Axial Field Electric Motor

Naval Undersea Warfare Center

Wednesday, April 01 2009

This axial field electric motor is optimized for high-power-density applications.

An axial field electric motor comprises one or more elements such as a rotor mounted for rotation and multiple axial flux permanent magnets carried by the rotor. The axial flux permanent magnets are oriented such that an associated magnetic flux produced thereby is at least substantially axially oriented. The axial flux permanent magnets are positioned around the rotor with alternating orientations of flux direction so that a flux direction of adjacent magnets is at least substantially axially oriented but opposite in direction. The radial flux permanent magnets are also carried by the rotor and oriented so that an associated magnetic flux produced is at least substantially radially oriented.

In one embodiment of the present invention, radial stator windings may be positioned so as to be substantially adjacent opposite axial front and rear sides of the hybrid rotor to thereby maximize forces that counteract axial vibration. A hybrid motor housing provides support and/or stator back iron for the radial stator and the axial stators. A radial air gap is defined between the radial stator and the hybrid rotor. A rotor back iron is positioned radially between the axial flux permanent magnets and the radial flux permanent magnets. A retaining ring surrounds the hybrid rotor and holds the components of the hybrid rotor together. A structure may comprise a non-magnetic separator and/or rotor structure such as an aluminum structure for the hybrid rotor that defines pockets for the permanent magnets and radial spacers.

Alternatively, the structure and spacers may be comprised of separate components, laminates, and the like. The motor may be utilized to create an electromagnetic feedback system that magnetically clamps and holds the rotor in its centrally aligned position, thereby reducing axial vibrations. Stator windings may be substantially perpendicular to the axis of the rotation of the hybrid rotor shaft. With the magnetic flux directed radially, either inwardly or outwardly, and with electron current in the direction as indicated either into the page or out of the page, then two forces will be produced in opposite directions on opposite radial ends of the hybrid rotor.

If the hybrid rotor attempts to warp, then the force produced on one side of the rotor will be greater than that produced in the opposite direction, tending to push the hybrid rotor back into a vertical position and thereby reducing axial vibrations produced due to warping or bending of the rotor. The feedback or centralizing effect will be greatest if the wires in the radial stator winding are oriented to be substantially perpendicular to the rotor axis, and positioned so that the stator windings are adjacent axially opposite sides of the radial flux permanent magnets.

If the orientation of stator windings is parallel to the hybrid rotor shaft or the axis thereof, then the stator windings produce a force that increases torque applied to the hybrid rotor. When the stator windings are at angles between parallel and perpendicular with respect to the rotor shaft, some feedback effects will be produced to reduce axial vibrations and some amount of force will be provided to increase torque of the hybrid rotor. Thus, the orientation of the stator windings can be selected as desired with these benefits in mind.

This work was done by Chahee P. Cho of the Naval Undersea Warfare Center.
NUWC-0008