IDLING ROTATIONAL SPEED CONTROL VALVE OF INTERNAL COMBUSTION ENGINE

PROBLEM TO BE SOLVED: To block pressure wave acted on a servo system, and prevent resonance of a servo machine by arranging a pressure bulk head which is changeably in a thrust direction between a valve and a diaphragm in a device formed in such a constitution that a valve element interposed in an air passage for bypassing a throttle valve is opened/closed by the diaphragm. SOLUTION: An umbrella valve opened/closed through a shaft by a diaphragm 10 is arranged on a position opposing to a valve seat in a bypass formed to bypass a throttle valve in a main passage. At this time, in the diaphragm 10, its outer peripheral rim is fastened by laminating with a body together with the outer peripheral rim of a cup shaped metal plate 6 in which an orifices 6a are formed. The outer peripheral wall thickness rim of a boots 7 is held and fixed on the inner bottom part of the metal plate 6 by a ring 29, and movement of the metal plate 6 is allowed. In the case where a filter 45 is clogged, the atmosphere is led from an air gap 6b between the metal plate 6 and the body 1, and smooth operation of the diaphragm 10 is secured.