| 摘要 |
The present invention provides a vacuum booster, which is constructed such that an area with which a cylinder communicates with a port communicating with a reservoir and being open to the cylinder is reduced at high temperature, so that a sufficient reaction force can be transmitted from a piston of a master cylinder to a valve mechanism at an initial stage of the braking operation, thus preventing vibration or noise from being generated in the valve mechanism. At high temperature, stop position, at which backward movement of the piston of the master cylinder is limited by an output member while a valve piston is at a non-operating position, is shifted forwards by a stop position shifting means, thus reducing the area with which the cylinder communicates with the port communicating with the reservoir and being open to the cylinder. At low temperature, while the valve piston is at the non-operating position, the stop position of the piston is not shifted, thus maintaining the area wide, with which the port communicates with the cylinder.
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