Exhaust purification system

TL;DR: In this paper, an exhaust purification system is provided with: a NOx storage-reduction catalyst 32 that stores NOx contained in exhaust, and, in an exhaust-rich state, reduces and purifies the stored NOx; and a nox purge rich control unit 140.

Abstract: An exhaust purification system is provided with: a NOx storage-reduction catalyst 32 that, in an exhaust-lean state, stores NOx contained in exhaust, and, in an exhaust-rich state, reduces and purifies the stored NOx; and a NOx purge rich control unit 140. When the catalyst temperature of the NOx storage-reduction catalyst 32 is greater than or equal to a catalyst temperature threshold Temp _cat_std and the NOx storage amount of the NOx storage-reduction catalyst is greater than or equal to a NOx storage amount threshold STR _thr_NOx , the NOx purge rich control unit 140 executes a NOx purge that reduces and purifies the stored NOx by putting the exhaust into a rich state via fuel injection control. When the catalyst temperature is greater than or equal to a catalyst temperature threshold Temp _cat_Hi that is higher than the catalyst temperature threshold Temp _cat_std , the NOx purge rich control unit 140 executes the NOx purge even if the NOx storage amount is less than the NOx storage amount threshold STR _thr_NOx .