Patent ID: 7475662

Claim:
An actuator for a valve lift controller controlling a lift amount of an intake valve and/or an exhaust valve, the actuator linearly driving a control shaft to change the lift amount according to an axial position of the control shaft, comprising: a feed screw mechanism including a screwed shaft which moves linearly along with the control shaft, and a rotation spindle which rotates in a circumferential direction, the feed screw mechanism converting a rotational movement of the rotation spindle into a linear movement of the screwed shaft; a protrusion protruding outwardly from the rotation spindle; an internal thread member engaging with an outer wall surface of the rotation spindle; a motor stator generating a magnetic field when energized; and a motor rotor positioning over the rotation spindle, the motor rotor sandwiched between the protrusion and the internal thread member in an axial direction of the rotation spindle, the motor rotor rotating along with the rotation spindle in the magnetic field generated by the motor stator, the motor rotor includes a cylindrical rotor core and a plurality of rotor magnets disposed in a circumferential direction of the rotor core, wherein the rotor magnets are disposed on an outer wall surface of the rotor core, and each rotor magnet generate a magnetic pole which is alternately reverse between adjacent rotor magnets the rotor core includes non-magnet portions on which no magnet is disposed and magnet portions on which magnets are disposed, the non-magnet portions are thicker than the magnet portions, and the rotor core includes an outer wall surface of which cross section is circle, and an inner wall surface which concaves toward the outer wall surface along a circumferential direction from a center portion of the non-magnet portions to a center portion of the magnet portion.