| 摘要 |
<p>PROBLEM TO BE SOLVED: To constantly and precisely control a catalyst oxygen storage quantity to be a target value by correcting output variation by deterioration of an air- fuel ration sensor on the catalyst upstream side. SOLUTION: A catalyst 3 having oxygen storage capacity is set in an engine exhaust passage, oxygen storage quantity is assumed in accordance with the output of an air-fuel ratio sensor 4 on the upstream side of the catalyst 3, and an air-fuel ratio is controlled so that the oxygen storage quantity matches with the target value. The air-fuel ratio is changed so as to decrease the oxygen storage quantity when output of an air-fuel ratio sensor 5 on the downstream side is on the lean side and to increase the oxygen storage quantity when it is on the rich side, and when the air-fuel ratio on the downstream side is on the same side as that before changing regardless of it, the output of the air-fuel ratio sensor 4 on the upstream side is corrected only by specified quantity.</p> |
