Title: Diaphragm actuator

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Abstract: A diaphragm actuator is operated by the pressure difference between a pressure chamber and a negative pressure chamber, and causes an operating shaft to slide through a wall portion of the negative pressure chamber. When the pressure in the negative pressure chamber is highly negative, ambient air leaks along a shaft seal and flows through the negative pressure chamber into a suction manifold of an engine, resulting in fluctuation of the air-fuel ratio. According to the present invention, the shaft seal includes a sealing diaphragm mounted on the wall portion, which supports a movable annular member. This annular member has a tapered surface by which an O-ring is compressed axially and radially inwardly against the operating shaft. The compression force applied to the O-ring increases as the negative pressure in the negative pressure chamber becomes higher. Another solution according to the present invention is to disconnect the negative pressure chamber from the suction manifold when a highly negative pressure at the low speed and low load operating condition of the engine is detected.


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