Abnormality judging system for exhaust gas purification apparatus of internal combustion engine

Abstract

The abnormality of an NHsensor is judged highly accurately. For this purpose, an abnormality judging system for an exhaust gas purification apparatus of an internal combustion engine comprises a selective catalytic reduction NOx catalyst which is provided at an exhaust gas passage of the internal combustion engine and which reduces NOx by using NHas a reducing agent, a supply device which supplies the reducing agent from an upstream side from the NOx catalyst, a NOx sensor which detects NOx and NHon a downstream side from the NOx catalyst, and an NHsensor which detects NHon a downstream side from the NOx catalyst, wherein it is judged that the NHsensor has any abnormality if an absolute value of a difference between an estimated NHconcentration as a difference between a detection value of the NOx sensor and an estimated value of a NOx concentration and an NHconcentration detected by the NHsensor is not less than a threshold value when NHflows out from the selective catalytic reduction NOx catalyst.