PROBLEM TO BE SOLVED: To lower the noise level of exhaust noise extending over the whole range of frequency by moving a valve in the axial lengthwise direction of a silencer main body by operation of a valve operation mechanism, and enabling a resonance hole to be selected into an acoustical closed state or an acoustical opened state. ;SOLUTION: The interior of a silencer main body 1 is divided into two parts, an expansion chamber 5 and a resonance chamber 6 with a partition plate 4. The partition plate 4 is formed with a resonance hole 12 on the position offset from a resonance pipe 9, and the extreme end of an exhaust introducing pipe 7 is positioned on the intermediate position of the resonance hole 12 and the expansion chamber 5. A valve 13 opening/closing the resonance hole 12 is arranged on the resonance chamber 6 side of the partition plate 4, and it is moved for opening/closing by a valve operation mechanism 14. This valve operation mechanism 14 is provided with an actuator 21 controlled according to engine speed, the position of the valve 13 against the resonance hole 12, namely the acoustical closed state or the acoustical opened state of the resonance hole 12 is selected by operating it, and hence exhaust noise is reduced extending over the wide range of frequency band.;COPYRIGHT: (C)1998,JPO
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