Patent ID: 8695568

Claim:
An inter-cylinder air-fuel ratio imbalance abnormality detection device, comprising: a catalyst that is provided in an exhaust passage of a multi-cylinder internal combustion engine; a pre-catalyst sensor that is an air-fuel ratio sensor provided upstream of the catalyst; a post-catalyst sensor that is an air-fuel ratio sensor provided downstream of the catalyst; an air-fuel ratio control unit that performs main air-fuel ratio control based on an output of the pre-catalyst sensor and auxiliary air-fuel ratio control based on an output of the post-catalyst sensor; a control amount calculation unit that calculates a control amount for the auxiliary air-fuel ratio control based on the output of the post-catalyst sensor; a revolution variation detection unit that detects a revolution variation of the internal combustion engine; an abnormality detection unit that detects an inter-cylinder air-fuel ratio imbalance abnormality on the basis of a detected value of the revolution variation; and a guard range reduction unit that reduces a guard range of the control amount during detection of the imbalance abnormality.