| 摘要 |
PURPOSE:To reduce the vibration sound and increase the engine output with a compact construction by providing in an inverting manner an exhaust gas expansion pipe provided within a muffler proper of a hollow box shape so that the downstream end opening within the muffler proper is directed toward the exhaust gas upstream side. CONSTITUTION:An exhaust muffler 6 suitable for a scooter type automatic bicycle has a hollow box shaped muffler proper 7 partitioned into two front and rear chambers, that is, a hollow chamber 10 and a first expansion chamber 11. The expan sion chamber 11 is communicated to external air via a tail pipe 12. Further, an exhaust gas expansion pipe 13 connected to the downstream end of the exhaust pipe 13 is introduced into the muffler proper 7. The exhaust gas pipe 13 has a diameter expanded part 16 the diameter L of which changes toward the exhaust gas downstream side and a diameter contracted part 19, and the contracted part 19 inverts the downstream side downwardly substantially in a U-shape toward the exhaust gas upstream side. The downstream side of the exhaust gas expansion pipe 13 is communicated with and connected to an inner side casing 21 provided in parallel to the lower part of the part moving from the diameter expanded portion 16 to the diameter contracted portion 19 of the exhaust gas expansion pipe 13.
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