Patent ID: 6467268
Filing Date: 2002-10-22
Classification: B60T

Abstract:
A brake master cylinder comprising:a cylinder housing formed by a body having an internal bore open at one end; a cylinder cap assembled to the internal bore at the open end of the body; a first piston positioned in the cylinder housing and slidably movable in an axial direction; a second piston positioned in the cylinder housing forwardly of the first piston and slidably movable in the axial direction; and a sleeve positioned in the cylinder housing and slidably supporting the first piston and the second piston, the second piston being retractable by a predetermined distance from a non-braking operation position of the second piston a pressure chamber formed between the second piston and the cylinder housing; a reservoir connecting port formed on the body and adapted to communicate with a reservoir; a reservoir communication conduit formed on the sleeve and extending at least partially in a radial direction, the reservoir communication conduit opening to an outer peripheral surface of the second piston to establish communication between the reservoir connecting port and the pressure chamber; a first cup seal positioned between the second piston and the body and located forward of the sleeve; a second cup seal positioned between the sleeve and the second piston and located rearward of the reservoir communication conduit; a piston port provided on the second piston, the piston port being positioned rearwardly of the first cup seal and establishing communication between the reservoir communication conduit and the pressure chamber during non-braking operation, the predetermined distance being defined by the total of a retracting distance of the second piston from the non-braking operation position to a position where an opening of the piston port and an opening of the reservoir communication conduit overlap one another and a predetermined additional distance; a spring retainer having a flange portion at a front end portion of the spring retainer, the flange portion contacting a rear end portion of the second piston; a rod having one end engageable with the spring retainer; a rod engaging member fixed to a bottom of an internal bore opening formed at a forward portion of the first piston, an end of the rod opposite the one end being engaged with the rod engaging member; a compressed spring positioned between the spring retainer and the rod engaging member; and the predetermined distance being equal to a moving distance of a radial projection provided on the flange portion from the rear end portion of the second piston to a rear stepped portion of a large diameter portion provided on a stepped internal bore of the cylinder housing.