Air/fuel ratio control system for an internal combustion engine

摘要

An air/fuel ratio control system for an internal combustion engine equipped with a three-way catalytic converter, comprises first and second fluid supply passages for supplying, for example, a secondary air or a supplemental fuel to the engine, and a flow control valve disposed in the first fluid supply passage for varying the amount of the secondary air or the supplemental fuel in accordance with a detected condition of the air/fuel ratio. An open/close valve is disposed in the second fluid supply passage for opening and closing the communication through the second fluid supply passage without regard to the air/fuel ratio signal and with a predetermined period which is shorter than a normal period of turning over of the air/fuel signal, thereby reducing the deviation of the actual air/fuel ratio from a central value of the air/fuel ratio control, to improve the efficiency of purification of emission by means of the three-way catalytic converter.