AIR-FUEL RATIO CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES

An air-fuel ratio control system for an internal combustion engine includes an air-fuel ratio sensor arranged in the exhaust system of the engine, for detecting the air-fuel ratio of exhaust gases from the engine. An ECU calculates an adaptive control amount, based on an output from the air-fuel ratio sensor, by using an adaptive controller having an adaptive parameter-adjusting mechanism, such that the air-fuel ratio of a mixture supplied to the engine is converged to a desired air-fuel ratio, and controls the air-fuel ratio of the mixture in a feedback manner, according to the adaptive control amount. When a particular engine operating condition in which the adaptive controller can become unstable in operation is detected, the adaptive parameters are initialized according to the adaptive control amount.