Apparatus and method for estimating concentration of vaporized fuel purged into intake air passage of internal combustion engine

摘要

In a, so-called, lean burn engine having a vaporized fuel processor, a concentration of a vaporized fuel purged into an intake air passage (so-called, a purge concentration) is estimated using a normal type oxygen concentration sensor. Whenever a predetermined interval of time has passed, the engine combustion condition is forcefully and temporarily transferred into a stoichiometric air-fuel mixture ratio combustion condition during which the purge concentration is estimated on the basis of an output signal from the oxygen concentration sensor during an air-fuel mixture ratio feedback control. <IMAGE>