| 摘要 |
<P>PROBLEM TO BE SOLVED: To reduce the amount of sulfate discharged in the air. <P>SOLUTION: NO<SB>x</SB>catalyst is disposed in the exhaust passage of an internal combustion engine in which the air-fuel ratio of an air-fuel mixture burnt in a combustion chamber is kept in a lean state, and an auxiliary catalyst having oxidizing capability is disposed in the exhaust passage downstream of the NO<SB>x</SB>catalyst. When QN indicating the amount of accumulated NO<SB>x</SB>in the NO<SB>x</SB>catalyst becomes greater than a tolerable value QNA, a rich spike for NO<SB>x</SB>for temporarily changing over the air-fuel ratio AFN of exhaust gas flowing in the NO<SB>x</SB>catalyst into a rich state is performed to reduce NO<SB>x</SB>in the NO<SB>x</SB>catalyst and decrease the amount of the accumulated NO<SB>x</SB>. The amount of SO<SB>x</SB>accumulated in the NO<SB>x</SB>catalyst is obtained without forming sulfate. When the SO<SB>x</SB>is large in amount, the rich air-fuel ratio AFR in the rich spike for NO<SB>x</SB>is reduced compared to that in a state where the SO<SB>x</SB>is small in amount. <P>COPYRIGHT: (C)2004,JPO |
