| 摘要 |
PROBLEM TO BE SOLVED: To quickly supply a reducing agent to the whole NOx occlusion-reduction catalyst. SOLUTION: A reducing agent injection valve 27 is arranged in the exhaust passage in the upstream of an NOx occlusion-reduction catalyst 17 arranged in the exhaust passage of an engine, an upstream side exhaust control valve 22 is arranged in the upstream of the injection valve, and a bypass control valve 21 is arranged in a bypass pipe 20 branched from the exhaust passage in the upstream of the exhaust control valve. When the engine is normally operated, the bypass control valve 21 is closed, the upstream side exhaust control valve 22 and the downstream side exhaust control valve 23 are fully opened, and NOx exhausted from a combustion chamber 3 is absorbed by the NOx occlusion-reduction catalyst 17. When the load on the engine is low, the bypass control valve 21 is fully opened, the upstream side exhaust control valve 22 and the downstream side exhaust control valve 23 are closed, and a reducing agent is supplied to the reducing agent injection valve 27. At this time, the exhaust passage in the downstream of the NOx occlusion-reduction catalyst 17, and a surge tank 10 are connected by an EGR pipe 24 to apply negative pressure to the exhaust- downstream end of the NOx occlusion-reduction catalyst 17. |
