| 摘要 |
<p>PURPOSE:To improve the deterioration judgement precision by detecting deterioration of a catalyst in accordance with a parameter indicating difference of upstream and downstream air-fuel ratio sensors of a three way catalyst by forcibly varying an air-fuel ratio with a specified frequency and specified amplitude with a specified air-fuel ratio on the side leaner than a stoichiometric air-fuel ratio as its center. CONSTITUTION:A three way catalyst 14 is arranged in an exhaust pipe 13 of an engine 1, and an upstream O2 sensor 16 and a downstream O2 sensor 17 are installed as air-fuel ratio sensors on upstream and downstream thereof. An electronic control unit (ECU) 5 controls a fuel injection valve 6 in accordance with input signals from various sensors and forcibly varies an air-fuel ratio by specified frequency and specified amplitude (perturbation). By bringing an average air-fuel ratio to be (14.9) on the side leaner than a stoichiometric air-fuel ratio (14.7) during execution of perturbation, deterioration judgement of the three way catalyst 14 is carried out from respective output average values of the upstream and downstream O2 sensors 16, 17. Consequently, it is possible to improve precision of the deterioration judgement.</p> |
