| 摘要 |
PROBLEM TO BE SOLVED: To efficiently execute an SOX poisoning elimination operation of a NOX storage/reduction catalyst. SOLUTION: The NOX storage/reduction catalyst 7 is disposed in an exhaust passage 2 of an engine 1, NOX in an exhaust gas is stored in the catalyst 7 during a lean air-fuel ratio operation of the engine, and the stored NOX is reduced by changing over the air-fuel ratio of the engine to a short-time rich air-fuel ratio. An electronic control unit (ECU) 30 carries out a SOX poisoning elimination operation for keeping the catalyst at high temperature and at a rich air-fuel ratio when SOX is stored in the catalyst 7, and SOX poisoning causing the degradation of NOX storage capability occurs. When an operation region of the engine is divided into a plurality of regions and the NOX storage capability of the catalyst 7 is lowered as compared with a determination value set for every operation region, the ECU determines that the SOX poisoning occurs in the region and carries out the SOX poisoning elimination operation. Thereby, the SOX poisoning elimination operation is executed only when it is really necessary, so that increase of fuel consumption and deterioration of exhaust gas quality can be prevented. COPYRIGHT: (C)2003,JPO
|
