Patent ID: 6978614
Filing Date: 2005-12-27
Classification: B60T

Abstract:
1. A hydraulic master cylinder ( 10 ) for a motor vehicle having a substantially axial body ( 12 ) with a bore ( 14 ) for retaining a primary piston ( 16 ) and a secondary piston ( 18 ) that are slidingly fitted in the back-to front direction respectively, and are actuated by the driver of the vehicle between a rest rear position and a forward position to develop a braking force and wherein each piston ( 16 , 18 ) is resiliently returned to the rest rear position defined by a first rear stop; at least one sealing means ( 48 , 50 ) being disposed between each piston ( 16 , 18 ) and the bore ( 14 ) to define a rear hydraulic-fluid supply chamber ( 56 , 60 ) and a front pressure chamber ( 58 , 62 ); each piston ( 16 , 18 ) having a bore ( 78 , 80 ) that is open in the forward direction and communicating with the front pressure chamber ( 58 , 62 ); each piston ( 16 , 18 ) having at least one substantially radial valve ( 82 , 84 ) that is opened into its periphery and into said bore ( 78 , 80 ), that moves between a let-through position that corresponds to the rest rear position of the piston ( 16 , 18 ) and wherein said valve ( 82 , 84 ) is situated rearwards of the sealing means ( 48 , 50 ) and connects the rear supply chamber ( 56 , 60 ) with the front pressure chamber ( 58 , 62 ), and said valve ( 82 , 84 ) having an isolating position that corresponds to the forward application position of the piston ( 16 , 18 ) in which the valve ( 82 , 84 ) is situated forwards of the sealing means ( 48 , 50 ) to separate the rear supply chamber ( 56 , 60 ) from the front pressure chamber ( 58 , 62 ) so as to produce a hydraulic braking pressure inside the front pressure chamber ( 58 , 62 ); and wherein the pressure chamber ( 62 ), associated with at least one piston ( 18 ), comprises at least one tubular cylindrical element ( 90 ) located outside the piston and retained axially in the body ( 12 ) of the master cylinder; and said tubular cylindrical element ( 90 ) extending axially rearwards of the sealing means ( 50 ) and when the piston ( 18 ) travels forwards obturating the radial valve ( 84 ) so as to obtain a closing travel (C m2 ) of the valve which is smaller than the distance between the valve ( 84 ) and the sealing means ( 50 ); characterised in that a substantially annular space ( 51 ) for the resupply of the front pressure chamber ( 58 , 62 ) is provided between the body of the master cylinder and the tubular cylindrical element ( 90 ), said space connecting the front pressure chamber ( 58 , 62 ) to the rear supply chamber ( 56 , 60 ), said sealing means ( 50 ) consists of a lip seal, accommodated in a groove ( 54 ) made in the bore ( 14 ) of the waster cylinder ( 10 ); and said piston ( 18 ) is made in a single piece; and said radial valve ( 84 ) has at least one through-hole ( 88 ) opening into the periphery and into the bore ( 80 ) of the piston ( 18 ); and said cylindrical element ( 90 ) includes an annular ring having an inner diameter equal to that of the piston ( 18 ) and is located adjacent to a back face of the lip seal ( 50 ) and is accommodated inside a complementary groove ( 120 ) provided in the master cylinder ( 10 ), said ring of said tubular cylindrical element ( 90 ) having a slit to facilitate insertion into said groove ( 120 ) from the rear part of the master cylinder ( 10 ); and said seal ( 50 ) includes a further lip ( 124 ) that bears on a front transverse face ( 126 ) of said tubular cylindrical element ( 90 ).