CATALYST DETERIORATION DISCRIMINATING DEVICE OF INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To prevent erroneous judgment in catalyst deterioration discrimination by providing a deterioration discriminating means for discriminating the presence or absence of deterioration of a three-way catalyst on the basis of the output of an air-fuel ration sensor when an intake air amount of an engine is in discrimination performing range. SOLUTION: An upstream O2 sensor 13 is provided upstream from a catalytic converter 12, and a downstream O2 sensor 15 is provided on a downstream exhaust pipe 14. A control circuit 10 performs basic control such as fuel injection control of an engine, ignition timing control, etc. The control circuit 10 feedback-controls an air-fuel ratio on the basis of outputs of the upstream O2 sensor 13 and the downstream O2 sensor 15. Moreover, the control circuit 10 calculates an orbit length LVOS of the output of the downstream O2 sensor and the orbit length LVOM of the output of the upstream O2 sensor 15, and judges that a catalyst is deteriorated when a ratio of the orbit length LVOS to LVOM becomes the predetermined specified value or more. Therefore, any error is not generated on catalyst deterioration discrimination.