Method and circuit configuration for determining a frictional value

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.

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.