Patent Document ID: 4723408
Application ID: 06904042
Patent Flag: 1

Claim One:
1. A method for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, repsectively, of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising the steps of: calculating a first air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor; calculating a second air-fuel ratio correction amount in accordance with the output of said downstream-side air-fuel ratio sensor; determining whether or not a change of density of air taken into said engine is larger than a predetermined value; calculating a learning correction amount so that a mean value of said first air-fuel ratio correction amount is brought close to a reference value, when the change of the intake air density is larger than said predetermined value; adjusting an actual air-fuel ratio in accordance with said first and second air-fuel ratio correction amounts, and said learning correction amount.