Hydraulic power boosters for vehicle braking systems

Claim 1

An hydraulic booster for a vehicle braking system comprising a housing having a bore, and a boost piston working in said bore to actuate a master cylinder piston, a pedal-operated input piston, and a second piston relative to which said input piston is movable, and said housing is provided with a boost chamber for subjecting said boost piston to hydraulic pressure, and a control chamber is defined between said input piston and said second piston, a boost-pressure control valve being provided for controlling a supply of hydraulic pressure to said boost chamber, said boost-pressure control valve being responsive to pressure in said control chamber, wherein a recuperation valve is located in said control chamber for controlling communication between said control chamber and a reservoir, said recuperation valve closing upon relative movement of said input piston towards said second piston, further movement of said input piston in the same direction causing pressurization of fluid trapped in said control chamber, a reservoir chamber in said housing providing communication between said reservoir and said recuperation valve, first seal means disposed between said boost chamber and said reservoir chamber, second seal means disposed between said control chamber and said reservoir chamber, said seal means being arranged that said control and booster chambers are separated from each other by said reservoir chamber so that upon failure of either of said seal means, fluid from the respective control or boost chamber flows directly into said reservoir chamber and cannot flow from said boost chamber directly into said control chamber or vice versa depending on which of said seal means fails, without first flowing into said reservoir chamber.