| 摘要 |
<P>PROBLEM TO BE SOLVED: To make a NOx storage reduction catalyst surely release NOx even if a temperature of the NOx storage reduction catalyst is low. <P>SOLUTION: The NOx storage reduction catalyst 24 absorbing NOx in exhaust gas when air fuel ratio of flow-in exhaust gas is lean and releasing absorbed NOx when air fuel ratio of flow-in exhaust gas becomes rich is arranged in an engine exhaust gas passage, and a fuel adding valve 28 is arranged in the engine exhaust gas passage in the upstream of the NOx storage reduction catalyst. Fuel is added from the fuel adding valve to make exhaust gas flowing into the NOx storage reduction catalyst temporally rich when NOx need to be released from the NOx storage reduction catalyst. When a temperature of the NOx storage reduction catalyst is lower than a predetermined established temperature, first temperature raise control for raising a temperature of the NOx storage reduction catalyst is executed under the existence of a large quantity of oxygen in a first part of a period of fuel addition from the fuel adding valve and second temperature raise control for raising a temperature of the NOx storage reduction catalyst is executed under the existence of a small quantity of oxygen in a later part of the period of fuel addition. <P>COPYRIGHT: (C)2008,JPO&INPIT |
