CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

This invention relates to a control device (72) for an internal combustion engine (10). An object of this invention is to prevent a deterioration in exhaust characteristics when a change to an air-fuel ratio on a theoretical air-fuel ratio side is requested in an internal combustion engine (10) during operation in a lean mode. The control device (72) controls an internal combustion engine equipped with a NOx storage-reduction catalyst in an exhaust passage. When a NOx amount stored in the NOx storage-reduction catalyst reaches a release threshold value (76 or 84), the control device executes rich control to cause the NOx to be released. In a state in which an air-fuel ratio of an air-fuel mixture belongs to a second region that is near a lean limit, the release threshold value (76) for determining the start of the rich control is set in the vicinity of the NOx storage capacity of the NOx storage-reduction catalyst. If the air-fuel ratio of the air-fuel mixture enters a first region that is near a theoretical air-fuel ratio, the control device changes the release threshold value (84) to a smaller value.