Patent ID: 6668813
Filing Date: 2003-12-30
Classification: F01N,F02D

Abstract:
An air-fuel ratio control device for an internal combustion engine, comprising:an air-fuel ratio sensor which is provided upstream of a catalytic converter provided in an exhaust system of said internal combustion engine and detects an air-fuel ratio of said internal combustion engine; an O2 sensor which is provided downstream of said catalytic converter and detects a concentration of oxygen after said catalytic converter; reference air-fuel ratio target value setting means for setting a reference air-fuel ratio target value based on the number of revolutions and filling efficiency of said internal combustion engine; O2 voltage target setting means for setting a target value of an output voltage of said O2 sensor based on the number of revolutions and filling efficiency of said internal combustion engine; air-fuel ratio target value correcting means for obtaining an air-fuel ratio target value correction value based on an output voltage of said O2 sensor and a target value set by said O2 voltage target setting means; forcible air-fuel ratio oscillation width target value correcting means for obtaining a forcible air-fuel ratio oscillation width target value used for forcible air-fuel ratio oscillation based on the number of revolutions and filling efficiency of said internal combustion engine; air-fuel ratio computing means for computing an air-fuel ratio target value based on outputs of said reference air-fuel ratio target value setting means, said air-fuel ratio target value correcting means, and said forcible air-fuel ratio oscillation width target value correcting means; air-fuel ratio correction value computing means for computing a correction value based on an air-fuel ratio target value computed by said air-fuel ratio target value computing means and an output of said air-fuel ratio sensor; injector driving time correction value computing means for obtaining a forcible air-fuel ratio oscillation width injector driving time correction value based on the number of revolutions and filling efficiency of said internal combustion engine; and injector driving time setting means for setting time for driving an injector based on a correction value from said air-fuel ratio correction value computing means and a correction value from said injector driving time correction value computing means, wherein a forcible air-fuel ratio oscillation prohibiting means prohibits forcible air-fuel ratio oscillation when the output voltage of said O2 sensor is below a predetermined value.