Patent ID: 7194946

Claim:
A pneumatic servomotor ( 12 ) for power-assisted braking for a motor vehicle, having a substantially cylindrical rigid casing ( 16 ) inside which a moving transverse partition ( 18 ) is movably mounted that is coupled to an actuating rod ( 22 ) for actuating an associated master cylinder ( 14 ), and that defines in leaktight manner and inside the casing ( 16 ) two pressure chamberS ( 24 , 26 ) in order to actuate the actuating rod ( 22 ), for actuating the associated master cylinder in which the moving transverse partition ( 18 ) has a central piston ( 20 ) that is secured to a peripheral skirt ( 28 ) which is made of sheet metal and which is covered, at least in the vicinity of its periphery ( 40 ), with a sealing diaphragm ( 30 ) made of an elastomer material and whose periphery ( 32 ) is fixed to the casing ( 16 ) in leaktight manner, said servomotor being characterized in that, in the vicinity of the periphery ( 40 ) of the skirt ( 28 ), said skirt is provided with a stamped annular recess ( 42 ) defining an internal groove ( 44 ) which serves to receive snugly a peripheral bead ( 46 ) which projects from the surface of the diaphragm ( 30 ) in order to fix said diaphragm ( 30 ) to the skirt ( 28 ) in leaktight manner, said recess ( 42 ) has outer edges ( 50 ) which serve to be flattened towards each other to close the internal groove ( 44 ) locally onto a neck ( 52 ) of the bead ( 46 ) to hold the diaphragm ( 30 ) stationary axially relative to the skirt ( 28 ), said bead ( 46 ) has a rounded end ( 58 ) arranged on the side of the neck ( 52 ) remote from the surface of the diaphragm, and that is complementary to the rounded end-wall ( 56 ) of the recess ( 42 ) inside the groove ( 44 ), said diaphragm ( 30 ) being fixed to the skirt ( 28 ) of the servomotor by an assembly device ( 60 ) comprising: a first disk ( 62 ) which presses against the side of the diaphragm ( 30 ) which is opposite from the bead ( 46 ) and from the recess ( 42 ) to urge the diaphragm ( 30 ) axially into contact with the skirt ( 28 ) so as to hold the bead ( 46 ) in the groove ( 44 ) inside the recess ( 42 ); and a second disk ( 64 ), arranged facing the first disk ( 62 ), which second disk is provided, facing the recess ( 42 ), with at least one peripheral crimping tool ( 66 ) which serves to crimp the two opposite outer edges ( 50 ) of the recess ( 42 ) towards each other locally at the neck ( 52 ) of the bead so that the corresponding edges ( 53 ) of the internal groove ( 44 ) fit snugly onto the neck ( 52 ) and hold the bead ( 46 ) stationary in the groove ( 44 ).