US Patent 7474955 Method and apparatus for air fuel ratio adjustment

The air fuel ratio of an engine adapted to run on a mixture of alcohol and gasoline can be adapted by a method wherein the air fuel ratio is controlled using an ethanol adaptation value, including reducing the enrichment factor from an initial value until a lean switch from rich conditions to lean conditions is detected, determining a first enrichment factor value at which the lean switch occurs, increasing the enrichment factor until a rich switch from lean conditions to rich conditions is detected, determining a second enrichment factor value at which the rich switch occurs, calculating the average value between the first enrichment factor value and the second enrichment factor value, adjusting the air fuel ratio using the average value.