Abnormality diagnosis system for exhaust gas purification apparatus

Abstract

An object of the disclosure is to provide a technology that enables abnormality diagnosis of an NOx trap catalyst to make the diagnosis that the NOx trap catalyst is abnormal even if the degree of deterioration of the NOx trap catalyst is relatively small yet. When performing abnormality diagnosis of an NOx trap catalyst, a system according to the disclosure performs a lean temperature raising process, which is the process of raising the temperature of the NOx trap catalyst to or above a predetermined temperature while keeping the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst at a lean air-fuel ratio. The system diagnoses abnormality of the NOx trap catalyst on the basis of the NOx storage efficiency of the NOx trap catalyst or a parameter correlating with that NOx storage efficiency after the completion of the lean temperature raise process.

Dependencies are inferred from the claim text.