Feedforward control of motor vehicle roll angle

• US 20050222728A1
• Filed: 12/21/2004
• Published: 10/06/2005
• Est. Priority Date: 04/01/2004
• Status: Active Grant

• Current Assignee: BWI Company Limited SA (Shougang Corporation)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Hac, Aleksander B., Bedner, Edward J.
• Granted Patent: US 7,502,675 B2
• Time in Patent Office: Days
• US Class Current: 701/38
• CPC Class Codes: B60W 10/184 with wheel brakes
• CPC Class Codes: B60W 2510/20 Steering systems
• CPC Class Codes: B60W 2540/18 Steering angle
• CPC Class Codes: B60W 40/10 related to vehicle motion
• CPC Class Codes: B60W 40/109 Lateral acceleration

Abstract

A technique for reducing excessive motor vehicle roll angle using a feedforward control comprises a number of steps. Initially, a steering angle and a speed of the-motor vehicle are determined. Next, a lateral acceleration of the vehicle is estimated based on the steering angle and the speed. Then, a lateral acceleration proportional and derivative (PD) term of the estimated lateral acceleration is determined and roll angle reduction is implemented when the lateral acceleration PD term exceeds a first threshold. The roll angle reduction may be achieved through application of a braking force to an outside front wheel of the vehicle. A magnitude of the braking force may be proportional to a difference between the lateral acceleration PD term and the first threshold.

Claims

1. A method for reducing excessive motor vehicle roll angle using a feedforward control, comprising the steps of:

determining a steering angle of a vehicle;

determining a speed of the vehicle;

estimating a lateral acceleration of the vehicle based on the steering angle and the speed;

determining a lateral acceleration proportional and derivative (PD) term of the estimated lateral acceleration; and

implementing roll angle reduction when the lateral acceleration PD term exceeds a first threshold.

2. The method of claim 1, wherein the step of implementing roll angle reduction when a lateral acceleration PD term exceeds a first threshold includes the step of:

applying braking force to an outside front wheel of the vehicle.

3. The method of claim 2, wherein the magnitude of the braking force is proportional to a difference between the lateral acceleration PD term and the first threshold.

4. The method of claim 1, further comprising the step of:

estimating a roll angle and roll rate from a vehicle roll model.

5. The method of claim 4, wherein the step of implementing roll angle reduction when the lateral acceleration PD term exceeds a first threshold further comprises the step of:

implementing roll angle reduction when one of the lateral acceleration PD term exceeds a first threshold and a roll angle PD term exceeds a second threshold.

6. The method of claim 5, wherein the step of implementing roll angle reduction when one of the lateral acceleration PD term exceeds a first threshold and a roll angle PD term exceeds a second threshold includes the step of:

applying braking force to an outside front wheel of the vehicle.

7. The method of claim 6, wherein the magnitude of the braking force is proportional to a difference between one of the lateral acceleration PD term and the first threshold and the roll angle PD term and the second threshold.

8. A method for feedforward brake-based roll angle stability enhancement, comprising the steps of:

providing a first transfer function that models a relationship between a steer angle of a motor vehicle and a steer induced lateral force;

providing a second transfer function that models a relationship between a total lateral force acting on the vehicle and a roll angle of the vehicle;

determining a desired system transfer function that models a desired relationship between the total lateral force acting on the vehicle and the roll angle of the vehicle;

selecting a feedforward control transfer function to provide a brake induced lateral force to the vehicle to achieve a desired roll angle for the vehicle, wherein the total lateral force includes the steer induced lateral force and the brake induced lateral force, and wherein the feedforward control transfer function is a function of the first transfer function, the second transfer function and the desired system transfer function; and

controlling brakes of the vehicle to reduce the roll angle of the vehicle responsive to the feedforward control transfer function.

9. The method of claim 8, wherein the step of controlling brakes of the vehicle responsive to the feedforward control transfer function includes the step of:

inhibiting braking when one of a tire slip angle is below a first predetermined angle and when the tire slip angle has a wrong sign.

10. The method of claim 8, wherein the first transfer function is motor vehicle speed dependent.

11. The method of claim 8, wherein the step of controlling brakes of the vehicle responsive to the feedforward control transfer function includes the step of:

inhibiting braking when a road surface coefficient of friction (COF) is below a reference COF.

12. A control system including a feedforward control for reducing excessive motor vehicle roll angle, the system comprising:

at least one sensor for providing a steering angle of a motor vehicle and a speed of the vehicle;

a control unit for estimating a lateral acceleration of the vehicle based on the steering angle and the speed coupled to the at least one sensor, the control unit determining a lateral acceleration proportional and derivative (PD) term of the estimated lateral acceleration; and

a motor vehicle subsystem coupled to the control unit, the control unit providing a command to the subsystem to implement roll angle reduction when the lateral acceleration PD term exceeds a first threshold.

13. The system of claim 12, wherein the roll angle reduction is achieved through application of a braking force to an outside front wheel of the vehicle.

14. The system of claim 13, wherein the magnitude of the braking force is proportional to a difference between the lateral acceleration PD term and the first threshold.

15. The system of claim 12, wherein the control unit also implements a vehicle roll model to estimate a roll angle and a roll rate.

16. The system of claim 15, wherein the control unit implements the roll angle reduction when one of the lateral acceleration PD term exceeds a first threshold and a roll angle PD term exceeds a second threshold.

17. The system of claim 16, wherein the roll angle reduction is implemented through application of a braking force to an outside front wheel of the vehicle.

18. The system of claim 17, wherein the magnitude of the braking force is proportional to a difference between one of the lateral acceleration PD term and the first threshold and the roll angle PD term and the second threshold.

19. A control system that implements feedforward brake-based roll angle stability enhancement, the system comprising:

at least one sensor for providing a steer angle of a motor vehicle;

a control unit coupled to the at least one sensor, the control unit implementing a feedforward control transfer function to provide a brake induced lateral force to the vehicle to achieve a desired roll angle for the vehicle, wherein the feedforward control transfer function is based on a first transfer function, a second transfer function and a desired system transfer function, and wherein the first transfer function models a relationship between the steer angle of the vehicle and a steer induced lateral force, the second transfer function models a relationship between a total lateral force acting on the vehicle and a roll angle of the vehicle and the desired system transfer function models a desired relationship between the total lateral force acting on the vehicle and the roll angle of the vehicle, where the total lateral force includes the steer induced lateral force and the brake induced lateral force; and

a brake subsystem coupled to the control unit, the control unit providing a command to the brake subsystem for controlling brakes of the vehicle to reduce the roll angle of the vehicle responsive to the feedforward control transfer function.

20. The system of claim 19, wherein the control unit inhibits braking when one of a tire slip angle is below a first predetermined angle and when the tire slip angle has a wrong sign.

21. The system of claim 19, wherein the first transfer function is motor vehicle speed dependent.

22. The system of claim 19, wherein the control unit inhibits braking when a road surface coefficient of friction (COF) is below a reference COF.