DETERIORATION DIAGNOSTIC DEVICE FOR EXHAUST EMISSION CONTROL DEVICE

PROBLEM TO BE SOLVED: To provide a catalyst evaluation method evaluating the presence or absence of deterioration of a catalyst with higher accuracy and hardly influenced by a catalyst condition at the time of evaluation. SOLUTION: This deterioration diagnostic device for an exhaust emission control device diagnoses the deterioration state of the exhaust emission control device arranged in an exhaust passage on the basis of the sensor value of an exhaust gas sensor provided on the downstream side of the exhaust emission control device, and is provided with a detecting signal generating means generating a detecting signal having a specific frequency component and calculating a fuel injection quantity by multiplying the detecting signal by a reference fuel injection quantity, and an exhaust emission control device evaluating means extracting a frequency response corresponding to the detecting signal from output of the exhaust gas sensor of an internal combustion engine to the fuel injection quantity and determining a state of the exhaust emission control device based on the frequency response. COPYRIGHT: (C)2005,JPO&NCIPI