Method for controlling air-fuel ratio for internal combustion engine and apparatus therefor

摘要

Disclosed is a method of controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine by the selective use of either one of a feedback control mode in which the control is made to maintain the air-fuel ratio at the stoichiometric level and a lean control mode in which the control is made to maintain at the leaner side of the stoichiometric level in accordance with the state of operation of the engine. In this method, the execution of the control in the lean control mode is prohibited for a predetermined period of time during acceleration of the engine at least when the speed of vehicle mounting the engine is below a predetermined speed, and the air-fuel ratio control is made in the feedback control mode in the period of time. Consequently, the period of engine operation in the lean control mode is maximized without impairing the driveability of the engine particularly when the engine is accelerated from low speed. Disclosed also is an apparatus suitable for carrying out this method.