JP2004056835A - Bonded magnet for motor and motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the cogging torque without dropping the output torque. <P>SOLUTION: A bonded magnet 10 is in the shape of a hollow cylinder which has a peripheral thick part 12 in its circumference, centering upon an axis 11. The range B of about 135° in electric angle is an electric angle section which generates torque mainly, and the range A of about 45° in the electric angle is a transition section where the direction of magnetic vector at the surface of a magnet changes. In the electric angle section B, it is magnetized so that the magnetic vector at the surface of the magnet may go roughly in the direction of the normal of the circumference of the peripheral thick part 12 and that the magnitude may be equal. Moreover, in the electric angle section A, it is magnetized as shown in Fig. so that the magnetic vector may have the tangent components of in circumferential direction and that the density of the surface magnetic flux in normal direction of the component of its normal may decrease or increase gradually accompanying the progress of the electric angle. The change properties of the surface magnetic flux density in the normal direction at the surface of the magnet at 2π(one cycle) in electric angle are ones shown in Fig. 2. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD 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]
As a permanent magnet for a motor, an anisotropic bonded magnet formed into a hollow cylindrical shape is known. This bonded magnet is oriented in a magnetic field by being formed in a state where a predetermined magnetic field distribution is generated. Patterns of the orientation magnetic field in a cross section perpendicular to the axis of the cylindrical bond magnet mainly include axial orientation, radial orientation, and polar orientation. Axial orientation is a method of orienting in a uniaxial direction in a cross section, and radial orientation is a method of orienting radially from the center of the cross section, that is, in a direction normal to the circumference.
[0003]
[Problems to be solved by the invention]
When a bonded magnet having such an orientation is used, for example, in a two-pole DC brush motor, the motor mainly exhibits the following characteristics. A motor using a bond magnet having an axial orientation has a small cogging torque but a small output torque because the surface magnetic flux density in the normal direction changes sinusoidally with a 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 substantially in a square wave with respect to a change in the electrical angle.
[0004]
As described above, the bond magnet using the conventional orientation method inevitably increases the cogging torque when trying to increase the output torque, and inevitably decreases the output torque when trying to reduce the cogging torque. There was a problem.
[0005]
Japanese Patent Application Laid-Open No. 5-144632 discloses that the distribution of the surface magnetic flux density along the axial direction is such that the end portion that does not contribute to the torque generation has a magnetic field oriented toward the center in the axial direction, thereby efficiently generating torque. It is suggested that Further, the publication proposes that in a magnetic field distribution in a cross section perpendicular to the axial direction, a magnetic field distribution generated basically in a normal direction is concentrated and oriented in a central region of a working arc surface. With such a magnetic field distribution, the magnetic field effectively contributes to torque generation.
[0006]
However, in this publication, the magnetic field distribution in a cross section perpendicular to the axis converges on the magnetic field in the center region of the acting arc, so that there is a problem that the cogged torque increases. In addition, the result of simulating the magnetic field distribution for the orientation method described in the same publication shows that the orientation distribution toward the center is not formed at the center of the working arc surface, and the normal direction is almost distributed over the entire circumference. It was a magnetic field distribution. Thus, in reality, it is considered that a magnetic field distribution oriented toward the center is not formed at the center of the working arc surface.
[0007]
Accordingly, an object of the present invention is to realize a bonded magnet for a motor having a large output torque and a small cogging torque.
[0008]
Means for Solving the Problems and Effects of the Invention
According to a first aspect of the present invention, there is provided a hollow cylindrical anisotropic bonded magnet having a surface magnetic flux density in a normal direction in a cross section perpendicular to an axis of the anisotropic bonded magnet. In the main section of the magnetic pole period, the magnitude of the surface magnetic flux density in the normal direction is equal, and in the transition section in which the direction of the magnetic pole changes, the absolute value of the surface magnetic flux density in the normal direction gradually decreases as the electrical angle increases. A bonded magnet for a motor, characterized in that the distribution is gradually increased.
According to a second aspect of the present invention, there is provided a motor having the motor bonded magnet 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 a cross section perpendicular to the axis of the hollow cylindrical anisotropic bonded magnet. That is, when the periodic change of the magnetic pole is represented by the electric angle as a variable, in the electric angle section mainly contributing to the generation of torque, the magnetic vector of the magnet surface in the cross section is oriented in the normal direction, and the magnetic vector The components in the normal direction, that is, the surface magnetic flux densities in the normal direction are equal in magnitude. Then, in the transition section in which the magnetic vector on the magnet surface changes, the magnetic vector on the magnet surface is gradually inverted as shown in FIG. 1A, and as shown in FIG. The absolute value of the surface magnetic flux density gradually decreases and increases with changes in the electrical angle. As a result, in the electrical angle section that mainly contributes to the torque generation, the radial orientation is obtained, and the output torque of the motor is large. On the other hand, in the transition section in which the magnetic pole changes, the surface magnetic flux density in the normal direction is magnetized so as to gradually decrease and increase with the change in the electrical angle. And the cogging torque is small. Thus, the motor characteristics can be improved.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on embodiments. Note that the present invention is not limited to the following embodiments.
(First embodiment)
FIG. 1 shows a configuration of a bonded magnet according to a specific embodiment of the present invention. For example, an Nd-Fe-B-based anisotropic rare-earth bonded magnet was used as the bonded magnet 10. The bonded magnet 10 has a hollow cylindrical shape having an outer peripheral thick portion 12 around a shaft 11. FIG. 1A is a cross-sectional view perpendicular to the axis 11.
[0011]
FIG. 1 shows a case of two-pole magnetization. A range B of about 135 degrees in electrical angle is an electrical angle section in which torque is mainly generated. 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 densities in the normal direction of the outer peripheral thick part 12 are substantially equal in magnitude. In the electrical angle section A, the magnetic vector on the surface is smoothly inverted with the change of the electrical angle 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 as shown in FIG. As shown in FIG. 1B, in the section B, the surface magnetic flux density in the normal direction is almost 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 smoothly decreases and increases gradually.
[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 bonded magnet 10 is made uniform along the direction of the axis 11. However, it is not necessary to magnetize uniformly along the direction of the axis 11.
[0013]
On the other hand, as a comparative example, a bonded magnet with radial orientation and axial orientation was manufactured. The dimensions are the same as the bonded magnet of the above embodiment. As shown in FIG. 3, the surface magnetic flux densities in the normal direction of the radially oriented and axially oriented bonded magnets change as shown in the figure. That is, in the radially oriented bond magnet, the surface magnetic flux density in the normal direction has a substantially constant value in the range of almost all electrical angles, and the magnetic flux density in the normal direction changes abruptly at the change point of the magnetic pole. On the other hand, in the bond magnet in the axial orientation, the surface magnetic flux density in the normal direction changes almost sinusoidally over one period of the electrical angle. FIG. 3 also shows the distribution of the surface magnetic flux density in the normal direction of the bonded magnet oriented as in this embodiment.
[0014]
Then, a DC brush motor was manufactured using these bond magnets as excitation magnets. The dimensions of the DC brush motor were all the same. The output torque and cogging torque of those motors were measured, respectively. Assuming that the output torque of the DC brush motor using the bond magnet of the radial orientation is 100% and the cogging torque is 100%, the output of the motor using the bond magnet of the axial orientation and the output of the motor of the bond magnet using the orientation of the present embodiment are used. FIG. 3 shows the measured values of the torque and the cogging torque.
[0015]
The cogging torque of the motor using the axially-oriented bonded magnet was greatly reduced to 0.5%, but the output torque was also significantly reduced to 65%. On the other hand, in the motor using the bonded magnet of the present embodiment, the cogging torque was able to be greatly reduced to 30% while the output torque was hardly reduced to 95%. That is, the cogging torque could be reduced by as much as 70% with only a decrease in the output torque of only 5%. This is a very significant improvement in motor performance.
[0016]
Next, a method of forming the orientation of 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 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 further outside the nib 33, guides 31 a and 31 b formed of a columnar soft magnetic material having an arc-shaped cross section and extending in the axial direction are provided. 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 cavity 32 is formed on the inner wall of the nib 33 and a core 32 made of a soft magnetic material is provided to penetrate the nib 33. To a cylindrical cavity 35 formed between the outer wall of the core 32 and the inner wall of the nib 33, a bonded magnet material mainly composed of magnet powder and resin powder is supplied. Pole pieces 41a and 41b are provided on both sides of the mold 30, and magnetic field generating coils 42a and 42b are provided so as to include the pole pieces 41a and 41b. The mold 30, the nib 33, and the inserts 34a and 34b are made of a non-magnetic material such as stainless steel.
[0017]
In the above configuration, by applying a direct current to the coils 42a and 42b, an orientation magnetic field perpendicular to the axis of the core 32 is formed between the pole pieces 41a and 41b. The pole piece 41a, the pole piece 41b, the guides 31a, 31b, and the core 32 are portions where the magnetic resistance in the magnetic circuit is extremely small, and the orienting magnetic field converges and flows into these portions. The magnetic permeability of the guides 31a, 31b is much larger than the magnetic permeability of the mold 30, the nib 33, and the inserts 34a, 34b. For this reason, 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 directed to the core 32 in a direction perpendicular to the wall surfaces of the guides 31a and 31b. You will be guided towards. Since there are no guides 31a and 31b in the inserts 34a and 34b and the mold 30 having low magnetic permeability, the orientation magnetic field perpendicular to the outer peripheral surface of the core 32 in this part is because there is no high magnetic permeability guide. , Almost weakened. At that time, in addition to the existence of the orientation magnetic field from near the end facing the core of one guide to the vicinity of the end facing the core of the other guide, since the core has high magnetic permeability, the magnetic resistance is small and the orientation magnetic field is small. Passes near the core. As a result, 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-described configuration, a section having an angle of 135 degrees around the axis 11 of the arc-shaped guides 31a and 31b corresponds to the section B in FIG. In addition, a section 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 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 characteristics gradually decrease and gradually increase. On the other hand, in the section B, the absolute value of the surface magnetic flux density is only in the normal direction, and the surface magnetic flux density can be made substantially constant in the section B. 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 bonded magnet with two poles, but in the case of quadrupole orientation, it can be manufactured by an apparatus as shown in FIGS. That is, a ring 51 made of soft magnetic material is provided in the cavity of the mold 30 and is divided into four parts by inserts 52a, 52b, 52c, and 52d made of a nonmagnetic material between the inside of the ring 51 and the nib 33. Provided permanent magnets 50a, 50b, 50c, 50d. These inserts are to avoid a magnetic short circuit between the permanent magnets. With this arrangement, in the same manner as described above, in the transition region where the magnetic pole changes in the case of quadrupole orientation, the surface magnetic flux density in the normal direction is given, and the absolute value of the surface magnetic flux density in the normal direction becomes the transition of the electrical angle. On the other hand, it is possible to have a characteristic of smoothly decreasing and increasing gradually. 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. The present applicant has finally made mass production possible in recent years. For example, the anisotropic rare earth bonded magnet 10 is manufactured by the manufacturing method of publication number p2001-7691A, registration number 2816668, and registration number 3060104. This anisotropic rare-earth bonded magnet having a maximum energy product of 10 MGOe to 28 MGOe can be manufactured at present.
[0021]
In addition, ferrite, samarium-cobalt, and samarium-iron-nitrogen materials can be used as the magnet powder. In addition, a known particle size or the like of the magnet powder can be used. For example, the average particle diameter is about 1 μm for a ferrite type, and about 1 to 100 μm for a rare earth type. As the resin, a known material can be used. Polyamide-based synthetic resin such as nylon 12, nylon 6, etc., polyvinyl chloride, vinyl acetate copolymer thereof, homo- or copolymerized vinyl-based synthetic resin such as MMA, PS, PPS, PE, PP, urethane, silicone And thermoplastic resins such as polycarbonate, PBT, PET, PEEK, CPE, Hypalon, neoprene, SBR and NBR, or thermosetting resins such as epoxy-based and phenol-based resins. Known mixing ratios of the magnet powder and the synthetic resin can be used. For example, it can be 40 to 90 vol%. In addition, a plasticizer, a lubricant, an antioxidant, a surface treatment agent and the like can be used according to the purpose.
[0022]
The following conditions can be adopted as the manufacturing conditions. Although a thermosetting resin is used in the embodiment, a thermoplastic resin may be used. In the embodiment, compression molding is used, but other known molding methods can be used. In this example, in order to simultaneously perform the magnetic field orientation and the compression molding, the heat compression molding in a magnetic field was used. First, the preforming conditions were as follows: the mold temperature was 120 ° C., the molding pressure was 2.5 t / cm ² , the molding time was 15 sec, and the orientation magnetic field was 2T. The orientation is as described above. The molding conditions were as follows: the mold temperature was 150 ° C., the molding pressure was 8.0 t / cm ² , and the molding time was 10 seconds. Magnetization was performed as follows. As a magnetization yoke, a soft magnetic core was arranged inside a cylindrical bond magnet as in FIG. The magnetizing magnetic field acts as a parallel magnetic field in a direction perpendicular to the axis of the cylindrical bond magnet similarly to the orientation magnetic field. The magnetizing method used a pulse magnetic field. 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 in a hollow cylindrical shape with high accuracy. Then, the anisotropic rare earth bonded magnet 10 is easily and accurately and symmetrically magnetized. A magnetic field is precisely and symmetrically generated inside the motor device.
[0024]
The above embodiment is an example of the embodiment of the present invention, and various other modifications are possible. For example, in the above embodiment, the anisotropic rare-earth bonded magnet 10 is magnetized in two poles, but may be larger than two poles. For example, four poles, six poles, or eight poles may be used. As the number of magnetic poles is increased, the magnetic path length is shortened accordingly, so that the magnetic flux traversing the armature coil increases.
[0025]
In the above embodiment, in the case of two-pole magnetization, a range B of about 135 degrees in electrical angle is defined as an electrical angle section in which torque is mainly generated, and a range A of about 45 degrees in electrical angle changes the magnetic pole. Transition section. However, the transition section may use a range of about 50 degrees, a range of about 30 degrees, a range of about 15 degrees, and the like. The range in which torque is mainly generated is the remaining electrical angle section. In the case of the 4-pole arrangement, the above-mentioned 1/2 is used for the transition section, in the case of the 6-pole arrangement, the above-mentioned 1/3 is used, and in the case of the 8-pole arrangement, the above-mentioned 1/4 is used.
[0026]
The bonded magnet of the present invention can be used for exciting a DC brush motor. In this case, the motor can be used for both the stator and the rotor, and the motor can be used for a DC brush motor, a brushless motor, a synchronous motor, and the like.
[Brief description of the drawings]
FIG. 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 normal direction with respect to an electrical angle. FIG. 4 is a characteristic diagram showing a density change characteristic.
FIGS. 2A and 2B are a cross-sectional view and a detailed view showing an orientation magnetic field distribution at the time of manufacturing the bonded magnet according to the embodiment. FIGS.
FIG. 3 shows the orientation magnetic field distribution, the magnetic vector distribution on the magnetized magnet surface, and the surface magnetic flux density distribution characteristic in the normal direction of the magnet surface according to the embodiment of the present invention. FIG. 4 is an explanatory diagram illustrating an axial alignment.
FIG. 4A is a cross-sectional view of an apparatus for orienting bonded magnets according to an embodiment of the present invention, and FIG. 4B is a cross-sectional view of the apparatus for orienting bonded magnets.
FIG. 5 is a cross-sectional view showing a detailed configuration inside a mold of the orientation processing apparatus.
6A is a cross-sectional view of an alignment processing apparatus for a quadrupole bonded magnet according to another embodiment, and FIG. 6B is a longitudinal sectional view of the alignment processing apparatus.
FIG. 7 is a cross-sectional view showing a detailed configuration of a mold of the alignment processing apparatus according to the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Anisotropic bond magnet 11 ... Shaft 12 ... Outer peripheral thick part 30 ... Die 31a, 31b ... Guide 32 ... Core 33 ... Nibs 34a, 34b ... Insert 35 ... Cavities 41a, 41b ... Pole pieces 42a, 42b ... Magnetic Generating coils 50a, 50b, 50c, 50d: permanent magnets

Claims (2)

In a hollow cylindrical anisotropic bonded magnet,
The surface magnetic flux density in a cross section perpendicular to the axis of the anisotropic bonded magnet is equal in the normal direction in the main section of the magnetic pole period, and normal in the transition section in which the direction of the magnetic pole changes. A bonded magnet for a motor, characterized in that the absolute value of the surface magnetic flux density in the direction has a distribution that gradually decreases and increases with an increase in the electrical angle. A motor having the bonded magnet for a motor according to claim 1.

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