| 摘要 |
PROBLEM TO BE SOLVED: To prevent overheat of a catalyst disposed to a bypass exhaust pipe for bypassing a main exhaust pipe. SOLUTION: A four-cylinder engine 1 has the bypass exhaust pipe 10 for bypassing the main exhaust pipe 8, and a front catalyst 11 is disposed in the middle of the bypass exhaust pipe. An open/close valve 12 driven by an actuator 12 is disposed to the main exhaust pipe 8, and is closed while warm-up has not been completed yet. Since an engine temperature reaches 850°C at 6000 rpm, sound speed at this time is 670 m/sec, and a fluctuation frequency is 200 Hz, one wavelength is 3.35 m, 3/4 wavelength is 2.5 m and a position of wave node is 0.8 m and 2.5 m. Therefore, an upstream end part of the bypass exhaust pipe is connected to a main exhaust pipe at 0.8 m from an intake valve 5, a downstream end part of the bypass exhaust pipe is connected to the main exhaust pipe at 2.5 m, and a main catalyst is disposed immediately after the connection point with the downstream end part. COPYRIGHT: (C)2005,JPO&NCIPI
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