JP2001314067A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem with conventional resin magnet rotors molded integrally with shafts that tooling change is required during molding depending on the shape or length of a shaft and resin magnet material is uneconomically used for parts irrelevant to field system. SOLUTION: A shaft 102a and a field magnet portion 101a are coupled with and secured to each other through an aluminum core 118a or the like. In this case an assembly of the field magnet 101a and the aluminum core 118a integrally molded or bonded together is secured on the shaft 102a. Thus, tooling change during molding is disused and aluminum material, laminated steel plates, or the like that is inexpensive is used for the coupling portion irrelevant to field system. As a result, productivity and cost effectiveness is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure of a resin magnet rotor in a brushless motor and a motor incorporating the same.

[0002]

2. Description of the Related Art FIG. 9A shows a conventional resin magnet rotor formed integrally with a shaft. In the figure, 901
Denotes a field magnet unit, 902 denotes a shaft, 903 denotes a bearing support unit for fixing the position of a bearing, and 904 denotes a connection unit that connects the field magnet unit 901 and the shaft 902 via the bearing support unit 903. 902a
Is a rotation preventing process for increasing the coupling strength between the bearing support portion 903 of the resin magnet and the shaft 902.
The field magnet section 901, the bearing support section 903, and the connecting section 904 are formed of a resin magnet material.

In general, the resin magnet rotor is simple to manufacture, and the field magnet portion 901, the connecting portion 904, and the bearing support portion 903 are formed simultaneously by integrally forming the rotor and the shaft, so that the processing cost can be reduced. Resin magnets are also used for parts unrelated to.

FIG. 9B shows a state in which a conventional resin magnet rotor is mounted on a motor. In the figure, 905
Is a bearing, 907 is a stator core formed by laminating a metal plate and winding a copper wire, 908 is a mold frame for molding them, and 909 is a bracket for fixing the rotor 906 together with the mold frame 908 via a bearing 905. Reference numeral 910 denotes a printed wiring board and a magnetic detection element 911.
Has been implemented.

[0005] The motor generates a magnetic field by passing a current through the winding of the stator core 907, and the rotor 906 is rotated by a suction repulsive force acting on the rotor 906.

[0006] Generally, the stator core 907 when the motor rotates.
The stator core 907 and the rotor 90 are arranged so that the magnetic attraction repulsive force of the rotor 906 against the
It is desirable to adjust the mechanical position of 6 and the magnetic flux distribution. However, actually, it is necessary to extend the field magnet portion 901 to the vicinity of the magnetic detection element 911, and the positional relationship of the rotor 906 with respect to the stator core 907 tends to be a positional relationship in which the magnetic center is shifted.

FIG. 10 shows the structure of a molding die for molding a conventional resin magnet rotor. FIG. 10 (B) is a view of the mold as viewed from above, and FIG. 10 (A) is a cross-sectional view along XX.

Reference numeral 912 denotes an orientation magnet for orienting the resin magnet material in a polar anisotropic manner, 913 denotes a shaft stopper for fixing a shaft, 917 denotes a cavity that controls the shape of the resin magnet rotor, and 914 denotes a gate through which the resin magnet material flows into the cavity 917. The mouth, 916 is the nozzle of the injection molding machine, and 915 is the nozzle 916 to the cavity 917.
It is a spool runner that connects to 915a indicates a runner, and 915b indicates a spool.

The resin magnet material is melted at a high temperature, and pressure is applied from a nozzle of an injection molding machine to be injected into a molding die. Therefore, it is injected into the cavity 917 from the gate port 914 via the spool runner 915.
Since a long shaft rotor may be formed, the runner has a structure avoiding the shaft 902. The shaft stopper 913 positions the shaft 902,
Depending on the length of the shaft 902, the shaft stopper 9
Rearrange 13 The length of the moldable shaft may be limited due to the structure of the mold.

[0010]

As described above, in the conventional resin magnet rotor integrally molded with the shaft, the field magnet portion, the connecting portion, and the bearing support portion are formed at the same time, so that the processing cost is low. There was such a problem.

Since resin magnets are used at the same time as the field magnets, such as at the connection portion and the bearing support portion, irrelevant to the field, the material cost is increased, and in the brushless motors to be mass-produced, there is a demand for the market. As a means for achieving a certain high efficiency, it is uneconomical to use a higher-performance and expensive resin magnet.

In terms of mechanical strength, since a soft resin is molded on a shaft having a small diameter, there is a tendency that the rotational strength and the detachment strength tend to be low. The shaft was expensive due to special processing.

In developing a rotor, it is generally desirable to adjust so that the magnetic attraction repulsion of the rotor with respect to the stator when the motor is rotating is not applied in the thrust direction. It took a lot of mold cost and mold production time to get the job done, and it was difficult to achieve the best results in a short development schedule.

In terms of manufacturing, the shaft is placed in a mold so as to form the field magnet portion, the bearing support portion, and the connection portion on the shaft. It was necessary to prepare only and to change the mold every time the shaft length changed, which was a factor to reduce the production volume.

[0015] Further, the length of the spool or runner up to the gate opening due to the presence of the shaft tends to decrease the temperature of the resin magnet material. The route was balanced, and the injection pressure and resin temperature were unbalanced, which had an adverse effect on polar orientation.

At the same time, a large amount of resin magnet remains on the spool runner and is reused by pulverization and drying. However, this is one factor that deteriorates magnetic properties.

According to the present invention, there is provided a brushless motor having a resin magnet rotor and a stator, wherein a connecting member is integrally formed at the time of molding the resin magnet rotor and then fixed to a shaft to improve the productivity of the resin magnet rotor. Aim.

[0018]

In order to solve this problem, the present invention provides a connecting member for fixing a field magnet portion and a shaft, and integrally forming the connecting member when forming the resin magnet rotor, or It is fixed to the shaft after bonding and fixing after molding.

Further, the amount of magnetic flux is increased by using this connecting member as a magnetic material, and the magnetic flux distribution of the rotor can be controlled by adjusting the fixing position of the connecting member.
Adjusting the magnetic center is also effective in reducing motor noise.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a brushless motor having a resin magnet rotor and a stator, wherein the resin magnet rotor is formed in a cylindrical shape and connects a shaft and a field magnet portion. A brushless motor characterized in that the connecting member is integrally formed when the field magnet is formed, and the connecting member is connected to the field magnet. A resin magnet rotor with a connecting member that fixes the field magnet section and the shaft section, and the connecting member is molded together when the field magnet is formed. It has the effect of improving tact.

According to a second aspect of the present invention, in a brushless motor having a resin magnet rotor and a stator, the resin magnet rotor is formed in a cylindrical shape, and a connecting member for connecting a shaft and a field magnet is formed. It is a brushless motor characterized in that the cylindrical field magnet portion and the connecting member are joined by bonding, and is a resin magnet rotor formed into a cylindrical shape, and only the field magnet portion is provided. After molding, the field magnet and the connecting member are bonded and fixed to the shaft, eliminating the need for changing the length of the shaft and changing the work of fixing the connecting member and the field magnet. There is an effect that the process and the production tact can have flexibility.

According to a third aspect of the present invention, there is provided the brushless motor according to the first or second aspect, wherein the connecting member for connecting the shaft and the field magnet portion is made of a magnetic material. A resin magnet rotor formed in a cylindrical shape, in which a connecting member for fixing a field magnet portion and a shaft is made of a magnetic material, and has an effect of increasing the amount of magnetic flux.

According to a fourth aspect of the present invention, there is provided the brushless motor according to the first or second aspect, wherein the thickness of the field magnet is different on both sides of the connecting member.
A resin magnet rotor formed in a cylindrical shape, provided with a connecting member for fixing the field magnet portion and the shaft,
The structure in which the thickness of the field magnet part is different on both sides of the connecting member makes it easier to position the connecting member to the field magnet part, or to fix the field magnet part and the connecting member. Has the effect of making it more robust.

According to a fifth aspect of the present invention, there is provided a brushless motor according to the first or second aspect, wherein a projection is provided on an outer periphery of a connecting member for connecting the shaft and the field magnet portion. A resin magnet rotor formed into a cylindrical shape, provided with a connecting member for fixing the field magnet portion and the shaft, and provided with a projection on the outer peripheral surface of the connecting member; Has the effect of strengthening the fixation.

According to a sixth aspect of the present invention, another hole is provided outside the shaft through hole of the connecting member for connecting the shaft and the field magnet portion.
3. A brushless motor according to claim 2, wherein the resin magnet rotor is formed in a cylindrical shape, and a connecting member for fixing the field magnet portion and the shaft is provided, and a plurality of connecting members are provided outside the shaft through hole of the connecting member. This has the effect of preventing the outer periphery of the connecting member from expanding when the shaft is swaged to the connecting member, and preventing the field magnet portion from being stressed.

According to a seventh aspect of the present invention, in the brushless motor according to the third aspect, the connecting member made of a magnetic material is disposed at a position offset from the center of the field magnet portion. A resin magnet rotor formed in a shape, provided with a connecting member for fixing the field magnet portion and the shaft, the connecting member being made of a magnetic material, and shorter than the field magnet, and the forming position of the connecting member is By adjusting the movement, the magnetic center of the motor with respect to the stator core is adjusted, and there is an effect that thrust vibration is suppressed and noise of the motor can be reduced.

According to an eighth aspect of the present invention, in the brushless motor according to the first or second aspect, the opposite side of the field magnet portion is assembled to a structure close to a stator core of the motor. A resin magnet rotor formed into a cylindrical shape, and a rotor provided with a connecting member for fixing the field magnet portion and the shaft, wherein a portion of the field magnet portion without a gate is located close to the stator core of the motor. The effect that the generated magnetic flux can be used effectively by placing the part not affected by the gate on the stator core side, not the part where the magnetic flux amount is reduced due to disordered orientation near the gate, .

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of the present invention will be described below.

(Embodiment 1) A specific embodiment of the present invention will be described with reference to FIG.

FIG. 1A shows a structure in which a field magnet portion 101a made of a resin magnet and a rotor shaft 102a are connected and fixed by a disk-shaped aluminum core 118a made of aluminum. The aluminum core 118a corresponds to a connecting portion 904 in a conventional rotor. The shaft 102a is provided with a shaft groove 103a for fixing an E-shaped retaining ring for holding a bearing, and a groove 104a for connecting the aluminum core 118a and the shaft 102a. When forming the field magnet portion 101a, the aluminum core 118a as a connecting member is put into a forming die and formed integrally. The integrally molded product is used as a crest 104a.
The shaft 102a and the aluminum core 118a are fixed by press-fitting the shaft 102a that has been processed as described above. Thereafter, an E-shaped retaining ring is inserted into the shaft groove 103a, and a bearing is press-fitted to complete the rotor.

Further, instead of an aluminum core as shown in FIG. 1B, a resin boss 119b may be integrally formed. The resin boss 119b may have a structure also serving as a bearing support, and the shaft groove 103b as shown in FIG. 1A may be omitted.

FIG. 2 shows a structure of a mold for insert-molding the aluminum core 218. FIG. 2B is a view of the mold as viewed from above, and FIG. 2A is a cross-sectional view taken along line XX. 212
Is an orientation magnet for orienting the resin magnet material in a polar anisotropic manner, 217 is a cavity controlling the shape of the resin magnet rotor, 214 is a gate port through which the resin magnet material flows into the cavity 217, 216 is a nozzle of an injection molding machine, 21
A spool runner 5 connects the nozzle 216 to the cavity 217. 215a is a runner, 215
b indicates a spool.

The resin magnet material is melted at a high temperature, and pressure is applied from a nozzle of an injection molding machine to be injected into a molding die. Gate 21 via spool runner 215
4 into the cavity 217. The absence of the shaft eliminates the need for the runner to avoid the shaft, applies pressure evenly to the four gates in the figure, and improves the polar orientation accuracy. Also, since there is no shaft, the runner 215
a becomes shorter.

The resin magnet material is generally used by crushing a formed spool / runner and reusing it after drying. By reducing the amount of reusable material, the characteristics of the resin magnet can be improved.

With the above structural measures, production tact time is improved by eliminating setup change of a molding die due to a difference in shaft length, and at the same time, characteristics of a resin magnet rotor are improved.

(Embodiment 2) As a specific embodiment, FIG.
Description will be made based on (C).

In the rotor configuration similar to that of the first embodiment, a field magnet portion 101c and an aluminum core 118c are fixed with an adhesive 123c. The bonded material is press-fitted into the shaft 102c on which the crest 104c has been processed, so that the shaft 102c and the aluminum core 118c are pressed.
Is fixed. Thereafter, an E-shaped retaining ring is inserted into the shaft groove 103c, and a bearing is press-fitted to complete the rotor.

By fixing the field magnet portion and the aluminum core which is the connecting member by bonding, it is possible to separate the forming of the field magnet portion and the bonding and fixing of the aluminum core, so that the production process and the production tact time are reduced. Can be given flexibility and productivity is improved.

(Embodiment 3) As a specific embodiment, FIG.
Description will be made based on (A).

In a rotor configuration similar to that of the first embodiment, a connecting member is made of a magnetic material. 320a has a thickness of 0.
A laminated core formed by laminating electromagnetic steel sheets of about 3 mm, 321a is a core caulking for caulking and fixing the electromagnetic steel sheets to each other, 322a
Is a shaft fixing caulking for caulking the shaft 302a and the laminated core 320a. Field magnet unit 30
1a (corresponding to 501 shown in FIG. 5A) corresponds to FIG.
As shown in the figure. 8 orientation magnets 512
(See FIG. 5 (B)) are arranged alternately with N poles and S poles, so that the magnetic path length of the field magnet section is increased.

FIG. 5B shows a case where the laminated core is integrally formed.
The magnetic field lines 524 from the oriented magnet 512 are drawn to the laminated core 520, which is a magnetic material, and concentrated at the center of the field magnet portion. As a result, the magnetic flux density of the field magnet portion 301a increases, and the lines of magnetic force interlinking with the stator core of the motor increase, contributing to an improvement in motor efficiency. Alternatively, an adhesive structure may be used as shown in FIG.

Further, as shown in FIG. 4, by increasing the thickness of the field magnet portion 401 on both sides of the laminated core 420 on the gate side from the opposite side of the gate, positioning for fixing the laminated core 420 is achieved, and especially adhesion is performed. In the case of assembling, workability can be improved. Also in the case of integral molding, the field magnet portion 401 and the laminated core 420 can be fixed more firmly.

(Embodiment 4) FIG.
A description will be given based on (A) and (B).

In the rotor configuration similar to that of the first embodiment, a plurality of protrusions 630b are provided on the outer periphery of the laminated core 620b, so that the biting between the field magnet portion 601a and the laminated core 620b is improved.

In the case of fixing by bonding, it acts as an adhesive groove for storing an adhesive, and can be fixed more firmly.

(Embodiment 5) As a specific embodiment, FIG.
A description will be given based on (C) and (D).

In the rotor configuration similar to that of the first embodiment, a shaft through hole 640d for penetrating the shaft is opened at the center of the laminated core 620c. Insert the shaft 602 into this hole and use the shaft fixing caulking 622
The shaft 602 and the laminated core 620c are connected and fixed.

The core groove 6 is provided outside the shaft through hole 640d.
30c is provided. When the shaft 602 is inserted into the shaft through hole 640d and the shaft fixing caulking 622 is performed, the outer circumference of the laminated core 620c becomes slightly larger due to the pressure at the time of caulking. When the outer circumference of the laminated core 620c becomes large, stress is applied to the field magnet portion 601c, and there is a possibility that the magnetic field magnet portion 601c is broken. By providing the core groove 630c outside the shaft through hole 640d, the bulge can be absorbed by the core groove 630c, and stress on the field magnet portion 601c can be eliminated.

(Embodiment 6) A specific embodiment will be described with reference to FIG.

A stator core 707 in which windings are wound around a core formed by laminating electromagnetic steel sheets is molded with resin. The rotor has the same configuration as that of the third embodiment, and the laminated core 720 is moved relative to the entire length of the field magnet 701.
Is moved to the opposite side of the output shaft. Since the lines of magnetic force at the time of orientation are concentrated on the laminated core 720, the magnetic flux distribution of the field magnet unit 701 changes depending on the position of the laminated core 720.

Generally, the stator core 707 when the motor is rotating
It is preferable that the magnetic attraction repulsive force of the rotor 706 be not applied in the thrust direction. However, in a motor of a specification that detects a rotor position by incorporating a circuit inside, it is necessary to extend the rotor end to the vicinity of the magnetic detection element 711. 701 is offset. Since magnetic flux gathers at the position of the laminated core 720, the position of the laminated core 720 is
By moving the shaft 702 in the thrust direction with respect to 01, the magnetic flux distribution of the field magnet unit 701 can be controlled, and the thrust vibration of the rotor can be adjusted to the minimum.

(Embodiment 7) A specific embodiment will be described with reference to FIG.

A stator core 7 in which a copper wire is wound around a core in which electromagnetic steel sheets are laminated is molded with resin.
As described in the sixth embodiment, an offset occurs between the stator core 807 and the field magnet unit 801.

In general, the rotor is configured such that the gate port 814 side is close to the stator core 807 as shown in FIG. The gate port 814 is in a direction perpendicular to the flow of the magnetic flux in the extremely anisotropic direction, and the orientation of the polar anisotropy is disturbed by the pressure of the injection molding. Become. In general, the gate side is configured to be closer to the stator core 807 in order to enhance the pole detection accuracy with respect to the magnetic detection element 811. In this embodiment, the rotor is assembled so that the stator core 807 is on the opposite side to the gate side. In this case, the effective magnetic flux is increased by setting the portion where the orientation is less disordered and the magnetic flux is large toward the stator core 807.

If there is a rotor gate on the magnetic detection element 811 side, the polar orientation accuracy tends to be poor. To prevent this, the position of the gate port 814 is provided at the outer peripheral position as much as possible so that the polar orientation can be reduced. The structure is to prevent disturbance.

The present embodiment is merely a representative example, and includes a resin magnet material, the number and position of gate ports, a material and a material of a connecting member, a type of a motor, the presence or absence of a mold of a motor body, and a shape and a structure of a stator core. However, the circuit type is not limited.

[0057]

As described above, according to the first aspect of the present invention, there is provided a resin magnet rotor formed into a cylindrical shape, wherein a connecting member for fixing the field magnet portion and the shaft portion is provided, and the connecting member is provided. Are molded together when forming a field magnet, which has the effect of eliminating setup changes due to shaft length and improving production tact.

According to a second aspect of the present invention, there is provided a resin magnet rotor formed into a cylindrical shape, wherein only the field magnet portion is formed, and then the field magnet portion and the connecting member are bonded and fixed. It is fixed to the shaft, eliminating the need for setup changes due to the length of the shaft, and separating the work of fixing the connecting member and the field magnet to allow flexibility in the production process and production tact. There is.

According to the third aspect of the present invention, there is provided a resin magnet rotor formed into a cylindrical shape, wherein the connecting member for fixing the field magnet portion and the shaft is made of a magnetic material. Has the effect of increasing.

According to the fourth aspect of the present invention, there is provided a resin magnet rotor formed in a cylindrical shape, wherein a connecting member for fixing the field magnet portion and the shaft is provided, and the field is provided on both sides of the connecting member. The thickness of the magnet part is made different so that the connecting member is fixed to the field magnet part, which makes positioning easier and makes the field magnet part and the connecting member more firmly fixed. is there.

According to the fifth aspect of the present invention, there is provided a resin magnet rotor formed into a cylindrical shape, wherein a connecting member for fixing the field magnet portion and the shaft is provided, and a projection is provided on the outer peripheral surface of the connecting member. Is provided, and there is an effect that the fixing between the field magnet portion and the connecting member is further strengthened.

According to a sixth aspect of the present invention, there is provided a resin magnet rotor formed into a cylindrical shape, wherein a connecting member for fixing the field magnet portion and the shaft is provided, and a shaft through hole of the connecting member is provided. Since several holes are provided on the outside, the outer periphery of the connecting member is prevented from expanding when the shaft is caulked to the connecting member, and there is an effect that stress is not applied to the field magnet portion.

According to the seventh aspect of the present invention, there is provided a resin magnet rotor formed into a cylindrical shape, wherein a connecting member for fixing the field magnet portion and the shaft is provided, and the connecting member is made of a magnetic material. And it is shorter than the field magnet, and by moving and adjusting the molding position of the connecting member,
There is an effect that the magnetic center of the motor with respect to the stator core is adjusted, thrust vibration is suppressed, and noise of the motor can be reduced.

According to the invention of claim 8, a resin magnet rotor formed into a cylindrical shape, wherein the rotor provided with a connecting member for fixing the field magnet portion and the shaft has a gate of the field magnet portion. Is assembled in such a way that the part without
By setting the portion not affected by the gate on the stator core side instead of the portion where the magnetic flux amount is reduced due to the disorder near the gate, the generated magnetic flux can be effectively used.

[Brief description of the drawings]

FIG. 1 (A) is a three-sided view of an integrally molded rotor of an aluminum core shown in Embodiment 1 of the present invention. (B) is a cross-sectional view showing a case where a connecting member is a resin boss. Sectional view of a rotor with adhesive

2A is a top view showing a molding die according to the first embodiment of the present invention. FIG. 2B is a sectional view taken along line XX shown in FIG. 2A.

3A is a three-sided view of a rotor in which a connecting member according to a third embodiment of the present invention has a laminated core of a magnetic material. FIG. 3B is a three-sided view of a rotor in which the laminated core shown in FIG.

FIG. 4 is a cross-sectional view of a rotor with a change in thickness on both sides of a laminated core according to a third embodiment of the present invention.

5A is a magnetic flux distribution diagram according to a third embodiment of the present invention. FIG. 5B is a cross-sectional view taken along line XX shown in FIG.

6A is a plan view of a boss provided with a protrusion according to the fourth embodiment of the present invention. FIG. 6B is a two-sided view of a laminated core provided with a protrusion according to the fourth embodiment of the present invention. Sectional view of a rotor provided with a through hole around a shaft hole shown in Example 5 (D) Plan view of laminated core shown in Example 5 of the present invention

FIG. 7 is a partial sectional view of a motor according to a sixth embodiment of the present invention.

FIG. 8 is a partial sectional view of a motor according to a seventh embodiment of the present invention.

9A is a three-view drawing of a conventional shaft-integrated rotor, and FIG. 9B is a partial cross-sectional view of a motor to which the conventional rotor is assembled.

10A is a cross-sectional view taken along line XX shown in FIG. 10B. FIG. 10B is a top view showing a conventional rotor mold.

[Explanation of symbols]

 101a-101c Field magnet part 102a-102c Shaft 103a, 103c Shaft groove 104a, 104c Rib 106a Rotor 114a Gate opening 118a, 118c Aluminum core 119b Resin boss 123c Adhesive

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H02K 29/00 H02K 29/00 Z (72) Inventor Hisakataka Kato 1006 Ojidoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Hiroaki Tanaka 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. AE08 5H019 AA09 AA10 CC03 CC08 EE14 5H621 GA01 GA04 HH01 JK13 JK17 5H622 AA03 CA01 CA05 PP03 PP10 PP19 PP20 QA03

Claims (8)

[Claims] 1. A brushless motor having a resin magnet rotor and a stator, wherein the resin magnet rotor is formed in a cylindrical shape, has a connecting member for connecting a shaft and a field magnet portion, and forms the field magnet. A brushless motor, wherein the connecting member is sometimes integrally formed and the field magnet and the connecting member are connected. 2. A brushless motor having a resin magnet rotor and a stator, wherein the resin magnet rotor is formed in a cylindrical shape, and has a connecting member for connecting a shaft and a field magnet portion, wherein the cylindrical field magnet is provided. A brushless motor, wherein the unit and the connecting member are joined by bonding. 3. The brushless motor according to claim 1, wherein a connecting member for connecting the shaft and the field magnet portion is made of a magnetic material. 4. The brushless motor according to claim 1, wherein the thickness of the field magnet is different on both sides of the connecting member. 5. The brushless motor according to claim 1, wherein a projection is provided on an outer periphery of a connecting member that connects the shaft and the field magnet portion. 6. The brushless motor according to claim 1, wherein another hole is provided outside the shaft through hole of the connecting member that connects the shaft and the field magnet portion. 7. The brushless motor according to claim 3, wherein the connecting member of the magnetic material is arranged at a position offset from the center of the field magnet portion. 8. The brushless motor according to claim 1, wherein the opposite side of the gate of the field magnet portion is assembled to a structure close to a stator core of the motor.