DC BRUSH MOTOR AND ITS PERMANENT MAGNET

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PROBLEM TO BE SOLVED : To reduce the size of a 1-200 W class motor. SOLUTION : In the brushless motor, an exciting magnet is formed of a hollow tubular anisotropic bond magnet 13 and magnetized with four poles. The anisotropic bond magnet 13 has a maximum energy product about five times as large as that of a conventional sintered ferrite magnet. Since four pole magnetization is employed, magnetic path length of a magnetic circuit per pole is decreased and a magnetic force contributive to impart torque is increased. When the torque is constant, the length of an electromagnetic rotator and the axial length of a permanent magnet can be decreased. Furthermore, the ratio of thickness w/d between a casing and the magnet is set in the range of 1-3 and the ratio d/a between the radial depth of an anisotropic rare earth bond magnet and the diameter of the electromagnetic rotator is set in the range of 0.015-0.07. Consequently, a 1-200 W class motor can be reduced in size and the motor performance index can be more than doubled.