Patent Document ID: 4831838
Application ID: 07124412
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, respectively, of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising the steps of: calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream-side air-fuel ratio sensor; calculating an air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameter; calculating a mean value of a number of successive maximum and minimum values of said air-fuel ratio correction amount; determining whether or not the mean value of said air-fuel ratio correction amount is larger than a variable reference value determined in accordance with an air-fuel ratio feedback control parameter, said reference value corresponding to a stoichiometric air-fuel ratio; increasing a learning correction amount when the mean value of said air-fuel ratio correction amount is larger than said reference value; decreasing said learning correction amount when the mean value of said air-fuel ratio correction amount is not larger than said reference value; and adjusting an actual air-fuel ratio in accordance with said air-fuel ratio correction amount and said learning correction amount.