ABNORMALITY DIAGNOSTIC DEVICE OF INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To provide an abnormality diagnostic device which can quickly and exactly diagnose an abnormality of an exhaust emission control catalyst.SOLUTION: An abnormality diagnostic device of an internal combustion engine having an external emission control catalyst 20 which can store oxygen is provided that comprises: a downstream-side air-fuel ratio sensor 41 disposed downstream from the catalyst; and a catalyst abnormality diagnostic device which diagnoses an abnormality of the exhaust emission control catalyst on the basis of an output air-fuel ratio of the downstream-side air-fuel ratio sensor when active air-fuel ratio control is performed. The catalyst abnormality diagnostic device calculates a maximum storable oxygen amount of the exhaust emission control catalyst on the basis of an oxygen amount which is stored into or discharged from the exhaust emission control catalyst within an air-fuel ratio inversion period in the active air-fuel ratio control, and diagnoses the abnormality of the exhaust emission control catalyst on the basis of the calculation result. Even when the calculated maximum storable oxygen amount is equal to or higher than a preset lower-limit storage amount, the catalyst abnormality diagnostic device determines that there is the abnormality in the exhaust emission control catalyst when a period during which the output air-fuel ratio of the downstream-side air-fuel ratio sensor is in the vicinity of a stoichiometric air-fuel ratio out of the air-fuel ratio inversion period or the ratio thereof is a reference value or less.