Air-fuel ratio control system for internal combustion engine

Abstract

An air-fuel ratio control system with a high accuracy for an internal combustion engine which is capable of particularly improving the transient response characteristic irrespective of the occurrence of an air-fuel ratio sensor delay and a fuel attachment. An in-cylinder air-fuel ratio is calculated on the basis of engine data obtained in advance so that an neural network (NN) receiving a fuel injection quantity involving the past value and air quantity estimating information such as an intake pressure and outputting a calculated in-cylinder air-fuel ratio undergoes learning. In the actual control, a difference between the in-cylinder air-fuel ratio estimated in the NN and the target air-fuel ratio is taken on the basis of information such as a fuel injection quantity varying with the time and the output of the NN is partially differentiated with respect to the fuel injection quantity, so that the difference therebetween is divided by the resultant partial differential coefficient to obtain a fuel correction amount whereby the in-cylinder air-fuel ratio coincides with the target air-fuel ratio. The fuel injection quantity is corrected with this correction amount to calculate a final fuel injection quantity. That is, the in-cylinder air-fuel ratio is controlled to approach the target air-fuel ratio so that the exhaust gas air-fuel ratio equals the target air-fuel ratio.