PURPOSE: To prevent air-fuel ratio control from its divergence by controlling a bypass air amount in accordance with a degree of changing an intake air amount, when air-fuel ratio is changed from a rich condition to a lean condition, and controlling the bypass air amount in accordance with a separate degree of changing during a lean period.
CONSTITUTION: A duty valve 3 for controlling a bypass air amount is interposed between bypass passages 3a, 3b of bypassing a throttle valve 2, and by controlling this duty valve 3 by a controller 200, air-fuel ratio of an engine is controlled to a target value. In a control device thus obtained, in the case of control in a transient period after changing air-fuel ratio, when the target air-fuel ratio is changed from a rich value to a lean value, in the point of changing time, in order to superpose an increase amount in accordance with an intake air amount relating to the then intake air amount, duty ratio in the duty valve 3 is increased. During the following lean control period, control of holding the superposed amount is performed to suppress a torque fluctuation.
OSHITA HIDEKI
TAKEUCHI HIROYUKI
