Permanent magnet type rotary electric device

A permanent magnet type rotary electric machine of reduced cogging torque, said machine having a permanent magnet element comprised of a plurality of permanent magnets of alternate polarity in a circumferential direction, said permanent magnets being of substantially the same shape and disposed circumferentially at equal intervals, an armature element juxtaposed to said permanent magnet element and having a number of circumferentially spaced core teeth around which coils are wound, said core teeth defining a number N of slots therebetween, said permanent magnet element and said armature element being supported for relative rotation, the magnitudes of torque exerted on the permanent magnets of N and S poles of the rotor are selected so that both of the torque values substantially cancel each other.

A method of making a permanent magnet type rotary electric machine of reduced cogging torque, said method comprising the steps of constructing a permanent magnet element comprised of a plurality of permanent magnets of alternate polarity in a circumferential direction with the permanent magnets being of substantially the same shape and disposed circumferentially at equal intervals, juxtaposing an armature element to the permanent magnet element and having a number of circumferentially spaced core teeth around which coils are wound, the core teeth define a number N of slots therebetween, supported the permanent magnet element and the armature element for relative rotation, selecting the number of poles P of the permanent magnet element as an even number no smaller than four, selecting the number of slots S so that it is not a multiple of P, and selecting the circumferential magnet angle made by the permanent magnets with respect to the axis of relative rotation to produce a cogging number that is an integral multiple substantially greater than the least common multiple of the number of slots S and the number of poles P.

A method of making magnet type rotary electric machine of reduced cogging torque, said machine having a permanent magnet element comprised of a plurality of permanent magnets of alternate polarity in a circumferential direction, said permanent magnets being of substantially the same shape and disposed circumferentially at equal intervals, an armature element juxtaposed to said permanent magnet element and having a number of circumferentially spaced core teeth around which coils are wound, said core teeth defining a number N of slots therebetween, said permanent magnet element and said armature element being supported for relative rotation, the magnitudes of torque exerted on the permanent magnets of N and S poles of the rotor are selected so that both of the torque values substantially cancel each other.