APPARATUS FOR DIAGNOSING DETERIORATION OF NOx CATALYST

摘要

This invention provides an apparatus for diagnosing the deterioration of an NO_x catalyst. In this apparatus, NO_x is supplied, to an occlusion/reduction-type NO_x catalyst, in such an amount that a criteria catalyst, which is in a boundary between a deteriorated state and a normal state, can occlude. Thereafter, a reducing agent in an amount corresponding to the NO_x amount is supplied by rich spike. The level of deterioration of the NO_x catalyst is determined based on the output of an NO_x sensor. In this apparatus, since the deterioration is determined based on only the level of the output of the NO_x sensor, the diagnosis of deterioration can be carried out with high accuracy. Further, since any excess reducing agent is not supplied during a period in which the catalyst is normal, and, thus, a deterioration in fuel consumption can be prevented.