| 摘要 |
PROBLEM TO BE SOLVED: To diagnose a deterioration state of an exhaust emission control device without arranging a NOsensor in an exhaust passage at a downstream side rather than a downstream-side SCR catalyst, in a system which diagnoses the deterioration of the exhaust emission control device having two SCR catalysts which are arranged in series along a flow of exhaust emission.SOLUTION: In a deterioration diagnosis system of an exhaust emission control device having an upstream-side SCR catalyst and a downstream-side SCR catalyst which is arranged at a downstream side rather than the upstream-side SCR catalyst, when an upstream-side NOpurification rate being a NOpurification rate of the upstream-side SCR catalyst is smaller than a lower limit value of the NOpurification rate which should be obtained in the upstream-side SCR catalyst and the downstream-side SCR catalyst as a whole, and when larger than a lower limit value of the NOpurification rate which should be singly obtained in the upstream-side SCR catalyst, a prescribed amount of additives are added from an adding device, and when a change amount of the upstream-side NOpurification rate before and after the addition is smaller than a prescribed threshold, it is diagnosed that the exhaust emission control device is deteriorated.SELECTED DRAWING: Figure 2 |
