EXHAUST EMISSION CONTROL SYSTEM AND METHOD FOR INTERNAL COMBUSTION ENGINES

摘要

An NOx storage-and-reduction type catalyst is used which exhibits a saturated NOx storage amount of 5 g or more as NO2 with respect to 1 liter of a catalyst volume at 500 DEG C, and rich spiking is controlled so that an actual NOx storage amount of the NOx storage-and-reduction type catalyst becomes 50% or less of the saturated NOx storage amount. Since the saturated NOx storage amount is large, the NOx storage amount is large even when it is 50% or less, it is possible to prolong intervals of the rich spiking. Then, since NOx storage component stores NOx preferentially into the sites which are likely to store and release NOx, a reduction efficiency is high. Therefore, while prolonging the intervals of the rich spiking and sustaining an effect of mileage improvement, it is possible to improve the reduction efficiency of NOx.