DE10354662B4 - Method and device for assisting the driver of a motor vehicle in driving-dynamic borderline situations - Google Patents

Abstract

Method for supporting the driver of a motor vehicle (14) in driving dynamics borderline situations, whereby a steering torque (M) is exerted on the steering wheel (13) in a driving dynamics critical situation so that the driver can recognize in which direction he has to steer in order to achieve the To stabilize the vehicle again, characterized in that the target yaw rate (dΨsoll / dt) is kept at a fixed value while a steering torque (M) is being applied and only then is a new value of the target yaw rate (dΨsoll / dt) calculated again, if a specified stability criterion is met.

Description

The invention relates to a method for assisting the driver of a motor vehicle in driving-dynamic limit situations according to the preamble of patent claim 1 and to a corresponding device according to the preamble of patent claim 6.

Vehicle dynamics regulations, such. B. ESP (Electronic Stability Program), increase the controllability of motor vehicles in borderline situations, such as oversteer in cornering. The term driving dynamics control is understood in the following to mean all systems which actively intervene in the driving operation of a vehicle by actuating an actuator. These include in particular systems such. B. ABS (anti-lock braking system), ASR (traction control), ESP, AFS (Active Front Steering) or EAS (Electronic Active Steering). Known vehicle dynamics regulations use in particular the brakes, the engine management or a steering actuator as actuators of the scheme.

In the vehicle dynamics control system ESP forms z. B. acting on a wheel wheel slip the controlled variable. The wheel slip is controlled in such a way that the vehicle shows a driving behavior adjusted as exactly as possible to the driver's request (cornering, acceleration, braking, etc.) without getting out of control. For this purpose, the vehicle dynamics control system determines an actual yaw rate (usually with the aid of a yaw rate sensor) and calculates a desired yaw rate that is dependent on the driver specifications. From the control deviation, a yawing moment is finally calculated, which is required to equalize the actual state variables to the desired state variables. The required yaw moment is then z. B. converted into control signals for the brake system or a steering actuator for influencing the steering.

In a critical driving situation, a driver can by his own wrong behavior, such. B. too strong braking or excessive steering of the steering, the driving situation quickly deteriorate again. If the driver reacts incorrectly in such borderline situations, there is a risk that the vehicle can no longer be brought under control, or at least that the time to stabilization takes much longer than would actually be necessary.

From the DE 101 41 425 A1 are known a method for generating a driving condition-dependent additive additional torque on the steering wheel of a vehicle and an apparatus for performing the method. The driver is assisted in stabilizing the driving state when undesired yawing movements occur. In this case, the additional torque is formed by means of a factor and the slip angle, wherein the additional torque predefines that steering wheel position which corresponds to one of the stabilization of the current driving state serving wheel position of the steerable vehicle wheels. The additional torque is transmitted to the steering wheel by means of an electric motor.

The features of the preambles of the independent claims are the DE 101 41 425 A1 taken.

It is therefore an object of the present invention to provide a method and a device for vehicle dynamics control, with which or the vehicle can be stabilized as quickly and conveniently.

This object is achieved according to the invention by the features specified in claim 1 and in claim 6. Further embodiments of the invention are the subject of dependent claims.

An essential aspect of the invention is the driver in a critical driving situation, such. As when oversteering the vehicle, to show how he behaves correctly. For this purpose, according to the invention, a steering torque (in a direction in which the vehicle stabilizes) is exerted on the steering wheel, which indicates to the driver in which direction he must steer in order to catch the skidding or oversteering vehicle as quickly as possible. The steering torque is preferably switched on when the control deviation of the yaw rate exceeds a predetermined threshold. Optionally, the steering torque could be switched even if another condition is met, indicating a critical driving situation, such. B. a high steering speed, possibly in combination with high lateral acceleration of the vehicle. The driver then senses a steering torque on the steering wheel that indicates which direction to steer in order to stabilize the vehicle.

The connection of the steering torque has the advantage that a vehicle can be stabilized in many cases solely by the steering intervention or the subsequent reaction of the driver, without any additional stabilization intervention by another system, such. As ESP, would be necessary. An additional stabilization intervention, such. B. a brake intervention, is only performed if necessary. Thus, the comfort and agility of the vehicle can be improved, which also benefits the driving pleasure.

In order to prevent that the countersteering of the driver is interpreted by the vehicle dynamics control system as a new direction request, it is provided, the driver's desire, ie the target yaw rate dΨ _soll / dt to hold a fixed value (the freeze yaw rate quasi freeze) to a stability criterion is satisfied to calculate based on a compensation torque, and after reaching the stability criterion to update the target yaw rate again according to the driver's request (steering wheel angle). The stability criterion mentioned may, for. B. be that the deviation of the yaw rate falls below a predetermined threshold or the gradient of the actual yaw rate falls below a predetermined value.

According to a preferred embodiment of the invention, the steering line is used in a first phase of the control to detect the driver's request. In this phase, no additional steering torque is switched. Occurs a critical driving situation, what z. B. can be assessed based on the deviation of the yaw rate (the P, I, or D component is assessed), the system goes into a second phase, in which the steering line is no longer used for the determination of the driver's request, but for the application of a steering torque is used for purposes of stabilization. The target yaw rate remains frozen in this phase. This can also be referred to as "dual use of the steering line", since in the first phase of the driver's request is determined from the steering wheel position, but this can not be done in a second phase, since there are additional moments acting on the steering wheel, not from Drivers originate and thus represent no driver's request.

The steering torque can z. B. by means of a servo device such. As a servomotor, or by means of another steering actuator, such. As an electric motor, exercised. In principle, any type of actuator can be used with which a steering torque can be exerted on the steering wheel.

Known servo devices are usually set up to assist the driver in a steering operation. In a driving-dynamic limit situation, the assisting steering torque can for example be constructed so that the driver is moved to countersteer. Optionally, a steering wheel, such. As a hydraulic or electric motor can be used to exert a steering torque and to point out the driver to the correct steering behavior.

The steering torque exerted by the steering actuator is preferably dimensioned such that it can be overridden by the driver. In particular, the steering torque is not so strong that the steering wheel slips out of the driver's hand. This has the advantage that the driver can continue to control the steering operation and determine the steering.

The steering torque caused by the steering actuator is preferably reduced again when the vehicle begins to stabilize again. A criterion for the stabilization is, for example, that the gradient of the actual yaw rate decreases again. The steering torque is therefore preferably reduced when the gradient of the actual yaw rate falls below a predetermined threshold.

If the actual yaw rate increases compared to the desired yaw rate after a first steering intervention, d. that is, if the vehicle again tends to get out of control, another torque intervention is preferably performed. The steering torque is preferably applied again when the deviation between the actual and target yaw rate is greater than a predetermined threshold and the gradient of the actual yaw rate exceeds a predetermined threshold. Thus, the vehicle can also be brought under control when the vehicle gets out of control again and the last unstable state is only a short time ago.

According to a preferred embodiment of the invention, the height of the adjusted steering torque is a function of the desired yaw rate, the control deviation or their derivative. Thus, the height of the steering torque can be better adapted to the current driving situation.

A vehicle dynamics control system for improving the lateral dynamic stability of a motor vehicle comprises a yaw rate sensor for determining the actual yaw rate, a control unit with an algorithm for calculating a target yaw rate on the basis of the driver's request, and a steering actuator that can be controlled by the control unit, by a steering torque apply to the steering when the vehicle is in a dynamic driving limit situation.

The invention will now be described by way of example with reference to the accompanying drawings. Show it:

1 a schematic representation of a vehicle dynamics control system (ESP) for slip angle and yaw rate control according to the prior art;

2a . 2 B the course of desired and actual yaw rate and a steering torque in a first driving situation;

3a . 3b the course of desired and actual yaw rate and a steering torque in a second driving situation; and

4a . 4b the course of target and actual yaw rate and a steering torque in a third driving situation.

1 shows the overall control system of a vehicle dynamics control (ESP) for performing a slip angle and yaw rate control, as it is already known from the prior art substantially. The vehicle dynamics control system shown here differs from known systems in that a steering actuator 9 is provided by a control unit 12 is driven in driving dynamics border situations such that the driver by a on the steering wheel 13 exerted steering torque M can detect in which direction he must steer in order to stabilize the vehicle as quickly as possible. Since an average rider in normal driving rarely experiences a situation where he has to intercept an oversteer vehicle, he often does not respond properly in such situations. By switching on the auxiliary torque M on the steering, he receives an indication of how he should respond best in the oversteer situation. The switched-on torque is preferably a pulse-shaped signal (square wave signal) with a fixed value.

The known control system includes the vehicle 14 as a controlled system, the sensors 1 - 5 for determining the controller input variables, the actuators 6 . 7 for influencing the braking and driving forces, as well as a hierarchically structured controller consisting of a superimposed driving dynamics controller 10 and a subordinate slip control 11 , The controller functions are in a control unit 12 implemented.

To control the slip angle or the yaw rate is the superimposed controller 10 the slip control 11 Setpoint values in the form of desired slip λ _So before. The target slip to be adjusted for the individual wheels _So λ is a function of the control difference between the actual and target behavior of the vehicle. The nominal behavior results from the signals of the steering wheel angle sensor 3 (Steering request), the form pressure sensor 2 (Delay request) and the engine management 7 (Driving torque request). From this, the target yaw rate dΨ _soll / dt is calculated, for example, by means of the so-called "single track model". The actual yaw rate results for example from the signal of the yaw rate sensor 4 ,

In a driving dynamic limit situation are in the vehicle dynamics controller 10 determined the required Sollschlüpfe for the individual wheels. The calculated set slips λ _So are then transferred to corresponding instructions for the "Brake hydraulics" actuators 6 and "engine management" 7 converted, which adjust the required braking or driving forces on the individual wheels to stabilize the vehicle.

The overall system is designed in this case such that in an unstable driving situation, first a control intervention on the steering 13 by means of the steering actuator 9 takes place and only if the vehicle does not stabilized, a supplementary brake or drive intervention is performed.

The operation of this steering auxiliary function is described below with reference to 2 - 4 exemplified in more detail.

2 shows the course of different yaw rates dΨ / dt, where dΨ _is / dt that of the yaw rate sensor 4 supplied actual yaw rate, dΨ _should / dt a considered by the vehicle dynamics control system (partially frozen) target yaw rate and dΨ _soll2 / dt determined by the driver's request or steering angle determined (actual) target yaw rate.

The time span between 0 and t1 describes a cornering, in which the driver steers ever further into a curve (the actual yaw rate dΨ _is / dt increases). From the selected by the driver steering wheel angle δ _L and the vehicle speed (the driver's request), taking into account the sensor 5 measured lateral acceleration and other geometric auxiliary variables, the target yaw rate dΨ _soll / dt are calculated. Overdriven the vehicle, so does the actual yaw rate dΨ _/ dt faster than they _should according to target specifications dΨ / dt should. D. h., The vehicle rotates too fast about the vertical axis with respect to the actual driver's request.

At time t1, the control deviation exceeds a predetermined threshold. At this moment is by driving the control unit 12 a steering wheel 9 activated, which exerts a steering torque M on the steering, indicating to the driver in which direction he should steer in order to stabilize the vehicle. The steering torque is dimensioned such that it can be overridden by an average driver. If the driver follows the specification of the steering system, the vehicle can be stabilized much faster than would be possible for an inexperienced driver.

In the said steering actuator 9 it is, for example, an electric servo motor or a hydraulic pump power steering, which is driven by an electronics accordingly. This makes it possible to exploit existing components. Optionally, a separate steering wheel can be used.

With the exercise of the steering torque M, it also comes after the time t1 to spin the vehicle (the actual yaw rate dΨ / dt increases dramatically), this phase of control loss _is relatively short and reaches its maximum already at time t2. The steering torque M is maintained in this example until the actual yaw rate dΨ _is / dt decreases again. That is, the threshold value for deactivating the torque M in the present case (dΨ _ist / dt) / dt = 0. Alternatively, another threshold value for resetting the steering torque M can be programmed.

The curve dΨ _soll2 / dt shows the course of the yaw rate determined from the steering angle. The countersteering is clearly recognizable. As can be seen, the driver, starting from a strong turned steering wheel position (time t1) steers in the opposite direction and thereby also exceeds the neutral position of the steering wheel 13 , After the time t2 he then steers back into the curve (rising target yaw rate).

The driver's countersteering has the following problem with vehicle dynamics control: If the vehicle is in an oversteer situation which the driver tries to stabilize by countersteering, this would be interpreted by the vehicle dynamics control system as a driver's desire to steer into an opposite turn (FIG. eg a right-hand turn if a left-hand bend was previously used uu). In fact, the vehicle is still in a left turn, which should continue to follow. The vehicle should only be stabilized in this left turn. It is therefore necessary to ignore the countersteering dΨ _soll2 / dt. For this purpose, the target yaw rate dΨ _soll / dt during the control phase on a "reasonable value" held (frozen). This meaningful value is a value given by the driver before the countersteering movement. In the present example, the target yaw rate dΨ _soll / dt taken into account by the system _is frozen to the value that existed at time t1 before the control threshold was exceeded. The desired yaw rate dΨ _soll / dt is then maintained at this value until a stability criterion is met, in the present case until the yaw rate sensor 4 supplied actual yaw rate dΨ _is / dt the frozen target yaw rate dΨ _soll / dt has approached so far that a predetermined threshold is exceeded. This is the case at time t3. Only at this time t3 is the actual steering angle taken into account again and a current value of the target yaw rate dΨ _soll / dt calculated. After the time t3, the vehicle has stabilized again.

3a shows the target and actual yaw rate dΨ _soll / dt or dΨ _is / dt in a driving situation at the beginning essentially the situation of 2a equivalent. The driver steers into a curve in which the vehicle oversteers and breaks out at time t1. When the maximum deviation between the actual and desired yaw rate dΨ _is exceeded / dt or dΨ _soll / dt, a steering torque M is again exerted on the steering. The steering torque M is reduced again at time t2. After time t2, the actual yaw rate dΨ _ist / dt _is reduced until time t3, when it reaches a minimum and then increases again. At time t3, the deviation between the actual yaw rate dΨ _ist / dt and the target yaw rate dΨ _soll / dt is even greater than a predetermined threshold value. At the same time, the gradient of the actual yaw rate exceeds a predetermined gradient threshold (here, for example, (dΨ _ist / dt) / dt = 0). If both criteria are met, the steering wheel becomes 9 activated again at time t3 to a steering torque M on steering and steering wheel 13 exercise.

In response to this, the driver again performs a countersteering movement (see actual, but not taken into account by the vehicle dynamics control target yaw rate dΨ _soll2 / dt), so that the actual yaw rate dΨ _ist / dt from time t4 again reduced. At time t4, the threshold value for the gradient of the actual yaw rate dΨ _ist / dt is again fallen below and thus the counter-torque M is reset.

At time t5, the actual yaw rate dΨ _ist / dt and the target yaw rate dΨ _soll / dt have again approached so far that the target yaw rate dΨ _soll / dt is updated and adapted to the actual driver's request.

4a shows the course of the actual yaw rate dΨ _ist / dt and the target yaw rate dΨ _soll / dt in a driving situation in which the driver deflects several times to stabilize the vehicle. In this case, between the times t1, t2; t4, t5 and t6, t7 a steering torque on the steering wheel 13 exercised. In contrast to the situation of 3a However, the target yaw rate is updated after the first countersteering movement, at time t3, since the difference between the actual yaw rate dΨ _ist / dt and the frozen target yaw rate dΨ _soll / dt is smaller than a predetermined threshold and the gradient of the actual Yaw rate dΨ _is / dt is less than zero. The same applies to the time t5 and the time t7.

At time t4, the target yaw rate is, however, maintained at a constant value, since the gradient of the actual yaw rate _is dΨ / dt exceeds the predetermined threshold value.

By the method for applying a steering torque described above, it is achieved that a driver can react correctly in borderline situations and bring the vehicle back under control quickly. The vehicle dynamics control system (eg ESP) must not start as long as the driver follows the instructions. If the vehicle nevertheless flings, the regulation intervenes and stabilizes the vehicle through braking or drive intervention.

LIST OF REFERENCE NUMBERS

1

wheel speed sensors

2

form sensor

3

Steering wheel angle sensor

4

Yaw rate sensor

5

Lateral acceleration sensor

6

pressure modulation

7

engine management

8th

Sensor signals for ESP

9

steering actuator

10

driving dynamics controller

11

slip controller

12

control unit

13

steering wheel

14

vehicle

dΨ _is / dt

Actual yaw rate

dΨ _should / dt

Target yaw rate (partially frozen)

dΨ _soll2 / dt

actual target yaw rate

tn

timings

M

steering torque

Claims (8)

Method for supporting the driver of a motor vehicle ( 14 ) in driving-dynamic limit situations, wherein in a dynamic driving situation critical steering torque (M) on the steering wheel ( 13 ), so that the driver can recognize in which direction he must steer in order to stabilize the vehicle, characterized in that the target yaw rate (dΨ _soll / dt) during the application of a steering torque (M) to a fixed value is held and only then a new value of the desired yaw rate (dΨ _soll / dt) is calculated when a predetermined stability criterion is met. A method according to claim 1, characterized in that the steering torque (M) is limited to a value that it can be overridden by the driver. A method according to claim 1 or 2, characterized in that the steering torque (M) is reduced when the gradient of the actual yaw rate (dΨ _is / dt) falls below a predetermined threshold. Method according to one of the preceding claims, characterized in that the height of the adjusted steering torque (M) is a function of the desired yaw rate (dΨ _soll / dt) or the control deviation. A method according to claim 3, characterized in that a further torque intervention takes place when the deviation between the actual (dΨ _ist / dt) and the desired yaw rate (dΨ _soll / dt) is greater than a predetermined threshold value and the gradient of the actual Yaw rate (dΨ _is / dt) exceeds a predetermined threshold. Device for assisting the driver of a motor vehicle ( 14 ) in driving-dynamic limit situations, containing: - a sensor system ( 2 - 7 . 11 ) for recognizing a driving-dynamic limit situation and - a controller ( 9 ) for applying a steering torque (M) to the steering wheel ( 13 ) in a driving-dynamic limit situation, characterized in that the target yaw rate (dΨ _soll / dt) during the application of a steering torque (M) is kept at a fixed value and only then a new value of the target yaw rate (dΨ _soll / dt ) is calculated when a given stability criterion is met. Apparatus according to claim 6, characterized in that the steering torque (M) is reduced when the gradient of the actual yaw rate (dΨ _is / dt) falls below a predetermined threshold. Apparatus according to claim 6 or 7, characterized in that a further auxiliary torque intervention is performed when the deviation between the actual (dΨ _ist / dt) and the desired yaw rate (dΨ _soll / dt) is greater than a predetermined threshold and the gradient the actual yaw rate (dΨ _ist / dt) exceeds a predetermined threshold.

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