Patent ID: 8051657
Filing Date: 2011-11-08
Classification: B60T

Abstract:
1. A plunger-typed master cylinder for brake system of vehicle, comprising: a cylinder body that has hydraulic pressure chambers where brake oil is supplied from an oil reservoir; a piston assembly comprising a pair of a primary piston and a floating piston that is each elastically supported by a spring in the hydraulic chambers and supplies hydraulic pressure to a brake when a booster is in operation; and seal cups comprising a pair of a floating cup and a primary cup that are spaced apart from each other on the primary piston and the floating piston, the outer circumferences of the seal cups are in contact with the insides of the hydraulic pressure chambers and the inner circumferences of the seal cups are in contact with the primary piston and the floating piston, respectively, and each seal cup has a deformation reference portion comprising a recess on a side of a body having outer and inner circumferences, closer to the outer circumference than to the inner circumference, to prevent deformation of the inner circumference from being transmitted to the outer circumference, wherein the primary cup has a ring-shaped body, an outer flange extends and inclines upward from a side of the body, an inner flange extends and declines from the side of the body at a predetermined distance from the outer flange, and the deformation reference portion is provided on a deformation reference line corresponding to the thickness of the outer flange, on the opposite side of the body to the side from which the outer flange and the inner flange extend.