EXHAUST EMISSION CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES

摘要

A particulate filter (18) is arranged in the engine exhaust passage in such a way that only the inner wall surface of a downstream end open cell (61d) of the particulate filter (18) is covered with a NOx adsorbent (62a) while the inner wall surface of an upstream end open cell (61u) is covered with an HC adsorbent (63a). Particulates in the exhaust are trapped by either the HC adsorbent (63a) or cell walls (60) of the particulate filter (18), and thereby prevented from reaching the NOx adsorbent (62a). When the catalyst temperature is low, NOx in the exhaust is adsorbed by the NOx adsorbent (62a), and hydrocarbon (HC) is adsorbed by the HC adsorbent (63a). When the catalyst temperature is high, the adsorbed NOx is desorbed from the NOx adsorbent (62a) and the adsorbed HC is desorbed from the HC adsorbent (63a) and reduces the NOx discharged from the NOx adsorbent (62a).