| 摘要 |
<P>PROBLEM TO BE SOLVED: To assuredly reduce purge NOx in the timing of reduce-purging NOx trap catalyst 13, if an exhaust emission control device includes the NOx trap catalyst 13 that traps NOx in exhaust in an exhaust passage 10 of an engine 1 when the air-fuel ratio of the flow-in exhaust gas is lean, and that reduce- purges the trapped NOx when the air-fuel ratio of the flow-in exhaust gas is rich. <P>SOLUTION: The temperature of a NOx trap catalyst 13 is detected by a sensor 24 or the like, when the catalyst temperature Tc is high, the air-fuel ratio of the exhaust gas is made rich using a normal method (for example, by performing EGR and controlling an inlet throttle valve). On the other hand, when the catalyst temperature is low, the air-fuel ratio of the exhaust gas is made rich using a method in which the amount of oxygen in the exhaust gas can be made smaller than by the normal method (for example, by stopping EGR and controlling the inlet throttle valve). <P>COPYRIGHT: (C)2003,JPO |
