Patent ID: 6848257

Claim:
A brake master cylinder ( 10 ) for a motor vehicle having an axial body ( 12 ) with a bore ( 14 ) therein that slideably receives at least one axial piston ( 16 , 18 ), said piston ( 16 , 18 ) being actuated by a driver of the vehicle between a rear position of rest and a forward position of application to pressurize fluid and create a braking force, said at least one axial piston ( 16 , 18 ) being elastically urged against a stop formed in said body ( 121 to define said rear position of rest, said master cylinder ( 10 ) having a front sealing means ( 26 , 28 ) and a rear sealing means ( 30 , 32 ) that are interposed between said piston ( 16 , 18 ) and said bore ( 14 ), said front sealing means ( 26 , 28 ) delimiting a rear supply chamber ( 34 , 38 ) from a front pressure chamber ( 36 , 40 ) within said bore ( 14 ), said body ( 12 ) having a radial supply duct ( 42 , 48 ) that connects an external reservoir of hydraulic fluid to said rear supply chamber ( 34 , 38 ) and opens between said front sealing means ( 26 , 28 ) and said rear sealing means ( 30 , 32 ), said body ( 12 ) having a drilling ( 50 , 52 ) that opens into said front pressure chamber ( 36 , 40 ) for supplying a braking circuit with pressurized fluid, said master cylinder ( 10 ) having means for placing said front pressure chamber ( 36 , 40 ) in communication with said rear supply chamber ( 34 , 38 ) with said piston ( 16 , 18 ) in said rest position and for inhibited said communication when said piston ( 16 , 18 ) is moved axially forward towards a position of application such that said front pressure chamber ( 36 , 40 ) is isolated from the rear supply chamber ( 34 , 38 ) to pressurized fluid in the front pressure chamber ( 36 , 40 ), characterized in that said front sealing means ( 26 , 28 ) comprises a front seal ( 25 , 28 ) that is mounted in a groove ( 110 , 112 ) of said body ( 12 ) said front seal ( 26 , 28 ) having an interior peripheral lip that contacts said piston ( 16 , 18 ) and lifts off the piston ( 16 , 18 ) when the piston ( 16 , 18 ) returns from a position of application to said position of rest to allow hydraulic fluid to flow between said bore ( 14 ) and a number of helical channels ( 128 ) and resupply said front pressure chamber ( 36 , 40 ) from said reservior by way of said radial supply duct ( 42 , 48 ), said body ( 12 ) having a front pair of annular bearing surfaces ( 120 , 122 , 124 , 126 ) located on each side of the front seal ( 26 , 28 ) to guide said piston ( 16 , 18 ) in the bore ( 14 ), said piston ( 16 , 18 ) having a front tublar portion ( 54 , 56 ) and a rear tublar portion ( 58 , 60 ) having a same outside diameter (D) with a rear bearing surface ( 62 , 64 ) of said front tubular portion ( 54 , 56 ) that slides in a bore ( 66 , 68 ) of said rear portion ( 58 , 60 ), retaining means ( 78 , 80 , 82 , 84 ) and elastic urging means ( 86 , 88 ) that is interposed between a rear face ( 70 , 72 ) of said front portion ( 54 , 56 ) and a closed end ( 74 , 76 ) of the bore ( 66 , 68 ) of the rear portion ( 58 , 60 ).