DE10354662A1 - Method for assisting the driver in driving-dynamic limit situations by applying a steering torque - Google Patents

Abstract

The invention relates to a method for assisting the driver of a motor vehicle in driving-dynamic limit situations in which the vehicle oversteers. In order to alert the driver to the correct steering behavior in borderline situations, a steering torque (M) is exerted on the steering wheel (13) by means of an actuator (9).

Description

The The invention relates to a method for assisting the driver of a motor vehicle in driving dynamics border situations according to the preamble of the claim 1 and a corresponding device according to the preamble of the claim 7th

Vehicle dynamics control, such as. ESP (Electronic Stability Program), increase the Controllability of motor vehicles in borderline situations, such as for example, when oversteer in cornering. Under the term vehicle dynamics control are in the Following all systems understood by controlling an actuator actively intervene in the driving operation of a vehicle. This includes in particular Systems such as e.g. ABS (antilock braking system), ASR (traction control), ESP, AFS (Active Front Steering) or EAS (Electronic Active Steering). Known driving dynamics regulations make use of the brakes in particular, the engine management or a steering actuator as actuators of Regulation.

at the vehicle dynamics control system ESP forms e.g. the at a wheel acting wheel slip the controlled variable. Of the Wheel slip is regulated so that the vehicle a possible exactly to the driver's request (cornering, acceleration, braking, etc.) adapted driving behavior shows, without getting out of hand. The Vehicle dynamics control system determines this an actual yaw rate (usually by means of a yaw rate sensor) and calculates one of the driver specifications dependent Target yaw rate. The control deviation eventually becomes a yawing moment calculated that needed is to the actual state variables the To adjust desired state variables. The required yaw moment is then given e.g. converted into control signals for the Brake system or a steering actuator for influencing the steering.

In A driver can correct a critical driving situation by his own wrong Behavior, such as too strong braking or too strong impact the steering, the driving situation quickly deteriorate again. If the driver reacts incorrectly in such borderline situations the danger that the vehicle is no longer under control or at least the time to stabilization much longer takes as needed.

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

Is solved this task according to the invention by the specified in claim 1 and in claim 7 Characteristics. Further embodiments of the invention are the subject of dependent claims.

One essential aspect of the invention is the driver in one critical driving situation, such as when oversteering the vehicle, to show how he behaves correctly. For this purpose, according to the invention, a moment (in one direction, in which the vehicle stabilizes) exerted on the steering wheel, the indicates to the driver in which direction he has to steer to the skidding or oversteering Vehicle as possible catch quickly again. The steering torque is then preferably switched when the deviation of the yaw rate a predetermined Threshold exceeds. Optionally, could the steering torque will be switched even if another condition Fulfills which indicates a critical driving situation, such as a high steering speed, possibly in combination with high lateral acceleration of the vehicle. The driver feels then on the steering wheel a steering torque that indicates to him in which direction he has to steer to stabilize the vehicle.

The Turning on the steering torque has the advantage that a vehicle in many cases solely by the steering intervention or the subsequent reaction the driver can be stabilized without an additional Stabilization intervention by another system, e.g. ESP, would be necessary. An additional one Stabilization intervention, such as a brake intervention, only becomes carried out, if necessary. This allows the comfort and agility of the vehicle be improved, which also benefits the driving pleasure.

In order to prevent that the counter-steering of the driver from the vehicle dynamics control system is interpreted as a new direction request, it is proposed to keep the driver's request, ie the target yaw rate dΨ _soll / dt to a fixed value (virtually freeze the target yaw rate) 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 stated stability criterion can be, for example, that the control deviation of the yaw rate falls below a predetermined threshold value or the gradient of the actual yaw rate falls below a predetermined value.

According to one preferred embodiment of Invention is the steering line in a first phase of the scheme used to capture the driver's request. At this stage will no additional Steering torque activated. If a critical driving situation occurs, what e.g. be judged by the control deviation of the yaw rate can (with the P, I, or D proportion is evaluated), so goes the system into a second phase, in the steering line no longer for the determination of the driver's request used, but for the application of a steering torque used for purposes of stabilization becomes. The target yaw rate remains frozen in this phase. This can also be called "dual Use of the steering line "referred be because in the first phase of the driver's request from the steering wheel position but this is not done in a second phase can be, because here are additional moments act on the steering wheel, which does not originate from the driver and thus represent no driver's request.

The Steering torque can e.g. by means of a servo device, e.g. one Servomotor, or by means of another steering actuator, such. an electric motor, exercised become. in principle Any kind of controller can be used with which a moment exercised on the steering wheel can be.

Known Servo devices are common set up so that they support the driver in a steering operation. In a driving dynamic boundary situation can be the supporting moment For example, be constructed so that the driver to countersteer is moved. Optionally, also a steering actuator, such as a hydraulic or electric motor can be used to exert a steering torque and to alert the driver to the correct steering behavior.

The exercised by the operator Steering torque is preferably such that it is overridden by the driver can be. 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 retains control of the steering operation and the driver Can determine steering.

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

takes the actual yaw rate opposite the desired yaw rate after a first steering intervention again, that is, the vehicle tends to get out of control again preferably another torque intervention performed. The Steering torque is preferably reapplied when the deviation between the actual and desired yaw rate is greater than a predetermined one Threshold and the gradient of the actual yaw rate a predetermined Threshold exceeds. Thus, the vehicle can also be brought under control, if the vehicle again except Control device and the last unstable state is only a short time ago.

According to one preferred embodiment of Invention is the height the set steering torque a function of the target yaw rate, the Control deviation or its derivation. This can be the height of the steering torque be better adapted to the particular driving situation.

A Vehicle dynamics control to improve the lateral dynamic stability of a Motor vehicle includes a yaw rate sensor for determining the actual yaw rate, a control unit with a Algorithm for calculating a target yaw rate based on the driver's request, and a steering actuator that can be controlled by the ECU, to apply a moment to the steering when the vehicle is moving is in a dynamic driving limit situation.

The Invention will be exemplified below with reference to the accompanying drawings explained in more detail. It demonstrate:

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 in fahrdyna border situations are controlled in such a way that the driver by one 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 desired slips λ _So are then converted into corresponding instructions for the actuators "brake hydraulics" 6 and "engine management" 7, which set 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 really should. That is, 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 torque M on the steering, which indicates to the driver in which direction he should steer in order to stabilize the vehicle. The counter 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 for deactivating the torque M in the present case (dΨ _soll / dt) / dt = 0. Alternatively, another threshold for the reset of the moment M can be programmed.

The curve dΨ _soll2 / dt shows the course of the yaw rate determined from the steering angle. That's it Countersteering well 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 the driver's desire to steer into an opposite turn (FIG. For example, a right turn if previously a left turn was 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 is fixed (frozen) during the control phase to a "reasonable value." This meaningful value is a value predefined by the driver before the countersteering movement The desired yaw rate dΨ _soll / dt is frozen to the value that was present at the time t1 before the control threshold was exceeded. The desired yaw rate dΨ _soll / dt is then held at this value until a stability criterion is met, in the present case up to that of 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 actual and desired yaw rate dΨ _is exceeded / dt or dΨ _soll / dt, a counter-torque M is again exerted on the steering. The counter-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 satisfied, the steering actuator 9 is re-activated at time t3 to a steering torque M on the 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 described above for applying a steering torque it is achieved that a driver reacts correctly in borderline situations and bring the vehicle back under control quickly. The Vehicle dynamics control system (e.g., ESP) must, as long as the driver Specifications follows, do not take action. However, if the vehicle is thrown, so the regulation intervenes and stabilizes the vehicle by braking or drive interventions.

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 (9)

Method for supporting the driver of a motor vehicle ( 14 ) in driving-dynamic limit situations, characterized in that in a critical driving situation a moment (M) on the steering wheel ( 13 ) so that the driver can see in which direction he has to steer in order to stabilize the vehicle again. Method according to claim 1, characterized in that that the moment (M) is limited to a value that it overrides by the driver can be. A method according to claim 1 or 2, characterized in that the moment (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. Method according to one of the preceding claims, characterized in that the desired yaw rate (dΨ _soll / dt) during the application of a moment (M) is kept at a fixed value and only then a new value of the desired yaw rate (dΨ _soll / dt) is calculated if a given stability criterion is met. Device for assisting the driver of a motor vehicle ( 14 ) in driving-dynamic limit situations, characterized by: - a sensor system ( 2 - 7 . 11 ) for recognizing a driving-dynamic limit situation and - a controller ( 9 ) for applying a torque (M) to the steering wheel ( 13 ) in a dynamic driving limit situation. Apparatus according to claim 7, characterized in that the moment (M) is degraded when the gradient of the actual yaw rate (dΨ _is / dt) falls below a predetermined threshold. Apparatus according to claim 7 or 8, 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.