Synchronous A.C. motor

A synchronous A.C. electrical motor comprising (A) a stator, bearings associated with the stator for supporting a rotor, the stator comprising a body of high permeability soft magnetic material arranged to have low eddy current losses, the body having a surface in the shape of a surface of revolution coaxial with the axis of the rotor, power windings energizable with input A.C. power disposed in the body adjacent to the surface of revolution to provide a rotating magnetic field about the axis when so energized, an excitation coil energizable with single phase A.C. disposed about a pole piece having a magnetizing face substantially at the surface of revolution, and (B) the rotor having three electrically and magnetically associated major components comprising (1) a first external layer of a high coercive force, low electrical conductivity magnetizable permanent magnetic material, the first layer having an exterior surface of revolution coextensive with and complementarily matching the surface of revolution of the stator with a rotational clearance space therebetween, (2) a second component upon which the first layer is placed in close contact to provide a low reluctance path for magnetic flux from the first layer, the second component comprising a body of high permeability material arranged to provide low eddy current losses therein, and (3) the third component closely physically associated with the second component and being spaced radially on the other side of the second component from the side on which the first layer is placed, the third component comprising a ferromagnetic material having high permeability and high electrical conductivity, and also having a selected high electrical resistance to the flow of transverse electrical currents, whereby during starting and at low rotor speeds the rotating magnetic field of the stator will generate transverse circulating electrical currents in the third ferromagnetic component that will react with the rotating magnetic field so as to apply a rotational torque to the rotor, and the selected high electrical resistance in the transverse direction in the third component providing for the inducing of relatively low amperage transverse currents in the component, and at higher speeds approaching synchronous speed, when the excitation coil is energized with A.C., the pole piece will be magnetized into successive strong north and south polarity and its magnetizing face will magnetize the first layer of permanent magnetic material into a controlled pattern of north and south magnetic poles that are at such a phase angle relative to the rotating magnetic field of the stator so as to produce a strong rotational torque capable of bringing the rotor up to synchronous speed.