Steer-by-wire systems and methods of operating thereof in vehicles
Described herein are steer-by-wire systems and methods of operating these systems in vehicles. A steer-by-wire system comprises a steering wheel assembly, comprising a steering wheel, sensors, and a torque generator. The system comprises a rack assembly, comprising a steering rack, sensors, and a rack actuator. The steering wheel assembly and the rack assembly are communicatively coupled by a steer-by-wire system controller, without having any direct mechanical links between the assemblies. In some examples, the controller instructs the rack assembly to control the steering rack position based on the steering input, such as changes in the steering wheel position. A steering map is used to determine the desired steering rack position based on the current steering wheel position. In some examples, a steering map is selected from a steering map set based on, e.g., the vehicle speed, vehicle direction, driver preference, and the like.
1. A method of maintaining an alignment between a steering wheel and a steering rack in a steer-by-wire system on a vehicle, the method comprising:
obtaining, at a steering wheel controller, a steering wheel position from a steering wheel position sensor coupled to the steering wheel;
obtaining, at the steering wheel controller, a steering rack position from a rack position sensor coupled to the steering rack;
determining, using the steering wheel controller, a rack position difference based on the steering wheel position and the steering rack position, wherein the rack position difference represents the alignment between the steering wheel and the steering rack; and
when the rack position difference is greater than a first alignment threshold, thereby requiring adjustment of the alignment between the steering wheel and the steering rack, and when vehicle propulsion is allowed, determining, using the steering wheel controller, at least one of
a steering wheel position target that is different from the steering wheel position and based on the rack position difference thereby ensuring the alignment between the steering wheel and the steering rack, or
a steering rack position target that is different from the steering rack position and based on the rack position difference thereby ensuring the alignment between the steering wheel and the steering rack.
2. The method of claim 1 , wherein the steering wheel position target is determined when the rack position difference is greater than the first alignment threshold.
3. The method of claim 1 , wherein the steering rack position target is determined when the rack position difference is greater than the first alignment threshold.
4. The method of claim 1 , wherein both the steering wheel position target and the steering rack position target are determined when the rack position difference is greater than the first alignment threshold.
5. The method of claim 1 , further comprising, when the vehicle propulsion is not allowed, determining only the steering wheel position target but not the steering rack position target.
6. The method of claim 1 , further comprising, when the vehicle propulsion is not allowed, comparing the rack position difference with a second alignment threshold that is greater than the first alignment threshold.
7. The method of claim 6 , further comprising, when the rack position difference is greater than the second alignment threshold:
sending a system calibration request from the steering wheel controller to a vehicle network, and
waiting at the steering wheel controller for a response from the vehicle network before determining the at least one of the steering wheel position target or the steering rack position target using the steering wheel controller.
8. The method of claim 1 , wherein, when the vehicle propulsion is not allowed, the adjustment of the alignment is performed only by rotating the steering wheel and not by moving the steering rack.
9. The method of claim 1 , wherein at least one of the steering wheel position target or the steering rack position target is determined by the steering wheel controller using an alignment map provided at the steering wheel controller.
10. The method of claim 9 , wherein the alignment map comprises values of the rack position difference, values of steering wheel position change, and values of steering rack position change.
11. The method of claim 10 , further comprising interpolating, by the steering wheel controller, a new set of values of the rack position difference, the steering wheel position change, and the steering rack position change based on existing values in the alignment map.
12. The method of claim 10 , wherein a higher value of the rack position difference corresponds to a higher value of the steering wheel position change.
13. The method of claim 10 , wherein a higher value of the rack position difference corresponds to a higher value of the steering rack position change.
14. The method of claim 9 , wherein the alignment map further comprises values of at least one of vehicle speed, steering angle difference, and propulsion state.
15. The method of claim 14 , wherein:
the alignment map comprises the values of the vehicle speed and the steering angle difference, and
a higher value of the vehicle speed corresponds to more responsive alignment.
16. The method of claim 1 , wherein the steering wheel position and the steering rack position are obtained periodically by the steering wheel controller.
17. The method of claim 1 , further comprising determining the steering wheel position target, by the steering wheel controller, from the steering wheel position using a steering map, wherein a difference between the steering wheel position target and the steering rack position is the rack position difference.
18. The method of claim 1 , wherein, when the rack position difference is greater than the first alignment threshold and when the vehicle propulsion is allowed, the vehicle is placed by the steering wheel controller into a limp mode.
19. The method of claim 1 , further comprising transmitting the steering wheel position target to a steering wheel actuator and rotating the steering wheel using the steering wheel actuator in accordance with the steering wheel position target.
20. The method of claim 1 , further comprising transmitting the steering rack position target to a rack actuator and moving the steering rack using the rack actuator in accordance with the steering rack position target.