| 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 space velocity SV for a catalyst of exhaust gas corresponding to the amount of oxygen in the exhaust gas per unit of time that flows into a NOx trap catalyst 13 is calculated. When this space velocity SV is small, 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 SV is large, 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 |
