MUFFLER FOR INTERNAL COMBUSTION ENGINE

PURPOSE:To prevent abrupt fluctuation of muffler characteristic in a muffler provided on an exhaust system of an internal combustion engine by providing an opening/closing valve on an exhaust system pipe, providing a damper mechanism which controls opening/closing operations of the valve, and thereby suppressing abrupt operation of the opening/closing valve. CONSTITUTION:A muffler 1 is arranged in an exhaust system of an internal combustion engine. A space inside an outer frame 2 is divided into a first chamber 5, a second chamber 6, a third chamber 7 by means of partition walls 3, 4. An inlet pipe 8 is introduced from outside of the muffler 1, penetrating the third and second chambers 7, 6, opened to and communicated with the first chamber 1 at its inner end. An outlet pipe 9 penetrates the first and second chambers 5, 6, being opened to and communicated with the third chamber 7 at its inner end, while opened to outside of the muffler 1 at its outer end. An opening/closing valve 13 is provided on a downstream end of an auxiliary inner pipe 12. The opening/closing valve 13 is fixed to a valve shaft 13a, and rotated together with the valve shaft 13a for opening/closing the downstream end of the auxiliary inner pipe 12. A damper mechanism 14 is provided for controlling opening/closing operations of the valve 13.