Air/fuel ratio control system for internal combustion engines, having atmospheric pressure compensating function

An air/fuel ratio control system for performing feedback control of the air/fuel ratio of a mixture being supplied to an internal combustion enging, which comprises:

• an O.sub.2 sensor for detecting the concentration of oxygen present in exhaust gases emitted from said engine;
• fuel quantity adjusting means for producing said mixture being supplied to said engine;
• an electrical circuit operatively connecting said O.sub.2 sensor with said fuel quantity adjusting means in a manner effecting feedback control operation in response to an output signal produced by said O.sub.2 sensor to control the air/fuel ratio of said mixture to a first predetermined preset value;
• a sensor for detecting atmospheric pressure to produce an output indicative thereof, and means for detecting operating conditions of said engine;
• wherein said electrical circuit including:
• first memory means storing a second predetermined preset value as a basic value of the air/fuel ratio of said mixture corresponding to a predetermined operating condition of said engine at a predetermined value of atmospheric pressure;
• second memory means storing a coefficient for providing a correction value corresponding to the difference between said predetermined value of atmospheric pressure and the value of actual atmospheric pressure;
• means for arithmetically calculating the sum of said basic value+(the value of actual atmospheric pressure-said predetermined value of atmospheric pressure).times.said correction coefficient;
• third memory means for storing said sum calculated by said arithmetic calculating means;
• and means responsive to said sum stored in said third memory means for controlling said fuel quantity adjusting means when said enging condition detecting means detects said predetermined engine operating condition.

An air/fuel ratio control system for performing feedback control of the air/fuel ratio of a mixture being supplied to an internal combustion engine, comprising:

• an O.sub.2 sensor for detecting the concentration of oxygen present in exhaust gases emitted from said engine;
• fuel quantity adjusting means for producing said mixture being supplied to said engine;
• a sensor for detecting atmospheric pressure to produce an output indicative thereof;
• means for detecting operating conditions of said engine;
• and
• an electrical circuit operatively connecting said O.sub.2 sensor with said fuel quantity adjusting means in a manner effecting feedback control operation in response to an output signal produced by said O.sub.2 sensor to control the air/fuel ratio of said mixture to a first predetermined preset value, said electrical circuit including:
• first memory means storing a plurality of different second predetermined preset values as basic values of the air/fuel ratio of said mixture individually corresponding to respective ones of different predetermined operating conditions of said enging at a predetermined value of atmospheric pressure;
• second memory means storing a plurality of different coefficients having predetermined values individually corresponding to respective ones of said predetermined operating conditions of said engine, for providing respective correction values corresponding to the difference between said predetermined value for atmospheric pressure and the value of actual atmospheric pressure;
• calculating means operable when said engine operating condition detecting means detects one of said different predetermined operating conditions of said engine, to arithmetically calculate the sum of (i) one of said basic values corresponding to said detected one predetermined operating condition of said engine and (ii) the product of the value of actual atmospheric pressure less said predetermined value of atmospheric pressure with one of said coefficients corresponding to said detected one predetermined operating condition of said engine;
• and
• means responsive to said sum calculated by said calculating means for controlling said fuel quantity adjusting means.