WO2005073044A1

WO2005073044A1 - Method and arrangement for controlling a motor vehicle torque transmitting clutch

Info

Publication number: WO2005073044A1
Application number: PCT/EP2004/014177
Authority: WO
Inventors: Manfred Steding; Stefan Fries; Klaus MÄTZSCHKER
Original assignee: Gkn Driveline International Gmbh
Priority date: 2004-01-30
Filing date: 2004-12-13
Publication date: 2005-08-11
Also published as: DE102004004870A1

Abstract

The invention concerns a method for controlling a motor vehicle torque transmitting clutch (34, 36) whose coupling state influences the distribution ratio of a torque between a first (24) and a second (26) wheel arrangement of the vehicle. The coupling state of the clutch (36) is controlled according to a deviation of an actual value of a yaw quantity, which is representative of the yaw behavior of the vehicle, from a set value of this yaw quantity. The yaw speed of the vehicle is preferably used as the yaw quantity. The set value of the yaw velocity is determined by a control unit (412) of the vehicle according to current values of the steering angle (α) of the vehicle and of the vehicle speed.

Description

Method and arrangement for controlling a motor vehicle torque transmission clutch

The invention is concerned with the active control of the torque distribution between the wheels of a motor vehicle.

Differential gears (differentials) are used in motor vehicles to enable different speeds between different wheels of the vehicle. A distinction is generally made between transverse differentials (axle differentials) and central differentials. Cross differentials allow speed differences between wheels of one axle of the vehicle, while central differentials allow such differences between wheels of different axles.

Differential locks counteract the compensating effect of the differential. Passive differential locks are known in which the locking effect depends on a speed difference. An example of such a differential lock dependent on the speed difference is a viscous clutch. The locking effect of the viscous coupling is based on fluid friction. There are also torque-dependent differential locks, for example the so-called Torsen differential. A targeted influencing of the blocking effect is not possible with passive systems.

In contrast to passive systems, the locking effect can be set in a defined manner with active differential locks. Controllable clutches are used as active differential locks, which can mostly be adjusted continuously between a fully open state, in which they transmit no torque and accordingly have no locking effect, and a fully closed state, in which they have a maximum share of the differential Transfer drive torque to be divided and develop a maximum locking effect accordingly. An example of a clutch used for active differential locks is a multi-plate clutch, in which the locking effect is based on the friction of friction plates against one another.

In all-wheel drive vehicles, all-wheel drive is often not permanent, but rather is implemented as a so-called "on demand" concept. In vehicles with this technology, the drive train contains a primary driven axle, whereby a secondary axle can be engaged by engaging a clutch. Such couplings are called distributor couplings below. Is the distributor coupling open, the secondary axle receives no drive torque, but if it is at least partially closed, part of the engine torque made available by the drive engine of the vehicle is directed to the secondary axle.

A distinction is also made between passive and active solutions for distributor couplings. For passive solutions, for example, viscous couplings are used, which respond to the occurrence of a slip (speed difference) between the primary and secondary axis and close automatically, the degree of closing being dependent on the slip. Active solutions include an actively controllable clutch, for example a multi-plate clutch.

Distributor clutches as well as lock-up clutches (ie clutches for differential locks) are therefore components that, due to their clutch condition, distribute a torque (drive torque or braking torque, depending on whether the vehicle engine is driving or braking) on different wheels - or generally wheel arrangements - of the vehicle determine. The term "wheel arrangement" is to be understood here to include both a single wheel and two or more wheels. For example, a distributor clutch connected centrally in the drive train between a front and a rear axle determines the ratio at which the torque is divided between the (several) wheels of these two axles. A locking clutch of a transverse differential, on the other hand, determines the ratio in which a drive torque made available to the relevant axle is divided between the (at least one) left and (at least one) right wheel of this axle.

In the case of controlled clutches for controlling the torque distribution in a vehicle, whether it be distributor clutches or locking clutches, the clutch has so far only been activated and only if a certain minimum speed difference between the wheels of the vehicle is detected. For this purpose, the wheel speed of the individual wheels is sensed and delivered to an electronic control unit, which uses this to determine the slip. A certain range of small speed differences is often permitted, for example, to disregard those speed differences that are already caused by different degrees of tire wear. It is also known to increase the control threshold with increasing speed and increasing steering angle of the vehicle. However, as soon as the detected speed difference exceeds the control threshold, the control unit sends a corresponding electronic command to the clutch. Depending on how strong the detected speed difference is, the clutch is closed to a greater or lesser extent in order to counteract the slip.

Again and again it happens that driving dynamically critical situations occur, for example a load change oversteer when cornering. The latter is caused by the driver suddenly taking the accelerator away. The gas removal results in a load change reaction of the vehicle, in which a considerable dynamic shift of weight from the back to the front can occur. The cornering forces of the rear wheels are temporarily reduced while they increase on the front wheels. This can change the vehicle's dynamic driving behavior to a noticeably oversteering behavior. Driving through a curve at a relatively high speed can even cause the rear of the vehicle to break out. Because most drivers are overwhelmed with sudden changes in the vehicle's driving dynamics due to lack of practice, such changes in driving behavior can pose significant safety problems.

Another example of a critical situation in terms of driving dynamics is acceleration in the curve. Here too, the vehicle may be oversteered to a greater or lesser extent, or the rear of the vehicle may break out.

Conventional systems for controlling active distributor or lock-up clutches are not prepared to deal with such situations that are critical in terms of driving dynamics, since they only respond to speed differences, but such speed differences do not necessarily occur more intensely when there are load changes or when accelerating in the curve.

The object of the invention is therefore to provide a safer and more stable driving behavior in a vehicle equipped with at least one actively controllable locking or distributor clutch.

In solving this problem, the invention is based on a method for controlling a motor vehicle torque transmission clutch, the clutch state of which influences the distribution ratio of a torque between a first and a second wheel arrangement of the vehicle. According to the invention, it is provided that the clutch state of the clutch is controlled as a function of a deviation of an actual value of a yaw variable representative of the yaw behavior of the vehicle from a target value of this yaw variable.

In the solution according to the invention, the actual yaw behavior of the vehicle can be approximated to a desired, predetermined yaw behavior by minimizing the deviation of the actual value of the yaw variable from the target value. This desired yaw behavior suitably corresponds to a stable driving behavior of the vehicle. Depending on the size of the deviation of the actual value from the target value of the yaw size, the clutch is more or less closed. If there is a critical situation in terms of driving dynamics, such as an excessively strong understeer or an excessively strong oversteer, the actual value of the yaw variable deviates from the target value. By appropriately actuating the clutch, the torque to be distributed over the two wheel arrangements can be redistributed so that the actual value of the yaw size approximates the desired value again. In this way, a closed control loop can be formed, which regulates differences between the actual value and the target value of the yaw variable.

The setpoint value of the yaw size can be determined on the basis of a theoretical vehicle model which provides a suitable setpoint value for the yaw size for different values of one or more input variables. Since it depends on the driving situation which setpoint is suitable for the yaw size, one or more operating parameters of the vehicle are preferably used as input values for determining the setpoint of the yaw size. The setpoint value of the yaw variable is expediently determined as a function of a current value of a steering angle of the vehicle, since depending on the curve curvature, a different degree of yaw of the vehicle is necessary. Since the speed of the vehicle when driving through a curve also determines how strong the vehicle yaws, the target value of the yaw rate is advantageously determined as a function of a current value of the vehicle speed. In addition, the vehicle model on which the determination of the target value of the yaw size is based can take into account the structural or geometric conditions of the vehicle, for example the steering geometry and / or the wheelbase of the vehicle. The relationship between the yaw variable target value and the variable input variables can be implemented in a control unit of the vehicle, for example in the form of a tabular database or in the form of an algorithm which is used to determine the target value of the Yaw magnitude calculated a mathematical equation or a set of such equations.

At least the yaw rate of the vehicle is expediently considered as the yaw variable. This can be determined directly, for example, with a yaw rate sensor. Otherwise, it is not excluded to use a second time derivative of the yaw angle of the vehicle (i.e. the yaw acceleration) as an yaw variable as an alternative or in addition.

As already indicated above, the two wheel arrangements can be arranged on a common axle and the clutch can be used as a controllable locking clutch of a transverse differential of this axle. Likewise, the two wheel arrangements can be arranged on different axles of the vehicle and the clutch can be used as a controllable locking clutch of a central differential of a transfer case of the vehicle that distributes the torque to the two axles. The two wheel assemblies can also be arranged on different axles of the vehicle and the clutch can be used as a controllable distributor clutch for distributing the torque to the two wheel assemblies.

The clutch preferably comprises an electromotive actuating unit which is controlled electrically to adjust the clutch state of the clutch. Basically any adjustment principles are conceivable. One possibility is an actuating mechanism with two axially opposite, rotatable disk parts which accommodate a ball arrangement between them, this ball arrangement being guided on at least one ramp track of at least one of the disk parts. By relative rotation of the two disk parts, a displacement of the ball arrangement along the at least one ramp path can be brought about, which influences the axial distance between the two disk parts.

The invention further relates to an arrangement for controlling a motor vehicle torque transmission clutch, the coupling state of which influences the distribution ratio of a torque between a first and a second wheel arrangement of the vehicle. According to the invention, this arrangement comprises an electronic control unit controlling the clutch, which is set up to determine the clutch state of the clutch as a function of a deviation of an actual value of a yaw variable representative of the yaw behavior of the vehicle from a target value thereof Control yaw size. The arrangement can have further features described above in connection with the method according to the invention.

In addition, the invention relates to a program code which is designed and designed to cause the method of the type described above to be carried out when executed on a program-controlled computer of a vehicle. Such a program code can be provided on a digital storage medium, such as a magnetically or optically readable information carrier disc, which is why the invention also extends to such a storage medium with machine-readable program code stored thereon for executing the method of the type described above.

The invention is explained below with reference to the accompanying drawings. They represent:

FIG. 1 schematically shows a first exemplary embodiment of a mechanical drive train of a motor vehicle with electrical and electronic components required for controlling locking clutches of the drive train,

FIG. 2 shows schematically a second exemplary embodiment of a mechanical drive train of a motor vehicle with electrical and electronic components required for controlling a distributor clutch of the drive train,

FIG. 3 shows an exemplary time diagram, which illustrates the effect of the invention in a load change process in the curve for a four-wheel vehicle with transfer case,

FIG. 4 shows an exemplary time diagram which illustrates the effect of the invention in a load change operation in the curve for a front-wheel drive vehicle, and

FIGS. 5a and 5b are exemplary time diagrams which illustrate the effect of the invention in a lane change maneuver for a four-wheel drive vehicle with a distributor clutch that can be activated as required.

A mechanical drive train of a motor vehicle is shown in FIG is generally designated 10. The drive train 10 contains a drive motor 12, from which engine torque that can be used to propel the vehicle is provided. The drive motor 12 can be, for example, an internal combustion engine or an electromotive drive unit. The drive motor 12 is followed by a change gear 14, which can be, for example, a manual transmission or a load-dependent automatic transmission. A clutch, not shown in FIG. 1, can be arranged between the drive motor 12 and the change gear 14. The engine torque of the drive motor 12 converted by the change gear 14 is divided by means of a transfer gear 16 in a predetermined symmetrical or asymmetrical relationship between a front axle 18 and a rear axle 20 of the vehicle. The part of the engine torque directed to the front axle 18 is divided by means of a first differential gear 22 onto a left and a right steered front wheel 24 or 26 of the vehicle. The distribution ratio of the drive torque available on the front axle 18 caused by the differential 22 is 50%: 50% in the unlocked case. Similarly, the portion of the engine torque allocated by the transfer case 16 to the rear axle 20 is divided equally between left and right rear wheels 30 and 32 of the vehicle by means of a second differential 28.

The transfer case 16 is assigned an infinitely controllable locking clutch 34, by means of which a central differential of the transfer case 16 can be partially or completely locked. The axle differentials (transverse differentials) 22, 28 are each also assigned a steplessly controllable locking clutch 36 or 38, which enables partial or complete locking of the differential in question. The locking clutches 34, 36, 38 are each mechanically coupled to an electromotive actuating unit 40, by means of which a desired clutch state of the respective locking clutch can be set. The actuating units 40 are controlled by an electronic control unit 42, which delivers corresponding electrical control signals to the actuating units 40. It goes without saying that each of the actuating units 40 and thus each of the locking clutches 34, 36, 38 can be controlled individually.

A serial bus arrangement 43 is used for electrical signal transmission from and to the control unit 42, which can be designed, for example, as a CAN (Controller Area Network) bus. Interfaces, protocols and electrical circuitry for signal transmission on a CAN bus are widely known and do not have to be are explained in more detail. It goes without saying that, as an alternative to a bus arrangement, the various electrical components of the vehicle can also be individually wired to the control unit 42.

The control unit 42 has a program-controlled microprocessor 44, which is provided in accordance with one in an electronic memory 46 of the control unit

42 stored control program generates suitable control signals for the actuators 40. The control program is indicated schematically in FIG. 1 at 48. To generate suitable control signals for the control units 40, the control unit 42 is dependent on information about various operating parameters of the vehicle. For this purpose, it can access various signals via the bus arrangement 43 which are representative of these operating parameters. For example, speed sensors 50 provide information about the speed of each of the wheels 24, 26, 30 32. From the measured wheel speeds, the control unit 42 can calculate any speed differences between the wheels of the front axle 18, between the wheels of the rear axle 20 and between the axles 18, 20. In addition, the control unit 42 can determine a speed of the vehicle according to methods known per se in the technical field.

If necessary, the control unit 42 can also access an engine torque signal which is representative of the engine torque provided by the drive motor 12 and is output by a schematically indicated torque sensor 52 on the bus arrangement 43. Furthermore, the control unit 42 can use the bus arrangement

43 have access to a pedal position signal, which indicates the position of an accelerator pedal 54 of the driver. The pedal position can be detected by a pedal position sensor 56, which can be a potentiometer sensor, for example.

The control unit 42 can also access a steering angle signal and, if desired, a gear position signal via the bus arrangement 43. The gear position signal can be provided by a gear position sensor 58 which detects the gear position of the change gear 14. The control unit 42 can recognize from the gear position signal whether and which gear is engaged. The steering angle signal is supplied by a rotation angle sensor 60, which detects the rotational position of a steering wheel 62 of the vehicle or a steering column carrying the steering wheel 62. The rotational position of the steering wheel 62 or the steering column is a measure of the α in FIG. plotted steering angle of the vehicle, ie the angular deviation of the front wheels 24, 26 from a straight-ahead position.

In addition, the control unit 42 receives (via the bus arrangement 43) from a yaw rate sensor 64 a yaw rate signal indicating the yaw rate (yaw acceleration) of the vehicle.

While FIG. 1 relates to the case of a vehicle with permanent all-wheel drive, FIG. 2 shows the drive train of a vehicle with optional all-wheel drive. This concept is also known as "on demand" technology. In FIG. 2, the same or equivalent components are provided with the same reference symbols as in FIG. 1, but supplemented by a lower case letter. In order to avoid unnecessary repetitions, only the differences from the exemplary embodiment in FIG. 1 are discussed below. The vehicle with the drive train shown in FIG. 2 is a vehicle with a front axle drive in which the rear axle can be switched on by means of a continuously variable distributor clutch 66a. The distributor clutch 66a is connected between the axle differentials 22a, 28a of the front axle 18a and the rear axle 20a. It replaces the transfer case 16 of the exemplary embodiment in FIG. 1 and allows the engine torque provided by the drive motor 12a to be divided as desired between the two axes 18a, 20a. The coupling state of the distributor clutch 66a can be set as desired by an electromotive actuating unit 40a which can be controlled by the control unit 42a.

Figures 1 and 2 are merely examples of powertrain configurations in which the invention can be used. It is understood that various other drive train configurations are conceivable. For example, in the "on demand" concept of FIG. 2, the rear axle 20a can form the primary driven axle, while the front axle 18a can be activated as a secondary axle if required. In this case, the distributor clutch 64a must be moved to a location between the change gear 14a and the front axle differential 22a. It can also be a vehicle with a pure front axle drive or rear axle drive, where only one axle is always driven. The equipping of the differentials with actively controllable locking clutches does not have to be as shown in FIGS. 1 and 2. For example, in FIG. 1 the actively controllable clutch 36 of the front axle differential 22 or / and the actively controllable clutch 38 of the rear axle differential 28 can be omitted or replaced by a passive, speed differential or torque-sensitive locking clutch. Vice versa in FIG. 2, one or both of the differentials 22a, 28a are provided with an actively controllable locking clutch. Regardless of the specific drive train configuration, the invention can be used with any actively controllable distributor or locking clutch, the clutch condition of which can be used to influence the distribution ratio of a drive torque to different wheels of the vehicle.

A control concept for the front axle locking clutch 36 of FIG. 1 is explained below. This control concept can be applied analogously to the two other locking clutches 34, 38 of FIG. 1, to the distributor clutch 66a of FIG. 2 and generally to any other locking and distributor clutch that influences the torque distribution in a drive train of a motor vehicle. Normally, the lock-up clutch 36 is open, i.e. it does not transmit any clutch torque. The front axle differential 22 then acts as an open differential. The control unit 42 responds to speed differences between the front wheels 24, 26. As soon as it detects such a speed difference, it outputs a control signal to the corresponding actuating unit 40, which causes the locking clutch 36 to be at least partially closed. The at least partial closing of the locking clutch 36 applies a locking torque to the differential 22 which counteracts the compensating action of the differential 22.

The control unit 42 is part of a control circuit which attempts to regulate speed differences between the front wheels 24, 26 to a minimum value equal to or close to zero. For this purpose, the control unit 42 contains a controller implemented in software or / and hardware, to which the detected speed difference is fed as a control difference. The signal output by the speed difference controller is then converted into a corresponding control signal for the actuating unit 40 in question. Since a slight speed difference can occur simply because of different wear of the front wheels 24, 26 or other asymmetries, a control threshold is expediently set below which the control unit 42 does not respond to speed differences.

To control the clutch state of the front axle lock-up clutch 36, the control unit 42 not only reacts to speed differences between the front wheels 24, 26 but also to deviations between the actual yaw behavior of the vehicle and a theoretical, stable yaw behavior. If the control unit 42 detects such a deviation in the yaw behavior, it controls that Locking clutch 36 associated actuator 40 so that the actual yaw behavior of the vehicle approximates the desired yaw behavior. For this purpose, the control unit 42 evaluates the yaw rate signal supplied by the yaw rate sensor 64. The control unit 42 continuously or periodically compares the current value of the yaw acceleration with a target value for the yaw acceleration, which it determines as a function of current values of the steering angle α and the vehicle speed. The yaw rate difference determined from this comparison is converted into a control signal which is used for the control of the relevant actuating unit 40. The partial or complete engagement of the locking clutch 36 as a function of the yaw rate difference results in a redistribution of the torque distributed to the front wheels 24, 26 (driving torque during engine operation of the drive motor 12 or drag or braking torque when the drive engine 12 is braking) counteracts the deviation of the actual yaw behavior of the vehicle from the desired yaw behavior and thus any instability.

For example, in a vehicle with a locking clutch controlled in the manner according to the invention in the front axle and / or in the rear axle, the actuation of the locking clutch in the event of a load change oversteer during cornering causes the longitudinal forces on the wheels of the axle in question to be redistributed, namely in such a way that there is a greater braking force on the outside wheel than on the inside wheel. The unequal pair of forces on the relevant axis causes an understeering yaw moment, which counteracts the load change oversteer.

A locking clutch in the transfer case of a vehicle with permanent all-wheel drive or a distributor clutch that can be activated as required (on-demand clutch) can also be controlled in the manner according to the invention in order to make maneuvers that are critical in terms of driving dynamics significantly less critical. For example, in a front-axle-driven vehicle, the rear axle of which can be activated by means of a distributor clutch, when changing lanes on slippery roads, high engine drag torques can act on the front wheels during push operation (with the gas removed) and therefore a comparatively strong brake slip occurs on the front wheels , The cornering forces on the front wheels decrease so much that the vehicle can no longer follow the steering movements of the wheels. It slips - understeering to the greatest extent - straight ahead. The invention, on the other hand, enables this unstable hold about the yaw rate difference that arises. By activating the distributor clutch depending on the yaw rate difference, the engine drag torque is partially diverted from the front axle to the rear axle, so that the cornering potential of the (steered) front wheels increases. The vehicle can then follow the steering angle specified by the driver. The average vehicle deceleration is also improved because the engine drag torque is now transmitted over all four wheels (assuming a two-axle vehicle with two wheels per axle).

The control concept according to the invention is also insensitive to influencing parameters such as the road coefficient of friction, the loading condition of the vehicle and the type of tire. Since the controlled variable in the exemplary embodiment considered here is the yaw rate difference, the stabilizing effect of the invention which improves the driving dynamics behavior can be achieved essentially in the same way on all road surfaces.

The diagram in FIG. 3 shows exemplary results for a four-wheel drive vehicle with a transfer case during a load change process in the curve. The vehicle has three differentials, namely a front axle differential, a rear axle differential and a center differential in the transfer case. A locking clutch is assigned to each of these differentials, by means of which the differential in question can be partially or completely locked. A curve 102 shows the course over time of the yaw rate of the vehicle in the event that all three differentials are open during the load change process, i.e. remain unlocked. One can see a strong increase in the yaw rate after the load change taking place at time t = 0 (sudden gas removal by the driver). This increase means a clear instability in the vehicle's dynamic driving behavior, which manifests itself in oversteer that is very difficult to master.

A curve 104 represents the case in which all three locking clutches are fully closed at the time of the load change. This results in a somewhat understeering driving behavior, which can be recognized from the decrease in yaw rate.

With the solution according to the invention, any time course of the yaw rate within the range covered by curves 102, 104 can be set by suitable tuning. A possible one when using the invention Achievable time course of the yaw rate during the load change process is represented by a curve 106. The position and shape of curve 106 can change depending on how strongly the individual locking clutches of the vehicle are closed when the load changes. The other curves 108, 110, 112 and 114 show exemplary time profiles of the yaw rate of the vehicle when only a part of the lock-up clutches is closed at the time of the load change, regardless of the yaw rate differences that occur. Curve 108 relates to the case in which only the front axle locking clutch is closed, curve 110 to the case in which only the rear axle locking clutch is closed, curve 112 to the case in which the center differential alone is locked, and curve 114 to In the event that the center differential and the rear axle differential are locked.

The exemplary time diagram of FIG. 4 was created for a front-wheel drive vehicle that is equipped with an electronic stability program (ESP). Depending on the speed of the wheels, the steering angle and lateral acceleration as well as the yawing moment of the vehicle, the electronic stability program effects braking interventions on the wheels and performance-reducing interventions on the drive motor of the vehicle. A curve 202 shows, by way of example, the course of the yaw rate of the vehicle over time when the front axle differential remains open during a load change process in the curve and the electronic stability program is switched off. The yaw rate increases after the load change (t = 0), so the vehicle oversteers. If the front axle differential or the locking clutch assigned to it is controlled in the manner according to the invention as a function of yaw rate differences and at the same time the electronic stability program remains switched off, a curve 204 is established. The desired weakening of the load change oversteer is clearly recognizable from the less rapidly increasing yaw rate. A similar weakening of the load change oversteer is also achieved by the electronic stability program with the differential open, as shown by a curve 206. However, it can be seen that a certain amount of time must elapse before the electronic stability program responds. Overall, the control process is also "rougher", which can be seen from the comparatively strong fluctuations in the yaw rate.

In the lower part of the diagram in FIG. 4, associated time profiles of the longitudinal acceleration of the vehicle are shown. Curve 212 relates to the case of the open differential when the electronic stability program is switched off, while curve 214 relates to the case of the open differential but when the electronic differential program is switched on represents electronic stability program and a curve 216 represents the case that the front axle lock clutch of the vehicle is regulated in the manner according to the invention depending on yaw rate differences. Since the correction in the electronic stability program is achieved, inter alia, by braking individual wheels, uncomfortable deceleration peaks can occur, which can be clearly seen on curve 214. The clutch control according to the invention, on the other hand, intervenes earlier than the electronic stability program and leads to a more uniform course of the yaw rate, with no significant jumps or irregularities occurring even when the vehicle is decelerating. If both the control concept according to the invention and the electronic stability program were activated in the example case considered here, Intervention of the electronic stability program would not be necessary as such, simply by controlling the front axle locking clutch, depending on yaw rate differences, the load change oversteer can be largely eliminated.

Finally, the diagrams in FIGS. 5a and 5b relate to the case in which a vehicle with a primarily driven front axle and a rear axle that can be optionally activated via a distributor clutch initiates a lane change maneuver with the gas removed ("overrun") at time t = 0. FIG. 5a shows exemplary time profiles of the steering wheel angle (dash-dotted curve), the theoretical yaw rate (dashed curve) and the actual yaw rate (dotted curve) with the distributor clutch open. FIG. 5b, on the other hand, shows exemplary time profiles of these parameters in the event that the distributor clutch of the vehicle is controlled as a function of yaw rate differences (difference between theoretical yaw rate and actual yaw rate).

When the distributor clutch is open, despite the very large steering wheel angle and correspondingly high theoretical or target yaw rate, only a very flat course of the actual yaw rate occurs. The vehicle can therefore only follow the driver's steering commands to a very limited extent (FIG. 5a). If, on the other hand, the distributor clutch is at least partially closed when there are deviations between the theoretical and the actual yaw rate, the yaw rate difference remains small. This means that the vehicle can follow the steering commands (Figure 5b). Accordingly, only smaller steering wheel angles are necessary in order to carry out the same lane change maneuver as when the distributor clutch is open.

Claims

Expectations

1. A method for controlling a motor vehicle torque transmission clutch (eg 36), the clutch state of which influences the distribution ratio of a torque between a first (24) and a second (26) wheel arrangement of the vehicle, characterized in that the clutch state of the clutch (36) depends on a deviation of an actual value of a yaw variable representative of the yaw behavior of the vehicle is controlled from a target value of this yaw variable.

2. The method according to claim 1, characterized in that a yaw rate of the vehicle is used as the yaw variable.

3. The method according to claim 1 or 2, characterized in that the target value of the L5 yaw rate is determined depending on a current value of a steering angle (α) of the vehicle.

4. The method according to any one of claims 1 to 3, characterized in that the target value of the yaw rate depending on a current value of a speed of the

> o vehicle is determined.

5. The method according to any one of claims 1 to 4, characterized in that the target value of the yaw rate is determined depending on a steering geometry and / or a wheel base of the vehicle.

! 5 6. The method according to any one of claims 1 to 5, characterized in that the two wheel assemblies (24, 26) are arranged on a common axle (18) and the clutch (36) as a controllable locking clutch of a transverse differential (22) of this axle serves.

! 0 7. The method according to any one of claims 1 to 5, characterized in that the two wheel assemblies (24, 26, 30, 32) are arranged on different axles (18, 20) of the vehicle and the clutch (34) as a controllable locking clutch a central differential of a transfer case (16) of the vehicle which distributes the torque to the two axles.

8. The method according to any one of claims 1 to 5, characterized in that the two wheel assemblies (24a, 26a, 30a, 32a) are arranged on different axles (18a, 20a) of the vehicle and the clutch (66a) serves as a controllable distributor clutch for distributing the torque to the two wheel assemblies.

9. The method according to any one of the preceding claims, characterized in that the clutch (36) comprises an electromotive actuating unit (40) which is electrically controlled to adjust the clutch state of the clutch.

10. Program code which is designed and designed to effect execution of the method according to one of the preceding claims when executed on a program-controlled computer of a motor vehicle.

11. Digital storage medium with machine-readable program code stored thereon, the program code being designed and designed to effect the execution of the method according to one of claims 1 to 9 when executed on a program-controlled computer of a motor vehicle.

12. An arrangement for controlling a motor vehicle torque transmission clutch, the clutch state of which influences the distribution ratio of a torque between a first and a second wheel arrangement of the vehicle, characterized by an electronic control unit (42) which controls the clutch and which is set up to depend on the clutch state of the clutch to control a deviation of an actual value of a yaw variable representative of the yaw behavior of the vehicle from a target value of this yaw variable, if desired in conjunction with further features of at least one of claims 2 to 9.