Anti-lock braking system

Claim 1

An anti-lock braking system for a motor vehicle that has four road wheels, means for braking each wheel, means for driving each wheel, and means for shifting between two-wheel and four-wheel drive, said shifting means incorporating a longitudinal differential between the front wheel drive shaft and the rear wheel drive shaft and a central lock for locking said longitudinal differential so as to drive said front and rear drive shafts at the same speed, said anti-lock braking system comprising: (a) at least one wheel speed sensor associated with one or more wheels for producing a signal representative of the respective wheel speed of said one or more wheel; (b) an evaluation circuit, responsive to the wheel speed signal of each wheel speed sensor, for producing a brake control signal for at least one wheel, said evaluation circuit including: (1) means, responsive to said shifting means, for producing a speed reference value which depends upon whether the central lock is engaged or disengaged, said reference value being reduced when the central lock is engaged; and (2) means, responsive to a wheel speed signal and to said reference value, for producing said brake control signal for at least one wheel in dependence upon the relative magnitudes of the represented wheel speed and said reference value; and (c) at least one brake pressure control unit, responsive to said brake control signal, for regulating the brake pressure applied to said at least one wheel.