Master cylinder for hydraulic brake system of motor vehicle

摘要

The invention concerns a main brake cylinder (10) for a hydraulic vehicle-brake system, the cylinder having a wall (12) enclosing a bore (14) extending along the longitudinal axis (A) of the cylinder. One end of the bore is closed off by an end wall forming part of the wall (12) of the cylinder (10) while the other end is closed off by a closure element (16) which forms a seal with the cylinder. Mounted in the bore (14) next to the closure element (16) so that it seals off the bore and can move axially is a piston (18) actuated by a rod which passes through the closure element. The piston has a centrally located valve (20) which allows fluid to flow between a reservoir and a pressure chamber (28) located inside the bore (14) and delimited by the end wall of the bore and the piston (18). When the piston (18) is not being actuated, the valve (20) is held in the open position by a component (transverse pin 34) holding up the closure element (16). In order to ensure a defined opening point in relation to the piston (18), even when the valve (20) is being opened against an overpressure, the closure element (16) consists of an annular elastomeric part (42) on the side facing the pressure chamber (28) and, detachably connected to the elastomeric part, immediately behind it along the longitudinal axis of the cylinder, another annular part (44) made of rigid material. The part (44) made of rigid material has an integral circular ridge (46) running round it, forming an essentially rigid stop, the cross-sectional diameter of the ridge being, at the most, approximately half the cross-sectional diameter of the elastomeric part (42) and the ridge penetrating completely or almost completely through the elastomeric part (42) in the axial direction.