WO2024158014A1 - Cylindrical magnetic body, outer rotor, and motor - Google Patents

Abstract

[Problem] To provide a cylindrical magnetic body which enables providing of an outer rotor with which motor torque can be enhanced, and a motor having said outer rotor. [Solution] This cylindrical magnetic body is characterized by having a multilayer structure comprising a transition metal layer, an intermediate layer, and a rare earth magnet layer in the stated order from the outer circumferential surface side to the inner circumferential surface side, and is characterized in that the intermediate layer and the rare earth magnet layer each contain a transition metal element and a rare earth element.

Description

Cylindrical magnetic body, outer rotor, and motor

This disclosure relates to a cylindrical magnetic body, an outer rotor having a cylindrical magnetic body, and a motor having the outer rotor.

In outer rotor motors, it is common for bonded or sintered magnets to be attached to the inner circumferential wall of the rotor. For example, Patent Document 1 discloses an outer rotor in which a cylindrical bonded magnet is arranged on the inner circumferential surface of the rotor core.

In conventional outer rotor motors, if the diameter of the outer rotor containing a bonded magnet or sintered magnet is reduced, it is difficult to obtain sufficient motor torque for practical use.

JP 2016-111738 A

The objective of the exemplary embodiment of the present disclosure is to provide an outer rotor capable of improving motor torque, a cylindrical magnetic body that can be used for the outer rotor, and a motor having the outer rotor.

In order to achieve the above object, the cylindrical magnetic body according to the present disclosure is
It has a multilayer structure including, from the outer peripheral surface side to the inner peripheral surface side, a transition metal layer, an intermediate layer, and a rare earth magnet layer, in the stated order, and both the intermediate layer and the rare earth magnet layer contain a transition metal element and a rare earth element.

By having the above-mentioned multi-layer structure, the cylindrical magnetic body can be used, for example, as part of the outer rotor of a motor, improving motor torque and enabling the motor to be made smaller.

Preferably, the average thickness of the rare earth magnet layer is 10 μm or more and 300 μm or less.

Preferably, there is no intervening layer between the transition metal layer and the intermediate layer in the multilayer structure, and between the intermediate layer and the rare earth magnet layer.

Preferably, the rare earth element contained in the intermediate layer is a rare earth element that has diffused from the rare earth magnet layer, and the transition metal contained in the intermediate layer is the same as the transition metal contained in the transition metal layer.

Preferably, the intermediate layer covers the entire inner circumferential surface of the transition metal layer in the circumferential direction,
The rare earth magnet layer covers the entire inner circumferential surface of the intermediate layer in the circumferential direction.

Preferably, the magnetization easy axis of the rare earth magnet layer is oriented in the radial direction,
The degree of orientation of the axis of easy magnetization is 90% or more with respect to the radial direction.

Preferably, the transition metal layer is a Co layer, the intermediate layer is a _{Sm2Co 17} layer, and the rare earth magnet layer is a SmCo ₅ layer.

The cylindrical magnetic body of the present disclosure can be used in the outer rotor of motors for various applications such as medical use and wristwatches, to control the magnetic fluid placed inside the cylinder, and to protect piping from plasma. For example, the magnet layer may have a multi-pole magnetization pattern in the circumferential or axial direction, and may be arranged on only a part of the cylinder. A motor having an outer rotor of the present disclosure may also have a stator inserted inside the outer rotor. A motor having an outer rotor of the present disclosure may further have a stator equipped with a magnetic sensor.

FIG. 1 is a cross-sectional view showing an outer rotor having a cylindrical magnetic body according to an embodiment of the present disclosure, showing a cross section perpendicular to the rotation axis of the outer rotor. 2(a) and (b) are examples of cross sections taken along line II-II in FIG. FIG. 3 is a schematic diagram showing an example of an arrangement of magnetization (magnetic poles) in the outer rotor shown in FIG. FIG. 4 is a cross-sectional view showing a motor having the outer rotor shown in FIG. 1, showing a cross section perpendicular to the rotation axis of the motor. FIG. 5 is a simplified diagram showing a cross section taken along line VV shown in FIG. FIG. 6 is a cross-sectional view showing a modified example of an outer rotor having a cylindrical magnetic body. FIG. 7 is a cross-sectional view showing yet another modified example of an outer rotor having a cylindrical magnetic body.

Below, one embodiment of the present disclosure will be described with reference to the drawings. Note that the shapes and the like depicted in the drawings of the present disclosure do not necessarily match the actual shapes and the like. This is because the shapes and the like may have been modified in each drawing for the purpose of explanation.

As shown in FIG. 1, the outer rotor 2 according to this embodiment includes a cylindrical magnetic body 10 having a multi-layer structure. In addition to the magnetic body 10, the outer rotor 2 may also include a rotor housing that supports the magnetic body 10, an engagement part for connecting the outer rotor 2 to the shaft, and other accessories such as a fan and gears.

As shown in FIG. 1, the magnetic body 10 has an outer peripheral surface 10a and an inner peripheral surface 10b, and preferably has an integral structure along the circumferential direction with no seams such as adhesive layers or gaps. In other words, the magnetic body 10 shown in FIG. 1 has a cylindrical shape. However, the magnetic body 10 only needs to have at least a cylindrical portion, and the shape of the magnetic body 10 is not necessarily limited.

The central axis AX shown in FIG. 1 is an imaginary line that passes through the center of the area surrounded by the inner peripheral surface 10a along the inner peripheral surface 10a, and the central axis AX of the magnetic body 10 coincides with the rotation axis of the outer rotor 2. Note that the Z axis in each drawing is parallel to the central axis AX, and the X axis, Y axis, and Z axis are perpendicular to each other.

The dimensions of the magnetic body 10 are not necessarily limited. For example, the outer diameter d1 of the magnetic body 10 is preferably 1 mm or more and 6 mm or less, and the inner diameter d2 of the magnetic body 10 is preferably 0.5 mm or more and 5 mm or less. The thickness of the magnetic body 10 is expressed as (d1-d2)/2, and is preferably, for example, 0.1 mm or more and 2 mm or less. Furthermore, the length L of the magnetic body 10 in the Z-axis direction may be, for example, 1 mm or more and 20 mm or less.

Magnetic body 10 has a multilayer structure that includes, from the outer peripheral surface side to the inner peripheral surface side, a transition metal layer 11, an intermediate layer 12, and a rare earth magnet layer 13, in the order listed. In magnetic body 10 having a multilayer structure, transition metal layer 11 is the base, and intermediate layer 12 and rare earth magnet layer 13 are laminated on the inner peripheral surface side of transition metal layer 11, in the order listed. Each layer (11-13) of magnetic body 10 is a continuous layer with no seams or breaks along the circumferential direction, as shown in Figure 1.

In the multilayer structure of the magnetic body 10, it is preferable that the inner peripheral surface of the transition metal layer 11 and the outer peripheral surface of the intermediate layer 12 are in direct contact with each other, and it is preferable that the inner peripheral surface of the intermediate layer 12 and the outer peripheral surface of the rare earth magnet layer 13 are in direct contact with each other. In other words, between the transition metal layer 11 and the intermediate layer 12, and between the intermediate layer 12 and the rare earth magnet layer 13 (between the layers in the multilayer structure), there may be a layer thinner than the resolution of 0.5 to 4 nm observable by a scanning electron microscope (SEM), but it is preferable that there is no intermediate layer made of a non-magnetic material such as an oxide layer, a resin layer, or an adhesive layer thicker than the resolution of 0.5 to 4 nm observable by an SEM. In this embodiment, "there is no intermediate layer" between the layers of the multilayer structure means that, as described above, the intermediate layer cannot be identified with the resolution observable by an SEM.

2(a) and (b) are examples of cross sections of the magnetic body 10 along the central axis AX. As shown in FIG. 2(a), the intermediate layer 12 preferably covers the entire circumferential direction of the inner circumferential surface of the transition metal layer 11, and the rare earth magnet layer 13 preferably covers the entire circumferential direction of the inner circumferential surface of the intermediate layer 12. However, the multilayer structure of the magnetic body 10 is not necessarily limited to the form shown in FIG. 2(a), and a part of the inner circumferential surface of the transition metal layer 11 may have a non-laminated region in which the intermediate layer 12 and the rare earth magnet layer 13 are not laminated. For example, in FIG. 2(b), the inner circumferential surface of the transition metal layer 11 has non-laminated regions 11b at both ends in the Z-axis direction that are not covered by the intermediate layer 12 and the rare earth magnet layer 13, and a multilayer structure is formed between the non-laminated regions 11b.

The outer peripheral surface 11a of the transition metal layer 11 may form the outer peripheral surface 10a of the magnetic body 10, as shown in Figures 1 and 2. Alternatively, a part or all of the outer peripheral surface 11a of the transition metal layer 11 may be covered with another layer. Examples of other layers located on the outer peripheral surface side of the transition metal layer 11 include layers of high-melting point nonmagnetic materials including W, Ta, Nb, or Mo. When a layer of high-melting point nonmagnetic material is present on the outer peripheral surface side of the transition metal layer 11, the average thickness of this layer of high-melting point nonmagnetic material is not particularly limited, and is preferably, for example, 0.5 μm or more and 25 μm or less, and more preferably 5 μm or more and 25 μm or less.

A part or the whole of the inner peripheral surface _13b of the rare earth magnet layer 13 may be covered with a layer containing _Sm2O3 and/or a protective layer containing Ni, Cu, Sn, etc. However, as shown in Figures 1 and 2, it is preferable that the inner peripheral surface 13b of the rare earth magnet layer 13 is exposed to the inner peripheral surface 10b of the magnetic body 10 and forms the inner peripheral surface 10b.

The characteristics of each layer (11 to 13) constituting the multilayer structure of the magnetic body 10 will be described in detail below. The composition of each layer may be analyzed by component analysis using, for example, inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence analysis (XRF), energy dispersive X-ray analysis (EDS), or wavelength dispersive X-ray analysis (WDS), and the crystal structure of each layer may be analyzed by X-ray diffraction (XRD), electron beam diffraction, or electron backscatter diffraction (EBSD). In addition, when measuring the thickness of each layer, it is preferable to divide the magnetic body 10 into equal parts and analyze at least three cross sections approximately perpendicular to the central axis AX, and it is preferable to measure the thickness at at least four points at equal intervals along the circumferential direction on each cross section. In other words, it is preferable to measure the thickness of each layer at at least 12 points distributed evenly in three-dimensional space, and calculate the average thickness and the standard deviation of the thickness.

In this embodiment, the transition metal layer 11 is a soft magnetic layer that mainly contains Co, and is the base material of the magnetic body 10. "Mainly contains Co" means that the content of Co is the highest in the layer, and the transition metal layer 11 may also contain other metal elements such as Cr, Mn, Fe, Ni, Cu, Pb, and Mo. The content of Co in the transition metal layer 11 is preferably, for example, 95 wt% or more, and more preferably 99 wt% or more.

The average thickness t1 of the transition metal layer 11 is not particularly limited and can be selected appropriately depending on the application of the motor, but it is preferable that it is, for example, 0.1 mm or more and 1.8 mm or less.

In this embodiment, the intermediate layer 12 is _a layer containing _Sm2Co17 as a main phase. The main phase _Sm2Co17 is an alloy of Sm and Co having a _Th2Zn17 type crystal structure, and is a soft magnetic material having a higher saturation magnetization than _SmCo5 described later. If the main _{phase Sm2Co17 has} a _Th2Zn17 type crystal structure, the _ratio of Sm atoms to Co atoms in _Sm2Co17 may be slightly deviated from the stoichiometric ratio. For example, other elements _such as Ti _{, Zr} , Nb, Ta, Cu, Ce, and Fe may be added to the intermediate layer 12 in order to improve the magnetic properties, and when other elements are added, the ratio of Sm atoms to Co atoms may be slightly deviated from the stoichiometric ratio.

In this embodiment, the term "main phase" refers to the phase having the highest content in a given layer. The intermediate layer 12 may contain _a phase (heterogeneous phase) whose composition and/or crystal structure is different from that of _Sm2Co17 , _a grain boundary phase, etc. The content of _Sm2Co17 in the intermediate layer 12 may be, for example, 70 wt% or more, preferably 80 wt% or more, more preferably 90 wt% or more, and even more preferably 95 wt% or more.

The average thickness t2 of the intermediate layer 12 is not particularly limited, but is preferably, for example, 1 μm or more and 100 μm or less. The percentage of the coefficient of variation of the thickness of the intermediate layer 12 is preferably, for example, 50% or less. The "coefficient of variation" is a coefficient that represents the variation in thickness, and is expressed as the ratio of the standard deviation of the thickness to the average thickness (standard deviation/average thickness).

In this embodiment, the rare earth magnet layer 13 is a hard magnetic layer containing _SmCo5 as a main phase. The main phase _SmCo5 is an alloy of Sm and Co having a _CaCu5 type crystal structure. If the main phase _SmCo5 has a _CaCu5 type crystal structure, the ratio of Sm atoms to Co atoms in _SmCo5 may be slightly deviated from the stoichiometric ratio. For example, other elements such as Ti, Zr, Nb, Ta, Cu, Ce, and Fe may be added to the rare earth magnet layer 13 in order to improve the magnetic properties, and when other elements are added, the ratio of Sm atoms to Co atoms may be slightly deviated from the stoichiometric ratio.

The rare earth magnet layer 13 may contain a phase (heterogeneous phase) whose composition and/or crystal structure is different from _SmCo5 , and a grain boundary phase. The content of _SmCo5 in the rare earth magnet layer 13 may be, for example, 70 wt% or more, preferably 80 wt% or more, more preferably 90 wt% or more, and even more preferably 95 wt% or more. Note that an example of the heterogeneous phase in the rare earth magnet layer 13 is an Sm-rich phase in which the ratio of Sm is higher than that of _SmCo5 .

The average thickness t3 of the rare earth magnet layer 13 is preferably 10 μm or more and 300 μm or less. The percentage of the thickness variation coefficient (standard deviation/average thickness) of the rare earth magnet layer 13 is preferably, for example, 50% or less. By reducing the variation coefficient, when the outer rotor 2 is assembled into a motor, the distance between the outer rotor 2 and the stator can be made as small as possible at a constant interval, which contributes to improving the motor torque.

Furthermore, the ratio (t3/t2) of the average thickness t3 of the rare earth magnet layer 13 to the average thickness t2 of the intermediate layer 12 is preferably 1 or more and 100 or less, and more preferably 5 or more and 100 or less. If the sum of the average thicknesses t1, t2, and t3 is T0, the ratio of t3 to T0 (t3/T0) may be 0.01 or more and less than 1. By controlling t3/t2 and/or t3/T0 within the above range, the magnetic properties of the cylindrical magnetic body can be further improved.

The Rz (maximum height difference) of the roughness curve based on the inner circumferential surface 13b of the rare earth magnet layer 13 is preferably 20 μm or less. When calculating the above Rz, it is preferable to obtain a roughness curve based on the contour line of the inner circumferential surface 13b in both a cross section perpendicular to the central axis AX and a cross section along the central axis AX. By making the Rz of the inner circumferential surface 13b 20 μm or less, when the outer rotor 2 having a cylindrical magnetic body is incorporated into a motor, the distance between the outer rotor 2 and the stator can be made as small as possible at a constant interval, which contributes to improving the motor torque.

The multi-layered magnetic body 10 is the rotor and also an element that constitutes the magnetic circuit in the motor. The rare earth magnet layer 13, which is a hard magnetic layer, is the magnet, and the transition metal layer 11 and intermediate layer 12, which are soft magnetic layers, act as a back yoke that collects magnetic flux.

The magnetization easy axis of the rare earth magnet layer 13 is preferably oriented in the radial direction. Here, the "radial direction" refers to a direction perpendicular to the central axis AX of the magnetic body 10, and "oriented in the radial direction" means that, as viewed from the direction of the central axis AX, the magnetization easy axis is arranged radially around the central axis AX. In addition, the magnetization easy axis of the rare earth magnet layer 13 is the crystal orientation [00L] of _SmCo5 , and it is preferable that the crystal orientation [00L] of _SmCo5 is oriented in the radial direction. L in the crystal orientation is any natural number, and [00L] indicates the same direction regardless of the natural number of L. L is, for example, 2.

In the outer rotor 2, the easy axis of magnetization of the rare earth magnet layer 13, which is a magnet, is oriented in the radial direction, which allows for a high surface magnetic flux density to be obtained. Furthermore, because the magnetic body 10 of the outer rotor 2 has a multi-layer structure that includes a transition metal layer 11, an intermediate layer 12, and a rare earth magnet layer 13, the degree of orientation of the rare earth magnet layer 13 can be improved compared to conventional sintered magnets or bonded magnets.

In the conventional outer rotors having sintered magnets or bonded magnets, the degree of orientation of the easy magnetization axis in the radial direction is at most 80%, and it is difficult to ensure an orientation degree of 90% or more. On the other hand, in the outer rotor 2 having the cylindrical magnetic body of this embodiment, the transition metal layer 11, the intermediate layer 12, and the rare earth magnet layer 13 are stacked in the order described above from the outer peripheral surface side to the inner peripheral surface side, so that the degree of orientation of the easy magnetization axis in the rare earth magnet layer 13 in the radial direction can be made 90% or more. Although the reason is not clear, it is presumed that the intermediate layer 12 is inserted between the transition metal layer 11 and the rare earth magnet layer 13, thereby obtaining a radial anisotropy with an orientation degree of 90% or more. In other words, in the rare earth magnet layer 13, the degree of orientation of the easy magnetization axis in the radial direction is preferably 90% or more, more preferably more than 90%, and even more preferably 95% or more.

By achieving a radial orientation of 90% or more, the surface magnetic flux density can be improved compared to conventional methods, and a sufficiently large motor torque can be obtained even if the outer rotor diameter is reduced (for example, the outer diameter d1 is 6 mm or less).

The direction in which the easy magnetization axis is oriented and the degree of orientation of the easy magnetization axis in the radial direction can be calculated by crystal orientation analysis using EBSD. The degree of orientation at each position of the rare earth magnet layer 13 is calculated using EBSD, and the degree of orientation can be calculated by averaging these values across the entire rare earth magnet layer 13.

The rare earth magnet layer 13, which is a magnet, is magnetized in the radial direction along the axis of easy magnetization, and has two or more magnetic poles on the inner peripheral surface 13b. For example, in FIG. 3, the arrangement of magnetic poles in the rare earth magnet layer 13 is shown by arrows, and the inner peripheral surface 13b of the rare earth magnet layer 13 has eight poles. There is no particular limit to the number of magnetic poles on the inner peripheral surface 13b of the rare earth magnet layer 13.

Below, an example of a method for manufacturing an outer rotor 2 having a cylindrical magnetic body is described.

The magnetic body 10 is preferably manufactured by a method that applies the molten salt immersion method. First, a cylindrical Co substrate and a reaction liquid containing an Sm source and a molten salt are prepared.

When preparing the reaction solution, a specific inorganic salt is first dehydrated by drying. Examples of inorganic salts include KCl (potassium chloride), LiCl (lithium chloride), and NaCl (sodium chloride). One type of inorganic salt may be used, or two or more types of inorganic salts may be used in combination. The dehydrated inorganic salt is heated to a specific temperature to melt the inorganic salt (molten salt). The temperature at which the inorganic salt is melted may be appropriately determined depending on the type of inorganic salt used, but is preferably 400°C or higher, more preferably 500°C or higher, and even more preferably 600°C or higher.

The Sm source is added to the above molten salt (molten inorganic salt) to obtain a reaction liquid. Examples of the Sm source include metallic Sm and Sm alloys. One type of Sm source may be used, or two or more types of Sm sources may be used. If the total of the number of moles of the Sm source and the number of moles of the inorganic salt in the reaction liquid is 100 mol%, the ratio of the Sm source in the reaction liquid is preferably, for example, 0.2 mol% to 6 mol%. When an additive element is added to the intermediate layer 12 and/or the rare earth magnet layer 13, a raw material containing the desired additive element may be added to the molten salt together with the Sm source.

Then, the above reaction liquid is brought into contact with the surface of the Co substrate, and a magnetic coating containing Sm is formed on the inner peripheral surface of the Co substrate by reactive diffusion of the Sm source in the molten salt to the surface of the Co substrate. This process is referred to as the reactive diffusion process. In this reactive diffusion process, if the Co substrate is directly immersed in the reactive liquid, a magnetic coating containing Sm is formed not only on the inner peripheral surface of the Co substrate, but also on the outer peripheral surface and end faces (surfaces perpendicular to the Z axis). Therefore, some measure is required to cause the Sm source to reactively diffuse only on the inner peripheral surface of the Co substrate, and to suppress reactive diffusion on the outer peripheral surface and end faces.

For example, it is preferable to form a mask of a high melting point material on the outer peripheral surface and end surface of the Co base. Examples of high melting point materials include W, Ta, Nb, Mo, or an alloy containing at least one of these elements. The mask of the high melting point material may be formed, for example, by a deposition method. After forming a mask of the high melting point material on the outer peripheral surface and end surface, the Co base is immersed in a reaction liquid, whereby the Sm source reacts and diffuses only on the inner peripheral surface of the Co base, forming a magnetic coating containing Sm on the inner peripheral surface. Alternatively, the Sm source may react and diffuse on the inner peripheral surface and outer peripheral surface of the Co base without forming a mask, forming a magnetic coating containing Sm on the inner peripheral surface and outer peripheral surface.

Instead of forming a mask of a high melting point material, a method of flowing a reaction liquid into a region surrounded by the inner surface of the Co substrate (inner region) may be adopted. For example, an inlet pipe is connected to both ends of the Co substrate, and a pump or mass flow controller is used to flow the reaction liquid into the inner region of the Co substrate at a constant flow rate. It is preferable to circulate the reaction liquid so that the reaction liquid that flows out from one end of the Co substrate flows back into the inner region. The method of flowing the reaction liquid into the inner region can improve the uniformity of the thickness of the magnetic coating compared to the case where the Co substrate is immersed in the reaction liquid.

In the reaction diffusion process, the temperature of the reaction liquid is maintained at a temperature at which the inorganic salt can be kept in a molten state. From the viewpoint of efficiently forming a magnetic coating, the temperature of the reaction liquid is preferably 500°C or more and 900°C or less, and more preferably 650°C or more and 800°C or less. The reaction time may be appropriately set according to the reaction temperature and the proportion of Sm source in the reaction liquid so that a magnetic coating of the desired thickness can be formed. For example, the reaction time may be 1 hour or more and 48 hours or less.

The magnetic film formed on the inner peripheral surface of the Co base in the reaction diffusion process is a precursor of the intermediate layer 12 and the rare earth magnet layer 13. Specifically, the magnetic film after the reaction diffusion process preferably contains _SmCo2 as the main phase. _SmCo2 is an alloy of Sm and Co having a _MgCu2 type crystal structure. As long as the main phase _SmCo2 has a _MgCu2 type crystal structure, the ratio of Sm atoms to Co atoms in _SmCo2 may be slightly deviated from the stoichiometric ratio. For example, when an additive element is added to improve the magnetic properties, the ratio of Sm atoms to Co atoms may be slightly deviated from the stoichiometric ratio.

In addition to the main phase, the magnetic coating may contain a heterophase, such as a Sm-rich phase having a higher ratio of Sm than _SmCo2 , and a grain boundary phase. The content of _SmCo2 in the magnetic coating may be 50 wt% or more, preferably 70 wt% or more, and more preferably 90 wt% or more.

Furthermore, after the reaction diffusion process, the Co substrate on which the magnetic coating is formed may be washed with an organic solvent such as ethanol or pure water.

Next, the Co base on which the magnetic film containing _SmCo2 is formed is heated at a predetermined temperature for a predetermined time (heating step). In this heating step, the reaction between _SmCo2 and the Co of the base progresses further, and an intermediate layer 12 containing _Sm2Co17 and a rare earth magnet layer 13 containing _SmCo5 are generated from the inner peripheral surface of the Co base and _the magnetic film.

The heating rate in the heating step is not particularly limited, and is preferably, for example, 1°C/min or more and 20°C/min or less. The holding temperature (attainment temperature) is preferably 800°C or more and 1200°C or less, more preferably 850°C or more and 1150°C or less, and even more preferably 900°C or more and 1100°C or less. The holding time at the above holding temperature is preferably, for example, 2 hours or more and 48 hours or less. In addition, the temperature drop rate during cooling after heating is preferably 5°C/min or more, more preferably 10°C/min or more, and even more preferably 20°C/min or more.

The atmosphere for the heating step is not particularly limited, but is preferably an inert gas atmosphere from the viewpoint of suppressing oxidation of the rare earth magnet layer 13. As the inert gas, for example, Ar gas, _N2 gas, or the like may be used.

By the above steps, the intermediate layer 12 and the rare earth magnet layer 13 are formed on the inner peripheral surface of the Co base in the order described above, and a magnetic body 10 having a multilayer structure is obtained. In particular, the above-mentioned manufacturing method obtains a multilayer structure in which a non-magnetic layer such as an adhesive layer is not interposed between the transition metal layer 11 (Co base) and the intermediate layer 12, and between the intermediate layer 12 and the rare earth magnet layer 13. If a mask of high melting point material is formed on the outer peripheral surface and end surface of the Co base, the mask of high melting point material may be removed after the heating step, or the mask of high melting point material may be left remaining. Also, if a mask of high melting point material is not formed on the outer peripheral surface and end surface of the Co base, a structure is obtained in which an intermediate layer and a rare earth magnet layer are formed on the outer peripheral surface of the Co base as well.

Next, an example of a motor using an outer rotor 2 having a cylindrical magnetic body according to this embodiment will be described. FIG. 4 is a schematic diagram showing a cross section perpendicular to the rotation axis of a motor 100 according to one embodiment, and FIG. 5 is a schematic diagram showing a simplified cross section along the rotation axis of the motor 100. As shown in FIGS. 4 and 5, the motor 100 has an outer rotor 2, a stator 50 inserted inside the outer rotor 2, and a shaft 60.

As shown in FIG. 4, the stator 50 is composed of a stator core 51 and a coil 52. The stator core 51 has a cylindrical portion 51a and teeth 51b protruding outward from the cylindrical portion 51a, and a coil 52 is formed on each of the teeth 51b. In FIG. 4, the stator core 51 has six teeth 51b, but the number of teeth 51b is not particularly limited. The coil 52 may be formed, for example, by winding a conductor having an insulating coating on its surface around the teeth 51b. The material of the stator core 51 is not particularly limited, and may be, for example, an electromagnetic steel sheet, SPCC (cold rolled steel sheet), an amorphous alloy, or magnetic powder. The powdered amorphous alloy or magnetic powder can be compression molded to form a stator core.

As shown in FIG. 5, the stator 50 is inserted into the area surrounded by the inner circumferential surface 10b of the magnetic body 10, and the multilayer structure of the magnetic body 10 surrounds the outer circumferential surface 50a of the stator 50. In other words, the inner circumferential surface 13b of the rare earth magnet layer 13 located at the innermost side of the multilayer structure faces the outer circumferential surface 50a of the stator 50.

In the motor 100, the shaft 60 is arranged to pass through the inside of the cylindrical portion 51a of the stator core 51. Although omitted in FIG. 5, the shaft 60 and the outer rotor 2 may be connected so that they rotate in unison. For example, a rotor housing including the outer rotor 2 made of magnetic material 10 may be connected to the shaft 60 via a bearing such as a bush or bearing. The motor 100 may also have a container that serves as the exterior, and the container may be connected to the stator 50.

The motor 100 can be used for a variety of purposes, including medical equipment and wristwatches.

The structure of the motor to which the outer rotor 2 is applied is not limited to the motor 100 shown in Figures 4 and 5. For example, the outer rotor 2 may be applied to a coreless motor or a frameless motor. In the case of a coreless motor, the stator may be formed without using a stator core, using a coil made of coreless wiring having a cylindrical shape, or a coil made of a flexible printed circuit board on which coil wiring is printed.

(Summary of the embodiment)
The cylindrical magnetic body of this embodiment has a multi-layer structure including, from the outer circumferential surface side toward the inner circumferential surface side, a transition metal layer 11, an intermediate layer 12, and a rare earth magnet layer 13 in the stated order.

By having the cylindrical magnetic body 10 have the multi-layer structure as described above, the easy magnetization axis of the rare earth magnet layer 13 can be oriented in the radial direction, and the degree of orientation of the easy magnetization axis in the radial direction can be improved compared to conventional sintered magnets and bonded magnets. Therefore, the outer rotor 2 having the cylindrical magnetic body 10 of this embodiment can obtain a high surface magnetic flux density. As a result, even if the outer diameter of the outer rotor 2 is reduced to 6 mm or less, a motor torque large enough for practical use can be obtained. Note that the degree of orientation of the easy magnetization axis in the rare earth magnet layer 13 in the radial direction is preferably 90% or more.

The average thickness t3 of the rare earth magnet layer 13 is preferably 10 μm or more and 300 μm or less. By controlling t3 within the above range, the magnetic properties of the cylindrical magnetic body can be further improved.

It is preferable that there be no intervening layers, such as adhesive layers, between the layers in the multilayer structure (i.e., between the transition metal layer 11 and the intermediate layer 12, and between the intermediate layer 12 and the rare earth magnet layer 13). By not interposing a protective layer, adhesive layer, or the like between the layers, the proportion of non-magnetic layers in the cylindrical magnetic body can be reduced and the proportion of magnets can be increased, thereby further improving the motor torque.

The above describes embodiments of the present disclosure, but the present disclosure is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit and scope of the present disclosure.

For example, the shape of the cylindrical magnetic body 10 is not limited to the cylindrical shape shown in Figures 1 and 2, and the planar shape defined by the outer circumferential surface 11a may be a shape other than a circle. For example, as shown in Figure 6, the outer circumferential surface 10a of the magnetic body 10 (i.e., the outer circumferential surface 11a of the transition metal layer 11) may have a gear structure. In this case, the shape of the tip of the gear, the number of teeth, and the pitch interval between the gears are not particularly limited.

Also, as a modification of the motor 100 shown in FIG. 5 or FIG. 6, the stator 50 may be equipped with a magnetic sensor 70 as shown in FIG. 7. In this case, the magnetic sensor detects the magnetic field generated by the opposing rare earth magnet layer 13. Since the rare earth magnet layer 13 is multi-pole magnetized as shown in FIG. 3, when the outer rotor 2 rotates, the direction of the magnetic field detected by the magnetic sensor 70 changes periodically. Therefore, by equipping the stator 50 with the magnetic sensor 70, it becomes possible to detect the rotation angle and rotation speed (speed) of the outer rotor 2.

The magnetic sensor 70 is preferably provided in a position where the influence of the magnetic field generated by the coil 52 is relatively small. A convex portion may be provided on the transition metal layer 11 so that the distance between the magnetic sensor 70 and the rare earth magnet layer 13 facing it is small. If a convex portion is provided on the transition metal layer 11, the distance between the magnetic sensor 70 and the rare earth magnet layer 13 is small, and the magnetic field from the rare earth magnet layer 13 detected by the magnetic sensor 70 is likely to be larger than the magnetic field generated by the coil 52, thereby improving the detection accuracy of the rotation angle and rotation speed.

The compositions of the transition metal layer 11, intermediate layer 12, and rare earth magnet layer 13 constituting the magnetic body 10 are not limited to the above combination. For example, in the above embodiment, the intermediate layer 12 and rare earth magnet layer 13 both contain Co as a transition metal element and Sm as a rare earth element, but the intermediate layer 12 and rare earth magnet layer 13 may contain at least one or more transition metals such as Fe and Ni other than Co, and may also contain at least one or more rare earth elements such as Nd, Pr, Dy, and Tb other than Sm. Specifically, the intermediate layer 12 may be a Sm ₂ Fe ₁₇ layer, a Nd ₂ Fe ₁₇ layer, or a Pr ₂ Fe ₁₇ layer, and is preferably a Sm ₂ Co ₁₇ layer. The rare earth magnet layer 13 may be _{a Sm2Fe17N3 layer} , _{a SmFe12} layer, a _NdFe12 layer, or a _PrFe12 layer, and is preferably a _SmCo5 layer. The transition metal layer 11 preferably contains at least one transition metal element overlapping with the intermediate layer 12, and more preferably contains the same element as the transition metal element contained in the intermediate layer 12. The rare earth element contained in the intermediate layer 12 is a rare earth element diffused from the rare earth magnet layer 13, and the transition metal contained in the intermediate layer 12 is preferably the same as the metal contained in the transition metal layer 11.

The cylindrical magnetic body of the present disclosure can be suitably used not only for outer rotors and motors, but also for controlling magnetic fluids placed inside the cylinder and protecting piping from plasma. In this case, the magnet layer may have a multi-pole magnetization pattern in the circumferential or axial direction, or may be arranged only in a part of the cylinder.

(Example)
The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

Example 1
A cylindrical Co substrate (outer diameter: 6.0 mm, thickness: 0.3 mm) was prepared. A mask made of Mo was formed on the outer peripheral surface of the Co substrate by a known method. Next, the inner peripheral surface of the Co substrate was polished with #120 abrasive paper for 5 minutes and washed with acetone.

LiCl was prepared and dehydrated by drying. The dehydrated LiCl was heated to 600°C in a metal Mo container by an external heater and melted. Sm metal powder was added to the molten LiCl as an Sm source. The Sm source was added so that the molar ratio of LiCl and Sm was LiCl:Sm=100:3. Next, a polished cylindrical Co base material was immersed in the molten LiCl. The reaction diffusion temperature was 700°C, and the reaction diffusion time was 30 hours. A laminate in which a _SmCo2 film was formed on the Co base material by the reaction diffusion process was obtained.

The obtained laminate was heated to 1050°C. Next, the laminate was heated at a holding temperature of 1050°C for 24 hours without applying a magnetic field to the laminate. After that, the laminate was cooled without applying a magnetic field to the laminate to obtain a cylindrical magnetic body. The heating rate was 0.15°C/sec, and the cooling rate was 50°C/sec. The atmosphere for the heating process was Ar. Finally, the Mo mask was removed.

Using an X-ray diffraction measurement device and an energy dispersive X-ray analysis device, it was confirmed that the structure of the obtained cylindrical magnetic body was a _Sm2Co17 film and _{a SmCo5} film formed in that order on the inner peripheral surface of a Co substrate. In addition, crystal orientation analysis using EBSD revealed that the cylindrical magnetic body was oriented in the radial direction, and the degree of orientation of the rare earth magnet layer was 90%.

The motor torque of the motor using the obtained cylindrical magnetic body as the outer rotor was obtained by simulation (JMAG). Specifically, the cylindrical magnetic body has a transition metal layer made of a Co base material with a diameter of 6.0 mm and a thickness of 0.3 mm. The inner peripheral surface of the Co base material is in contact with ₁₇ layers of _Sm2Co with a thickness of 0.05 mm as an intermediate layer. The inner peripheral surface of the intermediate layer is in contact with ₅ layers of SmCo with a thickness of 0.2 mm as a rare earth magnet layer. The rare earth magnet layer is magnetized in four poles in the radial direction, and the degree of orientation is 90%.

Example 2
A cylindrical magnetic body was produced in the same manner as in Example 1, except that the grit size of the abrasive paper was changed to a finer #4000. Using an X-ray diffraction measuring device and an energy dispersive X-ray analyzer, it was confirmed that the structure of the obtained cylindrical magnetic body was a _Sm2Co17 film and _{a SmCo5} film formed in this order on the inner peripheral surface of a Co base material. In addition, crystal orientation analysis using EBSD revealed that the cylindrical magnetic body was oriented in the radial direction, and the orientation degree of the rare earth magnet layer was 98%.

The motor torque was calculated by simulation under the same conditions as in Example 1 except that the above-mentioned cylindrical magnetic body was used, that is, the orientation degree of the rare earth magnet layer was 98%.

Example 3
Compared to Example 2, the thickness of the intermediate layer was set to 0.025 mm, and an intervening layer made of an adhesive (epoxy resin) having a thickness of 0.025 mm was further disposed between the rare earth magnet layer and the intermediate layer. The motor torque was obtained by simulation under the same conditions as in Example 2.

Comparative Example 1
In comparison with Example 1, the intermediate layer was an adhesive layer made of epoxy resin with a thickness of 0.05 mm, and the rare earth magnet layers were magnetized in parallel directions, and the motor torque was calculated by simulation. The orientation degree of the rare earth magnet layers was 100%.

Comparative Example 2
Compared to Example 1, the intermediate layer was an adhesive layer made of epoxy resin with a thickness of 0.05 mm, and the orientation degree of the rare earth magnet layer was 80%, but the motor torque was obtained by simulation in the same manner as in Example 1.

The simulation results for Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1.

The results shown in Table 1 show that by using the cylindrical magnetic body according to the present disclosure, motor torque can be improved compared to the comparative example equivalent to the conventional technology.

Example 10
A cylindrical magnetic body was produced in the same manner as in Example 2, except that no Mo mask was formed. Using an X-ray diffraction measuring device and an energy dispersive X-ray analyzing device, it was confirmed that the structure of the obtained cylindrical magnetic body was such that a _Sm2Co17 film and a _SmCo5 film were formed in this order on the inner peripheral surface of the Co base material, _and a _Sm2Co17 film and _{a SmCo5 film} were formed in this order on the outer peripheral surface of the Co base material. In addition, crystal orientation analysis using EBSD revealed that the cylindrical magnetic body was oriented in the radial direction, and the degree of orientation of the rare earth magnet layer was 98%.

REFERENCE SIGNS LIST 2 outer rotor 10 magnetic body 11 transition metal layer 12 intermediate layer 13 rare earth magnet layer 10a outer peripheral surface 10b inner peripheral surface 100 motor 50 stator 51 stator core 51a cylindrical portion 51b teeth portion 52 coil 60 shaft 70 magnetic sensor

Claims (10)

1. A multilayer structure including, from the outer peripheral surface side toward the inner peripheral surface side, a transition metal layer, an intermediate layer, and a rare earth magnet layer in the stated order;
   The intermediate layer and the rare earth magnet layer both contain a transition metal element and a rare earth element.
2. The cylindrical magnetic body according to claim 1, wherein the average thickness of the rare earth magnet layer is 10 μm or more and 300 μm or less.
3. The cylindrical magnetic body of claim 1, wherein there is no intervening layer between the transition metal layer and the intermediate layer in the multilayer structure, and between the intermediate layer and the rare earth magnet layer.
4. The cylindrical magnetic body according to claim 1, wherein the rare earth element contained in the intermediate layer is a rare earth element that has diffused from the rare earth magnet layer, and the transition metal contained in the intermediate layer is the same as the metal contained in the transition metal layer.
5. the intermediate layer covers the entire inner circumferential surface of the transition metal layer in the circumferential direction,
   2. The cylindrical magnetic body according to claim 1, wherein the rare earth magnet layer covers the entire inner circumferential surface of the intermediate layer in the circumferential direction.
6. The magnetization easy axis of the rare earth magnet layer is oriented in the radial direction,
   2. The cylindrical magnetic body according to claim 1, wherein the degree of orientation of the axis of easy magnetization is 90% or more with respect to the radial direction.
7. the transition metal layer is a Co layer;
   The intermediate layer is _{a Sm2Co17} layer,
   2. The cylindrical magnetic body according to claim 1, wherein the rare earth magnet layer is _five layers of SmCo.
8. An outer rotor comprising a cylindrical magnetic body according to any one of claims 1 to 7.
9. A motor having the outer rotor described in claim 8 and a stator inserted inside the outer rotor.
10. The motor of claim 9, characterized in that the stator is equipped with a magnetic sensor.

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