| 摘要 |
<P>PROBLEM TO BE SOLVED: To correctly determine whether a amount of sulfur stored in NO<SB>X</SB>catalyst should be reduced or not, while keeping good exhaust emission control action by the NO<SB>X</SB>catalyst. <P>SOLUTION: At two points with a time interval between them, a rich time purification ratios PER(1), PER(2), that are NO<SB>X</SB>purification ratios of NO<SB>X</SB>catalyst when an air-fuel ratio of inlet exhaust gas is switched to rich, and fuel consumptions SQF(1), (2) are detected to calculate a rich time purification ratio change rate DPE. A present rich time purification ratio PE is estimated based on the rich time purification ratio change rate DPE and a present fuel consumption SQF, and an accumulated amount of SO<SB>X</SB>is estimated based on the estimated present rich time purification ratio PE. When the accumulated amount of SO<SB>X</SB>is larger than a tolerance for SO<SB>X</SB>, an air-fuel ratio of exhaust gas flowing into the NO<SB>X</SB>catalyst is temporarily switched to be rich so as to reduce the accumulated SO<SB>X</SB>in the NO<SB>X</SB>catalyst. <P>COPYRIGHT: (C)2004,JPO |
