Advics Co., Ltd.

Toshiharu Okuda

Kaoru Tsubouchi

Koji Suzuki

Atsushi Yasuda

Katsuhiro Mita

Hideaki Iijima

A master cylinder includes a primary piston and a secondary piston, each formed with piston ports which include two different kinds of ports, i.e. first ports for ensuring communication between a reservoir and a pressure chamber of the master cylinder, and second ports through which brake fluid is sucked from the reservoir during automatic break control. The second ports are greater in number than the first ports and are positioned forwardly of the first ports so that the second ports are closed by primary cups which are provided on the inner wall of the cylinder body so as to be in sliding contact with the respective pistons before the first ports when the respective pistons are advanced. An annular wall having a greater inner diameter than the outer diameter of the pistons is formed on the inner wall of the cylinder body to support the back of each of the primary cups. An annular groove is formed in each piston so as to communicate with the first ports. The annular groove is preferably arranged so as to radially oppose the annular wall when the piston is in an inoperative position.

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Kariya, Japan

Toshiharu Okuda