Patent ID: 6484493
Filing Date: 2002-11-26
Classification: F01N,F02D,Y02T

Abstract:
An exhaust emission control device for internal combustion engine having a nitrogen oxide purification means provided in an exhaust system of an internal combustion engine for absorbing nitrogen oxide when an air-fuel ratio of exhaust gas becomes leaner than a stochiometric air-fuel ratio, and reducing the nitrogen oxide when the air-fuel ratio of exhaust gas becomes richer than the stochiometric air-fuel ratio, comprising:an oxygen concentration measurement means provided downstream from said nitrogen oxide purification means for measuring oxygen concentration in said exhaust gas; a time difference measuring means for measuring a time difference for an output signal from said oxygen concentration measurement means to change from lean to rich, when the air fuel ratio of the mixture supplied to said internal combustion engine changes from a condition leaner than the stochiometric air fuel ratio to a rich air-fuel ratio; a threshold value setting means for setting, in relation to said time difference, a predetermined first threshold value for judging if a purifying capacity of said nitrogen oxide purification means has deteriorated due to sulfur poisoning, and a predetermined second threshold value shorter than said first threshold value for judging if said nitrogen oxide purification means has heat-deteriorated; and a deterioration judging means for judging that said nitrogen oxide purification means has deteriorated due to sulfur poisoning when a measured time of said time measurement means is shorter than said first threshold value and longer than said second threshold value, and for judging that said nitrogen oxide purification means has heat-deteriorated when said measured time difference of said time difference measuring means is shorter than said second threshold value.