EXHAUST EMISSION PURIFYING DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To improve the NOx trap rate of a zeolite catalyst 18 and to reduce NOx to be discharged without being purified by suppressing the NOx desorption amount in a NOx desorption condition when NOx trap catalyst 20 to trap NOx is provided in the exhaust system of an engine 1 when air fuel ratio is lean, and further a zeolite catalyst 18 including zeolite, capable of trapping NOx at a time of a low temperature is provided on an upstream side. SOLUTION: Oxygen is fed to the zeolite catalyst 18 by making the air fuel ratio of the engine 1 lean or a second air supply. On the other hand, when the zeolite catalyst 18 is under a condition of the NOx desorption (the zeolist catalyst temperature detected by a thermal sensor 19 is higher than a predetermined value), and NOx trap catalyst 20 on a downstream side is deactivated (the NOx trap catalyst temperature detected by a thermal sensor 21 is lower than a predetermined value), the oxygen supply is stopped.