To highly accurately control EGR(exhaust gas recirculation) by accurately estimating the actual excess air factor in a cylinder by surely grasping the amount of the EGR air actually taken in the cylinder in an exhaust gas recirculation device.
The target excess air factor λ tgt in the cylinder is set in correspondence with driving conditions by means of a target excess air factor setting means 41, and the quantity of the fuel injected in the cylinder is set in correspondence with driving conditions by means of a fuel injection quantity setting means 51, and the true air quantity Ga supplied in the cylinder is calculated by means of an in-cylinder air quantity calculating means 52 based on the total intake air quantity detected by an in-cylinder intake air quantity detecting means 53 and the opening degree of an EGR valve detected by an opening degree detecting means. The actual excess air factor λ in the cylinder is then estimated based on the fuel injection quantity and true air quantity by means of an actual excess air factor estimating means 42 for controlling an EGR valve 25 so that the actual excess air factor λ estimated becomes equal to the target excess air factor λ tgt.
TANAKA TAMON
NISHIHARA SETSUO
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