Abnormality diagnosis device of internal combustion engine

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.