METHOD FOR ACTIVE STEERING SUPPORT IN A STUCK VEHICLE AND CONTROL UNIT

Abstract

A method for controlling an electrically actuatable steering actuator for a motor vehicle, wherein a check is carried out in order to determine whether a vehicle is stuck and a special control mode of the steering actuator is activated if a predefined condition is present, wherein the steering actuator is designed to set a steering angle in a manner independent of the driver and the steering actuator sets a steering angle profile in the special control mode.

Claims

1. A method for controlling an electrically actuatable steering actuator for a motor vehicle, comprising: checking in order to determine whether a vehicle is stuck and activating a special control mode of the steering actuator if a predefined condition is present, setting a steering angle by the steering actuator in a manner independent of the driver and setting a steering angle profile by the steering actuator in the special control mode.

2. The method as claimed in claim 1, wherein the steering angle profile corresponds to steering back and forth around a predefined reference value.

3. The method as claimed in claim 1, wherein the steering angle profile corresponds to a periodic profile with a predefined period and amplitude.

4. The method as claimed in claim 1, wherein a maximum steering angle and a minimum steering angle are predefined for the steering angle profile.

5. The method as claimed in claim 4, wherein the minimum steering angle and the maximum steering angle are determined according to an identified ground condition.

6. The method as claimed in claim 4, wherein the predefined minimum steering angle and the predefined maximum steering angle are temporally variable and are adapted while the special control mode is active.

7. The method as claimed in claim 1, wherein the special control mode is activated when a standstill of the motor vehicle is determined and the standstill lasts longer than a predefined time limit value.

8. The method as claimed in claim 1, wherein the special control mode is activated when a standstill of the motor vehicle is determined and a determined drive torque of the motor vehicle is above a predefined limit value.

9. The method as claimed in claim 1, wherein the special control mode is activated by an input by the driver.

10. The method as claimed in claim 1, wherein the special control mode is terminated when a movement of the vehicle in a longitudinal direction is determined.

11. The method as claimed in claim 1, wherein the special control mode is terminated by an input by the driver, wherein such an input is made, via a pushbutton, or by setting a brake pressure which is greater than a brake pressure limit value, or via a movement of the steering wheel, or by holding the steering wheel counter to the setting by the steering actuator during a predefined period.

12. The method as claimed in claim 1, wherein a drive torque is predefined by a control unit during the special control mode and the drive torque is applied to at least one driven axle.

13. The method as claimed in claim 12, wherein the drive torque is predefined by an assistance system.

14. A control unit of a motor vehicle, which comprises means for detecting when a vehicle is stuck and for controlling an electrically actuatable steering actuator of the motor vehicle, wherein a method as claimed in claim 1 is carried out by the control unit.

15. The method as claimed in claim 1, wherein the steering angle profile corresponds to steering back and forth around a neutral position.

16. The method as claimed in claim 3, wherein the periodic profile is a sine function.

17. The method as claimed in claim 12, wherein the drive torque is predefined by an automatic cruise control system.

18. The method as claimed in claim 2, wherein the steering angle profile corresponds to a periodic profile with a predefined period and amplitude.

19. The method as claimed in claim 5, wherein the predefined minimum steering angle and the predefined maximum steering angle are temporally variable and are adapted while the special control mode is active.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0038] An exemplary embodiment of an aspect of the invention will be discussed in more detail on the basis of two drawings. In the drawings, in a highly schematic illustration:

[0039] FIG. 1 shows an apparatus for carrying out a method according to an aspect of the invention; and

[0040] FIGS. 2A-2F show an exemplary profile of a plurality of variables while carrying out an exemplary method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] FIG. 1 shows an apparatus for carrying out a method according to an aspect of the invention. The apparatus is contained in a motor vehicle. In this case, 1a, 1b, 1c, 1d denote the wheels of the motor vehicle. The steerable wheels 1a and 1b of the vehicle can be set at a wheel angle 10a, 10b relative to the longitudinal axis of the vehicle.

[0042] The apparatus contains a steering wheel 4 at which a steering wheel angle 11 can be set. A sensor arrangement 2 measures the steering wheel angle 11 and/or the wheel angles 10a, 10b. The sensor arrangement 2 is connected to a control unit 6 and transmits the measured steering wheel angles 11 and/or wheel angles 10a, 10b to the control unit 6.

[0043] An electrically actuatable steering actuator 3 can be used to set a steering angle LW in a manner independent of the driver. As a result of a steering angle LW being set by the steering actuator 3, the wheel angles 10a, 10b and preferably the steering wheel angle 11 are set. The steering actuator 3 is connected to the control unit 6. If a special control mode is active, the control unit 6 transmits steering angle requirements, which correspond to a steering angle profile LW(t), to the steering actuator 3. The steering angle requirements are implemented by the steering actuator 3 by setting the steering angle profile.

[0044] According to the example, the apparatus has a drive unit 5, for example a vehicle drive motor which is connected to one or more vehicle axles and drives the wheels of the driven axles. The drive unit 5 is connected to the control unit 6. If the special control mode is present, the control unit transmits a drive torque requirement to the drive unit 5 according to the example, which drive torque requirement is implemented by the drive unit 5 as the drive torque.

[0045] According to the example, the drive unit 5 is connected to an input interface 7 (for example a pushbutton). The driver can activate and terminate the special control mode via this input interface 7.

[0046] According to the example, the drive unit 5 is likewise connected to means 8 which reveal a brake actuation by the driver, for example a brake light switch.

[0047] According to the example, the drive unit 5 is connected to means 9 for detecting a standstill of the vehicle. A duration of the standstill is either measured by the means for detecting a standstill 9 and transmitted to the control unit 6 or is captured by the control unit 6 itself. According to the example, the special control mode is activated if a standstill is detected by the means for detecting a standstill 9 and the duration of the standstill is longer than a predefined time limit value.

[0048] In one exemplary embodiment of an aspect of the invention, an engine torque of the drive unit 5, which is transmitted to the driven axles, is captured and is transmitted to the control unit 6. According to the example, the special control mode is activated when a standstill is detected by the means for detecting a standstill 9 and the captured engine torque of the drive unit 5 is above a predefined torque limit value. The special control mode is advantageously activated only when said conditions are present during a predefined period.

[0049] In another exemplary embodiment of an aspect of the invention, the speeds of the driven wheels are captured and are transmitted to the control unit 6. According to the example, the special control mode is activated when all of the following conditions have been met: [0050] a standstill has been determined by the means for detecting a standstill 9, [0051] a determined drive torque of the drive unit 5 is above a predefined limit value, [0052] all driven wheels of the vehicle have speeds greater than zero.

[0053] FIGS. 2A-2F show an exemplary profile of a plurality of variables while carrying out an exemplary method. In this case, the figure parts 2A, 2B, 2D and 2E show exemplary steering angle profiles 25, 26, 35 and 36 (temporal profiles LW(t)) set by a steering actuator (for example steering actuator 3 in FIG. 1) and the figure parts 2C and 2F show a status indicator 27 of a standstill detection means.

[0054] The time is respectively plotted on the x axes 21, 22, a steering angle is plotted on the y, axes 20 in the figure parts 2A, 2B, 2D and 2E and the value of the status indicator of the standstill detection means is plotted on the y axis 32 in the figure parts 2C and 2F.

[0055] FIGS. 2A, 2B and 2C each show a start of a special control mode and FIGS. 2D, 2E and 2F each show a termination of a special control mode.

[0056] At a first time 28, a standstill is detected and the status indicator 27 is set from zero (no standstill) to one (standstill detected). At the time 29, after a standstill is continuously considered to be detected for a period 31 which is longer than a predefined time limit value, a special control mode is then activated according to the example.

[0057] According to the example, a maximum steering angle value 23 and a minimum steering angle value 24 are predefined for the steering angle profile LW(t). The current steering angle at the start of the special control mode (input steering angle) 33, 34 is determined and is compared with the minimum and maximum steering angle values 23, 24.

[0058] Profile 25 in FIG. 2A shows the steering angle profile LW(t) set by the steering actuator in the special control mode in the event of the input steering angle 33 being greater than the maximum steering angle value 23. A profile accordingly reflected on the x axis is used, according to the example, if the input steering angle is less than the minimum steering angle value 24 and all subsequent considerations are similarly valid. The steering angle is first of all linearly reduced by the actuator, according to the example, until it is below the maximum steering angle value 23. In one preferred embodiment, a value for the gradient of the linear profile is predefined.

[0059] According to the example, the profile 25 then merges into a profile described by a sine function. The transition between the linear profile and the sinusoidal curve is advantageously effected in this case in such a manner that the profile can be continuously differentiated at any point since this is perceived to be particularly uniform by the driver.

[0060] Profile 26 in FIG. 2B shows the steering angle profile LW(t) set by the steering actuator in the special control mode in the event of the input steering angle being less than the maximum steering angle value 23, but greater than zero. A profile accordingly reflected on the x axis is used, according to the example, if the input steering angle 34 is less than zero but is greater than the minimum steering angle value 24. In this case, a point on the sinusoidal curve at which the sign function produces a value equal to the input steering angle is preferably determined as the starting point. The steering angle profile LW(t) now begins with the determined starting point and follows the profile 26.

[0061] As soon as the motor vehicle has propulsion again at the time 30 and a movement is carried out in the longitudinal direction, this is determined by the standstill detection means and the status indicator 27 of the standstill detection means is set to zero. According to the example, the special control mode is terminated when a standstill is no longer considered to be detected.

[0062] The special control mode is preferably not abruptly terminated, but rather the steering angle is reset by the steering actuator to a neutral position (straight-ahead position) after the end of the standstill.

[0063] In one preferred embodiment, the special control mode is terminated by linearly setting the steering angle set by the steering actuator, as shown by the steering angle profile 36 in FIG. 2E, from the value at the time 30 to zero (neutral position/straight-ahead position).

[0064] In a second preferred embodiment, the special control mode is terminated by reducing the amplitude with time, as illustrated in the profile 35 in FIG. 2D according to the example.

[0065] If the steering angle LW has been changed to the neutral position by the steering actuator, the special control mode can be terminated.