Patent ID: 6775978
Filing Date: 2004-08-17
Classification: B60T

Abstract:
A master cylinder (12) for use in a brake system having a housing (22) with a bore (20) therein, first (42) and second (44) pistons located in said bore (20) to define a first chamber (50) and a second chamber (52), said first chamber (50) being connected to a reservoir (32) by way of a passage (76) in said second piston (44) and a first port (28) in said housing (22) with said second chamber (52) being connected to said reservoir (32) by a second port (38) in said housing (22) to receive fluid and maintain a fluid level in said brake system at a desired level, first chamber (50) being connected to front wheel brakes (24) and said second chamber (52) being connected to rear (26) wheel brakes to effect a brake application in response to an input force being applied to said first (42) and second (44) pistons, said fluid communication between said first chamber (50) and said reservoir (32) being controlled by a first center port compensation valve (48â€²) that is characterized by a cylindrical member (126) with an axial bore (128) that extends from a first end (130) to a second end (132), said axial bore (128) having an annular shoulder (134) adjacent a groove (136) that retains a lip seal (125) near said second end (132), said cylindrical body (126) having an annular axial projection (127) that extends from said first end (130) for retaining a resilient ring (120) and an radial projection (138) that extends from said first end (130); a retainer (94) having a tubular body (96) with an external lip (98) on a first end and an internal lip (100) on a second end, said tubular body (96) concentrically receiving said cylindrical member (126); a return spring (90) located between said external lip (98) on said retainer (94) and said first piston (42) and a poppet spring (92) located between said radial projection (138) on said cylindrical member (126) and said internal lip (100) on said retainer (94); and a shaft (101) with a head (97) on a first end and threads (103) on a second end, said shaft (101) extending through said axial bore (128) of said cylindrical member (126) with said lip seal (125) engaging said shaft (101) and said threads (103) mating with corresponding threads (64) in said first piston (42) such that said head (97) is urged toward said annular shoulder (134) of said cylindrical body (126) and said return spring (90) is caged between said retainer (94) and first piston (42) to define limits for said first chamber (50) while said poppet spring (92) is caged between said radial projection (138) and said internal lip (100), said first piston (42) receiving an input force that moves said first piston (42) and compresses said return spring (90) such that said first piston (42) and said shaft (101) to move with respect to said retainer (94) to permit said poppet spring (92) to move said cylindrical body (126) and bring said resilient ring (120) into contact with a seat (40) that surrounds said passage (76) in said second piston (44) to interrupt fluid communication from said reservoir (32) through said passage (76) such that with subsequently movement said piston (42) pressurized fluid in chamber (50) that is communicated to said rear wheel brakes (36) to effect a brake application while said head (97) of said shaft (101) moves within the axial bore (128) of said first cylindrical member (126).