| 摘要 |
PROBLEM TO BE SOLVED: To provide a control method of an exhaust gas post-treatment device which can appropriately control timing for returning to a rich state after an S-purge, and urea water injection timing after PM regeneration.SOLUTION: A DOC 25, a NOx occlusion reduction catalyst 26 and a DPF 27 are connected to an exhaust pipe 20 at a downstream side of an exhaust pipe injector 23 which is arranged in the exhaust pipe 20 of an engine E. NOx in an exhaust gas is occluded by the NOx occlusion reduction catalyst 26 on condition that an air-fuel ratio is lean, and the occluded NOx is reduced and purified on condition that the air-fuel ratio is rich. At this time, PMs are regenerated by raising an exhaust gas temperature when the PMs are deposited on the DPF 27 by a prescribed amount, after that, the S-purge of sulfur occluded in the NOx occlusion reduction catalyst 26 is performed by further raising the exhaust gas temperature, a rich condition is prohibited during a period of the S-purge from a PM regeneration period, and after the completion of the S-purge, the rich-prohibited condition is continued until a difference between an inlet temperature of the DOC 25 and an outlet temperature of the NOx occlusion reduction catalyst 26 reaches a value not larger than a set threshold. |
