Rotor

Abstract

A rotor (10) for a rotating electric machine is described, the rotor (10) comprising a support disk (14) having opposing first and second faces, a support member (20), and a plurality of permanent magnets (22) attached to and carried by the support member, the support member being fixed to a first face of the support disk (14).

Description

[Technical field]

[0001] The present invention relates to a rotor for a rotating electric machine such as an electrically charged motor or generator, and in particular to a rotor suitable for use in an axial flux motor in which the stator cooperates with the rotor through an air gap, the air gap being transverse to the magnetic flux and primarily parallel to the axis of rotation, although it will be understood that the invention is not limited to such use. [Background technology]

[0002] GB 2468018 describes a machine comprising a series of coils wound around pole pieces spaced circumferentially around a stator and spaced axially (i.e. parallel to the axis of rotation of the rotor) from an associated rotor. The rotor has two stages comprising disks provided with permanent magnets facing either end of each electromagnetic coil of the stator.

[0003] The rotor stage typically comprises a hub region and an annular ring, the annular ring being of soft magnetic material and used to transfer magnetic flux between adjacent magnets, the magnets being surface mounted and spaced circumferentially around the rotor stage annular ring and arranged axially, i.e. parallel to the rotor axis of rotation. High rotational rotor speeds generate high centripetal forces on the rotor stage, especially the surface mounted magnets, and loss of magnet adhesion is a risk with this motor topology. The annulus and hub region are continuous and made of the same material, which can typically be ferromagnetic steel, but which is electrically conductive and experiences eddy current losses in use. To reduce eddy currents, the annular ring can carry a soft magnetic material, which can be a soft magnetic powder composite or laminated magnetic steel, which can carry magnetic flux substantially between adjacent surface mounted magnets, but this same-plane current flow is inhibited and has high electrical resistance in a plane substantially radial to the motor axis.

[0004] Two stator, one rotor axial flux motors are also known, where the one rotor includes circumferentially arranged magnets with pole faces facing across an air gap to a similarly arranged stator electromagnetic coil. Two rotor machines preferably have a rotor including a non-magnetic matrix having circumferentially arranged embedded magnets with their pole faces aligned primarily parallel to the axis of rotation, with magnetic north and south pole faces facing across the air gap towards the stator.

[0005] Two stator, one rotor axial flux machines have the advantage that the rotor cooperates with both stators and the magnetic field induced axial forces on the rotor are substantially balanced, so that the magnetic forces applied to them are substantially equal at rest and in use. Two stator, one rotor machines do not require a rotor magnetic yoke to move the permanent magnets, thus saving on yoke weight, and because the axial forces are substantially balanced, the rotor of such machines can be made relatively low stiffness. However, these advantages come at the expense of the two stators and their back yokes, which, when assembled, usually have an axial length larger than a one stator, two rotor axial flux machine. However, to obtain the short axial length, the rotor structure must achieve the stiffness and integrity at rest and under load.

[0006] It is advantageous in the motor of the present invention to minimize the air gap between the stator and rotor, thereby maximizing the torque generated by the opposing magnetomotive forces between the stator and rotor, consistent with the stiffness of the rotor stage and stack tolerances of the associated components. Minimizing the air gap between the stator and rotor can result in large axial loads between the rotor stage and the motor stator at rest and during operation, and it is preferable for the rotor to be stiff to resist bending that may otherwise interfere with the stator.

[0007] The problem that this invention seeks to solve is to achieve sufficient stiffness in the rotor stage to minimize motion to the stator while minimizing the mass of the rotor stage, minimizing eddy currents, and maximizing flux carrying capacity. Another problem of the motor of this invention is to maintain the integrity of the rotor stage which is rotated at high rotational speeds during normal operation, which speeds induce large centripetal forces on the magnets, thus putting stress on the attachment between the surface mounted magnets and the annular ring to which they are secured.

[0008] Another problem to be solved with the motor of the present invention is the thermal expansion mismatch between the rare earth transition metal composite magnet material and the rotor substrate made from magnetic steel on which the magnets are surface mounted. Temperature cycling can cause cracks in the bond between the magnets and the steel substrate. Furthermore, the ultimate operating temperature can be limited for similar reasons that prevent storage or transportation in locations where ambient temperatures can reach -40 degrees.

[0009] A further problem to be solved by the motor of the present invention is that the rotor may have a resonant frequency that coincides with the operating speeds typically used, and so there is value in damping vibrations whilst maintaining other properties.

[0010] Another problem that the motor of the present invention must solve is maintaining the peak temperature of commonly used permanent rare earth transition metal magnets at around 130 degrees, well below their Curie temperature. Eddy currents are generated in the permanent magnets during motor operation, and to reduce the eddy currents the magnets can be radially laminated, but laminations result in loss of useful magnetic material, are costly, and the number of laminations is limited by the cost / benefit balance. As a result, although the eddy currents are reduced, heat is still generated in the permanent magnets.

[0011] Most dynamoelectric machines are so-called radial flux machines, which have a rotor and a stator, with magnetic flux passing between the rotor and the stator in a radial direction, i.e. generally perpendicular to the axis of rotation, and rotate the rotor by the antagonistic action of the magnetic flux of the stator and the rotor. Radial flux machines generate significant centripetal forces as the rotor rotates. Radial flux machines have been mechanically improved to accommodate the centripetal forces by wrapping the rotor in fibers reinforced with a resin matrix. U.S. Patent Application Publication No. 2004 / 0021396 is one example, and U.S. Patent Application Publication No. 10-210690 is another example, where the fibers provide strength in the circumferential direction and maintain the structural integrity of the rotor against the centripetal forces.

[0012] While the majority of commercially available dynamoelectric machines are radial flux designs, there has been growing interest in axial flux machines such as those described herein. However, axial flux machines, especially those operated at high rotational speeds, present significant challenges due to the combination of axial and radial forces during operation.

[0013] It is an object of the present invention to provide a rotor in which at least some of the disadvantages associated with known rotor designs are overcome or the effects of these are reduced. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] British Patent No. 2468018 Specification [Patent Document 2] US Patent Application Publication No. 2004 / 0021396 [Patent Document 3] Japanese Patent Application Publication No. 10-210690 Summary of the Invention

[0015] The present invention provides a rotor for an electric rotating machine and a method for assembling a rotor for an electric rotating machine as defined by the independent claims attached hereto. Further advantageous embodiments are provided by the independent claims also attached hereto.

[0016] In particular, it describes a rotor for a rotating electric machine comprising a support disk having opposing first and second faces, a support member for receiving a plurality of permanent magnets, a plurality of permanent magnets mounted to and retained by the support member, and a retaining band extending around the permanent magnets and restricting or preventing radially outward movement of the permanent magnets in use, the retaining band being prestressed to apply a radially directed load inwardly against the plurality of magnets, the support member being fixed to the first face of the support disk.

[0017] By using a support member to hold the permanent magnets during construction of the rotor, fixing the support member and magnets to a first surface of the support disk, and using a prestressed retaining band to apply an inward, radially directed load to the magnets even when stationary, it is possible to construct a rotor that can achieve higher rpm than conventional rotors.

[0018] The support member may include a plurality of radially extending spokes, the spaces between adjacent spokes defining gaps for receiving respective permanent magnets.

[0019] Alternatively, the support member may comprise an annular portion having a plurality of spokes projecting radially therefrom, and each of the spaces between adjacent spokes may define a socket for receiving a respective permanent magnet.

[0020] The support member may be co-molded with the magnet and may be formed from a sheet molding compound (SMC) material.

[0021] Alternatively, the support member may be co-molded with the magnet and the support member may be formed from an injection molded polymer.

[0022] The spokes forming the annular portion and the support member may be formed from separate pieces.

[0023] In such a rotor, the annular portion may include a plurality of deformable structures extending radially outward, each of the deformable structures positioned on the annular portion to coincide with a respective spoke, each of the deformable structures contacting and providing a radial force against a respective spoke.

[0024] The annular portion may be formed from an injection molded polymer.

[0025] Each of the spokes may be formed from a unidirectional carbon strip, and the fibres of each of the carbon strips may be perpendicular to the axial length of the respective spoke.

[0026] Each of the spokes may be formed from a material having isotropic properties in a plane extending radially along the length of the respective spoke and in a plane extending perpendicular to the radial plane.

[0027] Each of the spokes may be formed from a magnetic material that may have a magnetic field alignment that is orthogonal to the magnetic field alignment of one or more of the plurality of permanent magnets.

[0028] The retaining band may comprise a composite material. By way of example it may comprise windings of a reinforcing fibrous material within a matrix of a suitable resin material. The fibrous material may be in the form of, for example, carbon fibre or glass fibre. Conveniently, the fibrous material is substantially hoop wound.

[0029] Preferably, the support member and permanent magnet are configured to react to loads imparted to the magnets by the retaining bands and substantially prevent the magnets from moving radially inward as a result of loads applied by the retaining bands.

[0030] To prevent relative movement between the support member and / or the permanent magnet and / or the support band, the gap between the support member and the permanent magnet and / or between the permanent magnet and the support band may be filled with a polymer resin.

[0031] The support member may be secured to the first surface of the support disc using an adhesive. Preferably, the permanent magnets may be secured to the support disc by bonding using a relatively low modulus adhesive.

[0032] It will be appreciated that just as the retaining bands serve to retain the permanent magnets against radial movement, the primary purpose of the adhesive material is to prevent the permanent magnets from lifting off the surface of the support disc.

[0033] By way of example, in the context of the present invention, a high modulus adhesive would be considered to have a modulus of elasticity greater than 500 MPa. Typically, epoxies have a modulus in the range of 1-5 GPa. A semi-rigid adhesive may have a modulus between 20 MPa and 500 MPa. A low modulus adhesive may have a modulus of elasticity of about 20 MPa or less. Typically, silicone adhesives have a modulus in the range of 1-2 MPa.

[0034] In use, the rotor is subjected to large loads resulting from centripetal effect and magnetic attraction and repulsion, as described below. It is important that the permanent magnets are held in place on the support disk, and through the use of a low modulus adhesive material, the magnets can be held in place on the support disk while accommodating limited movement between the magnets and the support disk. Low modulus materials typically exhibit high strain to failure, i.e., elongation under load. Whereas an epoxy adhesive, for example, can accommodate small amounts of elongation, a silicone adhesive can accommodate several hundred percent elongation. It is this strain capability or flexibility that allows it to accommodate relative movement between components.

[0035] The adhesive material preferably has good thermal conductivity, for example better than 0.5 W / m·K.

[0036] The support disk preferably comprises a first annular member, conveniently made of steel, to which is joined a second annular member. The second annular member is preferably a laminate. It may comprise a helically wound coil of laminated magnetic steel sheets. Such an arrangement has the advantage that it has a relatively high radial electrical resistance, preventing the generation of eddy currents, whilst allowing the traversal of magnetic flux.

[0037] The first and second annular members are conveniently bonded or secured to one another using a material of good thermal conductivity. By way of example, they may be secured to one another by epoxy bonding, silver brazing, soldering, or a suitable eutectic or eutectic region bonding medium. Preferably, the first and second annular members are bonded or secured to one another using a material having a thermal conductivity greater than 0.5 W / m·K, more preferably 10 W / mK.

[0038] We also describe a rotating electric machine comprising a stator and a rotatable rotor in the form of the rotor described above, said rotating electric machine being an axial flux machine such as a motor or generator, in which the rotor is positioned between a pair of rotors in the form described above.

[0039] Further, a method of assembling a rotor for a rotating electric machine comprising providing a support disk having opposing first and second faces, providing a support member having a plurality of permanent magnets attached thereto, positioning a prestressed retaining band to extend circumferentially around an outer radius of the permanent magnets, the retaining band applying an inwardly radially directed load to the permanent magnets to limit or prevent radially outward movement of the permanent magnets in use and in a prestressed state, and securing the support member to the first face of the support disk. The present invention describes a method comprising:

[0040] Providing a support member having a plurality of permanent magnets attached thereto comprises positioning a stiffener structure in a mold, the stiffener structure comprising a plurality of spokes projecting radially from an annular portion, each of the spaces between adjacent spokes defining a socket for receiving a respective permanent magnet; positioning a respective permanent magnet in each of the sockets; and coupling each of the permanent magnets to the stiffener structure.

[0041] The annular portion and each spoke of the stiffener structure may be in the form of a single piece. Alternatively, the annular portion and each spoke of the stiffener structure may be in the form of separate pieces.

[0042] Where the spokes and stiffener structures are formed in separate sections, the annular portion may comprise a plurality of deformable structures extending radially outward, each of the deformable structures being positioned on the annular portion to coincide with a respective spoke, such that when placed within the mold, each of the deformable structures contacts and provides a radial force against a respective spoke.

[0043] The annular portion may be formed from an injection molded polymer.

[0044] Each of the spokes may be formed from a unidirectional carbon strip, and the fibres of each of the carbon strips may be perpendicular to the axial length of the respective spoke.

[0045] Each of the spokes may be formed from a material having isotropic properties in a plane extending radially along the length of the respective spoke and in a plane extending perpendicular to the radial plane.

[0046] Each of the spokes may be formed from a magnetic material that may have a magnetic field alignment that is orthogonal to the magnetic field alignment of one or more of the plurality of permanent magnets.

[0047] In any of the above methods, coupling each of the permanent magnets to the stiffener structure may comprise injecting resin to fill gaps between one or more of the respective magnets and respective spokes and annular portion.

[0048] Alternatively, coupling each of the permanent magnets to the stiffener structure may comprise coupling each of the permanent magnets to the stiffener structure using an adhesive between each of the permanent magnets and a respective spoke and portion of the annular portion.

[0049] In an alternative method, providing a support member having a plurality of permanent magnets attached thereto comprises positioning a plurality of permanent magnets in a mold, the magnets being circumferentially disposed about an axis with gaps between each of the magnets, and forming a stiffener structure around the permanent magnets in the mold.

[0050] Forming a stiffener structure around the permanent magnets in the mold comprises using a plurality of SMC (sheet molding compound) preforms, each arranged as spokes projecting radially outward in the gaps between respective adjacent permanent magnets, and compressing the plurality of SMC preforms into the stiffener structure.

[0051] The stiffener structure includes an annular inner portion with the spokes formed therefrom.

[0052] The SMC preform may comprise a thermoset resin.

[0053] Providing a support member having a plurality of permanent magnets attached thereto comprises injection molding with a polymer to form a stiffener structure having a plurality of spokes projecting radially outwardly, each spoke being formed between adjacent permanent magnets.

[0054] The stiffener structure is formed with an annular inner portion with the spokes protruding therefrom, the annular inner portion being formed during injection molding using a polymer.

[0055] The injection molded polymer may comprise a polymer having fibers therein.

[0056] In any of the above methods, the retaining band may be a composite material. The retaining band may comprise windings of a reinforcing fibrous material within a matrix of a suitable resin material. The fibrous material may be substantially hoop wound.

[0057] In any of the above methods, the support member and permanent magnet may be secured to the first surface of the support disk using an adhesive, the adhesive may have a relatively low elastic modulus, the elastic modulus of the adhesive may be less than 20 MPa.

[0058] The adhesive material may have a higher thermal conductivity than epoxy. The adhesive material may have a thermal conductivity of greater than 0.5 W / m·K. [Brief description of the drawings]

[0059] The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a diagram showing a rotor according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a rotor according to an embodiment of the present invention. [Diagram 3] FIG. 3 is an exploded view of the rotor of FIGS. [Figure 4] FIG. 4 is a schematic diagram showing the rotor of FIGS. 1 to 3 in use. [Diagram 5] FIG. 5 is a diagrammatic representation showing a portion of the rotor and the loads it is subjected to. [Figure 6] FIG. 6 shows an inner radial ring of one embodiment of a support member. [Figure 7] FIG. 7 shows the inner radial ring of FIG. 6 in a mold with spokes before the resin-based filler is added. [Figure 8] FIG. 8 is an example of a UD pultrusion showing the cut lines for forming each of the spokes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] 1 to 3, a rotor 10 is shown for use in a rotating electric machine 12 (see FIG. 4), which in this embodiment takes the form of an axial flux motor. Although the rotor 10 is intended for use in an axial flux motor, it will be appreciated that the invention is not limited in this respect and the rotor 10, as shown or in modified form, may be used in, for example, a generator.

[0061] The rotor 10 includes a support disk 14 made from a first annular member 16 of steel to which a second annular member 18 is bonded or otherwise secured, for example by adhesive 18a or the like, the second annular member 18 being in the form of a helical coil of magnetic steel sheet material, the windings of which are laminated together in such a way as to form a body having a relatively high radial electrical resistance, reducing the generation of eddy currents therein, while readily allowing the traversal of magnetic flux between its faces. The first and second annular members 16, 18 are spaced very closely together and are bonded or otherwise secured together in such a way that thermal energy can be readily conducted therebetween. By way of example, the first and second annular members 16, 18 may be brazed together. Alternatively, they could be bonded together using a suitable epoxy adhesive (as shown), a suitable eutectic material, or the like.

[0062] The first annular member 16 serves as structural support for the remainder of the rotor 10 .

[0063] In the illustrated arrangement, steel is used for the first annular member 16, but it will be understood that other materials could be used. By way of example, a suitable ceramic or composite material could be used as desired.

[0064] A face of the second annular member 18 remote from the first annular member 16 has a support member 20 adhered thereto by an adhesive material 18b. In a first embodiment, the support member 20 is non-magnetic and shaped to define a central annular portion 20a from which extend a plurality of generally radially projecting spokes 20b. Adjacent ones of the spokes 20b define a socket or space therebetween in which a respective permanent magnet 22 is positioned. The permanent magnets 22 and the support member 20 are bonded to the second annular member 18 by using an adhesive material 18b. The adhesive material 18b may be any type of adhesive suitable for bonding the permanent magnets 22 and the support member 20 to the second annular member.

[0065] The adhesive material 18b may be, for example, an adhesive such as epoxy (or having similar properties or modulus of elasticity as an epoxy adhesive) that provides a strong and rigid bond between the magnet 22, the support member 20, and the second annular member. However, it is preferred that the adhesive material 18b has a low or relatively low modulus of elasticity and a relatively high thermal conductivity. By way of example, the adhesive material 18b may be in the form of a silicone base. Other examples of suitable materials include low modulus epoxy adhesives, polyurethane adhesives, acrylic adhesives, and nitrile phenolic adhesives. It will be understood that this list is not exhaustive and other materials may be used. To achieve the benefits of the invention, the strain, or elongation, to failure of the material should be sufficient to absorb all relative movement of the components that occurs in normal use, so that the stress in the adhesive does not carry significant radial loads. By way of example, the modulus of elasticity should be less than 20 MPa, and preferably in the range of 1 MPa to 5 MPa.

[0066] Surrounding the radially outer periphery of the magnets 22 are retaining bands 24, the purpose of which is to apply a radially inwardly directed load to the magnets 22 and force them into the sockets or spaces between the spokes 20b of the support member 20. The retaining bands 24 are of a fibre reinforced composite material. By way of example, they comprise windings of a suitable reinforcing fibre material, such as carbon fibre, embedded in a suitable resin material matrix. The retaining bands 24 are conveniently manufactured to have a relaxed diameter less than the outer diameter of the portion of the rotor 10 defined by the permanent magnets 22, and the retaining bands 24 are elastically stretched over the permanent magnets 22 during the assembly process in order to prestress the retaining bands 24 in such a way that they apply the aforementioned radially directed load to the magnets 22.

[0067] It will be appreciated that the retaining bands 24 exert relatively large radially inwardly directed loads on the magnets 22, and that one of the functions of the support members 20 is to react to these loads. When bonded with a low modulus adhesive, the support members 20 react to substantially all of the radially inwardly directed loads applied to the magnets 22 that would otherwise result in failure of the adhesive joint. The shape of the sides of the magnets 22 and the adjacent portions of the support members 20 is such that a locking force is generated between the magnets 22 and the support members 20 as a result of the hoop stresses generated in the retaining bands when installed. The locking force results from radially inwardly directed loads which press the sides of the magnets 22 against the sides of each leg of the support members 20 as a result of the wedge shape of the magnets 22. The magnets 22 therefore become locked to the support members 20 with their legs compressed between adjacent ones of the magnets 22, as shown diagrammatically in FIG. 5. The modulus of elasticity of this support member is important in enabling the rotor to function and react to loads, as the magnets are relatively stiff. By way of example, the support member 20 may be a material with a high carbon fiber content. Preferably, it should have a modulus of elasticity in excess of 20 GPa.

[0068] The support member 20 may be in an injection molded form, or alternatively may be, for example, a pressed form that is machined or finished substantially to the shape shown. However, in some embodiments, some manufacturing techniques (described below) allow the support member 20 to be formed without the inner annular portion 20a. For convenience, the support member 20 and magnets 22 are preassembled to form a subassembly that is then bonded as a unit to the second annular member 18 by adhesive 18b.

[0069] In a first manufacturing technique, the support member 20 is mounted in a mold as a single piece, i.e., the support member 20 includes an inner peripheral portion 20a and a plurality of spokes 20b. The production of the subassembly preferably includes filling any spaces or gaps between the magnet 22 and the support member 20 with, for example, a suitable resin-based filling substance, e.g., the magnet 22 and the support member 20 are positioned in a mold of suitable shape. The support member 20 may be designed to a slightly undersized size for this purpose, and its legs may be designed to a length such that, in use, they do not protrude radially outward of the magnet 22 and therefore do not engage the retaining band 24.

[0070] Alternatively, instead of providing the support member 20 as a single piece, the support member 20 may be provided as separate pieces, i.e., an inner annular ring 20a and separate spokes 20b, which are positioned in a mold with a plurality of magnets before a resin-based filler material is added between the gaps.

[0071] Figure 6 shows the inner radial ring of one embodiment of a support member. Figure 7 shows the inner radial ring of Figure 6 in a mold with spokes before the resin-based filler is added.

[0072] In such a manufacturing technique, the inner annular ring 20a may be provided with a plurality of deformable structures 20c spaced about its circumference, the purpose of each of the deformable structures 20c being to contact a respective spoke 20b and provide a radial force against the spokes 20b to hold them in place before the resin-based filler is added between the gaps. Once the resin-based filler is added, the structure is fixed in place.

[0073] When the support member 20 is provided as a separate piece, this allows the different pieces that comprise the support member 20 to be made from different materials having different properties.

[0074] For example, spokes 20b may include unidirectional (UD) carbon strips, such as those cut from a pultruded profile, which is a continuous manufacturing process primarily suited to producing UD strip material in large quantities with low labor.

[0075] FIG. 8 shows an example of a UD pultrusion showing the cut lines for forming each of the spokes 20b prior to assembly in a mold.

[0076] The use of spokes 20b comprising UD carbon fiber pultrusions significantly increases the stiffness of the spokes, particularly across their width. For example, the planar modulus across their width may be in the range of 110-130 Gpa, while the planar modulus along their length is in the range of 5 Gpa.

[0077] Alternatively, the spokes 20b may comprise an isotropic or quasi-isotropic material, for example a material that is isotropic in the XY plane (where the XY plane is the face of the support member and magnet). Such material combinations include glass fiber SMC (Sheet Moulding Compound), which may have an XY plane elastic modulus of 10-20 GPa, while carbon fiber SMC is higher, typically around 30-40 GPa - this can be increased by choosing a higher modulus grade of carbon fiber. In the Z plane (thickness direction), the elastic modulus is lower, for example in the range of 5-10 GPa.

[0078] The spokes 20b may instead include a magnetic material. In such an arrangement, the magnetic field alignment of the spokes 20b is arranged orthogonal to the magnetic field alignment of the permanent magnets 22. For example, if the permanent magnets are arranged as a NS pair, the spokes 20b may be arranged to have an EW alignment. Such an arrangement may provide a Halbach array, which may improve the magnetic performance of the rotor due to magnetic field enhancement.

[0079] In any of the manufacturing techniques mentioned above, the inner ring 20a may be injection molded, the material properties of which do not affect the performance of the rotor as much as the position of the magnets 22 and spokes 20b.

[0080] As previously mentioned, the inner ring 20a may alternatively be absent, in which case the permanent magnets 22 are held by the spokes 20b within the mold before the resin-based filler is added.

[0081] By producing the subassembly in this manner, it is possible to ensure that the magnets 22 are in intimate contact with the support member 20 and the filler material, minimizing or avoiding movement therebetween, so that subsequent application of the retaining band 24 should not result in significant movement of the magnets 22 that would cause stress or strain in the adhesive material 18b.

[0082] While the manufacturing technique described above uses a resin-based filler material once the components (inner ring 20a, spokes 20b, if applicable, and magnets 22) are positioned in a mold, an alternative technique involves using an adhesive between some or all of the components (inner ring 20a, spokes 20b, if applicable, and magnets 22). Such a technique provides a stronger bond strength between the respective components, particularly between the magnets 22 and spokes 20b, than would be the case if a resin-based filler material were used.

[0083] Broadly speaking, an alternative, co-molding, assembly technique involves positioning the magnets 22 in a suitable mold and molding the support member 20 in place between the magnets 22. Such co-molding techniques eliminate the need to fill gaps or spaces with a filler material because no gaps or spaces exist, and the magnets 22 and support member 20 are in intimate contact with one another as a result of the manner in which the support member 20 is formed.

[0084] In such co-molding techniques, the magnets 22 may be placed in a downstream tool and clamped or held in place. The SMC (Sheet Molding Compound) preform is uncured and flexible at this stage and is simply a rectangular piece of material cut. The SMC may include a thermosetting resin. The SMC preform is loaded into the tool and the upstream tool is introduced, compressing the SMC material and forcing it to flow into the final shape of the spokes 20b and inner ring 20a (although the tool may be shaped so that it does not place the inner ring 20a on the support member 20).

[0085] Using co-molding techniques, the load path from the magnets goes directly into the SMC material, producing a support member 20 and magnet 22 subassembly with high overall stiffness.

[0086] It will be appreciated that the rotor 10 described above is of single-sided configuration with magnets 22 coupled to a face of a support disk 14 consisting of first and second annular disks 16, 18 and a support member 20. In use, a pair of such rotors 10 are mounted on a common rotor shaft 26 and positioned such that a single stator 28 is axially positioned between the rotors 10, the stator 28 including coils which, in use, are energized to induce a magnetic field which cooperates with the permanent magnets 22 to drive the rotor 10, and the rotor shaft 26 is mounted such that they rotate. In some configurations, the rotors 10 may be mounted on bearings housed in the stator 28.

[0087] In use, rotation of the rotor 10 about its axis results in the magnets 22 being subjected to large centripetal loads, and the prestressed retaining bands 24 serve to counter these loads and hold the magnets 22 in place. The interaction between the magnetic flux of the permanent magnets 22 and the magnetic fields associated with the stator coils can result in large loads being applied to the permanent magnets 22 in a direction that pulls them away from the support disk 14 and / or causes the permanent magnets to twist or tilt relative to the support disk 14. If the permanent magnets 22 are bonded to the support disk 14 through the use of a low modulus adhesive material, the low modulus adhesive can accommodate such twisting movements and flex in use while maintaining the integrity of the bond between the permanent magnets 22 and the support disk 14. The low modulus adhesive material can also accommodate movements resulting from differential thermal expansion between parts of the rotor 10, particularly the magnets 22 and the second annular member 18, which is important as discussed previously herein.

[0088] Even if the support members 20 and permanent magnets 22 are bonded to the support disk by using an adhesive having a higher modulus of elasticity, the arrangement of the support members 20, permanent magnets 22, and prestressed bands 24 acts to prevent movement between the support disk and the magnets. Rotation of the rotor 10 about its axis in use causes the permanent magnets 22 to be subjected to large centripetal loads, and the prestressed retaining bands 24 act to counteract those loads and hold the permanent magnets 22 in place. Interaction between the magnetic flux of the permanent magnets 22 and the magnetic fields associated with the stator coils can cause the permanent magnets 22 to apply large loads in a direction that pulls them away from the support disk 14 and / or causes the permanent magnets to twist or tilt relative to the support disk 14, all of which are prevented by the adhesive.

[0089] The thermal conductivity of the material used to bond the permanent magnets 22 to the support disk 14, combined with the design of the support disk 14, allows for the conduction of thermal energy away from the magnets 22 for dissipation elsewhere in the motor.

[0090] It will be appreciated that the present invention is advantageous in that the permanent magnets are fixed to the remainder of the rotor 10 in a manner that makes it possible to avoid loss of the magnets and subsequent catastrophic damage to the motor during use, whilst still allowing the motor to operate at high speeds, e.g., in excess of 15,000 rpm, and in a variety of operating environments.

[0091] Although the rotor 10 described above is intended for use in a motor of the type in which a stator is positioned between a pair of single-sided rotors, the invention is not limited to such use and may be employed in other forms of motors and other forms of rotating electrical machines.

[0092] Although particular embodiments of the invention have been described herein, it will be understood that a wide range of modifications and variations can be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A rotor for a rotating electric machine, the rotor comprising: a support disk having opposing first and second surfaces; a support member for receiving a plurality of permanent magnets; a plurality of permanent magnets attached to and held by the support member; a retaining band extending around the permanent magnets and limiting or preventing radially outward movement of the permanent magnets in use, the retaining band being prestressed to apply a radially directed load inwardly to a plurality of the magnets; Equipped with The support member is fixed to the first surface of the support disk. Rotor.

2. the support member includes a plurality of radially extending spokes, the spaces between adjacent spokes defining gaps for receiving respective permanent magnets; The rotor according to claim 1 .

3. the support member comprises an annular portion having a plurality of spokes projecting radially therefrom, each of the spaces between adjacent spokes defining a socket for receiving a respective permanent magnet; The rotor according to claim 1 .

4. the support member is co-molded with the magnet and is formed from a sheet molding compound (SMC) material; A rotor according to claim 2 or 3.

5. the support member is co-molded with the magnet, the support member being formed from an injection molded polymer. The rotor according to claim 3.

6. the annular portion and the spokes are formed from separate pieces; The rotor according to claim 3.

7. the annular portion includes a plurality of deformable structures extending radially outward, each of the deformable structures positioned on the annular portion to coincide with a respective spoke; The rotor according to claim 6.

8. each of said deformable structures contacting and providing a radial force to a respective spoke; A rotor according to claim 7.

9. the annular portion is formed from an injection molded polymer; A rotor according to claim 6, 7 or 8.

10. each of said spokes being formed from a unidirectional carbon strip, the fibers of each of said carbon strips being perpendicular to the axial length of said respective spoke; The rotor according to claim 6.

11. each of said spokes is formed from a material having isotropic properties in a plane extending radially along the length of the respective spoke and in a plane extending perpendicular to the radial plane; The rotor according to claim 6.

12. each of said spokes being formed from a magnetic material; The rotor according to claim 6.

13. the magnetic material has a magnetic field alignment that is orthogonal to the magnetic field alignment of one or more of the plurality of permanent magnets. A rotor as claimed in claim 12.

14. The retaining band is a composite material. The rotor according to claim 1 .

15. The retaining band comprises windings of a reinforcing fibre material within a matrix of a suitable resin material. A rotor according to claim 14.

16. The reinforcing fiber material is hoop wound. A rotor as claimed in claim 15.

17. the support member and permanent magnet are configured to be responsive to a load applied to the magnet by the retaining band to prevent the magnet from moving radially inward as a result of the load applied by the retaining band; The rotor according to claim 1 .

18. a polymeric resin material between a portion of the permanent magnet, the support member and / or the retaining band; The rotor according to claim 4.

19. the support member and permanent magnet are secured to the first surface of the support disk using an adhesive; The rotor according to claim 1 .

20. The elastic modulus of the adhesive is less than 20 MPa; 20. The rotor of claim 19.

21. The adhesive has a higher thermal conductivity than epoxy.

20. The rotor of claim 19.

22. The adhesive has a thermal conductivity of greater than 0.5 W / m·K.

22. A rotor according to claim 21.

23. the support disk comprising a first annular member having a second annular member coupled thereto; The rotor according to claim 1 .

24. the first annular member is made of steel; 24. A rotor according to claim 23.

25. The second annular member is a laminate.

24. A rotor according to claim 23.

26. the second annular member is a stacked spirally wound coil; 26. A rotor as claimed in claim 25.

27. the first and second annular members are bonded or secured to one another using a material having a thermal conductivity greater than 10 W / mK; 24. A rotor according to claim 23.

28. A rotating electric machine having a stator and a rotatable rotor, the rotor having the configuration of claim 1, Rotating electric motor.

29. Equipped with an axial flux motor or axial flux generator, 29. The rotating electric machine according to claim 28.

30. The stator is positioned between a pair of rotors having the configuration of claim 1.

30. The rotating electric machine according to claim 29.

31. A method for assembling a rotor for a rotating electric machine, comprising the steps of: providing a support disk having opposing first and second surfaces; providing a support member having a plurality of permanent magnets attached thereto; positioning a prestressed retaining band extending circumferentially around an outer radius of the permanent magnet, the retaining band applying an inward, radially directed load to the permanent magnet in use and in a prestressed state to limit or prevent radially outward movement of the permanent magnet; securing the support member to the first surface of the support disk; A method comprising:

32. Providing a support member having a plurality of permanent magnets attached thereto, positioning a stiffener structure within the mold, the stiffener structure comprising a plurality of spokes projecting radially from the annular portion, each of the spaces between adjacent spokes defining a socket for receiving a respective permanent magnet; positioning a respective permanent magnet in each of said sockets; coupling each of the permanent magnets to the stiffener structure; 32. The method of claim 31 , comprising:

33. the annular portion and each spoke of the stiffener structure are in the form of a single piece; 33. The method of claim 32.

34. the annular portion and each spoke of the stiffener structure are in the form of a separate piece; 33. The method of claim 32.

35. the annular portion includes a plurality of deformable structures extending radially outward, each of the deformable structures positioned on the annular portion to coincide with a respective spoke; 35. The method of claim 34.

36. when placed within the mold, each of the deformable structures contacts and provides a radial force against a respective spoke; 36. The method of claim 35.

37. the annular portion is formed from an injection molded polymer; 37. The method of claim 34, 35 or 36.

38. each of said spokes being formed from a unidirectional carbon strip, the fibers of each of said carbon strips being perpendicular to the axial length of said respective spoke; 37. The method of any one of claims 34 to 36.

39. each of said spokes is formed from a material having isotropic properties in a plane extending radially along the length of the respective spoke and in a plane extending perpendicular to the radial plane; 35. The method of claim 34.

40. each of said spokes being formed from a magnetic material; 35. The method of claim 34.

41. the magnetic material has a magnetic field alignment that is orthogonal to the magnetic field alignment of one or more of the plurality of permanent magnets.

41. The method of claim 40.

42. coupling each of the permanent magnets to the stiffener structure comprises injecting resin to fill gaps between one or more of the respective magnets, each spoke, and an annular portion.

33. The method of claim 32.

43. coupling each of the permanent magnets to the stiffener structure comprises coupling each of the permanent magnets to the stiffener structure using an adhesive between each of the permanent magnets and a respective spoke and a portion of the annular portion.

33. The method of claim 32.

44. Providing a support member having a plurality of permanent magnets attached thereto, positioning a plurality of permanent magnets within a mold, the magnets being circumferentially disposed about an axis with gaps between each of the magnets; forming a stiffener structure around the permanent magnet in the mold; 32. The method of claim 31 , comprising:

45. forming a stiffener structure around the permanent magnet in the mold, using a plurality of SMC (sheet molding compound) preforms, each arranged as spokes projecting radially outwardly in the gaps between respective adjacent permanent magnets; compressing a plurality of said SMC preforms into said stiffener structure; 45. The method of claim 44, comprising:

46. the stiffener structure includes an annular inner portion with the spokes formed to protrude therefrom; 46. ​​The method of claim 45.

47. The SMC preform comprises a thermosetting resin.

47. The method of claim 45 or 46.

48. Providing a support member having a plurality of permanent magnets attached thereto, injection molding with a polymer to form a stiffener structure comprising a plurality of radially outwardly projecting spokes, each spoke being formed between adjacent permanent magnets; 45. The method of claim 44, comprising:

49. the stiffener structure is formed with an annular inner portion having the spokes protruding therefrom, the annular inner portion being formed during injection molding using a polymer; 49. The method of claim 48.

50. The injection molded polymer comprises a polymer having fibers therein.

50. The method of claim 48 or 49.

51. The retaining band is a composite material.

32. The method of claim 31 .

52. The retaining band comprises windings of a reinforcing fibre material within a matrix of a suitable resin material.

52. The method of claim 51.

53. The reinforcing fiber material is hoop wound.

53. The method of claim 52.

54. the support member and permanent magnet are secured to the first surface of the support disk using an adhesive; 32. The method of claim 31 .

55. The elastic modulus of the adhesive is less than 20 MPa; 55. The method of claim 54.

56. The adhesive has a higher thermal conductivity than epoxy.

55. The method of claim 54.

57. The adhesive has a thermal conductivity of greater than 0.5 W / m·K.

57. The method of claim 56.

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