| 摘要 |
<P>PROBLEM TO BE SOLVED: To supply secondary air to an exhaust emission control device with a simple structure. <P>SOLUTION: An NO<SB>x</SB>catalyst 22 is arranged in the exhaust passage of an internal combustion engine where the air-fuel ratio of air-fuel mixture to be burnt in a combustion engine is kept lean, and an auxiliary catalyst 23 having oxidizing ability is arranged in the exhaust passage on the downstream side of the NO<SB>x</SB>catalyst 22. An intake duct 13 between the compressor 15 of an exhaust air turbo charger and a cooling device 18 for cooling the air discharged from a compressor 15 is connected to an exhaust pipe 20b between the NO<SB>x</SB>catalyst 22 and the auxiliary catalyst 23 through a secondary air passage 31, and a secondary air control valve 33 is arranged in the secondary air passage 31. In order to reduce the accumulated SO<SB>x</SB>quantity in the NO<SB>x</SB>catalyst 22 when stopping the fuel supply in an engine decelerating operation, the secondary air control valve 33 is opened while temporarily holding the average air-fuel ratio of the exhaust gas carried into the NO<SB>x</SB>catalyst 22 in a rich state to supply the air discharged from the compressor 15 to the auxiliary catalyst 23 through the secondary air passage 31. <P>COPYRIGHT: (C)2004,JPO |
