Patent ID: 7049723

Claim:
A DC motor, comprising: a case: a rotor unit which is rotatably arranged within the motor and includes a single hollow cylindrical field magnet fixed to holder means into which a rotating shaft is press-fitted at a center thereof, said cylindrical field magnet being magnetized such that South and North poles alternate with each other in a circumferential direction thereof; and a stator unit which is circumferentially arranged around said rotor unit and is comprised of a ring arranged in the case and a plurality of stator yokes so arranged as to oppose said field magnet with a small gap, each of said stator yokes being formed by circumferentially stacking a large number of thin plates each of which constitutes a salient pole, and a plurality of coil units, each being formed by winding a magnet wire on a bobbin and mounted on each of said stator yokes; wherein the rotor unit includes a holder fitted at one end of the field magnet and a spring holder mounted at the other end of the field magnet, the spring holder being composed of a second holder fitted at the other end of the field magnet, a third holder and a spring sandwiched between the second holder and the third holder, and wherein each of the South and North poles has a plurality of stages formed in an axial direction and shifted from each other in the circumferential direction of said field magnet with a predetermined shift amount, boundaries between the South poles and the North poles being formed in a stepped shape in parallel with an axis of the rotating shaft.