AIR-FUEL RATIO FEEDBACK CONTROL METHOD FOR ELECTRONICALLY CONTROLLED ENGINE

摘要

PURPOSE:To enable to control the air-fuel ratio such that it is always kept at the theoretical air-fuel ratio, by correcting a reference value used for switching the mode of controlling the air-fuel ratio to 'lean' air-fuel ratio control or to 'rich' air-fuel ratio control when the minimum value of the output of an O2-sensor becomes out of a predetermined range in executing feedback control of the air-fuel ratio. CONSTITUTION:In operation of an engine, a control circuit 50 at first corrects a base fuel quantity calculated from the outputs of an air-flow meater 15 and an engine- speed sensor 29 according to the temperature of intake air and the air-fuel ratio detected by an O2-sensor 60, and then controls a fuel jinjection valve 20 according to the corrected injection quantity of fuel. Further, the output value of the O2-sensor 60 is compared with a reference value, and the mode of air-fuel ratio control is changed to 'lean' control or to 'rich' control according to the result of judgement whether the output value of the O2-sensor 60 is greater than said reference vlaue or not. With such an arrangement, the minimum value of the output signal of the sensor 60 is compared with a predetermined value range to correct said reference value in case that the minimum value becomes out of said value range. Thus, it is enabled to control the air-fuel ratio to keep it at the theoretical air-fuel ratio in spite of deterioration or other troubles of the O2-sensor 60.