Patent ID: 7243644

Claim:
An individual-cylinder air-fuel ratio estimation apparatus for an internal combustion engine including a plurality of cylinder groups, comprising: an air-fuel ratio sensor which is installed in a confluent exhaust pipe with exhaust manifolds of a plurality of cylinders in one of the cylinder groups of the internal combustion engine connected thereto, and which detects an air-fuel ratio of gases exhausted from the individual cylinders in the one of the cylinder groups and mixed at a confluence; and an individual-cylinder air-fuel ratio estimation circuitry for estimating individual-cylinder air-fuel ratios of the individual cylinders having exhausted the gases, on the basis of the air-fuel ratio of the mixed gas as detected by the air-fuel ratio sensor; the individual-cylinder air-fuel ratio estimation circuitry causing influences, which are ascribable to combustion intervals of adjacent combustion cylinders in the one of the cylinder groups, to be reflected on the estimation values of the individual-cylinder air-fuel ratios; wherein a plurality of combustion intervals between adjacent combustion cylinders in at least the one of the cylinder groups are established.