Torque motor with high torque poles and magnetic centering spring

Abstract

A two-pole limited angle torque motor including a rotor assembly having one or more permanent rotor magnets and a stator assembly including a stator coil and a pair of circumferentially spaced stator pole structures. Each pole structure includes a generally axially extending stator pole blade about which the stator coil circumferentially extends. A radially outwardly extending flange is at one end of one of the stator pole structures and at the opposite end of the other stator pole structure. The stator pole blades have a greater radial thickness adjacent the flanges thereof than at the opposite end of the blade to reduce the magnetic flux density of the stator pole structures in the region of the blades adjacent the flanges thereof. Also, the axial outer end faces of the flanges desirably protrude axially outwardly adjacent the radial inner ends thereof to make use of the fringing fields of the rotor magnet at the ends of the rotor assembly to increase the reluctance torque of the motor. At the ends of the stator assembly opposite the stator pole flanges on opposite sides of the rotor assembly are additional stator pole pieces. The blades of the stator pole structures terminate short of the other ends of the rotor magnet to provide room for the additional stator pole pieces at such other ends for a given rotor length whereby the motor has a substantially higher reluctance torque without significantly reducing the torque due to interaction of magnetic fields. Surrounding the stator assembly is an outer magnetic housing comprising two semi-cylindrical parts with air gaps between opposite sides thereof, said housing parts being rotatable relative to each other to change the size of one gap relative to the other or otherwise machinable to change both gaps equally for adjusting the reluctance torque of the motor.