METHOD AND DEVICE FOR DETERMINING A MAXIMUM COEFFICIENT OF FRICTION BETWEEN A TIRE AND AN UNDERLYING SURFACE

• US 20110166761A1
• Filed: 01/07/2011
• Published: 07/07/2011
• Est. Priority Date: 01/07/2010
• Status: Active Grant

• Current Assignee: Continental Automotive GmbH (Continental AG)
• Original Assignee: Continental Automotive GmbH (Continental AG)
• Inventors: Keller, Lothar, Kammann, Stefan
• Granted Patent: US 8,645,038 B2
• Time in Patent Office: Days
• US Class Current: 701/70
• CPC Class Codes: G01M 17/02 Tyres
• CPC Class Codes: G01N 19/02 Measuring coefficient of friction between materials testing of tyres G01M17/02; determinations of friction coefficient used in vehicle braking or traction control systems B60T8/172

Abstract

A method for determining a maximum coefficient of friction μ_max between a tire and an underlying surface entails empirically determining a reference curve μ_ref(S) of a coefficient of friction μ_ref as a function of a slip S between the tire and an underlying reference surface, determining a first momentary slip S₁ for the tire and a first momentary coefficient of friction μ₁ between the tire and the underlying surface at a first instant t₁, determining a second momentary slip S₂ for the tire and a second momentary coefficient of friction μ₂ between the tire and the underlying surface at a second instant t₂, computing a slope of the curve μ(S) of the coefficient of friction μ as a function of slip S, and computing the maximum coefficient of friction μ_max between the tire and the underlying surface by transforming the reference curve μ_ref(S) on the basis of the slope of the curve μ(S). With the aid of the vehicle devices present in any event in modern motor vehicles it is possible to use the information provided by the vehicle devices to be able to compute the momentary slip S and the momentary coefficient of friction μ. By comparing the momentary curve μ(S) that can be determined from the measuring points (μ₁; S₁) and (μ₂; S₂) with the empirically determined reference curve μ_ref(S) it is possible using a suitable mathematical method to very accurately estimate, in particular interpolate, the maximum coefficient of friction μ_max for the momentary material pairing of the tire with the underlying surface.

Claims

1. A method of determining a maximum coefficient of friction μ

_max between a tire and an underlying surface, the method which comprises;

empirically determining a reference curve μ

_ref(S) of a coefficient of friction μ

_ref as a function of a slip S between the tire and an underlying reference surface;

determining a first momentary slip S₁ for the tire and a first momentary coefficient of friction μ

₁ between the tire and the underlying surface at a first instant t₁;

determining a second momentary slip S₂ for the tire and a second momentary coefficient of friction μ

₂ between the tire and the underlying surface at a second instant t₂;

computing a slope of the momentary curve μ

(S) of the coefficient of friction μ

as a function of the slip S; and

computing the maximum coefficient of friction μ

_max between the tire and the underlying surface by transforming the reference curve μ

_ref(S) on the basis of the slope of the curve μ

(S).

2. The method according to claim 1, which further comprises integrating the maximum coefficient of friction μ

_max between the tire and the underlying surface in a drive-control system influencing a drive behavior of a motor vehicle.

3. The method according to claim 1, which comprises determining a maximum coefficient of friction μ

_max,x in a direction of travel of the tire and a maximum coefficient of friction μ

_max,y transverse to a direction of travel of the tire.

4. The method according to claim 1, wherein the transforming step comprises carrying out affine mapping of the reference curve μ

_ref(S).

5. The method according to claim 4, which comprises subjecting the reference curve μ

_ref(S) to exclusively mathematical rotatation and mathematical scaling.

6. The method according to claim 1, which comprises empirically determining a plurality of further reference curves μ

_ref(S) as a function of tire wear and tear, determining a momentary tire wear and tear with the aid of a tire control system, and correcting the reference curve μ

_ref(S) on a basis of the momentary tire wear and tear with the aid of the further reference curves μ

_ref(S).

7. The method according to claim 6, wherein the tire control system determines a tire-profile depth of the tire.

8. The method according to claim 1, which comprises determining tire data selected from the group consisting of tire dimensions, tire type, tire pressure, tire temperature, and tire-profile depth with a tire control system and correcting the reference curve μ

_ref(S) based on the tire data to take account of tire data deviating from momentary tire data when determining the reference curve μ

_ref(S).

9. The method according to claim 1, which comprises determining a relative acceleration component with a vehicle control device during a braking and/or an accelerating action.

10. The method according to claim 1, which comprises determining a relative wheel load.

11. The method according to claim 10, which comprises determining with the tire control system one or more of data concerning a surface of the tire momentarily supported on the underlying surface, pressure data, or tire data.

12. The method according to claim 1, which comprises determining a slip S of the tire by way of a wheel-speed sensor.

13. The method according to claim 1, which comprises making the maximum coefficient of friction μ

_max thus determined available to a drive-regulating system of a motor vehicle.

14. The method according to claim 13, which comprises further utilizing the maximum coefficient of friction μ

_max thus determined in a vehicle system selected from the group consisting of ABS, ESP, ESC.

15. The method according to claim 13, which comprises transmitting the maximum coefficient of friction μ

_max thus determined via a CAN bus within the motor vehicle.

17. The device according to claim 16, configured for carrying out the method according to claim 1.

16. A device for determining a maximum coefficient of friction μ

_max between a tire and an underlying surface, comprising;

a non-volatile memory having stored therein an empirically determined reference curve μ

_ref(S) of a coefficient of friction μ

_ref as a function of a slip S between the tire and an underlying reference surface;

a measuring system for determining a first momentary slip S₁ for the tire and a first momentary coefficient of friction μ

₁ between the tire and the underlying surface at a first instant t₁ and for determining a second momentary slip S₂ for the tire and a second momentary coefficient of friction μ

₂ between the tire and the underlying surface at a second instant t₂; and

a computing unit for computing a slope of the curve μ

(S) of the coefficient of friction μ

as a function of a slip S and for computing the maximum coefficient of friction μ

_max between the tire and the underlying surface by transforming the reference curve μ

_ref(S) on the basis of the slope of the curve μ

(S).