Patent ID: 7975470

Claim:
An apparatus for judging a condition of injection of reducing agent in an exhaust gas purification system comprising a reduction catalyst disposed in an exhaust system of an engine to reduce and purify nitrogen oxide in an exhaust gas, and a reducing agent injection supply means that mixes liquid reducing agent in an amount required depending on an engine operating state with air and injection-supplies this air-mixed reducing agent into the exhaust gas flowing on an upstream side of the reduction catalyst, wherein there is provided such a configuration that a condition of injection of the liquid reducing agent is judged by using at least one of a plurality of judgment means selected from: a first judgment means that judges that the condition of injection of the liquid reducing agent is abnormal when a consumption of the air during traveling of a predetermined distance is not within a predetermined range; a second judgment means that judges that the condition of injection of the liquid reducing agent is abnormal when a consumption of the air during consuming of a predetermined amount of fuel is not within a predetermined range; and a third judgment means that judges that the condition of injection of the liquid reducing agent is abnormal when a consumption of the air during traveling for a predetermined time is not within a predetermined range.