Air-fuel ratio judging method of internal combustion engine based on ion current

摘要

An air-fuel ratio judging method of an internal combustion engine based on an ion current for detecting an ion current generated in the combustion chamber of the internal combustion engine for each ignition, wherein a generation period during which an ion current generated exceeds a set judgment value is measured, a divisor for operating the variation rate of ion current generation period is operated based on a plurality of measured generation periods, the variation rate of ion current generation period is operated by assigning weights to the operated divisor in the direction of increasing it, and a decision is made that the air-fuel ratio is excessively high when the calculated variation rate is not lower than a predetermined value.