To meet contradictory characteristics that if a driving frequency is set to a lower value, pulsation of a plunger at a middle duty ratio becomes too large by producing a driving signal having a duty ratio proportional to the amount of intake air, etc., and varying the frequency of the driving signal in driving a flow control valve.
A control unit 16 uses a flow rate computing means 31 to compute the quantity Q of air required for controlling the next desired engine speed, if the internal combustion engine is at idle. In accordance with the computed quantity Q of air required, a driving signal having a duty ratio proportional to the quantity Q of intake air required is produced from a driving signal generating means 32, and is fed to a frequency changing means 33. The frequency of the driving signal is changed in proportion to an output duty ratio and in accordance with a conversion table stored in a storage means 34 in accordance with an output duty ratio T. A flow control valve 5 such as an idle speed control valve is controlled by the driving signal whose output duty ratio and frequency are determined.
ONO TAKAHIKO
MORIGUCHI TERUHIKO
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