Stator for axial flux machine

Abstract

A stator for an axial flux machine is provided having a plurality of stator bars disposed circumferentially spaced about an axis. Each of the stator bars has a set of windings wound thereon for generating a magnetic field substantially parallel to the axis. A plurality of radially outwardly disposed electrical interconnects for connecting two or more windings together are disposed radially outward of the plurality of stator bars and extend circumferentially along at least a portion of an outer circumference of the stator bars. A plurality of radially inwardly disposed electrical interconnects for connecting two or more windings together are also disposed radially inward of the stator bar and extend circumferentially along at least a portion of an inner circumference of the stator bar. The periphery of the stator is free of interconnects disposed radially outward along one or more portions.

Description

[0001] This application is a divisional application of the invention patent application with application date of May 11, 2020, application number 202080035092.0, and invention name “Stator for axial flux machine”. Technical Field

[0002] The present invention relates to the construction of electric machines, in particular stators for axial flux electric machines used as motors and generators. Background Art

[0003] There is a need to increase the power density of electric machines such as motors and generators. One reason for this is the growing interest in electric vehicles, both land vehicles and aircraft. However, the volume available for power sources, transmissions and auxiliary components is limited, and factors including power storage put further pressure on designers to increase the power density of electric machines in order to gain space and performance.

[0004] Improving the power density of electric machines often targets one or more cooling methods, motor topologies, and materials to typically achieve higher ampere-turns. While significant progress has been made in these approaches, there is still a strong motivation to further increase power density. Particularly for axial flux, segmented armature formats that increase the power rating of the machine raise additional issues because the internals of these machines have been designed for high power operation, often relying on efficient liquid coolant flow. Any redesign must maintain effective cooling while accommodating changes to increase power density.

[0005] One type of axial flux segmented armature machine is the Yokeless Segmented Armature (YASA) machine. Typical YASA machines are difficult to cool because they do not have a stator yoke through which heat can be conducted away from the stator. Prior art machines have immersed the stator coils in a flowing liquid coolant contained within the stator housing, thereby significantly increasing heat dissipation and therefore increasing power delivery. GB2511925 discloses additional improved cooling features for YASA type machines. The liquid coolant circulates around a chamber where it can contact not only the machine's motor stator coils, but also the coil faces and pole shoes, thereby improving heat dissipation of key components and increasing power density.

[0006] Thus, we have recognized a need for an improved electric motor architecture that is capable of achieving greater power density within a machine form factor. Summary of the invention

[0007] Therefore, the present invention provides a stator for an axial flux machine and an axial flux machine. Further optimized embodiments are also provided.

[0008] The present invention provides a stator for an axial flux machine, comprising: a plurality of stator bars, which are arranged circumferentially at intervals around an axis, each stator bar having a group of windings wound thereon for generating a magnetic field substantially parallel to the axis, the plurality of stator bars being arranged to provide a hollow area at the center of the axis, the stator bar having an outer periphery facing away from the axis and an inner periphery facing the axis; and a plurality of radially outwardly arranged electrical interconnects, which are used to connect two or more windings together, the plurality of radially outwardly arranged electrical interconnects being arranged radially outside the plurality of stator bars and extending circumferentially along at least a portion of the outer periphery of the stator bars; a plurality of radially inwardly arranged electrical interconnects, which are used to connect two or more windings together, the plurality of radially inwardly arranged electrical interconnects being arranged radially inside the stator bars and extending circumferentially along at least a portion of the inner periphery of the stator bars, wherein the outer periphery of the stator is free of radially outwardly arranged interconnects along one or more portions.

[0009] This arrangement provides a number of advantages. When the stator is enclosed within a housing, for a given size of housing, the size of the stator coils and the poles on which they are wound may be increased, extending into areas where there are no interconnecting wiring disposed outwardly, thereby increasing the maximum power output of the machine. As a result, a machine using such a stator will have a higher power output than a machine using a conventional stator of the same size.

[0010] Furthermore, instead of maintaining the same shape of housing as described above, a portion of such housing, corresponding to the area with no outwardly disposed interconnections to the stator, may be flattened to reduce the outer dimensions of the housing. This arrangement advantageously provides a stator of smaller diameter than a stator of equivalent size. Thus, a machine using such a stator may be smaller than a machine using a conventional stator because the dimensions of the stator bars and windings are not changed.

[0011] Radially inward portions of the stator corresponding to the one or more portions without radially outwardly disposed interconnects may include radially inwardly disposed electrical interconnects.

[0012] The stator may include one or more electrical transitions between the radially inward electrical interconnect and the radially outward electrical interconnect. Each of the one or more transitions between the radially inward electrical interconnect and the radially outward electrical interconnect may occur via a respective winding.

[0013] Using the windings themselves for the transition between the inner and outer electrical interconnects avoids the need for additional bus bars to achieve the transition. Such bus bars may add additional unnecessary radial dimensions to the stator.

[0014] Each set of windings may include a single winding layer on the stator bar, the winding layer including a strip conductor having a width across a surface of the strip conductor greater than a thickness through the strip conductor; wherein the windings are stacked along the stator bar in a direction substantially perpendicular to the axis such that adjacent strip conductor surfaces of the strip conductor abut each other.

[0015] The windings of the stator bars may be electrically connected in a three phase star arrangement, although other arrangements such as delta or delta star and known in the electric machine art are possible.

[0016] The stator may include a stator housing enclosing the stator bars, the stator housing having an annular sidewall at both ends of the stator bars and inner and outer circumferential sides of the stator bars facing radially inward and radially outward, respectively. One or more portions of the stator housing corresponding to the corresponding one or more portions of the outer circumference of the stator without the radially outwardly disposed interconnecting elements have a dimension between the outer circumferential side and the stator bars that is smaller than the dimension between the outer circumferential side and the stator bars at a region of the stator containing the radially outwardly disposed interconnecting elements.

[0017] This arrangement of the stator housing advantageously provides a stator having reduced radial dimensions compared to conventional stators, thereby enabling smaller machines to be provided without compromising the power output of such machines.

[0018] The stator housing may define a chamber containing a cooling fluid, the stator housing including a port for supplying the cooling fluid and a port for exhausting the cooling fluid. The housing and the stator bars may be arranged to allow cooling fluid to flow back and forth between an inner radius and an outer radius of the stator bars. The stator may include one or more blocks disposed in the stator housing between the stator housing and one or more corresponding stator bars, wherein the cooling fluid is forced to flow through gaps between the stator bars by virtue of the blocks.

[0019] In areas of the stator corresponding to respective one or more portions of the outer periphery of the stator without radially outwardly disposed interconnecting members, the outer peripheral side of the stator housing may abut against one or more stator bars, which abutment blocks the cooling fluid from flowing between the housing and the stator bars and forces the cooling fluid to flow between adjacent stator bars.

[0020] The stator may include two parts without an interconnection member disposed radially outward. The two parts without an interconnection member disposed radially outward may be circumferentially opposite to each other.

[0021] The present invention also provides an axial flux machine, comprising: a stator, comprising a plurality of stator bars arranged circumferentially spaced about an axis, each stator bar having a set of windings wound thereon for generating a magnetic field substantially parallel to the axis, the plurality of stator bars being arranged to provide a hollow region at the center of the axis, the stator bars having an outer periphery facing away from the axis and an inner periphery facing the axis; a rotor, comprising a set of permanent magnets and mounted for rotation about the axis of the machine, the rotor being spaced from the stator along the axis of the machine to define a gap between the stator and the rotor, wherein the stator The invention comprises: a plurality of radially outwardly arranged electrical interconnects for connecting two or more windings together, wherein the plurality of radially outwardly arranged electrical interconnects are arranged radially outside the plurality of stator bars and extend circumferentially along at least a portion of the outer circumference of the stator bars; and a plurality of radially inwardly arranged electrical interconnects for connecting two or more windings together, wherein the plurality of radially inwardly arranged electrical interconnects are arranged radially inside the stator bars and extend circumferentially along at least a portion of the inner circumference of the stator bars, and wherein the stator has no radially outwardly arranged interconnects along one or more portions.

[0022] As discussed above, this arrangement provides a number of advantages. When the stator is enclosed within a housing, for a given size housing, the size of the stator coils and the poles around which they are wound may be increased, extending into areas where there are no interconnecting wiring disposed outwardly, thereby increasing the maximum power output of the machine. As a result, a machine using such a stator will have a higher power output than a machine using a conventional stator of the same size.

[0023] Furthermore, instead of having a housing of the same shape as described above, a portion of such a housing corresponding to the area of ​​the stator without the outwardly disposed interconnects may be flattened to reduce the outer dimensions of the housing. This arrangement advantageously provides a stator of smaller diameter than a stator of equivalent size. Thus, a machine using such a stator may be smaller than a machine using a conventional stator because the dimensions of the stator bars and windings are not changed.

[0024] Radially inward portions of the stator corresponding to the one or more portions without radially outwardly disposed interconnects may include radially inwardly disposed electrical interconnects.

[0025] The stator of the machine may include one or more electrical transitions between radially inward electrical interconnects and radially outward electrical interconnects. Each of the one or more transitions between the radially inward electrical interconnects and the radially outward electrical interconnects may occur via a respective winding.

[0026] Each set of windings may include a single winding layer on the stator bar, the winding layer including a strip conductor having a width across a surface of the strip conductor greater than a thickness through the strip conductor; wherein the windings are stacked along the stator bar in a direction substantially perpendicular to the axis such that adjacent strip conductor surfaces of the strip conductor abut each other.

[0027] The windings of the stator bars may be electrically connected in a three phase star arrangement, although other arrangements such as delta or delta star and known in the electric machine art are possible.

[0028] The machine may include a stator housing enclosing the stator bars, the stator housing having annular sidewalls at both ends of the stator bars and inner and outer peripheral sides of the stator bars radially inward and radially outward, respectively. One or more portions of the stator housing corresponding to the corresponding one or more portions of the outer periphery of the stator without the radially outwardly disposed interconnecting elements have a dimension between the outer peripheral side and the stator bars that is smaller than the dimension between the outer peripheral side and the stator bars at the region of the stator containing the radially outwardly disposed interconnecting elements.

[0029] The housing may define a chamber containing a cooling fluid, the stator housing including a port for supplying the cooling fluid and a port for exhausting the cooling fluid.The housing and stator bars may be arranged to allow cooling fluid to flow back and forth between an inner radius and an outer radius of the stator bars.

[0030] The stator may include one or more blocks disposed in the stator housing between the stator housing and one or more corresponding stator bars, wherein the cooling fluid is forced to flow through the gaps between the stator bars by means of the blocks. In regions of the stator corresponding to corresponding one or more portions of the outer periphery of the stator without radially outwardly disposed interconnects, the outer peripheral side of the housing may abut against one or more stator bars, the abutment blocking the cooling fluid from flowing between the housing and the stator bars and forcing the cooling fluid to flow between adjacent stator bars.

[0031] The machine may include a second rotor including a set of permanent magnets and mounted for rotation about the axis of the machine, the second rotor being spaced apart from the stator along the axis of the machine to define a gap between the stator and the second rotor, and the second rotor being disposed on an opposite side of the stator from the rotor.

[0032] The machine may comprise two parts without a radially outwardly disposed interconnection. The two parts without a radially outwardly disposed interconnection may be circumferentially opposite each other.

[0033] In any of the above, the machine may be a motor or a generator. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0035] Figure 1a 1c show a general configuration of a dual-rotor axial flux machine, an example topology for an axial flux permanent magnet machine, and a schematic side view of a Yokeless Segmented Armature (YASA) machine, respectively;

[0036] FIG2 shows a perspective view of the YASA machine in FIG1c;

[0037] FIG3 shows a perspective exploded view of the stator and stator housing for a YASA machine;

[0038] Figure 4 A stator arrangement according to the invention is shown;

[0039] Figure 5 An example electrical interconnection for a stator coil is shown;

[0040] Figure 6 showing a star arrangement; and

[0041] Figure 7 A stator arrangement having a housing is shown;

[0042] Figure 8 A stator arrangement having a housing with a flattened portion is shown;

[0043] Fig. 9 A perspective view showing a region of the stator without an outwardly disposed interconnection;

[0044] Fig.10 shows an alternative example of electrical interconnection for the stator coils;

[0045] Fig.11 A stator arrangement is shown having a housing with two regions having no outwardly disposed interconnection members; and

[0046] Fig.12 A stator arrangement is shown having a housing with two flat parts. DETAILED DESCRIPTION

[0047] We will first discuss the background of the arrangement of an axial flux machine, which is an example of use of the stator of the present invention. Referring first to Figures 1c, 2 and 3 taken from our PCT application WO2012 / 022974, Figure 1c shows a schematic diagram of a yokeless segmented armature machine 10.

[0048] The yokeless segmented armature machine 10 comprises a stator 12 and two rotors 14a, 14b. The stator 12 is a collection of individual stator bars 16 circumferentially spaced around the axis of rotation 20 of the rotors 14a, 14b. Each stator bar 16 has its own axis (not shown), which is preferably but not necessarily arranged parallel to the axis of rotation 20. Each end of each stator bar is provided with a shoe 18a, 18b for the physical purpose of confining a coil 22, which is preferably an insulated wire of square / rectangular cross-section, thereby enabling a high packing factor. The coils 22 are connected to an electrical circuit (not shown) which, in the case of an electric motor, excites the coils so that the poles of the resultant magnetic field generated by the current flowing in the coils are opposite in adjacent coils 22.

[0049] The two rotors 14a, 14b carry magnets (e.g. permanent magnets) 24a, 24b facing each other, and (when the stator bars are tilted - not shown - the magnets are also the same) the coil 22 is located between the two rotors. Two air gaps 26a, 26b are provided between the respective shoes and the magnets 18a / 24a, 18b / 24b. A number of coils and magnets are provided spaced apart around the axis of rotation 20, and preferably there are different numbers of coils and magnets so that the coils do not all register with the corresponding magnet pairs at the same time and at the same rotational position of the rotor relative to the stator. This serves to reduce the cogging effect.

[0050] In the electric motor, the coils 22 are energized so that their polarity alternates for aligning the coils with different pairs of magnets at different times, thereby applying torque between the rotor and the stator. The rotors 14a, 14b are typically connected together (e.g., by a shaft, not shown) and rotate together about the axis 20 relative to the stator 12. A magnetic circuit 30 is provided by two adjacent stator bars 16 and two magnets 24a, 24b and back irons 32a, 32b, and is used for each rotor to link the magnetic flux between the back faces of each magnet 24a, 24b facing away from the corresponding coil 22. The stator bars 16 are enclosed in a housing extending across the air gaps 26a, 26b, and the housing defines a chamber supplied with a cooling medium.

[0051] Turning to FIG. 3 , a stator 12a is shown in which the stator coils are located between clamshell housings 42a, 42b of plastic material. These clamshell housings have an outer cylindrical wall 44, an inner cylindrical wall 46, and an annular radially arranged wall 48. In the prior art example of FIG. 3 , the radial wall 48 includes an inner recess 50 to receive the boots 18a, 18b of the stator bars 16 and to position the stator coil assembly (i.e., the stator bars 16, the coils 22, and the boots 18a, 18b) when the two clamshell housings 42a, 42b of the stator 12a are assembled together. The clamshell housings 42a, 42b define a space 52 inside the coils 22 and an outer defined space 54 around the outside of the coils 22, and there is a space 56 between the coils. The spaces 52, 54, 56 are interconnected to define a cooling chamber. Although not shown in FIG. 3 , when assembled, the clamshell housings 42a , 42b are provided with ports that allow a cooling medium, such as oil, to be pumped into the spaces 52 , 54 , 56 to circulate around the coils and cool them.

[0052] Turning now to the present invention, the concept relates to the electrical interconnection of the segmented armature in the YASA machine. Although fundamental to the operation, the electrical interconnection has not been considered as a source of significant increase in power density. However, the continued need to increase the power density of the machine has led to the surprising discovery that the interconnection of the armature coils coupled to the dual-purpose stator housing can significantly increase the power density of the YASA machine.

[0053] Briefly, the present invention provides a stator having a plurality of stator bars circumferentially spaced about an axis. Each stator bar has a set of windings wound thereon for generating a magnetic field substantially parallel to the axis. A plurality of radially outwardly disposed electrical interconnects for connecting two or more windings together are disposed radially outside the plurality of stator bars and extend circumferentially along at least a portion of the outer circumference of the stator bars. A plurality of radially inwardly disposed electrical interconnects for connecting two or more windings together are disposed radially inside the stator bars and extend circumferentially along at least a portion of the inner circumference of the stator bars. In the present invention, at least a portion of the outer circumference of the stator is free of radially outwardly disposed interconnects.

[0054] Turning now to the present invention, Figure 4 A simplified diagram of a stator 100 is shown, which includes a plurality of interconnected stator coil sets / windings 130. Each set of windings is wound around a respective stator bar 120, which preferably has stator shoes (not shown) at both ends to hold the windings 130 in place on the stator bars 120. Although the figure shows 18 stator bars 120, a skilled reader will appreciate that the number may be greater or less than 18. When current is passed through the windings 130, a magnetic field is generated.

[0055] The stator bars 120 are arranged circumferentially spaced about an axis 110, which is the axis of the machine using this stator arrangement and about which the rotor will rotate relative to the stator 100. The stator bars 120 have an outer periphery facing away from the axis and an inner periphery facing the axis. The magnetic field generated by the windings 130 is generally parallel to the axis 110. The stator bars 120 are arranged to provide a hollow area 140 in the center of the stator.

[0056] As for the windings 130 themselves, they can be multiple layers of coated wire of circular cross section. However, a preferred arrangement of the windings 130 is to use a single strip winding layer on the stator bar. The winding layer includes a strip conductor whose width across the strip conductor surface is greater than the thickness through the strip conductor. The windings are stacked along the stator bar in a direction generally perpendicular to the axis so that adjacent strip conductor surfaces of the strip conductor abut each other.

[0057] In the arrangement shown, a three-phase power supply (UVW) is input to the stator coil windings 130. Each winding is interconnected to a respective other winding 130 or to a power supply through a plurality of electrical interconnects 150, 160. Some electrical interconnects 150 are disposed radially outward of the stator bars 120 and extend circumferentially along at least a portion of the outer circumference of the stator bars 120. The interconnects may be positioned at different heights of the stator bars 120 and held in place relative to the stator bars 120 by a plurality of clamps (not shown) or spacers.

[0058] A plurality of radially inward electrical interconnects 160 are also provided. These electrical interconnects are provided radially inwardly relative to the stator bars and extend circumferentially along at least a portion of the inner circumference of the stator bars. As with the outward electrical interconnects 150, the inward electrical interconnects 160 may be positioned at different heights of the stator bars 120 and held in place relative to the stator bars 120 by a plurality of clamps (not shown) or spacers.

[0059] The interconnects between the connected windings 130 may transition between the inner and outer peripheries of the stator bars 120. In such a transition 180, this preferably occurs through the windings 130 themselves. That is, the windings 130 are wound around the stator bars 120 such that the connection at one end of the windings 130 terminates at the inner or outer periphery, and the connection at the other end of the windings 130 terminates at the outer or inner periphery, respectively. Using windings 130 to transition between one periphery and another eliminates the need for an additional interconnect between the two peripheries and would result in an increase in the width of the stator (in terms of the height of the stator bars, i.e., between one pole shoe and the other pole shoe).

[0060] Of course, alternatively, the windings 130 on the stator bars 120 may be wound to terminate at the same periphery, that is, the input and output of the windings 130 may both terminate at the inner periphery or both terminate at the outer periphery.

[0061] By carefully considering the connections of the various windings 130, transitions 180, and electrical interconnects 150, 160, the stator may be designed to have one or more portions 170 of the periphery of the stator bars 120 that are free of outwardly disposed electrical interconnects.

[0062] Figure 5 A simplified example connection scheme between all stator bars 120 and the power supply UVW is shown. Figure 4 Again, there are 18 stator bars in the exemplary arrangement. In this example, the windings 130 are connected as a three-phase star arrangement, although other connection schemes are possible. For example, a delta arrangement may be used, or a delta-star arrangement may be used, or other known arrangements may be used. Figure 6 A simplified star configuration used in the present invention is shown.

[0063] and Figure 4 Likewise, the stator 100 comprises an inwardly disposed electrical interconnect 160 and an outwardly disposed electrical interconnect 150. The transition 180 between the inner and outer peripheries of the stator bars 120 may occur through the windings 130 themselves. Furthermore, a portion 170 without an outwardly disposed electrical interconnect 150 is provided.

[0064] refer to Figure 7 , Figure 8 and Fig. 9 , the advantages of this arrangement will become apparent.

[0065] Figure 7 and Figure 8 With Figure 4 The stator 100 and all components are arranged identically, however, Figure 7 and Figure 8 A stator housing 200 encloses the stator 100 . Figure 7 and Figure 8 The difference between Figure 7 The stator housing 200 has a substantially circular shape. Figure 8 The stator housing 200 in FIG. 2 includes a flat portion 240 . Fig. 9 Show Figure 8 Perspective view of the arrangement in .

[0066] The stator housing 200 enclosing the stator bars 120 and the electrical interconnects 150, 160 has an annular sidewall 230 at both ends of the stator bars 120 and an inner peripheral side 210 and an outer peripheral side 220 respectively disposed radially inside and radially outside the stator bars 120. This arrangement of the stator housing 200 maintains the hollow area 140 at the center of the stator 100.

[0067] Figure 7 and Figure 8 Demo Figure 4 The advantages of the stator arrangement in FIG. 1 are related to the portion 170 where there is no outwardly arranged interconnecting member.

[0068] about Figure 7 For a given size of the stator housing 200, the size of the windings 130 and the stator bars 120 wound thereon may be increased, extending into the portion 170 where there are no externally disposed electrical interconnects 150, thereby increasing the maximum power output of the machine. Therefore, a machine using such a stator 100 may have a higher power output than a machine using a conventional stator of the same size.

[0069] about Figure 8 and Fig. 9 , replace with Figure 7 The stator housing 200 retains the same shape, and the flat portion 240 of the stator housing 200, corresponding to the portion 170 of the stator without the outwardly disposed electrical interconnect 150, has been flattened to reduce the dimension between the outer peripheral side 220 and the outer periphery of the stator bars 120. This arrangement advantageously provides a stator having a smaller diameter than a conventional stator. Therefore, a machine using the stator 100 of the present invention can be smaller than a machine using a conventional stator because the dimensions of the stator bars 120 and the windings 130 are not changed.

[0070] Even combined Figure 7 and Figure 8 The idea is to provide a stator with slightly larger stator bars 120 and windings 130 and a slightly smaller stator housing 200, which will allow the size of the stator 100 to be used.

[0071] Fig.10 An alternative example arrangement of stator interconnects is shown. Figure 5 Same, Fig.10 A simplified example connection scheme between all stator bars 120 and the power supply UVW is shown. There are 18 stator bars in the example arrangement. In this example, the windings 130 are connected as a three-phase star arrangement, although other connection schemes are possible. For example, a delta arrangement may be used, or a delta-star arrangement may be used, or other known arrangements may be used.

[0072] The stator 100 includes an inwardly disposed electrical interconnect 160 and an outwardly disposed electrical interconnect 150. The transition 180 between the inner periphery and the outer periphery of the stator bars 120 may occur through the windings 130 themselves.

[0073] However, an advantage of this particular arrangement of interconnects is that it provides two portions 170 of the electrical interconnect 150 that are not disposed outwardly.

[0074] Fig.11 and Fig.12 With Figure 4 The stator 100 and all components are arranged similarly, however, Fig.11 and Fig.12 A stator housing 200 encloses the stator 100 . Fig.11 and Fig.12 The difference between Fig.11 The stator housing 200 has a substantially circular shape. Fig.12 The stator housing 200 in FIG. 2 includes two flat parts 240 .

[0075] The stator housing 200 enclosing the stator bars 120 and the electrical interconnects 150, 160 has an annular sidewall 230 at both ends of the stator bars 120 and an inner peripheral side 210 and an outer peripheral side 220 respectively disposed radially inside and radially outside the stator bars 120. This arrangement of the stator housing 200 maintains the hollow area 140 at the center of the stator 100.

[0076] As reference Figures 7 to 9 In the example shown, the coils can be sized to fill the available space within the stator housing 200, thereby increasing the power output of the machine, or the housing can be sized smaller to reduce the outer dimensions of the machine without reducing the power output of the machine. Or a combination of these two advantages can be used.

[0077] When the two flat portions 240 are Fig.12 200 as being opposite one another, but the interconnects may alternatively be arranged such that the flat regions may be positioned at other angles circumferentially about the stator housing 200 relative to one another.

[0078] In any of the above examples, the stator housing 200 may also be configured and arranged to define a chamber containing a cooling fluid. In this case, the stator housing 200 also includes a port for supplying the cooling fluid and a port for discharging the cooling fluid, which may be oil or a dielectric fluid. The cooling fluid flows around the cavity in the stator housing 200 to cool the coil.

[0079] The cooling fluid may flow in the outer periphery (i.e., between the outer periphery side 220 of the stator housing 200 and the outer periphery of the stator bars 120), in the inner periphery (i.e., between the inner periphery side 210 of the stator housing 200 and the inner periphery of the stator bars 120), and between adjacent stator bars 120. Allowing the cooling fluid to flow in all of these channels within the housing provides an efficient and very effective cooling solution.

[0080] Blocks (not shown) may also be provided within the cavity, between the inner circumferential side 210 and the stator bars 120 or between the outer circumferential side 220 and the stator bars 120. The purpose of the blocks is to block the respective radially inner or radially outer cooling fluid flow paths and force the cooling fluid to flow between adjacent stator bars 120 and transition to the other cooling fluid flow paths. By placing blocks throughout the cavity, the cooling fluid can be made to meander through the cavity (i.e., the transition between the outer and inner cooling fluid flow paths) as it flows from the inlet to the outlet. This significantly improves the cooling performance of the stator.

[0081] exist Figure 8 , Fig. 9 and Fig.12 In the configuration of the stator housing 200 shown, the flat portion 240 of the stator housing 200 itself can perform the function of a block for the cooling fluid flow path. If the size of the flat portion 240 is appropriate relative to the corresponding stator bars 120, the housing can block the cooling fluid and force the cooling fluid between adjacent stator bars 120, that is, from the outer peripheral path between the outer peripheral side 220 of the stator housing 200 and the stator bars 120 to the inner peripheral path between the inner peripheral side 210 and the stator bars 120.

[0082] The stator 100 may be used to form an electrical machine, such as an electric motor or a generator. In such a machine, a rotor, including a set of permanent magnets, is mounted for rotation about the axis of the machine. The rotor is spaced apart from the stator 100 along the axis of the machine to define a gap between the stator 100 and the rotor. In a dual rotor configuration, a second rotor may be mounted on the side of the stator 100 opposite the first rotor and mounted for rotation about the axis relative to the stator 100. The first and second rotors may be tied together, or may operate independently.

[0083] As described above, electric machines of the type described herein are capable of converting mechanical energy into electrical energy and / or vice versa. When operating to convert mechanical energy into electrical energy, these machines operate as generators. When operating to convert electrical energy into mechanical energy, these machines operate as motors. A single electric machine can perform both functions.

[0084] No doubt many other effective alternatives will occur to the skilled person.It will be understood that the invention is not limited to the described embodiments and encompasses modifications by a skilled person falling within the scope of the appended claims.

Claims

1. A stator for an axial flux machine, comprising: a plurality of stator bars circumferentially spaced about an axis, each of the stator bars having a set of windings wound thereon to form a stator coil set for generating a magnetic field substantially parallel to the axis, the plurality of stator coil sets being arranged to provide a hollow area at the center of the axis, the stator coil set having an outer periphery radially facing away from the axis and an inner periphery radially facing the axis; a plurality of radially outwardly disposed electrical interconnects, each of the plurality of radially outwardly disposed electrical interconnects respectively connecting the outer peripheries of two or more windings together, the plurality of radially outwardly disposed electrical interconnects being disposed radially outward of the outer peripheries of the plurality of stator coil groups and extending circumferentially along at least a portion of the outer peripheries of the stator coil groups; and a plurality of radially inwardly disposed electrical interconnects, each of the plurality of radially inwardly disposed electrical interconnects respectively connecting inner circumferences of two or more windings together, the plurality of radially inwardly disposed electrical interconnects being disposed radially inward of the inner circumference of the stator coil assembly and extending circumferentially along at least a portion of the inner circumference of the stator coil assembly, wherein the outer periphery of the stator is free of radially outwardly disposed interconnections along only one or more portions, and The stator coil set and / or stator bars extend into the one or more portions of the outer circumference of the stator, thereby increasing the maximum power output of the stator.

2. The stator of claim 1, wherein radially inward portions of the stator corresponding to the one or more portions without radially outwardly disposed interconnects include radially inwardly disposed electrical interconnects.

3. The stator of claim 1, comprising one or more electrical transitions between the radially inward electrical interconnect and the radially outward electrical interconnect.

4. The stator of claim 3, wherein each of the one or more transitions between the radially inward electrical interconnect and the radially outward electrical interconnect occurs via a respective winding.

5. The stator of claim 1 , wherein each set of windings comprises a single winding layer on the stator bar, the winding layer comprising a ribbon wire having a width across a surface of the ribbon wire greater than a thickness through the ribbon wire; wherein the windings are stacked along the stator bar in a direction substantially perpendicular to the axis such that adjacent ribbon wire surfaces of the ribbon wire abut each other.

6. The stator of claim 1, wherein the windings of the stator coil assembly are electrically connected in a three-phase star arrangement.

7. The stator of claim 1, comprising a stator case enclosing the stator coil group, the stator case having annular side walls at both ends of the stator bar and inner and outer circumferential sides respectively radially inside and outside the stator coil group.

8. The stator of claim 7, wherein one or more portions of the stator housing corresponding to corresponding one or more portions of the outer periphery of the stator without radially outwardly disposed interconnects have a dimension between the outer periphery side and the stator bars that is smaller than a dimension between the outer periphery side and the stator bars at an area of ​​the stator containing radially outwardly disposed interconnects.

9. The stator of claim 7, wherein the housing defines a chamber containing a cooling fluid, the stator housing including a port for supplying the cooling fluid and a port for exhausting the cooling fluid.

10. The stator of claim 9, wherein the housing and stator bars are arranged to allow the cooling fluid to flow back and forth between an inner radius and an outer radius of the stator bars.

11. The stator of claim 10, wherein the stator comprises one or more blocks disposed in the stator housing between the stator housing and one or more corresponding stator bars, wherein the cooling fluid is forced through gaps between the stator bars by means of the blocks.

12. The stator according to claim 11, wherein the outer peripheral side of the housing abuts against one or more stator bars in the one or more portions without radially outwardly disposed interconnecting members, thereby blocking the flow of the cooling fluid between the housing and the one or more stator bars in the one or more portions without radially outwardly disposed interconnecting members.

13. The stator of claim 1 wherein there are two sections without a radially outwardly disposed interconnection.

14. A stator according to claim 13, wherein the two portions without the interconnection member disposed radially outwardly are circumferentially opposite each other.

15. An axial flux machine comprising: A stator comprising a plurality of stator bars circumferentially spaced about an axis, each of the stator bars having a set of windings wound thereon to form a stator coil set for generating a magnetic field substantially parallel to the axis, the plurality of stator coil sets being arranged to provide a hollow area at the center of the axis, the stator coil set having an outer periphery radially facing away from the axis and an inner periphery radially facing the axis; a rotor including a set of permanent magnets and mounted for rotation about the axis of the machine, the rotor being spaced from the stator along the axis of the machine to define a gap between the stator and the rotor, Wherein, the stator comprises: a plurality of radially outwardly disposed electrical interconnects, each of the plurality of radially outwardly disposed electrical interconnects respectively connecting together the outer peripheries of two or more windings, the plurality of radially outwardly disposed electrical interconnects being disposed radially outward of the outer peripheries of the plurality of stator bars and extending circumferentially along at least a portion of the outer periphery of the stator coil assembly; and a plurality of radially inwardly disposed electrical interconnects, each of the plurality of radially inwardly disposed electrical interconnects respectively connecting inner circumferences of two or more windings together, the plurality of radially inwardly disposed electrical interconnects being disposed radially inward of the inner circumference of the stator coil assembly and extending circumferentially along at least a portion of the inner circumference of the stator coil assembly, wherein the stator is free of radially outwardly disposed interconnects along only one or more portions; and Wherein the stator coil set and / or stator bars extend into the one or more portions of the outer circumference of the stator, thereby increasing the maximum power output of the axial flux machine.

16. The machine of claim 15, wherein radially inward portions of the stator corresponding to the one or more portions without radially outwardly disposed interconnects include radially inwardly disposed electrical interconnects.

17. The machine of claim 15, comprising one or more electrical transitions between the radially inward electrical interconnect and the radially outward electrical interconnect.

18. The machine of claim 17, wherein each of the one or more transitions between the radially inward electrical interconnect and the radially outward electrical interconnect occurs via a respective winding.

19. The machine of claim 15, wherein each set of windings comprises a single winding layer on the stator bar, the winding layer comprising a ribbon wire having a width across a surface of the ribbon wire that is greater than a thickness through the ribbon wire; wherein the windings are stacked along the stator bar in a direction substantially perpendicular to the axis such that adjacent ribbon wire surfaces of the ribbon wire abut one another.

20. The machine of claim 15, wherein the windings of the stator coil set are electrically connected in a three-phase star arrangement.

21. The machine of claim 15, comprising a stator housing enclosing the stator coil group, the stator housing having annular side walls at both ends of the stator bars between the stator and the rotor and inner and outer circumferential sides radially inside and outside the stator coil group, respectively.

22. A machine according to claim 21, wherein one or more portions of the stator housing corresponding to corresponding one or more portions of the outer periphery of the stator without radially outwardly arranged interconnecting members have a dimension between the outer periphery side and the stator bars that is smaller than the dimension between the outer periphery side and the stator bars at an area of ​​the stator containing radially outwardly arranged interconnecting members.

23. The machine of claim 21, wherein the housing defines a chamber containing a cooling fluid, the stator housing including a port for supplying the cooling fluid and a port for exhausting the cooling fluid.

24. The machine of claim 23, wherein the housing and the stator coil assembly are arranged to allow the cooling fluid to flow back and forth between an inner radius and an outer radius of the stator coil assembly.

25. The machine of claim 24, wherein the stator comprises one or more blocks disposed in the stator housing between the stator housing and one or more corresponding stator coil sets, wherein the cooling fluid is forced through gaps between the stator coil sets by means of the blocks.

26. A machine according to claim 25, wherein the outer peripheral side of the housing abuts one or more stator bars in the one or more portions without radially outwardly disposed interconnections, thereby blocking the flow of the cooling fluid between the housing and the one or more stator coil groups in the one or more portions without radially outwardly disposed interconnections.

27. The machine of claim 15, comprising a second rotor including a set of permanent magnets and mounted for rotation about the axis of the machine, the second rotor being spaced apart from the stator along the axis of the machine to define a gap between the stator and the second rotor, and the second rotor being disposed on a side of the stator opposite the rotor.

28. The machine of claim 15 wherein there are two sections without radially outwardly disposed interconnections.

29. A machine as claimed in claim 28, wherein the two portions without the interconnecting member disposed radially outwardly are circumferentially opposed to each other.

30. The machine of claim 15, wherein the machine is a motor or a generator.

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