| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purification method and an exhaust gas purification system which can prevent leaks of both non-purified NOx generated in the early stage of reproduction for the reproduction control of a NOx occlusion-reduction type catalyst and an unused reducing agent such as HC, CO generated in the late stage of reproduction. <P>SOLUTION: The exhaust gas purification system 10 is provided with the NOx occlusion-reduction type catalyst 50. The amount of the reducing agent is added which is commensurate with the amount of oxygen discharged in the early stage of reproduction control, and the first half rich control is performed which makes a target air/fuel ratio smaller than a theoretical air/fuel ratio. Then in the first half rich control, the completion of the discharge of the oxygen is determined by the concentration of oxygen on the downstream side of the NOx occlusion-reduction type catalyst 50. When it is determined that the discharge of the oxygen has been completed, the second half rich control, which is near the theoretical air/fuel ratio, is performed. The second half rich control makes the target air/fuel ratio larger than the first half rich control does. Thus, the reproduction of NOx of the NOx occlusion-reduction type catalyst 50 is performed. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
