EXHAUST EMISSION CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES

摘要

A particulate filter (18) is arranged in the exhaust passage of an engine. Only the inner wall surface of downstream end open cells (61d) of the particulate filter (18) is covered with a NOx adsorbent (62a), and the inner wall surface of the upstream end open cells (61u) is covered with a HC adsorbent (63a). The particulates in the exhaust gas are trapped in the HC adsorbent (63a) or the cell walls (60) of the particulate filter (18) and prevented from reaching the NOx adsorbent (62a). When the catalyst temperature is low, NOx in the inflowing exhaust gas is adsorbed in the NOx adsorbent (62a), and hydrocarbon (HC) is adsorbed in the HC adsorbent (63a). With the increase in the catalyst temperature, the adsorbed NOx is desorbed from the NOx adsorbent (62a), and the adsorbed HC is desorbed from the HC adsorbent (63a). This HC reduces the NOx desorbed from the NOx adsorbent (62a).