Air-fuel ratio control apparatus for internal combustion engine

An air-fuel ratio control apparatus for an internal combustion engine, the apparatus comprising:

• an air-fuel ratio sensing means for detecting an air-fuel ratio of exhaust gas, the air-fuel ratio sensing means being disposed in an exhaust path of the internal combustion engine and having an output characteristic which is nonlinear with respect to the air-fuel ratio of exhaust gas;
• an output deviation converting means for converting an output deviation to a first predetermined value if an output value of the air-fuel ratio sensing means is on a richer side of a predetermined target value and to a second predetermined value if the output value is on a leaner side of the target value, the output deviation being a difference between the output value and the target value, the first and second predetermined values having a same absolute value and opposite signs;
• a control input calculating means for calculating a control input to feedback-control the output value of the air-fuel ratio sensing means such that the output deviation converted by the output deviation converting means is to be zero;
• and
• an air-fuel ratio controlling means for controlling the air-fuel ratio of exhaust gas using the control input calculated by the control input calculating means.