GENERATORE DI PRESSIONE DI FRENATURA PER UN IMPIANTO FRENANTE IDRAULICO DI AUTOVEICOLI

A brake pressure generator for an automotive hydraulic brake system, wherein a booster piston (13) which is displaceable by an auxiliary hydraulic pressure in the direction of actuation is adapted to mechanically strike an annular piston (18) and is displaceable in the actuating direction. Sealingly guided within the annular piston (18) is a master cylinder piston (25) confining at least one working chamber (23) separable from an unpressurized supply reservoir (32), by a valve (31) controllable in way-responsive manner. Annular piston (18) is of a stepped-piston configuration and is provided with a section (19) facing pedal actuation (6) and being of a smaller diameter. According to the invention it is suggested that the pedal-sided section (19) of annular piston (18) is of a smaller diameter than that of the booster piston (13) to confine an annular chamber (22) which via a check valve (33) adapted to be switched open toward working chamber (23), is in communication with working chamber (23). A normally open two position-two way valve (42) is connected to annular chamber (22) and is adapted to be switched in response to the pressure in the booster chamber (5) into a locking position, which valve (42), in turn, is in communication with an unpressurized supply reservoir (32). Such a configuration will involve the advantage that a master cylinder piston (25) of a relatively small diameter mas be used. The ability for the booster piston (13) to be mechanically actuated by the brake pedal (6) through push rod (10) provides a safeguard in the event of a failure of the auxiliary pressure source and insures a minimum deceleration of the motor vehicle.