CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-234578, filed on 14 Dec. 2018, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a permanent magnet and a rotating electrical machine.

BACKGROUND

In the related art, as a rotating electrical machine, there has been known an IPM motor which is one type of inner rotor motor and in which a permanent magnet is embedded in a rotor (for example, Japanese Unexamined Patent Publication No. 2018-170940).

As the permanent magnet embedded in the rotor of the IPM motor, the inventors have been researching a permanent magnet having an arc shape cross-section, which more easily realizes a desired magnetic distribution than a rectangular parallelepiped permanent magnet, rather than the rectangular parallelepiped permanent magnet which has been adopted in the related art. If the permanent magnet having an arc shape cross-section has a planar reference surface in a surface thereof, positioning is facilitated when surface processing or the like is performed thereon. On the other hand, it is generally considered that it is difficult to form the reference surface with a high dimensional accuracy in a magnet surface, and if variations occur in the dimensions of the reference surface, variations occur also in rotor characteristics.

SUMMARY

After extensive research, the inventors have newly found a technique that is capable of easily forming the reference surface while preventing variations in rotor characteristics.

According to the present disclosure, there is provided a permanent magnet and a rotating electrical machine in which it is possible to easily form a reference surface while preventing variations in the characteristics of the rotating electrical machine.

A permanent magnet according to an aspect of the present disclosure has an arc shape cross-section defined by an outer arc, an inner arc, and a pair of end sides connecting an end point of the outer arc and an end point of the inner arc, and has a perpendicular reference surface provided in an inner peripheral surface defined by the inner arc and perpendicular to a direction of a bisector of an opening angle of the inner arc in the cross section.

The inventors have obtained the knowledge that even though there is a difference in the dimension of the perpendicular reference surface provided in the inner peripheral surface of the permanent magnet, almost no variations occur in the characteristics of a rotating electrical machine. That is, even though variations occur in the dimension of the perpendicular reference surface, variations in the characteristics of the rotating electrical machine are prevented. Therefore, according to the permanent magnet described above, it is possible to easily form a reference surface while preventing variations in the characteristics of the rotating electrical machine.

The permanent magnet according to another aspect is radially magnetized with reference to a virtual center positioned close to the inner arc in the cross section.

In the permanent magnet according to another aspect, a range of an opening angle θ of the inner arc is 10°≤θ≤90°.

According to an aspect of the present disclosure, there is provided a rotating electrical machine that includes a rotor having a shaft and a rotor core, a plurality of permanent magnets are attached to the rotor core to surround the shaft, and a stator disposed on an outer periphery of the rotor and having a plurality of coils, in which the permanent magnet has an arc shape cross-section defined by an outer arc, an inner arc, and a pair of end sides connecting an end point of the outer arc and an end point of the inner arc, and includes a perpendicular reference surface provided in an inner peripheral surface defined by the inner arc and perpendicular to a direction of a bisector of an opening angle of the inner arc in the cross section.

The inventors have obtained the knowledge that even though there is a difference in the dimension of the perpendicular reference surface provided in the inner peripheral surface of the permanent magnet, almost no variations occur in the characteristics of a rotating electrical machine. That is, even though variations occur in the dimension of the perpendicular reference surface, variations in the characteristics of the rotating electrical machine are prevented. Therefore, it is possible to easily form a reference surface of the permanent magnet while preventing variations in the characteristics of the rotating electrical machine.

