| 摘要 |
PROBLEM TO BE SOLVED: To suppress an unburnt gas from flowing out of an exhaust purification catalyst in addition to NOx.SOLUTION: An internal combustion engine comprises: an exhaust purification catalyst 20; a downstream-side air-fuel ratio sensor 41 which is arranged at a downstream side of the exhaust purification catalyst; and an air-fuel ratio control device 31 which controls an air-fuel ratio of an exhaust gas which flows into the exhaust purification catalyst. The air-fuel ratio control device performs: fundamental air-fuel ratio control for alternately and repeatedly switching the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst between a lean air-fuel ratio and a rich air-fuel ratio so that an oxygen occlusion amount OSA of the exhaust purification catalyst is alternately changed to an upper limit value Cup which is smaller than a maximum occlusive oxygen amount Cmax, and to a lower limit value Clow which is larger than zero; and temporary air-fuel ratio control for maintaining the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst at prescribed timing until an output air-fuel ratio AFdwn of the downstream-side air-fuel ratio sensor reaches a rich determination air-fuel ratio AFrich after the switching is performed a plurality of times repeatedly by the fundamental air-fuel ratio control.SELECTED DRAWING: Figure 6 |
