| 摘要 |
PROBLEM TO BE SOLVED: To inhibit a target air-fuel raito from being carelessly varied.SOLUTION: An internal combustion engine includes an exhaust emission control catalyst 40, and a downstream side sensor arranged on the downstream side of the exhaust emission control catalyst. A control device performs feedback control so that the air-fuel ratio of exhaust gas flowing into the exhaust emission control catalyst becomes a target air-fuel ratio. The target air-fuel ratio is changed over into a lean air-fuel ratio when the output air-fuel ratio of the downstream side sensor becomes a rich determined air-fuel ratio or lower, and changed over into a rich air-fuel ratio when the oxygen storage amount of the exhaust emission control catalyst after changeover is estimated to become a changeover reference storage amount or lower. Even when the catalyst oxygen storage amount is estimated to become the changeover reference storage amount or lower after the target air-fuel ratio is changed over into the lean air-fuel ratio, if the air-fuel ratio detected by the downstream side sensor is the rich determined air-fuel ratio or lower, the target air-fuel ratio is not changed over from the lean air-fuel ratio into the rich air-fuel ratio until the output air-fuel ratio of the downstream side sensor becomes higher than the rich determined air-fuel ratio.SELECTED DRAWING: Figure 11 |
