CN114731078A

CN114731078A - Rotor assembly for axial flux machine

Info

Publication number: CN114731078A
Application number: CN202080078100.XA
Authority: CN
Inventors: 乔治·哈德·米列海姆; 史蒂文·罗伯特·肖
Original assignee: eCircuit Motors Inc
Current assignee: eCircuit Motors Inc
Priority date: 2019-11-12
Filing date: 2020-11-06
Publication date: 2022-07-08
Also published as: TW202139568A; EP4059120A1; BR112022007921A2; AU2020382759A1; WO2021096767A1; MX2022005735A; KR20220100001A; JP2022553874A; CA3159768A1

Abstract

A rotor assembly for an axial flux electric machine may include at least one magnet and first and second support structures. The first support structure may be configured to attach the at least one magnet to the first support structure and provide a flux return path for the at least one magnet. The second support structure may be configured to attach to the first support structure so as to allow torque to be transferred between the at least one magnet and the second support structure via the first support structure, and the second support structure may also be configured to (a) attach to a rotatable shaft of the axial flux electric machine, or (B) serve as an output flange or an input flange of the axial flux electric machine.

Description

Rotor assembly for axial flux electric machine

Background

Permanent magnet axial flux motors and generators are known. Examples of such motors or generators (collectively referred to herein as "electric machines") are described in U.S. patent No.7,109,625, U.S. patent No.9,673,688, U.S. patent No.9,800,109, U.S. patent No.9,673,684, and U.S. patent No.10,170,953, as well as U.S. patent application publication No.2018-0351441 a1 ("the' 441 publication"), each of which is incorporated herein by reference in its entirety.

Disclosure of Invention

In some of the disclosed embodiments, a rotor assembly for an axial flux electric machine includes at least one magnet and first and second support structures. The first support structure is configured to attach the at least one magnet to the first support structure and provide a flux return path for the at least one magnet. The second support structure is configured to be attached to the first support structure so as to allow torque to be transferred between the at least one magnet and the second support structure via the first support structure, wherein the second support structure is further configured to (a) be attached to a rotatable shaft of the axial flux type electric machine, or (B) be used as an output flange or an input flange of the axial flux type electric machine.

In some embodiments, a method comprises: attaching at least one magnet to a first support structure for a rotor assembly of an axial flux type electric machine such that the first support structure provides a flux return path for the at least one magnet; and attaching a second support structure to the first support structure so as to allow torque to be transferred between the at least one magnet and the second support structure via the first support structure, the first support structure having the at least one magnet attached thereto, wherein the second support structure is further configured to (a) attach to a rotatable shaft of the axial flux machine, or (B) function as an output or input flange of the axial flux machine.

In some embodiments, a rotor assembly for an axial flux electric machine includes: at least one magnet; first means for providing a flux return path for at least one magnet; and a second device configured to be attached to the first device for transferring torque to or from the at least one magnet via the first device, wherein the second device is further configured to (a) be attached to a rotatable shaft of the axial flux machine, or (B) function as an output or input flange of the axial flux machine.

Drawings

Fig. 1 shows a cross-sectional view of an overall plan of an example axial flux air gap machine with a printed circuit board stator;

fig. 2 illustrates the tendency of the air gap in an axial flux motor to collapse due to deformation of the rotor support, which may result in interference with the stator;

FIG. 3A illustrates a cross-sectional view of an example rotor support having a taper included;

FIG. 3B illustrates a cross-sectional view of the example rotor support shown in FIG. 3A with the ring magnet attached thereto;

figure 4 shows how two rotor assemblies as shown in figure 3B can be mounted in an axial flux machine such that the equilibrium position of the rotors is equidistant from the gap centre line;

FIG. 5 illustrates an example magnet segment that may be used, for example, with rotor assemblies having a radius in excess of about four centimeters;

FIG. 6A illustrates an example of a first support structure or "rotor back iron" (back iron) of a rotor portion (e.g., a rotor half) constructed in accordance with some embodiments of the present disclosure;

FIG. 6B illustrates the first support structure shown in FIG. 6A with a set of magnet segments 502 mounted thereon;

FIG. 7 illustrates an example of a second support structure or "rotor support plate" constructed in accordance with some embodiments of the present disclosure;

FIG. 8A illustrates an example rotor assembly including a first support structure, such as shown in FIG. 6B, having a magnet segment mounted thereon, and a second support structure, such as shown in FIG. 7, prior to applying a final torque to the assembly screw;

FIG. 8B shows the rotor assembly of FIG. 8A when the screws have been tightened to design torque;

FIG. 9 shows the same rotor assembly as shown in FIG. 8B, but with the extent of the taper exaggerated for illustrative purposes;

fig. 10 shows a side view of a pair of pre-curved rotor assemblies, such as the one shown in fig. 9, illustrating how the rotor assemblies can be curved into a desired configuration when incorporated into an axial flux-type electric machine;

fig. 11A illustrates how two rotor assemblies as illustrated in fig. 8B can be installed in an axial flux type electric machine with the printed circuit board stator positioned within the generally uniform gap between the faces of the magnet segments;

FIG. 11B shows a cross-sectional view of the assembly shown in FIG. 11A;

figure 12A shows how two rotor assemblies as shown in figure 8B can be mounted in an axial flux machine without a shaft configuration;

FIG. 12B shows a cross-sectional view of the assembly of FIG. 12A;

fig. 13 illustrates a cross-sectional view of an example axial flux type electric machine in an outer-turn (out-runner) configuration, wherein the second support structures meet at an exterior of a stator configured to be mounted to a housing at an inner diameter of the stator; and

fig. 14 shows a cross-sectional view of an example axial flux-type electric machine with a single-sided rotor.

Detailed Description

This application incorporates by reference the entire contents of each of the following patent applications for all purposes: U.S. application serial No. 17/086,549 entitled "IMPROVED ROTOR assembly FOR AXIAL FLUX machine (IMPROVED ROTOR assembly FOR AXIAL FLUX machine") filed on 11/2/2020; U.S. provisional application No.62/934,059 entitled "IMPROVED ROTOR assembly FOR AXIAL FLUX machine (advanced ROTOR assembly FOR AXIAL FLUX machine)" filed on 12.11.2019; PRE-bent rotor FOR CONTROL OF magnet STATOR GAP IN AXIAL FLUX MACHINES (PRE-bent rotor FOR CONTROL OF magnet STATOR GAP IN AXIAL FLUX machine) filed on 18.5.2018 and published as U.S. patent application publication No.2018/0351441, entitled "PRE-bent rotor FOR CONTROL OF magnet STATOR GAP IN AXIAL FLUX machine", U.S. patent application serial No. 15/983,985; U.S. provisional patent application serial No. 62/515,251 entitled "PRE-curved rotor FOR CONTROL OF MAGNET STATOR GAP IN AXIAL FLUX machine (PRE-curved rotor FOR CONTROL OF MAGNET-STATOR GAP IN AXIAL FLUX machine"), filed on 6/5/2017; and U.S. provisional patent application serial No. 62/515,256 entitled AIR CIRCULATION IN AXIAL FLUX machine (AIR CIRCULATION IN AXIAL FLUX machine), filed on 6/5/2017. The present application also incorporates by reference, for all purposes, the entire contents of each of the following issued patents: U.S. patent nos. 7,109,625; U.S. patent nos. 9,673,688; U.S. patent nos. 9,800,109; U.S. patent nos. 9,673,684; and U.S. patent No.10,170,953.

Permanent magnet axial flux motors and generators, such as those described in the above-mentioned patent documents, may feature a planar Printed Circuit Board (PCB) stator assembly positioned between two rotor portions with permanent magnets, or between one rotor portion with one or more permanent magnets and a moving or stationary flux return yoke that effectively presents alternating north and south poles to the PCB stator. The interaction of the current supported by the stator and the magnetic flux density established by the rotor produces torque in motor operation, or applying torque to the rotor can induce current in the stator in generator operation.

In describing the geometry of an axial flux machine, the terms "axially," "radially," and "angularly" are generally used to describe the orientation of various components and/or the orientation of the magnetic flux lines. As used herein, the terms "axial" and "axially" refer to directions parallel to the axis of rotation of the rotor of the electric machine, the terms "radial" and "radially" refer to directions orthogonal to and intersecting the axis of rotation of the rotor of the electric machine, and the terms "angled" and "angularly" refer to directions along the curve of a circle in a plane orthogonal to the axis of rotation of the electric machine, wherein the center of the circle intersects the axis of rotation.

For rotors below a certain size, it is practical to use a single piece of magnetic material, sometimes referred to as a "ring magnet", which has been magnetized with alternating poles. Such ring magnets may be attached to a rotor support, sometimes referred to as a "back iron," which provides mechanical support for the magnets and provides a connection to the shaft of the motor.

In the' 441 publication, a method of "pre-bending" a rotor component is described in which the rotor support may be machined such that the stator-facing surfaces of the permanent magnets of the two respective halves of the rotor are "bent" when the rotor halves are in isolation and "flattened" when the two rotor halves are incorporated into an electric machine, such that the magnetic forces attract the rotor halves to each other and deflect the structural members and thus create a uniform gap between the opposing surfaces of the permanent magnets. In all examples disclosed in this document, a one-piece support structure is also used to provide a flux return path.

For larger motors, especially larger motors with radii in excess of eight centimeters, the use of ring magnets for magnet configurations may be impractical. Individual or segmented magnets for each pole can be more easily and economically produced and magnetized than one-piece magnets. The rotor support for the segmented magnets may also include recessed features or "pockets" that position the individual magnets in an alternating pole pattern. These pockets may confine the magnet radially and axially. Manufacturing the pockets may involve additional machining work as compared to a rotor support for a one-piece magnet having multiple poles. Additionally, the weight and inertia of the larger rotor may be important since the rotor support typically provides a flux return path via soft magnetic materials, such as steel. The magnet may be difficult to accurately place into the pocket and, once inserted into the pocket, difficult to remove. This can make it difficult to re-fit the rotor in the event of magnet damage or breakage, and can also potentially limit recovery and reuse of the magnetic material when the motor is out of service.

A rotor design is provided in which a rotor support for a portion of the rotor (e.g., a rotor half) may be made from multiple components, including at least a first support structure and a second support structure. In some implementations, the segmented magnet may be located on the first support structure. For example, the first support structure may be made of a first material, such as steel, which provides a flux return path for the rotor portion. The first support structure may be supported via a second support structure and connected to a shaft of the axial flux machine. In some implementations, the second support structure is made of a second material that is different from the first material. The first material may be selected for its magnetic properties. On the other hand, the second material may be selected for its stiffness, tensile strength, low weight, and/or manufacturability.

In some implementations, the first support structure can angularly and axially position the magnets, while the second support structure can radially position the magnets. Further, in some implementations, the first support structure may be supported by the second support structure in a manner such that the first support structure may be separate from the second support structure. In some such implementations, when the first support structure is separated from the second support structure, each magnet segment can be removed and replaced in the radial direction.

The designs described herein may be particularly advantageous for larger motors (e.g., with radii in excess of eight centimeters) that use segmented magnets. However, the principles described herein may also be applied to smaller motors using segmented or ring magnets. The design may be applied to any type of axial flux machine, including axial flux machines employing conventional stator structures, such as copper wire windings forming magnetic poles, and axial flux machines employing PCB-based stator structures, such as those described in the above-mentioned patent documents.

The function of the rotor in an axial flux type machine typically includes positioning the magnets, providing a flux return path, and maintaining the gap to a specified design geometry.

Magnet position may involve angularly constraining the magnets so that the magnets form an alternating series of poles that interact with the stator current density, resulting in a net production of torque. Further, the magnet is typically mechanically connected to the shaft such that the magnet can transfer torque to the shaft for useful mechanical output. The magnets may also be radially constrained to maintain the geometry of the poles. When a one-piece ring magnet is employed, the radial and angular constraints can be achieved by the integrity of the ring. However, if the rotor includes segmented magnets, these constraints need to be explicitly considered.

The flux return function of the rotor preferably completes the magnetic circuit between the poles without allowing a significant amount of flux to "leak" outside of the intended gap. Rotor flux outside the expected gap does not contribute to torque production/current generation and can induce and interact with currents in the resistive-increasing conductive material. Flux return functionality is typically achieved using soft magnetic materials, such as steel.

The maintenance of the axial position of the magnets or the gap between the magnet faces may be critical in many applications. When assembled on a shaft, the attractive forces between the rotor portions (e.g., rotor halves) tend to collapse the gap between the rotor portions where the stator is placed. Maintaining this gap at the design value may be important to motor/generator performance, and excessive reduction in gap size may result in mechanical interference between the rotor portion and the stator.

An attractive solution is to construct the rotor sections as an assembly of components, where the materials are optimized for the desired function. In some implementations, one or more magnet segments may be angularly oriented on a first support structure made of a soft magnetic material, such as steel. The first support structure may for example have a disc shape. In some implementations, the first support feature can be machined from a single piece of stock. In other implementations, the first support structure may be assembled from a plurality of separately formed components. The first support structure or "back iron" may serve as a flux return path or flux return yoke for the magnet segments. In some implementations, the piece can be made very quickly and accurately, for example, from flat sheet stock by a water jet process, a laser process, or a stamping process. This is possible to some extent because relatively few features are required and very little material needs to be removed. Minimizing the amount of soft magnetic material avoids time and energy consuming processing. Minimizing soft magnetic material may be important in some cases because minimizing soft magnetic material may reduce the moment of inertia of the motor, reduce the overall mass of the motor, and/or reduce the time constant of the motor.

In some implementations, the function of radially positioning the magnetic sections, the function of mechanically coupling the magnetic component to the shaft, and the function of maintaining the gap may be accomplished by a second support structure. In some implementations, such a second support structure may be made of a material (or materials) having a good strength/stiffness to weight ratio. Since there are no magnetic performance requirements, many relatively strong/rigid materials, such as magnesium alloys, carbon fiber composites, and aluminum, are candidates for the second component. These materials tend to be easier to form and machine in many cases than conventional machining of steel. Further, in some implementations, such a second support structure may be configured to perform additional functions, such as directly bonding components that would otherwise be mounted to the outer shaft. As explained in more detail below in connection with fig. 12A, 12B, 13, and 14, this configuration may facilitate the design of a "shaftless" motor, which may be more closely coupled to various load or torque sources.

The first and second support structures may be fastened together to form an integrated assembly in any of a number of ways. In some implementations, for example, the first and second support structures may be fastened to each other using locating pins, adhesives, and/or fasteners. In some implementations, such a two-piece assembly may allow the magnet segments to be easily manipulated and properly arranged for the rotor portion (e.g., rotor half) without clamps or other mechanisms to align and lower the magnet segments into their respective pockets. Because the first support structure does not need to radially constrain the magnet segments, the magnet segments can be inserted into the pocket from a radial direction with less force than if the magnet segments were axially inserted into the pocket before the first support structure is assembled to the second support structure. Thus, in some implementations, the first support structure may act as its own clamp to align and maintain play with adjacent magnet segments and direct the order of poles to the shaft so that the rotor halves are aligned on the final assembly. Once the magnet segments are assembled to the first support structure, the assembly comprising the first support structure and the magnet segments may be assembled to the second support structure, which may radially retain the magnet segments.

In some implementations, as an additional feature of a multi-piece rotor assembly as described herein, a "pre-bend" may be constructed in the second support structure, where it may be more easily machined. Thus, the first support structure may be machined flat in some such implementations. The two pieces may twist when the first support structure is assembled to the second support structure. In general, the assembly of the first and second support structures may approximate a frustum that angles away from the gap as the radius increases. When two such rotor portions are assembled to form a gap in the rotor, the magnetic attraction forces may further distort the assembly such that the gap is substantially uniform.

Some examples of advantages that may be realized with some implementations of the above methods and techniques include the following:

1. significant cost savings in machining operations for multi-piece designs are based on the various operations, materials and plays required to produce the correct geometry.

2. Greatly simplified clamp-less assembly of magnets with rotor back iron.

3. The mass of the soft magnetic material is minimized.

4. Applicable to magnet segments and ring magnet rotor types.

5. Easier recovery of magnetic material; removal in the radial direction.

Fig. 1 shows a cross-sectional view of an overall plan of an exemplary axial flux air gap type electric machine 100. As shown, the electric machine 100 may include a Printed Circuit Board (PCB) stator 102 and a rotor including a pair of

rotor portions

104a, 104b mechanically coupled to a shaft 108. As shown, the

rotor portions

104a, 104b may each include a

rotor support

112a, 112b, with the

respective ring magnets

110a, 110b attached to the rotor supports 112a, 112 b. In this case, each of the

rotor portions

104a, 104b (except for the

ring magnets

110a, 110 b) has a one-piece conventional structure, which requires that good stiffness, strength and magnetic properties be provided for the material selected for the rotor support 112.

Fig. 2 illustrates the tendency of the air gap 106 to collapse due to deformation of the rotor supports 112a, 112b, which may result in interference between the

ring magnets

110a, 110b and the stator 102, in an axial flux-type electric machine 200 similar to the axial flux-type electric machine 100 shown in fig. 1. Although the illustration is exaggerated, any rotor support 112 machined to the desired balancing geometry will experience some deflection.

FIG. 3A illustrates a cross-sectional view of an example rotor support 302 having a tapered surface 304 included. Fig. 3B shows a rotor portion 300 (e.g., a rotor half), the rotor portion 300 including both a rotor support 302 and a ring magnet 110 attached to a tapered surface 304. In some implementations, rotor support 302 may be configured such that outer edge 306 of rotor support 302 deforms to a desired equilibrium rotor position relative to the gap centerline upon assembly, as shown in fig. 4.

Fig. 4 illustrates how two rotor portions (e.g., half-rotor portions) such as rotor portion 300 shown in fig. 3B can be mounted in an axial flux-type motor 400 such that the equilibrium position of the rotors is equidistant from a centerline 402 of gap 106 between the rotor portions. As illustrated, the back 404a, 404B of the rotor supports 302a, 302B is distorted compared to fig. 3B due to the attractive force between the ring magnets 110a, 110B. Further, as also illustrated, when the rotor portion is installed in the electric machine 400, the

outer edges

306a, 306b of the

ring magnets

110a, 110b are deformed to a desired equilibrium rotor position relative to the centerline 402 of the gap 106.

Fig. 5 illustrates an exemplary magnet segment 502, which magnet segment 502 may be used, for example, with rotor assemblies having a radius in excess of about four centimeters. The magnet segments 502 may have several radii and dimensional tolerance parameters that may machine pockets that constrain the segments 502 in challenging planes. As shown, the magnet 502 may have an inner edge 504 and an outer edge 506, wherein the width W of the inner edge 504₁Width W of the outer edge 506₂Short.

Fig. 6A illustrates an example of a first support structure 602 or "rotor back iron" of a rotor portion (e.g., a rotor half) constructed in accordance with some embodiments of the present disclosure. As illustrated, in some implementations, the first support structure 602 can have an annular shape with a central opening 608 and can include positioning ribs 604 to receive magnet segments, such as the magnet segments 502 shown in fig. 5. Further, in some implementations, the first support structure 602 can include one or more pin and/or screw fastener holes 606, and the one or more pin and/or screw fastener holes 606 can be used to fasten the first support structure 602 to a second support structure 702, such as the second support structure 702 shown in fig. 7. In some implementations, the first support structure 602 can be made of steel.

Fig. 6B shows how the first support structure 602 can appear when a set of magnet segments 502 has been attached to the first support structure 602, for example by sliding the magnet segments 502 between the positioning ribs 604, but before the first support structure 602 is attached to the second support structure 702, as described below. As shown, the inner edge 504 of the magnet segment 502 may be positioned a first radial distance R from a center point 610 of the opening 608 of the first support structure 602₁And a magnetAn outer edge 506 of the segment 502 may be positioned at a second radial distance R from a center point 610 of the opening 608 of the first support structure 602₂To (3).

FIG. 7 illustrates an example of a second support structure 702 or "rotor support plate" constructed according to some embodiments of the present disclosure. As shown, in some implementations, the second support structure 702 may be configured to position the first support structure 602 to the shaft 108 (e.g., as shown in fig. 11A and 11B) to radially constrain the magnet segments 502 (e.g., via the circular lip 704) at the second radial distance R₂And/or features a tapered surface region 706 that determines how the rotor portion (e.g., rotor half) deforms on assembly. In some implementations, second support structure 702 may be fabricated using a turning type operation and/or a milling type operation. In some implementations, second support structure 702 may be made of a magnesium alloy, a carbon fiber composite, or aluminum.

Fig. 8A illustrates an example rotor assembly 800 prior to applying a final torque to an assembly screw 802, the example rotor assembly 800 including a first support structure 602 as shown in fig. 6B and a second support structure 702 as shown in fig. 7, the first support structure 602 having a magnet segment mounted thereon. In some implementations, the configuration shown in fig. 8A can be achieved, for example, by: magnet segments 502 are first positioned between positioning ribs 604 of first support structure 602, and first support structure 602 is then positioned within circular lip 704 of second support structure 702. As illustrated in fig. 8A, a gap 804 exists between the first support structure 602 and the second support structure 702 before the screw 802 is tightened.

Fig. 8B shows the rotor assembly 800 of fig. 8A when the screws 802 have been tightened to design torque. As shown, tightening the screw 802 may conform the first support structure 602 to the second support structure 702 such that the taper 808 corresponding to the tapered surface 706 (shown in fig. 7) may be transferred to the first support structure 602 and thus to the face 810 of the magnet segment 502.

Fig. 9 shows the same rotor assembly 800 as shown in fig. 8B, but the extent of the taper 808 is exaggerated for illustrative purposes. As illustrated in fig. 9, the magnet segments 502 (or alternatively, the ring magnet 110) may be attached to a surface of the first support structure 602 facing away from the second support structure 702 such that a face 810 of the magnet segments 502 (or a torus of the ring magnet 110) assumes the shape of the taper 808.

As illustrated in fig. 9, the extent of the taper 808 of the tapered surface 706 of the second support structure 702 may be measured by: identifying two

points

902, 904 on a surface of the second support structure 702 in contact with the first support structure 602, and a distance D between two

planes

906, 908 perpendicular to the axis of rotation 930 of the rotor assembly 800 and intersecting the first point 902 and the second point 904, respectively₁A determination is made. In some implementations, two contact points 902, 904 (with the inner radius R of the magnet segment 502) may be found₁And an outer radius R₂Aligned, or vice versa), wherein the distance D₁Substantially greater than zero. In this context, the term "substantially" is intended to exclude slight variations due to machining and/or material defects within the allowable range of tolerances. In some implementations, the distance D₁May be, for example, greater than "0.003" inches, or greater than "0.01" inches, or even greater than "0.02" inches. Additionally or alternatively, in some embodiments, two

contact points

902, 904 may be found, such that the distance D₁Ratio to the distance between two points and/or distance D₁Corresponding to the inner radius R of the magnet segment 502₁And an outer radius R₂The ratio of the difference between is substantially greater than zero. In some implementations, such a ratio may be, for example, greater than "0.002", or greater than "0.005", or even greater than "0.01".

As also illustrated in fig. 9, in some implementations, at least one point 910 can be found on a surface of second support structure 702 in contact with first support structure 602, where a ray 912 extending away from and perpendicular to the surface (such that ray 912 is aligned with the magnetization direction of the magnet) forms a substantially smaller than with a plane perpendicular to axis of rotation 930 "Angle alpha of 90 ″₁. In some implementations, the angle α₁May be, for example, less than "89.9" degrees, less than "89.7" degrees, or even less than "89.5" degrees. The point 910 may, for example, coincide with the inner radius R of the magnet segment 502₁Outer radius R of magnet segment 502₂Or some point alignment between the two radii.

Additionally or alternatively, and as also shown in fig. 9, when the first support structure 602 is attached to the second support structure 702, the degree of taper 808 transferred to the face 810 of the magnet segment 502 (or to the face of the ring magnet 110) may be measured by: identifying a distance D between a surface of the magnet segment 502 (or the ring magnet 110) orthogonal to the magnetization direction of the magnet segment 502 (or the ring magnet 110), e.g., two

points

914, 916 on a face 810 of the magnet segment 502 shown in FIG. 9, and two

planes

926, 928 perpendicular to the axis of rotation 930 and intersecting the first and

second points

914, 916, respectively₂A determination is made. In the example shown, the opposite surface of the magnet segment 502 that is in contact with the first support structure 602 is also orthogonal to the magnetization direction of the magnet segment 502. In some embodiments, it may be possible (at the inner radius R of the magnet segment 502)₁And an outer radius R₂Or vice versa) find two magnet surface points 914, 916, wherein the distance D₂Substantially greater than zero. In some implementations, the distance D₂May be, for example, greater than "0.002" inches, or greater than "0.005" inches, or even greater than "0.01" inches. Additionally or alternatively, in some embodiments, two magnet surface points 914, 916 may be found such that distance D₂Ratio to the distance between two points and/or distance D₂The ratio to the difference between the inner radius R1 and the outer radius R2 of the magnet section 502 is substantially greater than zero. In some implementations, such a ratio may be, for example, greater than "0.002", or greater than "0.005", or even greater than "0.01".

As also illustrated in fig. 9, in some implementations, at least one point 922 may be found on the following surface of the magnet segment 502: the magnetization direction of the surface and the magnet section 502 (or the ring magnet 11)To face 810 normal to and away from the first support structure 602, such as the magnet segment 502 shown in fig. 9, wherein rays 924 extending away from and perpendicular to the surface of the magnet (such that rays 924 are aligned with the magnetization direction of the magnet segment 502) form an angle a substantially less than "90" degrees with a plane perpendicular to the axis of rotation 930₂. In some implementations, the angle α₂May be, for example, less than "89.9" degrees, less than "89.7" degrees, or even less than "89.5" degrees. Point 922 may be located, for example, at an inner radius R of magnet segment 502₁Outer radius R of magnet segment 502₂Or at some point between the two radii. Further, as shown in fig. 9, the first support structure 602, the second support structure 702, and the magnet segment 502 may be configured and arranged such that a ray 924 (the ray 924 extending perpendicular to and away from a surface 810 of the magnet segment 502 facing away from the first support structure 602) intersects the plane 926.

As illustrated in fig. 10, when two

rotor assemblies

800a, 800b are attached to the shaft 108 (not shown in fig. 10) or otherwise installed in an axial flux-type electric machine, the magnetic flux of the

magnet segments

502a, 502b may create an attractive force in the gap 1002 between the

magnet segments

502a, 502b that bends the

rotor assemblies

800a, 800b such that the ends of the

rotor assemblies

800a, 800b move toward each other. The dashed lines in fig. 10 illustrate how the rotor assemblies 800a, 800B may be shaped after they are assembled into a motor or generator, such as described below in connection with fig. 11A-11B, 12A-12B, 13, and 14. In some implementations, the

rotor assemblies

800a, 800b may be pre-bent prior to assembly such that the surfaces of the two

magnet sections

502a, 502b that face each other are substantially parallel in the assembled motor or generator, thus making the width of the gap 1002 substantially uniform across the gap 1002. In other implementations, the

rotor assemblies

800a, 800b may be slightly "overbent" such that, once assembled, a taper is obtained that increases as a function of radius. While this may have the undesirable effect of reducing the gap at larger radii, it may allow for the use of a smaller average gap widthG, thus increasing the average magnetic field strength and maintaining the outer radius R of the

magnet segments

502a, 502b₂Play of (c).

As illustrated in fig. 10, the amount of bending experienced by the rotor assembly 800b when assembled may be measured, for example, by: identifying the outer radius R at the magnet segment 502b₂A point 1004, and a distance D for moving the point in a direction coincident with the axis of rotation 930 during assembly₃A determination is made. Distance D₃Can be measured, for example, by: a plane intersecting point 1004 and perpendicular to axis of rotation 930 is identified, and the distance such plane moves relative to another plane intersecting point 1006 at or near the center of rotor element assembly 800b and also perpendicular to axis of rotation 930 is determined. In some implementations, the distance D₃And may be greater than "0.001" inches, or greater than "0.005" inches, or even greater than "0.01" inches. Additionally or alternatively, in some implementations, the distance D₃The ratio to the average width G of the gap 1002 may be greater than "0.01", or greater than "0.05", or even greater than "0.1". Additionally or alternatively, the distance D₃The ratio to the average play distance between the magnet segments 502b and the surface of the stator 102 (not shown in fig. 10) may be greater than "0.25", greater than "0.5", or even greater than "1". Thus, in some implementations, the rotor assembly 800B may deflect as much as or greater than the average magnet/stator play distance.

Referring to fig. 9 in conjunction with fig. 10, it should be understood that in some embodiments, the

rotor assemblies

800a, 800b may be constructed and arranged such that when the

rotor assemblies

800a, 800b are installed in a motor or generator and cause deflection as illustrated in fig. 10, one or more of the following values may be reduced by fifty percent or more for each rotor assembly: (1) distance D between plane 906 and plane 908₁(2) distance D₁Ratio to the distance between point 902 and point 904 and/or distance D₁And the inner radius R of the magnet segment 502₁And an outer radius R₂Ratio of difference therebetween(3) the distance D between the plane 926 and the plane 928₂And (4) a distance D₂Ratio to the distance between

points

914 and 916 and/or distance D₂And the inner radius R of the magnet segment 502₁And an outer radius R₂The ratio of the difference between.

Fig. 11A illustrates how two rotor assemblies, such as rotor assembly 800 shown in fig. 8B, can be installed in an axial flux type electric machine 1100 with a stator 102 (e.g., a PCB-based stator) positioned within a substantially uniform gap between faces of magnet segments 502. Fig. 11B illustrates a cross-sectional view of the axial flux machine 1100 illustrated in fig. 11A. The "uniform gap" configuration shown in fig. 11A and 11B may result because, upon installation, the attractive forces between the opposing magnet segments 502 of the two rotor assemblies 800 may deflect the rotor assemblies 800 such that the first support structure 602 assumes its original, nominally flat shape (e.g., as shown in fig. 6A). Thus, the resulting gap between the faces of the magnet segments 502 may be substantially uniform as a function of radius.

Fig. 12A illustrates how two rotor assemblies, such as rotor assembly 800 shown in fig. 8B, can be installed in an axial flux type electric machine 1200 having a shaftless configuration. Fig. 12B illustrates a cross-sectional view of the axial flux type motor 1200 illustrated in fig. 12A. As illustrated, in some implementations, the axial flux electric machine 1200 may include a second support structure 1202, the second support structure 1202 being at least partially exposed to the environment outside the housing 1206, thus enabling the second support structure 1202 to also function as a mechanical connector for the electric machine 1200. For example, the external component may be mounted directly to exposed portion 1204 of second support structure 1202 or otherwise mechanically engaged with exposed portion 1204 of second support structure 1202. In some implementations, the configuration of first support structure 602 in axial flux machine 1200 may be the same as or similar to first support structure 602 in axial flux machine 1100 described above in connection with fig. 11A and 11B.

Fig. 13 shows an example of a "shaftless" axial flux type electric machine 1300 in an "outer turn" configuration. As shown, in such a configuration, the stator 102 may be fixedly coupled to the housing 1306 at the inner diameter, and the two

second support structures

1302a, 1302b may be fixedly coupled to each other at an exterior of the stator 102 (e.g., via one or more connectors 1304) and each may be rotatable relative to the housing 1306. In some implementations, the configuration of the first support structure 602 in the axial flux machine 1300 can be the same as or similar to the first support structure 602 in the axial flux machine 1100 described above in connection with fig. 11A and 11B.

Fig. 14 shows an example of a "shaftless" axial flux type electric machine 1400 with a single-sided rotor. In this configuration, one of the two rotor halves may be replaced with a magnetic material 1402, the magnetic material 1402 providing a flux return path and being secured to the housing 1404. As illustrated, the stator 102 may be placed between the fixed magnetic material 1402 and the magnet segments 502 of a single rotor assembly that includes a first support structure 602 (to which the magnet segments 502 may be mounted 602) and a second support structure 1406 (which second support structure 1406 may provide a mechanical connection between the magnetic elements and one or more components external to the motor 1400). In some implementations, the configuration of first support structure 602 in axial flux-type electric machine 1400 may be the same as or similar to first support structure 602 in axial flux-type electric machine 1100 described above in connection with fig. 11A and 11B.

Examples of inventive concepts/features/techniques

The following paragraphs describe examples of the novel concepts, features and/or techniques disclosed herein.

(A1) A rotor for an axial flux motor or generator, the rotor comprising at least one magnet disposed on a first support structure made of at least one first material, wherein the first support structure provides a flux return path for the at least one magnet and is connected to a shaft by a second support structure made of at least one second material.

(A2) A rotor as recited in paragraph (a1), wherein the at least one magnet includes a magnet segment and the first support structure provides radial alignment of the magnet segment.

(A3) A rotor as described in paragraph (a1) or paragraph (a2), wherein the at least one magnet includes a magnet segment and the first support structure is configured to be unattached from the second support structure to allow removal of the magnet segment by sliding in a radial direction.

(A4) A rotor as in any of paragraphs (a1) to (A3), the at least one magnet comprising a magnet segment, and wherein the first support structure comprises a rib that provides angular alignment of the magnet segment.

(A5) A rotor as in any of paragraphs (a1) to (a4), wherein the second support structure is configured such that an assembly comprising the first support structure and the at least one magnet becomes pre-bent when the assembly is attached to the second support structure.

(A6) A rotor as described in any of paragraphs (a1) to (a5), wherein the pre-bend feature is incorporated into the first support structure.

(A7) A rotor as described in any of paragraphs (a1) to (a6), wherein the first support structure is disc-shaped.

(A8) A rotor as in any of paragraphs (a1) to (a7), wherein the first support structure comprises a plurality of portions assembled to form a disc shape.

(A9) A rotor as in any of paragraphs (a1) to (A8), wherein the second support structure is configured to serve as an output or input flange of a motor or generator.

(B1) A rotor for an axial flux motor or generator, the rotor comprising a ring magnet disposed on a first support structure made of at least one first material, wherein the first support structure provides a flux return path for the ring magnet and is connected to a shaft by a second support structure made of at least one second material.

(B2) A rotor as recited in paragraph (B1), wherein the second support structure is configured such that an assembly comprising the first support structure and the ring magnet becomes pre-bent when the assembly is attached to the second support structure.

(B3) A rotor as described in paragraph (B1) or (B2), wherein the pre-curved section is incorporated into the first support structure.

(B4) A rotor as described in any of paragraphs (B1) to (B3), wherein the first support structure is disc-shaped.

(B5) A rotor as in any of paragraphs (B1) to (B4), wherein the first support structure comprises a plurality of portions assembled to form a disc shape.

(B6) A rotor as described in any of paragraphs (B1) to (B5), wherein the second support structure is configured to serve as an output or input flange of a motor or generator.

(C1) A rotor for an axial flux motor or generator, the rotor comprising at least one magnet disposed on a first support structure made of at least one first material, wherein the first support structure provides a flux return path for the at least one magnet and is attached to a second support structure made of at least one second material, the second support structure being configured to provide torque to a mechanical load or receive torque from a mechanical drive.

(C2) A rotor as recited in paragraph (C1), wherein the at least one magnet includes a magnet segment and the first support structure provides radial alignment of the magnet segment.

(C3) A rotor as described in paragraph (C1) or (C2), wherein the at least one magnet comprises a magnet segment and the first support structure is configured to be unattached from the second support structure to allow removal of the magnet segment by sliding in a radial direction.

(C4) A rotor as in any of paragraphs (C1) to (C3), the at least one magnet comprising a magnet segment, and wherein the first support structure comprises a rib that provides angular alignment of the magnet segment.

(C5) A rotor as in any of paragraphs (C1) to (C4), wherein the second support structure is configured such that an assembly comprising the first support structure and the at least one magnet becomes pre-bent when the assembly is attached to the second support structure.

(C6) A rotor as described in any of paragraphs (C1) to (C5), wherein the pre-bend feature is incorporated into the first support structure.

(C7) A rotor as described in any of paragraphs (C1) to (C6), wherein the first support structure is disc-shaped.

(C8) A rotor as recited in any of paragraphs (C1) to (C7), wherein the first support structure comprises a plurality of portions assembled to form a disk-shape.

(C9) A rotor as described in any of paragraphs (C1) to (C8), wherein the second support structure is configured to serve as an output or input flange of a motor or generator.

(D1) A rotor for an axial flux motor or generator, the rotor comprising a ring magnet disposed on a first support structure made of at least one first material, wherein the first support structure provides a flux return path for the ring magnet and is attached to a second support structure made of at least one second material, the second support structure being configured to provide torque to a mechanical load or receive torque from a mechanical drive.

(D2) A rotor as recited in paragraph (D1), wherein the second support structure is configured such that an assembly comprising the first support structure and the ring magnet becomes pre-bent when the assembly is attached to the second support structure.

(D3) A rotor as described in paragraph (D1) or paragraph (D2), wherein the pre-curved section is incorporated into the first support structure.

(D4) A rotor as described in any of paragraphs (D1) to (D3), wherein the first support structure is disc-shaped.

(D5) A rotor as described in any of paragraphs (D1) to (D4), wherein the first support structure comprises a plurality of sections assembled to form a disc shape.

(D6) A rotor as described in any of paragraphs (D1) to (D5), wherein the second support structure is configured to serve as an output or input flange of a motor or generator.

(E1) A rotor assembly for an axial flux electric machine, the rotor assembly comprising: at least one magnet; a first support structure configured to attach the at least one magnet to the first support structure and provide a flux return path for the at least one magnet; and a second support structure configured to be attached to the first support structure so as to allow torque to be transferred between the at least one magnet and the second support structure via the first support structure, wherein the second support structure is further configured to (a) be attached to a rotatable shaft of the axial flux type electric machine, or (B) be used as an output flange or an input flange of the axial flux type electric machine.

(E2) A rotor assembly as recited in paragraph (E1), wherein the second support structure is configured to be attached to a rotatable shaft of an axial flux electric machine.

(E3) A rotor assembly as recited in paragraph (E1), wherein the second support structure is configured to serve as an output flange or an input flange of an axial flux machine.

(E4) A rotor assembly as described in any one of paragraphs (E1) to (E3), wherein the first support structure is made of at least one first material; and the second support structure is made of at least one second material different from the at least one second material.

(E5) A rotor assembly as described in any one of paragraphs (E1) to (E4), wherein the at least one magnet comprises a magnet segment; and the second support structure is further configured to limit radial movement of the magnet segments when the magnet segments are attached to the first support structure and the second support structure is attached to the first support structure.

(E6) A rotor assembly as recited in paragraph (E5), wherein the second support structure further includes a circular lip configured to engage an outermost edge of the magnet segments to limit radial movement of the magnet segments.

(E7) A rotor assembly as described in paragraph (E5) or paragraph (E6), wherein the first support structure is further configured to allow the magnet segments to slide radially when the second support structure is unattached from the first support structure.

(E8) A rotor assembly as recited in any one of paragraphs (E5) to (E7), wherein the second support structure is further configured to be unattached from the first support structure, thereby allowing the magnet segments to be removed from the first support structure by sliding in a radial direction.

(E9) A rotor assembly as described in any one of paragraphs (E1) to (E8), wherein the at least one magnet comprises a magnet segment; and the first support structure further comprises a rib configured to limit angular movement of the magnet segments when the magnet segments are attached to the first support structure.

(E10) A rotor assembly as recited in any one of paragraphs (E1) to (E9), wherein the second support structure further comprises at least one surface that tapers in a radial direction so as to cause the first support structure to bend to conform to a shape of the at least one surface when the second support structure is attached to the first support structure.

(E11) A rotor assembly as described in any of paragraphs (E1) to (E4), (E9), or (E10), wherein the at least one magnet comprises an annular magnet configured to attach to the first support structure.

(E12) A rotor assembly as recited in any of paragraphs (E1) to (E11), wherein the second support structure is adapted to rotate about a rotational axis of the axial flux machine; the at least one magnet has a first surface orthogonal to the magnetization direction of the at least one magnet and facing away from the first support structure; the first support structure, the second support structure and the at least one magnet are constructed and arranged such that: if the first support structure, the second support structure and the at least one magnet are stationary with respect to the axis of rotation and are not affected by any other magnetic component, a distance between a first plane intersecting a first point on the first surface and perpendicular to the axis of rotation and a second plane intersecting a second point on the first surface and perpendicular to the axis of rotation is substantially greater than zero; the second point is at a greater radial distance from the axis of rotation than the first point; and the first support structure, the second support structure, and the at least one magnet are further constructed and arranged such that: a ray extending away from and perpendicular to the first surface at the second point intersects the first plane if the first support structure, the second support structure, and the at least one magnet are stationary relative to the axis of rotation and unaffected by any other magnetic component.

(E13) A rotor assembly as recited in paragraph (E12), wherein at least one magnet has an inner edge disposed at a first point; at least one magnet has an outer edge opposite the inner edge and disposed at a second point; and the first support structure, the second support structure, and the at least one magnet are further constructed and arranged such that: the ratio of the distance between the first plane and the second plane to the distance between the first point and the second point is larger than 0.002 if the first support structure, the second support structure and the at least one magnet are stationary with respect to the axis of rotation and are not affected by any other magnetic component.

(E14) A rotor assembly as described in any one of paragraphs (E1) to (E13), wherein the rotor assembly is mounted in an axial flux-type electric machine and the distance between the first plane and the second plane is substantially equal to zero.

(F1) A method, comprising: attaching at least one magnet to a first support structure for a rotor assembly of an axial flux type electric machine such that the first support structure provides a flux return path for the at least one magnet; and attaching a second support structure to the first support structure so as to allow torque to be transferred between the at least one magnet and the second support structure via the first support structure, the first support structure having the at least one magnet attached thereto, wherein the second support structure is further configured to (a) attach to a rotatable shaft of the axial flux type electric machine, or (B) function as an output flange or an input flange of the axial flux type electric machine.

(F2) A method as in paragraph (F1), wherein the second support structure is configured to be attached to a rotatable shaft of an axial flux electric machine.

(F3) A method as recited in paragraph (F1), wherein the second support structure is configured to serve as an output flange or an input flange of the axial flux machine.

(F4) A method as in any of paragraphs (F1) to (F3), wherein the first support structure is made of at least one first material; and the second support structure is made of at least one second material different from the at least one second material.

(F5) A method as in any of paragraphs (F1) to (F4), wherein the at least one magnet comprises a magnet segment, and attaching the second support structure to the first support structure further comprises attaching the second support structure to the first support structure such that the second support structure limits radial movement of the magnet segment.

(F6) A method as described in paragraph (F5), further comprising detaching the second support structure from the first support structure, thereby allowing the magnet segments to be removed from the first support structure by sliding in the radial direction.

(F7) A method as in any of paragraphs (F1) to (F6), wherein the second support structure further comprises at least one surface that tapers in a radial direction; and attaching the second support structure to the first support structure further comprises attaching the second support structure to the first support structure so as to bend the first support structure to conform to the shape of the at least one surface.

(F8) A method as in any of paragraphs (F1) to (F7), wherein the second support structure is adapted to rotate about a rotational axis of the axial flux machine; the at least one magnet has a first surface orthogonal to the magnetization direction of the at least one magnet and facing away from the first support structure; the first support structure, the second support structure and the at least one magnet are constructed and arranged such that: if the first support structure, the second support structure and the at least one magnet are stationary with respect to the axis of rotation and are not affected by any other magnetic component, the distance between a first plane intersecting a first point on the first surface and perpendicular to the axis of rotation and a second plane intersecting a second point on the first surface and perpendicular to the axis of rotation is substantially greater than zero; the second point is at a greater radial distance from the axis of rotation than the first point; and the first support structure, the second support structure, and the at least one magnet are further constructed and arranged such that: a ray extending away from and perpendicular to the first surface at the second point intersects the first plane if the first support structure, the second support structure, and the at least one magnet are stationary relative to the axis of rotation and unaffected by any other magnetic component.

(F9) A method as in paragraph (F8), wherein at least one magnet has an inner edge disposed at a first point; at least one magnet has an outer edge opposite the inner edge and disposed at a second point; and the first support structure, the second support structure, and the at least one magnet are further constructed and arranged such that: the ratio of the distance between the first plane and the second plane to the distance between the first point and the second point is larger than 0.002 if the first support structure, the second support structure and the at least one magnet are stationary with respect to the axis of rotation and are not affected by any other magnetic component.

(F10) A method as in any of paragraphs (F1) to (F9), further comprising mounting the rotor assembly in an axial flux-type electric machine such that the distance between the first plane and the second plane is substantially equal to zero.

Having thus described several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the disclosure. Accordingly, the foregoing description and drawings are by way of example only.

Various aspects of the present disclosure may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in this application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.

Further, the disclosed aspects may be implemented as methods, which have provided examples. The actions performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts concurrently, even though shown as sequential acts in illustrative embodiments.

Use of ordinal terms such as "first," "second," and "third," etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having," "containing," "involving," and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

What is claimed is:

Claims

1. a rotor assembly for an axial flux electric machine, the rotor assembly comprising:

at least one magnet;

a first support structure configured to attach the at least one magnet to the first support structure and provide a flux return path for the at least one magnet; and

a second support structure configured to be attached to the first support structure so as to allow torque to be transferred between the at least one magnet and the second support structure via the first support structure, wherein the second support structure is further configured to (A) be attached to a rotatable shaft of the axial flux type electric machine, or (B) serve as an output or input flange of the axial flux type electric machine.

2. The rotor assembly of claim 1, wherein:

the second support structure is adapted to rotate about a rotational axis of the axial flux machine;

the at least one magnet has a first surface orthogonal to a magnetization direction of the at least one magnet and facing away from the first support structure;

the first support structure, the second support structure and the at least one magnet are constructed and arranged such that: a distance between a first plane intersecting a first point on the first surface and perpendicular to the axis of rotation and a second plane intersecting a second point on the first surface and perpendicular to the axis of rotation is substantially greater than zero if the first support structure, the second support structure, and the at least one magnet are stationary relative to the axis of rotation and unaffected by any other magnetic component;

the second point is at a greater radial distance from the axis of rotation than the first point; and

the first support structure, the second support structure, and the at least one magnet are further constructed and arranged such that: a ray extending away from and perpendicular to the first surface at the second point intersects the first plane if the first support structure, the second support structure, and the at least one magnet are stationary relative to the axis of rotation and unaffected by any other magnetic component.

3. The rotor assembly of claim 2, wherein:

the at least one magnet has an inner edge disposed at the first point;

the at least one magnet has an outer edge opposite the inner edge and disposed at the second point; and

the first support structure, the second support structure, and the at least one magnet are further constructed and arranged such that: the ratio of the distance between the first plane and the second plane to the distance between the first point and the second point is greater than 0.002 if the first support structure, the second support structure and the at least one magnet are stationary with respect to the axis of rotation and are not affected by any other magnetic component.

4. A rotor assembly as claimed in claim 2 or claim 3, wherein the rotor assembly is mounted in the axial flux machine and the distance between the first and second planes is substantially equal to zero.

5. A rotor assembly as claimed in any one of claims 1 to 4, wherein:

the second support structure further comprises at least one surface that tapers in a radial direction so as to cause the first support structure to bend to conform to the shape of the at least one surface when the second support structure is attached to the first support structure.

6. A rotor assembly as claimed in any one of claims 1 to 5 wherein the second support structure is configured to be attached to a rotatable shaft of the axial flux machine.

7. A rotor assembly as claimed in any one of claims 1 to 5 wherein the second support structure is configured to act as an output or input flange of the axial flux machine.

8. A rotor assembly as claimed in any one of claims 1 to 7, wherein:

the first support structure is made of at least one first material; and

the second support structure is made of at least one second material different from the at least one first material.

9. A rotor assembly as claimed in any one of claims 1 to 8, wherein:

the at least one magnet comprises a magnet section; and

the second support structure is further configured to limit radial movement of the magnet segments when the magnet segments are attached to the first support structure and the second support structure is attached to the first support structure.

10. The rotor assembly of claim 9, wherein:

the second support structure further includes a circular lip configured to engage an outermost edge of the magnet segments to limit radial movement of the magnet segments.

11. A rotor assembly as claimed in claim 9 or claim 10, wherein:

the first support structure is further configured to allow the magnet segments to slide radially when the second support structure is disconnected from the first support structure.

12. A rotor assembly as claimed in any one of claims 9 to 11, wherein:

the second support structure is further configured to be capable of being detached from the first support structure, thereby allowing the magnet segments to be removed from the first support structure by sliding in a radial direction.

13. A rotor assembly as claimed in any one of claims 1 to 12, wherein:

the at least one magnet comprises a magnet section; and

the first support structure further comprises a rib configured to limit angular movement of the magnet segments when the magnet segments are attached to the first support structure.

14. A rotor assembly as claimed in any one of claims 1 to 8, wherein:

the at least one magnet comprises a ring magnet configured to attach to the first support structure.

15. A method, comprising:

attaching at least one magnet to a first support structure for a rotor assembly of an axial flux type electric machine such that the first support structure provides a flux return path for the at least one magnet; and

attaching a second support structure to the first support structure so as to allow torque to be transferred between the at least one magnet and the second support structure via the first support structure, the first support structure having the at least one magnet attached thereto, wherein the second support structure is further configured to (a) attach to a rotatable shaft of the axial flux machine, or (B) serve as an output or input flange of the axial flux machine.

16. The method of claim 15, wherein:

the second support structure is adapted to rotate about an axis of rotation of the axial flux machine;

17. The method of claim 16, wherein:

the at least one magnet has an inner edge disposed at the first point;

18. The method of any of claims 15 to 17, wherein:

the first support structure is made of at least one first material; and

19. The method of any of claims 15 to 18, wherein:

the at least one magnet comprises a magnet section, an

Attaching the second support structure to the first support structure further comprises attaching the second support structure to the first support structure such that the second support structure limits radial movement of the magnet segments.

20. The method of claim 19, further comprising:

disconnecting the second support structure from the first support structure to allow the magnet segments to be removed from the first support structure by sliding in a radial direction.