JPH01202143A - Stator for brushless dc motor - Google Patents

Abstract

PURPOSE:To reduce an overcurrent loss generated in a stator yoke and to contrive to improve a motor efficiency by fitting an apparatus with two stator yokes obtained by forming pole pieces through bending a soft magnetic metal plate and with an annular coil to be arranged between both stator yokes. CONSTITUTION:The cylinder part 31 of one of stator yokes 22, 24 is fitted into the cylinder part 30 of the other stator yoke in such manner that the outside surfaces of pole pieces 28, 29 of said stator yokes 22, 24 face the inner surface of a rotor magnet 14. In the pole pieces 28, 29, moreover, the spaces formed by both stator yokes 22, 24 are unperpendicularly combined with each other so that a magnetic imbalance is generated over the cylinder where an air gap is formed. Further, an apparatus is positioned and fixed by fitting of resin protrusions 35 respectively provided on both outside surfaces of a coil bobbin 32 into holes 36, 37 made in both stator yokes 22, 24 and by heat caulking of said resin protrusions 35.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a stator in a radial air gap type brushless DC motor using a permanent magnet rotor.

More specifically, this invention includes two stator yokes whose magnetic pole pieces are formed by bending soft magnetic metal plates, and an annular coil disposed between both stator yokes. A slit, notch, or hole is formed in one or both of the pole piece and the cylindrical part to increase the electrical resistance in the circumferential direction without increasing the magnetic resistance in the axial direction. This invention relates to a stator for a brushless DC motor that suppresses eddy current loss and improves motor efficiency.

[Conventional technology]

There are two types of stator structures for brushless DC motors: iron core type and iron core type. The iron-core stator has a structure in which a large number of electromagnetic steel plates punched into a predetermined shape are laminated and wires are wound around the slots.

In this case, the inner surface of the slot is insulated and the wire is wound by dividing into each slot.

In such a core stator, the winding must be divided into each slot as described above, which complicates the winding work and increases costs.

On the other hand, coreless stators are advantageous in terms of winding, but of course the efficiency of the magnetic circuit is poor due to the lack of an iron core.Therefore, in order to achieve the desired motor performance, high-performance permanent magnets are required. It is inevitable that this will be necessary and expensive.

Therefore, the present inventors first bent a soft magnetic metal plate to form magnetic pole pieces with half the number of magnetic poles of the rotor magnet as a solution to this problem.

proposed a brushless DC motor having a stator structure in which an annular coil is sandwiched between two stator yokes such that each pole piece faces a rotor magnet (Japanese Patent Application No. 177399/1982).

[Problem to be solved by the invention]

In this type of stator, the stator yoke plays a large role in the magnetic circuit, and its shape particularly has a large effect on motor characteristics (efficiency).

When the coil is energized when the motor is driven, a magnetic flux that changes in the axial direction is generated in the cylindrical portion that magnetically shorts the two stator yokes, so that an eddy current flows in the circumferential direction of the side surface of the cylindrical portion. Eddy currents also occur in the stator yoke and the magnetic pole piece that faces the magnet via the air gap. There was a problem in that the Joule loss (eddy current loss) caused by these eddy currents was large and the motor efficiency was poor.

In particular, the higher the motor speed is and the shorter the period of the alternating current flowing through the coil, the greater the loss due to eddy currents.

The purpose of this invention is to solve the above technical problems,
An object of the present invention is to provide a stator for a brushless DC motor that can reduce eddy current loss occurring in a stator yoke and improve motor efficiency.

[Means to solve the problem]

The present invention, which can achieve the above object, is a brushless DC motor stator having a structure in which there is an air gap in the radial direction between the low 9 IF stone and the stator magnetic pole piece, in which the magnetic pole piece is formed by bending a soft magnetic metal plate. It is equipped with a stake yoke and an annular coil arranged between both stator yokes, and the two stator yokes are magnetically short-circuited by a cylindrical part, and the cylindrical part or the magnetic pole piece has a slit or a notch. Alternatively, it is a stator of a brushless DC motor with holes formed therein.

The slits, notches, or holes may be formed only in the cylindrical part, only in the magnetic pole piece, or in both the cylindrical part and the magnetic pole piece.

It is desirable that the slits be as thin as possible and formed in the axial direction.In the case of holes, it is better to make them small in diameter and form a large number of them in the axial direction.

As for the structure of the stator yoke, the cylindrical portion may also be integrally formed by drawing, and the cylindrical portions of both stator yokes may be fitted together.

Alternatively, the cylindrical portion may be made of a soft magnetic material separate from both stator yokes and coupled to the stator yokes. In that case, it is also possible to mold the resin filled with powder of a soft magnetic material.

Note that the term "cylindrical" is used herein as a broad term that includes not only cylindrical shapes, but also polygonal cylindrical shapes and other irregularly shaped cylindrical shapes.

This invention can be applied to both outer rotor type and inner rotor type.

[Effect]

The stator yoke is manufactured by pressing a soft magnetic metal plate. The cylindrical part that magnetically short-circuits both stator yokes may be integrated with the stator yoke, or may be a separate member from the stator yoke, manufactured in a predetermined shape, and coupled to the stator yoke. The coil has a simple annular shape and can be easily wound using an automatic winding machine, since it is only necessary to sandwich the coil between the stator yokes from both sides after the coil is completed.

The magnetic pole pieces of the two stator yokes sandwiching the coil are arranged on the circumference and face the rotor magnet, forming a radial air gap. The position of the rotor magnet is detected by a magnetic pole detector, and the rotor rotates continuously by energizing the coils at the appropriate timing.

When the coil is energized, an alternating magnetic flux flows in the axial direction in the cylindrical portion of the stator yoke. As a result, an eddy current tends to flow in the cylindrical portion in the circumferential direction of the side surface. However, in the present invention, since slits, notches, holes, etc. are formed in the cylindrical portion, the electric resistance in the circumferential direction increases, making it difficult for current to flow, so that losses due to eddy currents can be suppressed. At this time, if slits or notches are provided long and thin in the axial direction, or if a large number of holes are arranged in the axial direction, the electric resistance in the circumferential direction becomes large, but the magnetic resistance in the axial direction is difficult to increase, and good results can be obtained.

Even if slits, notches, holes, etc. are formed in the magnetic pole piece instead of the cylindrical portion, eddy current loss can be suppressed for the same reason.

Therefore, even better motor characteristics can be obtained by providing slits or the like in both the cylindrical portion and the magnetic pole pieces.

If the cylindrical part is made of a separate member from the stator yoke,
The structure of the stator yoke is simplified and press working becomes easier. Furthermore, since the structure is simplified, it is possible to improve the precision of the parts, and both stator yokes can be made into the same shape. Furthermore, the cross-sectional area and material of the cylindrical portion can be arbitrarily changed regardless of the plate thickness of the stator yoke, which facilitates the design of the magnetic circuit.

〔Example〕

Figure 1 shows this invention as a 4-pole outer rotor type brushless D.
It is an exploded perspective view showing an example applied to a C motor.

The rotor 10 has a structure in which a rotor magnet 14 is attached to the inner peripheral surface of a cup-shaped rotor yoke 12, and a shaft 18 is fitted through a bush 16 fixed at the center. The rotor magnet 14 is made of a ring-shaped permanent magnet, and is magnetized with four poles in the radial direction. Of course, a combination of a plurality of segmented permanent magnets may also be used.

On the other hand, the stator 20 has first and second stator yokes 22 formed by bending the outer circumferential side of a soft magnetic metal plate.
．． It has a structure in which an annular coil 26 is sandwiched between 24 and 24. Here, the first and second stator yokes 22.24 each fan out in opposite directions from the center to form magnetic pole pieces 28.29 on the outer periphery, and integrally have a cylindrical portion 30.31 on the inner periphery. form a formed structure.

A feature of this embodiment is that axial slits 60.61 are formed in the cylindrical portions 30.31 of both stator yokes 22 and 24. Here, two slits 60, 61 are provided symmetrically about the central axis.

The coil 26 is a bobbin 3 having flanges at both ends of the winding core.
It has a structure in which a winding 33 is applied to the wire 2 and the end of the winding is connected to a pin terminal 34 by wrapping it around.

The first and second stator yokes 22 , 24 are arranged so that the outer surfaces of their pole pieces 28 , 29 just face the inner surface of the rotor magnet 14 , with the negative cylindrical portion 31 inside the other cylindrical portion 30 . In addition, the pole pieces are aligned so that a magnetic imbalance occurs on the circumference where the air gap is formed (i.e., the spatial angle formed by both stator yokes is non-perpendicular). . These positioning and fixing are performed by fitting the resin protrusions 35 provided on both outer surfaces of the coil pobbin 32 into holes 36, 37 formed in both stator yokes 22, 24, and thermally caulking the resin protrusions 35.

A magnetic pole detector 38 such as a Hall element is attached near the rotor magnet 14. This magnetic pole detector 38 is preferably provided near the magnetic neutral point of the first and second stator yokes 22 and 24 when they are combined and excited.

FIG. 2 shows a cross section of an example of a fan motor using a brushless DC motor having such a basic structure. Portions corresponding to the above-mentioned members are given the same reference numerals, and explanations thereof will be omitted. The rotor yoke 12 is fitted inside an impeller (impeller) 40 integrally molded from synthetic resin and fixed by heat caulking. Rotor lO shaft 18
is rotatably supported by bearings 44 and 45 attached to the case 42, and is held by an E-ring 48 while being preloaded by a spring 46. Stator is case 4
Can be attached to 2.

A circuit board 50 is attached to the inside of the case 42 with screws 51. Note that this circuit board 50 includes a coil excitation switching logic circuit, a switching element, and a magnetic pole detector 3.
8 etc. is mounted, and the pin terminal 34 of the coil 26 is also this circuit.

It is attached to the substrate 50. The necessary power is supplied externally by cord 52.

In the brushless DC motor of the above embodiment, the coil 26
Each magnetic pole piece 28 of the two stator yokes 22゜24 sandwiching the
．． 29 are arranged on the circumference and face the rotor magnets, forming an air gap in the radial direction. Rotor magnet 14
The position of the rotor is detected by the magnetic pole detector 38, and the rotor is continuously rotated by energizing the coil at a timing corresponding to the position.

By energizing the coil 26, the stator yokes 22 and 24
A magnetic flux that varies in the axial direction is generated in the cylindrical portion 30.31. As a result, eddy currents tend to flow in the cylindrical portions 30° and 31 in the circumferential direction of the side surfaces. However, since the slits 60.degree. 61 are formed in the cylindrical portion 30.31, the electrical resistance in the circumferential direction is large, and therefore eddy currents are suppressed, and as a result, loss can be reduced.

Note that the shape and number of slits formed in the cylindrical portion can be changed as appropriate. The embodiment shown in FIG. 3 is an example in which a slit 62 is formed from the upper end of the cylindrical portion 30 of the stator yoke 22 to the lower end.

Holes may be formed instead of slits. FIG. 4 shows an example. A large number of holes 63 are formed in the cylindrical portion 31 of the stator yoke 24 in an axial direction. Here, four rows are provided axially symmetrically.

FIGS. 5 to 7 show examples in which slits and notches are formed in the magnetic pole pieces. In FIG. 5, the pole piece 28 of the stator yoke 22
Three slits 64 extending in the axial direction are formed in each. Further, elongated holes 68 extending in the radial direction are also formed in the fan-shaped flat plate portion of the stator yoke 22. In FIG. 6, one square notch 65 is provided in the center. As shown in FIG. 7, an even larger parabolic notch 66 may be provided in the center. However, if it is too large, its function as a magnetic pole piece will be inhibited, so take this into account and set it to an appropriate size.

When slits, notches, holes, etc. are provided in these magnetic pole pieces, the eddy current loss 1 is also reduced for the same reason as when slits, etc. are formed in the cylindrical portion.

Therefore, from the above description, it is possible to provide slits, notches, holes, etc. in both the cylindrical part and the magnetic pole piece, thereby further reducing eddy current losses.

In the above embodiment, the cylindrical part is integrally press-molded with the stator yokes, and the cylindrical parts of both stator yokes fit together, but the cylindrical part is made of a soft magnetic material separate from both stator yokes. The present invention can also be applied to a stator structure in which two stator yokes and one cylindrical part are connected and a coil is arranged between them.

Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to only such configurations.
Although the above embodiment uses one stator having two stator yokes and one coil, it can also be applied to a motor having a structure in which a plurality of such stators are arranged in series in the axial direction. Further, although each of the above embodiments is an example of an outer rotor type, the present invention can also be applied to an inner rotor type.

〔Effect of the invention〕

The present invention includes a stator yoke in which a magnetic pole piece is formed by bending a soft magnetic metal plate as described above, and an annular coil disposed between both stator yokes. Since it is a stator of a brushless DC motor that is magnetically short-circuited and has slits, notches, or holes formed in the cylindrical portion or magnetic pole piece,
When the coil is energized, the magnetic flux changes in the axial direction in the cylindrical part of the stator yoke, and as a result, an eddy current tries to flow in the cylindrical part in the circumferential direction, but the electric resistance in the circumferential direction is large and it is difficult for the current to flow. Therefore, loss due to eddy current can be suppressed and motor efficiency can be improved. On the other hand, since magnetic flux flows through the magnetic pole pieces, eddy currents are generated, but the same effect as described above can be obtained by providing a cutout hole or the like.

In particular, if the slit is provided elongated in the axial direction or if a large number of holes are arranged in the axial direction, the electrical resistance in the circumferential direction increases, but the magnetic resistance in the axial direction is difficult to increase, and good results can be obtained.

If the cylindrical part is made of a separate member from the stator yoke,
The structure of the stake yoke is simplified, making it easier to press, making it possible to improve the precision of the parts.Since both stator yokes can be made into the same shape, it is easier to manufacture, and regardless of the plate thickness of the stator yoke, the cylindrical part Since the cross-sectional area and material of the magnetic circuit can be changed arbitrarily, the design of the magnetic circuit becomes easy, and the magnetic circuit can be designed with good efficiency.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing one embodiment of a brushless DC motor according to the present invention, FIG. 2 is a sectional view showing an example of the application of the present invention to a fan motor, and FIG. 3 is an exploded perspective view showing an example of a brushless DC motor according to the present invention. FIGS. 4 to 7 are perspective views showing still other embodiments of the stator yoke. 10...Rotor, 12...Rotor yoke, 14...
- Rotor magnet, 18... Shaft, 20... Stator, 22... First stator yoke, 24... Second
stator yoke, 26... annular coil, 28゜2
9... Magnetic pole piece, 30.31... Cylindrical part, 38...
Magnetic pole detector, 60, 61.64...slit, 63.
...hole, 65.66...notch. Patent applicant: Minebea Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4

Claims (7)

[Claims] 1. In the stator of a brushless DC motor, which has a structure in which there is an air gap in the radial direction between the rotor magnet and the stator pole piece, the stator yoke is formed by bending a soft magnetic metal plate to form the pole piece, and the stator yoke is arranged between both stator yokes. A brushless DC characterized in that the two stator yokes are magnetically short-circuited by a cylindrical part, and a slit, notch, or hole is formed in the cylindrical part. motor stator. 2. In the stator of a brushless DC motor, which has a structure in which there is an air gap in the radial direction between the rotor magnet and the stator pole piece, the stator yoke is formed by bending a soft magnetic metal plate to form the pole piece, and the stator yoke is arranged between both stator yokes. A brushless DC motor, characterized in that the two stator yokes are magnetically short-circuited by a cylindrical part, and a slit, notch, or hole is formed in the magnetic pole piece. stator. 3. In the stator of a brushless DC motor, which has a structure in which there is an air gap in the radial direction between the rotor magnet and the stator pole piece, the stator yoke is formed by bending a soft magnetic metal plate to form the pole piece, and the stator yoke is arranged between both stator yokes. The stator yoke is magnetically short-circuited by a cylindrical part, and a slit, notch or hole is formed in both the cylindrical part and the magnetic pole piece. Characteristic brushless DC motor stator. 4. 4. The stator according to claim 1, wherein the slit or notch is formed long in the axial direction. 5. 4. The stator according to claim 1, wherein a large number of holes are formed side by side in the axial direction. 6. 6. The stator according to claim 4, wherein the cylindrical portion is integrally press-molded with the stator yoke, and the cylindrical portions of both stator yokes fit together. 7. 6. A stator according to claim 4, wherein the cylindrical portion is made of a soft magnetic material separate from both stator yokes.