Hydraulic boosters for vehicle braking systems

Claim 1

An hydraulic booster for a vehicle braking system comprising a housing provided with a bore, an inlet for connection to a fluid pressure source, and an outlet for connection to a reservoir for fluid, a pedal-operated input piston, a boost piston working in said bore, a boost chamber, pressurisation of which operates said boost piston to provide an output force, boost valve means for controlling pressurisation of said boost chamber by controlling communication between said inlet and said boost chamber and between said outlet and said boost chamber, a control chamber, fluid in said control chamber being pressurised in response to operation of said pedal-operated input piston, said boost valve means being operable in response to pressure in said control chamber, and a recuperation valve for controlling communication between said control chamber and said boost chamber, said input piston including a valve-operating means for closing said recuperation valve to cut off communication between said control chamber and said boost chamber on initial movement of said input piston, said input piston also including means for pressurising fluid trapped in said control chamber following further movement of said input piston, said boost valve means being operative, in response to pressure in the control chamber, to pressurise said boost chamber, and said input piston has a pressure-responsive means on which said pressure in said boost chamber acts such that said valve-operating means is operative to close said recuperation valve.