Air-fuel ratio control system

摘要

An air-fuel ratio control system for controlling the air-fuel ratio of air-fuel mixture to be inducted into an automotive engine in order to accomplish feedback control of the air-fuel ratio into a stoichiometric level of feedforward control of the air-fuel ratio into a lean level. The air-fuel ratio control system is comprised of a control unit which is electrically connected to an oxygen sensor for detecting the air-fuel ratio and to a variety of sensors for detecting engine operating condition. The control unit is adapted to calculate an air-fuel ratio correction coefficient in accordance with the detected air-fuel ratio. The feedback control of the air-fuel ratio is accomplished in accordance with the air-fuel ratio correction coefficient. The control unit is further adapted to form a plurality of learning areas defined respectively by engine operating conditions. Learning is made in each learning area. At least a part of each learning area is under the feedback control. The control unit is adapted to further calculate a learning coefficient for the learning area corresponding to the detected engine operating condition, in accordance with the air-fuel ratio correction coefficient under the feedback control. The learning coefficient is memorized in the above-mentioned at least a part of each learning area. The feedforward control of the air-fuel ratio is accomplished in accordance with the learning coefficient in the learning area corresponding to the detected engine operating condition, thereby improving the precision of control in the feedforward control of the air-fuel ratio.