Patent ID: 8210091

Claim:
Brake booster comprising: a casing ( 2 ) of longitudinal axis (X); an assembly comprising a skirt ( 6 ) and a pneumatic piston ( 12 ) which is mounted to slide in a leaktight manner in the casing ( 2 ) along the longitudinal axis (X), said skirt-and-piston assembly ( 6 , 12 ) dividing the interior space ( 4 ) of the casing ( 2 ) into a low-pressure front chamber ( 8 ) and a variable-pressure rear chamber ( 10 ); a three-way valve ( 26 ) actuated by a control rod ( 28 ) mounted in a longitudinal passage ( 34 ) pierced in the pneumatic piston ( 12 ), the said control rod ( 28 ) being connected via a first longitudinal end to a brake pedal; a distributor-plunger ( 32 ) that can move, in the said piston, along the said longitudinal axis (X) under the control of a second end of the said control rod ( 28 ), the said distributor-plunger ( 32 ) comprising a sensor for applying the force of the control rod ( 28 ) to a hydraulic piston ( 122 ) of a master cylinder via a reaction device, the said skirt-and-piston assembly ( 6 , 12 ) transmitting a pneumatic boost force to the hydraulic piston ( 122 ) of the master cylinder; a sleeve ( 54 ) mounted to slide in a leaktight manner in the pneumatic piston ( 12 ) along the said longitudinal axis (X) over a set first travel (C); a securing means capable axially of connecting the said sleeve ( 54 ) to the pneumatic piston ( 12 ) when the said pneumatic piston has covered the set travel (C); and the said three-way valve ( 26 ) comprising a first valve seat ( 48 ) and a second valve seat ( 50 ) and a valve shutter ( 46 ) intended to be pressed against the first and/or second valve seat ( 48 , 50 ), the said second valve seat ( 50 ) being borne by a first longitudinal end of the distributor-plunger ( 32 ), the first valve seat being borne by a first longitudinal end of the said sleeve ( 54 ), characterized in that the securing means comprises a device for gradually moving the sleeve according to the movement of the piston.