WO2009090386A2

WO2009090386A2 - Improvements relating to electric motors and vehicles

Info

Publication number: WO2009090386A2
Application number: PCT/GB2009/000101
Authority: WO
Inventors: Martin Boughtwood
Original assignee: Qed Group Limited
Priority date: 2008-01-14
Filing date: 2009-01-14
Publication date: 2009-07-23
Also published as: WO2009090386A3

Abstract

A torque drive and control system for a vehicle having a plurality of driven wheels is disclosed. The system comprises a plurality of in-wheel electric motors for mounting within each respective driven wheel of the type having a plurality of coils forming a stator radially surrounded by a plurality of magnets forming a rotor; a control circuit within each electric motor for controlling a switching of voltage applied to coils of that motor to thereby control the accelerating or braking torque provided by the motor; means associated with each respective electric motor for detecting the speed of rotation of the motor; means for transmitting the speed of each motor to each other motor in the vehicle; wherein each control circuit is configured to adjust the torque provided by each respective motor in response to the detected speed of rotation of the motor and the speed of rotation of at least one other motor.

Description

Improvements relating to Electric Motors and Vehicles

FIELD OF THE INVENTION

This invention relates to improvements relating to electric motors or generators, as well as to a traction control system, a suspension system, an electric motor control system and an improved hand brake system for electric vehicles.

Accordingly, this patent application includes 5 broad areas of improvements relating to electrical vehicles, as described under subheadings A, B, C, D and E. For the avoidance of doubt, these different aspects may be used together in a single embodiment of the invention, or one or more of these aspects may be used in conjunction with another aspect, or on their own.

In the drawings, like reference numbers refer to like features.

A: ELECTRIC IN-WHEEL DRIVE ARRANGEMENT

The invention relates to electric vehicles, and particularly to a vehicle with in-wheel electric motors.

BACKGROUND OF THE INVENTION

Electric vehicles of various types powered by electric motors are known to the skilled person. In recent years, developments in electric motors have allowed in-wheel electric motors to be proposed for use in road vehicles. Motors of the type having a set of coils being part of the stator for attachment to a vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel are now being used in electric vehicle. These motors are sometimes referred to as "pancake" motors and may be three phase or, more recently, multiphase designs.

Advances in electric motor drive arrangements for vehicles are generally concentrated on the areas of power and efficiency to try and produce a vehicle having sufficient acceleration performance and range to be a realistic alternative to technologies such as the internal combustion engine.

SUMMARY OF THE INVENTION

We have appreciated that in-wheel electric motors can provide greater control over a vehicle than arrangements such as internal combustion engine drive with mechanical brakes. We have further appreciated that a new type of in- wheel motor drive that we have developed can be used in a vehicle in a new manner to improve vehicle handling.

The invention is defined in the accompanying independent claims, with preferred features set out in the dependent claims. An embodiment of the invention is a vehicle with separate in-wheel electric motors for each driven wheel arranged so that the torque provided by each electric motor at any instant is correctly matched to the prevailing driving conditions. This contrasts with earlier known ideas which only disclose managing torque in the event that a wheel loses grip in a form of traction control.

The invention may be embodied in a torque control method or by a computer program for operating a torque control method described above. The computer program for implementing the invention can be in the form of a computer program on a carrier medium. The carrier medium could be a storage medium, such as a solid state, magnetic, optical, magneto-optical or other storage medium. The carrier medium could be a transmission medium such as broadcast, telephonic, computer network, wired, wireless, electrical, electromagnetic, optical or indeed any other transmission medium.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same may be carried into effect reference is now made by way of example to the accompanying drawings in which: Figurei is an exploded view of a motor as used in an embodiment of the invention; Figure 2 is an exploded view of the motor of Figure 1 from an alternative angle; Figure 3 schematically shows schematically shows an example arrangement for a three phase motor as used in an embodiment of the invention; Figure 4 schematically shows an example arrangement of coils in one of the coil sub-sets shown in Figure 3 as used in an embodiment of the invention; Figure 5 schematically shows the coils of the embodiment in relation to the magnets;

Figure 6 schematically a control circuit; Figure 7 is a circuit diagram of the switching arrangement; and Figure 8 schematically shows a common control device; Figure 9 schematically shows a vehicle embodying the invention.

DETAILED DESCRIPTION

The embodiment of the invention described is vehicle having in-wheel electric motors. The motors are of the type having a set of coils being part of the stator for attachment to a vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel.

It is of importance that the electric motors are able to provide sufficient torque to both drive the vehicle and distribute torque between the wheels. Accordingly, the type of motor used in the embodiment will first be described, followed by the general principles of operation of the vehicle.

The in-wheel electric motors as used in the embodiment are shown in

Figures 1 and 2. The assembly can be described as a motor with built in electronics and bearing, or could also be described as a hub motor or hub drive as it is built to accommodate a separate wheel. Referring first to Figure 1 , the assembly comprises a stator 252 comprising a rear portion 230 forming a first part of the housing of the assembly, and a heat sink and drive arrangement 231 comprising multiple coils and electronics to drive the coils as well as a heat sink. The coil drive arrangement 231 is fixed to the rear portion 230 to form the stator 252 which may then be fixed to a vehicle and does not rotate during use.

A rotor 240 comprises a front portion 220 and a cylindrical portion 221 forming a cover, which substantially surrounds the stator 252. The rotor includes a plurality of magnets arranged around the inside of the cylindrical portion 221. The magnets are thus in close proximity to the coils on the assembly 231 so that magnetic fields generated by the coils in the assembly 231 generate a force on the magnets arranged around the inside of the cylindrical portion 221 of the rotor 240 thereby causing the rotor 240 to rotate.

The rotor 240 is attached to the stator 252 by a bearing block 223. The bearing block 223 can be a standard bearing block as would be used in a vehicle to which this motor assembly is to be fitted. The bearing block comprises two parts, a first part fixed to the stator and a second part fixed to the rotor. The bearing block is fixed to a central portion 233 of the wall 230 of the stator 252 and also to a central portion 223 of the housing wall 220 of the rotor 240. The rotor 240 is thus rotationally fixed to the vehicle with which it is to be used via the bearing block 223 at the central portion 225 of the rotor 240. This has a significant advantage in that a wheel rim and tyre can then be fixed to the rotor 240 at the central portion 225 using the normal wheel bolts to fix the wheel rim to the central portion of the rotor and consequently firmly onto the rotatable side of the bearing block 223. The wheel bolts may be fitted through the central portion 225 of the rotor through into the bearing block itself. A first advantage of this arrangement is that the whole assembly may be simply retrofitted to an existing vehicle by removing the wheel, bearing block and any other components such as the braking arrangement. The existing bearing block can then fitted inside the assembly and the whole arrangement fitted to the vehicle on the stator side and the normal rim and wheel fitted to the rotor so that the rim and wheel surrounds the whole motor assembly. Accordingly, retrofitting to existing vehicles becomes very simple. A second advantage is that there are no forces for supporting the vehicle on the outside of the rotor 240, particularly on the circumferential wall 221 carrying the magnets on the inside circumference. This is because the forces for carrying the vehicle are transmitted directly from the suspension fixed to one side of the bearing block (via the central portion of the stator wall) to the central portion of the wheel surrounding the rotor fixed to the other side of the bearing block (via the central portion of the rotor wall). This means that the circumferential wall 221 of the rotor is not subject to any forces that could deform the wall thereby causing misalignment of the magnets. No complicated bearing arrangement is needed to maintain alignment of the circumferential rotor wall.

Figure 2 shows an exploded view of the same assembly as Figure 1 from the opposite side showing the stator 252 comprising the rear stator wall 230 and coil and electronics assembly 231. The rotor 240 comprises the outer rotor wall 220 and circumferential wall 221 within which magnets 242 are circumferentially arranged. As previously described, the stator 252 is connected to the rotor 240 via the bearing block at the central portions of the rotor and stator walls.

Additionally shown in Figure 1 are circuit boards 80 carrying control electronics. Due to their kite shape these circuit boards can be referred to as kite boards. Additionally in Figure 2 a V shaped seal 350 is provided between the circumferential wall 221 of the rotor and the outer edge of the stator housing 230. Further, in Figure 2, a magnetic ring 227 comprising a commutation focusing ring and a plurality of magnets is provided for the purpose of indicating the position of the rotor with respect to the stator to a series of sensors arranged on the circuit boards 80 of the stator 252.

Figures 3 and 4 schematically show an example of the configuration of the electric motor of figures 1 and 2 as used in the embodiment of this invention. The motor 40 shown in Figure 3 is a three phase motor. The motor therefore has three coil sets. In this example, each coil set includes eight coil sub-sets. The coil sub-sets of each coil set are labelled 44, 46 and 48, respectively in Figure 3.

Each coil set includes pairs of coil sub-sets, which are arranged opposite each other around the periphery of the motor 40. However, it should be noted that there is no express need for each coil sub-set to have a corresponding coil subset located opposite from it on the opposite side of the periphery of the motor 40.

Each coil sub-set can be connected to a respective control device. The terminals for each coil sub-set of each coil set are labelled 54, 56 and 58, respectively in Figure 3. While the arrangement shown in Figure 3 includes a larger number of coil sub-sets, this does not significantly increase the size and bulk of the switching means which are used to operate the motor, as would be the case if the increased number of coil sub-sets were connected together in series. Instead, it is merely necessary to provide an additional control device incorporating relatively small switching devices for each additional coil sub-set.

These control devices are sufficiently small such that they can be located adjacent to their corresponding coil sub-sets.

As described above, each coil sub-set can include one or more coils. In this example, each coil sub-set includes three coils as is shown schematically in Figure 4. In Figure 4, these three coils are labelled 74A, 74B and 74C. The three coils 74A, 74B and 74C are alternately wound such that each coil produces a magnetic field which is anti-parallel with its adjacent coil/s for a given direction of current flow. As described above, as the permanent magnets of the rotor of the motor 40 sweep across the ends of the coils 74A, 74B and 74C, appropriate switching of the currents in the coils can be used to create the desired forces for providing an impulse to the rotor. As is shown schematically in Figure 4, each coil in a coil sub-set can be wound in series.

The reason that the coils 74A, 74B and 74C within each subset are wound in opposite directions to give antiparallel magnetic fields can be understood with respect to Figure 5 which shows the arrangement of the magnets 242 on the rotor surrounding the coils 44, 46 and 48 of the stator. For simplicity, the arrangement is shown as a linear arrangement of magnets and coils, but it will be understood that in the embodiment of the invention described the coils will be arranged around the periphery of the stator with the magnets arranged around the inside of the circumference of the rotor, as already described. The magnets 242 are arranged with alternate magnetic polarity towards the coils 44, 46 and 48. Each subset of three coils 74A, 74B and 74C thus presents alternate magnetic fields to the alternate pole faces of the magnets. Thus, when the left-hand coil of a subject has a repelling force against a North Pole of one of the magnets, the adjacent central coil will have a repelling force against a South Pole of the magnets and so on.

As shown schematically in Figure 5, the ratio of magnets to coils is eight magnets to nine coils. The advantage of this arrangement is that the magnets and coils will never perfectly align. If such perfect alignment occurred, then the motor could rest in a position in which no forces could be applied between the coils and the magnets to give a clear direction as to which sense the motor should turn. By arranging for a different number of coils and magnets around the motor, there would always be a resultant force in a particular direction whatever position the rotor and motor come to rest.

A particular benefit of the independent control of the coil subsets by the separate control devices is that a larger than normal number of phases can be arranged. For example, rather than a three phase motor, as described in Figure 3, higher numbers of phases such as twenty-four phase or thirty-six phase are possible with different numbers of magnets and coils. Ratios of coils to magnets, such as eighteen coils to sixteen magnets, thirty-six coils to thirty-two magnets and so on, are perfectly possible. Indeed, the preferred arrangement, as shown in Figures 1 and 2 is to provide 24 separate control "kite" boards 80, each controlling three coils in a sub-set. Thereby providing a twenty-four phase motor. The use of a multiphase arrangement, such as twenty-four phases, provides a number of advantages. The individual coils within each sub-set can have a larger inductance than arrangements with lower numbers of phases because each control circuit does not have to control large numbers of coils (which would require controlling a large aggregate inductance). A high number of phases also provides for lower levels of ripple current. By this it is meant that the profile of the current required to operate the motor undulates substantially less than the profile from, say a three-phase motor. Accordingly, lower levels of capacitance are also needed inside the motor. The high number of phases also minimises the potential for high voltage transients resulting from the need to transfer large currents quickly through the supply line. As the ripple is lower, the impact of the supply cabling inductance is lower and hence there is a reduction in voltage transient levels. When used in a braking arrangement, this is a major advantage, as in hard braking conditions, several hundred kilowatts need to be transferred over several seconds and the multiphase arrangement reduces the risk of high voltage transients in this situation.

The relative arrangement of magnets and coils, shown in Figure 5 can be repeated twice, three times, four times or indeed as many times as appropriate around 360 mechanical degrees of the rotor and stator arrangement. The larger the number of separate sub-sets of coils with independent phases, the lower the likelihood of high voltage transients or significant voltage ripple.

Figure 6 shows an example of a control device 80 in accordance with an embodiment of this invention. As described above, the control device 80 includes a number of switches which may typically comprise one or more semiconductor devices. The control device 80 shown in Figure 6 includes a printed circuit board

82 upon which a number of components are mounted. The circuit board 82 includes means for fixing the control device 80 within the motor, for example, adjacent to the coil sub-set which it the controls - directly to the cooling plate. In the illustrated example, these means include apertures 84 through which screws or suchlike can pass. In this example, the printed circuit board is substantially wedge-shaped. This shape allows multiple control device 80 to be located adjacent each other within the motor, forming a fan-like arrangement.

Mounted on the printed circuit board 82 of the control device 80 there can be provided terminals 86 for receiving wires to send and receive signals from a 92 control device as described below.

In the example shown in Figure 6, the control device 80 includes a number of switches 88. The switches can include semiconductor devices such as MOSFETs or IGBTs. In the present example, the switches comprise IGBTs. Any suitable known switching circuit can be employed for controlling the current within the coils of the coil sub-set associated with the control device 80. One well-known example of such a switching circuit is the H-bridge circuit. Such a circuit requires four switching devices such as those shown in Figure 6. The wires (e.g. copper wires) of the coil sub-sets can be connected directly to the switching devices 88 as appropriate, and interconnections between the switching devices 88 can be formed on the printed circuit board 82. Since the switching devices 88 can be located adjacent the coil sub-sets as described above, termination of the wires of the coil sub-sets at the switching devices 88 is made easier.

As shown in Figure 7, the control device includes semiconductor switches arranged in an H-bridge arrangement. The H-bridge is of course known to those skilled in the art and comprises four separate semiconductor switches 88 connected to a voltage supply (here 300 volts) and to ground. The coils of each sub-coil are connected across the terminals 81 and 83. Here a sub-coil 44 is shown connected across the terminals. Simplistically, to operate the motor and supply a voltage in one direction, switches 88A and 88D are closed and the other switch is left open, so that a circuit is made with current in one direction. To operate the motor this current direction is changed in harmony with the alternating magnetic polarity passing the coil. To change the direction of rotation of the motor, the timing and polarity of the current flow in the coil is changed to cause the resulting forces in the opposite direction. The direction of current flow in the coil is reversed when switches 88B and 88C are closed and the other two switches are left open. In practice, the technique of pulse width modulating is used to pulse width modulate the signal applied to the gate of the semiconductor switches to control the voltage applied to the coils. The braking arrangement operates in a manner not known in the prior art and will be described after describing the overall control arrangement.

A shown in Figure 8, a common control device 92 can be used to coordinate the operations of the multiple control devices 80 provided in the motor. In Prior motors, in which synchronization of the magnetic fields produced by the coils of each coil sub-set is automatically achieved by virtue of the fact that they are connected in series. However, where separate power control is provided for each coil sub-set, automatic synchronization of this kind does not occur. Accordingly, in accordance with an embodiment of this invention, a common control device 92 such as that shown in Figure 8 can be provided to ensure correct emulation of a polyphase system incorporating series-connected coils. As described above in relation to Figure 7, terminals 86 can be provided at the multiple control devices 80 to allow interconnections 90 to be formed between the multiple control devices 80 and the common control device 92.

The interconnections 90 can pass signals between the common control device 92 and the control devices 80 such as timing/synchronization signals for appropriate emulation of a polyphase series-connected system.

In an alternative embodiment, each control unit can operate independently, without the need of a central control device. For example, each control unit can have independent sensors to detect a position of a rotor of the motor, which would dispense with the need to provide synchronisation signals of the kind described above. Instead, each control unit would receive a demand signal enabling it to control the voltage applied to its associated coils in isolation.

It is stressed that the preferred embodiment does not require any form of central control device for the operation of each wheel incorporating a motor. Preferably, each motor is self-contained and, within each motor, the control circuits 80 are self-contained and depend upon nothing other than a torque demand signal to operate. This means that the elements are able to continue to function and to deliver demanded torque levels, irrespective of any other failures within the total drive system. In a system incorporating a plurality of wheels each having a motor, each motor incorporates all the intelligence needed to manage its actions. Each motor understands its position on the vehicle and controls its actions accordingly. Preferably, each motor is further provided with information regarding the other motors such as the speed, torque and status and are based on each motor's knowledge of its position on the vehicle and the state and status of the other motors it can determine the optimum level of torque that it should apply for a given demanded torque. Even without this other information, though, the motor can continue to respond to a demanded torque.

As discussed above, motors constructed according to an embodiment of this invention can allow for highly responsive torque control. The use of separate motors for each wheel of a vehicle can allow for increased flexibility in handling torque control for the vehicle. Moreover, the short response times for torque control afforded by a motor according to an embodiment of this invention can enhance this flexibility.

A schematic view of a vehicle embodying the invention is shown in Figure

9 including showing possible forces on the vehicle and wheels at a given instant. As previously described, each wheel of a vehicle can be controlled by its own motor and corresponding drive software, thereby allowing each motor to handle its own torque control. This means that each motor can handle, for example, a skid situation independently of the other wheels. Moreover, the fast response times (e.g. within a single PWM period of, for example 50 μs) afforded by embodiments of this invention can allow intricate control of the torque applied to each wheel independently, for increased effectiveness in handling.

To provide the appropriate toque, various parameters are determined, such as speed of rotation, angle of turn and acceleration. These could be provided by sensors. A speed sensor can be provided by measurement of the back EMF provided by the coils to determine the angular velocity of the wheel. Similarly, the acceleration sensor may be provided by determining the rate of change of angular velocity of the motor by measuring the back EMF from the coils. As an alternative, separate magnetic sensors may be provided within each motor. The angle of turn of the wheel may be measured by a separate sensor mounted within the suspension arrangement of the wheel to determine the angle of the wheel with respect to the vehicle body.

Whilst the measurement of speed of each wheel, direction of turn of the vehicle and acceleration of each wheel could be determined by separate sensors, these are preferably determined by logic within each of the control circuits 80 shown in Figure 6 and in conjunction with communicating information between the control circuits of each wheel within a network, such as shown in Figure 8. The controllers within each wheel determine the speed of rotation of that wheel by monitoring the back EMF, by separate sensors or otherwise. In addition, the angular acceleration is determined using one of the same techniques. The controllers within each wheel receive parameters indicating the speed of rotation and rate of angular acceleration of the other wheels in the vehicle, as well as the indication of the position of each wheel in the vehicle. Within each control circuit, contro⁾ logic can then determine based on the angular velocity of each wheel, the position of each wheel and the angular acceleration of each wheel whether the wheel has traction or is entering a skid condition. If it is determined that the wheel is likely to be about to skid or in the process of skidding, then a traction control mode operates to reduce the torque applied to that wheel by the motor. On the other hand, if the wheel is not determined to be skidding then the control logic remains in a torque share mode in which the torque provided by an electric motor to a given wheel may be increased where the control logic determines that a wheel is on the outside of a turn and so should receive an increase in the torque provided.

The logic within each control device for providing the appropriate torque settings may be referred to as torque share logic. The logic is able to operate by determining an angle turn of a vehicle in the manner described above. As an alternative, the controller area network linking the motors together may distribute the angular speed of each wheel to controllers of other wheels and the torque share logic may determine the appropriate torque for a wheel based on the relative speeds of the wheels alone, without the step of determining the angle of turn of the vehicle.

The torque share logic can determine the absolute or relative torque required of a wheel and switch power to the coils accordingly, either as an absolute level, but more preferably as a relative level. For example, the torque share logic could determine a torque difference needed in comparison to another wheel as a percentage of the RPM of the two wheels up to a maximum percentage difference. The maximum percentage difference would ensure that each wheel operates within a sensible range of torque difference in comparison to other wheels.

Whilst not essential to the invention, a master controller shown as the common control device 92, in Figure 8, can retain information received from each wheel as to speed, torque and acceleration and then provide instruction signals to the controllers within each wheel to specify the appropriate torque to provide. As previously explained, it is the relative velocities of the wheels that are crucial, to determining the appropriate torque to provide within the limits of traction. The master controller could operate to determine an average vehicle speed based on the average velocities of the wheels at a given time (taking into account any known slip of the wheels) and act as a master controller to instruct the controllers within the wheels how torque should be distributed amongst the wheels of the vehicle. The function as to the percentage difference of torque to apply may be a function of the average speed of the vehicle, as well as the speed of each of the wheels.

It is important to stress that unlike known arrangements, the invention operates by distribution of torque amongst wheels not velocity. The motor itself, as already described, is arranged to provide torque control rather than speed control.

In accordance with an embodiment of this invention, motor control is by a high speed continuous range torque loop which can also provide traction control. This can allow the response to be smoother and the achieved grip to be greater than a mechanically modulated torque management system. The motor drives can be networked together by a controller area network (CAN). This can allow information regarding, for example, skid events to exchanged between the motor drives for coordinated action to be taken. In one example, this information includes acceleration data indicative of the angular acceleration of each wheel. A sharp increase in angular acceleration can be interpreted as a wheel slip of a wheel skid.

According to an embodiment of the invention, sensors such as internal magnetic angle sensors can be provided in the motor of each wheel or in the wheels themselves. These sensors can detect the angular velocity of each wheel. By taking the first derivative of the angular velocity determined by the sensors, the angular acceleration of each wheel can be determined for wheel. In another embodiment, wheel torque requirements can be detected by comparing each wheel speed with that of the other wheels. As described above, wheel torque requirement could be detected by detecting changes in the angular velocity of a wheel. There are a number of ways in which the torque applied to a wheel can be reduced for regaining traction. For example, a combination of a calculated step reduction in torque followed by a linear reduction could be applied until it is detected that traction been regained. Alternatively, the torque could be dropped to zero or a very low value. The time taken for the wheel to stabilise back to the average vehicle speed could then be determined. This would give enough information to find the grip coefficient of the tyre as the rotational inertia of the wheel is known in advance. In turn, this measurement can then be used to modulate the torque produced in the wheel motor.

As described above, the motor drives of a vehicle can be networked together by, for example, a controller area network (CAN). Networking of this kind can allow the motor drives to communicate for providing improved awareness of each motor drive as to the overall condition of the vehicle. For example, in such a configuration, the motor drives can provide for the maintenance of left/right torque balance across the four wheels of, for example, a car. This can allow a significant left/right imbalance, which could alter the steering direction of the car or even spin it around, to be corrected for.

B: ELECTRIC MOTOR CONTROL

The invention relates to controlling electric motors, in particular to current sensing and control in in-wheel or hub electric motors.

BACKGROUND OF THE INVENTION

Known electric motor systems typically include a motor and a control unit for controlling power to the motor. Known types of electric motor include the induction motor, brushless permanent magnet motor, switched reluctance motor and synchronous slip ring machine. Three phase electric motors are the most common kind of electric motor available.

Figure 10 shows a schematic representation of a typical three phase motor. In this example, the motor includes three coil sets. Each coil set produces a magnetic field associated with one of the three phases of the motor. In a more general example, N coil sets can be used to produce an N-phase electric motor. Each coi) set can include one or more sub-sets of coils which are positioned around a periphery of the motor. In the present example, each coil set includes four such sub-sets - the coil sub-sets of each coil set are labelled 14, 16 and 18, respectively in Figure 10. As shown in Figure 10, the coil sub-sets 14, 16, 18 are evenly distributed around the motor 10 to co-operate in producing a rotating magnetic field within which a central rotor 12, which typically incorporates one or more permanent magnets, can rotate as shown by the arrow labelled C. The coil sub-sets of each coil set are connected together in series as shown by the connections 24, 26 and 28 in Figure 10. This allows the currents in the coils of each coil set to be balanced for producing a substantially common phase. The wires of each coil set are terminated as shown at 34, 36 and 38 in Figure 10. Typically, one end of the wire for each coil set is connected to a common reference terminal, while the other wire is connected to a switching system for controlling the current within all of the coils of that coil set. Typically then, current control for each coil set involves controlling a common current passing through a large number of coils.

As shown in Figure 11, each coil sub-set can include one or more coils. In particular, Figure 11 shows the coils 24A, 24B in one of the coil sub-sets 14. In this example, there are two coils per coil sub-set. The two coils are wound in the opposite directions, and are interconnected so that the current flowing in each coil is substantially the same. As the poles of the rotor 12 sweep across the coils 24A, 24B₁ switching of the current in the coils 24A, 24B can produce the appropriate magnetic field for attracting and repelling the rotor for continued rotation thereof. The magnetic field produced by the two oppositely wound coils 24A, 24B is referred to as belonging to the same phase of this three phase motor. Every third coil sub-set arranged around the periphery of the motor 10 produces a magnetic field having a common phase. The coils and the interconnections may typically comprise a single piece of wire (e.g. copper wire) running around the periphery of the motor and wound into coils at the appropriate locations.

For a three phase electric motor, the switching system is almost invariably a three phase bridge circuit including a number of switches. Such switching systems require current sensing circuitry in at least two of the three coils in order to determine the current flowing in the coil, and hence the magnetic field produced by the coil. The measured current is then used by the motor control circuitry in a closed loop to determine how to subsequently adjust the voltage applied to the coil depending upon requirements.

Because each coil is independently powered via the connections 34, 36, and 38, it is necessary for at least two of the circuits 34, 36, and 38 to have a separate current sensor. This allows the voltage applied to each coil set 34, 36, 38 to be controlled depending upon the actual current flowing in the coil sets 34 and subsets 14, 16, 18. Accordingly as the number of separate control circuits increases it is desirable to avoid the need for separate current sensing apparatus for each circuit.

Almost all electronic control units for electric motors today operate by some form of pulse width modulation (PWM) voltage control. PWM control works by using the motor inductance to average out an applied pulse voltage to drive the required current into the motor coils. Using PWM control an applied voltage is switched across the motor windings for a minimum period dictated by the power device switching characteristic. During this on period, the current rises in the motor winding at a rate dictated by its inductance, the applied voltage and the motor back emf. The PWM control then sequentially modulates the applied voltage so that the current in the winding matches the desired value so that precise control of the current is achieved.

SUMMARY OF THE INVENTION

Aspects of the invention are defined in the accompanying claims. According to an aspect of the invention, there is provided an electric motor. The motor includes one or more separate coil sets arranged to produce a magnetic field of the motor. Each coil set includes a plurality of coil sub-sets. Each coil sub-set includes one or more coils. The magnetic field produced by the coils in each coil set have a substantially common phase. The motor also includes a plurality of control devices each coupled to a respective coil sub-set for controlling the instantaneous voltage applied to the coils of that respective coil sub-set. Each control device may operate without requiring an input synchronisation signal. A key aspect of the present invention is that it operates in an entirely open loop manner - that is without the need for any feedback from current sensors. Thus the control device is pre equipped with all of the known characteristics of the motor and control device such that for any given input or torque demand, the system knows precisely what voltage to apply at any instant so that the resulting current is the most optimum current for that instant. The control devices include means for monitoring a back EMF within the coils of that coil sub-set. This allows the current within a coil-subset to be determined so that the control device can adjust voltage applied to the coil subset in response to the monitored back EMF and determined current in the coil sub-set. This allows for high-speed power control without the need for additional current sensors to be included for each coil-subset.

The control devices can include one or more switches for applying a pulsed voltage to the one or more coils of a coil sub-set. PWM control of the currents in the motor coils can be enhanced due to the increased number of turns which can be included in the coils. Because smaller switching device can be used, significant savings in cost, weight and heat dissipation can be made.

The control device can adjust a pulse of the pulsed voltage (e.g. a width of the pulse) in response to the monitored back EMF for high speed power control. The control devices can operate independently of one another because each control device comprises sufficient logic to determine the position of the rotor and so to apply the appropriate voltage to control the current in the respective coil subset. The control devices can receive a demand signal from an external device, such as a brake pedal sensor, and apply appropriate coil control based on the coil characteristics, the position of the rotor and the demand signal.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which:

Figure 10 schematically shows an example arrangement for a three phase motor;

Figure 11 schematically shows the arrangement of coils in one of the coil sub-sets shown in Figure 10;

Figure 12 is an exploded view of a motor embodying the invention; Figure 13 is an exploded view of the motor of Figure 12 from an alternative angle;

Figure 14 schematically shows an example coil arrangement for a three phase motor according to an embodiment of this invention;

Figure 15 schematically shows an example arrangement of coils in one of the coil sub-sets shown in Figure 12 according to an embodiment of the invention; Figure 16 schematically shows schematically shows an example arrangement for a three phase motor according to an embodiment of this invention;

Figure 17 schematically shows an example arrangement of coils in one of the coil sub-sets shown in Figure 16 according to an embodiment of the invention;

Figure 18 schematically shows the coils of the embodiment in relation to the magnets; Figure 19 schematically shows an example of a control device in accordance with an embodiment of this invention; Figure 20 is a circuit diagram of the switching arrangement; Figure 21 schematically shows an arrangement in which a common control device is used to coordinate the operation of a plurality of control devices;

DETAILED DESCRIPTION

The embodiment of the invention described is an electric motor for use in a wheel of a vehicle. The motor is of the type having a set of coils being part of the stator for attachment to a vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel. For the avoidance of doubt, the various aspects of the invention are equally applicable to an electric generator having the same arrangement. In addition, some of the aspects of the invention are applicable to an arrangement having the rotor centrally mounted within radially surrounding coils.

The physical arrangement of the embodying assembly is best understood with respect to Figures 12 and 13, showing a 24-phase motor. The assembly can be described as a motor with built in electronics and bearing, or could also be described as a hub motor or hub drive as it is built to accommodate a separate wheel.

Referring first to Figure 12, the assembly comprises a stator 252 comprising a rear portion 230 forming a first part of the housing of the assembly, and a heat sink and drive arrangement 231 comprising multiple coils and electronics to drive the coils as well as a heat sink. The coil drive arrangement 231 is fixed to the rear portion 230 to form the stator 252 which may then be fixed to a vehicle and does not rotate during use. The coils themselves are formed on tooth laminations 235 which together with the drive arrangement 231 and rear portion 230 form the stator 252.

A rotor 240 comprises a front portion 220 and a cylindrical portion 221 forming a cover, which substantially surrounds the stator 252. The rotor includes a plurality of magnets 242 arranged around the inside of the cylindrical portion 221. The magnets are thus in close proximity to the coils on the assembly 231 so that magnetic fields generated by the coils in the assembly 231 generate a force on the magnets 242 arranged around the inside of the cylindrical portion 221 of the rotor 240 thereby causing the rotor 240 to rotate. The rotor 240 is attached to the stator 252 by a bearing block 223. The bearing block 223 can be a standard bearing block as would be used in a vehicle to which this motor assembly is to be fitted. The bearing block comprises two parts, a first part fixed to the stator and a second part fixed to the rotor. The bearing block is fixed to a central portion 233 of the wall 230 of the stator 252 and also to a central portion 225 of the housing wall 220 of the rotor 240. The rotor 240 is thus rotationally fixed to the vehicle with which it is to be used via the bearing block 223 at the central portion 225 of the rotor 240. This has a significant advantage in that a wheel rim and tyre can then be fixed to the rotor 240 at the central portion 225 using the normal wheel bolts to fix the wheel rim to the central portion of the rotor and consequently firmly onto the rotatable side of the bearing block 223. The wheel bolts may be fitted through the central portion 225 of the rotor through into the bearing block itself. A first advantage of this arrangement is that the whole assembly may be simply retrofitted to an existing vehicle by removing the wheel, bearing block and any other components such as the braking arrangement. The existing bearing block can then fitted inside the assembly and the whole arrangement fitted to the vehicle on the stator side and the normal rim and wheel fitted to the rotor so that the rim and wheel surrounds the whole motor assembly. Accordingly, retrofitting to existing vehicles becomes very simple.

A second advantage is that there are no forces for supporting the vehicle on the outside of the rotor 240, particularly on the circumferential wall 221 carrying the magnets on the inside circumference. This is because the forces for carrying the vehicle are transmitted directly from the suspension fixed to one side of the bearing block (via the central portion of the stator wall) to the central portion of the wheel surrounding the rotor fixed to the other side of the bearing block (via the central portion of the rotor wall). This means that the circumferential wall 221 of the rotor is not subject to any forces that could deform the wall thereby causing misalignment of the magnets. No complicated bearing arrangement is needed to maintain alignment of the circumferential rotor wall.

The rotor also includes a focussing ring and magnets 227 for position sensing discussed later. Figure 13 shows an exploded view of the same assembly as Figure 12 from the opposite side showing the stator 252 comprising the rear stator wall 230 and coil and electronics assembly 231. The rotor 240 comprises the outer rotor wall 220 and circumferential wall 221 within which magnets 242 are circumferentially arranged. As previously described, the stator 252 is connected to the rotor 240 via the bearing block at the central portions of the rotor and stator walls.

Additionally shown in Figure 12 are circuit boards 80 carrying control electronics described later. Due to their kite shape these circuit boards can be referred to as kite boards. Additionally in Figures 12 and 13 a V shaped seal 350 is provided between the circumferential wall 221 of the rotor and the outer edge of the stator housing 230, again described in detail later. Further, in Figure 13, a magnetic ring 227 comprising a commutation focusing ring and a plurality of magnets is provided for the purpose of indicating the position of the rotor with respect to the stator as well as a series of sensors arranged on the circuit boards

80 of the stator 252. This is also described in greater detail later.

Coil Control: Example No. 1

Figure 14 schematically shows an example of an electric motor in accordance with an embodiment of this invention. In this example, the motor is generally circular. However, it will be appreciated that embodiments of this invention can employ other topologies. For example a linear arrangement of coils for producing linear movement is envisaged.

The motor 40 in this example is a three phase motor. Again, it will be appreciated that motors according to this invention can include an arbitrary number of phases (N = 1, 2, 3...). Being a three phase motor, the motor 40 includes three coil sets. In this example, each coil set includes two coil sub-sets. The coil sub-sets of each coil set are labelled 44, 46 and 48, respectively. The coil sub-sets 44, 46 and 48 are arranged around a periphery of the motor 40. In this example, each coil sub-set is positioned opposite the other coil sub-set in that coil set, although such an arrangement is not strictly essential to the working of the invention. Each coil sub-set includes one or more coils, as described below in relation to Figure 15. The motor 40 can include a rotor (not shown in Figure 14) positioned in the centre of the circle defined by the positioning of the various coils of the motor, thereby to allow rotation of the rotor within the rotating magnetic field produced by the coils. Preferably, though, the rotor is arranged around the coils as previously disclosed in Figures 12 and 13. The rotor may typically comprise one or more permanent magnets arranged to rotate such that their poles sweep across the ends of the coils of the motor 40. Appropriate switching of voltages applied to the coils of the coil sub-sets allows synchronized attraction and repulsion of the poles of the permanent magnet of the rotor to produce the rotating action of the motor 40. It will be appreciated that Figure 14 is highly schematic and, in practice, the coil sub-sets will be arranged at the outer periphery of the stator with the rotor magnets surrounding the coils.

Each coil set 44, 46, 48 includes one or more coils. As shown in Figure 15, in the present example, there is a single coil per coil sub-set. An example with more than one coil per coil sub-set is described below in relation to Figures

16 and 17. Where more than one coil is provided in a given coil sub-set, these coils can generally be wound in opposite directions such that the magnetic field produced by each coil is in an anti-parallel configuration with respect to the magnetic field in an adjacent coil. As described above, appropriate switching of the current in the coils causes the permanent magnets of the rotor to rotate.

As shown in Figure 14, in accordance with an embodiment of this invention, the coil or coils of each coil sub-set can be connected to a separate control device 80. In Figure 14, it is schematically shown that each coil sub-set is connected to the terminals 54, 56, 58 of respective control devices 80. Accordingly, the coils of corresponding coil sub-sets within a given coil set are not connected in series. Instead, each coil sub-set is individually controlled and powered. The connections to the control device and the coils of each coil sub-set can be formed using, for example, a single piece of wire (e.g. copper wire) as is shown schematically in Figure 15.

There are numerous advantageous to providing individual power control for the coils of each coil sub-set.

Since there is no need to run connecting wires around the periphery of the motor providing series interconnections for the coils of each coil sub-set, less wire is used in manufacturing the motor. This reduces manufacturing costs as well as reducing the complexity of the motor construction. The reduction in wire also reduces conduction losses.

By providing individual power control for the coils of each coil sub-set, and by using a larger number of turns per coil than would be achievable using a motor in which the coils of each coil sub-set are connected in series, the total inductance of the motor can be greatly increased. In turn, this allows far lower current to be passed through each coil sub-set whereby switching devices having a lower power rating can be used for current control. Accordingly, switching devices which are, cheaper, lighter and less bulky can be used to operate the motor.

The use of lower currents also reduces heat dissipation problems and lowers switching losses due to the faster speed of the smaller switching devices which can be employed. The fact that smaller switching devices can operate at higher frequencies allows for finer and more responsive motor control. Indeed, torque adjustment can take place on the basis in a highly responsive manner, with adjustments being able to be made within a single PWM period. A typical PWM period according to an embodiment of the invention is approximately 50 μs.

Another advantage of the use of smaller switching devices is that they can be located proximal the coils which they control. In prior electric motors, where relatively large switching devices have been employed to control the operation of coil sub-sets connected in series, the control device is sufficiently large that it can not be included with the other motor components (e.g. stator, rotor, etc.) but instead has been provided separately. In contrast, since small switching devices can be used, in accordance with an embodiment of this invention the switching devices and the control devices in which those switching devices are incorporated can be located in, for example the same housing/casing as the other motor components. Further detail regarding an example of a control device incorporating switching devices is given below in relation to Figures 19 and 20.

Coil Control: Example No. 2

Figures 16 and 17 show another example arrangement for a motor 40 in accordance with an embodiment of this invention. The motor 40 shown in Figure 14 is a three phase motor. The motor therefore has three coil sets. In this example, each coil set includes eight coil sub-sets. The coil sub-sets of each coil set are labelled 44, 46 and 48, respectively in Figure 16. In common with the example described above in relation to Figure 14, each coil set includes pairs of coil sub-sets which are arranged opposite each other around the periphery of the motor 40. Again, however, it should be noted that there is no express need for each coil sub-set to have a corresponding coil sub-set located opposite from it on the opposite side of the periphery of the motor 40.

As described above in relation to Figure 16, each coil sub-set can be connected to a respective control device 80. The terminals for each coil sub-set of each coil set are labelled 54, 56 and 58, respectively in Figure 16. While the arrangement shown in Figure 16 includes a larger number of coil sub-sets than, for example, the arrangement shown in Figure 12, this does not significantly increase the size and bulk of the switching means which are used to operate the motor as would be the case if the increased number of coil sub-sets were connected together in series. Instead, it is merely necessary to provide an additional control device 80 incorporating relatively small switching devices as described above for each additional coil sub-set. As described above, these control devices 80 are sufficiently small such that they can be located adjacent to their corresponding coil sub-sets within, for example, the same casing as the motor 40.

As described above, each coil sub-set can include one or more coils. In this example, each coil sub-set includes three coils as is shown schematically in

Figure 17. In Figure 17, these three coils are labelled 74A, 74B and 74C. The three coils 74A, 74B and 74C are alternately wound such that each coil produces a magnetic field which is anti-parallel with its adjacent coil/s for a given direction of current flow. As described above, as the permanent magnets of the rotor of the motor 40 sweep across the ends of the coils 74A, 74B and 74C, appropriate switching of the voltage applied to the coils can be used to create the desired forces for providing an impulse to the rotor. As is shown schematically in Figure

15, each coil in a coil sub-set can be wound in series.

The reason that the coils 74A, 74B and 74C within each subset are wound in opposite directions to give antiparallel magnetic fields can be understood with respect to Figure 18 which shows the arrangement of the magnets 242 on the rotor surrounding the coils 44, 46 and 48 of the stator. For simplicity, the arrangement is shown as a linear arrangement of magnets and coils, but it will be understood that in the embodiment of the invention described the coils will be arranged around the periphery of the stator with the magnets arranged around the inside of the circumference of the rotor, as already described.

The magnets 242 are arranged with alternate magnetic polarity towards the coil subsets 44, 46 and 48. Each subset of three coils 74A, 74B and 74C thus presents alternate magnetic fields to the alternate pole faces of the magnets. Thus, when the left-hand coil of a subset has a repelling force against a North Pole of one of the magnets, the adjacent central coil will have a repelling force against a South Pole of the magnets and so on.

As shown schematically in Figure 18, the ratio of magnets to coils is eight magnets to nine coils. The advantage of this arrangement is that the magnets and coils will never perfectly align. If such perfect alignment occurred, then the motor could rest in a position in which no forces could be applied between the coils and the magnets to give a clear direction as to which sense the motor should turn. By arranging for a different number of coils and magnets around the motor, there would always be a resultant force in a particular direction whatever position the rotor and motor come to rest.

N-phase electric motor

A particular benefit of the independent control of the coil subsets by the separate control devices is that a larger than normal number of phases can be arranged. For example, rather than a three phase motor, as described in Figure 16, higher numbers of phases such as twenty-four phase or thirty-six phase are possible with different numbers of magnets and coils. Ratios of coils to magnets, such as eighteen coils to sixteen magnets, thirty-six coils to thirty-two magnets and so on, are perfectly possible. Indeed, the preferred arrangement, as shown in Figures 12 and 13 is to provide 24 separate control "kite" boards 80, each controlling three coils in a sub-set. Thereby providing a twenty-four phase motor. The use of a multiphase arrangement, such as twenty-four phases, provides a number of advantages. The individual coils within each sub-set can have a larger inductance than arrangements with lower numbers of phases because each control circuit does not have to control large numbers of coils (which would require controlling a large aggregate inductance). A high number of phases also provides for lower levels of ripple current. By this it is meant that the profile of the current required to operate the motor undulates substantially less than the profile from, say a three-phase motor. Accordingly, lower levels of capacitance are also needed inside the motor. The high number of phases also minimize the potential for high voltage transients resulting from the need to transfer large currents quickly through the supply line. As the ripple is lower, the impact of the supply cabling inductance is lower and hence there is a reduction in voltage transient levels. When used in a braking arrangement (described later), this is a major advantage, as in hard braking conditions, several hundred kilowatts need to be transferred over several seconds and the multiphase arrangement reduces the risk of high voltage transients in this situation.

The relative arrangement of magnets and coils, shown in Figure 18 can be repeated twice, three times, four times or indeed as many times as appropriate around 360 mechanical degrees of the rotor and stator arrangement.

The larger the number of separate sub-sets of coils with independent phases, the lower the likelihood of high voltage transients or significant voltage ripple.

In accordance with an embodiment of this invention, a plurality of coil subsets with individual power control can be positioned adjacent each other in the motor. In one such example, three coils such as those shown in Figure 17 could be provided adjacent each other in a motor but would not be connected in series to the same control device 80. Instead, each coil would have its on control device 80.

Where individual power control is provided for each coil sub-set, the associated control devices can be operated to run the motor at a reduced power rating. This can be done, for example, by powering down the coils of a selection of the coil sub-sets.

Reduced coil subset operation

By way of example, in Figure 16 some of the coil sub-sets are highlighted with a '*'. If these coil sub-sets were to be powered down, the motor would still be able to operate, albeit with reduced performance. In this way, the power output of the motor can be adjusted in accordance with the requirements of a given application. In one example, where the motor is used in a vehicle such as a car, powering down of some of the coil sub-sets can be used to adjust the performance of the car. In the example shown in Figure 16, if each of the coil sub-sets indicated with an '*' were powered down, the remaining coil sub-sets wou\d result in a configuration similar to that shown in Figure 14, although of course there are three coils per coil sub-set as opposed to the single coil per coil sub-set shown in Figure 14.

Powering down of one or more of the coil sub-sets has the further benefit that in the event of a failure of one of the coil sub-sets, other coil sub-sets in the motor 40 can be powered down resulting in continued operation of the motor 40 in a manner which retains a balanced magnetic field profile around the periphery of the motor for appropriate multiphase operation. In contrast, in prior systems involving series interconnection of the coils of the coil sub-sets, a failure in the coils or interconnections associated with any given coil set is likely to be catastrophic and highly dangerous, given the large currents involved. Moreover, a failure anywhere within the coils or interconnections between the coils of a given coil set would result in the motor not being able to continue functioning in any way whatsoever.

In summary, individual power control for the coil sub-sets in accordance with an embodiment of this invention allows independent powering up and or powering down of selected coil sub-sets in order to react to differing powering requirements and/or malfunctions or failures within the coil sub-sets.

Control Circuitry

Figure 19 shows an example of a control device 80 in accordance with an embodiment of this invention. As described above, the control device 80 includes a number of switches which may typically comprise one or more semiconductor devices. The control device 80 shown in Figure 19 includes a printed circuit board 82 upon which a number of components are mounted. The circuit board 82 includes means for fixing the control device 80 within the motor, for example, adjacent to the coil sub-set which it the controls - directly to the cooling plate. In the illustrated example, these means include apertures 84 through which screws or suchlike can pass. In this example, the printed circuit board is substantially wedge-shaped. This shape allows multiple control device 80 to be located adjacent each other within the motor, forming a fan-like arrangement.

In the example shown in Figure 19, the control device 80 includes a number of switches 88. The switches can include semiconductor devices such as MOSFETs or IGBTs. In the present example, the switches comprise IGBTs. Any suitable known switching circuit can be employed for controlling the current within the coils of the coil sub-set associated with the control device 80. One well known example of such a switching circuit is the H-bridge circuit. Such a circuit requires four switching devices such as those shown in Figure 19. The wires (e.g. copper wires) of the coil sub-sets can be connected directly to the switching devices 88 as appropriate, and interconnections between the switching devices 88 can be formed on the printed circuit board 82. Since the switching devices 88 can be located adjacent the coil sub-sets as described above, termination of the wires of the coil sub-sets at the switching devices 88 is made easier.

As shown in Figure 20, the control device includes semiconductor switches arranged in an H-bridge arrangement. The H-bridge is of course known to those skilled in the art and comprises four separate semiconductor switches 88 connected to a voltage supply (here 300 volts) and to ground. The coils of each sub-coil are connected across the terminals 81 and 83. Here a sub-coil 44 is shown connected across the terminals. Simplistically, to operate the motor and supply a voltage in one direction, switches 88A and 88D are closed and the other switch is left open, so that a circuit is made with current in one direction. To operate the motor this current direction is changed in harmony with the alternating magnetic polarity passing the coil. To change the direction of rotation of the motor, the timing and polarity of the current flow in the coil is changed to cause the resulting forces in the opposite direction. The direction of current flow in the coil is reversed when switches 88B and 88C are closed and the other two switches are left open. In practice, the technique of pulse width modulating is used to pulse width modulate the signal applied to the gate of the semiconductor switches to control the voltage applied to the coils. The braking arrangement operates in a manner not known in the prior art and will be described after describing the overall control arrangement.

As shown in Figure 21, a common control device 92 can be used to coordinate the operations of the multiple control devices 80 provided in the motor. In prior motors, in which synchronization of the magnetic fields produced by the coils of each coil sub-set is automatically achieved by virtue of the fact that they are connected in series. However, where separate power control is provided for each coil sub-set, automatic synchronization of this kind does not occur. Accordingly, in accordance with an embodiment of this invention, a common control device 92 such as that shown in Figure 21 can be provided to ensure correct emulation of a polyphase system incorporating series-connected coils. As described above in relation to Figure 20, terminals 86 can be provided at the multiple control devices 80 to allow interconnections 90 to be formed between the multiple control devices 80 and the common control device 92.

In an alternative and preferred embodiment, each control unit can operate independently, without the need of a central control device. For example, each control unit can have independent sensors to detect a position of a rotor of the motor, which would dispense with the need to provide synchronisation signals of the kind described above. Instead, each control unit would receive a demand signal enabling it to control the voltage applied to its associated coils in isolation.

Other control signals such as power up/power down control signals can also be sent/received via the interconnects. These signals can also include signals for adjusting/defining the voltage pulses applied by the control device 80 to the coils of its associated coil sub-set for powering the motor.

For example, in accordance with an embodiment of this invention, means can be provided for monitoring a back EMF within the coil or coils of a coil subset. The task of emulating a motor with series connected coil sub-sets as described above is complicated by virtue of the back EMF associated with the motor. In a series connected system, the back EMFs are also in series and this gives rise to a smooth sine wave back EMF profile. Accordingly, in a series configuration the sinusoidal back EMF minimises the bandwidth required from the drive electronics when controlling the current in the coils.

In contrast, the reduced number of coil sub-sets connected in series in accordance with an embodiment of this invention can result in a non sinusoidal back EMF. Accordingly a more agile control system is desirable in order to ensure that the currents in the coils remain sinusoidal, or more often remain in a form that closely matches the back emf.

According to an embodiment of this invention, near instantaneous compensation can be provided for back EMF and further adjusting for any variations in a system dc supply voltage. The means for measuring the back EMF can include a current sense device fitted to provide feedback of the actual current flowing in the coil or coils of each coil sub-set. In one example, a simple series resistor of suitably low value in series with the switching devices can be employed. For example, in one embodiment two resistors can be provided in the bottom emitter of a "H" bridge power stage.

As the back EMF changes with rotor angle and rotor velocity, this results in a change in the rate of change of current in the coil. This rate of change of current can be detected across a resistor or other current sense device as a change in voltage. This change can then be differentiated to produce a voltage which is proportional to the back EMF.

Similarly, the supply voltage can be applied to a capacitor at the start of each PWM period. The resulting voltage ramp can be added to the back EMF signal and combined as a feed forward term to modify the current PWM period up or down. Thus both supply variation and back EMF changes substantially instantly adjust the PWM period and hence voltage applied to the coil, resulting in rapid adjustment of coil current to follow the demanded value.

Embodiments of the invention control the motor in a number of different ways, without the need for current sensors in the coil subset, as described below.

Open-loop voltage control

With open loop voltage control, embodiments of the invention include a control device that is pre-programmed with the motor characteristics. Embodiments of the invention may be hard wired into the circuitry, with the use of appropriate logic and software, or with a suitable pre-programmed chip.

The characteristics are stored in the form of specific values, specific relationships, specific constants and a multi dimensional look up table of instant by instant values.

The specific values comprise the motor coil resistance, transistor volt drop, diode volt drop, etc.

Specific relationships comprise the motor inductance variation with rotor angle, magnet flux variation with temperature, coil resistance with temperature, motor torque constant variation with torque, transistor and diode volt drop variation with temperature etc.

The values stored in the multi dimensional look up table are specific voltage waveforms for rising and falling quadrants, as well as the different stored waveforms required depending upon whether the motor is operating in the generating or regenerative braking mode. These voltage values are complex values based on motor type, measured back emf versus rotor angle, together with adjustments made to compensate for rotor speed and coil inductance variations with rotor angle. The battery supply voltage level is a dynamic variable also used in computing the instantaneous required voltage.

Thus in this preferred embodiment there is no sensor input other than rotor angle position. In particular, there are no current sensors. In this way embodiments of the invention are able to determine what voltage needs to be applied to the coil based on the torque required from the motor by the user without the need for current sensing apparatus in the coil. This embodiment has the advantage that a current sensor is not needed for each coil subset. In particular, for electric motors with a large number of phases, it is particularly advantageous to not need current sensing apparatus in each coil. This avoids the need for additional hardware which reduces the efficiency of the motor and necessarily increases its weight.

Partly derived and partly measured back emf

The second method of motor control without current sensors in the coil-subsets is the derived and partly measured back emf embodiment. In this embodiment, the back emf is determined by the following method.

With rotor angle position information along with the supply voltage and knowledge of the motor coil inductance etc, it is possible to derive back emf by measuring the voltage across the coil at suitable instants. The voltage across the coil without the influence of back emf would be the supply volts (during a pwm on period). However, the back emf is present when the motor is rotating and this adds to or subtracts from the measured voltage. Therefore, at any instant it is possible to determine back emf and taking account of the instantaneous speed, the period of the applied voltage can be adjusted to suit the demanded torque

This allows the controller to adjust the pulse of the pulsed applied voltage in response to the back EMF without the need for an additional current sensor.

This embodiment has the advantage that additional current sensors are not required in each coil subset. Since the current in each coil sub set must be individually determined, this embodiment avoids the need for additional current sensors for each of the subsets.

Embodiments of the invention use appropriate logic and may be implemented in software or hard wired into an electric motor or can be embodied in a chip.

This is particularly advantageous in the case of a 24-phase motor as shown in figures 12 and 13, because of the large number of coil subsets. Embodiments of the invention avoid the need for current monitoring apparatus for each of the coil subsets.

In a further example, a sense coil can be provided. Sense coils can be provided around, for example, a sub-set of coil teeth of the kind described below. The sense coil then can be monitored at appropriate times for the back EMF voltage. This in turn can be used in a similar manner as described above to feed forward a term to adjust PWM period in mid-cycle, response to the magnitude of the back EMF.

In embodiments where each drive module generates its own PWM signal, back EMF correction thus can take place in a manner which is not synchronised with the other modules resulting in a distributed random spread spectrum.

Alternatively the control devices can have their PWM generators synchronised by an off board device such as the common control device 92.

The control device can also optionally include means for monitoring a temperature within the motor, for example within the coils sub-set associated with that control device 80. The control device can be configured automatically to respond to the temperature measurement to, for example, reduce power to the coils sub-set to avoid overheating. Alternatively, the temperature measurement can be passed onto the common control device 92 from each control device 80, whereby the common control device 92 can . monitor the overall temperature within the motor and adjust the operation of the control devices 80 accordingly.

Noise Reduction

In accordance with an embodiment of the invention, EMI noise can be reduced by providing for staggered switching of the switches within each control device 80. By including a slight delay between the switching of the various switching devices in the motor, a situation can be avoided in which a large number of switching events occur in a short amount of time, leading to a peak in EMI noise. Thus, the staggering of the switching within the switches 88 of the control devices 80 can spread the EMI noise associated with the switching events during operation of the motor across a wider time period thereby avoiding an EMI noise peak. This kind of spreading of the switching events can be coordinated locally at the individual control devices 80 or could alternatively be coordinated by the common control device 92 using adjusted timing signals sent via the interconnections 90.

Power Supply

Although the control devices 80 described in this application can provide individual power control for the coils of each coil sub-set in a motor, and although this may be achieved using various kinds of switching devices and arrangements, the control device system cells can be coupled to a common power source such as a DC power supply. A particularly useful arrangement for the DC power supply is to provide a circular bus bar. Because the control circuit 80 are arranged in a ring, the DC power feed may also be arranged as a ring. This provides increased safety in that there is a current path around each side of the ring (in the same way as a domestic ring main) and so breakage of the DC supply at one point will not prevent power reaching the control circuits. In addition, because current can flow from the source power supply to each control circuit by two routes through the circular bus bar, the current demand on the bus bar is halved.

Braking Arrangement

A number of the features already described provide a significant advantage when implemented in a motor within a vehicle wheel in providing a safe mechanism for applying a braking force and thereby avoid the need for a separate mechanical braking arrangement. The motor itself can provide the braking force and thereby return energy to the power supply, such that this arrangement may be termed "regenerative" braking. When operating in this mode, the motor is acting as a generator.

The braking arrangement makes use of the considerable redundancy built into the motor assembly as a whole. The fact that each separate coil sub-set 44, shown in Figures 16 and 17, is independently controlled by a switching circuit 80 means that one or more of the switching circuits may fail without resulting in a total loss of braking force. In the same way that the motor is able to operate with reduced power when providing a driving force by intentionally switching some of the switching circuits to be inoperable, the motor can operate with a slight reduction in braking force if one or more of the switching circuits fail. This redundancy is inherent in the design already described but makes the motor a very effective arrangement for use in a vehicle, as it can replace both the drive and braking arrangement.

A further reason why the motor assembly can provide an effective braking arrangement is in relation to the handling of power. As already mentioned, the use of multiple independently controlled coils means that the current through each coil when operating in a generating mode need not be as high as the current through an equivalent arrangement with fewer phases. It is, therefore, simpler to deliver the power generated by the coils back to the power source.

To ensure safe operation of the braking arrangement, even in the event of failure of the power source, the circuitry 80 for each individual coil sub-set is itself powered by an electricity supply derived from the wheel itself. As the wheel rotates, it generates a current as the magnets pass the coils. If the power supply fails, this current is used to supply power to the switches 80.

A further redundancy measure is in providing separate physical sensors connected to the brake pedal (or other mechanical brake arrangement) of the vehicle, one sensor for each wheel. For example, in a typical four-wheeled car, four separate brake sensor arrangements would be physically coupled to the brake pedal with four separate cables going to the four separate motors. Accordingly, one or more of these separate electrical sensors connected to the mechanical brake pedal or, indeed, the separate cables could fail and still one or more of the wheels will be controlled to operate a braking force. By virtue of the ability of the control units to communicate with each other, software features allow the failure of any sensor or it's cable to have no effect on the motor operation. This is achieved by each motor being able to arbitrate the sensor information and use the sensor data from the other motors if it's sensor data is disparate with the other three sensors.

A yet further redundancy measure is the use of a so-called dump resistor. In the event of failure of the power supply, the energy generated by the wheel, when providing a braking force, needs to be dissipated. To do this, a resistance is provided through which the electrical power generated by the wheel may be dissipated as heat. The use of the multiphase design with separate electrical switching of each sub-coil allows the use of distributed resistance, so that each sub-coil may dissipate its power across a resistance and the dump resistance as a whole may therefore be distributed around the wheel. This ensures that the heat thereby generated can be evenly dissipated through the mass of the wheel and the cooling arrangement.

Referring again to Figure 20, the mode of operation of the switch 80 for each coil sub-set 44 is as follows when in a braking mode. The upper switches 88A and 88B are opened and switch 88C operated in on / off pwm mode to control the voltage generated by the coil. As the magnet passes the coil sub-set 44, the voltage at connection point 83 rises. When the switch 88C is then opened as part of the pwm process, the voltage at point 83 rises to maintain the coil current and so energy is returned to the power supply (via the diode across switch 88B). This arrangement effectively uses the coils of the motor itself as the inductor in a boost form of DC-to-DC converter. The switching of the controls in the H bridge circuit controls the DC voltage that is provided back to the power source.

The boost type dc / dc converter switching strategy employed for regenerative braking has a further distinct advantage in that it reduces battery loading. In known systems regenerative mode operates by switching the top switches to provide the battery volts in series with the motor coil and its back emf. This requires the current to be established through the battery. Hence even though the coil is generating, it depletes the battery state of charge by virtue of its current having to flow through the battery in the discharge direction. By employing the DC-to DC converter arrangement described above, the coil establishes its current locally by an effective short circuit across the coil, created by the bottom switches. When the generated current is established it is then directed back to the battery in the charge direction. So whilst both regimes collect the transient energy when the bottom switch turns off in the normal pwm sequence, the conventional system consumes battery current whilst establishing the generated current flow, whereas the arrangement here described consumes no battery current. When the voltage generated by the coil falls below say four volts, the current can no longer flow due to the voltage dropped across the switches or diodes used within the H bridge circuit. In the embodiment, a voltage of approximately 1.75 volts per mile per hour is generated and so at speeds below 3 miles per hour, this situation arises. At this speed, the switching strategy changes to a form of DC plugging. In DC plugging the phase of all voltages is arranged to be the same. This common phase of all voltages results in the removal of rotation force and the application of a static force. The static force attempts to hold the rotor in one position. Thus normal pwm control is used but with each coil subset having it's applied voltage in phase with all others. This DC mode of operation is particularly beneficial at low speeds, as it ensures safe stopping of the vehicle. When the vehicle has come to a complete rest, the vehicle will stay at rest, as any movement of the rotor is resisted by the static field. There is thus no risk that the motor would accidentally move forwards or backwards.

The dump resistor arrangement already described may also be used in the event that the battery is simply full and energy needs to be dissipated when braking. If the voltage across the supply goes over a given threshold then energy may be switched to the dump resistor.

Embodiments of this invention can provide a highly reliable motor or generator, at least in part due the separateness of the power control for the coil sub-sets as described above. Accordingly, a motor or generator according to this invention is particularly suited to applications in which a high degree of reliability is required.

A further safety feature, particularly beneficial when incorporated in a vehicle, is that the motor can supply power not only to the switches within the motor, but also to remote aspects of a whole system, including a master controller processor, shown as common control device 92, in Figure 21 , and to other sensors, such as the break pedal sensor. In this way, even if there is a total failure of power supply within the vehicle, the braking arrangement can still operate.

For example, applications such as wind turbines depend for their success and take up on cost and reliability. Typical turbine systems will run for 25 years and ideally should require minimum in service down time for maintenance / breakdown etc. By incorporating the drive electronics into a compact form with compact windings, as can be achieved according to an embodiment of this invention, the total system cost can be minimised. In accordance with an embodiment of this invention, independent power control of the coil sub-sets can allow continued operation even under partial failure the system.

In particular vertical axis turbines which are recently growing in popularity due to their efficient operation can benefit from the incorporation of a motor according to this invention. This is because of the high power to weight ratio which can be achieved, which allows for lower mast head mass and hence less cost for support column / structure.

Military, marine aircraft and land based drive systems are all currently less reliable than would be desired due to the dependence on single device reliability in classic 3 phase bridge topologies. Again, using a motor according to an embodiment of this invention, the reliability of such vehicles could be improved.

It will be clear from the foregoing description that electric motors generally include a complex arrangement of interconnections and windings. As described above, the manufacture of an electric motor incorporating such features is a laborious and time consuming process. The time and effort which is required to construct an electric motor is generally exacerbated by the use of, for example, copper wire for the windings and interconnections. Wire of this kind is often relatively thick (in order to be able to handle high currents) and is difficult to manipulate. Damage to electric insulation provided on the wire can be difficult to avoid during motor construction, again due to the difficulty in manipulating the wire. Access to the relevant parts of a motor for installing the windings and interconnections is often limited and inhibited by other components of the motor.

It will be clear from the foregoing that embodiments of this invention are applicable to electric generators as well as to electric motors, due in part to the structural and conceptual similarity between the two. For example, an electric generator can benefit from separate power termination of the coils of a coils subset as described above. Furthermore, the coil mounting system described above is equally applicable to the construction of the arrangement of coils in a generator and a motor.

C: VEHICLE WITH IN-WHEEL MOTOR BRAKE

The invention relates to electric vehicles and electric motors, and in particular electric vehicles of the type using in-wheel electric motors.

BACKGROUND OF THE INVENTION

Vehicles using in-wheel electric motors are known. The challenge in recent years has been to develop electric motor technology to provide greater power and efficiency to extend the speed, acceleration and range of electric vehicles. Various designs of in-wheel electric motor are known, including multiphase designs. A known three phase design will first be briefly described by way of background.

Figure 22 shows a schematic representation of a typical three phase motor. In this example, the motor includes three coil sets. Each coil set produces a magnetic field associated with one of the three phases of the motor. In a more general example, N coil sets can be used to produce an N-phase electric motor. Each coil set can include one or more sub-sets of coils which are positioned around a periphery of the motor. In the present example, each coil set includes four such sub-sets - the coil sub-sets of each coil set are labelled 14, 16 and 18, respectively in Figure 22. As shown in Figure 22, the coil sub-sets 14, 16, 18 are evenly distributed around the motor 10 to co-operate in producing a rotating magnetic field within which a central rotor 12, which typically incorporates one or more permanent magnets, can rotate as shown by the arrow labelled C. The coil sub-sets of each coil set are connected together in series as shown by the connections 24, 26 and 28 in Figure 22. This allows the currents in the coils of each coil set to be balanced for producing a substantially common phase. The wires of each coil set are terminated as shown at 34, 36 and 38 in Figure 22. Typically, one end of the wire for each coil set is connected to a common reference terminal, while the other wire is connected to a switching system for controlling the current within all of the coils of that coil set. Typically then, current control for each coil set involves controlling a common current passing through a large number of coils. As shown in Figure 23, each coil sub-set can include one or more coils.

In particular, Figure 23 shows the coils 24A, 24B in one of the coil sub-sets 14. In this example, there are two coils per coil sub-set. For a three phase electric motor, the switching system is almost invariably a three phase bridge circuit including a number of switches. Typical power electronic switches including the Metal Oxide Silicon Field Effect Transistor (MOSFET) and the Insulated Gate Bipolar Transistor (IGBT) exhibit two principal losses: switching losses and conduction losses.

While switching losses decrease with switching speed, a faster switching speed also leads to increased electromagnetic interference (EMI) noise. This problematic trade off between switching speed and EMI noise is compounded at higher power ratings (e.g. for a larger motor), since larger switches are required. The inductance associated with a power switch and its connection system increases with the physical size of the switch. This inductance impacts the switching speed of the power device and the switching speed of a power device is typically therefore limited by its physical size. Accordingly, for high power ratings larger switches must be used, but larger switches involve slower switching speeds and therefore larger switching losses. Moreover, the cost of a power device increases roughly with the square of the size of the device. Conduction losses also increase with increased power.

Including switching losses and conduction losses, the total losses are approximately proportional to the square of the power. This imposes serious thermal management problems for the motor since, for example, a doubling of the power leads to a four fold increase in thermal losses. Extracting this heat without elevating the temperature of the device above its safe operating level becomes the limiting factor in what power the device can handle. Indeed, today larger power devices having intrinsic current handling capabilities of, for example, 500A are restricted to 200A due to thermal constraints.

Consider a conventional three phase motor with a given power rating. If a larger power rating is desired, this can be achieved by producing a motor with a larger diameter. For a larger motor diameter, the peripheral speed of the rotor increases for a given angular velocity. For a given supply voltage this requires that the motor coils to have a reduced number of turns. This is because the induced voltage is a function of the peripheral speed of the rotor and the number of turns in the coils. The induced voltage must always be at or below the supply voltage. However, the reduced number of turns in the coils leads to a reduced inductance for the motor, since the inductance of the motor is proportional to the square of the number of turns.

Almost all electronic control units for electric motors today operate by some form of pulse width modulation (PWM) voltage control. PWM control works by using the motor inductance to average out an applied pulse voltage to drive the required current into the motor coils. Using PWM control an applied voltage is switched across the motor windings for a minimum period dictated by the power device switching characteristic. During this on period, the current rises in the motor winding at a rate dictated by its inductance and the applied voltage. The PWM control is then required to switch off before the current has changed too much so that precise control of the current is achieved.

As discussed above, the use of larger power devices leads to a slower switching speed, while a larger motor also has a lower inductance. For higher power motors, these two factors inhibit the effectiveness of PWM as a control system because the current in the motor coils rises more rapidly (due to the low inductance of the motor due to the fewer number of turns in the coils) but the PWM control is more coarse (due to the slow switching speed achievable using high power switching devices).

A known solution to this problem is to introduce additional inductance in the motor in the form of current limiting chokes in series with the motor windings. This added inductance increases the rise time of the current in the motor coils. However, the chokes are typically as large or larger than the motor itself and as they carry the full current they dissipate a large additional heat loss as well as being a substantial extra volume, weight and cost.

In all such known motor arrangements, development effort has been concentrated on providing higher power for acceleration and low losses for greater vehicle range from a given battery source. SUMMARY OF THE INVENTION

We have appreciated that in-wheel electric motors may also be used to provide a braking torque and, furthermore, that an in-wheel electric motor can provide the full braking torque needed for a vehicle without the need for additional mechanical braking. The invention resides first in the appreciation that an in- wheel electric motor can provide the full braking torque needed by a vehicle. Also, the invention resides in the appreciation that, to provide full braking torque, an in-wheel electric motor must be able to convert high transient power loads into electricity and be able to deliver this back to a source or load. The invention further resides in an arrangement which allows high power to be converted into electrical current by an in-wheel motor without producing high transient currents.

The invention is defined in the accompanying independent claims, with preferred features set out in the dependent claims.

An embodiment of the invention uses a combination of techniques by which the kinetic energy of a vehicle may be converted to electrically power in an in-wheel motor without producing currents beyond the capabilities of the electrically system including coils, switched and power connections. The invention is applicable to electric vehicles such as cars with 4 in-wheel electric motors (one per wheel), capable of high speed travel at speeds in excess of 60Mph. The embodiment of the invention is capable of producing a braking force that delivers in excess of 20OkW of power over a few seconds, thereby decelerating a vehicle of mass on the order 1.5 tons from 60Mph in around 5 seconds. A motor embodying the invention is capable of such power conversion and yet only has a mass of the order 30Kg.

The motor includes one or more separate coil sets arranged to produce a magnetic field of the motor. Each coil set includes a plurality of coil sub-sets. Each coil sub-set includes one or more coils. The magnetic field produced by the coils in each coil set have a substantially common phase. The motor also includes a plurality of control devices each coupled to a respective coil sub-set for controlling a current in the coils of that respective coil sub-set. The electric motor embodying the invention uses a new technique of coil switching for the purpose of avoiding high transient currents. The control devices can include one or more switches for applying a pulsed voltage to the one or more coils of a coil sub-set. Pulse width modulation (PWM) control of the currents in the motor coils can be enhanced due to the increased number of turns which can be included in the coils. Because smaller switching device can be used, significant savings in cost, weight and heat dissipation can be made. The new technique of switching involves staggering the switching of the switches so that switching pulses of a coil are staggered in relation to switching pulses of other coils. The staggering of the pulses is such that the currents received from each of the coils has peaks and troughs of waveform at different times, thereby summing to an approximately DC current with a ripple rather than high peaks and troughs.

Control of the currents in the coils of the motor is further enhanced because the current in each coil sub-set can be controlled independently of the current in another coil sub-set. Because all of the coils of each coil set are not connected in series, the coil or coils of each coil sub-set can have a larger number of turns. The increased number of turns in each coil increases the overall inductance of the motor. This means that lower currents can be used in the coils of each coil sub-set, which leads to fewer heat dissipation problems, and which allows smaller switching devices to be used. The use of smaller switching devices in turn allows for faster switching speeds and lower switching losses.

Some of the control devices can include means for monitoring a back

EMF within the coils of that coil sub-set. The control device can adjust a pulse of the pulsed voltage (e.g. a width of the pulse) in response to the monitored back EMF for high speed power control.

Since smaller components (e.g. switching devices) can be used, they can be housed within a casing of the motor, in contrast to known systems using large, bulky switching devices. For example, the control devices can be located adjacent their respective coil sub-sets within the motor thereby simplifying termination of the coil windings. The casing of the motor can include one or more apertures dimensioned such that the control devices can be accessed one at a time, depending on the orientation of the rotor/casing and the control devices. The electric motor is thus operable in a braking mode. In the braking mode control devices coupled to a respective coil sub-set for controlling a current in the one or more coils of the respective coil sub-set are operable by current drawn from the coils. Since the control devices can operate from current drawn from the coils, a fail-safe braking arrangement is provided as the control devices can continue to operate (and thereby control braking) even in the event of failure of the power supply. Preferably, each control device is arranged so that it is operable from current from one sub-set of coils when in a braking mode. This ensures that there is redundancy built into the braking arrangement, as, in the event of failure of a coil, other coils and control devices would still be operable to provide a braking force.

The motor preferably also includes a capacitance coupled between the coils and a connection for a power supply. The capacitance ensures that current can continue to be supplied to the control devices when a transition occurs between a power consuming mode and non-power consuming mode. The motor also includes a resistance selectively coupled to the control devices such that in an emergency braking mode power from the coils may be consumed by the resistance. An emergency braking mode is one in which a power supply is unable to receive power from the coils, for example, because the power supply such as a battery has failed, a battery is full or a connection has failed. The resistance is preferably arranged very close to the control devices and coils thereby reducing the risk of connection failure.

The embodiment of the invention is a motor comprising a cooling arrangement. The motor includes a plurality of coils arranged around a circumference and a cooling channel disposed immediately adjacent the plurality of coils through which a coolant fluid may be pumped. Circulated - gives the option of convective flow. Key point here is the multi faceted cooling plate. It encloses the windings on three sides and provides faces for the attachment of the electronic power devices, the dump power devices and the dump resistor. In fact another key point is that the stator assembly comprising the coils, teeth and back iron is assembled directly onto the cooling plate. The assembly is then potted onto the cooling plate using thermally conductive material - epoxy filled with aluminium oxide or aluminium nitride or carbon for example. This potting process is important due to the mechanical integrity imparted to the whole assembly - all parts are as one and more able to withstand vibration and shock. The potting further improves the electrical strength of the insulation system in that it prevents any air pockets within the winding system. Because of the high switching speeds dv/dt is high and this induces electrical stress in the insulation medium of the windings. Air pockets would risk ionization and lead to early failure of the insulation. In electronically controlled motors or generators this insulation breakdown brought on by the repeated electrical stress induced through the switching events is a major reliability issue - potting reduces this risk by a very large degree. Potting is best done under vacuum, but low viscosity potting material can be used in atmospheric pressure. The potting is of critical value in improving the thermal conductivity between the heat generating windings and laminations and the heat sinking cooling plate with it's cooling fluid inside. The potting is further of great benefit in that it allows the winding system to be fully immersed in water with no risk of electrical failure. This is important due to the need to make the electrical system immune to condensation or other water ingress.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same may be carried into effect reference is now made by way of example to the accompanying drawings in which:

Figure 22 schematically shows an example arrangement for a three phase motor;

Figure 23 schematically shows the arrangement of coils in one of the coil sub-sets shown in Figure 22;

Figure 24 is an exploded view of a motor embodying the invention; Figure 25 is an exploded view of the motor of Figure 24 from an alternative angle;

Figure 26 schematically shows an example coil arrangement for a three phase motor according to an embodiment of this invention;

Figure 27 schematically shows an example arrangement of coils in one of the coil sub-sets shown in Figure 24 according to an embodiment of the invention; Figure 28 schematically shows schematically shows an example arrangement for a three phase motor according to an embodiment of this invention;

Figure 29 schematically shows an example arrangement of coils in one of the coil sub-sets shown in Figure 7 according to an embodiment of the invention; Figure 30 schematically shows the coils of the embodiment in relation to the magnets;

Figure 31 schematically shows an example of a control device in accordance with an embodiment of this invention;

Figure 32 is a circuit diagram of the switching arrangement; and Figure 33 schematically shows an arrangement in which a common control device is used to coordinate the operation of a plurality of control devices.

DETAILED DESCRIPTION

The embodiment of the invention described is an electric vehicle and an electric motor for use in a wheel of a vehicle. The motor is of the type having a set of coils being part of the stator for attachment to a vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel. The vehicle is operable in a braking mode in which the electric motors provide the full braking torque.

The physical arrangement of the embodying assembly is best understood with respect to Figures 24 and 25. The assembly can be described as a motor with built in electronics and bearing, or could also be described as a hub motor or hub drive as it is built to accommodate a separate wheel.

Referring first to Figure 24, the assembly comprises a stator 252 comprising a rear portion 230 forming a first part of the housing of the assembly, and a heat sink and drive arrangement 231 comprising multiple coils and electronics to drive the coils as well as a heat sink. The coil drive arrangement 231 is fixed to the rear portion 230 to form the stator 252 which may then be fixed to a vehicle and does not rotate during use. The coils themselves are formed on tooth laminations 235 which together with the drive arrangement 231 and rear portion 230 form the stator 252. A rotor 240 comprises a front portion 220 and a cylindrical portion 221 forming a cover, which substantially surrounds the stator 252. The rotor includes a plurality of magnets 242 arranged around the inside of the cylindrical portion 221. The magnets are thus in close proximity to the coils on the assembly 231 so that magnetic fields generated by the coils in the assembly 231 generate a force on the magnets 242 arranged around the inside of the cylindrical portion 221 of the rotor 240 thereby causing the rotor 240 to rotate.

The rotor 240 is attached to the stator 252 by a bearing block 223. The bearing block 223 can be a standard bearing block as would be used in a vehicle to which this motor assembly is to be fitted. The bearing block comprises two parts, a first part fixed to the stator and a second part fixed to the rotor. The bearing block is fixed to a central portion 233 of the wall 230 of the stator 252 and also to a central portion 225 of the housing wall 220 of the rotor 240. The rotor 240 is thus rotationally fixed to the vehicle with which it is to be used via the bearing block 223 at the central portion 225 of the rotor 240. This has a significant advantage in that a wheel rim and tyre can then be fixed to the rotor 240 at the central portion 225 using the normal wheel bolts to fix the wheel rim to the central portion of the rotor and consequently firmly onto the rotatable side of the bearing block 223. The wheel bolts may be fitted through the central portion 225 of the rotor through into the bearing block itself. The rotor also includes a focussing ring and magnets 227 for position sensing discussed later.

Figure 25 shows an exploded view of the same assembly as Figure 24 from the opposite side showing the stator 252 comprising the rear stator wall 230 and coil and electronics assembly 231. The rotor 240 comprises the outer rotor wall 220 and circumferential wall 221 within which magnets 242 are circumferentially arranged. As previously described, the stator 252 is connected to the rotor 240 via the bearing block at the central portions of the rotor and stator walls.

Additionally shown in Figure 24 are circuit boards 80 carrying control electronics described later. Due to their kite shape these circuit boards can be referred to as kite boards. Additionally in Figures 24 and 25 a V shaped seal 350 is provided between the circumferential wall 221 of the rotor and the outer edge of the stator housing 230, again described in detail later. Further, in Figure 25, a magnetic ring 227 comprising a commutation focusing ring and a plurality of magnets is provided for the purpose of indicating the position of the rotor with respect to the stator to a series of sensors arranged on the circuit boards 80 of the stator 252. This is also described in greater detail later.

Figure 26 schematically shows an example of an electric motor in accordance with an embodiment of this invention. In this example, the motor is generally circular.

The motor 40 in this example is a three phase motor. Again, it will be appreciated that motors according to this invention can include an arbitrary number of phases (N = 1 , 2, 3...). Being a three phase motor, the motor 40 includes three coil sets. In this example, each coil set includes two coil sub-sets. The coil sub-sets of each coil set are labelled 44, 46 and 48, respectively. The coil sub-sets 44, 46 and 48 are arranged around a periphery of the motor 40. In this example, each coil sub-set is positioned opposite the other coil sub-set in that coil set, although such an arrangement is not strictly essential to the working of the invention. Each coil sub-set includes one or more coils, as described below in relation to Figure 27.

The motor 40 can include a rotor (not shown in Figure 26) positioned around the coils as previously disclosed in Figures 24 and 25. The rotor may typically comprise one or more permanent magnets arranged to rotate such that their poles sweep across the ends of the coils of the motor 40. Appropriate switching of currents in the coils of the coil sub-sets allows synchronized attraction and repulsion of the poles of the permanent magnet of the rotor to produce the rotating action of the motor 40. It will be appreciated that Figure 26 is highly schematic and, in practice, the coil sub-sets will be arranged at the outer periphery of the stator with the rotor magnets surrounding the coils.

Each coil set 44, 46, 48 includes one or more coils. As shown in Figure 27, in the present example, there is a single coil per coil sub-set. An example with more than one coil per coil sub-set is described below in relation to Figures 28 and 29. Where more than one coil is provided in a given coil sub-set, these coils can generally be wound in opposite directions such that the magnetic field produced by each coil is in an anti-parallel configuration with respect to the magnetic field in an adjacent coil. As described above, appropriate switching of the current in the coils causes the permanent magnets of the rotor to rotate.

As shown in Figure 26, in accordance with an embodiment of this invention, the coil or coils of each coil sub-set can be connected to a separate control device 80. In Figure 26, it is schematically shown that each coil sub-set is connected to the terminals 54, 56, 58 of respective control devices 80.

Accordingly, the coils of corresponding coil sub-sets within a given coil set are not connected in series. Instead, each coil sub-set is individually controlled and powered. The connections to the control device and the coils of each coil sub-set can be formed using, for example, a single piece of wire (e.g. copper wire) as is shown schematically in Figure 27. There are numerous advantageous to providing individual power control for the coils of each coil sub-set.

Another advantage of the use of smaller switching devices is that they can be located proximal the coils which they control. In prior electric motors, where relatively large switching devices have been employed to control the operation of coil sub-sets connected in series, the control device is sufficiently large that it cannot be included with the other motor components (e.g. stator, rotor, etc.) but instead has been provided separately. In contrast, since small switching devices can be used, in accordance with an embodiment of this invention the switching devices and the control devices in which those switching devices are incorporated can be located in, for example the same housing/casing as the other motor components. Further detail regarding an example of a control device incorporating switching devices is given below in relation to Figures 31 and 32.

Figures 28 and 29 show another example arrangement for a motor 40 in accordance with an embodiment of this invention. The motor 40 shown in Figure 5 is a three phase motor. The motor therefore has three coil sets. In this example, each coil set includes eight coil sub-sets. The coil sub-sets of each coil set are labelled 44, 46 and 48, respectively in Figure 28. In common with the example described above in relation to Figure 26, each coil set includes pairs of coil sub-sets which are arranged opposite each other around the periphery of the motor 40. Again, however, it should be noted that there is no express need for each coil sub-set to have a corresponding coil sub-set located opposite from it on the opposite side of the periphery of the motor 40.

As described above in relation to Figure 28, each coil sub-set can be connected to a respective control device 80. The terminals for each coil sub-set of each coil set are labelled 54, 56 and 58, respectively in Figure 28. While the arrangement shown in Figure 28 includes a larger number of coil sub-sets than, for example, the arrangement shown in Figure 24, this does not significantly increase the size and bulk of the switching means which are used to operate the motor, as would be the case if the increased number of coil sub-sets were connected together in series. Instead, it is merely necessary to provide an additional control device 80 incorporating relatively small switching devices as described above for each additional coil sub-set. As described above, these control devices 80 are sufficiently small such that they can be located adjacent to their corresponding coil sub-sets within, for example, the same casing as the motor 40.

As described above, each coil sub-set can include one or more coils. In this example, each coil sub-set includes three coils as is shown schematically in Figure 29. In Figure 29, these three coils are labelled 74A, 74B and 74C. The three coils 74A, 74B and 74C are alternately wound such that each coil produces a magnetic field which is anti-parallel with its adjacent coil/s for a given direction of current flow. As described above, as the permanent magnets of the rotor of the motor 40 sweep across the ends of the coils 74A, 74B and 74C₁ appropriate switching of the currents in the coils can be used to create the desired forces for providing an impulse to the rotor. As is shown schematically in Figure 27, each coil in a coil sub-set can be wound in series.

, The reason that the coils 74A, 74B and 74C within each subset are wound in opposite directions to give antiparallel magnetic fields can be understood with respect to Figure 30 which shows the arrangement of the magnets 242 on the rotor surrounding the coils 44, 46 and 48 of the stator. For simplicity, the arrangement is shown as a linear arrangement of magnets and coils, but it will be understood that in the embodiment of the invention described the coils will be arranged around the periphery of the stator with the magnets arranged around the inside of the circumference of the rotor, as already described.

As shown schematically in Figure 30, the ratio of magnets to coils is eight magnets to nine coils. The advantage of this arrangement is that the magnets and coils will never perfectly align. If such perfect alignment occurred, then the motor could rest in a position in which no forces could be applied between the coils and the magnets to give a clear direction as to which sense the motor should turn. By arranging for a different number of coils and magnets around the motor, there would always be a resultant force in a particular direction whatever position the rotor and motor come to rest.

A particular benefit of the independent control of the coil subsets by the separate control devices is that a larger than normal number of phases can be arranged. For example, rather than a three phase motor, as described in Figure 28, higher numbers of phases such as twenty-four phase or thirty-six phase are possible with different numbers of magnets and coils. Ratios of coils to magnets, such as eighteen coils to sixteen magnets, thirty-six coils to thirty-two magnets and so on, are perfectly possible. Indeed, the preferred arrangement, as shown in Figures 24 and 25 is to provide 24 separate control "kite" boards 80, each controlling three coils in a sub-set. Thereby providing a twenty-four phase motor. The use of a multiphase arrangement, such as twenty-four phases, provides a number of advantages. The individual coils within each sub-set can have a larger inductance than arrangements with lower numbers of phases because each control circuit does not have to control large numbers of coils (which would require controlling a large aggregate inductance). A high number of phases also provides for lower levels of ripple current. By this it is meant that the profile of the current required to operate the motor undulates substantially less than the profile from, say a three-phase motor. Accordingly, lower levels of capacitance are also needed inside the motor. The high number of phases also minimise the potential for high voltage transients resulting from the need to transfer large currents quickly through the supply line. As the ripple is lower, the impact of the supply cabling inductance is lower and hence there is a reduction in voltage transient levels. When used in a braking arrangement (described later), this is a major advantage, as in hard braking conditions, several hundred kilowatts need to be transferred over several seconds and the multiphase arrangement reduces the risk of high voltage transients in this situation.

The relative arrangement of magnets and coils, shown in Figure 30 can be repeated twice, three times, four times or indeed as many times as appropriate around 360 mechanical degrees of the rotor and stator arrangement. The larger the number of separate sub-sets of coils with independent phases, the lower the likelihood of high voltage transients or significant voltage ripple.

In accordance with an embodiment of this invention, a plurality of coil subsets with individual power control can be positioned adjacent each other in the motor. In one such example, three coils such as those shown in Figure 29 could be provided adjacent each other in a motor but would not be connected in series to the same control device 80. Instead, each coil would have its on control device 80.

Where individual power control is provided for each coil sub-set, the associated control devices can be operated to run the motor at a reduced power rating. This can be done, for example, by powering down the coils of a selection of the coil sub-sets. Figure 31 shows an example of a control device 80 in accordance with an embodiment of this invention. As described above, the control device 80 includes a number of switches which may typically comprise one or more semiconductor devices. The control device 80 shown in Figure 31 includes a printed circuit board 82 upon which a number of components are mounted. The circuit board 82 includes means for fixing the control device 80 within the motor, for example, adjacent to the coil sub-set which it the controls - directly to the cooling plate. In the illustrated example, these means include apertures 84 through which screws or suchlike can pass. In this example, the printed circuit board is substantially wedge-shaped. This shape allows multiple control device 80 to be located adjacent each other within the motor, forming a fan-like arrangement.

In the example shown in Figure 31, the control device 80 includes a number of switches 88. The switches can include semiconductor devices such as MOSFETs or IGBTs. In the present example, the switches comprise IGBTs. Any suitable known switching circuit can be employed for controlling the current within the coils of the coil sub-set associated with the control device 80. One well known example of such a switching circuit is the H-bridge circuit. Such a circuit requires four switching devices such as those shown in Figure 31. The wires (e.g. copper wires) of the coil sub-sets can be connected directly to the switching devices 88 as appropriate, and interconnections between the switching devices 88 can be formed on the printed circuit board 82. Since the switching devices 88 can be located adjacent the coil sub-sets as described above, termination of the wires of the coil sub-sets at the switching devices 88 is made easier.

As shown in Figure 32, the control device includes semiconductor switches arranged in an H-bridge arrangement. The H-bridge is of course known to those skilled in the art and comprises four separate semiconductor switches 88 connected to a voltage supply (here 300 volts) and to ground. The coils of each sub-coil are connected across the terminals 81 and 83. Here a sub-coil 44 is shown connected across the terminals. Simplistically, to operate the motor and supply a voltage in one direction, switches 88A and 88D are closed and the other switch is left open, so that a circuit is made with current in one direction. To operate the motor this current direction is changed in harmony with the alternating magnetic polarity passing the coil. To change the direction of rotation of the motor, the timing and polarity of the current flow in the coil is changed to cause the resulting forces in the opposite direction. The direction of current flow in the coil is reversed when switches 88B and 88C are closed and the other two switches are left open. In practice, the technique of pulse width modulating is used to pulse width modulate the signal applied to the gate of the semiconductor switches to control the voltage applied to the coils. The braking arrangement operates in a manner not known in the prior art and will be described after describing the overall control arrangement.

As shown in Figure 33, a common control device 92 can be used to coordinate the operations of the multiple control devices 80 provided in the motor. In prior motors, in which synchronization of the magnetic fields produced by the coils of each coil sub-set is automatically achieved by virtue of the fact that they are connected in series. However, where separate power control is provided for each coil sub-set, automatic synchronization of this kind does not occur. Accordingly, in accordance with an embodiment of this invention, a common control device 92 such as that shown in Figure 33 can be provided to ensure correct emulation of a polyphase system incorporating series-connected coils. As described above in relation to Figure 32, terminals 86 can be provided at the multiple control devices 80 to allow interconnections 90 to be formed between the multiple control devices 80 and the common control device 92.

A particular feature of the embodiment of the invention that allows the motor to provide the full braking torque is the use of staggered PWM switching for the purpose of current control. As already described, when operating in a motor mode, the voltage across the coils is controlled by PWM switching by the switches in control circuits 80. When in braking mode, the PWM switching is arranged so that the switches within a given wheel provide staggered switching such that the current profile delivered by each coil through the switches is offset in relation to the current profile from other switches within the wheel. As a result, the sum of such currents has an approximately DC form with a current ripple.

To achieve the staggered switching, each control device communicates with other control devices within the motor to establish a timing pattern to evenly distribute the switching over continuous rotation of the wheel. The communication may be by inter control device communication across a network. Alternatively the control devices can have their PWM generators synchronised by an off board device such as the common control device 92. A further possibility is that the timing of the switching is established with respect to some other parameter such as the position of the rotor, back EMF from the coils and so on.

It is particularly important to note that the timing pattern of the PMW switching, including a slight delay between the switching of the various switching devices in the motor, avoids peaks in current delivered to a power source in a manner not previously known. This kind of spreading of the switching events can be coordinated locally at the individual control devices 80 or could alternatively be coordinated by the common control device 92 using adjusted timing signals sent via the interconnections 90.

Although the control devices 80 described in this application can provide individual power control for the coils of each coil sub-set in a motor, and although this may be achieved using various kinds of switching devices and arrangements, the control device system cells can be coupled to a common power source such as a DC power supply. The connection may be referred to as a power connector, a DC bus, a battery connection, as supply line or the like. A particularly useful arrangement for the DC power supply is to provide a circular bus bar. Because the control circuit 80 are arranged in a ring, the DC power feed may also be arranged as a ring. This provides increased safety in that there is a current path around each side of the ring (in the same way as a domestic ring main) and so breakage of the DC supply at one point will not prevent power reaching the control circuits. In addition, because current can flow from the source power supply to each control circuit by two routes through the circular bus bar, the current demand on the bus bar is halved.

The braking arrangement makes use of the considerable redundancy built into the motor assembly as a whole. The fact that each separate coil sub-set 44, shown in Figures 28 and 29, is independently controlled by a switching circuit 80 means that one or more of the switching circuits may fail without resulting in a total loss of braking force. In the same way that the motor is able to operate with reduced power when providing a driving force by intentionally switching some of the switching circuits to be inoperable, the motor can operate with a slight reduction in braking force if one or more of the switching circuits fail. This redundancy is inherent in the design already described but makes the motor a very effective arrangement for use in a vehicle, as it can replace both the drive and braking arrangement.

A further reason why the motor assembly can provide an effective braking arrangement is in relation to the handling of power. As already mentioned, the use of multiple independently controlled coils means that the current through each coii when operating in a generating mode need not be as high as the current through an equivalent arrangement with fewer phases. It is, therefore, simpler to deliver the power generated by the coils back to the power source.

Referring again to Figure 32, the mode of operation of the switch 80 for each coil sub-set 44 is as follows when in a braking mode. The upper switches 88A and 88B are opened and switch 88C operated in on I off pwm mode to control the voltage generated by the coil. As the magnet passes the coil sub-set 44, the voltage at connection point 83 rises. When the switch 88C is then opened as part of the pwm process, the voltage at point 83 rises to maintain the coil current and so energy is returned to the power supply (via the diode across switch 88B). This arrangement effectively uses the coils of the motor itself as the inductor in a boost form of DC-to-DC converter. The switching of the controls in the H bridge circuit controls the DC voltage that is provided back to the power source.

The boost type dc / dc converter switching strategy employed for regenerative braking has a further distinct advantage in that it reduces battery loading. In known systems regenerative mode operates by switching the top switches to provide the battery volts in series with the motor coil and its back emf. This requires the current to be established through the battery. Hence even though the coil is generating, it depletes the battery state of charge by virtue of its current having to flow through the battery in the discharge direction. By employing the DC-to DC converter arrangement described above, the coil establishes its current locally by an effective short circuit across the coil, created by the bottom switches. When the generated current is established it is then directed back to the battery in the charge direction. So whilst both regimes collect the transient energy when the bottom switch turns off in the normal pwm sequence, the conventional system consumes battery current whilst establishing the generated current flow, whereas the arrangement here described consumes no battery current.

When the voltage generated by the coil falls below say four volts, the current can no longer flow due to the voltage dropped across the switches or diodes used within the H bridge circuit. In the embodiment, a voltage of approximately 1.75 volts per mile per hour is generated and so at speeds below 3 miles per hour, this situation arises. At this speed, the switching strategy changes to a form of DC plugging. In DC plugging the phase of all voltages is arranged to be the same. This common phase of all voltages results in the removal of rotation force and the application of a static force. The static force attempts to hold the rotor in one position. Thus normal pwm control is used but with each coil subset having it's applied voltage in phase with all others. This DC mode of operation is particularly beneficial at low speeds, as it ensures safe stopping of the vehicle. When the vehicle has come to a complete rest, the vehicle will stay at rest, as any movement of the rotor is resisted by the static field. There is thus no risk that the motor would accidentally move forwards or backwards.

Embodiments of this invention can provide a highly reliable motor or generator, at least in part due the separateness of the power control for the coil sub-sets as described above. Accordingly, a motor or generator according to this invention is particularly suited to applications in which a high degree of reliability is required. A further safety feature, particularly beneficial when incorporated in a vehicle, is that the motor can supply power not only to the switches within the motor, but also to remote aspects of a whole system, including a master controller processor, shown as common control device 92, in Figure 33, and to other sensors, such as the break pedal sensor. In this way, even if there is a total failure of power supply within the vehicle, the braking arrangement can still operate.

D: THREE WHEEL ELECTRIC VEHICLE

The invention relates to three wheel electric vehicles, and particularly to a vehicle with in-wheel electric motors.

BACKGROUND OF THE INVENTION

Three wheel vehicles of various types powered by electric motors are known to the skilled person. In recent years, developments in electric motors have allowed in-wheel electric motors to be proposed for use in road going three wheel vehicles. Motors of the type having a set of coils being part of the stator for attachment to a vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel are now being used in electric vehicle. These motors are sometimes referred to as "pancake" motors and may be three phase or, more recently, multiphase designs.

Three wheel electric vehicles are typically of the type having two rear wheels driven by a common axle and a tilting front wheel, the tilt angle of which is controllable by a steering wheel or by handlebars. Such vehicles are similar to motor bikes in terms of the way the vehicle is handled for cornering by both turning and tilting the front wheel in the direction of the turn.

The alternative approach uses two front wheels and a single rear wheel. This can provide better aerodynamic performance by allowing the vehicle shape to closely resemble the classic teardrop aerodynamic form, being wider at the front than at the rear. However, with such an approach it becomes much more complex to provide a tilting mechanism between the front wheels and the vehicle body to tilt the vehicle body when cornering. The disadvantage of a non-tilting three wheel configuration is instability - the vehicle will tip over in a turn before it will slide, unless the centre of mass is much closer to the ground or the wheelbase is much wider than a similar four wheel vehicle. To improve stability some three wheelers are designed as tilting three wheelers so that they lean while cornering like a motorcyclist would do. The tilt may be controlled manually or by computer. SUMMARY OF THE INVENTION

We have appreciated the desirability of improving the stability of three wheel vehicles. We have further appreciated the need to reduce weight and avoid complex tilting mechanisms.

An embodiment of the invention provides a three wheel vehicle of the type having two driven front wheels and a rear wheel, the front wheels having in wheel electric motors. The in wheel electric motors are attached to pivotable connection arms pivotably mounted to the body of the vehicle. The pivotable connection is such that the body of the vehicle may be raised or lowered by application of torque to the wheel. This allows the tilt of the body to be controlled by the independent control of torque to each driving wheel.

The embodiment of the invention significantly reduces the complexity of the steering and tilting mechanism for providing vehicle stability. The preferred embodiment is a form of suspension control system for a vehicle with each pivotable connection being a suspension arm of the vehicle and being independently powered by a respective motor. The system includes a control unit for selectively adjusting a torque applied to each wheel to apply a force to each respective suspension arm. The control unit can be operable to selectively adjust a torque applied to each wheel to apply a force to each respective suspension arm to alter a height of the vehicle.

The invention may also be embodied in a suspension control method or by a computer program for operating a suspension control method described above. The computer program for implementing the invention can be in the form of a computer program on a carrier medium. The carrier medium could be a storage medium, such as a solid state, magnetic, optical, magneto-optical or other storage medium. The carrier medium could be a transmission medium such as broadcast, telephonic, computer network, wired, wireless, electrical, electromagnetic, optical or indeed any other transmission medium. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 34 is an exploded view of a motor as used in an embodiment of the invention; Figure 35 is an exploded view of the motor of Figure 34 from an alternative angle; Figure 36 schematically shows an example arrangement for a three phase motor as used in an embodiment of the invention; Figure 37 schematically shows an example arrangement of coils in one of the coil sub-sets shown in Figure 36 as used in an embodiment of the invention; Figure 38 schematically shows the coils of the embodiment in relation to the magnets;

Figure 39 schematically shows an example of a wheel mounted on a suspension arm; and

Figure 40 schematically shows a 3 wheel vehicle embodying the invention.

DETAILED DESCRIPTION

The embodiment of the invention described is three wheel vehicle having in-wheel electric motors. The motors are of the type having a set of coils being part of the stator for attachment to a vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel.

It is of importance that the electric motors are able to provide sufficient torque to both drive the vehicle and provide control over the vehicle attitude when cornering. Accordingly, the type of motor used in the embodiment will first be described, followed by the general principles of operation of the three wheel vehicle. The in-wheel electric motors as used in the embodiment are shown in Figures 34 and 35. The assembly can be described as a motor with built in electronics and bearing, or could also be described as a hub motor or hub drive as it is built to accommodate a separate wheel.

Referring first to Figure 34, the assembly comprises a stator 252 comprising a rear portion 230 forming a first part of the housing of the assembly, and a heat sink and drive arrangement 231 comprising multiple coils and electronics to drive the coils as well as a heat sink. The coil drive arrangement 231 is fixed to the rear portion 230 to form the stator 252 which may then be fixed to a vehicle and does not rotate during use.

The rotor 240 is attached to the stator 252 by a bearing block 223. The bearing block 223 can be a standard bearing block as would be used in a vehicle to which this motor assembly is to be fitted. The bearing block comprises two parts, a first part fixed to the stator and a second part fixed to the rotor. The bearing block is fixed to a central portion 233 of the wall 230 of the stator 252 and also to a central portion 223 of the housing wall 220 of the rotor 240. The rotor 240 is thus rotationally fixed to the vehicle with which it is to be used via the bearing block 223 at the central portion 225 of the rotor 240. This has a significant advantage in that a wheel rim and tyre can then be fixed to the rotor 240 at the central portion 225 using the normal wheel bolts to fix the wheel rim to the central portion of the rotor and consequently firmly onto the rotatable side of the bearing block 223. The wheel bolts may be fitted through the central portion 225 of the rotor through into the bearing block itself. A first advantage of this arrangement is that the whole assembly may be simply retrofitted to an existing vehicle by removing the wheel, bearing block and any other components such as the braking arrangement. The existing bearing block can then fitted inside the assembly and the whole arrangement fitted to the vehicle on the stator side and the normal rim and wheel fitted to the rotor so that the rim and wheel surrounds the whole motor assembly. Accordingly, retrofitting to existing vehicles becomes very simple.

Figure 35 shows an exploded view of the same assembly as Figure 34 from the opposite side showing the stator 252 comprising the rear stator wall 230 and coil and electronics assembly 231. The rotor 240 comprises the outer rotor wall 220 and circumferential wall 221 within which magnets 242 are circumferentially arranged. As previously described, the stator 252 is connected to the rotor 240 via the bearing block at the central portions of the rotor and stator walls.

Additionally shown in Figure 34 are circuit boards 80 carrying control electronics. Due to their kite shape these circuit boards can be referred to as kite boards. Additionally in Figure 35 a V shaped seal 350 is provided between the circumferential wall 221 of the rotor and the outer edge of the stator housing 230.

Further, in Figure 35, a magnetic ring 227 comprising a commutation focusing ring and a plurality of magnets is provided for the purpose of indicating the position of the rotor with respect to the stator to a series of sensors arranged on the circuit boards 80 of the stator 252.

Figures 49 and 50 schematically shows an example of the configuration of the electric motor of figures 34 and 35 as used in the embodiment of this invention. The motor 40 shown in Figure 36 is a three phase motor. The motor therefore has three coil sets. In this example, each coil set includes eight coil sub-sets. The coil sub-sets of each coil set are labelled 44, 46 and 48, respectively in Figure 36. Each coil set includes pairs of coil sub-sets which are arranged opposite each other around the periphery of the motor 40. However, it should be noted that there is no express need for each coil sub-set to have a corresponding coil sub-set located opposite from it on the opposite side of the periphery of the motor 40.

Each coil sub-set can be connected to a respective control device. The terminals for each coil sub-set of each coil set are labelled 54, 56 and 58, respectively in Figure 36. While the arrangement shown in Figure 36 includes a larger number of coil sub-sets, this does not significantly increase the size and bulk of the switching means which are used to operate the motor as would be the case if the increased number of coil sub-sets were connected together in series. Instead, it is merely necessary to provide an additional control device incorporating relatively small switching devices for each additional coil sub-set. These control devices are sufficiently small such that they can be located adjacent to their corresponding coil sub-sets.

As described above, each coil sub-set can include one or more coils. In this example, each coil sub-set includes three coils as is shown schematically in Figure 37. In Figure 37, these three coils are labelled 74A, 74B and 74C. The three coils 74A, 74B and 74C are alternately wound such that each coil produces a magnetic field which is anti-parallel with its adjacent coil/s for a given direction of current flow. As described above, as the permanent magnets of the rotor of the motor 40 sweep across the ends of the coils 74A, 74B and 74C, appropriate switching of the currents in the coils can be used to create the desired forces for providing an impulse to the rotor. As is shown schematically in Figure 37, each coil in a coil sub-set can be wound in series.

The reason that the coils 74A, 74B and 74C within each subset are wound in opposite directions to give antiparallel magnetic fields can be understood with respect to Figure 38 which shows the arrangement of the magnets 242 on the rotor surrounding the coils 44, 46 and 48 of the stator. For simplicity, the arrangement is shown as a linear arrangement of magnets and coils, but it will be understood that in the embodiment of the invention described the coils will be arranged around the periphery of the stator with the magnets arranged around the inside of the circumference of the rotor, as already described. The magnets 242 are arranged with alternate magnetic polarity towards the coils 44, 46 and 48. Each subset of three coils 74A, 74B and 74C thus presents alternate magnetic fields to the alternate pole faces of the magnets. Thus, when the left-hand coil of a subject has a repelling force against a North Pole of one of the magnets, the adjacent central coil will have a repelling force against a South Pole of the magnets and so on.

As shown schematically in Figure 38, the ratio of magnets to coils is eight magnets to nine coils. The advantage of this arrangement is that the magnets and coils will never perfectly align. If such perfect alignment occurred, then the motor could rest in a position in which no forces could be applied between the coils and the magnets to give a clear direction as to which sense the motor should turn. By arranging for a different number of coils and magnets around the motor, there would always be a resultant force in a particular direction whatever position the rotor and motor come to rest.

A particular benefit of the independent control of the coil subsets by the separate control devices is that a larger than normal number of phases can be arranged. For example, rather than a three phase motor, as described in Figure 36, higher numbers of phases such as twenty-four phase or thirty-six phase are possible with different numbers of magnets and coils. Ratios of coils to magnets, such as eighteen coils to sixteen magnets, thirty-six coils to thirty-two magnets and so on, are perfectly possible. Indeed, the preferred arrangement, as shown in Figures 34 and 35 is to provide 24 separate control "kite" boards 80, each controlling three coils in a sub-set, thereby providing a twenty-four phase motor. The use of a multiphase arrangement, such as twenty-four phases, provides a number of advantages. The individual coils within each sub-set can have a larger inductance than arrangements with lower numbers of phases because each control circuit does not have to control large numbers of coils (which would require controlling a large aggregate inductance). A high number of phases also provides for lower levels of ripple current. By this it is meant that the profile of the current required to operate the motor undulates substantially less than the profile from, say a three-phase motor. Accordingly, lower levels of capacitance are also needed inside the motor. The high number of phases also minimize the potential for high voltage transients resulting from the need to transfer large currents quickly through the supply line. As the ripple is lower, the impact of the supply cabling inductance is lower and hence there is a reduction in voltage transient levels. When used in a braking arrangement (described later), this is a major advantage, as in hard braking conditions, several hundred kilowatts need to be transferred over several seconds and the multiphase arrangement reduces the risk of high voltage transients in this situation.

The relative arrangement of magnets and coils, shown in Figure 38 can be repeated twice, three times, four times or indeed as many times as appropriate around 360 mechanical degrees of the rotor and stator arrangement.

The use of separate motors for each wheel of the vehicle of the type described above provides appropriate characteristics to enable handling suspension control for the vehicle. The short response time for torque control afforded by the type of motor described provides this flexibility.

As shown in Figure 39, in accordance with one embodiment of the invention, the suspension control system for each wheel 330 includes a suspension arm 340. This is shown as a leading arm suspension arrangement as used in a front wheel of a vehicle. In Figure 39, the normal direction of travel of the vehicle with respect to the surface 350 is shown by the arrow labelled Z. Accordingly, as shown in Figure 39, the wheel 330 rotates in the direction indicated by the arrow labelled X. If additional torque is applied to the wheel in the direction indicated by the arrow labelled X, this will tend to impart a force on the suspension arm 340, whereby the suspension arm 340 will tend to lower in the direction indicated by the arrow labelled Y. In this example, the wheel 330 is a front wheel of a vehicle such as a car. The lowering of the suspension arm 340 in the direction indicated by the arrow labelled Y, would therefore cause the front of the vehicle in locality of the wheel 330 to lower also. In this way, by adjusting the torque to the wheel of a vehicle, a suspension control system for a vehicle can be implemented. In this example, lowering the front of the vehicle when torque is applied to the front wheel helps to counteract the effect of the centre of gravity of the vehicle tending to cause the vehicle body to lower at the back and rise at the front when accelerating.

It should be appreciated that, in the case of Figure 39, an increase in torque applied in the direction indicated by the arrow, X, tends to lower the suspension arm in the direction indicated by the arrow Y due to the suspension arm being in a leading position relative to the direction of motion, Z. However, in the case where the suspension arm is in a trailing position relative to the direction of motion (which would be represented by figure 39 with the direction, Z, reversed and the direction of the torque, X, pointing anti-clockwise) an increase in torque would tend to raise the suspension arm (i.e. the direction "Y" would also be reversed). Therefore, the arrangement of a suspension arm in a trailing or leading position can be used to determine whether an increase in torque to the wheel will cause the suspension arm, and therefore the portion of the vehicle in the locality of the wheel, to be raised or lowered.

In accordance with the embodiment of this invention, there can be provided a suspension control system in which the torque applied to each wheel of a vehicle can be selectively adjusted for adjusting the suspension and/or height of the vehicle. The control system can be implemented by a control unit which can be provided either for each respective wheel or which can be provided as a central control unit operable to control a plurality of wheels. Each wheel can is powered by an electric motor of the kind described above. In such embodiments, the fine control and swift response times afforded by the motor described above can enhance the responsiveness of the suspension control. The control devices for controlling the suspension can be networked together using a control area network (CAN) as described above.

In a first example of a situation in which the ability to independently control the suspension of a plurality of wheels using torque control is where a vehicle is travelling around a corner. When a vehicle is travelling round a corner, it may be desirable to tilt the vehicle such that the side of the vehicle on the outside of the corner rises up with respect to the side of vehicle on the inside of the comer.

This can be used to counterbalance the tendency of the outside of the vehicle to tilt downwards toward the surface of the road. In this example, more torque can be provided to the outer front wheel of the vehicle (i.e. the wheels of the vehicle on the outside of the corner) in order to raise that part of the vehicle. Conversely, less torque can be provided to the wheel on the inside of the corner. This would lower the suspension of the vehicle on the inside of the corner as desired.

The above example describes a situation in which pairs of wheels in the vehicle are controlled together, to raise, or lower a portion of the vehicle. In another example, the front wheels of a vehicle and the back wheel of the vehicle can be controlled to act against each other having the effect of raising the overall level of the vehicle. In particular, more/less torque can be provided to the front/rear wheels of a vehicle for effectively pushing the suspension arms of the wheels of the front and rear of the vehicle toward each other, thereby causing them both to rise up.

A highly schematic view of a three wheel vehicle embodying the invention is shown if Figure 40. In this example, the vehicle includes a front wheel 331 connected via a leading arm suspension arm 341 to a vehicle body 400. Two rear wheels 330 are also driven by the same type of electric motor as already described. Optionally, the front wheel is driven by an in-wheel electric motor.

The embodiment of the invention is able to control the attitude of the body by use of torque applied independently to the two front wheels due to the very responsive and high torque capabilities of the motors described. The torque control may be implemented in many ways but is preferably achieved by independent control within each wheel. The parameters that be may used to determine the appropriate torque to demand include steering direction sensors and vehicle attitude and yaw sensors. By providing independent control electronics in each wheel, the inputs of rate of turn, attitude, yaw, torque and others may be used in calculations within the control circuit within each wheel to determine the torque that should be provided at any instant.

The sensors could include independent sensors within each suspension arm to determine the vehicle attitude at each wheel as well as the angle of turn of the wheel in relation to the direction of travel. In conjunction with the speed of the wheel and torque demanded by any torque demand request on depressing the vehicle accelerator pedal, the appropriate torque may be determined.

In the preferred embodiment, the motor of each wheel is preferably controlled by one or more control circuits within each wheel, which are able to demand the appropriate torque from the motor based on the speed of that wheel, the torque demanded and the speed of other wheels. As an example, the vehicle shown schematically in Figure 40, if turning to the left, would tend, due to the centre of gravity of the vehicle, to lean to the right. The wheel on the outside of the turn would sense that it is travelling faster than the wheel on the inside and thus that the vehicle is turning. To compensate for the lean to the right, the motor on the outside of the turn produces an increase in torque, pushing the trailing arm upwards and raising the vehicle body at that point.

The vehicle width may be relatively narrow, such that the distance between the rear wheels is small. In this arrangement, the vehicle body may lean more and would lean "into" corners in the manner of a motorbike. Similarly, using relatively long trailing arms in the rear wheels would also cause the vehicle to "lean" more.

The vehicle may, of course, have two wheels at the front and a single wheel at the rear (and would then be arranged as it the direction of travel were in the opposite direction in Figure 40). Optionally, the rear wheel is driven by an in- wheel electric motor.

In one embodiment having two wheels at the front and a single wheel at the rear, the suspension arms of the front wheels are arranged to be trailing the direction of motion such that an increase in torque causes the suspension arms to rise. In this case, when the vehicle turns left (for example), the right hand side of the vehicle would tilt downwards toward the surface of the road. By applying an increased torque to the right hand side front wheel the right hand side of the vehicle can be raised up.

E: HAND BRAKE

The invention relates to hand or parking brakes; in particular to hand or parking brakes for use with electric vehicles driven by in-wheel electric motors.

BACKGROUND OF THE INVENTION

Known hand or parking brake mechanisms generally comprise a braking mechanism such as a drum brake mechanism which is activated by a lever located near the driver of the vehicle. Since the brake mechanism is located near one of the wheels of the vehicle, an activation cable is needed to connect the brake mechanism to the lever. A problem with such conventional hand brake devices is that they typically require large static forces to remain in the activation cable system while the brake is applied. This results in cable stretch and the need for regular adjustment of the actuation cable.

Furthermore, the provision of a hand brake for in-wheel electric motor (hub motor) vehicles requires major modifications to known hand brake systems to allow the provision of parking brake. This is because the space normally occupied by the hand brake mechanism is taken up by the electric motor. Known electric motor systems typically include a motor and a control unit for controlling power to the motor. Known types of electric motor include the induction motor, brushless permanent magnet motor, switched reluctance motor and synchronous slip ring machine. Three phase electric motors are the most common kind of electric motor available. Figure 41 shows a schematic representation of a typical three phase motor. In this example, the motor includes three coil sets. Each coil set produces a magnetic field associated with one of the three phases of the motor. In a more general example, N coil sets can be used to produce an N-phase electric motor. Each coil set can include one or more sub-sets of coils which are positioned around a periphery of the motor. In the present example, each coil set includes four such sub-sets - the coil sub-sets of each coil set are labelled 14, 16 and 18, respectively in Figure 41. As shown in Figure 41 , the coil sub-sets 14, 16, 18 are evenly distributed around the motor 10 to co-operate in producing a rotating magnetic field within which a central rotor 12, which typically incorporates one or more permanent magnets, can rotate as shown by the arrow labelled C. The coil sub-sets of each coil set are connected together in series as shown by the connections 24, 26 and 28 in Figure 41. This allows the currents in the coils of each coil set to be balanced for producing a substantially common phase. The wires of each coil set are terminated as shown at 34, 36 and 38 in Figure 41. Typically, one end of the wire for each coil set is connected to a common reference terminal, while the other wire is connected to a switching system for controlling the current within all of the coils of that coil set. Typically then, current control for each coil set involves controlling a common current passing through a large number of coils.

As shown in Figure 42, each coil sub-set can include one or more coils. In particular, Figure 42 shows the coils 24A, 24B in one of the coil sub-sets 14. In this example, there are two coifs per coil sub-set. The two coils are wound in the opposite directions, and are interconnected so that the current flowing in each coil is substantially the same. As the poles of the rotor 12 sweep across the coils 24A, 24B, switching of the current in the coils 24A, 24B can produce the appropriate magnetic field for attracting and repelling the rotor for continued rotation thereof. The magnetic field produced by the two oppositely wound coils 24A, 24B is referred to as belonging to the same phase of this three phase motor. Every third coil sub-set arranged around the periphery of the motor 10 produces a magnetic field having a common phase. The coils and the interconnections may typically comprise a single piece of wire (e.g. copper wire) running around the periphery of the motor and wound into coils at the appropriate locations.

SUMMARY OF THE INVENTION

Aspects of the invention are defined in the accompanying claims.

Embodiments of the invention provide an in-wheel electric motor comprising a rotor, stator and mechanical parking brake operable to prevent relative rotation of the rotor and stator. Embodiments of the invention provide an in-wheel electric motor including a mechanical parking brake. Known parking brake systems are not suitable for use with in-wheel electric motor because the space normally occupied by the hand brake mechanism has been taken up by the electric motor.

Preferably, the mechanism includes a two-lever actuation mechanism.

This has the advantage that it does not require large static forces to remain in the actuation cable when the brake is applied. This means that the cable does not stretch and avoids the need for regular adjustment of the actuation cable. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 41 schematically shows an example arrangement for a three phase motor; Figure 42 schematically shows the arrangement of coils in one of the coil sub-sets shown in Figure 41; Figure 43 is an exploded view of a motor embodying the invention;

Figure 44 is an exploded view of the motor of Figure 43 from an alternative angle;

Figure 45 schematically shows an example coil arrangement for a three phase motor according to an embodiment of this invention;

Figure 46 schematically shows an example arrangement of coils in one of the coil sub-sets shown in Figure 43 according to an embodiment of the invention;

Figure 47 shows an exploded detailed view of the hand brake mechanism according to an embodiment of the invention; and

Figure 48 shows a further exploded detailed view of the hand brake mechanism according to an embodiment of the invention.

DETAILED DESCRIPTION

The embodiment of the invention described is a hand brake for use in a wheel of a vehicle, preferably a vehicle powered by in-wheel electric motors. The motor is of the type having a set of coils being part of the stator for attachment to a vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel. For the avoidance of doubt, the various aspects of the invention are equally applicable to an electric generator having the same arrangement. In addition, some of the aspects of the invention are applicable to an arrangement having the rotor centrally mounted within radially surrounding coils.

The physical arrangement of the motor assembly is best understood with respect to Figures 43 and 44, showing a 24-phase motor. However embodiments of the invention are equally applicable to motor of any phase, that is to say a multiphase electric motor. These figures show expanded perspective views of the motor in which the components of the motor have been moved away from their in-use position so that each component of the motor can be easily seen. The assembly can be described as a motor with built in electronics and bearing, or could also be described as a hub motor or hub drive or in-wheel motor as it is built to accommodate a separate wheel.

Referring first to Figure 43, the assembly comprises a stator 252 comprising a rear portion 230 forming a first part of the housing of the assembly, and a heat sink and drive arrangement 231 comprising multiple coils and electronics to drive the coils as well as a heat sink. The coil drive arrangement

231 is fixed to the rear portion 230 to form the stator 252 which may then be fixed to a vehicle and does not rotate during use. The coils themselves are formed on tooth laminations 235 which together with the drive arrangement 231 and rear portion 230 form the stator 252.

A rotor 240 comprises a front portion 220 and a cylindrical portion 221 forming a cover, which substantially surrounds the stator 252. The rotor includes a plurality of magnets 242 arranged around the inside of the cylindrical portion 221. The magnets are thus in close proximity to the coils on the assembly 231 so that magnetic fields generated by the coils in the assembly 231 generate a force on the magnets 242 arranged around the inside of the cylindrical portion 221 of the rotor 240 thereby causing the rotor 240 to rotate.

The rotor 240 is attached to the stator 252 by a bearing block 223. The bearing block 223 can be a standard bearing block as would be used in a vehicle to which this motor assembly is to be fitted. The bearing block comprises two parts, a first part fixed to the stator and a second part fixed to the rotor. The bearing block is fixed to a central portion 233 of the wall 230 of the stator 252 and also to a central portion 225 of the housing wall 220 of the rotor 240. The rotor 240 is thus rotationally fixed to the vehicle with which it is to be used via the bearing block 223 at the central portion 225 of the rotor 240. This has a significant advantage in that a wheel rim and tyre can then be fixed to the rotor 240 at the central portion 225 using the normal wheel bolts to fix the wheel rim to the central portion of the rotor and consequently firmly onto the rotatable side of the bearing block 223. The wheel bolts may be fitted through the central portion 225 of the rotor through into the bearing block itself. A first advantage of this arrangement is that the whole assembly may be simply retrofitted to an existing vehicle by removing the wheel, bearing block and any other components such as the braking arrangement. The existing bearing block can then fitted inside the assembly and the whole arrangement fitted to the vehicle on the stator side and the normal rim and wheel fitted to the rotor so that the rim and wheel surrounds the whole motor assembly. Accordingly, retrofitting to existing vehicles becomes very simple.

The rotor also includes a focussing ring and magnets 227 for position sensing as described in our co-pending British application number GB 0713695.5.

Figure 44 shows an exploded view of the same assembly as Figure 43 from the opposite side showing the stator 252 comprising the rear stator wall 230 and coil and electronics assembly 231. The rotor 240 comprises the outer rotor wall 220 and circumferential wall 221 within which magnets 242 are circumferentially arranged. As previously described, the stator 252 is connected to the rotor 240 via the bearing block at the central portions of the rotor and stator walls.

Additionally shown in Figure 43 are circuit boards 80 carrying control electronics. These are described in our co-pending British patent application number 0713695.5. Due to their kite shape these circuit boards can be referred to as kite boards. Additionally in Figures 3 and 4 a V shaped seal 350 is provided between the circumferential wall 221 of the rotor and the outer edge of the stator housing 230, again described in our co-pending British patent application number 0713695.5. Further, in Figure 44, a magnetic ring 227 comprising a commutation focusing ring and a plurality of magnets is provided for the purpose of indicating the position of the rotor with respect to the stator to a series of sensors arranged on the circuit boards 80 of the stator 252. This is also described in greater detail in our co pending British patent application number 0713695.5.

Figure 45 schematically shows an example of an electric motor in accordance with an embodiment of this invention. In this example, the motor is generally circular. The motor 40 in this example is a three phase motor. Again, it will be appreciated that motors according to this invention can include an arbitrary number of phases (N = 1, 2, 3...). Being a three phase motor, the motor 40 includes three coil sets. In this example, each coil set includes two coil sub-sets. The coil sub-sets of each coil set are labelled 44, 46 and 48, respectively. The coil sub-sets 44, 46 and 48 are arranged around a periphery of the motor 40. In this example, each coil sub-set is positioned opposite the other coil sub-set in that coil set, although such an arrangement is not strictly essential to the working of the invention. Each coil sub-set includes one or more coils, as described below in relation to Figure 46. The motor 40 can include a rotor (not shown in Figure 45) positioned in the centre of the circle defined by the positioning of the various coils of the motor, thereby to allow rotation of the rotor within the rotating magnetic field produced by the coils. Preferably, though, the rotor is arranged around the coils as previously disclosed in Figures 43 and 44. The rotor may typically comprise one or more permanent magnets arranged to rotate such that their poles sweep across the ends of the coils of the motor 40. Appropriate switching of currents in the coils of the coil sub-sets allows synchronized attraction and repulsion of the poles of the permanent magnet of the rotor to produce the rotating action of the motor 40. It will be appreciated that Figure 45 is highly schematic and, in practice, the coil sub-sets will be arranged at the outer periphery of the stator with the rotor magnets surrounding the coils.

Each coil set 44, 46, 48 includes one or more coils. As shown in Figure 46, in the present example, there is a single coil per coil sub-set. Where more than one coil is provided in a given coil sub-set, these coils can generally be wound in opposite directions such that the magnetic field produced by each coil is in an anti-parallel configuration with respect to the magnetic field in an adjacent coil. As described above, appropriate switching of the current in the coils causes the permanent magnets of the rotor to rotate.

A particular benefit of the independent control of the coil subsets by the separate control devices is that a larger than normal number of phases can be arranged. For example, rather than a three phase motor, as described in Figure 47, higher numbers of phases such as twenty-four phase or thirty-six phase are possible with different numbers of magnets and coils. Ratios of coils to magnets, such as eighteen coils to sixteen magnets, thirty-six coils to thirty-two magnets and so on, are perfectly possible. Indeed, the preferred arrangement, as shown in Figures 43 and 44 is to provide 24 separate control "kite" boards 80, each controlling three coils in a sub-set. Thereby providing a twenty-four phase motor. The use of a multiphase arrangement, such as twenty-four phases, provides a number of advantages. The individual coils within each sub-set can have a larger inductance than arrangements with lower numbers of phases because each control circuit does not have to control large numbers of coils (which would require controlling a large aggregate inductance). A high number of phases also provides for lower levels of ripple current. By this it is meant that the profile of the current required to operate the motor undulates substantially less than the profile from, say a three-phase motor. Accordingly, lower levels of capacitance are also needed inside the motor. The high number of phases also minimize the potential for high voltage transients resulting from the need to transfer large currents quickly through the supply line. As the ripple is lower, the impact of the supply cabling inductance is lower and hence there is a reduction in voltage transient levels. When used in a braking arrangement (described later), this is a major advantage, as in hard braking conditions, several hundred kilowatts need to be transferred over several seconds and the multiphase arrangement reduces the risk of high voltage transients in this situation.

As shown in Figure 45, in accordance with an embodiment of this invention, the coil or coils of each coil sub-set can be connected to a separate control device 80. In Figure 45, it is schematically shown that each coil sub-set is connected to the terminals 54, 56, 58 of respective control devices 80. Accordingly, the coils of corresponding coil sub-sets within a given coil set are not connected in series. Instead, each coil sub-set is individually controlled and powered. The connections to the control device and the coils of each coil sub-set can be formed using, for example, a single piece of wire (e.g. copper wire) as is shown schematically in Figure 46. There are numerous advantageous to providing individual power control for the coils of each coil sub-set. Since there is no need to run connecting wires around the periphery of the motor providing series interconnections for the coils of each coil sub-set, less wire is used in manufacturing the motor. This reduces manufacturing costs as well as reducing the complexity of the motor construction. The reduction in wire also reduces conduction losses.

Another advantage of the use of smaller switching devices is that they can be located proximal the coils which they control. In prior electric motors, where relatively large switching devices have been employed to control the operation of coil sub-sets connected in series, the control device is sufficiently large that it can not be included with the other motor components (e.g. stator, rotor, etc.) but instead has been provided separately. In contrast, since small switching devices can be used, in accordance with an embodiment of this invention the switching devices and the control devices in which those switching devices are incorporated can be located in, for example the same housing/casing as the other motor components.

As can be seen from figures 41 to 46, the provision of an in-wheel electric motor means that conventional hand brake systems cannot be used with in-wheel electric motors because the motor has already taken up the space normally occupied by the hand brake. Figure 47 shows an exploded view of the hand brake mechanism. In general, the mechanism is mounted on the rear portion of the stator 230. The mechanism comprises a pair of substantially semi-circular shaped levers, otherwise known as arms or braking arms 1506, 1507. These are pivotally mounted at one end on the rear portion of the stator 230 by way of a nut 1509, bolt 1503 and washer 1508 which pass through substantially circular holes at one end of the semi-circular shaped levers 1506, 1507and pivotally secure the levers 1506, 1507 to the rear portion of the stator 230. Alternatively, a single arm could be used provided that sufficient braking force can be applied. Indeed a single arm could be provided which is arranged to pivot around the bolt 1503.

The arm or arms 1506, 1507 may be made out of steel or other suitable material. Preferably, as shown in figure 47, the substantially semi-circular shaped levers 1506, 1507 further comprise an additional layer on their inner surface, which lines the levers or arms and contacts with the drum 243 to provide braking. This may be a conventional friction material such as Ferodo^R™ brake pad or brake liner. Ferodo^R™ is a registered trade mark of Federal-Mogul Friction Products Limited, United Kingdom. It will be appreciated by those skilled in the art that the levers 1506, 1507 need not be in fact semi-circular; other configurations will be known to those skilled in the art. For example, the levers could be substantially straight, but lined with curved friction material.

The levers are pivotally secured to the rear portion of the stator 230 by the bolt 1503 passing through a substantially circular hole in the rear portion of the stator 230. Preferably, the substantially circular holes in one end of the semicircular shaped levers 1506, 1507 are first lined with a tubular pivot spacer 1512 of slightly smaller diameter than the circular holes in on end of the semi-circular shaped levers. The pivot spacer 1512 is then mounted on the bolt 1503. It is preferable to have a pivot spacer 1512 because this reduces wear between the bolt and the holes in the levers, as well as providing a snug, yet rotatable mounting of the levers on the bolt 1503. Preferably the bolt 1503 also passes through a bonded seal 1504 so that the motor is substantially a sealed unit.

However other pivotal connecting means will be apparent to those skilled in the art. The other ends of the levers 1506, 1507 are connected to the brake actuator mechanism 1505 which is described below in greater detail with reference to figure 48.

The hand brake actuator mechanism comprises a pair of actuator levers 605, 606. The levers are pivotally mounted on a hand brake bracket 601 by way of pivot pins 609 passing through holes in the actuator levers 605, 606. The pivot pins 609 are secured in position by an e clip 610, however other pivotal attachment means will be apparent to those skilled in the art. Preferably, the holes in the hand brake actuator levers 605, 606 are lined with bushes 604 to reduce friction and to ensure a snug fit of the pivot pins 609 within the hoes in the actuator levers 605, 606. The hand brake bracket is in turn mounted onto the rear portion of the stator 230 by way of a self-clinching stud 1502 and a washer 1510 and nut 1511 , best seen in figure 47. The hand brake bracket 601 fixes the position of rotation of the actuator levers 605, 606 with respect to the hand brake bracket, however it does allow the actuator levers 605, 606 to rotate substantially about the axis of the pivot pins 609. The two actuator levers 605, 606 are also attached to each other by means of a shoulder bolt 613, washer 607, nylon washer 614, further washer 607 and nut 608. The shoulder bolt passes through a substantially circular hole in one of the levers but through a substantially oblate hole in the other lever. The connection of the two actuator levers 605, 606 is such that it allows both rotational motion of the two levers with respect to the hand brake bracket 601 as well as allowing some translational motion between the two actuator levers since the shoulder bolt 613 is able to slide along the oblate hole in one of the actuator levers 606 as the two levers rotate about their pivot points. Preferably an additional nylon washer 614 is provided to reduce sliding and rotational frictional forces.

The brake is applied or activated so that relative rotation of the rotor with respect to the stator is prevented by way of activation means 602. The activation means is simply mechanical way of applying a force in a particular direction to the actuator 1505, in particular to the levers 605, 606. In one embodiment shown in figure 47, the activation means is a brake actuator shaft 602. The shoulder bolt passes through a hole in a brake actuator shaft, 602, as well as through the holes in the actuator levers 605, 606.

The handbrake actuator shaft 602 is substantially cylindrical in shape and is positioned approximately perpendicular to the longest axis of the hand brake bracket 601. Furthermore, the shaft 602 also passes through a hole approximately in the centre of the hand brake bracket 601. In an alternative embodiment, the activation means may comprise an activation cable, which may be directly or indirectly linked to the original (hand) brake activation cable. The cable may then be directly joined to the shoulder bolt via a hole in the shoulder bolt through which the activation cable may pass. The cable can then be attached by metal crimps or other means known to those skilled in the art such as a clamping nut and bolt.

Preferably, the hole in the hand brake bracket 601 is lined with a bush 603 to reduce friction and to ensure a snug fit of the hand brake actuator shaft 602. In this way, the hand brake actuator shaft 602, the hand brake bracket 601 and the hand brake actuator levers 605 and 606 all lie substantially in the same plane.

One of the hand brake actuator levers 606 contacts the flat surface 1513 of one of the semi-circular levers 1506 via a cam roller 612 which is in turn preferably mounted on a bush 611. Similarly, the other actuator lever 605 contacts a flat surface on the other semi-circular lever 1507 via a cam roller 612 which is in turn preferably mounted on a bush 611. The cam rollers 612 and bushes 611 are pivotally mounted on substantially tubular protrusions of the actuator levers 605, 606 by way of the pivot pins 609, e clips 610. The protrusions extend approximately parallel to the axis of rotation of the actuator levers about the hand brake bracket 601 , in the direction of rotation of the pivot pins 609.

The cam rollers 612 are not attached or fixed to the flat surfaces 1513 of the semi-circular levers 1506, 1507, however the rollers 612 contact the flat surfaces 1513 in such a way as they can slide over the flat surfaces, as well as rotate around a pivot point above the flat surfaces 1513.

The hand brake is shown in the non-activated position in figure 47. In this position, the interior diameter of the levers 1506, 1507 is greater than the exterior diameter of the drum 243, thereby allowing the wheel to rotate freely without substantial hindrance.

To activate the hand brake, the driver of the vehicle pulls the activation means, preferably the shaft 602 so that the shaft 602 moves in towards the rear portion of the stator. That is to say that the shoulder bolt 613 (and hence the actuator shaft 602) moves towards the rear portion of the stator 230. The actuator shaft may be pulled by way of a conventional hand brake cable which is, in turn, linked to the hand brake driver activation lever, near the driver.

The action of the actuator shaft moving towards the rear portion of the stator causes the shoulder bolt 613 as well as the ends of the hand brake actuation levers pivotally connected to the shoulder bolt 613 to also move towards the rear portion of the stator. The actuator shaft must in practice be as short as possible so that as it projects outside the motor through the rear portion of the stator as little as possible. However the shaft must be long enough so that its movement provides enough movement for the actuation levers 605 606 to provide a mechanical advantage.

The hand brake actuator levers are also pivotally connected to the hand brake bracket 601 by the pivot pins. Since the distance between the axes of rotation of the pivot pins 609 is fixed by the spacing of the holes in the hand brake bracket, the shoulder bolt 613 is forced to slide down the oblate hole in one of the hand brake actuator levers as the shoulder bolt 613 moves towards the rear portion of the stator 230. This action causes the cam rollers 612, bushes 611, mounted on the substantially tubular protrusions of the actuation levers to be drawn closer together to each other, as well as rotating closer to the rear portion of the stator 230. This causes the cam rollers 612 to roll or slide across the flat surfaces 1513 of the semi-circular levers from the edge of the flat surface further away from the rear portion of the stator, to the edge of the flat surface nearer to the rear portion of the stator. This in turn draws the two semi-circular halves of the hand brake levers 1506, 1507 together, and reduces the overall diameter of the two levers 1506, 1507. As the two arms of the hand brake actuation levers 605, 606 become substantially parallel to the rear portion of the stator, the two inner surfaces of the two levers 1506, 1507 grip onto the hand brake drum surface.

Preferably, the braking arms 1506, 1507 are semi flexible. This semi- flexibility has the advantage that it allows deformation of the arms 1506, 1507 so that it has good contact with the drum. This allows the mechanism to be lighter with a uniform fit around the drum. Furthermore, the semi flexibility of the arms helps ensure a positive locking of the mechanism when the actuator shaft is moved by the activation means - the brake cable used to activate the brake.

As the levers 1506, 1507 grip the drum, and the substantially semi-circular levers 1506, 1507 are subject to a tensile force.

However, this tensile force is directed substantially parallel to the longest axis of the hand brake actuator bracket, and because the arms of the hand brake levers 605 and 606 are now substantially parallel to the rear portion of the stator 230, as well as being substantially parallel to the main axis of the hand brake bracket 601 , this tensile force of the semicircular hand brake levers 1506, 1507 cannot open the mechanism. This is because the direction of force required to initiate the opening of the levers 605, 606 is substantially perpendicular to the tensile force of the semi-circular halves of the hand brake levers 1506, 1507, trying to force the ends near the flat surfaces 1513 open.

In this way, the hand brake mechanism remains locked with the interior surfaces of the levers 1506, 1507 gripping the exterior surface of the drum 243, with only a minimal or zero tensile force needing to be applied to the hand brake actuator shaft 602, or any cable actuating the shaft. The mechanism is opened by releasing the small maintaining force applied by the user to shaft 602 causing the shaft to move away from (or towards depending upon the angle of viewing) the rear portion of the stator. This may be achieved by known hand brake systems using levers and ratchets. Preferably hand brake actuator shaft 602 biasing means is also provided

(not shown in the figures). The biasing means tends to move the hand brake actuator shaft and hence the shoulder bolt 613 away from the rear portion of the stator when the small locking force applied to the shaft 602 via a cable (not shown) is released. The biasing means may comprise a coil spring which is mounted on the actuator shaft. The spring is arranged so that it is coupled to the shaft 602 and the hand brake bracket 1505 such that it tends to move the shoulder bolt 613 towards the rear portion of the stator. The spring or biasing means may conveniently be located between the rear portion of the stator 230 and the hand brake bracket 601. This causes the shoulder bolt 613 to move away from the rear portion of the stator. This causes the bolt 613 to slide within the oblate hole of one of the levers at the same time as the cam rollers 612 move further away from each other, as well as moving further away from the rear portion of the stator. This pushes the two halves of the semicircular levers 1506, 607 apart, releasing the semi-circular levers from the drum 243.

Preferably the surface of the drum 243 comprises hard, anodised surface or comprises a Keronite^R™ coating. Keronite^R™ is a registered trade mark of Keronite International Limited, United Kingdom. Such treating of the surface of the drum allows high static braking force, with low friction rotation and long life. Keronite^R™ coating allows the surface of metals such as aluminium and magnesium to be treated to that the surface is a hard, dense ceramic with high resistance to corrosion and wear.

Embodiments of the invention have the advantage that they provide a lightweight, hand brake which compact so that it is suitable for incorporation in an in-wheel electric motor, which requires low or zero force to maintain the brake in the locked position.

Embodiments of the invention provide an over centring brake mechanism which acts on two brake shoes that in turn act on an internal extension of the motor rotor, the drum, 243. The over centring mechanism ensures high forces can be applied to the rotor by the brake pads, whilst the sustaining force required from the input lever or cable is minimal. Furthermore, the mass of the mechanism is much less than that of conventional mechanisms, meaning that it is light weight so that it is suitable for use in electric vehicles with in-wheel or other electric motors where the weight of the vehicle must be kept to a minimum. The internal rotor extension (drum) 243 provides a solid and lightweight reaction surface directly on the rotor, which is suitable for use in in-wheel electric motors. Embodiments of the invention have the advantage that they contain the static braking force substantially within the lever system and thus prevent stretch of the activation cable.

The rotor inner wall provide for lightweight braking surface, providing a drum surface. This is much lighter drum than in conventional hand brakes which require a heavy internal surface.

Embodiments of the invention also have the advantage that the rotor wall also performs the function of segregating the motor sensor system from the brake and power electronics and thus they reduce the radio interference (EMC interference) in the sensitive position sensor signals. Embodiments of the invention provide a light and powerful hand brake mechanism which can be incorporated into in-wheel electric motors. Conventional hand brake system do not provide such a hand brake mechanism.

Furthermore, incorporating a holding or parking bake mechanism in a very compact lightweight wheel motor is extremely difficult with conventional hand brakes.

Embodiments of the invention also have the advantage that the mechanism is contained within a wheel motor and is designed to allow retrofitting to an existing brake cable system on a car or other vehicle.

As it is a legal requirement that vehicles are fitted with a suitable parking brake or hand brake, the present invention allows unrestricted public use of in- wheel electric motors on public vehicles, by providing a hand or parking brake mechanism incorporated into an in-wheel electric motor which can be easily retrofitted to cars or other vehicles which are being converted into electric or hybrid vehicles. Furthermore certain countries such as the United States have legislation regarding certain minimum standards for vehicular hand or parking brakes. Amongst these are that a 1.6 Tonne vehicle must remain static on a gradient of 18%. This equates to providing a force at the parking brake of approximately 4500 Newtons. Although conventional hand brakes can achieve this, they are not suitable for use in in-wheel electric motors, and furthermore, they suffer the problem of cable stretch, as previously described. Furthermore, embodiments of the invention also have the advantage that only a relatively small force is required to activate the hand brake. In some countries, it is a legislative requirement that the force required to activate the hand brake by the driver must be less than 400 Newtons. The dual actuator levers 605, 606 of the present invention has the advantage that a large braking force can be applied to the arms 1506, 1507 with minimal force less than 400 Newtons needing to be applied via the actuator shaft because of the mechanical advantage of the mechanism.

Claims

1. A torque drive and control system for a vehicle having a plurality of driven wheels, comprising: a plurality of in-wheel electric motors for mounting within each respective driven wheel of the type having a plurality of coils forming a stator radially surrounded by a plurality of magnets forming a rotor; a control circuit within each electric motor for controlling a switching of voltage applied to coils of that motor to thereby control the accelerating or braking torque provided by the motor; means associated with each respective electric motor for detecting the speed of rotation of the motor; means for transmitting the speed of each motor to each other motor in the vehicle; wherein each control circuit is configured to adjust the torque provided by each respective motor in response to the detected speed of rotation of the motor and the speed of rotation of at least one other motor.

2. A torque drive and control system for a vehicle having a plurality of driven wheels, comprising: a plurality of in-wheel electric motors for mounting within each respective driven wheel of the type having a plurality of coils forming a stator radially surrounded by a plurality of magnets forming a rotor; a control circuit within each electric motor for controlling a switching of voltage applied to coils of that motor to thereby control the accelerating or braking torque provided by the motor; means associated with each respective electric motor for detecting the speed of rotation of the motor; means for determining an angle of turn of the vehicle; wherein each control circuit is configured to adjust the torque provided by each respective motor in response to the detected speed of rotation of the motor and the angle of turn of the vehicle.

3. A torque drive and control system according to claim 1 or 2, wherein each motor comprises a plurality of control circuits, each control circuit being connected to a respective sub-set of the coils.

4. A torque drive and control system according to claim 1 , 2 or 3, wherein each control circuit is operable to perform torque control independently of other control circuits in the system according to predetermined rules.

5. A torque drive and control system according to any preceding claim, wherein each control circuit includes torque share logic arranged to instruct the motor the appropriate torque to provide.

6. A torque drive and control system according to any preceding claim, wherein each control circuit is configured to increase the torque provided by the motor if it is determined that the motor is on the outside of a turn in comparison to a wheel determined to be on the inside of a turn.

7. A vehicle comprising: a plurality of wheels, each wheel being independently powered by a respective motor; and a torque drive and control system of any preceding claim.

B

8. An electric motor comprising: a plurality of coils arranged to produce a magnetic field of the motor, a plurality of magnets; and a control device coupled to the coils controlling the switching of voltage applied to the coils wherein the control device is operable to adjust a pulse of the pulsed voltage in response to a determination of the torque required from the motor without use of current sensors.

9. An electric motor according to claim 8 in which the coils comprise one or more separate coil sets arranged to produce a magnetic field of the motor, each coil set comprising a plurality of coil sub-sets, each coil subset comprising one or more coils

10. An electric motor according to claim 9 in which the magnetic field produced by the coils in each coil set having a substantially common phase.

11. An electric motor according to claim 10 further comprising a plurality of control devices each coupled to a respective coil sub-set for independently controlling a current in the coils of said respective coil subset.

12. An electric motor according to claim 11 further comprising means for monitoring a back EMF within the coils of that coil sub-set.

13. An electric motor according to claim 12 wherein the control device adjusts the pulse of the pulsed voltage in response to the monitored back EMF.

14. An electric motor according to claim 8 in which each control device is operable to control current in a respective coil subset without an input synchronisation signal.

15. The electric motor of claim 8, further comprising a sensor arranged to detect the position of a rotor of the motor to generate a position signal, wherein each control device is operable to control current in a respective coil sub-set using the position signal.

16. The electric motor of claim 9, wherein each control device has an associated sensor to detect the position of the rotor to generate a position signal for the respective control device.

17. The electric motor according to any one of claims 8-16, wherein each control unit is operable to receive a demand signal and arranged to control current in a respective coil sub-set based on the demand signal.

18. The electric motor of claim 10, wherein each control unit comprises a circuit board and wherein the associated sensor is mounted on the circuit board.

19. The electric motor of claim 12, wherein the circuit board is arranged on a stator of the motor and a rotor of the motor comprises a plurality of magnets, wherein the sensor detects the position of the magnets and thereby detects the position of the rotor.

20. The electric motor of according to any one of claims 8-19, wherein each coil sub-set comprises a plurality of adjacent coils.

21. The electric motor of claim 16, wherein the monitoring of the back EMF is used to determine the position of the rotor to thereby control adjust a pulse of the pulsed voltage.

22. The electric motor of claim 16 or 17, wherein adjusting a pulse of the pulsed voltage in response to the monitored back EMF comprises adjusting a width of the pulse.

23. The electric motor according to any one of claims 8-22 comprising a motor casing, wherein the control devices are housed within the casing.

24. The electric motor of claim 19, wherein the control devices are located adjacent their respective coil sub-sets within the motor.

25. The electric motor according to any one of claims 8-24, wherein each control device is operable to control a temperature of its respective coil sub-set by adjusting a current within the coils of that coil sub-set.

26. The electric motor according to any one of claims 8-25, comprising a common control device configured to coordinate the operation of the plurality of control devices.

27. The electric motor of claim 26, wherein the common control device is configured to coordinate the operation of the plurality of control devices to control the current in the one or more coils of each respective coil sub-set such that each coil set produces a magnetic field having a substantially common phase.

28. The electric motor of claim 26 comprising a plurality of separate coil sets, wherein the common control device is configured to coordinate the plurality of control devices to provide polyphase current emulation within the coils.

29. The electric motor of claim 11 , wherein the plurality of control devices are configured to provide staggered switching of the currents in the coils of the motor within a polyphase cycle of the motor.

30. The electric motor of any one of claims 26 to 29, wherein the common control device is operable to selectively disable one or more of the control devices to allow fractional power operation.

31. The electric motor according to any one of claims 8-30, wherein each control device is coupled to a common dc power supply.

32. The electric motor of claim 31 , wherein each control device is disconnectable from the common dc power supply in the event of a failure.

33. The electric motor of claim 32 wherein each control device includes a fuse arrangement to disconnect the control device from the common dc power supply in the event of a failure.

34. The electric motor according to any one of claims 8-33, wherein each control device is coupled to receive power generated by coils of the motor, whereby each control device continues to receive power in the event of failure of a common dc power supply.

35. The electric motor according to any one of claims 8-34, wherein coils of the motor are connectable to control devices external to the motor to thereby supply power generated by coils to the external devices in the event of failure of a dc power supply.

36. The electric motor of claim 35 and an external device comprising at least brake sensor, wherein the coils of the motor are coupled to the brake sensor to supply power generated by coils to the brake sensor.

37. The electric motor of claim 35 or 36 and an external device comprising at least an external controller, wherein the coils of the motor are coupled to the external controller to supply power generated by coils to the external controller.

38. The electric motor according to any one of claims 8-37, wherein the coil sets are arranged to produce a rotating magnetic field, and wherein the motor further comprises a rotatable magnet or magnets.

39. A vehicle comprising the motor according to any one of claims 8-38.

40. An electric motor operable in a braking mode comprising: a plurality of coils arranged to produce a magnetic field of the motor; a plurality of magnets; and a control device connected to a dc supply coupled to the coils controlling the current in the coils; wherein, in braking mode, the control device is operable to adjust a pulse of the pulsed voltage in response to a determination of the torque required from the motor without the use of current sensors.

41. An electric motor according to claim 8 further comprising: means for determining one or more instantaneous motor values; a look-up table for storing sets of one or more known motor values, each set of values associated with as particular motor control pulsed voltage and motor torque; means for comparing one or more of the determined instantaneous motor values to one or more of the stored sets of motor values and applying a pulsed voltage associated with one of the stored sets of values in dependence upon the comparison.

42. A method for determining the voltage to be applied to an electric motor comprising: determining the torque required from the motor; controlling the switching of a pulsed voltage applied to the coils in response to a determination of the torque required from the motor without use of current sensors.

43. A method for determining the voltage applied to an electric motor comprising: determining one or more instantaneous motor values including the rotor speed and the battery voltage supply level; determining the back emf across the coil in dependence upon the determined instantaneous voltage across the coil, the battery voltage supply level and the instantaneous rotor speed; wherein the voltage applied to the coil is determined by comparing the determined back emf with back emf values stored in a look up table, each stored value associated with a stored particular motor coil voltage and desired torque value and selecting a voltage to be applied to the motor coil in dependence upon the determined back emf and the torque required from the motor without the use of current sensors.

44. An electric motor comprising: a plurality of coils arranged to produce a magnetic field of the motor, a plurality of magnets; a control device coupled to the coils controlling the switching of voltage applied to the coils; means for determining one or more instantaneous motor values including the rotor speed and the battery voltage supply level; and means for determining the back emf across the coil in dependence upon the determined instantaneous voltage across the coil, the battery voltage supply level and the instantaneous rotor speed; wherein the voltage applied to the coil is determined by comparing the determined back emf with back emf va)ues stored in a look up table, each stored value associated with a stored particular motor coil voltage and desired torque value and selecting a voltage to be applied to the motor coil in dependence upon the determined back emf and the torque required from the motor without the use of current sensors.

45. An electric vehicle comprising a plurality of wheels, each wheel having an in-wheel electric motor, the electric motor of each wheel being operable in a braking mode and each electric motor comprising: one or more separate coil sets arranged to produce a magnetic field of the motor, each coil set comprising a plurality of coil sub-sets, each coil sub-set comprising one or more coils, the magnetic field produced by the coils in each coil set having a substantially common phase; a plurality of control devices each coupled to a respective coil subset for independently controlling a current in the one or more coils of said respective coil sub-set; and a common power connection between the control devices and a power source; wherein each control device comprises switches arranged to switch the coils in the braking mode using pulse width modulation switching so arranged that the current profile delivered by each control device to the common power connection is offset in relation to other control devices so that full braking torque may be provided by the electric motors whilst avoiding current peaks on the common power connection.

46. The electric vehicle of claim 45, further comprising a sensor arranged to detect the position of a rotor of the motor to generate a position signal, wherein each control device is operable to control current in a respective coil sub-set using the position signal.

47. The electric vehicle of claim 46, wherein each control device has an associated sensor to detect the position of the rotor to generate a position signal for the respective control device.

48. The electric vehicle of any one of claims 45 to 47, wherein each coil subset comprises a plurality of adjacent coils.

49. The electric vehicle of claim 45, wherein at least one of the control devices comprises means for monitoring a back EMF within the coils of that coil sub-set, and wherein the control device is operable to adjust a pulse of the pulsed switching in response to the monitored back EMF.

50. The electric vehicle of claim 49, wherein the monitoring of the back EMF is used to determine the position of the rotor to thereby control adjust a pulse of the pulsed switching.

51. The electric vehicle of claim 49 or 50, wherein adjusting a pulse of the pulsed voltage in response to the monitored back EMF comprises adjusting a width of the pulse.

52. The electric vehicle of claim 49 or 50, wherein adjusting a pulse of the pulsed voltage in response to the monitored back EMF comprises adjusting a timing of the pulse.

53. The electric vehicle of any one of claims 45 to 52, further comprising an interconnection between control devices, wherein the control devices are arranged to stagger switching with respect to one another by communication on the interconnection.

54. The electric vehicle of any one of claims 45 to 53, comprising a common control device configured to coordinate the operation of the plurality of control devices to ensure staggered switching of the switches.

55. The electric vehicle of claim 54, wherein the common control device is configured to coordinate the operation of the plurality of control devices to control the current in the one or more coils of each respective coil sub-set such that each coil set produces a magnetic field having a substantially common phase.

56. The electric vehicle of claim 54 comprising a plurality of separate coil sets, wherein the common control device is configured to coordinate the plurality of control devices to provide polyphase current emulation within the coils.

57. The electric vehicle of claim 56, wherein the plurality of control devices are configured to provide staggered switching of the currents in the coils of the motor within a polyphase cycle of the motor.

58. The electric vehicle of any one of claims 45 to 57, wherein each control device is coupled to receive power generated by coils of the motor, whereby each control device continues to receive power in the event of failure of a common dc power supply.

59. The electric vehicle of claim 58 and an external device comprising at least brake sensor, wherein the coils of the motor are coupled to the brake sensor to supply power generated by coils to the brake sensor.

60. The electric vehicle of claim 58 or 59 and an external device comprising at least an external controller, wherein the coils of the motor are coupled to the external controller to supply power generated by coils to the external controller.

61. The electric vehicle of any one of claims 45 to 60 wherein each control device comprises an H-bridge switching arrangement having first and second switches coupled to a first side of the dc supply and third and fourth switches coupled to a second side of the dc supply and configurable so that, in the regenerative braking mode, the first and second switches on the first side of the dc supply are opened, the third switch on the second side of the dc supply is closed and the fourth switch on the second side of the dc supply repeatedly opened and closed.

62. The electric vehicle of claim 61 , wherein the fourth switch is repeatedly opened and closed by pulse width modulation.

63. The electric vehicle of claim 61 or 62, further comprising a diode arrangement such that, when the fourth switch is repeatedly opened and closed, a voltage is applied from the coil sub-set to the dc supply via the diode to regenerate the dc supply.

64. The electric vehicle of claim 61 , 62 or 63, further configurable so that, when the speed of the motor drops below a given value, the control devices are operable, in a non-regenerative mode, to apply voltages to the coil sets in a common phase.

65. The electric vehicle of any of claims 61 to 64, further comprising a dump resistor coupled to the control device and configured to receive current from the control device in the event that power cannot be returned to the DC supply.

66. The electric vehicle of claim 65, wherein the dump resistor is configured to receive current in the event that the DC supply is a battery that is full, the voltage across the supply goes over a given threshold or the DC supply fails.

67. An electric motor as described according to any one of claims 45 to 66.

68. An in-wheel electric motor for a road vehicle capable of providing the full braking torque for a vehicle.

69. A vehicle comprising a plurality of wheels each with in-wheel electric motors, the electric motors capable of providing the full braking torque for the vehicle.

70. A three wheel electric vehicle having two driven wheels toward a first end and one wheel toward a second end and a vehicle body, the driven wheels having in-wheel electric motors and each being coupled to the vehicle body by respective suspension arrangements of the type allowing the vehicle body to rise or lower in height, the attitude of the vehicle at each wheel being controllable by control of the torque provided by the electric motors within the driven wheels.

71. A three wheel electric vehicle according to claim 70, wherein the suspension arrangements of the driven wheels include an offset such that application of torque between the wheel and the suspension arrangement in one direction causes part of the suspension arrangement to rotate in the opposite direction thereby altering the attitude of the vehicle.

72. A three wheel electric vehicle according to claim 70 or 71 , wherein the suspension arrangements each comprise a suspension arm, the attitude of the vehicle at each wheel being controllable by application of torque between the respective wheel and suspension arm.

73. A three wheel electric vehicle according to claim 72, wherein the driven wheels are the rear wheels of the vehicle and the suspension arms are trailing arms.

74. A three wheel electric vehicle according to claim 73, wherein the driven wheels are the front wheels of the vehicle and the suspension arms are leading arms.

75. A three wheel electric vehicle according to any one of claims 70 to 74, wherein the one wheel toward the second end also has an in-wheel electric motor.

76. A three wheel electric vehicle according to any one of claims 70 to 75, wherein the driven wheels are arranged so as to increase the torque provided by the outer of the driven wheels when turning the vehicle.

77. A three wheel electric vehicle according to any one of claims 70 to 76, wherein the electric motors comprise a plurality of coil sets within a stator and surrounding magnets in a rotor.

78. A three wheel electric vehicle according to claim 77, wherein each coil set comprises a plurality of coil sub-sets, each coil sub-set comprising one or more coils, the magnetic field produced by the coils in each coil set having a substantially common phase.

79. A three wheel electric vehicle according to claim 77 or 78, having a plurality of control devices each coupled to a respective coil sub-set for independently controlling a current in the coils of said respective coil subset, each control device being operable to control current in a respective coi! sub-set without an input synchronisation signal.

80. A three wheel electric vehicle according to any one of claims 70 to 79, each wheel includes a control circuit arranged to determine the appropriate torque for the respective wheel to provide and to thereby control the electric motor.

81. A three wheel electric vehicle according to claim 80, wherein each control circuits includes an input from a sensor arranged to determine the relative position of the suspension to determine the attitude of the vehicle at the wheel.

82. A three wheel electric vehicle according to claim 80, wherein each control circuit includes an input from a sensor arranged to determine the relative direction of turn of the wheel.

83. A three wheel electric vehicle according to claim 80, further comprising a sensor arranged to detect the position of a rotor of the motor to generate a position signal, wherein each control device is operable to control current in a respective coil sub-set using the position signal.

84. A three wheel electric vehicle according to claim 72, wherein the driven wheels are rear wheels of the vehicle and the suspension arms are trailing arms.

85. A three wheel electric vehicle according to claim 72, wherein the driven wheels are front wheels of the vehicle and the suspension arms are leading arms.

86. An in-wheel electric motor comprising a rotor, stator, and mechanical parking brake operable to prevent relative rotation of the rotor and stator.

87. An in-wheel electric motor according to claim 86 further comprising: a. a first arm pivotally mounted on the stator b. a brake drum mounted on the rotor rotatable with respect to the stator; and c. activation means coupled to the arm wherein in use the brake is activated by applying a force to the activation means which causes the arm to contact the drum.

88. An in-wheel electric motor according to claim 87 further comprising: a. a second arm pivotally mounted on the stator, the arm coupled to the activation means, wherein, in use the activation means causes both the first and second arms to contact the drum.

89. An in-wheel electric motor according to claims 87 or 88 further comprising: a. locking means coupled to the first or second arms or both wherein, in use, a force applied to activation means causes the locking means to move the arm(s) from a first position in which the stator and rotor are able to rotate substantially freely to a second locked and braked position in which the arms contact the drum wherein substantially zero maintaining force is applied to the activation means once the locking means is locked in position.

90. An in-wheel electric motor according to any one of claims 87 to 89 in which one or both of the arms are flexible thereby deforming to the shape of the drum when the brake is applied.

91. An in-wheel electric motor according to any one of claims 87 to 90 in which the brake is housed within the motor.

92. An in-wheel electric motor according to any one of claims 87 to 91 in which the arms comprise two opposable arms.

93. An in-wheel electric motor according to any one of claims 87 to 92 in which electric motor is a multiphase electric motor.

94. An in-wheel electric motor according to any one of claims 87 to 93 in which the motor comprises a plurality of separate coils.

95. An in-wheel electric motor according to any one of claims 87 to 94 in which the arms are arranged to clamp around the drum.

96. An in-wheel electric motor according to any one of claims 87 to 95 in which the levers clamp substantially completely around the drum.

97. An in-wheel electric motor according to any one of claims 87 to 96 further comprising a pair of actuator levers, each lever pivotally connected at one end to the rear portion of the stator, the levers pivotally connected to each other and to the activation means at the other end wherein in use, the activation means causes the levers to rotate and slide with respect to each other thereby clamping the arms on the drum.

98. An in-wheel electric motor according to any one of claims 87 to 97 in which the activation means further comprises biasing means for biasing the arms such that they are non-contacting with the drum.

99. An in-wheel electric motor according to any one of claims 87 to 98 in which the motor comprises coils positioned on a stator surrounded by magnets mounted on a rotor.