Patent ID: 6698202
Filing Date: 2004-03-02
Classification: B60T

Abstract:
A master cylinder comprising:a stepped cylinder comprising a large diameter cylinder portion and a small diameter cylinder portion; a stepped piston comprising a large diameter piston portion slidably inserted into the large diameter cylinder portion and a small diameter piston portion slidably inserted into the small diameter cylinder portion; a reservoir for storing a brake fluid; and a reverse flow checking opening and closing portion for partitioning an inside of the stepped cylinder into a large diameter pressurizing chamber and a small diameter hydraulic chamber, and for permitting the brake fluid to flow from a large diameter pressurizing chamber side to a small diameter hydraulic chamber side, the reverse flow checking opening and closing portion being opened by a reduction in volume of the large diameter pressurizing chamber by sliding movement of the stepped piston toward the small diameter hydraulic chamber side; and a control valve for gradually reducing a hydraulic pressure of the large diameter pressurizing chamber in accordance with a rise in a hydraulic pressure of the small diameter hydraulic chamber; wherein the control valve comprises a valve piston and a valve spring for urging the valve piston within a valve cylinder; and the valve piston reduces the hydraulic pressure of the large diameter pressurizing chamber when propulsive force produced by the hydraulic pressure of the small diameter hydraulic chamber and propulsive force produced by the hydraulic pressure of the large diameter pressurizing chamber exceed an urging force produced by the valve spring; wherein the control valve comprises at least two ring seals between the valve cylinder and the valve piston to partition an inside of the valve cylinder, and a chamber formed between the at least two ring seals and the small diameter hydraulic chamber communicate with each other; wherein the valve spring is at a first side of the valve piston, a relief chamber communicating the reservoir and the large diameter pressurizing chamber is at a second side of the valve piston, and the control valve comprises an opening and closing valve mechanism for establishing or cutting off communication between the relief chamber and the large diameter pressurizing chamber; wherein the valve cylinder is partitioned by the two ring seals into a relief chamber, a chamber formed between the two ring seals, and a damper chamber that stores the valve spring; and wherein the valve piston comprises a throttle path one end of which opens to the relief chamber and the other end of which opens to the damper chamber.