Patent ID: 6672052
Filing Date: 2004-01-06
Classification: F01N,F02D,Y02T

Abstract:
An exhaust gas purifying apparatus for purifying exhaust gases generated by an internal combustion engine, said exhaust gas purifying apparatus comprising:a NOx trap material disposed in an exhaust gas passage to absorb NOx while an air-fuel ratio of an exhaust gas is leaner than a stoichiometric air-fuel ratio and release NOx while an air-fuel ratio of an exhaust gas is richer than said stoichiometric air-fuel ratio; and control means for estimating an amount of NOx absorbed by said NOx trap material, for making an air-fuel ratio richer so as thereby to cause said NOx trap material to release NOx when said amount of NOx absorbed by said NOx trap material is greater than a specified amount, for estimating an amount of sulfur absorbed by said NOx trap material, and for making an air-fuel ratio richer and rising an exhaust gas temperature so as thereby to cause said NOx trap material to perform sulfur releasing when said amount of sulfur absorbed by said NOx trap material is greater than a first specified amount; wherein said control means conditionally restricts said sulfur releasing of said NOx trap material and restrains said air-fuel ratio from being made richer when said amount of sulfur absorbed by said NOx trap material is larger than a second specified amount that is larger than said first specified amount.