| 摘要 |
PURPOSE:To enhance a buffer action, by providing plural communicating holes for the inner circumferential wall surface of a brake room along the sliding direction of a piston so as to communicate the brake room with the inside of a cylinder, and fitting a subpiston into the brake room. CONSTITUTION:A brake room 7 in which a subpiston 5 is fitted to the internal surface of the covering member 4 of a cylinder 1 is formed, and plural communicating holes 12a-12e which communicate with communicating grooves 10 are formed on a boss 8. As the subpiston 5 is fitted into the brake room 7 deeper, the communicating holes 12a-12e are closed gradually by the circumferential surface of the subpiston 5, and the transmitting area of an operational fluid in the cylinder 1 and the operational fluid in the brake room 7 becomes gradually smaller, so that strong braking force works gradually. Thus, a sufficient buffer action can be obtained even by a low viscous operational fluid.
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