METHOD FOR DETERMINING A GEAR RACK FORCE OF A STEER-BY-WIRE STEERING SYSTEM, STEER-BY-WIRE STEERING SYSTEM AND VEHICLE

Abstract

Technologies and techniques for determining a gear rack force of a steer-by-wire steering system that includes a steering handle, for specifying a steering angle as a function of a steering handle position. A vehicle wheel actuator is configured to set the steering angle by movement of a gear rack of the steering system, by applying an actuating force, the gear rack being coupled to at least one vehicle wheel. A reaction force actuator may produce a reaction force on the steering handle in accordance with a gear rack force. Friction operation is determined, in which gear rack movement does not occur when the steering handle position is changed, and, if friction operation is present, the gear rack force is determined on the basis of the actuating force of the vehicle wheel actuator.

Claims

1-10. (canceled)

11. A system for determining a gear rack force in a steer-by-wire steering system, comprising: a steering element, configured to specify a steering angle as a function of a position of a steering element; a vehicle wheel actuator, configured to set the steering angle by moving a gear rack in the steering system coupled to at least one vehicle wheel by applying an actuation force thereto; a reaction force actuator, for generating a reaction force on the steering element in accordance with a gear rack force; a steering control unit, configured to determine if a friction-burdened operation is present, in which the gear rack does not move when the position of the steering element is changed, determine a new gear rack force based on the actuation force of the vehicle wheel actuator, and generating a feedback torque to the steering element.

12. The system of claim 11, wherein the steering control unit is configured to determine the new gear rack force using the actuation force of the vehicle wheel actuator when the friction-burdened operation is determined.

13. The system of claim 11, wherein the steering control unit is configured to define the actuation force by the actuation value of a regulator.

14. The system of claim 13, wherein the regulator is configured to detect one of (i) a position of the steering element, or (ii) a value generated on the basis thereof, as a target value.

15. The system of claim 13, wherein the regulator is further configured to detect one of (i) a position of the gear rack, or (ii) a value generated on the basis thereof, as an actuation value

16. The system of claim 15, wherein the actuation value comprises an actuation value for a power electronics system in the vehicle wheel actuator that is configured to control an electric motor in the vehicle wheel actuator for generating the actuation force in accordance with the actuation value.

17. The system of claim 15, wherein, if the steering control unit determines that the friction-burdened operation is not present, the new gear rack force is determined using a gear rack position value.

18. The system of claim 17, wherein the gear rack position value is determined using a rotor position sensor in the vehicle wheel actuator.

19. The system of claim 11, the movement of the gear rack is determined by a movement of a component in the vehicle wheel actuator.

20. A method for operating a steer-by-wire steering system, comprising: specifying, via a steering element, a steering angle as a function of a position of a steering element; setting, via a vehicle wheel actuator, the steering angle by moving a gear rack in the steering system coupled to at least one vehicle wheel by applying an actuation force thereto; generating, via a reaction force actuator, a reaction force on the steering element in accordance with a gear rack force; determining, via a steering control unit, if a friction-burdened operation is present, in which the gear rack does not move when the position of the steering element is changed, determining, via the steering control unit, a new gear rack force based on the actuation force of the vehicle wheel actuator, and generating, via the steering control unit, a feedback torque to the steering element.

21. The method of claim 20, wherein determining the new gear rack force comprises using the actuation force of the vehicle wheel actuator when the friction-burdened operation is determined.

22. The method of claim 20, further comprising defining, via the steering control unit, the actuation force by the actuation value of a regulator.

23. The method of claim 22, wherein defining the actuation force comprises detecting one of (i) a position of the steering element, or (ii) a value generated on the basis thereof, as a target value.

24. The method of claim 22, wherein defining the actuation force comprises detecting one of (i) a position of the gear rack, or (ii) a value generated on the basis thereof, as an actuation value

25. The method of claim 24, wherein the actuation value comprises an actuation value for a power electronics system in the vehicle wheel actuator that is configured to control an electric motor in the vehicle wheel actuator for generating the actuation force in accordance with the actuation value.

26. The method of claim 24, wherein, if the determining establishes that the friction-burdened operation is not present, the new gear rack force is determined using a gear rack position value.

27. The method of claim 26, wherein the gear rack position value is determined using a rotor position sensor in the vehicle wheel actuator.

28. The method of claim 20, wherein the movement of the gear rack is determined by a movement of a component in the vehicle wheel actuator.

29. A system for determining a gear rack force in a steer-by-wire steering system, comprising: a steering element, configured to specify a steering angle as a function of a position of a steering element; a vehicle wheel actuator, configured to set the steering angle by moving a gear rack in the steering system coupled to at least one vehicle wheel by applying an actuation force thereto; a reaction force actuator, for generating a reaction force on the steering element in accordance with a gear rack force; a steering control unit, configured to define the actuation force by the actuation value of a regulator determine if a friction-burdened operation is present, in which the gear rack does not move when the position of the steering element is changed, determine a new gear rack force based on the actuation force of the vehicle wheel actuator, and generating a feedback torque to the steering element.

30. The system of claim 29, wherein the regulator is configured to detect one of (i) a position of the steering element, or (ii) a value generated on the basis thereof, as a target value, and wherein the regulator is further configured to detect one of (a) a position of the gear rack, or (b) a value generated on the basis thereof, as an actuation value

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Aspects of the present disclosure shall be explained below in reference to the drawings. Therein:

[0039] FIG. 1 shows a schematic drawing illustrating the principles of a steering system according to an exemplary embodiment of the present disclosure; and

[0040] FIG. 2 shows a flow chart for a method according to the present disclosure, which can be executed by the steering system in FIG. 1.

DETAILED DESCRIPTION

[0041] A (steer-by-wire) steering system 1 according to an exemplary embodiment is shown in FIG. 1 as a schematic drawing illustrating the principles of the present disclosure. The steering system 1 is part of a vehicle 14, indicated by a broken line.

[0042] In this example, the steering system 1 includes a steering element 2 in the form of a steering wheel, which is connected to an input shaft 3. There is a torque sensor 4 on the input shaft 3 for detecting a manual steering torque M.sub.H exerted by the driver, and a reaction force actuator 5 for generating a feedback torque M.sub.FF applied to the steering element 2, corresponding to the generation of a reaction force, or resulting in a corresponding reaction force, and which can be converted into such. The conversion of the feedback torque M.sub.FF and reaction force can take place taking the size or leverage of the feedback actuator 5, input shaft 3, and/or steering element 2 into account.

[0043] In addition, an angular position (i.e., setting) φ.sub.L of the steering element 2 can be determined, for example, with the torque sensor 4 or a separate sensor (not shown), e.g. a rotor position sensor in the reaction force actuator 5. Using this angular position φ.sub.L and/or the manual steering torque M.sub.H, as well as their changes, in particular, it is possible to determine whether or not the position of the steering element 2 has changed.

[0044] The steer-by-wire steering system 1 may also include a control unit in the form of a steering control unit 6 and a vehicle wheel actuator 11, comprising a power electronics system 7 and an electric servomotor 8, which is connected to a gear rack 9, e.g., via a spherical head or sprocket gearing. The electric servomotor 8 may be configured with a rotor position sensor 10, from which rotor angle signals φ.sub.R can be converted back to the gear rack position.

[0045] A steering angle may be determined in the steering control unit 6 based on the manual steering torque M.sub.H and other input variables, e.g., the motor vehicle speed, as the target value, in a manner known per se, which is to be set on the vehicle wheels by the vehicle wheel actuator 11 or its servomotor 8 via the gear rack 9. For this, the steering control unit 6 generates an actuation value, or an actuation signal S for the power electronics system 7. The actuation value S can also be referred to as a gear rack position specification, wherein the desired steering angle is set via the corresponding predefined gear rack position. The rotor angle signal φ.sub.R can be used as the actual signal for determining the actuation value S (e.g., by converting it to an actual gear rack position). The steering control unit 6 therefore serves as a regulator for the gear rack position and the (vehicle wheel) steering angle set therewith.

[0046] The actuation value S can also be converted to a torque exerted by the servomotor and an actuation force F acting on the gear rack 9 (e.g., resulting from a gear ratio in the spherical head gearing). This conversion can likewise be carried out by the steering control unit 6, and used to set the feedback torque M.sub.FF when a friction-burdened operation has been detected.

[0047] A friction-burdened operation is preferably detected by the determination device 20 in the steering control unit 6. The determination device 20 may evaluate the rotor angle signal φ.sub.R and the torque and/or angular position signals M.sub.H, φ.sub.L associated with the steering element 2. In particular, the determination device 20 checks the relationships of these signals to one another, e.g., with regard to whether changes in the torque and/or angular position signals M.sub.H, φ.sub.L, which indicate changes in the position of the steering element, agree with the expected changes in the rotor angle signal φ.sub.R. The latter corresponds to a change in the gear rack position, and therefore a movement of the gear rack.

[0048] If instead, none of these changes are detected, and in particular, the position of the steering element is changed, without resulting in a change in the rotor angle signal φ.sub.R, the determination device 20 determines a friction-burdened operation. In this case, it can be assumed that actuation forces F generated by the servomotor 8 dissipate entirely through internal friction, such that the gear rack does not move. A friction-burdened operation also includes scenarios in which a predefined steering movement is not implemented, e.g. because the vehicle wheels are blocked (e.g. by a curb), and the gear rack does not move.

[0049] The present disclosure exploits this in that the actuation forces F of the servomotor 8 generated in the friction-burdened operation are used to set an appropriate feedback torque M.sub.FF at the steering element 2. This is based on the idea that these actuation forces F in the friction-burdened operation correspond to the currently active gear rack force. Even if the gear rack does not move, and there is significant internal friction, the driver can still be given a realistic feedback through the steering element 2. This improves the operability of the steering system 1 from the perspective of the driver.

[0050] In normal operation, distinguished by the absence of a friction-burdened operation, and changes in the position of the steering element result in expected movements of the gear rack 9, a feedback torque M.sub.FF may be determined by the steering control unit 6 on the basis of the current rotor angle signal φ.sub.R and/or a change therein. In particular, the presence of a gear rack force can be assumed in the manner known per se using a model, and a value for the feedback torque M.sub.FF can be determined on the basis of this gear rack force. In the friction-burdened operation described above, this is difficult utilizing the prior art, or can only be achieved imprecisely, because the rotor angle signal φ.sub.R remains unchanged, despite the manual steering torque M.sub.H that has been generated. In other words, the gear rack force and/or reaction force are determined differently in normal operation than in the friction-burdened operation.

[0051] A flow chart for a method according to the present disclosure is shown in FIG. 2, which can be executed with the steering system 1 shown in FIG. 1. (Any) changes in the position of the steering element are determined in step S1. This can take place, for example, based on the signals M.sub.H, φ.sub.L explained above. (Any) movement of the gear rack is determined in step S2. This can be determined, for example, based on changes in the rotor angle signal φ.sub.R.

[0052] A friction-burdened operation is determined in step S3, for which any changes or movements determined in steps S1 and S2 in the manner described above are compared. If a friction-burdened operation is determined (arrow N), a typical setting of the feedback torque M.sub.FF takes place in step S4, e.g., based on a model-based determined gear rack force, in which the actuation force F of the servomotor 8 is less strong, or can also remain unaccounted for. In particular in this case, it cannot be assumed from the relationships in the friction-burdened operation that further force components, e.g., counterforces when redirecting the vehicle wheels, arise and can affect the gear rack force.

[0053] If a friction-burdened operation is determined (arrow Y), the feedback torque M.sub.FF is determined in step S5 based on the current gear rack force, which is set to the actuation force F.

LIST OF REFERENCE SYMBOLS

[0054] 1 steering system [0055] 2 steering element [0056] 3 input shaft [0057] 4 torque sensor [0058] 5 reaction force actuator [0059] 6 steering control unit/regulator [0060] 7 power electronics system [0061] 8 servomotor [0062] 9 gear rack [0063] 10 rotor position sensor [0064] 11 vehicle wheel actuator [0065] 14 vehicle [0066] 20 determination device [0067] M.sub.H manual steering torque [0068] φ.sub.R rotor angle signal [0069] φ.sub.L angular position