Air–Fuel Ratio Control Device

Abstract: Provided is an air-fuel ratio control device capable of performing accurate air-fuel ratio feedback control regardless of variation in resistance values due to manufacturing tolerances and changes over time in an oxygen sensor. The air-fuel ratio control device includes: an excess ratio calculation unit (25) that, using a data map that associates a plurality of air excess ratio values  with temperatures T and voltage values VHG of a detection unit of a resistance-type oxygen sensor, calculate an air excess ratio ; a lookup table that associates rich-side threshold values RREF and lean-side threshold values LREF with the temperatures T; a characteristics examination unit (40) that acquires a crest value of the voltage values VHG by setting a target air excess ratio cmd to a stoichiometric neighborhood and examines whether the crest values are in a rich region, a stoichiometric region, or a lean region; and a calibration unit (41) that calibrates the data map and the lookup tables using an affine transformation procedure so that the crest values correspond to the rich-side threshold value RREF and the lean-side threshold value LREF according to the examination. Fig. 2

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