| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent misdetection of catalyst deterioration and to attain an accurate deterioration judgment by installing a deterioration detection prohibiting means to prohibit the detection of deterioration of a catalyfic means at a time when the amplitude of output in an oxygen content sensor is the prescribed value or less. SOLUTION: A three-way catalyst 16 for purifying exhaust is installed in an exhaust pipe 12. An upstream side oxygen sensor 14 is installed in an upstream position of this catalyst 16, and also a downstream side oxygen sensor 15 of the catalyst 16 is installed therein, detecting oxygen content in the exhaust gas each. The detected value is fed to an engine controlling electronic control unit 5. Feedback in the case of monitoring deterioration in the three-way catalyst 16 is controlled on the basis of output alone in the downstream side oxygen sensor 15. When a fluctuation in the output of downstream side oxygen sensor 15 small, deterioration monitoring is set so as not to be executed. When this catalyst 16 is new in particular, misjudgment due to a fact that the output is stagnant around the reference value, and that accurate oxygen storage time is undetectable is prevented.</p> |
