Update authorization of reference level of the air-fuel ratio is judged the air-fuel ratio control unit

摘要

PROBLEM TO BE SOLVED: To provide an air-fuel ratio controller wherein a reference value of an air-fuel ratio is not updated in a condition where a catalyst is deteriorated.;SOLUTION: In the air-fuel ratio controller of an internal combustion engine for controlling the air-fuel ratio, a control input for controlling the air-fuel ratio is obtained to converge the output of an exhaust gas sensor arranged in an exhaust pipe at a target value using a change-over function. The manipulated value is added on the reference value to obtain a target air-fuel ratio. A function for representing an ellipse having the value of the change-over function and the output of the exhaust gas sensor as variables is defined to obtain a value of a function representing the ellipse. According to the value of the function representing the ellipse, the reference value is judged or not to permit updating. When the reference value is updated, the reference value is updated based on an integration value of the change-over function. When the catalyst is judged to be deteriorated, the reference value is not updated to stably detect the deterioration of the catalyst.;COPYRIGHT: (C)2004,JPO