阅读说明：本技术 轴向磁通电机和辅助组件 (Axial flux machine and auxiliary assembly ) 是由 C·R·莱恩斯 S·A·J·肖尔 B·C·汤姆斯 M·P·弗雷泽 于 2020-01-29 设计创作，主要内容包括：本发明涉及一种用于轴向磁通电机的定子壳体,该定子壳体在形状上是管状的并且基本上是圆柱形的,壳体的内表面包括多个凹部,每个凹部构造成接收轴向磁通电机的定子的导电线圈的外部部分。每个凹部的垂直于轴向磁通电机的旋转轴线的横截面优选地是细长的,每个细长的凹部的主要尺寸基本上在轴向磁通电机的径向方向上延伸。(The present invention relates to a stator housing for an axial-flux electric machine, the stator housing being tubular and substantially cylindrical in shape, an inner surface of the housing including a plurality of recesses, each recess configured to receive an outer portion of a conductive coil of a stator of the axial-flux electric machine. A cross-section of each recess perpendicular to the axis of rotation of the axial-flux electric machine is preferably elongate, a major dimension of each elongate recess extending substantially in a radial direction of the axial-flux electric machine.)

1. A stator housing for an axial-flux electric machine, the housing being tubular and substantially cylindrical in shape, an inner surface of the housing including a plurality of recesses, each recess configured to receive an outer portion of a conductive coil of a stator of the axial-flux electric machine.

2. A stator housing according to claim 1, wherein a cross-section of each recess perpendicular to the axis of rotation of the axial-flux electric machine is elongate with a major dimension extending substantially in a radial direction of the axial-flux electric machine.

3. The stator housing of claim 2, wherein each elongated recess has an aspect ratio of between about 5 and about 15.

4. A stator housing according to claim 1, 2 or 3, wherein the side wall of each recess is substantially parallel to the axis of rotation of the axial-flux electric machine.

5. The stator housing of any one of claims 1 to 4, wherein the circumferential distance between adjacent recesses is between about 1 and about 3 times the width of each recess.

6. The stator housing of any of the preceding claims, further comprising an annular ring configured to form an annular channel adjacent to a circumferential outer surface of the stator housing.

7. The stator housing of claim 6, further comprising a spacer configured to separate the annular channel, the spacer extending from a first axial end of the stator housing to a second axial end of the stator housing.

8. The stator housing of claim 7, wherein the spacer mechanically couples the stator housing to the annular ring.

9. The stator housing of claim 7 or 8, characterized in that the annular ring comprises a cooling fluid inlet arranged adjacent to a first side of the spacer and a cooling fluid outlet arranged adjacent to a second side of the spacer, the inlet and outlet being in fluid communication with an annular channel.

10. A stator housing according to any of the preceding claims, characterized in that the housing is formed by extrusion.

11. The stator housing of claim 10, wherein the plurality of recesses are formed by a first set of projections extending from an inner surface of the stator housing and a second set of projections extending from the inner surface of the stator housing, wherein the first set of projections are integrally formed with the stator housing and the second set of projections are separately formed and positioned within the stator housing.

12. The stator housing of claim 11, wherein the second set of protrusions are mechanically attached to the stator housing.

13. A stator housing according to claim 11 or 12, characterized in that the first set of protrusions is interleaved with the second set of protrusions.

14. The stator housing of claim 13, wherein the first set of projections are interleaved with the second set of projections such that each projection from the first set of projections is adjacent to a projection from the second set of projections.

15. The stator housing of any one of claims 11 to 14, wherein each of the second set of protrusions comprises a key configured to engage with a corresponding slot formed in an inner surface of the extruded stator housing to mechanically attach each protrusion thereto.

16. The stator housing of any one of claims 11 to 14, wherein each of the second set of protrusions comprises a slot configured to engage with a corresponding key formed on an inner surface of the extruded stator housing to mechanically attach each protrusion thereto.

17. A stator housing according to any of claims 10 to 16, characterized in that the stator housing is extruded as a single component.

18. The stator housing according to any one of claims 10 to 16, characterized in that the stator housing is formed from a plurality of circumferentially interlocked extruded segments.

19. A stator housing according to any one of claims 10 to 18 when dependent on any one of claims 6 to 9, wherein the annular ring is formed by extrusion.

20. A stator housing according to claim 19 when dependent on any one of claims 7 to 9, wherein the spacer is formed by a groove formed on one of the inner surface of the annular ring and the outer surface of the stator housing and a key formed on the other of the inner surface of the annular ring and the outer surface of the stator housing.

Technical Field

The invention relates to an axial flux machine and features thereof.

Background

Electrical machines, including motors and generators, have become very widely used. However, our concerns about the reliance on and pollution caused by fossil fuels powering internal combustion engines are creating political and commercial pressures to expand the use of electric machines to new applications and expand their use in existing applications. Motors are increasingly used in vehicles such as electric cars, motorcycles, ships, and airplanes. They are also used in energy generation applications, such as generators in wind turbines.

In order to meet the requirements of these applications, it is necessary to design a motor that has both suitable performance characteristics (such as speed and torque) and high efficiency. The efficiency of the motor is crucial in almost all applications: for example, it can both increase the range of an electric vehicle and reduce the required battery capacity. Reducing the required battery capacity in turn may reduce the weight of the vehicle, which leads to further efficiency gains.

One known type of electric machine is an axial flux machine. As the name implies, the direction of the flux lines being cut during operation of the axial flux machine is parallel to the axis of rotation of the axial flux machine. This is in contrast to a radial flux machine, where the direction of the flux lines cut during operation of the radial flux machine is perpendicular to the axis of rotation of the radial flux machine. While radial flux machines are more common, axial flux machines have been used in certain applications where form factor (relatively small axial extent) and performance characteristics (such as high torque to weight ratio) are of concern.

One example of a yokeless axial flux machine using a concentrated winding arrangement is described in international patent application publication No. WO 2018/015293 a 1. The stator assembly of the axial flux machine comprises circumferentially distributed discrete stator teeth, each having ferromagnetic material around which an electrical winding is present. This is commonly referred to as a yokeless and segmented armature machine. A radially inwardly extending elongated portion of the stator housing is provided for cooling and provides structure for receiving stator teeth. While such axial flux machines can achieve high efficiencies, it is desirable to improve efficiencies, particularly over a wide range of operating parameters. Furthermore, even though the inwardly radially extending elongated portion of the housing provides some structure for receiving discrete stator teeth, there are still difficulties associated with accurately positioning and bonding each stator tooth into the stator housing, and each stator tooth must be wound around a spool-like structure containing ferromagnetic material. It would be desirable to provide a stator that can be more easily and accurately assembled.

Disclosure of Invention

Embodiments described herein provide a rotor, a housing, a cooling arrangement, a flux guide, and a mechanical stack for an axial flux machine that includes a plurality of electrically conductive coils that provides high machine efficiency and ease of manufacture.

Throughout this disclosure, unless otherwise defined, in a cylindrical polar coordinate systemTerms such as "radial", "axial", "circumferential", and "angle" are used in the context of cylindrical polar coordinatesThe direction of the axis of rotation of the motor is parallel to the z-axis. That is, "axial" meansParallel to the axis of rotation (i.e. along the z-axis), "radial" means any direction perpendicular to the axis of rotation, and "angle" is in the azimuthal directionThe above angle, and "circumferential" refer to the azimuthal direction about the axis of rotation.

Terms such as "radially extending" and "axially extending" should not be construed to imply that the features must be completely radial or completely parallel to the axial direction. For purposes of illustration, the current carrying conductors will still experience lorentz forces for angles less than 90 degrees, although it is well known that the lorentz experienced by the current carrying conductors in a magnetic field is greatest when the direction of current flow is substantially perpendicular to the direction of magnetic flux. Thus, deviations from the parallel and perpendicular directions will not change the basic operating principle.

The invention is defined in the independent claims, to which reference should now be made. Preferred features are set out in the dependent claims.

Rotor

According to a first aspect of the present disclosure there is provided a rotor for an axial flux electric machine, the rotor comprising a substantially flat disc portion, the outer edge having a lip formed thereon, the lip extending away from the disc portion along the axis of rotation of the electric machine, the rotor further comprising a plurality of circumferentially distributed permanent magnets fixed thereon, wherein the permanent magnets are fixed on the substantially flat disc portion on the same side from which the lip extends, the outer circumferential edge of each permanent magnet abutting the lip.

Preferably, each of the plurality of permanent magnets is formed of a single permanent magnet. Alternatively, each permanent magnet may be formed from a plurality of separate segments. The separate segments may be stacked adjacent to each other in a radial or circumferential direction.

Preferably, the plurality of permanent magnets comprises an even number of permanent magnets. Preferably, circumferentially adjacent magnets are arranged such that they have opposite polarities. That is, each north pole is circumferentially adjacent to two south poles, and each south pole is circumferentially adjacent to two north poles.

Preferably, the permanent magnets are fixed on the planar surface of the rotor by an adhesive.

The plurality of permanent magnets are preferably circumferentially spaced apart. The rotor may further include a plurality of non-magnetic spacers configured to circumferentially space adjacent ones of the plurality of permanent magnets apart. Each non-magnetic spacer is preferably fixed on a flat surface of the rotor. The spacers may be secured by adhesive or mechanical fasteners. Each spacer is preferably elongate and arranged such that the major dimension extends substantially in a radial direction. Each spacer preferably has a thickness substantially equal to the thickness of one of the permanent magnets. The opposite sides of each of the spacers are preferably substantially parallel.

Alternatively, the planar surface of the rotor may include a plurality of protrusions configured to circumferentially space adjacent ones of the plurality of permanent magnets apart. The height of each protrusion in the direction extending axially from the rotor plate is preferably smaller than the thickness of the permanent magnet. For example, the ratio of the thickness of the permanent magnet to the height of each protrusion may be between 2 and 10, more preferably between 4 and 10. Advantageously, ensuring that the height of the protrusions is less than the thickness of the permanent magnets ensures that there is not excessive flux leakage between the permanent magnets.

Each projection may be elongate and arranged such that the major dimension extends substantially in a radial direction. In this example, a single protrusion may be provided between adjacent permanent magnets. Alternatively, a plurality of protrusions may be provided between adjacent magnets. In this example, each protrusion may be: a circle having a diameter substantially equal to a width of a space between adjacent magnets; and an oval shape having a minor dimension substantially equal to the width of the space between adjacent magnets; a rectangle substantially equal to the width of the space between adjacent magnets and having a major dimension substantially less than the radial length of the permanent magnet; or any other suitable shape.

Preferably, the permanent magnets are shaped such that they are narrower towards the centre of the rotor and wider towards the edges of the rotor, such that the profile of the plurality of permanent magnets tapers evenly from their narrow ends to their wide ends.

Stator housing

According to a second aspect of the present disclosure, there is provided an extruded stator housing for an axial-flux electric machine, wherein the housing is tubular and substantially cylindrical in shape, an inner surface of the housing including a plurality of recesses, each recess configured to receive at least an outer portion of a conductive coil of a stator of the axial-flux electric machine.

According to one aspect of the present invention, a stator housing for an axial-flux electric machine is provided, the housing being tubular and substantially cylindrical in shape, an inner surface of the housing including a plurality of recesses, each recess configured to receive an outer portion of a conductive coil of a stator of the axial-flux electric machine.

A cross-section of each recess perpendicular to the axis of rotation of the axial-flux electric machine is preferably elongate, a major dimension of each elongate recess extending substantially in a radial direction of the axial-flux electric machine. Each elongated recess preferably has an aspect ratio of between about 5 and about 15. The aspect ratio of each recess may be between about 7 and about 12, more preferably between about 7 and about 10.

The side wall of each recess is preferably substantially parallel to the axis of rotation of the axial-flux electric machine.

The circumferential distance between adjacent recesses is between about 1 and about 3 times the width of each recess.

The stator housing preferably further comprises an annular ring configured to form an annular channel adjacent a circumferential outer surface of said stator housing. The stator housing preferably further comprises a spacer configured to separate the annular channel, the spacer extending from the first axial end of the stator housing to the second axial end of the stator housing. In this way, the spacer positions the annular ring relative to the stator housing outer surface to form an annular channel, and partitions the annular channel to form a C-shape. The spacer preferably mechanically couples the stator housing to the annular ring. The annular ring preferably includes a cooling fluid inlet disposed adjacent a first side of the spacer, and a cooling fluid outlet disposed adjacent a second side of the spacer, the inlet and outlet being in fluid communication with the annular channel. As will now be appreciated, the spacers separate the annular passages such that the flow of cooling fluid travels circumferentially around the annular passages.

In a preferred example of the present invention, the stator housing is formed by extrusion. In this preferred example, the plurality of recesses are preferably formed by a first set of projections extending from an inner surface of the stator housing and a second set of projections extending from the inner surface of the stator housing, wherein the first set of projections are integrally formed with the stator housing and the second set of projections are formed separately from the stator housing and positioned within the stator housing. The second set of protrusions is preferably mechanically attached to the stator housing. The first set of projections is preferably interleaved with the second set of projections.

Advantageously, forming the stator housing and the recess in this way improves the manufacturability of the stator housing. The minimum thickness of any feature of the extrusion tool used to form the stator housing may be increased such that the tool life is significantly increased.

The first set of projections is preferably interleaved with the second set of projections such that each projection from the first set of projections is adjacent to a projection from the second set of projections.

Each of the second set of protrusions may include a key configured to engage with a corresponding groove formed in an inner surface of the extruded stator housing to mechanically attach each protrusion thereto. Alternatively, each of the second set of protrusions includes a slot configured to engage with a corresponding key formed on the inner surface of the extruded stator housing to mechanically attach each protrusion thereto.

The second set of protrusions may be formed by extrusion.

The stator housing may be extruded as a single component. That is, the main tubular body of the stator housing may be formed as a single component. Alternatively, the stator housing may be formed from a plurality of circumferentially interlocked extruded segments. In one example, the shell may be extruded as a plurality of interlocking arcuate segments. The housing may be formed from two, three, four, five or more interlocking arcuate segments. In one further example, the extrusion housing may be formed of two sections, a first outer section and a second inner section, the inner section comprising a plurality of recesses. The inner section may comprise a plurality of sub-sections, each sub-section comprising at least one recess. The second inner section is preferably interlocked with the first outer section.

When the stator housing comprises an annular ring, the annular ring is preferably formed by extrusion. When the annular ring is spaced apart from the outer surface of the tubular body of the stator housing by the spacer, the spacer is preferably formed of a groove formed on one of the inner surface of the annular ring and the outer surface of the stator housing and a key formed on the other of the inner surface of the annular ring and the outer surface of the stator housing.

Preferably, the extrusion casing has an outer surface shaped so as to increase the total surface area of the outer surface of the extrusion casing.

The outer surface of the extruded casing may include fins or heat sinks.

Cooling down

According to a third aspect of the present disclosure there is provided a stator housing for an axial flux electric machine, wherein the housing further comprises at least one recess or channel in which a liquid cooling arrangement is accommodated.

The housing may comprise at least two recesses or channels arranged on opposite axial ends of said housing, in which recesses or channels the liquid cooling arrangement is accommodated.

The or each recess or channel may be substantially annular. The or each recess or passage may be substantially adjacent to an outer portion of a conductive coil in a stator of an axial-flux electric machine.

The inner surface of the housing preferably includes a plurality of recesses, each recess configured to receive at least an outer portion of a conductive coil of a stator of an axial-flux electric machine. Each recess is preferably elongate, a major dimension of each elongate recess extending substantially in a radial direction of the axial-flux electric machine. The side of each recess is preferably substantially parallel to the axis of rotation of the axial-flux electric machine. The circumferential distance between adjacent recesses is preferably between about 1 and about 3 times the width of the recesses.

Preferably, the liquid cooling arrangement within the housing comprises a tube for receiving a cooling liquid, the tube being in contact with the housing, or otherwise in contact with the housing by a heat transfer material, to improve heat transfer between the housing and the tube. The heat transfer material may be one of: a resin; paste (paste); and putty (putty).

Preferably, the tubes forming the liquid cooling arrangement provide an inlet and an outlet on the exterior face of the housing.

Alternatively, the recess or channel may be configured to directly receive the cooling liquid, the housing further comprising at least one plate configured to seal the at least one recess or channel.

The housing may further comprise at least one further channel provided on an axial end of said housing. Preferably, the further channel is in fluid communication with the at least one recess or channel. The additional channel may be located axially between the rotor of the axial-flux electric machine and a controller of the axial-flux electric machine. In this manner, a single liquid cooling arrangement may cool both the axial-flux electric machine and the controller for the axial-flux electric machine.

The housing may also include an outer annular channel disposed adjacent a circumferential surface of the housing. Preferably, the outer annular channel is in fluid communication with the or each further recess or channel.

Preferably, the liquid cooling arrangement is connected to a closed loop cooling system, wherein the cooling liquid enters the inlet of the cooling arrangement within the housing, surrounds the tubes, and exits the outlet of the cooling arrangement, enters the radiator or heat exchanger, passes through the pump, and then returns into the inlet of the cooling arrangement.

The stator housing may be formed by extrusion as described above, followed by machining of the at least one recess or channel.

Mechanical stack

According to a fourth aspect of the present disclosure, there is provided a stacked axial-flux motor assembly comprising a plurality of axial-flux motors as described herein stacked mechanically in series.

In this way, where the stacked axial-flux motor assembly is an electric motor, the total torque provided by the axial-flux motor assembly to the output shaft is the sum of the torques provided by the rotors of each axial-flux motor to the shaft.

Alternatively, where the stacked axial-flux motor assembly is a generator, the total torque provided to the input shaft of the axial-flux motor assembly is distributed substantially equally to the rotor of each axial-flux motor.

Preferably, each axial-flux electric machine includes a shaft mechanically coupled to a rotor of the axial-flux electric machine, wherein each shaft is mechanically coupled to a respective shaft of an adjacent axial-flux electric machine.

Alternatively, the stacked axial-flux motor assembly includes a single shaft mechanically coupled to each rotor of each axial-flux motor. In some embodiments, a stacked axial flux motor assembly may comprise: n stators, where N is an integer greater than 1, arranged about a common axis; and M rotors, where M ═ N +1, wherein the or each rotor is disposed between adjacent stators, the rotors comprising permanent magnets on opposite sides of the rotors.

Preferably, the plurality of stacked axial flux machines are controlled by a single controller.

Preferably, the plurality of stacked axial flux machines are controlled by a single controller integrated into the stacked axial flux assembly.

Alternatively, each of the plurality of stacked axial flux machines is controlled by a respective controller. The controllers may be integrated into their respective axial-flux machines.

Laminated flux guide

According to a fifth aspect of the present disclosure, there is provided a laminated flux guide for an axial-flux electric machine as described herein, the flux guide comprising a plurality of laminations. The flux guide has a base surface and an opposite surface inclined (tapered) with respect to the base surface, the laminations being parallel to the base surface. In use, the flux guide is arranged such that each lamination is substantially in a plane extending in a radial direction and an axial direction of the axial flux machine.

Preferably, the laminations are arranged such that the three edges of each lamination are substantially coplanar in a direction perpendicular to the base plane. The flux guide is preferably shaped so as to maximally fill a space defined by adjacent circumferential conductive coils of a stator of an axial-flux electric machine as described herein.

Preferably, the laminations are formed from electrical steel. For example, the electrical steel may be a grain-oriented electrical steel. The laminations are preferably stacked such that the grains of each lamination in the stack have the same grain direction. In particular, the stacking is such that, when arranged in a stator of an axial flux electric machine, the stacked crystal grains are oriented substantially parallel to the axis of rotation of the axial flux machine, thereby being aligned with the axial flux lines generated by the permanent magnets of the rotor.

Preferably, the flux guide comprises an outer layer of a material that is preferably electrically insulating. The outer layer preferably covers at least the inclined surface. More preferably, the outer layer is configured to extend around the base surface and the inclined surface and thereby wrap around the flux guide.

There is also provided a stator for an axial-flux electric machine as described herein, the stator comprising a plurality of flux guides as described

There is also provided a method of manufacturing a flux guide, the method comprising: cutting an electrical steel sheet to provide a plurality of laminations; and stacking the laminations to provide a base surface and a surface that is inclined relative to the base surface to form a tapered lamination stack. The laminates are preferably secured to each other using an adhesive. The laminations are preferably arranged so that the three edges of each lamination are substantially coplanar in a direction perpendicular to the base plane.

Preferably, the method of manufacture comprises providing laminations comprising grain oriented electrical steel, such as c.r.g.o transformer core steel, and stacking the laminations such that the grain direction of each lamination in the stack is substantially aligned. The lamination stack may then be insulated by wrapping the lamination stack in a housing of electrically insulating material.

According to a sixth aspect of the present disclosure, a conductive coil for a stator of an unbounded axial-flux electric machine having distributed windings is provided. The conductive coil includes a first active section and a second active section. Each active section extends in a generally radial direction substantially perpendicular to the axis of rotation of the electric machine and comprises a plurality of winding turn portions stacked parallel to the axis of rotation such that a cross-section perpendicular to the radial direction of each active section is elongated with its major dimension parallel to the axis of rotation. The second active sections are spaced apart in a circumferential direction and axially offset from the first active sections.

This type of conductive coil provides for easy manufacture of a stator using the conductive coil configuration, as well as high machine efficiency. For example, the electrically conductive coil may form a structure in which a magnetic flux guide, such as a lamination stack, may be placed. This allows the stator to be manufactured quickly and also with high accuracy, which improves the efficiency of the machine. In addition, the axial offset of the active sections facilitates stacking of the coils in the axial and circumferential directions. The use of axially stacked winding turns also mitigates the skin effect and proximity effect in the active section. This is because the cross-section of each winding turn is smaller and since the winding turns are connected in series, the current is deterministically controlled to flow over the entire axial extent of each active section. This reduces heat generation and improves flux linkage.

According to this sixth aspect, the conductive coil may optionally comprise a plurality of pairs of active sections connected in series with each other. Adjacent pairs of active segments may circumferentially overlap to define a second type of space for receiving a flux guide. The second type of space is a circumferential space between two adjacent active sections of different pairs of active sections of the coil. Like the active section defining it, the circumferential space extends substantially radially and may be elongated in the radial direction. The active segment pairs of each such additional pair of each coil advantageously increase the number of slots per phase per pole by one. This may reduce losses and thus improve efficiency, as a greater number of slots per phase per pole may result in a more accurate sinusoidal flux density. Furthermore, the number of active sections per coil may be varied proportionally according to the radius of the machine.

According to a seventh aspect of the present disclosure, there is provided an electrically conductive coil for a stator of a yokeless, axial flux machine. The conductive coil includes two pairs of active sections. Each active section extends in a generally radial direction substantially perpendicular to the axis of rotation of the electric machine. The generally radially extending active sections of each pair of active sections are spaced apart in the circumferential direction. The two pairs of active sections partially overlap in the circumferential direction to define a second type of space for receiving the flux guide. The second type of space is a circumferential space between two adjacent active sections of different pairs of active sections of the coil. The circumferential space extends substantially radially and may be elongate, as do the active sections defining it.

The conductive coil of the type according to the seventh aspect provides for easy manufacture of a stator constructed using the conductive coil, and high machine efficiency. For example, when a plurality of such coils are circumferentially distributed around the stator ring, the resulting coil structure will have circumferentially distributed spaces (of the second type) in which flux guides may be disposed. This allows the stator to be manufactured quickly, with a large number of flux guides, and also with a high degree of accuracy (which improves the efficiency of the machine). Furthermore, since each coil has (at least) two pairs of spaced-apart active sections, the coil will provide the stator with (at least) two slots per pole per phase, which makes the magnetic flux density generated by the stator more sinusoidal, with less significant harmonic components. For sinusoidally varying currents, the average torque produced by the motor is caused by the interaction of the fundamental magnetic field components and not by the harmonic components. This is advantageous because harmonic components in the circumferential spatial flux density lead to larger eddy currents being generated in the permanent magnets of the rotor, which in turn leads to higher losses and increased heat generation. Furthermore, any other harmonic component in the winding magnetomotive force distribution may cause increased losses in the flux guide. Still further, the number of active segment pairs per coil may be varied proportionally according to the radius of the machine and/or by selecting the span (pitch) between the active segments forming each pair. Thus, each additional pair of active sections per coil increases the number of slots per phase per pole by one, and therefore higher efficiencies can be obtained, especially as the size of the machine increases.

According to this seventh aspect, each active section may optionally comprise a plurality of winding turn portions stacked parallel to the axis of rotation, such that a cross section perpendicular to the radial direction of each active section is elongated with its major dimension parallel to the axis of rotation. The axially stacked insulated winding turns may mitigate the skin effect and proximity effect of the active section. This reduces heating (due to better distribution of current through the conductor cross-section) and improves flux linkage.

According to a seventh aspect, each pair of active sections may optionally be axially offset from each other. Axially offsetting the active sections facilitates stacking of the coils in both the axial and circumferential directions, which provides flexibility in the span (spacing) between each pair of active sections and improves the structural rigidity of the complete winding due to the interlocking nature of the coils. It also increases the flux linkage in the core and thus increases the generation of torque.

The following optional features may also be applied to the conductive coil of the sixth aspect and the conductive coil of the seventh aspect.

In use, current flows in opposite radial directions along the active sections forming a pair of active sections (i.e. current flows in an opposite direction along the second active section to current flowing along the first active section).

Each active section may be only a single winding turn width. Alternatively, each active section may be a plurality of winding turn widths. That is, each active section may include a plurality of circumferentially stacked winding turn portions. If each active section does comprise a plurality of circumferentially stacked winding turn portions, the number of circumferentially stacked winding turn portions is preferably smaller than the number of axially stacked winding turn portions, such that the major dimension of the coil cross-section perpendicular to the radial extension direction of the active section is parallel to the axis of rotation. For example, the active section may be only two winding turn portions wide, but comprise more than two winding turn portions in the axial direction. For example, the ratio of the number of axially stacked winding turn portions to the number of circumferentially stacked winding turn portions may be greater than or equal to three, preferably greater than or equal to five, more preferably greater than or equal to seven. A coil having a partial width greater than one winding turn increases the overall length of the conductor, which in turn increases the impedance of the coil. The higher impedance may allow the use of a controller with a lower switching rate, which may reduce cost in some cases.

The winding turn portions of the first and second generally radially extending active sections of a pair of active sections may have proximal ends at an inner radius and distal ends at an outer radius. The proximal ends of the winding turn portions may be connected by an inner loop section and the distal ends by an outer loop section, such that, in use, current flows in opposite radial directions along a pair of radially extending active sections.

The outer loop section may be configured to form an outer portion of the coil that is substantially parallel to the axis of rotation. The axially parallel portions of the coils may be axially inserted into the bore of the stator housing, which improves the ease of manufacture of the stator. Furthermore, the extended nature of the outer portion of the coil provides a greater surface area for mechanical locking of the coil and cooling at the outer periphery of the stator.

Each outer loop section may have any shape, but preferably may be substantially semi-circular or rectangular, such that the outer portion of the coil is a semi-circular disc or rectangular surface. The surface of the outer part may also be curved, for example involute shaped. These surfaces create a large surface area, but also require a relatively limited conductor length, which reduces material costs.

Additionally or alternatively, the outer loop section may be configured to form a substantially involute portion of the coil. The involute portions (which maintain a substantially constant gap between adjacent conductive elements) provide a radially interlocking arrangement of circumferentially distributed coils. There may be two substantially involute outer portions of the coil connecting the outer portions of the coil to the two active sections.

The inner loop section may be configured to form an inner portion of the coil that is substantially parallel to the axis of rotation. The inner portion is substantially parallel to the axis of rotation, thereby occupying as little circumferential space as possible. This is very important for the invaluable physical space at the stator inner diameter

Each inner loop section may have any shape, but preferably may be substantially semi-circular or rectangular, such that the inner portion of the coil is a semi-circular disc or rectangular surface. The surface may also be curved, for example, in the shape of an involute. These shapes require a relatively limited conductor length to implement, which reduces material costs.

The inner loop section may be configured to form a substantially involute portion. The involute portions (which maintain a substantially constant gap between adjacent conductive elements) provide a radially interlocking arrangement of circumferentially distributed coils. There are two substantially involute inner portions of the coil that connect the inner portions of the coil to the two active sections.

The number of active segment pairs may be an integer multiple of 2. Using an integer multiple of two pairs of active sections can easily allow each coil to be made of multiple identical conductive elements, which reduces manufacturing costs.

The electrically conductive coil may be configured such that, in use, current flows in the same direction along adjacent active sections of the coil separated by one of the spaces for the flux guide. This avoids that the current generation flowing in these adjacent active sections has an opposite effect on the torque generation.

The pairs of active sections constituting one coil may be integrally formed, or formed by connecting a plurality of individual elements in series, each element including a pair of active sections. The connection can be made, for example, using ferrules, by soldering or by welding. The individual elements may be formed by winding, gluing and forming conductors, which may be performed using known techniques that are relatively inexpensive to implement. Integrally formed components can be expensive, but can also allow for more complex coil topologies that cannot or are difficult to implement using conventional winding techniques. Further, by integrally forming the elements, the number of constituent parts of the stator is reduced.

The conductive coil may include a first connection portion and a second connection portion for connecting the conductive coil to a power source. The first connection portion and the second connection portion may extend parallel to the rotation axis. The connecting portions may extend in the same parallel direction or in opposite parallel directions. The parallel extending connection portions allow a very simple connection of the coil to a power supply.

The first connection portion and the second connection portion of the coil may be provided near the radially outer end of the coil. In this way, the connection may be made close to the outer radius of the stator assembly where there is a larger circumferential space than, for example, at the inner radius of the stator assembly. This means that the connection is less densely stacked, which provides ease of manufacture and provides a more reliable electrical connection.

There is also provided a stator for an axial-flux electric machine, the stator comprising a plurality of conductive coils according to the sixth aspect. There is also provided a stator for an axial-flux electric machine, the stator comprising a plurality of conductive coils according to the seventh aspect. In either case, the plurality of electrically conductive coils may be distributed circumferentially around the stator.

The plurality of electrically conductive coils may be arranged in sets, each set corresponding to a pole of the stator.

Each conductive coil may be configured to be connected to one phase of a multi-phase power supply.

Circumferentially adjacent electrically conductive coils may be configured to be connected to different phases of a multi-phase power supply such that for an N-phase power supply, the stator comprises a plurality of sets of N electrically conductive coils, each set comprising one coil for each phase of the N-phase power supply, each set of coils corresponding to one pole of the stator.

For each phase of the multi-phase power supply, each second coil of the stator connected to that phase may be connected to a common bus. In this way, the winding can be divided into two interleaved sections that connect half the total number of coils of each phase to one of the busbars of the two phases.

Circumferentially adjacent conductive coils may circumferentially overlap to define a first type of space for receiving a flux guide. Each space of the first type may be a circumferential space between two adjacent active sections of two different coils. The spaces of the first type extend in a radial direction and may be elongated in the radial direction, similar to the active sections that define them. Since the coils of the stator naturally form the structure for receiving the flux guides, the stator will be manufactured quickly and also with a high degree of precision, which improves the efficiency of the machine.

The stator may further comprise flux guides positioned in the spaces of the first type and/or the second type.

The stator may further include a stator housing. The stator housing may comprise circumferentially distributed and axially extending apertures for receiving an outer portion of the conductive coil substantially parallel to the axis of rotation. As mentioned above, this provides for easier and more accurate manufacturing and heat transfer from the conductive parts of the stator to the stator housing.

An axial-flux electric machine including such a stator is also provided. The axial flux machine may comprise a pair of opposed rotors disposed on opposite sides of a stator; each rotor may be dedicated to only one stator, or one or more rotors may be shared between two axially aligned stators.

A method of manufacturing a stator for an axial-flux electric machine is also provided. The method includes positioning a plurality of conductive coils in a stator housing such that the plurality of coils are distributed circumferentially around the stator housing. Each conductive coil includes a first active section and a second active section, each active section extending in a generally radial direction substantially perpendicular to a rotational axis of the electric machine and including a plurality of winding turn portions stacked parallel to the rotational axis such that a cross-section perpendicular to the radial direction of each active section is elongated with a major dimension parallel to the rotational axis. The second active sections are spaced apart in a circumferential direction and axially offset from the first active sections.

The stator housing may include a plurality of circumferentially distributed and axially extending bores. In this case, positioning the plurality of electrically conductive coils in the stator housing may include positioning an axially extending portion of the respective coil in one of the axially extending bores for each respective electrically conductive coil. This increases ease of assembly, accuracy of assembly, mechanical locking, and cooling and efficiency in use.

Each conductive coil may include a plurality of pairs of active sections connected in series with one another, wherein adjacent pairs of active sections circumferentially overlap to define a second type of space for receiving a flux guide. The second type of space may be a circumferential space between two adjacent active sections of the same coil, but which are different pairs of active sections of the coil. The method also includes positioning a flux guide in the space. As mentioned above, advantageously, each additional pair of active sections per coil increases the number of slots per phase per pole by one, which may reduce losses and thus improve efficiency. Furthermore, the number of active sections per coil can be varied proportionally to the radius of the machine, so that higher efficiency can be achieved on larger machines.

Another method of manufacturing a stator for an axial-flux electric machine is provided. The method includes positioning a plurality of conductive coils in a stator housing such that the plurality of coils are distributed circumferentially around the stator housing. Each conductive coil includes two pairs of active segments, each extending in a generally radial direction substantially perpendicular to the axis of rotation of the electric machine. The generally radially extending active sections of each pair of active sections are spaced apart in the circumferential direction. The two pairs of active sections each partially overlap in a circumferential direction to define a second type of space for receiving the flux guide. The second type of space is a circumferential space between two adjacent active sections of different pairs of active sections of the same coil. The method also includes positioning a flux guide in the space.

In this second method, each active section may comprise a plurality of winding turn portions stacked parallel to the axis of rotation such that a cross-section perpendicular to a radial direction of each active section is elongated with its major dimension parallel to the axis of rotation. This reduces heating as the current is more evenly distributed through the conductive cross section. The active sections of each pair may be axially offset from each other. Axially offsetting the active sections facilitates stacking of the coils in both the axial and circumferential directions, provides flexibility in span (spacing) between each pair of active sections, and improves the structural rigidity of the complete winding due to the interlocking nature of the coils.

In both methods, the conductive coils may be positioned such that circumferentially adjacent conductive coils circumferentially overlap and thereby define a first type of space for receiving the flux guide. Each space of the first type may be a space between two adjacent active sections of two different coils. Both methods may further include positioning the flux guide in the first type of space.

Both methods may further include impregnating at least a portion of the stator with a bonding compound such as a resin. This may enhance the stator assembly to protect it from the mechanical and electromagnetic forces to which it is subjected during use. The means for connecting the coil to the power supply may be non-impregnated with the binding compound, advantageously allowing access to the connection after impregnation.

In accordance with another aspect of the claimed disclosure, a stator for an axial-flux electric machine is provided. The stator includes a plurality of circumferentially distributed conductive coils. Each of the plurality of conductive coils is configured to be connected to one phase of a multi-phase power supply and includes at least one pair of active sections. Each active section extends in a generally radial direction substantially perpendicular to the axis of rotation of the electric machine. The generally radially extending active sections of each pair of active sections are spaced apart in the circumferential direction. Circumferentially adjacent conductive coils circumferentially overlap to define a first type of space for receiving a flux guide. Each space of the first type is a circumferential space between two adjacent active sections of two different coils.

Like the active section, the circumferential space extends substantially radially and may be elongated in the radial direction.

The electrically conductive coils of such a stator form a structure in which a magnetic flux guide, such as a lamination stack, can be placed. This allows the stator to be manufactured quickly and also with high accuracy, which improves the efficiency of the machine. In addition, the number of flux guides and correspondingly the number of slots per pole per phase of the stator can easily be increased and can easily be varied in proportion to the radius of the machine. Increasing the number of slots per phase per pole can make the circumferential space flux density in the stator and two machine air gaps more sinusoidal with lower harmonic distortion. For sinusoidally varying phase currents, the average torque produced by the motor is more due to the interaction of the fundamental magnetic field components than to the harmonic components. This is advantageous because harmonic components in the circumferential spatial flux density lead to larger eddy currents in the permanent magnets of the rotor, which leads to higher losses and increased heat. Furthermore, any other harmonic component in the winding magnetomotive force distribution may cause increased losses in the flux guide.

In use, current flows in opposite radial directions along the active sections of a pair of active sections forming a coil.

Each conductive coil may include a plurality of pairs of active sections connected in series with one another. Adjacent pairs of active sections may circumferentially overlap to define a second type of space for receiving a flux guide. The second type of space may be a circumferential space between two adjacent active sections of the same coil but belonging to different pairs of active sections of the coil. The circumferential space extends substantially radially and may be elongated in the radial direction, as defined by the active section. Each additional pair of active sections per coil increases the number of slots per phase per pole by one, which can reduce losses and thus improve efficiency. Advantageously, the number of active sections per coil may be varied proportionally according to the radius of the motor.

The number of pairs of active sections may be an integer multiple of 2. Using multiple pairs of active sections that are an integer multiple of two readily allows each coil to be made of multiple identical conductive elements, which reduces manufacturing costs.

The pairs of active sections constituting one coil may be integrally formed, or formed by connecting a plurality of individual elements in series, each element including a pair of active sections. The connection can be made, for example, using ferrules, by soldering or by welding. The individual elements may be formed by winding, gluing and forming the conductors, which may be performed using known winding techniques that are relatively inexpensive to implement. Integrally formed components can be expensive, but can also allow for more complex coil topologies that cannot or are difficult to implement using conventional winding techniques. Further, by integrally forming the elements, the number of constituent parts of the stator is reduced.

The stator may further comprise flux guides, such as electrical steel laminations, located in the first and/or second type of space. The flux guide axially guides the magnetic flux between corresponding magnetic poles on the opposing rotor. These flux guides may have a high magnetic permeability at least in the axial direction and, therefore, for a specific arrangement of the permanent magnets, the flux density in the stator is increased.

The plurality of electrically conductive coils may be arranged in sets, each set corresponding to a pole of the stator. Circumferentially adjacent electrically conductive coils may be configured to be connected to different phases of a multi-phase power supply such that for an N-phase power supply, the stator comprises a plurality of sets of N electrically conductive coils, the N electrically conductive coils of each set comprising one coil for each phase of the N-phase power supply, each set of coils corresponding to one pole of the stator.

The stator may be configured such that, in use, current flows in the same direction along adjacent active sections separated by one of the second type of spaces for the flux guides. This avoids that the currents flowing in these adjacent active sections have an opposite effect on the torque production.

The active sections of each pair of active sections may be axially offset from each other. Axially offsetting the active sections facilitates stacking of the coils in both the axial and circumferential directions, which provides flexibility in the span (spacing) between each pair of active sections and improves the structural rigidity of the complete winding due to the interlocking nature of the coils.

Each active section may comprise a plurality of winding turn portions stacked parallel to the axis of rotation such that a cross-section perpendicular to a radial direction of each active section is elongated with its major dimension parallel to the axis of rotation. Axially stacking the insulated winding turns mitigates skin and proximity effects in the active section. This is because the cross-section of each winding turn is smaller and because the winding turns are connected in series, the current flow is deterministically controlled over the entire axial extent of each active section. This reduces heating (since the current is distributed more evenly throughout the conductive cross section) and improves flux linkage.

Each active section may have only one winding turn width. Alternatively, each active section may be a plurality of winding turn widths. That is, each active section may include a plurality of circumferentially stacked winding turn portions. If each active section does comprise a plurality of circumferentially stacked winding turn portions, the number of circumferentially stacked winding turn portions is preferably smaller than the number of axially stacked winding turn portions, such that the major dimension of the coil cross-section perpendicular to the radial extension direction of the active section is parallel to the axis of rotation. For example, the active section may be only two winding turn portions wide, but comprises more than two winding turn portions in the axial direction. For example, the ratio of the number of axially stacked winding turn portions to the number of circumferentially stacked winding turn portions may be greater than or equal to three, preferably greater than or equal to five, more preferably greater than or equal to seven. A coil that is larger than the width of one winding turn portion increases the overall length of the conductor, which in turn increases the impedance of the coil. The higher impedance may allow the use of a controller with a lower switching rate, which may reduce cost in some cases.

The winding turn portions of the first and second generally radially extending active sections may have proximal ends at an inner radius and distal ends at an outer radius. The proximal ends of the winding turn portions may be connected by an inner loop section and the distal ends may be connected by an outer loop section, such that, in use, current flows in opposite radial directions along a pair of radially extending active sections.

The outer loop section may be configured to form an outer portion of the coil that is substantially parallel to the axis of rotation. The axially parallel portions of the coils may be axially inserted into the bore of the stator housing, which improves the ease of manufacture of the stator. Furthermore, the expandability of the portion of the coil provides a greater surface area for the mechanical locking of the coil and the cooling at the outer periphery of the stator.

The stator may further comprise a stator housing comprising circumferentially distributed and axially extending apertures for receiving an outer portion of the electrically conductive coil substantially parallel to the axis of rotation. As mentioned above, this provides for easier and more accurate manufacturing and improves heat transfer from the conductive components of the stator through the stator housing.

Each outer loop section may have any shape, but preferably may be substantially semi-circular or rectangular, such that the outer portion of the coil is a semi-circular disc or rectangular surface. The surface may also be curved, for example, in the shape of an involute. These surfaces create a large surface area, but also require a relatively limited conductor length for a given axial extent of the coil, which reduces material costs.

The outer loop section may be configured to form a substantially involute portion of the coil. The involute portions (which maintain a substantially constant gap between adjacent conductive elements) provide a radially interlocking arrangement of circumferentially distributed coils. There may be two substantially involute outer portions of the coil connecting the outer portions of the coil to the two active sections.

The inner loop section may be configured to form an inner portion of the coil that is substantially parallel to the axis of rotation. The inner portion is substantially parallel to the axis of rotation, thereby occupying as little circumferential space as possible. This is important because the physical space at the inner radius of the stator is at a premium.

The inner circuit section may have any shape, but preferably may be substantially semi-circular or rectangular, such that the inner portion is a semi-circular disc or rectangular surface. The surface may also be curved, for example, in the shape of an involute. These shapes require a relatively limited conductor length to implement, which reduces material costs.

The inner loop section may be configured to form a substantially involute portion of the coil. The involute portions provide a radially interlocking arrangement for circumferentially distributed coils. There are two substantially involute inner portions of the coil that connect the inner portions of the coil to the two active sections.

The stator may further comprise connection means for connecting the electrically conductive coil to a multi-phase power supply. The connection means may be provided axially above a plane perpendicular to the axis of rotation and axially above the electrically conductive coil, and/or may be provided below a plane perpendicular to the axis of rotation and axially below the electrically conductive coil. Positioning the connection means above and/or below the coils allows the coils to be easily connected to the connection means and also means that the connection can be accessed even after impregnation of the stator assembly. This prevents a faulty connection which renders the entire stator unusable.

Each of the plurality of electrically conductive coils may comprise a pair of connection portions extending substantially parallel to the axis of rotation for connecting the electrically conductive coil to the connection means. The connecting portions may extend in the same parallel direction or in opposite parallel directions. The parallel extending connection portions allow a very simple connection of the coil to the connection means.

The connecting means may comprise a plurality of busbars or a plurality of busbar segments, which may be annular.

For each phase of the multi-phase power supply, each second coil of the stator connected to that phase may be connected to a common bus. In this way, the winding can be divided into two interleaved sections that connect half the total number of coils of each phase to one of the busbars of the two phases.

There is also provided a yokless axial flux machine comprising any of the above stators.

The yokeless axial flux machine may further comprise a pair of opposed rotors arranged on opposite sides of the stator, each rotor comprising a plurality of circumferentially distributed permanent magnets defining a pole pitch of the machine. The angle by which each active segment pair is spaced may be different from the pole pitch of the machine defined by the permanent magnets. While the angle by which each pair of active regions is spaced may be the same as the pole pitch, the use of different angles facilitates a long or short pitch of the winding.

The angle by which each pair of active sections is spaced may be less than the pole pitch. Using a smaller angle allows a short pitch to be achieved, which can be used to further reduce harmonics in the stator magnetic field.

One of a pair of opposing rotors may be shared between the stator and an axially aligned second stator.

In accordance with yet another aspect of the claimed disclosure, a method of manufacturing a stator of an axial-flux electric machine is provided. The method includes positioning a plurality of conductive coils in a stator housing such that the plurality of coils are distributed circumferentially around the stator housing. The conductive coils are positioned such that circumferentially adjacent conductive coils circumferentially overlap, thereby defining a first type of space that receives the flux guide. Each space of the first type is a circumferential space in a region where two coils overlap. The method also includes positioning a flux guide in the first type of space.

The electrically conductive coils of such a stator form a structure in which a magnetic flux guide, such as a lamination stack, can be placed. This allows the stator to be manufactured quickly and also with high accuracy, which improves the efficiency of the machine.

Each conductive coil may include a plurality of pairs of active sections connected in series with one another. Adjacent pairs of active segments may circumferentially overlap to define a second type of space for receiving a flux guide. The second type of space may be a circumferential space between two adjacent active sections of the same coil, but which are non-paired active sections of the coil. In this case, the method may further comprise positioning the flux guide in a second type of space. This not only provides additional structure for placing the flux guide, but also allows for the manufacture of motors with a greater number of slots per pole per phase. This may reduce harmonics in the stator field and improve motor efficiency, as explained above.

The stator housing may include a plurality of circumferentially distributed and axially extending bores. In this case, positioning the plurality of electrically conductive coils in the stator housing may include positioning an axially extending portion of the respective coil in one of the axially extending bores for each respective electrically conductive coil. This increases ease of assembly, accuracy of assembly, mechanical locking, and cooling and efficiency in use.

The method may further include impregnating at least a portion of the stator with a bonding compound such as a resin. This may enhance the stator assembly to protect it from the mechanical and electromagnetic forces to which it is subjected during use. The means for connecting the coil to the power supply may be non-impregnated with the binding compound, advantageously allowing access to the connection after impregnation.

Any feature in one aspect of the disclosure may be applied to other aspects of the disclosure in any suitable combination. In particular, method aspects may apply to apparatus aspects, and vice versa. Furthermore, any, some, and/or all features of one aspect may be applied to any, some, and/or all features of any other aspect in any suitable combination.

It should also be appreciated that particular combinations of the various features described and defined in any aspect of the present disclosure may be implemented and/or supplied and/or used independently.

Drawings

Embodiments of the present disclosure will now be further described, by way of example only, with reference to the accompanying drawings, in which:

fig. 1A is a side view of an axial flux machine showing a stator assembly, a rotor and a shaft;

figure 1B is a perspective view of the axial flux machine of figure 1A;

fig. 2A is a perspective view of a rotor and a shaft of the axial flux machine of fig. 1A-1B;

fig. 2B is a plan view of one rotor of the axial flux machine of fig. 1A-B and 2A, more clearly showing the permanent magnets of the rotor;

fig. 3 is a cross-sectional side view of an axial flux machine, showing additional details not visible in fig. 1A-1B and 2A-2B;

FIG. 4A is a perspective view of the conductive components of the stator assembly of the axial flux machine including 48 conductive coils;

FIG. 4B is a side view of the conductive components of the stator assembly of FIG. 4A;

FIG. 4C is a plan view of the conductive components of the stator assembly of FIGS. 4A and 4B;

figure 5A shows plan and bottom views of a single conductive coil element having a pair of radially extending active sections;

figure 5B shows two perspective views of the conductive coil element of figure 5A;

figure 5C shows two side views of the conductive coil element of figures 5A and 5B;

figure 5D illustrates front and rear views of the conductive coil element of figures 5A-5C;

FIG. 5E is a plan view of a portion of a stator including a plurality of the conductive elements of FIGS. 5A-5D distributed circumferentially around the stator, showing the spaces created by their overlap;

fig. 5F is a plan view illustrating the stator of fig. 5E;

FIG. 5G is a plan view of the conductive element showing how the conductive element is wound in a flat plane;

FIG. 5H is a side view of the conductive element shown in FIG. 5G;

FIG. 5I is a perspective view of the conductive element shown in FIGS. 5G and 5H;

FIG. 5J is a plan view of an alternative conductive coil element;

FIG. 5K is a plan view of a stator employing a plurality of the conductive coil elements of FIG. 5J;

fig. 6A shows a plan view and a bottom view of a conductive coil comprising two pairs of circumferentially overlapping radially extending active sections connected in series;

fig. 6B shows two perspective views of the conductive coil of fig. 6A;

figure 6C shows two side views of the pair of conductive coils of figures 6A and 6B;

figure 6D illustrates front and rear views of the conductive coil of figures 6A-6C;

FIG. 7A is a front view showing the conductive coil of FIGS. 6A-6D connected to a pair of bus bars;

FIG. 7B is a perspective view of the conductive coil of FIGS. 6A-6D connected to a pair of bus bars;

FIG. 7C is a plan view of the pair of conductive coils of FIGS. 6A-6D connected to a pair of bus bars;

FIG. 8A is a perspective view of eight conductive coils connected to the same pair of bus bars;

FIG. 8B is a plan view of eight conductive coils connected to the same pair of bus bars;

FIG. 9A is a front view of two circumferentially adjacent conductive coils connected to respective pairs of busbars;

FIG. 9B is a perspective view of two circumferentially adjacent conductive coils connected to respective pairs of busbars;

FIG. 9C is a plan view of two circumferentially adjacent conductive coils connected to respective pairs of busbars;

FIG. 10 is a perspective view of six adjacent conductive coils showing an alternative way of connecting the conductive coils to a three-phase power supply;

fig. 11A is a plan view of one half of the conductive components of a sixteen-pole, three-phase stator assembly, which includes 24 conductive coils, each having two pairs of radially-extending active sections;

FIG. 11B is a perspective view of the stator assembly of FIG. 11A;

FIG. 12A is a perspective view of a stator assembly including a stator housing that houses conductive coils of the stator assembly;

FIG. 12B is a plan view of the stator assembly of FIG. 12A showing how the electrically conductive coil is received in the stator housing bore;

FIG. 12C is a perspective view of the stator assembly of FIGS. 12A and 12B showing bus bars and phase connections;

fig. 13 is a flowchart showing a manufacturing method of the stator; and

figure 14 is an efficiency diagram illustrating the efficiency of an axial flux machine including the stator assembly of figures 12A-12C for a range of torque and speed values;

fig. 15 is a perspective view of a rotor plate for an axial-flux electric machine as described herein;

fig. 16A is a perspective view of an alternative rotor for an axial-flux electric machine, as described herein;

fig. 16B is a perspective view of another alternative rotor for an axial-flux electric machine, as described herein;

fig. 17A is a perspective view of an extrusion housing for an axial-flux electric machine as described herein;

fig. 17B is a plan view of an extrusion housing for an axial-flux electric machine as described herein;

fig. 18 is a perspective view of a housing including a cooling system for an axial-flux electric machine as described herein;

fig. 19 is a perspective view of two stacked axial-flux electric machines as described herein;

fig. 20 is a schematic view of an alternative axial-flux electric machine including a shared rotor;

21A, 21B, and 21C illustrate views of a flux guide for an axial-flux electric machine as described herein;

fig. 22 is a plan view of a multi-piece extrusion housing for an axial-flux electric machine; and

fig. 23 is a plan view of a portion of an alternative multi-piece extrusion housing for an axial-flux electric machine.

Like reference numerals are used for like elements throughout the specification and drawings.

Detailed Description

Embodiments of the present disclosure will now be described with reference to axial flux motor 100. Although electric motor 100 is described, it should be appreciated that the present disclosure may be equally practiced in other types of axial-flux electric machines, such as generators.

Overview of axial flux machine

Fig. 1A and 1B illustrate the main components of axial flux motor 100. Axial flux motor 100 includes a stator assembly 1, two rotors 2a, 2b disposed on opposite sides of stator assembly 1, and a shaft 3. The shaft includes a drive end 3a and a non-drive end 3 b. The rotors 2a, 2b are fixedly mounted to the shaft 3. In use, the stator 1 of the axial flux motor 100 remains stationary and the rotors 2a, 2b and shaft 3 rotate together relative to the stator 1. It should be appreciated that various components typically present in motor 100, such as the rotor cover plate and the means for connecting the stator to a power source, have been omitted from fig. 1A and 1B for clarity

Although fig. 1A-1B show two rotors 2a, 2B and a single stator 1, it will be appreciated that other configurations are possible. For example, one of the rotors 2a, 2b may be shared between two axially aligned stators. That is, there may be two stators and three rotors, with one of the three rotors being shared between the two stators.

Fig. 2A and 2B show the rotors 2A, 2B and the shaft 3 of the motor 100 without the stator assembly 1. As is particularly clear from fig. 2B, each rotor 2a, 2B comprises a plurality of circumferentially distributed permanent magnets 21, 22, 23, 24. The magnets 21, 22, 23, 24 are, for example, rare earth magnets such as NdFeB magnets. Circumferentially adjacent magnets, such as permanent magnets 21 and 22, have opposite polarities. That is, each north pole 23 is circumferentially adjacent to two south poles 22, 24, and each south pole 22 is circumferentially adjacent to two north poles 21, 23.

Although not visible in fig. 2A and 2B, the rotors 2A, 2B are mounted such that the opposing permanent magnets have opposite poles. I.e. the north pole on rotor 2a faces the south pole on rotor 2b and vice versa. Thus, the magnets of the two rotors 2a, 2b generate a magnetic field with axial lines of magnetic flux between the two rotors 2a, 2 b.

As will be understood by those skilled in the art, the stator assembly 1 described herein is yoke-free but not iron-free. The yoke is an additional structural element present in some stators for directing the lines of magnetic flux between opposite poles of the rotor magnetic field. That is, the yoke completes the magnetic circuit within the stator. Since the axial flux machine 100 described herein utilizes a pair of opposing rotors 2a, 2b whose opposing permanent magnets have opposite polarities, no yoke is required to complete the magnetic circuit because the flux is unidirectional. Having a stator without a yoke reduces the overall weight of the axial flux machine, which is very beneficial in many practical applications. In addition, since there is no loss due to a change in magnetic flux density in the yoke region, it improves efficiency.

The circumferential (angular) spacing a of the centers of two adjacent permanent magnets 21, 22 of the rotors 2a, 2b defines the pole pitch of the axial flux motor 100. Note that the average span β of the permanent magnets may be equal to or less than the pole pitch α of the motor 100. In fig. 2A-2B, adjacent magnets are separated by a non-magnetic spacer, so that the average span β of the permanent magnets 21-24 is less than the pole pitch α of the motor 100. In one example, β is about 3/4 of α. The ratio of β to α can be selected to reduce circumferential, spatial harmonic distortion of the permanent magnetic flux density in the stator 1. As will be appreciated, it is not necessary to provide non-magnetic spacers so that the span β of the permanent magnets 21-24 is less than the pole pitch α of the motor 100. For example, the permanent magnets 21-24 may be fixed to the rotor at their desired spaced locations using an adhesive or the like.

The rotors 2A, 2B shown in fig. 2A-2B have sixteen circumferentially distributed permanent magnets 21-24 and thus sixteen poles. However, this is merely an example, and in practice may be greater or less than sixteen poles, depending in part on the intended application. For example, the poles are typically present in pairs (and therefore there is typically an even number of poles), and the number of poles is limited to some extent by the radius of the rotors 2a, 2b, which will depend on the size of the motor suitable for the intended application. The rotors 2a, 2b may for example have eight poles or thirty-two poles.

Turning to fig. 3, a cross-sectional view of axial flux motor 100 of fig. 1-2 is shown with additional detail. Since the disclosures described herein relate primarily to the electrically conductive components 10 of the stator assembly 1, which will be described in more detail below with reference to fig. 4-12, only a brief overview of the components of fig. 3 will be provided. Those skilled in the art will be familiar with the components of an axial flux machine, such as axial flux motor 100, and will also appreciate that not all of the features shown in fig. 3 are essential to an axial flux machine, and that these features may be implemented in a number of different ways.

In addition to the stator 1, the drive-end rotor 2a, the non-drive-end rotor 2b and the shaft 3, fig. 3 also shows a drive-end rotor cover plate 4a and a non-drive-end rotor cover plate 4b, which surround the rotors 2a, 2b and generally seal the electric motor 100 against the ingress of foreign objects. A rotor spacer ring 4c spaces the rotors 2a, 2b apart. The O-ring seals 8a, 8b and dynamic seal 9 further seal the interior of the motor 100. The rotation of the rotors 2a, 2b is assisted by a drive end bearing 6a and a non-drive end bearing 6b, the drive end bearing 6a and the non-drive end bearing 6b maintaining a gap 5 between the permanent magnets of the rotors 2a, 2b and the stator 1. Also shown is an encoder assembly 7, which encoder assembly 7 includes an encoder mount 71, an on-shaft position encoder 72 and an associated encoder sensor magnet 73.

Conductive coil and stator

The conductive component 10 of the stator assembly 1, including the conductive coil 12, will now be described with reference to fig. 4-12. It should be appreciated that although a particular example having a particular number of stator poles 11, conductive coils 12, and current phases is described, this is not intended to limit the scope of the claims.

Turning briefly to fig. 12A to 12C, a stator assembly 1 is shown, it being seen that the stator assembly 1 includes an annular or ring-shaped stator housing 20 which houses the electrically conductive components 10 of the stator 1. The core of the stator assembly 1 comprises radially extending active sections of the conducting components 10 of the stator and flux guides 30 in the form of a stack of laminations, wherein the axial flux provided by the rotor magnets interacts with radially flowing current flowing through the conducting components 10 to generate a torque that rotates the rotors 2a, 2 b. A flux guide 30 in the form of a lamination stack is positioned in the space between the radially extending active sections of the electrically conductive assembly 10 of the core, which flux guide 30 may comprise a grain-oriented electrical steel sheet surrounded by an electrical insulation. The flux guide 30, which is in the form of a laminated stack, serves to guide the flux generated by the permanent magnets 21-24 between the current-carrying conductors.

Turning now to fig. 4A to 4C, the electrically conductive assembly 10 (which will be referred to simply as "stator 10" from now on) is shown without the stator housing 20 or the flux guide 30 in the form of a lamination stack being shown. As can best be appreciated from the top down view of fig. 4C, the stator 10 has distributed windings and comprises a plurality (in this case 16) of circumferentially distributed stator poles 11a, 11b, … …, 11p, each comprising a plurality of electrically conductive coils 12. Each conductive coil 12 is connected to one phase of a multi-phase power supply via a connection means 15,16, in this example the connection means 15,16 take the form of a bus bar. In this particular example, the stator 10 is configured for use with a three-phase power supply such that each pole 11a-11p of the stator has three conductive coils 12.

It will be appreciated that in the case of sixteen poles 11a-11p and three conductive coils 12 per pole, the stator 10 of fig. 4A-4C has a total of 48 circumferentially distributed conductive coils 12. However, as can be seen from the top down view of fig. 4C, the stator 10 actually has 96 radially extending active segments. Furthermore, as can be seen from the side view of fig. 4B, there are two layers of radially extending active segments that are axially offset, providing a total of 192 radially extending active segments. The reason for this will become apparent from the description of fig. 5-9. In summary, each conductive coil 12 includes one or more conductive elements 120, each including a pair of axially offset, radially extending active segments. Each conductive coil 12 of the stator 10 of fig. 4A-4B includes two such conductive elements 120, and since each conductive element 120 includes a pair of axially offset radially extending segments, a total of 192 radially extending active segments results.

The conductive components of the stator 10 may be made of any combination of one or more conductive materials. However, the conductive member 10 is preferably made of copper.

Fig. 5A-5D are various views of a single conductive element 120. As mentioned above, and as will be explained in more detail below, each conductive coil 12 is comprised of one or more conductive elements 120. It will be appreciated that where each conductive coil 12 is comprised of one conductive element 120, the conductive coil 12 and the conductive element 120 are equivalent. Fig. 6A-6D illustrate the conductive coil 12 comprised of two conductive elements 120 and 120', which will be described below.

Returning to fig. 5A-5D, as can best be appreciated from the top-down view of fig. 5A, where the axis of rotation is perpendicular to the plane of the page, the conductive element 120 includes a pair of circumferentially spaced, radially extending active segments 121a, 121 b. These radially extending active sections 121a, 121b are referred to as "active" sections because when the conductive coils 12 are located in the stator they are disposed within the stator core and thus interact with the magnetic field provided by the magnets of the rotors 2a, 2 b. It will be appreciated that the flux linkage is at least close to maximising as the active section extends in a generally radial direction which is generally perpendicular to the axial flux in the core.

The angle γ by which the two active sections 121a, 121b are spaced apart will be referred to as the coil span. The coil span may be the same as or different (smaller or larger) than the pole pitch a (defined by the angle between the centers of the permanent magnets of the rotor). Preferably, the coil span γ is less than the pole pitch α. For example, γ may be about 5/6 of α. By making γ smaller than α, a short pitch of the winding can be implemented, which reduces the spatial harmonic content of the winding magnetomotive force (mmf).

Turning to fig. 5E and 5F, they show a sixteen-pole, three-phase stator 10 'that is similar to the stator 10 of fig. 4A-4C, but differs in that each coil 12 of the stator 10' has only one conductive element 120 (a pair of active segments 121a, 121 b). That is, in fig. 5E and 5F, the coil 12 and the conductive element 120 are equivalent. Like stator 10, the electrically conductive coils 120a, 120b, 120c of stator 10' are circumferentially distributed around the stator, and circumferentially adjacent coils circumferentially overlap.

As is particularly clear from fig. 5E, the circumferential overlap of the coils 120a, 120b, 120c defines the circumferential space between the active sections of the coils. These circumferential spaces, which are elongated in the radial direction, can receive the flux guides 30. Spaces such as the marked spaces 141a, 141b, 141c will be referred to as spaces of the first type. As can be seen, a first type of space 141a, 141b, 141c is defined between the active sections of the different coils. For example, the space 141b is between one of the two active sections of the coil 120a and one of the two active sections of the coil 120 c. However, it should be appreciated that the two coils defining the particular spaces 141a, 141b, 141c of the first type may depend on various factors, including the number of phases per stator pole, the number of poles, and the selected coil span γ.

Returning now to fig. 5A-5D, as can be seen from fig. 5B and 5D, the two active sections 121a, 121B are axially offset from each other. This facilitates stacking of the conductive coils 12 in the circumferential direction and also facilitates circumferential stacking of the conductive elements 120, where each conductive coil 12 has a plurality of conductive elements 120. As will be discussed in more detail with reference to fig. 14, this allows for more stator poles and more slots per pole per phase, both of which may provide higher efficiency. Furthermore, the winding can easily be short-pitched.

As can be seen in each of fig. 5B, 5C and 5D, each conductive element 120 is formed from a continuous length of wound conductor. The outermost winding of the conductor length terminates at a first connection portion 128, which first connection portion 128 will be referred to as an outer tail portion 128. The outer tail 128 extends substantially parallel to the axial direction. This facilitates convenient connection of the coil 12 to a multi-phase power supply, as will be described in more detail below. The innermost winding turn portion terminates at a second connection portion 129, which second connection portion 129 will be referred to as an inner tail portion 129.

As can also be seen in each of fig. 5B, 5C and 5D, a length of conductor forming the conductive element 120 is wound such that there are a plurality of winding turn portions 131a, 131B stacked parallel to the axis of rotation of the electrical machine. The cross section of the resulting conductive element 120 perpendicular to the radial direction of each active section 121a, 121b is elongated with its major dimension parallel to the axis of rotation. In the example of fig. 5A-5D, there are fourteen axially stacked winding turn portions 131a, 131b, but this is not intended to limit the disclosure, as other numbers are equally possible.

Fig. 5G, 5H and 5I show how the conductive element 120 is formed by winding a length of conductor. As shown in fig. 5G, the conductor is wound in a single plane around a pair of support elements 301, 302 (which extend perpendicularly out of the plane of the page) to form a flat planar winding having a plurality (in this case fourteen) of turns or layers. The windings are flat as best appreciated from fig. 5H and 5I. The innermost winding terminates at the inner tail 129 and the outermost winding terminates at the outer tail 128.

The flat winding shown in fig. 5G-5I has been formed, and the three-dimensional shape of the conductive element 120 is formed by bending or deforming the flat winding into the shape shown in fig. 5A-5D. Bending may be performed using a bending tool, as is known in the art. For example, a bending tool having an axially offset inner male profile block may be pushed against the outer female shape to bend the flat winding, thereby axially offsetting the active sections from each other. The outer tail 128 and the inner tail 129 may be individually bent as desired.

To make the bending process easier, the flat winding may first be given extra strength so that the winding retains its shape during bending. In one example, the conductor has an external adhesive layer that is heat or solvent activated so that after winding, the turns/layers can be bonded together to hold the shape.

It should be appreciated that conductive element 120 may be wound in a variety of different ways, as can be seen in particular in fig. 5G-5I, and the particular windings shown are not intended to limit the present disclosure.

Some alternatives include:

although the winding in fig. 5G has been wound around the support elements 301, 302 in a counter-clockwise direction, the length of the conductor may equally be wound in a clockwise direction.

Although the outermost turn of the winding is terminated such that the outer tail 128 passes into the active section 121a, 121b of the conductive element 120, this is not necessary. The outer turn may terminate at any point of the turn, for example, such that the outer tail 128 passes into the loop section of the turn rather than the active section.

Although fourteen axially stacked winding turns are shown in fig. 5, more or less than fourteen turns are possible.

Although the winding is one turn/layer thick (see in particular fig. 5H), it may be more than one turn/layer thick. In this case, each conductive element 120 will include a plurality of circumferentially stacked winding turn portions. Although any number of circumferentially stacked winding turn portions is possible, the number is preferably smaller than the number of winding turn portions in the axial direction, such that the cross section of the conductive element 120 (which is perpendicular to the radial direction of each active section 121a, 121b) still has a major dimension parallel to the axis of rotation. For example, the ratio of the number of axially stacked turns to the number of circumferentially stacked turns may be greater than three, and may preferably be greater than five.

As will be appreciated from the above, in use, current will flow in opposite directions (i.e. inwards and outwards parallel to the radial extension direction) along the two active sections 121a, 121b of the conductive element 120. The reversal of the direction of the current flow is provided by the outer loop section 122 of the winding turn portions 131a, 131b and the inner loop section 125 of the winding turn portions 131a, 131 b. Each outer loop section 122 includes a first portion 123 and a pair of second portions 124a, 124b (one for each of the pair of active sections 121a, 121b) connecting the active sections 121a, 121b to the first portion 123. Similarly, each inner loop section 125 includes a first portion 126 and a pair of second portions 127a, 127b (one for each of the pair of active sections 121a, 121b) connecting the active sections 121a, 121b to the first portion 126.

As can be seen from fig. 5B, 5C and 5D, the outer first portions 123 together form an outer portion 133 of the coil element 120, the surface of which is substantially parallel to the axis of rotation. In the particular example of fig. 5A-5D, the outer first portion 123 is generally semi-circular, and thus the outer portion 133 is a generally flat semi-circular disc 133, although other shapes are possible. For example, each outer first portion 123 may have a shape corresponding to three sides of a rectangle, such that they together form an outer portion 133 having a flat rectangular surface. As another example, the outer portion 133 of the conductive element 120 formed by the outer first portion 123 need not be flat or planar: this is illustrated in fig. 5J, which shows a conductive element 120 "having an outer portion 133", the outer portion 133 "having a curved profile and thus a curved surface. Fig. 5K shows a plan view of a stator 10 "comprising such conductive elements, which can be compared with fig. 4C (although it is noted that the stator 10" does not show any connection means 15, 16).

The surface 133 formed by the outer first portion 123 may be used to facilitate cooling due to its relatively large surface area. Furthermore, since the outer portions 133 of the coils 120 are substantially parallel to the axis of rotation, the stator housing 20 may be provided with an axially extending bore 25, which bore 25 axially receives the outer portions 133 of the coil elements 120', 120 "to provide a mechanical lock and improve the cooling effect. This will be explained in more detail below.

The inner first portions 126 together form an inner portion 136 of the coil element 120. The inner portion 136 shown in fig. 5B-5D is substantially identical to the outer portion 133 described above, and the outer portion 133, similar to the above, may be parallel to the axis of rotation, and it may have various shapes and contours. However, the inner portion 136 will generally play less of a role in the cooling and stacking of the coil 12, and thus the inner portion 126 may be configured to reduce the total amount of conductor per conductive element 120 to reduce cost.

With respect to the outer second portions 124a, 124b and the inner second portions 127a, 127b, although they appear substantially straight in fig. 5A-5D, in practice they are slightly curved. In particular, the shape of each outer first portion 124a, 124b is a segment of a first involute, and thus the first portions 124a, 124b together form an outer substantially involute portion 134a, 134b of the coil element 120. Similarly, each inner second portion 127a, 127b is shaped as a segment of a second involute, and thus the first portions 127a, 127b together form inner substantially involute portions 137a, 137b of the coil element 120. The importance of the involute will be described with reference to fig. 6A to 6D.

Although it has been described above that the conductive element 120 is formed by winding a length of conductor, this is not essential. The conductive element 120 may be manufactured in other ways, including by being integrally formed.

Further, while element 120 is illustrated as being wound from a length of conductor and including stacked winding turn portions 131a, 131b, this is preferred, but not required. For example, instead of axially extending stacked winding turn portions 131a, 131b, each conductive element 120 may be formed by a single axially extending conductive strip. In some cases, a single axially extending conductive strip may be more preferred than a plurality of axially stacked winding turn portions 131a, 131b, but, as will be described below, the use of stacked winding turn portions 131a, 131b advantageously helps to mitigate skin and proximity effects that otherwise would lead to increased losses.

As described above, each conductive coil 12 may include only one conductive element 120. However, for reasons explained in more detail below, each conductive element preferably comprises two or more circumferentially overlapping conductive elements. An example of a conductive coil comprising two circumferentially overlapping conductive elements 120, 120' will now be described with reference to fig. 6A-6D.

Fig. 6A shows a top and bottom view of the conductive coil 12 including two conductive elements 120, 120'. The features of each of the two conductive elements 120, 120' are the same as the features of the single conductive element 120 described above with reference to fig. 5A-5D, and therefore their features will not be described again.

To form the conductive coil 12, two identical conductive elements 120, 120 'are electrically connected together in series at their inner tail portions 129, 129'. In the example shown herein, the inner tails 129, 129' are connected using a ferrule 130. However, there are other ways of connecting the inner tails 129, 129', such as brazing or welding. To connect the two elements 120, 120', one of the two conductive elements 120, 120' is rotated 180 ° about an axis extending vertically in the plane of the page of fig. 6A, so that the outer tails 128, 128' of the two conductive elements 120, 120' are in opposite directions and the inner tails 129, 129' are adjacent and therefore easily connected by the ferrule 130. Alternatively, the conductive coil 12 comprising two conductive elements may be integrally formed as a single piece.

The resulting conductive coil 12 has two pairs of circumferentially overlapping, spaced apart active sections 121a, 121 b; 121a ', 121 b'. Notably, the overlap of the two pairs of active sections defines two spaces 142a, 142 b. A first space 142a is defined between one (first) active section 121a of the first conductive element 120 of the coil 12 and one (first) active section 121a 'of the second conductive element 120' of the coil 12. A second space 142b is defined between the other (second) active section 121b of the first conductive element 120 of the coil 12 and the other (second) active section 121b 'of the second conductive element 120' of the coil 12. That is, the two spaces 142a, 142b are two different pairs of active sections 121a, 121b of the same coil 12; 121a ', 121 b'; 121b, 121 b'. This type of space will be referred to as a second type of space. Like the spaces of the first type, the spaces 142a, 142b of the second type provide space for the flux guide 30 in the form of a lamination stack. This makes it easier to construct the stator assembly 1, and also increases the number of slots per pole per phase of the stator assembly 1, which can improve the efficiency of the motor.

Having now described the first type of spaces 141a-141c (i.e. the spaces defined between active sections of different coils) and the second type of spaces 142a-142b (i.e. the spaces defined between active sections of the same coil but different pairs), it should be noted that the first and second types of spaces may coincide when a plurality of coils 12 defining the second type of space are provided in the stator 10 to define the first type of space. This is best seen in fig. 11A, which shows a sixteen-pole, three-phase stator in which each coil 12 includes two conductive elements 120, 120'. Only half of the conductive coil 12 is shown in fig. 11A-11B so that these spaces can be clearly seen. Whether the first type of space and the second type of space coincide may depend on a number of factors, including the selected coil span γ, the number of stator poles, and the number of phases.

Returning to fig. 6A-6D, it can also be seen from fig. 6A and 6B that there is a gap 143a between the second portions 124a, 124a 'of the outer loop sections 122, 122' (which form a pair of outer involute portions 134a, 134a 'of the two conductive elements 120, 120'). Likewise, there is a gap 143b between the second portions 124b, 124b ' (which form another pair of outer involute portions 134b, 134b ') of the outer loop segments 122, 122 '. There is also a gap 144a between the second portions 127a, 127a ' (which form a pair of inner involute portions 137a, 137a ') of the inner loop segments 125, 125 '. Finally, there is also a gap 144b between the second portions 127b, 127b ' (which form another pair of outer involute portions 137b, 137b ') of the inner loop segments 125, 125 '. The width of these gaps 143a, 143b, 144a, 144b remains substantially constant along the length of the involute portions of the conductive elements 120, 120' due to the geometric nature of the involute. This advantageously reduces the resulting diameter of the motor for a given rating and loss in the coils.

Although the conductive coil 12 has been described as having two conductive elements 120, 120', it should be appreciated that the conductive coil 12 may have any integer number of conductive elements 120, including more than two. Increasing the number of conductive elements per conductive coil 12 will increase the number of spaces of the second type defined by circumferentially adjacent active sections of conductive elements 120, which in turn increases the number of slots per phase per pole in the stator 1. This can result in the generation of a stator magnetic field having a more accurate sinusoidal flux density and less significant harmonic distortion. This advantageously reduces the generation of eddy currents in the permanent magnets of the rotors 2a, 2b, which in turn reduces heating losses and thus provides higher motor efficiency. However, it will be appreciated that the number of conductive elements 120 per conductive coil 12 will generally be limited by size constraints. For example, for a given conductor cross-section (i.e., the cross-section of the wire wound around the winding) and a given radius of the stator, the number of conductors that can fit circumferentially into a single coil span γ is limited.

There may be several further considerations if the coil 12 is to have more than two conductive elements. For example:

if the coil is formed by connecting a plurality of conductive elements 120 (e.g. by means of a ferrule 130), it may be preferable to provide several types of conductive elements to facilitate a simpler connection of adjacent conductive elements. For example, the conductive element 120 described above may be used for two circumferentially outer conductive elements, as their outer tail portions 128 will be connected to a power source. However, one or more inner conductive elements between the outer conductive elements will be connected to the conductive elements at both their inner tail 129 and outer tail 128, so a second type of conductive element may be provided for connection, the second type of conductive element having an outer tail 128 that is adapted in a similar manner relative to the inner tail 129. Alternatively, each coil 12 may be formed as an integral unit, rather than by the connection of three or more separate conductive elements.

An integer multiple of two conductive elements 120 per coil 12 may be better than an odd number of conductive elements 120 per coil 12. If an integer multiple of two elements 120 is used, the outer tails 128 of the two circumferentially outermost elements 120 will be directed in opposite parallel directions as shown in fig. 6A-6D. Although this is not required, it provides a more straightforward and clear connection of the coil 12 using connection means, as will be described below with reference to fig. 7-10.

Although a stator 10 having a single axial layer of circumferentially distributed coils 12 (a single layer of coils 12 having axially offset active sections) has been described, it will be appreciated that each stator may have multiple axially stacked coil layers. In this case, the spaces of the first type and/or the spaces of the second type of each layer may advantageously substantially coincide in the circumferential direction. This will advantageously allow for the insertion of an axially longer flux guide 30, which axially longer flux guide 30 may extend through the axial length of the plurality of axially stacked layers, providing further gains in ease and speed of assembly.

Connecting a coil to a polyphase power supply

The manner in which the plurality of circumferentially distributed electrically conductive coils 12 are connected to the multi-phase power supply will now be described. It will be appreciated that in practice there are many different ways in which this can be achieved, and that those skilled in the art will appreciate many different ways. Thus, the present disclosure is not limited to any particular connection arrangement. However, the described way of connecting the electrically conductive coil 12 provides a particularly clean and well-organized set of connections, the described way of connecting the electrically conductive coil 12 making use of the connecting means 15,16, the connecting means 15,16 being provided above/below a plane perpendicular to the axis of rotation in the axial direction and above/below the electrically conductive coil in the axial direction. Furthermore, the connection is easy to perform, which reduces the possibility of poor connection, and the stator can be impregnated with resin without impregnating the connection device, which allows the connection portion to be inspected and fixed even after impregnating the stator assembly.

Referring first to fig. 4B, there are first connection means 15 provided axially above a plane perpendicular to the axis of rotation of the electric motor 100 and above the conductive coil 12. There is also a second connection means 16 provided axially below a plane perpendicular to the axis of rotation of the electric motor 100 and axially below the conductive coil 12. In the case of the stator 10, the stator 10 is configured for use with a three-phase power supply, the connection means 15 and 16 comprising being provided for each of the three phases. However, it can be extended to multi-phase power supplies having any number of phases.

In the particular connection arrangement of fig. 4A-4C, which is referred to as a parallel connection arrangement, each of the connection devices 15,16 comprises three phase connections and one star connection. That is, the first connection device 15 includes a first phase connection 151 for a first phase of the power supply, a second phase connection 152 for a second phase of the power supply, a third phase connection 153 for a third phase of the power supply, and a star connection 154. Similarly, the second connecting means 16 comprises a first phase connection 161 for a first phase of the power supply, a second phase connection 162 for a second phase of the power supply, a second phase connection 163 for a third phase of the power supply, and a star connection 164.

In the depicted example, the connection portions 151-153, 161-163 and the star-shaped connection portions 154, 164 are in the form of annular bus bars, the outer peripheries (although this could equally be inner peripheries) of which substantially coincide with the axially extending outer tail portions 128, 128' of the conductive coil. The connection buses 151-153, 161-163 are themselves connected to a power supply via input ports 1510-1530, 1610-1630.

In the parallel connection arrangement shown, each conductive coil 12 is connected to one phase of the power supply by one of the phase connections (as an example, phase connection 151) connecting the coil 12 to one of the connection devices 15,16 and a star connection (in this example, star connection 164) connecting to the other connection device 15, 16. The connection of a conductive coil 12 to a phase connection 151 and a star ring 164 is shown in fig. 7A-7C and will now be described with reference to fig. 7A-7C.

Fig. 7A-7C show one conductive coil 12 having two conductive elements 120, 120', the two conductive elements 120, 120' being connected to a first phase connection 151 from a first connecting means 15 and to a star connection 164 from a second connecting means 16. Since the outer tail portions 128, 128' of the conductive coil 12 extend in the axial and opposite directions, and since the peripheries of the bus bars 151, 164 coincide with the axially extending outer tail portions 128, 128', the outer tail portions 128, 128' are easily connected to the connection portions 151, 164.

To make the connection even easier, the ring-shaped bus bars 151, 164 are provided with circumferentially spaced receiving means 151a-h, 164a-x for receiving the axially extending outer tails 128, 128' of the coils 12. In the three-phase parallel connection arrangement shown, each star connection 154, 164 will be connected to half of all coils 12, while each phase connection 151, 161, 163 will be connected to only one of the six coils 12. Thus, in this example, the number of equally spaced receiving means 164a-x of the star connection 164 is three times that of the first phase connection 151.

Returning to fig. 4A-4C, each pole 11a-11p of the stator 10 includes one conductive coil 12 for each phase (i.e., each pole 11a-11p has 3 conductive coils 12 because the stator is configured for use with a three-phase power supply), and circumferentially adjacent conductive coils 12 are connected to different phases. This is shown in fig. 11A and 11B for a sixteen-pole stator 10, which sixteen-pole stator 10 is connected to a three-phase power supply, but only one half of the conductors are shown, so that only 24 conductive coils 12 distributed in the circumferential direction can be seen.

In view of this, in the three parallel connection arrangements shown in fig. 4, 7-9 and 11-12, each sixth conductive coil 12 will be connected to the connection means 15,16 in the same way. This is shown in fig. 8A and 8B. There may be eight equally spaced conductive coils 12a-12g connected to the same phase connection 151 and the same star ring 164. Although not shown in fig. 8A-8B, it will be appreciated that the middle between each coil will be another coil 12 connected to the same phase of the power supply, but through a complementary set of bus bars. I.e. to the phase connection 161 and the star connection 154.

The conductive coils 12 corresponding to the other phases of the power supply will be connected in substantially the same manner as described above for one phase. To illustrate this, fig. 9A-9C show how two circumferentially adjacent conductive coils 12 are connected in a parallel connection arrangement.

Fig. 9A-9C show two circumferentially adjacent conductive coils 12a, 12 b. The conductive coil 12a is connected in a similar manner to the conductive coil 12 in fig. 7A-7C. That is, the coil 12a is connected to the second phase connection portion 152 and the star connection portion 164. The coil 12b circumferentially adjacent to the coil 12a is connected to a different phase of the power supply and thus to a different pair of bus bars. Specifically, the circumferentially adjacent coils 12b are connected to the third phase connection 163 of the second connection device 16 and the star connection 154 of the first connection device without loss of generality.

The connection of the conductive coil 12 has been described above with reference to a parallel connection arrangement. However, other connection arrangements are possible. To illustrate this, fig. 10 shows an alternative arrangement, which will be referred to as a series connection arrangement.

In the series connection arrangement of fig. 10, the first connection means 15' above the conductive coil 12 differs from the connection means 15 of fig. 4, 7-9 and 11-12 in that it does not comprise a star connection: it includes only a first phase connection part 151', a second phase connection part 152 ', and a third phase connection part 153 '. However, the second connection device 16' is identical to the second connection device 16 of fig. 4, 7-9 and 11-12 in that it has a three-phase connection 161 ', 162 ', 163' and a star connection 164 '. In order to compensate for the lack of star connections in the first connection means 15', the conductive coils 12 are connected in a different manner. The phase connections 151'-153' of the first connecting means 15 'also serve twice as many conductive coils 12 and therefore have additional receiving means compared to the receiving means of the second connecting means 16' and the first and second connecting means 15,16 arranged in parallel.

Fig. 10 shows a series connection arrangement of two circumferentially adjacent stator poles 11 and 11'. Similar to the parallel connection arrangement, each pole 11, 11' includes one conductive coil for each pole, such that each pole has three coils: pole 11 is comprised of electrically conductive coils 12a, 12b and 12c, while pole 11 'is comprised of electrically conductive coils 12a', 12b 'and 12 c'. Also as with the parallel connection arrangement, circumferentially adjacent coils are connected to different phases. However, while coils of the same phase but adjacent poles (e.g. 12a and 12a') in a parallel connection arrangement are connected substantially independently and form independent current paths, in a series connection arrangement their connections are related and they are part of the same current path.

Considering only the connection to the coils 12a, 12a ' of the same phase, the coil 12a of the first pole 11 is connected by its external tail to the phase connection 153' of the first connection means and to the phase connection 163' of the second connection means. The coil 12a ' of the second adjacent pole 11' is connected to the phase connection 153' of the first connection means 15' and to the star connection 164' of the second connection means. Thus, the current path may be considered to travel from phase connection 163 'through coil 12a, then along phase connection 153', then through coil 12a 'to star connection 164'.

Different connection arrangements may be used for different practical applications. For example, the series-connected arrangement described above theoretically provides a machine torque constant (measured in Nm/a) that is up to twice the machine torque constant provided by the parallel arrangement described above. This would be preferable for some (but certainly not all) practical applications.

Although the connection means 15, 15 'have been described as being above the coil 12 and the connection means 16, 16' as being below the coil, it will be appreciated that two pairs 15, 16; 15', 16' may be above the coil 12 or two pairs 15, 16; 15', 16' may be below the coils. In this case, it may be preferable to manufacture the coil 12 with its outer tails 128, 128' extending in the same axial direction rather than in opposite axial directions.

Furthermore, although the connection means 15,16, 15 'and 16' are described as continuous ring-shaped busbars, this is only one way of implementing the connection means. For example, the connecting means may not be continuous or annular, but may take the form of a series of two or more circumferentially distributed bus-sections. Many other kinds of connection means will occur to those skilled in the art.

Stator manufacturing

The above-described features and configuration of the electrically conductive coil 12 provide for particularly efficient and effective manufacture of a stator including a plurality of circumferentially distributed coils 12. Of particular importance is the fact that the coils 12 themselves provide a structure into which the flux guides 30, for example in the form of a lamination stack, are provided. This makes the placement of the flux guide 30 in the stator assembly 1a relatively straightforward and precise operation, especially in contrast to many known manufacturing techniques, which may involve winding the coil around a bobbin-like structure containing the lamination stack and then individually fixing (e.g., using glue) the wound bobbin-like structure into the stator housing. Various other advantages will be described.

Fig. 13 is a flow chart illustrating a method 500 for manufacturing a stator.

Method 500 includes providing 510 a plurality of conductive coils, such as conductive coil 12 described above. Preferably, the electrically conductive coil 12 has a plurality of circumferentially overlapping pairs of circumferentially spaced radially extending active sections (as in the coils 12 of fig. 6A-6D) such that each coil 12 provides the second type of space. However, the coil 12 may have only a pair of spaced apart active sections (as in the coils of fig. 5A-5D). By connecting the plurality of conductive elements 120 in series or in any other manner, the conductive coil 12 may be formed as a single unitary piece.

At 520, the method 500 includes positioning the plurality of conductive coils 12 in the stator housing such that the plurality of coils are distributed circumferentially around the stator housing. Preferably, the electrically conductive coils are positioned such that circumferentially adjacent electrically conductive coils circumferentially overlap, thereby defining a space of a first type for receiving the flux guide. By providing an appropriate number of coils 12 having an appropriate coil span γ within the housing, the circumferential overlap of circumferentially adjacent coils 12 can be ensured. As described above, where the coil 12 has multiple pairs of active sections such that the coils each define a space of the second type, the spaces of the first and second types may coincide with one another.

The stator housing 20 may be provided with a plurality of circumferentially spaced axially extending bores 25 for receiving the coils 12. This makes positioning of the coil 12 in the stator housing easier and more accurate. Advantageously, if the coil 12 is formed with an axially extending outer portion 133, the axially extending outer portion 133 may be received within the axially extending bore 25. Since the axially extending outer portions 133 have a large surface area, they provide a good mechanical locking of the coil 12 in the stator housing so that assembly with glue (for example) is not necessary, and also provide a cooling source for the stator. The circumferentially distributed holes 25 for the receiver coils 12 can be seen most clearly in fig. 12A-12C.

Optionally, at 530, the method 500 includes positioning a flux guide 30 (such as a lamination stack) in a space (a first type and/or a second type of space) defined by the coil 12. As explained above, the overlapping of adjacent coils creates a first type of space 141a, 141b, 141c between the active sections of the different coils. If the coils 12 each include more than one pair of radially extending active sections (as shown in fig. 6A-6D), then multiple pairs of the second type of spaces 142a, 142a' would also be defined within each conductive coil 12. In each case, the flux guide may also be positioned within the space. Since the coils 12 themselves provide a defined space for the structure, the positioning of the lamination stack into the structure is straightforward, fast and accurate. In combination with the provision of the holes 25 for receiving the coils 12 in the stator housing 20, this means that both components of the stator core (the active sections of the coils 12 and the flux guides 30) can be positioned quickly and very accurately compared to many known techniques. It will be appreciated that the precisely positioned core assembly reduces losses and therefore improves machine efficiency.

Optionally, at 540, the method 500 includes connecting the plurality of coils 12 to the connection means 15,16 so that the coils can be connected to a multi-phase power supply. This may be done in any desired manner, for example using busbars in a parallel or series connection arrangement, as described above.

Optionally, at 550, the method 500 includes impregnating at least a portion of the stator assembly 1 in a bonding compound, such as a resin. This enhances the stator structure and thus protects the stator assembly 1 from electromagnetic and mechanical forces to which it is subjected in use. Furthermore, the heat conduction between the stator components can be improved if the binding compound has a significantly higher heat transfer coefficient than air.

If the connection means 15,16 are provided axially above and/or below the coil 12 as described above, impregnation of the stator can be performed before or after the coil is connected to the connection means. Furthermore, and advantageously, if the connection means 15,16 themselves are not impregnated, the connection can be tested, changed and, if necessary, replaced after impregnation. This is highly desirable because a faulty connection in a resin impregnated stator can result in the entire stator being unusable and unfixed.

Efficiency of the machine

It has been found that an axial flux machine 100 comprising the stator assembly 1 described herein provides not only high peak efficiency but also high efficiency over a wide range of operating parameters. While high peak efficiencies are often mentioned, in practice these peak efficiencies are rarely achieved, particularly in applications that require the machine to perform over a range of operating parameters. Thus, for many applications, efficiency over a wide range of parameters is a more meaningful measure in practice.

To illustrate this, fig. 14 is an efficiency graph showing the measured efficiency of an axial flux machine including the stator assembly of fig. 12A-12C for a range of torque and speed values typically used in many applications. The efficiency map includes a profile of constant efficiency. As can be seen, in addition to a high peak efficiency (93%), the efficiency is still high for almost all regions of the efficiency map, and even at relatively low speeds of 500rpm, with torques up to 30Nm, the efficiency is still high (over 80%).

The high efficiency that the stator assembly 1 can achieve may have many different reasons. Some of which will now be described.

First, as explained above, the nearly self-forming structure of the conductive components of the stator 10 provided by the geometry of the coils 12 allows for very precise placement of the components of the stator core. The accurate placement of the components of the core means that the coupling between the stator field and the rotor field is better and the symmetry around the stator circumference is high, which improves the generation or torque.

Another significant advantage is the production of stator fields with more accurate sinusoidal flux densities. As will be appreciated by those skilled in the art, the greater the number of slots per phase per pole in the stator, the more sinusoidal the magnetic flux density may be. The coils 12 and stator 10 described above may provide an increased number of slots per pole per phase by increasing the number of conductive elements 120 per conductive coil 12, and the number may be easily scaled up (e.g., if the radius of the stator may be increased for a particular application). One advantage of a high sinusoidal flux density is that the flux density has a relatively low harmonic content. At low harmonic contents, the coupling of the rotor field and stator field is more involved in the fundamental component of the magnetic flux density and less involved in the interaction with the harmonic component. This reduces the generation of eddy currents in the rotor magnets, which in turn reduces losses due to heating. In contrast, many known axial flux motors utilize a concentrated winding arrangement that provides only a limited number (e.g., a small number) of slots per phase per pole, which produces a more trapezoidal flux density with more significant harmonic components.

Although the coils 12 may be implemented using axially extending strips, they are preferably implemented using the axially stacked winding arrangements shown in fig. 5A-5D and 6A-6D. Although many motor manufacturers may consider this a disadvantage because it would consider reducing the fill factor in the stator core, the inventors have found that this disadvantage can be remedied by reducing skin and proximity effects that cause current to flow around the outside of the conductor cross-section and mainly the axially outside of the active section. The number of windings in the axial direction may be chosen to balance these two considerations.

Rotor

As described above, the axial-flux electric machine includes two rotors 2a and 2b disposed on opposite sides of the stator assembly 1 and attached to the shaft 3. One of the rotors 2a may be fixed to the drive end 3a of the shaft 3 and the other of the rotors 2a may be fixed to the non-drive end 3b of the shaft.

The rotors 2a, 2b are mounted on the shaft 3 such that the opposing permanent magnets have opposite poles, such that the north pole on the rotor 2a faces the south pole on the rotor 2b, and vice versa. Thus, the magnets of the two rotors 2a, 2b generate a magnetic field with axial lines of magnetic flux between the two rotors 2a, 2 b.

The rotors 2A, 2B shown in fig. 2A-2B and discussed above comprise sixteen circumferentially distributed permanent magnets 21-24 and thus sixteen poles. The structural rotors 2a, 2b may be such that the rotors 2a, 2b are formed by a rotor plate 1500 as shown in fig. 15, the rotor plate 1500 comprising flat faces 1502 (flat plates) for receiving permanent magnets. It will of course be understood that the rotor plate 1500 is identical for both rotors 2a and 2 b.

The rotor plate 1500 includes a lip 1504 on the outermost edge that protrudes from the face 1502 and is operable to improve retention of the permanent magnets 21-24. This may have the following advantageous effects: under rotation of the rotors 2a, 2b, the permanent magnets 21-24 are less likely to become dislodged from the rotors 2a, 2b, thereby improving the lifetime of the axial flux machine.

The improved fixation of the permanent magnets 21-24 on the rotor plate 1500 may also reduce the possibility that the rotors 2a, 2b of the axial flux machine may become unbalanced, which may also increase the lifetime and performance of the axial flux machine.

According to the present disclosure, the permanent magnets 21-24 may be non-segmented, that is, each permanent magnet 21-24 is formed of a single permanent magnet, rather than a plurality of permanent magnets. This reduces the complexity of the construction of the axial flux machine, which in turn may improve the ease of manufacture, lifetime and overall simplicity of the axial flux machine.

Due to the limited presence of eddy currents in the permanent magnets 21-24, the non-segmented permanent magnets 21-24 may be used in an axial flux machine according to the present disclosure. The limited presence of eddy currents in the permanent magnets 21-24 may be due to the axial flux machine being driven by a fundamental magnetic field component and less by a harmonic component. This reduces eddy currents generated in the permanent magnet, which in turn reduces losses due to heating.

The permanent magnets 21-24 may be fixed to the rotor plate 1500 by an adhesive. Alternatively, where the rotor plate 1500 is formed of ferrous metal, the permanent magnets may simply be held in place by magnetic forces generated by the permanent magnets themselves.

As discussed above with respect to fig. 2A-2B, adjacent magnets are separated by a non-magnetic spacer. Each spacer may be retained by a fastener, such as a threaded fastener. In the alternative shown in fig. 16A, such a spacer is not required. In this alternative, the rotor 1600 includes a rotor plate 1500 and a plurality of permanent magnets as described above. The permanent magnets in this example are fixed to the rotor plate by bonding them with an adhesive. It has been found that this, in combination with the magnetic force between the permanent magnets and the rotor plate, is sufficient to hold the permanent magnets in place and to maintain the spaces 1602 between adjacent magnets.

As again discussed above with respect to fig. 2A-2B, in the examples shown in fig. 2A-2B and 16A, each permanent magnet is not segmented and therefore has a single unitary body. An alternative example is shown in fig. 16B, where the rotor 1604 likewise includes a rotor plate 1500 and a plurality of substantially identical permanent magnets 1606. In the example of fig. 16B, each permanent magnet 1606 is formed of a plurality of permanent magnet segments 1608a, 1608B, 1608c, and 1608 d. The permanent magnet segments 1608a-1608d are arcuate segments that are radially stacked adjacent to one another such that the north poles are oriented in the same direction. Another alternative (not shown) is to form each segmented permanent magnet from a plurality of elongated permanent magnet segments stacked circumferentially adjacent to each other such that the north poles are oriented in the same direction.

In another alternative example (not shown) of the rotor 2a, 2b, a rotor may be provided in which the spacers are formed integrally with the rotor plate. In this example, the height of each spacer extending in the axial direction from the rotor plate is smaller than the thickness of the permanent magnet. In this way, excessive leakage flux between adjacent permanent magnets can be prevented. For example, the height of each spacer may be less than 50%, more preferably less than 20%, of the thickness of the permanent magnet.

Stator housing

Axial-flux electric machines described herein may include an extruded stator housing such that conductive coil 12 of stator assembly 1 is disposed within the housing. As can be seen in fig. 17A and 17B, the housing 1700 is generally tubular and cylindrical in shape, and has an inner face 1702 and an outer face 1704.

The exterior face may be shaped to increase the total surface area of the exterior face of the extruded shell, such as including fins 1706 or heat sinks formed therein.

As the surface area of the outer surface of the axial-flux motor is increased, extruded housing 1700 of the axial-flux motor may increase the rate at which thermal energy is dissipated from the axial-flux motor. Cooling of an axial-flux electric machine will be discussed in more detail below.

Previously proposed axial flux motor housings have employed stacked stamped plates to reduce eddy currents in the housing. As discussed above, the presence of eddy currents is limited in an axial-flux motor according to the present disclosure, and as discussed above, this may be an effect of an axial-flux motor being driven by a fundamental magnetic field component and less by a harmonic component.

The limited presence of eddy currents may enable the housing 1700 of an axial flux electric machine according to the present disclosure to be formed from extruded sections as opposed to stacked stamped plates. This in turn may lead to improved manufacturability and/or cost savings; for example, the complexity of assembly may be reduced, and thus assembly time may be reduced.

Forming housing 1700 of axial-flux electric machine as a single extruded section may also increase the structural rigidity of the axial-flux electric machine. It also reduces weight.

Additionally, the extruded housing of the axial flux electric machine includes a series of recesses on its interior face 1702 that accommodate the exterior sections of the coils 12 of the stator assembly 1 to improve heat dissipation from the coils 12. This will be discussed in more detail later.

Cooling down

As briefly described above, an extruded housing as described above may be used to improve the cooling performance of an axial-flux electric machine according to the present disclosure.

As mentioned above, the outer face of the extruded housing of the axial flux machine may be shaped to increase the total surface area of the outer face of the extruded housing, for example comprising fins or heat sinks formed therein. Therefore, it would be advantageous to maximize heat transfer from the stator assembly 1 of an axial flux machine to the extrusion housing.

Efficient cooling of an axial-flux electric machine according to the present disclosure may also be facilitated by the shape and orientation of the coils within the axial-flux machine, and in particular by the shape and orientation of the outer portions of the coils 12 at the outer edge of the stator 1. The cooling performance of an axial-flux electric machine may be improved by increasing the rate at which heat can be dissipated from coils 12 of stator 1.

In order to increase the rate at which heat energy can be dissipated from stator 1, the heat energy may advantageously be transferred into the extruded housing of the axial flux machine. For this purpose, the inner face of the extrusion casing of the axial flux machine may comprise a lip, recess or face shaped so as to be in thermal contact with the outer portion of the coil 12 of the stator 1 and thus enable heat to be transferred from the coil 12 of the stator into the extrusion casing of the axial flux machine. As mentioned above, the outer portion of each coil 12 has a surface substantially parallel to the axis of rotation, wherein the inner face of the housing comprises a complementary recess for the outer portion of each coil.

The coils 12 of the stator are encapsulated in a potting compound having a high heat transfer capability to promote efficient transfer of thermal energy from the coils 12 of the stator. Additionally, a heat transfer paste or compound may be placed between the flat section of each coil 12 and the interior face of the extruded housing to further improve heat transfer capability.

The heat energy can then be dissipated to the air by a heat sink or heat sink extruded out of the exterior face of the housing.

The extrusion housing may further comprise recesses, channels or the like to accommodate the liquid cooling arrangement therein. The liquid cooling arrangement may be used to increase the rate at which thermal energy is dissipated from the axial-flux electric machine and thus improve the cooling performance of the axial-flux electric machine. Advantageously, the recess or channel may be provided such that it is immediately adjacent to the curved portion of the outer section of the coil.

Liquid cooling (e.g., water cooling) may provide more efficient cooling performance than air cooling. This is because the specific heat capacity of water is greater than that of air, and the specific heat capacity of water is more than four times that of air.

Such a liquid cooling arrangement is shown in figure 18. The liquid cooling arrangement within the extrusion casing 1800 may, for example, include a tube 1802 formed of a material having high heat transfer properties, such as copper, and may be in contact with the extrusion casing directly, or in addition by a heat transfer paste or putty, to improve heat transfer between the extrusion casing and the tube 1802. A tube 1802 forming a liquid cooling arrangement provides an inlet 1804 and an outlet 1806 on the exterior face of the extrusion housing 1800. Another tube (not shown) is provided on the opposite face of the extrusion housing 1800 and provides a similar inlet 1808 and outlet 1810.

Cooling water is fed into the inlet 1804, 1808 of each tube and removed from the outlet 1806, 1810 of the tube. The cooling water is supplied at a reduced temperature into the inlet of the tube and may be fed out of the outlet into a radiator, heat exchanger, phase change cooler or the like before being returned to the inlet. This may be considered a cooling "loop". If the axial-flux electric machine is to be used in, for example, a vehicle, the thermal energy transferred from the axial-flux electric machine to the cooling water through the heat exchanger may be used to heat the cabin of the vehicle, or to maintain the temperature of the vehicle battery pack.

Heat sinks and/or heat sinks may be used in conjunction with the liquid cooling arrangement to maximize the rate at which heat energy is dissipated from the axial flux machine.

The cooling circuit may be a closed loop system such that cooling liquid (e.g. water) passes around a cooling channel which may form a cooling arrangement into an inlet of the cooling arrangement within the extrusion housing and out of an outlet of the cooling arrangement into a radiator, heat exchanger or the like (to transfer thermal energy from the cooling liquid into the air), or possibly via a pump to another cooling or heating system and then back into the inlet of the cooling arrangement.

Where the cooling circuit is a closed loop system and the circuit includes a radiator, the radiator may include forced cooling in the form of one or more fans to promote airflow through the radiator and improve cooling performance of the cooling circuit.

As described above, in the case of a vehicle, heat may be transferred from the cooling circuit of the axial flux machine and into, for example, the heating circuit or heater of the vehicle to maintain the temperature of the vehicle battery pack. Maintaining the temperature of the battery pack in the vehicle may improve the performance of the battery pack; the low temperature may reduce the performance of the battery pack, thereby shortening the range of the vehicle.

If the axial-flux electric machine is installed in a large vehicle, such as a bus or coach, the available space for cooling the axial-flux electric machine may be large. Thus, the cooling circuit may comprise a large radiator or heat exchanger and may provide thermal energy to a circuit that provides heating for the occupants of the vehicle. Alternatively, if the cooling circuit is a closed loop circuit, the space may be utilized for cooling by using a large radiator.

A liquid cooling arrangement may also be advantageous in the case of a mechanically stacked axial-flux electric machine as described below. For a plurality of axial-flux electric machines stacked together, air cooling may be insufficient, so, for example, the liquid-cooling arrangement of a first axial-flux electric machine in the stack may be connected to the liquid-cooling arrangement of a second axial-flux electric machine in the stack, and so on. In one example, the outlet of the liquid cooling arrangement of the first axial flux machine is connected to the inlet of the liquid cooling arrangement of the second axial flux machine in the stack.

The liquid may then pass through a cooling arrangement of both the first axial flux machine and the second axial flux machine. In an alternative example, a radiator or heat exchanger may be placed between the outlet of the cooling arrangement of the first axial flux machine and the inlet of the second axial flux machine in the stack. This may increase the cooling capacity.

In another example, the axial-flux electric machine is mechanically fixed to the controller such that the controller and the axial-flux electric machine form a single unit, and the cooling arrangement in the axial-flux electric machine is configured to cool both the axial-flux electric machine and the controller. In this example, a cooling plate may be provided between the axial-flux electric machine and the controller, the cooling plate being hollow and having an inlet and an outlet for connection to a cooling circuit or the like.

In yet another example, the axial-flux electric machine is electrically attached rather than mechanically attached to the controller. Another cooling passage may be provided in the controller and a cooling circuit that cools the axial-flux electric machine may be extended to pass coolant through the cooling passage in the controller to also cool the controller.

Mechanical stack

An advantage of the modular and yoke-less nature of the axial-flux electric machine described above is that multiple entities of the axial-flux electric machine may be stacked on a single shaft (or mechanically coupled to provide the effect of a single shaft) to form stacked axial-flux electric machine assembly 1900. One example of such an arrangement is shown in fig. 19. In this example, two substantially identical axial-flux electric machines as described herein are mechanically stacked together and mechanically coupled such that the combined torque output of the two axial-flux electric machines is provided on a single output shaft.

It will be appreciated that the stacked axial-flux motor assembly may include any number of axial-flux motors, i.e., any number of axial-flux motors may be stacked to provide a combined output on a single output shaft.

Each axial-flux motor of the stacked axial-flux motor assembly may be controlled by its own separately provided controller. Alternatively, each axial flux machine may have its own integrated controller.

Fig. 20 shows a schematic view of an alternative "stacked" axial-flux electric machine 2000. In this example, the assembly 2000 includes two stators 2002, 2004 and three rotors 2006, 2008, and 2010. Stators 2002 and 2004 are as described herein. Rotors 2006 and 2010 are also described herein. However, the rotor 2008 is provided with permanent magnets on opposite faces, and is therefore "shared" by both the stator 2002 and the stator 2004. The rotors 2006, 2008 and 2010 are disposed on a single shaft (not shown).

Laminated flux guide

As described above, the stator of an axial magnetic flux machine utilizes a plurality of flux guides distributed circumferentially around the stator, each flux guide positioned in a radially elongated space defined by circumferentially adjacent electrically conductive coils. In a broad sense, the purpose of the flux guide is to increase the flux density generated by the coil and the permanent magnet.

A magnetic flux guide according to the present embodiment will now be described with reference to fig. 21A, 21B, and 21C.

The flux guide 2100 according to the present embodiment is made of metal, which is configured to increase the axial magnetic flux density generated by the permanent magnet and the coil of the stator. Here, the magnetic flux guide is made of a laminated sheet of grain-oriented electrical steel, such as cold-rolled grain-oriented (c.r.g.o) steel. These sheets are cut to form rectangular laminations. The first set 2102 of laminates is cut to substantially the same size in all three dimensions-each having the same thickness and the same surface height and surface width. The second set 2104 of laminations are cut to have the same thickness and the same size in one of the two surface dimensions, respectively. The thickness and dimensions are the same as those of the first set 2102. However, the laminations of the second set 2104 have a progressively reduced size in the other surface dimension compared to the size of the first set of laminations in that dimension.

The laminations are then stacked in size order with the largest lamination (first set of laminations) forming the base of the stack and the smallest lamination at the top of the stack. The laminations are also arranged such that each lamination is aligned with its adjacent laminations along at least three edges, resulting in a stack that tapers in a direction of increasing surface dimension of the second set. This results in a stepped appearance of one surface of the entire stack of laminations.

In this embodiment, the stack of laminations is then wrapped in an insulating material, such as a meta-aramid polymer (meta-aramid polymer) wrap, to form a stack of laminations having a tapered shape, as best shown in fig. 21B. Electrically insulating the stack after lamination is preferred, since electrically insulating the stack after lamination provides the best performance when providing the flux guide in the stator. However, it will be appreciated that the lamination stack may not be insulated after stacking, thereby providing the flux guide 2106-in which case the lamination stack may be disposed directly in the stator.

The grains of the electrical steel are oriented in substantially a particular single direction. The individual laminations are stacked such that the grains of each lamination in the stack have the same grain direction. The stack of laminations is then positioned between adjacent coils of the stator such that the grain orientation of the stack of laminations is substantially parallel to the axis of rotation. In this way, the grain direction is aligned with the axial flux lines generated by the stator in operation. This alignment of the grains of steel serves to direct the magnetic flux generated by the circumferentially distributed electrically conductive coils and the magnetic flux generated by the permanent magnets on the rotor. This has the effect of increasing the magnetic flux density compared to the magnetic flux density produced by the coil and the permanent magnet in the absence of the flux guide.

As described above, the interval between adjacent coils increases in the radial direction. As a result, the space defined by adjacent coils tapers toward the center of the stator. The lamination stack (flux guide) thus has a tapering shape in the manner described above. In particular, the tapering of the flux guide substantially matches the variation in spacing of adjacent coils. This is done to maximize the amount of flux guide material between adjacent coils, thereby maximizing the effect of the flux guide on the flux density when the stator is in use.

Other features of the stator casing

Further examples of stator housings for use with axial-flux electric machines described herein are shown in fig. 22 and 23. As described above, the conductive coil 12 of the stator assembly 1 is provided within the stator housing 2200. Similar to the stator housing shown in fig. 17A and 17B, the housing 2200 is generally tubular and cylindrical in shape, having an inner surface 2202 and an outer surface 2204.

Also, similar to the stator housing of fig. 17A and 17B, a series of recesses 2206 are provided in the inner surface of the stator housing, which recesses accommodate the outer sections of the coils 12 of the stator assembly 1 to improve heat dissipation from the coils 12. As discussed above, the outer portion of each coil 12 has a surface that is substantially parallel to the axis of rotation. The recess 2206 forms a complementary feature for receiving this outer portion of the coil. In this way, heat transfer between the coil 12 and the stator housing 2200 is improved. In addition, the rigidity of the torque transmission and connection between the coil 12 and the stator is improved.

The coils 12 of the stator are encapsulated in a potting compound having a high heat transfer capability to promote efficient transfer of thermal energy from the coils 12 of the stator. Additionally, a heat transfer paste or compound may be placed between the flat section of each coil 12 and the interior face of the extruded housing to further improve heat transfer capability.

As can be seen, a cross-section of each recess perpendicular to the axis of rotation of the axial-flux electric machine is elongate, a major dimension of each elongate recess extending substantially in a radial direction of the axial-flux electric machine. In this example, each elongated recess has an aspect ratio of about 8.

The stator housing 2200 also includes an annular ring 2208, the annular ring 2208 configured to form an annular channel 2210 adjacent to a circumferential outer surface of the stator housing. The stator housing 2200 includes a spacer 2212 configured to separate the annular passages. The spacers 2212 extend from the first axial end of the stator housing to the second axial end of the stator housing. The spacers 2212 position the annular ring 2208 relative to the stator housing outer surface to form annular passages 2210, and partition the annular passages to form a C-shape.

The spacers 2212 include slots formed in the outer surface of the tubular body and keys formed on the inner surface of the annular ring 2208. The slots and keys engage to mechanically couple the stator housing to the annular ring. The annular ring includes a cooling fluid inlet (not shown) disposed adjacent a first side of the spacer and a cooling fluid outlet (not shown) disposed adjacent a second side of the spacer, the inlet and outlet being in fluid communication with the annular channel.

The axial ends of the stator housing 2200, annular ring 2208 and annular passage 2210 are sealed and mechanically coupled by end plates (not shown) that also house bearings for receiving the motor shaft. Recesses may be provided in the end plate to receive the end faces of the stator housing and the annular ring. The end plates are coupled to the stator housing using fasteners such as bolts (e.g., which engage threaded holes 2211).

As can be seen, the tubular body of the stator housing includes a protrusion with a threaded bore 2211 formed therein. Thus, the annular ring 2208 is shaped such that the annular passage 2210 has substantially the same width along its circumferential length. However, the width is reduced near the protrusion including the threaded hole, which may improve fluid flow through the channel. Thus, the annular ring 2208 is undulating or similarly raised in shape.

This example of the stator housing may be coupled to a cooling system as described above, and as will now be appreciated, the spacers separate the annular channels such that the flow of cooling fluid travels circumferentially around the annular channels.

In the example shown in fig. 22, the stator housing 2200 is formed by extrusion. To improve the life of the extrusion tool, the minimum thickness of any feature of the tool is maximized by forming the recess 2206 in two stages. The first set of projections 2214 or fingers are integrally formed with the tubular body of the stator housing. The second set of fingers 2216 are also formed separately by extrusion and then mechanically coupled to the stator housing 2200. The fingers 2216 include slots 2218, the slots 2218 configured to engage corresponding keys 2220 integrally formed on the inner surface 2202 of the stator housing 2200.

As can be seen, the wall thickness of the tubular body of the stator housing is similar to the wall thickness of the fingers 2214, which also improves manufacturability of the stator housing by extrusion.

An alternative stator housing 2300 is shown in fig. 23. The features of the stator housing 2300 are the same as the stator housing 2200 except that the recess 2302 is formed in a different manner.

In this example, the recesses 2302 are again formed by a first set of protrusions 2304, fingers, integrally formed with the tubular body 2306 of the stator housing. Likewise, the second set of protrusions 2308, the fingers, are formed separately and then mechanically coupled to the stator housing. In this example, the fingers 2308 include keys 2310, the keys 2310 configured to engage corresponding slots 2312 provided in the inner surface of the stator housing.

In an alternative to using extrusion, the stator housing may be formed by stacking a plurality of stamped plates. The stamped plates may be mechanically coupled together, or may be welded or brazed together, or a combination thereof.

Various embodiments having various optional features are described above. It will be appreciated that any combination of one or more optional features is possible, in addition to any mutually exclusive feature.