DETECTION OF AIR-FUEL RATIO

摘要

PURPOSE:To exactly detect the air-fuel ratio of a supplied gaseous mixture by calculating an excess oxygen quantity by correcting the oxygen concn. detected by an oxygen sensor provided in an exhaust passage with a NOx concn. and computing the air-fuel ratio therefrom. CONSTITUTION:An electronic controller 20 computes the oxygen concn. from the oxygen pump current of an oxygen sensor 17 provided in the exhaust passage 3. The controller 20 determines the concn. of the NOx by the three- dimensional map of the NOx previously stored according to the rotating speed, load and target air-fuel ratio of an engine. The controller corrects the oxygen concn. by adding the oxygen quantity contained in the NOx and determines the result thereof as the excess oxygen quantity. This excess oxygen quantity attains the value approximate to the oxygen quantity when the supplied gaseous mixture make perfect combustion. The controller 20 computes the air-fuel ratio from the excess oxygen quantity. The air-fuel ratio of the supplied gaseous mixture is exactly detected in this way.