| 摘要 |
<P>PROBLEM TO BE SOLVED: To improve purification rate of nitrogen oxide in a selective catalytic reduction catalyst while avoiding complication of a system composition and suppressing rise in cost. <P>SOLUTION: In an exhaust emission control device, whether the present NO/NOx ratio is larger than 0.5 or not is determined (S2). If the NO/NOx ratio is larger than 0.5, a post injection amount is set based on engine rotation frequency NE and the NO/NOx ratio (S4) to execute post injection. The execution of the post injection raises temperature of exhaust gas exhausted from an engine and promotes oxidation reaction of an oxidation catalyst, and the NO/NOx ratio of the exhaust gas supplied to the SCR (selective catalytic reduction) catalyst is controlled to be 0.5. The NOx purification rate of the SCR catalyst can be improved thereby without complicating the system composition, which can suppress the rise in cost. <P>COPYRIGHT: (C)2010,JPO&INPIT |
