JP4304930B2 - Magnetization method of rare earth magnet and rare earth magnet - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetizing method for a rare earth magnet, and more particularly to a magnetizing method suitable for magnetizing a rare earth magnet used by being fixed to a rotor of a rotating machine.
[0002]
[Prior art]
Currently, two types of rare earth magnets, rare earth / cobalt magnets and rare earth / iron / boron magnets, are widely used in various fields.
[0003]
In particular, rare earth / iron / boron magnets (hereinafter referred to as “RT- (M) -B magnets”, where R is a rare earth element including Y, and T is Fe or a mixture of Fe and Co and / or Ni. , M is an additive element (for example, at least one of Al, Ti, Cu, V, Cr, Ni, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, W), B is boron or boron and carbon Has the highest maximum magnetic energy product among various magnets, and its price is relatively low, so it is actively adopted in various electronic devices.
[0004]
For example, rare earth magnets are used in various rotating machines (motors and the like) for the purpose of obtaining high energy efficiency or reducing the size and weight. For example, JP 2000-41372 A discloses a movable magnet type DC torque motor 10 as shown in FIG.
[0005]
This DC torque motor 10 has a rotor 1 in which permanent magnets 5 and 6 are fixed in a cylindrical shape around a cylindrical iron core (for example, soft iron) 4 centering on a shaft 3, and a substantially U-shape. A first magnetic pole portion 7 and a second magnetic pole portion 8 that are opposed to the rotor 1 with a predetermined gap are formed at the end portions, respectively, and a stator 2 with a coil 9 wound around the base portion (upper side in the figure). Have. Here, the stator 2 is formed by superimposing electromagnetic steel strips having a saturation magnetic flux density of 1.6 T (Tesla) or more, for example.
[0006]
The permanent magnets 5 and 6 disclosed in the above publication are semi-cylindrical (bow-shaped) permanent magnets that are magnetized in opposite directions. For example, the magnet 5 has an N pole on the front surface (outer peripheral surface) side and an S pole on the back surface (inner surface) side, while the magnet 6 has an S pole on the front surface (outer peripheral surface) side and an N pole on the back surface (inner surface) side. Has been. Instead of the magnets 5 and 6, an integrally formed cylindrical magnet (not shown) may be used.
[0007]
[Problems to be solved by the invention]
When magnetizing the magnets 5 and 6 used in the rotor of the motor 10 described above in a cylindrical arrangement, or when magnetizing an integrally formed cylindrical magnet, It has been found that there is a problem that, when magnetized by applying a magnetic field once in the radial direction, the boundary portion of the regions magnetized in opposite directions (corresponding to the magnets 5 and 6 in FIG. 5) is not sufficiently magnetized. . In such an incompletely magnetized magnet, the average magnetic flux density decreases, or the angle range in which a desired surface magnetic flux density can be obtained becomes narrow. Furthermore, in the angular distribution (around the axis) of the surface magnetic flux density, an extreme value is generated near the boundary portion, and the linearity of the change in the surface magnetic flux density is lowered. As a result, it is difficult to accurately adjust the angle of the rotating machine. The performance of the rotating machine may not be fully demonstrated.
[0008]
The present invention has been made in view of the above-mentioned points, and one of its purposes is that when magnetizing magnets arranged in a cylindrical shape so as to form mutually magnetized regions in the opposite directions, It is an object of the present invention to provide a magnetizing method in which a magnet is magnetized more reliably in a predetermined direction than before. Another object of the present invention is to provide a magnet magnetized by such a magnetizing method and a high-performance rotating machine using the magnet, particularly a rotating machine capable of adjusting the angle with high accuracy.
[0009]
[Means for Solving the Problems]
The method for magnetizing a rare earth magnet according to the present invention comprises a step of preparing a rare earth magnet arranged to form a cylinder, and applying a first external magnetic field to the rare earth magnet to move the cylinder from the inside to the outside. A first magnetization step for forming a first region that is magnetized and a second region that is magnetized from the outside to the inside, and the boundary between the first region and the second region, Including a second magnetization step of applying a second external magnetic field so that an external magnetic field component in a direction that forms an angle greater than 0 ° and less than 50 ° with the direction of the external magnetic field component applied in the magnetization step In this way, the above object is achieved.
[0010]
In a preferred embodiment, the rare-earth magnet is supported so as to be rotatable relative to the magnetic circuit around the axis of the cylinder, and the first magnetizing is performed at a first position relative to the magnetic circuit. A step is executed, and after the rare earth magnet is rotated relative to the magnetic circuit about the axis, the second magnetization step is executed.
[0011]
In a preferred embodiment, a dipole magnet having one each of the first region and the second region is formed along the circumference of the cylinder.
[0012]
The angle formed between the direction of the external magnetic field component applied in the first magnetization step and the direction of the external magnetic field component applied in the second magnetization step at the boundary between the first region and the second region is 20 ° or more and 40 ° or less, and more preferably 25 ° or more and 35 ° or less.
[0013]
The first external magnetic field and the second external magnetic field preferably have substantially the same intensity. For example, it is preferable to generate the first external magnetic field and the second external magnetic field using the same magnetic circuit under the same conditions, and change only the relative position (angle around the axis) of the rare earth magnet with respect to the magnetic circuit. Various known magnetic circuits can be used as the magnetic circuit.
[0014]
The rare earth magnet is preferably a radially oriented anisotropic sintered magnet.
[0015]
Since the rare earth magnet according to the present invention is magnetized using any one of the above magnetizing methods, it has excellent magnetic properties.
[0016]
The rare earth magnet according to the present invention is a cylindrical rare earth magnet having a first region magnetized from the inside to the outside of the cylinder and a second region magnetized from the outside to the inside. The surface magnetic flux density continuously changes without taking an extreme value at the boundary between the first region and the second region.
[0017]
In a preferred embodiment, in the first region or the second region, an angle range in which the surface magnetic flux density takes a maximum value is 120 ° or more and 140 ° or less.
[0018]
In a preferred embodiment, the angle range from the point where the surface magnetic flux density is zero to the maximum value is 20 ° or more and 30 ° or less.
[0019]
Since the rotating machine according to the present invention includes the rare earth magnet manufactured by the above manufacturing method, the rotating machine has excellent characteristics and is suitably used for a valve opening control device and the like.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a magnetizing method for a rare earth magnet according to the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.
[0021]
As shown in FIGS. 1A and 1B, the rare earth magnet magnetization method according to the present invention includes at least two magnetization steps.
[0022]
First, a rare-earth magnet 22 (also referred to as a magnet before magnetization) is prepared so as to form a cylinder 22a. The rare earth magnet 22 may be an integrally formed rare earth magnet, or a plurality of arcuate magnets fixed to the surface of a cylindrical rotor (step (a)).
[0023]
Next, by applying a first external magnetic field H1 to the rare earth magnet 22, a first region R1 that is magnetized from the inside to the outside of the cylinder 22a and a second region R2 that is magnetized from the outside to the inside. Are formed (step (b)). At this time, the magnetization direction of the boundary portion BR between the first region R1 and the second region R2 of the rare earth magnet 22 is not stable. In particular, in a radially oriented anisotropic rare earth sintered magnet, since the crystal grains are oriented in the radial direction, the crystal grains in the boundary portion BR are in a direction perpendicular to the orientation direction (that is, a tangential direction to the cylinder 22a). It will receive a magnetizing magnetic field and will not be magnetized well. Conventionally, only this magnetization process has been executed.
[0024]
In the magnetization method of the present invention, the direction of the external magnetic field component applied in the first magnetization step (represented here by H1) and 0 ° to the boundary portion BR between the first region R1 and the second region. The second external magnetic field H2 is applied so that an external magnetic field component (represented by H2 here) in a direction that forms an angle of less than 50 ° is applied (step (c)). The magnetization direction of the crystal grains in the boundary portion BR is determined by the second external magnetic field H2. The strengths of the first external magnetic field H1 and the second external magnetic field H2 are preferably substantially equal. In addition, you may perform this 1st magnetization process and / or a 2nd magnetization process in multiple times. The strengths of the external magnetic fields H1 and H2 are appropriately set according to the rare earth magnet to be used, but in the case of a radially oriented RT- (M) -B magnet, it is set to 2T to 4T.
[0025]
In FIGS. 1A and 1B, for the sake of simplicity, the external magnetic field H1 or H2 in the same direction is applied to the entire rare earth magnet 22, but this is not necessarily required. For example, an external magnetic field component in a different direction may be applied between the boundary portion BR and the vicinity of the center of each of the regions R1 and R2.
[0026]
Below, the example using the radial orientation RT- (M) -B type anisotropic sintered magnet which is excellent in magnetic characteristics and excellent in flatness of the surface magnetic flux density (maximum value) will be described. The radial ring magnet (reference numeral 112 in FIG. 2) used here is manufactured as follows, for example.
[0027]
First, rare earth alloy powder is produced by a rapid cooling method (cooling rate: 10 ² to 10 ⁴ ° C / sec) such as a strip casting method (see the specification of US Pat. No. 5,383,987). This powder is press-molded under an orientation magnetic field in which the magnetic field strength in the cavity is 0.4 MA / m or more to produce a molded body having a density of 3.5 g / cm ³ or more. The obtained compact is sintered (1000 ° C. to 1100 ° C. under Ar atmosphere for 2 to 5 hours), and further subjected to an aging treatment (400 ° C. to 600 ° C. for 3 to 7 hours) to produce a radial ring magnet. . The radial ring magnet has, for example, an outer diameter of 29 mmφ, an inner diameter of 25 mmφ, and a height of 12 mm. In addition, since a radial ring magnet is manufactured by a well-known method, detailed description of the manufacturing method is abbreviate | omitted here (for example, refer Unexamined-Japanese-Patent No. 2001-192705). The radial ring magnet may be formed by bonding a plurality of arcuate magnets (molded bodies) in a ring shape (cylindrical shape). Of course, also in this case, the orientation of the magnetic particles in the finally obtained radial ring magnet is set to be radial orientation, and the sintered magnet has magnetic anisotropy in the radial direction from the center of the ring.
[0028]
In the present embodiment, magnetization was performed using the magnetizing apparatus 100 shown in FIG.
[0029]
The magnetizing apparatus 100 includes a columnar rotor 110 fixed to a shaft 103, and a magnetic circuit 120 (120a and 120b) that generates an external magnetic field with respect to the rotor 110. The shaft 103 is supported by a support base 130 so as to be rotatable. As will be described later, in order to change the relative position of the magnetized radial ring magnet 112 and the magnetic circuit 120 at a predetermined degree of rotation (θ) about the shaft 103, for example, grooves provided at a predetermined angle are provided. A clamped rotation mechanism 132 may be provided. Thus, by providing a mechanism that rotates step by step by a predetermined angle, the control of the rotation angle θ can be easily performed with good reproducibility.
[0030]
The magnetic circuit 120 has a yoke 122 (122a and 122b), and a coil 124 (124a and 124b) connected to a capacitor power source (not shown) is wound around the yoke 122. A cylindrical radial ring magnet 112 is disposed on the outer periphery of the columnar rotor 110. The magnetic circuits 120a and 120b generate an external magnetic field (for example, H1 and H2 in FIG. 1) in a predetermined direction with respect to the radial ring magnet 112. As the magnetic circuit 120, other known magnetic circuits such as an air-core coil may be used. Further, a radial ring magnet having four or more poles can be magnetized by appropriately changing the shape of the magnetic pole of the magnetic circuit.
[0031]
First, a predetermined external magnetic field (about 3 T) was applied from the magnetic circuits 120 a and 120 b with the radial ring magnet 112 in the first position with respect to the shaft 103. The first position may be an arbitrary position.
[0032]
FIG. 3 shows the results of measuring the angle dependence of the surface magnetic flux density Bg (T: Tesla) of the radial ring magnet 112 obtained by executing only the first magnetization step using a Gauss meter equipped with a Hall element probe. Shown in (a). The measurement angle is a boundary line between the N-pole region (region R1 magnetized toward the outer periphery) and the S-pole region (region R2 magnetized toward the inner periphery) of the obtained radial ring magnet 112. The direction passing through the center of the N region and the center axis of the radial ring magnet 112 is equivalent to 0 °.
[0033]
Next, after the first magnetizing step is executed, the first magnetizing step is performed at a second position where the radial ring magnet 112 is rotated by a certain angle θ around the axis 103 with respect to the first position. The same external magnetic field was applied. The angle dependence of the surface magnetic flux density Bg of the radial ring magnet 112 obtained when the rotation angle θ is 20 ° and 40 ° is shown in FIG. 3B (the same result was obtained at 20 ° and 40 °). ). FIG. 3C shows the angle dependency of the surface magnetic flux density Bg of the radial ring magnet 112 obtained when the rotation angle θ is 30 °.
[0034]
As shown in FIGS. 3A to 3C, the surface magnetic flux density Bg along the circumference of the radial ring magnet is at the boundary portion BR (see FIG. 1) between the first region R1 and the second region R2. The value takes zero, and then the value (absolute value) increases and takes the maximum value in each of the first region R1 and the second region R2, then passes through the flat region, and again reaches zero in the boundary portion BR. It becomes. Strictly speaking, the maximum value in each of the first region R1 and the second region R2 is a maximum value, and the value of the surface magnetic flux density Bg in the flat region is slightly smaller than the maximum value (maximum value). Become. Here, a flat region between two maximum values in each of the first region R1 and the second region R2 is referred to as a “maximum value region” where the surface magnetic flux density B takes a maximum value.
[0035]
First, as is apparent from the graph of FIG. 3A, the boundary portion BR (see FIG. 1) between the first region R1 and the second region R2 is sufficiently magnetized in a single magnetization step. Therefore, the angle range (50 ° to 150 ° and 220 ° to 330 °) of the maximum value region where the surface magnetic flux density Bg takes the maximum value is narrow, and the average magnetic flux density is also low. Further, the surface magnetic flux density Bg does not continuously change in the vicinity of the boundary portion BR, and takes extreme values (maximum value and minimum value). Further, in the vicinity of the boundary portion BR, the angle range from the point where the surface magnetic flux density Bg is zero to the maximum value exceeds 30 °.
[0036]
Thus, when magnetized only in the first magnetizing step, the angle range of the maximum value region of the surface magnetic flux density Bg is relatively narrow, less than 120 °, in each of the first region R1 and the second region R2, In addition, since an extreme value appears in the change in the surface magnetic flux density Bg at the boundary portion BR between the first region R1 and the second region R2, when a radial ring magnet 122 having such characteristics is used, for example, a rotating machine is configured. Not only is energy efficiency low, it also generates large vibrations. Furthermore, it is difficult to make a precise position (angle) sensor using such a radial ring magnet.
[0037]
On the other hand, the characteristics of the radial ring magnet obtained by using the magnetization method of the present invention are as shown in FIGS. 3B and 3C, compared with FIG. It can be seen that the angle range where Bg takes the maximum value is wide and the average magnetic flux density is also high. The angle range of the maximum region is 30 ° to 150 ° and 210 ° to 330 ° in the example shown in FIG. 3B, and 20 ° to 150 ° and 195 in the example shown in FIG. ° to 330 °.
[0038]
Further, in the vicinity of the boundary portion BR between the first region R1 and the second region R2, the surface magnetic flux density monotonously increases or decreases, and the extreme value (maximum value or minimum value) seen in FIG. ) Does not exist. In particular, the radial ring magnet 112 when the rotation angle θ shown in FIG. 3C is 30 ° has a wide angle range where the maximum value is obtained, and the average magnetic flux density is also high. Furthermore, it can be seen that the change in the surface magnetic flux density Bg near the boundary portion BR between the first region R1 and the second region R2 is very smooth.
[0039]
As described above, by performing the first magnetization step and the second magnetization step, the angle range of the maximum value region of the surface magnetic flux density Bg is 120 ° to 140 °, and the surface magnetic flux density Bg is zero. A radial ring magnet having an angle range from 20 ° to 30 ° can be obtained. Further, the surface magnetic flux density Bg of the radial ring magnet monotonously increases or decreases without taking an extreme value in the vicinity of the boundary portion BR between the first region R1 and the second region R2, and the linearity of the change in the surface magnetic flux density Bg Is expensive.
[0040]
FIG. 4 shows an angle range in which the surface magnetic flux density Bg of various radial ring magnets 112 obtained by changing the rotation angle θ takes a maximum value, and an angle range in which the surface magnetic flux density takes a value more than half of the maximum value. The results of plotting the values divided by 360 degrees against the rotation angle θ are shown. The rotation angle θ = 0 ° indicates a case where only the first magnetization step is executed. When the rotation angle θ is 50 °, almost the same result as in the case of θ = 0 ° is obtained.
[0041]
As is apparent from the graph of FIG. 4, by adopting the magnetization method according to the present invention and setting the rotation angle θ to more than 0 ° and less than 50 °, the angle range where the surface magnetic flux density Bg takes the maximum value and the maximum value It can be seen that the angle range taking half the value is increased compared to the conventional magnetization method (corresponding to the rotation angle θ = 0 ° in FIG. 4). Furthermore, by setting the rotation angle θ in the range of 20 ° or more and 40 ° or less, as shown in FIG. 3B, the surface magnetic flux density Bg at the boundary portion BR between the first region R1 and the second region R2 is increased. The extreme value does not appear in the change, and it changes continuously and smoothly. Furthermore, by making the rotation angle θ within 30 ° ± 5 °, the change in the surface magnetic flux density Bg at the boundary portion BR becomes smoother. When the rotation angle θ is about 30 °, the surface magnetic flux density B changes most smoothly as shown in FIG.
[0042]
As described above, when the magnetization method according to the present invention is used, the radial ring magnet in which the boundary portion BR of the regions (the first region R1 and the second region R2) magnetized in opposite directions is more reliably magnetized than before. Is obtained. If such a radial ring magnet is used to form a rotating machine as shown in FIG. 5, a rotating machine with high energy efficiency and less vibration can be obtained. Such a rotating machine is suitably used for applications that require high-precision control of the angle of a throttle valve control device, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-41372.
[0043]
【The invention's effect】
According to the present invention, when magnetizing a magnet arranged in a cylindrical shape so as to form regions that are oppositely magnetized to each other, magnetization is performed such that the vicinity of the boundary of the region is more reliably magnetized in a predetermined direction than before. A method is provided. Moreover, a high-performance rotating machine is provided by using a magnet magnetized by such a magnetizing method. When the rare earth magnet according to the present invention is used, torque ripples of motors and actuators are reduced, and energy efficiency is improved.
[0044]
In particular, a magnet obtained by magnetizing a radially oriented RT- (M) -B-based sintered magnet using the magnetizing method of the present invention is a high-performance rotating machine or a highly accurate position (angle). ) It is suitably used for a sensor for detection. Of course, the present invention is not limited to rare earth sintered magnets but can be used to magnetize various rare earth magnets including bonded magnets.
[Brief description of the drawings]
FIGS. 1A and 1B are diagrams schematically showing a method of magnetizing a rare earth magnet according to the present invention. FIG. 1B shows a method for magnetizing a rare earth magnet after the first magnetizing step shown in FIG. The second magnetizing step shown is executed.
FIG. 2 is a diagram schematically showing a magnetizing apparatus 100 used for executing a magnetizing method according to an embodiment of the present invention.
FIGS. 3A to 3C are graphs showing the angle dependence of the surface magnetic flux density Bg of a radial ring magnet. FIG. 3A shows a graph obtained by a conventional magnetizing method. FIGS. c) shows what is according to the invention.
FIG. 4 is a graph for explaining a difference in magnetic characteristics of a radial ring magnet depending on a rotation angle θ.
FIG. 5 is a view showing a known rotating machine in which a rare earth magnet according to the present invention is preferably used.
[Explanation of symbols]
22 Rare earth magnet 22a Cylinder 100 Magnetizer 103 Shaft 110 Rotor 112 Radial ring magnet 120, 120a, 120b Magnetic circuit 122, 122a, 122b Yoke 124a, 124b Coil 130 Support base 132 Rotating mechanism H1, H2 External magnetic field

Claims (11)

Providing a rare earth magnet arranged to form a cylinder;
A first external magnetic field is applied to the rare earth magnet to form a first region that is magnetized from the inside to the outside of the cylinder and a second region that is magnetized from the outside to the inside. The magnetization process;
An external magnetic field component is applied to the boundary between the first region and the second region in a direction that forms an angle greater than 0 ° and less than 50 ° with the direction of the external magnetic field component applied in the first magnetization step. A second magnetization step of applying a second external magnetic field,
A magnetizing method for a rare earth magnet. The rare earth magnet is supported so as to be rotatable relative to the magnetic circuit around the axis of the cylinder, and the first magnetizing step is executed at a first position relative to the magnetic circuit,
After rotating the rare earth magnet relative to the magnetic circuit about the axis, the second magnetization step is performed;
The method for magnetizing a rare earth magnet according to claim 1.   The rare earth magnet magnetization method according to claim 1 or 2, wherein a dipole magnet having one each of the first region and the second region is formed along a circumference of the cylinder.   The angle formed by the direction of the external magnetic field component applied in the first magnetization step and the direction of the external magnetic field component applied in the second magnetization step at the boundary between the first region and the second region is The method for magnetizing a rare earth magnet according to any one of claims 1 to 3, wherein the method is 20 ° or more and 40 ° or less.   The method for magnetizing a rare earth magnet according to any one of claims 1 to 4, wherein the first external magnetic field and the second external magnetic field have substantially the same strength.   The method for magnetizing a rare earth magnet according to claim 1, wherein the rare earth magnet is a radially oriented anisotropic sintered magnet.   A method for producing a rare earth magnet, comprising a magnetization step performed using the magnetization method according to claim 1.   A rare earth magnet manufactured by the manufacturing method according to claim 7. A cylindrical rare earth magnet,
A first region magnetized from the inside to the outside of the cylinder;
A second region magnetized from outside to inside,
At the boundary between the first region and the second region, the surface magnetic flux density continuously changes without taking an extreme value ,
In the first region or the second region, an angle range in which the surface magnetic flux density takes a maximum value is 120 ° to 140 °,
A rare earth magnet having an angle range from a point of zero surface magnetic flux density to a maximum value of 20 ° or more and 30 ° or less . A rotating machine comprising the rare earth magnet according to claim 9 . A valve opening control device comprising the rotating machine according to claim 10 .

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