Patent ID: 6651429
Filing Date: 2003-11-25
Classification: B60T

Abstract:
In a master cylinder including:(a) a cylinder body having a cylindrical bore and an opening provided through a circumferential wall of the cylinder body for a relief port in the bore communicating with the interior of a hydraulic reservoir: (b) a piston slidably inserted into said cylindrical bore to thereby form a hydraulic pressure generating chamber in said cylindrical bore; (c) an annular cup seal having an inner circumferential lip portion contacting with said piston, an outer circumferential lip portion slidably contacting with an inner circumferential wail of said cylindrical bore, and a base portion connecting said lip portions, said lip portions so arranged as to face to said hydraulic pressure generating chamber and said opening, whereby said cup seal is positioned to cut communication between said hydraulic pressure generating chamber and said hydraulic reservoir through said relief port when portions of said outer circumferential lip pass by said opening; and (d) the improvement comprising two coil springs in tandem urging said piston into its inoperative position, with the winding directions being equal to each other; and an engaging member having a spring receiving portion engaged with either of said coil springs and an inner surface contacting with a top end of said inner circumferential lip portion of said cup seal and having a circumferential portion protruding into a space formed by said inner circumferential lip portion, said outer circumferential lip portion and said base portion without contact with said inner circumferential lip; said outer circumferential lip and said base portions, and said cup seal sliding in said cylindrical bore without rotation, whereby the contact pressure between said outer circumferential lip portion and said inner circumferential wall of said cylindrical bore is larger than the contact pressure between said inner circumferential lip portion and said piston, when said piston moves in its operative direction to seal said opening; and said cup seal sliding in said cylindrical bore with rotation together with said piston, whereby the contact pressure between said inner circumferential lip portion and said piston is larger than the contact pressure between said outer circumferential lip portion and said inner wall of said cylindrical bore, when said piston moves in said inoperative direction to unseal said opening.