Air Fuel Ratio Control Device

Abstract: Provided is an air-fuel ratio control device (1) that is capable of accurately detecting an air-fuel ratio over an extended period regardless of the specifications of an internal combustion engine. This air-fuel ratio control device (1) reads a signal value from an oxygen concentration sensor (2) provided so as to contact exhaust of a four-cycle internal combustion engine, and calculates, by means of an air-fuel ratio control unit, the air-fuel ratio of the exhaust on the basis of a signal value VH that was read. The signal value VH based on the oxygen in gas that is not the exhaust is eliminated on the basis of changes in the signal value VH from the oxygen concentration sensor (2) with respect to a crank angle of the internal combustion engine, during a period T1 from when an exhaust valve of the internal combustion engine opens to when the valve closes; and the abovementioned calculation is performed on the basis of the signal value VH after said elimination.

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