DETERIORATION DIAGNOSTIC DEVICE FOR EXHAUST EMISSION CONTROL DEVICE

摘要

PROBLEM TO BE SOLVED: To accurately diagnose the deterioration of a selective reduction catalyst by using a sensor for measuring the air-fuel ratio of exhaust gas flowing into an exhaust emission control device including the SCR catalyst and a sensor for measuring the air-fuel ratio of the exhaust gas flowing out of the exhaust emission control device.SOLUTION: In a period for executing induction processing as processing for inducing a water-gas-shift reaction in a catalyst arranged further upstream of the SCR catalyst by means of changing the air-fuel ratio of exhaust gas exhausted from an internal combustion engine from a lean air-fuel ratio into a predetermined rich air-fuel ratio, a deterioration diagnostic device for the exhaust emission control device uses air-fuel ratio sensors for measuring the air-fuel ratio of the exhaust gas flowing into the SCR catalyst and the air-fuel ratio of the exhaust gas flowing out of the SCR catalyst, respectively, and diagnoses the deterioration of the SCR catalyst on the basis of values measured by the sensors. It executes the induction processing when the amount of NHadsorbed onto the SCR catalyst is a predetermined amount or lower.SELECTED DRAWING: Figure 5