EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To optimally control driving switching from a lean air-fuel ratio to a rich air-fuel ratio by accurately understanding an NOx absorbing level. SOLUTION: In an internal combustion engine where an NOx storage catalyst 15 is arranged in an exhaust pipe 12 and driving of a lean air-fuel ratio leaner than a stoichiometric air-fuel ratio is carried out under a required driving condition, air-fuel ratio sensors 16 and 17 for generating outputs proportional to an oxygen content in exhaust gas are provided in respective exhaust pipes 12 before and after the NOx storage catalyst 15, and an NOx absorbing level determining means 18 is provided for determining the NOx absorbing level of the NOx storage catalyst 15 based on the outputs of the air-fuel ratio sensors 16 and 17 during lean air-fuel ratio driving.