| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device improving NOx conversion rate in a wide operation range by suitably controlling flow rate of exhaust gas passing through an oxidation catalyst and getting ratio of NO and NO<SB>2</SB>in exhaust gas introduced in a reducing catalyst close to a predetermined ratio. <P>SOLUTION: NOx reducing catalyst 16 reducing and converting NOx with using reducing agent is provided in an exhaust pipe 12 of an engine 10. Flow rate control valves 20A, 20B capable of controlling a exhaust gas passage area in multiple stages, and oxidation catalysts 22A, 22B having different oxidation capacity oxidizing NO to NO<SB>2</SB>are provided in branch pipes 12A, 12B branching the exhaust pipe 12 positioned in an exhaust gas upstream thereof into two respectively. A control unit 26 operates exhaust gas volume flow quantity Fe based on intake air volume flow quantity Fi detected by an air flow sensor 26 and fuel consumption rate C read from an engine control unit 30, and suitably controls flow rate control valves 20A, 20A according to exhaust gas volume flow rate Fe and catalyst temperature T indirectly detected by an exhaust gas temperature sensor 24 to make ratio of NO and NO<SB>2</SB>in exhaust gas introduced to the NOx reducing catalyst 16 close to the predetermined ratio. <P>COPYRIGHT: (C)2007,JPO&INPIT |
