Patent ID: 8671665

Claim:
An exhaust gas purifying apparatus for an internal combustion engine, comprising: a first catalyst provided in an exhaust passage of said engine, which can remove NOx in exhaust gases from said engine when an air-fuel ratio of an air-fuel mixture burning in said engine is in the vicinity of the stoichiometric ratio; a second catalyst provided downstream of said first catalyst, which can remove NOx in the exhaust gases using a reducing agent; reducing-agent supply means for supplying the reducing agent to said second catalyst; air-fuel ratio control means for controlling the air-fuel ratio; and determining means for determining an execution condition of a lean operation in which the air-fuel ratio is set to a lean air-fuel ratio which is leaner than the stoichiometric ratio, wherein said air-fuel ratio control means controls the air-fuel ratio to a rich air-fuel ratio which is richer than the stoichiometric ratio, during a lean transition period from the time the execution condition is satisfied, when switching the air-fuel ratio from an air-fuel ratio in the vicinity of the stoichiometric ratio to the lean air-fuel ratio, and said air-fuel ratio control means controls the air-fuel ratio to the lean air-fuel ratio after the lean transition period has elapsed.