EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of restricting the influence of the determination of abnormality to the exhausting characteristic and the operability at the minimum by carrying out the detection of abnormality of an oxygen concentration sensor provided downstream from an NOx emission control device with the optimal timing. SOLUTION: At the engine starting time point (t0), when the output TVO2 of an O2 sensor 19 is lower than the reference voltage TVREF, if the sensor output TVO2 exceeds the reference voltage TVREF before carrying out of the lean operation or during the carry-out of the deterioration determination of a NOx emission control device 15, the O2 sensor is judged to be normal. When the O2 sensor output TVO2 doesn't exceed the reference voltage TVREF till the conclusion of the deterioration determining process, the operation for enriching the air-fuel ratio is prolonged, and when the O2 sensor output TVO2 exceeds the reference voltage TVREF, the O2 sensor is judged to be normal, and when it doesn't exceed, the O2 sensor is judged to be abnormal.