| 摘要 |
<p>PROBLEM TO BE SOLVED: To conduct determination of catalyst deterioration at favorable precision while improving exhaust purifying efficiency. SOLUTION: Sensors for detecting an air-fuel ratio of exhaust gas or if it is rich or lean are respectively installed on the upstream side and the downstream side of catalyst for purifying exhaust, and sub-feedback(sun-F/B) control for reflecting output of the downstream side sensor on air-fuel ratio feedback control is conducted. As catalyst deterioration determination executing conditions are satisfied, a gain of an integration term and a skip term of a sub-F/B correction coefficient is changed into a large valve, so if deterioration of catalyst exists or not is largely reflected on the output of the downstream side sensor. In the case of the catayst being normal, the amplitude and frequency of the output of the downstream side sensor are not so much enlarged even when the gain of the sub-F/B correction coefficient is changed into the large valve, but in the case of the catalyst being deteriorated, the amplitude and frequency of the output of the downstream side sensor are relatively largely increased. By making relative evaluation of the output of the downstream side sensor to the reference of output of the upstream side sensor, if deterioration of the catalyst exists or not can be determined at favorable precision.</p> |
