Patent ID: 7801666

Claim:
An air-fuel ratio detection apparatus of an internal combustion engine having a plurality of cylinders, comprising: an air-fuel ratio detection means disposed upstream of a catalyst in an exhaust pipe for detecting an air-fuel ratio of exhaust gas flowing through a confluent portion into which the exhaust gas discharged from each cylinder flows; a detection timing computation means for computing a detection timing at which the air-fuel ratio of the exhaust gas discharged from each cylinder is respectively detected by the air-fuel ratio detection means; an air-fuel ratio change means for compulsorily changing the air-fuel ratio of the exhaust gas discharge from each cylinder; a deviation estimation means for estimating a deviation between a reference air-fuel ratio and the air-fuel ratio of the exhaust gas discharged from each cylinder, the air-fuel ratio being detected by the air-fuel ratio detection means at said detection timing; and an air-fuel ratio change quantity computation means for computing an air-fuel ratio change quantity compulsorily changed by the air-fuel ratio change means, wherein the deviation estimation means estimates said deviation on the basis of the air-fuel ratio change quantity, the air-fuel ratio detected by the air-fuel ratio detection means before the air-fuel ratio is compulsorily changed by the air-fuel ratio change means, and the air-fuel ratio detected by the air-fuel ratio detection means after the air-fuel ratio is compulsorily changed by the air-fuel ratio change means.