Rotors for axial flux machines

Abstract

A method of manufacturing a rotor for an axial flux permanent magnet machine, the machine having a stator including a set of coils wound on respective stator bars and spaced circumferentially about an axis of the machine, and a rotor including a rotor body carrying a set of permanent magnets on a layer of metal laminations and mounted for rotation about the axis, the rotor and stator being spaced along the axis to define a gap therebetween along which magnetic flux in the machine is generally axial, the method including brazing the metal laminations to the rotor body and bonding the set of permanent magnets to the metal laminations.

Description

[Technical field]

[0001] This specification describes a method of manufacturing a rotor for an axial flux permanent magnet machine, the rotor produced by the method, and machines incorporating the rotor. [Background technology]

[0002] Axial flux permanent magnet machines typically have a disk-like or ring-like rotor and stator structure arranged around an axis. The stator includes a set of coils, each of which may be parallel to the axis. The rotor, mounted on bearings, carries a set of permanent magnets bonded to the rotor by adhesive. The bearings allow the rotor to rotate about a driven shaft by the magnetic field from the stator coils.

[0003] Figure 1a shows a typical arrangement of an axial flux machine with a pair of rotors R1, R2 on either side of a stator S, although a simpler construction could omit one of the rotors. There is an air gap G between the rotor and stator and in an axial flux machine the direction of the magnetic flux through the air gap is substantially axial.

[0004] Depending on the arrangement of the rotor's north and south poles, various configurations of axial flux permanent magnet machines exist. Figure 1b shows the basic configurations of torus NS machines, torus NN machines (NN pole arrangements have a thicker yoke since the magnetic flux has to flow through the thickness of the yoke) and YASA (yokeless segmented armature) forms.

[0005] The diagram of the YASA form shows a cross section through two coils, with the cross-hatched areas indicating the windings around each coil.

[0006] As mentioned above, the permanent magnets of known axial flux permanent magnet machines are bonded to the rotor structure by an adhesive, e.g., a polymer adhesive. The adhesive helps to maintain the relative position of the magnets and may also electrically isolate the magnets from the rotor body to reduce eddy currents, which can disadvantageously increase heat generation and reduce efficiency. To further reduce eddy currents in the rotor body, an intervening layer of laminated magnetic steel sheets may be provided between the magnets and the rotor structural body. Thus, the magnets are bonded to the laminations by an adhesive, and the laminations themselves are bonded to the rotor body by an adhesive. The presence of the laminations and both adhesive layers electrically insulates the magnets from the rotor body, thereby reducing eddy currents.

[0007] Although adhesive bonds work well to locate the magnets and reduce eddy currents, they are subject to substantial stresses and strains when exposed to the high temperatures and rotational speeds that can occur in the YASA configuration, increasing the risk of component failure, for example, due to bond cracking and other damage, and reducing the rotor's lifespan.

[0008] Furthermore, the adhesive bond of the laminations to the rotor body is usually electrically insulating. While this is usually not an issue in most applications, when certain types of machining, such as grinding, turning, milling, are applied to achieve coplanarity of the lamination surfaces, these processes can cause the exposed surfaces of the lamination layers to fuse together or become rough at the machined surfaces, thereby substantially reducing the ability of the laminations to prevent eddy currents, and limiting the subsequent deburring process due to the electrical insulation of the laminations. As a result, once the laminations are adhesively bonded to the rotor body, it is not easy to machine the surfaces of the laminations, and usually requires that any machining and deburring be done before the laminations are bonded to the rotor, which can be impractical.

[0009] To overcome the problems associated with wire EDM, electrochemical grinding, conventional EDM, cutting, stamping, acid etching, and precision punching, U.S. Patent No. 5,333,636 proposes a method of wrapping a soft magnetic metal ribbon around a toroid and applying an adhesive to mechanically restrain the ribbon.

[0010] US Patent No. 5,399,636 proposes a method in which multiple layers of amorphous metal strips are laminated together by adhesive bonding to form a generally three-dimensional part. The adhesive means is described as providing sufficient structural integrity to allow the component to be handled and used or incorporated into a larger structure. US Patent No. 5,399,636 emphasizes that a method of forming a laminate without introducing burrs or other edge defects is preferred, since such burrs or edge defects cannot be easily removed in the method of US Patent No. 5,399,636 without damaging the laminate structure, for example by introducing surface roughness at or near the cut surface. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] US Patent Application Publication No. 2004 / 0250408 [Patent Document 2] US Patent Application Publication No. 2004 / 0150285 [Patent Document 3] International Publication No. 2012 / 022974 Summary of the Invention [Problem to be solved by the invention]

[0012] Generally speaking, the problems of adhesively bonding electrical steel laminations to the rotor body in the YASA configuration are solved by replacing the adhesive bond between the rotor body and the laminations with a brazed bond. [Means for solving the problem]

[0013] summary Brazed joints are stronger, more crack resistant, and more rigid than adhesive joints, and therefore can withstand higher temperatures and higher rotational speeds for longer periods of time without failure than when the laminations are bonded to the rotor body using adhesives. The increased rigidity and joint strength also synergistically allows for stronger and faster coplanarization processes, and because the brazed joints are metallic and conductive, they can be followed by an electrically enhanced chemical etching process, such as ECM, to remove lamination layers that have been inadvertently fused or roughened by the machining process. Unlike many other machining processes, electrically enhanced etching processes, such as ECM, are amenable to implementation on a production line. Thus, the brazed joints not only improve the strength and rigidity of the rotor, but also allow for more efficient processes to be used on a production line. This approach runs counter to that of known methods that teach that the laminations should be electrically insulated (e.g., with adhesives) to reduce eddy currents. The inventors have recognized that any increase in eddy currents that may occur with the introduction of brazed joints is substantially offset by the advantages provided by stronger joints and enabling efficient processes such as ECM. Furthermore, the rigidity of the joint of the brazed laminations to the rotor body reduces the possibility of damage to the interlamination structure, i.e., delamination of the metal laminations, which may occur when metal laminations are joined using adhesives. In particular, the rigid brazed joints to the rotor body reduce the relative movement of the interstitial layers as their surfaces are machined, so that they can withstand substantially higher forces than if the laminations were joined to the rotor body using adhesives. Thus, machining can be performed after the laminations are joined to the rotor body, thereby simplifying the manufacturing process.

[0014] For example, the surfaces of the laminations facing away from the rotor body may be machined by turning, milling, grinding, and / or CO2 blasting in a first machining step. However, advantageously, the braze bond now allows these steps to be followed or even replaced by ECM, providing a highly coplanar, smooth, clean surface before bonding a set of permanent magnets to it without damaging the delicate lamination structure. The coplanar, smooth, and clean surface between the laminations and the permanent magnets provides improved performance and life of the rotor, physical integrity of the laminations, and electrical insulation between the turns (i.e., between the layers of the interlamination structure), and the bonded magnets help reduce eddy currents in the rotor body. In contrast, if machining is performed on lamination surfaces bonded to the rotor body with adhesive, the lack of stiffness in the laminations may result in substantial damage to the lamination structure at the machined surface, and at least many of the benefits of ECM may not apply. Therefore, with an adhesive-based approach, the only options are to either apply less aggressive machining techniques that result in a less smooth and dirtier surface to which to bond the permanent magnets, or simply not perform any machining, resulting in substandard rotor performance and lifespan.

[0015] Thus, according to a first aspect, there is provided a method of manufacturing a rotor for an axial flux permanent magnet machine having a stator comprising a set of coils wound on respective stator bars and spaced circumferentially about an axis of the machine, and a rotor comprising a rotor body carrying a set of permanent magnets on a layer of metal laminations and mounted for rotation about the axis, the rotor and stator being spaced along the axis and defining an air gap therebetween, where the magnetic flux in the machine is generally axial, the method comprising brazing the metal laminations to the rotor body and joining the set of permanent magnets to the metal laminations.

[0016] Optionally, the method includes electrochemically machining the surfaces of the metal laminations to deburr the surfaces after brazing the metal laminations to the rotor body and before joining the set of permanent magnets.

[0017] Advantageously, as discussed above, ECM provides a highly coplanar, smooth and clean surface without damaging the delicate laminate structure prior to bonding a set of permanent magnets thereto, and, unlike other deburring methods, is highly suitable for implementation on a production line.

[0018] Optionally, the method includes applying a filling compound to the metal laminate to fill interlaminar spaces of the metal laminate.

[0019] Advantageously, filling the interlaminar spaces after the metal laminations are bonded to the rotor body further enhances the stiffness of the lamination structure since the lamination layers are sandwiched between layers of the filling compound. This further improves its ability to withstand the high rotational forces and high temperatures generated by the YASA form during operation, as well as allowing the structure to withstand higher forces during any subsequent machining processes. Furthermore, the filling compound allows the laminations to be machined without cutting fluids or other machining fluids, such as oils, being trapped between the lamination layers. In other words, the filling compound seals and electrically insulates adjacent lamination layers.

[0020] Optionally, applying the filling compound includes performing vacuum pressure impregnation (VPI) with a resin.

[0021] VPI is a type of resin transfer molding process in which the rotor body, along with the metal laminations brazed thereto, is completely submerged in resin. Through a combination of dry and / or wet vacuum and / or pressure cycles, the resin is forced, i.e., impregnated, into the spaces between the laminations, resulting in a monolithic structure comprising the resin and the metal laminations. An example VPI process may include placing the rotor body with the bonded laminations into a closed tool, drawing a vacuum, and injecting resin, optionally under pressure, into the tool to allow the resin to penetrate the spaces between the laminations. The resin is then allowed to harden and cool, creating a monolithic structure. Advantageously, the VPI process ensures that the impregnating resin is absorbed throughout most, if not all, of the lamination structure, leaving no spaces. This not only improves the stiffness of the metal laminations as discussed above, but it also prevents any contaminants from entering the spaces between these laminations, thereby improving the performance of the rotor.

[0022] Optionally, brazing includes applying a braze compound to a surface of the rotor body, disposing metal laminations on the braze compound on the rotor body, and heating the braze compound to bond the metal laminations to the rotor body. Optionally, the heating is performed in a humpback furnace or a vacuum brazing furnace.

[0023] Advantageously, one or both major surfaces of the rotor body, for example a disk-like shape defining a central axial hole therethrough, may have a valley-like shape between two raised sides into which the laminations may be received. This valley-like shape thus advantageously provides a space into which a brazing compound, such as a brazing powder, may be deposited using automated means on a production line. With the brazing compound deposited on the rotor body, the metal laminations may be placed thereon, the raised sides serving to accurately position the metal laminations thereon. Once the laminations are placed on the rotor body with the brazing compound between them, heat is applied, which melts the brazing compound, which brazes the laminations to the rotor body to join them. A humpback furnace or a vacuum brazing furnace may advantageously be used as part of a production line for carrying out the method of the present disclosure.

[0024] Optionally, the method may include quenching and tempering the rotor body and the joined metal laminations. Optionally, the quenching includes gas quenching.

[0025] Advantageously, quenching and tempering the rotor body and bonded metal laminations ensures that the desired metal grain structure is achieved. Advantageously, quenching with gas, for example instead of oil, ensures that there are no contaminants between the layers of the lamination structure that would otherwise degrade rotor performance and life.

[0026] Optionally, the method may include flattening the rotor body and metal laminations, for example in a press, to correct for distortions that may occur during the brazing or heat treatment cycle after the aforementioned quenching and tempering. Flattening is a plastic deformation of the assembly and thus may involve bending the rotor body and metal laminations into a predetermined, e.g., flat, shape.

[0027] Optionally, prior to joining the metal laminations to the rotor body, the method includes identifying which surfaces of the metal laminations are flatter than other surfaces of the metal laminations, whereby brazing is performed at the identified flatter surfaces.

[0028] Typically, metal laminations as contemplated in this disclosure are manufactured by winding metal sheets into a roll. This process results in one side of the metal lamination being smoother or flatter than the other side. The inventors have recognized that the braze joint of the flattest or smoothest surface will provide a substantially stronger joint to the rotor body, thereby further enhancing and enabling the benefits of a stiffer laminate structure as described above. Thus, advantageously, one can identify which surface of the metal lamination is the smoothest and use that surface to create the braze joint, resulting in a rotor with improved performance.

[0029] Optionally, permanent magnets are bonded to the metal laminations with an adhesive after the metal laminations are brazed to the rotor body.

[0030] According to a second aspect, there is provided an axial flux permanent magnet machine comprising a stator comprising a set of coils wound on each stator bar and spaced circumferentially about an axis of the machine, and a rotor carrying a set of permanent magnets on a layer of metal laminations and mounted for rotation about said axis, the rotor and stator being spaced along the axis and defining an air gap therebetween, where the magnetic flux in the machine is generally axial, and the rotor comprising a rotor body and a brazed joint between the metal laminations and the rotor body.

[0031] Optionally, the metal laminate comprises an electrochemically engineered surface.

[0032] As previously mentioned, electrochemically machined surfaces are highly coplanar, smooth, and clean surfaces, which therefore help improve rotor performance and life, the physical integrity of the laminations, and the electrical insulation between turns and to the attached magnets, and reduce eddy currents in the rotor body, as compared to metal lamination surfaces machined using other techniques.

[0033] Optionally, the axial flux permanent magnet machine comprises a filling compound, for example a resin, in the interlaminar spaces of the metal laminations.

[0034] Optionally, the axial flux permanent magnet machine comprises an adhesive bond between the metal laminations and the set of permanent magnets and the metal laminations.

[0035] As will be appreciated, the axial flux permanent magnet machines described herein have all of the advantages discussed above in connection with the described methods, which are provided by the increased strength, stiffness, and electrical conductivity resulting from the brazed joint between the metal laminations and the rotor body and / or the fill compound within the metal laminations.

[0036] According to a third aspect, there is provided a rotor for an axial flux permanent magnet machine, the rotor comprising a rotor body carrying a set of permanent magnets on a layer of metal laminations, and a brazed joint between the metal laminations and the rotor body.

[0037] As will be appreciated, the rotors described herein have all of the advantages discussed above in connection with the described methods, which are provided by the increased strength, stiffness, and electrical conductivity resulting from the brazed joint between the metal laminations and the rotor body and / or the filler compound within the metal laminations.

[0038] According to a fourth aspect, there is provided a method of joining metal laminations to a rotor body of a rotor, the method including applying a braze compound to a surface of the rotor body, disposing metal laminations on the braze compound on the rotor body, and heating the braze compound to join the metal laminations to the rotor body.

[0039] Optionally, the method includes subjecting a surface of the metal lamination to electrochemical machining to deburr said surface after brazing the metal lamination to the rotor body.

[0040] Optionally, the method includes applying a filling compound to the metal laminate to fill interlaminar spaces of the metal laminate.

[0041] Advantageously, the method of the present disclosure is not limited to manufacturing rotors of the axial flux permanent magnet machines described above, but rather may be used generally to join metal laminations to the rotor body of any type of rotor to provide the advantages described above.

[0042] According to a fifth aspect, there is provided a method of processing a metal laminate, the method comprising subjecting a surface of the metal laminate to electrochemical processing.

[0043] Advantageously, the disclosed method is not limited to manufacturing rotors of the above-mentioned axial flux permanent magnet machines or to joining metal laminations to rotors, and in particular, the method of the present invention provides the above-mentioned advantages when used for machining any metal laminations in general.

[0044] For example, the method may be particularly applicable to efficiently and effectively deburr and smooth the surfaces of disk-like or toroidal shaped parts of metal laminates, which are manufactured by winding a metal sheet around a central axis, with the layers of metal laminate running parallel to and / or around said axis. The method is therefore particularly suited to scenarios in which it is desired to ensure that the layers of the laminate do not become bonded, roughened or fused together. That is, the method is particularly effective in preventing roughening or damage that may be introduced into the machined surfaces by other machining or deburring methods. Such metal laminate parts find use in and components of electric motors, generators, and other magnetic machines, as well as in other devices and systems. Thus, in one example, the metal laminate parts referred to in this method may be described as metal lamination parts of electric motors, generators, and / or other magnetic machines.

[0045] An axial flux permanent magnet machine as described above and as used in the above described method may be, for example, a motor or a generator.

[0046] These and other aspects of the present invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0047] [Figure 1a] FIG. 1 is a diagram showing a typical configuration of a two-rotor axial flux machine. [Figure 1b] 1A-1D illustrate example configurations of axial permanent magnet machines, including a schematic side view of a yokeless and segmented armature (YASA) machine. [Figure 1c] This is an enumeration diagram of YASA machines. [Diagram 2] FIG. 1c is a perspective view of the YASA machine of FIG. [Diagram 3] FIG. 2 is an exploded perspective view of the stator and stator housing of a YASA machine. [Figure 4]FIG. 2 is an exploded view of the rotor of the axial flux permanent magnet machine of the present invention. [Figure 5a] FIG. 4 shows metal laminations 403 joined to the rotor body after brazing. [Figure 5b] FIG. 5b shows a cross section through line AA in FIG. 5a. [Figure 6a] FIG. 1 illustrates an exemplary VPI tool. [Figure 6b] FIG. 2 is a cross-sectional view of a portion of the rotor body and metal laminations to which a filler has been applied. [Figure 7] FIG. 2 shows a cross section of an assembled rotor according to the present invention. [Figure 8] FIG. 1 illustrates a method according to the present disclosure. [Figure 9] FIG. 1 illustrates a method according to the present disclosure. [Figure 10] FIG. 1 illustrates a method according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] Like elements are indicated with like reference numbers. Detailed Description Figures 1c, 2 and 3 are taken from US Patent No. 5,399,933, with Figure 1c showing details of an exemplary yokeless and segmented armature (YASA) machine 10. Machine 10 may function as a motor or as a generator.

[0049] The machine 10 comprises a stator 12 and, in this example, two rotors 14a,b. The stator 12 comprises a set of individual stator bars 16 spaced circumferentially around a machine axis 20, which also defines the axis of the rotors 14a,b. Each bar 16 carries a stator coil 22 and typically has an axis arranged parallel to the axis of rotation 20. Each end 18a,b of the stator bars is provided with a shoe 27, which serves to confine the coils of the stator coils 22 and may also diffuse the magnetic field generated by the stator coils. The stator coils 22 may be formed from insulated wire of square or rectangular cross section so that a high packing factor may be achieved. In the motor, the stator coils 22 are connected to an electric circuit (not shown) which energizes the coils, such that the poles of the magnetic field generated by the current flowing through the stator coils are opposite in adjacent stator coils 22.

[0050] The two rotors 14a,b carry permanent magnets 24a,b facing each other with a stator coil 22 between them. If the stator bars are tilted (not shown), the magnets are tilted as well. There are air gaps 26a,b between each shoe and magnet pair 17 / 24a, 27 / 24b. In one example motor, when the stator coil 22 is energized, its polarity alternates, causing the coils to align with different magnet pairs at different times, resulting in a torque being applied between the rotor and stator.

[0051] The rotors 14a,b are generally connected to each other, for example by a shaft (not shown), and rotate together about the machine axis 20 relative to the stator 12. In the illustrated example, the magnetic circuit 30 is formed by two adjacent stator bars 16, the two magnet pairs 24a,b, and two backplates 32a,b, one for each rotor, connecting the magnetic flux between the back faces of each magnet pair 24a,b facing away from each coil 22. The backplates 32a,b, also called back irons, comprise a magnetic material, typically a ferromagnetic material, but not necessarily iron. This magnetic material does not have to be a permanent magnet. The stator coils 16 are housed in a housing that defines a chamber for the rotor and the stator and in which a cooling medium can be provided.

[0052] FIG. 3 shows the stator 12a in which the stator coils are placed between clamshells 42a,b of plastic material. These clamshells have an outer cylindrical wall 44, an inner cylindrical wall 46, and an annular end wall 48. In FIG. 3, the end wall 48 includes an inner pocket 50 for receiving the shoes 18a,b of the stator bar 16 and serves to position the stator coil assemblies 16, 22, 18a,b when the two clamshell housings 42a,b of the stator 12a are assembled together. The stator housings 42a,b define, on the inside, a space 52 for the coils 22 and, on the outside, a space 54 around the outer surface of the coils 22, with a space 56 between the coils. The spaces 52, 54, 56 are interconnected to define a cooling chamber. Although not shown in FIG. 3, when assembled, the stator housings 42a,b include ports that allow a cooling medium, such as oil, to be pumped into the spaces 52, 54, 56 and circulate around the coils to cool them.

[0053] The coil cores may be laminated with interlaminate insulation parallel to the desired magnetic flux direction. However, the coil cores may also be formed from soft iron particles (Soft Magnetic Composite - SMC) coated with electrical insulation, bonded together by an insulating matrix, and molded into the desired shape. An exemplary SMC includes glass-bonded iron particles, a thin layer of glass (typically less than 10 μm) that bonds the iron particles and electrically insulates them from each other, leaving some residual porosity. The shoes 27 may be molded from the SMC, for example, using a high temperature and high pressure compression process. Conveniently, the shoes and stator bars may be formed separately and then assembled.

[0054] 4 shows an exploded view of the rotor of the axial flux permanent magnet machine of the present invention. The rotor comprises a rotor body 401 carrying a set of permanent magnets 402 on metal lamination layers 403. That is, the metal laminations 403 have an inner structure made up of electrically isolated layers that help reduce eddy currents.

[0055] The rotor body 401 is constructed from a metal such as steel to provide structural strength to the rotor and defines an axial bore 404 through its center. The rotor body of FIG. 4 is provided with a ridge or outer wall 405a on the outer periphery and a ridge or inner wall 405b on the inner periphery which collectively provide a valley or U-shape in the main surface of the rotor body to help receive and position the metal laminations 403 therein. The shape of the rotor body 401 may be stamped or machined to the desired tolerances prior to placement of the metal laminations 403 therein.

[0056] The metal laminations 403 may comprise, for example, magnetic steel. Other suitable materials are also contemplated. Although not shown, the metal laminations 403 are created by rolling a metal sheet of a desired width and thickness into a roll of a desired diameter to provide a helical or concentric annular interlaminar structure around the axial hole 406 with spaces between the layers determined by the roll tension. The spaces electrically insulate each layer of the metal laminations 403 from its immediately adjacent neighbors to minimize eddy currents in the metal laminations 403 and magnetically isolate the rotor body 401 from the permanent magnets 402 bonded to the surface of the metal laminations 403 to prevent eddy currents in the rotor body 401.

[0057] 4 are provided as segmented magnets shaped to allow for their arrangement into a ring that conforms to the shape of the rotor body and metal laminations, however, it is envisioned that other shapes and arrangements of permanent magnets may also be used, for example, a single monolithic ring magnet, as dictated by the particular application.

[0058] To assemble the rotor of FIG. 4, a brazing compound 407, such as a powder, e.g., a nickel-based brazing powder, is deposited on the surface of the rotor body 401 to which the metal laminations 403 are to be brazed. The metal laminations 403 are then placed (410) on the surface of the rotor body and heat is applied. As will be appreciated, brazing requires sufficient heat to melt the brazing compound 407, but not so hot that it melts the parent materials being joined. For example, heat of about 600-1200°C, e.g., about 1100°C, may be used depending on the brazing compound used. The heat may be applied using a furnace, such as a belt-type humpback furnace when part of a production line, or a vacuum brazing furnace. After heating, the brazing compound cools and solidifies, thereby joining the metal laminations 403 to the rotor body 401 in a brazed joint.

[0059] Optionally, quenching (e.g., in an inert or alternative gas such as nitrogen) and, if necessary, tempering may be performed to achieve the desired metal grain structure, as will be understood by those skilled in the art.

[0060] After the metal laminations 403 are brazed to the rotor body 401, an adhesive 411, e.g., a polymer adhesive, is applied to the exposed surfaces of the metal laminations 403 and a set of permanent magnets 402 are placed thereon in the desired locations to complete the adhesive bond to the metal laminations 403.

[0061] 5a and 5b exemplarily show the metal lamination 403 joined to the rotor body after brazing has been completed. FIG. 5b shows a cross section through line AA in FIG. 5a. As described above, the brazing joint provided by the brazing compound 407 after heating and cooling securely fixes the lamination layers in their position on the rotor body. The lamination layers seen in FIG. 5b provide an example of an interlamination structure, i.e., the layers of the roll of metal sheet are arranged in a spiral or concentric ring manner with spaces between the layers, going around the valleys or U-shaped sections provided by the raised portions or walls 405a, 405b of the rotor body 401. The lamination layers are aligned in a direction away from the rotor body 401.

[0062] Optionally, after brazing is completed, the metal laminations 403 and rotor body 401 may be flattened or otherwise plastically deformed to achieve the desired flatness for a given application, which may be done, for example, with a press die or other tool.

[0063] 6a and 6b illustratively show an optional step of providing a filler compound, such as a resin, to fill the interlaminar spaces of the metal laminations 403 after the metal laminations 403 are brazed to the rotor body 401. As previously described, VPI may be used. FIG. 6a shows an exemplary VPI tool 600 with an enclosed space 601 with a set of conduits 602 in which wet and dry vacuum cycles with a filler compound 603, such as a resin, may be performed to impregnate the interlaminar spaces of the metal laminations 403 with the filler compound.

[0064] 6b illustratively shows a cross-section similar to that of FIG. 5b, but this time after a filling compound 603 has been applied and the metal laminate 403 has been impregnated with the filling compound 603. As discussed above, the filling compound further improves the strength and stiffness of the laminate structure of the metal laminate 403.

[0065] FIG. 6b further illustrates that a layer of fill compound 603 may remain on the top surface of the metal laminations 403. However, as discussed above, the increased strength of the brazed joint 407 allows physical machining techniques to be applied with reduced risk of damaging the laminations. Furthermore, the electrical conductivity of the brazed joint in turn also allows ECM to be applied to remove burrs on the outer surface of the metal laminations 403, providing the benefits of ECM described herein that are not possible with other types of deburring. In this way, the exposed surfaces of the metal laminations 403 may be clean, coplanar, and smooth prior to bonding of the permanent magnet sets with adhesive 411, thereby improving rotor performance and life, lamination physical integrity, and electrical insulation between turns.

[0066] 7 exemplarily illustrates a cross-section of an assembled rotor 700 according to the present disclosure taken through a line corresponding to line AA in FIG. 5a. Like elements are designated with like reference numerals. As described above, the rotor comprises a rotor body 401, a set of permanent magnets 402, and a layer of metal laminations 403. The metal laminations 403 and the rotor body 401 are joined by a braze joint 407, while the set of permanent magnets 402 and the metal laminations are joined by an adhesive joint 411. The top surface of the metal laminations 403 (i.e., the surface facing away from the rotor body 401) may be an electrochemically machined surface.

[0067] As previously described, when assembled, the rotor may be placed in axial alignment with the stator of FIG. 3 to create an axial flux permanent magnet machine having a YASA configuration.

[0068] 8 is a flow chart of a method 800 of manufacturing a rotor for an axial flux permanent magnet machine according to the present disclosure. The machine includes a stator with a set of coils wound on respective stator bars and spaced circumferentially about the axis of the machine, and a rotor including a rotor body carrying a set of permanent magnets on a layer of metal laminations and mounted for rotation about the axis, the rotor and stator being spaced along the axis to define an air gap therebetween, within which the magnetic flux in the machine is generally axial. The method 800 includes brazing (801) the metal laminations to the rotor body and bonding (802) the set of permanent magnets to the metal laminations.

[0069] 9 is a flow chart of a method 900 of joining metal laminations to a rotor body of a rotor according to the present disclosure. The method 900 includes applying a braze compound to a surface of the rotor body (901), placing metal laminations on the braze compound on the rotor body (902), and heating the braze compound to join the metal laminations to the rotor body (903).

[0070] 10 is a flow chart of a method 1000 for machining a metal laminate according to the present disclosure. The method 1000 includes electrochemically machining (1001) a surface of a metal laminate.

[0071] As used herein, the terms top and bottom, horizontal and vertical are used to describe the relative positions of such surfaces and directions relative to one another and are not intended to limit the present disclosure to any given orientation within a coordinate system. The terms top and bottom, horizontal and vertical are used for convenience of description in conjunction with the figures provided herein. Thus, a top surface is on the opposite side of a structure from a bottom surface. Similarly, an inner surface is on the opposite side of a structure from an outer surface, regardless of the structure's orientation in a coordinate system.

[0072] No doubt many other effective alternatives will occur to those skilled in the art, and it will be understood that the invention is not limited to the described embodiments, but encompasses modifications that are within the scope of the claims appended hereto and that are obvious to those skilled in the art.

[0073] For example, while a brazing compound is described as being applied to the rotor body, the reverse is also envisioned. For example, a brazing compound could instead be applied to the metal laminations and the rotor body placed thereon prior to brazing. Similarly, while an adhesive is described as being applied to the metal laminations before the magnets are placed thereon, it is also envisioned that the reverse is possible. For example, an adhesive could instead be applied to the magnets to achieve the same desired effect.

Claims

1. 1. A method of manufacturing a rotor for an axial flux permanent magnet machine, the machine having a stator comprising a set of coils wound on respective stator bars and spaced circumferentially about an axis of the machine, and a rotor comprising a rotor body carrying a set of permanent magnets on layers of metal laminations and mounted for rotation about said axis, the rotor and stator being spaced along the axis to define an air gap therebetween in which magnetic flux in the machine is generally axial, the method comprising: brazing the metal laminations to the rotor body; and bonding the set of permanent magnets to the metal laminations.

2. 2. The method of claim 1, further comprising electrochemically machining a surface of the metal laminations to deburr the surface after brazing the metal laminations to the rotor body and prior to attachment of the set of permanent magnets.

3. 3. The method of claim 1 or 2, comprising applying a filling compound to the metal laminate to fill interlaminar spaces of the metal laminate.

4. 4. The method of claim 3, wherein applying the filling compound comprises vacuum pressure impregnation with a resin.

5. The method according to any one of claims 1 to 4, wherein the brazing comprises: applying a braze compound to a surface of the rotor body; disposing the metal laminations on the braze compound on the rotor body; and heating the braze compound to join the metal laminations to the rotor body.

6. 6. The method of claim 5, wherein the heating is performed using a humpback furnace or a vacuum brazing furnace.

7. 7. A method as claimed in claim 5 or 6, comprising quenching and tempering the rotor body and the joined metal laminations.

8. 8. The method of claim 7, wherein the quenching comprises a nitrogen gas quench.

9. A method according to any one of claims 5 to 8, comprising planarising the rotor body and the metal laminations after said quenching and tempering.

10. 10. A method according to any one of claims 1 to 9, comprising identifying which surfaces of the metal laminate are flatter than other surfaces of the metal laminate, and wherein the brazing is performed at the identified surfaces.

11. The method according to any one of the preceding claims, characterized in that the permanent magnets are bonded to the metal laminations by an adhesive.

12. 1. An axial flux permanent magnet machine, comprising: a stator comprising a set of coils wound on each stator bar and spaced circumferentially about an axis of the machine; a rotor carrying a set of permanent magnets on a layer of metal laminations and mounted for rotation about said axis; the rotor and the stator are spaced apart along the axis to define a gap therebetween in which magnetic flux within the machine is generally axial; 11. The machine of claim 1, wherein the rotor comprises a rotor body and a braze joint between the metal laminations and the rotor body.

13. 13. The axial flux permanent magnet machine of claim 12, wherein the metal laminations include an electrochemically machined surface.

14. 14. The axial flux permanent magnet machine of claim 13 including a fill compound disposed in interlaminar spaces of the metal laminations.

15. 15. The axial flux permanent magnet machine of claim 14, wherein the filling compound comprises a resin.

16. 16. An axial flux permanent magnet machine according to any one of claims 13 to 15, characterised in that it comprises an adhesive bond between the metal laminations and the set of permanent magnets, and the metal laminations.

17. 1. A rotor for an axial flux permanent magnet machine, the rotor comprising: a rotor body carrying a set of permanent magnets on a layer of metal laminations; a brazed joint between the metal laminations and the rotor body.

18. 1. A method of joining metal laminations to a rotor body of a rotor, the method comprising: applying a braze compound to a surface of the rotor body; disposing the metal laminations on the braze compound on the rotor body; and heating the braze compound to join the metal laminations to the rotor body.

19. 20. The method of claim 18, further comprising electrochemically machining a surface of the metal laminations to deburr the surface after the metal laminations are brazed to the rotor body.

20. 20. The method of claim 18 or 19, comprising applying a filling compound to the metal laminate to fill interlaminar spaces of the metal laminate.

21. 13. A method for processing a metal laminate, the method comprising subjecting a surface of the metal laminate to an electrochemical process.

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