| 摘要 |
<p>PROBLEM TO BE SOLVED: To detect deterioration of a catalyst with high accuracy by arranging a first and a second catalyst deterioration detecting means for detecting deterioration of an exhaust catalyst, and determining deterioration of the catalyst on the basis of an output of the means. SOLUTION: O2 sensors 16, 18 are disposed upstream and downstream from a catalytic converter rhodium 15 arranged in an exhaust system. Of the sensors, an output of the downstream O2 sensor 18 crosses reference voltage to the lean side or a rich side after a prescribed delay time is lapsed, with respect to changes (from a rich condition to a lean condition, and from the lean condition to the rich condition) of skip state of an air-fuel ratio correcting coefficient. Delay times T1, T2 from a time point when the air fuel ratio correcting coefficient is changed from the rich condition to the lean condition and from the lean condition to the rich condition, until when output voltage of the sensor 18 is reference voltage VR2 and less and or more is counted. The delay times T1, T2 are found out by prescribed times, an average of the delay times T1, T2 are calculated, and deterioration of the catalyst 15 is determined from its average value.</p> |
