Method and circuit configuration for determining a frictional value

Claim 3

The method according to claim 1, which further comprises approximating the coefficient of friction in the approximating step with the equation μ(s)=As+B√s, wherein A and B are parameters for the approximation, μ is the coefficient of friction, and s is the wheel slip.

Claim 4

The method according to claim 1, which further comprises approximating the coefficient of friction in the approximating step with the equation ##EQU21## wherein A, B and C are parameters for the approximation, μ is the coefficient of friction, and s is the wheel slip.

Claim 5

The method according to claim 1, which further comprises estimating, in the estimating step, the coefficient of friction μ with the following recursive estimation algorithm: μ(n)=μ(n-1)+k(n)(y(n)-X* μ(n-1)), in which ##EQU22## is a variable formed from the measured values, ω R is an angular speed of the respective wheel, and n is a dummy index of consecutive measurement instants; ##EQU23## is a vehicle parameter, m A is a portion of a vehicle mass on the respective wheel, r R is a rolling radius of the wheel, and Θ R is a mass moment of inertia of the wheel; ##EQU24## is an amplification factor for error feedback; and P(n-1)=10 q *(y(n-1)-X* μ(n-1)) 2 is a covariance of an estimation error at a measurement time n-1;

Claim 6

The method according to claim 1, which further comprises determining the coefficient of friction as a function of a wheel slip with a recursive estimation algorithm.

Claim 7

The method according to claim 5, which further comprises determining the coefficient of friction on the basis of a model ##EQU25## in which A and B are curve parameters with a vector representation b T = AB! calculated from the measured wheel slip values with the vector representation X T = s√s! and from a previously ascertained coefficient of friction μ(n-1), and determining a current coefficient of friction μ(n) with the following estimation algorithm: μ(n)=X.sup.T (n)*b(n) in which b(n)=b(n-1)+k(n-1)(μ(n)-X.sup.T (n)b(n-1) k(n)=P(n-1)X(n)(1+X.sup.T (n)P(n-1)X(n)).sup.-1 P(n-1)=10.sup.q *|μ(n-1)-X.sup.T (n-1)b(n-1)|.sup.2 *I and I is a unit matrix.

Claim 8

The method according to claim 1, which further comprises determining the coefficient of friction μ(s) on the basis of a model ##EQU26## wherein A, B, and C are parameters for the approximation, and s is the wheel slip.

Claim 9

The method according to claim 5, which further comprises transmitting the frictional value determined in the determining step to an anti-lock brake system or a traction control system.

Claim 10

A circuit configuration for determining a coefficient of friction between a motor vehicle tire and a road surface, comprising: a plurality of sensors disposed at a motor vehicle for continuously measuring an angular speed of a wheel and a braking pressure at a wheel; an evaluation circuit connected to said sensors and receiving the signals from the sensors, said evaluation circuit being programmed to calculate and angular acceleration from the angular speed measured by a respective one of said sensors; and to evaluate a coefficient of friction between a motor vehicle tire and a road surface from the angular acceleration and from the braking pressure with a recursive estimation algorithm.

Claim 11

A circuit configuration for determining a coefficient of friction between a motor vehicle tire and a road surface, comprising: a plurality of sensors disposed at a motor vehicle for continuously measuring an angular speed of a wheel and a braking pressure at a wheel; an evaluation circuit connected to said sensors and receiving the signals from the sensors, said evaluation circuit being programmed to calculate and angular acceleration from the angular speed measured by a respective one of said sensors; and to evaluate a coefficient of friction between a motor vehicle tire and a road surface from the angular acceleration and from the braking pressure with a recursive estimation algorithm.

Claim 12

The circuit configuration according to claim 9, which further comprises means for connecting an output of said evaluation circuit to an anti-lock brake system.

Claim 13

The circuit configuration according to claim 9, which further comprises means for connecting an output of said evaluation circuit to a traction control system.

Claim 14

In an anti-lock brake system or a traction control system in which a coefficient of friction between a motor vehicle tire and a road surface is utilized as a control parameter, an improved circuit configuration for determining the coefficient of friction between the motor vehicle tire and the road surface, the improvement which comprises: a plurality of sensors disposed at the motor vehicle for continuously measuring a vehicle travel speed, an angular speed of a wheel, and a braking pressure at a wheel; an evaluation circuit connected to said sensor and receiving the signals from said sensors, the evaluation circuit being programmed for calculating an angular acceleration from the angular speed measured by a respective one of said sensors; for calculating a wheel slip from the vehicle travel speed and from the angular acceleration; for approximately a dependency of the coefficient of friction between the tire and the road surface from the wheel slip with a non-linear approximation equation; and for determining a current estimated value of the coefficient of friction between the motor vehicle tire and the road surface from measurement values ascertained in an immediately preceding instant with a recursive estimation algorithm.

Claim 15

In an anti-lock brake system or a traction control system in which a coefficient of friction between a motor vehicle tire and a road surface is utilized as a control parameter, an improved circuit configuration for determining the coefficient of friction between the motor vehicle tire and the road surface, the improvement which comprises: a plurality of sensors disposed at the motor vehicle for continuously measuring a vehicle travel speed, an angular speed of a wheel, and a braking pressure at a wheel; an evaluation circuit connected to said sensor and receiving the signals from said sensors, the evaluation circuit being programmed for calculating an angular acceleration from the angular speed measured by a respective one of said sensors; for calculating a wheel slip from the vehicle travel speed and from the angular acceleration; for approximately a dependency of the coefficient of friction between the tire and the road surface from the wheel slip with a non-linear approximation equation; and for determining a current estimated value of the coefficient of friction between the motor vehicle tire and the road surface from measurement values ascertained in an immediately preceding instant with a recursive estimation algorithm.