Air-fuel ratio control apparatus for an internal combustion engine

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

• operative state detection means for detecting an operative state of said internal combustion engine;
• purge quantity control means for controlling a quantity of purge air that is introduced into an engine intake system, based on a detection output of said operative state detection means;
• purge quantity calculation means for calculating said purge air quantity that is introduced into said engine intake system by said purge quantity control means;
• purge rate calculation means for calculating a purge rate from said purge air quantity calculated by said purge quantity calculation means and from said operative state detected by said operative state detection means;
• an air-fuel ratio sensor for sensing an air-fuel ratio of an air-fuel mixture supplied to said internal combustion engine;
• air-fuel ratio control means for controlling an air-fuel ratio feedback correction coefficient which makes a correction so that said air-fuel ratio of said air-fuel mixture, which is supplied to said internal combustion engine, becomes a target value, based on an output of said air-fuel ratio sensor;
• purge air concentration calculation means for calculating a purge air concentration from said purge rate and said air-fuel ratio feedback correction coefficient;
• purge air concentration correction means for calculating a purge air concentration correction coefficient, based on said purge rate and said purge air concentration;
• and
• fuel injection quantity calculation means for calculating an injection quantity of fuel which is supplied to said internal combustion engine, based on said air-fuel ratio feedback correction coefficient and said purge air concentration correction coefficient.