Resonator type silencer

Abstract

A resonator type silencer in which the resonance frequency is variable in accordance with engine speed of an automotive engine. The silencer is comprised of a casing connected through a neck section to a duct through which intake air or exhaust gas flows. A cylindrical rotatable member is disposed in the casing and rotatably supported on a rotatable shaft, forming an annular space between it and the inner peripheral surface of the casing. A stationary partition wall is fixedly disposed inside the cylindrical rotatable member and extends radially. A movable partition wall is disposed in the casing and extends from the rotatable shaft to the cylindrical rotatable member. The movable partition wall defines, in cooperation with the stationary partition wall, a tuning chamber inside the cylindrical movable member. A movable blocking wall is disposed in the casing to block the annular space thereby to define a peripheral passage in communication with the neck section. A part of the cylindrical rotatable member is cut out to form a communication with the peripheral passage. The cylindrical rotatable member is driven to rotate in accordance with engine speed, thereby changing the length of the peripheral passage communicating with the neck section and the volume of the tuning chamber to alter the resonance frequency of the silencer.