Patent ID: 8047064

Claim:
An apparatus for detecting an abnormality of inter-cylinder air-fuel ratio dispersion in a multi-cylinder internal combustion engine, comprising: a catalytic element that is disposed in an exhaust passage of the multi-cylinder internal combustion engine to purify exhaust gas by oxidizing at least hydrogen contained in the exhaust gas; a first air-fuel ratio sensor that detects a first exhaust gas air-fuel ratio as an air-fuel ratio of exhaust gas that has not passed through the catalytic element; a second air-fuel ratio sensor that detects a second exhaust gas air-fuel ratio as an air-fuel ratio of exhaust gas that has passed through the catalytic element; an abnormality detector that detects an abnormality of inter-cylinder air-fuel ratio dispersion on a basis of a divergence state of a detected value of the second exhaust gas air-fuel ratio to a lean side from a detected value of the first exhaust gas air-fuel ratio; and an abnormal cylinder specifier that forcibly reduces fuel injection amounts in cylinders individually when an abnormality of dispersion is detected by the abnormality detector, detects a divergence state of the detected value of the second exhaust gas air-fuel ratio to the lean side from the detected value of the first exhaust gas air-fuel ratio at this time, and specifies as an abnormal cylinder that one of the cylinders in which a value indicating the divergence state has become smaller than at a time of detection of the abnormality of dispersion.