| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control method and an exhaust emission control system capable of improving NOx purification rate while preventing deterioration of fuel economy and HC discharge to atmosphere in an exhaust emission control system using a NOx occlusion reduction type catalyst for control of NOx in exhaust gas. <P>SOLUTION: When it is determined that air fuel ratio of exhaust gas need to be made rich to recover NOx occlusion capacity of the NOx occlusion reduction type catalyst, after setting air fuel ratio of exhaust gas to a predetermined first target air fuel ratio Ft1 set higher than stoichiometric condition by performing intake system rich control for reducing air fuel ratio of exhaust gas by controlling at least one of EGR quantity and intake air quantity, fuel system rich control for reducing air fuel ratio by adding fuel in exhaust gas is performed in addition to intake system rich control to make air fuel ratio of exhaust gas set to a predetermined second target air fuel ratio Ft2 set lower then the first target air fuel ratio Ft1. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
