Patent ID: 6338243
Filing Date: 2002-01-15
Classification: F01N,F02D,Y02T

Abstract:
An exhaust emission control system for an exhaust system for an internal combustion engine, having a nitrogen oxide removing means for absorbing nitrogen oxides contained in exhaust gases in an exhaust lean condition and reducing the absorbed nitrogen oxides in an exhaust rich condition, said control system comprising;a first oxygen concentration sensor provided upstream of said nitrogen oxide removing means for detecting the oxygen concentration in the exhaust gases; a second oxygen concentration sensor provided downstream of said nitrogen oxide removing means for detecting the oxygen concentration in the exhaust gases; first measuring means for measuring a first response delay time period from the time when the output value from said first oxygen concentration sensor has changed to a value indicative of a rich air-fuel ratio, to the time when the output value from said second oxygen concentration sensor becomes a value indicative of a rich air-fuel ratio, after changing the air-fuel ratio of the air-fuel mixture to be supplied to the engine from a lean region to a rich region with respect to a stoichiometric ratio; second measuring means for measuring a second response delay time period from the time when the output value from said first oxygen concentration sensor has changed to a value indicative of a lean air-fuel ratio, to the time when the output value from said second oxygen concentration sensor becomes a value indicative of a lean air-fuel ratio, after changing the air-fuel ratio from the rich region to the lean region with respect to the stoichiometric ratio; and deterioration determining means for determining deterioration of said nitrogen oxide removing means according to the first and second response delay time periods, wherein said deterioration determining means includes correcting means for correcting the first response delay time period according to the second response delay time period, and determines the deterioration according to the first response delay time period corrected by said correcting means.