| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent deterioration of three-way catalyst from being eroneously discriminated in a device determinating deterioration of three-way catalyst based on output of an oxygen sensor on the lower stream side of the three-way catalyst by estimating an oxygen balance in the three-way catalyst, and stopping deterioration determination of the three-way catalyst when the oxygen balance is over the set threshold value. SOLUTION: In this internal combustion engine, an air-fuel ratio sensor 11 on the upper stream is on the upper stream side of three-way catalyst for exhaust emission control, an oxygen sensor 12 on the lower stream side is on the lower stream side, respectively provided. A fuel quantity is controlled by an air-fuel ratio feedback control means 13 at least according to the output of the upper stream side air-fuel ratio sensor 11, and deterioration of the three- way catalyst is determinated by a deterioration determinating means 14 at least based on the output of the lower stream side oxygen sensor 12. In this case, an oxygen balance estimation means 15 estimating the oxygen balance in the three-way catalyst is provided, and when the estimated oxygen balance is over the set threshold value, deterioration determination of the three-way catalyst by the deterioration determinating means 14 is stopped by a deterioration determination stopping means 16 so as to prevent deterioration from being eroneously determinated.</p> |
