| 摘要 |
PROBLEM TO BE SOLVED: To prevent erroneous learning affected by rich spike control for controlling reducingly NOx occluded in a NOx catalyst to enhance learning precision. SOLUTION: The rich spike control is executed to make rich an air-fuel ratio transitorily in every establishment of rich-spike control executing conditions during a lean operation. NOx is occluded thereby in the NOx catalyst 24 during the lean operation, and the occluded NOx is reducedly controlled by the rich spike control to be discharged. The learning for parameters (a fuel correction factor, an evaporated gas concentration, a crank angular-veocity deviation, a target air-fuel ratio and the like) affected by an air-fuel ratio variation and a rotation variation by the rich spike control is prohibited during execution of the rich spike control and within a prescribed time after the finish of the rich spike control, because the air-fuel ratio is varied transitorily to generate the rotation variation when the rich spike control is executed, and the learning precision is prevented thereby from lowered by the rich spike control to enhance precision for engine control and precision for abnormality diagnosis.
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