| 摘要 |
PURPOSE:To improve a NOx purifying rate of a lean NOx catalyst by cooling the lean NOx catalyst in a temperature region where the bed temperature of the lean NOx catalyst shows the activity and then stopping the cooling to carry out the cooling- heating cycle for raising the catalyst bed temperature. CONSTITUTION:An exhaust system of an internal combustion engine 2 capable of lean combustion for an automobile is provided with a lean NOx catalyst 4 and a bypass path 6 for bypassing the catalyst and further a bypass valve 8 therebetween for changing over the flow of exhaust. On the basis of a signal from a running condition detecting means 10 for detecting the running condition of the internal combustion engine 2, a fuel injection amount and ignition timing are controlled by a combustion control means 12 and the change-over of the bypass valve 8 is controlled by a bypass controlling means 14. Then, in the bypass control means 4, when the internal combustion engine 2 is run with a small exhaust amount of NOx and the catalyst bed temperature exceeds a first predetermined temperature, the bypass valve 8 is changed over to bypass the catalyst, and when the catalyst bed temperature is under a second predetermined temperature, the bypass valve 8 is changed over not to bypass the catalyst. |
