EXHAUST EMISSION CONTROL DEVICE FOR ENGINE

摘要

PROBLEM TO BE SOLVED: To improve exhaust emission control performance.SOLUTION: An exhaust passage 10 of an engine 2 includes: an NOx occlusion catalyst 11 for occluding NOx in exhaust gas; and a selective reduction catalyst 13 provided downstream of the NOx occlusion catalyst 11 for reducing and eliminating NOx by using ammonia generated by hydrolyzing urea water. An engine control unit 30 of the engine estimates NOx occlusion amount Qa of the NOx occlusion catalyst 11, performs purge control for reducing and eliminating NOx occluded in the NOx occlusion catalyst 11 by increasing an exhaust temperature of the engine 2 and making an air-fuel ratio of the exhaust gas stoichiometric or rich when the NOx occlusion amount Qa exceeds a predetermined value A, and performs temperature increase control for making the air-fuel ratio of the exhaust gas lean and increasing the exhaust temperature to an activation temperature of the selective reduction catalyst 13 or higher when the NOx occlusion amount Qa becomes larger than a predetermined value C that is set larger than the predetermined value A and larger than a slip determination value B of the NOx occlusion catalyst 11.SELECTED DRAWING: Figure 1