Method for controlling an engine

Abstract

A device for controlling an engine includes: a first control circuit having a first controller, and a second control circuit having a second controller, the controllers being designed to control a state variable of the engine in each case. The second controller is disposed in such a way that it lies closer to the engine than the second controller in terms of signal technology.

Claims

1. A system for controlling an electric motor of a vehicle, the system comprising: a first control device which includes a first controller to control a torque of the electric motor, the first controller outputting a first signal variable to a data bus as a function of an actual torque of the electric motor and a setpoint torque; and a second control device connected downstream from the first control device via the data bus, the second control device receiving the first signal variable over the data bus and including: a second controller to control a speed of the electric motor, the second controller generating a second signal variable as a function of an actual speed of the electric motor and a setpoint speed; and a unit which forms a resulting signal variable as a function of the first and second signal variables; wherein the second controller is situated closer to the electric motor than the first controller in terms of signal technology.

2. The system as recited in claim 1, wherein the first control device and the second control device are disposed in such a way that a signal propagation time of the second signal variable to the unit is shorter than a signal propagation time of the first signal variable to the unit.

3. The system as recited in claim 1, wherein the second controller is directly connected to the unit.

4. The system as recited in claim 1, further comprising an inverter which generates a control variable as a function of the resulting signal variable, wherein the control variable is used to control the electric motor.

5. The system as recited in claim 1, wherein the unit which forms the resulting signal variable is a control unit which specifies, as a function of a driving state of the vehicle, one of at least two different control modes in which the control of the electric motor is implemented.

6. The system as recited in claim 1, wherein the unit is configured to selectively implement a pure torque control as a function of a driving condition of the vehicle by generating the resulting signal variable as a function of the first signal variable but not the second signal variable.

7. The system as recited in claim 6, wherein the unit implements the pure torque control in response to a wheel slip of the vehicle being below a predetermined threshold.

8. The system as recited in claim 1, wherein the unit is configured to selectively implement a pure speed control as a function of a driving condition of the vehicle by generating the resulting signal variable as a function of the second signal variable but not the first signal variable.

9. The system as recited in claim 1, wherein the unit is configured to selectively implement a combined torque and speed control as a function of a driving condition of the vehicle by generating the resulting signal variable as a function of both the first signal variable and the second signal variable.

10. The system as recited in claim 9, wherein the unit implements the combined torque and speed control in response to a wheel slip of the vehicle being above a predetermined threshold.

11. A method for controlling an electric motor of a vehicle, the method comprising: generating a first signal for use in controlling a torque of the electric motor using a first controller of a first control device, the first signal variable being a function of an actual torque of the electric motor and a setpoint torque, and outputting the first signal variable to a data bus; generating a second signal for use in controlling a speed of the electric motor using a second controller of a second control device connected downstream from the first control device via the data bus, the second signal variable being a function of an actual speed of the electric motor and a setpoint speed, the second control device receiving the first signal variable over the data bus; and forming a resulting signal variable as a function of the first and second signal variables using a unit of the second control device, wherein the second controller is situated closer to the electric motor than the first controller in terms of signal technology.

12. The method as recited in claim 11, wherein the first and second controllers are disposed in such a way that a signal propagation time of the second signal to the unit is shorter than a signal propagation time of the first signal to the unit.

13. The method as recited in claim 11, further comprising generating a control variable to control the electric motor as a function of the resulting signal variable using an inverter.

14. A device for controlling an electric motor of a vehicle, the device comprising: a controller to control a speed of the electric motor, the controller generating a signal variable as a function of an actual speed of the electric motor and a setpoint speed; and a unit which forms a resulting signal variable as a function of the signal variable and an additional signal variable that the device receives over a data bus from an additional device, connected upstream from the device via the data bus, having an additional controller to control a torque of the electric motor, the additional signal variable being a function of an actual torque of the electric motor and a setpoint torque, wherein the controller is configured to be situated closer to the electric motor than the additional controller in terms of signal technology.

15. The system as recited in claim 1, wherein the first control device is an electronic stability program control device.

16. The system as recited in claim 1, wherein the unit is a summation unit to form a resulting signal variable as a function of the first and second signal variables, and the system further comprises an inverter to generate a current signal as a function of the resulting signal variable to control the electric motor.

17. The system as recited in claim 16, wherein the inverter is disposed in the second control device.

18. The device as recited in claim 14, wherein the control device and the additional control device are disposed in such a way that a signal propagation time of the signal variable to the unit is shorter than a signal propagation time of the additional signal variable to the unit.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows A block circuit diagram of a control device according to one specific embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(2) FIG. 1 shows a block circuit diagram of a specific embodiment of a device according to the present invention for the control of an engine 1, in this case, an electric motor which drives the front axle of a vehicle, for example.

(3) The control device in the present example includes two controllers 3, 5, i.e., a torque controller 3 and an engine speed controller 5, which control electric motor 1 as a function of the driving state either individually or jointly. At low wheel slipthe vehicle is in a stable state , a pure torque control is preferably implemented. Engine speed controller 5 remains inactive in this case. In the event that the wheel slip at at least one wheel exceeds a predefinable threshold value, on the other hand, a combined control is preferably implemented, in which control variable I, which is the engine operating current in the case at hand, is formed while taking both controller output variables (signal variables S.sub.1 and S.sub.2) into account. The individual control mode is controlled by a control unit 14, which is connected to second controller 5 and is able to optionally activate or deactivate the latter or to modify its control amplification.

(4) Torque controller 3 is part of a first control circuit 15, and the engine speed controller is part of a second control circuit 16.

(5) The control device in the illustrated example includes two control devices 2 and 4, which are connected via a data bus 12 and thus are connected in series in terms of signal technology. Torque controller 3 is integrated in first control device 2, and engine speed controller 5 is integrated in second control device 4, in the form of software.

(6) First control device 2 is preferably the particular control device that is responsible for the electronic stability control of the vehicle, such as the ESP control device.

(7) If active, both controllers 3, 5 output a signal variable S.sub.1 and S.sub.2 at their respective outputs, which is transmitted to a unit 10 which uses signal variables S.sub.1 and S.sub.2 to form a resulting signal variable S. The controller outputs are thus connected to unit 10 in each case.

(8) In the example at hand, unit 10 is a summator, which adds up the two signal variables S.sub.1 and S.sub.2. Resulting signal S is finally forwarded to an inverter 6, which converts it into a corresponding current value I.

(9) Unit 10 and inverter 6 are integrated in control device 4, as is second controller 5. Control unit 14 is likewise situated in control device 4. The output of inverter 6 is connected to electric motor 1.

(10) Torque controller 3 ascertains first signal variable S.sub.1 as a function of a previously determined setpoint torque M.sub.setpoint and an actual engine torque. The individual torques are calculated in the known manner while taking wheel speeds n.sub.wheel into account. Wheel speeds n.sub.wheel are measured with the aid of rate-of-rotation sensors (not shown).

(11) Engine speed controller 5 ascertains second signal variable S.sub.2 as a function of a previously determined setpoint engine speed n.sub.eng,setpoint and a measured actual engine speed n.sub.eng. Setpoint engine speed n.sub.eng,setpoint of the motor is calculated with the aid of a device 8 which is included in first control device 2. It is ultimately transmitted to second control device 4 via data bus 12.

(12) The setpoint engine speed n.sub.eng,setpoint may be calculated according to the following equation, for example:

(13) $n_{\mathrm{eng},\mathrm{setpoint}}=\frac{30}{}\frac{i_D{i}_G}{r_{\mathrm{wheel}}}{v}_{\mathrm{wheel},\mathrm{setpoint}}$
where
i.sub.D is the translation of a differential gear of the vehicle,
i.sub.G is the translation of the vehicle transmission coupled to electric motor 1,
r.sub.wheel denotes the radius of the driven wheels, and
v.sub.wheel,setpoint denotes an average setpoint speed of the driven wheels.

(14) To form the control difference for the engine speed control, a unit 13 is provided, which in this case is integrated in second control device 4. The control difference is subsequently output to engine speed controller 5. Engine speed controller 5 may be a PDT1 controller, for example. The control amplifications for the P and D component can be selected as a function of the vehicle speed and/or the average engine torque, for example.

(15) To determine the control mode, a control unit 14 is provided, as previously mentioned, which sets the control mode as a function of the driving state. The driving state is monitored by a unit 9 in this case, which outputs a variable that describes the driving state, e.g., Z.sub.1 or Z.sub.2, to control unit 14 via data bus 12. Unit 9 determines the current wheel slip of the driven wheels, for instance, and generates a signal Z.sub.1 when the wheel slip is smaller than a predefined threshold value, that is to say, when the vehicle is in a stable driving state, and a signal Z.sub.2 when the wheel slip is greater than a predefined threshold value, which means that the vehicle is in an unstable driving state.

(16) In the stable driving state, a pure torque control is preferably implemented. In the unstable driving state, on the other hand, a combined control is carried out, in which both controllers 3, 5 participate. Because the reaction times in engine speed control circuit 16 are considerably lower than in torque control circuit 15, a more rapid reduction of the control deviation is achieved overall, and fewer control oscillations arise in the control circuit in addition.