| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a method for judging the deterioration of an exhaust gas cleaning catalyst device, capable of judging the deterioration state of the catalyst device without performing special control of the air-fuel ratio of air-duel mixture for forming exhaust gas to be supplied to the catalyst device to judge the deterioration state of the catalyst device, particularly, capable of precisely judging the deterioration state of the catalyst device while securing required cleaning performance of the catalyst device. SOLUTION: The target air-fuel ratio of exhaust gas in the upstream of a catalyst device 4 is found on the basis of the output of an O2 sensor 7 in the downstream of the catalyst device 4 so as to obtain required cleaning performance, and the air-fuel ratio of an internal combustion engine 1 is so controlled that the detected output of an air-fuel ratio sensor 6 in the upstream of the catalyst device 4 may be converged to the target air-fuel ratio. In controlling, the deterioration state of the catalyst device 4 is judged on the basis of the target air-fuel ratio or the detected output of the air-fuel ratio sensor 6.</p> |
