Patent ID: 8230846

Claim:
An air-fuel ratio control device for an internal combustion engine having an exhaust path in which a catalyst capable of occluding oxygen is installed, the air-fuel ratio control device comprising: an oxygen sensor which is installed downstream of the catalyst; and reflection coefficient calculation means for calculating a reflection coefficient, which reflects an output value of the oxygen sensor in the calculation of a fuel injection amount and increases or decreases to have a consequence on the air-fuel ratio of an exhaust gas; wherein the reflection coefficient calculation means fixes the reflection coefficient at a predetermined value for providing a lean air-fuel ratio when the output value of the oxygen sensor is greater than a reference value corresponding to a stoichiometric air-fuel ratio and smaller than an upper threshold value set at a value smaller than the maximum output value of the oxygen sensor, and fixes the reflection coefficient at a predetermined value for providing a rich air-fuel ratio when the output value of the oxygen sensor is smaller than the reference value and greater than a lower threshold value set at a value greater than the minimum output value of the oxygen sensor, and increases or decreases the reflection coefficient in accordance with a change in the output value of the oxygen sensor when the output value of the oxygen sensor is greater than the upper threshold value and when the output value of oxygen sensor is smaller than the lower threshold value.