JPH11308794A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brushless motor, wherein cogging torque can be reduced and magnets can be firmly held. SOLUTION: This motor is constituted of a stator and a rotor 19 installed rotatably in the stator. The rotor 19 is constituted of a yoke 22 having a rotary shaft at the center, a plurality of magnets 23 whose inner and outer surfaces are formed into circular arc surfaces and which are located on the outer surface of the yoke 22 and a cylindrical can 25 put on the outer surface of the magnets 23. The adjacent ends of the magnets 23 are formed thin parts 24, because parts of the inner surfaces of the ends are removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor provided with a plurality of magnets divided along a circumferential direction on an outer peripheral surface of a rotor.

[0002]

2. Description of the Related Art A brushless motor has been widely used for various purposes because of its advantage that there is no mechanical contact between a brush and a commutator as compared with a conventional brush motor.

[0003] A general structure of a brushless motor includes a stator and a rotor rotatably accommodated and supported in the stator. As shown in FIG.
A plurality of magnets 4 each having an inner surface and an outer surface formed on an outer peripheral surface of a yoke 3 provided with a rotation shaft 2 at a central portion thereof and having an inner surface and an outer surface formed in a circular arc surface concentric with the outer peripheral surface of the yoke 3 have an inner peripheral surface thereof. It is provided by bonding and fixing.

Further, in the case of a motor in which the rotor 1 is rotated at a high speed, a cylindrical can 5 is attached to the outer peripheral surface of the magnet 4 in order to prevent the magnet 4 from peeling and scattering. The inner peripheral surface of the can 5 is bonded and fixed to the outer surface of the magnet 4.

The adjacent magnets 4 in the circumferential direction are magnetized with different polarities. For this reason, since the magnetization polarity alternates at the boundary between the adjacent magnets 4 due to the rotation of the rotor 1, a large cogging torque is generated, which may cause vibration.

In order to reduce the cogging torque, the inventor has removed the outer surface of the adjacent magnet 4 along the circumferential direction as shown in FIG.
It is considered that the cogging torque is reduced by forming the cogging torque.

However, when the outer surface of the end of the magnet 4 is removed to form the thin portion 4a,
Of the magnet 4 and the inner peripheral surface of the can 5 bonded to the outer surface of the magnet 4 are reduced.
In some cases, the holding state becomes unstable.

Therefore, when the rotor 1 is rotated at a high speed and used, not only is the magnet 4 easily peeled off from the yoke 3 due to centrifugal force, but also the gap between the inner peripheral surface of the can 5 and both ends of the outer surface of the magnet 4 can be increased. When the magnet 4 separates from the rotor 1, the end may collide with the inner peripheral surface of the can 5 due to centrifugal force. Then, since the can 5 may be protruded and deformed outward by the magnet 4, the deformed portion may come into contact with the inner surface of the stator.

[0009]

As described above, in the conventional brushless motor, a large cogging torque is generated at the boundary between the magnets provided on the outer peripheral surface of the rotor and divided in the circumferential direction, so that vibration is generated. Therefore, if the outer surface of the boundary of the magnet is removed to reduce the cogging torque to make it thinner, the holding state of the magnet by the can is impaired, so the magnet is easily peeled, and the can is deformed. There is a risk of frustration.

It is an object of the present invention to provide a brushless motor capable of reducing cogging torque and securely holding a magnet without being separated from a yoke by a can.

[0011]

According to a first aspect of the present invention, there is provided a stator having a stator and a rotor rotatably provided in the stator, wherein the rotor has a yoke provided with a rotation shaft at a central portion; A plurality of magnets, the inner surface and the outer surface of which are formed in an arcuate surface and are provided on the outer peripheral surface of the yoke by being divided into a plurality in the circumferential direction, and a cylindrical can attached to the outer peripheral surfaces of these magnets, Adjacent ends of the magnet are formed in thin portions from which inner surfaces of the ends are removed.

According to the first aspect of the present invention, the cogging torque can be reduced by removing the inner surface side of the adjacent end of the magnet provided on the outer peripheral surface of the yoke to reduce the cogging torque. Since the joint area between the outer surface of the can and the inner peripheral surface of the can, that is, the holding area of the magnet by the can is not reduced, the magnet can be securely held by the can without peeling from the yoke.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 2 shows a brushless motor 11, which has a stator 12.
And the stator 12 is held by a motor case 13. The motor case 13 is formed by molding resin or a premix, and is integrated by inserting the stator 12 at the time of molding.

A hollow portion 14 is formed on one side of the motor case 13 and an opening 15 is formed on the other side. A first bearing 16 is housed and held in the hollow portion 14, and the opening 15 is closed by a bracket 18 holding a second bearing 17 on the inner surface thereof.

The rotor 1 is provided in the internal space of the stator 12.
9 are accommodated. One end of the rotating shaft 21 provided on the rotor 19 is rotatably supported by the first bearing 16 and protrudes from the hollow portion 14 to the outside of the motor case 13. The other end of the rotating shaft 21 is the second shaft. It is rotatably supported by a bearing 17.

The rotor 19 has a yoke 22, as shown in FIG.
Is provided. A ferrite magnet 23 divided into four parts in the circumferential direction is bonded and fixed to the outer peripheral surface of the yoke 22. Adjacent circumferential end faces of the magnets 23 are joined.

The magnet 23 has an inner surface and an outer surface formed in a curved surface concentric with the outer peripheral surface of the yoke 22, and the inner surface of both ends along the circumferential direction is indicated by a hatched portion C in FIG. Has been removed. As a result, both ends of the magnet 23 are thinner than the other portions.
Is formed. The portion of the inner surface of the magnet 23 other than the thin portion 24 is an arc surface concentric with the yoke 22. The thin portion 24 is formed so as to gradually become thinner toward the end.

A cylindrical can 25 is attached to the outer periphery of the magnet 23 with its inner peripheral surface adhered to the outer surface of the magnet 23. That is, the magnet 23 is held in a state where the entire outer surface is adhered to the inner peripheral surface of the can 25. Thereby, by forming both ends of the magnet 23 in the thin portion 24, a gap G is generated between the inner surfaces of both ends and the outer peripheral surface of the yoke 22. In this state, the magnet 23 peels off from the yoke 22. However, since the entire outer surface of the magnet 23 is held by the inner peripheral surface of the can 25, the magnet 23 does not rattle.

According to the brushless motor 11 having the above-described structure, both ends of the magnet 23 along the circumferential direction of the yoke 22 are formed in the thin portion 24. Therefore, the cogging torque generated by the alternation of the magnetizing polarities at the ends of the adjacent magnets 24 is reduced, so that it is possible to suppress the occurrence of vibrations due to the rotation of the rotor 19.

Since the thin portion 24 of the magnet 23 is formed by removing the inner surfaces of both ends in the circumferential direction of the magnet 23, a gap G is formed between the inner surface of the end of the magnet 23 and the outer surface of the yoke 22. Although it occurs, the outer surface and can 25
There is no gap between the inner peripheral surface and the inner peripheral surface.

Therefore, since the magnet 23 has its entire outer surface securely held by the inner peripheral surface of the can 25, it is difficult for the magnet 23 to peel off from the outer peripheral surface of the yoke 22. Even if the magnet 23 may be peeled off from the yoke 22, the outer surface is in close contact with the inner peripheral surface of the can 25. Deformation of the stator 12
There is no rubbing of the inner peripheral surface of the.

That is, the cogging torque can be reduced by removing the inner surfaces of both ends along the circumferential direction of the magnet 23 to form the thin portion 24, and the outer surface of the magnet 23 and the inner circumferential surface of the can 25 can be reduced. Are in contact with each other without any gap, so that the magnet 23 can be reliably held by the can 25 even if the magnet 23 is separated from the yoke 22.

Means for forming the thin portions 24 at both ends along the circumferential direction of the magnet 23 is to form the magnet 23 with a uniform thickness, and then to the inner surfaces of both ends of the magnet 23 by hatching portions indicated by C in FIG. May be removed by grinding.
When the mold 3 is molded, it may be molded in advance so that both end portions become the thin portions 24. From the viewpoint of productivity, the latter means is more advantageous.

[0024]

According to the first aspect of the present invention, the inner surface of the adjacent end of the magnet provided on the outer peripheral surface of the yoke is removed to make the magnet thin. Therefore, the cogging torque can be reduced, and the joint area between the outer peripheral surface of the magnet and the inner peripheral surface of the can, that is, the holding area of the magnet by the can is not reduced.
The magnet can be securely held by the can without being separated from the yoke.

[Brief description of the drawings]

FIG. 1 is a sectional view of a rotor showing an embodiment of the present invention.

FIG. 2 is a sectional view showing a schematic configuration of the brushless motor.

FIG. 3 is an explanatory view of forming a thin portion at an end of the magnet.

FIG. 4 is a sectional view of a rotor showing a conventional example.

FIG. 5 is a sectional view of a rotor showing another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 ... Stator 19 ... Rotor 22 ... Yoke 23 ... Magnet 24 ... Thin part 25 ... Can

Claims (1)

[Claims] 1. A rotor having a stator and a rotor rotatably provided in the stator, wherein the rotor has a yoke provided with a rotation shaft at a center portion, and the yoke has an inner surface and an outer surface formed in arcuate surfaces. A plurality of magnets provided on the outer peripheral surface of the magnet so as to be divided into a plurality in the circumferential direction; and a cylindrical can attached to the outer peripheral surface of the magnets. A brushless motor characterized in that it is formed in a thin portion from which the inner surface of the portion has been removed.