METHOD FOR OPERATING A STEER-BY-WIRE STEERING SYSTEM, AND STEER-BY-WIRE STEERING SYSTEM

Abstract

A method is disclosure for operating a steer-by-wire vehicle steering system with a steering wheel in a shut-down state of the vehicle. According to one step of the method, after the vehicle has been shut down a procedure is carried out to monitor whether the steering wheel of the vehicle is being moved. If a movement of the steering wheel is ascertained and the movement exceeds a defined first limiting value, the movement of the steering wheel is damped by a damping unit of the steering system. If no movement of the steering wheel exceeding the first limiting value was ascertained for a defined time period, no further monitoring of a movement of the steering wheel and no further damping of the movement of the steering wheel are undertaken, so long as the vehicle is shut down. If, alternatively or additionally, a movement of the steering wheel exceeds a second limiting value, which is lower than the first limiting value, but does not exceed the first limiting value was ascertained within the defined time period and it is ascertained on the basis of an evaluation of the movement profile of the movement of the steering wheel that the movement was not caused by a user, likewise no further monitoring of a movement of the steering wheel and also no further damping of the movement of the steering wheel are undertaken, so long as the vehicle is shut down. Moreover, a steer-by-wire steering system for a vehicle is specified.

Claims

1. A method for operating a steer-by-wire steering system of a vehicle with a steering wheel in a shut-down state of the vehicle, the method comprising: after a vehicle has been shut down, a procedure is carried out to monitor whether the steering wheel of the vehicle is being moved, if a movement of the steering wheel is ascertained and the movement exceeds a defined first limiting value, the movement of the steering wheel is damped by a damping unit f the steering system, if no movement of the steering wheel that exceeds the first limiting value was ascertained for a defined period of time and/or a movement of the steering wheel that exceeds a second limiting value, which is lower than the first limiting value, but does not exceed the first limiting value was ascertained within the defined period of time and it is ascertained based on an evaluation of a movement profile of the movement of the steering wheel that the movement was not caused by a user, no further monitoring of movement of the steering wheel and also no further damping of the movement of the steering wheel are undertaken, so long as the vehicle is shut down.

2. The method as claimed in claim 1, wherein a movement of the steering wheel is detected based on a rotational speed of the steering wheel and/or based on a change in a position of the steering wheel.

3. The method as claimed in claim 1, wherein the damping unit is switched off when the vehicle is being shut down.

4. The method as claimed in claim 1, wherein a monitoring period after the shut down of the vehicle is extended if after the shut down of the vehicle a movement of the steering wheel that exceeds the first limiting value is ascertained within the defined period of time.

5. The method as claimed in claim 1, wherein monitoring of the movement of the steering wheel is intensified if an ascertained movement of the steering wheel lies between the first limiting value and the second limiting value.

6. The method as claimed in claim 1, wherein after the shut down of the vehicle, a timer begins to run, the running-time of which corresponds to the defined period of time, the timer being reset to a starting value if an active movement of the steering wheel was ascertained within the running-time.

7. The method as claimed in claim 1, wherein a detected movement profile of the steering wheel is evaluated by an algorithm, and the monitoring of the steering wheel movement is terminated if the movement profile indicates that the steering wheel movement was not caused by a user.

8. A steer-by-wire steering system for a vehicle, which has been set up to execute a method as claimed in claim 1, comprising: a steering wheel, with a damping unit which is configured to damp, in an active state, a movement of the steering wheel, and with a monitoring unit which has been set up to detect a movement of the steering wheel in an inactive state of the damping unit and to activate the damping unit if the detected movement of the steering wheel exceeds a first limiting value or the detected movement exceeds a second limiting value, which is lower than the first limiting value, but does not exceed the first limiting value and it was ascertained on the basis of an evaluation of the movement profile of the movement of the steering wheel that the movement was caused by a user.

9. The steer-by-wire steering system as claimed in claim 8, wherein the steering system is configured to deactivate the monitoring unit if no movement of the steering wheel that exceeds the first limiting value is detected within a defined period of time and/or a movement of the steering wheel that exceeds the second limiting value but does not exceed the first limiting value was ascertained within the defined period of time and it was ascertained based on an evaluation of the movement profile of the movement of the steering wheel that the movement was not caused by a user.

10. The method as claimed in claim 2, wherein the damping unit is switched off when the vehicle is being shut down.

11. The method as claimed in claim 10, wherein a monitoring period after the shut down of the vehicle is extended if after the shut down of the vehicle a movement of the steering wheel that exceeds the first limiting value is ascertained within the defined period of time.

12. The method as claimed in claim 11, wherein monitoring of the movement of the steering wheel is intensified if an ascertained movement of the steering wheel lies between the first limiting value and the second limiting value.

13. The method as claimed in claim 12, wherein after the shut down of the vehicle, a timer begins to run, the running-time of which corresponds to the defined period of time, the timer being reset to a starting value if an active movement of the steering wheel was ascertained within the running-time.

14. The method as claimed in claim 13, wherein a detected movement profile of the steering wheel is evaluated by an algorithm, and the monitoring of the steering wheel movement is terminated if the movement profile indicates that the steering wheel movement was not caused by a user.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0028] Further advantages and features of the disclosure arise out of the following description and the accompanying drawings, to which reference is made. In the drawings:

[0029] FIG. 1 shows schematically a steering system according to the disclosure,

[0030] FIG. 2 shows a progression of the angular velocity of the steering wheel, and

[0031] FIG. 3 shows a flowchart that illustrates a method according to the disclosure.

DETAILED DESCRIPTION

[0032] FIG. 1 illustrates schematically a steer-by-wire steering system 10 for a vehicle with a steering wheel 12.

[0033] The steering system 10 includes a rack 14. The rack 14 is connected to a wheel-carrier via tie rods, which for the sake of simplicity are not represented, in such a manner that a linear displacement of the rack 14 results in a rotation of the wheel-carriers about their steering axle.

[0034] Moreover, the steering system 10 includes an actuator unit 16, a damping unit 18 and a monitoring unit 20.

[0035] The actuator unit 16 serves for setting a wheel-positioning angle in respect of wheels 22, 24 of the vehicle on the basis of a steering angle of the steering wheel 12.

[0036] For this purpose, in the exemplary arrangement that is represented the actuator unit 16 includes a servomotor 26 and also a pinion 28 which engages the rack 14.

[0037] In an alternative exemplary arrangement, which for the sake of simplicity is not represented, the actuator unit 16 includes, instead of a rack 14 and a pinion 28, electromotive servo actuators, one servo actuator being assigned to each wheel 22, 24.

[0038] In the steer-by-wire steering system 10 there is no mechanical coupling between the steering wheel 12 and the wheels 22, 24. Instead, a wheel-positioning angle is set by the servomotor 26.

[0039] For this purpose, the pinion 28, which is in interlocked engagement with the rack 14, is rotated by the servomotor 26, as a result of which the rack 14 is moved linearly.

[0040] A sensor 30which, for example, is an angle sensorhas been set up in order to detect a steering angle of the steering wheel 12.

[0041] On the basis of the detected steering angle, a wheel-positioning angle requirement is determined, and the actuator unit 16 is triggered accordingly.

[0042] The damping unit 18 has been set up to apply a torque to the steering wheel 12. For this purpose, the damping unit 18 includes a steering actuator 32.

[0043] In addition, the damping unit 18 includes a position sensor 34 which can detect a position of the steering actuator 32.

[0044] In addition, the damping unit 18 includes a control unit 36 for outputting a desired damping torque.

[0045] The damping unit 18 simulates a resistance in the course of steering on the steering wheel 12. As a result, the damping unit 18 damps movements of the steering wheel 12 and in this way prevents the steering wheel 12 from striking against an end stop at high speed. In addition, a haptic feedback is given to the driver by the damping.

[0046] The monitoring unit 20 has been set up to detect a movement of the steering wheel 12, for example also when the damping unit 18 has been switched off or is in a standby mode.

[0047] The movement of the steering wheel 12 can be detected on the basis of a rotational speed of the steering wheel and/or on the basis of a change in the position of the steering wheel.

[0048] The monitoring unit 20 includes at least one sensor 38 which has been set up to detect a movement of the steering wheelfor example, a speed of the steering wheel.

[0049] This sensor 38 may be, for instance, the same sensor 30 which detects the steering angle of the steering wheel 12.

[0050] However, it is also conceivable that the sensor 38 is a separate sensor.

[0051] In addition to this, the monitoring unit 20 may have been set up to access further sensors of the steering system 10for example, the position sensor 34.

[0052] The monitoring unit 20 has been set up to activate the damping unit 18 if the detected movement of the steering wheel 12 exceeds a first limiting value.

[0053] In addition, the monitoring unit 20 has been set up to take a movement of the steering wheel into account only when this movement exceeds a second limiting value, which is lower than the first limiting value.

[0054] Movements that lie below the second limiting value are, for example, so slight that they are to be ignored.

[0055] The monitoring unit 20 has, in addition, been set up to activate the damping unit if the detected movement exceeds the second limiting value but not the first limiting value and it was ascertained on the basis of an evaluation of the movement profile of the movement of the steering wheel that the movement was caused by a user.

[0056] In addition to this, the steering system 10 has been set up to deactivate the monitoring unit 20that is to say, to switch it offif no movement of the steering wheel that was caused by a user is detected within a defined period of time. This means that no movement of the steering wheel is detected that exceeds the first limiting value or that lies between the first limiting value and the second limiting value and is assigned to a user by evaluation of the movement profile.

[0057] For the purpose of evaluating the detected movements of the steering wheel and also for the purpose of triggering and, where appropriate, deactivating the damping unit 18, the monitoring unit 20 likewise includes a control unit 40.

[0058] A movement of the steering wheel detected by the monitoring unit 20 is illustrated in FIG. 2. Such a movement of the steering wheel is possible in a shut-down state of the vehicle if the damping unit 18 has been deactivated.

[0059] The illustrated scenario arises, for instance, if a user turns the steering wheel 12 in the shut-down and switched-off state of the vehicle.

[0060] In the illustrated example, the angular velocity w or rotational speed of the steering wheel 12 increases continuously from time t.sub.0 until t.sub.max. Prior to time t.sub.0, the steering wheel 12 is at rest.

[0061] At time t.sub.1, the speed of the steering wheel 12 reaches the value w.sub.2, which corresponds to the second limiting value. In the exemplary arrangement, the monitoring unit 20 therefore takes the movement of the steering wheel into account starting from time t.sub.1, whereas movements between t.sub.0 and t.sub.1 are ignored.

[0062] At time t.sub.2, the speed of the steering wheel 12 reaches the value w.sub.1, which corresponds to the first limiting value. In the case of movements that exceed the first limiting value, the monitoring unit 20 assumes, without further analysis, that these movements were caused by direct application of force to the steering wheel 12that is to say, by a user who is located in the vehicle.

[0063] At time t.sub.max, an end stop has been reached, and the angular velocity of the steering wheel drops abruptly from w.sub.max to zero.

[0064] Such a striking of the steering wheel 12 against an end stop is to be avoided.

[0065] In accordance with an exemplary arrangement of the disclosure, there is therefore provision that the monitoring unit 20 activates the damping unit 18 as required, in order to damp a movement of the steering wheel 12.

[0066] A method according to the disclosure for operating a steer-by-wire steering system 10 is illustrated in FIG. 3 on the basis of a flowchart.

[0067] In a step S1, the vehicle is shut down and switched off; more specifically, the engine/motor of the vehicle is switched off.

[0068] Immediately after the engine/motor has been switched off, the vehicle is in a state of rest, in which parts of the vehicle system may still be active.

[0069] In one exemplary arrangement, the monitoring unit 20 is still active for the time being.

[0070] With the shutdown of the vehicle, in addition a timer begins to run. The running-time of the timer corresponds to the defined period of time after which the monitoring unit 20 is to be deactivated if no movement of the steering wheel 12 was ascertained within the defined period of time. For instance, the running-time of the timer amounts to 20 minutes.

[0071] Accordingly, after the timer has run down, no further monitoring of a movement of the steering wheel 12 and also no further damping of the movement of the steering wheel take place, so long as the vehicle is shut down.

[0072] The damping unit 18 is switched off for the time being when the vehicle is being shut down.

[0073] The monitoring unit 20 monitors, in step S2, whether the steering wheel of the vehicle is being moved.

[0074] The measurement of a movement of the steering wheel can be undertaken either continuously or at fixed time-intervals. The time-intervals may be very short and may amount to 50 milliseconds, for instance.

[0075] If condition B1, that a fixed time-interval has elapsed, has arisen (labeled in the flowchart by y for yes), in step S3 an evaluation is undertaken in the monitoring unit 20 for the purpose of ascertaining a movement of the steering wheel 12.

[0076] If a condition is not satisfied, this is labeled in the flowchart by n for no.

[0077] If it is ascertained in step S3 that condition B2, according to which the second limiting value was exceeded, is satisfied, the timer continues to run for the time being.

[0078] Condition B3 implies that the timer has not yet run down in the course of the implementation of step S3.

[0079] If, in addition to condition B2, condition B4 is also satisfied, according to which the detected movement of the steering wheel exceeds the first limiting value, in step S5 the movement of the steering wheel 12 is damped by the damping unit 18. The time at which step S5 takes place corresponds to time t.sub.2 in FIG. 2.

[0080] If condition B4 has arisen, the timer is reset to its initial value. Accordingly, if, after the shutdown of the vehicle, a movement of the steering wheel 12 that exceeds the first limiting value is ascertained within the defined period of time, a period of monitoring after the shutdown of the vehicle is extended.

[0081] If merely condition B2 is satisfiedthat is to say, if an ascertained movement of the steering wheel 12 lies between the first and second limiting valuesthe movement profile of the movement of the steering wheel is evaluated, in order to ascertain whether the movement was caused by a user. If this is the case, the movement of the steering wheel 12 is likewise damped by the damping unit 18, and the timer is reset to its initial value.

[0082] Prior to the activating of the damping unit 18, a procedure is carried out to check whether condition B5that the vehicle has been shut downis actually satisfied.

[0083] For instance, a procedure is carried out to check whether the speed of the vehicle amounts to 0 km/h.

[0084] As a result, it is guaranteed that the damping unit 18 is not activated unintentionally during a trip.

[0085] If merely condition B2 is satisfied, in addition a monitoring of the movement of the steering wheel is intensified, this being undertaken in step S6. The intensification of the monitoring takes place, when it was not possible to ascertain unequivocally whether a movement of the steering wheel that lies between the first and second limiting values was caused by a user. The time at which step S6 takes place corresponds to time t.sub.1 in FIG. 2.

[0086] An intensification of the monitoring is undertaken, for instance, by virtue of the fact that the monitoring unit 20 accesses further sensors in order to obtain additional measured values. For instance, in this case the monitoring unit 20 can access the position sensor 34 or a torque sensor which is not represented in the figures.

[0087] If, after the intensification of the monitoring, the monitoring unit 20 ascertains that condition B6 obtains, according to which an active movement of the steering wheel 12 has occurred, step S5 takes place, and the damping unit 18 is activated.

[0088] If the monitoring unit 20 ascertains that no active movement of the steering wheel 12 has occurred, step S3 is implemented again, and a movement of the steering wheel continues to be monitored.

[0089] If no active movement of the steering wheel 12 is ascertained within the defined period of time after the shutdown of the vehicle, the monitoring unit 20 andto the extent that this was activethe damping unit 18 are switched off in step S7.

[0090] Consequently no further monitoring of a movement of the steering wheel occurs.

[0091] It is conceivable that a detected movement profile of the steering wheel 12 is evaluated, in the control unit 40 of the monitoring unit 20 by an algorithm, in order to ascertain whether or not an ascertained movement of the steering wheel has been undertaken by a user.

[0092] In addition, it is possible that under certain conditions, which are labeled in the flowchart by B7, a monitoring of a movement of the steering wheel from the beginning is dispensed with. Such a condition is, for instance, that a vehicle is intended for transportation on a car train. If condition B7 is satisfied, step S7 is undertaken directly, and the monitoring unit 20 is deactivated.