Patent ID: 6082345
Filing Date: 2000-07-04
Classification: F02B,F02D

Abstract:
In an air fuel ratio control system for an internal combustion engine having an exhaust system, including an oxygen concentration sensor arranged in said exhaust system, said oxygen concentration sensor having an output characteristic that an output thereof is substantially proportional to concentration of oxygen present in exhaust gases from said engine, and feedback control means responsive to the output of said oxygen concentration sensor, for carrying out feedback control of an air-fuel ratio of a mixture supplied to said engine so as to make the air-fuel ratio equal to a desired air-fuel ratio, the improvement comprising:activated state-detecting means for detecting an activated state of said oxygen concentration sensor; andcorrection-limiting means for limiting correction of the air-fuel ratio of said mixture by said feedback control means, depending upon the activated state of said oxygen concentration sensor detected by said activated state-detecting means,wherein said activated state-detecting means comprises internal resistance-detecting means for detecting internal resistance of said oxygen concentration sensor,said correction-limiting means sets (a) lower limit value of an amount of correction of the air-fuel ratio of said mixture to a larger value and/or (b) an upper limit value of the amount of correction of the air-fuel ratio of said mixture to a smaller value when the internal resistance of said oxygen concentration sensor detected by said internal resistance-detecting means is higher than a value of said internal resistance to be assumed when said oxygen concentration sensor has a temperature thereof falling in a predetermined activation temperature range within which said oxygen concentration sensor can be activated.