Method for determining slip threshold value for propulsion slip adjustment of motor vehicle

PURPOSE: To prevent idle running of a driving wheel quickly by expanding a predetermined acceleration curve into a performance graph of friction coefficient and then associating a slip threshold value with the friction coefficients determined from the performance graph. CONSTITUTION: Vehicle speed, vehicle acceleration, wheel and driving wheel slips are determined by a means 14 in accordance with the peripheral speed of the wheel detected by a means 13, and after comparing the slip of each wheel with a slip threshold value by a means 16, a driving means 17 and a braking means 18 are controlled in accordance with the result of the comparison to adjust a driving slip. In this case, a curve of the acceleration reachable from the stop of the vehicle is determined as functions of friction coefficient for various vehicle forms. Then taking the running resistance relating to vehicle speed into consideration, the curve is expanded into a performance graph of friction coefficient relating to vehicle speed and vehicle acceleration. Then a slip threshold value is associated with each of the friction coefficients determined from the performance graph. Thus it is possible to prevent idle running of the driving wheel quickly.