| 摘要 |
An exhaust gas purification apparatus includes an NOx reduction catalytic converter disposed in an engine exhaust passage to reductively purify NOx in exhaust gas using ammonia or its precursor as a reducing agent, a first concentration sensor which detects an ammonia concentration in an exhaust gas moving on a downstream side of the NOx reduction catalytic converter, and a control unit which incorporates therein a computer. The control unit conducts calculation to estimate an ammonia concentration in the exhaust gas moving on the downstream side of the NOx reduction catalytic converter, and when a difference between the ammonia concentration detected by the first concentration sensor and the estimated ammonia concentration by the calculation becomes larger than a first predetermined value, determines that the NOx reduction catalytic converter is deteriorated. |
