Acceleration/deceleration induced real-time identification of maximum tire-road friction coefficient

• US 20070061061A1
• Filed: 09/15/2005
• Published: 03/15/2007
• Est. Priority Date: 09/15/2005
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Hermiz, Sarmad, Salman, Mutasim
• Granted Patent: US 7,751,961 B2
• Time in Patent Office: Days
• US Class Current: 701/80
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 8/172 Determining control parameters used in the regulation, e.g. by calculations involving measured or detected parameters B60T8/17551 takes precedence

Abstract

A method for classifying a road surface condition by estimating the maximum tire/road surface coefficient of friction and actively inducing acceleration or deceleration. In one embodiment, the induced acceleration/deceleration is provided by applying torque to the driven wheels of the vehicle. The speeds of the driven and non-driven wheels are measured. The tire/road surface coefficient of friction and the driven wheel slip ratio are calculated from the wheel speeds. The tire/road surface coefficient of friction and the wheel slip ratio are used to determine the slope of the wheel slip/coefficient of friction curve, which is used to classify the road surface condition.

Claims

1. A method for determining a road surface condition for a vehicle, said method comprising:

determining a plurality of operating parameters;

determining whether the vehicle is traveling along a substantially straight line or along a curve;

changing the vehicle speed for a predetermined period of time;

determining a tire/road surface coefficient of friction from the change in vehicle speed;

determining a wheel slip ratio from the change in vehicle speed; and

determining the road surface condition based on the tire/road surface coefficient of friction and the wheel slip ratio.

2. The method according to claim 1 wherein determining the road surface condition includes calculating a slope of a curve that defines a function between the tire/road surface coefficient of friction and the wheel slip ratio.

3. The method according to claim 2 wherein determining the tire/road surface coefficient of friction and the wheel slip ratio includes using the speed of wheels of the vehicle.

4. The method according to claim 3 wherein determining the tire/road surface coefficient of friction, determining the wheel slip ratio and determining the slope of the curve includes using the equations:

5. The method-according to claim 1 wherein determining the wheel slip ratio includes determining the wheel slip ratio of the driven wheels of the vehicle.

6. The method according to claim 1 wherein determining the plurality of operating parameters includes determining an ambient temperature, determining whether vehicle windshield wipers are on, determining a previewed road curvature and determining a previous road surface condition.

7. The method according to claim 6 wherein determining a previewed road curvature includes using maps and GPS.

8. The method according to claim 1 wherein determining if the vehicle is traveling along a straight line or a curve includes using a yaw rate sensor and/or a hand-wheel angle sensor.

9. The method according to claim 1 further comprising determining whether a vehicle cruise control is on, where determining the tire/road surface coefficient of friction, the wheel slip ratio and the road surface condition is performed only if the cruise control is on.

10. The method according to claim 1 wherein changing the vehicle speed includes changing the vehicle speed by about two kilometers per hour.

11. The method according to claim 1 wherein determining the road surface condition includes determining whether the road surface is icy or snowy.

12. A method for determining a road surface condition for a vehicle stability system, said method comprising:

changing the speed of the vehicle;

determining a tire/road surface-coefficient of friction;

determining a wheel slip ratio; and

determining a slope of a curve that defines a function of the tire/road surface coefficient of friction and the wheel slip ratio.

13. The method according to claim 12 further comprising determining the road surface condition from the slope of the curve.

14. The method according to claim 12 wherein determining the tire/road surface coefficient of friction and the wheel slip ratio includes using the speed of wheels of the vehicle.

15. The method according to claim 12 wherein determining the wheel slip ratio includes determining the wheel slip ratio of the driven wheels of the vehicle.

16. A system for determining a road surface condition for a vehicle, said system comprising:

means for determining a plurality of operating parameters;

means for determining whether the vehicle is traveling along a substantially straight line or along a curve;

means for changing the vehicle speed;

means for determining a tire/road surface coefficient of friction from the change in vehicle speed;

means for determining a wheel slip ratio from the change in vehicle speed; and

means for determining the road surface condition based on the tire/road surface coefficient of friction and the wheel slip ratio.

17. The system according to claim 16 wherein the means for determining the road surface condition includes means for calculating a slope of a curve that defines a function between the tire/road surface coefficient of friction and the wheel slip ratio.

18. The system according to claim 16 wherein the means for determining the tire/road surface coefficient of friction and the wheel slip ratio uses the speed of wheels of the vehicle.

19. The system according to claim 16 wherein the means for determining the wheel slip ratio determines the wheel slip ratio of the driven wheels of the vehicle.

20. The system according to claim 16 wherein the means for determining the plurality of operating parameters includes means for determining an ambient temperature, means for determining whether vehicle windshield wipers are on, means for determining a previewed road curvature and means for determining a previous road surface condition.

21. The system according to claim 20 wherein the means for determining a previewed road curvature uses maps and GPS.

22. The system according to claim 16 wherein the means for determining if the vehicle is traveling along a straight line or a curve includes using a yaw rate sensor and/or a hand-wheel angle sensor.