Patent ID: 7040093

Claim:
Penetration master cylinder, comprising at least a body ( 1 ) in which a cylindrical bore ( 10 ) is provided along an axis of symmetry (X), a piston ( 2 ) fitted for a sliding axial travel inside the bore ( 10 ), at least between a rest position and a pressure-rise position, and a sealing cup ( 3 ) having a long bent portion ( 31 ), stationarily housed inside a groove ( 11 ) provided in the bore ( 10 ), a lip ( 32 ) applied against a cylindrical wall ( 20 ) of the piston ( 2 ), in a sealing manner, so as to define a pressure chamber ( 4 ) inside the bore ( 10 ), and a bottom portion ( 33 ) joining the long bent portion ( 31 ) to the lip ( 32 ), wherein the cylindrical wall ( 20 ) of the piston provides a cavity ( 40 ), intended for the pressure chamber ( 4 ), and exhibits at least a first resupply port ( 51 ) having a determined first cross-sectional area and disposed adjacent to the bottom portion ( 33 ) of the cup ( 3 ) in the rest position of the piston ( 2 ), a position in which said first port ( 51 ) causes the pressure chamber ( 4 ) to communicate with a resupply passage ( 6 ), which is located inside the body ( 1 ) and outside the chamber ( 4 ), characterised in that it comprises at least a second port ( 52 ) having a smaller cross-sectional area than that of the first port, and in that the first and second ports ( 51 , 52 ) are comparatively nearer and farther from the lip ( 32 ) of the cup ( 3 ), respectively, in the rest position of the piston ( 2 ), in which the second port ( 52 ) causes the pressure chamber ( 4 ) to communicate with the resupply passage ( 6 ).