JPH05236685A - Brushless dc motor - Google Patents

Abstract

PURPOSE:To improve the mechanical strength of a rotor by forming the end of the permanent magnet buried in the rotor of a brushless DC motor into convex shape. CONSTITUTION:For a brushless DC motor, a permanent magnet 2b is buried to turn the direction perpendicular to the radial direction of a rotor core 2a, and also the end in the direction perpendicular to the radial direction of the rotor core 2a of the permanent magnet 2b is made in convex shape. Therefore, the stress concentration at the end of the permanent magnet 2b can be dispersed in nearly all range of the convex face. Hereby, the stress concentration in the place, where great stress concentration was occurring in a conventional rotor, can be reduced, and the mechanical strength of the rotor 2 can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor including an armature having an armature winding wound around an armature core and a rotor having a permanent magnet embedded in the rotor core.

[0002]

2. Description of the Related Art Conventionally, a motor has been adopted as a drive source for a compressor or the like, paying attention to advantages such as easy electric control. In addition, although there are various types of motors, at present, it is possible to easily obtain a rotating magnetic field by using a three-phase AC power supply, a commutator is not required, and it is robust, low-priced, and easy to handle. The three-phase induction motor is most commonly used because of its advantages. However, in the induction motor, not only is the armature winding wound around the armature core, but the rotor winding is also wound around the rotor core.
Since current also flows through the rotor winding during operation, even if it is assumed that there is no mechanical loss, the output is more than the input due to the secondary copper loss due to the current flowing in the rotor winding. It can be reduced and efficiency cannot be increased so much.

Focusing on this point, instead of winding the rotor winding around the rotor iron core, a permanent magnet is attached to the rotor iron core to reduce secondary copper loss to zero, and permanent operation can be achieved. Magnet motors have been proposed. This permanent magnet motor has a structure in which at least one pair of permanent magnets is provided on the outer circumference of a rotor core (hereinafter referred to as a surface magnet structure), and at least one pair of permanent magnets is embedded inside the rotor core. It is roughly divided into those having the above structure (hereinafter referred to as an embedded magnet structure).

In the surface magnet structure, a permanent magnet is simply attached to the surface of the rotor core,
When the rotor is rotated at a high speed, the permanent magnet is likely to peel off, and the rotor cannot be rotated at a high speed. Therefore, a reinforcing method for firmly integrating the permanent magnet and the rotor core by using metal fittings and bolts, a bind wire made of a non-magnetic material, a metal tube made of a non-magnetic material, and the like is applied.

On the other hand, in the case of the embedded magnet structure, since the permanent magnet is embedded inside the rotor core, peeling of the permanent magnet can be prevented, and it is possible to cope with higher speed rotation than that of the surface magnet structure. Therefore, a permanent magnet motor having an embedded magnet structure is adopted for applications requiring high-speed rotation. As a specific configuration of the above-mentioned embedded magnet structure, as shown in FIG. 8, a relatively thin rectangular parallelepiped permanent magnet 92 is embedded inside a rotor core 91 in a state of being oriented in a direction perpendicular to the radial direction. At the same time, in order to prevent magnetic flux short-circuiting inside the rotor core, a magnetic flux short-circuit extending continuously to the end face of the permanent magnet 92 in the direction perpendicular to the radial direction and extending to a position close to the outer circumference of the rotor core 91. A structure has been proposed in which a gap 93 for prevention is formed, and a portion continuous to the outer end of the gap 93 is used as the magnetic flux short circuit portion 94.

[0006]

When the embedded magnet structure shown in FIG. 8 is used for high-speed rotation, centrifugal force is generated at the end of the permanent magnet 92 embedded in the rotor core 91. Since the stress concentration becomes remarkably large as compared with other portions and damage is likely to occur, there is an inconvenience that even if the embedded magnet structure is adopted, it is not possible to cope with high speed rotation.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a brushless DC motor having an embedded magnet structure capable of significantly reducing local stress concentration and simplifying rotor manufacturing work. It is intended to be provided.

[0008]

In order to achieve the above object, the brushless DC motor of claim 1 has permanent magnets embedded so as to be oriented in a direction perpendicular to the radial direction of the rotor core. The end of the permanent magnet in the direction perpendicular to the radial direction of the rotor core is formed into a convex curved surface.

In the brushless DC motor according to a second aspect of the present invention, the entire range of the permanent magnet is curved so that the central portion parallel to the axis of the rotor is recessed.

[0010]

According to the brushless DC motor of the present invention, the end of the permanent magnet embedded in the rotor core at a predetermined position in the direction perpendicular to the radial direction is formed in a convex curved surface. Therefore, when a relatively thin rectangular parallelepiped permanent magnet was used, significant stress concentration occurred at the edge, but it was possible to disperse it in almost the entire range of the convex curved surface, The mechanical strength of the child as a whole can be greatly improved. Further, regarding the manufacturing work, when manufacturing the permanent magnet, it is only necessary to make the end portion a convex curved surface in advance, and no extra work is required, so that the complexity of the work can be greatly suppressed.

In the brushless DC motor of claim 2, since the permanent magnet is curved over the entire range so that the central portion is recessed, a relatively thin rectangular parallelepiped permanent magnet is used. In this case, significant stress concentration occurred at the end corners, but it can be dispersed not only in the almost entire range of the convex curved surface of the end but also in the curved part other than the end, and the mechanical properties of the rotor as a whole The strength can be greatly improved. Also,
Also in manufacturing work, when manufacturing permanent magnets, make the end part a convex curved surface in advance and curve the entire range, and change the shape of the permanent magnet insertion hole formed in the rotor core to the cross-sectional shape of the permanent magnet. Since it only needs to be adapted and no extra work is required, the complexity of work can be greatly suppressed.

[0012]

Embodiments will now be described in detail with reference to the accompanying drawings showing embodiments. 4 is a longitudinal sectional view showing an embodiment of the brushless DC motor of the present invention, FIG. 3 is a perspective view showing the structure of a rotor, FIG. 2 is a perspective view showing the shape of a permanent magnet, and FIG. 1 is a structure of the rotor. FIG.

As shown in FIG. 4, the brushless DC motor includes an armature 1 formed by winding an armature winding around a plurality of slits formed on the inner surface of a substantially cylindrical armature core, and an inner diameter of the armature 1. The rotor 2 has at least one pair (two pairs in the illustrated embodiment) of permanent magnets 2b embedded in a rotor core 2a having a slightly smaller outer diameter.
In the rotor 2 shown in FIGS. 1 and 3, permanent magnets 2b are embedded in a direction perpendicular to the radial direction of the rotor 2, and in order to prevent short circuit of magnetic flux generated by the adjacent permanent magnets 2b,
A gap 2c for preventing a magnetic flux short circuit is formed extending in the radial direction from the end of the permanent magnet 2b to the vicinity of the outer end of the rotor core 2a. The permanent magnet 2b has a convex curved surface at its end portion in the direction perpendicular to the radial direction of the rotor 2 (see FIG. 2). The portion remaining outside the void 2c is the magnetic flux short circuit portion 2d.

It is possible to use a ferrite magnet as the permanent magnet 2b, but it is preferable to use a rare earth magnet. The permanent magnet 2b is inserted into the corresponding hole of the rotor core 2a with an adhesive such as an epoxy intervening. In the case of the brushless DC motor having the above configuration, since the end of the permanent magnet 2b is formed into a convex curved surface, the stress concentration at the end of the permanent magnet 2b can be dispersed over almost the entire range of the convex curved surface. High-speed rotation can be achieved without employing any other reinforcing method, and peeling and damage of the permanent magnet 2b during high-speed rotation can be reliably prevented.

Next, a manufacturing operation of the rotor 2 having the above structure will be described. For example, a silicon steel plate is punched into a clearance fitting dimension with respect to a permanent magnet, or wire cutting is performed to obtain a unit silicon steel plate (see FIG. 5). A plurality of unit silicon steel plates obtained as described above are laminated and pressed into the shaft of the rotor 2. Then, the permanent magnet 2b is inserted into the magnet insertion portion of the laminated silicon steel plates with the epoxy adhesive interposed, and fixed by the adhesive to obtain the rotor 2 having the embedded magnet structure. As the epoxy adhesive, it is preferable to use one having an adhesive force of 1 to ² kg / mm ² or more when the rotor has an outer diameter of about 60 mm.

As is clear from the above description, since the openings to be formed in the silicon steel plate only need to be the portions into which the permanent magnets 2b are inserted and the voids 2c, the openings in the silicon steel sheet need not be formed as compared with the case where the openings for bolting are formed. The processing on the steel plate can be simplified, and the reinforcing work can be simplified as compared with the case where the bolt is inserted and the nut is tightened. Then, only by performing the simplified work, the local stress concentration can be significantly reduced as compared with the conventional rotor, and the mechanical strength of the rotor 2 can be significantly improved.

[0017]

[Embodiment 2] FIG. 6 is a longitudinal sectional view showing a rotor in another embodiment of the brushless DC motor of the present invention, and FIG. 7 is a perspective view showing the shape of a permanent magnet. The only difference is that the permanent magnet 2b is curved over the entire range. More specifically, the permanent magnet 2b is curved with a predetermined curvature with reference to a central portion parallel to the axis of the rotor 2, and the central portion is positioned so as to directly face the axis of the rotor 2. In addition, the orientation is set so that the central part is closer to the axis.

Therefore, when a rectangular parallelepiped permanent magnet is embedded, a large stress concentration is likely to occur near the end portion of the permanent magnet 2 near the outer periphery of the rotor 2, and the stress concentration during high speed rotation is reduced to the end of the permanent magnet 2b. Since it can be dispersed in the convex curved surface of the portion and the entire curved portion, the permanent magnet 2b can be prevented from peeling off and being damaged during high-speed rotation, and the mechanical strength of the rotor 2 as a whole can be greatly improved.

[0019]

As described above, according to the first aspect of the present invention, by simply changing the shape of the end portion of the permanent magnet, the stress concentration at the place where a remarkably large stress concentration occurs in the conventional rotor is significantly increased. It is possible to reduce the mechanical strength of the rotor, and it is possible to significantly improve the mechanical strength of the rotor, and it is possible to significantly reduce the complexity of the work because no extra work such as drilling is required. ..

According to the second aspect of the present invention, since the shape of the permanent magnet as a whole is also changed, the stress concentration can be further greatly reduced, the mechanical strength of the rotor can be greatly improved, and the manufacturing work can be performed. Also, since it is not necessary to perform extra work such as drilling, there is a peculiar effect that the complexity of work can be significantly suppressed.

[Brief description of drawings]

[0021]

FIG. 1 is a vertical sectional view showing the structure of a rotor in an embodiment of a brushless DC motor of the present invention.

[0022]

FIG. 2 is a perspective view showing the shape of a permanent magnet.

[0023]

FIG. 3 is a perspective view showing a rotor in one embodiment of the brushless DC motor of the present invention.

[0024]

FIG. 4 is a vertical sectional view schematically showing an embodiment of the brushless DC motor of the present invention.

[0025]

FIG. 5 is a plan view showing a unit silicon steel sheet.

[0026]

FIG. 6 is a vertical cross-sectional view showing the structure of a rotor in another embodiment of the brushless DC motor of the present invention.

[0027]

FIG. 7 is a perspective view showing the shape of a permanent magnet.

[0028]

FIG. 8 is a schematic view showing an example of a rotor having an embedded magnet structure.

[0029]

[Explanation of symbols]

1 armature 2 rotor 2a rotor core 2
b Permanent magnet

Claims (2)

[Claims] 1. An armature (1) formed by winding an armature winding around an armature core, and a permanent magnet (2b) around a rotor core (2a).
A brushless DC motor including a rotor (2) in which a permanent magnet (2b) is embedded in a rotor core (2a).
Is embedded so as to face in a direction perpendicular to the radial direction of, and the end of the permanent magnet (2b) in the direction perpendicular to the radial direction of the rotor core (2a) is formed into a convex curved surface. Brushless DC motor characterized by. 2. The brushless DC motor according to claim 1, wherein the entire range of the permanent magnet (2b) is curved so that a central portion parallel to the axis of the rotor is recessed.