| 摘要 |
<p>PURPOSE: To precisely determine whether a catalyst deteriorates or not without reducing a deterioration determining execution frequency for the catalyst. CONSTITUTION: O2 sensors 13, 15 are arranged individually on a catalyst converter 12 upstream side and on a downstream side exhaust passage in an internal combustion engine 1. In a control circuit 10, an engine air-fuel ratio is feedback controlled to a theoretical air-fuel ratio on the basis of outputs from the O2 sensors 13, 15, while deterioration in a catalyst is determined on the basis of the output orbital length of the O2 sensors 13, 15 during execution of the feedback control. By means of the control circuit 10, a present catalyst temperature is estimated from an engine intake air quantity, and a range, in which deterioration determination is carried out on the basis of this catalyst temperature, for the intake air quantity is set. In the control circuit 10, catalyst deterioration determination based on the O2 sensor output orbital length is carried out only when the intake air quantity detected by means of an air flow meter 3 is within the set range for the deterioration determining intake air quantity.</p> |
