Motor and motor manufacturing apparatus

Abstract

Flat rolled magnetic steel sheets and strip or a die is turned in the press forming process. Rotor cores are stacked with turning through an angle which is an odd number multiple of about (360° / (number of slots in the motor×natural number n×2)) and stator cores are stacked with turning through an angle which is an odd number multiple of (360° / (number of poles in the motor×natural number n×2)). Stacking with turning through an angle which is an odd number multiple converts the phases of cogging torques into mutually opposite phases and cancels and reduces the cogging torque caused by magnetic anisotropy.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of U.S. application Ser. No. 10 / 792,915 filed Mar. 15, 2004 which is currently pending.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a motor and a motor manufacturing apparatus, in particular, to cogging torque reduction. [0004] 2. Description of the Related Art [0005] In motors comprising a rotor with a magnet embedded therein and a stator having slots provided equidistantly in a circumference and a coil portion formed therein by winding in the slots, those motors being rotationally driven by the torque of the magnet and the reluctance torque of the coil, when the rotor rotates, a pulsating cogging torque is generated in the rotor. [0006] When the magnet disposed inside the rotor forms a magnetic circuit in which the generated magnetic flux is closed via the slots in the stator, the total sum of electromagnetic attraction forces at a rotation angle ...

AI Technical Summary

Benefits of technology

[0015] It is an object of the present invention to reduce the cogging torque caused by magnetic anisotropy of rotor or stator cores in a motor.

[0016] In accordance with the present invention, the cogging torque caused by magnetic anisotropy is reduced by obtaining different rolling directions in a plurality of cores which are to be stacked, during core manufacture by press forming, and preventing matching of rolling directions in the stacked cores. Turning flat rolled magnetic steel sheets and strip serving as a core workpiece through a prescribed angle or turning a die through a prescribed angle in the course of press forming makes it possible to eliminate the dependence of rotation on the pitch of poles, slots, or outer shape.

[0017] The inventors have experimentally discovered that the cogging torque caused by magnetic anisotropy is generated with a period which a natural number multiple of the number of slots and a natural number multiple of the number poles. Accordingly, based on the characteristic of the generation period of the cogging torque caused by magnetic anisotropy, in the rotation angle of flat rolled magnetic steel sheets and strip or die in the press forming process, the rotor cores are stacked with turning through an angle which is an odd number multiple of about (360° / (number of slots in the motor×natural number n×2)) and the stator cores are stacked with turning through an angle which is an odd number multiple of about (360° / (number of poles in the motor×natural number n×2)). Stacking with turning through the angle which is an odd number multiple causes the phases of cogging torque to cancel each other by the opposite phase and makes it possible to reduce the cogging torque of the motor. When stacking is conducted with turning through an angle which is an even number multiple, the cogging torque phases become in phase and the cogging torque is not cancelled and cannot be reduced.

Problems solved by technology

However, the cogging torque component caused by magnetic anisotropy is impossible to reduce by such methods.

Furthermore, stacking the cores while rotating them so as to obtain an almost uniform arrangement in the entire stacked core at a pitch of poles, slots, or outer shape can be also considered as means for averaging the scattering of the core thickness or the scattering caused by the core shape associated with die accuracy, but such a uniform arrangement cannot reduce the cogging torque caused by magnetic anisotropy.

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