Direct current motor having poles arranged to minimize cogging torque

Claim 1

A direct current motor, comprising: a cylindrical armature rotatable on its axis, said armature having a multiplicity of slots uniformly spaced apart circumferentially around the armature; and an even number of one-piece permanent magnet poles circumferentially spaced apart around the armature and radially spaced therefrom by narrow airgaps, said poles being so shaped and located with respect to each other that cogging torque tending to occur between the armature and one-half of said number of poles is countered and cancelled by cogging torque tending to occur between the armature and the other half of said number of poles, said poles having outer body portions which are symmetrical in shape about their central planes passing through the axis of said armature, said central planes of said poles being spaced apart by 360*/N, where N is a total number of poles, and said poles having inner body portions adjacent said armature which are asymmetrical with respect to said central planes so that the point of maximum permeance in said airgap of each pole occurs (360*/N) + OR - phi from the point of occurrence of maximum permeance of each adjacent pole where phi is the angle in electrical degrees between the points of occurrence of maximum and minimum permeance respectively of each pole.