Air-fuel mixture ratio control device

Abstract

An air-fuel ratio control device for controlling the air-fuel ratio of a mixture to be supplied into an internal combustion engine. The device has a control circuit adapted to produce, in accordance with the offset of the output of an oxygen sensor in the exhaust system of the engine from a reference value corresponding to the desired air-fuel ratio, a control signal for making the air-fuel ratio coincide with the command air-fuel ratio. The device further has a mixture supplying means including means for adjusting the air-fuel ratio in accordance with the control signal. The air-fuel ratio adjusting means includes an actuator incorporating a step motor adapted to change the opening area of fuel passage or air bleed passage of a carburetor. The control circuit has means for temporarily stopping the step motor for a predetermined time length before the stepping speed or the stepping direction of the motor is changed, to assure the correct operation of the step motor and, hence, a precise control of the air-fuel ratio.

Dependencies are inferred from the claim text.