Method and apparatus for determining an individual wheel surface coefficient of adhesion

• US 6,549,842 B1
• Filed: 10/31/2001
• Issued: 04/15/2003
• Est. Priority Date: 10/31/2001
• Status: Expired due to Fees

• Current Assignee: BWI Company Limited SA (Shougang Corporation)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Hac, Aleksander Boguslaw, Bodie, Mark Olen
• Primary Examiner(s): LOUIS JACQUES, JACQUES H
• Application Number:
  US10/003,713
• Time in Patent Office: 531 Days
• Field of Search: 701/80, 701/70, 701/73, 701/90, 180/197, 73/9, 731/05, 731/46, 303/140, 303/143, 303/149, 303/150, 303/189
• 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

The present invention provides a method of estimating a coefficient of adhesion between a road surface and a plurality of tires disposed on a vehicle. An estimated coefficient of adhesion for each of the plurality of tires is provided. First values of longitudinal and lateral forces on the tires are determined from a first set of vehicle dynamic parameters requiring no explicit knowledge of the coefficient of adhesion; and second values of the same forces are determined from a second set of vehicle parameters in an analytic tire model including the estimated value of the coefficient of adhesion. Differences between the first and the second values of the forces on the tires are determined in the longitudinal and lateral directions. Longitudinal and lateral adaptation speeds are determined for each of the plurality of tires; and a coefficient of adhesion adjustment for each of the plurality of tires is estimated from the differences and the adaptation speeds. The estimated coefficients of adhesion for each of the plurality of tires are updated with the estimated coefficient of adhesion adjustments in a reiterative process minimizing the differences.

Claims

1. A method of determining a coefficient of adhesion between a road surface and each of a plurality of tires disposed on a vehicle, comprising:

providing an estimated coefficient of adhesion for each of the plurality of tires;

determining for each of the plurality of tires a longitudinal adaptation speed as a function of a tire longitudinal force value;

determining for each of the plurality of tires a lateral adaptation speed as a function of a tire lateral force value;

estimating for each of the plurality of tires a coefficient of adhesion adjustment, each being based on the longitudinal adaptation speed and the lateral adaptation speed; and

updating for each of the plurality of tires the estimated coefficient of adhesion with the estimated coefficient of adhesion adjustments.

2. The method of claim 1, wherein for each of the plurality of tires the tire longitudinal force value and the tire lateral force value are based on a tire longitudinal slip value, a tire slip angle, a tire normal force value and the estimated coefficient of adhesion.

3. The method of claim 2, wherein determining the tire longitudinal slip value and tire slip angle further comprise:

measuring a vehicle yaw rate;

receiving a wheel speed value for each of the plurality of tires;

determining a front wheel steer angle value;

determining a rear wheel steer angle value;

calculating the tire longitudinal slip value based on each of the wheel speed values and the vehicle yaw rate; and

calculating the tire slip angle based on each of each of the wheel speed values and each of the wheel steer angle values and the vehicle yaw rate.

4. The method of claim 2, wherein determining the tire normal force value comprises:

receiving a vehicle lateral acceleration value;

estimating a vehicle longitudinal acceleration value by passing a vehicle reference speed value through a differentiator;

calculating a longitudinal load transfer value based on the vehicle longitudinal acceleration value;

calculating a lateral load transfer value based on the vehicle lateral acceleration value; and

summing the longitudinal load transfer value and the lateral load transfer value.

5. The method of claim 1, further comprising determining a vehicle handling state.

6. The method of claim 5, wherein the vehicle handling state is a state selected from the group consisting of a linear state of handling, a nonlinear state of handling, a quick transient state of handling and an approximate steady state of handling.

7. The method of claim 1, wherein the coefficient of adhesion has an initial value of 1.

8. The method of claim 1, wherein the plurality of tires comprises a pair of front tires and a pair of rear tires and the estimated coefficients of adhesion for each of the rear tires is updated using a coefficient of adhesion for a corresponding one of the front tires.

9. A method of determining a coefficient of adhesion between a road surface and a plurality of tires disposed on a vehicle, comprising:

providing an estimated coefficient of adhesion for each of the plurality of tires, the plurality of tires including at least two front tires and at least two rear tires;

determining a tire longitudinal slip value and a tire slip angle for each of the plurality of tires;

determining a tire normal force value for each of the plurality of tires;

determining a first tire longitudinal force value and a tire lateral force value for each of the plurality of tires, the first tire longitudinal force value and the tire lateral force value being based on the tire longitudinal slip value, the tire slip angle, the tire normal force value and the coefficient of adhesion;

determining an axle lateral force value;

determining a second tire longitudinal force value for each of the plurality of tires;

determining a vehicle handling state;

determining a longitudinal adaptation speed;

determining a lateral adaptation speed;

estimating a coefficient of adhesion adjustment for each of the plurality of tires based on the longitudinal adaptation speed and the lateral adaptation speed; and

updating the estimated coefficients of adhesion for each of the plurality of tires with the estimated coefficient of adhesion adjustment.

10. A computer usable media for storing a program for determining a coefficient of adhesion between a road surface and a plurality of tires disposed on a vehicle, comprising:

computer readable program code that determines a longitudinal adaptation speed as a function of a tire longitudinal force value for each of the plurality of tires;

computer readable program code that determines a lateral adaptation speed as a function of a tire lateral force value for each of the plurality of tires;

computer readable program code that estimates for each of the plurality of tires a coefficient of adhesion adjustment, each being based on the longitudinal adaptation speed, the lateral adaptation speed and a provided coefficient of adhesion; and

computer readable program code that updates for each of the plurality of tires the estimated coefficient of adhesion with the estimated coefficient of adhesion adjustments.

11. The program of claim 10, wherein the tire longitudinal force value and the tire lateral force value are based on a tire longitudinal slip value, a tire slip angle, a tire normal force value and the coefficient of adhesion.

12. The program of claim 11, wherein determining the tire longitudinal slip value and tire slip angle further comprise:

computer readable program code that measures a vehicle yaw rate;

computer readable program code that receives a wheel speed value for each of the plurality of tires;

computer readable program code that determines a front wheel steer angle value;

computer readable program code that determines a rear wheel steer angle value;

computer readable program code that calculates the tire longitudinal slip value based on each of the wheel speed values and the vehicle yaw rate; and

computer readable program code that calculates the tire slip angle based on each of the wheel speed values and each of the wheel steer angle values and the vehicle yaw rate.

13. The program of claim 11, wherein the tire normal force determination further comprises:

computer readable program code that receives a vehicle lateral acceleration value;

computer readable program code that estimates a vehicle longitudinal acceleration value by passing a vehicle reference speed value through a differentiator;

computer readable program code that estimates a longitudinal load transfer value based on the vehicle longitudinal acceleration value;

computer readable program code that calculates a lateral load transfer value based on the vehicle lateral acceleration value; and

computer readable program code that sums the longitudinal load transfer value and the lateral load transfer value.

14. The program of claim 10, further comprising:

computer readable program code that determines a vehicle handling state.

15. An apparatus for determining a coefficient of adhesion between a road surface and a plurality of tires disposed on a vehicle, comprising:

means for determining a longitudinal adaptation speed as a function of a tire longitudinal force value for each of the plurality of tires;

means for determining a lateral adaptation speed as a function of a tire lateral force value for each of the plurality of tires;

means for estimating for each of the plurality of tires a coefficient of adhesion adjustment, each being based on the longitudinal adaptation speed and the lateral adaptation speed and a provided coefficient of adhesion; and

means for updating for each of the plurality of tires the estimated coefficient of adhesion with the estimated coefficient of adhesion adjustments.

16. The apparatus of claim 15, wherein the tire longitudinal force value and the tire lateral force value are based on a tire longitudinal slip value, a tire slip angle, a tire normal force value and the coefficient of adhesion.

17. The apparatus of claim 15, wherein determining the tire longitudinal slip value and tire slip angle further comprise:

means for measuring vehicle yaw rate;

means for receiving a wheel speed value for each of the plurality of tires;

means for receiving a front wheel steer angle value;

means for receiving a rear wheel steer angle value;

means for estimating a vehicle longitudinal speed value;

means for estimating a vehicle lateral speed value;

means for calculating the tire longitudinal slip value based on each of the wheel speed values and the vehicle yaw rate; and

means for calculating the tire slip angle based on each of the wheel speed values and each of the wheel steer angle values and the vehicle yaw rate.

18. The apparatus of claim 15, wherein the tire normal force determination further comprises:

means for receiving a vehicle lateral acceleration value;

means for estimating a vehicle longitudinal acceleration value by passing a vehicle reference speed value through a differentiator;

means for calculating a longitudinal load transfer value based on the vehicle longitudinal acceleration value;

means for calculating a lateral load transfer value based on the vehicle lateral acceleration value; and

means for summing the longitudinal load transfer value and the lateral load transfer value.

19. The apparatus of claim 15, further comprising means for determining a vehicle handling state.

20. A braking system disposed within an automobile, comprising:

means for providing an estimated coefficient of adhesion for each of a plurality of tires;

means for determining a longitudinal adaptation speed as a function of a tire longitudinal force value;

means for determining a lateral adaptation speed as a function of a tire lateral force value; and

means for estimating for each of the plurality of tires a coefficient of adhesion adjustment, each being based on the longitudinal adaptation speed and the lateral adaptation speed.

21. The method of claim 20, further comprising means for updating the estimated coefficients of adhesion for each of the plurality of tires with the estimated coefficient of adhesion adjustment.

22. A method of determining a coefficient of adhesion between a road surface and a tire disposed on a vehicle, comprising:

providing an estimated value of the coefficient of adhesion;

determining a first value of a force on the tire from a first set of vehicle dynamic parameters requiring no explicit knowledge of the coefficient of adhesion;

determining a second value of the force on the tire from a second set of vehicle parameters in an analytic tire model including the estimated value of the coefficient of adhesion;

determining a difference between the first and the second values of the force on the tire;

updating the estimated value of the coefficient of adhesion in direction to reduce the difference; and

repeating the previous steps using the updated value of the coefficient of adhesion as the provided value thereof.

23. The method of claim 22 wherein the step of updating the estimated value of the coefficient of adhesion comprises:

determining a vehicle handling state;

in response to the vehicle handling state, determining a speed of adaptation; and

adjusting the estimated value of the coefficient of adhesion in magnitude derived from the speed of adaptation.

24. The method of claim 23 wherein the force on the tire is a lateral force.

25. The method of claim 24 wherein the force on the tire is calculated using dynamic equations of the vehicle in a yaw plane.

26. The method of claim 24 wherein the speed of adaptation is set to a reset value so that no adaptation occurs if the vehicle is determined to be in a linear range of handling behavior based on a function of a magnitude of a yaw rate error between a desired yaw rate and an actual yaw rate of the vehicle.

27. The method of claim 24 wherein the first set of vehicle parameters comprises a vehicle lateral acceleration and a vehicle yaw rate.

28. The method of claim 23 wherein the force on the tire is a longitudinal force.

29. The method of claim 28 wherein the force on the tire is calculated using equations describing rotary dynamics of the tire.

30. The method of claim 28 wherein the speed of adaptation is set to a reset value so that no adaptation occurs when the difference between the first and second values of the force on the tire is lesser in magnitude than a first threshold value and a low pass filtered difference between the first and second values of the force on the tire is lesser in magnitude than a second threshold value.

31. The method of claim 28 wherein the first set of vehicle parameters comprises a wheel speed, a driving torque, a braking torque and a rolling resistance moment.

32. The method of claim 23 wherein the speed of adaptation is set to a reset value so that no adaptation occurs when a longitudinal acceleration of the vehicle exceeds a reference vehicle acceleration threshold.

33. The method of claim 22 wherein the second set of vehicle parameters comprises a tire longitudinal slip value, a tire slip angle and a tire normal force value as well as the estimated value of the coefficient of adhesion.

34. A method of determining coefficients of adhesion between a road surface and a set of a front tire and a rear tire disposed on a vehicle, comprising:

providing an estimated value of the coefficient of adhesion for the front tire;

determining a first value of a force on the front tire from a first set of vehicle dynamic parameters requiring no explicit knowledge of the coefficient of adhesion;

determining a second value of the force on the front tire from a second set of vehicle parameters in an analytic tire model including the estimated value of the coefficient of adhesion;

determining a difference between the first and the second values of the force on the front tire;

updating the estimated value of the coefficient of adhesion of the front tire in direction to reduce the difference and storing the resulting updated estimated value;

repeating the previous steps using the updated value of the coefficient of adhesion of the front tire as the provided value thereof; and

repeatedly deriving the coefficient of friction of the rear tire from one of the stored updated estimated values of the coefficient of friction for the front tire determined at an earlier time determined responsive to vehicle speed.

35. The method of claim 34 wherein the earlier time is earlier by a time duration approximating the time required for the rear tire to travel the distance between the front and rear tires at the vehicle speed.