DEVICE FOR DETECTING DETERIORATION OF NOx CATALYST OF SELECTIVE REDUCTION TYPE

摘要

The purpose of the present invention is to detect, with higher accuracy, a deterioration of an NOx catalyst of the selective reduction type disposed in the exhaust passage of an internal combustion engine. This device for detecting a deterioration of a selective reduction type NOx catalyst is equipped with an NOx removal percentage calculation unit that calculates the percentage of NOx removal with the selective reduction type NOx catalyst on the basis of the NOx concentration of exhaust that flows into the selective reduction type NOx catalyst and the NOx concentration of the exhaust that flows out of the selective reduction type NOx catalyst. When the temperature of the selective reduction type NOx catalyst is not lower than a temperature (Tc0) at which the percentage of NOx removal with the selective reduction type NOx catalyst, the degree of deterioration of which is the upper limit of a permissible range, starts decreasing as the temperature of the selective reduction type NOx catalyst rises, then whether the selective reduction type NOx catalyst has deteriorated or not is assessed on the basis of the NOx removal percentage.