To provide an actuator significantly reducing a deformation amount in a diametrically expanding direction of a torsion spring than ever before, while securing good startability of an engine.
A ball screw shaft 45 is rotated by an electric motor 36 to rectilinearly travel a ball nut 46 in an axial direction to perform rotation control of a control shaft 32, and thereby to variably control a valve lift amount of an intake valve. During stop of the engine, a first spur gear 60 and a second spur gear 61 are rotated by a spring force of the torsion spring 62 of a rotation imparting mechanism 39 to rotate the ball screw shaft 45 in one direction. Thereby, the ball nut 46 is made to travel to an approximately intermediate position in an axial direction, that is, in a direction to control the intake valve to a large working angle side to automatically control the valve lift amount of the intake valve to an intermediate lift suitable for starting.
NAKAMURA MAKOTO
Hiromichi Kobayashi
Tomioka Kiyoshi