Brushless D.C. motor having asymmetrically positioned poles

Claim 1

A brushless direct current motor comprising: an outer rotor for rotation in a first circumferential direction about an axis, the rotor having a first magnetized portion of a first magnetic polarity which extends in a circumferential arc having a first angle; an inner stator coaxially aligned within the rotor, the stator having a generally cylindrical core and having a first pair of T-shaped poles projecting radially outward from the core and circumferentially spaced from one another in the first circumferential direction by an angle which is greater than the first angle, and having a second pair of T-shaped poles projecting radially outward from the core and circumferentially spaced from one another in the first circumferential direction by an angle which is greater than the first angle, each T-shaped pole having a radially aligned body and a circumferentially aligned head; an air gap separating an inner surface of the rotor and the heads of the first and second pairs of T-shaped poles; a first winding wound on the bodies of the first pair of poles to cause the head of a first pole of the first pair of T-shaped poles to have the first magnetic polarity and the head of a second pole of the first pair of T-shaped poles to have a second magnetic polarity when the first winding is energized; a second winding wound on the bodies of the second pair of poles to cause the head of a first pole of the second pair of T-shaped poles to have the first magnetic polarity and the head of a second pole of the second pair to have the second magnetic polarity when the second winding is energized; magnetic sensing means for sensing angular position of the rotor; and a control circuit connected to and responsive to the magnetic sensing means for alternately energizing the first and second windings in synchronism with the sensed angular position of the rotor to cause rotation of the rotor in the first circumferential direction.