JP2003319585A - Permanent magnet motor and method for forming anisotropic pole magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a permanent magnet motor which can suppress the increase in a cogging torque without eliminating the drop in output characteristics when anisotropic pole magnets are used. <P>SOLUTION: The magnet 21 for constituting the rotor 24 of the permanent magnet motor is formed of a magnetic field integral mold in the state that a frame 9 is inserted into molds 14 to 16 or the like. In this case, the radial thickness L2 of the pole end of the magnet 21 is formed to become a ratio of 86.7% with respect to the size L1 of a pole central part. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polar anisotropic magnet having an even number of magnetic poles only on the gap side facing a stator, and a yoke arranged on the side opposite to the gap side and made of a soft magnetic material. And a method for forming a polar anisotropic magnet used in the motor.

[0002]

4 and 5 show an example of the structure of an outer rotor type motor using polar anisotropic magnets. FIG. 4 shows a rotor 1 and FIG. 5 shows a stator 2. It is a thing. First, in FIG. 5, the stator core 3
Includes a yoke portion 4 having an annular shape, and a large number of teeth 5 provided on the outer peripheral portion of the yoke portion 4 so as to radially project. In this case, the stator core 3 is formed in an annular shape by connecting a plurality of divided cores (not shown) divided in the circumferential direction in the circumferential direction. Each of the split cores is formed by laminating a large number of steel plates made of silicon steel plates punched into a predetermined shape.

On the outer surfaces of the yoke portion 4 and each tooth 5 of the stator core 3, a covering member 6 made of an insulating resin (for example, polybutylene resin) is provided by molding so as to cover almost all of them. The covering member 6 includes a plurality of mounting portions 7 which are located on the inner peripheral side of the yoke portion 4.
Are provided integrally. The attachment portion 7 is used when attaching the stator core 3 to a mechanical portion (not shown) of a washing machine, which is an attachment target. And
A coil 8 is wound around each tooth 5 to form the stator 2.

On the other hand, the rotor 1 shown in FIG. 4 is composed of a frame (rotor yoke) 9 and a magnet 10. The frame 9 is formed into a flat, so-called bottomed cylindrical cup shape by pressing a magnetic material such as a steel plate, and has a shaft support mounting hole 11 in the center.
In addition, in FIG. 4, the frame 9 is shown in a state of being turned upside down. An annular portion 12 is formed around the frame 9, and a plurality of ventilation holes 13 formed by cutting and raising are radially arranged in an intermediate portion between the annular portion 12 and the shaft support mounting hole 11. There is.

A shaft (not shown) is mounted in the shaft support mounting hole 11 of the rotor 1 via the shaft support, and the shaft rotates via a bearing (not shown). Freely supported.

The magnet 10 is a so-called plastic magnet, and is made of a magnetic resin in which magnetic powder is mixed with a ferrite nylon binder. The magnet 10 is arranged on the inner peripheral side of the annular portion 12 of the frame 9 and faces the stator 2.

Further, in this case, the magnet 10 has anisotropy by being oriented in a magnetic field such that the directionality of magnetism is a predetermined direction at the time of molding. That is, as shown in FIG. 6, polar anisotropy is provided by orienting the magnetic field in the magnet 10 so that only the magnetic poles are permeable.

In FIG. 6, the magnet 10 is attached to the molds 14 and 1.
Mold 15 that is also an oriented magnet at the same time as molding by 5
The state in which magnetic field orientation is performed by the collecting magnets 16a and 16b arranged on both sides thereof is shown by cutting out one magnetic pole. By having polar anisotropy like this,
The magnetic force of the magnetic poles can be increased as compared with those having other anisotropy such as isotropicity, axial anisotropy, and radial anisotropy, and the characteristics of the motor can be improved correspondingly, and the magnet 10 The thickness can also be reduced.

Further, the annular portion 12 of the frame 9 does not need to have a role of forming a magnetic path, and needs only a mechanical role of supporting the magnet 10. Therefore, the thickness of the annular portion 12 may be any thickness as long as mechanical strength is ensured, and it is possible to reduce the weight by forming the annular portion 12 thinner than before.

The magnet 10 of the rotor 1 is magnetized to have 48 poles, and the stator core 3 has 36 slot portions on its outer peripheral portion. The coil 8 is wound around the stator core 3 by the three-phase direct winding method.

In the motor having such a structure, the radial thickness of the magnet 10 is formed to be substantially uniform as shown in FIG. For example, if the above-mentioned dimension is set to 1/2 of the generally economical magnetic pole pitch, there is a portion in which the magnetization direction of the magnetic pole portion should be inclined in the radial direction (normal direction) where it should originally be in the circumferential direction. The demagnetization resistance against the armature reaction that occurs during rotation may be reduced. Further, since the magnetic flux density distribution in the air gap becomes trapezoidal, a large cogging torque or torque ripple occurs. Furthermore, as shown in FIG. 7, when the magnet 10 is integrally molded with the frame 9, as shown in FIG. Since the magnetization direction is more concentrated in the radial direction than in the case of not being integrally molded as shown in (1), the magnetic flux density distribution tends to be remarkably trapezoidal.

This problem can be largely avoided by making the wall thickness of the magnet 10 equal to the magnetic pole pitch, but even if the above size is set to 1/2 or more of the magnetic pole pitch, the total magnetic flux amount hardly increases. However, it does not contribute to the improvement of the output of the motor, and the demerit that the weight increases and the cost increases becomes large.

In addition, the extremely anisotropic magnet 10 is
There is a problem that permanent demagnetization is likely to occur because the internal magnetic path length at the magnetic pole end portion becomes short. When permanent demagnetization occurs in the magnet 10, the output characteristics initially set in the motor deteriorate, which is not preferable.

The present invention has been made in view of the above circumstances, and an object thereof is to suppress an increase in cogging torque without reducing output characteristics when a polar anisotropic magnet is used. (EN) Provided is a permanent magnet type motor capable of achieving the above, and a method for forming a polar anisotropic magnet used for the motor.

[0015]

In order to achieve the above object, a permanent magnet type motor according to claim 1 has a substantially annular shape or a segmented shape forming a part of an annular shape, and is on the side of the air gap facing the stator. A polar anisotropic magnet having an even number of magnetic poles, and a yoke arranged on the side opposite to the air gap side and made of a soft magnetic material, It is characterized in that the thickness in the radial direction at the magnetic pole end portion is formed so as to have a ratio of 85% to 88% with respect to the dimension of the magnetic pole center portion.

That is, the magnitude of the air gap magnetic flux density in the motor is proportional to the magnetic path length in the magnet if the air gap length is constant.
Therefore, if the radial thickness at the magnetic pole end of the polar anisotropic magnet is made shorter than the size at the magnetic pole center,
Since the magnetic path length in the magnet at the magnetic pole end portion is also shortened and the air gap magnetic flux density is reduced, the magnetic flux density distributions can be approximated to have a sinusoidal waveform. Therefore, generation of cogging torque can be suppressed. Further, in the conventional configuration, there is no portion where the internal magnetic path length is shortened at the magnetic pole end, so permanent demagnetization does not occur at that portion, and it is possible to suppress the characteristic fluctuation of the motor over time.

By the way, as described above, if the wall thickness of the magnetic pole end of the polar anisotropic magnet is shortened with respect to the size of the magnetic pole center, the amount of magnetic flux is reduced accordingly, so that the output of the motor is reduced. Will be invited. Therefore, according to the result of the experiment conducted by the inventor of the present invention, if the thickness of the magnetic pole end portion is formed to be 85% to 88% of the central portion of the magnetic pole, the motor It has been found that the balance between the induced voltage generated during rotation and the cogging torque is optimum.

In this case, as described in claim 2, it is preferable that the polar anisotropic magnet is formed by magnetic field integral molding with the yoke inserted in a mold. That is, as described above, if a magnet having a uniform wall thickness is integrally formed with the yoke to make it anisotropic, the direction of magnetization is concentrated in the radial direction and the air gap magnetic flux density distribution becomes closer to a trapezoidal wave shape. I will end up. Therefore, if the polar anisotropic magnet is formed integrally with the yoke and is made anisotropic, the air gap magnetic flux density distribution can be improved more effectively.

Further, as described in claim 3, it is preferable that the surface of the polar anisotropic magnet located on the air gap side is formed so as to form a convex cylindrical surface for each magnetic pole. That is, by making the surface shape from the magnetic pole center portion to the magnetic pole end portion a cylindrical surface shape, the air gap magnetic flux density distribution changes gently, and the distribution state can be made closer to a sine wave shape.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS. The same parts as those in FIGS. 4 to 7 are designated by the same reference numerals and the description thereof will be omitted. Only different parts will be described below. FIG. 2 is a view corresponding to FIG. 4, and FIG. 1A is a perspective view showing a part of the frame 9 and the magnet (polar anisotropic magnet) 21 of this embodiment, and FIG.
Is a view corresponding to FIG. 7.

That is, the molded shape of the magnet 21 is a cylindrical surface in which the magnetic pole surface 22 facing the stator (stator) 2 is convex toward the gap side. The magnetic pole surface 22 becomes a magnetic pole by being magnetized later, and has a convex shape toward the center of the magnetic pole. In order to form the magnetic pole surface 22 in such a shape, a mold 23 made of a non-magnetic material is arranged on the inner peripheral side.

As shown in FIG. 1B, if the wall thickness of the magnet 21 at the center of the magnetic pole is L1 and the wall thickness at the end of the magnetic pole is L2, then L2 is 86.7% of L1 ( The wall thickness ratio) is set. Other configurations are the same as the conventional one, and the above constitutes the rotor 24.

Next, the operation of this embodiment will be described with reference to FIG. The air gap magnetic flux density in the motor is
It is determined by the equation (1). (Air gap magnetic flux density) ∝ (Magnet magnetic path length) / {(Magnet magnetic path length) + (Gap length) · 2} (1) That is, the magnitude of the air gap magnetic flux density in the motor is the air gap length. Is constant, it is proportional to the magnetic path length in the magnet. If the magnet 21 is formed integrally with the frame 9 and is made extremely anisotropic, the magnetizing direction is concentrated in the radial direction, so that the air gap magnetic flux density distribution becomes closer to a trapezoidal wave shape.

Therefore, as in this embodiment, the magnet 2
When the radial thickness L2 at the magnetic pole end portion of No. 1 is made smaller than the dimension L1 at the magnetic pole center portion, the state of being extremely anisotropic compared to the conventional magnet 10 is basically the same. Since the magnetic path length in the magnet at the magnetic pole end portion is shortened and the air gap magnetic flux density is reduced, the magnetic flux density distribution can be approximated to have a sinusoidal waveform. Therefore, generation of cogging torque can be suppressed.

The wall thickness ratio, which is the ratio of the dimensions L1 and L2, is defined by the equation (2): (wall thickness ratio) = (L2 / L1) × 100 [%] (2) If the wall thickness ratio is made smaller, the magnetic flux distribution density will be closer to a sinusoidal shape, which is suitable from the viewpoint of suppressing the generation of cogging torque. However, on the other hand, the amount of magnetic flux is reduced by that amount, resulting in a reduction in motor output. Further, when the magnet 21 is formed by integral molding, if the wall thickness ratio becomes too small, so-called "melt flow" deteriorates, leading to deterioration in moldability. From the above, it is necessary to set the thickness ratio to an optimum value in consideration of the trade-off between the output characteristic of the motor and the cogging torque and the formability.

Therefore, the inventor of the present invention has made the magnet 2
A radial anisotropic magnet formed of the same material as that of No. 1 is formed in the same shape as a motor for a washing machine disclosed in, for example, Japanese Patent No. 2905119 (basically, as shown in FIGS. Based on the case where the cogging torque was minimized (the same as that shown), the magnets of the same type as the magnet 21 were made to have the same shape, and the wall thickness ratio was changed for comparison. The result is shown in Figure 4.
Shown in.

The horizontal axis of FIG. 3 is the wall thickness ratio of the magnet, and the vertical axis is the relative value based on the induced voltage and cogging torque generated in the permanent magnet type motor constructed using the magnet. It is shown. That is, 10 on the vertical axis
0% corresponds to the level of the induced voltage and the cogging torque when the cogging torque of the motor using the radial anisotropic magnet is minimized.

In FIG. 3, it is desirable that the induced voltage exceeds 100% in terms of maximizing the output characteristics of the motor or downsizing the motor with the same output characteristics. Further, since the cogging torque causes noise and vibration, it is desirable that the cogging torque be less than 100%. It can be seen that the wall thickness ratio that satisfies these contradictory conditions at the same time is in the range of about 85% to 88%. In this embodiment, the induced voltage is exactly 1 based on FIG.
A wall thickness ratio of 86.7%, which is 00%, was selected.

As described above, according to the present embodiment, the magnet 21 constituting the rotor 24 of the permanent magnet type motor is formed by magnetic field integral molding with the frame 9 inserted in the molds 14 to 16 and the like. At that time, the radial thickness dimension L2 at the magnetic pole end portion of the magnet 21 was formed so as to be 86.7% of the dimension L1 at the magnetic pole center portion.

That is, if the dimension L2 is made shorter than the dimension L1, the magnetic path length in the magnet at the magnetic pole end is also shortened and the air gap magnetic flux density is reduced, so that the magnetic flux density distribution becomes sinusoidal. You can get closer. Therefore, it is possible to suppress the generation of cogging torque when the motor rotates. Further, in the conventional configuration, there is no portion where the internal magnetic path length is shortened at the magnetic pole end, so permanent demagnetization does not occur at that portion, and it is possible to suppress the characteristic fluctuation of the motor over time.

By adjusting the wall thickness ratio to 86.7%, the balance between the induced voltage generated when the motor rotates and the cogging torque can be optimized, so that the conventional radial anisotropic magnet is used. The output ratio equivalent to that of the conventional motor can be obtained, the generation ratio of the cogging torque can be reduced, and the motor can be driven with low vibration and low noise.

Further, in the structure of the present embodiment, there is no portion where the internal magnetic path length is shortened at the magnetic pole end portion of the conventional structure, so that permanent demagnetization does not occur at that portion, and the time-lapse of the motor is eliminated. It is also possible to suppress characteristic variations.

According to this embodiment, the magnet 21
Since the magnetic pole surface 22 is formed so as to form a convex cylindrical surface for each magnetic pole, it is possible to gently change the air gap magnetic flux density distribution and bring the distribution state closer to a sinusoidal shape.
Therefore, generation of cogging torque can be further suppressed.

The present invention is not limited to the embodiments described above and shown in the drawings, but the following modifications or expansions are possible. The wall thickness ratio may be set in the range of 85% to 88%. The polar anisotropic magnet is not limited to the one formed in an integral ring shape, and may be, for example, a segment shape divided at a plurality of locations. In that case, it is preferable to divide the magnetic poles at the central portion because the magnetic path extending between the magnetic poles is hardly divided. In addition, the polar anisotropic magnet does not necessarily have to be formed by magnetic field integral molding with the yoke inserted in the mold. Only the polar anisotropic magnet is separately molded and polar anisotropic, and then combined with the yoke. It may be configured.
It may be applied to an inner rotor type permanent magnet type motor.

According to the permanent magnet type motor of the present invention, the radial thickness of the magnetic pole end of the polar anisotropic magnet is 85% to 88% of the size of the magnetic pole center. Since it is formed as described above, the air gap magnetic flux density distribution can be approximated so as to have a sine wave shape, and generation of cogging torque can be suppressed while maintaining the output characteristics of the motor.

[Brief description of drawings]

1 is an embodiment of the present invention, (a) is a perspective view showing a frame of a permanent magnet type motor and a part of a magnet;
(B) shows a state in which a magnet is molded from a mold and at the same time magnetic field orientation is performed by cutting out one magnetic pole.

FIG. 2 is a perspective view showing a configuration example of a rotor in an outer rotor type motor using polar anisotropic magnets.

FIG. 3 is a diagram showing a magnet wall thickness ratio on the horizontal axis and a relative value on the basis of the induced voltage and cogging torque generated in the permanent magnet motor on the vertical axis.

FIG. 4 is a view corresponding to FIG. 2 showing a conventional technique.

FIG. 5 is a perspective view showing a configuration of a stator.

FIG. 6 is a view corresponding to FIG. 1 (b) (however, when the frame is not integrally molded)

FIG. 7 is a view equivalent to FIG.

[Explanation of symbols]

2 is a stator (stator), 9 is a frame (yoke), 1
4, 15, 16, and 23 are molds, 21 is a magnet (polar anisotropic magnet), and 24 is a rotor.

Claims (6)

[Claims] 1. A polar anisotropic magnet having a substantially annular shape or a segment shape forming a part of an annular shape, having an even number of magnetic poles only on the gap side facing the stator, and arranged on the side opposite to the gap side. And a yoke made of a soft magnetic material, the permanent magnet type motor having a radial thickness at a magnetic pole end portion of the polar anisotropic magnet with respect to a dimension at a magnetic pole center portion. A permanent magnet motor, characterized in that it is formed to have a ratio of 85% to 88%. 2. The permanent magnet type motor according to claim 1, wherein the polar anisotropic magnet is formed by magnetic field integral molding with the yoke inserted in a mold. 3. The surface of the polar anisotropic magnet located on the gap side is
The permanent magnet type motor according to claim 1 or 2, wherein each magnetic pole is formed so as to form a convex cylindrical surface. 4. A polar anisotropic magnet having an approximately annular shape or a segmented shape forming a part of an annular shape and having an even number of magnetic poles only on the air gap side facing the stator, and arranged on the opposite side to the air gap side. And a yoke formed of a soft magnetic material to form a polar anisotropic magnet of a permanent magnet type motor, the radial thickness dimension of a magnetic pole end of the polar anisotropic magnet. Is formed so as to have a ratio of 85% to 88% with respect to the size of the central portion of the magnetic pole. 5. The method for forming a polar anisotropic magnet according to claim 4, wherein the polar anisotropic magnet is formed by magnetic field integral molding with the yoke inserted in a mold. 6. The surface of the polar anisotropic magnet located on the void side is
The method for forming a polar anisotropic magnet according to claim 4 or 5, wherein each magnetic pole is formed so as to form a convex cylindrical surface.