APPARATUS FOR DIAGNOSIS OF ABNORMALITY IN EXHAUST GAS PURIFICATION SYSTEM

摘要

In an exhaust gas purification system in which an aqueous urea solution is added to a NOx selective reduction catalyst (which is placed in an exhaust gas passage in an internal combustion engine) by means of a urea addition device, a sensor for detecting the concentration of ammonia is arranged on the downstream side of the NOx catalyst. The addition of a predetermined amount of the aqueous urea solution is carried out during the fuel cut.Based on the output from the sensor, the abnormality in at least one of the urea addition device and the aqueous urea solution is detected. By adding the aqueous urea solution during the fuel cut, it becomes possible to prevent the reactive consumption between urea and NOx, and it becomes also possible to produce an output corresponding to the amount of the aqueous urea solution from the sensor. By comparing the output state with a normal one, it can be detected whether or not a proper amount of an aqueous urea solution having proper quality is added.