WO2010015451A1

WO2010015451A1 - Onboard electric system for a motor vehicle

Info

Publication number: WO2010015451A1
Application number: PCT/EP2009/057424
Authority: WO
Inventors: Markus Beck; Christian Gaertner; Roman Lahmeyer
Original assignee: Robert Bosch Gmbh
Priority date: 2008-08-06
Filing date: 2009-06-16
Publication date: 2010-02-11
Also published as: DE102008041027A1; CN102119477A; EP2311169A1

Abstract

The invention relates to an onboard electric system for a motor vehicle comprising an electric generator (1), a battery (4), a generator controller (6), and at least one consumer load (7, 8) being supplied by the generator (1) and the battery (4). The generator controller (6) is configured in order to provide the generator (1) with a target output voltage (U_soll+U_diff). The generator controller (6) is equipped to detect the load state (SOC) and the load current (l_ist) of the battery (4), and to vary the target output voltage (U_soll+U_diff) of the generator (6) until the load current (l_ist) assumes an amperage (l_soll) that is predetermined as a function of the load state.

Description

description

title

On-board electrical system for a motor vehicle

The present invention relates to an on-board electrical system for a motor vehicle.

State of the art

DE 100 52 315 A1 discloses an on-board electrical system with an electric generator, a battery which can be charged by the generator, a generator control unit for controlling the power output of the generator and at least one load supplied by the generator and the battery. The generator control unit is able to specify to the generator a desired output voltage, which provides this at its terminals.

In addition, a SoII- battery current is given in this known on-board electrical system. In order to set this desired battery current, the control unit varies the electrical power delivered to certain consumers.

Usually, the generator of a vehicle on-board electrical system is connected to the battery and the consumers via an electrical line of not insignificant length, in which, depending on the current consumption of the battery and the consumer, a voltage drop occurs, which may be several tenths of a volt. If the power consumed by the consumers is so strong that the voltage at the terminals of the battery terie falls below its rest voltage, the battery is discharged. Substituting, in order to exclude excessive discharge of the battery, the target voltage of the generator high, so flows a strong charging current when the power consumption of the generators is low, and the battery is kept on averaged over a high state of charge, in which the energy efficiency of the store is relatively low. The generator must therefore apply an unnecessarily high power to keep the battery in its state of charge. When the state of charge of the battery is constantly high, the efficiency of energy recovery by operation of the generator in the event of a power failure is also low.

Advantages of the invention

The present invention allows a more accurate control of the state of charge of the battery. By the more accurate control, it is possible to keep the battery on average at a lower state of charge, in which the efficiency of the charging is better, without running the risk that the battery reaches a critically low state of charge, in which they do not supply the consumers can ensure more.

This is achieved by the generator control unit is set up in an on-board electrical system of the type specified to detect the state of charge and the charging current of the battery and to vary the nominal output voltage of the generator until the charging current assumes a charging state-dependent predetermined current.

For this purpose, the generator control unit preferably comprises a first control circuit which responds to a terminal voltage of the battery in order to vary the setpoint output voltage of the generator until the terminal voltage corresponds to a desired value, and a second control loop which varies this setpoint value of the terminal voltage Charge state dependent set preset charging current. In spite of controllable charging current intensity, the terminal voltage which can be tapped on the battery is kept constant, an adequate supply of consumers is secured at all times.

The strength of the battery charging current is preferably predetermined as a function of a deviation between an actual and a desired state of charge of the battery. By giving the charging current as a continuous function of the deviation, the charging on average can take place at low currents and correspondingly low voltage losses on the line, which in turn increases the efficiency of the on-board electrical system.

The nominal state of charge of the battery is preferably predetermined as a function of temperature. At a high battery temperature, a relatively low state of charge is sufficient to provide, for example, the currents required to start the vehicle, while at low temperature, safe starting can only be ensured with a significantly higher state of charge. The energetic efficiency of charging, that is, the ratio of electric energy which can be retrieved from the battery to the amount of energy used to charge the battery, is lower the higher the state of charge of the battery is. Therefore, lowering the target high-temperature state of charge also increases the efficiency of the system.

If, for example due to a change in temperature, the actual state of charge of the battery is higher than the desired state of charge, the charging current can also be negative, as a battery discharging current, be specified.

In order to prevent the occurrence of impermissible voltage values in the electrical system, a value limiter can be connected between an output for the nominal generator output voltage of the control unit and a control input of the generator. - A -

The generator control unit may conveniently be implemented by a microprocessor system and an operating program executed by it. In particular, if such a microprocessor system in addition to the control of the generator still other tasks, it is expedient that the microprocessor system is set up to detect the utilization of the generator and suspend the execution of the operation for generator control when the generator is fully utilized. Thus, the computing power not required for the generator control in this time other tasks of the microprocessor system is available.

Further features and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying figures.

characters

Show it:

1 is a block diagram of the on-board electrical system of a motor vehicle;

Fig. 2 is a block diagram of the generator control apparatus of the on-board electrical system of Fig. 1;

3 shows an example of a first characteristic curve used in the control unit; and

4 shows an example of a second characteristic curve used in the control unit.

Description of the embodiments

In the diagram of FIG. 1, 1 designates a generator, 2 a generator regulator, which regulates an output voltage supplied by the generator 1 at its output terminals to a desired value, which is controlled by a 4 is a vehicle battery, 5 is a battery sensor, 6 is a generator control unit for supplying a control signal which the generator controller 2 sets the setpoint of the output voltage, 7, 8 consumers and 9 an electrical line which is an output terminal of the generator. 1 with the battery 4 and the consumers 7, 8 connects.

The generator 1 and the generator controller 2 are combined in a unit of known type. The control signal specifying the target output voltage of the generator 1 on the line 3 is the only control signal which the generator controller 2 processes. The control signal may e.g. a PWM signal with a representative of the desired output voltage of the generator duty cycle act. Alternatively, the line 3 may also be a bus line on which the control signal for the generator controller 2 is transmitted in digital form, optionally alternately in time with control signals for other functional groups of a motor vehicle.

The generator controller 2 is connected within an assembly formed by him and the generator 1 with output terminals of the generator 1 to detect the voltage applied thereto, to compare with the specified voltage from the control signal and optionally the duty cycle of excitation currents with which he the generator. 1 is applied to vary until agreement between the desired output voltage and the tapped at the terminals of the generator 1 actual output voltage is achieved.

The current intensity which the generator 1 must supply in order to maintain the setpoint output voltage at its terminals is variable depending on the number and consumption values of the consumers 7, 8 which are active at the same time. Accordingly, the voltage drop on the line 9 between the generator 2 and the battery 4 is variable. The generator control unit 6 is provided to counteract voltage fluctuations caused by the consumers 7, 8 at the terminals of the battery 4 and to keep the battery 4 at a desired state of charge. An exemplary structure of the control unit 6, with which this goal is achieved, is shown schematically in FIG. The control unit 6 receives as input values from the battery _sensor 5 measured values of the terminal voltage Ui _{st of} the battery 4, the current flowing through the battery 4 current I, the temperature T and the state of charge SOC of the battery 4. In a memory 10 of the controller 6, a characteristic is stored which specifies a desired state of charge of the battery 4 as a function of its temperature.

Fig. 3 shows an example of the course of this characteristic. The nominal state of charge SOC_soll is not higher than 80% at any temperature, since the closer the battery comes to its maximum charging capacity, the lower the energy efficiency of the charging process. In a temperature range of about -30 to +20 ⁰ C, the nominal state of charge gradually decreases from 80 to about 65%. At temperatures above 20 ⁰ C, the desired state of charge is substantially constant. The temperature dependence of the desired state of charge takes into account the temperature dependence of the internal battery resistance; In order to safely start the vehicle with the help of the battery 4, in a cold climate due to poor mobility and possibly also reduced number of mobile charge carriers in the battery 4, a higher state of charge is required than when warm.

Referring again to FIG. 2, the memory 10 is polled on the basis of the temperature measurement value T originating from the battery sensor 5 in order to obtain a value of the setpoint charge state SOC_soll corresponding to the current battery temperature, which is then displayed in a differential amplifier 11 with the signals reported by the battery sensor 5 Actual state of charge SOC is compared. In a simplified embodiment of the invention, the input for the temperature reading T and the memory 10 can also be omitted, and the differential amplifier is instead connected to a fixed value signal representing a constant desired state of charge, the selected between 50 and 95% of the charging capacity of the battery 4 can be.

A representative of the difference between the actual and desired state of charge SOC or SOC_soll output signal of the differential amplifier 11 is used to query a second memory 12. This stores a characteristic curve, a desired charging current l _so n the battery 4 in response to the deviation delta -SOC = SOC-SOC_soll specified between setpoint and actual state of charge. An example of the course of this characteristic is shown in FIG. 4. If actual and nominal state of charge are the same, the charging current is 0; if the actual state of charge remains behind the desired state, then the charging current increases rapidly with increasing deviation. If the nominal state of charge of the battery is lower than the actual state, a (negative) current flow discharging the battery is permitted. The discharging current with positive deviation is usually weaker than the charging current in the case of a strong negative deviation. The fact that the charging current is always different from zero when the actual and target state of charge does not coincide exactly ensures that the battery is charged during a large part of the generator operating time, but only with a weak current, so that losses due to voltage drop occur the line 9 remain low.

A second differential amplifier 13 receives the target value _so l n of the charging current from the memory 12 at its non-inverting and true and charging current l | _St from the battery sensor 5 at its inverting input. The differential amplifier 13 thus provides a representative of the difference between the nominal and actual charging current of the battery signal to an integral proportional controller consisting of an amplifier 14, an integrator stage 15 and an adder 16 for adding the output signals of the amplifier 14 and the integrator stage 15th The output of the adder 16 then assumes a constant value when the temperature measured by the sensor 5 charging current l _ιst and the desired charging current l _as n equal to, the level which the output signal of the adder 16 then assumes, not by the by the components 10 to 16 is defined by a control circuit to be described hereinafter, which uses the output signal of the adder 16 as an input signal.

By in the second control loop, a differential amplifier 17 _st to the non-inverting input connected to the output of the adder 16 and the inverting input with the temperature measured by sensor 5 battery terminal voltage Ui is connected, the output signal of the adder 16 receives the function of a target voltage U _as n for the battery 4. As in the first control circuit, the output of the differential amplifier 17 is connected to an integral proportional controller consisting of an amplifier 18, an integrator stage 19 and an adder 20 for adding the output signals of the amplifier 18 and the integrator stage 19. The output signal of the adder 20 thus depends together with a deviation of the battery terminal voltage U _ιst from its nominal value and is designated in the figure with U _d i _ff . Another adder 21 adds the signals U _so n and Udi _ff and gives the sum U _SO ιι + U _dlff via a level limiter 22 as a target output voltage signal for the generator 1 to the line 3. This has the consequence that U _dlff exactly then converges to a fixed value when the battery voltage U | measured by the sensor 5 _St agrees with U _so n, that is, when U _{dlff represents} the voltage difference by which the output voltage of the generator 1 relative to U _so n must be increased to make the battery _voltage U _ιs t Uson.

The level limiter 22 suppresses excessive fluctuations in the output signal Usoiι + Udi _{ff of} the adder 21, which could possibly occur during a Nach¬ regulating process and limits the possible values of the generator set voltage to an interval of, for example, 10.0 to 15.5 V, in which a proper functioning of the consumer 7, 8 is ensured.

Thus, the generator control unit 6 ensures, on the one hand, a continuously sufficient voltage supply to the loads 7, 8 and, on the other hand, a desired, not unnecessarily high, state of charge of the battery 4.

Between the output of the adder 21 and the control line 3, according to a preferred development, a switch 23 can still be provided, which responds to fuel cut of the vehicle engine and, in the case of fuel cut, instead of the output signal of the adder 21 or the level limiter 22, a constant signal with the line 3 combines. This constant signal corresponds to a high or the maximum output voltage which the generator 1 is able to supply. Shut-off is often used when driving downhill or rolling out in front of a traffic light, in situations where the kinetic energy of the vehicle is greater than required. By using the switch 23, the generator power is set high in such a case, this kinetic energy can be recovered in part via the generator 1 and stored in the battery 4, which reduces the amount of fuel required for the operation of the generator 1.

Since the generator control unit specifies only the output voltage U _SO ιι + U _dlff of the generator 1, it is the object of the generator controller 2, adjust the power of the generator or the strength of the fed to the generator 1 excitation current so that this requirement is met. According to a further developed embodiment of the generator controller 2 to the generator control unit 6 - for example, via the line 3 - a signal back, which is representative of the degree of utilization of the generator, eg for the duty cycle of an energized in windings of the generator exciter current. If the generator control unit is constructed as a microprocessor system and the control circuits described above are each implemented in the form of software, then the microprocessor system may receive a signal of the Generator controller 2, which indicates high or maximum utilization of the generator 1, use by suspending the execution of the second control loop until the signal of the generator controller 2 again indicates a generator power below a predetermined limit. Thus, in a time in which the generator would not be able to provide the compensated output voltage U _so n + Udiff, the computing time required for the calculation of U _d i _ff can be saved and used for other purposes.

Claims

claims

1. Vehicle electrical system for a motor vehicle with an electric generator (1), a battery (4), a generator control unit (6) and at least one by the generator (1) and the battery (4) fed consumers (7, 8), wherein the generator control unit (6) is arranged to give the generator (1) a desired output voltage (U-So _I i ⁺ Udi _ff ), characterized in that the generator control unit (6) is set, the state of charge (SOC) and charging current (l _ιst) of the battery (4) to detect and SoII- output voltage (U _soll + Udι _ff) of the generator (6) to vary, until the charging current (l _ιst) a state of charge depending on predetermined current (Isoii) assumes.

2. on-board electrical system according to claim 1, characterized in that a first control circuit (17-20) of the generator control unit (6) to a

Terminal voltage (U | _St ) of the battery (4) is responsive to vary the _desired output voltage (Usoii + U _dlff ) of the generator (6) until the terminal voltage (U | _St ) corresponds to a setpoint (U _so n), and a second control loop (13-16) of the generator control unit (6) varies the setpoint value (U _so n) of the terminal voltage in order to set the charging current intensity (1 _so n) as a function of the charging state.

3. on-board electrical system according to claim 1 or 2, characterized in that the strength of the battery charging current (L _so n) in response to a deviation (delta-SOC) between actual and nominal

Charge state (SOC, SOC_soll) of the battery (4) is specified.

4. On-board electrical system according to claim 3, characterized in that the strength of the battery charging current (L _so n) as a continuous function the deviation (delta SOC) between actual and nominal state of charge of the battery is specified.

5. Onboard electrical system according to claim 3 or 4, characterized marked, that the desired state of charge (SOC_soll) of the battery is temperature-dependent predetermined.

6. On-board electrical system according to one of claims 3 to 5, characterized in that in the event that the actual state of charge (SOC) of the battery (4) is higher than the desired state of charge (SOC_soll), the

Battery charge current (l _so n) is specified negative.

7. On-board electrical system according to one of the preceding claims, characterized in that between an output for the SoII generator output voltage (U _so n) and a control input of

Generator (1) a value limiter (22) is connected.

8. On-board electrical system according to one of the preceding claims, characterized in that the generator control unit (6) is implemented by a microprocessor system and an operating program executed by this and that the microprocessor system is adapted to detect the utilization of the generator (1) and the execution of the operating program suspend when the generator (1) is at full capacity.