Method and device for determining a maximum coefficient of friction between a tire and an underlying surface
View Patent ↗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 S 1 for the tire and a first momentary coefficient of friction μ 1 between the tire and the underlying surface at a first instant t 1 , determining a second momentary slip S 2 for the tire and a second momentary coefficient of friction μ 2 between the tire and the underlying surface at a second instant t 2 , 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).
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 S 1 for the tire and a first momentary coefficient of friction μ 1 between the tire and the underlying surface at a first instant t 1 ;
determining a second momentary slip S 2 for the tire and a second momentary coefficient of friction μ 2 between the tire and the underlying surface at a second instant t 2 ;
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.
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 S 1 for the tire and a first momentary coefficient of friction μ 1 between the tire and the underlying surface at a first instant t 1 and for determining a second momentary slip S 2 for the tire and a second momentary coefficient of friction μ 2 between the tire and the underlying surface at a second instant t 2 ; 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).
17. The device according to claim 16 , configured for carrying out the method according to claim 1 .