| 摘要 |
<p>PROBLEM TO BE SOLVED: To precisely carry out catalyst deterioration discrimination in accordance with output of an air-fuel ratio sensor and output of a catalyst downstream side O2 sensor without erroneous judgement caused by variation of an engine air-fuel ratio by carrying out air-fuel ratio feed-back control in accordance with output of an air-fuel ratio sensor provided on the catalyst upsream side. SOLUTION: An air-fuel ratio sensor (A/F sensor) 45 is provided on the upstream side of an exhaust purifying catalyst provided in an exhaust passage of an engine. The engine carries out sub air-fuel ratio feed-back control to compensate dispersion of output characteristics of the A/F sensor 45 by varying a control center of air-fuel ratio feed-back control by the A/F sensor 45. Additionally, an O2 sensor 46 is provided in a exhaust system on the downstream of a catalyst converter 38. Additionally, an engine electronic control unit 70 is a microcomputer system to carry out catalyst deterioration discrimination processing in addition to air-fuel ratio control. Consequently, it is possible to precisely carry out catalyst deterioration discrimination without erroneous judgement caused by air-fuel ratio variation.</p> |
