Patent ID: 7528515
Filing Date: 2009-05-05
Classification: H02K

Abstract:
1. A small DC motor, comprising: a motor frame having two ends and a side wall; wherein the side wall surrounds a magnet and a rotor and is formed by four straight side portions and four connecting portions; wherein each of the connecting portions is located between a pair of the side portions; wherein the magnet includes four separate adjacent magnet sections, each magnet section having a different polarity from an adjacent magnet section, wherein each magnet section has an outer surface conforming to the motor frame and an arc shaped inner surface forming a portion of a border for a circular opening containing the rotor so that the cross section of each magnet section through a plane perpendicular to the axis of the rotor varies in width according to the shape of the side wall of the motor frame; wherein each of the side portions is in contact with at least two magnet sections and each of the connecting portions is in contact with only a single adjacent magnet section; and wherein, in a plane perpendicular to the rotational axis of the rotor, each of the connecting portions extends in a direction substantially perpendicular to a line extending from the center of the circular opening through a midpoint of the arc shaped inner surface of the adjacent magnet section so that, for each magnet section, the ratio of a radial minimum thickness of the magnet section to the radial maximum thickness of the magnet section is between about 1:2 to about 1:3.