Patent ID: 6519932
Filing Date: 2003-02-18
Classification: F01N,F02D,Y02T

Abstract:
An exhaust gas purification apparatus for an internal combustion engine comprising:a NOx catalyst arranged in an exhaust gas passage of said internal combustion engine; and air fuel ratio control means for selecting one of an engine operation with lean air fuel ratio, operation with stoichiometric air fuel ratio, and operation with rich air fuel ratio, depending on an engine operation state, wherein said air fuel ratio control means temporarily forces engine operation with rich air fuel ratio when said engine operation state is shifted from said engine operation with lean air fuel ratio to said engine operation with stoichiometric air fuel ratio, wherein said air fuel ratio control means stops said forced engine operation with rich air fuel ratio based on a signal from a timer, and wherein a period during which said forced engine operation with rich air fuel ratio is performed is dependent on a degree of richness of said rich air fuel ratio of said forced engine operation, and said degree of richness is based on either one of or a plurality of a rotation speed of said internal combustion engine, an engine load, and an air quantity.