Air/Fuel Ratio Control Apparatus for Internal Combustion Engine

An air/fuel ratio control apparatus for an internal combustion engine as is applied to the internal combustion engine, having:

• a catalyst which is disposed in an exhaust passage of the internal combustion engine;
• an upstream-side air/fuel ratio sensor which is disposed in a part of the exhaust passage as lies in an upstream of the catalyst;
• a downstream-side air/fuel ratio sensor which is disposed in a part of the exhaust passage as lies in a downstream of the catalyst;
• and
• fuel injection means for injecting fuel in compliance with an instruction;
• the air/fuel ratio control apparatus comprising:
• command basic-fuel-injection-quantity acquisition means for acquiring a fuel quantity for obtaining a target air/fuel ratio, as a command basic fuel injection quantity, from an in-cylinder intake air quantity which is estimated on the basis of a running state of the internal combustion engine;
• main-feedback-correction-magnitude calculation means for calculating a main feedback correction magnitude on the basis of a value obtained after a value which is based on a difference between an output value of the upstream-side air/fuel ratio sensor and a predetermined upstream-side target value has been subjected to predetermined high-pass filtering, or a value obtained after the output value of the upstream-side air/fuel ratio sensor has been subjected to predetermined high-pass filtering;
• sub-feedback-correction-magnitude calculation means for calculating a sub-feedback correction magnitude on the basis of an output value of the downstream-side air/fuel ratio sensor and a predetermined downstream-side target value;
• command basic-fuel-injection-quantity correction means for correcting the command basic fuel injection quantity so that a fuel quantity which the fuel injection means actually injects when it has received the injection instruction of the fuel of the command basic fuel injection quantity may become a quantity which is required for making an actual air/fuel ratio of a mixture to be fed into the engine, the target air/fuel ratio;
• command final-fuel-injection-quantity calculation means for calculating a command final fuel injection quantity in such a way that the corrected command basic fuel injection quantity is corrected by the main feedback correction magnitude and the sub-feedback correction magnitude;
• and
• air/fuel ratio control means for feedback-controlling the air/fuel ratio of the mixture to be fed into the engine, in such a way that the injection instruction of the fuel of the command final fuel injection quantity is given to the fuel injection means, wherein
• said command basic-fuel-injection-quantity correction means is configured so as to calculate a parameter value for correcting the command basic fuel injection quantity, on the basis of the output value of the upstream-side air/fuel ratio sensor, the command final fuel injection quantity, the target air/fuel ratio, and the command basic fuel injection quantity, and to correct the command basic fuel injection quantity by using the parameter value.