JP2005102499A - Cylindrical field magnet and motor using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radially anisotropic cylindrical field magnet which realizes a remarkable reduction in a cogging torque and to provide a motor using the same. <P>SOLUTION: The cylinder field magnet 1 includes a peripheral surface 12 of an anti-armature side having a circular shape, by forming a mixture of an anisotropic magnetic powder and a binder in a ring shape and magnetic field orienting radially the mixture, having a plurality of pole surfaces 13 alternately formed with peripheral polarities at a predetermined pitch by radially magnetizing a peripheral surface 11 of an armature side in such a manner that the peripheral center of the pole surfaces 13 is most protruded to the armature side, an adjacent boundary of the pole surfaces 13 are most recessed to the anti-armature side, the pole surfaces 13 each has a waveform curved shape gradually separated from the armature toward the boundary from the peripheral center and has the maximum magnetic energy (BH)max of 13 MGOe or more in a radial direction. A field element of the radially anisotropic magnet field type motor includes the cylinder field magnet 1 and a soft magnetic field yoke 2 brought into contact with the peripheral surface 12 of the anti-armature side of the cylinder field magnet 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cylindrical field magnet having radial anisotropy and a motor using the magnet.

Conventionally, for spindle motors such as hard disk drive motors and CD-ROM drive motors, there are simple permanent magnet type motors having a field element having a permanent magnet as a field pole and an armature that rotates relative to the field element. It is used.
In this type of motor, it is usually the highest priority to reduce the cogging torque. For this reason, the following proposals have conventionally been made.
Japanese Patent Laid-Open No. 6-217478 discloses that a field magnet of a magnet field type motor is manufactured by attaching segment magnets to the outer peripheral surface of a yoke alternately with a predetermined polarity in the circumferential direction. . Each segment magnet has an inner peripheral surface formed in an arc shape, and the radial thickness of the magnetic pole boundary between the segment magnets is within the range of 0.3 to 0.7 times the radial thickness of the magnetic pole central portion. And the shape of the outer peripheral surface of the permanent magnet is proposed to be a curved surface represented by a predetermined mathematical expression.

The field element disclosed in Japanese Patent Laid-Open No. 8-336249 proposes to provide a groove at the magnetic pole end of a ring-shaped magnet to smooth the change in magnetic flux density at the magnetic pole end.
According to Japanese Patent Laid-Open No. 9-213521, in a ring magnet that is magnetized in the radial direction, the armature side circumferential surface is a circle, and the counter armature side circumferential surface is complicated on each side. It has been proposed to produce a field element by a substantially polygonal cylindrical radial anisotropic field magnet having a curved surface shape.
JP-A-6-217478 JP-A-8-336249 JP-A-9-213521

  In recent years, strong radial anisotropic segment magnets with (BH) max of 13 MGOe or more have been adopted for field elements in order to reduce the size of motors and to advance permanent magnet fabrication technology. It has been found that a field element having such a high (BH) max has a problem that cogging torque cannot be sufficiently reduced by the various conventional techniques described above.

  The present invention has been made in view of the above problems. By using a radial anisotropic magnet having a (BH) max of 13 MGOe or more, the present invention has an excellent torque to weight ratio and a marked reduction in cogging torque compared to the prior art. It is an object to be solved to provide a field element of a realized radial anisotropic magnet field type motor.

According to the first aspect of the present invention, in the radially anisotropic cylindrical field magnet used for the motor, a mixture of anisotropic magnetic powder having magnetic anisotropy and a binder is formed in a ring shape and a magnetic field is radially applied. A plurality of magnetic pole surfaces that are oriented and have a circumferential surface on the side opposite to the armature, and the circumferential surface on the armature side are alternately formed with a predetermined pitch in the circumferential direction by radial magnetization. The center of the magnetic pole surface in the circumferential direction protrudes most toward the armature side, the boundary between the magnetic pole surface and the adjacent magnetic pole surface is recessed most toward the anti-armature side, and the electromagnetic due to insufficient lateral flow of the radial anisotropic magnet A cylindrical field magnet having a corrugated curved surface that prevents a sudden change in the circumferential magnetic field strength of the air gap and having a maximum magnetic energy (BH) max of 13 MGOe or more.
The cylindrical field magnet and a soft magnetic field yoke in contact with the peripheral surface of the cylindrical field magnet on the counter armature side constitute a field element of a radial anisotropic magnet field type motor. Thus, it has been found for the first time that the ratio of the cogging torque to the effective torque can be remarkably reduced as compared with the prior art.
As in the invention of claim 2, the corrugated curved surface shape may be a corrugated curved surface shape in which the radius of curvature gradually decreases from the armature as it goes from the center in the circumferential direction to the boundary portion. In this case, the case where the radius of curvature is locally constant is included.

Hereinafter, the effect by the structure of the cylindrical field magnet of this structure is demonstrated.
First, the present inventors investigated the cause of the cogging torque increase when a radial anisotropic magnet having a maximum magnetic energy (BH) max of 13 MGOe or more is used in the various conventional techniques.

As a result, the following was found.
First, it was found that when a segment-shaped radial anisotropic magnet was affixed to the circumferential surface of the yoke, the cogging torque increased significantly for the following reasons.
That is, in a field element manufactured by pasting such a segment magnet (hereinafter also referred to as a segment magnet pasting type field element), variation in gaps between segment magnets adjacent in the circumferential direction, and segment magnet and yoke Variation in the thickness of the adhesive layer between the two and the magnetic field strength of the electromagnetic gap between the field element and the armature varies, which increases the cogging torque.

In the conventional isotropic magnet, the variation in the magnetic flux distribution due to the above-described variation is caused by the magnetic flux flowing in the circumferential direction in the segment magnet, thereby partially or entirely bypassing the yoke and adjacent in the circumferential direction. This is significantly mitigated by direct flow between isotropic segment magnets.
However, when a segment magnet made of a radial anisotropic magnet is used to obtain a high torque, such a lateral flow effect of the magnetic flux can hardly be expected, and the magnetic flux flows only through the yoke. For this reason, the variation in the gap between the segment magnets adjacent to each other in the circumferential direction and the variation in the thickness of the adhesive layer between the segment magnet and the yoke are directly reflected in the magnetic field strength of the electromagnetic gap. It was found that the cogging torque increased.

  That is, in a field element manufactured by pasting such a segment magnet (hereinafter also referred to as a segment magnet pasting type field element), variation in gaps between segment magnets adjacent in the circumferential direction, and segment magnet and yoke Variation in the thickness of the adhesive layer between the two and the magnetic field strength of the electromagnetic gap between the field element and the armature varies, which increases the cogging torque.

  Next, when a groove is simply formed at the magnetic pole end of a ring-shaped magnet, the cogging torque is reduced with an isotropic magnet, but when a radial anisotropic magnet is used, the cogging torque is noticeable for the following reasons. It was found to increase. That is, when a square groove is formed at the end of such a magnetic pole, in the case of a conventional isotropic magnet, the surface shape of the magnetic pole is discontinuously changed, and the local magnetic resistance at each part in the circumferential direction is suddenly changed. On the other hand, when magnetized, magnetic flux flows laterally in the isotropic magnet in the circumferential direction, thereby mitigating sudden changes in the magnetic flux density of the electromagnetic gap in the circumferential direction.

However, in radial anisotropic magnets, it is almost impossible to expect the magnetic flux to flow in the circumferential direction in the magnet, and such a steep step on the magnetic pole surface suddenly changes the circumferential distribution of the magnetic field strength of the electromagnetic gap. It has been found that the cogging torque increases for the following reasons.
In view of the above, field elements simply provided with a groove on the magnetic pole surface of a cylindrical field magnet or a segment magnet are applied to a radial anisotropic magnet due to a sudden increase in cogging torque due to the above-described reason. It has been found that it cannot withstand practical use in applications sensitive to cogging torque.

  Next, when a cylindrical field magnet is formed by a radial anisotropic magnet and the peripheral surface on the counter armature side is a substantially polygonal shape having complicated curved surfaces on each side, naturally, the cylindrical field magnet A yoke of the same shape is fitted to the peripheral surface of the polygonal anti-armature side, but it is extremely difficult to accurately make such a fitting surface with a dimensional tolerance of ± 0.05 mm or less. Therefore, the variation in the gap on the fitting surface causes a significant increase in the cogging torque in the radial anisotropic magnet as described above.

  In view of the above-described conventional problems, in the field element of this configuration, first, a radial anisotropic magnet having a maximum magnetic energy (BH) max of 13 MGOe or more is adopted as the field magnet while suppressing an increase in physique. Radial anisotropy is achieved by increasing the effective torque and eliminating the variation of the adhesive layer and the gap between the segment magnets by forming it into a cylindrical shape, and making the armature side circumferential surface a corrugated surface. Preventing sudden changes in the magnetic field strength in the circumferential direction of the electromagnetic gap due to insufficient magnetic flux lateral flow of the magnet, and making the yoke side (counter armature side) circular in shape eliminates machining of the magnet side peripheral surface of the yoke, It is intended to reduce the cogging torque by greatly reducing the gap variation between them.

  Eventually, according to this configuration, a field element having an excellent effective torque / cogging torque ratio can be realized by a large effective torque and a small cogging torque by the radial anisotropic magnet.

The invention according to claim 3 is the cylindrical field magnet according to claim 1 or 2, wherein the cylindrical field magnet is a field magnet used in a spindle motor.
According to a fourth aspect of the present invention, in a motor having a radially anisotropic cylindrical field magnet, the yoke, the cylindrical field magnet fixed to the inner peripheral surface of the yoke, and the interior of the cylindrical field magnet The cylindrical field magnet is formed by forming a mixture of anisotropic magnetic powder having magnetic anisotropy and a binder in a ring shape and orienting the magnetic field in the radial direction. The armature-side peripheral surface has a circular shape, and the armature-side peripheral surface has a plurality of magnetic pole surfaces in which polarities are alternately formed at predetermined pitches in the circumferential direction by magnetization in the radial direction. The center in the circumferential direction of the magnetic pole protrudes most toward the armature side, the boundary between the magnetic pole face and the adjacent magnetic pole face is recessed most toward the anti-armature side, and the magnetic field strength in the circumferential direction of the electromagnetic gap due to insufficient magnetic flux lateral flow of the radial anisotropic magnet It has a corrugated surface shape that prevents sudden changes in the maximum magnetic energy of 13 MGOe or more ( A motor, characterized in that it comprises a H) max.

In the invention of claim 5, the corrugated curved surface shape of the cylindrical field magnet is a corrugated curved surface shape in which the radius of curvature gradually decreases from the armature toward the boundary portion from the center in the circumferential direction on the magnetic pole surface. The motor according to claim 4.
The invention according to claim 6 is the motor according to claim 4 or 5, wherein the motor is a spindle motor.
The invention according to claim 7 is the motor according to any one of claims 4 to 6, wherein the motor has a cogging torque of 4 gfcm or less.

  The field yoke is fitted into the peripheral surface of the cylindrical field magnet on the side opposite to the armature, and between the peripheral surface on the side opposite to the armature of the cylindrical field magnet and the magnet side peripheral surface of the field yoke. According to the configuration in which the radial length of the air gap is less than 0.5% of the radius of the peripheral surface on the counter armature side of the cylindrical field magnet, the cylindrical field magnet and the field yoke are fitted. As a result of setting the gap to be less than 0.5% of the radius of the peripheral surface on the counter armature side of the cylindrical field magnet, it was found that the cogging torque can be satisfactorily suppressed.

  That is, the present inventors have found that the radial anisotropic magnet having an excellent maximum magnetic energy (BH) max has an isotropic variation in the gap between the minute cylindrical field magnet and the yoke fitted thereto. It has been found that a large cogging torque increase is caused due to the absence of the lateral flow of magnetic flux as in the case of a magnet. Therefore, the ratio of the cogging torque / effective torque is reduced to a practically sufficient range even when the radial anisotropic magnet and the yoke are fitted by reducing the fitting gap to less than the above value. It was found that it can be reduced.

  When manufacturing a radial anisotropic magnet, a cylindrical field magnet and a field yoke are formed by insert molding. Such insert integral molding causes a significant increase in cost compared to single molding of a cylindrical field magnet by press molding and its fitting and adhesion, and is not usually used. According to this manufacturing method, the gap between the cylindrical field magnet and the field yoke can be made substantially zero, and it has been found that the cogging torque can be greatly reduced for the above-described reason. Further, the effective torque can be increased.

NdFeB-based, SmFeN-based, SmCo-based, etc. can be adopted as the radial anisotropic magnetic powder, and a resin, an inorganic material, a low melting point metal, or the like can be adopted as the binder.
Preferred aspects of the invention are described with reference to the following examples.

A pressure of about 10 ton / cm ² was applied in the mold while magnetically orienting the NdFeB-based anisotropic magnetic powder at a temperature of 150 ° C. in the radial direction, and FIG. 1 (Example), FIG. 2 (Comparative Example 1), FIG. The magnets shown in (Comparative Examples 2 and 3) and FIG. 4 (Comparative Example 4) were manufactured. Here, the maximum magnetic energy product (BH) max of the magnet is 17 MGOe.

  Here, the magnet shape of the embodiment has an outer diameter of 21.6 mm, an inner diameter of 19.4 mm, a depth of t4.5 mm, and the arc radius R of the corrugated portion is 8 mm. The yoke material is SUM22 steel, which has an outer diameter of φ22.6 mm, an inner diameter of φ21.6 mm, and a depth of t4.5 mm. For magnetization, a voltage of 1800 V was applied, and 12 poles of radial magnetization were applied.

  The magnet shape of Comparative Example 1 is the shape of a magnet for one pole of Example 1, the outer diameter arc radius is 10.8 mm, the maximum wall thickness is 1.1 mm, the inner diameter side arc radius is 8 mm, and the depth is t4.5 mm. The segment magnet was manufactured by compression molding. Twelve segment magnets were attached to the yoke made of SUM22 with an adhesive. Thereafter, a voltage of 1800 V was applied to perform radial magnetization.

  The magnet shape of the comparative example 2 has an outer diameter of 21.6 mm, an inner diameter of 19.4 mm, a depth of t4.5 mm, a groove portion angle of θ, and θ = 7.5 deg, which is the most effective, of the comparative example 2. The magnet shape was used, and the case of θ = 9 deg was the magnet shape of Comparative Example 3. The yoke material is SUM22 steel, the shape is an outer diameter φ22.6 mm, the inner diameter φ21.6 mm, and the depth is t4.5 mm. For magnetization, a voltage of 1800 V was applied, and 12 poles of radial magnetization were applied.

  The magnet shape of the comparative example 4 has an inner diameter of 19.4 mm, an outer diameter of a regular dodecagon, a circumscribed circle diameter of 21.6 mm, and a depth of t4.5 mm. Incidentally, the yoke material is SUM22 steel, the outer diameter is φ22.6 mm, the inner diameter side is a regular dodecagon, the diameter of the circumscribed circle is φ21.6 mm, and the depth is t4.5 mm. For magnetization, a voltage of 1800 V was applied, and 12 poles of radial magnetization were applied.

  A motor was assembled using each rotor, and the motor characteristics were examined. As the motor characteristics, cogging torque and back electromotive force constant were measured. The counter electromotive force constant is calculated by calculating ke = E / N (V / krpm) from the measured wave height value E of the voltage generated in correlation when the motor is forcibly rotated at N = 1800 rpm. Obtained by the formula. The results are shown in Table 1.

According to Table 1, in all the comparative examples, the cogging torque is remarkably large, whereas in the present embodiment, the cogging torque is significantly smaller than that of the comparative example, and the level of Tc ≦ 4 gfcm of the spindle motor is shown. It became clear that he was satisfied.

  Further, as a total evaluation of the motor performance, it is preferable to increase the counter electromotive force constant and reduce the cogging torque. From this viewpoint, Ke / Tc is used as one index. Furthermore, regarding the fitting property between the yoke and the magnet, A was evaluated when it was good, B was evaluated when it was not very good, and C was evaluated when it was poor. As an evaluation regarding the cogging torque, it is essential that Tc ≦ 4 gfcm for the application of the spindle motor. Accordingly, A was determined to be 4 gfcm or less, B was determined to be 5 to 9 gfcm, and C was determined to be C when the 10 gfcm or more was completely out of use.

  As is clear from the above results, it has been clarified that Comparative Examples 1 to 4 as compared with the prior art are not practically usable from the viewpoint of cogging torque. On the other hand, only the embodiment which is the product of the present invention can reduce the cogging torque to an extremely small value, and also shows a good result for the back electromotive force. The motor performance Ke / Tc is compared with the comparative example. It was revealed that the performance was about 7 times better.

  The present invention can be used for a motor having a very small cogging torque. For example, it is effective for a sundle motor.

It is a schematic cross section of the field rotor of an Example. 6 is a schematic cross-sectional view of a field rotor of Comparative Example 1. FIG. 6 is a schematic cross-sectional view of a field rotor of Comparative Example 2. FIG. 10 is a schematic cross-sectional view of a field rotor of Comparative Example 4. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cylindrical field magnet which consists of a radial anisotropic magnet 2 ... Field yoke 3 ... Segment magnet 11 ... Armature side peripheral surface 12 ... Anti-armature side peripheral surface 13 ... Magnetic pole surface

Claims (7)

In the radial anisotropic cylindrical field magnet used for motors,
A mixture of anisotropic magnetic powder having magnetic anisotropy and a binder is formed in a ring shape and magnetically oriented in the radial direction, and the peripheral surface on the counter armature side has a circular shape,
The peripheral surface on the armature side has a plurality of magnetic pole surfaces in which polarities are alternately formed at a predetermined pitch in the circumferential direction by magnetization in the radial direction,
The center of the magnetic pole surface in the circumferential direction protrudes most toward the armature side, the boundary portion between the magnetic pole surface and the adjacent magnetic pole surface is recessed most toward the anti-armature side, and electromagnetic gaps due to insufficient magnetic flux lateral flow of the radial anisotropic magnet It has a corrugated curved surface that prevents sudden changes in circumferential magnetic field strength,
A cylindrical field magnet having a maximum magnetic energy (BH) max of 13 MGOe or more.   2. The cylinder according to claim 1, wherein the corrugated curved surface shape is a corrugated curved surface shape in which the radius of curvature gradually decreases from the armature toward the boundary portion from the circumferential center in the magnetic pole surface. Field magnet.   The cylindrical field magnet according to claim 1 or 2, wherein the cylindrical field magnet is a field magnet used for a spindle motor. In a motor having a radial anisotropic cylindrical field magnet,
York,
The cylindrical field magnet fixed to the inner peripheral surface of the yoke;
An armature disposed inside the cylindrical field magnet,
The cylindrical field magnet is
A mixture of anisotropic magnetic powder having magnetic anisotropy and a binder is formed in a ring shape and magnetically oriented in the radial direction, and the peripheral surface on the counter armature side has a circular shape,
The peripheral surface on the armature side has a plurality of magnetic pole surfaces in which polarities are alternately formed at a predetermined pitch in the circumferential direction by magnetization in the radial direction,
The center of the magnetic pole surface in the circumferential direction protrudes most toward the armature side, the boundary portion between the magnetic pole surface and the adjacent magnetic pole surface is recessed most toward the anti-armature side, and electromagnetic gaps due to insufficient magnetic flux lateral flow of the radial anisotropic magnet It has a corrugated curved surface that prevents sudden changes in circumferential magnetic field strength,
A motor having a maximum magnetic energy (BH) max of 13 MGOe or more.   The corrugated curved surface shape of the cylindrical field magnet is a corrugated curved surface shape in which the radius of curvature gradually decreases from the armature toward the boundary portion from the circumferential center in the magnetic pole surface. The motor according to claim 4.   The motor according to claim 4, wherein the motor is a spindle motor.   The motor according to any one of claims 4 to 6, wherein the motor has a cogging torque of 4 gfcm or less.