Master brake cylinder for two-circuit braking systems

Claim 1

In a hydraulic brake booster for a vehicle brake system of the type having primary and secondary sides and actuated by a brake pedal and which includes valve means for controlling both the interconnection of a storage source with a pressure alternation chamber in the booster as well as the interconnection of the pressure alternation chamber with a relief station, the booster being connected with a hydraulic dual circuit main cylinder having a return spring biased double piston for pressurizing the primary and secondary sides of the system and which further includes a locking protection device arranged to cooperate with an electronic switching circuit which controls a valve mechanism for controlling the application of hydraulic fluid in the two brake systems, the improvement comprising: sensing means communicating with said dual circuit main cylinder for indicating an abnormally low braking pressure in one of said braking circuits; and hydraulic means actuated whenever said sensing means detects an abnormally low braking pressure for causing said double piston to execute a series of pumping strokes to raise the pressure to normal in said circuit.