Patent ID: 7234384

Claim:
A pneumatic brake booster ( 10 ) for a motor vehicle, having a rigid casing ( 12 ) inside which there can move a transverse partition ( 14 ) delimiting in a sealed manner a front chamber ( 16 ), subjected to a first pressure (P 1 ), and a rear chamber ( 18 ), subjected to a second pressure (P 2 ) that varies between the first pressure (P 1 ) and a pressure (P a ) higher than the first pressure (P 1 ), acting on an actuating rod ( 28 ) of a master cylinder associated with the booster ( 10 ) via a reaction disk ( 32 ), a tubular moving piston ( 22 ) which is slideably mounted in the casing ( 12 ) and is secured to the moving partition ( 14 ), a control rod ( 38 ) moving in the piston ( 22 ) selectively as a function of an axial input force directed forward against the action of a return force exerted on the rod ( 38 ) by a return spring ( 138 ), movements of the control rod ( 38 ) determining the openings and closings of at least one axial inlet valve ( 52 ) which is interposed between a pressure source subjected to the pressure (P a ) higher than the first pressure (P 1 ) and the rear chamber ( 18 ) and of at least one axial re-equalizing valve ( 50 ) that is axially offset with respect to the inlet valve ( 52 ), which is interposed between the front chamber ( 16 ) and the rear chamber ( 18 ), to actuate the moving partition ( 14 ), and a plunger ( 46 ), slideably mounted in the piston ( 22 ), passing through the moving partition ( 14 ) and secured to the end of the control rod ( 38 ), to act directly upon the actuating rod ( 28 ) of the master cylinder via the reaction disk ( 32 ), a first transverse sealing element ( 132 ) for the axial inlet valve ( 52 ), secured to the rear end ( 48 ) of the plunger ( 46 ); and a first complementary transverse sealing element ( 134 ) for the axial re-equalizing valve ( 50 ), comprising at least one portion of the rear face ( 90 ) of the moving partition ( 14 ), the improvement comprising: a first tubular sleeve ( 136 ), fixed around the plunger ( 46 ) in the moving piston ( 22 ), which is returned elastically away from the moving partition ( 14 ), a transverse face ( 140 ) of which comprises the first transverse sealing element ( 132 ) for the axial inlet valve ( 52 ), a floating second tubular sleeve ( 142 ), surrounding the first sleeve ( 136 ), which is axially mobile with respect to the moving piston, which is returned elastically towards the moving partition ( 14 ), a rear internal transverse face ( 144 ) of which comprises a complementary second sealing element ( 146 ) for the axial inlet valve ( 52 ), and a front external transverse face ( 148 ) of which comprises a complementary external second sealing element ( 150 ) for the re-equalizing valve ( 50 ), the first sleeve ( 136 ) being slideably mounted in the moving piston ( 22 ) with a travel (d) which is determined by first bayonet-fitting means ( 154 ) interposed between said first sleeve ( 136 ) and the moving piston ( 22 ) and which are locked against rotation by the second sleeve ( 142 ).