EXHAUST EMISSION CONTROL SYSTEM

摘要

PROBLEM TO BE SOLVED: To perform an effective prevention of NH3 slip or an erroneous diagnosis when an exhaust temperature is rapidly increased at an exhaust emission control system.SOLUTION: This invention relates to an exhaust emission control system comprising SCR41; a NOx sensor 22 arranged at the downstream side of SCR41; and a NOx purifying control part 51 for controlling an amount of injection of urea water to SCR41 and performing an abnormality diagnosis on the basis of the detected value of the NOx sensor 22. The control system further comprises an exhaust gas temperature sensor 21 getting a temperature of exhaust gas flowing into SCR21; a temperature increasing rate calculation part 54 for calculating a temperature increasing rate in which the exhaust gas temperature got at the exhaust gas temperature sensor 21 reaches from the predetermined first temperature to the second temperature; and a prohibition part 55 for prohibiting an abnormality diagnosis performed by NOx purifying control part 51 when the temperature increasing rate calculated by the temperature increasing rate calculation part 54 is higher than a predetermined determination threshold.