Patent ID: 6843163

Claim:
A pneumatic brake booster comprising a rigid casing ( 10 ) locally shaped into a hollow shaft ( 3 ) pierced with an opening ( 30 ), a moving partition ( 4 ), a hub ( 5 ) secured to the moving partition ( 4 ), an annular seal ( 6 ) and position-setting means ( 71 , 72 ), the moving partition ( 4 ) sealingly delimiting front and rear chambers ( 11 , 12 ) of variable and complementing volumes inside the rigid casing ( 10 ), the hub ( 5 ) being cylindrical and slideably mounted in the opening ( 30 ) of the hollow shaft ( 3 ) between a rest position and at least one active position, the seal ( 6 ) being arranged between the hub ( 5 ) and the hollow shaft ( 3 ), and the position-setting means ( 71 , 72 ) fixing the rest position of the hub ( 5 ) with respect to the casing ( 10 ), characterized in that the seal ( 6 ) comprises an elastomeric material ( 61 ) shaped into an annulus and an annular metal insert ( 62 ), in that, in a region (Zr) of radial narrowing of the insert, the elastomeric material ( 61 ) is in sealed contact with the hollow shaft ( 3 ) in a space radially external to the insert ( 62 ), and in sealed contact with the hub ( 5 ) in a space radially internal to the insert ( 62 ), in that, in a region (Ze) of radial widening of the insert, the insert ( 62 ) is housed in the hollow shaft ( 3 ) such that it can slide axially without radial clearance, and in that the position-setting means ( 71 , 72 ) comprise a first pair ( 71 ) of restraining surfaces ( 711 , 712 ), one ( 711 ) of which consists of a first end ( 621 ) of the insert ( 62 ) and the other ( 712 ) of which is formed on the hollow shaft ( 3 ), and a second pair ( 72 ) of restraining surfaces ( 721 , 722 ) one ( 721 ) of which consists of a second end ( 622 ) of the insert ( 62 ) and the other ( 722 ) of which is formed on the hub ( 5 ).