| 摘要 |
PROBLEM TO BE SOLVED: To prevent discharge of HC into the air at the early stage of the NOx purge in particular while suppressing needless fuel consumption by minimizing the degree of air-fuel ratio enrichment for an NOx purge and a S purge when executing the NOx purge and S purge during operation of an engine 1 in which a preliminary catalyst 24 and an NOx occlusion type main catalyst 26 are respectively provided to the upstream side and downstream side of an exhaust system. SOLUTION: A plurality of cylinders 2, 2, ... of an engine 1 are sorted into a rich side and a lean side for NOx purge. An air-fuel ratio is controlled to be slightly richer than a theoretical air-fuel ratio in average. Thereby, the generation quantity of CO which is a reducing agent component reacting from relatively low temperature is increased. The HC and NOx during rich and lean exhaust are purified by a preliminary catalyst 24 on the upstream side. The exhaust containing abundantly only CO is fed to a main catalyst 26 on the downstream side. As a result, even if the temperature of the catalyst 26 is decreased, the device prevents discharge of the HC or the like into the air and can promptly activate the catalyst 26 by reaction heat of the CO. COPYRIGHT: (C)2006,JPO&NCIPI
|
