Patent ID: 7210665

Claim:
An actuator, comprising: (a) a rotor assembly comprising an output shaft having a first screw portion with a male screw on an outer circumference of the output shaft, and having a plain rod portion, a sleeve having a second screw portion with a female screw on an inner circumference of the sleeve, the sleeve rotatably supported by bearings disposed respectively at both axial ends of the sleeve, wherein the first screw portion is threadedly engaged with the second screw portion so as to convert a rotary motion of the sleeve into a linear motion of the output shaft, and a magnet fixedly disposed at an outer circumference of the sleeve; (b) a stator assembly that rotates the magnet, and comprises a coil, a bobbin having the coil wound therearound, and stator yokes coupled to each other so as to sandwich the bobbin; (c) a valve plug attached to the output shaft; (d) a pin inserted orthogonally through the plain rod portion so as to protrude therefrom in a radial direction; (e) a hollow cylindrical housing attached to the stator assembly; and (f) fail-safe mechanism integrally built in the hollow cylindrical housing, the fail-safe mechanism comprising a coil spring disposed around the output shaft inside the hollow cylindrical housing, and a spring holder disposed around the output shaft inside the hollow cylindrical housing, and having slits extending parallel to the axial direction of the output shaft, the spring holder being so arranged that ends of the pin protrude into the slits whereby the slits restrict rotation of the output shaft and guide the pin in the axial direction, wherein the valve plug is moved to a predetermined position by a restoring force of the coil spring when the power supply to the stator assembly is interrupted.