JP4029679B2 - Bond magnet for motor and motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hollow cylindrical anisotropic bonded magnet used for a motor and a motor using the bonded magnet.
[0002]
[Prior art]
An anisotropic bonded magnet formed into a hollow cylindrical shape is known as a permanent magnet for a motor. The bond magnet is shaped in a state where a predetermined magnetic field distribution is generated, thereby orienting the magnetic field. The orientation magnetic field pattern in the cross section perpendicular to the axis of the cylindrical bonded magnet mainly includes axial orientation, radial orientation, and polar orientation. Axial alignment is a method of aligning in a uniaxial direction in the cross section, and radial alignment is a method of aligning radially from the center of the cross section, that is, in the normal direction of the circumference.
[0003]
[Problems to be solved by the invention]
When such a bonded magnet is used in, for example, a two-pole DC brush motor, the motor mainly exhibits the following characteristics. In a motor using an axially oriented bonded magnet, the cogging torque is small but the output torque is small because the surface magnetic flux density in the normal direction changes sinusoidally with respect to the change in electrical angle. On the other hand, a motor using a radially oriented bonded magnet has a large output torque but a large cogging torque because the surface magnetic flux density in the normal direction changes in a substantially square wave with respect to a change in electrical angle.
[0004]
As described above, the bond magnet using the conventional orientation method inevitably increases the cogging torque when the output torque is increased, and the output torque inevitably decreases when the cogging torque is decreased. There was a problem.
[0005]
Japanese Patent Application Laid-Open No. 5-144632 discloses an efficient generation of torque with respect to the distribution of the surface magnetic flux density along the axial direction by setting the magnetic field orientation toward the center in the axial direction at the end that does not contribute to torque generation. It is proposed to plan. Further, the publication proposes that the magnetic field distribution generated in the normal direction in the magnetic field distribution in the cross section perpendicular to the axial direction is basically oriented in the central region of the working arc surface. With such a magnetic field distribution, the magnetic field effectively contributes to torque generation.
[0006]
However, this publication has a problem that the cogging torque increases because the magnetic field distribution in a cross section perpendicular to the axis converges around the magnetic field in the central region of the working arc. In addition, as a result of simulating the magnetic field distribution for the orientation method described in the publication, the orientation distribution toward the center is not formed in the central portion of the working circular arc surface, and the normal direction is distributed over almost the entire circumference. Magnetic field distribution. Thus, in reality, it is considered that the magnetic field distribution oriented toward the center is not formed in the central portion of the working arc surface.
[0007]
Therefore, an object of the present invention is to realize a bonded magnet for a motor that has a large output torque and a small cogging torque.
[0008]
[Means for solving the problems and operational effects of the invention]
The structure of the invention according to claim 1 for solving the above problems is the hollow cylindrical anisotropic rare earth bonded magnet, in a cross section perpendicular to the axis of the anisotropic rare earth bonded magnet, the main section of the magnetic pole cycle In the transition section where the magnetic vector on the magnet surface is oriented so as to face the normal direction, the surface magnetic flux density in the normal direction is equal, and the magnetic pole direction changes , the magnetic vector on the magnet surface is A bond magnet for motors characterized by being oriented so that it gradually inverts with increasing angle, and the distribution of the absolute value of the surface magnetic flux density in the normal direction gradually decreasing and gradually increasing with increasing electrical angle. is there.
A second aspect of the present invention is a motor having the bonded magnet for a motor according to the first aspect. As the anisotropic bonded magnet, it is effective to use an anisotropic rare earth bonded magnet, for example, an Nd—Fe—B based anisotropic rare earth bonded magnet.
[0009]
The present invention is characterized by the distribution of the surface magnetic flux density in the normal direction in the cross section perpendicular to the axis of the hollow cylindrical anisotropic bonded magnet. That is, when the periodic change of the magnetic pole is expressed as an electrical angle as a variable, in the electrical angle section that mainly contributes to the generation of torque, the magnetic vector on the magnet surface is in the normal direction in the cross section, and the magnetic vector The components in the normal direction, that is, the surface magnetic flux density in the normal direction are equal in magnitude. In the transition section in which the magnetic vector on the magnet surface changes, the magnetic vector on the magnet surface is gradually reversed as shown in FIG. 1A, and the normal direction is obtained as shown in FIG. The absolute value of the surface magnetic flux density gradually decreases and gradually increases as the electrical angle changes. As a result, in the electrical angle section that mainly contributes to torque generation, radial orientation is obtained, and therefore the output torque of the motor is large. On the other hand, in the transition section where the magnetic pole changes, the surface magnetic flux density in the normal direction is magnetized so as to gradually decrease and increase with respect to the transition of the electrical angle, so there is a sudden change in the surface magnetic flux density in the normal direction. There is no cogging torque. In this way, the motor characteristics can be improved.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on embodiments. In addition, this invention is not limited to the following embodiment.
(First embodiment)
FIG. 1 shows the configuration of a bonded magnet according to a specific embodiment of the present invention. As an example, the bond magnet 10 is an Nd-Fe-B anisotropic rare earth bond magnet. The bond magnet 10 has a hollow cylindrical shape having an outer peripheral thick portion 12 around the shaft 11. FIG. 1A is a cross-sectional view perpendicular to the shaft 11.
[0011]
FIG. 1 shows the case of dipole magnetization. A range B of about 135 degrees in electrical angle is an electrical angle section in which torque is mainly generated. Further, a range A of about 45 degrees in electrical angle is a transition section in which the magnetic pole changes. In the electrical angle section B, the surface magnetic flux density in the normal direction of the outer peripheral thick portion 12 is approximately equal in magnitude. In the electrical angle section A, the magnetic vector on the surface is smoothly reversed as the electrical angle changes as shown in the figure. The change characteristic of the surface magnetic flux density in the normal direction at an electrical angle of 2π (one cycle) is the characteristic shown in FIG. As shown in FIG. 1B, in the section B, the surface magnetic flux density in the normal direction is substantially constant, and in the section A, the surface magnetic flux density in the normal direction increases as the electrical angle θ increases. The absolute value gradually decreases and increases smoothly.
[0012]
The distribution of the surface magnetic flux density in the normal direction in the longitudinal sectional view parallel to the axis 11 of the bond magnet 10 is made uniform along the direction of the axis 11. However, it is not necessary to uniformly magnetize along the direction of the axis 11.
[0013]
On the other hand, as a comparative example, a bonded magnet having a radial orientation and an axial orientation was manufactured. The dimensions are the same as those of the bonded magnet of the above embodiment. As shown in FIG. 3, the surface magnetic flux density in the normal direction of the radially oriented and axially oriented bonded magnets changes as shown in the figure. That is, in a radially oriented bonded magnet, the surface magnetic flux density in the normal direction takes a substantially constant value in the range of almost all electrical angles, and the magnetic flux density in the normal direction changes suddenly at the change point of the magnetic pole. On the other hand, in the axially oriented bonded magnet, the surface magnetic flux density in the normal direction changes almost sinusoidally over one period of the electrical angle. Further, the distribution of the surface magnetic flux density in the normal direction of the bonded magnet oriented as in this embodiment is also shown in FIG.
[0014]
Then, a DC brush motor was manufactured using these bonded magnets as exciting magnets. The dimensions of the DC brush motor were all the same. The output torque and cogging torque of these motors were measured. The output of a DC brush motor using a radially oriented bonded magnet is 100%, the cogging torque is 100%, a motor using an axially oriented bonded magnet, and a motor of a bonded magnet using the orientation of this embodiment. The measured values of torque and cogging torque are shown in FIG.
[0015]
The cogging torque of the motor using the axially oriented bonded magnet is greatly reduced to 0.5%, but the output torque is also greatly reduced to 65%. In contrast, in the motor using the oriented bonded magnet of this example, the output torque was hardly reduced to 95%, and the cogging torque could be greatly reduced to 30%. In other words, the cogging torque could be reduced by 70% with only a 5% decrease in output torque. This is a very effective improvement for motor performance.
[0016]
Next, the orientation forming method for the bonded magnet will be described based on an example in which compression molding is performed. 4A is a plan sectional view of the device, and FIG. 4B is a longitudinal sectional view of the device. FIG. 5 is a detailed cross-sectional view of a portion including the cavity 35 of the mold 30. A cylindrical nib 33 is provided outside the cavity 35 of the mold 30, and guides 31 a and 31 b made of a columnar soft magnetic body having an arcuate cross section and extending in the axial direction are provided outside the nib 33. is set up. Inserts 34a and 34b made of a non-magnetic material are provided at positions where the guides 31a and 31b do not exist. A core 32 made of a soft magnetic material with a cavity 35 formed in the inner wall of the nib 33 is disposed through the nib 33. A bonded magnet material mainly composed of magnet powder and resin powder is supplied to a cylindrical cavity 35 formed between the outer wall of the core 32 and the inner wall of the nib 33. Pole pieces 41a and 41b are disposed on both sides of the mold 30, and magnetic field generating coils 42a and 42b are disposed so as to enclose the pole pieces 41a and 41b. The mold 30, the nib 33, and the inserts 34a and 34b are made of a nonmagnetic material such as stainless steel.
[0017]
In the above configuration, by applying a direct current to the coils 42a and 42b, an alignment magnetic field perpendicular to the axis of the core 32 is formed between the pole piece 41a and the pole piece 41b. The pole piece 41a, the pole piece 41b, the guides 31a and 31b, and the core 32 are portions in which the magnetic resistance in the magnetic circuit is extremely small, and the orientation magnetic field converges on the portions and flows. The magnetic permeability of the guides 31a and 31b is much larger than the magnetic permeability of the mold 30, the nib 33, and the inserts 34a and 34b. Therefore, as is clear from FIG. 2, the parallel orientation magnetic fields output from the pole pieces 41a and 41b converge on the guides 31a and 31b, and are applied to the core 32 in the direction perpendicular to the wall surfaces of the guides 31a and 31b. You will be guided towards. Since the guides 31a and 31b are not present in the low-permeability inserts 34a and 34b and the mold 30, the orientation magnetic field perpendicular to the outer peripheral surface of the core 32 in this portion is not provided with the high-permeability guide. , Almost weaken. At that time, in addition to the presence of the orientation magnetic field from the vicinity of the end facing the core of one guide to the vicinity of the end facing the core of the other guide, the core has a high permeability, so the magnetic resistance is small and the orientation magnetic field Passes near the core. Thereby, the orientation magnetic field is gradually reversed in the tangential direction in the cavity 35 corresponding to the transition section in which the direction of the magnetic pole of the magnet changes.
[0018]
In the above configuration, a section having an angle of about 135 degrees centered on the axis 11 of the arc-shaped guides 31a and 31b corresponds to the section B in FIG. Further, an angle where the guides 31a and 31b do not exist, that is, a section of about 45 degrees corresponds to the transition section A in FIG. With such a configuration, a surface magnetic flux density distribution in the normal direction as shown in FIGS. 1 and 3 can be obtained. Regarding the magnetic flux distribution of the cavity 35, the orientation magnetic field rotates in the transition section A, so that the absolute value of the surface magnetic flux density in the normal direction is smooth with respect to the transition of the electrical angle as shown in FIG. The characteristic gradually decreases and gradually increases. On the other hand, in the section B, the surface magnetic flux density is only in the normal direction where the absolute value is constant, and in the section B, the surface magnetic flux density can be made almost constant. With such a configuration, the surface magnetic flux density in the normal direction as shown in FIG.
[0019]
The above example is an example of a bond magnet that is dipolarly oriented, but when it is quadrupolarly oriented, it can be manufactured by an apparatus as shown in FIGS. That is, a ring 51 made of soft magnetism is provided in the cavity of the mold 30 and divided into four by inserts 52a, 52b, 52c and 52d made of a nonmagnetic material between the inside of the ring 51 and the nib 33. Permanent magnets 50a, 50b, 50c, and 50d are provided. These inserts are to avoid magnetic shorts between permanent magnets. Similar to the above, this arrangement gives a normal surface magnetic flux density in the transition region where the magnetic pole changes in the case of the quadrupole orientation, and the absolute value of the normal surface magnetic flux density becomes the transition of the electrical angle. On the other hand, it can be a characteristic of gradually decreasing and gradually increasing. With such a configuration, a large number of bonded magnets can be manufactured with one mold.
[0020]
The anisotropic rare earth bonded magnet 10 is also called a plastic magnet, and is typically formed by mixing Nd—Fe—B based magnet powder with a resin material. Mass production is finally possible in recent years by the present applicant. For example, this anisotropic rare earth bonded magnet 10 is manufactured by the manufacturing method of publication number p2001-7691A, registration number 2816668, registration number 3060104. This anisotropic rare earth bonded magnet can now be manufactured with a maximum energy product of 10 MGOe to 28 MGOe.
[0021]
In addition, materials such as ferrite, samarium-cobalt, and samarium-iron-nitrogen can be used as the magnet powder. Moreover, a well-known thing can be used for the particle size etc. of magnet powder. For example, the average particle diameter is about 1 μm for ferrite and about 1 to 100 μm for rare earth. A known material can be used for the resin. Polyamide-based synthetic resins such as nylon 12 and nylon 6, polyvinyl chloride, vinyl acetate copolymers thereof, vinyl-based synthetic resins such as MMA, PS, PPS, PE, and PP, or urethane, silicone Further, thermoplastic resins such as polycarbonate, PBT, PET, PEEK, CPE, hypalon, neoprene, SBR, and NBR, or thermosetting resins such as epoxy and phenol can be used. As the blending ratio of the magnet powder and the synthetic resin, known ones can be used. For example, it can be 40-90 vol%. In addition, plasticizers, lubricants, antioxidants, surface treatment agents and the like can be used depending on the purpose.
[0022]
The following conditions can be adopted as the manufacturing conditions. In the embodiment, a thermosetting resin is used, but a thermoplastic resin may be used. Although compression molding was used in the examples, other known molding methods can be used. In this example, in order to perform magnetic field orientation and compression molding at the same time, heating compression molding in a magnetic field was used. First, the pre-molding conditions were a mold temperature of 120 ° C., a molding pressure of 2.5 t / cm ² , a molding time of 15 sec, and an orientation magnetic field of 2T. The orientation method is as described above. The main molding conditions were a mold temperature of 150 ° C., a molding pressure of 8.0 t / cm ² , and a molding time of 10 sec. Magnetization was performed as follows. As a magnetized yoke, a soft magnetic core was arranged inside a cylindrical bonded magnet as in FIG. The magnetizing magnetic field acts as a parallel magnetic field in a direction perpendicular to the axis of the cylindrical bonded magnet, like the orientation magnetic field. As a magnetization method, a pulsed magnetic field was used. The magnetizing magnetic field is about 4T.
[0023]
Further, since the anisotropic rare earth bonded magnet 10 is manufactured by resin molding, it is formed into a precise hollow cylindrical shape. The anisotropic rare-earth bonded magnet 10 is easily magnetized symmetrically with high accuracy. Magnetic fields are generated accurately and symmetrically within the motor device.
[0024]
The above-described example is an example of an embodiment of the present invention, and various other modifications can be considered. For example, in the above embodiment, the anisotropic rare earth bonded magnet 10 is two-pole magnetized, but it may be more than two poles. For example, four poles, six poles, and eight poles may be used. If the number of magnetic poles is increased, the magnetic path length is shortened accordingly, so that the magnetic flux traversed by the armature coil increases.
[0025]
In the above embodiment, in the case of dipole magnetization, a range B of about 135 degrees in electrical angle is mainly set as an electrical angle section for generating torque, and a magnetic pole changes in range A of about 45 degrees in electrical angle. It is set as a transition section. However, the transition interval may be in the range of about 50 degrees, the range of about 30 degrees, the range of about 15 degrees, or the like. The range where torque is mainly generated is the remaining electrical angle section. Further, in the case of the 4-pole arrangement, the above-mentioned transition interval is ½, in the case of the 6-pole arrangement, the ３ is used, and in the case of the 8-pole arrangement, the ¼ is used.
[0026]
The bonded magnet of the present invention can be used for excitation of a DC brush motor. In this case, it can be used for both the stator and the rotor, and the motor can be used for a brushless motor, a synchronous motor, etc. in addition to a DC brush motor.
[Brief description of the drawings]
1A is a cross-sectional view showing a distribution of surface magnetic flux density of a bonded magnet according to a specific embodiment of the present invention, and FIG. 1B is a surface magnetic flux in a direction normal to an electrical angle. The characteristic view which showed the change characteristic of the density.
FIGS. 2A and 2B are a cross-sectional view and a detailed view showing an orientation magnetic field distribution during manufacture of the bonded magnet according to the embodiment.
FIG. 3 shows the orientation magnetic field distribution of the bonded magnet according to the embodiment of the present invention, the magnetic vector distribution of the magnetized magnet surface, and the surface magnetic flux density distribution characteristics in the normal direction of the magnet surface; Explanatory drawing demonstrated compared with the thing of axial orientation.
4A is a cross-sectional view of a bonded magnet orientation processing apparatus according to an embodiment of the present invention, and FIG. 4B is a cross-sectional view of the orientation processing apparatus.
FIG. 5 is a cross-sectional view showing a detailed configuration in a mold of the orientation processing apparatus.
6A is a transverse cross-sectional view of a quadrupole-oriented bonded magnet orientation processing apparatus according to another embodiment, and FIG. 6B is a longitudinal cross-sectional view of the orientation processing apparatus.
FIG. 7 is a cross-sectional view showing a detailed configuration of a mold of an orientation processing apparatus according to the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Anisotropic bonded magnet 11 ... Shaft 12 ... Thick part 30 of outer periphery ... Mold 31a, 31b ... Guide 32 ... Core 33 ... Nib 34a, 34b ... Insert 35 ... Cavity 41a, 41b ... Pole piece 42a, 42b ... Magnetic Generating coils 50a, 50b, 50c, 50d ... Permanent magnets

Claims (2)

In hollow cylindrical anisotropic rare earth bonded magnet,
In a cross section perpendicular to the axis of the anisotropic rare earth bonded magnet, in the main section of the magnetic pole period, the magnetic vector of the magnet surface is aligned so that the normal direction, the normal direction of the surface magnetic flux density magnitude In the transition zone where the magnetic pole direction changes , the magnetic vector on the magnet surface is oriented so that it gradually reverses with increasing electrical angle, and the absolute value of the surface magnetic flux density in the normal direction increases with increasing electrical angle. The bond magnet for motors is characterized in that the distribution is gradually reduced and gradually increased. A motor having the bonded magnet for a motor according to claim 1.

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