APPARATUS FOR DETECTING DETERIORATION OF NOx SELECTIVE REDUCTION CATALYST

摘要

An object of the invention is to detect deterioration of an NOx selective reduction catalyst provided in an exhaust passage of an internal combustion engine with improved accuracy. An apparatus for detecting deterioration of NOx selective reduction catalyst according to the invention has an NOx purification rate calculation unit that calculates the NOx purification rate in the NOx selective reduction catalyst based on the NOx concentration in the exhaust gas flowing into the NOx selective reduction catalyst and the NOx concentration in the exhaust gas flowing out of the NOx selective reduction catalyst. A determination as to whether the NOx selective reduction catalyst is deteriorated or not is made based on the NOx purification rate at a time when the temperature of the NOx selective reduction catalyst is equal to or higher than a temperature (Tc0) at which the NOx purification rate will start to decrease with a rise in the temperature of the NOx selective reduction catalyst if the degree of deterioration of the NOx selective reduction catalyst is at the upper limit of an allowable range.