JP7845047B2 - Permanent magnet fields, rotating machines, linear motors - Google Patents

Description

This disclosure relates to permanent magnet fields, etc.

For example, a technique for suppressing thermal demagnetization of the permanent magnet field of electric motors such as rotating machines and linear motors is known (see Patent Document 1).

Patent Document 1 describes a rotor for an embedded magnet synchronous motor in which the shape of the magnetic flux short-circuit prevention holes is designed, and a metal plate is placed to attenuate the reverse polarity magnetic field through thermal loss, thereby reducing the eddy currents generated in the permanent magnets and suppressing the temperature rise of the permanent magnets.

Japanese Patent Publication No. 2014-87076

However, Patent Document 1 does not consider situations such as an overcurrent flowing through the armature coil, resulting in a rapid increase in the temperature of the permanent magnet. Therefore, in the configuration of Patent Document 1, the temperature of the permanent magnet may rise to a level that causes demagnetization. Thus, there is room for improvement in terms of suppressing thermal demagnetization of the permanent magnet field.

Therefore, in light of the above-mentioned challenges, the objective is to provide a technology that can more effectively suppress thermal demagnetization of permanent magnet fields.

To achieve the above objective, in one embodiment of this disclosure,
Permanent magnets and
The permanent magnet is provided adjacent to a heat-absorbing member ,
The heat-absorbing member includes a first material capable of absorbing heat from the permanent magnet due to the latent heat during the phase transition, and a second material having a greater thermal conductivity than the permanent magnet, in a manner that is mixed together.
The second material described above is a flat powder,
The aforementioned powders are arranged such that their flattened spreading direction intersects with the contact surface between the permanent magnet and the heat-absorbing member .
A permanent magnet field is provided.

In other embodiments of this disclosure,
Equipped with the aforementioned permanent magnet field,
A rotating machine is provided.

Furthermore, in yet another embodiment of this disclosure,
Equipped with the aforementioned permanent magnet field,
A linear motor is provided.

According to the above-described embodiment, thermal demagnetization of the permanent magnet field can be suppressed more effectively.

This is a cross-sectional view showing an example of a rotating machine.

The embodiments will be described below with reference to the drawings.

[Configuration of a rotating machine]
Referring to Figure 1, the configuration of the rotating machine 1 according to this embodiment will be described.

Figure 1 is a cross-sectional view showing an example of a rotating machine 1. Specifically, it is a cross-sectional view taken from a plane perpendicular to the rotation axis (shaft 30) of the rotating machine 1.

As shown in Figure 1, the rotating machine 1 includes a stator 10, a rotor 20, and a shaft 30.

For example, the rotating machine 1 is a synchronous machine driven by a three-phase alternating current supplied from an external source.

The stator 10 is positioned radially outward from the rotor 20, centered on the rotation axis of the rotating machine 1 (hereinafter simply referred to as "radial direction"). The stator 10 is fixed to the housing of the rotating machine 1 (not shown).

The stator 10 is the armature and includes an iron core 11 and a coil 12.

The iron core 11 functions as a magnetic path for the magnetic field generated by the armature current of the coil 12. The iron core 11 is formed from a soft magnetic material, such as electrical steel sheet or compacted magnetic core. The iron core 11 includes a back yoke portion 11A and a teeth portion 11B.

The back yoke portion 11A has a roughly cylindrical shape. The term "roughly" is used to allow for manufacturing tolerances, and the same intent applies hereafter.

The teeth portion 11B protrudes radially inward from the inner circumferential surface of the back yoke portion 11A. Multiple teeth portions 11B (six in this example) are provided and arranged at approximately equal intervals in the circumferential direction (hereinafter simply referred to as "circumferential direction") around the rotation axis of the rotating machine 1. Between adjacent teeth portions 11B, slots (hereinafter conveniently referred to as "coil slots") are formed for housing the coils 12.

Furthermore, the number of teeth 11B, that is, the number of coil slots formed between two adjacent teeth 11B, may be five or fewer, or seven or more. For example, if the rotating machine 1 is driven by three-phase AC, the number of teeth 11B (coil slots) may be 12 or 24.

The coil 12 is wound around the teeth 11B and carries the armature current. For example, as shown in Figure 1, the coil 12 is wound around each teeth 11B using a concentrated winding method. Alternatively, the coil 12 may be wound across multiple teeth 11B using a distributed winding method.

Electrical insulation is ensured between the iron core 11 and the coil 12 by the insulating portion.

For example, the insulating portion is an insulating film made of PET (Polyethylene Terephthalate) placed between the iron core 11 and the coil 12. Alternatively, the insulating portion may be an insulating coating formed on the conductor of the coil 12.

The rotor 20 is positioned radially inward relative to the stator 10. The rotor 20 faces the stator 10 radially, separated by a predetermined air gap AG.

The rotor 20 is a permanent magnet field and includes an iron core 21, a permanent magnet 22, a cavity 23, and a heat-absorbing member 24.

The iron core 21 functions as a magnetic path for the magnetic field generated by the armature current of the stator 10 (coil 12) and the magnetic field generated by the permanent magnet 22. The iron core 11 is formed from a soft magnetic material, such as electromagnetic steel sheet or powdered magnetic core.

The iron core 21 has a cylindrical shape that is approximately concentric with the rotation axis of the rotating machine 1. A through hole is provided at the radial center of the iron core 21, penetrating in the axial direction (hereinafter simply referred to as "axial direction") along the rotation axis of the rotating machine 1. The shaft 30 is fixed to the iron core 21 by being inserted through this through hole in the axial direction.

Furthermore, the iron core 21 is provided with slots (hereinafter referred to as "magnet slots" for convenience) for embedding permanent magnets 22.

The permanent magnet 22 generates a magnetic field that links with the stator 10, which acts as the armature. The permanent magnet 22 is, for example, a neodymium sintered magnet or a ferrite magnet.

Multiple permanent magnets 22 (four in this example) are provided and are arranged at approximately equal intervals in the circumferential direction at predetermined radial positions inside the outer circumferential surface of the iron core 21.

Furthermore, the number of permanent magnets 22 may be three or fewer, or five or more.

The permanent magnet 22 has an elongated, roughly rectangular shape, with one set of sides being significantly longer than the other set of sides when viewed in the axial direction. The longer sides are positioned approximately perpendicular to the radial direction at approximately the center. The permanent magnet 22 is magnetized such that its short sides have opposite polarities (north and south poles).

Note that the shape of the permanent magnet 22 in Figure 1 is just an example, and the permanent magnet 22 may have other shapes. For example, when viewed in the axial direction, the permanent magnet 22 may have a V-shape or U-shape that is convex inward in the radial direction. Furthermore, if the permanent magnet 22 has a V-shape when viewed in the axial direction, the V-shape may be realized by combining two elongated rectangular magnet members. In this case, the two magnet members are magnetically arranged in parallel. Also, if the permanent magnet 22 has a U-shape when viewed in the axial direction, the U-shape may be realized by a single magnet member forming a curved shape, or by combining multiple elongated rectangular magnet members. In this case, the multiple magnet members are magnetically arranged in parallel. Furthermore, multiple permanent magnets 22 may be arranged in series in the radial direction.

The permanent magnets 22 are arranged such that the magnetic poles on the faces of the permanent magnets 22 facing the stator 10 are different from those of other permanent magnets 22 adjacent to them in the circumferential direction. For example, if the south pole is magnetized on the face of one permanent magnet 22 facing the stator 10, then the north poles will be magnetized on the faces of other permanent magnets 22 adjacent to that permanent magnet 22 in the circumferential direction that face the stator 10.

The cavity 23 is positioned adjacent to both ends of the permanent magnet 22 in a direction perpendicular to the main magnetic flux. In this example, when viewed in the axial direction, the cavity 23 is positioned adjacent to both ends of the permanent magnet 22 in a direction along the longer side of the substantially rectangular shape.

The cavity 23 functions as a flux barrier that suppresses short circuits of magnetic flux at both ends in the direction perpendicular to the main magnetic flux of the permanent magnet 22. This prevents a decrease in the magnetic flux linked with the stator 10 due to a short circuit of the magnetic flux of the permanent magnet 22, thus preventing a decrease in the torque of the rotating machine 1.

Note that the shape of the cavity 23 in Figure 1 is just one example; any shape may be used for the cavity 23 as long as its function as a flux barrier is ensured.

In the iron core 21, the cavity 23 and the magnet slot are formed as a single, interconnected cavity. During the manufacturing process of the rotating machine 1, the permanent magnet 22 is inserted into the portion of the integrated cavity corresponding to the magnet slot and then fixed in place.

The heat-absorbing member 24 is positioned adjacent to the permanent magnet 22 and is capable of absorbing heat from the permanent magnet 22. This allows the heat-absorbing member 24 to absorb heat from the permanent magnet 22, suppressing the temperature rise of the permanent magnet 22. Therefore, even in situations where the temperature of the permanent magnet 22 rises rapidly and heat dissipation through the structural heat dissipation path alone is insufficient to avoid reaching a temperature range where thermal demagnetization occurs, the heat-absorbing member 24 can suppress thermal demagnetization of the permanent magnet 22. In particular, in situations where the temperature of a portion of the permanent magnet 22 rises rapidly, the time lag between the heat dissipation and the heat dissipation path becomes large, making thermal demagnetization more likely. The heat-absorbing member 24 effectively suppresses thermal demagnetization of the permanent magnet 22 in such cases.

The heat absorbed by the heat-absorbing member 24 is released to the permanent magnet 22 and the iron core 21, etc., as the temperature of the permanent magnet 22 decreases, and is then dissipated to the outside of the rotor 20 through the normal heat dissipation path.

For example, as shown in Figure 1, the heat-absorbing member 24 is made of a material with a magnetic permeability lower than that of the iron core 21, i.e., a non-magnetic material, and is placed in the cavity 23. Specifically, the heat-absorbing member 24 may be embedded in a portion of the cavity 23 adjacent to the permanent magnet 22. This allows the cavity 23 to function as both a flux barrier and a heat-absorbing component from the permanent magnet 22. Therefore, the heat-absorbing member 24 can be efficiently positioned while avoiding any impact on the magnetic circuit of the rotating machine 1.

Note that the shape of the heat-absorbing member 24 in Figure 1 (triangular in cross-section) is just one example. Any shape may be used for the heat-absorbing member 24, as long as it is effective in absorbing heat from the permanent magnet 22, for example, by maximizing the contact area with the permanent magnet 22.

For example, the heat-absorbing member 24 includes a material that is nonmagnetic and has a phase transition (phase change) temperature lower than the temperature range in which thermal demagnetization of the permanent magnet 22 occurs, and is capable of absorbing heat from the permanent magnet 22 by latent heat during the phase transition (hereinafter referred to as a "latent heat-absorbing material" for convenience). The latent heat-absorbing material is, for example, a vanadium oxide such as vanadium dioxide ( _VO2 ).

Vanadium dioxide has a phase transition temperature of around 67°C between its low-temperature insulating phase and high-temperature metallic phase. This allows for suppression of thermal demagnetization, even when using low-grade permanent magnets 22 that exhibit thermal demagnetization at temperatures around 70°C.

The heat-absorbing member 24 may include, in addition to the latent heat-absorbing material, a non-magnetic material with a higher thermal conductivity than the latent heat-absorbing material (hereinafter, for convenience, referred to as a "high thermal conductivity material"). The high thermal conductivity material is, for example, copper. This allows for faster heat transfer from the permanent magnet 22 to the heat-absorbing member 24.

For example, the heat-absorbing member 24 is a sintered body formed by sintering a compacted powder, which is created by mixing fine powders of both a latent heat-absorbing material and a high thermal conductivity material and then press-molding it. In this case, the latent heat-absorbing material may be a material with a thermal conductivity significantly lower than that of the high thermal conductivity material, such as the vanadium oxide mentioned above. While there is a positive correlation between thermal conductivity and electrical conductivity, and eddy currents can be generated in the high thermal conductivity material due to the leakage magnetic flux of the permanent magnet 22 linking the heat-absorbing member 24, the latent heat-absorbing material mixed with the high thermal conductivity material can suppress the generation of eddy currents. Therefore, heat can be transferred more quickly from the permanent magnet 22 to the heat-absorbing member 24 while suppressing heat generation in the heat-absorbing member 24 due to eddy currents.

The high thermal conductivity material may be arranged in the heat-absorbing member 24 such that it facilitates heat conduction in a direction intersecting the contact surface between the permanent magnet 22 and the heat-absorbing member 24. Specifically, the latent heat-absorbing material may be arranged in the heat-absorbing member 24 such that its thermal conductivity in a specific direction intersecting the contact surface between the permanent magnet 22 and the heat-absorbing member 24 is higher than its thermal conductivity in other directions. This allows for increasing the thermal conductivity in a specific direction from the permanent magnet 22 towards the interior of the heat-absorbing member 24 while minimizing the volume ratio of the high thermal conductivity material in the heat-absorbing member 24. Therefore, more heat can be absorbed from the permanent magnet 22 to the heat-absorbing member 24 more quickly. Furthermore, by limiting the volume ratio of the high thermal conductivity material, the generation of eddy currents in the high thermal conductivity material due to the leakage flux of the permanent magnet 22 linking the heat-absorbing member 24 can be suppressed. Therefore, heat can be transferred more quickly from the permanent magnet 22 to the heat-absorbing member 24 while suppressing heat generation in the heat-absorbing member 24 due to eddy currents.

For example, the heat-absorbing member 24 is a sintered body similar to the one described above, and the high thermal conductivity material is a flat powder with a small thickness and a flat shape that spreads laterally. This ensures that during press molding, the orientation of the high thermal conductivity material powder aligns with the direction corresponding to its small thickness, resulting in a configuration where the powders are aligned in a laterally spreading direction. Therefore, by configuring the heat-absorbing member 24 so that the direction in which the high thermal conductivity material powders are aligned intersects with the contact surface between the permanent magnet 22 and the heat-absorbing member 24, the thermal conductivity in a specific direction from the permanent magnet 22 towards the interior of the heat-absorbing member 24 can be increased.

Furthermore, the high thermal conductivity material may be formed into a sheet and attached to a component made of a latent heat-absorbing material, or positioned between components made of latent heat-absorbing materials. This allows the heat-absorbing component 24 to be configured such that the direction in which the sheet-like high thermal conductivity material spreads intersects with the contact surface between the permanent magnet 22 and the heat-absorbing component 24, thereby increasing the thermal conductivity in a specific direction from the permanent magnet 22 towards the interior of the heat-absorbing component 24.

The shaft 30 is attached integrally to the rotor 20 such that it penetrates the rotor 20 axially and both of its axial ends are exposed. The shaft 30 is rotatably supported by bearings at both of its axial ends within the housing of the rotating machine 1. Specifically, the shaft 30 may have a cylindrical shape extending axially and be fitted into the aforementioned through-hole provided in the iron core 21 so that both of its axial ends are exposed. This allows the rotor 20 to rotate integrally with the shaft 30.

[Other embodiments]
Next, other embodiments will be described.

The embodiments described above may be modified or altered as appropriate.

For example, in the above embodiment, the heat-absorbing member 24 may be provided adjacent only to one of the two ends of the permanent magnet 22 in the direction perpendicular to the main magnetic flux. For instance, if the rotation direction of the rotating machine 1 is limited to one direction, the heat-absorbing member 24 is provided only at the end of the permanent magnet 22 that is prone to thermal demagnetization in the direction perpendicular to the main magnetic flux.

Furthermore, in the embodiments and variations described above, the heat-absorbing members 24 may be provided adjacent to only some of the permanent magnets 22 among the multiple permanent magnets 22 of the rotor 20. For example, if some permanent magnets 22 that are highly likely to experience thermal demagnetization have been identified through experiments or computer simulations, the heat-absorbing members 24 may be provided only to those specific permanent magnets 22.

Furthermore, in the embodiments and variations thereof described above, the heat-absorbing member 24 may be embedded in the cavity 23 so as to fill the entire cavity 23.

Furthermore, in the embodiments and variations described above, the heat-absorbing member 24 may be provided in place of, or in addition to, the cavity 23, at another location adjacent to the permanent magnet 22. For example, the heat-absorbing member 24 may be provided adjacent to the axial end of the permanent magnet 22.

Furthermore, in the embodiments described above and examples of their modifications and changes, the heat-absorbing member 24 may include, in addition to or instead of the latent heat-absorbing material, a material with a specific heat sufficiently greater than that of the permanent magnet 22.

Furthermore, the technical concepts, including the configuration of the permanent magnet field (rotor 20) of the rotating machine 1 in the above-described embodiments and examples of their modifications and changes, may also be adopted for the permanent magnet field of a linear motor. In this case, the permanent magnet field may be either the movable element or the stator.

Furthermore, in the embodiments and variations/modifications described above, the permanent magnets in the permanent magnet field may employ a Halbach arrangement and include a main magnet that generates a magnetic flux linked with the armature, and an auxiliary magnet that strengthens the magnetic flux on the pole surface of the main magnet facing the armature. In this case, considering, for example, predictions of thermal demagnetization based on experiments or computer simulations, the heat-absorbing member may be placed adjacent to both the main magnet and the auxiliary magnet, or adjacent to only one of them.

[Effect]
Next, the operation of the permanent magnet field according to this embodiment will be explained.

Conventionally, efforts have been made to prevent permanent magnet field overheating due to eddy currents in the magnetic circuit, and to design the structure to allow heat generated in the permanent magnet and surrounding components to dissipate easily.

However, even with a properly designed magnetic circuit, if an unexpectedly large overcurrent flows through the armature coil, a rapid temperature rise in the permanent magnet can occur, potentially leading to thermal demagnetization. Furthermore, in situations where the temperature rises rapidly in a portion of the permanent magnet, structural design alone may not be sufficient to dissipate the heat, potentially resulting in thermal demagnetization. Neodymium magnets, in particular, exhibit high residual magnetic flux density and coercivity, making them suitable for creating powerful permanent magnet fields. However, their high temperature dependence of coercivity makes them highly susceptible to thermal demagnetization, and even when the temperature drops, the magnetic force may not recover.

In contrast, in this embodiment, the permanent magnet field comprises a permanent magnet and a heat-absorbing member. The permanent magnet field is, for example, a rotor 20. The permanent magnet is, for example, a permanent magnet 22. The heat-absorbing member is, for example, a heat-absorbing member 24. Specifically, the heat-absorbing member is provided adjacent to the permanent magnet.

This allows the heat from the permanent magnet to be absorbed by the adjacent heat-absorbing member, even if, for example, the temperature of the permanent magnet rises rapidly due to an overcurrent in the armature coil, or if the temperature of a part of the permanent magnet rises rapidly. Therefore, thermal demagnetization of the permanent magnet can be suppressed more effectively.

Furthermore, in this embodiment, the permanent magnet field may include an iron core in which the permanent magnets are embedded. The iron core is, for example, core 21. Specifically, the permanent magnets may generate a magnetic flux that links with the armature. The armature is, for example, the stator 10. The iron core may also have a cavity positioned adjacent to the end perpendicular to the main magnetic flux of the permanent magnets. The cavity is, for example, cavity 23. The heat-absorbing member may be placed in the cavity.

This allows for effective utilization of the cavity designed to suppress leakage flux from the permanent magnet, thereby suppressing thermal demagnetization of the permanent magnet.

Furthermore, in this embodiment, the heat-absorbing member may include a first material (latent heat-absorbing material) capable of absorbing heat from the permanent magnet due to the latent heat during the phase transition.

This allows for the suppression of thermal demagnetization of permanent magnets by using a first material having a phase transition temperature lower than the temperature range in which thermal demagnetization occurs.

Furthermore, in this embodiment, the heat-absorbing member may include a second material (high thermal conductivity material) having a higher thermal conductivity than the permanent magnet.

This allows heat to be absorbed more quickly from the permanent magnet to the heat-absorbing material.

Furthermore, in this embodiment, the second material may be arranged in the heat-absorbing member such that it facilitates heat conduction in a direction intersecting the contact surface between the permanent magnet and the heat-absorbing member.

This allows for selectively increasing the thermal conductivity in the direction from the permanent magnet to the heat-absorbing member without increasing the volume ratio of the second material in the heat-absorbing member. Therefore, the volume ratio of the first material can be maintained relatively high. Consequently, more heat can be absorbed from the permanent magnet to the heat-absorbing member more quickly.

Furthermore, in this embodiment, the second material may be a flattened powder. The powder of the second material may be mixed with the first material such that the direction perpendicular to its thickness intersects with the contact surface between the permanent magnet and the heat-absorbing member.

This allows the heat-absorbing material to absorb more heat from the permanent magnet more quickly.

Furthermore, in this embodiment, the first material may be vanadium oxide.

This suppresses the temperature rise above the phase transition temperature of vanadium oxide (approximately 67°C), and as a result, thermal demagnetization can be suppressed even when low-grade permanent magnets are used. Furthermore, by using vanadium oxide with a sufficiently lower electrical conductivity than the second material, the generation of eddy currents associated with the leakage flux of the permanent magnet linked to the heat-absorbing member can be suppressed.

While embodiments have been described in detail above, this disclosure is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist described in the claims.

1 Rotating machine 10 Stator 11 Iron core 11A Back yoke section 11B Teeth section 12 Coil 20 Rotor 21 Iron core 22 Permanent magnet 23 Cavity section 24 Heat absorption member 30 Shaft

Claims (5)

Permanent magnets and
The permanent magnet is provided adjacent to a heat-absorbing member ,
The heat-absorbing member includes a first material capable of absorbing heat from the permanent magnet due to the latent heat during the phase transition, and a second material having a greater thermal conductivity than the permanent magnet, in a manner that is mixed together.
The second material described above is a flat powder,
The aforementioned powders are arranged such that their flattened spreading direction intersects with the contact surface between the permanent magnet and the heat-absorbing member .
Permanent magnet field. The iron core in which the aforementioned permanent magnet is embedded is provided,
The permanent magnet generates a magnetic flux that links with the armature,
The iron core has a cavity that is positioned adjacent to the end in a direction perpendicular to the main magnetic flux of the permanent magnet,
The heat-absorbing member is arranged in the cavity.
The permanent magnet field according to claim 1. The first material is vanadium oxide.
The permanent magnet field according to claim 1 or 2 . A permanent magnet field according to any one of claims 1 to 3 ,
Rotating machine. A permanent magnet field according to any one of claims 1 to 4 ,
Linear motor.