Hydraulic pressure control system for split brake system

Claim 1

A hydraulic pressure control system for a split brake system which comprises: a tandem master cylinder having first and second hydraulic pressure sources; at least first and second rear wheel cylinders; a first brake pressure supply line communicating said first source with said first rear wheel cylinder; a second brake pressure supply line communicating said second source with said second rear wheel cylinder; a first hydraulic pressure control device positioned within said first supply line for controlling output hydraulic pressure transmitted therefrom with respect to hydraulic pressure transmitted from said first source; and a second hydraulic pressure control device including a housing positioned within said second supply line and including a balance piston mounted in said housing and a first passage formed in said housing for controlling output hydraulic pressure transmitted therefrom with respect to input hydraulic pressure transmitted from said second source in response to output hydraulic pressure transmitted from said first control device, said second hydraulic pressure control device further including a by-pass passage formed in said housing, a second piston disposed within said housing, one end thereof receiving hydraulic pressure from said first source and the other end thereof receiving hydraulic pressure transmitted through said valve means which is normally open by said balance piston and second valve means disposed within said first passage such that said first passage is normally open for passing fluid between said valve means and said second supply line such that said second valve means also normally closes said by-pass passage and, upon failure of said supply line, said second valve means opens said by-pass passage and, at the same time, interrupts communication between said first passage and said balance piston.