Air-fuel ratio control system for internal combustion engines

摘要

An air-fuel ratio control system for an internal combustion engine has a sensor which detects the air-fuel ratio of exhaust gases in an exhaust passage of the engine emitted from a plurality of cylinders. An air-fuel ratio of a mixture supplied to each of a plurality of cylinders is estimated, based on the detected air-fuel ratio and a model representative of a behavior of the exhaust passage. A cylinder-by-cylinder air-fuel ratio control amount is calculated for use in controlling the air-fuel ratio of the mixture supplied to the each of the cylinders in a feedback manner responsive to the estimated air-fuel ratio of the mixture such that the estimated air-fuel ratio of the mixture supplied to the each of the cylinders is converged to a desired air-fuel ratio. A learned value of the cylinder-by-cylinder air-fuel ratio control amount is calculated. When the difference between the detected air-fuel ratio and the estimated air-fuel ratio of the mixture supplied to the each of the cylinder is larger than a predetermined value, the calculation of the learned value of the cylinder-by-cylinder air-fuel ratio control amount is inhibited.