Patent ID: 7344203

Claim:
A master cylinder comprising a cylinder body, a primary cup supported on an inner periphery of said cylinder body, and a piston inserted in said cylinder body so as to be in sliding contact with an inner periphery of said primary cup, said piston defining a pressure chamber in said cylinder body, said cylinder body being integrally formed with an annular wall behind said primary cup, said annular wall having a greater inner diameter than the inner diameter of said cylinder body to define an annular passage between said annular wall and said piston, said annular wall having a front end face that faces the primary cup and supports the primary cup, said annular wall having a rear end face, the inner diameter of the annular wall which is greater than the inner diameter of the cylinder body extending from the front end face of the annular wall to the rear end face of the annular wall so that said annular passage extends rearward from the front end face of the annular wall to the rear end face of said annular wall, wherein a connecting passage of annular configuration having a greater radial dimension than said annular passage is defined between the inner periphery of said cylinder body and said piston behind said annular wall so as to communicate with said annular passage, said connecting passage being adapted to communicate with a reservoir, the rear end face of said annular wall facing the connecting passage, wherein said piston is formed with circumferentially spaced piston ports arranged to be in direct radial communication with said annular passage when the master cylinder is not actuated, and the annular passage being dimensioned to permit brake fluid flow through the annular passage when the master cylinder is not actuated so that when the master cylinder is not actuated the brake fluid is able to flow from said connecting passage to said pressure chamber through said annular passage and said piston ports.