WO2008096140A1

WO2008096140A1 - Transmission system

Info

Publication number: WO2008096140A1
Application number: PCT/GB2008/000422
Authority: WO
Inventors: William Wesley Martin; Richard John Evan Thompson
Original assignee: Zeroshift Limited
Priority date: 2007-02-09
Filing date: 2008-02-06
Publication date: 2008-08-14
Also published as: GB2459618A; GB0915576D0; GB0702548D0

Abstract

A multi-path transmission system (88) for a heavy goods vehicle (HGV) or other large vehicle that is arranged to perform instantaneous or substantially instantaneous gear changes. The transmission system (88) includes first and second shafts (1,3), a first gear element rotatably mounted on the first shaft (16), a first selector assembly (33) for selectively locking the first gear element (16) for rotation with the second shaft (3) from the following operational modes: lock the first gear element (16) for rotation with the second shaft (3) in the clockwise and anti-clockwise directions; lock the first gear element (16) for rotation with the second shaft (3) in the clockwise direction and not lock in the anti-clockwise direction; and lock the first gear element (16) for rotation with the second shaft (3) in the anti-clockwise direction and not lock in the clockwise direction.

Description

Transmission System

The present invention relates to a transmission system and in particular but not exclusively to a multi-path transmission system for a heavy goods vehicle (HGV) or other large vehicle.

A typical multi-path transmission system may have twelve normal forward gear ratios plus a crawler gear and a reverse gear. The twelve forward gears may be provided by three gear pairs, plus a splitter on the input and a range changer on the output. When the ratio changer is set in the low range, the three gear pairs provide first, second and third gear ratios. When the ratio changer is set in the high range, the three gear pairs provide fourth, fifth and sixth gear ratios. By employing the splitter, six additional intermediate gear ratios can be made available (commonly referred to as first split, second split and so on). Synchromesh is usually provided to make gear changing easier.

Changing gear in a multi-path gear box may involve selecting a different gear pair, operating the splitter or selecting a different range, or simultaneously carrying out two or three of these separate operations. The process may also involve operating a clutch and/or adjusting the engine speed to match the rotational speeds of the various gear components. The process of changing gear may therefore be highly complex. Frequently, automated gearshift systems are employed to sequence these operations in the correct order and to control the engine speed throughout the operation. Even with an automated system, the process of changing gear may be very slow, typically taking several seconds. As a result, there may be a prolonged interruption in the delivery of torque to the driving wheels. This may cause the vehicle to slow appreciably, particularly if it is driving up an incline. The loss of drive can be so significant, for example on steep inclines, that by the time the new gear has been selected the drive conditions are such that the new gear is no longer suitable and another gear, typically a lower gear, is required.

The rotating components of multi-path transmission systems for HGVs are much larger than those of car transmission systems and thus the selector mechanisms employed have to handle transfers of very large inertia that take place when changing gear in such transmission systems. This leads to different design considerations than for car transmission systems and has focused the attention of those skilled in the art on the use of conventional shift mechanisms to ensure that designs are robust and readily controllable. Instantaneous transmission systems that allow gear changes to be made with no appreciable interruption in the delivery of torque to the wheels have been designed for use in other vehicles such as cars. An instantaneous gear selector mechanism typically has four modes of operation with respect to each of the rotatably mounted gear wheels associated with it:

Fully engaged in both torque directions (fully in gear);

Disengaged in both torque directions (neutral);

Engaged in the forward torque direction while disengaged in the reverse torque direction;

Disengaged in the forward toque direction while engaged in the reverse torque direction.

The last two modes enable a discrete ratio transmission system to have the ability to shift up or down ratios instantly under load without torque interruption. In some embodiments it is not necessary to have a neutral position.

Cars generally have much simpler transmission systems with typically between four and six gear pairs and no splitter or range changer. Examples of instantaneous transmission systems include those described in WO2004/099654, WO2005/005868, WO2005/005869, WO2005/024261, WO2005/026570, WO 2006/123128, WO 2006/123166, WO 2006/095140 and WO 2007/132209 the contents of which are incorporated herein by reference. These all employ a dog-type selector mechanisms for changing gear.

The known transmissions mentioned above have a plurality of gear trains for transmitting drive between transmission input and output shafts. For a first gear train, a first gear wheel is rotatably mounted on either a transmission input shaft or an output shaft and a second gear wheel is fixed to the other shaft, in mesh with the first gear wheel. A second gear train comprising third and fourth gear wheels is similarly arranged. The transmission also includes at least one gear selector mechanism that is located between the rotatably mounted gear wheels that is arranged to selectively lock them for rotation with the shaft on which they are mounted. When a gear wheel from a gear train is locked for rotation with the shaft, drive is transmitted between the input and output shafts via that gear train. The arrangement of the transmission is such that when drive is transmitted between the input and output shafts via one of the gear trains the gear selector mechanism can select a new gear train under power without first disengaging the first gear train, by locking the rotatably mounted gear wheel of the second gear train to its shaft. Thus momentarily, drive is transmitted between the input and output shaft via two gear trains simultaneously. The new gear train then overdrives the first gear train for at least one accelerating and at least one decelerating shift type and the selector mechanism disengages the first gear wheel. Drive is then transmitted between the input and output shafts via the new gear train only. Since it is not necessary to open the clutch when changing gear the transmission provides uninterrupted power through a gearshift.

It is an object of the present invention to provide a transmission system, and in particular a multi-path transmission system for a heavy goods vehicle, that mitigates at least some of the aforesaid disadvantages.

According to one aspect of the invention there is provided a multi-path transmission system for a heavy goods vehicle (HGV) or other large vehicle that is arranged to perform instantaneous or substantially instantaneous gear changes.

The problem described above relating to loss of drive when selecting a lower gear when driving up a hill relates to so called "kickdown shifts", which are accelerating downshifts. Early versions of instantaneous type selector assemblies had difficulties performing this type of shift and this initially prejudiced the inventors against the applicability of instantaneous type selector mechanisms to multipath transmission systems. However, through their efforts to refine the systems for controlling the transmission system, kickdown shifts are now fully achievable. The inventors have realised that the problem of slow gear changes within multipath transmissions systems can be overcome by using instantaneous selector mechanisms.

Advantageously the multi-path transmission system can be used in other large vehicles such as agricultural vehicles or excavation vehicles.

According to another aspect of the invention there is provided a transmission system including first and second shafts, a first gear element rotatably mounted on the first shaft, and a first selector assembly for selectively locking the first gear element for rotation with the second shaft from the following operational modes: lock the first gear element for rotation with the second shaft in the clockwise and anti-clockwise directions; lock the first gear element for rotation with the second shaft in the clockwise direction and not lock in the anti- clockwise direction; and lock the first gear element for rotation with the second shaft in the anti-clockwise direction and not lock in the clockwise direction.

The invention enables instantaneous shifts to take place in a multi-path transmission systems since it enables instantaneous shifts to take place between split shafts.

Advantageously the transmission system includes a second selector assembly for selectively locking the first gear element for rotation with the first shaft from the following operational modes: lock the first gear element for rotation with the first shaft in the clockwise and anticlockwise directions; lock the first gear element for rotation with the first shaft in the clockwise direction and not lock in the anti-clockwise direction; and lock the first gear element for rotation with the first shaft in the anti-clockwise direction and not lock in the clockwise direction. This enables the first gear element to be part of a gear train that can function as a splitter gear and also as a regular gear as determined by the operational modes selected by the first and second selector assemblies. If the first gear element is selected by both the first and second selector assemblies drive can be transmitted directly between the first and second shafts. For example, the first and second shafts can be output and input shafts respectively that are arranged substantially coaxially and drive can be directly applied from the input shaft to the output shaft substantially instantaneously by the first and second selector assemblies selecting the first gear element.

Advantageously the transmission system includes a second gear element rotatably mounted on the second shaft, wherein the first selector assembly is arranged to selectively lock the second gear element for rotation with second shaft from the following operational modes: lock the second gear element for rotation with the second shaft in the clockwise and anticlockwise directions; lock the second gear element for rotation with the second shaft in the clockwise direction and not lock in the anti-clockwise direction; and lock the second gear element for rotation with the second shaft in the anti-clockwise direction and not lock in the clockwise direction. This enables the first and second gear elements to provide split high and low gear options when they are part of first and second gear trains in a multipath transmission system. The first selector mechanism can perform instantaneous gearshifts between the first and second gear elements.

Advantageously the transmission system includes a third shaft arranged substantially parallel to the first and second shafts.

Advantageously the transmission system includes a first gear train arranged to communicate drive between the first and third shafts, wherein the first gear train includes the first gear element and at least one additional gear element. Advantageously the, or one of the, additional gear element(s) can be fixed for rotation with the third shaft.

Advantageously the transmission system includes a second gear train arranged to communicate drive between the second and third shafts, wherein the second gear train includes the second gear element and at least one additional gear element. Advantageously the, or one of the, additional gear element(s) can be fixed for rotation with the third shaft.

Advantageously the transmission system can include a third gear train including arranged to communicate drive between the first and third shafts, said third gear train including a third gear element rotatably mounted on the first shaft and at least one additional gear element. Advantageously the, or one of the, additional gear element(s) can be fixed for rotation with the third shaft.

The second selector assembly is arranged to selectively lock the third gear element for rotation with the first shaft from the following operational modes: lock the third gear element for rotation with the first shaft in the clockwise and anti-clockwise directions; lock the third gear element for rotation with the first shaft in the clockwise direction and not lock in the anti-clockwise direction; and lock the third gear element for rotation with the first shaft in the anti-clockwise direction and not lock in the clockwise direction. This enables instantaneous gearshifts to take place between the first and third gear trains.

Advantageously the transmission system may include additional gear trains for communicating drive between the first and third shafts, for example which each include a gear element rotatably mounted on the first shaft and a gear element fixed for rotation with the third shaft. Advantageously the transmission system can include additional gear selector assemblies for selectively locking the rotatably mounted gear elements for rotation with the first shaft. For example, another selector assembly of the type described herein can be mounted on the first shaft between each pair of additional rotatably mounted gear elements to enable instantaneous shifts to take place for the additional gear trains. Preferably the multipath transmission system includes between two and ten gear trains, and more preferably between three and six gear trains.

Advantageously each of the gear selector assemblies can be arranged to select the following operational mode: not lock the gear element for rotation with the first or second shaft as the case maybe in the clockwise or anticlockwise directions, i.e. can select a neutral condition.

Advantageously each of the gear selector assemblies can include first and second sets of engagement members arranged to selectively lock its respective gear element for rotation with the first or second shaft as the case maybe and an actuator system for selecting between the operational modes, said actuator system having a first actuator member for moving the first set of engagement members, a second actuator member for moving the second set of engagement members, a first actuator device for actuating the first actuator member and a second actuator device for actuating the second actuator member independently of the first actuator device.

Advantageously the or each selector assembly is arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition.

Preferably the or each selector assembly is arranged such that when a decelerating force is transmitted the first set of engagement members engages the engaged gear element, and the second set of engagement members is in an unloaded condition, and when a driving force is transmitted the second set of engagement members drivingly engages the engaged gear element, and the first set of engagement members is then in an unloaded condition.

Advantageously the actuator system can be arranged to bias the loaded set of engagement members towards an unengaged gear element without disengaging the loaded set of engagement members from the engaged gear element. Advantageously the transmission system can include a gear range changing device arranged to adjust the output drive characteristics of the transmission system. Preferably the range changing device is an epicyclic range changer connected to the first shaft.

Advantageously the transmission system can include an electronically programmable control system for controlling operation of the or each gear selector assembly. For example, the control system may include a processing device that is programmed to control operation of the selector assemblies. This can prevent transmission lock up occurring by appropriate sequence control. Advantageously the control system can be arranged to move the unloaded set of engagement members out of engagement from the engaged gear element before actuating the other gear selector assembly to engage the new gear wheel. This is an important factor in preventing transmission lock up when torque reversals occur during a shift requiring the operation of more than one selector assembly since it removes the set of engagement elements out of engagement with the current gear wheel that would otherwise lock the transmission if a torque reversal occurred.

The control system can also be arranged to bias the loaded set of engagement members towards the unengaged gear wheel until the loaded set of engagement members are free to move.

Advantageously the transmission system can include means for determining the direction of torque in the transmission system when receiving a request for a gearshift. Preferably the transmission includes a sensor device, such as a speed sensor for detecting the rotational speed of at least one transmission component or transmission input, and the control system determines from the sensor device the rate of change of rotational speed. This enables the sensor device to determine the direction of torque in the transmission, that is whether there is an accelerating or braking force being applied. Instead of using a sensor device, the direction of torque can be determined by calculation from other known quantities, including the engine speed.

The transmission may also include means for preventing the direction of torque in the transmission changing during a gearshift. Advantageously the control system is arranged to issue control signals to adjust the output of a drive source. Preferably the control system is connected to an engine control unit via a communication means such as a Controller Area Network (CAN) bus. The control signals instruct the engine control unit to adjust the engine output as required. The control system can also be arranged to issue control signals for controlling the clamp load between input and output sides of a clutch device. Preferably the control system controls the operation of a clutch actuator, which in turn controls the clutch device. Controlling both the clutch and the engine control system provides the best gear shift results.

According to one embodiment of the invention, there is provided a multipath transmission system for a heavy goods vehicle (HGV) or similar vehicle including input, output and counter shafts, a first gear train for communicating drive between the output shaft and the counter shaft having a first gear element rotatably mounted on the output shaft and a gear element fixed for rotation with the counter shaft, a second gear train for communicating drive between the input shaft and the counter shaft having a second gear element rotatably mounted on the input shaft and a gear element fixed for rotation with the counter shaft, a first selector assembly for selectively locking each of the first and second gear elements for rotation with the input shaft from the following operational modes: lock the gear element for rotation with the input shaft in the clockwise and anti-clockwise directions; lock the gear element for rotation with the input shaft in the clockwise direction and not lock in the anti-clockwise direction; and lock the gear element for rotation with the input shaft in the anti-clockwise direction and not lock in the clockwise direction, and a second selector assembly for selectively locking the first gear element for rotation with the output shaft from the following operational modes: lock the first gear element for rotation with the output shaft in the clockwise and anti-clockwise directions; lock the first gear element for rotation with the output shaft in the clockwise direction and not lock in the anti-clockwise direction; and lock the first gear element for rotation with the output shaft in the anti-clockwise direction and not lock in the clockwise direction. This provides a multipath HGV transmission system having a splitter gear arrangement that can perform instantaneous gearshifts between split high and low positions.

Each selector assembly is arranged to select a new gear train while the current gear tram is still engaged and thus can perform instantaneous gearshifts. Advantageously the or each selector assembly used in the transmission system or multipath transmission system can include first and second sets of engagement members that are moveable into and out of engagement with two gear elements and an actuator system for actuating the engagement members, wherein the gear selector assembly is arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition and the actuator system is arranged to move the unloaded set of engagement members into driving engagement with the unengaged gear element to effect a gear change.

Advantageously the or each selector assembly can be arranged such that when a braking force is transmitted the first set of engagement members drivingly engages the engaged gear wheel, and the second set of engagement members is in an unloaded condition, and when a driving force is transmitted the second set of engagement members drivingly engages the engaged gear wheel, and the first set of engagement members is then in an unloaded condition.

Advantageously the actuator system for the or each selector assembly can be arranged to include a first actuator device for actuating the first set of engagement members and a second actuator device for actuating the second set of engagement members independently of the first actuator device. Preferably the actuator system includes a first actuator member for moving the first set of engagement members and a second actuator member for moving the second set of engagement members, which can be actuated by the first and second actuator devices respectively.

Preferably the actuator assembly includes at least one resilient means arranged to move at least one of the first and second sets of engagement members into engagement with the first and second gear elements when the engagement members are in unloaded conditions. Preferably the or each resilient means is arranged to bias at least one of the first and second sets of engagement members towards the first or second gear element when the engagement members are drivingly engaged with a gear element.

Preferably the or each selector assembly is arranged such that when the first and second sets of engagement members engage one of the first and second gear elements the backlash when moving between acceleration and deceleration is less than or equal to five degrees. Preferably each of the rotatably mounted gear elements includes drive formations that can be engaged by the first and second sets of engagement members. For example, the first and second gear elements can include first and second groups of dogs respectively. For example, the first and second groups of dogs can each comprise between two and twelve dogs, evenly distributed on the first and second gears respectively. Preferably the first and second groups of dogs each comprise between two and four dogs, and more preferably three dogs.

Advantageously the first gear element includes first and second sets of drive formations, wherein the first set of drive formations are arraigned for engagement by the first selector assembly and the second set of drive formations are arranged for engagement by the second selector assembly.

The first and second sets of engagement members preferably comprise between two and eight members, more preferably between two and four members, and more preferably still three members.

Advantageously the first shaft may include keyways arranged such that the first and second sets of engagement members can slide axially along the keyways and to radially restrain the positions of the sets of engagement members. Preferably the cross-section of the keyways is one of T-shaped, slotted, and dovetailed.

According to another aspect of the invention there is provided a multipath transmission system for a heavy goods vehicle (HGV) or similar vehicle including first and second rotatable shafts and first and second gear elements, said first gear element being rotatably mounted on the first shaft and said second gear element being rotatably mounted on the second shaft, a gear selector assembly for selectively transmitting torque between the second shaft and the first gear element and between the second shaft and the second gear element, said selector assembly including first and second sets of engagement members that are moveable into and out of engagement with the first and second gear elements and an actuator system for actuating the engagement members, wherein the gear selector assembly is arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition and the actuator system is arranged to move the unloaded set of engagement members into driving engagement with the unengaged gear element to effect a gear change.

Advantageously drive can be transmitted between the first and second shafts via a third shaft. Advantageously the transmission system includes a first gear train for transmitting drive between the first and third shafts, said first gear train including the first gear element and another gear element that is fixed for rotation with the third shaft and a second gear train for transmitting drive between the second and third shafts, said second gear train including the second gear element and another gear element fixed for rotation with the first shaft.

Advantageously the multipath transmission system can include a second selector assembly similar to the first selector assembly that is arranged to engage the first gear element to selectively lock it for rotation with the first shaft.

Advantageously the transmission system can include additional gear trains for transmitting drive between the first and third shaft.

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

Figure Ia is a schematic representation of a transmission system layout according to the invention;

Figure Ib is a schematic of a vehicle drive system including a transmission system in accordance with the invention;

Figure Ic is a schematic representation of a selector mechanism used in the transmission system of Figure Ia;

Figure 2 is a schematic illustrating the arrangement of a group of dogs on a side of a gear wheel (teeth not shown for clarity);

Figure 3 is a schematic that illustrates the interaction of a selector mechanism and the dogs on the side of a gear wheel; Figure 4 is an isometric view of an engagement element from the selector mechanism;

Figures 5a-f illustrate diagrammatically operation of one of the selector mechanisms;

Figure 6 shows the transmission system in a neutral configuration; and

Figures 7 to 18 show the transmission system in various forward drive configurations representing respectively first gear, first split, second gear, second split, third gear, third split, fourth gear, fourth split, fifth gear, fifth split, sixth gear, and sixth split.

As shown in figure Ia, the transmission system 88 includes an input shaft 3, an output shaft 1 and a countershaft 6. Drive is transferred between the various drive shafts 1,3,6 by a set of six mainshaft gears 8,10,12,14,16,18 carried by the input and output shafts 3,1 and six countershaft gears S',10',12',14',16',18' carried by the countershaft 6.

The six countershaft gears 8',10',12',14',16',18' ^₆ attached directly to the countershaft 6 for rotation therewith. As seen from right to left in figure Ia, these countershaft gears are a reverse gear 8', crawler gear 10', first gear 12', second gear 14', splitter high/third gear 16' and splitter low gear 18'. The mainshaft gears 8,10,12,14,16,18 carried by the input and output shafts 3,1 are mounted on bearings (not shown) so as to be rotatable relative thereto. Five of these mainshaft gears are rotatably mounted on the output shaft 1 : these are from right to left a reverse gear 8 (R), crawler gear 10 (C), first gear 12 (1^st), second gear 14 (2^nd) and splitter high/third gear 16 (H/3^rd). A mainshaft splitter low gear 18 (L) is rotatably mounted on the input shaft 3. The transmission system also includes a reverse idler gear 19 that transfers drive from the mainshaft reverse gear 8 to the countershaft reverse gear 8', and a conventional epicyclic range changer mechanism 22.

As previously mentioned, the mainshaft gears 8,10,12,14,16,18 are rotatably mounted on the respective input/output shafts 3,1. To transfer drive from the respective shaft to the primary gear, each gear has associated with it a selector mechanism 29,31,33. Each of these selector mechanisms may, for example, be of the type described in one or more of described in WO2004/099654, WO2005/005868, WO2005/005869, WO2005/024261 and WO2005/026570, the contents of which are incorporated by reference herein. However, the selector mechanisms 29,31,33 are preferably arranged as described below. Figure Ib is a schematic diagram of a drive system including a transmission system 88 in accordance with the invention. The drive system can be used in lorries and other heavy vehicles such as agricultural vehicles, excavators and cranes, and includes an engine 80, an engine control unit 82, a sensor system 84 for determining the direction of torque in the transmission, a clutch device 86 such as a friction clutch, a transmission system 88, and a transmission control unit 90.

The engine 80 is typically an internal combustion engine in a vehicle but may be an electric motor for electric vehicles or any other suitable drive source. The output of the engine 80 is largely determined by the driver loading a throttle input device 81 (typically a throttle pedal), which is connected to the engine via a throttle interface 83 and the engine control unit 82. The engine control unit 82 is arranged to monitor and adjust the output of the engine 80 in accordance with instructions received from the user and the transmission control unit 90. The engine control unit 82 may be a throttle potentiometer type system or alternatively an electronic control system (sometimes called a "drive by wire" system).

The engine control unit 82 communicates with the transmission control unit 90 via a Controller Area Network (CAN) bus.

The transmission control unit 90 is a software driven automatic control system that is programmed to produce smooth gearshifts and prevent certain transmission failure modes occurring, for example transmission lockup due to impermissible gearshifts. In order to fulfil its primary functions the transmission control unit 90 controls the sequencing of shift operations in the transmission system 88, the torque in the transmission system via the clutch 88 and engine 80 using a clutch actuator 92 and the engine control unit 82 respectively. In order to achieve this, the transmission control unit 90 receives inputs to determine the direction of torque in the transmission. This can be calculated from existing vehicle sensors for detecting engine and road speeds and from a knowledge of the geometry of the transmission system or can be from clutch sensors 93 or a transmission torque direction sensor 84. The transmission control unit 90 also determines the operational conditions of selector assemblies 29,31,33, for example by determining their positions from a knowledge of the transmission system and controlling actuation of the selector assemblies 29,31,33 and / or by using one or more transmission position sensors 96. Optionally, the transmission control unit 90 can also receive inputs from one or more of the following devices: a transmission output shaft speed sensor 98, and a user operated gear selection input device 94 for manual and semi-automatic transmissions.

The torque value in the transmission is determined in part by the output of the engine 80 and in part by the operational condition of the clutch 86, which determines the maximum permissible torque that can be transmitted to the transmission (clutch torque limit) according to the clamp load between the input and output sides of the clutch. The clamp load between the input and output sides of the clutch is determined by the transmission control unit 90 via the clutch actuator 92. Reducing the clamp load between the clutch plates allows controlled relative rotational movement between the input and output sides of the clutch device 86 to control the value of torque transmitted. A typical value for speed difference can be 25rpm when operating around 4000rpm (4000rpm on one side of the clutch to 4025rpm on the other side).

The input and output clutch sensors 93 detect the speeds of the input and output sides of the clutch 86 respectively. The readings from the sensors 93 are monitored by the transmission control unit 90, which determines whether relative rotational movement is occurring and the direction of torque according to the values received from the sensors 93. The transmission control unit 90 is arranged to control the clutch actuator 92 and select the clutch clamp load in order to transmit the desired amount of torque to the transmission 88.

The drive system may include one or more clutch clamp load sensors (not shown) in order to detect slip between the input and output sides of the clutch 86.

The optional sensor system 84 for determining the direction of torque in the transmission, may include an accelerometer for determining whether the vehicle is accelerating or decelerating such as a mercury switch, a pair of load cells arranged to detect strain in transmission components wherein from a comparison of the outputs of each load cell it is possible to determine the torque direction (see WO 2005/005869), a sensor for detecting throttle position and/or a sensor for determining the rate of change in velocity in a rotating transmission component, such as an output shaft. In each case, it is the transmission control unit 90 that determines the direction of torque based on signals received from the sensor(s) used. Any other suitable way of determining the direction of torque in the transmission can be used.

Optionally, the system can include a speed sensor 98 for detecting the output speed of the transmission. This can assist the transmission control unit 90 to determine which gear is engaged, since it can be programmed with details of the gear ratios and knows the input speed from the output side of the clutch sensor 93. Also, the readings from the speed sensor 98 can be used by the transmission control unit 90 to take into account the effect of changing road conditions on the direction of torque in the transmission 88.

Selector and actuator mechanisms

Each selector mechanism 29,31,33 is similar and is mounted on its shaft in a similar manner. The structure of the first gear selector mechanism 29 and the way that it selectively engages the crawler gear 10 and the first gear 12 will now be described. However the general structure and principles of operation are applicable to the second and third gear selector mechanisms 31,33 and their respective gear wheels.

The gear selector mechanism 29 is arranged to engage drive formations 20 located on the crawler gear 10 and the first gear 12. The drive formations 20 on each gear wheel 10,12 comprise groups of dogs (similar drive formations are located on the mainshaft gears 8,10,12,14,16,18 carried by the input and output shafts 3,1).

The first dog group 20 is located on one side of the crawler gear 10. The dogs are preferably formed integrally with the crawler gear 10, but this is not essential. The first dog group 20 comprises three dogs evenly circumferentially distributed about the gear face, i.e. the angle subtended between the centres of a pair of dogs is approximately 12Cf (see Figures 2 and 3). The second dog group 20, comprises three dogs and is similarly arranged on one side of the first gear 10. Three dogs are used because this arrangement provides large engagement windows, that is the spaces between the dogs, to receive the engagement elements and because of its inherent self-centring affect and even load distribution. Large engagement windows provide greater opportunities for the first gear selector mechanism 29 to fully engage the gear wheels 10,12 before transmitting drive thereto. If the first gear selector mechanism 29 drives a gear wheel when only partially engaged it can lead to damage of the dogs and / or the first gear selector mechanism 29. The splitter high/third gear 16 has drive formations on two sides since it can be selected by the second and third selector mechanisms 31,33.

The crawler and first gears 10,12 are mounted spaced apart on the output shaft 1 and are arranged such that the sides including the first and second dog groups face each other.

The first gear selector mechanism 29 includes the first and second sets of engagement elements 35,36 and the actuator assembly 38.

The first and second sets of engagement elements 35,36 are mounted on the output shaft 1 between the crawler and first gears 10,12. The first set of engagement elements 35 comprises three engagement elements 28 that are evenly distributed about the output shaft 1 such that their bases face inwards, and the axes of the elements 28 are substantially parallel. The second set of engagement elements 36 comprises three engagement elements 30 which are similarly arranged about the output shaft 1 (see Figure 3).

The sets of engagement elements 35,36 are mounted on a sleeve 34 which is mounted on the output shaft 1 between the crawler and first gears 10,12 (see Figures Ia, Ie and 3). The sets of engagement elements 35,36 are arranged to rotate with the output shaft 1 but are able to slide axially along the sleeve 34 and the output shaft 1 in response to a switching action of the actuator assembly 38. To facilitate this, the sleeve 34 includes six keyways 41 formed in its curved surface with each engagement element 28,30 having a complementary formation in its base. The keyways 41 can be arranged to be non-radially restraining or to be radially restraining. If the keyways 41 are radially restraining, they may have substantially T-shaped profiles such that the elements are radially and tangentially (but not axially) restrained within the keyways 41 (see Figure 3). Alternatively, the keyways 41 can have slotted or dovetailed profiles to radially restrain the elements, or any other suitable shape.

Preferably the engagement elements 28,30 are configured to be close to the output shaft 1 to prevent significant cantilever effects due to large radial distances of loaded areas thus reducing the potential for structural failure.

The arrangement of the element sets 35,36 is such that elements of a particular set are located in alternate keyways 41 and the element sets 35,36 can slide along the sleeve 34. The elements in each element set are rigidly connected to each other by an annular connector member 100 and move as a unit. The connector member 100 also acts to radially restrain the engagement elements. Each element set 35,36 can move independently of the other. The connector member 100 has a groove 102 formed in its outer curved surface that extends fully around the circumference of the connector member. The elements 28 in the first set of engagement elements 35 are preferably integrally formed with its connector member 100, though this is not critical. The elements 28 are evenly distributed about the connector member 100. The second set of engagement elements 36 comprises three elements 30, which are held in a similar fixed arrangement by a second connector member 100. When there is relative movement between the first and second sets of elements 35,36, the connector member 100 of the first element set 35 moves over the second set of elements 36 and the connector member 100 of the second element set 36 slides over the first set of elements 35.

Each element 28 in the first element set 35 has a first end 28a arranged to engage the first group of dogs 20 attached to the first gear wheel 13 and a second end 28b arranged to engage the second group of dogs 20 on the third gear wheel 17. The first and second ends 28a,28b typically have the same configuration but are opposite handed, for example the first end 28a is arranged to engage the first group of dogs 20 during deceleration (reverse torque direction) of the first gear wheel 13 and the second end 28b is arranged to engage the second group of dogs 20 during acceleration (forward torque direction) of the third gear wheel 17 (see Figure 4). Each element 30 in the second element set 36 is similarly arranged, except that the first end 30a is arranged to engage the first group of dogs 20 during acceleration of the second gear wheel 15 and the second end 30b is arranged to engage the second group of dogs 20 during deceleration of the third gear wheel 17.

When both the first and second sets of engagement elements 35,36 engage a gear wheel drive is transmitted between the input and output shafts 3,1 whether the gear is accelerating or decelerating.

The first and second ends 28a,30a,28b,30b of each element include an engagement face 43 for engaging the dogs 20, a ramp 45, an end face 42 and may include a shoulder 44 (see Figure 4). The end faces 42 limit the axial movement of the engagement elements 28,30 by abutting the sides of the gear wheels. The engagement faces 43 may be angled to complement the sides of the dogs 20a so that as the engagement elements 28,30 rotate into engagement, there is face-to-face contact to reduce wear. Each ramp 45 is preferably helically formed and slopes away from the end face 42. The angle of inclination of the ramp 45 is such that the longitudinal distance between the edge of the ramp furthest from the end face 42 and the plane of the end face 42 is larger than the height of the dogs 20. This ensures that the transmission does not lock up when there is relative rotational movement between the engagement elements 28,30 and the dogs 20 that causes the ramp 45 to move towards engagement with the dogs 20. The dogs 20 do not crash into the sides of the engagement elements 28,30 but rather engage the ramps 45. As further relative rotational movement between the dogs 20 and the engagement elements 28,30 occurs, the dogs 20 slide across the ramps 45 and the helical surfaces of the ramps cause the engagement elements 28,30 to move axially along the output shaft 1 away from the dogs 20 so that the transmission does not lock up.

The arrangement of the gear selector mechanism 29 is such that it inherently prevents lockup of the transmission occurring when selecting a new gear.

When the elements of the first and second sets 35,36 are interleaved, as in Figure 3, the engagement faces 43 of the first ends 28a of the first set of elements 35 are adjacent the engagement faces 43 of the first end 30a of the second set of elements 36. When the first and second sets of elements 35,36 are fully engaged with a gear, a dog 20 is located between each pair of adjacent engagement faces 43. The dimensions of the dogs 20 and the ends of the elements are preferably such that there is little movement of each dog between the engagement face 43 of the acceleration element and the engagement face 43 of the deceleration element when the gear moves from acceleration to deceleration, or vice versa, to ensure that there is little or no backlash in the gear.

The actuator assembly 38 includes first and second actuators 46,64 and first and second actuator members 48,58. The first and second actuators 46,64 are force generator actuators and preferably part of an electrical system for example, an electro-mechanical system or an electro-hydraulic system. The first and second actuator members 48,58 are mechanical drive members that transmit force from the first and second actuators to 46,64 to the sets of engagement members 35,36 and are preferably in the form of independently controllable forks. Accordingly, the first set of engagement elements 35 is driven by the first actuator 46 via the first fork 48 and the second set of engagement elements 36 is driven by the second actuator 64 via the second fork 58. Thus the first and second sets of engagement elements

35,36 move totally independently of each other. Alternatively, the first and second sets of engagement members can be arranged to have some interdependence such as the arrangement of WO 2004/099654, which only has a single actuator for controlling actuation of both sets of engagement elements.

Each fork 48,58 is arranged to extend approximately 180 degrees around the groove 102 of its respective set of engagement elements and includes a semi-annular part that is located within the groove 102. Each set of engagement elements 35,36 can rotate relative to its respective fork 48,58 and is caused to move axially along the input shaft 3 by the actuator member 48,58 applying a force to the connector member 100.

The actuator assembly 38 can optionally include resilient devices, such as helical springs (not shown). The springs are arranged to bias the first and second sets of engagement elements 35,36 to move in an axial direction when they are in driving engagement with a gear wheel and are unable to move. For example, the forks 48,58 can be suspended at their remote ends in a cradle and can be arranged to move a limited amount with respect to the cradle 68 against the action of the springs 66.

Operation of the first and second actuators 46,64, and hence movement of the first and second sets of engagement elements is controlled by the transmission control unit 90. When transmission position sensors 96 are used, they are arranged for determining the operational conditions of selector mechanisms 29,3133 in the transmission. Typically the position sensors 96 monitor the positions of the actuator members 48,58 and hence the positions of the sets of engagement elements to determine whether they are engaged with a gear wheel or not. However, they can be arranged to monitor the positions of the sets of engagement elements directly in some applications to obtain the same effect. Typically there are the same number of position sensors 96 as there are sets of engagement elements or actuator members 48,58. In this case, there are two position sensors per selector mechanism 29,31,33, giving six in total.

Conveniently the position sensors 96 can be included in the actuators 46,64 to provide a compact arrangement. The position sensors 96 can be of any suitable type such as hall effect type sensors. ^

If position sensors 96 are not used, the positions of the sets of engagement elements 35,36 are calculated by the transmission control unit 90 from the known geometry of the transmission and the controlled actuation of the sets of engagement elements 35,36.

The transmission control unit 90 is an electronic logic control system driven by software that is arranged to control operation of the first and second actuators 48,64 and hence the first and second sets of engagement elements 35,36. It is the sequence programming that enables the transmission control unit 90 to automatically control the transmission to prevent conflict shifts occurring. Being able to control the actuation of the first and second sets of engagement elements 35,36 totally independently by use of first and second actuators 46,64 and the first and second actuator members has the advantage that the magnitude and the timing of application of the biasing force applied by each actuator can be independently and accurately controlled. This means that even at low rotational gear speeds the engagement elements sets 35,36 do not accidently disengage from the engaged gear wheel and thus no loss of drive is experienced.

Optionally, the transmission control unit 90 can have two layers of control: a first layer for controlling operation of the selector mechanisms 29,31,33 and a second level that monitors operation of the first level of control to ensure that the first layer of control is operating correctly.

The transmission 88 can be fully automatic, that is gear selections are made by the transmission control unit 90 when the engine control unit 82 detects predetermined operational conditions, for example when the engine 80 reaches a particular speed in a particular gear. Alternatively, gear selection can be made by the user of the drive system by initiating the gear selection input device 94, for example a gear lever (manual) or switches located adjacent the steering wheel (semi-automatic). The transmission 88 can be arranged such that it is possible to select between the automatic and manual modes.

Operation of a single gear selector mechanism

The operation of the first gear selector mechanism 29 will now be described with reference to Figures 5a-5f which for clarity illustrate diagrammatically the movement of the first and second sets of engagement element 35,36 by the relative positions of only one element from each set.

Figure 5a shows the first and second element sets 35,36 in a neutral position, that is, neither element set is engaged with a gear wheel. Figure 5b shows the first and second element sets moving into engagement with the crawler gear 10 under the action of the first and second actuators 46,64 in response to a gearshift request from the input device 94. Preferably, the clutch is opened for the first gearshift.

Figure 5 c shows a condition when the crawler gear 10 is fully engaged, that is, the elements 28,30 are interleaved with the first group of dogs 20. The first and second actuators 46,64 are activated such that the actuator members 48,58 maintain the first and second element sets 35,36 in engagement with the first gear wheel 13. Accordingly, drive is transferred through the crawler gear 10 to the output shaft 1 via the first element set 35 when decelerating and via the second element set 36 when accelerating.

Whilst accelerating (crawler gear 10 rotating in the direction of arrow B in Figure 5 c) using the crawler gear 10, the engagement faces 43 of the elements of the first element set 35 are not loaded, whilst the engagement faces 43 of the elements of the second element set 36 are loaded. When a user, or an engine control unit 82 wishes to engage the first gear 12 an input signal is sent from the input device 94 or the engine control unit 82 to the transmission control unit 90. The transmission control unit 90 sends a signal to the clutch actuator 92 to reduce the clutch clamp load until the transmission control unit 90 detects relative rotational movement between the input and output sides of the clutch based on signals received from the clutch sensors 93. For example, the transmission control unit 90 may detect around a 1% difference in rotational speeds. The transmission control unit 90 also actuates the first actuator 46 to drive the first actuator member 48, which causes the elements 28 of the first element set 35 to slide axially along the keyways 41 in the sleeve 34 thereby disengaging the first element set

35 from the crawler gear 10 (see Figure 5d).

The second actuator 64 is activated to move the second actuator member 58 and hence the second element set 36 towards the first gear 12. However, because the second element set 36 is loaded, i.e. is driving the crawler gear 10, it cannot be disengaged from the crawler gear 10, and the second element set 36 remains stationary, with the second actuator 64 and when used at least one helical spring 66 biasing it towards the first gear wheel 12.

When the first element set 35 slides axially along the output shaft 1, the engagement faces 43 engage the second group of dogs 20 (see Figure 5e). The torque spike caused by the engagement can be reduced by allowing further relative rotation of the input and output sides of the clutch 86. The engagement elements 28 then begin to drive the first gear 12 in the direction of Arrow C in Figure 5e and drive is transmitted between the output shafts 3, and counter 6 via first gear train 12,12 . As this occurs, the second element set 36 ceases to be loaded, and is free to disengage from the first group of dogs 20. Since the second element set 36 is biased by the second actuator 64 (and the helical spring 66 if used) it slides axially along the keyways 41 in the sleeve 34 thereby completing the disengagement of the crawler gear wheel 10 from the output shaft 1. The second element set 36 slides along the keyways 41 until it engages the first gear 12, thereby completing engagement of the first gear wheel 12 with the output shaft 1 (see Figure 5f).

The transmission control unit 90 restores clutch clamp load using the clutch actuator 92 and returns control of the engine 80 to the driver. This is done smoothly so that it is imperceptible to the driver.

This method for selecting gear trains substantially eliminates torque interruption since the first gear train 12 is engaged before the crawler gear 10 is disengaged, thus momentarily, the crawler and first gears 10,12 are simultaneously engaged and locked for rotation with the output shaft 1, until the newly engaged gear wheel overdrives the original gear wheel. Thus gearshifts are instantaneous since there is no loss of drive when changing gear.

When a gear is engaged by both the first and second element sets 35,36 it is possible to accelerate or decelerate with very little backlash occurring when switching between the two conditions. Backlash is the lost motion experienced when the dog moves from the engagement face 43 of the acceleration element to the engagement face 43 of the deceleration element when moving from acceleration to deceleration, or vice versa. A conventional dog- type transmission system has approximately 30 degrees of backlash. A typical transmission system for a car in accordance with the current invention has backlash of less than four degrees. Backlash is reduced by minimising the clearance required between an engagement member and a dog during a gearshift: that is, the clearance between the dog and the following engagement member (see measurement 'A' in Figure 5b). The clearance between the dog and the following engagement member is in the range 0.5mm - 0.03mm and is typically less than 0.2mm. Backlash is also a function of the retention angle, that is, the angle of the engagement face 43, which is the same as the angle of the undercut on the engagement face of the dog 20a. The retention angle influences whether there is relative movement between the dog and the engagement face 43. The smaller the retention angle, the less backlash that is experienced. The retention angle is typically between 0 and 15 degrees.

Transition from the first gear 12 to the crawler gear 10 whilst decelerating is achieved by a similar process.

Whilst decelerating in the first gear 12 the engagement surfaces 43 of the elements of the first element set 35 are not loaded, whilst the engagement surfaces 43 of the elements of the second element set 36 are loaded. When a user, or an engine control unit 82 wants to engage the first gear train 5 a signal is sent from the input device 94 or the engine control unit 82 to the transmission control unit 90. The transmission control unit sends a signal to the clutch actuator 92 to reduce the clutch clamp load until the transmission control unit 90 detects relative rotational movement between the input and output sides of the clutch based on signals received from the clutch sensors 93. The transmission control unit 90 then synchronises the engine speed via the engine control unit 82 to the new gear wheel to be selected. The transmission control unit 90 actuates the first actuator 46 to move the first actuator member 48 axially, causing the first element set 35 to slide axially in the keyways 41 along the input shaft 3 in the direction of the crawler gear 10, thereby disengaging the first element set 35 from the first gear wheel 12.

The transmission control system activates the second actuator 64 however since the second element set 36 is loaded, i.e. it is drivingly engaged with the dogs 20 on the third gear wheel 17, it remains stationary but is urged towards the first gear wheel 13.

As the first element set 35 slides axially in the keyways 41 and engages the dogs 20 on the crawler gear 10 and begins to drive the crawler gear 10 such that energy is transmitted between the output and counter 6, shafts 3, via the crawler gear train 10,10'. The torque spike caused by the engagement is minimised due to the speed synchronisation step. However if a torque spike is generated its effect is mitigated by further relative rotation of the input and output sides of the clutch 86. As this occurs, the second element set 36 ceases to be loaded and biasing of the second actuator 64 (and the helical spring(s) 66 if used) causes it to slide axially within the key ways 41 along the input shaft 3 towards the crawler gear 10, thereby completing disengagement of the first gear 12. The second element set 36 continues to slide within the keyways 41 along the output shaft 1 until it engages the crawler gear 10, thereby completing engagement of the crawler gear 10 with the output shaft 1.

The transmission control unit 90 restores clutch clamp load using the clutch actuator 92 and control of the engine 80 is returned to the driver.

Kick-down shifts, that is a gearshift from a higher gear train to a lower gear train but where acceleration takes place, for example when a vehicle is travelling up a hill and the driver selects a lower gear to accelerate up the hill, require a brief torque interruption to allow disengagement of the driving element set. For example, when accelerating in first gear the first gear wheel 12 is fully engaged by the first and second sets of engagement elements 35,36 and the first element set 35 drivingly engages the dogs 20. When a kick-down shift is requested by the user via the input device 94 or the engine control unit 82, the transmission control unit 90 reduces the clutch clamp load using the clutch actuator 92 until controlled relative rotational movement between the input and output sides of the clutch is detected by the transmission control unit 90 via the clutch sensor 93 readings. The engine speed is then adjusted to synchronise with the new gear speed (crawler gear in this case), which typically involves increasing the engine speed. The transmission control unit 90 is able to synchronise the speed since it is programmed with information relating to the gear ratios for each gear train and can determine the currently engaged gear and the new gear to be selected. Synchronising the engine speed in this manner has a smoothing effect when engaging the new gear and prevents the vehicle from lurching when the gear is selected. The clutch clamp load is then further reduced as is the throttle in order to maintain the new ratio speed. The loaded 35 and the unloaded element sets 36 are then disengaged from the third gear wheel 17 by actuating the first and second actuators 46,64 such that loaded set disengages the first gear 12 prior to the unloaded set 36 engaging the crawler gear 10. The torque spike caused by the engagement is minimised due to the speed synchronisation step. However if a torque spike is generated its effect is mitigated by further relative rotation of the input and output sides of the clutch 86. In practice it is preferable to reduce the torque transmittable by the clutch to zero, or near zero, or at least sufficiently low such that the actuators 46,64 are able to move the sets of engagement before disengaging the loaded set of engagement elements 35. Although the shift is not entirely instantaneous, it is very quick and the power interruption is lower than previous methods and may not even be noticed by the driver. The first element set 35 is then moved across into engagement with the crawler gear 10 to complete the kick-down shift. After which, the torque is reinstated by the engine control unit 82, the clutch clamp load is restored by the clutch actuator 92 and control of the engine 80 is returned to the user.

When the unloaded second element set 36 is disengaged from the first gear 12, it can alternatively be held in the neutral position until after the loaded first element set 35 is disengaged from the first gear 12. The second element set 36 can then be moved into engagement with the crawler gear 10, after which the torque and clutch are reinstated. This shift is not instantaneous.

Transmission Layout

The transmission system layout uses a multi-gear multi-path layout, which uses discrete gear ratios and instantaneous selector mechanisms 29,31,33 to facilitate instantaneous torque handover gear shifts for a variety of different ratios. In the example given the layout is a twelve plus two transmission with twelve main gear ratios plus one crawler ratio and one reverse gear ratio. It will be apparent to the skilled person that additional (or less) gear trains can be used in the transmission system to make it suitable for different vehicles.

The first selector mechanism 29 includes first and second sets of engagement elements 35,36 (Y,Z in Figures 6 to 18) for selectively locking respectively the crawler gear 10 and first gear 12 to the output shaft 1. Each set of engagement members 35,36 is connected to an actuator assembly 38, which is described below. By actuating the sets of engagement members 35,36 it is possible to connect the crawler gear 10 and/or first gear 12 to the output shaft 1 to transfer drive between that gear and the shaft 1. Moving the actuator assembly 38 engages one gear and disengages the other without any appreciable interruption in the torque transferred through the transmission. The second selector mechanism 31 is similar to the first selector mechanism 29 and includes a first and second sets of engagement members 35,36 (W,X in Figures 6 to 18) for selectively locking respectively the second gear 14 and third/splitter high gear 16 for rotation with the output shaft 1 and an actuator assembly 38. By activating the actuator assembly 38 it is possible to connect the second gear 14 and/or third/splitter high gear 16 to the output shaft 1 to transfer drive between that gear and the shaft.

The third selector mechanism 33 is again similar to the first selector mechanism 29 and includes first and second sets of engagement members 35,36 (U, V in Figures 6 to 18) for selectively locking respectively the third/splitter high gear 16 and the splitter low gear 18 to the input shaft 3 and an actuator assembly 38. By activating the actuator assembly 38 it is possible to connect the third/splitter high gear 16 and/or the splitter low gear 18 to the input shaft 3 to transfer drive between that gear and the shaft. The third/splitter high gear 16, the splitter low gear 18, their complementary countershaft gears 16',18', and the third selector mechanism 33, together comprise an input splitter 60.

In order to achieve the different ratios an input splitter 60 is used on the input side of the transmission and a range changer 22 is used on the output shaft of the transmission. It is feasible to incorporate a neutral position between the splitter ratios which will aid engine synchronisation during certain shifts.

Power enters the transmission through the input shaft 3 and is transferred to the countershaft 6 through either one of two gear ratios (split low and split high) provided by the input splitter 60. The first selector mechanism 29 with no neutral position transmits the input power to the countershaft 6 through either the split low gear ratio or the split high gear ratio.

The mainshaft gears 12,14,16 are then selectively locked for rotation with the output shaft 1 and power is transferred to the output shaft 1 through the selected ratio, according to the operational conditions of the first, second and third selector mechanisms 29, 31 , 33.

The high splitter gear 16 is also third gear. This means that when third/split high is selected by the second and third selector mechanisms 31,33 power travels directly from the input shaft 3 to the output shaft 1 and is not transferred through the countershaft 6. The range changer 22 provides a two ratio final drive for the transmission. The torque paths for the various selected ratios remain the same once the range changer 22 has been changed from its initial low ratio to its alternative high ratio.

Operation of the transmission system is sequenced as described below with reference to figures 7 to 19, wherein the following references are used:

First selector mechanism 29:

First set of engagement elements Y = Drive ring for 1^st Second set of engagement elements Z = Overun ring for 1^st Second selector mechanism 31: First set of engagement elements W = Drive ring for H/3^rd : Overun ring for 2nd

Second set of engagement elements X = Overun for H/3^rd : Drive ring for 2^nd Third selector mechanism 33:

First set of engagement elements U = Drive ring for Low: Overun ring for High Second set of engagement elements V = Overun ring for Low: Drive ring for High

1. Power - on shifts

1.1 Up-shift:lst-M^st split

• Positive engine torque maintained

• Clutching maintained

• The third selector mechanism 33 is actuated: Positive torque maintains the first set of engagement elements U in drive, the first set of engagement elements is pre-loaded,

Second set of engagement elements V moves from split low to split high position

• Drive relieved off first set of engagement elements U and moves into split high position to complete the shift

1.2 Up-shift: 1^st split -*2^nd • Positive engine torque maintained

• Clutching maintained • First selector mechanism 29 is actuated: First set of engagement elements Y maintained in 1^st gear due to positive driving torque, and is pre-loaded, Second set of engagement elements Z moves to neutral position

• Second selector mechanism 31 actuated to move from neutral position to engage 2ⁿ gear. First and Second sets of engagement elements W & X engage 2ⁿ gear

• First set of engagement elements Y relieved of driving torque, and due to preloading moves into neutral position

• Torque decreased (Throttle and clutch modulation)

• Third selector mechanism 33 actuated: First set of engagement elements U maintained in split high due to overrun torque, and is pre-loaded, Second set of engagement elements V moves from split high to split low position

• First set of engagement elements U relieved of torque and due to pre-loading moves from split high to split low position

• Torque increased (Throttle and clutch modulation)

1.3 Up-shift: 1^st ^2^nd

• Positive engine torque maintained

• Clutching maintained

• First selector mechanism 29 actuated and moves from 1^st gear position to neutral position: First set of engagement elements Y maintained in 1^st gear due to positive driving torque, and is pre-loaded, Second set of engagement elements Z moves from

1^st gear to neutral position

• The second gear selector mechanism 31 is actuated and moves from neutral position into 2^nd gear position: First and second sets of engagement elements W & X engage in 2^nd. First set of engagement elements W takes up driving torque. • First set of engagement elements Y relieved of torque, due to pre-loading moves into neutral position ^

1.4 Down-shift: 1^st split -» 1^st

• Drive torque decreased (Throttle and clutch modulation)

• Third selector mechanism 33 actuated and moves from split high to split low position: First set of engagement elements U is maintained in split high position due to overrun torque, and is pre-loaded, Second set of engagement elements V engages in split low gear

• Torque increased (Throttle and clutch modulation)

1.5 Down-shift: 2^nd -» 1^st split

• Positive engine torque maintained

• Third selector mechanism 33 actuated and moves from split low to split high: First set of engagement elements U is maintained in split low due to drive torque, and is preloaded, Second set of engagement elements V engages in split high gear • First set of engagement elements U is relieved of torque and due to pre-loading moves from split low to split high position.

• Torque decreased (Throttle and clutch modulation)

• The second selector mechanism 31 actuated and moves from 2^nd gear to neutral position: First set of engagement elements W maintained in 2^nd gear due to overrun torque, and is pre-loaded, Second set of engagement elements X moves from 2^nd gear to neutral position

• First selector mechanism 29 actuated and moves from neutral position into 1^st gear position: First and second sets of engagement elements Y & Z engage in 1^st gear. Second set of engagement elements Z takes up overrun drive. • First set of engagement elements W relieved of driving torque, due to pre-loading moves from 2^nd gear to neutral position

• Torque increased (Throttle and clutch modulation) 1.6 Down-shift: 2^nd split -> 1^st split

• Torque decreased (Throttle and clutch modulation)

• Second selector mechanism 31 actuated and moves from 2" gear position into neutral position: First set of engagement elements W maintained in gear due to torque reversal, and is pre-loaded, Second set of engagement elements X moves from 2^nd gear into neutral position

• First selector mechanism 29 actuated and moves from neutral position into 1^st gear position: First and second sets of engagement elements Y & Z engage in 1^st gear. Second set of engagement elements Z takes up overrun drive • First set of engagement elements W relieved of torque and due to pre-loading moves into neutral position

• Torque decreased (Throttle and clutch modulation)

1.7 Down-shift: 2^nd -» 1^st

• Torque decreased (Throttle and clutch modulation) • Second selector mechanism 31 actuated and moves from 2^nd gear position into neutral position: First set of engagement elements W maintained in gear due to torque reversal, and is pre-loaded, Second set of engagement elements X moves into neutral position

• First selector mechanism 29 actuated and moves from neutral position into 1^st gear position: First and second sets of engagement elements Y & Z engage in 1^st gear.

Second set of engagement elements Z takes up overrun drive

• First set of engagement elements W relieved of torque and due to pre-loading moves into neutral position

• Torque increased (Throttle and clutch modulation)

2. Power-off shifts

2.1 Up-shift: lst^ 1^st split

• Torque increased (Throttle modulation) • Third selector mechanism 33 actuated and moves from split low to split high position: First set of engagement elements U is maintained in split low position due to driving torque, and is pre-loaded, Second set of engagement elements V moves from split low to split high gear position • Drive relieved off set of engagement elements U and due to pre-loading moves from split low to split high position

• Torque decreased (Throttle modulation)

2.2 Up-shift: 1st split -»2nd

• Torque increased (Throttle modulation)

• First selector mechanism 29 actuated and moves into neutral position: First set of engagement elements Y maintained in 1^st gear due to driving torque, and is preloaded, Second set of engagement elements Z moves to neutral position

• Second selector mechanism 31 actuated and moves from neutral position into 2^nd gear position: First and second sets of engagement elements W & X engage in 2^nd gear. Second set of engagement elements X takes up drive torque.

• First set of engagement elements Y relieved of driving torque, due to pre-loading moves from 1^st to neutral position

• Torque decreased (Throttle modulation)

• Third selector mechanism 33 actuated and moves from split high to split low position: First set of engagement elements U is maintained in split high position due to overrun torque, and is pre-loaded, Second set of engagement elements V moves from split high to split low position.

2.3 Up-shift: 1st ->2nd

• Torque increased (Throttle modulation)

• First selector mechanism 29 actuated and moves from 1^st gear position to neutral position: First set of engagement elements Y maintained in 1^st gear due to positive driving torque, and is pre-loaded, Second Set of engagement elements Z moves from 1^st to neutral position

• Second selector mechanism 31 actuated and moves from neutral position into 2^nd gear position: First and second sets of engagement elements W & X engage in 2^nd . Second set of engagement elements X takes up drive torque.

• First set of engagement elements Y relieved of torque, due to pre-loading moves from 1st into neutral position

• Torque decreased (Throttle modulation)

2.4 Down-shift: 1st split -> 1^st • Third selector mechanism 33 actuated and moves from split high to split low position:

First set of engagement elements U maintained in split high due to overrun torque, and is pre-loaded, Second set of engagement elements V moves from split high to split low position

• First set of engagement elements U relieved of torque, due to pre-loading moves into split low position

2.5 Down-shift: 2nd -> 1st split

• Torque increased (Throttle modulation)

• Third selector mechanism 33 actuated and moves from split low to split high position: First set of engagement elements U maintained in split low position due to drive torque, and is pre-loaded, Second set of engagement elements V moves from split low to split high position

• Torque decreased (Throttle modulation)

• Second selector mechanism 31 actuated and moves from 2^nd to neutral position: First set of engagement elements W maintained in 2^nd gear position due to overrun torque, and is pre-loaded, Second set of engagement elements X moves from 2^nd to neutral position

• First selector mechanism 29 actuated and moves from neutral position to 1^st gear position: First and second sets of engagement elements Y & Z move from neutral to 1^st gear position. Second set of engagement elements Z takes up overrun drive. • First set of engagement elements W relieved of torque, pre-loaded spring unloads and moves set of engagement elements W from 2^nd to neutral position

2.6 Down-shift: 2nd split ->lst split

• First selector mechanism 29 actuated and moves from neutral position to 1^st gear position: First and second sets of engagement elements Y & Z move from neutral to 1 ^st gear position. Second set of engagement elements Z takes up overrun drive

• First set of engagement elements W relieved of torque, due to pre-loading moves from 2^nd into neutral position

2.7 Down-shift: 2nd -> 1st

• Second selector mechanism 31 actuated and moves from 2ⁿ to neutral position: First set of engagement elements W maintained in 2^nd gear position due to overrun torque, and is pre-loaded, Second set of engagement elements X moves from 2^nd to neutral position

• First selector mechanism 29 actuated and moves from neutral position to 1^st gear position: First and second sets of engagement elements Y & Z move from neutral to 1^st gear position. Second Set of engagement elements Z takes up overrun drive

Noise Vibration and Harshness improvements can be achieved through clutch modulation during shift events. A neutral position can be applied to the splitter hub allowing engine synchronisation during splitter shifts, for some applications.

It will be appreciated by the skilled person that the invention is not to be considered as strictly limited to the above embodiment and that modifications can be made that fall within the scope of the invention, for example the number of gear trains included and the specific type of selector assemblies used.

Claims

1. A transmission system including first and second shafts, a first gear element rotatably mounted on the first shaft, and a first selector assembly for selectively locking the first gear element for rotation with the second shaft from the following operational modes: lock the first gear element for rotation with the second shaft in the clockwise and anticlockwise directions; lock the first gear element for rotation with the second shaft in the clockwise direction and not lock in the anti-clockwise direction; and lock the first gear element for rotation with the second shaft in the anti-clockwise direction and not lock in the clockwise direction.

2. A transmission system according to claim 1, including a second selector assembly for selectively locking the first gear element for rotation with the first shaft from the following operational modes: lock the first gear element for rotation with the first shaft in the clockwise and anti-clockwise directions; lock the first gear element for rotation with the first shaft in the clockwise direction and not lock in the anticlockwise direction; and lock the first gear element for rotation with the first shaft in the anti-clockwise direction and not lock in the clockwise direction.

3. A transmission system according to anyone of the preceding claims, including a second gear element rotatably mounted on the second shaft, wherein the first selector assembly is arranged to selectively lock the second gear element for rotation with second shaft from the following operational modes: lock the second gear element for rotation with the second shaft in the clockwise and anti-clockwise directions; lock the second gear element for rotation with the second shaft in the clockwise direction and not lock in the anti-clockwise direction; and lock the second gear element for rotation with the second shaft in the anti-clockwise direction and not lock in the clockwise direction.

4. A transmission system according to any one of the preceding claims, including a third shaft arranged substantially parallel to the first and second shafts.

5. A transmission system according to claim 4, including a first gear train arranged to communicate drive between the first and third shafts, wherein the first gear train includes the first gear element and at least one additional gear element.

6. A transmission system according to claim 4 or 5 when dependent on claim 2, including a second gear train arranged to communicate drive between the second and third shafts, wherein the second gear train includes the second gear element and at least one additional gear element.

7. A transmission system according to any one of claims 4 to 6, including a third gear train arranged to communicate drive between the first and third shafts, said third gear train including a third gear element rotatably mounted on the first shaft and at least one additional gear element.

8. A transmission system according to claim 7, wherein the second selector assembly is arranged to selectively lock the third gear element for rotation with the first shaft from the following operational modes: lock the third gear element for rotation with the first shaft in the clockwise and anti-clockwise directions; lock the third gear element for rotation with the first shaft in the clockwise direction and not lock in the anticlockwise direction; and lock the third gear element for rotation with the first shaft in the anti-clockwise direction and not lock in the clockwise direction.

9. A multipath transmission system for a heavy goods vehicle (HGV) or similar vehicle including input, output and counter shafts, a first gear train for communicating drive between the output shaft and the counter shaft having a first gear element rotatably mounted on the output shaft and a gear element fixed for rotation with the counter shaft, a second gear train for communicating drive between the input shaft and the counter shaft having a second gear element rotatably mounted on the input shaft and a gear element fixed for rotation with the counter shaft, a first selector assembly for selectively locking each of the first and second gear elements for rotation with the input shaft from the following operational modes: lock the gear element for rotation with the input shaft in the clockwise and anti-clockwise directions; lock the gear element for rotation with the input shaft in the clockwise direction and not lock in the anti-clockwise direction; and lock the gear element for rotation with the input shaft in the anti-clockwise direction and not lock in the clockwise direction, and a second selector assembly for selectively locking the first gear element for rotation with the output shaft from the following operational modes: lock the first gear element for rotation with the output shaft in the clockwise and anti-clockwise directions; lock the first gear element for rotation with the output shaft in the clockwise direction and not lock in the anti-clockwise direction; and lock the first gear element for rotation with the output shaft in the anti-clockwise direction and not lock in the clockwise direction.

10. A multipath transmission system according to claim 11, including a third gear train for transmitting drive between the output shaft and the counter shaft, the third gear train including a third gear element rotatably mounted on the output shaft and another gear element fixed for rotation with the counter shaft.

11. A multipath transmission according to claim 12, wherein the second selector assembly is arranged to selectively lock the third gear element for rotation with the output shaft from the following modes: lock the third gear element for rotation with the output shaft in the clockwise and anti-clockwise directions; lock the third gear element for rotation with the output shaft in the clockwise direction and not lock in the anticlockwise direction; and lock the third gear element for rotation with the output shaft in the anti-clockwise direction and not lock in the clockwise direction.

12. A transmission system or multipath transmission system according to any one of the preceding claims, wherein the or each selector assembly includes first and second sets of engagement members that are moveable into and out of engagement with two gear elements, and an actuator system for actuating the engagement members, wherein the gear selector assembly is arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition and the actuator system is arranged to move the unloaded set of engagement members into driving engagement with the unengaged gear element to effect a gear change.

13. A transmission system or multipath transmission system according to claim 14, wherein the or each selector assembly is arranged such that when a braking force is transmitted the first set of engagement members drivingly engages the engaged gear wheel, and the second set of engagement members is in an unloaded condition, and when a driving force is transmitted the second set of engagement members drivingly engages the engaged gear wheel, and the first set of engagement members is then in an unloaded condition.

14. A transmission system or multipath transmission system according to claim 14 or 15, wherein the actuator system can be arranged to include a first actuator device for actuating the first set of engagement members and a second actuator device for actuating the second set of engagement members independently of the first actuator device.

15. A transmission system or multipath transmission system according to any one of the preceding claims, wherein the or each rotatably mounted gear element includes drive formations that can be engaged by a selector assembly.

16. A transmission system or multipath transmission system according to any one of the preceding claims, wherein the first gear element includes a first set of drive formations for engagement by a first selector assembly and a second set of drive formations for engagement by a second selector assembly.

17. A transmission system or multipath transmission system according to any one of the preceding claims, including an electronically programmable control system for controlling operation of the or each gear selector assembly.

18. A transmission system or multipath transmission system according to any one of the preceding claims, including a gear range changing device arranged to adjust the output drive characteristics of the transmission system.

19. A multi-path transmission system for a heavy goods vehicle (HGV) or other large vehicle that is arranged to perform instantaneous or substantially instantaneous gear changes.