PURPOSE: To prevent the fluctuation of an air-fuel ratio upon switching and avoid unstable combustion or a torque shock by a method wherein the increasing or decreasing of an injection amount is delayed or gradually increased or decreased in accordance with the delay of response of the suction air of operating cylinders side which is generated upon switching the number of operating cylinders.
CONSTITUTION: When all cylinders operation is switched to the partial cylinders operation, a fuel injection interrupting circuit 25 and a fresh air interrupting valve and an exhaust gas recirculating valve driving circuit 27 are operated at an instant when the output of an OR circuit 23 has become H, and fuel for resting side cylinders #4W#6 is interrupted while the fresh air interrupting valve is opened to increase the suction air volume of operating side cylinders #1W#3. A fuel injection constant switching circuit 26, for switching the injection amount for the operating side cylinders #1W#3 into two times thereof, is operated with some time delay by the operation of an integrating circuit 30. On the contrary, when the partial cylinders operation is switched to the all cylinders operation, the to the delay of decreasing output of the integrating circuit 30 is reduced with a time delay corresponding the air for operating cylinders #1W#3 after the output of the OR circuit 23 is switched and thereby preventing the air-fuel ratio from becoming excessively thin immediately after the switching.
ISHIZAWA SHIZUO
AIHARA HISAMOTO
KAMEGAYA SHIGERU
NAKATSURU KAZUHIRO
