EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To reduce an HC exhaust amount after starting an engine. SOLUTION: A three-way catalyst 22 and an HC absorption catalyst 23 are arranged in series in an exhaust pipe 21. When a temperature of the HC absorption catalyst 23 is low after starting the engine, an HC in exhaust gas is absorbed into the HC absorption catalyst 23. After that, when a temperature of the HC absorption catalyst 23 rises up to an HC desorption temperature region, a target air-fuel ratio in the upstream of the HC absorption catalyst 23 is changed over to an air-fuel ratio on a lean side more than an ordinary air-fuel ratio in accordance with an output of an oxygen sensor 26 in the downstream of the HC absorption catalyst 23. Consequently, since an air-fuel ratio of exhaust gas flowing into the HC absorption catalyst 23 is controlled to the lean side, oxygen concentration in the exhaust gas is increased, and an HC desorbed from the HC absorption catalyst 23 and oxygen in the exhaust gas react easily to accelerate the purification of the desorbed HC and reduce an HC exhaust amount. Moreover, since an air-fuel ratio in the downstream of the catalyst 23 is monitored by the oxygen sensor 26 in the downstream of the HC absorption catalyst 23, an increase of NOx due to excessive lean can be prevented.