| 摘要 |
<P>PROBLEM TO BE SOLVED: To restrain the generation of an ammonia slip while improving reduction efficiency, in a selective reduction catalyst system for reducing NOx by adding urea water. <P>SOLUTION: This exhaust emission control device has a catalyst 50 arranged in an exhaust passage 10 of an internal combustion engine 1 and selectively reducing the NOx included in exhaust gas with ammonia generated by hydrolyzing the urea water as a reducing agent, and a means 100 for controlling a urea water adding valve 62 for adding the urea water from the catalyst upstream side of the exhaust passage and an injection quantity of the urea water 63 according to a catalyst state. The control means 100 improves the dispersiveness of the reducing agent in the catalyst 50 by temporarily injecting urea exceeding a predetermined quantity when a state of being smaller than a predetermined value in the injection quantity of the urea water 63 is continued for a predetermined time. <P>COPYRIGHT: (C)2011,JPO&INPIT |
