Patent ID: 7121186

Claim:
A pneumatic servomotor for assisted braking, comprising a casing ( 2 ) having a longitudinal axis (X) and in which a low- pressure chamber ( 10 ) and a variable-pressure chamber ( 8 ) are defined, in an airtight manner, by a moving partition wall ( 12 ) bearing a pneumatic piston ( 18 ) in its middle part, a three-way valve ( 20 ), arranged at the rear part of the pneumatic piston ( 18 ) and controlled by an actuating rod ( 27 ), the three-way valve comprising a first valve ( 22 ) for a re-equalization between the low-pressure chamber ( 10 ) and the variable-pressure chamber ( 8 ), and a second valve ( 24 ) for the high-pressure supply of the variable-pressure chamber ( 8 ), said second valve ( 24 ) comprising a valve seat, borne by a first longitudinal end of a distributor plunger ( 28 ) and receiving a longitudinal end of the actuating rod ( 27 ), said distributor plunger ( 28 ) having, at a second longitudinal end in the opposite direction relative to the first longitudinal end, a finger ( 30 ), which is perpendicular to the longitudinal axis (X) and which comes into contact with a face of a reaction disk ( 32 ) on a braking operation, said reaction disk ( 32 ) being accommodated in a housing ( 34 ) integral with a push rod ( 36 ) for providing an output force to actuate a master cylinder corresponding to an input force applied to said actuating rod ( 27 ), said housing ( 34 ) comprising a pneumatic braking-assistance device (D) fitted with a cage ( 38 ), a first closed longitudinal end of which is integral with the push rod ( 36 ) while a second open longitudinal end is closable by an annular ring ( 44 ) integral with the cage ( 38 ) and by a reaction piston ( 42 ) fitted for a sliding travel inside the ring ( 44 ) along the longitudinal axis (X), said reaction piston ( 42 ) being reactionnally kept against the ring ( 44 ) by a resilient means ( 40 ) having a prestress (ch) and bearing by a rear end on the closed first end of the cage ( 38 ), and wherein an area consisting of the rear faces ( 50 , 52 ) of the annular ring ( 44 ) and of the reaction piston ( 42 ), respectively, constitutes the front longitudinal end of the housing ( 34 ) of the reaction disk, characterized in that said device comprises plastically-deformable means ( 68 , 74 ) for the adjustment of a ratio of the input force to the output force to facilitate a quick stop for a vehicle.