| 摘要 |
PROBLEM TO BE SOLVED: To adjust the catalyst temperature without generating hunting. SOLUTION: A NOX occlusion catalyst 7 is disposed in an exhaust passage 3 of an internal combustion engine 1. A loop-shaped exhaust pipe 9b is provided on an inlet part of the catalyst 7, and a regular exhaust passage to directly feed the exhaust emission to an inlet exhaust passage 9a of the catalyst 7 from the exhaust passage 3 and a cooled exhaust passage to feed the exhaust emission to the catalyst 7 after dropping the temperature of the exhaust emission through the exhaust pipe 9b can be switched by an exhaust control valve 9c. An electronic control unit (ECU) 30 detects the exhaust temperature by an exhaust temperature sensor 9d disposed at the catalyst inlet, and switches the exhaust flow to the cooled exhaust passage when the exhaust temperature is higher than the first predetermined temperature, and switches the exhaust flow to the regular exhaust passage when the exhaust temperature is lower than the second predetermined temperature. In addition, the ECU raises the first predetermined temperature, or drops the second predetermined temperature when the temperature of the exhaust pipe 9b constituting the cooled exhaust passage is low, preventing the hunting of the control valve 9. COPYRIGHT: (C)2003,JPO
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