Rotor and Permanent Magnet Motor

Abstract

The rotor (1) includes a shaft (2) and a rotor (3) that includes a bonded magnet (4) and is fixed to the shaft (2). The bonded magnet (4) has a volume resistivity of 10 8 The magnet comprises hard magnetic ferrite particles (6) having a resistivity of Ω·cm or more, and a resin (5). The dielectric loss between the inner and outer peripheral surfaces of the bonded magnet (4) in the rotor (3) is 70 or less.

Description

[Technical field]

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

[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 devices such as blowers and ventilation fans. In permanent magnet motors using bonded magnets, a potential difference called shaft voltage occurs between the inside and outside of the bearing that supports the rotor, and if this potential difference becomes excessive, a small current flows inside the bearing, causing electrolytic corrosion in the bearing. If this electrolytic corrosion progresses, it can lead to malfunctions such as abnormal noises coming from the bearing, so a countermeasure was required.

[0003] It is known that the potential difference applied to the bearing is closely related to the capacitance that changes according to 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 to 12 pF when the measurement frequency is 10 kHz. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2013 / 042282 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above conventional electric motor, it is difficult to stably control the capacitance of the bonded magnet provided in the rotor, and the capacitance is prone to variation. Therefore, even in the above conventional electric motor, there is a problem that electrolytic corrosion of the bearings may occur.

[0006] The present disclosure has been made in consideration of the above, and has an object to obtain a rotor that can suppress variations in capacitance that cause electrolytic corrosion more than ever before. [Means for solving the problem]

[0007] In order to solve the above problems and achieve the object, the rotor according to the present disclosure includes a shaft and a rotor including a bonded magnet and fixed to the shaft. The bonded magnet has a volume resistivity of 10 8 The magnet contains hard magnetic ferrite particles with a dielectric constant of Ω·cm or more, and a resin. The dielectric loss between the inner and outer peripheral surfaces of the bonded magnet in the rotor is 70 or less. The hard magnetic ferrite particles include first hard magnetic ferrite particles having 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 having an average particle size of 0.05 μm or more and 1 μm or less, and the content of the second hard magnetic ferrite particles is 5 mass% or more and 40 mass% or less. Effect of the Invention

[0008] The rotor according to the present disclosure has an advantage that the variation in capacitance that causes electrolytic corrosion can be suppressed more effectively than in the past. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic example of a rotor according to a first embodiment; [Diagram 2] FIG. 1 is a schematic diagram showing an example of the configuration of a typical bonded magnet. [Diagram 3] FIG. 1 is a schematic diagram showing an example of the configuration of a typical bonded magnet. [Figure 4] FIG. 1 is a schematic diagram showing an example of the structure of hard magnetic ferrite particles contained in the bonded magnet of the rotor according to the first embodiment; [Diagram 5] FIG. 2 is a schematic diagram showing an example of the polar anisotropic orientation of hard magnetic ferrite particles inside the bonded magnet of the rotor according to the first embodiment; [Figure 6]FIG. 1 is a diagram showing an example of the relationship between the magnetization easy axis and the magnetization direction of hard magnetic ferrite particles. [Figure 7] FIG. 1 is a diagram showing an example of the relationship between the magnetization easy axis and the magnetization direction of hard magnetic ferrite particles. [Figure 8] FIG. 1 is a diagram showing an example of the relationship between the magnetization easy axis and the magnetization direction of hard magnetic ferrite particles. [Figure 9] FIG. 1 is a schematic diagram showing an example of polar anisotropic magnetization of a bonded magnet used in a rotor according to embodiment 1. [Figure 10] FIG. 1 is a cross-sectional view showing a schematic example of a structure of a rotor according to a first embodiment; [Figure 11] 1 is a flowchart showing an example of a procedure for a manufacturing method of a rotor according to the first embodiment. [Figure 12] FIG. 11 is a cross-sectional view showing a schematic example of a configuration of a permanent magnet motor according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A rotor and a permanent magnet motor according to embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0011] Embodiment 1 Fig. 1 is a cross-sectional view showing a schematic example of a rotor according to the first embodiment. As shown in Fig. 1, the rotor 1 according to the first embodiment has a shaft 2 and a rotor 3 fixed to the shaft 2. The rotor 3 includes a bonded magnet 4. In this example, the rotor 3 is made of the bonded magnet 4. The bonded magnet 4 has a configuration in which hard magnetic ferrite particles 6, which are hard magnetic particles, are dispersed in a resin 5.

[0012] 2 and 3 are diagrams showing an example of the configuration of a typical bonded magnet. FIG. 2 shows an example of the configuration of a bonded magnet 54 immediately after molding, and FIG. 3 shows an example of the configuration of a bonded magnet 54 after some time has passed since molding. In general, a bonded magnet 54 is formed by binding hard magnetic particles 56 with a binder component made of resin 55. In addition, in order to strengthen the magnetic force, the filling amount of the hard magnetic particles 56 is often relatively high. Immediately after molding of the bonded magnet 54, the hard magnetic particles 56 are closely attached to each other due to the binding force of the resin 55, which is the binder component, as shown in FIG. 2. However, as time passes, the binding force of the resin 55 loosens slightly due to the springback phenomenon. As shown in FIG. 3, after some time has passed since molding, the distance between the hard magnetic particles 56 may become greater than that shown in FIG. 2 immediately after molding. At this time, if the volume resistivity of the hard magnetic particles 56 contained in the bonded magnet 54 is low, this will cause variation in the electrical performance of the bonded magnet 54. If the volume resistivity of the hard magnetic particles 56 is low, it will be particularly prone to variation in the dielectric properties, which is a factor in the fluctuation of the electrostatic capacitance that causes electrolytic corrosion in motor equipment.

[0013] Consider the case where the volume resistivity of the hard magnetic particles 56 is low. In one example, as shown in FIG. 2, when the distance between the hard magnetic particles 56 immediately after molding is close, a conductive path is formed in the bonded magnet 54, making it easier for electricity to flow. In the case of an AC electric field, since electrical conductivity and dielectric loss are physically proportional, when electrical conductivity is high, the dielectric loss of the bonded magnet 54 increases and the dielectric constant shows a high value. On the other hand, as shown in FIG. 3, when the distance between the hard magnetic particles 56 is increased due to the springback phenomenon, the conductive path in the bonded magnet 54 decreases and the characteristics become like an insulator. As a result, the electrical conductivity becomes lower than in the case of FIG. 2, the dielectric loss in the bonded magnet 54 decreases, and the dielectric constant becomes lower. In this way, when the volume resistivity of the hard magnetic particles 56 contained in the bonded magnet 54 is low, the dielectric characteristics, i.e., the dielectric constant and dielectric loss, vary depending on the distance between the hard magnetic particles 56. As a result, the capacitance varies, inducing 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 has a volume resistivity of 10 8 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 in the bonded magnet 4 varies due to the springback phenomenon, there is almost no change in the electrical conductivity in the bonded magnet 4, so the dielectric characteristics are less likely to change. In other words, whether some of the insulating hard magnetic ferrite particles 6 are in contact or not, the inside of the bonded magnet 4 is in a state where electricity does not easily flow. 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 may be a ferromagnetic material having spontaneous magnetization and a volume resistivity equal to or higher than a value at which the material is considered to be an insulator. 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 22Y-type hexagonal ferrite such as M-type hexagonal ferrite is 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 distributed and inexpensive. Furthermore, hexagonal ferrite having a composition in which a part of the metal element Ba, Sr or Fe of the above hexagonal ferrite is replaced with a transition metal element may also be used.

[0016] FIG. 4 is a diagram showing a schematic example of the structure of a hard magnetic ferrite particle contained in the bonded magnet of the rotor according to the first embodiment. The hard magnetic ferrite particle 6 contained in the bonded magnet 4 of the rotor 1 according to the first embodiment is a hexagonal crystal system, and has a plate-like particle shape as shown in FIG. 4. The hard magnetic ferrite particle 6 has a characteristic that the crystal grows so that the c-plane, which is a plane perpendicular to the c-axis of the hexagonal crystal structure, becomes the long side of the plate-like particle. In addition, the aspect ratio of the long axis and the short axis of the plate-like particle tends to increase as the crystal grows. 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 in the plane perpendicular to the c-axis, i.e., in the c-plane.

[0017] On the other hand, the axis of easy magnetization of the hard magnetic ferrite particles 6 is in the c-axis direction. In order to increase the magnetic force of the bonded magnet 4, it is important to control the orientation of the crystals, that is, the orientation of the plate-shaped hard magnetic ferrite particles 6, when filling the resin 5. From this point of view, it is easier to control the orientation of the hard magnetic ferrite particles 6 filled in the bonded magnet 4 when the hard magnetic ferrite particles 6 are relatively large in particle size and have a large aspect ratio. However, there is a problem that the plate-shaped coarse particles have poor packing properties, that is, it is difficult to achieve high packing. In addition, when such coarse particles with poor packing properties are to be highly packed, the pressure during molding must be significantly increased, which also causes a problem that changes over time due to the springback phenomenon as shown in Figures 2 and 3 are likely to occur. For this reason, in order to increase the magnetic force of the bonded magnet 4 and enable high packing, it is preferable to use coarse particles with a relatively large particle size and fine particles with a relatively small particle size in combination for 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. When the content of the second hard magnetic ferrite particles is less than 5% by mass, it is easy to control the orientation in the entire bonded magnet 4, but it is difficult to achieve high packing. When the content of the second hard magnetic ferrite particles is more 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 small, so that the orientation in the entire bonded magnet 4 is deteriorated and the desired magnetic force cannot be obtained. For this reason, the content of the second hard magnetic ferrite particles is desirably 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 about 5 hours to 10 hours using an electric furnace to obtain hard magnetic ferrite particles 6. 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 at this time is the diameter of a volume-equivalent sphere.

[0020] In addition, the aspect ratio of the hard magnetic ferrite particles 6 is determined by taking a photograph of the cross section of the bonded magnet 4 at a magnification ranging from several hundred to several thousand times using a scanning electron microscope (SEM), measuring the long axis and short axis of the hard magnetic ferrite particles 6 from the obtained photograph, and calculating the ratio of the long axis to the short 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 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 8 If the resistivity is less than Ω·cm, the material will be more semiconductive than insulating. For this reason, as shown in Figures 2 and 3, when 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 vary accordingly. 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 Since the hard magnetic ferrite particles 6 have a resistivity of Ω·cm or more, which is a value that is higher than the value that can be considered an insulator, the electrical properties are unlikely to fluctuate even if the distance between the hard magnetic ferrite particles 6 in the bonded magnet 4 changes. As a result, the variation in capacitance in the bonded magnet 4 can be suppressed. Here, the volume resistivity of the hard magnetic ferrite particles 6 is obtained by measuring the volume resistivity 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 about 5 hours to 10 hours using an electric furnace, and the hard magnetic ferrite particles 6 obtained are used as a sample. The volume resistivity of the hard magnetic ferrite particles 6 can be obtained 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 the first embodiment may be non-oriented or oriented. When oriented, the orientation may be radial, axial, radial, or polar anisotropic. FIG. 5 is a schematic diagram showing an example of polar anisotropic orientation of the hard magnetic ferrite particles inside the bonded magnet of the rotor according to the first embodiment. When oriented, it is preferable that the c-plane of the hard magnetic ferrite particles 6 is polar anisotropically oriented as shown in FIG. 5, from the viewpoint of improving the demagnetization resistance of the bonded magnet 4 and obtaining a strong magnetic force.

[0023] 6 to 8 are diagrams showing an example of the relationship between the magnetization easy axis and the magnetization direction of the hard magnetic ferrite particles. The magnetization form of the bonded magnet 4 is preferably magnetized in a direction perpendicular to the c-plane, that is, in the direction of the magnetization easy axis AEM, along the orientation of the hard magnetic ferrite particles 6. As shown in FIG. 6 and FIG. 7, when the direction of the magnetization easy axis AEM of the hard magnetic ferrite particles 6 does not coincide with the magnetization direction MD, the magnetic force is difficult to improve. In the case of FIG. 6, the direction of the magnetization easy axis AEM is inclined by 90° to the magnetization direction MD, and magnetization in the direction of the magnetization easy axis AEM is not possible. In the case of FIG. 7, the direction of the magnetization easy axis AEM intersects with the magnetization direction MD at an angle greater than 0° and less than 90°, and although not as difficult as in the case of FIG. 6, it is difficult to magnetize in the direction of the magnetization easy axis AEM, and it is difficult to improve the magnetic force.

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

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

[0026] One example of the structure of rotor 1 is a structure in which bonded magnets 4 are attached directly to shaft 2, but the structure of rotor 1 according to embodiment 1 is not limited to this. FIG. 10 is a cross-sectional view that shows a schematic example of the structure of the rotor according to embodiment 1. As shown in FIG. 10, rotor 1 may have a structure in which bonded magnets 4 are attached to 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 are connected to each other within the bonded magnet 4, forming a conductive path, and the volume resistivity of the bonded magnet 4 decreases. That is, the electrical conductivity of the bonded magnet 4 increases. In this case, the dielectric loss of the bonded magnet 4 increases significantly, causing the dielectric constant of the bonded magnet 4 to increase. Such an increase in the dielectric constant causes electrolytic corrosion in a permanent magnet motor having the rotor 1. For this reason, it is important to suppress the dielectric loss in order to suppress the increase in the dielectric constant, which is the cause of electrolytic corrosion. The bonded magnet 4 of the rotor 1 according to the first embodiment contains hard magnetic ferrite particles 6 whose volume resistivity is equal to or higher than the value at which the bonded magnet 4 becomes an insulator, so that a conductive path is unlikely to be generated inside the bonded magnet 4, and the dielectric loss is suppressed to a low value. As a result, the increase in the dielectric constant is also suppressed, making it possible to suppress the occurrence of electrolytic corrosion in a permanent magnet motor having the rotor 1. Here, the dielectric loss and relative dielectric constant of bonded magnet 4 refer to values ​​calculated from the 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 formulas (1) and (2).

[0028] Dielectric constant = C × ln(b / a) ÷ (2π × ε0) (1) Dielectric loss = tan Δ × relative 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 the hard magnetic ferrite particles 6 in the bonded magnet 4 of the rotor 1 according to the first embodiment is preferably 70 wt% or more and 95 wt% or less. In particular, when the content of the hard magnetic ferrite particles 6 is 75 wt% or more and 90 wt% or less, the hard magnetic ferrite particles 6 are easily mixed and dispersed in the resin 5, and the workability and moldability are good, and the magnetic force of the bonded magnet 4 is also good, which is preferable. If the content of the hard magnetic ferrite particles 6 is less than 70 wt%, the bonded magnet 4 may not have the desired magnetic force. On the other hand, if the content of the 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 cause problems in the 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, from the viewpoint of moldability, a thermoplastic resin is preferable. An example of the thermoplastic resin is a polymer or copolymer of at least one monomer selected from the group consisting of ethylene, propylene, butadiene, isoprene, styrene, methacrylic acid, acrylic acid, methacrylic acid ester, acrylic acid ester, 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, polyether ether ketone, polyether sulfone, and polyarylate. In addition, additives such as flame retardants can be added within a range that does not impair the desired magnetic and dielectric properties.

[0032] The size of bonded magnet 4 used in rotor 1 according to embodiment 1, specifically the radius of the inner circumferential surface, the radius of the outer circumferential surface, and the thickness, may be changed appropriately 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 a metal or an alloy from the viewpoint 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, rotor 1 according to embodiment 1 is equipped with bonded magnets 4 that are capable of suppressing variations in electrostatic capacitance that are a cause of electrolytic corrosion.

[0035] Next, a method for manufacturing the rotor 1 according to the first embodiment will be described. FIG. 11 is a flow chart showing an example of the procedure 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 performed according to a method known in the art. As an example of the mixing method, a single-screw extruder or a multi-screw extruder is generally used, but other than the above extruders, a Banbury mixer, a roller, a co-kneader, a blast mill, a Prabender blastograph, etc. can also be used. The resin composition can be prepared by operating these in a batch or continuous manner. In addition, it is also possible to carry out so-called mold blending, in which the thermoplastic resin pellets and the hard magnetic ferrite particles 6 are mixed to form a mixture, and the mixture is used as a molding resin and melt-kneaded in the heating cylinder of a molding machine without melt-kneading.

[0036] The prepared resin composition is then heated and melted at a temperature at which the thermoplastic resin melts, and a bonded magnet 4 is formed by molding into a predetermined shape (step S13). The shape may be any shape suitable for use as the bonded magnet 4 for the rotor 1, and is preferably a block shape. In addition, a crushing process step for crushing the prepared resin composition can be provided before the resin composition is heated and melted in step S13. It is preferable to subject the prepared resin composition to a crushing process, since this can improve the workability of the heat melting process. Examples of molding methods include injection molding and uniaxial press molding. At this time, a magnetic field orientation permanent magnet and a magnetic field orientation yoke can be arranged in the mold so as to form a polar anisotropic orientation magnetic field of similar shape in the circumferential direction. This makes it preferable to orient the hard magnetic ferrite particles 6 during molding. Furthermore, when molding the bonded magnet 4, the shaft 2 can be set in the mold and molded as one piece. In this way, molding the shaft 2 and the bonded magnet 4 as one piece is preferable from the viewpoint of productivity.

[0037] Next, a magnetizing device is used to apply a magnetic field with 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 a specified shape (step S14). There are no particular limitations on the method for magnetizing the bonded magnet 4, and it can be performed in accordance with any method known in the art. 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 manner, the rotor 1 according to embodiment 1 is manufactured.

[0038] In the first embodiment, the rotor 1 includes a shaft 2 and a rotor 3 including a bonded magnet 4 and 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 having 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, bonded magnet 4 has insulating properties 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, there is an effect of being able to provide a rotor 1 that can suppress variations in capacitance that cause electrolytic corrosion.

[0039] It is also preferable that the filling amount of the hard magnetic ferrite particles 6 in the bonded magnet 4 is 70 wt% or more and 95 wt% or less. This makes it easier 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.

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

[0041] Embodiment 2 Fig. 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 Fig. 12. Permanent magnet motor 10 according to embodiment 2 includes rotor 1 having rotating body 3 including bonded magnet 4 fixed to shaft 2, two bearings 11 arranged on both sides of bonded magnet 4 in the extension direction of shaft 2 and supporting shaft 2 of rotor 1, stator 12 having winding coil 14 wound around stator core 13, and conductive housing 15. Rotor 1 has the configuration described in embodiment 1.

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

[0043] Next, the mechanism of occurrence of electrolytic corrosion that causes the abnormal noise of the bearing 11 will be explained. Between the shaft 2 of the rotor 1 and the bearing 11, and between the bonded magnet 4 of the rotor 1 and the winding coil 14, an axial voltage determined by the voltage distribution according to the respective capacitances is generated. At this time, the smaller the capacitance, the larger the axial voltage due to the voltage distribution. Therefore, when the dielectric loss and dielectric constant of the bonded magnet 4 are large, the capacitance between the bonded magnet 4 of the rotor 1 and the winding coil 14 becomes relatively large, and the capacitance between the shaft 2 and the bearing 11 becomes relatively small. Therefore, the voltage distribution between the shaft 2 and the bearing 11 becomes large, and an excessive axial voltage is generated. At this time, if the axial voltage generated between the shaft 2 and the bearing 11 becomes higher than the discharge start voltage, an electric discharge occurs, and electrolytic corrosion occurs in the bearing 11.

[0044] Permanent magnet motor 10 according to the second embodiment uses rotor 1 equipped with bonded magnet 4 with low dielectric loss and dielectric constant as described in the first embodiment. 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 sharing between shaft 2 and bearing 11. In other words, the axial voltage generated between shaft 2 and bearing 11 is suppressed to less than the discharge start voltage. This makes it possible to suppress the occurrence of electrolytic corrosion in bearing 11.

[0045] As described above, the permanent magnet motor 10 according to the second embodiment includes the rotor 1 described in the first embodiment, the bearing 11 supporting the shaft 2 of the rotor 1, and the stator 12. The rotor 1 includes the bonded magnet 4 having a small dielectric loss and dielectric constant as described in the first embodiment. Since the capacitance between the bonded magnet 4 and the winding coil 14 becomes relatively small and the capacitance between the shaft 2 and the bearing 11 becomes relatively large, the voltage sharing between the shaft 2 and the bearing 11 becomes small. In other words, the shaft voltage generated between the shaft 2 and the bearing 11 is suppressed to less than the discharge start voltage. As a result, there is an effect of being able to provide a permanent magnet motor 10 capable of suppressing the occurrence of electrolytic corrosion in the bearing 11. EXAMPLES

[0046] Hereinafter, the rotor 1 of the present disclosure will be described in detail with reference to examples and comparative examples, but the scope of the present disclosure is not limited thereto.

[0047] The hard magnetic ferrite particles 6 used in the following examples and comparative examples are manufactured by crushing a bulk body of hard magnetic ferrite using known methods such as coarse crushing with an Attritor (registered trademark) and fine crushing with a ball mill. For various hard magnetic ferrite particles 6 manufactured under different crushing 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 manufactured hard magnetic ferrite particles. Here, the material of the hard magnetic ferrite particles 6 is M-type hexagonal ferrite (BaFe 12 O 19 ).

[0048] [Table 1]

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

[0050] [Table 2]

[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, are 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. Next, this resin composition is injection molded using a mold at a molding pressure of 5 MPa so as to be integrated with the shaft 2 to obtain a bonded magnet 4. At this time, the M-type hexagonal ferrite particles are polar anisotropically oriented by magnetic field orientation. After that, the molded bonded magnet 4 is demagnetized once, and then polar anisotropically magnetized using a magnetizing device to obtain a rotor 1 for evaluation. The fine particle content of No. A M-type hexagonal ferrite particles is 30 wt%, and the volume resistivity is 10 8 The dielectric loss of the bonded magnet 4 thus obtained is 68.

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

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

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

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

[0056] [Example 6] A rotor 1 for evaluation is obtained in the same manner as in Example 1, except that the M-type hexagonal ferrite particles of No. G are 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. G is 42 wt %, and the volume resistivity is 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 thus obtained is 68.

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

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

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

[0061] The ratio of the magnetic flux density of the bonded magnet 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 magnet 4 is evaluated by using the magnetic flux density of Example 1 as a reference to evaluate the magnetic flux density obtained in each example and each comparative example. In other words, the ratio of the magnetic flux density of the bonded magnet 4 is calculated by dividing the magnetic flux density obtained in each example and each comparative example by the magnetic flux density of Example 1. In addition, each of the obtained rotors 1 is 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, and further, 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 a reference to evaluate the axial voltage obtained in each example and each 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 each 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 the hard magnetic ferrite particles 6 having a resistivity of Ω·cm or more are filled and the bonded magnet 4 has a dielectric loss of 70 or less, the axial voltage generated between the shaft 2 and the bearing 11 is low, and the occurrence of electrolytic corrosion is suppressed. 9 Ω cm or 10 10In the case of Example 2 or Example 3, which has a high 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 Ω cm lower than 10 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 the bearing 11 was higher than in Example 1, indicating that electrolytic corrosion was occurring. Furthermore, even when filled with hard magnetic ferrite particles 6 whose volume resistivity is equal to or exceeds the value at which the magnet can be considered an insulator, as in Comparative Example 2, electrolytic corrosion can occur if the bonded magnet 4 has high dielectric loss. This is thought to be due to the fact that the conductive paths formed by the connections between the hard magnetic ferrite particles 6 were increased by increasing the molding pressure.

[0066] As can be seen from the above results, according to Examples 1 to 8, it is possible to provide a rotor 1 equipped with a bonded magnet 4 that can suppress the variation in capacitance that causes electrolytic corrosion. Furthermore, according to Examples 1 to 8, it is possible to 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 the embodiments may be combined with each other. Also, parts of the configurations may be omitted or modified without departing from the spirit of the invention. [Explanation of symbols]

[0068] 1 rotor, 2 shaft, 3 rotating body, 4 bonded magnet, 5 resin, 6 hard magnetic ferrite particles, 8 other components, 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, a rotor including a bonded magnet and fixed to the shaft; Equipped with The bonded magnet has a volume resistivity of 10 8 The hard magnetic ferrite particles have a resistivity of Ω cm or more, and a resin, A rotor characterized in that the dielectric loss between the inner peripheral surface and the outer peripheral surface of the bonded magnet in the rotor is 70 or less.

2. 2. The rotor according to claim 1, wherein the bonded magnet has a polar anisotropic orientation in the direction perpendicular to the c-axis of the hard magnetic ferrite particles, and is polar anisotropically magnetized along the polar anisotropic orientation so that the outer circumferential surface of the bonded magnet becomes a magnetic pole.

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

4. 2. The rotor according to claim 1, wherein the hard magnetic ferrite particles include first hard magnetic ferrite particles having 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 having an average particle size of 0.05 μm or more and 1 μm or less.

5. 2. The rotor according to claim 1, wherein the hard magnetic ferrite particles are magnetoplumbite ferrite particles.

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

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