| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a device for diagnosing catalyst degradation, in which a cost increase is suppressed and which can determine to what extent a catalyst has degraded. <P>SOLUTION: The device for diagnosing the catalyst degradation includes: a selective reduction type catalyst 25 which is provided in an exhaust passage 19 of an engine 10 and which reduces and purifies NOx contained in exhaust gas circulating through the exhaust passage 19; an NO<SB POS="POST">2</SB>ratio obtaining means 33 for obtaining an NO<SB POS="POST">2</SB>ratio as a ratio of NO<SB POS="POST">2</SB>to NOx contained in the exhaust gas circulating through the selective reduction type catalyst 25; a NOx purification ratio obtaining means 34 for obtaining a NOx purification ratio as a ratio of NOx reduced and purified by the selective reduction type catalyst 25, on the basis of the amount of NOx on the upstream and downstream sides of the selective reduction type catalyst 25; and a degradation determining means 35 for determining the degree of the degradation of the selective reduction type catalyst 25 on the basis of the NO<SB POS="POST">2</SB>ratio obtained by the NO<SB POS="POST">2</SB>ratio obtaining means 33, the NOx purification ratio obtained by the NOx purification ratio obtaining means 34, and a temperature of the selective reduction type catalyst 25. <P>COPYRIGHT: (C)2012,JPO&INPIT |
