Air-fuel ratio controlling method and apparatus therefor

An apparatus for controlling the air-fuel ratio of a mixture to be supplied to an internal combustion engine comprising:

• sensor means for sensing various operating conditions of said engine, said sensor means including an air-fuel ratio sensor for sensing the air-fuel ratio from the composition of exhaust gases therefrom;
• input port means connected to said sensor means to receive therefrom data indicative of operating conditions of said engine;
• timer means for measuring an elapsed time interval;
• interrupt control means for generating an interrupt request signal;
• random access memory means at least part of which functions as a nonvolatile memory;
• read-only memory means storing a program and constants;
• a presettable counter;
• power amplifier means connected to said presettable counter to drive fuel injection valve means for an interval of time corresponding to the content of said counter;
• and
• a microprocessor connected to said input port means, said timer means, said interrupt control means, said random access memory means, said read-only memory means and said presettable counter to respond to starting of said engine to initialize said random access memory means in accordance with said program stored in said read-only memory means and execute said program comprising the following steps as a main routine:
• at intervals of a time determined by an elapsed time indicative data from said timer means, increasing or decreasing integrated data read out from said random access memory means by a predetermined value in accordance with output signal data of said air-fuel ratio sensor read out from said input port means and storing said varied integrated data in said random access memory means;
• determining whether engine operating condition indicative data read out from said input port means is indicative of an abnormal condition;
• when said engine is not in abnormal condition, at intervals of another time determined by another elapsed time indicative data from said timer means, increasing or decreasing correction data read out from one of storage locations of said nonvolatile memory part determined by said engine operation condition indicative data by a predetermined value in accordance with the value of said varied integrated data and storing said varied correction data in said one of storage locations of said nonvolatile memory part;
• when said engine is in abnormal condition, resetting all the correction data stored in said storage locations of said nonvolatile memory part to a predetermined value;
• said microprocessor being responsive to said interrupt request signal from said interrupt control means to execute as an interrupt handling routine the following steps of said program in said read-only memory means;
• reading said engine operating condition indicative data from said input port means and storing the same in said random access memory means;
• computing a base fuel injection amount in accordance with said engine operating condition indicative data stored in said random access memory means;
• correcting said computed base fuel injection amount in accordance with said varied integrated data and said varied correction data stored in said random access memory means;
• and setting a value corresponding to said corrected fuel injection amount in said presettable counter.