METHOD FOR CONTROLLING A STEER-BY-WIRE STEERING SYSTEM WITH A REDUCED FEEDBACK IN AUTOMATIC DRIVE MODE

Abstract

A steer-by-wire steering system may include an actuation control system to actuate road wheels via a rack and pinion steering gear and a steering wheel control system to simulate a steering feel of a mechanically linked steering system to a steering device. The actuation control system may have a second control unit, and the steering wheel control system may have a first control unit and an actuator. An automatic driving electronic control unit may decide if a drive mode is vehicle-controlled or driver-controlled. If driver-controlled, the first control unit may rotate the steering wheel by a turning angle by activating the actuator according to a pre-set function depending on a rotation angle of a pinion to simulate the steering feel. If vehicle-controlled, the first control unit may rotate the steering wheel by a reduced turning angle by activating the actuator according to a fraction of the pre-set function.

Claims

1.-12. (canceled)

13. A method for controlling a steer-by-wire steering system for a motorized vehicle, the steer-by-wire steering system comprising a steering device control system for simulating a steering feel to a steering device, with the steering device control system including a first control unit; an actuation control system for actuating road wheels via a rack and pinion steering gear, with the actuation control system including a second control unit and an actuator; and an automatic driving electronic control unit for deciding based on input signals if a drive mode corresponds to vehicle-controlled steering or driver-controlled steering, the method comprising: detecting a status of the drive mode; and reporting the status to the first control unit via the automatic driving electronic control unit, wherein if the drive mode reported to the first control unit corresponds to driver-controlled steering, the method comprises rotating the steering device by a first steering device turning angle by activating the actuator according to a pre-set function depending on a rotation angle of a pinion of the rack and pinion steering gear to simulate the steering feel, wherein if the drive mode reported to the first control unit corresponds to vehicle-controlled steering, the method comprises rotating the steering device by a second steering device turning angle by activating the actuator according to the pre-set function multiplied by a factor of less than one.

14. The method of claim 13 wherein the factor is a function with at least one variable.

15. The method of claim 13 wherein the factor is linear.

16. The method of claim 13 wherein the factor is dependent on the first steering device turning angle or the second steering device turning angle.

17. The method of claim 13 wherein the second steering device turning angle is less than the first steering device turning angle.

18. The method of claim 13 wherein the second steering device turning angle in vehicle-controlled steering is reduced relative to the first steering device turning angle in driver-controlled steering.

19. The method of claim 13 wherein under vehicle-controlled steering the method comprises setting a steering device turning torque to a predefined value.

20. The method of claim 13 wherein the steer-by-wire steering system comprises hands-on-off detection that provides one of the input signals for the automatic driving electronic control unit.

21. The method of claim 13 comprising providing an indication as to whether a driver's hand or hands are touching the steering device as one of the input signals for the automatic driving electronic control unit.

22. The method of claim 13 wherein the factor has a value between 0 and 0.5.

23. The method of claim 13 wherein the factor has a value between 0 and 0.25.

24. The method of claim 13 wherein the factor is 0.

25. A steer-by-wire steering system for a motorized vehicle comprising: a steering device control system for simulating a steering feel to a steering device, with the steering device control system including a first control unit; an actuation control system for actuating road wheels via a rack and pinion steering gear, with the actuation control system including a second control unit and an actuator; and an automatic driving electronic control unit for deciding based on input signals if a drive mode corresponds to vehicle-controlled steering or driver-controlled steering, wherein the automatic driving electronic control unit is configured to report a status of the drive mode to the first control unit, wherein under driver-controlled steering the first control unit is configured to activate the actuator according to a pre-set function depending on a rotation angle of a pinion of the rack and pinion steering gear to rotate the steering device by a first steering wheel turning angle to simulate the steering feel, wherein under vehicle-controlled steering the first control unit is configured to activate the actuator according to the pre-set function multiplied by a factor of less than one to rotate the steering device by a second steering wheel turning angle.

26. The steer-by-wire steering system of claim 25 wherein the second steering device turning angle is less than the first steering device turning angle.

27. The steer-by-wire steering system of claim 25 wherein the second steering device turning angle in vehicle-controlled steering is reduced relative to the first steering device turning angle in driver-controlled steering.

28. The steer-by-wire steering system of claim 25 comprising means for detecting whether a driver's hand or hands are contacting the steering device, which is used as one of the input signals for the automatic driving electronic control unit.

29. The steer-by-wire steering system of claim 25 comprising an electronic clutch arrangement configured to decouple movement of the steering device from movement of the road wheels.

Description

[0022] FIG. 1 shows a steer-by-wire steering system in a schematic illustration,

[0023] FIG. 2 shows a schematic illustration of the steer-by-wire steering system with control and signal lines from the steering wheel control system to the steering gear, and

[0024] FIG. 3 shows a steer-by-wire steering system in a schematic illustration with an electronic clutch arranged between the steering wheel and the steering gear.

[0025] FIG. 1 is a schematic representation of a steer-by-wire steering system 1 that comprises an actuation control system 2 to actuate road wheels 3 and a steering device control system 4 to simulate the steering feel of a conventional mechanically linked steering system. A steering device 5, which is in the example a steering wheel but which can also be a joystick, is connected to a driver input shaft 6. Position sensors 7 and torque sensor 8 are operably connected to driver input shaft 6. Position sensors 7 electronically detect the angular position of the driver input shaft 6, while the torque sensor 8 electronically detects and evaluates the torsional force acting on the driver input shaft 6. The angular displacement of the steering wheel 5 is detected, transmitted to the actuation control system 2 via a signal line 99, processed in the actuation control system 2, and applied to a servo motor 9 to move the steerable road wheels 3 via a rack 101 and pinion 102 system 10 in a defined angle (3.

[0026] As shown in FIG. 2, the steering device control system 4 includes a steering device actuator 11 to provide a passive steering system feel similar to current production hydraulic or electric assisted rack and pinion systems to the steering wheel 5. The steering device actuator 11 includes an electric motor having a motor shaft rotatively driven by the motor and connected to the driver input shaft 6. Within the steering device control system 4 the steering device actuator 11 electronically communicates with a first control unit 12 via control and signal lines 13. The first control unit 12 communicates via the signal lines 99 electronically the values detected by the sensors 7, 8 to a second control unit 14 being part of the actuation control system 2. The actuation control system 2 further comprises an actuator 9 assigned to the steering gear 10 to move the steerable road wheels 3. The second control unit 14 receives signals from the first control unit 12 and gives feedback of road wheel 3 movement to the first control unit 12.

[0027] Since there is no direct mechanical coupling between the actuation control system 2 and the steerable wheels 3, the driver does not receive any feedback from the road surface through the steering mechanism. Therefore, the steering device actuator 11 generates a reaction torque to the steering wheel 5, based upon a number of steering parameters such as vehicle speed, steering device angle 1, the steering device angle speed v1, v2, the steering device turning acceleration, the yaw rate of the vehicle, road surface condition, and further driving parameters of the vehicle.

[0028] The steer-by-wire system of FIGS. 1 and 2 has half-automated driving incorporated, which allows a transition from vehicle controlled steering (automatic drive mode) to driver controlled steering (manual drive mode).

[0029] An automatic driving electronic control unit (ECU) 120 is present which sets the current drive mode and adjusts the steering system accordingly. The autonomous driving electronic control unit 120 decides based on input signals from the first 12 and second control unit 14 which steering mode is needed. A hands-on-off detection can for example be one of the input signals. The detection of whether there is contact between the driver's hands and the steering wheel (referred to as hands-on-off detection for short) can be made when the driver carries out active steering movements or when the driver wants to override automatic steering and take control of the vehicle, grasping the steering wheel is one way for the driver to commandeer control of the vehicle. In addition, the steering wheel 5 can be the means to transfer control of the vehicle to an automatic steering system.

[0030] Hands-on-off detection can be carried out by the steering angle and torque sensors 7, 8.

[0031] When the steering system 1 is in manual drive mode. The steering wheel 5 communicates directly with the road wheels 3 and the actuator 9 of the steering wheel control system 11 gives an artificial feedback to the driver.

[0032] When the steering system changes to automatic drive mode, the automatic driving electronic control unit 120 provides instructions to the first control unit 12 which receives signals 99 from the second control unit 14 and provides information to the actuator 9 of the steering wheel control system 11 for generating an artificial reduced visual steering wheel 5 movement.

[0033] In automatic drive mode the steering device angle 2 and/or steering device angle speed v1 (road wheel to steering wheel transmission) is reduced in comparison to a steering device turning angle 1 and/or a steering device angle speed v2. The visual feedback movement of the steering wheel 5 is decoupled of the actual rack 101 movement and is controlled by the first control unit 12 in such a way that only slow and small movements are generated without disturbing the driver. This way the offset between the steering wheel 5 and the road wheel 3 is reduced with respect to complete uncoupling of the road wheel 3 to steering wheel 5 transmission. When returning to manual drive mode, the angle difference between the current position of the steering wheel and the position of the steering wheel according to the current position of the road wheels is thus smaller. In another embodiment it is advantageous to further limit the torque t1 applied by the steering wheel actuator 9 to the steering wheel 5 to increase the safety of the driver.

[0034] It is further possible to completely decouple the steering wheel movement from the movement of the road wheels electronically, so the second control unit 14 sends no movement signals to the first control unit 12, or by an electronic clutch arrangement 40, as shown in FIG. 3, so that the steering wheel actuator 9 does not execute any movement of the steering wheel 5 during automatic drive mode.