Exhaust gas purifying apparatus and method for internal combustion engine

摘要

An apparatus is provided for purifying an exhaust gas discharged from an internal combustion engine, which comprises a first exhaust gas passage including a nitrogen oxide removing catalyst and a three way catalyst, a second exhaust gas passage including the three way catalyst, a gas flow regulator for selectively directing the exhaust gas to the first and second exhaust gas passages, and a control unit which directs the exhaust gas to the first exhaust gas passage (thereby passing exhaust gas first through the nitrogen oxide removing catalyst and thereafter through the three way catalyst) when the temperature of the nitrogen oxide removing catalyst is within a hydrocarbon adsorbing range of temperature thereof while the engine is warming up, and to the second exhaust gas passage (thereby passing the exhaust gas only through the three way catalyst) when the temperature of the nitrogen oxide removing catalyst exceeds the hydrocarbon adsorbing range of temperature thereof.