| 摘要 |
A master cylinder includes a cylinder body, primary cups supported on the inner periphery of the cylinder body, and a primary piston and a secondary piston inserted in the cylinder body so as to be in sliding contact with the respective primary cups. The cylinder body is integrally formed with annular walls behind the respective primary cups. The annular walls have a greater inner diameter than the inner diameter of the cylinder body to define annular passages between the annular walls and the respective pistons. Connecting passages having a greater radial dimension than the annular passage are defined between the inner periphery of the cylinder body and the respective pistons behind the respective annular walls so as to communicate with a reservoir. While the master cylinder is not actuated, piston ports formed in the respective pistons communicate with the reservoir through the respective annular passages and connecting passages. Brake fluid can thus be sucked smoothly into the respective pressure chambers both during a return stroke of the pistons and during automatic brake control such as vehicle stability control.
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