| 摘要 |
PURPOSE:To assure stable secondary air in the entire range of rotational frequency of an engine without deteriorating a silencing function, by providing a straight expanded pipe portion behind a venturi portion provided in an exhaust gas inlet pipe, and by setting the length of said pipe portion at least twice larger than the inside diameter of the pipe portion. CONSTITUTION:A catalytic muffler 1 has a cylindrical body comprising an outer cylindrical wall, a front partition plate 3 and a rear partition plate 4. Six chambers including a first chamber 10 and a sixth chamber 15 are defined in the direction of flow or secondary air, by four partition plates 5-8 and an inner cylindrical wall 9 in the body of the muffler 1. An exhaust gas inlet pipe 16 extends through the partition plates 3, 5-7 so that the rear end 16B of the pipe 16 is opened into the second chamber 11. A straight expanded pipe portion 16A is provided behind the venturi portion 20, 21 of the inlet pipe 16. The length L of the expanded pipe portion 16A is set at least twice larger than the inside diameter D of the inlet pipe 16. As a result, the cutoff frequency based on the damping of reflected waves is suppressed to attain the purpose.
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