| 摘要 |
PROBLEM TO BE SOLVED: To maintain highly accurate control by promoting activation of an exhaust catalyst when starting an engine and by preventing control valves from becoming high temperature when the engine becomes high temperature. SOLUTION: Exhaust emission control secondary air is supplied to an exhaust pipe 20 extending from the engine 15 via the first and second control valves 33 and 34 and first and second air introducing pipes 23 and 24 from a secondary air cleaner 22. The first and second air introducing pipes 23 and 24 are laid in a shroud 37 for surrounding the periphery of the engine 15 by forming the respective upper sides as flexible pipe parts 23a and 24a, and forming the respective lower sides as metallic pipe parts 23b and 24b. The exhaust catalyst 41 is arranged in a muffler 21 connected with the rear end of the exhaust pipe 20. When the exhaust gas temperature is a low state when starting the engine, the exhaust gas temperature is raised by heating the metallic pipe parts 23b and 24b by heat of the engine 15, to activate the exhaust catalyst 41. When the exhaust gas temperature becomes sufficiently high, the first and second air introducing pipes 23 and 24 are forcibly cooled by cooling air sent into the shroud 37, to prevent the high temperature rise in the first and second control valves 33 and 34. COPYRIGHT: (C)2006,JPO&NCIPI |
