METHOD FOR CONTROLLING A STEER-BY-WIRE STEERING SYSTEM OF A ROAD VEHICLE WITH FEEDBACK ACTUATOR POSITION CALIBRATION

Abstract

A method for calibrating a position of a feedback actuator of a steer-by-wire steering system of a road vehicle includes moving the feedback actuator to a first end stop of the feedback actuator and from there moving the feedback actuator to a second end stop, recording a position of the two end stops and based thereon determining a newly defined center position, moving the feedback actuator to the newly defined center position, and storing the newly defined center position in a memory as an offset value of an absolute steering wheel angle.

Claims

1. A method for calibrating a position of a feedback actuator of a steer-by-wire steering system of a road vehicle, the method comprising: moving the feedback actuator to a first end stop of the feedback actuator and from there moving the feedback actuator to a second end stop; recording a position of the two end stops and based thereon determining a newly defined center position; moving the feedback actuator to the newly defined center position; and storing the newly defined center position in a memory as an offset value of an absolute steering wheel angle.

2. The method according to claim 1, further comprising: if the end stops change, recording modified end stop positions, and setting functions performed by the steering system using the positions of the two end stops to the modified end stop positions.

3. The method according to claim 1, wherein stored feedback actuator end stop positions are updated during operation of the feedback actuator if an actual position of the feedback actuator is at a steering wheel angle greater than a stored position.

4. The method according to claim 1, wherein stored feedback actuator end stop positions are updated during operation of the feedback actuator if a mechanical end stop is determined to be at a steering wheel angle smaller than a previously stored steering wheel angle.

5. The method according to claim 4, wherein determining if the mechanical end stop is at a steering wheel angle smaller than the previously stored steering wheel angle is based on at least one of an estimated motor torque, a direction of the estimated motor torque, or a combination of a feedback actuator position and movement.

6. The method according to claim 1, further comprising using updated feedback actuator end stop positions in feedback actuator position-related functions for a torque request.

7. The method according to claim 1, further comprising adjusting a position request to send to a road wheel actuator updated feedback actuator end stop positions.

8. A steer-by-wire steering system for a road vehicle comprising: a feedback actuator; a road wheel actuator; and a controller configured or programmed to control the feedback actuator and the road wheel actuator; wherein the controller is configured or programmed to perform the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Example embodiments of the present invention will now be described with reference to the drawings.

[0017] FIG. 1 is a schematic view of a steer-by-wire-steering system.

[0018] FIG. 2 is a block diagram representing feedback actuator end stop calibration.

[0019] FIG. 3 is a block diagram representing end stop adaptation of the steering system.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

[0020] FIG. 1 is a schematic drawing of a steer-by-wire steering system 1 with a steering shaft 2 connected to a steering wheel 3. There is no mechanical connection between the steering wheel 3 and the road wheels 4. A road wheel actuator 5 operates a gear rack 6 via a recirculating ball gear.

[0021] When a driver operates the steering wheel 3, the steering shaft 2 is rotated, which is detected by a shaft sensor, which is not shown in the drawings. A controller is configured or programmed to calculate an operation signal for the road wheel actuator 5 from the signal detected by the shaft sensor. By operating the gear rack 6 with the operation signal, the road wheels 4 are turned. At the same time, forces introduced in the gear rack 6 from the road wheels 4 are recognized by another sensor not shown in the drawings, and a feedback signal is calculated, which is applied to the steering shaft 2 by a steering wheel actuator 7, also called a feedback actuator, so that the operator can recognize the feedback in the steering wheel 3.

[0022] As shown in FIG. 2, the position of the feedback actuator can be calibrated 8 during operation of the vehicle, after some time automatically or in a workshop.

[0023] In a first step of the calibration process, the feedback actuator moves to a first end stop and from there moves to a second end stop, e.g., with position control. The end stops are mechanically defined. The position of the two end stops is recorded. With the recorded information, the feedback actuator is moved back to a newly defined center position where it remains 9. The newly defined center position is stored in a memory as an offset value of the absolute steering wheel angle.

[0024] The feedback actuator torque and or position actuation could be used for this calibration procedure.

[0025] If the end stops change during the lifetime of the steering system, the position of the changed end stop is recorded 10 and the functions in the system is set to the modified end stop positions 11 (see FIG. 3).

[0026] In detail, the stored feedback actuator end stop positions are updated during operation if the actual position of the feedback actuator is at a steering wheel angle greater than the stored position, and an algorithm detects the mechanical end stop at a steering wheel angle that is smaller than a previously stored steering wheel angle. The algorithm can detect the mechanical end stops based on an estimated motor torque, a direction of the estimated motor torque, and/or a combination of a feedback actuator position and movement.

[0027] The updated feedback actuator end stop positions are then used in feedback actuator position-related functions for a torque request (e.g., end stop feeling provision).

[0028] Additionally, it is possible to adjust a position request send to the road wheel actuator (virtual gear ratio) to the updated feedback actuator end stop positions.

[0029] While example embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.