| 摘要 |
PROBLEM TO BE SOLVED: To suppress the lowering of output performance due to an increase in exhaust emission resistance while sufficiently securing the dispersion of urea water in an exhaust emission passage in a urea SCR system. SOLUTION: A mixing means 15 for promoting the mixing of the urea water supplied by a urea water supply means 13 with exhaust emission is installed between the urea water supply means 13 and a selective reduction catalyst 16 in the exhaust emission passage 3. The exhaust emission control device comprises: a bypass passage 21 bypassing the mixing means 15 by communicating the downstream side of the urea water supply means 13 with the upstream side of the selective reduction catalyst 16; a control valve 32 capable of controlling the communication state of the bypass passage 21; and a control means 50 for controlling the operating state of the control valve 32. The control means 50 controls the control valve 32 to open the bypass passage 21 when an engine load is equal to or higher than a predetermined value or an engine rotational speed is equal to or higher than a predetermined value. COPYRIGHT: (C)2009,JPO&INPIT
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