| 摘要 |
PROBLEM TO BE SOLVED: To prevent the thermal deterioration of a catalyst by setting the air-fuel ratio state according to the operating state of an engine, and holding the air-fuel ratio in a middle air-fuel ratio once over a prescribed time. SOLUTION: An exhaust pipe 14 is connected to an exhaust manifold 12, and a muffler is connected to the exhaust pipe 14 through a small-sized proximity three way catalyst 20 and an exhaust emission control catalytic device 30. The exhaust emission control catalytic device 30 is provided with occlusive NOX catalyst 30a and a three way catalyst 30b, a ECU(electronic control unit) 40 having a CPU or the like is set between the occlusive NOX catalyst 30a and the catalyst 30b. An air-fuel ratio state is set to the ECU 40 according to the operating state of the engine 1, and the air-fuel ratio is held in a prescribed air-fuel ratio of the middle once over a prescribed time. |
