Rotor and permanent magnet motor

Abstract

A rotor (1) comprises: a shaft (2); and a rotor (3) that includes a bonded magnet (4) and that is fixed to the shaft (2). The bonded magnet (4) includes: hard-magnetism ferrite particles (6) having a volume resistivity of 108 Ω⋅cm or more; and resin (5). The dielectric loss between the inner peripheral surface and the outer peripheral surface of the bonded magnet (4) in the rotor (3) is 70 or less.

Description

Rotor and Permanent Magnet Motor

[0001] The present disclosure relates to a rotor including a permanent magnet and a permanent magnet motor.

[0002] A known configuration of permanent magnet motors is to use a bonded magnet made of hard magnetic powder and resin for the rotor's rotating body. Such permanent magnet motors are widely used in motor equipment such as blowers and ventilation fans. Permanent magnet motors using bonded magnets have a problem in that a potential difference known as shaft voltage occurs between the inside and outside of the bearing that supports the rotor. If this potential difference becomes excessive, a minute current flows inside the bearing, causing electrolytic corrosion in the bearing. If this electrolytic corrosion progresses, it can lead to abnormal noise from the bearing, so a solution was needed.

[0003] It is known that the potential difference applied to the bearing is closely related to the capacitance, which changes depending on the dielectric constant of the bonded magnet of the rotor. Therefore, Patent Document 1 discloses an electric motor that includes a stator, a rotor in which a rotor made of a resin magnet and a shaft are integrally formed, a bearing, and a conductive bracket, and in which the capacitance between the shaft and the outer periphery of the rotor is 3 pF or more and 12 pF or less when measured at a frequency of 10 kHz.

[0004] International Publication No. 2013 / 042282

[0005] However, in the conventional motors described above, it is difficult to stably control the capacitance of the bonded magnets provided in the rotor, and the capacitance is prone to variation. As a result, even in the conventional motors described above, there is a problem in that electrolytic corrosion of the bearings may occur.

[0006] The present disclosure has been made in view of the above, and has an object to obtain a rotor that can suppress variations in capacitance that cause electrolytic corrosion more than conventional rotors.

[0007] In order to solve the above-mentioned problems and achieve the object, the rotor according to the present disclosure includes a shaft and a rotating body including a bonded magnet and fixed to the shaft. The bonded magnet has a volume resistivity of 10 8The bonded magnet has a dielectric loss of 70 or less between the inner and outer peripheral surfaces of the rotating body.

[0008] The rotor according to the present disclosure has the effect of being able to suppress variations in capacitance that cause electrolytic corrosion more effectively than in the past.

[0009] FIG. 1 is a cross-sectional view schematically showing an example of a rotor according to embodiment 1; FIG. 1 is a diagram showing an example of the configuration of a general bonded magnet; FIG. 1 is a diagram showing an example of the structure of hard magnetic ferrite particles contained in the bonded magnet of the rotor according to embodiment 1; FIG. 1 is a diagram showing an example of the polar anisotropic orientation of hard magnetic ferrite particles inside the bonded magnet of the rotor according to embodiment 1; FIG. 1 is a diagram showing an example of the relationship between the easy axis of magnetization and the magnetization direction of hard magnetic ferrite particles; FIG. 1 is a diagram showing an example of the relationship between the easy axis of magnetization and the magnetization direction of hard magnetic ferrite particles;

[0010] Hereinafter, a rotor and a permanent magnet motor according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0011] Embodiment 1. Figure 1 is a cross-sectional view that schematically shows an example of a rotor according to embodiment 1. As shown in Figure 1, rotor 1 according to embodiment 1 has a shaft 2 and a rotating body 3 fixed to shaft 2. Rotating body 3 includes a bonded magnet 4. In this example, rotating body 3 is made of bonded magnet 4. Bonded magnet 4 has a configuration in which hard magnetic ferrite particles 6, which are hard magnetic particles, are dispersed in resin 5.

[0012] Figures 2 and 3 are schematic diagrams showing an example of the configuration of a typical bonded magnet. Figure 2 shows an example of the configuration of a bonded magnet 54 immediately after molding, and Figure 3 shows an example of the configuration of a bonded magnet 54 some time after molding. Typically, a bonded magnet 54 is molded by binding hard magnetic particles 56 with a binder component made of resin 55. Furthermore, to strengthen the magnetic force, the hard magnetic particles 56 are often packed relatively heavily. Immediately after molding of the bonded magnet 54, the hard magnetic particles 56 are tightly packed together due to the binding force of the binder component, resin 55, as shown in Figure 2. However, over time, the binding force of the resin 55 loosens slightly due to the springback phenomenon. As shown in Figure 3, after some time has passed since molding, the distance between the hard magnetic particles 56 may become greater than in Figure 2 immediately after molding. In this case, if the volume resistivity of the hard magnetic particles 56 contained in the bonded magnet 54 is low, this will cause variations in the electrical performance of the bonded magnet 54. If the volume resistivity of the hard magnetic particles 56 is low, variations in the dielectric properties, which are a factor in fluctuations in electrostatic capacitance that can cause electrolytic corrosion in motor equipment, are particularly likely to occur.

[0013] Consider the case where the volume resistivity of the hard magnetic particles 56 is low. For example, as shown in Figure 2, when the distance between the hard magnetic particles 56 is short immediately after molding, a conductive path is formed within the bonded magnet 54, making it easier for electricity to flow. In the case of an AC electric field, electrical conductivity and dielectric loss are physically proportional, so high electrical conductivity increases the dielectric loss of the bonded magnet 54 and increases the dielectric constant. On the other hand, as shown in Figure 3, when the distance between the hard magnetic particles 56 increases due to the springback phenomenon, the conductive paths within the bonded magnet 54 decrease, resulting in insulator-like properties. This results in lower electrical conductivity compared to the case shown in Figure 2, reduced dielectric loss within the bonded magnet 54, and a lower dielectric constant. Thus, when the volume resistivity of the hard magnetic particles 56 contained in the bonded magnet 54 is low, the dielectric properties, i.e., the dielectric constant and dielectric loss, vary depending on the distance between the hard magnetic particles 56. This results in variations in capacitance and induces electrolytic corrosion. In other words, it is believed that the volume resistivity of the hard magnetic particles 56 is the cause of the variation in capacitance in the bonded magnet 54.

[0014] For this reason, insulating hard magnetic particles are used in the bonded magnet 4 used in the rotor 1 according to the first embodiment. As shown in FIG. 1, an example of the insulating hard magnetic particles is a particle having a volume resistivity of 10 8 The bonded magnet 4 has insulating hard magnetic ferrite particles 6 with a resistance of Ω-cm or more. Furthermore, the bonded magnet 4 used in the rotor 1 according to the first embodiment has a low dielectric loss of 70 or less. With this configuration, even if the distance between the hard magnetic ferrite particles 6 within the bonded magnet 4 fluctuates due to the springback phenomenon, there is almost no change in the electrical conductivity within the bonded magnet 4, making it difficult for the dielectric properties to change. In other words, whether some of the insulating hard magnetic ferrite particles 6 are in contact or not, electricity does not easily flow inside the bonded magnet 4. As a result, the electrostatic capacitance is stabilized, making it possible to suppress electrolytic corrosion.

[0015] The hard magnetic ferrite particles 6 contained in the bonded magnet 4 of the rotor 1 according to the first embodiment are ferromagnetic materials having spontaneous magnetization and having a volume resistivity equal to or greater than the value at which they are considered to be insulators. An example of such hard magnetic ferrite particles 6 is BaFe 12 O 19 , SrFe 12 O 19 M-type hexagonal ferrites such as BaFe 18 O 27 , SrFe 18 O 27 W-type hexagonal ferrites such as Ba3Co2Fe 24 O 41 , Sr3Co2Fe 24 O 41 Z-type hexagonal ferrites such as BaZnFe 12 O 22 Y-type hexagonal ferrites such as M-type hexagonal ferrite and M-type hexagonal ferrite are also called magnetoplumbite-type hexagonal ferrite. These may be used alone or in combination of two or more. Among these, M-type hexagonal ferrite is particularly suitable because it is widely available and inexpensive. Furthermore, hexagonal ferrites having a composition in which a part of the metal elements Ba, Sr, or Fe in the above hexagonal ferrites is substituted with a transition metal element may also be used.

[0016] FIG. 4 is a diagram showing a schematic example of the structure of hard magnetic ferrite particles contained in the bonded magnet of the rotor according to embodiment 1. The hard magnetic ferrite particles 6 contained in the bonded magnet 4 of the rotor 1 according to embodiment 1 are hexagonal crystals and have a plate-like particle shape as shown in FIG. 4. These hard magnetic ferrite particles 6 are characterized by crystal growth in which the c-plane, which is a plane perpendicular to the c-axis of the hexagonal crystal structure, becomes the long plane of the plate-like particle. Furthermore, the greater the crystal growth, the greater the aspect ratio of the long diameter to the short diameter of the plate-like particle tends to become. In FIG. 4, the direction perpendicular to the c-plane is the c-axis, which is the crystal axis, and the a-axis or b-axis, which is the crystal axis, exists within the plane perpendicular to the c-axis, i.e., within the c-plane.

[0017] On the other hand, the easy axis of magnetization of the hard magnetic ferrite particles 6 is in the c-axis direction. To increase the magnetic force of the bonded magnet 4, it is important to control the crystal orientation, i.e., the orientation of the plate-shaped hard magnetic ferrite particles 6, when filling the resin 5. From this perspective, it is easier to control the orientation of the hard magnetic ferrite particles 6 filled into the bonded magnet 4 when the particles are relatively large and have a high aspect ratio. However, plate-shaped coarse particles have the problem of poor packing properties, making them difficult to achieve high packing. Furthermore, to achieve high packing properties with such coarse particles, the molding pressure must be significantly increased, which can lead to changes over time due to the springback phenomenon shown in Figures 2 and 3. Therefore, to increase the magnetic force of the bonded magnet 4 and enable high packing, it is preferable to use a combination of relatively large coarse particles and relatively small fine particles as the hard magnetic ferrite particles 6.

[0018] Therefore, the hard magnetic ferrite particles 6 contained in the bonded magnet 4 of the rotor 1 according to the first embodiment preferably include first hard magnetic ferrite particles having an average particle size of 3 μm to 8 μm and an aspect ratio of 1.5 to 3, and second hard magnetic ferrite particles having an average particle size of 0.05 μm to 1 μm. The content of the second hard magnetic ferrite particles is preferably 5% by mass to 40% by mass, and more preferably 10% by mass to 30% by mass. If the content of the second hard magnetic ferrite particles is less than 5% by mass, it is easy to control the orientation throughout the bonded magnet 4, but it becomes difficult to achieve high packing. Furthermore, if the content of the second hard magnetic ferrite particles is greater than 40% by mass, it is possible to achieve high packing of the first hard magnetic ferrite particles, but the content of the first hard magnetic ferrite particles is relatively low, which deteriorates the orientation throughout the bonded magnet 4 and makes it difficult to obtain the desired magnetic force. Therefore, the content of the second hard magnetic ferrite particles is preferably 5% by mass or more and 40% by mass or less.

[0019] Here, the average particle size of the hard magnetic ferrite particles 6 is determined by measuring the particle size of the hard magnetic ferrite particles 6 filled in the bonded magnet 4. Specifically, the bonded magnet 4 is heat-treated and incinerated in an air atmosphere at a temperature of 500°C to 800°C for a period of approximately 5 to 10 hours using an electric furnace, to obtain hard magnetic ferrite particles 6, which are used as a sample. The average particle size of the hard magnetic ferrite particles 6 can be determined by measuring the particle size distribution of this sample using a laser diffraction / scattering method. The average particle size of the hard magnetic ferrite particles 6 determined in this case is the diameter of a volume-equivalent sphere.

[0020] The aspect ratio of the hard magnetic ferrite particles 6 can be determined by taking a photograph of the cross section of the bonded magnet 4 using a scanning electron microscope (SEM) at a magnification ranging from several hundred to several thousand times, measuring the major axis and minor axis of the hard magnetic ferrite particles 6 from the obtained photograph, and calculating the ratio of the major axis to the minor axis.

[0021] The volume resistivity of the hard magnetic ferrite particles 6 contained in the bonded magnet 4 of the rotor 1 according to the first embodiment is set to 10 8 The volume resistivity of the hard magnetic ferrite particles 6 is preferably 10 Ω·cm or more. 9 More preferably, it is 10 Ω cm or more. 10 It is more preferable that the volume resistivity of the hard magnetic ferrite particles 6 is 10 Ω·cm or more. 8 If the resistivity is less than Ω·cm, the magnet will be more semiconductive than insulating. Therefore, as shown in Figures 2 and 3, if the distance between the hard magnetic ferrite particles 6 in the bonded magnet 4 varies, the electrical properties of the bonded magnet 4 will vary, and the capacitance will also vary. On the other hand, the hard magnetic ferrite particles 6 used in the rotor 1 according to the first embodiment have a volume resistivity of 10 8 Because the resistivity is Ω·cm or more, which is above the value at which the hard magnetic ferrite particles 6 can be considered an insulator, the electrical properties are less likely to fluctuate even if the distance between the hard magnetic ferrite particles 6 within the bonded magnet 4 changes. As a result, it is possible to suppress variations in the electrostatic capacitance of the bonded magnet 4. Here, the volume resistivity of the hard magnetic ferrite particles 6 is determined by measuring the volume resistivity of the hard magnetic ferrite particles 6 filled into the bonded magnet 4. Specifically, the bonded magnet 4 is heat-treated and incinerated in an air atmosphere at a temperature of 500°C to 800°C for a period of approximately 5 to 10 hours using an electric furnace, to obtain hard magnetic ferrite particles 6, which are used as a sample. The volume resistivity of the hard magnetic ferrite particles 6 can be determined by measuring this sample with a powder resistance measuring device.

[0022] The orientation of the hard magnetic ferrite particles 6 in the bonded magnet 4 of the rotor 1 according to embodiment 1 may be non-oriented or oriented. When oriented, the orientation can be radial, axial, radial, or polar anisotropic. Figure 5 is a schematic diagram showing an example of the polar anisotropic orientation of the hard magnetic ferrite particles inside the bonded magnet of the rotor according to embodiment 1. When oriented, it is preferable that the c-planes of the hard magnetic ferrite particles 6 be polar anisotropically oriented, as shown in Figure 5, from the viewpoint of improving the demagnetization resistance of the bonded magnet 4 and obtaining a strong magnetic force.

[0023] Figures 6 to 8 are diagrams showing an example of the relationship between the easy axis of magnetization and the magnetization direction of hard magnetic ferrite particles. The magnetization mode of the bonded magnet 4 is preferably magnetized in a direction perpendicular to the c-plane, i.e., in the direction of the easy axis of magnetization AEM, along the orientation of the hard magnetic ferrite particles 6. As shown in Figures 6 and 7, when the direction of the easy axis of magnetization AEM of the hard magnetic ferrite particles 6 does not coincide with the magnetization direction MD, it is difficult to improve the magnetic force. In the case of Figure 6, the direction of the easy axis of magnetization AEM is tilted 90° relative to the magnetization direction MD, making it impossible to magnetize in the direction of the easy axis of magnetization AEM. In the case of Figure 7, the direction of the easy axis of magnetization AEM intersects with the magnetization direction MD at an angle greater than 0° but less than 90°. Although not as difficult as in the case of Figure 6, it is difficult to magnetize in the direction of the easy axis of magnetization AEM, making it difficult to improve the magnetic force.

[0024] On the other hand, as shown in Figure 8, when the direction of the easy axis AEM of magnetization of the hard magnetic ferrite particles 6 coincides with the magnetization direction MD, it is easier to improve the magnetic force. Therefore, by orienting the hard magnetic ferrite particles 6 and magnetizing them in the direction of the easy axis AEM, it is possible to improve the magnetic force of the bonded magnet 4. Figure 9 is a schematic diagram showing an example of polar anisotropic magnetization of the bonded magnet used in the rotor according to embodiment 1. When magnetizing, it is preferable that the c-plane, which is the longitudinal surface of the hard magnetic ferrite particles 6, is polar anisotropically oriented, and that the outer peripheral surface of the ring-shaped bonded magnet 4 is polar anisotropically magnetized along the polar anisotropic orientation, as shown in Figure 9. This type of polar anisotropic magnetization makes it possible to improve the magnetic force.

[0025] The rotating body 3 of the rotor 1 according to the first embodiment includes a bonded magnet 4. When the rotating body 3 includes a bonded magnet 4 and rotor components other than the bonded magnet 4, the structure of the rotating body 3 may be a surface magnet type in which the bonded magnet 4 is attached in a ring shape to the outer surface of the rotor component, or an embedded magnet type in which the bonded magnet 4 is embedded inside the rotor component. In the case of a surface magnet type, bonded magnets 4 of various shapes can be used, such as a ring magnet in which a ring-shaped bonded magnet 4 is attached to the outer surface of the rotor component so as to cover the outer surface of the ring-shaped rotor component, or an arc magnet in which an arc-shaped bonded magnet 4 is attached along the outer surface of the ring-shaped rotor component. In the case of a ring magnet, the outer and inner surfaces of the bonded magnet 4 may be circular, elliptical, or wavy. In the case of an embedded magnet type, bonded magnets 4 of various shapes can be used, such as an arc magnet in which an arc-shaped bonded magnet 4 is embedded inside the rotor component, or a flat magnet in which a flat-shaped bonded magnet 4 is embedded inside the rotor component.

[0026] One example of the structure of the rotor 1 is a structure in which the bonded magnets 4 are attached directly to the shaft 2, but the structure of the rotor 1 according to embodiment 1 is not limited to this. Fig. 10 is a cross-sectional view that schematically shows one example of the structure of the rotor according to embodiment 1. As shown in Fig. 10, the rotor 1 may have a structure in which the bonded magnets 4 are attached to the shaft 2 via another member 8. The other member 8 corresponds to a rotor component member. An example of the other member 8 is a metal member.

[0027] The bonded magnet 4 of the rotor 1 according to the first embodiment has a dielectric loss of 70 or less, preferably 50 or less, and more preferably 30 or less. If the volume resistivity of the hard magnetic ferrite particles 6 contained in the bonded magnet 4 is lower than the value considered to be an insulator, the hard magnetic ferrite particles 6 within the bonded magnet 4 will connect to each other, forming conductive paths and lowering the volume resistivity of the bonded magnet 4. In other words, the electrical conductivity of the bonded magnet 4 will increase. In this case, the dielectric loss of the bonded magnet 4 will increase significantly, causing the dielectric constant of the bonded magnet 4 to increase. This increase in dielectric constant can cause electrolytic corrosion in permanent magnet motors that include the rotor 1. For this reason, suppressing dielectric loss is important in order to suppress the increase in dielectric constant, which causes electrolytic corrosion. The bonded magnet 4 of the rotor 1 according to the first embodiment contains hard magnetic ferrite particles 6 with a volume resistivity equal to or higher than the value at which the bonded magnet 4 becomes an insulator, making it difficult for conductive paths to be formed within the bonded magnet 4 and keeping the dielectric loss low. As a result, the increase in dielectric constant is also suppressed, making it possible to suppress electrolytic corrosion in permanent magnet motors that include the rotor 1. Here, the dielectric loss and relative dielectric constant of bonded magnet 4 refer to values ​​calculated from the values ​​of capacitance C and dielectric tangent tan Δ measured between the inner and outer circumferential surfaces of bonded magnet 4 in rotating body 3 using the following equations (1) and (2).

[0028] Dielectric constant = C × ln(b / a) ÷ (2π × ε0) (1) Dielectric loss = tan Δ × dielectric constant (2)

[0029] Here, a is the radius from the center of shaft 2 to the inner peripheral surface of bonded magnet 4, b is the radius from the center of shaft 2 to the outer peripheral surface of bonded magnet 4, and ε0 is the dielectric constant of a vacuum.

[0030] The content of hard magnetic ferrite particles 6 in the bonded magnet 4 of the rotor 1 according to embodiment 1 is preferably 70 wt% or more and 95 wt% or less. In particular, when the content of hard magnetic ferrite particles 6 is 75 wt% or more and 90 wt% or less, it is preferable because it makes it easy to mix and disperse the hard magnetic ferrite particles 6 in the resin 5, improves workability and moldability, and also improves the magnetic force of the bonded magnet 4. If the content of hard magnetic ferrite particles 6 is less than 70 wt%, it may not be possible to obtain a bonded magnet 4 with the desired magnetic force. On the other hand, if the content of hard magnetic ferrite particles 6 exceeds 95 wt%, it becomes difficult to mix and disperse the hard magnetic ferrite particles 6 in the resin 5, which may hinder workability and moldability.

[0031] The resin 5 used in the bonded magnet 4 of the rotor 1 according to the first embodiment can be a thermosetting resin or a thermoplastic resin. Among these, thermoplastic resins are preferred from the standpoint of moldability. Examples of thermoplastic resins include polymers or copolymers of at least one monomer selected from the group consisting of ethylene, propylene, butadiene, isoprene, styrene, methacrylic acid, acrylic acid, methacrylic acid esters, acrylic acid esters, vinyl chloride, tetrafluoroethylene, acrylonitrile, maleic anhydride, and vinyl acetate, as well as at least one resin selected from the group consisting of polyphenylene ether, chlorinated polyethylene, silicone resin, polyamide, polyimide, polycarbonate, polyester, polyacetal, polyphenylene sulfide, polyethylene glycol, polyetherimide, polyketone, polyetheretherketone, polyethersulfone, and polyarylate. Additives such as flame retardants can also be added to the resin as long as they do not impair the desired magnetic and dielectric properties.

[0032] The size of the bonded magnet 4 used in the rotor 1 according to the first embodiment, specifically the radius of the inner circumferential surface, the radius of the outer circumferential surface, and the thickness may be changed as appropriate depending on the application.

[0033] The shaft 2 used in the rotor 1 according to the first embodiment is not particularly limited, but is preferably made of a metal or an alloy from the viewpoints of durability and cost. Examples of metals that can be used for the shaft 2 include iron, stainless steel, aluminum, and copper.

[0034] As described above, the rotor 1 according to the first embodiment is provided with bonded magnets 4 that can suppress variations in electrostatic capacitance that cause electrolytic corrosion.

[0035] Next, a method for manufacturing the rotor 1 according to the first embodiment will be described. Fig. 11 is a flowchart showing an example of the steps of the method for manufacturing the rotor according to the first embodiment. First, a thermoplastic resin as the resin 5 is heated and melted (step S11). Next, a thermoplastic resin having a volume resistivity of 10 8 Hard magnetic ferrite particles 6 having a resistance of Ω·cm or more are mixed and dispersed to prepare a resin composition (step S12). The mixing method for preparing the resin composition is not particularly limited and can be carried out in accordance with methods known in the art. As an example of a mixing method, a single-screw extruder or a multi-screw extruder is generally used. In addition to the above extruders, a Banbury mixer, a roller, a co-kneader, a blast mill, a Prabender blotograph, etc. can also be used. The resin composition can be prepared by operating these in a batch or continuous manner. Alternatively, instead of melt-kneading, so-called mold blending can be carried out by mixing thermoplastic resin pellets and hard magnetic ferrite particles 6 to form a mixture, and then using the mixture as a molding resin and melt-kneading it in the heating barrel of a molding machine.

[0036] The prepared resin composition is then heated and melted at a temperature at which the thermoplastic resin melts, forming a bonded magnet 4 molded into a predetermined shape (step S13). The shape may be any suitable shape for use as the bonded magnet 4 for the rotor 1, preferably a block shape. Furthermore, a crushing process can be performed on the prepared resin composition before the resin composition is heated and melted in step S13. Crushing the prepared resin composition is preferable because it improves the workability of the heat-melting process. Examples of molding methods include injection molding and uniaxial press molding. In this case, a magnetic field alignment permanent magnet and a magnetic field alignment yoke can be placed in the mold to form a polar anisotropic alignment magnetic field of similar shape in the circumferential direction. This preferably aligns the hard magnetic ferrite particles 6 during molding. Furthermore, when molding the bonded magnet 4, a shaft 2 can be set in the mold and molded integrally. Integrating the shaft 2 and bonded magnet 4 in this manner is advantageous from the perspective of productivity.

[0037] Next, a magnetizing device is used to apply a magnetic field of a strength that reaches the saturation point of the maximum magnetic flux density of the hard magnetic ferrite particles 6, thereby magnetizing the bonded magnet 4 molded into the specified shape (step S14). There are no particular restrictions on the method for magnetizing the bonded magnet 4, and it can be carried out in accordance with any method known in the relevant technical field. Examples of methods for magnetizing the bonded magnet 4 include a static magnetic field generation method using a DC electromagnet and a pulsed magnetic field generation method using a capacitor-type magnetizer. In this way, the rotor 1 according to embodiment 1 is manufactured.

[0038] In the first embodiment, the rotor 1 includes a shaft 2 and a rotating body 3 that includes a bonded magnet 4 and is fixed to the shaft 2. The bonded magnet 4 has a volume resistivity of 10 8The bonded magnet 4 comprises hard magnetic ferrite particles 6 with a resistivity of Ω-cm or more and resin 5, and the dielectric loss of the bonded magnet 4 is 70 or less. With this configuration, the bonded magnet 4 retains the properties of an insulator, both immediately after molding of the bonded magnet 4 and after springback has occurred over time since molding, making it difficult for conductive paths to be generated inside the bonded magnet 4. As a result, it has the effect of providing a rotor 1 that can suppress variations in capacitance that cause electrolytic corrosion.

[0039] Furthermore, it is preferable that the filling amount of hard magnetic ferrite particles 6 in bonded magnet 4 be 70 wt % or more and 95 wt % or less. This makes it easier to mix and disperse hard magnetic ferrite particles 6 in resin 5, improving workability and moldability, and also improving the magnetic force of bonded magnet 4.

[0040] Furthermore, the hard magnetic ferrite particles 6 contained in the bonded magnet 4 preferably include first hard magnetic ferrite particles with an average particle size of 3 μm or more and 8 μm or less and an aspect ratio of 1.5 or more and 3 or less, and second hard magnetic ferrite particles with an average particle size of 0.05 μm or more and 1 μm or less. This makes it easier to control the orientation throughout the bonded magnet 4, while enabling high packing without significantly increasing the pressure during molding, and has the effect of producing a bonded magnet 4 with the desired magnetic force.

[0041] Embodiment 2. Figure 12 is a cross-sectional view showing a schematic example of the configuration of a permanent magnet motor according to embodiment 2. A permanent magnet motor 10 according to embodiment 2 will be described below with reference to Figure 12. Permanent magnet motor 10 according to embodiment 2 includes a rotor 1 having a rotating body 3 including bonded magnets 4 fixed to a shaft 2, two bearings 11 arranged on either side of bonded magnet 4 in the extension direction of shaft 2 and supporting shaft 2 of rotor 1, a stator 12 having a stator core 13 wound with winding coils 14, and a conductive housing 15. Rotor 1 has the configuration described in embodiment 1.

[0042] The operation of permanent magnet motor 10 will now be described. Permanent magnet motor 10 becomes an electromagnet when an alternating current flows through winding coils 14 of stator 12. At this time, the south and north poles of the magnetic field generated at regular intervals by winding coils 14 wound around each stator core 13 alternate. This generates a magnetic repulsive force with bonded magnet 4 of rotor 1, causing rotating body 3 of rotor 1 to rotate at high speed and function as a motor.

[0043] Next, we will explain the mechanism by which electrolytic corrosion, which causes abnormal noise from bearing 11, occurs. Between shaft 2 of rotor 1 and bearing 11, and between bond magnet 4 and winding coil 14 of rotor 1, a shaft voltage is generated that is determined by the voltage distribution according to the respective capacitances. At this time, the smaller the capacitance, the greater the shaft voltage due to the voltage distribution. For this reason, if the dielectric loss and dielectric constant of bond magnet 4 are high, the capacitance between bond magnet 4 of rotor 1 and winding coil 14 becomes relatively large, and the capacitance between shaft 2 and bearing 11 becomes relatively small. As a result, the voltage distribution between shaft 2 and bearing 11 becomes large, and excessive shaft voltage occurs. At this time, if the shaft voltage generated between shaft 2 and bearing 11 becomes higher than the discharge inception voltage, a discharge occurs, and electrolytic corrosion occurs in bearing 11.

[0044] Permanent magnet motor 10 according to embodiment 2 uses rotor 1 equipped with bonded magnet 4 with low dielectric loss and dielectric constant, as described in embodiment 1. This makes the capacitance between bonded magnet 4 of rotor 1 and winding coil 14 relatively small, and the capacitance between shaft 2 and bearing 11 relatively large. This reduces the voltage distribution between shaft 2 and bearing 11. In other words, the axial voltage generated between shaft 2 and bearing 11 is kept below the discharge start voltage. This makes it possible to suppress the occurrence of electrolytic corrosion in bearing 11.

[0045] As described above, permanent magnet motor 10 according to embodiment 2 includes rotor 1 described in embodiment 1, bearing 11 that supports shaft 2 of rotor 1, and stator 12. Rotor 1 includes bonded magnet 4 with low dielectric loss and dielectric constant as described in embodiment 1. The capacitance between bonded magnet 4 and winding coil 14 is relatively small, and the capacitance between shaft 2 and bearing 11 is relatively large, so the voltage distribution between shaft 2 and bearing 11 is small. In other words, the axial voltage generated between shaft 2 and bearing 11 is kept below the discharge start voltage. As a result, there is an effect of providing permanent magnet motor 10 that can suppress the occurrence of electrolytic corrosion in bearing 11.

[0046] Hereinafter, the rotor 1 of the present disclosure will be described in detail using examples and comparative examples, but the scope of the present disclosure is not limited by these examples.

[0047] The hard magnetic ferrite particles 6 used in the following examples and comparative examples are produced by pulverizing a bulk hard magnetic ferrite using known methods such as coarse pulverization using an Attritor (registered trademark) and fine pulverization using a ball mill. For various hard magnetic ferrite particles 6 produced under different pulverization conditions, the particle size distribution is measured by a laser diffraction / scattering method, and the content of fine particles of 0.05 μm or more and 1 μm or less is calculated. Table 1 shows the characteristics of the produced hard magnetic ferrite particles. Here, the material of the hard magnetic ferrite particles 6 is M-type hexagonal ferrite (BaFe 12 O 19 )

[0048]

[0049] Table 2 shows the manufacturing conditions and characteristic evaluation results of the bonded magnets according to the examples and comparative examples.

[0050]

[0051] Example 1 In Example 1, 900 parts by mass of No. A M-type hexagonal ferrite particles, which are hard magnetic ferrite particles 6, were added to 100 parts by mass of chlorinated polyethylene resin, which is resin 5, and mixed at a temperature of 180°C to obtain a resin composition. This resin composition was then injection molded using a mold at a molding pressure of 5 MPa so as to be integrated with shaft 2, to obtain bonded magnet 4. During this process, the M-type hexagonal ferrite particles were polar anisotropically oriented by magnetic field orientation. The molded bonded magnet 4 was then demagnetized once and then polar anisotropically magnetized using a magnetizer to obtain a rotor 1 for evaluation. The fine particle content of No. A M-type hexagonal ferrite particles was 30 wt%, and the volume resistivity was 10 8 The dielectric loss of the bonded magnet 4 thus obtained is 68 Ω·cm.

[0052] Example 2 A rotor 1 for evaluation was obtained in the same manner as in Example 1, except that the M-type hexagonal ferrite particles of No. B were used instead of the M-type hexagonal ferrite particles of No. A. The content of fine particles in the M-type hexagonal ferrite particles of No. B was 30 wt %, and the volume resistivity was 10 9 The dielectric loss of the bonded magnet 4 thus obtained is 50.

[0053] [Example 3] A rotor 1 for evaluation was obtained in the same manner as in Example 1, except that the M-type hexagonal ferrite particles of No. C were used instead of the M-type hexagonal ferrite particles of No. A. The content of fine particles in the M-type hexagonal ferrite particles of No. C was 30 wt %, and the volume resistivity was 10 10 The dielectric loss of the bonded magnet 4 thus obtained is 30.

[0054] Example 4 A rotor 1 for evaluation was obtained in the same manner as in Example 1, except that the M-type hexagonal ferrite particles of No. E were used instead of the M-type hexagonal ferrite particles of No. A. The content of fine particles in the M-type hexagonal ferrite particles of No. E was 4 wt %, and the volume resistivity was 10 8 The dielectric loss of the bonded magnet 4 thus obtained is 58 Ω·cm.

[0055] [Example 5] A rotor 1 for evaluation was obtained in the same manner as in Example 1, except that the M-type hexagonal ferrite particles of No. F were used instead of the M-type hexagonal ferrite particles of No. A. The content of fine particles in the M-type hexagonal ferrite particles of No. F was 10 wt %, and the volume resistivity was 10 8 The dielectric loss of the bonded magnet 4 thus obtained is 64.

[0056] Example 6 A rotor 1 for evaluation was obtained in the same manner as in Example 1, except that the M-type hexagonal ferrite particles of No. G were used instead of the M-type hexagonal ferrite particles of No. A. The fine particle content of the M-type hexagonal ferrite particles of No. G was 42 wt %, and the volume resistivity was 10 8 The dielectric loss of the bonded magnet 4 thus obtained is 70.

[0057] Example 7 A rotor 1 for evaluation is obtained in the same manner as in Example 1, except that the M-type hexagonal ferrite particles are radially oriented by magnetic field orientation. The dielectric loss of the bonded magnet 4 obtained in this manner is 68.

[0058] Example 8 A rotor 1 for evaluation was obtained in the same manner as in Example 1, except that radial magnetization was performed using a magnetizing device. The dielectric loss of the bonded magnet 4 obtained in this manner was 68.

[0059] Comparative Example 1 A rotor 1 for evaluation was obtained in the same manner as in Example 1, except that the M-type hexagonal ferrite particles of No. D were used instead of the M-type hexagonal ferrite particles of No. A. The content of fine particles in the M-type hexagonal ferrite particles of No. D was 30 wt %, and the volume resistivity was 10 6 The dielectric loss of the bonded magnet 4 thus obtained is 100.

[0060] Comparative Example 2 A rotor 1 for evaluation was obtained in the same manner as in Example 1, except that the molding pressure during injection molding was changed to 50 MPa. The dielectric loss of the bonded magnet 4 thus obtained was 75.

[0061] The ratio of the magnetic flux density of the bonded magnets 4 is evaluated for the rotors 1 obtained in the above examples and comparative examples. Specifically, the ratio of the magnetic flux density of the bonded magnets 4 is evaluated by using the magnetic flux density of Example 1 as the reference and determining the magnetic flux density obtained in each example and comparative example. In other words, the ratio of the magnetic flux density of the bonded magnets 4 is calculated by dividing the magnetic flux density obtained in each example and comparative example by the magnetic flux density of Example 1. Each of the obtained rotors 1 is then incorporated into a permanent magnet motor 10 for evaluation, and the ratio of the axial voltage between the shaft 2 and the bearing 11 is evaluated. Furthermore, the presence or absence of electrolytic corrosion in the bearing 11 of the permanent magnet motor 10 is visually evaluated. The ratio of the axial voltage between the shaft 2 and the bearing 11 is evaluated by using the axial voltage of Example 1 as the reference and determining the axial voltage obtained in each example and comparative example. In other words, the ratio of the axial voltage between the shaft 2 and the bearing 11 is calculated by dividing the axial voltage obtained in each example and comparative example by the axial voltage of Example 1.

[0062] As shown in Table 2, the volume resistivity is 10 8 In Examples 1 to 8, in which hard magnetic ferrite particles 6 of Ω cm or more were filled and the dielectric loss of the bonded magnet 4 was 70 or less, the axial voltage generated between the shaft 2 and the bearing 11 was low, and the occurrence of electrolytic corrosion was suppressed. In particular, when the volume resistivity of the hard magnetic ferrite particles 6 was 10 9 Ω cm or 10 10 In the case of Example 2 or Example 3, where the volume resistivity is as high as Ω·cm, the axial voltage is further suppressed to a low level, and it is clear that the higher the volume resistivity, the greater the effect of suppressing the occurrence of electrolytic corrosion.

[0063] Furthermore, when focusing on the particle size of the hard magnetic ferrite particles 6, it can be seen that Examples 1 to 3 and Example 5, which contain fine particles of 0.05 μm or more and 1 μm or less in the range of 10% to 30%, have a high magnetic flux density ratio of the bonded magnet 4 and a strong magnetic force.

[0064] Regarding the orientation of the hard magnetic ferrite particles 6 and the magnetization of the bonded magnet 4, a comparison of Example 1 with Examples 7 and 8, which use the same hard magnetic ferrite particles 6, shows that polar anisotropic orientation and polar anisotropic magnetization improves the magnetic force.

[0065] On the other hand, the volume resistivity is 10 8 10 Ω cm or less 6 In Comparative Example 1, which was filled with hard magnetic ferrite particles 6 of Ω cm, the axial voltage generated between the shaft 2 and bearing 11 was higher than in Example 1, indicating the occurrence of electrolytic corrosion. Furthermore, even when filled with hard magnetic ferrite particles 6 whose volume resistivity is equal to or exceeds the value at which they can be considered an insulator, as in Comparative Example 2, electrolytic corrosion can occur if the dielectric loss of the bonded magnet 4 is high. This is thought to be because the significantly increased molding pressure increased the number of conductive paths formed by the connections between the hard magnetic ferrite particles 6.

[0066] As can be seen from the above results, Examples 1 to 8 provide a rotor 1 equipped with bonded magnets 4 that can suppress variations in capacitance that cause electrolytic corrosion. Also, Examples 1 to 8 provide a permanent magnet motor 10 that can suppress the occurrence of electrolytic corrosion in bearings 11.

[0067] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0068] 1 rotor, 2 shaft, 3 rotating body, 4 bonded magnet, 5 resin, 6 hard magnetic ferrite particles, 8 other members, 10 permanent magnet motor, 11 bearing, 12 stator, 13 stator core, 14 winding coil, 15 housing, AEM easy axis of magnetization, MD magnetization direction.

Claims

1. A shaft and a rotating body including a bonded magnet, the rotating body being fixed to the shaft, wherein the bonded magnet has hard magnetic ferrite particles with a volume resistivity of 10 8 Ω·cm or more and a resin, and a rotor characterized in that a dielectric loss between an inner peripheral surface and an outer peripheral surface of the bonded magnet in the rotating body is 70 or less.

2. The bonded magnet has a direction of a plane perpendicular to the c-axis of the hard magnetic ferrite particles being magnetically anisotropically oriented, and is magnetically anisotropically magnetized such that the outer peripheral surface of the bonded magnet serves as a magnetic pole along the magnetically anisotropic orientation. The rotor according to claim 1, characterized in that.

3. The rotor according to claim 1 or 2, characterized in that the filling amount of the hard magnetic ferrite particles in the bonded magnet is 70 wt% or more and 95 wt% or less.

4. The hard magnetic ferrite particles include first hard magnetic ferrite particles having an average particle diameter of 3 μm or more and 8 μm or less and an aspect ratio of 1.5 or more and 3 or less, and second hard magnetic ferrite particles having an average particle diameter of 0.05 μm or more and 1 μm or less. The rotor according to any one of claims 1 to 3, characterized in that.

5. The rotor according to any one of claims 1 to 4, characterized in that the hard magnetic ferrite particles are magnetoplumbite type ferrite.

6. A permanent magnet motor comprising: the rotor according to any one of claims 1 to 5; and a bearing that supports the shaft of the rotor.

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