Hydraulic vehicle servo brake

Claim 1

A hydraulic vehicle servo brake with a master cylinder comprising at least one stepped main-piston assembly, having an annular step connecting an enlarged main piston part to a tapered main piston part with an annular chamber provided at the annular step of the main piston, with a booster piston positively engaged with the main piston and being adapted to be acted upon by a brake pedal and by controlled auxiliary pressure in a control pressure chamber that is supplied by a brake valve governed by the brake pedal, with a first annular seal sealing the booster piston in relation to the control pressure chamber, with a second annular seal sealing the main piston in relation to the annular chamber, as well as with a valve disposed in the annular chamber which, when the brake pedal is not depressed, is opened due to the main piston being in an inactive position and connects the annular chamber with a supply reservoir and which will close upon depression of the brake pedal causing a slight advance movement of the main piston into an active position, wherein after closing of said valve, said annular chamber will be connected to a pressure chamber defined by of the main piston and a wheel-slip detecting brake control unit will shut off the connection to the annular chamber by way of valve means upon wheel slip detection and wherein an annular gap closed by two annular seals and connected to the supply reservoir by way of a port is arranged on the enlarged main piston part so that the annular chamber will be connected to the supply-reservoir port in the presence of a brake pedal travel in its active position which is sufficient for performing a panic stop that is not boosted by the controlled auxiliary pressure wherein the booster piston (12') and the tapered main piston part (12") are united to form an integral piston (26) of constant diameter, on the integral piston the first and the second annular seals (15, 16) are provided at a close axial distance from one another, the supply reservoir being connected by a bore (17) and said port to said annular gap located between said two annular seals.