Patent ID: 7059115

Claim:
An air/fuel ratio control method for an internal combustion engine comprising the steps of: detecting an output of an air/fuel ratio sensing means indicative of an air/fuel ratio of exhaust gases at a location downstream of a catalyst in an exhaust passage of said internal combustion engine; setting a target air/fuel ratio for converging the output of said air/fuel ratio sensing means to a predetermined target value such that the output of said air/fuel ratio sensing means fluctuates over a predetermined amplitude and at a predetermined frequency higher when the output of said air/fuel ratio sensing means is near said predetermined target value than when the output of said air/fuel ratio sensing means is not near said predetermined target value; and controlling the air/fuel ratio of an air/fuel mixture supplied to said internal combustion engine in accordance with the set target air/fuel ratio, wherein said target air/fuel ratio is set based on one of a Δ modulation algorithm, a ΔΣ modulation algorithm and a ΣΔ modulation algorithm, and wherein said step of setting a target air/fuel ratio setting includes; calculating a predicted value for a value indicative of the output of said air/fuel ratio sensing means based on a prediction algorithm; and calculating said target air/fuel ratio based on said calculated predicted value in accordance with said one modulation algorithm.