| 摘要 |
PROBLEM TO BE SOLVED: To provide a sub-muffler capable of reducing booming noise in an engine low rotating region and reducing back pressure rise in an engine high rotating region. SOLUTION: This sub-muffler 10 is devised so that an opening and closing valve 14 closes an exhaust passage R1 in the case engine speed is in a low rotating region. Then, booming noise is reduced as exhaust gas enters a clearance 24 from a first opening 31 provided in front of the opening and closing valve 14 after passing the exhaust passage R1 downstream, passes this clearance 24 upstream, enters a return passage R2 from a second opening 32 thereafter and is discharged outside of the sub muffler 10 by passing this return passage R2 downstream. At this time, back pressure rise is restrained as exhaust gas introduced to the sub muffler 10 can pass the opening and closing valve 14 in an open state after passing the exhaust passage 1 downstream.
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