Vehicle Stability Control System and Method

• US 20090112435A1
• Filed: 10/30/2007
• Published: 04/30/2009
• Est. Priority Date: 10/30/2007
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Xu, Li, Salib, Albert Chenouda, Meyers, Joseph Carr, Eisele, Daniel Domek, Brown, Todd Allen
• Granted Patent: US 8,170,767 B2
• Time in Patent Office: Days
• US Class Current: 701/78
• CPC Class Codes: B60T 2230/02 Side slip angle, attitude angle, floating angle, drift angle
• CPC Class Codes: B60T 8/1755 Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve road vehicle drive control systems for control of driving stability otherwise than by controlling a particular sub-unit B60W30/02
• CPC Class Codes: B60W 10/04 including control of propulsion units
• CPC Class Codes: B60W 10/18 including control of braking systems
• CPC Class Codes: B60W 10/20 including control of steering systems
• CPC Class Codes: B60W 2050/0033 Single-track, 2D vehicle model, i.e. two-wheel bicycle model
• CPC Class Codes: B60W 30/045 Improving turning performance

Abstract

A method and system for controlling vehicle stability may comprise determining whether a vehicle is oversteering or understeering and, if the vehicle is oversteering or understeering, determining an amount by which to reduce a speed of the vehicle to correct for understeering or oversteering and applying brake pressure to at least the rear brakes of the vehicle to reduce vehicle speed. The method and system also may comprise determining an engine torque reduction amount based on vehicle oversteer or understeer conditions, reducing engine torque by the determined amount or to zero if the determined amount of engine torque reduction is greater than an actual engine torque, and applying braking to at least the rear brakes of the vehicle if the determined amount of engine torque reduction is greater than the actual engine torque.

Claims

1. A method for controlling vehicle stability, the method comprising:

determining whether a vehicle is oversteering or understeering;

if the vehicle is oversteering or understeering, determining an amount by which to reduce a speed of the vehicle to correct for understeering or oversteering; and

applying brake pressure to at least rear brakes of the vehicle to reduce the vehicle speed.

2. The method of claim 1, further comprising, upon initially applying brake pressure to the rear wheels, adding balance to the vehicle while slowing the vehicle by swinging a rear tire force vector backwards until it is in parallel with a front tire force.

3. The method of claim 2, further comprising applying brake pressure to front and rear brakes of the vehicle simultaneously after applying brake pressure to the rear brakes of the vehicle.

4. The method of claim 3 wherein, if brake pressure is applied to the front and rear brakes of the vehicle simultaneously, the brake pressure is applied so that the front and rear tire force vectors are kept in parallel and are further rotated backwards.

5. The method of claim 4, wherein the magnitude of the brake pressure applied to each brake is in proportion to the normal force on the wheel to which the brake pressure is applied.

6. The method of claim 1, further comprising determining oversteer and understeer by comparing a target vehicle yaw rate with an actual vehicle yaw rate.

7. The method of claim 1, further comprising desensitizing control during transient maneuvers using control deadbands.

8. A method for controlling vehicle stability, the method comprising:

determining an engine torque reduction amount based on vehicle oversteer or understeer conditions;

reducing engine torque by the determined engine torque reduction amount or to zero if the determined amount of engine torque reduction is greater than an actual engine torque; and

applying braking to at least rear brakes of the vehicle if the determined engine torque reduction amount is greater than the actual engine torque.

9. The method of claim 8, wherein the amount of the engine torque reduction request that is greater than the actual engine torque is converted to a normalized negative longitudinal force, and the normalized negative longitudinal force is converted to a brake pressure for at least the rear brakes of the vehicle.

10. The method of claim 9, wherein the normalized negative longitudinal force may be reduced to prevent brake pressure from getting so high that lateral tire force is washed out.

11. The method of claim 9, wherein the normalized negative longitudinal force may be reduced to prevent rapid brake pressure buildup from increasing a path radius of the vehicle.

12. The method of claim 11, wherein the normalized negative longitudinal force is controlled to prevent a sudden decrease in the vehicle'"'"'s path radius.

13. A system for controlling vehicle stability, the system comprising:

a controller for receiving one or more of input signals from vehicle sensors and calculations from previously-executed code, determining whether a vehicle is oversteering or understeering and, if the vehicle is oversteering or understeering, determining a requested amount by which to reduce a speed of the vehicle to correct for understeering or oversteering, wherein the controller sends a signal to apply brake pressure to at least rear brakes of the vehicle to reduce vehicle speed by the requested amount.

14. The system of claim 13 wherein, upon initially applying brake pressure to the rear wheels, balance is added to the vehicle while slowing the vehicle by swinging a rear tire force vector backwards until it is in parallel with a front tire force vector.

15. The system of claim 14, wherein brake pressure is applied to front and rear brakes of the vehicle simultaneously after application of brake pressure to the rear brakes of the vehicle.

16. The system of claim 15 wherein, if brake pressure is applied to the front and rear brakes of the vehicle simultaneously, the brake pressure is applied so that the front and rear tire force vectors are kept in parallel and are further rotated backwards.

17. The system of claim 16, wherein the magnitude of the brake pressure applied to each brake is in proportion to the normal force on the wheel to which the brake pressure is applied.

18. The system of claim 13, wherein the controller determines oversteer and understeer by comparing a target vehicle yaw rate with an actual vehicle yaw rate.

19. The system of claim 13, wherein the controller desensitizes control during transient maneuvers using control deadbands.