Patent ID: 7934378
Filing Date: 2011-05-03
Classification: B60T,F16J

Abstract:
1. Brake master cylinder ( 10 ) for a motor vehicle, of the type which comprises a substantially axial body ( 12 ) inside a bore ( 14 ) of which is slideably mounted at least one axial piston ( 16 , 18 ) which is capable of being actuated by a driver of the vehicle between a rear rest position and a forward braking force application position, and which is returned elastically toward its rear rest position, of the type in which the bore ( 14 ) comprises two seals, front ( 30 , 34 ) and rear ( 32 , 36 ), which are interposed between the piston ( 16 , 18 ) and the bore ( 14 ), the front seal ( 30 , 34 ) delimiting, in the bore ( 14 ), a rear supply chamber ( 38 , 42 ) and a front pressure chamber ( 40 , 44 ), of the type in which the body ( 12 ) comprises a radial supply duct ( 46 , 52 ) which connects an external hydraulic fluid reservoir to the rear supply chamber ( 38 , 42 ) and which opens out between the two seals ( 30 , 32 , 34 , 36 ), of the type in which the body ( 12 ) comprises a braking circuit supply hole ( 54 , 56 ) which opens into the front pressure chamber ( 40 , 44 ), of the type in which the piston comprises a bore ( 58 , 60 ), open to the front, communicating on the one hand with the front pressure chamber ( 40 , 44 ) and on the other hand with the periphery of said piston ( 16 , 18 ) by way of at least one hole ( 62 , 64 ) which, when the piston ( 16 , 18 ) occupies its rear rest position, is arranged between the two seals ( 30 , 32 , 34 , 36 ) so as to open communication between the front pressure chamber ( 40 , 44 ) and the rear supply chamber ( 38 , 42 ) and which, when the piston ( 16 , 18 ) is moved axially forward toward its application position, is capable of passing beyond the front seal ( 30 , 34 ) in order to isolate the front pressure chamber ( 40 , 44 ) from the rear supply chamber ( 38 , 42 ) and thus allow a braking pressure to be established in the front pressure chamber ( 40 , 44 ), of the type in which at least each front seal ( 30 , 34 ) is accommodated in a groove in the body of the master cylinder and comprises three concentric lips with an axial orientation, in particular, a first inner lip ( 80 ) of which a free end ( 82 ) is arranged in contact with the periphery of the piston ( 16 , 18 ), a second central lip ( 84 ) of which the free end ( 86 ) is arranged, in a rest position, in contact with a front face ( 88 ) of the groove ( 70 , 72 ), and a third outer lip ( 90 ) of which a free end ( 92 ) is arranged, in a rest position, in contact with a peripheral bottom face ( 94 ) of the groove ( 70 , 72 ), the second central lip ( 84 ) and the third outer lip ( 90 ) being capable, when the front pressure chamber ( 40 , 44 ) is exposed to a partial vacuum caused by the return of the piston ( 16 , 18 ) from its forward application position to its rest position or else by the activation of a trajectory control device forming part of the braking circuit, of separating from the front face ( 88 ) and from the bottom peripheral face ( 94 ) of the groove ( 70 , 72 ) so as to allow the front pressure chamber ( 40 , 44 ) to be resupplied by the reservoir, characterized in that the groove ( 70 , 72 ) comprises a chamfer ( 93 ) which extends from the bore to at least one intermediate portion ( 96 ) of the front face ( 88 ) of the groove ( 70 , 72 ) with which the end ( 86 ) of the second central lip ( 84 ) is in contact in its rest position, and in that said end ( 86 ) of the second central lip ( 84 ) has a reduced cross section to facilitate the separation by tilting of the second central lip ( 84 ) in order to cause the separation by tilting of the third outer lip ( 90 ), with the aim of facilitating the resupply of the reservoir by means of the front pressure chamber ( 40 , 44 ) or else the resupply of the front pressure chamber ( 40 , 44 ) by the reservoir.