| 摘要 |
A pneumatic booster includes a casing, a diaphragm secured to the casing to partition the inside of the casing into a front chamber which is communicated with a negative-pressure source and a rear chamber, a valve body secured to the inner peripheral portion of the diaphragm, a vacuum valve provided in the valve body to allow the front and rear chambers to be selectively communicated with and cut off from each other, an atmospheric valve provided in the valve body to allow the rear chamber to be selectively communicated with and cut off from the atmosphere, an input rod for actuating the vacuum and atmospheric valves, and an output rod adapted to receive the force of displacement of the diaphragm. The atmospheric valve is composed of first and second valve portions provided in series along a communicating passage between the rear chamber and the atmosphere. The first and second valve portions are closed successively in the mentioned order when the atmospheric valve is closed. The booster further includes orifices for providing communication between the rear chamber and the atmosphere during the period of time from the instant the first valve portion is closed until the second valve portion is closed. Thus, it is possible to give a driver a feeling of stable and favorable braking at all times and also to improve the durability of the booster.
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