Rotor of an electric motor with magnetic mounting device and electric motor with the rotor

Abstract

Rotor (10, 10', 10"), wherein the rotor (10, 10', 10") of an electric motor (100) is provided with several magnets (16, 16a, 16b, 16c) arranged in the circumferential direction, a holding element (20, 20a, 20b) which is formed concentrically on an outer side in a radial direction of the multiple magnets (16, 16a, 16b, 16c) with respect to the rotor (10, 10', 10") in order to hold the multiple magnets (16, 16a, 16b, 16c), wherein the retaining element (20, 20a, 20b) is formed from several tubular elements (201, 202, 203) which have different diameters and are arranged concentrically, wherein the diameter of the individual tubular elements (201, 202, 203) is widened and a compression holding force directed radially inwards acts as an elastic restoring force from the retaining elements (20, 20a, 20b) on the magnets (16, 16a, 16b, 16c); wherein an excess of one of the tubular elements of any two tubular elements adjacent to each other in the radial direction, among the several tubular elements (201, 202, 203) is designed such that it is larger than the excess of the other tubular element positioned on the outside in the radial direction of the tubular element in question; wherein the multiple tube sections contain fiber-reinforced resin configured such that fibers run at least in one circumferential direction; and wherein the tubular element (201) positioned furthest inwards in the radial direction among the several tubular elements (201, 202, 203) is designed such that its tensile strength is greater than that of each of the other tubular elements (202, 203).

Description

Background of the invention 1. Field of the invention

[0001] The present invention relates to a rotor with a magnetic holding device and an electric motor with the rotor. 2. Description of the state of the art

[0002] A known synchronous electric motor includes a rotor with a plurality of magnets arranged circumferentially on one surface thereof. If a higher speed is desired in this type of electric motor, it is necessary to provide sufficient holding strength for the magnets to prevent them from detaching from the rotor due to centrifugal force.

[0003] JP H11-89 142 A discloses a rotor of an electric motor including a rotational axis, a sleeve provided in an outer periphery of the rotational axis, a cylindrical permanent magnet arranged on an outer periphery of the sleeve, and a holding member made of carbon fiber reinforced plastic and provided on an outer periphery of the permanent magnet to cover the permanent magnet.

[0004] JP 2013-169103 A discloses an electric motor rotor including a cylindrical protective tube designed to surround a plurality of magnets. The protective tube is attached to the rotor in such a way that it has an increased diameter when filled with resin, and therefore, the protective tube is pressed against the magnets on a radially inner side due to the recovery force of the protective tube. According to this prior art, the magnets can be held in place without adhesive.

[0005] To rotate a rotor at high speed, even greater holding strength of the magnets is required. For example, when the carbon-reinforced plastic holding member disclosed in JP H11-89142 A is adopted, the holding strength can be increased by thickening the holding member. However, since stress is generated concentrically on an inner diameter side, simply increasing the thickness of the holding member is not effective. In addition, when a thickened holding member is adopted, a distance between the magnets of the rotor and the stator (magnetic gap) becomes larger, resulting in reduced torque. Furthermore, it is costly and requires a high degree of skill to form a thickened carbon-fiber reinforced plastic member, possibly causing defects in the internal structure and deteriorating the holding strength.

[0006] To improve the holding function of the magnets, interference of the holding members can be increased to increase an amount of extension in the circumferential direction. However, especially when the holding member is made of FRP formed from a sheet-like material wound around a jig, a terminal end portion of the sheet-like material or a portion nearby may not be able to extend far enough, so these portions detach or separate from the holding member, thereby deteriorating the reliability of the rotor. In addition, due to increasing interference of the holding member, large recovery force acts on the holding member, and a fiber on an outer peripheral side may get caught in a gap between fibers on an inner peripheral side, and thus the intended holding force may be lost.

[0007] According to a known prior art, the magnets and the protective tube are held by the internal pressure of a filler material, as disclosed in JP 2013-169103 A. In this case, a filler material is thermoplastic injected by injection molding. The internal pressure generated by the resin is small enough with respect to the tensile strength of the resin that the resin is not deformed. In other words, this known prior art can only be applied to the case where it is only necessary to provide a fastening force that can be borne by the plastic. When the rotor with such a structure is operated at high speed, the following problems arise. (1) The protective tube is expanded due to the centrifugal force corresponding to the self-weight of the protective tube, but the filler material cannot follow the expansion of the protective tube after reaching a certain limit.As a result, the fastening force acting on the protective tube is lost, and the protective tube begins to idle. The protective tube scrapes the filler material with its inner wall and eventually detaches from the rotor with noise. (2) Compared to the centrifugal force corresponding to the weight of the magnets with comparable density to iron, the fastening force by the resin filler material is very weak and may not be sufficient to secure the magnets against the centrifugal force. Therefore, when the rotor reaches a certain speed, the magnets begin to move to a radially outer side and in one rotational direction, idling, and destroying the filler material. Accordingly, the structure disclosed in JP 2013-169 103 A is not suitable for increasing the speed. Furthermore, further background information on the field of the invention is known from WO 2008 / 012 637 A1 and DE 296 10 872 U1.

[0008] Therefore, there is a need for a rotor that can increase the efficiency and reliability of an electric motor. Brief description of the invention

[0009] This object is achieved by the invention defined in the independent claims. Advantageous further developments are set forth in the dependent claims.

[0010] According to a first aspect, there is provided a rotor of an electric motor comprising a plurality of magnets arranged in a circumferential direction, the rotor further comprising a holding member provided concentrically with the rotor on a radially outer side of the plurality of magnets for holding the plurality of magnets, the holding member including a plurality of tubular members arranged concentrically with each other and having diameters that differ from each other, the respective tubular members having expanded diameters such that a pressing holding force acts radially inward on the magnets due to an elastic recovery force of the holding member, any two tubular members of the plurality of tubular members adjacent to each other in a radial direction are configured such that one of the two tubular members has an interference greater than that of the other tubular member located on a radially outer side; and the plurality of tubular members contain fiber-reinforced resin configured such that fibers extend at least in one circumferential direction, and wherein a tubular member of the plurality of tubular members located at an innermost position in a radial direction has a tensile strength higher than that of any other tubular members.

[0011] According to a second aspect, in the rotor according to the first aspect, any two tubular members of the plurality of tubular members adjacent to each other in a radial direction are configured such that one of the two tubular members has a modulus of elasticity less than or equal to that of the other tubular member located on a radially outer side.

[0012] According to a third aspect, in the rotor according to the first or second aspect, a tubular member of the plurality of tubular members located at an innermost position in a radial direction has a tensile strength higher than that of any other tubular members.

[0013] According to a fourth aspect, in the rotor according to any one of the first to third aspects, at least one tubular member of the plurality of tubular members located at an outermost position in a radial direction has a cylindrical shape before assembly.

[0014] According to a fifth aspect, there is provided an electric motor comprising the rotor according to any one of the first to fourth aspects.

[0015] These and other objects, features and advantages of the present invention will become more apparent in light of the detailed description of exemplary embodiments thereof as illustrated by the drawings. Short description of the drawings Fig. 1 is a longitudinal sectional view illustrating an electric motor according to an embodiment of the present invention. Fig. 2 is a cross-sectional view illustrating an electric motor according to a variation. Fig. 3 is a cross-sectional view illustrating a rotor according to a first embodiment of the invention. Fig. Figure 4 is a diagram showing stress applied in a support member of the rotor of Fig. 3 is generated. Fig. 5 is an exploded perspective view illustrating the rotor according to the first embodiment. Fig. 6 is a cross-sectional view illustrating a rotor according to a second embodiment. Fig. Figure 7 is a diagram showing stress applied in a support member of the rotor of Fig. 6 is generated. Fig. 8 is a cross-sectional view illustrating a rotor according to a comparative example; and Fig. 9 is a diagram showing stress generated in a holding member of the rotor according to the comparative example. Detailed description of the invention

[0016] Embodiments of the present invention will now be described below with reference to the accompanying drawings. Constituent elements of the illustrated embodiment may be resized relative to one another for a better understanding of the invention.

[0017] Fig. 1 is a longitudinal sectional view illustrating an electric motor 100 according to an embodiment of the present invention. The electric motor 100 is, for example, a surface permanent magnet (SPM) motor in which magnets are mounted on the surface of a rotor. The electric motor 100 includes a rotor 10 and a stator 50 arranged concentrically with each other. The electric motor 100 is designed to generate rotational power due to magnetic interaction between the rotor 10 and the stator 50.

[0018] The stator 50 includes a cylindrical iron core 52 formed with slots (not shown) running parallel to an axial direction, and coils 54 wound through the slots. The stator 50 is attached to a housing 102 of the electric motor 100, which surrounds the stator 50. During operation of the motor 100, a three-phase alternating current, for example, is supplied to the coils 54 to generate a rotating magnetic field around the rotor 10.

[0019] The rotor 10 includes a sleeve 14, which is press-fitted, for example, to an outer periphery of a cylindrical rotor shaft coupled to, for example, a spindle of a machine tool, and a holding member 20 attached to an outer periphery of the magnets 16 for holding the magnets 16. The rotational shaft 12 is rotatably supported by a bearing (not shown) about a rotational axis line X during operation of the electric motor 100. The sleeve 14, the magnets 16, and the holding member 20 of the rotor 10 are designed to rotate together with the rotational shaft 12.

[0020] The sleeve 14 has a flange 14a that gradually protrudes radially outward at one end of the sleeve 14. The flange 14a is formed with a fluid channel 18 that connects the outer side 22 of the rotor 10 to a gap 24 between the inner peripheral surface of the sleeve 14 and the outer peripheral surface of the rotation axis 12. The fluid channel 18 is formed with a threaded hole 18a that opens to the outer side 22. The sleeve 14 is also formed with an annular groove at both ends of the sleeve in the axial direction, and a sealing member 26, such as an O-ring, is mounted in the annular groove.

[0021] In this document, “radially outward” means a direction away from the rotational axis line X in the cross-section, “radially inward” means a direction towards the rotational axis line X in the cross-section, and “the axial direction” means a direction parallel to the rotational axis line X.

[0022] In this embodiment, the rotor 10 is attached to the rotational axis 12 by oil pressure fitting. Accordingly, the diameter of the rotor 10 is expanded due to the oil pressure provided in the gap 24 between the sleeve 14 and the rotational axis 12 through the fluid channels 18, which are arranged in a circumferential direction of the sleeve 14 and spaced from each other. During this process, a supply nozzle for supplying the oil is screwed into the threaded hole 18a. At least one fluid channel is used as an air hole.

[0023] The oil introduced into the gap 24 is sealed by the sealing member 26 provided at opposite ends of the sleeve 14, preventing it from leaking to the outside 22 of the rotor 10. The oil also lubricates the contact surface between the inner peripheral surface of the sleeve 14 and the outer peripheral surface of the rotation axis 12. This facilitates the sliding of the sleeve 14 in the axial direction to a predetermined position relative to the rotation axis 12.

[0024] The inner peripheral surface of the sleeve 14 and a portion of the outer peripheral surface of the rotation axis 12 that receives the sleeve 14 may have a tapered surface configured to have a gradually decreasing diameter from one end to the other. In this case, the sleeve 14 and the rotation axis 12 are positioned such that the sleeve 14 is moved from the smaller diameter side to the larger diameter side of the rotation axis 12, and a predetermined interference is achieved when the sleeve 14 remains at a predetermined position.

[0025] The magnet 16 includes a plurality of permanent magnets arranged in the circumferential direction on the outer peripheral surface of the sleeve 14. For example, the respective permanent magnets of the magnet 16 have a rod-like shape and form a plurality of permanent magnet groups integrally formed with resin.

[0026] As further described below, the holding member 20 is formed by concentrically attaching a plurality of tubular members with diameters that differ from each other to the rotor 10. The respective tubular members are attached to the rotor 10 with the increased diameters according to a predetermined interference. This allows the tubular members to provide sufficient recovery force to the magnets 16 radially inward to hold the magnets 16 against centrifugal force generated when the rotor 10 is rotating. The more the rotor speed increases, the greater the recovery force is required. In this connection, as the interference of the tubular members increases, the recovery force becomes larger. Accordingly, the interference of the tubular members is determined according to the necessary recovery force, depending on the rotor speed.

[0027] The respective tubular elements are tubes made of non-magnetic materials, for example. The tubular elements can be made of titanium alloy or stainless steel. In addition to the material's inherent properties, the mechanical properties can be modified through a heat treatment or by adjusting the thickness.

[0028] Alternatively, the tubular members may be made of fiber-reinforced plastic (hereinafter referred to as "FRP"), which is formed of a plurality of fibers interlocked by a resin serving as a binder. For example, the tubular member may be formed into a predetermined shape conforming to the external shape of a jig by wrapping a prepreg sheet around the jig and then heating the resin to cure it. The FRP used for the tubular member may be a material with high specific strength (tensile strength per unit density), such as carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, boron fiber, titanium alloy fiber, ultra-high molecular weight polyethylene, and polybutylene terephthalate fiber, or the like.

[0029] The tubular members may have different mechanical properties. For example, an inner tubular member provided on a radially inner side has the following feature compared to another tubular member provided on a radially outer side of the inner tubular member. The inner tubular member is made of a material with sufficiently high tensile strength in the circumferential direction, radial direction, and axial direction, respectively. For example, the inner tubular member is formed of a thin tube made of non-magnetic metal. Alternatively, in the inner tubular member made of FRP, a fiber ratio is increased in every direction except the circumferential direction. The FRP of the inner tubular member may contain various types of fibers combined with each other. In either case, the material with high tensile strength can be adopted.

[0030] Alternatively, in the case where at least two tubular members are made of FRP in which fibers extend in the circumferential direction, a tubular member on a radially inner side is configured to contain matrix resin having a larger Izod impact strength than that of a tubular member on a radially outer side, or in other words, to have a higher fracture resistance. "Fibers extending in a circumferential direction" means that fibers are wound to extend in a direction perpendicular to the axial direction of the tubular member, or alternatively, to extend in a direction at an angle within a predetermined range with respect to the direction perpendicular to the axial direction.

[0031] On the other hand, a tubular member in the intermediate position in the radial direction may be made of a material having a modulus of elasticity in the circumferential direction larger than that of the tubular member on the radially inner side. For example, when the tubular member in the intermediate position is made of FRP, a ratio of fibers extending in the circumferential direction is increased. Alternatively, a fiber having such a property may be selected. Further, for example, an outer tubular member provided on the radially outer side of the tubular member in the intermediate position is made of a material having a larger modulus of elasticity in the circumferential direction, so that it has a smaller amount of expansion.This allows the expansion amount of the outermost tubular member to be small, and consequently, the outer tubular member provided on the outermost layer of the support member can be prevented from coming off or loosening at the terminal end portions thereof, which are formed by winding the sheet material to form the FRP. In addition to these effects, in cases where greater strength against external forces is required, for example, to protect the surface of the rotor, the outermost tubular member may be a thin tube made of non-magnetic metal.

[0032] When the intermediate tubular member is inserted between the inner tubular member and the outer tubular member, it is unlikely to be subjected to external force because it is inserted between the other tubular members on the inside and outside. Therefore, the intermediate tubular member is primarily designed to increase elasticity in the circumferential direction for holding the magnets. For this purpose, the material of the intermediate tubular member can be selected with elasticity in the circumferential direction in mind.For example, the material of the intermediate tubular member is selected such that the elastic modulus of the intermediate tubular member in the circumferential direction is equal to or larger than that of the inner tubular member and smaller than that of the outer tubular member, and that the interference of the intermediate tubular member is equal to or smaller than that of the inner tubular member and larger than that of the outer tubular member.

[0033] Of the plurality of pipe members, any two pipe members adjacent to each other in the radial direction may be designed such that one of the pipe members has an interference equal to or greater than that of the other pipe member provided on the radially outer side.

[0034] The interference of the tubular member can be defined as the increased diameter of the tubular member attached to the rotor compared to the diameter of the tubular member before attachment to the rotor. In other words, the variation in the diameter before and after attachment. For tubular members with a non-circular shape, where the diameter cannot be directly obtained, an imaginary circle is defined such that the diameter has the same length as the circumferential length of the tubular member in cross-section. Then, the changes in the diameter of the imaginary circle are calculated to obtain the interference of the tubular member.

[0035] Of the plurality of tubular members, materials may be selected for any two tubular members adjacent to each other in the radial direction such that one of the tubular members has a Young's modulus in the circumferential direction equal to or smaller than that of the other tubular member provided on the radially outer side. For example, metal or FRP may be selected for the respective tubular members as needed, or alternatively, the extension direction of the fibers may be adjusted as needed to satisfy the above-described relationship of the Young's modulus in the circumferential direction.

[0036] In the case where at least two tubular members are made of FRP with fibers extending in a circumferential direction, a tubular member on a radially inner side stretches to a greater extent than a tubular member on a radially outer side. Therefore, the matrix resin of the tubular member on a radially inner side can be configured to have a higher Izod impact strength, or in other words, higher fracture resistance.

[0037] Furthermore, among the multiple tubular members constituting the support member, the innermost tubular member in the radial direction may be designed to have higher tensile strength than any other tubular members. For example, the innermost tubular member may be made of FRP, in which the ratio of fibers extending in the circumferential direction is maximized, or of a non-magnetic metal with high tensile strength.

[0038] Each tubular member may have a cylindrical shape before being attached to the rotor. In this case, the tubular member has a cylindrical shape when no external force acts on it. The "cylindrical shape" means a substantially cylindrical shape in cross-section. The tubular member with a cylindrical shape is advantageously easy to form and therefore inexpensive to manufacture. In addition, it is easy to produce a cylindrical tubular member with uniform thickness and strength, which contributes to stable quality and performance. In particular, in the case where the tubular member is made of FRP in which the fibers run in a circumferential direction, it is advantageous that a cylindrical tubular member is not prone to defects such as stress in fibers.On the other hand, a tubular member on the innermost side in a radial direction may have a non-cylindrical shape and correspond to an outer edge of the magnets to reduce stress concentration.

[0039] The holding member made of the plurality of tubular members having the features described above has the following advantages. (1) Since the support member for holding the rotor magnets has a multi-layer structure composed of multiple tubular members, stress can be distributed among the respective tubular members, unlike the prior art, in which stress is concentrated near the inner peripheral surface of the support member. This reduces the maximum stress generated in the innermost layer of the support member. As a result, the rotor can advantageously operate at higher speeds, and the power output of the electric motor can be increased. (2) When the support member has a multi-layer structure, the maximum stress generated in the support member can be reduced, allowing the support member to be thinner. As a result, a magnetic gap can be narrowed, and the magnetic resistance can be reduced. This increases the amount of magnetic flux, resulting in increased torque with the same electric current. This also means that the electric motor can have increased power output at the same speed. Therefore, the efficiency of the electric motor can be advantageously improved. (3) When the interference of the tubular member provided on the radially inner side is equal to or greater than that of the tubular member on the radially outer side, the assembly process of the tubular members can be facilitated. Specifically, when the interference of each tubular member is designed in this way, the size differences between the tubular members can be increased, thereby enabling the assembly process for fitting the tubular members to each other to be carried out smoothly. As a result, the manufacturing cost of the electric motor can be reduced. (4) When the tubular member has a small interference on the radially outer side, the amount of expansion of the tubular member constituting the outermost layer of the holding member in the circumferential direction can be reduced. Accordingly, even in the case where the tubular member is formed by winding a sheet material, the terminal ends of the sheet material can be prevented from coming off when the tubular member expands. In addition, the fiber on the outer peripheral side can be prevented from digging into the fibers on the inner peripheral side. This can improve the durability of the rotor, and therefore the reliability of the electric motor can be improved. Alternatively, since the rotor can be operated at a higher speed due to the improved reliability, the output of the electric motor can be advantageously increased. (5) When the tubular member provided on the radially inner side has a large interference, the recovery force generated in the tubular member on the inner peripheral side is increased, and the force for directly supporting the magnets against the centrifugal force during rotation can be increased. This also achieves the effect of increasing the maximum speed of the rotor and the power output of the electric motor. (6) When the support member is formed of the tubular members having different mechanical properties, the tubular members may be arranged to have appropriate mechanical properties depending on the positions in the radial direction. For example, the tubular members with high tensile strength may be provided on the inner peripheral side where the load is likely to be large, and the tubular members having a property for protecting the rotor from the external force (for example, the air friction resistance property) may be provided on the outer peripheral side to prevent the rotor from being damaged. For example, since the innermost tubular member is in contact with the magnets, the innermost tubular member should have sufficiently high tensile strength not only in the circumferential direction but also in every direction.Accordingly, if the innermost tubular member is made of a material having desirable properties, the rotor can be prevented from being damaged and the reliability of the electric motor can be improved.

[0040] In the case where the support member is made of FRP, a tubular member on a radially inner side can be more flexible, or in other words, configured to have a higher Izod impact strength than a tubular member on a radially outer side. This can prevent engine damage. (7) When the support member is made of FRP, the strength in each direction can be easily adjusted by adjusting the ratio of fibers running in different directions to each other. When the tubular member is made of FRP containing a material with high specific strength, such as carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, boron fiber, titanium alloy fiber, ultra-high molecular weight polyethylene, and polybutylene terephthalate fiber, or the like, the centrifugal force acting on the tubular member can be reduced. As a result, most of the recovery force generated by the tubular member can be used to hold the magnets against the centrifugal force acting on the magnets. Therefore, the material with high specific strength is advantageously used to form the tubular member. (8) It is advantageous that the tubular member with a circular cross-section can be easily formed as required, and is less likely to generate internal structural defects. Furthermore, the manufacturing cost can be reduced.

[0041] Fig. Fig. 2 is a longitudinal sectional view showing a rotor 10' according to a variation of the rotor 10 shown in Fig. 1. In this variation, the magnet 16 is formed of three magnets 16a, 16b, and 16c arranged in the axial direction. In contrast, the holding member 20 is formed of two holding members 20a and 20b. The other configurations of the rotor 10' are the same as those of the rotor 10.

[0042] The magnets 16a, 16b, and 16c may have the same size or different sizes in the axial direction. For example, the sizes of the magnets 16a, 16b, and 16c in the axial direction may be 30 mm, 40 mm, and 50 mm, respectively. Likewise, the holding members 20a and 20b may have the same size or different sizes in the axial direction. Only one of the magnet 16 and the holding member 20 may have a discrete structure. As described above, the magnet 16 and the holding member 20 may have different discrete structures. In any case, the holding member 20 extends over the entire length of the outer circumference of the magnet 16 in the axial direction.

[0043] The magnet may also have a discrete structure in the circumferential direction. In this case, the magnet may be arranged in a substantially circular arc shape in the circumferential direction. Due to the compressive force acting radially inward on the magnets, the discrete magnets arranged in the circumferential direction can be prevented from breaking into pieces. Furthermore, the discrete magnets arranged in the circumferential direction can be easily increased in size compared to an integrally formed cylindrical magnet, and therefore, the electric motor with a larger power output can be advantageously designed.

[0044] Fig. 3 is a cross-sectional view illustrating a rotor 10 according to a first embodiment of the present invention. As illustrated, the support member 20 includes a first tubular member 201 provided on the outer periphery of the magnet 16, and a second tubular member 202 provided on the outer periphery of the first tubular member 201. According to this embodiment, since the stress generated in the support member 20 is distributed between the first tubular member 201 and the second tubular member 202, the maximum stress is reduced. In the illustrated embodiment, the magnet 16 includes four magnets arranged in the circumferential direction with a gap S therebetween.

[0045] Fig. 8 is a cross-sectional view illustrating a rotor 110 according to a comparative example. The support member in this comparative example includes only one tubular member 120. Fig. 9 is a diagram of the load generated in the support member of the rotor 110. The horizontal axis of the diagram represents rotational positions of the support member 20 from the outer peripheral surface O to the inner peripheral surface I of the tubular member 120. The vertical axis represents the magnitude of the load generated in the tubular member 120. As shown in Fig. 9, the load is generated concentrically in a region near the inner peripheral surface I of the tubular member 120.

[0046] Fig. Figure 4 is a diagram of the load generated in the support member 20 of the rotor 10, which is shown in Fig. 3. The horizontal axis of the diagram represents radial positions from the outer peripheral surface O2 to the inner peripheral surface I2 of the second tubular member 202 and from the outer peripheral surface O1 to the inner peripheral surface I1 of the first tubular member 201. The vertical axis of the diagram represents the magnitude of the stress generated in the first tubular member 201 and the second tubular member 202, respectively. The dashed line in the diagram of Fig. 4 represents the load generated in the comparative example shown in Fig. 9 is shown.

[0047] As in Fig. As shown in Figure 4, the maximum stress generated in the support member 20 in the first embodiment is smaller than that of the comparative example. Furthermore, the difference in stress between the innermost position (the inner peripheral surface I1 of the first tubular member 201) of the support member 20 and the outermost position (the outer peripheral surface O2 of the second tubular member 202) is also smaller. Accordingly, according to the first embodiment, the stress is distributed over the entire portion of the support member 20.

[0048] In the diagram shown in Fig. As shown in Figure 4, the area between the curve showing a relationship between the radial position and the load (load curve) and the horizontal axis is proportional to the tensile force acting on the tubular member in the circumferential direction. The tensile force in the circumferential direction is proportional to the compressive force pressing the magnet radially inward. Therefore, if the area A1 defined by the load curve and the horizontal axis remains equal to the corresponding area B in the comparative example (see Fig. 9), the pressing force for holding the magnet is substantially the same, and at the same time, the maximum stress generated in the tubular member can be reduced.

[0049] As in Fig. As shown in Figure 4, even if the holding member is formed of multiple tubular members, relatively large stress is still generated in the tubular member on the radially inner side. The innermost tubular member, which is in direct contact with the magnet, is subject to stress concentration at contact positions with the corners of the magnet and the like. Accordingly, it is particularly advantageous for the tubular member on the radially inner side to have the increased tensile strength. Although the tubular member with high tensile strength is generally expensive, if only one or some of the tubular members have the increased tensile strength, the cost can be reduced.

[0050] Fig. Figure 5 is an exploded perspective view illustrating a rotor according to an embodiment of the present invention. The rotor part with a sleeve 14 and magnets 16 is shown in Fig. 5 in the state before attachment to the rotation axis, which is not shown. In this embodiment, the magnets 16 are arranged in four groups in the circumferential direction on the outer peripheral surface of the sleeve 14, and each group includes three magnets 16a, 16b, and 16c.

[0051] The first tubular member 201 and the second tubular member 202, which form the support member 20, are sequentially attached to the rotor part. Alternatively, after attaching the second tubular member 202 to the outer peripheral surface of the first tubular member 201, the inner peripheral surface of the first tubular member 201 may be mounted to the outer peripheral surface of the rotor part. Note that in this embodiment, the order of attachment of the respective parts is not limited.

[0052] Next, the exemplary configurations of the first tubular member 201 and the second tubular member 202 of the holding member 20 according to the first embodiment will be described. (Example 1)

[0053] The first tubular member 201 is made of FRP containing carbon fiber or glass fiber, which have a low elastic modulus and are relatively expensive. The fibers are wound multiple times to have a strength sufficient to withstand most of the force for holding the magnets. For example, the resin is also used as a binder and is used to form the first tubular member 201. Alternatively, a prepreg sheet containing the fibers is formed and then wound around a jig into a tubular shape, and then the resin is heated to harden to form the tubular member 201. In contrast, the second tubular member 202 is made of a material with relatively high tensile strength and a high elastic modulus, such as carbon fiber.

[0054] The first tubular member 201, made of a material with a small elastic modulus in the circumferential direction, is provided with greater interference than the second tubular member 202. Before and after attachment, the expansion amount of the first tubular member 201 is greater than the expansion amount of the second tubular member 202. Generally, when the tubular member is formed by repeatedly winding a sheet material, there is an increased risk of the terminal end of the sheet material coming off as the expansion amount of the tubular member increases. However, according to this embodiment, since the compressive force acts on the outer periphery of the first tubular member 201 from the second tubular member 202 to press the terminal end of the first tubular member 201, the terminal end can be prevented from coming off. Furthermore, since the holding force for holding the magnet can be realized largely by an inexpensive material, the overall cost can be reduced. (Example 2)

[0055] The first tubular member 201 is a tube made of a non-magnetic metal, such as austenitic stainless steel, titanium, or titanium alloy. This type of metal tube generally exhibits isotropy and high tensile strength in both the axial and circumferential directions. If the first tubular member 201 is made of this type of metal at the innermost layer, the first tubular member 201 can be prevented from being damaged even if it comes into contact with a corner portion of the magnet or an unevenly stepped portion of the magnet.

[0056] In contrast, the second tubular member 202 is made of FRP containing, for example, carbon fiber, with numerous fibers extending in the circumferential direction to exhibit a high elastic modulus. Therefore, when the second tubular member 202 provided on the radially outer side is made of a material with a high elastic modulus, a large recovery force acts on the second tubular member 202 even when the second tubular member 202 has an interference smaller than that of the first tubular member 201. As a result, the holding force for holding the magnet can be increased. This makes it possible to increase the maximum rotational speed, and thereby increase the power output of the electric motor.

[0057] Fig. 6 is a cross-sectional view illustrating a rotor 10" according to a second embodiment of the present invention. The rotor 10" in this embodiment includes a first tubular member 201 provided on the outer periphery of the magnet, a second tubular member 202 fitted onto the outer peripheral surface O1 of the first tubular member 201, and a third tubular member 203 provided on the outer peripheral surface O2 of the second tubular member 202.

[0058] Fig. Fig. 7 is a diagram showing the tendency of the load distribution generated in the holding member 20 of the rotor, which is in Fig. 5. The horizontal axis represents radial positions from the outer peripheral surface O3 to the inner peripheral surface I3 of the third tubular member 203, from the outer peripheral surface O2 to the inner peripheral surface I2 of the second tubular member 202, and from the outer peripheral surface O1 to the inner peripheral surface I1 of the first tubular member 201. The vertical axis of the diagram represents the magnitude of the stress generated in the first tubular member 201, the second tubular member 202, and the third tubular member 203, respectively. The dashed line of the diagram in Fig. Figure 7 represents the load generated in the comparative example shown in Fig. 9 is shown.

[0059] As in Fig. As shown in Figure 7, according to the support member 20 having the three tubular members 201, 202, and 203, the maximum load can be reduced compared to the comparative example. When the support member 20 has the same thickness, the respective tubular members 201, 202, and 203 have a thinner thickness than the first embodiment. Therefore, when the support member is formed from many tubular members, each tubular member can be thinner and is easier to manufacture. In addition, a high-quality tubular member without structural defects, in other words, a tubular member with higher strength, can be advantageously produced. Furthermore, the yield rate can be increased, and as a result, the manufacturing cost can also be reduced. In addition, the thinner tubular member results in a smaller magnetic gap, which contributes to the increased torque and improved efficiency of the electric motor, and therefore the performance of the electric motor can be improved.Furthermore, the thinner tubular member makes it possible to reduce the amount of material used for the support member and the cost can be reduced.

[0060] For example, with reference to Fig. 7, when the area A2 defined by the load curve and the horizontal axis in this embodiment is equal to the corresponding area B in the comparative example (see Fig. 9), the press-holding force acting on the magnet in this embodiment is comparable to the comparative example, and at the same time, the maximum stress generated in the tubular members can be reduced.

[0061] The order of assembly of the rotor 10" according to this embodiment is not limited in any specific way, as described with reference to Fig. 5. This also applies to the case where the holding member is formed from four or more tubular members.

[0062] Next, exemplary configurations of the first tubular member 201, the second tubular member 202, and the third tubular member 203 of the holding member 20 will be described. (Example 3)

[0063] The first tubular member 201, which forms the innermost layer, is made of, for example, FRP containing glass fiber, carbon fiber with a low elastic modulus, or aramid fiber. If the first tubular member 201 is made of a material with a high cushioning effect and high toughness, formability, and ductility, the first tubular member 201 can be prevented from being damaged even if stress concentration occurs due to the uneven shape of the magnet.

[0064] The second tubular member 202 is made of a material having a larger elastic modulus than the first tubular member 201. For example, the second tubular member 202 is made of carbon fiber with a larger elastic modulus than the first tubular member 201. The second tubular member 202 is provided with an interference fit comparable to that of the first tubular member 201. As a result, a larger recovery force can be generated in the second tubular member than in the first tubular member. This allows the second tubular member 202 to provide most of the holding action for holding the magnet. Furthermore, since the second tubular member is sandwiched between the first tubular member 201 and the third tubular member 203, stress concentration due to the external shape of the magnet can be avoided, and there is no risk of the terminal end of the sheet material coming off.To take advantage of this, the second tubular member 202 is provided with a relatively larger interference and a relatively larger elastic modulus to provide the majority of the magnet-holding effect. Furthermore, considering the strength in the radial direction, if the tubular member 202 is provided with a relatively larger tensile force, the large holding force for holding the magnet can be provided.

[0065] The third tubular member 203 is made of a material having a Young's modulus equal to or greater than that of the second tubular member 202. When the third tubular member 203 is made of a material with a high Young's modulus at the outermost layer of the holding member, the third tubular member 203 can be provided with relatively smaller interference compared to the inner tubular members. As a result, the wound sheet material can be prevented from coming off at its connecting end. Furthermore, the fiber can be prevented from digging into the inner peripheral side. Furthermore, productivity during assembly can be improved due to the larger gap for loose fitting. Furthermore, the third tubular member 203 can provide some of the holding force for holding the magnet. The third tubular member 203 can be made of FRP or a non-magnetic metal such as titanium alloy. (Example 4)

[0066] The first tubular member 201 and the second tubular member 202 are made of materials having comparable elastic moduli. The first tubular member 201 and the second tubular member 202 can be made of the same material. Even if the tubular members are made of the same material, the stress is distributed among the tubular members, and therefore, the maximum stress can be reduced, which is advantageous as described above. As the respective tubular members become thinner, the tubular member can be easily formed from the sheet-like material, and properties such as tensile strength and durability can be improved. In addition, since the yield rate is improved, the manufacturing cost can be reduced. The thinner support member also results in a smaller magnetic gap, thereby improving the torque and efficiency of the electric motor, and therefore, the performance of the electric motor can be improved.The thinner retaining member is also advantageous in that, since the amount of material used for the retaining member can be reduced, costs can be reduced. Furthermore, since the maximum load can be reduced, the maximum rotational speed can be increased.

[0067] In contrast, the third tubular member 203 is made of a material with a relatively large elastic modulus. The third tubular member 203 is provided with a small interference. Even if the interference is small, since the third tubular member 203 has a relatively large elastic modulus, a sufficiently large recovery force is generated in the third tubular member 203. Accordingly, the terminal end of the sheet material wound to form the second tubular member 202 can be prevented from coming off the third tubular member 203 due to the compressive force. In addition, since the third tubular member 203 has a small interference, the terminal end of the sheet material wound to form the third tubular member 203 can be prevented from coming off.

[0068] In the case where at least the first and second tubular members 201 and 202 are made of FRP in which fibers extend in a circumferential direction, the FRP matrix fiber of the first tubular member 201 may be configured to have a larger Izod impact strength than the FRP matrix fiber of the second tubular member 202. According to this configuration, the support member 20 can be prevented from being damaged. For example, the first tubular member 201 may contain acrylic resin as the matrix resin, and the second tubular member 202 may contain epoxy resin as the matrix resin. Alternatively, both of the first and second tubular members 201 and 202 may contain epoxy resin as the matrix resin, and the respective materials of the first and second tubular members 201 and 202 may be selected such that the glass transition temperature of the matrix resin of the first tubular member 201 is lower than that of the matrix resin of the second tubular member 202.This allows the rotor to have high fracture resistance or to be expected to operate at higher speeds. (Example 5)

[0069] The first tubular member 201 is a thin tube made of non-magnetic metal. Therefore, even if the magnet has a rough surface and stress concentration tends to occur at a portion contacting the magnet, the first tubular member can be prevented from being damaged.

[0070] The second tubular member 202 is made of, for example, FRP. The second tubular member is made of a material having a modulus of elasticity greater than that of the first tubular member in the circumferential direction and an interference smaller than that of the first tubular member. Since the first tubular member is a metal tube, there is no risk of the fiber of the second tubular member digging into the first tubular member. Therefore, the second tubular member can be provided with an interference comparable to that of the first tubular member. As a result, the second tubular member can be designed to provide the majority of the holding force for holding the magnet. In contrast, the third tubular member 203 is made of a material having a modulus of elasticity greater than that of the second tubular member 202, for example, FRP.The third tubular member 203 is provided with a smaller interference than that of the first tubular member and the second tubular member. As a result, the fibers of the second tubular member 202 can be prevented from coming off or becoming loose. Furthermore, since the third tubular member 203 has a small interference, the connecting end of the web material of the third tubular member can be prevented from coming off.

[0071] Examples are described where the holding member contains three tubular members.

[0072] For simplicity, we consider the case where an imaginary line connecting the contours of the magnets is circular. In the case where the imaginary line is not circular, the same explanation applies based on an imaginary circle, where an equivalent diameter of the circle is replaced by a circumferential length of the magnets.

[0073] The outer diameter of the magnets before attachment to the rotation axis is 80 mm. The sizes of the first tubular member 201, the second tubular member 202, and the third tubular member 203 are as follows: the first pipe link: the inner diameter is 80.1 mm, the thickness is 0.5 mm and the outer diameter is 81.1 mm; the second pipe link: the inner diameter is 81.2 mm, the thickness is 0.5 mm and the outer diameter is 82.2 mm; and the third pipe link: the inner diameter is 82.4 mm, the thickness is 0.5 mm and the outer diameter is 83.4 mm.

[0074] In this case, since the inner diameter of the second tubular member 202 is larger than the outer diameter of the first tubular member 201, the fit therebetween is a loose fit with an interference of 0.1 mm. Since the inner diameter of the third tubular member 203 is larger than the outer diameter of the second tubular member 202, the fit therebetween is a loose fit with an interference of 0.2 mm. Accordingly, the tubular members 201, 202, and 203 can be easily assembled.

[0075] In this example, the interference is set to 0.6 mm, or in other words, the magnet is attached to the rotation axis by a press fit such that the outer diameter of the magnet is increased to 80.6 mm. The press fit can be achieved using oil pressure or a conical die.

[0076] In the case where the interference of the magnet is set to 0.6 mm, the sizes of the tubular members 201, 202 and 203 are as follows (the changes in strength are small enough to be neglected): the first pipe section: the inner diameter is 80.6 mm and the outer diameter is 81.6 mm; the second pipe section: the inner diameter is 81.6 mm and the outer diameter is 82.6 mm; and the third pipe section: the inner diameter is 82.6 mm and the outer diameter is 83.6 mm.

[0077] Accordingly, the interferences of the first tubular member 201 and the second tubular member 202 and the third tubular member 203 are 0.5 mm, 0.4 mm and 0.2 mm, respectively.

[0078] According to this embodiment, the tubular members 201, 202, and 203 are assembled to each other by a loose fit, thus improving productivity. In contrast, the second tubular member 202 has a relatively large interference. Therefore, if the second tubular member 202 is made of a material with a relatively high elastic modulus, most of the holding force for holding the magnet can be provided by the second tubular member 202.

[0079] In embodiments of the present invention, a film may be interposed between the respective tubular members or between the tubular member and the outer peripheral surface of the magnet to increase the holding force for holding the magnet. The film may also have the effect of increasing the tightness between the members that contact each other. Alternatively, a film or a lubricant may be used between the members to improve productivity during the assembly process. Impact of the invention

[0080] According to the invention, the rotor magnets are held by a plurality of tubular members arranged concentrically with the rotor. Therefore, the load that would otherwise tend to concentrate on the inner circumference of the support member is distributed among the respective tubular members, and thus, the maximum load generated in these tubular members can be reduced. The maximum rotational speed of the rotor can be increased without compromising rotor reliability. As a result, the power output of the electric motor can be increased.

[0081] Although the various embodiments and modifications of the present invention have been described above, it will be apparent to those skilled in the art that other embodiments and modifications can also provide the functions and effects intended by the present invention. Specifically, one or more of the constituent elements of the above-described embodiments and modifications may be omitted or substituted, or any known means may be further added without departing from the scope of the present invention. Furthermore, it will be apparent to those skilled in the art that the invention can also be practiced by any combination of the features of the various embodiments expressly or implicitly disclosed in this specification.

Claims

[1] Rotor (10, 10', 10"), wherein the rotor (10, 10', 10") of an electric motor (100) is provided with a plurality of magnets (16, 16a, 16b, 16c) arranged in the circumferential direction, a holding element (20, 20a, 20b) which is concentrically formed on an outer side in a radial direction of the plurality of magnets (16, 16a, 16b, 16c) with respect to the rotor (10, 10', 10") in order to hold the plurality of magnets (16, 16a, 16b, 16c), wherein the holding element (20, 20a, 20b) is formed from a plurality of tubular elements (201, 202, 203) which have different diameters from one another and are arranged concentrically, the diameter of the individual tubular elements (201, 202, 203) being expanded and a compression holding force directed inward in the radial direction acting as an elastic restoring force from the holding elements (20, 20a, 20b) to the magnets (16, 16a, 16b, 16c); wherein an interference of one of the tubular elements of any two tubular elements adjacent to each other in the radial direction among the plurality of tubular elements (201, 202, 203) is designed to be larger than the interference of the other tubular element positioned on the outside in the radial direction of the tubular element in question; wherein the plurality of tubular members contain fiber-reinforced resin configured such that fibers extend at least in one circumferential direction; and wherein the tubular member (201) positioned furthest inward in the radial direction among the plurality of tubular members (201, 202, 203) is configured such that its tensile strength is greater than that of each of the other tubular members (202, 203). [2] The rotor (10, 10', 10") according to claim 1, wherein the elastic modulus of one of the tubular members of any two tubular members adjacent to each other in the radial direction among the plurality of tubular members (201, 202, 203) is made smaller than the elastic modulus of the other tubular member positioned on the outside in the radial direction of the tubular member in question. [3] A rotor (10, 10', 10") according to any one of claims 1 or 2, wherein at least two tubular members among the plurality of tubular members (201, 202, 203) are made of a fiber-reinforced resin formed such that the fibers extend in the circumferential direction, and with respect to each matrix resin of the fiber-reinforced resin, the further inward in the radial direction the tubular member made of the fiber-reinforced resin is positioned, the greater the Izod impact value of the matrix resin. [4] The rotor (10, 10', 10") according to any one of claims 1 to 3, wherein the tubular member (203) positioned outermost in the radial direction among the plurality of tubular members (201, 202, 203) has a cylindrical shape in the state before its attachment, and wherein the other tubular members (201, 202) of the plurality of tubular members have a non-cylindrical shape. [5] Electric motor (100) provided with a rotor (10, 10', 10") according to one of claims 1 to 4.

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