EXHAUST EMISSION CONTROL SYSTEM

摘要

PROBLEM TO BE SOLVED: To easily allow precise and sure determination of deterioration all the time, even in a catalytic converter low in oxygen storage ability. SOLUTION: In the deterioration determination for the catalytic converter, a means for varying forcibly an air-fuel ratio modulates an air-fuel ratio (S10) to make an average oxygen storage amount occluded in the catalytic converter in a lean air-fuel ratio and released from the catalytic converter in a rich air- fuel ratio less than a break-through amount in a non-deteriorated condition of the ctalytic converter and more than a break-through amount in a deteriorated condition of the converter.