Apparatus and method for detecting abnormality of inter-cylinder air-fuel ratio dispersion in multi-cylinder internal combustion engine

An apparatus for detecting an abnormality of inter-cylinder air-fuel ratio dispersion in a multi-cylinder internal combustion engine, comprising:

• a hydrogen concentration sensor disposed in an exhaust passage of the multi-cylinder internal combustion engine to detect a concentration of hydrogen in exhaust gas;
• an abnormality detector that detects an abnormality of inter-cylinder air-fuel ratio dispersion on a basis of an output of the hydrogen concentration sensor;
• and
• an abnormal cylinder specifier that forcibly reduces a fuel injection amount in each of cylinders when an abnormality of dispersion is detected by the abnormality detector, acquires an output of the hydrogen concentration sensor at this time, and specifies as an abnormal cylinder that one of the cylinders in which the output indicates that the concentration of hydrogen has become lower than at a time of detection of the abnormality of dispersion.

A method for detecting an abnormality of inter-cylinder air-fuel ratio dispersion in a multi-cylinder internal combustion engine equipped with 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, and 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, comprising:

• detecting 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
• forcibly reducing fuel injection amounts in cylinders individually when an abnormality of dispersion is detected by the abnormality detector, detecting the 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 specifying 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.