Patent ID: 6955047
Filing Date: 2005-10-18
Classification: B60T

Abstract:
1. A master cylinder comprising a cylinder body formed with a cylinder opening to a booster mounting surface of said cylinder body, said booster mounting surface being formed for mounting a booster thereon; a piston entering a constant-pressure chamber of said booster at the rear end portion thereof and operable by an output shaft of said booster; a piston guide provided at the rear end portion of said cylinder for slidably guiding said piston inserted thereinto; a fluid-tight seal member provided between said cylinder and said piston for fluid-tightly partitioning the front portion of said cylinder as a fluid pressure chamber; a drain port opening at a drain portion which said fluid-tight seal member defines at the rear portion of said cylinder for communicating with a reservoir; an internal seal stepped portion formed by radially outwardly expanding an opening portion of said cylinder which opens to said booster mounting surface; an annular spacing formed by partitioning said internal seal stepped portion with the front end surface of said booster secured to said booster mounting surface and with the external surface of said piston; and an annular complex elastomeric seal member fit in said annular spacing, wherein a first surface of said elastomeric seal member forms a slide seal portion formed at the internal surface of said complex seal member for fluid-tightly partitioning said drain portion and said constant-pressure chamber from each other in sliding contact with the external surface of said piston; a second surface of said elastomeric seal member forms an air-tight seal portion formed at the rear end surface of said complex seal member for air-tightly partitioning said constant-pressure chamber from the atmosphere in contact with the front end surface of said booster and a third surface of said elastomeric seal member forms a fixed seal portion formed at the external surface of said complex seal member for fluid-tightly partitioning said drain portion from the atmosphere in contact with the internal surface of the internal seal stepped portion, said slide seal portion, said air-tight seal portion and said fixed seal portion being formed as parts of a single seal.