JP2007281437A - Anisotropic ferrite magnet, and motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anisotropic ferrite magnet by dry molding capable of reducing cogging torque and torque ripple. <P>SOLUTION: The anisotropic ferrite magnet by dry molding has an inner-periphery surface and an outer-periphery surface opposite to the inner one, has an arcuate section, and has magnetic anisotropy in the radial direction. In a Bd distribution graph using the circumferential measurement region length of the inner or outer-periphery surface and surface magnetic flux density Bd as vertical and horizontal axes, respectively, when the maximum and minimum of Bd in the inner-periphery surface are set to Bdi(max) and Bdi(min), respectively, and the maximum and minimum of Bd on the outer-periphery surface are set to Bdo(max) and Bdo(min), respectively; the conditions of Ro=Bdo(min)/Bdo(max)≥0.5 and Ri/Ro=äBdi(min)/Bdi(max)}/äBdo(min)/Bdo(max)}<1.0 should be met. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a ferrite magnet manufactured using a dry molding method and having an arc shape and anisotropy in the radial direction, and a motor using the ferrite magnet.

  Motors used in home appliances and automobile electrical components are required to have high performance, small size, and light weight. Such a motor is a DC motor, and an arc-shaped anisotropic ferrite magnet is used as the magnet. These motor magnets are anisotropic so that the radial direction is the easy axis of magnetization. These magnets are required to have a large surface magnetic flux density Bd on the inner peripheral surface side and a uniform distribution of the surface magnetic flux density Bd on the inner peripheral surface side in the circumferential direction. If the fluctuation of the surface magnetic flux density Bd is large in the circumferential direction of the inner peripheral surface, cogging torque and torque ripple are increased, and good motor characteristics cannot be obtained. Here, the cogging torque refers to a change of the torque with respect to the rotation angle based on the magnetic attractive force generated between the stator and the rotor of the motor. Moreover, torque ripple means the fluctuation range of torque.

  The arc-shaped anisotropic ferrite magnet is manufactured using dry molding or wet molding. Wet molding has good orientation, but increases the manufacturing cost. On the other hand, in dry molding, the orientation tends to be disturbed at both ends of the arc-shaped anisotropic ferrite magnet, and it is difficult to obtain good motor characteristics.

  In order to solve such problems of dry molding, Patent Document 1 proposes a method for preventing disorder of orientation at both ends of a magnet when manufacturing an arc-shaped ferrite magnet having anisotropy in the radial direction. ing. In other words, Patent Document 1 uses a dry molding apparatus provided with an orientation ferromagnetic material to obtain a molded body having anisotropic directions aligned in the radial direction. For this reason, an arc-shaped anisotropic ferrite magnet having a large surface magnetic flux density Bd on the inner peripheral surface side and a uniform distribution can be obtained. Therefore, the motor using the anisotropic ferrite magnet of Patent Document 1 is characterized by being strong and having a small cogging torque. Conventionally, cracks frequently occur in the vicinity of both ends of the inner peripheral surface during sintering due to disorder in orientation at both ends of the magnet. However, in Patent Document 1, there is extremely little disorder in orientation at both ends of the magnet. Therefore, such cracks are drastically reduced.

Japanese Patent No. 2777693

According to Patent Document 1, an anisotropic ferrite magnet that can improve the characteristics of a motor can be provided, but the demand for improving the characteristics continues.
The present invention has been made based on such a technical problem, and an object thereof is to provide an anisotropic ferrite magnet in which cogging torque and torque ripple are further reduced. Another object of the present invention is to provide a motor using such an anisotropic ferrite magnet.

Patent Document 1 focuses on the surface magnetic flux density Bd distribution on the inner peripheral surface of a ferrite magnet having an arc shape and anisotropy in the radial direction. However, when actually assembled as a motor, the magnet forms a magnetic circuit with the case, adjacent magnets, etc., so the surface magnetic flux density Bd distribution on the outer peripheral surface of the anisotropic ferrite magnet also affects the motor characteristics. There was found. In other words, cogging torque and torque ripple can be reduced by making the surface magnetic flux density Bd distribution on the outer peripheral surface uniform and making the degree of uniformity higher than the surface magnetic flux density Bd distribution on the inner peripheral surface. That is, the anisotropic ferrite magnet of the present invention has an inner peripheral surface and an outer peripheral surface opposite to the inner peripheral surface, has a circular cross section, and has a magnetic anisotropy in its radial direction. In the Bd distribution graph, which is an isotropic ferrite magnet, the horizontal axis represents the measurement area length in the circumferential direction of the inner circumferential surface or outer circumferential surface, and the vertical axis represents the surface magnetic flux density Bd.
The maximum and minimum values of Bd on the inner peripheral surface are respectively Bdi (max), Bdi (min),
When the maximum value and the minimum value of Bd on the outer peripheral surface are Bdo (max) and Bdo (min), respectively.
Condition of Ro = Bdo (min) / Bdo (max) ≧ 0.5 and Ri / Ro = {Bdi (min) / Bdi (max)} / {Bdo (min) / Bdo (max)} <1.0 It is characterized by satisfying.

In the anisotropic ferrite magnet of the present invention, Ri / Ro = {Bdi (min) / Bdi (max)} / {Bdo (min) / Bdo (max)} ≦ 0.9, and further Ri / Ro = It is preferable to satisfy the condition of {Bdi (min) / Bdi (max)} / {Bdo (min) / Bdo (max)} ≦ 0.8.
In the anisotropic ferrite magnet of the present invention, when the area surrounded by the Bd distribution curve on the inner peripheral surface and the horizontal axis is Ai, and the area surrounded by the Bd distribution curve on the outer peripheral surface and the horizontal axis is Ao, Ai /Ao=0.95 to 1.9 is preferably satisfied.
Furthermore, in the anisotropic ferrite magnet of the present invention, it is preferable that the condition of Ri = Bdi (min) / Bdi (max) ≧ 0.4 is satisfied.

A motor using an anisotropic ferrite magnet of the present invention includes a stator, a rotor that can rotate with respect to the stator, and an anisotropic ferrite magnet that is fixed to the stator. Is an anisotropic ferrite magnet by dry molding having an inner peripheral surface and an outer peripheral surface opposite to the inner peripheral surface, having a circular arc cross section and having magnetic anisotropy in the radial direction. In the Bd distribution graph with the horizontal axis representing the circumferential region or the circumferential region of the outer circumferential surface and the vertical axis representing the surface magnetic flux density Bd,
The maximum and minimum values of Bd on the inner peripheral surface are respectively Bdi (max), Bdi (min),
When the maximum value and the minimum value of Bd on the outer peripheral surface are Bdo (max) and Bdo (min), respectively.
Condition of Ro = Bdo (min) / Bdo (max) ≧ 0.5 and Ri / Ro = {Bdi (min) / Bdi (max)} / {Bdo (min) / Bdo (max)} <1.0 It is characterized by satisfying.

  According to the present invention, an anisotropic ferrite magnet that can reduce cogging torque and torque ripple can be provided. By using the anisotropic ferrite magnet of the present invention, a motor having excellent characteristics can be obtained.

  As shown in FIG. 1, the anisotropic ferrite magnet 1 according to the present invention has a circular cross section and has anisotropy (indicated by an arrow) in the radial direction. The anisotropic ferrite magnet 1 has an inner peripheral surface 2 and an outer peripheral surface 3, and is sometimes referred to as a so-called anisotropic segment magnet. This anisotropic ferrite magnet 1 is manufactured using a dry molding method. This molding method will be described later.

The magnet of the present invention is characterized by a surface magnetic flux density Bd distribution in the circumferential direction of the outer peripheral surface 3 (hereinafter, simply referred to as Bd or Bd distribution), and a Bd distribution in the circumferential direction of the inner peripheral surface 2. The Bd distribution relationship in the circumferential direction of the outer peripheral surface 3 is also characteristic.
The Bd distribution in the circumferential direction of the inner peripheral surface 2 and the outer peripheral surface 3 is measured by the procedure shown in FIGS. First, the anisotropic ferrite magnet 1 incorporated in the magnetic case 4 is magnetized by a predetermined method using the inner surface magnetized yoke 5 shown in FIG. In the Bd measurement, as shown in FIG. 3, the Hall element 6 is disposed near the inner peripheral surface 2 of the magnetized anisotropic ferrite magnet 1. The Hall element 6 at this time is positioned at the center of the inner peripheral surface 2 in the height direction (vertical direction in FIG. 3) and is placed in contact with the peripheral surface or as close as possible. Then, by rotating the anisotropic ferrite magnet 1 in the circumferential direction, the Bd distribution from one end A to the other end B in the circumferential direction of the peripheral surface can be measured. The anisotropic ferrite magnet 1 is rotated so that the distance between the Hall element 6 and the peripheral surface does not vary. Although FIG. 3 shows the measurement for the inner peripheral surface 2, the same measurement is performed for the outer peripheral surface 3.

  The Bd distribution measured as described above is plotted in a Bd distribution graph in which the horizontal axis is the measurement region length (the locus of the Hall element 6 from one end A to the other end B) and the vertical axis is Bd. A Bd distribution curve as shown is obtained. As the Bd distribution curve, two Bd distribution curves of the Bd distribution curve on the inner peripheral surface 2 and the Bd distribution curve on the outer peripheral surface 3 can be obtained.

In FIG. 4, the maximum and minimum values of Bd on the inner peripheral surface 2 are Bdi (max) and Bdi (min), respectively, and the maximum and minimum values of Bd on the outer peripheral surface 3 are Bdo (max) and Bdo (min), respectively. And In addition, although the polarities of the inner peripheral surface 2 and the outer peripheral surface 3 are opposite, Bdi (max), Bdi (min), Bdo (max), and Bdo (min) are specified by their absolute values. .
In the above, the anisotropic ferrite magnet 1 according to the present invention satisfies the condition of Ro = Bdo (min) / Bdo (max) ≧ 0.5. The value obtained by Ro = Bdo (min) / Bdo (max) (1) represents the uniformity of Bd on the outer peripheral surface 3. That is, the larger the value obtained by the equation (1), the more uniform the Bd on the outer peripheral surface 3. In the anisotropic ferrite magnet 1 according to the present invention, this Ro is 0.5 or more. Ro is ideally 1.0, but it is not easy to obtain such a value. Considering that other conditions according to the present invention are satisfied, the upper limit of Ro is about 0.75.

  Further, the anisotropic ferrite magnet 1 according to the present invention satisfies the condition of Ri / Ro = {Bdi (min) / Bdi (max)} / {Bdo (min) / Bdo (max)} <1.0. It is characterized by. Ri / Ro = {Bdi (min) / Bdi (max)} / {Bdo (min) / Bdo (max)} (2) is the uniformity of Bd (Ri) on the inner circumferential surface 2 and the outer circumferential surface 3. It is a ratio of uniformity (Ro) of Bd. Therefore, when the value obtained by Expression (2) is less than 1.0, Bd on the outer peripheral surface 3 shows a more uniform distribution than the inner peripheral surface 2. As will be apparent from the examples to be described later, Ri / Ro has been 1.0 or more because conventionally, the uniformity of the Bd distribution on the inner peripheral surface 2 has been exclusively considered. Ri / Ro according to the present invention is preferably 0.9 or less, more preferably 0.8 or less. However, since Ri / Ro is small means that Ri itself is small, Ri / Ro is preferably 0.5 or more, and more preferably 0.6 or more.

In the anisotropic ferrite magnet 1 of the present invention, when the area surrounded by the Bd distribution curve and the horizontal axis of the inner peripheral surface 2 is Ai, and the area surrounded by the Bd distribution curve and the horizontal axis of the outer peripheral surface 3 is Ao, Ai / Ao = 0.95-1.9, preferably Ai / Ao = 1.0-1.5. The anisotropic ferrite magnet 1 in which Ai / Ao is too small has insufficient magnetic properties on the inner peripheral surface 2 side. On the other hand, in order to obtain Ai / Ao exceeding 1.9, the density difference between the inner peripheral surface 2 and the outer peripheral surface 3 of the molded body must be remarkably increased. For this reason, cracks frequently occur during firing, which may make molding impossible. Further preferable Ai / Ao is 1.0 to 1.3.
In the present invention, in the Bd distribution graph, Bd on the inner peripheral surface 2 is preferably uniform, and Ri = Bdi (min) / Bdi (max) ≧ 0.4 is preferable. Ri, like Ro, is very ideally 1.0, but it is not easy to obtain such a value. Considering that other conditions according to the present invention are satisfied, Ri has an upper limit of about 0.75.

There is no material limitation on the anisotropic ferrite magnet 1 to which the present invention is applied. In this, the anisotropic whose main phase is M-type (Magnet Plumbite-type) ferrite represented by the general formula of MO.6Fe ₂ O ₃ or MFe ₁₂ O ₁₉ (M = Ba or Sr). It is suitable to apply to a magnetic ferrite magnet. In this M-type ferrite, a part of M can be replaced with rare earth elements (La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). Moreover, a part of Fe can be substituted with one or two of Co and Ni.

In order to obtain the anisotropic ferrite magnet 1 according to the present invention, it is important to use a characteristic forming apparatus in a magnetic field. Hereinafter, the dry magnetic field forming apparatus 20 will be described.
FIG. 5 is a cross-sectional view of the main part of the dry magnetic field molding apparatus 20. The dry magnetic field molding apparatus 20 includes a die 21, an upper punch 22, a lower punch 23, a cavity 24 composed of the die 21 and the lower punch 23, and a coil 25. The dry magnetic field molding apparatus 20 includes hard nonmagnetic portions 22 a and 23 a on the cavity 24 side of the upper punch 22 and the lower punch 23.

The upper punch 22 forms the outer peripheral surface 3 of the anisotropic ferrite magnet 1. Therefore, the shape of the molding surface 22s of the hard nonmagnetic portion 22a of the upper punch 22 is concave. The upper punch 22 is made of a nonmagnetic material. Therefore, the entire upper punch 22 including the hard nonmagnetic portion 22a is made of a nonmagnetic material.
The lower punch 23 forms the inner peripheral surface 2 of the anisotropic ferrite magnet 1. Therefore, the shape of the molding surface 23s of the hard nonmagnetic portion 23a of the lower punch 23 is convex. The lower punch 23 is made of a magnetic material except for the hard non-magnetic portion 23a constituting the molding surface.

  By configuring the upper punch 22 from a non-magnetic material, a radial magnetic field is applied from the lower punch 23 into the cavity 24 when a magnetic field is applied by the coil 25. In other words, the orientation of the anisotropic ferrite magnet 1 does not converge on the outer peripheral surface 3 or a partial deviation of the orientation direction does not occur and the anisotropic ferrite magnet 1 can be uniformly anisotropic in the radial direction.

  The material of the nonmagnetic material constituting the upper punch 22 is not particularly limited, and for example, stainless steel, copper beryllium alloy, high manganese steel, bronze, brass, nonmagnetic super steel, etc. can be used, and two or more kinds of materials can be used. May be combined.

On the other hand, the material of the magnetic material constituting the lower punch 23 is not particularly limited and may be any material that is generally used. For example, carbon steel, carbon tool steel, alloy tool steel, die steel, or the like is used.
As the hard non-magnetic portions 22a and 23a of the upper punch 22 and the lower punch 23, it is most preferable to use stellite which is a Co-based hard alloy, but any non-magnetic and wear-resistant material may be used. Magnetic super steel or the like can be used.

  The material of the die 21 may be a non-magnetic material, and the same material as the upper punch 22 can be used. Further, a wear-resistant material such as nonmagnetic super steel or stellite can be provided on the inner wall surface of the die 21 constituting the cavity 24.

  The cavity 24 is a space excluding a portion occupied by the lower punch 23 fitted therein in the space of the die hole 21 a penetrating in the vertical direction of the die 21. Then, the ferrite powder to be molded is filled in the cavity 24 and the upper punch 22 enters the cavity 24, whereby the ferrite powder is pressure-molded in cooperation with the lower punch 23.

  In the dry magnetic field molding apparatus 20, a magnetic jig 27 having a lower surface 27 s having a shape substantially along the arc of the molding surface 22 s of the upper punch 22 is mounted above the upper punch 22. The curvature radius r1 of the lower surface 27s is set to be larger than the curvature radius r2 when the upper punch 22 is positioned immediately before the completion of molding so as to be concentric with the arc of the molding surface 22s of the upper punch 22. ing. That is, when the upper punch 22 is positioned immediately before the completion of molding, the arc of the molding surface 22 s of the upper punch 22 and the arc of the lower surface 27 s of the magnetic body jig 27 are not concentric, and the lower surface 27 s of the magnetic body jig 27 is not concentric. The center of the arc is located closer to the lower punch 23 than the center of the arc of the molding surface 22s. By providing the magnetic material jig 27 on the upper punch 22 side made of a non-magnetic material, the magnetic field strength applied to the cavity 24 by the coil 25 is increased. Further, by making the shape of the lower surface 27 s of the magnetic body jig 27 approximately along the molding surface 22 s of the upper punch 22, radial orientation is facilitated. The area of the lower surface 27s of the magnetic jig 27 may be made large enough not to bias the end orientation of the anisotropic ferrite magnet 1 obtained. Furthermore, the dry magnetic field molding apparatus 20 increases the thickness of the central portion in the width direction of the magnetic body jig 27 by setting the curvature radius r1 to be larger than the curvature radius r2 than when r1 = r2. . Therefore, the magnetic flux can be focused to some extent at the center portion in the width direction of the anisotropic ferrite magnet 1. By doing so, the Bd at the central portion in the width direction of the outer peripheral surface 3 of the anisotropic ferrite magnet 1 where Bd generally decreases is increased, and the uniformity of the Bd distribution on the outer peripheral surface 3 of the anisotropic ferrite magnet 1 is increased. Can be improved. The material of the magnetic body jig 27 may be a normal magnetic body, and for example, carbon steel, carbon tool steel, alloy tool steel, die steel, etc. are used.

  The basic configuration of the above dry magnetic field forming apparatus 20 is described in Patent Document 2. However, in the dry magnetic field molding apparatus 20 described in FIG. 2 of Patent Document 2, when the upper punch 22 is positioned immediately before the completion of molding, the curvature radius r1 of the lower surface 27s is an arc of the molding surface 22s of the upper punch 22. And the concentric circle (curvature radius r2) (r1 = r2). In this regard, the dry magnetic field molding apparatus 20 is different from FIG.

Japanese Patent Laid-Open No. 10-270276

A molded body was produced using the dry magnetic field molding apparatus 20 having the configuration shown in FIG. The magnetic field forming apparatus 20 has the following specifications.
Curvature radius of molding surface 22s of upper punch 22: 16.4 mm
Curvature radius of molding surface 23s of lower punch 23: 11.1 mm
Cavity 24 width: 26.93 mm
Cavity 24 length (depth): 24.56 mm
Curvature radius of lower surface 27s of magnetic body jig 27: Example 1 = 73 mm, Example 2 = 71 mm, Comparative Example 3 = 66 mm

The molding space of the dry magnetic field molding apparatus 20 was filled with the raw material powder of the anisotropic ferrite magnet, and pressure molded in the magnetic field to obtain an arc-shaped molded body having anisotropy in the radial direction. . The composition of the raw material powder, the molding pressure, and the applied magnetic field strength are as follows.
Raw material powder composition: Sr _0.95 La _0.05 Co _0.03 Fe _11.97 O ₁₉
Molding pressure (total pressure): 2.5 ton
Magnetic field strength: 6 kOe (480 kA / m)
Next, the compact was sintered to obtain an arc-shaped anisotropic ferrite magnet. As for the dimensions of the obtained anisotropic ferrite magnet, the radius of curvature of the outer peripheral surface is 13.25 mm, the radius of curvature of the inner peripheral surface is 8.9 mm, the width in the cross section including the radial direction is 22.6 mm, and the length is 21. It was 2 mm.

For comparison, an anisotropic ferrite magnet similar to the above was prepared except that a molded body obtained by the following molding method in a magnetic field was used.
Comparative Example 1: A magnetic field molding apparatus in which the orientation magnetic bodies 61 and 62 were removed from the magnetic field molding apparatus shown in FIG.
Comparative Example 2: A magnetic field molding apparatus having the configuration shown in FIG. 4 of Patent Document 1 was used.
Comparative Example 3: A magnetic field molding apparatus having the configuration shown in FIG.
In the dry magnetic field molding apparatus 20 described in FIG. 2 of Patent Document 2, as described above, when the upper punch 22 is positioned immediately before the completion of the molding with the curvature radius r1 of the lower surface 27s, the molding of the upper punch 22 is performed. It is set to be concentric with the arc of the surface 22s (curvature radius r2) (r1 = r2), and r1 = r2 = 66 mm.

Bd was measured by the method described above for the anisotropic ferrite magnets of Examples 1 and 2 and Comparative Examples 1 to 3 obtained above.
6 to 10 show the Bd distribution curves of the inner and outer peripheral surfaces of the anisotropic ferrite magnets of Examples 1 and 2 and Comparative Examples 1 to 3. FIG. Further, Bdi (max), Bdi (min), Bdo (max), Bdo (min), Ai, and Ao were obtained from each Bd distribution curve. From each obtained value, Ri, Ro, Ri / Ro, and Ai / Ao were obtained. The results are shown in Table 1.
The obtained anisotropic ferrite magnet was incorporated into a motor, and cogging torque and torque ripple were measured. This motor includes a stator and a rotor that can rotate with respect to the stator, and has a known configuration in which an anisotropic ferrite magnet is fixed to the stator. The results are shown in Table 1.
Furthermore, using this motor, the electromotive force Ec when the rotor was rotated by external driving was measured. The results are shown in Table 1. Ec is an index of motor characteristics, and the larger the value, the larger the output can be obtained.

As shown in Table 1, when comparing the anisotropic ferrite magnets according to Examples 1 and 2 and the anisotropic ferrite magnets according to Comparative Examples 1 to 3, Ro is 0. The Bd distribution on the outer peripheral surface is more uniform than that of the anisotropic ferrite magnets of Comparative Examples 1 to 3 having Ro of less than 0.5. Further, the anisotropic ferrite magnets according to Examples 1 and 2 have Ri / Ro of less than 1.0, and compared with the anisotropic ferrite magnets of Comparative Examples 1 to 3 in which Ri / Ro is 1.0 or more, The Bd distribution on the outer peripheral surface is more uniform than the Bd distribution on the inner peripheral surface.
As the Ri / Ro becomes lower, the cogging torque and the torque ripple are reduced, and the motor using the anisotropic ferrite magnet according to the first and second embodiments where the Ri / Ro is less than 1.0 has the rotation and output. Uniformity can be ensured.

  Further, in Examples 1 and 2, the cogging torque and the torque ripple are reduced, and the electromotive force Ec is also improved with respect to the comparative example 1. Thus, the electromotive force Ec is reduced together with the cogging torque and the torque ripple. The ability to improve indicates that the present invention is a very effective technique for improving the characteristics of the motor.

1 is a perspective view of an anisotropic ferrite magnet according to the present invention. It is a figure which shows the magnetization method for the measurement of the surface magnetic flux density Bd in the inner peripheral surface and outer peripheral surface of an anisotropic ferrite magnet. It is a figure which shows the measuring method of the surface magnetic flux density Bd in the inner peripheral surface and outer peripheral surface of an anisotropic ferrite magnet. It is a graph which shows the surface magnetic flux density Bd distribution curve in the inner peripheral surface and outer peripheral surface of an anisotropic ferrite magnet. It is sectional drawing which shows schematic structure of the shaping | molding apparatus in a magnetic field used for this invention. 4 is a graph showing a surface magnetic flux density Bd distribution curve of an anisotropic ferrite magnet according to Example 1. 6 is a graph showing a surface magnetic flux density Bd distribution curve of an anisotropic ferrite magnet according to Example 2. 6 is a graph showing a surface magnetic flux density Bd distribution curve of an anisotropic ferrite magnet according to Comparative Example 1. 6 is a graph showing a surface magnetic flux density Bd distribution curve of an anisotropic ferrite magnet according to Comparative Example 2. 10 is a graph showing a surface magnetic flux density Bd distribution curve of an anisotropic ferrite magnet according to Comparative Example 3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Anisotropic ferrite magnet, 2 ... Inner peripheral surface, 3 ... Outer peripheral surface, 4 ... Case, 5 ... Inner surface magnetizing yoke, 6 ... Hall element, 20 ... Dry magnetic field molding apparatus, 21 ... Die, 22 ... Upper part Punch, 22a ... hard nonmagnetic part, 23 ... lower punch, 23a ... hard nonmagnetic part, 24 ... cavity, 25 ... coil, 27 ... magnetic body jig, 27s ... bottom surface

Claims (15)

An anisotropic ferrite magnet by dry molding having an inner peripheral surface and an outer peripheral surface facing the inner peripheral surface, having a circular cross section and having magnetic anisotropy in the radial direction,
In the Bd distribution graph in which the horizontal axis represents the measurement area length in the circumferential direction of the inner peripheral surface or the outer peripheral surface and the vertical axis represents the surface magnetic flux density Bd,
The maximum and minimum values of Bd on the inner peripheral surface are respectively Bdi (max), Bdi (min),
When the maximum value and the minimum value of the Bd on the outer peripheral surface are Bdo (max) and Bdo (min),
An anisotropic ferrite magnet characterized by satisfying the conditions of Ro ≧ 0.5 and Ri / Ro <1.0.
However, Ro = Bdo (min) / Bdo (max),
Ri = Bdi (min) / Bdi (max)   The anisotropic ferrite magnet according to claim 1, wherein the condition of Ri / Ro ≦ 0.9 is satisfied.   The anisotropic ferrite magnet according to claim 1, wherein the condition of Ri / Ro ≦ 0.8 is satisfied.   When the area surrounded by the Bd distribution curve and the horizontal axis on the inner peripheral surface is Ai, and the area surrounded by the Bd distribution curve and the horizontal axis on the outer peripheral surface is Ao, Ai / Ao = 0.95 to 1.9. The anisotropic ferrite magnet according to any one of claims 1 to 3, wherein the following condition is satisfied.   The anisotropic ferrite magnet according to claim 4, wherein the condition of Ai / Ao = 1.0 to 1.5 is satisfied.   The anisotropic ferrite magnet according to claim 4, wherein the condition of Ai / Ao = 1.0 to 1.3 is satisfied.   The anisotropic ferrite magnet according to claim 1, wherein the condition of Ro ≦ 0.75 is satisfied.   The anisotropic ferrite magnet according to claim 1, wherein the condition of 0.5 ≦ Ri / Ro is satisfied.   The anisotropic ferrite magnet according to claim 1, wherein the condition 0.6 ≦ Ri / Ro is satisfied.   The anisotropic ferrite magnet according to claim 1, wherein the condition of Ri ≧ 0.4 is satisfied.   The anisotropic ferrite magnet according to claim 10, wherein the condition of Ri ≦ 0.75 is satisfied.   2. The anisotropic ferrite magnet according to claim 1, wherein the anisotropic ferrite magnet has a magnetoplumbite type ferrite containing Sr, La, Co, and Fe as a main phase. A stator,
A rotor rotatable with respect to the stator;
An anisotropic ferrite magnet fixed to the stator,
The anisotropic ferrite magnet is
A ferrite magnet by dry molding having an inner peripheral surface and an outer peripheral surface facing the inner peripheral surface, having a circular arc cross section and having magnetic anisotropy in the radial direction,
In the Bd distribution graph in which the horizontal axis represents the measurement area length in the circumferential direction of the inner peripheral surface or the outer peripheral surface and the vertical axis represents the surface magnetic flux density Bd,
The maximum and minimum values of Bd on the inner peripheral surface are respectively Bdi (max), Bdi (min),
When the maximum value and the minimum value of the Bd on the outer peripheral surface are Bdo (max) and Bdo (min),
A motor satisfying the conditions of Ro ≧ 0.5 and Ri / Ro <1.0.
However, Ro = Bdo (min) / Bdo (max),
Ri = Bdi (min) / Bdi (max) The anisotropic ferrite magnet is
Ro ≦ 0.75,
The motor according to claim 13, wherein a condition of 0.5 ≦ Ri / Ro ≦ 0.9 is satisfied. The anisotropic ferrite magnet is
The motor according to claim 14, wherein a condition of 0.4 ≦ Ri is satisfied.

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