Rotor for electric machine

Abstract

A rotor for an electric machine is provided. The rotor has a structural member having a curved support surface that extends about an axis of rotation of the rotor. A plurality of magnets are disposed on the curved support surface and arranged in an array about the axis of rotation of the rotor. The array includes first and second magnets having different radial sizes. The rotor further includes a plurality of spacers between the curved support surface and a radial end face of at least some of the plurality of magnets to space the plurality of magnets from the curved support surface in a radial direction. The plurality of spacers includes a plurality of first spacers, each first spacer being adjacent to a radial end face of one of the plurality of first magnets. The shape of the spacer is determined to conform to both the curved support surface of the structural member and the radial end face of its associated magnet, where the radial end faces of at least some of the plurality of magnets are flat.

Description

Technical Field

[0001] The invention relates to a rotor for an electric machine, such as a generator for an aircraft engine. The invention also relates to a method for producing a rotor for an electric machine and to an electric machine for a generator for an aircraft. Background Art

[0002] An electric machine (motor or generator) generally includes a rotor configured to rotate on an axis relative to a stationary stator. The rotor and stator also include an air gap between them. The interaction of the magnetic fields of the respective components produces an induced electromotive force (EMF) and / or current. In a permanent magnet electric machine (such as a permanent magnet generator), the magnetic field of the rotor is generated by permanent magnets, which, in the case of a generator, induce an AC voltage in the stator windings when the stator windings pass through the moving magnetic field of the permanent magnets.

[0003] As will be appreciated by those skilled in the art of electric machine design, a permanent magnet rotor typically includes a structural member (such as a rotor body) defining a curved support surface extending about the axis of rotation of the rotor, and a plurality of magnets mounted on the curved support surface and arranged in an array about the axis of rotation of the rotor. Iron losses (such as eddy currents induced in the magnetic portion of the machine) may result in inefficiencies, for example, due to electrical resistance and associated heat losses. Summary of the invention

[0004] The arrangement of the polarity of the permanent magnets of the rotor can affect how the magnetic flux interacts with the associated stator. In some arrangements of the rotor, for example where the plurality of magnets includes a first set of magnets of one type and / or orientation and a second set of magnets of another type and / or orientation, the magnetic requirements of the magnets may be different.

[0005] According to a first aspect of the present invention, there is provided a rotor for an electric machine, the rotor comprising:

[0006] a structural member having a curved support surface extending about an axis of rotation of the rotor;

[0007] a plurality of magnets disposed on the curved support surface and arranged in an array around the rotation axis of the rotor, the array comprising:

[0008] a first plurality of magnets having a first radial size; and

[0009] a plurality of second magnets having a second radial dimension greater than the first radial dimension; and

[0010] a plurality of spacers disposed between the curved support surface and at least some of the plurality of magnets, wherein the plurality of spacers include a plurality of first spacers disposed between the curved support surface and a radial end surface of each of the plurality of first magnets to space the plurality of first magnets apart from the curved support surface in a radial direction.

[0011] By this arrangement, the spacer can compensate for magnets of different sizes, thereby allowing magnets of different sizes to be used more easily than existing arrangements. In known arrangements, in order to avoid inconsistencies in the air gap spacing between the rotor and the stator, magnets of the same size are typically used, even if this results in a set of magnets being too large for this application (thereby causing unnecessary cost and weight), or a series of slots are machined into the curved support surface of the structural member to allow the larger magnet to be partially recessed into the support surface to compensate for its larger size. With this arrangement, no such machining step is required. On the contrary, the spacer allows the use of smaller magnets when appropriate, which generally reduces the amount of magnetic material. As a result, a cheaper and lighter rotor can be formed. Compared with known arrangements, the provision of a spacer can also allow a greater degree of size difference between the first magnet type and the second magnet type, in which the size difference is limited by the extent to which material can be removed from the structural member to accommodate the larger magnet. The spacer can be in direct contact with one or both of the curved support surface and the plurality of magnets, or indirect contact via one or more intermediate components.

[0012] The plurality of spacers may further include a plurality of second spacers disposed between the curved support surface and a radial end surface of each of the plurality of second magnets. The plurality of first spacers may each have a first radial thickness, and the plurality of second spacers may each have a second radial thickness less than the first radial thickness.

[0013] The size of the plurality of first spacers and the plurality of second spacers is preferably determined so that the array defined by the plurality of magnets has a substantially uniform diameter. Preferably, the difference between the first radial thickness and the second radial thickness of the first spacer and the second spacer is substantially the same as the difference between the first radial size and the second radial size of the first magnets and the second magnets. In the case where the magnet is located radially outside the structural member, the array can have a substantially uniform outer diameter. In the case where the magnet is located radially inside the structural member, the array can have a substantially uniform inner diameter. As used herein, the term "substantially uniform diameter" means that the diameter defined by the plurality of magnets at the opposite radial ends of the structural member varies less than 10%, preferably less than 5%, and more preferably less than 2% around the circumference of the array. This minimizes the variation in the size of the air gap and the variation in the magnetic flux in the air gap.

[0014] This configuration is particularly advantageous when the annular rotor sleeve is to be applied to a final rotor assembly, as it may provide a more uniform stress distribution for the rotor sleeve.

[0015] One or more of the magnets may have a curved radial end face. In such an embodiment, the spacers may be curved on one or both radial faces. In certain preferred embodiments, the plurality of spacers are shaped to conform to both the curved support surface of the structural member and the radial end face of each of the plurality of magnets, wherein the radial end faces of at least some of the plurality of magnets are flat.

[0016] Magnets with flat or tapered radial end faces can be easier to manufacture than magnets with curved ends, but additional machining of structural members may generally be required to provide a flat interface against which magnets with flat ends may abut. Providing spacers therebetween that conform to the curved support surface and to the magnets with flat ends can simplify manufacture and assembly of the rotor because it reduces or eliminates the need to machine the support surface or to manufacture the magnets with curved faces that closely match the curvature of the support surface.

[0017] The plurality of spacers may be provided as part of the same integral structure.One or more of the plurality of spacers may be defined by a slotted sheet wrapped around the curved support surface in a circumferential direction.

[0018] With this arrangement, the plurality of spacers can be handled together as one piece and assembled to the rotor in a single step. This can speed up manufacturing.

[0019] Alternatively, the plurality of spacers may comprise a plurality of discrete spacer bars forming a discontinuous array of spacer elements about the axis of rotation of the rotor.

[0020] One or more of the plurality of discrete spacers may be associated with a plurality of magnets. That is, one or more of the plurality of discrete spacers may be adjacent to a plurality of magnets. In this way, one or more of the plurality of discrete spacers may be adjacent to or abut two or more magnets. In this embodiment, the discrete spacers are arranged as a plurality of sections around the circumference of the rotor, whereby the number of sections is less than the number of magnets. One or more of the plurality of discrete spacers may be adjacent to only a single magnet. In this way, each individual magnet may be handled during assembly together with the discrete spacers fixed to its radial end face. Explained with reference to a method according to another aspect of the invention, the magnets may be protected in this manner during handling.

[0021] The first spacer and the second spacer can be formed of the same material composition. In certain embodiments, the plurality of first spacers are formed of a first material composition, and the plurality of second spacers are formed of a second material composition different from the first material composition. With this arrangement, the material properties can be independently selected as needed. In some embodiments, the first spacer and the second spacer can be formed of the same material with different amounts or types of coloring. This can make it easier to distinguish the first spacer and the second spacer from each other, thereby reducing the risk of misalignment during assembly. This may be particularly beneficial if the size difference between the first spacer and the second spacer is not easily observed by the eye.

[0022] The plurality of spacers may extend along only a portion of the axial extent of the plurality of magnets. For example, the plurality of spacers may be spaced apart along the axial direction of a given magnet. The plurality of spacers may extend along the entire axial extent of the plurality of magnets.

[0023] The plurality of spacers may include radially extending protrusions adjacent to the axial ends of the plurality of magnets to limit movement of the magnets in the axial direction. The radially extending protrusions may form end caps on the axial ends of the plurality of magnets.

[0024] In this way, during assembly, the axial position of the magnet can be maintained by the spacer itself, without the need for additional clamps or retaining components. In addition, during manufacture, the axial end faces of the magnet can be at least partially covered by these spacers and thus protected during handling.

[0025] The rotor may further include a plurality of soft magnetic elements between the magnet and the structural member. The soft magnetic elements may advantageously change the magnetic flux characteristics of the rotor. The soft magnetic elements may be positioned between the spacers and the magnets. In certain embodiments, the rotor may further include a plurality of soft magnetic elements embedded in the plurality of spacers. With this arrangement, the soft magnetic elements do not need to be handled separately from the spacers. This may also reduce the risk of the soft magnetic elements becoming displaced during or after assembly.

[0026] The multiple spacers can be formed by polymers. Suitable polymers include polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), polyetherketone (PEK), polyphenylene sulfide (PPS), polyamideimide (PAI) or any other suitable polymer. The multiple spacers can include soft magnetic composite (SMC) materials. "Soft magnetic composite" can be defined as a material including ferromagnetic granular material. The particles can be dispersed in an electrically insulating material. The average particle size can be less than 100 μm. The material can have a powdered or powdered particle size and distribution. Unlike the grains or adjacent particles that can be found in a single ferromagnetic sheet or layer, the particles of the soft magnetic composite in the intermediate layer can be substantially electrically insulated from each other. In this way, compared with laminated components, the maximum size of induced eddy currents across it can be significantly reduced. In particular, the eddy currents in the rotor can be significantly reduced by reducing the maximum geometric range of any single conductive part of the ferromagnetic material. In the soft magnetic composite, the maximum uninterrupted range of the conductive ferromagnetic material is limited by the particle size. In some embodiments, the multiple spacers can include both SMC and polymers. In these embodiments, the polymer may improve the material properties of the spacer.

[0027] The multiple magnets can be arranged into any suitable array. For example, these permanent magnets can be arranged into a Halbach array or a Halbach-type array. For the Halbach array, a magnetic field is generated by adjacent permanent magnets arranged to have an orientation change relative to each other. This can be done with a 90° orientation change between adjacent permanent magnets. In this arrangement, the magnetic field on one side of the array can be increased or enhanced, while the opposite side exhibits a magnetic flux in which the magnetic field is reduced to a negligible amount. In the rotor, the magnetic field can be amplified in a radial direction relative to the rotor and reduced in the opposite radial direction relative to the rotor. For example, in a Halbach-type array, there can be any appropriate discrete orientation change angle between the magnets. It should be understood that the Halbach-type array is an array in which adjacent magnets in the array are rotated in a specific orientation order, which causes the magnetic fields of the magnets constituting the array to be combined in a manner that enhances the resulting magnetic field on one side of the array and minimizes the magnetic field on the other side. Therefore, the Halbach-type array can achieve an effect comparable to the Halbach array, although the configuration may be different from the strict definition of the Halbach array.

[0028] The multiple magnets can be arranged in a Halbach array. The Halbach array produces a stronger field in one radial direction, while reducing the field to near zero in the opposite radial direction. Therefore, this configuration advantageously guides the magnetic flux to the stator, thereby minimizing the leakage of the magnetic flux in the opposite direction and improving the overall electromagnetic performance of the motor. Halbach arrays (which can be linear or arranged around a cylindrical geometry) are typically produced using curved or tapered wedge magnets. It may be expensive to manufacture curved or tapered wedge magnets. When using a Halbach array, the optimal size of magnets of different orientations changes. It has been found that the present invention is particularly beneficial for rotors having magnets arranged in a Halbach array, because these magnets can be sized according to their optimal size without the need to machine the structural members of the rotor to produce recesses for accommodating larger magnets in the same structure. In high-pole machines, the number of slots required may be greater, thereby increasing the cost and duration of manufacturing. The present invention also enables the use of magnets with flat ends without the need to modify the curved support surface of the structural member.

[0029] According to a second aspect of the present invention, there is provided an electric machine for use in a generator of an aircraft, the electric machine comprising: a stator; and a rotor according to the first aspect of the present invention.

[0030] According to a third aspect of the present invention, there is provided a method for forming a rotor of an electric machine, the method comprising the following steps:

[0031] providing a structural member having a curved support surface extending about an axis of rotation of the rotor;

[0032] Arranging a plurality of magnets in an array on the curved support surface about the axis of rotation of the rotor, the array comprising a plurality of first magnets having a first radial size and a plurality of second magnets having a second radial size greater than the first radial size; and

[0033] A plurality of spacers are positioned between the curved support surface and at least some of the plurality of magnets by positioning a plurality of first spacers between the curved support surface and radial end surfaces of the plurality of first magnets to space the plurality of first magnets apart from the curved support surface in a radial direction.

[0034] The step of positioning a plurality of spacers between the curved support surface and at least some of the plurality of magnets may further include positioning a plurality of second spacers, each second spacer being adjacent to a radial end surface of one of the plurality of second magnets. In some embodiments, the plurality of first spacers each have a first radial thickness, and the plurality of second spacers each have a second radial thickness that is less than the first radial thickness.

[0035] The step of positioning a plurality of spacers between the curved support surface and the plurality of magnets can be performed by positioning the plurality of spacers on the curved support surface before subsequently positioning the plurality of magnets on the plurality of spacers to arrange the plurality of magnets into an array on the curved support surface. In certain embodiments, the plurality of magnets can be fixed to the plurality of spacers before positioning the plurality of magnets and the plurality of spacers together on the curved support surface. The plurality of magnets can be fixed to the plurality of spacers in any suitable manner. For example, using an adhesive, such as a contact adhesive.

[0036] The plurality of spacers may be formed on one or more corrugated sheets. The corrugated sheets form an integral structure, the plurality of spacers being defined by the integral structure. In such an embodiment, the step of positioning the plurality of spacers may be performed by wrapping the slotted sheet around the curved support surface in a circumferential direction and subsequently securing the plurality of magnets to the slotted sheet. Alternatively, the plurality of spacers may include a plurality of discrete spacer bars, each of the plurality of discrete spacer bars being secured to one of the plurality of magnets prior to being mounted on the curved support surface.

[0037] By securing the magnet to the spacer before mounting both the magnet and the spacer on the curved support surface, the spacer can provide protection for the magnet during assembly. Magnets can be fragile and can break easily during handling. When handling the magnet, the spacer can provide a physical cushion to reduce the risk of damage to the magnet.

[0038] The plurality of spacers may be planar. The plurality of spacers may include one or more radially extending protrusions at one or both axial ends. The radially extending protrusions may limit any movement of the magnet in the axial direction and better maintain the positioning of the magnet during assembly, or otherwise improve the ease of assembly or the need for additional clamps.

[0039] Each magnet may be a unitary body. The plurality of magnets may each include a plurality of laminated sheets. The laminated sheets may be stacked in situ on the plurality of spacers to form the plurality of magnets.

[0040] In this way, the spacer provides a base on which the magnet can be formed. Once the magnet is formed, this advantageously provides protection for the magnet during processing without the need to subsequently fix the magnet to the spacer (without any reinforcement).

[0041] The plurality of spacers may be formed of a polymer.

[0042] The plurality of spacers may be formed by injection molding. The plurality of spacers may be otherwise formed by extrusion, rotational molding, thermoforming or any other suitable form of molding or additive manufacturing.

[0043] This method provides a repeatable process for mass production of spacers, which in turn can result in more predictable mechanical properties and reduced costs. This is particularly desirable in high pole count motors where a large number of spacer bars may be required.

[0044] The method may further include the step of arranging a plurality of soft magnetic elements between the plurality of magnets and the plurality of spacers. The soft magnetic elements may be arranged as one or more soft magnetic material layers arranged between the plurality of magnets and the plurality of spacers. During the process of forming the spacers, the plurality of soft magnetic elements may be embedded in the plurality of spacers.

[0045] The method of the present invention may further comprise providing any of the features of the product as described above or in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Further features and advantages of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0047] Figure 1 shows a perspective cross-sectional view of a rotor according to a first aspect of the present invention;

[0048] Figure 2 Shows Figure 1 an enlarged cross-sectional view of a portion of a rotor;

[0049] Figure 3 yes Figure 1 An exploded view of the rotor;

[0050] Figure 4 A cross-sectional view of a discrete spacer bar is shown;

[0051] Figure 5 shows a perspective view of a magnet and associated spacer bars during assembly;

[0052] Figure 6 shows a block diagram illustrating an electric machine according to yet another aspect of the present invention;

[0053] Figure 7 an enlarged cross-sectional view showing an alternative rotor; and

[0054] Figure 8 A flow chart illustrating a method according to another aspect of the invention is shown. DETAILED DESCRIPTION

[0055] In this context, the present disclosure provides improvements in the assembly of electric machines. Specifically, in this context, the present disclosure relates to an improved rotor body and a method of manufacturing the same, whereby electromagnetic performance can be enhanced and weight can be reduced.

[0056] Figure 1 A perspective view of a rotor 100 according to a first embodiment of the present invention is shown. The rotor 100 includes a structural member 110, which may include a ferromagnetic material. The rotor 100 further includes a permanent magnet array 120 arranged around the rotation axis A of the rotor 100. The structural member 110 of the rotor 100 may be a cylindrical shaft arranged to rotate around the rotation axis A, preferably a hollow shaft. The structural member 110 may have a substantially annular cross-section. The structural member 110 may include a ferromagnetic material, examples of which include steel. The structural member 110 may include electrical steel (such as silicon steel) or be composed thereof. The ferromagnetic material may be continuous in the axial, radial and / or circumferential directions of the structural member 110. The structural member 110 may include a laminated component, which includes alternating steel layers and electrically insulating material layers. The laminate may be positioned in a plane perpendicular to the rotation axis A. However, forming a structural component from a solid material substance (such as a ferromagnetic material) may provide advantages in terms of structural strength. In some examples, the structural member 110 may include or be formed of a non-magnetic material (such as a carbon fiber composite material). Alternatively or additionally, the structural member 110 may include a ferromagnetic material layer. The ferromagnetic material layer may be disposed between the structural member and the permanent magnet array. The structural member 110 defines a curved support surface 111 that extends around the axis of rotation A of the rotor, and the permanent magnet array is mounted on the curved support surface. The structural member 110 may be connected to a radially extending flange 112, and the rotor is mounted to a rotor shaft (not shown) by the radially extending flange. Depending on whether the rotor 100 is operated in a motor or in a generator, the shaft may transmit a rotational drive to the rotor 100 or receive a rotational drive from the rotor 100.

[0057] like Figure 1 As shown, the magnet array 120 includes a plurality of first magnets 121 and a plurality of second magnets 122 alternating around the circumference of the rotor 100. The first magnets 121 and the second magnets 122 may differ from each other in structure, size, and / or magnetic orientation.

[0058] The magnets 121 to 122 in the permanent magnet array can include any suitable hard magnetic material, such as ferrite, alnico, and / or rare earth materials such as neodymium. Each of these magnets includes a north pole and a south pole. These magnetic poles define a north-south plane (not shown) that extends longitudinally therebetween. Specifically, the north-south plane defines a plane that separates the north pole from the south pole. The magnets 121, 122 can be arranged such that the angular range around the rotor 100 has alternating north and south poles. The north-south planes of the plurality of first magnets 121 can be arranged in a first direction. The north-south planes of the plurality of second magnets 121 can be arranged in a second direction. For example, the first direction can be perpendicular to the second direction.

[0059] In the illustrated embodiment, the magnet array 120 is arranged such that the plurality of first magnets 121 alternate with the plurality of second magnets 122 in the circumferential direction to form a Halbach array. Those skilled in the art will understand that the magnet array 120 does not have to be arranged in this specific manner. For example, the magnets can be arranged in any suitable array that enhances the magnetic field in a radial direction. Thus, this embodiment can equally depict a Halbach-type array configured to produce a comparable magnetic field.

[0060] Figure 2 is shown Figure 1 An enlarged cross-sectional view of a portion of the rotor 100 shown. Figure 2 Each of the magnets 121, 122 shown includes a radially inner end face 131, a radially outer end face 132, a first circumferential face 133, and a second circumferential face 134. In the depicted embodiment, each face 131 to 134 of each magnet in the array is substantially flat. It should be understood that one or more of the magnet array 120 can include curved radial end faces. Preferably, the radially inner end face 131 is flat. In some embodiments, only a certain portion of the magnet array 120 can include one or more flat radial end faces. For example, one-tenth, preferably at least one-eighth, preferably at least one-sixth, preferably at least one-fourth, preferably at least one-half, preferably at least three-fourths, preferably at least seven-eighths or more of the magnet array 120 can have flat radial end faces. In the most preferred arrangement, each of the magnet array 120 includes flat faces.

[0061] The rotor 100 further includes a plurality of spacers 140. The plurality of spacers 140 are disposed between the curved support surface 111 and the radially inner end surface 131 of each of the plurality of magnets. In this manner, the plurality of spacers 140 space the plurality of magnets 120 from the curved support surface 111 in the radial direction. The plurality of spacers 140 may include a plurality of first spacers 141 each adjacent to the radially inner end surface 131 of one of the plurality of first magnets 121 and a plurality of second spacers 142 each adjacent to the end surface of one of the plurality of second magnets 122. The spacers 140 may indirectly contact one or both of the curved support surface 111 and its corresponding magnet via one or more intermediate components (not shown). In the illustrated embodiment, each spacer 140 is connected to the radially inner end surface 131 of a single magnet in the magnet array 120 and to the curved support surface 111.

[0062] The plurality of spacers 140 are configured to modify the outer diameter OD defined by the magnet array 120. When implementing a particular magnet array (such as a Halbach array), the different orientations of the north-south planes of the plurality of magnets may affect the optimal size of the magnets. Therefore, in some embodiments, the plurality of first magnets 121 can be formed to include a different size than the plurality of second magnets 122. In the illustrated embodiment, the plurality of first magnets 121 are smaller than the plurality of second magnets 122 in the radial direction. It should be understood that, alternatively, the plurality of first magnets 121 can be larger than the plurality of second magnets 122 in the radial direction. Optionally, there may be additional plurality of magnets that define additional radial ranges.

[0063] In order to compensate for the different sizes of the first magnet and the second magnet, the size of the first spacer 141 is different from the size of the second spacer 142. Figure 2 , the first spacer is larger than the second spacer 142 in the radial direction. By configuring the first spacer and the second spacer so that the radial size difference between the first spacer and the second spacer is similar to the radial size difference between the first magnet and the second magnet, the variation of the outer diameter OD of the magnet array 120 can be minimized. Preferably, the sizes of the first spacer and the second spacer are determined so that the radial size difference between the first spacer and the second spacer is substantially the same as the radial size difference between the first magnet and the second magnet, and the outer diameter of the magnet array 120 is substantially constant. This minimizes the variation of the air gap of the assembled motor (not shown), which may otherwise be caused by using two sets of magnets having different radial sizes and also having different radial ranges from each other. As Figure 2 As shown, the rotor 100 may further include a composite sleeve 150 extending around the outer diameter of the magnet array 120 to help retain the magnets in place during rotation of the rotor 100 .

[0064] The plurality of spacers 141, 142 may be formed from a continuous ring of material extending around the entire circumference of the structural member 110. The plurality of spacers 141, 142 may be formed from one or more sheets of material wrapped around the circumference of the structural member (see Figure 7 ). In the rotor 100 of the first embodiment, a plurality of spacers 141, 142 are formed by a plurality of discrete segments or spacer bars that form a discontinuous array of spacer elements around the rotation axis A of the rotor 110. The discontinuity between adjacent spacer bars can be aligned with the discontinuity between adjacent magnets. Adjacent magnets and / or spacer bars can be adjacent to each other or separated by optional gaps. In the illustrated embodiment, each spacer bar is associated with a single magnet of the plurality of magnets 121, 122. That is, a single spacer bar is adjacent to the radially inner end face 131 of a single magnet 120. It should be understood that while this can be a configuration of one or more magnets 120 and one or more associated spacers 140, this feature is not required. For example, each spacer bar can be associated with multiple magnets.

[0065] The intermediate layer formed by the spacers 141 to 142 can have a thickness between 0.1 mm and 10 mm, preferably between 0.5 mm and 5 mm, more preferably between 1 mm and 3 mm. This thickness can be an average thickness averaged around the intermediate layer. This thickness can be measured in the radial direction relative to the rotation axis A. Each of the spacers 141 to 142 can include a plurality of sublayers. These optional sublayers can be stacked on top of each other in the radial direction. The cumulative thickness of the optional sublayers can fall within one of the above ranges.

[0066] Preferably, the plurality of spacers 140 extend substantially along the entire axial extent of the magnet array 120 .

[0067] refer to Figure 3 , the magnet array 120 extends in the axial direction of the rotor 100. That is, the magnet array 120 extends parallel to the rotation axis A of the rotor 100. Each magnet in the array may be a single structure extending along the entire axial extent of the array. Alternatively, one or more magnets in the array may be formed by a plurality of axial segments positioned end to end in the axial direction. Figure 3 In the embodiment of the present invention, each first magnet 121 in the array is formed by six axial segments 121a to 121f, and each second magnet in the array is formed by six axial segments 122a to 122f. It should be understood that one or more of these magnets may include fewer or otherwise more axial segments. Figure 1The rotor 100 shown is a high pole count rotor, wherein the array has more than 30, 40 or 50 permanent magnets. It will be appreciated that the present disclosure may be extended to rotors having different numbers of permanent magnets to thereby provide the rotor with different numbers of poles. In a similar manner, one or more of the plurality of spacers may be a single structure extending along the entire axial extent of the array. Alternatively, one or more spacers may be formed from a plurality of axial segments positioned end to end in the axial direction. Figure 3 , each first spacer 141 is formed of six axial segments, and each second spacer is formed of six axial segments. It will be appreciated that one or more of these spacers may include fewer or otherwise more axial segments. In this manner, each magnet segment may be secured to its associated spacer segment prior to assembly on the rotor 100, and may thereby be protected by its associated spacer segment during handling.

[0068] The spacers 141 and 142 may be directly adjacent to the structural member 110, or may be fixed to the structural member 110 via a retention layer (not shown) that may include an adhesive. Similarly, at least one of the permanent magnets 121 to 122 may be directly adjacent to the spacers 141 and 142, or may be fixed to the spacers 141 to 142 via a retention layer (not shown) that may include an adhesive. There may be a rotor sleeve 150 that is disposed around the rotor 100, preferably around a plurality of permanent magnets 121 to 122, to fix the components of the rotor 100. A plurality of spacers 140 may be formed by molding. For example, a plurality of spacers 140 may be formed by injection molding. A plurality of spacers 140 may be otherwise formed by rotational molding, thermoforming, or any other suitable form of molding or additive manufacturing. Alternatively, the plurality of spacers 140 may be extruded. This is particularly effective when forming a plurality of spacers 140 of congruent geometry. It will be appreciated that when two or more pluralities of spacers 140 are formed by extrusion, corresponding pluralities of dies having different cross-sectional profiles are required.

[0069] Figures 1 to 3 The rotor 100 shown is configured to be arranged concentrically within the stator. In the arrangement shown, the permanent magnet arrays 121 to 122 are located radially outside the structural member 110. In this way, the rotor 100 is configured to rotate concentrically within the stator (not shown). It should be understood that these teachings can also be applied to rotors of outer rotor configurations, in which the rotor rotates around the stator positioned radially inside the rotor. In this alternative arrangement, the permanent magnet array and spacers 141 to 142 can be positioned radially inside the structural member 110.

[0070] The rotor 100 may further include a radially extending end cap 113 fixed at one or both axial ends of the structural member. The end cap 113 may be annular in shape. The end cap 113 helps retain the magnets and spacers in the axial direction during assembly and operation.

[0071] Figure 4 1 is a schematic side cross-sectional view of the spacers 141, 142 of the rotor 100 taken through a radial plane. The spacers have an upper (radially outer) surface 144, the shape of which is determined to correspond to the geometry of the radial inner end face of the magnet used therewith. In the illustrated embodiment, the upper surface 144 is flat. It should be understood that the upper surface 144 can have any suitable geometry, such as concave, convex, beveled, recessed or conical. The spacers 141, 142 also have a lower (radially inner) surface 145, the shape of which is determined to conform to the curved support surface. When used in conjunction with a magnet including a flat radial end face, it is a particularly advantageous feature to provide the lower surface 145 with the same radius of curvature as the curved support surface, which would not otherwise conform to the shape of the support surface without further machining steps.

[0072] The spacers 141, 142 also include an optional soft magnetic element 146. Figure 4As shown, the soft magnetic element 146 can be fixed to the upper surface 144 of the spacer 141, 142. This can be achieved by adhesive, fastening or any other suitable fixing means. The soft magnetic element 146 can advantageously change the magnetic flux characteristics of the rotor. In the case where the soft magnetic element 146 is fixed to the upper surface 144 of the spacer 141, 142, the soft magnetic element 146 is positioned adjacent to the magnets 121, 122 in use. That is, the soft magnetic element 146 can be at least partially connected to the magnets 121, 122. Alternatively, the soft magnetic element 146 can be embedded in the body of the spacer 142. For example, in the case where the spacer is injection molded, the soft magnetic element 146 can be a soft magnetic sheet that is embedded in the spacer by overmolding. The spacer may include a soft magnetic composite material. Soft magnetic composite materials are generally referred to using the acronym "SMC". SMC materials include soft magnetic particles. These particles may include ferromagnetic materials, such as iron. SMC can be derived from powder. The spacer can be formed using a powder metallurgy process. The average particle size of such a powder can be in the range of 5 μm to 200 μm. The average particle size can advantageously be less than 200 μm, less than 150 μm, less than 100 μm, less than 75 μm or less than 50 μm. Smaller particle sizes are preferred in reducing the extent to which any intra-particle eddy currents may be induced. The particles of the powder can be at least partially coated in an electrically insulating material. This can be achieved by mixing or dispersing the particles in an electrically insulating material. In this way, the conductive and magnetically conductive particles in the SMC can be electrically insulated from at least some adjacent conductive and magnetically conductive particles by means of an electrically insulating layer or a partial electrically insulating layer. Soft magnetic composites can be contrasted with laminated components having, for example, alternating macroscopic layers (e.g., steel layers and electrically insulating resin layers). In soft magnetic composites, the maximum size along which current can flow may be limited by particle size. Unlike the ferromagnetic layers of laminated components, the particles in soft magnetic composites can be discontinuous. In addition, the magnetic and electrical properties of soft magnetic composites can be isotropic, meaning that such physical properties are similar when measured in different directions; this contrasts with laminated components that are anisotropic, making their physical properties dependent on the direction in which they are measured. In a laminate, a single layer of conductive and magnetically conductive material can extend a significant distance in a single plane, cylindrical or linear direction. The conductive and magnetically conductive particles in SMCs typically have a maximum overall dimension of less than one centimeter, or less than one millimeter, and can have a maximum overall dimension smaller than this, such as the sizes described above.

[0073] Figure 52 is an exploded perspective view of a portion of an alternative embodiment of a spacer 240, showing two spacer segments 240a, 240b and two magnet segments 221a, 221b. The spacer 240 includes a lower (radially inner) surface 245 that is shaped to conform to a curved support surface. Thus, the lower surface 245 can be contoured, or include a contoured surface. Figure 5 , the lower surface 245 comprises a concave surface. In this embodiment, each magnet segment is formed by a stack of laminate sheets 225 arranged on one of the spacer segments. The laminate sheets are shown as being stacked axially. In other embodiments, the laminate sheets may be stacked radially or circumferentially. In this embodiment, the spacer 240 has radially extending protrusions 247 arranged at the axial ends of the magnet. The radially extending protrusions form end caps at the axial ends of the array and may eliminate the need for separate end caps (such as Figure 3 ). Further, during assembly and handling, the protrusions 247 form a protective layer on the ends of the magnets to reduce the risk of damage. One or more of these spacers may include one or more visible markings 251 by which different types of spacers can be easily identified. The visual markings 251 may include, but are not limited to, text or graphics indicating the type of spacer. Figure 5 In the embodiment of FIG. 2 , the visual marker 251 is a graphic indicating the direction of the north-south plane of the magnet.

[0074] Figure 6 A schematic diagram of an electric machine 300 that can incorporate a rotor of the present disclosure is shown. The electric machine 300 includes a rotor 100 and a stator 320 that can rotate relative to the stator about an axis of rotation A. In the illustrated arrangement, the stator 320 includes a stator core that is arranged about the axis of rotation A and includes a plurality of slots defined by a plurality of stator teeth, the slots having stator windings arranged therein. The stator 320 is typically configured as an annular member that includes a hole in which the rotor 100 is rotatably mounted. The rotor 100 is typically mounted on a shaft 330 that is arranged to rotate about the axis of rotation A. When the rotor 100 and the stator 320 are in an operating position, an air gap 315 is formed between the rotor 100 and the stator 320.

[0075] Rotation of the rotor 100 relative to the stator 320 can induce an electromotive force in the stator windings, which is due to the changing magnetic field generated by the permanent magnet array that the stator windings experience rotation. In this way, the motor 300 can be used as a generator. In this configuration, the rotor 100 is usually driven to rotate by a prime mover 340 (such as an aircraft engine) via a shaft 330. When the rotor 100 rotates around the rotation axis A in the hole of the stator 320, the magnetic field of the rotor 100 also rotates. This causes a rotating magnetic field, which interacts with the electrical conductors of the stator 320 and thus generates a voltage, which can then be supplied to an electrical accessory or component 350. The motor 300 can also be configured to operate as an electric motor by providing a current from a power supply 350 to the windings of the stator 320. Current is provided to the windings of the stator, thereby generating a time-varying magnetic field, which rotates the rotor 100. The rotor 100 then rotates the shaft 330, and can therefore be used to transmit drive to the prime mover 340.

[0076] Figure 7 An enlarged cross-sectional view of a portion of a rotor 400 according to a second embodiment is shown. The second embodiment has similar structure and operation to the first embodiment discussed above, and like reference numerals are used to represent like features. Thus, Figure 7 Each of the magnets 421, 422 shown includes a radially inner end face 431, a radially outer end face 432, a first circumferential face 433, and a second circumferential face 434. In the depicted embodiment, each face 431 to 434 of each of the magnet array is substantially flat. It should be understood that one or more of the magnet array 420 may include a curved radial end face. Preferably, the radially inner end face 431 is flat. In some embodiments, only a portion of the magnet array 420 may include one or more flat radial end faces. For example, one tenth, preferably at least one eighth, preferably at least one sixth, preferably at least one quarter, preferably at least one half, preferably at least three quarters, preferably at least seven eighths, or more of the magnet array 420 may have a flat radial end face. In the most preferred arrangement, each of the magnet array 420 includes a flat face.

[0077] The rotor further includes a plurality of spacers 440. The plurality of spacers 440 are disposed between the curved support surface 411 and the radially inner end surface 431 of each of the plurality of magnets. In this way, the plurality of spacers 440 space the plurality of magnets 420 from the curved support surface 411 in the radial direction. The plurality of spacers 440 may include a plurality of first spacers 441 each adjacent to the radially inner end surface 431 of one of the plurality of first magnets 421 and a plurality of second spacers 442 each adjacent to the end surface of one of the plurality of second magnets 422. The spacers 440 may indirectly contact one or both of the curved support surface 411 and its corresponding magnet via one or more intermediate components (not shown). In the illustrated embodiment, each spacer 440 is connected to the radially inner end surface 431 of a single magnet in the magnet array 420 and to the curved support surface 411.

[0078] Unlike the first embodiment, the plurality of spacers 440 of the rotor 400 are defined by an integral structure between the curved support surface 411 and the magnet. In this embodiment, the spacer is defined by a slotted sheet 448 wrapped around the structural member. For this embodiment, it is preferred that the slotted sheet 448 is fixed to the curved support surface 411 before the magnet is arranged on the spacer. This can be achieved by applying an adhesive to the radial inner surface of the slotted sheet 448, or the radial outer surface of the curved support surface 411, and then winding the slotted sheet 448 around the curved support surface 411 in the circumferential direction. The slotted sheet 448 forms an intermediate layer between the magnet and the structural member, which separates the magnet 420 from the curved support surface 411. The slotted sheet 448 can extend around the entire circumference of the structural member. In other embodiments, a plurality of slotted sheets can be arranged around the rotation axis A and combined to form an intermediate layer so that each sheet extends only around a portion of the circumference of the structural member.

[0079] The slotted sheet 448 may be directly adjacent to the curved support surface 411, or it may be fixed to the curved support surface 411 via a retention layer (not shown) that may include an adhesive. Similarly, at least one of the permanent magnets may be directly adjacent to the slotted sheet 448, or it may be fixed to the slotted sheet 448 via an additional retention layer (not shown) that may include an adhesive. The thickness of the slotted sheet 448 may be between 0.1 mm and 10 mm, preferably between 0.5 mm and 5 mm, and more preferably between 1 mm and 3 mm. When the spacer 440 is included, the slotted sheet 448 has a circumferentially varying thickness. Therefore, the thickness mentioned may be an average thickness, a maximum thickness, or a minimum thickness averaged around the slotted sheet.

[0080] The rotor may further include a composite sleeve 450 extending around the outer diameter of the magnet array 420 to help retain the magnets in place during rotation of the rotor.

[0081] Figure 8 A method of assembling a rotor 100 for an electric machine 300 is presented. The method may include one or more steps in combination with any aspect of the rotor described above. The method includes a step S8.1 of providing a structural member for the rotor. The method further includes a step S8.2 of arranging a plurality of magnets on a curved support surface of the structural member of the rotor, and a step S8.3 of positioning a plurality of spacers between the curved support surface and the plurality of magnets to space the plurality of magnets from the curved support surface. Step S8.3 may be performed, for example, before step S8.2 by arranging the plurality of spacers on the curved support surface before subsequently fixing the plurality of magnets to the plurality of spacers. In this method, the plurality of spacers may be arranged on a slotted sheet before the magnets are arranged on the slotted sheet, and the slotted sheet is arranged on the curved support surface. Preferably, steps S8.2 and S8.3 are performed by fixing the plurality of spacers together with the plurality of magnets and arranging both the spacers and the magnets together on the curved support surface of the structural member. The plurality of magnets may be glued to the plurality of spacers. The plurality of magnets may each be an integral component. The plurality of magnets may each comprise a plurality of laminated sheets stacked and bonded together on one of the plurality of spacers. The sheets may be magnetized to form each magnet before or after being fixed to the spacers. The sheets or magnets may be magnetized in situ on the structural member. The method may further comprise a step S8.4 of winding a rotor sleeve (e.g., a rotor sleeve made of carbon fiber) around the permanent magnet array.

[0082] The method steps described above are arranged in an exemplary order of execution. However, it should be understood that these method steps can be performed in a number of different orders depending on the requirements. For example, the magnets can be magnetized at any stage. Similarly, the spacers can be mounted to the rotor before the magnets are mounted. For example, this can be an advantageous order when the spacers are defined on a continuous slotted sheet.

[0083] Various modifications may be made to all of the above-described embodiments, whether by way of addition, deletion, and / or substitution, to provide further embodiments, any and / or all of which are intended to be encompassed by the appended claims.

[0084] The invention may also be described or defined in accordance with one or more of the following clauses:

[0085] 1. A rotor for an electric motor, the rotor comprising:

[0086] a structural member having a curved support surface extending about an axis of rotation of the rotor;

[0087] a plurality of magnets disposed on the curved support surface and arranged in an array around the rotation axis of the rotor, the array comprising:

[0088] a first plurality of magnets having a first radial size; and

[0089] a plurality of second magnets having a second radial dimension greater than the first radial dimension; and

[0090] A plurality of spacers are disposed between the curved support surface and at least some of the plurality of magnets, wherein the plurality of spacers include a plurality of first spacers disposed between radial end surfaces of each of the plurality of first magnets to space the plurality of first magnets from the curved support surface in a radial direction.

[0091] 2. A rotor according to claim 1, wherein the plurality of spacers further include a plurality of second spacers, which are arranged between the curved support surface and the radial end surface of each of the plurality of second magnets, wherein the plurality of first spacers each have a first radial thickness, and the plurality of second spacers each have a second radial thickness less than the first radial thickness.

[0092] 3. The rotor of clause 2, wherein the plurality of first spacers and the plurality of second spacers are sized such that the array defined by the plurality of magnets has a substantially uniform outer diameter.

[0093] 4. A rotor according to any preceding clause, wherein each of the plurality of spacers is shaped to conform to both the curved support surface of the structural member and the radial end faces of the magnets with which it is associated, wherein the radial end faces of at least some of the plurality of magnets are flat.

[0094] 5. A rotor according to any preceding clause, wherein the plurality of spacers are defined by a slotted sheet wrapped around the curved support surface in a circumferential direction.

[0095] 6. A rotor according to any one of clauses 1 to 4, wherein the plurality of spacers comprises a plurality of discrete spacer bars forming a discontinuous array around the axis of rotation of the rotor.

[0096] 7. A rotor according to clause 6, wherein each of the plurality of discrete spaced bars is connected to only one of the plurality of magnets.

[0097] 8. A rotor according to clause 2 or clause 3, wherein the plurality of first spacers are formed from a first material composition and the plurality of second spacers are formed from a second material composition different from the first material composition.

[0098] 9. A rotor according to any preceding clause, wherein the plurality of spacers extend along the entire axial extent of the plurality of magnets.

[0099] 10. The rotor of clause 9, wherein the plurality of spacers include radially extending protrusions adjacent axial ends of the plurality of magnets to limit movement of the magnets in an axial direction.

[0100] 11. A rotor according to any preceding clause, further comprising a plurality of soft magnetic elements embedded in the plurality of spacers.

[0101] 12. A rotor according to any preceding clause, wherein the plurality of spacers are formed from a polymer.

[0102] 13. A rotor according to any preceding clause, wherein the plurality of magnets are arranged in a Halbach array.

[0103] 14. An electric machine for use in a generator of an aircraft, the electric machine comprising:

[0104] stator; and

[0105] A rotor according to any of clauses 1 to 13.

[0106] 15. A method for forming a rotor for an electric machine, the method comprising the steps of:

[0107] providing a structural member having a curved support surface extending about an axis of rotation of the rotor;

[0108] Arranging a plurality of magnets in an array on the curved support surface around the rotation axis of the rotor, the array comprising:

[0109] a first plurality of magnets having a first radial size; and

[0110] a plurality of second magnets having a second radial dimension greater than the first radial dimension; and

[0111] A plurality of spacers are positioned between the curved support surface and at least some of the plurality of magnets by positioning a plurality of first spacers between the curved support surface and radial end surfaces of the plurality of first magnets to space the plurality of first magnets apart from the curved support surface in a radial direction.

[0112] 16. A method as described in clause 15, wherein the step of positioning a plurality of spacers between the curved support surface and at least some of the plurality of magnets further includes positioning a plurality of second spacers between the curved support surface and radial end surfaces of the plurality of second magnets to space the plurality of second magnets from the curved support surface in a radial direction, wherein the plurality of first spacers each have a first radial thickness, and the plurality of second spacers each have a second radial thickness that is less than the first radial thickness.

Claims

1. A rotor for an electric motor, the rotor include: a structural member having a curved support surface extending about an axis of rotation of the rotor; a plurality of magnets disposed on the curved support surface and arranged in an array around the rotation axis of the rotor, the array comprising: a plurality of first magnets having a first radial size; and a plurality of second magnets having a second radial size greater than the first radial size; and a plurality of spacers disposed between the curved support surface and at least some of the plurality of magnets, wherein the plurality of spacers include a plurality of first spacers disposed between radial end surfaces of each of the plurality of first magnets to space the plurality of first magnets from the curved support surface in a radial direction, wherein each of the plurality of spacers is shaped to conform to both the curved support surface of the structural member and a radial end surface of an associated magnet of the plurality of magnets, and wherein the radial end surfaces of at least some of the plurality of magnets are flat.

2. The rotor according to claim 1, in, The plurality of spacers further include a plurality of second spacers disposed between the curved support surface and a radial end surface of each of the plurality of second magnets, wherein the plurality of first spacers each have a first radial thickness, and the plurality of second spacers each have a second radial thickness that is smaller than the first radial thickness.

3. The rotor according to claim 2, in, The plurality of first spacers and the plurality of second spacers are sized such that the array defined by the plurality of magnets has a substantially uniform outer diameter.

4. A rotor according to any preceding claim, in, The plurality of spacers are defined by a slotted sheet wrapped around the curved support surface in a circumferential direction.

5. A rotor according to any one of claims 1 to 3, in, The plurality of spacers includes a plurality of discrete spacer bars that form a discontinuous array about the rotational axis of the rotor.

6. The rotor according to claim 5, in, Each of the plurality of discrete spacer bars is connected to only one of the plurality of magnets.

7. A rotor according to claim 2 or claim 3, in, The plurality of first spacers are formed of a first material composition, and the plurality of second spacers are formed of a second material composition different from the first material composition.

8. A rotor according to any preceding claim, in, The plurality of spacers extend along the entire axial extent of the plurality of magnets.

9. The rotor according to claim 8, in, The plurality of spacers include radially extending protrusions adjacent to axial ends of the plurality of magnets to limit movement of the magnets in an axial direction.

10. A rotor according to any preceding claim, further comprising a plurality of soft magnetic elements embedded in the plurality of spacers.

11. A rotor according to any preceding claim, in, The plurality of spacers are formed of a polymer.

12. A rotor according to any preceding claim, in, The plurality of magnets are arranged in a Halbach array.

13. An electric machine for use in a generator of an aircraft, the electric machine include: stator; as well as A rotor as claimed in any one of claims 1 to 12.

14. A method for forming a rotor of an electric machine, the method The following steps are involved: providing a structural member having a curved support surface extending about an axis of rotation of the rotor; Arranging a plurality of magnets in an array on the curved support surface around the rotation axis of the rotor, the array comprising: a plurality of first magnets having a first radial size; and a plurality of second magnets having a second radial size greater than the first radial size; and positioning a plurality of spacers between the curved support surface and at least some of the plurality of magnets to space the plurality of first magnets apart from the curved support surface in a radial direction by positioning a plurality of first spacers between the curved support surface and radial end surfaces of the plurality of first magnets; wherein each of the plurality of spacers is shaped to conform to both the curved support surface of the structural member and a radial end surface of an associated magnet of the plurality of magnets, and wherein the radial end surfaces of at least some of the plurality of magnets are flat.

15. The method according to claim 14, in, The step of positioning a plurality of spacers between the curved support surface and at least some of the plurality of magnets further includes positioning a plurality of second spacers between the curved support surface and radial end surfaces of the plurality of second magnets to space the plurality of second magnets apart from the curved support surface in a radial direction, wherein the plurality of first spacers each have a first radial thickness, and the plurality of second spacers each have a second radial thickness that is less than the first radial thickness.

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