Patent ID: 6835357
Filing Date: 2004-12-28
Classification: F01N,F02D,Y02T

Abstract:
An exhaust emission control system for an internal combustion engine, comprising:nitrogen oxides removing means provided in an exhaust system of said engine for removing nitrogen oxides in exhaust gases in a condition where an air-fuel ratio of an air-fuel mixture to be supplied to said engine is set to a lean region with respect to a stoichiometric ratio; an oxygen concentration sensor provided downstream of said nitrogen oxides removing means for detecting the concentration of oxygen in the exhaust gases; deterioration determining means for determining deterioration of said nitrogen oxides removing means on the basis of an output of said oxygen concentration sensor after the air-fuel ratio has been changed from the lean region to a rich region with respect to the stoichiometric ratio; and abnormality determining means for determining abnormality of said oxygen concentration sensor on the basis of an output of said oxygen concentration sensor during a period in which the air-fuel ratio is kept in the rich region with respect to the stoichiometric ratio immediately after execution of the deterioration determination by said deterioration determining means.