Apparatus for and method of controlling air-fuel ratio of internal combustion engine, and recording medium storing program for controlling air-fuel ratio of internal combustion engine

摘要

A target value Vtgt for an output Vout of an O₂ sensor 8 (an exhaust gas sensor) disposed downstream of a catalytic converter 4 is set variably depending on a temperature T_O2 of an active element 10 of the O₂ sensor 8 by a target value setting unit 18, and the air-fuel ratio of an exhaust gas is controlled by an air-fuel ratio control unit 17 to converge the output Vout to the target value Vtgt. An exhaust gas temperature Tgd is estimated by an exhaust temperature observer 19, and the temperature T_O2 of the active element 10 is sequentially estimated by an element temperature observer 20 using the estimated value of the exhaust gas temperature Tgd. A heater 13 of the O₂ sensor 8 is controlled by a heater controller 22 to keep the temperature T_O2 of the active element 10 at a predetermined target value R. The air-fuel ratio is thus controlled to maintain a desired exhaust gas purifying capability of the catalytic converter irrespective of the temperature of the active element of the exhaust gas sensor.