To prevent the operating condition of an internal combustion engine from being unstable when a reference duty ratio takes a value different from an actual reference duty ratio.
This valve system includes a cam 12 for opening an intake valve 11 and an actuator 20 for moving the cam 12 so that the distance of the cam 12 from a reference position is changed. When a duty ratio for the actuator is the reference duty ratio, the cam 12 is not moved but moved when the duty ratio is shifted from the reference ratio. The opened amount of the intake valve becomes zero while the distance of the cam 12 from the reference position is taking a predetermined value or less. When the target opened valve amount is zero, the duty ratio is so controlled that the distance of the cam from the reference position takes the predetermined value or less and the duty ratio at this time is updated as the reference duty ratio.
IRISAWA YASUYUKI
Jun Tsuruta
Masaya Nishiyama
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