CATALYST DETERIORATION JUDGING DEVICE OF INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To detect the slight deterioration of a catalyst. SOLUTION: The air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio based on the output signal of an air-fuel ratio sensor 21 arranged in an exhaust gas passage on the upstream side of a three-way catalyst 16 and the output signal of an air-fuel ratio sensor 22 arranged in an exhaust gas passage on the downstream side of the three-way catalyst 16. The output signal of the air-fuel ratio sensor 22 is frequency analyzed to judge whether or not the three-way catalyst 16 is slightly deteriorated from the output signal intensity of the air-fuel ratio sensor 22 at the frequency in which e.g. an engine is revolved by 720 deg. crank angle.