INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To always accurately determine the deterioration of NOx catalyst regardless of the state of the NOx sensor. SOLUTION: The temperature of the NOx catalyst 19, which occludes NOx in the exhaust in an excess oxygen atmosphere and discharges the occluded NOx in a decreased oxygen atmosphere, is detected by a temperature sensor 21. Also, the NOx concentration downstream of the NOx catalyst 19 is detected by a NOx sensor 22. The deterioration state value of the NOx catalyst 19 is determined based on the purification rate of NOx at low and high temperatures corresponding to temperature information against time and concentration information against time. Then, the deterioration state value and the deterioration determination value are compared to determine the deterioration of the NOx catalyst 19. Further, deterioration of the NOx catalyst 19 is determined by relative detected values of the NOx sensor 22. Accordingly, deterioration of the NOx catalyst 19 is always accurately determined regardless of the state of the NOx sensor 22.