Importance

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Abstract

An exhaust gas purifying device for an engine comprises an exhaust gas purifying catalyst with an electric heater arranged in the exhaust passage capable of temporarily adsorbing NO.sub.X in the inflowing exhaust gas therein. A NO.sub.X adsorbing capacity of the exhaust gas purifying catalyst becomes larger when a temperature of the exhaust gas purifying catalyst becomes higher. The heater is turned on and is turned off alternately and repeatedly to thereby increase and reduce the catalyst temperature. NO.sub.X in the inflowing exhaust gas is adsorbed in the exhaust gas purifying catalyst when the catalyst temperature falls, and the adsorbed NO.sub.X is desorbed from the exhaust gas purifying catalyst and reduced when the catalyst temperature increases. The catalyst temperature is controlled to increase to a first upper threshold temperature, at which the NO.sub.X adsorbing capacity of the exhaust gas purifying catalyst is substantially zero, and is controlled to fall to a first lower threshold temperature, at which the NO.sub.X adsorbing capacity of the exhaust gas purifying catalyst is substantially a maximum.

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First Claim