| 摘要 |
<p>PURPOSE:To prevent occurrence of erroneous diagnosis by suspending deterioration judgment of an exhaust emission control catalyst when a knocking signal of an engine is detected. CONSTITUTION:In general cases, rich and lean inversion number ratios of upstream and downstream side air-fuel ratio detection means (sensors) 32 are obtained by means of an inversion number ratio calculation means, and based on the result, deterioration of an exhaust emission catalyst is judged by means of a deterioration judgment means. In the case that knocking occurs at an engine l, however, a combustion temperature is increased in a cylinder by natural firing, and oxygen is consumed by a large amount. HC is decreased while NOx is increased. The inversion number ratio similar to one at the time of catalyst deterioration is temporaily detected. Erroneous judgment may occur when the catalyst 10 is not deteriorated. In order to avoid this, a deterioration judgment suspension means suspends deterioration judgment of the exhaust emission control catalyst for a specified time when knocking of an engine is detected by a knocking detection means. When detection 16 of the knocking signal is stopped, deterioration judgment of the catalyst 10 is restarted for preventing of occurrence of erroneous diagnosis.</p> |
