Electric machine

Abstract

To provide a motor comprising a structure for preventing breakage of a magnet or a magnet holding part even if the magnet holding part is thermally shrunk.SOLUTION: An electric machine comprises: a rotor core 21; a plurality of magnets 22 disposed on a surface of the rotor core 21 in a thrust generation direction (S direction); and a magnet holding part 23 disposed between the magnets 22 and 22. The magnet holding part 23 includes: a protrusion 23a extending from the rotor core 21 through a gap between the magnets 22 and 22 in a radial direction (T direction) which is a direction orthogonal with the thrust generation direction (S direction); and a claw 23b extending from a tip end of the protrusion 23a to a position where the claw is superposed with the magnet 22. A compression layer 24 whose elasticity modulus is lower than that of the magnet 22 is provided at a position where the compression layer is compressed in a case where the magnet holding part 23 is thermally shrunk.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric machine having a structure in which magnets are arranged on the surface of a core, such as an SPM (Surface Permanent Magnet) motor. [Background technology]

[0002] 2. Description of the Related Art Conventionally, SPM motors are known as electric machines having magnets arranged on the surface (for example, Patent Document 1).

[0003] An SPM motor consists of a rotor with magnets and a stator. The rotor is constructed by attaching a rotor core to a shaft and arranging magnets on the surface of the rotor core. The stator is arranged on the outer periphery of the rotor and has teeth extending toward the rotor and coils wound around the teeth.

[0004] This SPM motor has a magnet holder called an inset type to hold the magnets on the surface. This magnet holder is composed of a protrusion that protrudes from the rotor core in the outer diameter direction between the magnets, and a claw that extends from the tip of the protrusion in a direction overlapping with the magnet, and the magnet holder restricts the circumferential and radial movement of the magnets during rotation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2020-78177 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when this motor is used in a low-temperature environment, the difference in the linear expansion coefficient between the magnet holding part and the magnet causes the magnet holding part to compress the magnet in the radial direction due to the difference in thermal contraction, generating thermal stress in the magnet and magnet holding part, which may damage the magnet, the magnet holding part, or both. The thermal stress increases the lower the environmental temperature and the larger the magnet.

[0007] This problem is not limited to SPM motors, but is similar to that of linear motors, etc., so long as the motor has a structure in which magnets are held by a magnet holder.

[0008] The present invention has been made with an eye on these problems, and aims to realize an electric machine with a new structure that can prevent damage to the magnet or the magnet holding part even if the magnet holding part undergoes thermal contraction. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention takes the following measures.

[0010] That is, the electric machine of the present invention comprises a core, a plurality of magnets arranged on the surface of the core along the thrust generation direction, and a magnet holding portion arranged between the magnets, wherein the magnet holding portion includes a protrusion extending from the core through between the magnets in a direction perpendicular to the thrust generation direction, and a claw portion extending from the tip of the protrusion to a position overlapping with the magnet, and is characterized in that a compression layer having a lower elastic modulus than the magnet is provided at a position where it is compressed when the magnet holding portion is thermally contracted.

[0011] With this structure, when the magnet holding part thermally shrinks, the compression layer compresses and deforms, reducing the stress generated in the magnet holding part, effectively preventing damage to the magnet and magnet holding part due to thermal stress.

[0012] In this case, it is preferable that the magnet is divided in a direction perpendicular to the thrust generating direction, and the compressed layer is provided between the divided magnets.

[0013] With this configuration, when the magnet holding portion thermally shrinks in the direction perpendicular to the thrust generation direction, the compression layers provided in the divided gaps are compressed and deformed, reducing the stress generated in the magnet holding portion. Moreover, although the cross section through which the magnetic flux that induces eddy currents passes remains the same, because the magnet is divided, the cross section surrounded by the eddy currents flowing in the magnet is smaller, which also leads to a reduction in eddy current loss if the compression layers are made of an insulating material. Increasing the number of divisions allows the thickness of each compression layer to be smaller, stabilizing the strength and increasing the effect of reducing eddy current loss.

[0014] Alternatively, it is also preferable that the compressed layer is provided between the magnet and the surface of the core, or between the magnet and the claw portion of the magnet holding portion.

[0015] Even if a compression layer is provided in this position, when the magnet holding portion undergoes thermal contraction in a direction perpendicular to the thrust generation direction, the compression layer undergoes compression deformation, thereby reducing the stress generated in the magnet and the magnet holding portion.

[0016] It is also preferable that the compressed layer is provided between the magnet and the protrusion of the magnet holding portion.

[0017] By providing a compression layer at this position, the compression layer is compressed and deformed by the action of stress in the direction of thrust generation, making it easier to insert the magnet.In addition, the ease of resin filling and the filling rate improve when inserting the magnet, regardless of whether it is in liquid, sheet, or solid form, and stress relaxation due to the difference in thermal deformation between the magnet and the core at low temperatures becomes possible.

[0018] It is also preferable to provide a deformation allowing portion at a position facing the compression layer, which allows deformation in which the compression layer extends in a direction intersecting the compression direction as a result of compression of the compression layer.

[0019] If the volume of the compression layer remains almost unchanged, the provision of the deformation allowance portion can induce appropriate compression deformation of the compression layer.

[0020] The thickness of the compression layer is preferably set within a range in which the expected amount of compression does not exceed the compression strength.

[0021] Adhesives that simply adhere a magnet to a core will break when compressed and lose their function as an elastic body, but by designing the compression layer to be within the compression strength, it can function effectively as the compression layer of the present invention. Effect of the Invention

[0022] According to the electric machine of the present invention described above, even if the magnet holding portion undergoes thermal contraction, the compression layer undergoes compressive deformation, thereby reducing the stress generated in the magnet holding portion, thereby making it possible to effectively prevent damage to the magnets and magnet holding portion due to thermal stress. [Brief description of the drawings]

[0023] [Figure 1] 1 is a schematic cross-sectional view of a motor as an electric machine according to an embodiment of the present invention; [Diagram 2] 2 is a diagram showing an expanded view of the inset structure in FIG. 1 together with a comparative example. [Diagram 3] FIG. [Figure 4] FIG. 13 is a diagram showing a first modified example of the present invention. [Diagram 5] FIG. 11 is a diagram showing a second modified example of the present invention. [Figure 6] FIG. 11 is a diagram showing a third modified example of the present invention. [Figure 7] FIG. 11 is a diagram showing a fourth modified example of the present invention. [Figure 8] FIG. 13 is a diagram showing a fifth modified example of the present invention. [Figure 9] FIG. 13 is a diagram showing a sixth modified example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0025] FIG. 1 is a schematic cross-sectional view showing an example in which an electric machine according to the present invention is applied to a motor M which is a rotary motor.

[0026] Motor M is an inner rotor type as shown in FIG. 1(a), and is constructed by attaching a rotor 2, which serves as a movable part, to a shaft 1 so that they can rotate together, and disposing a stator 3 on the outer periphery of rotor 2.

[0027] The stator 3 includes a stator core 31, which is a core configured in a substantially cylindrical shape, a plurality of teeth 32 formed integrally with the stator core 31 from equiangular positions toward the inner circumference, and coils 33 wound around each of the teeth 32. A power supply device (not shown) is connected to the coils 33, and the coils 33 are configured to generate a rotating magnetic field for rotating the rotor 2 by supplying power.

[0028] The rotor 2 is disposed on the inner peripheral side of the stator 3 with a predetermined gap therebetween. The rotor 2 includes a rotor core 21, which is a core configured in a substantially cylindrical shape, and a magnet (permanent magnet) 22 disposed on the outer peripheral surface along the rotor core 21.

[0029] The magnets 22 are sector-shaped and arranged in the thrust generation direction (S direction), i.e., in the circumferential direction of the rotor core 21, in the same number as the number of poles, and are configured to have a roughly annular shape overall. As shown by arrow H in Fig. 1(b), each magnet 22 is arranged so that its orientation direction (direction of easy magnetization) faces the radial direction (T direction), which is perpendicular to the thrust generation direction (S direction). The magnets 22 are made of a rare earth magnet, such as a neodymium magnet or a samarium-cobalt magnet.

[0030] The magnets 22 are held in the rotor core 21 by magnet holders 23, which are called inset type. The magnet holders 23 are configured in a T-shape including protrusions 23a extending from the rotor core 21 between the magnets 22 in a radial direction (T direction) perpendicular to the thrust generating direction (S direction), and claws 23b extending from the tips of the protrusions 23a to positions overlapping with the outer circumferential surfaces of the magnets 22 located on both sides toward the leading and lagging sides of the rotation direction. The magnet holders 23 restrict the movement of the magnets 22 in the circumferential direction (S direction) during rotation by the protrusions 23a, and restrict the movement in the radial direction (T direction) by the claws 23b. The magnet holders 23 are made of, for example, an electromagnetic steel plate similar to that of the rotor core 21.

[0031] 1 is merely a schematic diagram, the claws 23b may be embedded in recesses provided on the outer circumferential surface of the magnet 22 so that the outer periphery of the claws 23b coincides with the outer circumferential surface of the magnet 22.

[0032] Fig. 2(a) shows the inset structure of Fig. 1(a) linearly developed. The magnet 22 is actually divided into magnet pieces 22a, 22a, and a compressed layer 24 is provided between the magnet pieces 22a, 22a.

[0033] Fig. 2(b) shows a conventional inset structure as a comparative example. In this conventional structure, a single block-shaped magnet 22 is placed between magnet holders 23, 23 arranged in the circumferential direction (S direction). Magnet holder 23 also has a protrusion 23a and a claw 23b. There is no gap between magnet 22 and magnet holder 23 in the circumferential direction (S direction) and radial direction (T direction), or the gap is kept extremely small, restricting movement of magnet 22.

[0034] For this reason, when this motor M is used in a low-temperature environment, the magnet holding portion 23 will thermally shrink, compressing the magnet 22 radially as indicated by the white arrow in the figure, generating thermal stress in the magnet 22 and the magnet holding portion 23, which may result in damage to the magnet 22, the magnet holding portion 23, or both.

[0035] Regarding the linear expansion coefficient of the magnet 22, if the magnet 22 is a neodymium magnet, for example, the linear expansion coefficient in the direction parallel to the orientation direction (direction of easy magnetization) is 7×10 -6 [1 / °C] in the direction perpendicular to the orientation direction (perpendicular to the magnetization), and approximately 0 [1 / °C] in the direction perpendicular to the orientation direction. This linear expansion coefficient is calculated to shrink by approximately 0.1% when the temperature drops by 140°C. On the other hand, when the magnet holder 23 is made of electromagnetic steel plate, the expansion coefficient is 12×10 -6 [1 / ℃], which is larger than that of a magnet.

[0036] The amount of contraction (amount of expansion) ΔX is given by: ΔX = X × α × ΔT … (1) It is expressed as:

[0037] In this embodiment, if the orientation direction of magnet 22 is the radial direction (T direction) and the length (thickness) of magnet 22 in the radial direction is X1, the length of magnet holding part 23 that substantially holds magnet 22 is the distance X2 from the base end position of protrusion 23a, i.e., the outer circumferential surface 21a of yoke 21 to the lower surface 23b1 of claw portion 23b, and if magnet 22 is held without any gaps, then X1 = X2 (= X). Therefore, in formula (1), if the temperature difference ΔT between magnet 22 and magnet holding part 23 is also the same under the same environment, the linear expansion difference ΔX between magnet 22 and magnet holding part 23 is determined by the linear expansion coefficient difference Δα.

[0038] As a result, the contraction of the magnet holding portion 23, which has a larger linear expansion coefficient than the magnet 22, becomes dominant, and the distance X2 between the claw portion 23b and the rotor core surface 21a becomes smaller than the thickness X1 of the magnet 22, causing compression of the magnet 22 as indicated by the white arrow in the figure.

[0039] Therefore, in this embodiment, in the inset structure shown in Fig. 1(a) as described above, the magnet 22 is divided into a plurality of magnet pieces 22a as shown in Fig. 2(a). A compression layer 24 having a lower elastic modulus than the magnet 22 is provided between the magnet pieces 22a, 22a adjacent in the radial direction (T direction), and the compression layer 24 is deformed by the compression stress when the magnet holding part 23 is thermally contracted. Although the magnet pieces are given the same reference numeral 22a, their thicknesses do not necessarily have to be the same (the same applies below).

[0040] The compressed layer 24 is made of an elastic material, and is disposed with almost no gaps in the circumferential and radial directions with a uniform thickness over almost the entire area between the inner circumferential magnet piece 22a and the outer circumferential magnet piece 22a between the magnet holding parts 23, 23. In the direction perpendicular to the paper surface of Figures 1(a) and 2(a) (axial direction of shaft 1), the compressed layer 24 is also disposed with almost no gaps in the axial direction between the inner circumferential magnet piece 22a and the outer circumferential magnet piece 22a between the magnet holding parts 23, 23 with a uniform thickness over almost the entire area.

[0041] Examples of the material for the compressed layer 24 include epoxy, acrylic, silicone, and urethane materials. The manufacturing method is to pour a material between the magnet pieces 22a and harden it, or to sandwich the compressed layer 24 in a sheet shape between the magnet pieces 22a and 22a and assemble them.

[0042] In this case, the thickness of the compression layer 24 is set within a range in which the expected amount of compression does not exceed the compression strength. The thickness of the compression layer 24 may also be determined in consideration of the strength of the magnets 22 and the rotor core 21.

[0043] If the compression layer 24 has compression characteristics as shown by line A (yield point A1) in Fig. 3, the compression amount ΔX will not reach the yield point A1, but if the compression layer 24 has compression characteristics as shown by line B (yield point B1) in Fig. 3, the compression amount ΔX will exceed the yield point B1, and the compression layer 24 will lose its function as an elastic body due to compression. For example, if the length of the magnet holding portion 23 of the rotor 2 shown in Fig. 1 is 10 mm, when the ambient temperature drops by 200°C from 20°C to -180°C, the compression amount by the magnet holding portion 23 will be 10mm x 200°C x (12 x 10-6 -7×10 -6 ) ≒ 0.01 mm. If a normal adhesive layer (thickness 0.1 mm) were to undergo this shrinkage, the adhesive layer would be compressed by about 10%, which corresponds to the case of line B in Figure 3, and there is a risk that the adhesive layer's elastic function will be destroyed.

[0044] In contrast, in this embodiment, the thickness D and material of the compression layer 24 shown in Fig. 2(a) are set so that the amount of shrinkage ΔX does not exceed the yield point A1 as shown by line A in Fig. 3 even if thermal shrinkage occurs due to a scheduled temperature difference. For example, the thickness of the compression layer 24 is set to about 0.2 mm, which is twice the thickness of a normal adhesive layer (0.1 mm), and the compression ratio is set to within 5% even if there is a temperature change of 200°C, thereby avoiding destruction and ensuring the function as an elastic body.

[0045] The above is a simple example, but the compressive stress actually generated in the compression layer 24 is determined by the thickness of the magnet 22 (the length of the magnet holding portion 23), the angle of the magnetization direction, the linear expansion coefficient of the magnet 22, the environmental temperature, the thickness of the compression layer 24, the Young's modulus of the compression layer 24, etc., so the compression layer 24 must not be destroyed by this compressive stress. An example of the thickness per layer of the compression layer 24 is 0.01 mm to 1.0 mm, preferably 0.03 mm to 0.8 mm, and more preferably 0.05 mm to 0.5 mm, and the total number of compression layers 24 is increased as necessary.

[0046] As described above, the motor M, which is an electric machine of this embodiment, comprises a rotor core 21, a plurality of magnets 22 arranged on the surface of the rotor core 21 along the thrust generation direction (S direction), and a magnet holding portion 23 arranged between the magnets 22, 22, and the magnet holding portion 23 is configured to include a protrusion 23a extending in a radial direction (T direction) that is perpendicular to the thrust generation direction (S direction) from the rotor core 21 through the magnets 22 and between the magnets 22, and a claw portion 23b extending from the tip of the protrusion 23a to a position overlapping with the magnet 22.

[0047] A compression layer 24 having a lower elastic modulus than the magnet 22 is provided at a position where the magnet holding portion 23 is compressed when it is thermally contracted.

[0048] With this structure, when magnet holding portion 23 thermally contracts, compressive layer 24 undergoes compressive deformation, reducing the stress generated in magnet 22 and magnet holding portion 23. This makes it possible to effectively prevent magnet 22 (magnet piece 22a) and magnet holding portion 23 from being damaged by thermal stress.

[0049] In particular, in this embodiment, the magnet 22 is divided in a direction (T direction) perpendicular to the thrust generating direction (S direction), and a compressed layer 24 is provided between the divided magnet pieces 22a, 22a.

[0050] With this configuration, when magnet holding portion 23 thermally contracts in the radial direction (T direction) perpendicular to the thrust generation direction (S direction), compression layer 24 provided between magnet pieces 22a, 22a undergoes compression deformation, reducing stress generated in magnet 22 and magnet holding portion 23. Furthermore, by dividing magnet 22 into magnet pieces 22a, 22a, the cross section through which the magnetic flux that induces eddy currents passes remains unchanged, but because the magnet is divided, the cross-sectional area surrounded by the eddy currents flowing in the magnet becomes smaller, so if the compression layer is made of an insulating material, this can reduce eddy current loss and ultimately improve motor efficiency.

[0051] As described above, the motor M of this embodiment can effectively reduce stress generated in the magnet 22 and the magnet holder 23, so that an inset type SPM motor can be established even in low-temperature environments such as high-altitude environments, space environments, and environments cooled with liquid nitrogen. This makes it possible to effectively realize a smaller, lighter, and more powerful motor M.

[0052] Although one embodiment of the present invention has been described above, the specific configuration of each part is not limited to the above-mentioned embodiment. Below, several modified examples will be described, but the same reference numerals are used to designate parts common to the above embodiment, and explanations are omitted except for parts that require special explanation.

[0053] (Variation 1) 4, the number of divisions in the radial direction (T direction) of magnet 22 may be two or more. By increasing the number of divisions, not only the total thermal stress but also the eddy current loss in each magnet piece 22a can be reduced, resulting in reduced heat generation due to loss and improved efficiency of motor M.

[0054] In this case, since the compressed layers 24 are in series, if the thickness of the compressed layers 24 needs to be 0.2 mm, for example, the sum of the thicknesses D of the individual compressed layers 24 only needs to satisfy this value. The thicknesses D of the compressed layers 24 do not need to be the same value.

[0055] (Variation 2) In addition, since the dividing surface need not be parallel to the thermal contraction direction of magnet holding portion 23, compressed layer 24 may be configured at an incline, as shown in Fig. 5. Even if compressed layer 24 is formed between magnet pieces 22a, 22a in this structure, when magnet holding portion 23 thermally contracts in the radial direction (T direction) perpendicular to the thrust generation direction (S direction), the radial direction (T direction) component of compressed layer 24 is compressed and deformed, thereby reducing the stress generated in magnet 22 and magnet holding portion 24.

[0056] Such an oblique compression layer 24 is also effective when applied to a rotating machine having a flux-concentration type magnet arrangement such as a Halbach magnet.

[0057] (Variation 3) 6, the magnet 22 may be divided in the circumferential direction (S direction) and radial direction (T direction), and the compressed layer 24 may be formed between the magnet pieces 22a, 22a in the radial direction (T direction) and between the magnet pieces 22a, 22a in the circumferential direction (S direction). In this way, it is possible to reduce the thermal stress of the compressed layer 24 in the radial direction (T direction) and at the same time further reduce the eddy current loss of the magnet 22 compared to the first modification.

[0058] (Variation 4) 7, the magnet 22 may not be divided, and a compressed layer 24 having a thickness D may be provided between the magnet 22 and the surface 21a of the rotor core 21, or between the magnet 22 and the lower surface 23b1 of the claw portion 23b of the magnet holding portion 23. Even if the compressed layer 24 is provided at this position, when the magnet holding portion 23 thermally contracts in a direction (T direction) perpendicular to the thrust generating direction (S direction), the compressed layer 24 is compressed and deformed, thereby reducing the stress generated in the magnet 22 and the magnet holding portion 23. In this case, the gap between the magnet 22 and the magnet holding portion 23 can be made larger, which has the advantage that the magnet 22 can be easily inserted into the rotor core 21. Here, too, the thickness D of each compressed layer 24 does not need to be the same.

[0059] In this example, a compressed layer 24 is also provided in the gap in the circumferential direction (S direction) between the protrusion 23a of the magnet holding portion 23 and the magnet 22. This improves the ease of filling the resin and the filling rate when the magnet is inserted, regardless of whether it is in liquid, sheet or solid form, and also makes it possible to alleviate stress caused by the difference in thermal deformation between the magnet and the core at low temperatures.

[0060] (Variation 5) Furthermore, as shown in Figure 8(b) which corresponds to the BB line break in Figure 8(a), it is desirable to provide a deformation-permitting portion S at a position facing the compressed layer 24, which allows the compressed layer 24 to deform in a direction (S direction) intersecting the compression direction (T direction) when the compressed layer 24 is compressed.

[0061] If the volume of the compression layer 24 is to remain almost the same, other portions need to expand in order for the compression layer 24 to be compressed. Therefore, by providing the deformation-permitting portion S, it is possible to induce an appropriate compressive deformation of the compression layer 24.

[0062] (Variation 6) Alternatively, as shown in FIG. 9, the magnet 22 with the compressed layer 24 interposed therebetween may be held by a shrink ring 25 instead of by an inset mold.

[0063] In this case, protrusions 23b rise from rotor core 21 through between magnets 22a in a direction (T direction) perpendicular to the thrust generation direction (S direction), but the tips of protrusions 23b do not extend to a position where they press against the surface of magnet 22. For this reason, the outer periphery of magnet 22 is pressed by shrink ring 25 to restrict radial movement.

[0064] Providing the compression layer 24 in such a structure also has the effect of suppressing eccentricity caused by misalignment of the magnet 22 by pressing in the shrink ring 25. In addition, the compression layer 24 can reduce the stress on the shrink ring 25 and the magnet 22 that occurs when the shrink ring 25 is pressed in, preventing damage to the shrink ring 25 and the magnet 22. Furthermore, reducing the stress allows the press-in allowance to be increased, so that a large pretension (a force that shrinks in the radial direction) can be applied to the shrink ring 25, eliminating the gap between the shrink ring 25 and the magnet 22 that occurs during high-speed rotation, enabling high-speed rotation.

[0065] (Variation 7) The above has described the case where the electric machine is a rotary electric motor (motor), but if in Figures 2 to 9, S is the linear direction in which thrust is generated, and T is the direction perpendicular to this, then it can also be used as a linear-motion machine such as a linear motor.

[0066] Other configurations can also be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0067] M: Electric machine (motor) 21...Core (rotor core) 22...Magnet 23…Magnet holder 23a...Protrusion 23b...Claw part 24…Compressed layer

Claims

1. a core, a plurality of magnets arranged in the core along the thrust generating direction, and a magnet holding portion arranged between the magnets, the magnet holding portion including a protrusion extending from the core through between the magnets in a direction perpendicular to the thrust generating direction, and a claw portion extending from the tip of the protrusion to a position overlapping with the magnet, A compression layer having a lower elastic modulus than the magnet is provided at a position where the magnet holding portion is compressed when thermally contracted, An electric machine characterized in that the magnet is divided in a direction perpendicular to the thrust generation direction between the core and the claw portion of the magnet holding part, and the compression layer is provided between the divided magnets.

2. The electric machine according to claim 1 , wherein the compressible layer is provided between the magnet and the core or between the magnet and the claws of the magnet holder.

3. An electric machine as described in claim 1, wherein the magnet is divided in the thrust generating direction between adjacent protrusions of the magnet holding portion, and the compression layer is provided between the divided magnets.

4. 4. The electric machine according to claim 1, wherein the compressible layer is provided between the magnet and the protrusion of the magnet holder.

5. The electric machine according to claim 1 or 3, further comprising a deformation-permitting portion provided at a position facing the compressible layer, the deformation-permitting portion allowing the compressible layer to deform and expand in a direction intersecting the compressive direction when the compressible layer is compressed.

6. 4. The electric machine according to claim 1, wherein the thickness of the compressible layer is set within a range in which a predetermined amount of compression does not exceed the compressive strength.

7. An electric machine as described in any one of claims 1 to 6, wherein the magnet is arranged on the surface of the core.

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