Patent ID: 8171913

Claim:
An intake system for an internal combustion engine, comprising: a duct defining an intake passage inside the duct, wherein intake air is supplied to a combustion chamber of the engine through the intake passage; and a cantilevered valve including a plate-like valve main body that opens and closes the intake passage of the duct, a rotatable shaft that supports the valve main body, and a valve extension portion that extends from the valve main body in a valve opening direction of the valve main body, wherein: the duct includes: a reduced passage portion that is formed between an inner wall of the duct and the valve main body at least when the valve main body is held in a valve fully closed position; an accommodating recess that accommodates the valve main body and the valve extension portion at least when the valve main body fully opens the intake passage; and a pressure introduction passage that is formed between an inner wall of the duct and the valve main body at least when the valve main body fully closes the intake passage and that communicates with a space between the valve main body and the valve extension portion at least when the valve main body fully closes the intake passage; the valve extension portion includes a sealing part, the duct and the sealing part defining therebetween a clearance of predetermined, constant value over an entire valve operation range from a fully open position to a fully closed position of the valve main body; and the clearance has a smaller flow passage sectional area than the reduced passage portion.