| 摘要 |
PROBLEM TO BE SOLVED: To raise a control accuracy to the theoretical air fuel ratio of the air fuel ratio of an exhaust gas flowing in a storage reduction type NOX catalyst at SOX release time. SOLUTION: When the temperature of NOX catalyst 12 is increased, first and fourth cylinders are made to a rich cylinder operated by a rich air fuel ratio and second and third cylinders are made to a lean cylinder operated by a lean air fuel ratio. When the air fuel ratio feedback control by a cylinder group for feedback controlling the air fuel ratio is carried out based on the output signal of an upper streamside air fuel ratio sensor 18 provided on the upper stream of NOX catalyst 12, by correcting the feedback target value based on the rich coefficient representing the rich degree of the air fuel ratio in the rich cylinder and air amount, a flow in exhaust average air fuel ratio is controlled to a theoretical air fuel ratio substantially.
|
