Axial flux electric machine pole pieces with conductive ribbons

Abstract

Axial flux electric machines and associated methods are disclosed herein. One disclosed axial flux electric machine includes a stator having a plurality of pole pieces, a rotor spaced from the stator in an axial direction of the axial flux electric machine, and coiled ribbons of conductive material forming at least a portion of the pole pieces in the plurality of pole pieces. The axial direction of the coiled ribbons of conductive material is substantially parallel to the axial direction of the axial flux electric machine. In some embodiments of the disclosed axial flux electric machine, the coiled ribbons of soft magnetic material are coiled into interleaved composite coils that, together with the coiled ribbons of conductive material, form at least a portion of the pole pieces for the axial flux electric machine.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 403,281, filed September 1, 2022, which claims the benefit of U.S. Provisional Patent Application No. 18 / 241,159, filed August 31, 2023, which are hereby incorporated by reference in their entireties for all purposes. [Background technology]

[0002] background Axial-flux electric machines were first patented in 1889 by Nikola Tesla in U.S. Patent No. 405,858. However, the use of such machines in the commercial market was largely uncommon until the invention of high-performance neodymium-iron-boron (Nd-Fe-B) permanent magnet material in 1983. Since then, axial-flux electric machines have been rapidly and widely adopted due to their high efficiency and compact nature compared to other technologies. The emergence of environmentally friendly technologies such as electric vehicles has further increased the application space of axial-flux electric machines. Today, axial-flux electric machines are used in electric vehicles, robots of various sizes and types, and electric or hybrid propulsion systems for aircraft. It is generally desirable to reduce the power losses generated by electric machines, thereby improving the machine's energy conversion efficiency. It is also desirable to keep electric machines lightweight and compact, thereby reducing their upfront manufacturing costs.

[0003] Axial flux electric machines typically include a stationary assembly and a rotating assembly. In its most basic form, an axial flux electric machine includes at least three components: a stator, a rotor, and a rotor shaft. The stator is the stationary component, and the rotor and rotor shaft are the rotating components. An axial flux electric machine can also include two or more stators or two or more rotors. Two examples of axial flux electric machines are shown in FIG. 1 , where axial cross section 100 illustrates an axial flux electric machine with one rotor and two stators, and axial cross section 110 illustrates an axial flux electric machine with one stator and two rotors. Radial cross section 111 illustrates the stator of either axial flux electric machine. Radial cross section 112 illustrates the rotor of either axial flux electric machine. As used herein, the term radial cross section refers to a view provided by viewing the axial flux electric machine in the direction of the axis of the axial flux electric machine, and the term axial cross section refers to a view provided by viewing the axial flux electric machine along the radius of the rotor of the axial flux electric machine. Axial flux electric machines work by exchanging electrical energy and rotational momentum of rotating parts using a magnetic field that is in the direction of motion of the rotating parts.

[0004] The manner in which electrical energy and rotational momentum are exchanged in an axial flux electric machine depends on the specific design of the machine. For axial electric motors, designs can include permanent magnets and controllably magnetized magnets. The permanent magnets can be on the rotor or the stator, and the controllably magnetized magnets can be on either the rotor or the stator. Stator 101 and rotor 102 can be the stator and rotor on two different types of illustrated axial flux electric machines, as shown in FIG. 1. In the example provided, the permanent magnets are on the rotor, while the stator can be controllably magnetized to rotate the rotor. However, in an alternative example, the permanent magnets are on the stator, and the rotor can be controllably magnetized.

[0005] The controllably magnetized magnet can include conductive coil windings and soft magnetic material. In the axial flux electric machine of FIG. 1, the stator includes coil windings 105, the coils made from a conductive material, and the terminals of the conductive coil are exposed to the outside and energized by an external electric circuit. Typical conductive materials for the coils are aluminum and copper. As shown in FIG. 1, a conductive wire is coiled around a trapezoidal pole piece 106 to form the coil windings 105. Such pole pieces are manufactured using a complex molding process using soft magnetic materials and laminations. The soft magnetic material allows the device to be configurably magnetized under the influence of an electric current applied to the coiled wire.

[0006] The rotor can be connected to a rotor shaft to transfer the rotor's rotational momentum to an external system. As shown in FIG. 1, the rotor 102 can house a circular array of permanent magnets 103 of distinctly spaced alternating magnetic poles and be coupled to a rotor shaft 109. The rotor is typically supported by one or more bearings 108, which allow the rotor to rotate about an axis of rotation while maintaining a substantially uniform air gap between the rotor and the stator. In the example axial flux motor of FIG. 1, when the stator coils are energized, current flowing through the coils generates a magnetic field between two adjacent coils with alternatingly opposite polarities. The magnetic flux generated by the coils repels or attracts the permanent magnets in their vicinity, inducing torque and rotation of the rotor. The rotor shaft coupled to the rotor then transmits torque to an externally connected load. Summary of the Invention [Problem to be solved by the invention]

[0007] overview Disclosed herein are electric machines and associated methods and systems for converting electrical power into rotating mechanical power and vice versa. The electric machines may be permanent magnet synchronous AC electric machines in the form of axial flux electric machines. The axial flux electric machines may be either motors or generators.

[0008] Prior art axial-flux electric machines have several drawbacks. For example, they do not utilize the flux-carrying capacity of electrical steel and underutilize the flux of permanent magnets. Furthermore, manufacturing trapezoidal pole pieces using laminated electrical steel is typically difficult because standard electrical steel stamping and joining methods are not readily available. Another possibility for solving this problem is to use soft magnetic composites formed using soft magnetic materials such as iron or silicon steel, which allow individual pole pieces to be sintered into the desired shape and concentrate the rotor's permanent magnet flux. However, soft magnetic composites typically achieve lower saturation levels of magnetic flux. [Means for solving the problem]

[0009] Certain embodiments of the invention disclosed herein provide pole pieces having conductive ribbons that, in certain embodiments, overcome the shortcomings of the prior art approaches discussed above and enable alternative, lower cost manufacturing processes while significantly reducing losses in the electric machine.

[0010] In certain embodiments of the present invention, an axial flux electric machine is provided. The axial flux electric machine includes a stator having a plurality of pole pieces, a rotor spaced from the stator in an axial direction of the axial flux electric machine, and coiled ribbons of conductive material forming at least a portion of the pole pieces in the plurality of pole pieces. The axial direction of the coiled ribbons of conductive material is substantially parallel to the axial direction of the axial flux electric machine. In some embodiments, the axial flux electric machine further includes coiled ribbons of soft magnetic material forming at least a portion of the pole pieces. In these embodiments, the coiled ribbons of soft magnetic material and the coiled ribbons of conductive material can generally be coiled in interleaved composite material coils. In some embodiments, the axial flux electric machine further includes coiled ribbons of insulating material forming at least a portion of the pole pieces, and the coiled ribbons of soft magnetic material, the coiled ribbons of conductive material, and the coiled ribbons of insulating material are generally coiled in interleaved composite material coils. In some embodiments, the conductive material is at least partially coated in an insulating material such that the ribbon of conductive material comprises a conductive core that is insulated from the ohmic contacts when the conductive material is coiled either on itself or in an interleaved composite coil. The coating can extend the entire circumference of the ribbon segment, or it can be partial, covering only the top or bottom of the ribbon segment.

[0011] In a particular embodiment of the present invention, an axial flux electric machine is provided, the axial flux electric machine comprising a stator having a plurality of pole pieces, a rotor spaced from the stator in an axial direction of the axial flux electric machine, and a coil of conductive material forming at least a portion of a pole piece in the plurality of pole pieces, the coil of conductive material forming the pole piece as a free-standing structure.

[0012] In a particular embodiment of the present invention, an axial flux electric machine is provided. The axial flux electric machine includes a stator having a plurality of pole pieces, a rotor spaced from the stator in an axial direction of the axial flux electric machine, and a coiled ribbon of conductive material forming at least a portion of a pole piece in the plurality of pole pieces. The radial surface area of ​​the coiled ribbon forms at least half of the radial surface area of ​​the pole pieces. As used herein, the term "radial surface area" refers to a surface area measured perpendicular to the axial direction of the axial flux electric machine.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate various embodiments of the systems, methods, and various other aspects of the present disclosure. Those skilled in the art will understand that element boundaries (e.g., boxes, groups of boxes, or other shapes) depicted in the figures represent example boundaries. Perhaps, in some examples, one element may be designed as multiple elements, or multiple elements may be designed as one element. In some examples, an element shown as an internal component of one element may be implemented as an external component of another element, and vice versa. Furthermore, elements may not be drawn to scale. A non-limiting and non-exhaustive description is provided with reference to the following drawings. The components in the figures are not necessarily to scale, emphasis instead being placed on illustrating principles. [Brief explanation of the drawings]

[0014] [Figure 1] 1 shows an axial flux electric machine according to the prior art; [Figure 2] 1 is an exploded view of an example axial flux electric machine in accordance with certain embodiments of the present invention; [Figure 3] FIG. 2 illustrates an example rotor, in accordance with certain embodiments of the present invention. [Figure 4] FIG. 2 illustrates an example of a stator, in accordance with certain embodiments of the present invention. [Figure 5] FIG. 1 illustrates an example of interleaved composite coils, in accordance with certain embodiments of the present invention. [Figure 6] FIG. 2 illustrates an example of a piece of composite ribbon, in accordance with certain embodiments of the present invention. [Figure 7] FIG. 10 is a close-up view of an example of a turn corner of an interleaved composite coil, in accordance with certain embodiments of the present invention. [Figure 8] FIG. 1 illustrates a composite coil, in accordance with certain embodiments of the present invention. [Figure 9] FIG. 2 illustrates an example of an assembled pole piece having a first interleaved composite material coil and a second interleaved composite material coil, according to certain embodiments of the present invention. [Figure 10] FIG. 10 is an exploded view of the assembled pole piece of FIG. [Figure 11] 10A-10C illustrate a process for forming folds in an interleaved composite coil, according to certain embodiments of the present invention. [Figure 12] 10A-10C illustrate pole pieces having folds as internal electrical connections in accordance with certain embodiments of the present invention. [Figure 13] 10A-10C illustrate folds for a composite coil, in accordance with certain embodiments of the present invention. [Figure 14] FIG. 1 illustrates a set of coil pairs with additional magnetic flux and external electrical connections in accordance with certain embodiments of the present invention. [Figure 15] FIG. 2 illustrates an example of a stator housing, in accordance with certain embodiments of the present invention. [Figure 16] FIG. 10 illustrates another example of a stator housing, in accordance with certain embodiments of the present invention. [Figure 17] 1 is a cross-sectional view of an example of an assembled axial flux electric machine in accordance with certain embodiments of the present invention; [Figure 18] 1 is a cross-sectional view of an example of an assembled axial flux electric machine having a mechanical differential assembly in accordance with certain embodiments of the present invention. [Figure 19] FIG. 2 illustrates an example of gears of a mechanical differential assembly, in accordance with certain embodiments of the present invention. [Figure 20]FIG. 1 illustrates an example of a mechanical differential assembly, in accordance with certain embodiments of the present invention. [Figure 21] FIG. 1 illustrates an example of an axially stacked axial flux electric machine in accordance with certain embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Detailed Description Reference will now be made in detail to implementations and embodiments of the various aspects and variations of the systems and methods described herein. While several exemplary variations of the systems and methods are described herein, other variations of the systems and methods may involve aspects of the systems and methods described herein combined in any suitable manner having all or some combination of the described aspects.

[0016] Methods and systems related to electric machines according to the above summary are disclosed in detail herein. The methods and systems disclosed in this section are non-limiting embodiments of the present invention, are provided for illustrative purposes only, and should not be used to limit the overall scope of the present invention. It should be understood that the disclosed embodiments may or may not overlap with each other. Thus, portions of one embodiment or a specific embodiment thereof may or may not fall within the scope of another embodiment or a specific embodiment thereof, and vice versa. Different embodiments from different aspects may be combined or practiced separately. Although it may be apparent to those skilled in the art, many different combinations and subcombinations of the exemplary embodiments shown within the broad framework of the present invention that are not explicitly shown or described should not be construed as being excluded.

[0017] FIG. 2 illustrates an exploded view of an axial flux electric machine 200 (hereinafter, an axial flux electric machine is often referred to as a machine or an electric machine) according to certain embodiments of the present invention. The machine has one stator 201 and two rotors 202, 203, with one rotor on one side of the stator and the other rotor on the other side of the stator. The stator and rotors are axially arranged along the rotor's axis of rotation. The rotors are adjacent to the stator, but a gap exists between them. When assembled, the rotors are spaced from the stator in the axial direction of the axial flux electric machine to form this gap. For example, the space between the stator and rotors can be on the order of 0.1 millimeters to 3 millimeters. The machine includes an external support structure in the form of an external housing comprising external housing components 204, 205, a rotor shaft 208, and rotor support bearings 206, 207. When assembled, the rotor shaft is fixedly connected to each of the two rotors 202, 203. The bearings 206, 207 are in turn supported by the stator housing. The bearings 206, 207 allow the rotor shaft to rotate relative to the fixed stator as described above. The stator includes stator electrical contact terminals 211, 212, 213 for supplying current to the stator from an external power source. Each rotor 202, 203 includes a permanent magnetic disk 209, 210 on the side of the rotor facing the stator 201.

[0018] In certain embodiments of the present invention, the axial flux electric machine may include only one rotor and one stator. In other embodiments of the present invention, the axial flux electric machine may include only one rotor and two stators, such that one stator is on one side of the rotor and the other stator is on the other side of the rotor. In alternative embodiments, the axial flux electric machine may include more rotors and stators that transmit torque to a shared rotor shaft. In certain embodiments of the present invention, two rotors driven by a single stator can distribute torque to two separate rotor shafts. In certain embodiments, two rotors driven by a single stator can be connected to a mechanical differential assembly so that they transmit torque to a shared rotor shaft having two portions that can rotate independently of each other. In some embodiments, the rotor shaft is hollow.

[0019] FIG. 3 illustrates a rotor 300 according to one embodiment of the present invention. Permanent magnetic disks 301 are attached to a rotor support structure 302, which mechanically supports the disks. The permanent magnetic disks 301 are magnetized to generate a substantially axial magnetic field with alternating north and south magnetic poles, as shown in FIG. 3. In another embodiment, the permanent magnetic disks 301 are realized by joining multiple permanent magnets together or by joining multiple permanent magnets to the rotor support structure 302. In either embodiment, it is not necessary for the permanent magnets to fill the entire volume of the permanent magnetic disks 301, as depicted in FIG. 3. The rotor support structure of each rotor is then attached to the rotor shaft 208 (FIG. 2) so that all portions of the rotor spin at the same rotational speed about the axis defined by the support bearings 206, 207 (FIG. 2), allowing for torque transfer without relative movement at the interface between the rotor shaft and the rotor support structure.

[0020] FIG. 4 illustrates a stator 400 according to a specific embodiment of the present invention. Stator 400 includes a plurality of stator electrical contact terminals 402, 403, 404. The stator further includes a plurality of pole pieces, such as pole piece 401. In this example, each pole piece includes two interleaved composite coils (only one interleaved composite coil is shown in FIG. 4). For each pole piece, the second interleaved composite coil is axially adjacent to the illustrated interleaved composite coil and is therefore hidden from view in FIG. 4.

[0021] In certain embodiments, each pole piece may include only one interleaved composite coil or multiple interleaved composite coils. As described below, in some embodiments, each pole piece may include multiple interleaved composite coils, including adjacent coils coiled in the same direction, with adjacent coils coiled in the same direction from the outside of the coil to the inside of the coil and adjacent coils coiled in the same direction from the inside of the coil to the outside of the coil. As used herein, the term "direction" when used with respect to winding direction may be either counterclockwise or clockwise from a fixed reference plane. As used herein, the term "inward" may refer to a coil that winds from the outside of the coil to the inside, and "outward" may refer to a coil that winds from the inside of the coil to the outside of the coil. Thus, the conductive ribbons and coiled interleaved composite coils disclosed herein each lie in the axial direction of the axial flux electric machine and generate additive magnetic flux with other coils coiled in the same direction. In particular, inwardly and counterclockwise coiled ribbons generate the same magnetic flux as outwardly and counterclockwise coiled ribbons. Thus, the interleaved composite coil shown as part of pole piece 401 in FIG. 4 and the second interleaved composite coil forming part of pole piece 401 are both wound in the same direction, thereby generating additional magnetic flux axially relative to stator 400.

[0022] FIG. 5 illustrates an interleaved composite coil 500 according to a specific embodiment of the present invention. The interleaved composite coil 500 is formed by coiling a composite ribbon 501 inward and counterclockwise (i.e., counterclockwise from the outside of the coil to the inside of the coil). When installed, the axial direction of the interleaved composite coil is substantially parallel to the axial direction of the axial-flux electric machine. FIG. 6 illustrates a piece of composite ribbon 600 according to an embodiment of the present invention. The composite ribbon 600 is then formed by alternating, from right to left in FIG. 6, a ribbon of soft magnetic material 601, a ribbon of insulating material 602, a ribbon of conductive material 603, and a ribbon of second insulating material 604, with one ribbon of insulating material on each side of the ribbon of conductive material. The material for the ribbon of soft magnetic material can be one of iron, silicon steel, magnetic cobalt alloy, amorphous steel, and any other suitable material. The material for the ribbon of conductive material can be one of copper, aluminum, and any other suitable material. Instead of separate ribbons of material, the insulating material can be part of the ribbon of conductive material, part of the ribbon of soft magnetic material, or both. The insulating material can be part of the ribbon in that it covers at least a portion of the conductive material or the soft magnetic material. The covering material can be partial because its ends need to have ohmic connections to the bias voltage source. However, within the coil, all sides of the ribbon can be covered with insulating material. A cross section can look similar to Figure 6, with an optional additional layer of insulating material along the illustrated exposed surface of the ribbon of soft magnetic material 601.

[0023] As shown in FIG. 6 , each ribbon of a particular material has two cross-sectional linear dimensions: W, the ribbon width measured in the axial direction of the interleaved composite coil 500, and T, the ribbon thickness measured in the radial direction of the interleaved composite coil 500. A composite ribbon can include multiple ribbons of the same material. For example, two ribbons of conductive material can be pressed together within the composite ribbon. This has the beneficial effect of doubling the thickness of the conductive material, thereby reducing the ohmic resistance of the conductive material by half (assuming all other factors are constant). This is particularly beneficial because, when an interleaved composite coil is energized during operation, the poles of its magnetic flux alternate; the lower the resistance through the conductive material, the faster the pole change. In this way, the thickness of the coiled ribbon of conductive material, and therefore the performance of the axial flux electric machine, can be easily tuned; a thicker ribbon results in lower resistance and faster pole switching speeds, and conversely, a thinner ribbon results in higher resistance and slower pole switching speeds. However, increasing the thickness of the coiled ribbon of conductive material in this manner increases the weight of the machine and increases manufacturing costs. These principles also apply to the width of the ribbon W. The appropriate design thickness of the ribbon can be determined as a trade-off between weight, manufacturing cost, and performance.

[0024] 7 is a close-up view of a turn corner of an interleaved composite coil according to certain embodiments of the present invention. The interleaved composite coil is formed by coiling a composite ribbon, such that the interleaved composite coil generally comprises a coiled ribbon 701 of soft magnetic material, a coiled ribbon 702 of insulating material, a coiled ribbon 703 of conductive material, and a coiled ribbon 704 of a second insulating material, each of which is generally coiled within the interleaved composite coil. Adjacent turns of the interleaved composite coil are separated by an air gap 705. The ribbons coiled in this manner may form part of the pole piece 401 of FIG. 4.

[0025] In certain embodiments, the interleaved composite coil 500 may not include any coiled ribbons of insulating material. For example, the ribbons of conductive material, and thus the coiled ribbons of conductive material, may be coated with an electrically insulating film or otherwise covered with insulating material. Alternatively, the various ribbons in the interleaved composite coil 500 may each be separated by an air gap instead of insulating material. In some embodiments, the composite ribbon 600 may not include any ribbons of soft magnetic material, and as a result, the interleaved composite coil may not include any coiled ribbons of soft magnetic material. In certain embodiments, the coiled ribbons of conductive material and at least one other coiled ribbon of conductive material are pressed together and generally wound within a composite conductive coil; in such embodiments, the interleaved composite coil comprises a composite conductive coil.

[0026] In certain embodiments, the axial direction of the interleaved composite material coils is substantially parallel to the axial direction of the axial flux electric machine, such that each of the constituent coiled ribbons of the interleaved composite material coils has an axial direction substantially parallel to the axial direction of the axial flux electric machine. Thus, for example, in the embodiment of FIG. 7 , the axial direction of coiled ribbon 703 of conductive material is substantially parallel to the axial direction of the axial flux electric machine. The coiled ribbons of conductive material form winding sets, with air gaps 705 separating adjacent windings within the winding set. In this manner, the coiled ribbons of conductive material form at least two complete concentric turns.

[0027] In certain embodiments of the present invention, the coiled ribbon of conductive material entirely forms the pole piece 401 of FIG. 4 . This contrasts with the prior art axial flux electric machines described above in that the conductive material is not wound around a central structure, such as the trapezoidal pole piece 106 shown in FIG. 1 . In this manner, the present invention avoids the complex manufacturing processes associated with constructing such a central structure. Furthermore, the ribbon of conductive material can be wound into a coil of any geometric shape, including, for example, rectangular, circular, triangular, pie, pentagonal, etc. This provides a particular benefit in that the pole piece can be shaped to conform to different geometries, as necessitated by alternative design constraints for the axial flux electric machine. In certain embodiments, the contour of the coiled ribbon of conductive material forms a polygon, as seen in FIG. 5 . Furthermore, using these approaches, the soft magnetic material, if present, can be distributed across the entire surface area of ​​the pole piece, as opposed to being present only in the center of the pole piece, leaving room for outer windings, as in the pole piece 106 of FIG. 1 . In certain embodiments, the annulus defined by the innermost turn of the coiled ribbon of conductive material and the outermost turn of the coiled ribbon of conductive material forms at least half of the radially measured surface area of ​​the pole piece of the axial-flux electric machine. Therefore, the coiled ribbon of conductive material and any soft magnetic material within the same interleaved composite coil can be distributed across the entire surface area of ​​the pole piece. The fact that the soft magnetic material is distributed across a larger portion of the pole piece leads to improved motor efficiency. In certain embodiments, the coiled ribbon of conductive material has a diameter that is at least half of the radially measured surface area of ​​the coiled ribbon of conductive material. In certain embodiments, the radial surface area of ​​the coiled ribbon of conductive material forms at least half of the radial surface area of ​​the pole piece. Figure 5 illustrates an interleaved composite coil having a radial surface area that is the entire radial surface area of ​​the pole piece, since the entire pole piece is defined by the interleaved composite coil.

[0028] In certain embodiments of the present invention, coils of conductive material form pole pieces as freestanding structures. In certain embodiments of the present invention, interleaved composite material coils form pole pieces as freestanding structures. Thus, the pole pieces do not require a substrate in addition to the ribbon of material from which they are formed. For example, interleaved composite material coil 500 can function as a freestanding structure in that the coiled ribbons are themselves pole pieces and do not require a substrate for support. As a result, pole pieces formed in accordance with certain embodiments of the present invention disclosed herein are not limited by compatibility with any substrate with respect to the type of material that can be used to form the pole pieces. Furthermore, the thickness and width of the ribbons are not constrained by compatibility with what a given substrate supports. This added degree of flexibility is a significant improvement over prior art approaches.

[0029] 5, an interleaved composite coil 500, according to certain embodiments, has two ends: an outer coil end at the outer periphery of the coil for the outermost turn of the coil, and an inner coil end at the center of the coil for the innermost turn of the coil. A coiled ribbon of conductive material within the interleaved composite coil presents an external electrical contact terminal 503 at the outer coil end and an internal electrical contact terminal 502 at the second end. The direction of the bend toward the external electrical contact is counterclockwise and opposite the direction of the coil wound outward from the center of the coil.

[0030] In certain embodiments, the coiled ribbon of conductive material includes at least two straight sides. For example, the interleaved composite coil 500 of Figure 5 includes a coiled ribbon of conductive material formed with two straight sides, the straight sides intended to engage radial segments of the stator housing.

[0031] In certain embodiments, the ribbons disclosed herein can have a variety of dimensions. For example, a coiled ribbon of conductive material has a thickness of less than 1 millimeter measured in a radial direction of the coiled ribbon of conductive material. In some embodiments, a coiled ribbon of conductive material has a width of at least 1 millimeter measured in an axial direction of the coiled ribbon. In certain embodiments, the dimensions of any coiled ribbon of soft magnetic material wrapped with a coiled ribbon of conductive material can have comparable measurements. In some embodiments, the thickness of the coiled ribbon of soft magnetic material measured in a radial direction of the coiled ribbon of soft magnetic material and the thickness of the coiled ribbon of conductive material measured in a radial direction of the coiled ribbon of conductive material are significantly different. As previously discussed, ribbon dimensions can be increased to reduce the resistance of the ribbon or decreased to reduce the weight of the axial flux electric machine. Additionally, the width of the conductive ribbon can be kept small to reduce the effects of eddy currents.

[0032] FIG. 8 illustrates a composite interleaved composite material coil 800 comprised of an interleaved composite material coil 801 and a second interleaved composite material coil 802, which can be used to illustrate certain embodiments of the present invention. The two illustrated interleaved composite material coils in FIG. 8 can have properties similar to those of interleaved composite material coil 500. For example, interleaved composite material coil 801 can include a coiled ribbon of conductive material, and second interleaved composite material coil 803 can include a second coiled ribbon of conductive material. As illustrated, the coiled ribbon of conductive material that is part of interleaved composite material coil 801 is coiled in a first direction (i.e., counterclockwise), and the second coiled ribbon of conductive material that is part of second interleaved composite material coil 803 is also coiled in the first direction (i.e., counterclockwise). Furthermore, the second coiled ribbon of conductive material and the coiled ribbon of conductive material are adjacent in the axial direction of the axial flux electric machine. Due to this configuration, the axial magnetic flux of each coiled ribbon of conductive material is additive. Furthermore, the illustrated approach provides the significant benefit that the combined conductivity of the two coils is equivalent, resulting in higher switching speeds, while the width of each individual ribbon is cut in half compared to a single coil with the same conductivity. This is important because wider ribbons have been shown to generate eddy currents, which tend to reduce the switching speed and efficiency of the pole pieces. The number of separate coiled ribbons in a composite interleaved composite material coil, such as that shown in Figure 8, can be increased substantially beyond two to further benefit from this effect. At the same time, ribbons can be bonded to adjacent ribbons using an insulating adhesive to still maintain a cumulative structural width sufficient for the composite coil to function as a freestanding structure. In the illustrated case, the second coiled ribbon of conductive material and the coiled ribbon of conductive material each have a width of less than 5 centimeters measured in the axial direction of the axial-flux electric machine. In certain embodiments of the present invention, the number of coiled ribbons of conductive material can be increased to the point where the coiled ribbons of conductive material are instead individual strands of conductive material within a Litz wire.

[0033] FIG. 9 illustrates an example of an assembled pole piece 900 having a first interleaved composite material coil 901 and a second interleaved composite material coil 902, in accordance with certain embodiments of the present invention. The interleaved composite material coils may include coiled ribbons of conductive material. In certain embodiments, each interleaved composite material coil has an external electrical contact terminal and an internal electrical contact terminal. The external electrical contact terminal may be a positive contact terminal or a negative contact terminal, depending on the configuration of the axial electric machine. Furthermore, the internal electrical contact terminals of different interleaved composite material coils may be coupled to one another. In the particular configuration illustrated in FIG. 9, the internal electrical contacts of the two coils may be coupled to one another, and one of the external electrical contact terminals may be a positive contact terminal, while the other external electrical contact terminal may be a negative contact terminal. As illustrated, the first interleaved composite material coil 901 is wound inward in a clockwise direction, and the second interleaved composite material coil 902 is wound outward in a clockwise direction. Thus, two adjacent coils can generate additional magnetic flux and form a continuous electrical circuit from the positive contact terminal to the negative contact terminal, both terminals located outside the stator to which the assembled pole piece 900 is mounted.

[0034] FIG. 10 shows an exploded view 1000 of the assembled pole piece 900. The exploded view shows two interleaved composite coils, each divided into two main coils of material that make up the composite coil for a total of four coils. The first interleaved composite coil 1001 has an external electrical contact terminal 1003 and an internal electrical contact terminal 1004 on a coiled ribbon of conductive material that is part of the composite coil. The second interleaved composite coil 1002 has an external electrical contact terminal 1005 and an internal electrical contact terminal 1006 on a coiled ribbon of conductive material that is part of the composite coil. The internal electrical contact terminals 1004 and 1006 are each electrically connected to a conductive pin 1007. The conductive pin 1007 contacts the innermost turn of the coiled ribbon and the innermost turn of the second coiled ribbon, forming part of the conductive path between the two external contact terminals. In this way, the external electrical contact terminal 1003 of the first interleaved composite material coil 1001 is ohmically connected to the external electrical contact terminal 1005 of the second interleaved composite material coil 1002, and a conductive path is formed between the two external electrical contact terminals.

[0035] Connections between separate axially spaced coils of conductive material within an axial electric machine can be provided in a variety of ways. In the examples of FIGS. 9 and 10, the connections are provided by conductive pins. In other embodiments, the conductive path between the two external electrical contact terminals is formed differently. For example, in an alternative embodiment, a single ribbon of conductive material can be formed integrally with both coils. Thus, an interleaved composite material coil having such a single ribbon of conductive material can coil inwardly in a first plane from the first external electrical contact terminal toward the center of the pole piece, bend from the first plane in which the first coil is located into a second plane in which the second coil is located, and then coil outwardly in the second plane from the center of the pole piece to the second external electrical contact terminal. In other words, the coiled ribbon of conductive material within the first interleaved composite material coil (e.g., 1008) and the second coiled ribbon of conductive material within the second interleaved composite coil (e.g., 1009) can be part of a single continuous strip of conductive material. A single continuous strip of conductive material may be folded according to the process described below with reference to Figure 11. Thus, in certain embodiments, the conductive pathway between axially spaced coils may include a fold within such single continuous strip of conductive material connecting a coiled ribbon of conductive material with a second coiled ribbon of conductive material.

[0036] FIG. 11 illustrates a process for forming interconnections in the form of folds within a single continuous strip of conductive material. In step 1100, a single continuous strip of conductive material can be provided. As shown, the strip of material can be folded in step 1101 such that the folded portion forms the outline of a right triangle with the top surface of the original, unfolded strip of material. Next, in step 1102, the folded portion can be refolded so that the strip of material is oriented in the same direction on both sides of the fold. The location of the fold in step 1102 can be selected so that there is a sufficient offset between the plane occupied by the original, unbent side of the strip of material and the bent side of the strip of material, such that the two planes occupied thereby are spaced far enough apart to form the coils of a magnetic pole piece. Because the strip of material is oriented in the same direction on both sides of the fold, the coils formed on both sides of the fold wind in the same direction, and their magnetic flux is additive.

[0037] Figure 12 shows a pole piece 1201 formed using this approach shown in Figure 11, where two interleaved composite coils are formed from a single continuous strip of conductive material and a single continuous strip of soft magnetic material, with both strips of material folded according to the process of Figure 11. As shown, the pole piece includes two external electrical contacts, and the two coils are oriented so that their magnetic flux is additive (i.e., both coils are wound counterclockwise, with coil 1202 wound inward and coil 1203 wound outward).

[0038] FIG. 13 illustrates a folding pattern that allows a set of composite coils to utilize internal electrical connections in the folding configuration described with reference to FIGS. 11 and 12. The composite coil can be the composite coil described with reference to FIG. 8, which can include an internal connection so that two composite coils are connected to another composite coil oriented as with reference to FIGS. 9 and 10. FIG. 1300 illustrates a top-down view of the folding, and FIG. 1310 illustrates a bottom-up view of the folding. As illustrated, two single ribbons of conductive material and two single ribbons of soft magnetic material are folded so that they form a composite coil, transfer to a different plane, and then form a second composite coil. Because the strips of material are oriented in the same direction on both sides of the folding, both composite coils can wind in the same direction and have additional magnetic flux. At the same time, one composite coil can wind inward and the other composite coil can wind outward so that the pole piece formed by the two composite coils can have two external electrical connections.

[0039] FIG. 14 illustrates a set of coil pairs arranged such that the coils all have additive magnetic flux, with each pair of coils forming a single conductive path that enters the center of the coil and returns to the exterior of the coil, thereby presenting both a positive contact terminal and a negative contact terminal at the exterior of the coil. A set of coil pairs can form a pole piece for an axial-flux electric machine according to the present disclosure. While FIG. 14 includes two pairs of coils, indicated by pair 1400 and pair 1410, a set of coil pairs according to the present disclosure can include any number of coil pairs within the set, so long as the illustrated pattern persists. For example, a set of pairs forming a pole piece can include two, three, or four pairs of coils. Individual coils within a pair can also be composite coils, as described with reference to FIG. 8.

[0040] 14 includes a coiled ribbon of conductive material wound inwardly in a first direction and at least one additional coiled ribbon of conductive material wound in the first direction (e.g., the outer coil of pair 1400 and the outer coil of pair 1410), and a second coiled ribbon of conductive material wound in a second direction and at least one additional coiled ribbon of conductive material wound in the second direction (e.g., the inner coil of pair 1400 and the inner coil of pair 1410), where the at least one additional coiled ribbon of conductive material wound in the first direction and the at least one additional coiled ribbon of conductive material wound in the second direction are positioned adjacent to each other in the axial direction of the axial flux electric machine, such that the magnetic flux of the coiled ribbon of conductive material, the second coiled ribbon of conductive material, the at least one additional coiled ribbon of conductive material wound in the first direction, and the at least one additional coiled ribbon of conductive material wound in the second direction are additive. Patterns according to the present disclosure can also be described with reference to the inward or outward winding of the coils and the direction of the coils. In that pattern, each coil winds in the same direction, with the A coil winding inward and the B coil winding outward, or vice versa. Thus the pattern is AB-BA-AB-BA, and the pattern continues as many times as necessary to form a pole piece with the overall axial machine constraints in place, such as minimizing the weight and other constraints of the axial flux electric machine.

[0041] In certain embodiments of the invention, an axial flux electric machine comprises a first pair of coiled ribbons of conductive material. For example, the coiled ribbon of conductive material described with reference to FIG. 9 and a second coiled ribbon of conductive material can form the first pair of coiled ribbons of conductive material. The first pair of coiled ribbons of conductive material can be those of pair 1400. The axial flux electric machine can comprise at least one additional pair of coiled ribbons of conductive material, such as pair 1410, where the at least one additional pair of coiled ribbons of conductive material and the first pair of coiled ribbons of conductive material form a set of pairs of coiled ribbons of conductive material. As shown, all of the coiled ribbons of conductive material in a set of pairs of coiled ribbons of conductive material are coiled in a first direction, each pair of coiled ribbons of conductive material in the set of pairs of coiled ribbons of conductive material has an inwardly wound coil and an outwardly wound coil, and the sets of pairs of coiled ribbons of conductive material are arranged adjacent to each other in the axial direction of the axial-flux electric machine such that the inwardly wound coil of one pair is never adjacent to the outwardly wound coil of another pair. Using this approach, all of the coils are additive in terms of their magnetic flux, and each pair of coils provides two external electrical contacts. The pairs of coils may share a common conductive connection at their internal contact, such as a common conductive pin.

[0042] FIG. 15 illustrates an example of a stator housing 1500 for assembling and housing pole pieces within a stator, according to certain embodiments of the present invention. The stator housing includes a set of pole piece sections 1501. The shape of the pole piece sections in FIG. 15 is not a limitation of the embodiments of the present invention disclosed herein. Indeed, a benefit of using certain embodiments of the present invention disclosed herein is the ability to shape the ribbon to form pole pieces of widely different sizes, allowing the ribbon to accommodate a diverse array of pole piece section designs. In other embodiments, the stator housing can be formed by joining together a first stator housing 1601 and a second stator housing 1602, as shown in FIG. 16. The stator housing may be primarily fabricated using metal, polymer, or composite materials with separate components mechanically joined together using one of several known joining methods, such as adhesives, fasteners, rivets, etc. The pole pieces are attached to the stator housing and fitted into the pole piece sections, i.e., one pole piece within one pole piece section. Figure 4 shows a view of one side of the stator with the pole pieces assembled in this manner. In certain embodiments, the stator housing is overmolded onto the pole pieces.

[0043] As described in connection with FIG. 9 , each assembled pole piece 900 includes two interleaved composite coils 901, 902. In certain embodiments, each pole piece is electrically connected to a conductive bus bar, not depicted in this figure, via the pole piece's two external electrical contact terminals 1003, 1005. In this manner, all pole pieces for that stator are connected via the bus bar. The bus bar is then electrically connected to the stator's electrical contact terminals 402, 403, 404. In some embodiments, some or all of the pole piece's external electrical contact terminals or the stator's electrical contact terminals are positioned along the outer diameter of the stator. For example, in FIG. 4 , the stator's electrical contact terminals are positioned along the outer diameter of the stator. In some embodiments, some or all of the pole piece's external electrical contact terminals or the stator's electrical contact terminals are positioned along the inner diameter of the stator.

[0044] In a pole piece assembled in a stator as described above, the first interleaved composite coil 901 and the second interleaved composite coil 902 of the pole piece are separated by a small gap that ensures the conductive coils maintain a minimum distance to avoid any electrical breakdown of the air due to electrical potentials generated during operation. Alternatively, the gap is filled with insulating oil, which increases the gap's dielectric strength and allows for a narrower gap. Alternatively, insulating oil flows through the gap, enabling heat transfer from the coils to an external heat sink. This is achieved by connecting an oil passage to a pump that maintains a flow of insulating oil in the gap between the first interleaved composite coil 901 and the second interleaved composite coil 902.

[0045] Figure 17 shows a cross-section of the axial-flux electric machine of Figure 2 assembled with the various components of the machine described above. Figure 17 shows rotor support structure 1701 and permanent magnet disks 1702 for a first portion of the rotor on one side of the stator, rotor support structure 1703 and permanent magnet disks 1704 for a second portion of the rotor on the other side of the stator opposite the first portion of the rotor, pole pieces 1705, rotor shaft 1706, rotor support bearings 1707, 1708, and an outer housing with outer housing parts 1709, 1710. The stator is secured to the housing via stator support structure 1711. Portions of the axial-flux electric machine above rotor shaft 1706 with similar shading are alternative parts of the same circular component.

[0046] FIG. 18 shows a cross-sectional view of a particular embodiment of an axial-flux electric machine including a first rotor shaft 1801, a second rotor shaft 1802, and a mechanical differential assembly 1803. The mechanical differential assembly transfers torque from the rotor to the rotor shafts and allows differential rotation between the two rotor shafts using gears, pinion gears, and other components. Allowing differential rotation allows relative rotational motion of the two rotor shafts. FIG. 19 shows an example of gearing for a mechanical differential assembly with two shafts 1901, 1902 and associated gears. In FIG. 18, the mechanical differential assembly is located inside the axial-flux electric machine. In an alternative embodiment, the differential mechanical assembly can be located outside the machine. In such an embodiment, as shown in FIG. 20, the rotor is coupled to a hollow main rotor shaft 2001, a differential assembly 2002 is located just outside the axial-flux electric machine, and one of the rotor shafts passes through the hollow main shaft from one side of the machine to the differential assembly located on the other side of the machine. A differential assembly 1502 transfers torque from the main rotor shaft to a first rotor shaft 1503 and a second rotor shaft 1504 that pass through the hollow main shaft, but using gears and pinion gears and other components, creates a rotational difference between the two rotor shafts.

[0047] In certain embodiments of the invention, two or more axial-flux electric machines as described above can be axially stacked to form a single motor assembly. The two motors can be connected to a common rotor shaft or to separate rotor shafts. FIG. 21 shows an axial-flux electric machine with two axial-flux electric machines 2100, 2110 forming a single motor assembly. The motor assembly includes two stators, each including a plurality of composite coils 2101, with a rotor having permanent magnets 2102. The two rotors are connected to a rotor shaft 2103 via a rotor support 2104. In alternative embodiments, the two rotors can be connected to different rotor shafts. In the illustrated embodiment, the two stators may be electrically connected, or they may be powered by completely separate circuits.

[0048] While the specification has been described in detail with reference to particular embodiments of the invention, it will be understood that alterations, variations, and equivalents to these embodiments may readily occur to those skilled in the art upon achieving the above understanding. These and other modifications and variations to the invention may be practiced by those skilled in the art without departing from the scope of the invention, which is more particularly set forth in the appended claims.

[0049] While this specification has been described in detail with reference to specific embodiments of the present invention, it will be understood that modifications, variations, and equivalents to these embodiments may readily occur to those skilled in the art upon achieving the above understanding. While the examples of this disclosure have generally been directed to axial flux electric machines in the form of axial flux motors, the embodiments disclosed herein are equally applicable to axial flux generators. As another example, the composite coils disclosed herein can be used in place of any of the individual coils described herein. Furthermore, at any point where interleaved composite coils are referenced, independent coated ribbons of conductive material can be used instead. These and other modifications and variations to the present invention may be practiced by those skilled in the art without departing from the scope of the invention, which is more particularly set forth in the appended claims.

Claims

[Claim 1] An axial magnetic flux electromachine, A stator (101; 400) having multiple magnetic pole pieces, A rotor (102; 300) spaced apart from the stator (101; 400) in the axial direction of the aforementioned axial magnetic flux electromachine, A coiled ribbon (603; 703) of a conductive material forming at least a portion of the pole pieces (1201; 1705) among the plurality of pole pieces, Equipped with, The axial direction of the coiled ribbon (603; 703) of the conductive material is substantially parallel to the axial direction of the axial flux electromachine. Axial magnetic flux electromechanism.

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