CONTROL SYSTEM IN A FOUR-WHEEL-DRIVE MOTOR VEHICLE AND METHOD FOR CONTROL

Abstract

A control system in a four-wheel-drive motor vehicle for the distribution of drive forces at least from a drive of the motor vehicle to wheels of the first and second axles of the motor vehicle, at least including:

a distribution device for distributing the drive forces to the first and second axles; rotation rate sensors for detecting the rotation rate of the two axles and/or the wheels of the motor vehicle, a central control device that is connected to a distribution controller and the sensors and a vehicle communication system, wherein the distribution controller is attached to the distribution unit and performs control both to a setpoint torque and to a setpoint rotation rate, and thusin a drive-dependent and switchable mannerdetermines a distribution ratio of the drive forces to be distributed to the first and second axles on the basis of the ratio between the torque and the setpoint torque or between the setpoint rotation rate and the setpoint rotation rate.

Claims

1. Control system in a four-wheel-drive motor vehicle for distributing drive forces at least of a drive of the motor vehicle to wheels of the first and second axles of the motor vehicle, at least comprising: a distribution device for distributing the drive forces to the first and second axles; rotational speed sensors for sensing the rotational speed of the two axles and/or of the wheels of the motor vehicle, a central control device which is connected to a distributor control unit is and to the sensors and to a vehicle communication system, wherein the distributor control unit is mounted on the distributor unit and performs adjustment both to a setpoint torque and to a setpoint rotational speed, and in doing so determines a transmission ratio to the drive forces which are to be distributed to the first and second axles as a function of the travel and in a switch-able fashion, on the basis of the ratio between the torque and the setpoint torque or between the rotational speed and the setpoint rotational speed.

2. Control system according to claim 1, wherein the distribution controller is composed of a component with setpoint torque adjustment and a component for adaptive rotational speed adjustment.

3. Control system according to claim 1, wherein at least the component for adaptive rotational speed adjustment is attached directly to the distributor device.

4. Control system according to claim 1, wherein the input inter-face between the distributor adjustment device and the central controller (11) processes, via the vehicle communication, both a setpoint torque (M_setp 10 ms) and a target corridor for the rotational speed (nFrax_10 ms) and a target corridor for the rotational speed (nFrax_setp) of the first axle or a differential rotational speed of the first and second axles.

5. Control system according to claim 1, wherein the control system can be switched over between adjustment modes, and that a setpoint torque, setpoint rotational speed or both manipulated variables can be processed.

6. Method for distributing drive forces at least of a drive of the motor vehicle to wheels of the first and second axles of the motor vehicle, at least comprising: a distribution device for distributing the drive forces to the first and second axles; rotational speed sensors for sensing the rotational speed of the two axles and/or of the wheels of the motor vehicle, a central control device which is connected to a distributor control unit and to the sensors and to a vehicle communication system, wherein the distributor control unit adjusts both to a setpoint torque and to a setpoint rotational speed, and in doing so determines a transmission ratio to the drive forces to be distributed to the first and second axles, as a function of the travel and in a switchable fashion, on the basis of the ratio between the torque and the setpoint torque or between the rotational speed and the setpoint rotational speed.

7. Method according to claim 6, wherein the input and output variables of the adjustment device are transferred to a vehicle communication system in such a way that the transit times do not have any influence on the rapid adjustment.

8. Method according to claim 6 or 7, wherein two closed-loop control circuits are used, wherein a first closed-loop control circuit adjusts to a setpoint rotational speed, while the second closed-loop control circuit adjusts to the setpoint torque.

9. Method according to one of claims 6 to 8, wherein the second closed-loop control circuit is designed to be faster for the setpoint torque than the first closed-loop control circuit.

10. Method according to one of claims 6 to 9, wherein the switching over between the two adjustment devices is carried out by defining a range for the rotational speed of the primary axle.

11. Method according to one of claims 6 to 9, wherein the switching over takes place between the two adjustment devices selection of a travel mode.

Description

DRAWINGS

[0023] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0024] FIG. 1 shows a schematic view of a motor vehicle with four-wheel drive with a control system according to an embodiment of the present invention,

[0025] FIG. 2 shows a schema of the control,

[0026] FIG. 3 shows a schematic of a control system in the prior art,

[0027] FIG. 4 shows a schematic of a control system according to the invention.

DESCRIPTION OF THE INVENTION

[0028] FIG. 1 shows schematic of a motor vehicle with four-wheel drive with a control system according to the invention contained therein.

[0029] As shown in FIG. 1, the motor vehicle with four-wheel drive has an engine 1 and a gearbox 2 connected to it as a unit, wherein the engine 1 and the gearbox 2 together form a drive. The gearbox 2 is a distribution unit that distributes the drive forces in different ways known to the person skilled in the art to a first drive shaft 3 and a second drive shaft 4. The respective drive force is transferred to a primary axle 10 and a secondary axle 20 via a front differential 5 and a rear differential 6.

[0030] In this example, rotation rate sensors 8 are attached to the wheels 7.

[0031] The vehicle can be driven by a combustion engine, by one or more electric motors or by both drive systems.

[0032] The control system is structured hierarchically and consists at least of a driving dynamics master control unit 11 and a distribution control unit 12. In the embodiment shown, the master control unit 11 is connected to rotation rate sensors, which are the wheel rotation rate sensors. The communication is carried out via the vehicle communication system, for example via a bus system, such as the commonly used CAN bus.

[0033] As usual, the signals of the wheel rotation rate sensors can be received together by a central control unit of the vehicle, which is not represented in the figure. This is where signal preparation takes place. However, the raw signals of the sensors can also be used directly at the master controller.

[0034] As an alternative to wheel rotation rate sensors, other rotation rate sensors in the drive train can also be used for control, for example on articulated shafts or gearboxes.

[0035] The distribution control unit 12 is used in particular for controlling the longitudinal slip, wherein on the basis of a control variable, in particular a setpoint slip specification, a manipulation variable, for example a setpoint torque, a setpoint current etc., is output to an actuator, for example a clutch, in the distribution gearbox 2. The control error is formed by generating the difference between the setpoint slip and the actual slip, wherein the actual slip value is formed on the basis of the rotation rate recorded by the rotation rate sensors.

[0036] In FIG. 2, control to a setpoint slip is represented schematically.

[0037] A control variable w(t) is represented by the setpoint slip specification of the master control unit 11 or the driving dynamics controller. The control error e(t) is formed by forming the difference between the setpoint slip and the actual slip. The actual slip value or the controlled variable y(t) is formed on the basis of the wheel rotation rate information. Other rotation rate sensors of the drive train, for example on the gearbox and/or on the drive shafts 3, 4, could also be used to determine the actual rotation rate. This is particularly useful if these measuring points are positioned closer to the actuator, i.e. on the actuator of a coupling to the distribution unit 2 and/or have a faster transmission frequency than the wheel rotation rate sensors.

[0038] The setpoint slip controller 13, which is attached close to the actuator, consists, for example, of proportional, integral, and differential parts (PID controller) with an anti-wind-up measure. The setpoint slip controller 13 can carry out slip control without dynamically relevant signals such as lateral acceleration, yaw rate, engine torques, etc. The output variable u(t) of the setpoint slip controller 13 close to the actuator is adapted to the subsequent control path of the actuator, for example the clutch, and can be designed differently. This means that for example a setpoint torque M(t), a setpoint current i(t), a valve position x(t), or an appropriate interface variable can be transferred. In addition to the coupling system and the actuator system, the drive train is also part of this control path.

[0039] The interference variable d(t) can either be generated in the actuator, for example a change in a coefficient of friction of a multi-plate clutch, or may act in the drive train. By taking into account such disturbances, both stationary changes and time-dependent changes in the characteristic properties of the actuator, for example a deviation of the transferred torque, are taken into account and regulated. As a result, the requirements on torque accuracy are reduced, which significantly reduces control complexity.

[0040] The integrated slip control is a mandatory installation on or in the control unit of the actuator in order to avoid latency times from the bus communications. It also opens up the possibility of implementing the controller in a faster computing cycle, which improves the control quality. The control quality is also highly dependent on the control dynamics of the control path.

[0041] In FIG. 3, control to a torque is shown schematically as a longitudinal distribution L, wherein the driving dynamics master control unit 11 is shown on the left. This passes a setpoint torque to the control circuit of the distribution controller 12. The control is carried out in a 10 ms cycle time until the signal is output to the actuator.

[0042] FIG. 4 shows the integrated slip control of the longitudinal distribution L. In addition to the previously received setpoint torque M_Soll 10 ms, a target corridor for the front axle rotation rate nFrax_Soll 10 ms or the differential rotation rate of the axles, in the form of MIN and MAX values from the master controller 11 are transferred and processed (10 ms) in the distribution controller 12. The setpoint rotation rate can be set as a fixed signal value, which serves the controller as a control variable, but it can also be a permissible corridor in the form of an upper and a lower control threshold and can be used for control.

[0043] In the distribution controller, a slip controller 13 runs in a faster task, for example in 2 ms, which changes the setpoint torque at a suitable point based on the setpoint/actual front axle rotation rate control error. For this, it is also necessary to read the wheel rotation rate signals quickly enough.

[0044] The main difference from the prior art is that a setpoint rotation rate is processed instead of a setpoint torque, wherein both control variables can also be received and processed.

[0045] The control provides standard driving of the vehicle in setpoint torque mode. However, the front axle setpoint rotation rate is constantly sent from the master controller to the distribution controller.

[0046] As long as the front axle actual rotation rate remains within the specified range, only control to the setpoint torque is carried out in the distribution controller.

[0047] As soon as the front axle rotation rate leaves the specified range, the superimposed slip-based control is activated and the torque is adapted accordingly. The master can therefore influence the transition conditions by varying the rotation rate corridor.

[0048] Other approaches are also conceivable, in which the vehicle is adjustable under torque control in normal mode and under rotation rate control in sports mode.

[0049] Thus, it is possible to switch between the two control strategies and to activate the highly dynamic slip-based control only in states relevant to driving dynamics or as required.

[0050] This is particularly important because the controlling the torque requires an increased load on the actuator in favor of a lower clutch load.

[0051] The motivation for this alternative concept is to be able to regulate the slip difference more finely. This results in a reduction in the thermal load on the multi-plate clutch while maintaining maximum driving dynamics.

[0052] There are also new possibilities in the development of drive control that also lead to simplifications and reductions in development costs at this point.

[0053] Apart from the distribution controller described above, the controller can also be used to determine the coefficient of friction between the tire and the road surface, to work as a safety monitoring function or to compare the accuracy of two clutches in a twin application for use in a torque splitter.

[0054] This type of control works better the more dynamically the actuator of the clutch can be regulated. Preconditions for this are suitable power of the actuator, high levels of stiffness in the mechanical components of the clutch actuator system, and high levels of stiffness of the components in the axial force flow of the clutch.

[0055] The requirements regarding torque accuracy are decreasing. In particular, errors concerning the nature of the gradient (for example changes in the coefficient of friction of the tribological system due to oil aging) can be easily adjusted. Offset errors can also be eliminated but more strongly affect performance in driving conditions involving predictive control.

[0056] The new type of control led to a significant reduction in the power dissipation in the clutch in certain driving conditions.

[0057] This leads, inter alia, to a significantly improved situation of the thermal load on the multi-clutch system.

LIST OF REFERENCE DESIGNATIONS

[0058] 1 engine [0059] 2 gearbox [0060] 3 first output shaft [0061] 4 second output shaft [0062] 5 front differential [0063] 6 rear differential [0064] 7 wheels [0065] 8 rotation rate sensors [0066] 10 primary axle [0067] 11 master control unit for driving dynamics [0068] 12 distribution control unit [0069] 13 setpoint slip controller [0070] 20 secondary axle