Patent ID: 8407983

Claim:
An abnormality diagnosis device of an internal combustion engine that has a catalyst provided in an exhaust passage of the internal combustion engine for purifying exhaust gas, an upstream sensor provided upstream of the catalyst for sensing an air-fuel ratio or a rich/lean state of the exhaust gas and a downstream sensor provided downstream of the catalyst for sensing the rich/lean state of the exhaust gas and that performs main feedback control for correcting a supply air-fuel ratio based on an output of the upstream sensor and sub feedback control for correcting a control amount related to the main feedback control based on an output of the downstream sensor, the abnormality diagnosis device comprising: a control unit, including a computer processor, the control unit being configured at least to perform: an exhaust gas purification rate deterioration degree determination for determining a deterioration degree of an exhaust gas purification rate based on a time in which a sub feedback correction amount used in the sub feedback control is guarded with a predetermined guard value; and an abnormality diagnosis for determining whether there exists an abnormal state where the exhaust gas purification rate is deteriorated due to a variation in the air-fuel ratio among cylinders based on the deterioration degree of the exhaust gas purification rate determined by the exhaust gas purification rate deterioration degree determination, wherein the exhaust gas purification rate deterioration degree determination calculates the deterioration degree of the exhaust gas purification rate by integrating an intake air quantity during a period, in which the sub feedback correction amount is continuously guarded with the guard value, and the abnormality diagnosis determines whether there exists the abnormal state when the catalyst and both of the upstream sensor and the downstream sensor are in normal condition.