System and method of controlling vehicle steer-by-wire systems with adjustable steering feel

• US 6,728,615 B1
• Filed: 02/03/2003
• Issued: 04/27/2004
• Est. Priority Date: 02/03/2003
• Status: Expired due to Term

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Inventors: Yao, Yixin, Stout, Gregory J.
• Primary Examiner(s): Jeanglaude, Gertrude A.
• Application Number:
  US10/356,441
• Time in Patent Office: 449 Days
• Field of Search: 701/41, 701/42, 701/43, 701/44, 701/33, 180/402, 180/403, 180/444, 180/443, 180/445, 180/446, 180/447
• US Class Current: 701/41
• CPC Class Codes: B62D 6/008 Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications

Abstract

The present invention involves a system and method of controlling a steer-by-wire system to produce adjustable steering feel for A vehicle driver by providing control of reaction torque on a steering wheel of a vehicle. The method includes a quantitative description for the steering feel which is obtained by establishing a relationship of steering wheel reaction torque and steering wheel angle, road wheel torque, and vehicle speed. The system and method include steer-by wire system closed-loop feedback controls with inner torque loop, steering wheel rate feedback loop, and steering wheel angular position feedback loop to implement providing the steering feel, active steering wheel return with the different rotation rate, steering wheel stop according to the road wheel angular position in a parking state, and directional angle reference generation to road wheels.

Claims

1. A method of controlling a steer-by-wire system to produce adjustable steering feel for a vehicle driver by providing control of reaction torque on a steering wheel of a vehicle, the method comprising:

providing a steering wheel sub-system control to produce steering feel for a vehicle driver, to provide the active steering wheel return with the different rotation rate, to provide the steering wheel stop according to the road wheel angular position in the parking state, and to generate the directional reference angle to road wheels;

providing a road wheel control sub-system to make road wheel angle tracking for the road wheel directional reference angles within a servo control system structure having road wheel angular position feedback and road wheel angular rate feedback;

applying the equivalent road wheel toque, the steering wheel rate and the steering angle as feedback signals to construct a closed-loop control system for the steering wheel sub-system including the inner torque loop, the steering wheel rate feedback loop, and the steering wheel angular position feedback loop with the steering wheel controller to implement the steering functions of steering feel, active steering wheel return, steering wheel stop according to the road wheel angular position, and directional reference angle generation;

describing the action toque produced by vehicle driver to turn the steering wheel to be the disturbance torque for steering wheel closed-loop control system;

receiving steering wheel action torque from the vehicle driver by using steering wheel connected to the steering wheel motor;

receiving steering angle from the steering wheel control sub-system;

receiving steering wheel reference angle being based on road wheel angles from the road wheel control sub-system;

receiving steering angular rate from the steering wheel control sub-system;

receiving the equivalent road wheel toque from the road wheel control sub-system;

receiving vehicle speed from the vehicle speed sensor measurement or estimation;

calculating the steering wheel angle error based on the steering wheel angle and steering wheel reference angles;

determining a steering wheel angle control variable based on steering wheel angle error using the steering wheel controller;

determining a steering wheel angular rate feedback control variable based on steering wheel angular rate using the rate loop compensator,

describing quantitatively for steering wheel reaction toque based on steering wheel angle, road wheel torque and vehicle speed;

generating the steering wheel reaction torque control variables from the steering wheel controller including adjustable controller parameters based on the steering wheel angle and the equivalent road wheel torque; and

applying torque control variable of the steering wheel controller to control the reaction torque produced by the steering wheel motor to obtain the adjustable steering feel and other steering functions.

2. The method of claim 1 wherein steering wheel reaction toque which represents steering feel for the driver is described quantitatively based on the variable relationships between the steer-by-wire system and the steering wheel control unit in the steer-by-wire system.

3. The method of claim 2 wherein variables of steer-by-wire system include the reaction torque τ

_c, the steering wheel angle θ

_s and equivalent road wheel torque τ

_d, and vehicle speed.

4. The method of claim 2 wherein variables of steering wheel control unit include the equivalent reaction torque variable u_s(t), input variable u_i(t);

the input variable u_r(t), and vehicle speed.

5. The method of claim 2 wherein the equivalent reaction torque variable u_s(t) is proportional to the reaction torque τ

_c affected by the input variable u_i(t) of and the input variable u_r(t), where input variable u_i(t) is proportional to the steering wheel angle θ

_s and the input variable u_r(t) is proportional to the equivalent road wheel torque τ

_d.

6. The method of claim 5 wherein the variable relationships between the steer-by-wire system and steering wheel control unit, variables u_s(t), u_i(t) and u_r(t) can be used to describe steer-by-wire system variables including reaction toque τ

_c(t), steering wheel angle θ

_s and road wheel torque τ

_r.

7. The method of claim 6 wherein the description quantitatively of the equivalent reaction torque u_s(t) in the steering wheel control unit is given in the following equation:

8. The method of claim 7 both of functions f(u_i(t),v_c) and f(u_r(t),v_c) may be linear or nonlinear functions of input variables u_i(t), u_r(t) and vehicle speed.

9. The method of claim 8 By adjusting the parameters of two functions f(u_i(t),v_c) and f(u_r(t),v_c), the equivalent reaction torque u_s(t) will change with variable u_i(t) and u_r(t). The change of vehicle speed V_c will automatically adjust the parameters of the functions f(u_i(t),v_c) and f(u_r(t),v_c) to cause the change of function values such that the equivalent reaction torque u_s(t) produces the relative changes.

10. The method of claim 8 adjustable controller parameters may be determined in the every sampling time based on quantitative description of the equivalent reaction torque u_s(t).

11. The method of claim 2 wherein according to the variable relations between steering wheel control unit and steering wheel control system, an equation to describe the reaction torque τ

_c may be further provided as follows;

12. The method of claim 11 wherein the equation gives the quantitative description for reaction toque τ

_c(t) based on steering wheel angle θ

_s, road wheel torque τ

_r and vehicle speed V_s.

13. The method of claim 11 wherein the equation gives the quantitative description for the steering feel according to reaction toque τ

_c(t).

14. The method of claim 1 wherein the vehicle driver turns the steering wheel to control the vehicle direction and to produce an action for steering wheel sub-system with the closed-loop feedback controls.

15. The method of claim 14 wherein the action of the vehicle driver turning steering wheel produce an action toque for the steering wheel and its assembly.

16. The method of claim 15 wherein an action toque on the steering wheel produced by the vehicle driver is described and defined as an equivalent external disturbance torque for steering wheel closed-loop control system.

17. The method of claim 16 wherein when an external disturbance torque which represents the driver'"'"'s steering action is exerted to the steering wheel feedback control sub system, the steering wheel control sub-system produces a reaction torque to reject the equivalent disturbance torque. Thus, a driver holding the steering wheel of the vehicle will feel the reaction torque change in the process of turning the steering wheel.

18. The method of claim 15 wherein by automatically adjusting parameters of the steering wheel feedback controller in steering wheel control sub-system and vehicle variables, the reaction torque will change with the vehicle variables and steering wheel system variables (the steering wheel angle, steering wheel rate and road wheel torque).

19. The method of claim 1 wherein calculating the steering wheel angle error includes:

determining the steering wheel angle error between the steering wheel reference angle and the actual received steering wheel angle by using the steering wheel angle negative feedback.

20. The method of claim 1 wherein generating the steering wheel reaction torque control variables from the steering wheel controller includes:

determining the steering wheel angular control variable based on the steering wheel angle error using the steering wheel controller in the steering wheel closed-loop control system;

determining the equivalent road wheel torque based on the estimation for actual road wheel toque;

determining the steering wheel reaction torque control variable using the steering wheel controller including adjustable controller parameters based on the steering wheel angular control variable and the equivalent road wheel torque.

21. The method of claim 1 wherein the equivalent road wheel torque signal can be obtained by the estimation methodology as road wheel torque.

22. The method of claim 21 wherein equivalent road wheel torque estimation signal can be obtained from the control signals of the controller output of the road wheel feedback control system.

23. The method of claim 22 wherein the equivalent road wheel torque signal is proportional to the road wheel control signals, and the equivalent road wheel torque signal may change according to the road wheel system operating conditions, external disturbances and the road conditions.

24. The method of claim 1 wherein the some steering functions are produced by applying the steering wheel closed-loop control sub-system includes the inner torque loop, the steering wheel rate feedback loop, and the steering wheel angular position feedback loop with the steering wheel controller to implement the steering functions.

25. The method of claim 24 wherein steering functions produced by the steering wheel closed-loop control sub-system includes the steering feel, active steering wheel return, steering wheel stop according to the road wheel angular position, and directional reference angle generation.

26. The method of claim 25 wherein steering feel is produced from the steering wheel closed-loop control sub-system.

27. The method of claim 25 wherein active steering wheel return is produced from the steering wheel closed-loop control sub-system.

28. The method of claim 25 wherein steering wheel stop according to the road wheel angular position is produced from the steering wheel closed-loop control sub-system.

29. The method of claim 25 wherein directional reference angle is produced from the steering wheel closed-loop control sub-system.

30. A steer-by-wire system to produce adjustable steering feel for the vehicle driver by providing the control of the reaction torque on the steering wheel, the system comprising:

a steering wheel control sub-system having a steering wheel controlled plant and a steering wheel controller producing the steering feel for a vehicle driver, the active steering wheel return with the different rotation rate, the steering wheel stop according to the road wheel angular position in the parking state, and the directional reference angle to road wheels; and

a road wheel control sub-system to make road wheel angle tracking for the road wheel directional reference angles having the road wheel controlled plant and road wheel controller.

31. The system of claim 30 wherein steering wheel control sub-system having the steering wheel controller includes the inner torque loop, the steering wheel rate feedback loop, and the steering wheel angular position feedback loop.

32. The system of claim 30 wherein road wheel control sub-system having the steering wheel controller includes road wheel angular position feedback loop and road wheel angular rate feedback loop within a servo control system structure.

33. The system of claim 30 wherein the steering wheel controlled plant of the steering wheel control sub-system includes:

a steering wheel shaft and a steering wheel attached to the steering wheel shaft;

a steering wheel position sensor attached to the steering wheel shaft or a steering wheel motor actuator for sensing a steering wheel angle;

a steering wheel motor amplifier in electrical communication with the steering wheel controller; and

a steering motor actuator for receiving motor torque control variable from the steering wheel motor amplifier for produce the torque on the steering wheel.

34. The system of claim 30 wherein the road wheel controlled plant of the road wheel control sub-system includes:

a left road wheel angle sensor attached to a left road wheel motor actuator and a right road wheel sensor attached to a right road wheel motor actuator for sensing a left and right road wheel angles;

a left road wheel motor amplifier in electrical communication with the road wheel controller and a right road wheel motor amplifier in electrical communication with the road wheel controller for receiving motor torque control variables to provide the road wheel motor actuator control values; and

a left road wheel motor actuator in electrical communication with the left road wheel amplifier and attached adjacent to the left road wheel and a right road wheel motor actuator in electrical communication with the right road wheel amplifier and attached adjacent to the right road wheel for applying torque to the corresponding road wheel based on torque control signal received from the corresponding motor amplifier.