Wide air gap permanent magnet motors

Claim 1

In an electrical machine comprising a permanent magnet having a predetermined remanent flux density, a core separated from said permanent magnet by a gap, said magnet, said core and said gap forming a magnetic circuit in which said magnet is at a magnetic flux density and a magnetic field intensity determined by the size of said gap, the product of said flux density and said field intensity corresponding to an energy product, said magnet having a predetermined maximum energy product which occurs at a flux density lower than said remanent flux density, an electrically-conductive winding interposed within said gap between said permanent magnet and said core, and means for permitting relative motion between said permanent magnet and said winding, the improvement which comprises: (a) means for substantially maximizing the energy product of said magnet by making the size of said gap sufficiently large to limit the flux density of said magnet to a flux density substantially nearer to that corresponding to said predetermined maximum energy product than to said remanent flux density; (b) said magnet having an effective magnetization curve of a slope corresponding substantially to the slope of the effective magnetization curve of any one of barium ferrite, strontium ferrite and rare earth permanent magnets; and (c) said gap being virtually filled with said winding.