Speed control of a D.C. electric motor

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

• at least one pair of opposing field pole members, each having a shank portion mounted to said yoke member, a face portion defined by a plurality of field pole leg members extending radially inwardly to form a bore for receiving said armature, and a core portion for providing a magnetic path between said shank portion and said face portion;
• a field coil wound around said shank portion of each of said field pole members;
• and
• a plurality of separately excitable field control coils wound individually around said field pole leg members of each of said field pole members, said field control coils being operable to shift the magnetic flux generated by said field coils across said face portions when one or more of said field control coils are energized magnetically subtractive to the flux generated by said field coils, such that the magnetic field generated by said field coils is shifted away from said subtractively energized field control coil(s) and concentrated over a predeterminable portion of said field pole face portions.

A method of controlling the speed of a D.C. electric motor having a yoke, an armature, a pair of opposing field poles, each of said field poles including a shank portion mounted to said yoke, a face portion defined by a plurality of field pole legs extending radially inwardly to form a bore for receiving said armature, and a core portion for providing a magnetic path between said shank portion and said face portion, a field coil wound around said shank portion of each of said field poles, and a plurality of separately excitable field control coils wound individually around said field pole legs of each of said field poles, comprising the steps of:

• (a) energizing one or more of said field control coils magnetically subtractive to the flux generated by said field coils for increasing the speed of said D.C. electric motor by causing the magnetic flux generated by said field coils to shift across said face portions such that the magnetic flux generated by said field coils is shifted away from said subtractively energized field control coil(s) and concentrated over a predeterminable portion of said field pole face portions;
• (b) de-energizing said subtractively energized field control coil(s) for decreasing the speed of said D.C. electric motor;
• and
• (c) energizing one or more of said field control coils magnetically additive to the flux generated by said field coils for further decreasing the speed of said D.C. electric motor.

A method of variably controlling the speed of a D.C. electric motor having a yoke, an armature, a pair of opposing field poles, each of said field poles including a shank portion mounted to said yoke, a face portion defined by a plurality of field pole legs extending radially inwardly to form a bore for receiving said armature, and a core portion for providing a magnetic path between said shank portion and said face portion, a field coil wound around said shank portion of each of said field poles, and a plurality of separately excitable field control coils wound individually around said field pole legs of each of said field poles, coprising the steps of:

• (a) energizing all of said field control coils magnetically additive to the flux generated by said field coils at a starting condition to produce a first speed;
• (b) de-energizing said field control coils in a predetermined sequence for providing gradual increases in the speed of said D.C. electric motor from said starting condition to produce other speeds differing from said first speed;
• (c) energizing said field control coils magnetically subtractive to the flux generated by said field coils in a predetermined sequence for further increasing the speed of said D.C. electric motor;
• (d) de-energizing said subtractively energized field control coils in a predetermined sequence for providing gradual decreases in the speed of said D.C. electric motor;
• and
• (e) energizing said field control coils magnetically additive to the flux generated by said field coils for further decreasing the speed of said D.C. electric motor.