Anti-skid control system for motor vehicles

Claim 1

An anti-skid control system for a motor vehicle having front righthand, rear lefthand, front lefthand and rear righthand wheels and equipped with an X-type two-channel piping brake apparatus wherein one of the two channels is associated with the front righthand and rear lefthand wheels while the other channel is associated with the front lefthand and rear righthand wheels, means for controlling said two channels independently of each other, said anti-skid control system comprising; first valve means provided in a piping connecting a rear wheel cylinder to a modulator for increasing and reducing brake fluid pressure in a respective one of said two channels, said valve means being arranged to be closed only when the rear wheel tends to be locked earlier than the front wheel; and check valve means provided in parallel with said first valve means, said check valve means being arranged to only permit the brake pressure fluid to flow from said rear wheel cylinder to said modulator, said first valve means comprising a normally open solenoid valve adapted to be opened and closed in response to a signal derived from a control circuit for controlling said modulator, said control circuit including a select-low circuit for selecting the lower one of the front and rear wheel speeds in said respective one of the two channels and being arranged to control said modulator on the basis of the wheel speed selected by said select-low circuit, said control circuit further including a subtracter for subtracting the rear wheel speed from the front wheel speed in said respective one of the two channels so as to provide an output representing the difference between the two wheel speeds; a comparator for comparing the output of said subtracter with an amount corresponding to a predetermined speed difference ΔV and providing an output pulse when the output of said subtracter exceeds said amount corresponding to said predetermined speed difference ΔV; and a flip-flop circuit arranged to be reset by the output pulse of said comparator and reset by a brake fluid pressure reducing signal supplied from said control circuit to said modulator; said first valve means being controlled in opening and closing by the output of said flip-flop circuit.