| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device with a NOx storage type catalyst 38 in an exhaust passage 34 for an engine 1, maximizing the purification of exhaust gas by keeping the NOx storage capacity of the catalyst 38 to a maximum at all times. <P>SOLUTION: The NOx storage amount of the NOx catalyst 38 is estimated in accordance with the operation history of the engine 1. When the estimated NOx storage amount exceeds a boundary value (a target storage amount) sufficient to keep the NOx storage capacity of the NOx catalyst 38 at nearly 100%, NOx purge is performed to release stored NOx for reduction and purification (SA5-SA7). As the boundary value is smaller with the deterioration of the NOx catalyst 38, the target storage amount as a threshold value for the NOx purge is corrected to be smaller. <P>COPYRIGHT: (C)2004,JPO |
