| 摘要 |
<p>PURPOSE:To perform a degradational diagnosis in a highly accurate manner by setting a criterional value on the basis of magnitude in an air-fuel ratio variation by means of feedback control at time of comparing the turnover frequency ratio of each air-fuel ratio sensor at both upstream and downstream sides of a catalytic converter, with the criterional value and judging the extent of catalytic degradation. CONSTITUTION:Mainly, on the basis of the turnover of rich or lean of a detected air-fuel ratio in an air-fuel ratio sensor 1 at the upstream side, the air-fuel ratio of an internal combustion engine 3 is controlled by a feedback control means 4. The ratio of each turnover frequency of rich and lean in the upstream side air-fuel sensor 1 and a downstream side air-fuel ratio sensor 2 is found out by a calculating means 5. In addition, the turnover frequency ratio is compared with a criterional value, and catalytic degradation is judged by a judging means 6. Moreover, on the basis of magnitude of an air-fuel ratio variation by means of a feedback control means 4, for example, the amplitude and period or the like of a feedback compensation factor, the said criterional value is set by a setting means 7.</p> |
