Patent ID: 6357224
Filing Date: 2002-03-19
Classification: F01N,F02B,F02D,Y02T

Abstract:
An engine exhaust gas purifying apparatus comprising:an NOx trapping agent arranged within an exhaust gas passage, trapping an NOx in an exhaust gas in accordance with an adsorption or an absorption when an air-fuel ratio in the exhaust gas is lean and discharging or reducing the NOx when the air-fuel ratio is a stoichiometric air-fuel ratio or the rich air-fuel ratio; air-fuel ratio changing means temporarily changing the air-fuel ratio of the exhaust gas from the lean air-fuel ratio to the stoichiometric air-fuel ratio or the rich air-fuel ratio at a predetermined cycle; particular component detecting means detecting a particular component in the exhaust gas downstream said NOx trapping agent; NOx discharge or reduction completion judging means judging on the basis of a detecting result of said particular component detecting means at a time of temporarily changing the air-fuel ratio of the exhaust gas to the stoichiometric air-fuel ratio or the rich air-fuel ratio by said air-fuel ratio changing means that a discharge or reduction of the NOx trapped by said NOx trapping agent is completed; and NOx discharge or reduction completion time detecting means detecting a time required for purifying the NOx, wherein a control parameter of said air-fuel ratio changing means is changed on the basis of a result obtained by comparing a time (TD) detected by the NOx discharge or reduction completion time detecting means with a predetermined value (TTD) previously set; and wherein a difference between the values TD and TTD is made small at a time of changing the control parameter of said air-fuel ratio changing means on the basis of the result of comparison between said detected time TD and the predetermined value TTD.