JP2003007534A - Method for magnetizing permanent magnet, permanent magnet and motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for magnetizing a permanent magnet, a permanent magnet and a motor by which cogging torque can be greatly reduced and a high torque constant can be also obtained. SOLUTION: When a permanent magnet 12 is magnetized, its magnetic flux density is changed like a trapezoidal wave in the circumferential direction, its value at the central part of magnetic pole is set as a specified value, those at both ends are set to zero, and then the transition rate is set to 35-60%. The permanent magnet 12 is used for a stator 10 of a motor M.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a permanent magnet magnetizing method, a permanent magnet and a motor. For more details,
The present invention relates to a method of magnetizing each magnetic pole magnetized in a permanent magnet used in a motor, a permanent magnet magnetized by the magnetizing method, and a motor using the magnetized permanent magnet.

[0002]

2. Description of the Related Art Conventionally, a DC brushless motor using a permanent magnet in a rotor has been used for HDD (hard disk drive), FDD (floppy (registered trademark) disk drive) and the like. An example of such a DC brushless motor (hereinafter, simply referred to as a motor) is shown in FIG.
This motor M ′ has a required number, for example, nine drive coils 1
An outer rotor type motor in which a rotor 102 having a cylindrical permanent magnet 102a rotates outside a stator 101 having 01a, 101a, ...
On the inner peripheral surface of a, an even number of magnetic poles having different polarities are alternately magnetized at a predetermined interval in the circumferential direction in a predetermined magnetization pattern, for example, 12 magnetic poles at a pitch of 30 °.

The torque constant of the motor M'using a permanent magnet is proportional to the interlinking magnetic flux interlinking with the drive coil 101a. Therefore, in order to obtain a high torque constant, each magnetic pole is magnetized with a rectangular wave. That is, as shown in FIG. 11, the direction of the magnetic field is fixed in the radial direction, the magnetic flux density changes like a rectangular wave in the circumferential direction, and is 0 at both ends of the magnetic pole, and becomes a constant value at other positions. It is desirable that the magnetization is performed in a magnetization pattern.

However, in such rectangular wave magnetization, a large cogging torque comparable to the torque constant is generated and the rotor 102 cannot be rotated smoothly. Therefore, in actuality, radial sine wave magnetization, that is, in FIG. As shown, the direction of the magnetic field is fixed in the radial direction, the magnetic flux density changes sinusoidally in the circumferential direction, and is magnetized in a magnetization pattern such that the magnetic pole has a maximum at the center and zero at both ends. Or, it is usual that skew magnetization, that is, the rectangular wave magnetization is applied to each magnetic pole, and the permanent magnet is magnetized in a magnetization pattern in which a skew (twist) of a predetermined angle is applied ( See, for example, JP-A-5-315136 and JP-A-2-101949).

According to such radial sine wave magnetization and skew magnetization, the cogging torque is 1/50 to 1 of the torque constant.
Although it can be reduced to about / 60 and the rotor 102 can be smoothly rotated, there is a problem that the torque constant is reduced to about 60 to 75% of that in the case of rectangular wave magnetization.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and it is a permanent magnet magnetizing method, a permanent magnet and a permanent magnet magnetizing method that can significantly reduce the cogging torque and obtain a high torque constant. The purpose is to provide a motor.

[0007]

According to the method of magnetizing a permanent magnet of the present invention, the magnetization of the permanent magnet is changed to a predetermined value at the center of the magnetic pole by changing the magnetic flux density like a trapezoidal wave in the plane direction and at both ends. 0
And the transition rate is set to 35 to 60%.

In the permanent magnet magnetizing method of the present invention, it is preferable that the transition rate is 45 to 50%.

The permanent magnet of the present invention is characterized by being magnetized by the above method.

Therefore, the permanent magnet of the present invention is used in a motor.

[0011]

Since the present invention is constructed as described above, a high torque constant can be obtained even though the cogging torque can be greatly reduced.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described based on the embodiments with reference to the accompanying drawings, but the present invention is not limited to such embodiments.

FIG. 1 shows a sectional view of a motor using a permanent magnet to which a permanent magnet magnetizing method according to an embodiment of the present invention is applied. As shown in FIG. 1, the motor M is an outer rotor type motor in which the rotor 20 rotates outside the stator 10.

The stator 10 is formed by laminating a required number of steel plates having a predetermined shape, and has a cylindrical stator yoke 1
1 and a predetermined distance in the circumferential direction of the outer peripheral surface of the stator yoke 11,
For example, nine substantially T-shaped salient poles 12, 12, ... Radially provided at a pitch of 40 ° are provided.
The drive coils 13, 13, 13, ... Are wound around 2 ,.

The drive coil 13 comprises a three-phase drive coil, that is, a U-phase drive coil 13U, a V-phase drive coil 13V and a W-phase drive coil 13W, and is adjacent to the U-phase drive coil 13U in the clockwise direction in FIG. The V-phase drive coil 13V is located in the V-phase drive coil 13V, the W-phase drive coil 13W is located next to the V-phase drive coil 13V, and the U-phase drive coil 13U is located next to the W-phase drive coil 13W.
It is wound around 2, 12, ...

The rotor 20 includes a cylindrical permanent magnet 21 and
Cylindrical rotor yoke 22 fitted onto permanent magnet 21
And a rotary shaft 23 that rotates integrally with the permanent magnet 21 and the rotor yoke 22 at the axial center of the rotor 20.

The permanent magnet 21 is formed by molding various permanent magnets such as a ferrite magnet, an alnico magnet, an Sm-Co type magnet, and a rare earth-Fe type magnet into a cylindrical body, and the inner peripheral surface thereof and the stator 10 described above. The inner diameter is adjusted so that a predetermined gap (hereinafter referred to as a gap), for example, a gap of about 0.2 mm is generated between the salient pole 12 and the tip end surface. Further, an even number of magnetic poles having different polarities are alternately magnetized on the inner peripheral surface at predetermined intervals in the circumferential direction (plane direction), for example, 12 magnetic poles at a pitch of 30 °. The permanent magnet magnetizing method of the present invention is particularly effective for radial anisotropic magnets, but is also applicable to isotropic magnets.

As shown in FIG. 2, the direction of the magnetic field is fixed to each of the magnetic poles in the radial direction, the magnetic flux density changes in the circumferential direction (plane direction) like a trapezoidal wave, and the central portion of the magnetic poles (hereinafter referred to as "flat"). In a region), it is magnetized in a magnetizing pattern such that it has a constant value and changes linearly from both ends of the flat region and becomes 0 at both ends of the magnetic pole. In the following explanation,
The region in which the magnetic flux density changes linearly is called the transition region, and the ratio of this transition region to one magnetic pole is called the transition ratio.

Here, the torque constant is kept high, for example, 85% or more of that in the case of rectangular wave magnetization, and the cogging torque is practically usable as a motor, for example, 25 of the torque constant.
According to experiments conducted by the present inventors, it has been found that the transition rate may be set to 35 to 60% in order to reduce it to less than or equal to%. Further, in order to obtain a torque constant as high as about 90% in the case of rectangular wave magnetization and to reduce the cogging torque to 5% or less of the torque constant, the transition rate is determined by the experiments conducted by the present inventors. According to this, it was also found that it may be set to 45 to 50%.

The rotor yoke 22 is a cylindrical body having an inner diameter slightly larger than the outer diameter of the permanent magnet 21, and is fitted onto the permanent magnet 21 so that its inner peripheral surface is fixed to the outer peripheral surface of the permanent magnet 21.

The rotating shaft 23 is fixed to the center of a lid member 24 which is arranged so as to cover one open end of the rotor 20 and which is integrated with the rotor yoke 22, and rotates integrally with the permanent magnet 21 and the rotor yoke 22. It is possible. Here, the diameter of the rotating shaft 23 is smaller than the inner diameter of the stator yoke 11.

As described above, according to this embodiment, trapezoidal wave magnetization with a predetermined transition rate is performed on each magnetic pole of the permanent magnet 21, so that the cogging torque can be greatly reduced and a high torque constant can be obtained. You can

[0023]

EXAMPLES Hereinafter, the present invention will be described more specifically based on more specific examples.

Examples 1 to 3 and Comparative Examples 1 to 5 As shown in FIG. 3, the transition rates are 40% (Example 1), 47% (Example 2) and 53% (Example), respectively. The motor M of the embodiment was prototyped by setting to 3). In addition, Example 1
The material of the permanent magnet of each motor of Example 3 is NP-8L (trade name of Daido Steel Co., Ltd.), and the material of the stator is 3% S.
It is regarded as i-Fe.

For comparison, as shown in FIG. 3 together, the transition rate is 0% (Comparative example 1: square wave magnetization),
Outer rotor type motors having 12 magnetic poles and 9 salient poles, which were set to 13% (Comparative Example 2), 27% (Comparative Example 3) and 67% (Comparative Example 4) and were configured in the same manner as the embodiment, were manufactured.

Further, as Comparative Example 5, an outer rotor type motor having 12 magnetic poles and 9 salient poles, which was constructed in the same manner as in the embodiment, was manufactured by subjecting each magnetic pole of a permanent magnet to radial sine wave magnetization.

The materials of the permanent magnets of the motors of Comparative Examples 1 to 5 are NP-8 as in Examples 1 to 3.
L and the material of the stator is 3% Si-Fe.

FIG. 4 shows the measurement results obtained by measuring the magnetic flux density of the gap portion of one magnetic pole magnetized in the permanent magnet of each motor of Examples 1 to 3 and Comparative Examples 1 to 5. The measurement results of the surface magnetic flux densities of the two adjacent magnetic poles are shown in FIG. 5 for reference.

Further, Examples 1 to 3 and Comparative Example 1
-For each motor of Comparative Example 4, motor torque (torque constant) at a rotor rotation angle of 0 degrees when a current of 1 A is supplied to the drive coil, cogging at a rotor rotation angle of 0 degrees and 2.5 degrees in a non-excited state The measurement results obtained by measuring the respective torques are shown in FIG. 6, and the motor of Example 2 in which the cogging torque at the rotor rotation angle of 2.5 degrees was the minimum and the motor of Comparative Example 1 in which the cogging torque was the maximum were FIG. 7 shows the measurement results obtained by measuring the cogging torque by changing the rotor rotation angle from 0 degree to 10 degrees.

FIG. 8 shows the measurement results of the interlinkage magnetic flux interlinking with the drive coil of each of the motors of Examples 1 to 3 and Comparative Examples 1 to 5 as a chain of the motor of Comparative Example 1. The magnetic flux is shown as relative to 100. In addition, FIG.
In addition, the torque constants of the motors of Examples 1 to 3 and Comparative Examples 1 to 5, cogging torque at a rotor rotation angle of 2.5 degrees in the non-excited state, and a value obtained by dividing the cogging torque by the torque constant. Is shown in a table.

From FIG. 7, the cogging torque changes depending on the rotor rotation angle. However, when the magnetizing waveform is changed, the cogging torque does not originally generate the cogging torque.
It can be seen that the cogging torque at all rotor rotation angles except (for example, 0 degree) is similarly reduced. That is, it is understood that if the cogging torque at the rotor rotation angle at which a large cogging torque is generated is reduced, the cogging torque at other rotor rotation angles is naturally reduced. Therefore, in the following description, the cogging torque at the rotor rotation angle of 2.5 degrees at which the cogging torque close to the maximum value is generated will be taken as an example for comparison and examination.

From FIGS. 6, 7 and 9, the cogging torque showing the maximum value in the motor of Comparative Example 1 (transition rate: 0%) in which the rectangular wave is magnetized decreases as the transition rate increases, After the transition rate became 0 near 47%, it started to increase again. Specifically, in the motors of Comparative Example 2 (transition rate: 13%) and Comparative Example 3 (transition rate: 27%), the torque constants are 110% and 74%, respectively, which are very large. In the motor of the ratio: 40%, the torque constant is 21%, which is reduced to a practical level as a motor, and in the motor of the second embodiment (transition ratio: 47%), the torque constant is 4%. , A value close to that of the motor of Comparative Example 5 in which the radial sine wave is magnetized.
The motor of Example 3 (transition rate: 53%) has a torque constant of 23%, which is still a practical level as a motor, but the motor of Comparative Example 4 (transition rate: 67%) has a torque constant. , Which is 29% of that of the motor, which is practically difficult to use as a motor. That is, it is understood that the transition rate may be set to 35 to 60% in order to reduce the cogging torque to a practical level as a motor (25% or less of the torque constant).

Further, from FIGS. 6, 8 and 9, the torque constant showing the maximum value in the motor of Comparative Example 1 (transition rate: 0%) in which the rectangular wave was magnetized was gradually increased as the transition rate increased. In the motor of Example 3 (transition rate: 53%), which is still as high as 88% of that of the motor of Comparative Example 1, Comparative Example 4
In the motor of (transition rate: 67%), the motor of Comparative Example 1 is 82%, which is close to the motor of Comparative Example 5 in which the radial sine wave is magnetized. That is, it is understood that the transition rate needs to be 60% or less in order to obtain a torque constant as high as 85% or more in the case of rectangular wave magnetization.

From the above, the measurement results shown in FIGS. 6 to 9 can obtain a high torque constant of 85% or more in the case of rectangular wave magnetization by setting the transition rate to 35 to 60%. In addition, the cogging torque can be reduced to 25% or less of the torque constant to a practical level as a motor, and in particular, by adopting a transition rate of 45 to 50%,
It is possible to obtain a torque constant as high as 90% of the case of square wave magnetization, and cogging torque is 5% of the torque constant.
It shows that it can be reduced to the following.

Although the present invention has been described above based on the embodiments and examples, the present invention is not limited to such embodiments and examples, and various modifications can be made. For example, in the embodiments and examples, the number of phases of the drive coil is three, but the number of phases is not limited to this, and may be a single phase, for example.

In the embodiments and examples,
Although the outer rotor type motor is described as an example, the present invention is not limited to this, and the permanent magnet magnetizing method of the present invention can be applied to, for example, an inner rotor type motor or a flat type motor.

[0037]

As described in detail above, according to the present invention,
It is supposed that each magnetic pole of the permanent magnet is magnetized so that the magnetic flux density changes like a trapezoidal wave in the circumferential direction and becomes a constant value at the central portion of the magnetic pole, 0 at both ends, and a transition rate becomes a predetermined value. Therefore, it is possible to significantly reduce the cogging torque and obtain an excellent effect that a high torque constant can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a motor using a permanent magnet to which a permanent magnet magnetizing method according to an embodiment of the present invention is applied, in which FIG. 1 (a) is a sectional view in a direction orthogonal to an axial direction. ,same
(b) shows a cross-sectional view of the main part in the axial direction.

2A and 2B are diagrams illustrating a magnetization pattern of a permanent magnet of the motor, FIG. 2A shows a magnetization waveform, and FIG. 2B shows a magnetization distribution in one magnetic pole.

FIG. 3 shows examples 1 to 3 and comparative examples 1 to 4;
FIG. 6 is a diagram showing a magnetization waveform of one magnetic pole magnetized in a permanent magnet of each motor of FIG.

FIG. 4 shows examples 1 to 3 and comparative examples 1 to 5;
FIG. 4 is a graph showing the measurement results of the magnetic flux density in the gap portion of one magnetic pole magnetized in the permanent magnet of each motor.

FIG. 5 is a graph showing examples 1 to 3 and comparative examples 1 to 5;
FIG. 6 is a graph showing the measurement results of the surface magnetic flux densities of two adjacent magnetic poles magnetized by the permanent magnet of each motor.

FIG. 6 shows examples 1 to 3 and comparative examples 1 to 4
1. For each motor, the motor torque (torque constant) at a rotor rotation angle of 0 degree when a current of 1 A is supplied to the drive coil, the rotor rotation angle at a non-excitation state of 0 degree, and 2.
It is a graph which shows the measurement result which each measured the cogging torque in 5 degrees.

FIG. 7: For each motor of Example 2 and Comparative Example 1,
It is a graph which shows the measurement result which measured the cogging torque by changing a rotor rotation angle from 0 degree to 10 degrees.

FIG. 8 is a graph showing examples 1 to 3 and comparative examples 1 to 5;
FIG. 4 is a graph chart relatively showing the measurement results of measuring the interlinkage magnetic flux interlinking with the drive coil of each of the motors.

9 is a graph showing examples 1 to 3 and comparative examples 1 to 5; FIG.
2 is a table showing the torque constants of the respective motors, the cogging torque at a rotor rotation angle of 2.5 degrees in the non-excited state, and the values obtained by dividing the cogging torque by the torque constant.

FIG. 10 is a cross-sectional view showing an example of a conventional motor.

11A and 11B are explanatory diagrams of rectangular wave magnetization, where FIG. 11A shows a magnetization waveform and FIG. 11B shows a magnetization distribution in one magnetic pole.

FIG. 12 is an explanatory diagram of radial sine wave magnetization,
(a) shows the magnetization waveform, and (b) shows the magnetization distribution in one magnetic pole.

[Explanation of symbols]

10 Stator 11 Stator yoke 12 salient poles 13 Drive coil 20 rotor 21 Permanent magnet 22 rotor yoke 23 rotation axis M motor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryo Omatsuzawa             2-30, Daido-cho, Minami-ku, Nagoya-shi, Aichi             Daido Steel Co., Ltd. Technology Development Laboratory F-term (reference) 5H621 AA02 GA04 GB10 HH01                 5H622 AA02 CA01 CA05 CA10 PP11                       QB02

Claims (4)

[Claims] 1. The magnetization of a permanent magnet is changed to a predetermined value at the center of the magnetic pole by changing the magnetic flux density like a trapezoidal wave in the surface direction, and is set to 0 at both ends, and the transition rate is set to 35 to 60%. A method for magnetizing a permanent magnet, which is characterized in that 2. The permanent magnet attachment method according to claim 1, wherein the transition rate is 45 to 50%. 3. A permanent magnet, which is magnetized by the permanent magnet magnetizing method according to claim 1. 4. A motor comprising the permanent magnet according to claim 3.