| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve NOx purifying efficiency and fuel consumption by controlling rich spike so as to be gradually rich while detecting an NOx desorbing characteristic in an NOx occluding catalyst at the time of rich spike. SOLUTION: An exhaust emission control device for an internal combustion engine is provided with an NOx occluding catalyst 7 adsorption-holding NOx in exhaust at the time of a lean air-fuel ratio and desorbing and reducing the adsorption-held NOx at the time of a rich air-fuel ratio, and sensors 15, 17 for detecting air-fuel ratios upstream and downstream of the NOx occluding catalyst 7. When the NOx adsorption-holding quantity of the NOx occluding catalyst 7 reaches the specified value, the air-fuel ratio is temporarily made rich, and the degree of richness is gradually heightened. This enrichment control is completed when the air-fuel ratios upstream and downstream of the catalyst almost coincide with each other. HC can therefore be supplied in proper quantity for NOx desorbing and reducing reaction, and reaction can be completed in a short period of time.</p> |
