Patent ID: 6145305
Filing Date: 2000-11-14
Classification: B01D,F01N,Y02T

Abstract:
A system for diagnosing deterioration of a NOx-occluded catalyst installed in an exhaust stream of an internal combustion engine, said catalyst occluding NOx in the exhaust gas when the engine exhaust gas led to the catalyst shows a leaner air/fuel ratio and releasing NOx therefrom when said engine exhaust gas shows a stoichiometric and/or richer air/fuel ratio, said system comprising:an inlet NOx concentration estimating unit which estimates NOx concentration at an inlet part of said catalyst;an outlet NOx concentration detecting unit which detects NOx concentration at an outlet part of said catalyst; anda deterioration degree judging unit which judges a deterioration degree of the catalyst in accordance with a rate of the minimum value of NOx concentration detected by said detecting unit for a predetermined period to a value of NOx concentration estimated by said estimating unit at the time when said minimum value of NOx concentration is detected, said predetermined period being a period between a time when the engine exhaust gas shows the stoichiometric and/or richer air/fuel ratio and a subsequent time when the engine exhaust gas shows the stoichiometric and/or richer air/fuel ratio.