The invention concerns a pneumatic servo brake booster comprising a mobile piston (22) stressing an actuator rod (34) of a master cylinder (28) in response to the actuation of a plunger (56) whereof one front end, passing through the piston (22) and forming a first probe (62) is capable, in the extreme actuating position of the plunger (56), of penetrating into a reaction disc (44) interposed between the piston (22) and the actuating rod (34) to transmit to the plunger (56) the reaction force of the master cylinder (28). The invention is characterised in that it comprises a second probe (68), which is capable, when the control rod (46) is actuated at a speed higher than a predetermined speed, of being locked by a one-way clutch device (70), then of being driven by the piston to cause the second probe (68) to penetrate into the reaction disc (44) to enable the first probe (52) to apply a braking force more rapidly.
展开▼
