Air-fuel ratio control system for use in an internal combustion engine

Claim 1

In an air-fuel ratio control system for an internal combustion engine including an exhaust sensor located in an exhaust path of said internal combustion engine and control means for effecting a feedback control to match an air-fuel ratio with a target value in accordance with a detection signal from said exhaust sensor, the improvement wherein said control means includes a correction section for correcting variations in the detection signal from the exhaust sensor to enable the air-fuel ratio to achieve the target value, said correction section comprising: means for determining whether predetermined implementation conditions of correction determination are satisfied; means for detecting a response time that elapses from an occurrence of a change in an operating state of the engine until the detection signal from the exhaust sensor achieves a determination signal value; and means for governing the feedback control over the air-fuel ratio in accordance with said detected response time to correct the feedback control, said governing means including: means for determining a difference time between said detected response time and a response reference time which represents a response time of said exhaust sensor in a normal state; means for determining a ratio value of said difference time to said response reference time; means for calculating a correction constant based upon a predetermined number of accumulated ratio values; and means for determining whether said correction constant falls within a correctable range of variations.