Speed control of a D.C. electric motor

An improved D.C. electric motor of the type having an armature, a commutator, and a brush assembly, wherein the improvement comprises:

• a yoke member;
• and
• at least one pair of opposing pole means associated with said yoke member for generating a magnetic field which is variable across a face portion of said pole means, each of said pole means including a plurality of separately excitable field control coils for selectively varying the density and direction of the magnetic flux along said face portion of said pole means;
• wherein each of said pole means includes a field pole member having a shank portion mounted to said yoke member, a plurality of spaced, generally radially extending field pole leg members associated with said face portion, and a core portion interposed radially between said shank portion and said face portion for providing a magnetic path between said shank portion and said face portion, and a field coil wound around said shank portion of said field pole member, and wherein said field control coils are wound individually around said field pole leg members of said field pole member and are operable to shift the magnetic flux generated by said field coil across said face portion when one or more of said field control coils are energized magnetically subtractive to the flux generated by said field coil, such that the magnetic flux generated by said field coil is shifted away from said subtractively energized field control coil(s) and concentrated over a predeterminable portion of said field pole face portion;
• wherein at least a portion of the magnetic flux generated by at least one of said field control coils energized magnetically subtractive to the magnetic flux generated by said field coils cuts at least one of the coils of said armature;
• wherein said face portion is constructed to provide for a continuous, generally cylindrical surface as the bore for receiving said armature.