Algorithm for steering angle command to torque command conversion

• US 9,150,246 B2
• Filed: 12/06/2013
• Issued: 10/06/2015
• Est. Priority Date: 12/06/2013
• Status: Expired due to Fees

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Lee, Jin-Woo, Ghoneim, Youssef A.
• Primary Examiner(s): EL CHANTI, HUSSEIN A
• Application Number:
  US14/099,719
• Publication Number:
  US 20150158524A1
• Time in Patent Office: 669 Days
• Field of Search: 701/41
• US Class Current: 1/1
• CPC Class Codes: B62D 1/28 non-mechanical , e.g. following a line or other known markers
• CPC Class Codes: B62D 15/025 Active steering aids, e.g. helping the driver by actively influencing the steering system after environment evaluation B62D1/28 takes precedence
• CPC Class Codes: B62D 6/001 the torque NOT being among the input parameters
• CPC Class Codes: B62D 6/002 computing target steering angles for front or rear wheels B62D7/159 takes precedence
• CPC Class Codes: B62D 6/08 responsive only to driver input torque

Abstract

A system and method for converting a vehicle steering angle command to a vehicle steering torque command for a vehicle steering system in a vehicle. The method estimates a self-aligning torque that defines the torque that maintains a vehicle steering wheel at a neutral steering position or to a position that makes no slip angle at the road wheel, applies known total steering torque commands to the steering system at a plurality of sample time steps where the known steering torque commands include the self-aligning torque, and measures a vehicle steering angle at each time step. The method then models the steering system of the vehicle using the torque commands, the measured steering angles, a system delay and a plurality of unknown parameters.

Claims

1. A method for converting a vehicle steering angle command to a vehicle steering torque command for a vehicle steering system in a vehicle, said method comprising:

estimating a self-aligning torque that defines the torque that maintains a vehicle steering wheel at an initial steering angle;

applying known total steering torque commands to the steering system at a plurality of sample time steps where the known steering torque commands include the self-aligning torque;

measuring, using a steering angle sensor, a vehicle steering angle at each time step; and

modeling the steering system of the vehicle using the torque commands, the measured steering angles, a system delay and a plurality of steering system parameters for a plurality of different vehicle speeds, wherein modeling the steering system includes performing an off-line process to determine an off-line steering model and an on-line process to correct the off-line steering model in real time during vehicle operation.

2. The method according to claim 1 wherein estimating a self-aligning torque includes employing dynamic equations.

3. The method according to claim 2 wherein the dynamic equations include:

4. The method according to claim 1 wherein estimating a self-aligning torque includes using an empirical data set that models the self-aligning torque as a multi-dimensional look-up table based on vehicle speed, steering angle and other vehicle parameters.

5. The method according to claim 4 wherein estimating a self-aligning torque using the empirical method includes driving the vehicle with a known initial steering angle and a predetermined vehicle speed, applying a steering torque to the steering system, increasing the steering torque until it maintains the steering wheel at the initial steering wheel angle and repeating these steps at predetermined steering wheel angles and vehicle speeds to populate the look-up table.

6. The method according to claim 1 wherein modeling the steering system includes using the equation:

7. The method according to claim 6 wherein the plurality of time steps includes a current time step and a previous time step, and wherein the equation is converted to the equation:

8. The method according to claim 7 wherein the equation is solved by a least-square process to identify the steering system parameters and define the steering model.

9. The method according to claim 7 wherein the pure time delay is determined by a step response test that includes applying a step torque command and measuring a time difference until the steering wheel moves.

10. The method according to claim 1 wherein the plurality of different vehicle speeds include a low vehicle speed, a medium vehicle speed and a high vehicle speed.

11. The method according to claim 1 wherein correcting the steering model on-line during vehicle operation includes using the equations:

12. A method for converting a vehicle steering angle command to a vehicle steering torque command for a vehicle steering system in a vehicle, said method comprising:

estimating a self-aligning torque that defines the torque that maintains a vehicle steering wheel at an initial steering angle using dynamic equations or an empirical data set that models the self-aligning torque as a multi-dimensional look-up table based on vehicle speed, steering angle and other vehicle parameters;

applying known total steering torque commands to the steering system at a plurality of sample time steps where the known steering torque commands include the self-aligning torque;

measuring, using a steering angle sensor, a vehicle steering angle at each time step;

modeling the steering system of the vehicle off-line at a plurality of vehicle speeds using the torque commands, the measured steering angles, a system delay and a plurality of steering system parameters, wherein modeling the steering system includes using the equation;

13. The method according to claim 12 wherein the dynamic equations include:

14. The method according to claim 12 wherein estimating a self-aligning torque using the empirical method includes driving the vehicle with a known initial steering angle and a predetermined vehicle speed, applying a steering torque to the steering system, increasing the steering torque until it maintains the steering wheel at the initial steering wheel angle and repeating these steps at predetermined steering wheel angles and vehicle speeds to populate the look-up table.

15. The method according to claim 12 wherein the plurality of time steps includes a current time step and a previous time step, and wherein the equation is converted to the equation:

16. The method according to claim 12 wherein the pure time delay is determined by a step response test that includes applying a step torque command and measuring a time difference until the steering wheel moves.

17. The method according to claim 12 wherein correcting the steering model on-line during vehicle operation includes using the equations:

18. A conversion system for converting a vehicle steering angle command to a vehicle steering torque command for a vehicle steering system in a vehicle, said conversion system comprising:

means for estimating a self-aligning torque that defines the torque that maintains a vehicle steering wheel at an initial steering angle;

means for applying known total steering torque commands to the steering system at a plurality of sample time steps where the known steering torque commands include the self-aligning torque;

means for measuring a vehicle steering angle at each time step; and

means for modeling the steering system of the vehicle using the torque commands, the measured steering angles, a system delay and a plurality of steering system parameters for a plurality of different vehicle speeds, wherein the means for modeling the steering system performs an off-line process to determine an off-line steering model and an on-line process to correct the off-line steering model in real time during vehicle operation.

19. The conversion system according to claim 18 wherein the means for the steering system includes uses the equation:

20. The system according to claim 19 wherein the plurality of time steps includes a current time step and a previous time step, and wherein the equation is converted to the equation: