JPH07108082B2 - Abduction type brushless DC motor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a radial air gap type brushless DC motor using a permanent magnet rotor.

More specifically, the present invention comprises two stator yokes each having a magnetic pole piece formed by bending a soft magnetic metal plate, and an annular coil arranged between the two stator yokes. Are magnetically short-circuited by forming a slit, a notch or a hole in one or both of the magnetic pole piece and the tubular portion to increase the electric resistance in the circumferential direction without increasing the magnetic resistance in the axial direction. The present invention relates to a stator of a brushless DC motor that suppresses eddy current loss and improves motor efficiency.

[Conventional technology]

There are iron core type and non-iron core type stator structures for brushless DC motors. The iron-core stator has a structure in which a large number of electromagnetic steel plates punched into a predetermined shape are laminated and wound in the slots. In this case, the inner surface of the slot is insulated,
The winding is performed by dividing each slot.

In such an iron-core stator, the winding work must be divided into each slot as described above, which complicates the winding work and causes a cost increase.

On the other hand, the ironless core type stator is advantageous in terms of winding, but naturally the efficiency of the magnetic circuit is poor due to the absence of an iron core, and therefore a high-performance permanent magnet is required to achieve the desired motor performance. It is unavoidable that it becomes necessary and expensive.

Therefore, the inventors of the present invention have previously made it possible to solve such problems by using two stator yokes each of which is formed by bending a soft magnetic metal plate to form half the number of magnetic pole pieces of the rotor magnet. We proposed a brushless DC motor with a stator structure in which an annular coil is sandwiched so as to face a magnet (Japanese Patent Application No. 62-177399).

[Problems to be Solved by the Invention]

In this type of stator, the stator yoke plays a large role in the magnetic circuit, and in particular, its shape greatly affects the 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 tubular portion that magnetically short-circuits the two stator yokes, so that an eddy current flows in the circumferential direction of the side surface of the tubular portion. In addition, an eddy current is generated in the magnetic pole piece facing the magnet via the stator yoke and the air gap. The Joule loss (eddy current loss) due to these eddy currents is large and there is a problem that the motor efficiency is poor.

In particular, as the motor speed increases and the cycle of the alternating current flowing through the coil decreases, the loss due to the eddy current increases.

The object of the present invention is to solve the above technical problems,
An object of the present invention is to provide a stator of a brushless DC motor capable of reducing the eddy current loss generated in the stator yoke and improving the motor efficiency.

[Means for Solving the Problems]

The present invention is an outer rotation type brushless DC motor having a rotor and a stator. Here, in the rotor, a rotor magnet is attached to an inner peripheral surface of a cup-shaped rotor yoke, and a shaft is fixed by a bush fixed at the center.
The stator has two stator yokes each having a magnetic pole piece formed by bending the outer circumference of a soft magnetic metal plate, and a soft magnetic cylindrical shape that is interposed between the two stator yokes and magnetically shorts the inner peripheral edges thereof. Section and an annular coil located on the outer peripheral side of the soft magnetic cylindrical section, having an air gap in the radial direction between the stator pole piece and the rotor magnet, and the soft magnetic cylindrical section in the axial direction. The structure has long slits or notches.

The slit or notch may be formed only in the tubular portion, or may be formed in both the tubular portion and the pole piece.
It is desirable that the slit be formed as thin as possible and formed in the axial direction.

As the structure of the stator yoke, the tubular portions may be integrally formed by drawing, and the tubular portions of both the stator yokes may be fitted together. Alternatively, the tubular portion may be made of a soft magnetic material different from that of both stator yokes, and may be coupled to the stator yokes. In that case, the resin may be molded with a soft magnetic material powder.

It should be noted that the term "cylindrical" is used herein as a term having a broad concept including not only a cylindrical shape but also a polygonal cylindrical shape and other irregularly shaped cylindrical shapes.

The present invention can be applied to both the outer rotor type and the inner rotor type.

[Action]

The stator yoke is manufactured by pressing a soft magnetic metal plate. The tubular portion that magnetically short-circuits the two stator yokes may be integrated with the stator yoke, or may be formed as a member separate from the stator yoke and formed into a predetermined shape to be coupled to the stator yoke. The coil has a simple annular shape, and after the coil is completed, it may be sandwiched by the stator yokes from both sides, so that the coil can be easily wound by using an automatic winding machine.

The magnetic pole pieces of the two stator yokes that sandwich the coil are arranged on the circumference and face the rotor magnet, and an air gap in the radial direction is formed. The position of the rotor magnet is detected by the magnetic pole detector, and the rotor is continuously rotated by energizing the coil at a timing corresponding thereto.

By energizing the coil, an alternating magnetic flux flows in the axial direction in the tubular 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 the slits, notches, holes, etc. are formed in the cylindrical portion, the electric resistance in the circumferential direction becomes large, and it becomes difficult for current to flow, so that loss due to eddy current can be suppressed. At this time, if slits or notches are elongated in the axial direction or a large number of holes are arranged in the axial direction, the electric resistance in the circumferential direction increases, but the magnetic resistance in the axial direction hardly increases, and good results are obtained.

Therefore, if a slit or the like is formed in both the tubular portion and the magnetic pole piece, better motor characteristics can be obtained.

If the tubular part is composed of a member separate from the stator yoke,
The structure of the stator yoke is simplified and press working becomes easy. Further, since the structure is simple, the precision of the parts can be improved, and both stator yokes can have the same shape. Further, the cross-sectional area and material of the tubular portion can be changed arbitrarily regardless of the plate thickness of the stator yoke, which facilitates the design of the magnetic circuit.

〔Example〕

FIG. 1 shows the invention of a 4-pole outer rotor type brushless DC.
It is an exploded perspective view showing an example applied to a motor.

The rotor 10 is a bush in which a rotor magnet 14 is attached to the inner peripheral surface of a cup-shaped rotor yoke 12 and is fixed to the center.
It is a structure in which a shaft 18 is fitted by means of 16. The rotor magnet 14 is composed of a ring-shaped permanent magnet, and is 4 in the radial direction.
It is extremely magnetized. Of course, a combination of a plurality of segment-shaped permanent magnets may be used.

On the other hand, the stator 20 includes the first and second stator yokes 22, 24 formed by bending the outer peripheral side of the soft magnetic metal plate.
This is a structure in which the annular coil 26 is sandwiched by. Here, the first and second stator yokes 22 and 24 spread out in a fan shape from the center in opposite directions, and the pole pieces on the outer peripheral side.
28 and 29 are formed, and the cylindrical portions 30 and 31 are integrally formed on the inner peripheral side.

The feature of this embodiment is that the cylindrical portion 3 of both stator yokes 22 and 24 is
The point is that axial slits 60 and 61 are formed at 0 and 31.
Here, two slits 60 and 61 are provided symmetrically with respect to the central axis.

The coil 26 has a structure in which a bobbin 32 having flanges at both ends of a winding core is provided with a winding 33, and a winding terminal is entwined with a pin terminal 34 for connection.

In the first and second stator yokes 22 and 24, one cylindrical portion 31 is fitted into the other cylindrical portion 30 so that the outer surfaces of the magnetic pole pieces 28 and 29 are just opposite to the inner surface of the rotor magnet 14. In addition, the magnetic pole pieces have a magnetic imbalance on the circumference where the air gap is formed (that is,
(So that the space angle formed by both stator yokes is non-right angle)
Can be combined. The positioning and fixing are performed by fitting resin projections 35 provided on both outer surfaces of the coil bobbin 32 with holes 36, 37 formed in both stator yokes 22, 24 and heat caulking the resin projections 35.

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

A cross section of an example of a fan motor using a brushless DC motor having such a basic structure is shown in FIG. The parts corresponding to the respective members are designated by the same reference numerals, and the description thereof will be omitted. A rotor yoke 12 is fitted inside an impeller (impeller) 40 integrally formed of synthetic resin, and fixed by thermal caulking. The shaft 18 of the rotor 10 is a case
It is rotatably supported by bearings 44 and 45 attached to 42, and is held by an E ring 48 while being preloaded by a spring 46. The stator is attached to the case 42.

A circuit board 50 is attached to the inside of the case 42 with screws 51. A coil excitation switching logic circuit, a switching element, a magnetic pole detector 38, etc. are mounted on the circuit board 50, and the pin terminals 34 of the coil 26 are also mounted on the circuit board 50. The required power is externally supplied by the cord 52.

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

When the coil 26 is energized, a magnetic flux that changes in the axial direction is generated in the cylindrical portions 30 and 31 of the stator yokes 22 and 24. As a result, eddy currents tend to flow through the cylindrical portions 30 and 31 in the circumferential direction of the side surface. However, since the slits 60 and 61 are formed in the cylindrical portions 30 and 31, the electric resistance in the circumferential direction is large, so that the eddy current is suppressed, and as a result, the loss can be reduced.

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 the slit 62 is formed from the upper end to the lower end of the cylindrical portion 30 of the stator yoke 22.

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

FIGS. 5 to 7 show examples in which slits or notches are formed in the pole pieces. In FIG. 5, the magnetic pole piece 28 of the stator yoke 22 is formed with three slits 64 extending in the axial direction. Further, the fan-shaped flat plate portion of the stator yoke 22 is also formed with an elongated hole 68 extending in the radial direction. In FIG. 6, one square notch 65 is provided at the center. As shown in FIG. 7, a larger parabolic notch 66 may be provided at the center. However, if it is too large, the function as a magnetic pole piece is hindered, so in consideration of it, the size is set to an appropriate size.

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

Therefore, from the above description, slits, notches, holes, etc. may be provided in both the cylindrical portion and the magnetic pole pieces, which can further reduce the eddy current loss.

In the above-mentioned embodiment, the cylindrical portion is integrally press-molded with the stator yoke, and the structure is such that the cylindrical portions of both stator yokes fit together. However, the cylindrical portion 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 portion are coupled to each other and a coil is arranged therebetween.

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

〔The invention's effect〕

This invention comprises 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 arranged between both stator yokes, and a tubular portion is provided 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 tubular portion or magnetic pole pieces, the tubular portion of the stator yoke is axially magnetic flux by energizing the coil. Eddy current tends to flow in the cylindrical portion in the circumferential direction, but the electrical resistance in the circumferential direction is large and it is difficult for the current to flow, so loss due to eddy current can be suppressed and motor efficiency can be improved. . On the other hand, since magnetic flux also flows through the magnetic pole pieces, eddy current is generated, but the effect similar to the above can be obtained by providing a notch or a hole.

In particular, when slits are elongated in the axial direction or a large number of holes are arranged in the axial direction, the electric resistance in the circumferential direction increases, but the magnetic resistance in the axial direction hardly increases, and good results are obtained.

If the tubular part is composed of a member separate from the stator yoke,
The structure of the stator yoke is simplified, press work is facilitated, the precision of parts can be improved, both stator yokes can be formed in the same shape, which facilitates the manufacture, and the tubular portion regardless of the thickness of the stator yoke. Since the cross-sectional area and the material can be arbitrarily changed, the magnetic circuit can be easily designed and the magnetic circuit can be efficiently designed.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a brushless DC motor according to the present invention, FIG. 2 is a sectional view showing an example in which the present invention is applied to a fan motor, and FIG. FIG. 4 is a perspective view showing an embodiment, and FIGS. 4 to 7 are perspective views showing still another embodiment of the stator yoke. 10 ... Rotor, 12 ... Rotor yoke, 14 ... Rotor magnet, 16 ... Bush, 18 ... Shaft, 20 ... Stator, 22 ... First stator yoke, 24 ... Second stator yoke, 26 ...... Toroidal coil, 28,29 …… Pole piece, 30,
31 …… Cylinder part, 32 …… Bobbin, 33 …… Winding, 38 …… Magnetic pole detector, 60,61,62,64 …… Slit, 63 …… Hole, 65,66…
… Notches.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 56-10066 (JP, A) JP 61-240850 (JP, A) JP 62-293959 (JP, A)

Claims (4)

[Claims] 1. An outer rotation type brushless DC motor having a rotor (10) and a stator (20), wherein the rotor (10) has a rotor magnet (14) on an inner peripheral surface of a cup-shaped rotor yoke (12). The shaft (18) is fixed by the bush (16) fixed to the center, and the stator (20) is formed by bending the outer peripheral side of the soft magnetic metal plate to form two pole pieces (28, 29). Stator yoke (22,
24) and both stator yokes (22, 24)
The soft magnetic cylindrical part (30,3
1) and an annular coil (26) located on the outer peripheral side of the soft magnetic cylindrical portion (30, 31), and the stator pole piece (28, 29).
With an air gap in the radial direction between the rotor magnet (14) and the rotor magnet (14), and the soft magnetic cylindrical portion (30, 31) has axially long slits (60, 61, 62) or notches. Brushless DC motor. 2. The outer rotor type brushless DC motor according to claim 1, wherein the stator (20) has a slit (64) or a notch (65) in which the magnetic pole pieces (28, 29) are long in the axial direction. 3. The stator (20) includes a soft magnetic cylindrical portion (30, 3).
1) is press-formed integrally with the stator yokes (22, 24), and the tubular parts (30, 31) of both stator yokes (22, 24)
The outer rotation type brushless DC motor according to claim 1 or 2, wherein: 4. The outer rotation type brushless DC motor according to claim 1, wherein the stator (20) has a soft magnetic cylindrical portion made of a member separate from both stator yokes.