| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent deterioration in emission by properly knowing the present NOx occlusion function in a NOx catalyst, and also to prevent deterioration in fuel economy by recovering the allowable occlusion amount of the NOx catalyst. SOLUTION: An amount of a required reducing agent required for reducing NOx occluded in the present NOx catalyst 24 is calculated, based on an output from an A/F sensor 32, and a straight line representing a relationship between the occlusion amount of the NOx catalyst 24 and the amount of the required reducing agent is calculated. According to the result of comparison between the straight line and the occlusion amount of the present NOx catalyst 24, allowable occlusion amount of the NOx catalyst 24 is set. When the allowable occlusion amount is decreased, depending on a degree of sulfur poisoning in the NOx catalyst 24, air-fuel ratio rich control and temperature rise are carried out and the allowable occlusion amount is recovered. Accordingly, the present NOx occlusion function in the NOx catalyst 24 can be known properly, whereby the deterioration in emission can be prevented, and the deterioration in the fuel economy can be prevented, by recovering the allowable occlusion amount of the NOx catalyst 24.</p> |
