Method to control the operation of wheels of a vehicle to prevent slipping or skidding, and brake locking

A system for controlling braking operation of a wheel forming at least one controlled wheel of a vehicle, comprising

• means (6) for continuously measuring the instantaneous braking pressure P.sub.B being applied to the wheel (1);
• means (2) for continuously measuring the instantaneous rolling speed V.sub.R of the wheel (1) over a roll-off surface;
• means for determining, from said continuously measured braking pressure P.sub.B and wheel speed V.sub.R, the instantaneous value of the coefficient of friction .mu. between the wheel circumference and the roll-off surface of the wheel;
• and
• means (7) for controlling the level of braking pressure being applied to said wheel based on the determined coefficient of friction .mu.,
• wherein said determining means for determining said coefficient of friction .mu. includes
• (1) means for solving, by utilizing the measured values of braking pressure P.sub.B and wheel speed V.sub.R, at a strobing instant K and a subsequent strobing instant K+1, one of the linear differential equations:
• V.sub.R(K+1) =p.sub.2 *V.sub.R(K) -p.sub.1 *P.sub.B(K) +c.sub.1 * (1)
• V.sub.RN(K+1) =p.sub.2 .multidot.V.sub.RN(K) -p.sub.1 P.sub.BN(K) +c.sub.1 ( 1N)
• wherein the subscript N denotes a normalizing value and the superscript * denotes a not normalized value;
• wherein the parameters (p.sub.1 *, p.sub.2 * and c.sub.1 *) and (p.sub.1, p.sub.2 and c.sub.1), respectively, are estimated;
• and
• (2) means (14) for calculating the coefficient of friction .mu. in accordance with the respective relationships:
• ##EQU16## wherein clock means (10) are provided furnishing strobing pulses at constant strobing intervals T.sub.A ;
• wherein
• the instantaneous values (p.sub.2 *, p.sub.1 *, c.sub.1 *) or, respectively, (p.sub.2, p.sub.1, c.sub.1) are estimated values based on measured values of braking pressure P.sub.B or P.sub.BN, respectively, and wheel speed V.sub.R or V.sub.RN, respectively;
• and
• R.sub.R or T.sub.R, respectively are constant values defined as ##EQU17## and wherein .theta..sub.R is the moment of inertia of the wheel (1), G.sub.F the weight of the vehicle or a portion to the specific wheel and r.sub.R the mean radius of the wheel.