Patent ID: 6844647

Claim:
In a brushless permanent magnet motor comprised of a stator of magnetic material having a multiplicity of electrically energizable stator pole elements at locations spaced circumferentially about an axis of said motor, and a coaxial rotor rotatable about said axis and having a circumferential array of permanent magnets effectively disposed on an outer surface thereof and in a closely proximate, magnetically interactive, facing relationship to said stator pole elements; the improvement wherein said rotor comprises a cylindrical shell component and a cylindrical inner component disposed concentrically within said shell component with an outer surface of said inner component in magnetically close proximity to an inner surface of said shell component; said shell and inner components being conjointly rotatable and displaceable relative to one another, to selectively establish first and second relative positions, in at least one of the axial direction and a rotational direction; said shell component having an array of first magnetic elements extending circumferentially thereabout, and said inner component having an array of second magnetic elements, comprising permanent magnets, extending circumferentially thereabout for producing magnetic flux at said outer surface thereof; said first and second magnetic elements being dimensioned, configured, and arranged to cooperatively generate relatively strong magnetic fields in said first relative position of said inner and shell components, and thereby to produce maximal values of flux density in the magnetic interaction between said stator pole elements and said permanent magnets, and to generate magnetic fields that are weak, relative to said relatively strong magnetic fields, in said second relative position of said inner and shell components and thereby to produce values of flux density in such magnetic interaction that are reduced substantially from said maximal values of flux density.