Laminated Winding Stator Electric Machine

Abstract

A laminated winding stator for an axial-flux electric machine configured for use with a multi-phase power source is provided. The laminated winding stator includes a first stator portion including a first plurality of conductive coils and a second stator portion including a second plurality of conductive coils. Each conductive coil of the first and second plurality of conductive coils includes at least a pair of active portions, each active portion extending in a generally radial direction substantially perpendicular to an axis of rotation of the electric machine. The first and second stator portions are axially aligned and each include a space between adjacent active portions for housing a flux guide, the space in the first stator portion being circumferentially aligned with the space in the second stator portion.

Description

[Technical field]

[0001] The present invention relates to a laminated winding stator electric machine, and in particular to a laminated winding stator assembly for a laminated wound yokeless stator axial-flux electric machine, and other components of the stator assembly. [Background technology]

[0002] Electric machines, such as electric motors and generators, are already in very widespread use. However, reliance on fossil fuels to power internal combustion engines and concerns about the pollution they cause are creating political and commercial pressures to open the use of electric machines to new applications and to expand their use in existing applications. Electric machines are increasingly being used in vehicles such as electric cars, motorcycles, boats, and aircraft. They are also used in energy generation applications, for example as generators in wind turbines.

[0003] To meet the demands of these applications, electric machines need to be designed with both suitable performance characteristics such as speed and torque, as well as high efficiency. Electric machine efficiency is critical in almost all applications, for example it can increase the range of electric vehicles while reducing the battery capacity required. Reducing the battery capacity required can further reduce the weight of the vehicle, which leads to further efficiency improvements. In addition to electrical efficiency, efficient use of materials is also a key consideration. It is preferable for electric machines to use as little material (e.g. copper) as possible, both for environmental and cost reasons, and also to reduce weight (which also helps to increase the efficiency and range of the electric machine and vehicle).

[0004] One known type of electric machine is the axial flux machine. As the name suggests, the direction of the magnetic flux lines cut during operation of an axial flux machine is parallel to the axis of rotation of the machine. This is in contrast to radial flux machines, where the direction of the magnetic flux lines cut during operation of the machine is perpendicular to the axis of rotation of the machine. Although radial flux machines are more common, axial flux machines have been used in some applications where their form factor (relatively small in the axial direction) and performance characteristics (such as high torque-to-weight ratio) are appreciated.

[0005] An example of a yokeless axial-flux machine is described in US Pat. No. 5,399,633. This document discloses a conductive coil of a yokeless axial-flux electric machine stator having distributed windings, a stator including a plurality of such coils, a yokeless axial-flux electric machine including such a stator, and a method of manufacturing the stator. The conductive coil includes a first active section and a second active section, each of which includes a plurality of winding turn portions extending in a generally radial direction substantially perpendicular to the axis of rotation of the electric machine and stacked parallel to the axis of rotation such that a cross section perpendicular to the radial direction of each active section is elongated with a long dimension parallel to the axis of rotation. The second active section is circumferentially spaced and axially offset from the first active section. This document also describes an example of a laminated winding stator with two stator sections developed by the present inventors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] British Patent No. 2580918 Specification Summary of the Invention [Means for solving the problem]

[0007] The embodiments described herein provide conductive coils and stators for axial flux machines with multiple conductive coils that improve mechanical efficiency, ease of manufacture, and provide good thermal conduction from the coils to the stator housing to aid in cooling.

[0008] In this disclosure, unless otherwise specified, terms such as "radial," "axial," "circumferential," and "angular" are used with respect to a cylindrical polar coordinate system (r, θ, z) in which the direction of the axis of rotation of the electric machine is parallel to the z-axis. That is, "axial" means parallel to the axis of rotation (i.e., along the z-axis), "radial" means any direction perpendicular to the axis of rotation, "angle" is the azimuthal angle θ, and "circumferential" refers to the azimuthal direction about the axis of rotation.

[0009] Terms such as "radially extending" and "axially extending" should not be understood to imply that a feature must be exactly radial or exactly axially parallel. For example, it is known that the Lorentz force experienced by a current carrying conductor in a magnetic field is greatest when the direction of the current is exactly perpendicular to the direction of the magnetic flux, but a current carrying conductor may also experience the Lorentz force at angles less than 90°. Thus, deviations from the parallel and perpendicular orientations do not change the underlying principles of operation.

[0010] The invention is defined in the independent claims referred to below. Preferred features are set out in the dependent claims.

[0011] According to a first aspect of the present invention, there is provided a laminated winding stator for an axial-flux electric machine configured for use with a multi-phase power source, the laminated winding stator comprising a first stator portion including a first plurality of conductive coils and a second stator portion including a second plurality of conductive coils, each conductive coil of the first and second plurality of conductive coils including at least a pair of active parts, each active part extending in a generally radial direction substantially perpendicular to a rotational axis of the electric machine, the first and second stator portions being axially aligned and each including a space between adjacent active parts for housing a flux guide, the spaces of the first stator portion being circumferentially aligned with the spaces of the second stator portion, and each conductive coil of the first plurality of conductive coils being electrically connected to a corresponding conductive coil of the second plurality of conductive coils to form a set of conductive coils.

[0012] Utilizing two stator parts instead of one large stator reduces the amount of winding material required, and therefore the weight of the electric machine, without reducing the power output of the electric machine, because less material is needed to connect the active parts for a given (total) cross-sectional area of ​​the active parts with two stator parts compared to one large stator (i.e. the active parts of both stator parts combined compared to the large stator).

[0013] The circumferentially aligned spaces in the first and second stator parts may be configured to accommodate a common flux guide. The conductive coils of such a stator form a structure in which a flux guide, such as a lamination pack, can be placed. This reduces the number of components that need to be assembled (compared to when both stator parts have their own flux guides) and allows the stator to be manufactured quickly and with high precision, improving the efficiency of the electric machine. In particular, this is achieved by means of aligning the two stator parts in the form of a common flux guide. Furthermore, the number of flux guides and correspondingly the number of slots per pole per phase of the stator can be easily increased, which can be easily varied according to the radius of the electric machine. Increasing the number of slots per pole per phase allows the circumferential spatial flux density in the stator and the two machine air gaps to be more sinusoidal with low harmonic distortion. With sinusoidally varying phase currents, the average torque generated by the electric machine is derived more from the interaction of the fundamental magnetic field components and less from harmonic components. This is advantageous because high eddy currents in the rotor permanent magnets due to harmonic components in the circumferential spatial flux density lead to high losses and increased heating. Furthermore, additional harmonic components in the winding magnetomotive force distribution can lead to increased losses in the flux guides.

[0014] A flux guide, such as a lamination pack, which may include grain oriented electrical steel sheets surrounded by electrical insulation, may be positioned within each aligned space set. The flux guides pass magnetic flux axially between corresponding poles of the opposing rotors. These flux guides may have high magnetic permeability, at least in the axial direction, thereby increasing the magnetic flux density of the stator for certain arrangements of permanent magnets.

[0015] Optionally, the active portions of each active portion pair are circumferentially spaced apart and circumferentially adjacent conductive coils overlap circumferentially.

[0016] Optionally, the spaces include a first type of spaces, each space of the first type being a circumferential space between two adjacent active portions of two different conductive coils.

[0017] Optionally, each conductive coil includes a plurality of pairs of active parts connected in series with each other, adjacent pairs of active parts overlapping in the circumferential direction, and the spaces include a second type of space, each space of the second type being a circumferential space between two adjacent active parts of the same conductive coil but different pairs of active parts of that conductive coil. The circumferential spaces may extend substantially radially and be radially elongated, as may the active parts defining the circumferential space. Each additional pair of active parts per coil per stator section increases the number of slots per pole per phase by one, thereby reducing losses and thus improving efficiency. Advantageously, the number of active parts per coil may be varied according to the radius of the machine.

[0018] The number of active pairs can be an integer multiple of 2. Using an integer multiple of 2 makes it easier to fabricate each coil from multiple identical conductive elements, reducing manufacturing costs.

[0019] The pairs of active parts of each conductive coil may be integrally formed or may be formed by connecting in series a number of separate elements, each of which includes a pair of active parts. The connection may be made, for example, with ferrules, by brazing, or by welding. The separate elements may be formed by winding, joining, and shaping the conductors, which may be done using known winding techniques, which are relatively inexpensive to implement. Integral formation of elements may be expensive, but may also allow for more complex coil topologies that are not or are difficult to achieve with normal winding techniques. Furthermore, integrally formed elements reduce the number of components of the stator.

[0020] In use, current can flow in the same direction along adjacent active parts that are separated by one of the second type of spaces, thereby preventing current flowing through those adjacent active parts from having an adverse effect on torque production.

[0021] Optionally, in use, current flows in radially opposite directions along the active portions of each active portion pair of each conductive coil. This may be achieved by having the first and second generally radially extending active portion winding turn portions have proximal ends positioned at an inner radius and distal ends positioned at an outer radius. The proximal ends of the winding turn portions may be connected by an inner loop portion and the distal ends may be connected by an outer loop portion such that in use, current flows in radially opposite directions along the radially extending active portion pair.

[0022] The outer loop portion may be configured to form an outer portion of the coil that is substantially parallel to the axis of rotation. The ability to axially insert the axially parallel portion of the coil into an opening in the stator housing improves ease of stator manufacture. Additionally, the flared nature of that portion of the coil provides a greater surface area for mechanical locking of the coil and cooling at the periphery of the stator. As previously mentioned, the use of two stator portions rather than a single large stator with the same total cross-sectional area of ​​the active portion reduces the cost and weight of the electric machine by reducing the amount of material required to form the outer loop portion.

[0023] Each outer loop portion may have any shape, but is preferably substantially semicircular or rectangular, such that the outer portion of the coil is a semidisk-shaped or rectangular surface. The surfaces may also be curved, for example involute shaped. These surfaces provide a large surface area, but also require a relatively limited conductor length for a given axial extent of the coil, thereby reducing material costs.

[0024] The outer loop portion may be configured to form a substantially involute portion of the coil, which maintains a substantially constant gap between adjacent conductive elements, resulting in a radially interlocking arrangement of the 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 portions.

[0025] The inner loop portion may be configured to form an inner portion of the coil that is substantially parallel to the axis of rotation. Because it is substantially parallel to the axis of rotation, the inner portion occupies a minimal amount of circumferential space. This is important because there is limited physical space at the inner radius of the stator compared to the outer radius.

[0026] The inner loop portion may have any shape, but preferably may be substantially semicircular or rectangular, such that the inner portion has a semidisk-like or rectangular surface. The surface may also be curved, for example an involute shape. These shapes reduce material costs by requiring a relatively limited conductor length to implement.

[0027] The inner loop portion may be configured to form a substantially involute portion of the coil, which results in a radially interlocking arrangement of the circumferentially distributed coils. There may be two substantially involute inner portions of the coil connecting the inner portion of the coil to the two active portions.

[0028] Optionally, the active parts of each active part pair may be axially offset from one another. Axially offsetting the active parts facilitates axial and circumferential coil stacking, allowing for span (pitch) freedom between each active part pair, and also improves the structural rigidity of the complete winding due to coil intermeshing.

[0029] Optionally, each active part may include multiple axially and / or circumferentially stacked winding turn portions. Axial stacking of the winding turns, preferably insulated winding turns, reduces skin and proximity effects in the active parts, since the cross section of each winding turn is smaller and, assuming the winding turns are connected in series, the current is deterministically controlled to flow over the entire axial length of each active part. This reduces heating as the current is spread more evenly over the conductive cross section.

[0030] Optionally, each active part may be one winding turn wide. Alternatively, each active part may be multiple winding turns wide. That is, each active part may include multiple circumferentially stacked winding turn portions. When each active part includes multiple circumferentially stacked winding turn portions, it is preferred that the number of circumferentially stacked winding turn portions is less than the number of axially stacked winding turn portions, and the major dimension of the cross section of the coil perpendicular to the radial direction of the active part is parallel to the axis of rotation. For example, the active part may be only two winding turn portions wide, but may include three or more 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 3 or more, preferably 5 or more, more preferably 7 or more. A coil that is larger than one winding turn wide increases the overall length of the conductor, which further increases the impedance of the coil. A higher impedance may allow the use of a controller with a lower switching speed, which may potentially reduce costs.

[0031] Optionally, the active portions of each conductive coil for each conductive coil set are circumferentially aligned with one another.

[0032] Optionally, each active portion of each conductive coil for each conductive coil set is circumferentially offset from one another by an integer number of spaces.

[0033] Optionally, in the case of an N-phase power supply, each conductive coil in each conductive coil set is connected to the same phase.

[0034] In this case, the laminated winding stator may include multiple poles, with each pole including an integer M multiple of the N sets of conductive coils, with M sets of conductive coils per phase.

[0035] Optionally, for each conductive coil set, a conductive coil of the first plurality of conductive coils is connected in series to a conductive coil of the second plurality of conductive coils by a connector.

[0036] When the conductive coil sets are connected by connectors in this manner, the laminated winding stator may further comprise a first busbar arrangement and a second busbar arrangement, the first busbar arrangement including a first busbar and star connection for each phase and the second busbar arrangement including a second busbar for each phase. For each of the N phases, each conductive coil from the first plurality of conductive coils of the first conductive coil set of a first pole may be connected to the first busbar for that phase, each conductive coil from the first plurality of conductive coils of the last conductive coil set of a last pole may be connected to the star connection of the first busbar arrangement, and each conductive coil from the second plurality of conductive coils may be connected to the second busbar for that phase, thereby forming a current path from the first pole to the last pole through the conductive coil set and second busbar for that phase.

[0037] Additionally, a first busbar arrangement can be located at a first axial end of the laminated winding stator, and a second busbar arrangement can be located at a second axial end of the laminated winding stator. Positioning the busbar arrangements at the first and second ends (e.g., above and / or below the coils) allows for easy connection of the coils to the busbar arrangements, and also means that the connections may be accessible even after the stator assembly is impregnated with resin or otherwise encapsulated (such as by high pressure plastic encapsulation or overmolding processes). This prevents a poor connection from rendering the entire stator unusable.

[0038] For each phase, the second busbar of the second busbar configuration may also include a number of second busbar sections configured to connect each conductive coil set of that phase in series to form a current path from the first pole to the last pole.

[0039] The first busbar arrangement can be axially adjacent to the first stator portion in a first direction along the axis of the laminated winding stator, and similarly, the second busbar arrangement can be axially adjacent to the second stator portion in a second direction opposite the first direction along the axis of the laminated winding stator.

[0040] As an alternative to connecting the conductive coils of each set in series, they may be connected in parallel, i.e., for each conductive coil pair, a conductive coil of the first plurality of conductive coils may be connected in parallel to a conductive coil of the second plurality of conductive coils by one or more connectors.

[0041] According to a second aspect of the present invention there is provided an electric machine configured for use with a polyphase power source, the electric machine comprising a laminated winding stator of the first aspect of the present invention (including any suitable combination of the additional features discussed above), a first rotor portion disposed at a first axial end of the laminated winding stator, and a second rotor portion disposed at a second axial end of the laminated winding stator.

[0042] Optionally, a third rotor portion is axially disposed between the first stator portion and the second stator portion.

[0043] Optionally, each rotor section includes a number of magnetic poles equal to the number of poles of the laminated winding stator. The angle separating the active parts of each pair may be different from the pole pitch of the electric machine defined by the permanent magnets. The angle separating the active parts of each pair may be the same as the pole pitch, but using a different angle facilitates long or short pitch winding of the windings. The angle separating the active parts of each pair may be less than the pole pitch. Using a smaller angle allows single pitch winding, which can be used to further reduce harmonics in the stator magnetic field.

[0044] Each of the magnetic poles may include one or more permanent magnets, which are arranged such that circumferentially adjacent magnetic poles have opposite polarities.

[0045] Corresponding poles of opposing rotors may face each other, in which case they may be circumferentially aligned. Alternatively, they may be circumferentially offset. A circumferential offset between the rotors may reduce cogging torque.

[0046] If corresponding poles of opposing rotors are circumferentially offset, the circumferential offset may be an angle equal to half the angle between circumferentially adjacent spaces.

[0047] The poles may occupy an annular sector about the axis of rotation of the rotor or have a generally annular sector shape. In some cases, especially when the shape is generally annular sector, the edges of the poles may be distorted so that they are not radial. In this case, the edges of the poles may not be aligned with the edges of the flux guides.

[0048] According to a third aspect of the present invention, there is provided a conductive coil for use in a first stator portion of a laminated wound stator of the first aspect of the present invention (including any suitable combination of the additional features discussed above in relation to the first aspect), the conductive coil comprising at least a pair of active portions, a first terminal portion and a second terminal portion, the first terminal portion configured to extend axially in a first direction for connection to a first busbar arrangement, the second terminal portion configured to extend axially in a second direction for connection to a connector, and the second terminal portion having an extension portion configured to extend in the second direction beyond the second stator portion.

[0049] According to a fourth aspect of the present invention, there is provided a conductive coil for use in a second stator portion of the laminated winding stator of the first aspect, when the coils of each conductive coil set are connected in series and when the laminated winding stator comprises first and second busbar arrangements, the conductive coil comprising at least a pair of active portions, a first terminal portion and a second terminal portion, the first terminal portion configured to extend axially in a second direction for connection to the second busbar arrangement and the second terminal portion configured to extend axially in the second direction for connection to a connector.

[0050] The terminal portions may extend substantially parallel to the axis of rotation of the electric machine. Parallel extending connection portions allow a very simple connection of the coil to the connection means.

[0051] Any feature of one aspect of the present disclosure may be applied to any other aspect of the present disclosure in any suitable combination. In particular, method aspects may be applied 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.

[0052] It is also to be understood that specific combinations of the various features described and defined in any aspect of the present disclosure can be implemented and / or provided and / or used independently.

[0053] Embodiments of the invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0054] [Figure 1] 1 is a side view of an electric machine according to an embodiment of the present invention; [Diagram 2] 1 is a side view of an electric machine according to an embodiment of the present invention; [Figure 3A] FIG. 2 is a perspective view of the rotor and shaft of the axial flux machine of FIG. 1. [Figure 3B] FIG. 2B is a plan view of one rotor of the axial-flux machine of FIGS. 1A and 2A, showing more clearly the permanent magnets of the rotor. [Figure 4] FIG. 2 is a plan view of a stator according to an aspect of the present invention. [Figure 5A] 1A and 1B show top and bottom views of a single conductive coil element having a pair of radially extending active portions. [Figure 5B] 5B shows two perspective views of the conductive coil element of FIG. 5A. [Figure 5C] 5A and 5B show two side views of the conductive coil element of FIG. 5B. [Figure 5D] 5A-5C depict front and rear views of the conductive coil element. [Figure 5E] FIG. 5B 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, illustrating the spacing resulting from the overlap. [Figure 5F] FIG. 5F is a plan view showing the stator of FIG. 5E. [Figure 5G] 1 is a plan view of a conductive element illustrating how the conductive element may be wound onto a flat surface. [Figure 5H] FIG. 5C is a side view of the conductive element shown in FIG. 5G. [Figure 5I] FIG. 5C is a perspective view of the conductive element shown in FIGS. 5G and 5H. [Figure 6A] 1A and 1B show top and bottom views of a conductive coil including two pairs of circumferentially overlapping, radially extending active portions connected in series. [Figure 6B] 6B shows two perspective views of the conductive coil of FIG. 6A. [Figure 6C] 6A and 6B show two side views of the conductive coil pair of FIG. 6A and FIG. 6B. [Figure 6D] 6A-6C depict front and rear views of the conductive coil. [Figure 7A] 4 illustrates a connection pattern of a stator according to an aspect of the present invention. [Figure 7B] 4 illustrates a connection pattern of a stator according to an aspect of the present invention. [Figure 7C] 4 illustrates a portion of a stator connection pattern according to an aspect of the present invention. [Figure 7D] 4 illustrates an alternative connection pattern for a stator according to an aspect of the present invention. [Figure 8A] 1 illustrates a coil according to an embodiment of the present invention. [Figure 8B] 1 illustrates a coil according to an embodiment of the present invention. [Figure 8C] 1 illustrates a coil according to an embodiment of the present invention. [Figure 8D] 1 illustrates yet another coil according to an aspect of the present invention. [Figure 8E] 1 illustrates yet another coil according to an aspect of the present invention. [Figure 8F] 1 illustrates yet another coil according to an aspect of the present invention. [Figure 8G] 8A to 8C and the coils in FIGS. 8D to 8E are shown. [Figure 8H] 8A to 8C and the coils in FIGS. 8D to 8E are shown. [Figure 9] 1 illustrates the material savings obtained by embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Like reference numbers are used throughout the description and figures to refer to like elements.

[0056] An embodiment of the present disclosure will now be described with reference to an axial-flux motor 100. Although motor 100 is described, it should be understood that the present disclosure may be practiced with other types of axial-flux electric machines, such as generators, as well.

[0057] Axial Flux Machine Overview 1 shows the main components of an axial-flux motor 100. The axial-flux motor 100 includes a stator assembly 1 (also referred to as a laminated winding stator 1 or simply stator 1), two rotors 2a, 2b arranged on either side of the stator assembly 1, and a rotation axis 3. The laminated winding stator 1 includes a first stator portion 1a and a second stator portion 1b. The first stator portion 1a and the second stator portion 1b are axially aligned (i.e. the rotation axis 3 is also the common axis of both stator portions 1a, 1b).

[0058] The first stator portion 1a includes a first plurality of conductive coils and the second stator portion 1b includes a second plurality of conductive coils. As will be described in more detail below, each conductive coil 12 of both the first and second plurality of conductive coils includes at least a pair of active portions. Each active portion extends in a generally radial direction substantially perpendicular to the axis of rotation 3 of the electric machine 100. Each stator portion 1a, 1b includes spaces between adjacent active portions that house flux guides. The spaces of the first stator portion 1a are circumferentially aligned with the spaces of the second stator portion 1b.

[0059] In practice there will typically be a shaft along axis 3, which typically includes a drive end and a non-drive end. The rotors 2a, 2b are fixedly mounted to the shaft. In use, the stator 1 of the axial flux motor 100 remains stationary and the rotors 2a, 2b and the shaft rotate together relative to the stator 1. It will be appreciated that various components typically present in the motor 100, such as rotor cover plates and means for connecting the stator to a power source, have been omitted from Figure 1 for the sake of clarity.

[0060] Figure 2 shows yet another embodiment of an electric machine 200 in which a third rotor 2c is disposed between the first stator portion 1a and the second stator portion 1b. However, it can be seen that in other respects the electric machine 200 is substantially similar to the electric machine 100 shown in Figure 1.

[0061] 3A and 3B show rotors 2a, 2b and shafts 3a, 3b arranged along a rotational axis 3 of a motor 100 (without a stator assembly 1). As is particularly clear from FIG. 3B, each rotor 2a, 2b includes 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.

[0062] Although not visible in Figures 3A and 3B, the rotors 2a, 2b are mounted such that opposing permanent magnets have opposite polarity, i.e., the north pole of rotor 2a faces the south pole of rotor 2b and vice versa. As a result, the magnets of the two rotors 2a, 2b generate a magnetic field with axial magnetic flux lines between the two rotors 2a, 2b.

[0063] As will be appreciated by those skilled in the art, the stator assembly 1 described herein is yokeless but not ironless. A yoke is an additional structural element present in some stators to guide the magnetic flux lines between the opposing poles of the rotor magnetic field. That is, the yoke completes the magnetic circuit within the stator. The axial flux machine 100 described herein utilizes a pair of opposing rotors 2a, 2b with opposing permanent magnets having opposite polarities, and therefore does not require a yoke to complete the magnetic circuit since the magnetic flux is unidirectional. Having a yokeless stator reduces the overall weight of the axial flux machine, which is highly beneficial in many practical applications. Additionally, efficiency is improved since there are no losses due to changes in magnetic flux density in the yoke area.

[0064] The circumferential (angular) separation α 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 can be less than or equal to the pole pitch α of the motor 100. In Figs. 3A, 3B, adjacent magnets are separated by non-magnetic spacers, 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 the circumferential spatial harmonic distortion of the permanent magnet flux density of the stator 1. As will be appreciated, it is not necessary to provide a non-magnetic spacer so that the span β of the permanent magnets 21-24 can be less than the pole pitch α of the motor 100. For example, the permanent magnets 21-24 can be attached to the rotor with an adhesive or the like at their required spacing.

[0065] The rotors 2a, 2b shown in Figures 3A, 3B have 16 circumferentially distributed permanent magnets 21-24 and therefore 16 poles. However, this is merely an example and in practice there may be more or less than 16 poles, to some extent depending on the intended application. For example, the poles are usually present in pairs (so there is usually an even number of poles) and the number of poles is limited to some extent by the radius of the rotors 2a, 2b, which varies depending on the size of the motor suitable for the intended application. The rotors 2a, 2b may have, for example, 8 to 32 poles.

[0066] Conductive Coil and Stator We now describe the conductive components 10, including the conductive coils 12, of the stator assembly 1. Although specific examples of particular numbers of stator poles 11, conductive coils 12, and current phases are described, it should be understood that this is not intended to limit the scope of the claims.

[0067] The core of the stator assembly 1, where axial magnetic flux provided by the rotor magnets interacts with current flowing radially through the conductive component 10 to generate torque that rotates the rotors 2a, 2b, includes the radially extending active portions of the stator conductive component 10 and flux guides, in this example in the form of lamination packs. The flux guides, in the form of lamination packs which may include grain oriented electrical steel sheets surrounded by electrical insulation, are positioned in the spaces between the radially extending active portions of the core conductive component 10. The flux guides, in the form of lamination packs, serve to pass the magnetic flux generated by the permanent magnets (e.g. 21-24) between the current carrying conductors.

[0068] With reference to Figure 4, a conductive component 10 forming the stator portions 1a, 1b (hereafter simply referred to as "stator portion 10") is shown without a stator housing or a flux guide in the form of a lamination pack. As can be seen from the top view of Figure 4, the stator portion 10 has a distributed winding and comprises a number (in this case 16) circumferentially distributed stator poles 11a, 11b, ..., 11p, each of which includes a number of conductive coils 12. Each conductive coil 12 is connected to one phase of a polyphase power supply via connection means 15, which in this example takes the form of a busbar. In this particular example, the stator portion 10 is configured for use with a three-phase power supply, so that there are three conductive coils 12 per stator pole 11a-11p.

[0069] With 16 poles 11a-11p and three conductive coils 12 per pole, it will be appreciated that the stator portion 10 of FIG. 4 has a total of 48 circumferentially distributed conductive coils 12. However, from the top view of FIG. 4, it can be seen that this stator portion 10 actually has 96 radially extending active portions. Furthermore, not visible in the plan view of FIG. 4, but as will become apparent from subsequent figures, there are two axially offset layers of radially extending active portions, resulting in a total of 192 radially extending active portions. The reason for this will become apparent from the description of FIGS. 5-9. In summary, each conductive coil 12 includes one or more conductive elements 120, each of which includes a pair of axially offset radially extending active portions. Each conductive coil 12 of the stator portion 10 of FIG. 4 includes two such conductive elements 120, with each conductive element 120 including a pair of axially offset radially extending portions, resulting in a total of 192 radially extending active portions.

[0070] The conductive components of the stator portion 10 may be made of any combination of one or more conductive materials, however, it is preferred that the conductive components 10 are made of copper.

[0071] Figures 5A-5D show various views of a single conductive element 120. As noted above and described in more detail below, each conductive coil 12 is composed of one or more conductive elements 120. It will be understood that in the case of one conductive element 120 per conductive coil 12, the conductive coil 12 and the conductive element 120 are equivalent. Figures 6A-6D show a conductive coil 12 composed of two conductive elements 120 and 120', as described below.

[0072] 5A-5D, as best seen in the top view of FIG. 5A, in which the axis of rotation is perpendicular to the page, conductive element 120 includes a pair of circumferentially spaced apart, radially extending active conductive portions 121a, 121b. These radially extending active portions 121a, 121b are referred to as "active" portions because they are located within the stator core to interact with the magnetic field provided by the magnets of rotors 2a, 2b when conductive coil 12 is positioned in the stator. It will be appreciated that because the active portions extend in a generally radial direction that is generally perpendicular to the axial magnetic flux of the core, the flux linkage is at least close to a maximum.

[0073] The angle γ that separates the two active parts 121a, 121b is called the coil span. The coil span may be the same as the pole pitch α (defined as the angle between the centers of the permanent magnets of the rotor) or may be different (smaller or larger). 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 less than α, a fractional pitch winding of the windings can be implemented, which reduces the space harmonic content of the winding magnetomotive force (mmf).

[0074] 5E and 5F, these show a 16-pole, 3-phase stator portion 10', which is similar to the stator portion 10 of FIG. 4, except that each coil 12 of the stator portion 10' has only one conductive element 120 (a pair of active portions 121a, 121b). That is, in FIG. 5E and 5F, the coils 12 and conductive elements 120 are identical. Like the stator portion 10, the conductive coils 120a, 120b, 120c of the stator portion 10' are distributed circumferentially around the stator, with circumferentially adjacent coils overlapping circumferentially.

[0075] As is particularly clear from FIG. 5E, the circumferential overlap of the coils 120a, 120b, 120c defines circumferential spaces between the active parts of the coils. These radially elongated circumferential spaces can accommodate flux guides. The spaces labeled 141a, 141b, 141c, etc., are referred to as spaces of a first type. Thus, the spaces of the first type 141a, 141b, 141c are defined between the active parts of the different coils. For example, the space 141b is between one of the two active parts of the coil 120a and one of the two active parts of the coil 120c. However, it should be understood that the two coils that define a particular space 141a, 141b, 141c of the first type may vary depending on various factors, including the number of phases per stator pole, the number of poles, and the selected coil span γ.

[0076] Returning now to Figures 5A-5D, as can be seen from Figures 5B and 5D, the two active parts 121a, 121b are axially offset from one another. This facilitates circumferential stacking of the conductive coils 12, and also facilitates circumferential stacking of the conductive elements 120 when there are multiple conductive elements 120 per conductive coil 12. This allows for more stator poles and more slots per pole per phase, both of which can improve efficiency. Additionally, the windings can be easily wound with short pitch.

[0077] As can be seen in each of Figures 5B, 5C, and 5D, each conductive element 120 is formed from a single continuous length of wound conductor. The outermost turn of this length of conductor terminates in a first terminal portion 128, referred to as the outer tail 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 source, as will be described in more detail below. The innermost winding turn portion terminates in a second terminal portion 129, referred to as the inner tail 129.

[0078] As can also be seen in each of Figures 5B, 5C, and 5D, the length of conductor forming conductive element 120 is wound such that there are a number of winding turn portions 131a, 131b stacked parallel to the axis of rotation of the electric machine. A cross section of conductive element 120 taken perpendicular to the radial direction of each active portion 121a, 121b is elongated with the long dimension parallel to the axis of rotation. In the example of Figures 5A-5D, there are 14 axially stacked winding turn portions 131a, 131b, although other numbers are possible and this is not intended to limit the disclosure.

[0079] Figures 5G, 5H, and 5I show how the conductive element 120 can be formed by winding a single conductor. As shown in Figure 5G, the conductor is wound in a single plane around a pair of support elements 301, 302 (projecting perpendicularly out of the page) to form a flat, planar winding of multiple (in this case 14) turns or layers. The flatness of the winding is best seen in Figures 5H and 5I. The innermost turn terminates in an inner tail 129 and the outermost turn terminates in an outer tail 128.

[0080] Once the flat windings shown in Figures 5G-5I are formed, the three-dimensional shape of the conductive element 120 is formed by bending or deforming the flat windings into the shapes shown in Figures 5A-5D. The bending can be performed using a bending tool as known in the art. For example, a bending tool having an axially offset inner male profile block can be pressed against an outer female block to bend the flat windings such that the active portions are axially offset from one another. The outer tails 128 and inner tails 129 can be bent separately as desired.

[0081] To facilitate the bending process, the flat windings may be initially reinforced so that the windings maintain their shape during bending. In one example, the conductor has a heat or solvent activated outer bonding layer to bond the turns / layers together after winding and allow them to maintain their shape.

[0082] 5G-5I, it should be understood that the conductive element 120 can be wound in a variety of different ways and that the disclosure is not intended to be limited to the particular windings shown. - The windings in FIG. 5G are wound counterclockwise around the support elements 301, 302, however it is also possible to wind a single conductor in a clockwise direction. - The outermost turn of the winding is terminated, but not necessarily, such that the outer tail 128 leads to the active part 121a, 121b of the conductive element 120. The outer turn may terminate at any point on the turn, for example the outer tail 128 may lead to a loop part of the turn rather than to an active part. Although 14 axially stacked winding turns are shown in FIG. 5, there may be more or less than 14 turns. - the thickness of the winding is 1 turn / layer (see in particular FIG. 5H), but may be 2 turns / layer or more thick. In this case, each conductive element 120 will include a number of circumferentially stacked winding turn portions. Any number of circumferentially stacked winding turn portions is possible, but preferably less than the number of axially stacked winding turn portions, so that the cross section of the conductive element 120 perpendicular to the radial direction of each active part 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 can be 4 or more, preferably 6 or more.

[0083] As can be seen above, in use, current flows in opposite directions (i.e. inwards and outwards parallel to the radial expansion direction) along the two active parts 121a, 121b of the conductive element 120. The reversal of the current direction is obtained by the outer loop parts 122 of the winding turn portions 131a, 131b and the inner loop parts 125 of the winding turn portions 131a, 131b. Each of the outer loop parts 122 includes a first portion 123 and a pair of second portions 124a, 124b (one for each of the pair of active parts 121a, 121b) connecting the active parts 121a, 121b to the first portion 123. Similarly, each of the inner loop portions 125 includes a first portion 126 and a pair of second portions 127a, 127b (one for each of the pair of active portions 121a, 121b) connecting the active portions 121a, 121b to the first portion 126.

[0084] As can be seen in Figures 5B, 5C, and 5D, the outer first portions 123 together form an outer portion 133 of the coil element 120 having a surface substantially parallel to the axis of rotation. In the particular example of Figures 5A-5D, the outer first portions 123 are substantially semicircular, such that the outer portion 133 is a substantially flat semicircular plate 133, although other shapes are possible. For example, each of the outer first portions 123 may have a shape corresponding to three sides of a rectangle, such that together they form the 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 portions 123 need not be flat or planar.

[0085] The surface 133 formed by the outer first portion 123 can be used to facilitate cooling through a relatively large surface area. Additionally, because the outer portion 133 of the coil 120 is substantially parallel to the axis of rotation, the stator housing can be provided with axially extending openings that axially receive the outer portions 133 of the coil elements 120', 120'', providing mechanical locking and improved cooling.

[0086] The inner first portion 126 together form the inner portion 136 of the coil element 120. The inner portion 136 shown in Figures 5B-5D is substantially similar to the outer portion 133 described above, may be parallel to the axis of rotation like the outer portion 133 described above, and may be of various shapes and profiles. However, because the inner portion 136 generally plays a lesser role in cooling and lamination of the coil 12, the inner portion 126 may be configured to reduce the total amount of conductor per conductive element 120 to reduce costs.

[0087] Regarding the outer second portions 124a, 124b and the inner second portions 127a, 127b, they appear substantially straight in Fig. 5A-5D, but are actually slightly curved. In particular, the shape of each of the outer first portions 124a, 124b is a part of a first involute, so that the first portions 124a, 124b together form the outer substantially involute portions 134a, 134b of the coil element 120. Similarly, the shape of each of the inner second portions 127a, 127b is a part of a second involute, so that the first portions 127a, 127b together form the inner substantially involute portions 137a, 137b of the coil element 120. The significance of the involute will be explained with reference to Figs. 6A-6D.

[0088] Although the conductive element 120 has been described above as being formed by winding a length of conductor, this is not required and the conductive element 120 can be manufactured in other ways, including being integrally formed.

[0089] Additionally, while the illustrated elements 120 are wound from a single conductor and include stacks of winding turn portions 131a, 131b, this is preferred but not required. For example, rather than an axially extending stack of winding turn portions 131a, 131b, each conductive element 120 can be formed from a single axially extending conductive strip. In some cases, a single axially extending conductive strip may be preferred over multiple axially stacked winding turn portions 131a, 131b, but as described below, the use of stacked winding turn portions 131a, 131b can advantageously help reduce skin and proximity effects that can lead to increased losses.

[0090] As noted above, each conductive coil 12 may include only one conductive element 120. However, for reasons described in more detail below, each conductive element preferably includes two or more circumferentially overlapping conductive elements. An example of a conductive coil including two circumferentially overlapping conductive elements 120, 120' will now be described with reference to Figures 6A-6D.

[0091] 6A shows top and bottom views of a conductive coil 12 including two conductive elements 120, 120'. The features of each of the two conductive elements 120, 120' are the same as those of the single conductive element 120 described above with reference to Figures 5A-5D, and therefore these features will not be described again.

[0092] To form the conductive coil 12, two identical conductive elements 120, 120' are electrically connected in series with each other at their inner tails 129, 129'. In the example shown here, the inner tails 129, 129' are connected using a ferrule 130. However, there are other ways to connect 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 perpendicular to the plane of the paper in 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 can be more easily connected to the ferrule 130. Alternatively, the conductive coil 120 including the two conductive elements can be integrally formed as a single piece.

[0093] The resulting conductive coil 12 has two circumferentially overlapping, spaced apart pairs of active parts 121a, 121b; 121a', 121b'. In particular, the overlap of the two pairs of active parts defines two spaces 142a, 142b. The first space 142a is defined between one (first) active part 121a of the first conductive element 120 of the coil 12 and one (first) active part 121a' of the second conductive element 120' of the coil 12. The second space 142b is defined between the other (second) active part 121b of the first conductive element 120 of the coil 12 and the other (second) active part 121b' of the second conductive element 120' of the coil 12. That is, the two spaces 142a, 142b are circumferential spaces between adjacent active parts 121a, 121a'; 121b, 121b' of two different active part pairs 121a, 121b; 121a', 121b' of the same coil 12. This type of space is referred to as the second type of space. Like the first type of space, the second type of space 142a, 142b provides space for flux guides such as lamination packs. This makes the stator assembly 1 easier to manufacture and also increases the number of slots per pole per phase of the stator assembly 1, thereby increasing the efficiency of the motor.

[0094] Although a first type of spaces 141a-141c (i.e., spaces defined between active portions of different coils) and a second type of spaces 142a, 142b (i.e., spaces defined between active portions of the same coil but different pairs) have been described, it should be noted that the first and second type of spaces may coincide if multiple coils 120 defining the second type of spaces are provided in the stator portion 10 to define the first type of spaces. Whether the first and second type of spaces coincide may depend on several factors, including the selected coil span γ, the number of stator poles, and the number of phases.

[0095] Returning to Figures 6A-6D, it can also be seen from Figures 6A and 6B that there is a gap 143a between the second portions 124a, 124a' of the outer loop portions 122, 122' that form the outer involute portions 134a, 134a' of one pair of the two conductive elements 120, 120'. Similarly, there is a gap 143b between the second portions 124b, 124b' of the outer loop portions 122, 122' that form the outer involute portions 134b, 134b' of the other pair. There is also a gap 144a between the second portions 127a, 127a' of the inner loop portions 125, 125' that form the inner involute portions 137a, 137a' of one pair. Finally, there is also a gap 144b between the second portions 127b, 127b' of the inner loop portions 125, 125' that form the other pair of outer involute portions 137b, 137b'. Due to the geometric properties of the involute, the width of these gaps 143a, 143b, 144a, 144b is substantially constant along the length of the involute portion of the conductive elements 120, 120'. This advantageously reduces the motor diameter and coil losses obtainable for a given rating.

[0096] Although the conductive coil 12 has been described with two conductive elements 120, 120', it should be understood that the conductive coil 12 may have any integer number of conductive elements 120, including three or more. Increasing the number of conductive elements per conductive coil 12 further increases the number of slots per pole per phase of the stator 1 by increasing the number of spaces of the second type defined by the circumferentially adjacent active parts of the conductive elements 120. This may lead to the generation of a stator magnetic field with a more truly sinusoidal magnetic flux density with less harmonic distortion. This advantageously reduces the generation of eddy currents in the permanent magnets of the rotors 2a, 2b, further reducing heating losses and thus resulting in higher motor efficiency. However, it will be understood that the number of conductive elements 120 per conductive coil 12 is generally limited by size constraints. For example, for a given cross section of a conductor (i.e., the cross section of the wire of the wound winding) and a given radius of the stator, there is a limited number of conductors that can be fitted circumferentially into a single coil span γ.

[0097] If the coil 12 has more than two conductive elements, some additional considerations may arise. For example: When forming a coil by connecting a number of conductive elements 120 (e.g. by ferrules 130), it may be preferable to provide several types of conductive elements to make the connection of adjacent conductive elements simpler. For example, the conductive element 120 described above may be used as the two circumferentially outer conductive elements, since its outer tail 128 is connected to the power supply. However, since one or more inner conductive elements between the outer conductive elements are connected to conductive elements at both their inner and outer tails 129, a second type of conductive element may be provided to make the connection easier, having an outer tail 128 adapted similarly 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 preferred over an odd number of conductive elements 120 per coil 12. When an integer multiple of two conductive elements 120 are used, the outer tails 128 of the two circumferentially outermost elements 120 are oriented in parallel opposite directions, as shown in Figures 6A-6D. This is not required, but may result in simpler connections of the coils 12 in some cases, as will be further described below.

[0098] Connecting the Coil to a Multiphase Power Supply Next, a method of connecting the multiple circumferentially distributed conductive coils 12 to a multi-phase power supply will be described. It should be understood that in practice there are many different ways in which this can be achieved, as will occur to those skilled in the art. The invention is therefore not limited to any particular connection configuration. However, the described method of connecting the conductive coils 12, utilizing connection means axially above / below the plane perpendicular to the axis of rotation and axially above / below the conductive coils, provides a particularly neat and orderly series of connections. Furthermore, the ease of connection reduces the possibility of connection failure, and the stator can be resin-impregnated or otherwise encapsulated (such as by using a high pressure plastic encapsulation or overmolding process) without impregnating or encapsulating the connection means, allowing the connections to be inspected and fixed even after impregnation of the stator assembly.

[0099] 4, there is a first connection means 15 provided axially above the stator portion 10 and axially above the conductive coils 12 in a plane perpendicular to the axis of rotation of the motor 100. When two such stator portions 10 are used in accordance with the present invention, a second connection means is similarly positioned on the opposite side of the other stator portion, i.e., at either axial end of the combination of the first and second stator portions.

[0100] The first connection means 15 and the second connection means can be implemented in various ways. In one embodiment, the first and second connection means comprise a first and a second busbar arrangement, respectively. The first busbar arrangement comprises a first busbar per phase configured to power the electric machine, and the second busbar arrangement likewise comprises an equal number of second busbars, again one for each phase. For example, in the case of a three-phase device, each busbar arrangement comprises three busbars, one for each phase. More generally, in the case of an N-phase device, each busbar arrangement comprises N busbars, one for each phase. Furthermore, the first busbar arrangement also comprises a star connection that can be connected to a neutral point.

[0101] In one particular example, the connecting means is a busbar that is continuous and annular about the axis of the stator, although this is but one way of implementing the connecting means. For example, the connecting means need not be continuous or annular, but instead may take the form of a series of two or more circumferentially distributed busbar sections. This may be particularly the case where a laminated winding stator includes multiple poles connected in series. In this case, the busbar may include multiple separate sections, each connecting adjacent poles of the stator.

[0102] Each bus bar in the bus bar arrangement is formed from a conductive material, such as copper, and is insulated from the other bus bars. Many other types of connection means will occur to those skilled in the art.

[0103] The conductive coils of each stator portion are arranged in corresponding sets, each set including a coil from each stator portion. In other words, each conductive coil of the first plurality of conductive coils has a corresponding conductive coil of the second plurality of conductive coils. The coils of each coil set are interconnected by one or more connectors, also referred to as jumpers. The coil sets are arranged in multiple poles and connected to desired phases of the electric machine via a busbar arrangement and connectors.

[0104] For each phase, a first pole may be defined as including a set of conductive coils (first coil set), one coil from the first plurality of conductive coils and one coil from the second plurality of conductive coils, that are connected to a first busbar for that phase.

[0105] Similarly, for each phase, the last pole may be defined as including a different set of coils (last coil set) from the two stator sections. It should be noted that the last pole may or may not be adjacent to the first pole, and the terms "first pole" and "last pole" do not imply a physical location. The coils from the first plurality of conductive coils of this last coil set are connected to a star connection in the first busbar configuration. Note that since the star connection is the neutral connection, all of the corresponding coils per phase may be connected to the same star connection.

[0106] With respect to the second busbar configuration, each conductive coil from the second plurality of conductive coils is connected to the second busbar for that phase such that a current path is formed from the first pole to the last pole through the conductive coil set and the second busbar for that phase.

[0107] Such a connection configuration is shown in Figures 7A and 7B, both of which show a laminated winding stator with adjacent poles connected in series.

[0108] 7A and 7B show diagrams of a laminated winding stator with first stator portion 719 and second stator portion 721, first busbar arrangement 723 and second busbar arrangement 725, respectively, and a number of connectors 727, also referred to as jumpers 727 in FIG. 7A. The first busbar arrangement 723 includes three first busbars A1, B1, C1, one for each phase, and a star connection S, and is located at a first axial end of the laminated winding stator. The second busbar arrangement 725 includes three second busbars A2, B2, C2, one for each phase, and is located at a second end of the laminated winding stator. The multiple connectors 727 or jumpers 727 provide connections between the coils of the two stator portions 719, 721 and are located between the coils of the laminated winding stator and the second busbar arrangement 725.

[0109] As is evident from the number of first and second busbars, both laminated winding stators of Figures 7A and 7B are configured for use with a three-phase power source. In Figure 7A, the three phases are designated by the letters A, B, and C, whereas in Figure 7B, the three phases are designated by different line styles (solid, dashed, and dotted) along with the letters A, B, and C. Each stator section includes twelve conductive elements. In Figure 7A, each conductive element is designated by a "bottom" section, two "core" sections, and a "top" section. These terms are used for ease of explanation, not to imply absolute orientation, and are used with respect to the longitudinal axis of the laminated winding stator (which is coaxial with the axis of rotation when assembled into an electric machine). The second busbar 725 is at the "top" end of the stator, whereas the first busbar 723 is at the "bottom" end of the stator. The "top" and "bottom" portions of the conductive elements correspond to the terminal portions of each conductive element within the coil nearest each end of the stator, while the "core" portions correspond to active portions 121a and 121b as shown in Figures 5A-5D.

[0110] It will be understood that both Figures 7A and 7B are merely two different schematic diagrams to aid in understanding the electrical connections of the laminated winding stator according to the present disclosure, and therefore the locations of the components of the laminated winding stator and coils in Figures 7A and 7B do not precisely correspond to the physical locations of the components.

[0111] The conductive elements of each stator section are divided into two groups of six conductive elements (P1 and P2 in FIG. 7B), each group corresponding to a pole of the laminated winding stator. Thus, the laminated winding stator of FIGs. 7A and 7B is a two-pole device, although it will be understood that the connection methods described below are applicable to stators with any number of poles.

[0112] Within each group (i.e., for each pole), the conductive elements are arranged into coils. Each coil includes two adjacent conductive elements connected in series and corresponds to a single phase. Boxes 719a and 721a in Figure 7B each correspond to one coil and thus represent two adjacent conductive elements connected in series.

[0113] Exemplary current paths are shown in Figures 7A and 7B by arrows following the current in phase B.

[0114] Initially, the current travels along the first busbar of phase B, busbar B1, as indicated by arrow 701. From busbar B1, the current then passes through the coils of the first pole of the first stator section 719, as indicated by arrow 703. That is, within the first stator section, the current passes through the coils corresponding to phase B in the group corresponding to the first pole. Because the conductive elements in each coil are connected in series, the current actually passes first through the first conductive element of the coil and then through the second conductive element of the coil. However, in FIG. 7A, for the sake of clarity, arrow 703 is shown extending from a lower portion of the first conductive element of the coil to an upper portion of the second conductive element of the coil, whereas in FIG. 7B, arrow 703 extends from one side of the box to the other, representing that in each case the current flows sequentially through both conductive elements.

[0115] From the top portion of the second B coil in the first stator portion 719, the current travels in the direction of arrow 705a to jumper 727. As shown in FIG. 7A, the connection to the first busbar B1 is at the bottom portion of the coil (e.g., in the form of outer tail 128 as shown in FIGS. 5A-5B), while the connection to the jumper 727 is at the top portion. From the jumper 727, the current path continues along arrow 705b to the second stator portion 721, passing through the corresponding coil in the second stator portion 721 (indicated by arrow 707) before entering the second busbar B2 (indicated by arrow 709a). This completes the portion of the current path through the first pole (P1 in FIG. 7B) of the laminated winding stator.

[0116] The current path continues down the second busbar B2 (indicated by arrow 711), and follows arrow 713 to the coils of the second pole (P2 in FIG. 7B) of the second stator part 721. From these coils, the current continues back to the jumper 727 in the direction of arrow 715a, before passing through the coils of the second pole of the first stator part 719 (indicated by arrows 715b and 717). After passing through the coils of the first stator part 719 of the second pole (arrow 717), the connection terminates in the star connection S, as indicated by arrow 729. This completes the portion of the current path through the second (in this case last) pole (P2 in FIG. 7B).

[0117] The current paths of the other two phases A and C are also equivalent and all end in the same star connection S. It will be appreciated that the sum of the currents at the "neutral" star point is always zero, i.e., the current flowing from a particular phase returns via the other phase.

[0118] 7A and 7B show how current flows through an exemplary stator between different coils, while FIG. 7C shows how current flows in the coils through adjacent conductive elements. In FIG. 7C, the current path is shown from the first busbar B1 to the second busbar B2 through a set of conductive coils (four conductive elements), one coil of the first stator part 719, and one coil of the second stator part 721. From the first busbar B1, the current enters the first conductive element of the first coil, for example through the tail 128, at arrow 801a. The current then passes through each winding of the first conductive element through the two "core" parts, i.e. active parts 121a, 121b. The current passes through each active part 121a, 121b multiple times (equal to the number of winding turns of the conductive element), at arrow 803a. After passing through each winding of the active parts 121a, 121b, the current then passes from the end of the first conductive element to the second conductive element (but in the same coil as the first conductive element) at arrows 805a and 807. The current then passes to the active parts 121a, 121b (arrow 801b) and then through the active parts 121a, 121b of the second conductive element a number of times equal to the number of winding turns at arrow 803b. Once the current has passed through all of the winding turns of the active parts 121a, 121b of the second conductive element of the first coil, the current then leaves the first oil at the "top" portion (arrow 805b) before proceeding to the second coil (arrow 809).

[0119] It should be noted that although arrow 809 goes directly from the first coil to the second coil, the current actually passes between the first and second coils through a jumper (arrows 705a, 705b in FIG. 7A). Arrow 809 is shown in FIG. 7C in a manner that does not obscure the current path within the coils themselves.

[0120] Upon entering the first conductive element of the second coil at the "bottom" portion, the current travels to the active portion 121a, 121b of the first conductive element of the second coil (arrow 811a). The current then passes through the active portion 121a, 121b at arrow 813a a number of times equal to the number of winding turns before leaving the first conductive element of the second coil (along arrows 815a and 817) and entering the second conductive element of the second coil. The current then travels to the active portion 121a, 121b (arrow 811b) and then passes through the active portion 121a, 121b of the second conductive element at arrow 813b a number of times equal to the number of winding turns. Once the current has passed through all of the windings of the active portion 121a, 121b of the second conductive element of the second coil, the current then leaves the second coil at the "top" portion (arrow 815b) and travels to the second busbar B2.

[0121] When viewed axially, in one stator portion, the current travels between the conductive elements in a clockwise direction, while in the other stator portion, the current travels in a counterclockwise direction. To avoid confusion, it should also be noted that the current may travel in opposite directions between the conductive elements in the first and second stator portions, but flows in the same radial direction along the circumferentially aligned active parts in the two stator portions. For example, as shown in FIG. 7C, in the first stator portion 719, the current first passes through the left conductive element of the first coil and then the right conductive element, while in the second stator portion 721, the current first passes through the right conductive element of the second coil and then the left conductive element. In other words, the first conductive element of the first coil is the left conductive element and the second conductive element of the first coil is the right conductive element, whereas the first conductive element of the second coil is the right conductive element and the second conductive element of the second coil is the left conductive element. In this sense, the terms "first" and "second" when applied to the conductive coils in the description of Figures 7A-7D relate to their relative order along the current path, and it will be understood that the terms left and right are used with reference to the position of the conductive elements in the schematic diagram of Figure 7A.

[0122] It should be noted that the capital and lower case letters in Figures 7A and 7C refer to the direction of current flow through the active portion or whether the active portion is the "first" (e.g., 121a) or "second" (e.g., 121b) active portion within the stator portion. That is, as can be seen in Figures 5E and 5F and, e.g., Figures 6A-6D, when the conductive elements are stacked, current flows in opposite directions along the first and second active portions of each conductive element, and the conductive elements are arranged such that all of the first active portions of the stator portions are at one level within the stator (e.g., a first distance from the first end of the stator) and all of the second active portions of the stator portions are at a different level within the stator (e.g., a second distance from the first end of the stator that is different from the first distance). For example, in Figures 7A and 7C, capital letters may refer to a first active part (e.g., where current flows radially inward for a given direction of a magnetic field when in use) and lowercase letters may refer to a second active part (e.g., where current flows radially outward for a given direction of a magnetic field when in use).

[0123] 7A-7C show one possible connection scheme for two poles. However, there may be more poles. In this case, the first and / or second busbar may include multiple separate busbar portions that may connect adjacent poles (electrically) in series. For example, the second coil of the first pole may be connected to the second coil of the second pole by a first portion of the second busbar. The first coil of the second pole may be connected to the first coil of the third pole by a first portion of the first busbar. The second coil of the third pole may be connected to the second coil of the fourth pole by a second portion of the second busbar, and so on. It will be appreciated that this connection method may be extended to accommodate any number of poles.

[0124] In addition to being connected in series, coils or poles may be connected in parallel. For example, a first pole may be connected in parallel with a second and third pole by connecting the first coil of each pole to a first busbar and then connecting the second coil of each pole to a second busbar (the first and second busbars are not split as in the above example). In this case, the second busbar is a star connection to which each phase connects.

[0125] A schematic diagram of such a laminated winding stator is shown in Figure 7D. The laminated winding stator of Figure 7D is configured for use with a three-phase power supply. Components relating to different phases are shown with different line types. The first phase components are drawn with dotted lines, the second phase components with dashed lines, and the third phase components with solid lines. A star connection S common to each phase is drawn with dashed and dotted lines.

[0126] The laminated winding stator comprises a first busbar arrangement 723 including first busbars A1, B1, C1 per phase disposed at a first axial end of the laminated winding stator and a star connection S disposed at a second axial end of the laminated winding stator. The stator coils are disposed in the first stator portion 719 and the second stator portion 721. A connector 727 or jumper 727 is provided between the second stator portion 721 and the star connection S for electrically connecting the first stator portion 719 and the second stator portion 721.

[0127] Two poles P1, P2 are shown and for each phase, poles P1, P2 include coils in a first stator portion 719 and a second stator portion 721. Each coil in the first stator portion 719 and the second stator portion 721 is represented by a box, coil 719a, 721a, etc. The coils include one or more conductive elements connected in series, although the conductive elements themselves are not shown.

[0128] A representative current path starts at the first busbar A1, passes through coil 719a of the first stator portion 719, through connector 727a to coil 721a of the second stator portion 721 before entering the star terminal S. It will be appreciated that this current path is repeated in parallel for each phase between the first busbar arrangement 723 and the star terminal S. It will again be appreciated that the sum of the currents at the "neutral" star point is always zero; i.e., current flowing from a particular phase returns via the other phase.

[0129] Depending on the required use case, different combinations of series and parallel connections can be used. For example, it has been found that in low voltage (and high current) applications it is advantageous to connect the coils of the two stator parts in parallel, but the different poles within each stator part can be connected in series in any way. On the other hand, in high voltage (and constant current) applications it has been found to be preferable to connect the coils of the two stator parts in series.

[0130] Furthermore, each stator section does not necessarily have to have the same configuration. For example, each stator section may have a different coil span (the angle γ at which the two active parts 121a, 121b of the conductive element are separated). This means that each stator section may have a different amount of fractional pitch windings (some with fractional pitch windings and some without). Each stator section may also have a different winding factor, which may improve the fundamental of the electric machine.

[0131] Connection to the connectors / jumpers and bus bars can be made using the terminal portions or tails of the coil, such as terminal portion 128 of Figures 5A-5D and 6A-6D. Depending on the connection pattern used, a coil with different arrangements of terminal portions may be required. For example, a coil may be required where both terminal portions extend in different axial directions (as shown in Figures 6A-6D), whereas a coil may be required where the terminal portions extend in the same axial direction. Furthermore, the length of the terminal portions will vary depending on whether a first or second bus bar configuration is being connected and whether the coil is positioned in the first or second stator portion.

[0132] For example, consider the case where the coils are connected as disclosed in FIG. 7A. The first coil of the first pole (i.e., the coil having the current path represented by the line 703) requires a connection to the first busbar B1 at the first axial end (located at the bottom of FIG. 7A) and a connection to the connector (jumper) at the second axial end (top of FIG. 7A). The connection to the first busbar B1 is at the lower part of the stator part, whereas the connection to the connector is from the upper part. Thus, the first terminal part (connection to the first busbar) needs to extend in the opposite direction to the second terminal part (connection to the jumper). Furthermore, the first terminal part only needs to extend a short distance from the first stator part to the first busbar, whereas the second terminal part needs to extend from the first stator part beyond the second stator part and connect to the jumper at the second end. Thus, the second terminal part needs to be of sufficient length and also of a suitable position and shape so as not to interfere with the second stator part.

[0133] Such a coil 12 is depicted in Figures 8A, 8B, and 8C. Generally, the coil is similar to that shown in Figures 6A-6D, and corresponding reference numbers are used for like aspects. With reference to the position of the coil when in the stator section, Figure 8A shows a view parallel to the axis of the stator section (i.e., a top view of the coil), Figure 8B shows a view parallel to the circumferential direction of the stator section (i.e., a side view of the coil), and Figure 8C shows two perspective views of the coil. As with the coil in Figures 6A-6D, in the coil in Figures 8A-8C, the terminal portions 128, 128' extend in opposite directions such that, when assembled into the stator, one terminal portion 128 extends toward one end of the stator (e.g., the second axial end) and the other terminal portion 128' extends toward the other end of the stator (e.g., the first axial end). Terminal portions 128, 128' also both extend from the outer portion of the coil. However, unlike the coil shown in Figures 6A-6D, terminal portion 128 extends axially (parallel to the axis of rotation if part of an electric machine) much further than terminal portion 128'. This allows terminal portion 128, when the coil is positioned on the first stator portion, to extend beyond the second stator portion to contact a connector at the second axial end of the stator that is on the opposite side of the second stator portion from the first stator portion. Note also that to bypass the second stator portion in this manner, terminal portion 128 extends radially beyond the outer edge of the body of the coil. This is best seen in the side view of the coil shown in Figure 8B. This allows terminal portion 128 to pass radially outward of the circumferentially aligned coil of the second stator portion to contact a connector.

[0134] With regard to the second coil of the first pole (i.e., the coil of the second stator part with the current path represented by line 707), this coil requires a different arrangement of the terminal parts. In this case, as shown in FIG. 7A, both terminal parts should extend in the same direction, toward the second axial end to connect to the connector 727 and the second bus bar B2. In some cases, these terminal parts should also be of similar length, but this depends on how the second bus bar and jumper are positioned relative to each other and exactly where the terminals extend from the coil. FIGS. 8D, 8E, and 8F show one exemplary coil 12″. As with FIGS. 8A-8C, FIG. 8D shows a top view of the coil, FIG. 8E shows a side view, and FIG. 8F shows two perspective views. Generally, the coil is similar to that shown in FIGS. 8A-8C and is labeled with corresponding reference numbers. Thus, both terminal parts are located on the outer portion of the coil (i.e., the portion that is at the outer radius of the stator part when assembled). However, in Figures 8D-8F, terminal portions 128'', 128''' both extend in the same axial direction.

[0135] 8G and 8H show how the coils 12, 12'' shown in FIGS. 8A-8C and 8D-8F can be positioned relative to each other when placed in their respective stator portions to allow connection to the necessary connectors and busbars. That is, the coils 12 are positioned in a first stator portion and the coil 12'' is a circumferentially aligned coil in a second stator portion. In particular, it can be seen in FIGS. 8G and 8H how the tail 128 extends radially outward from the coil 12, past the outside of the coil 12'' and tail 128'' to allow connection to a connector (positioned above the coil in the illustrated view). It can also be seen that while the axially extending portions of the tails 128 and 128'' are both circumferentially aligned (i.e., both are on the same radial line but at different distances from the center of the stator), both tails 128 and 128'' have bends that allow connection to the necessary busbars and connectors.

[0136] Mechanical Efficiency It has been found that the axial flux machine 100 with the stator assembly 1 described herein provides high efficiency over a wide range of operating parameters as well as high peak efficiency. High peak efficiency is often quoted but is rarely achieved in practice, especially in applications where the machine needs to function over a range of operating parameters. Hence, efficiency over a wide parameter range is a more realistic and meaningful measure for many applications.

[0137] There may be several different reasons for the high efficiency achievable by the stator assembly 1, some of which are explained below.

[0138] First, as mentioned above, the nearly self-forming structure of the conductive components of the stator 10 imparted by the geometry of the coils 12 allows for very precise placement of the stator core components. Precise placement of the core components means that there is better coupling of the stator and rotor magnetic fields and greater symmetry around the stator, improving torque generation.

[0139] Another significant advantage is the generation of a stator magnetic field with a more sinusoidal flux density. As will be appreciated by those skilled in the art, the greater the number of slots per pole per phase of the stator, the closer the flux density can be to a sinusoid. The coils 12 and stator 10 described above can be configured to have a greater number of slots per pole per phase by increasing the number of conductive elements 120 per conductive coil 12, which can be easily increased (e.g., if the stator radius can be increased in a particular application). The advantage of a highly sinusoidal flux density is that the flux density has a relatively low harmonic content. With less harmonic content, the coupling of the rotor and stator magnetic fields contains more of the fundamental component of the flux density and interacts less with the harmonic components. This reduces the generation of eddy currents in the rotor magnet, which further reduces losses due to heating. In contrast, many known axial flux motors utilize concentrated winding configurations that offer only a limited number of slots per pole per phase (e.g., fractional), which generate a much more trapezoidal flux density with more harmonic content.

[0140] The coil 12 can be implemented with axially extending strips, but is preferably implemented with an axially stacked winding configuration as shown in Figures 5A-5D and 6A-6D. Many motor manufacturers may consider this a disadvantage as it may be considered to reduce the packing factor of the stator core, but the inventors have found that this is compensated for by the reduction in skin and proximity effects which cause current to flow in the outer regions of the conductor cross-sections and primarily in the axially outer portions of the active parts of those conductors. The number of axial turns may be selected to balance these two considerations.

[0141] A further particular advantage of the use of the laminated wound stator disclosed herein is that it reduces the amount of copper (or other material) used at the end portions of the coils, i.e. less material is used for the active connections. This is shown in FIG.

[0142] Semicircle 901 represents the area of ​​material used for the connection of the active parts when only one stator part is used (and therefore can be considered as a proxy for the volume of material), while semicircles 903a and 903b represent the area used when two stator parts are used. It can be seen that, if the width of the active parts is the same (lines 907a and 907b have the same total length as line 905), the total area is significantly smaller. This means that the amount of material required can be reduced without reducing the power generated by the motor. In fact, considering that the radius of semicircles 903a and 903b is half that of semicircle 901, the amount of material required for the connection of the active parts when two stator parts are used is only half that required for one stator part. This results in both a reduction in cost and an important weight saving, which can help, for example, to increase the range of electric vehicles powered by motors incorporating such stators.

[0143] A number of embodiments having various optional features have been described above. It will be understood that, except for mutually exclusive features, any combination of one or more of the features is possible.

Claims

1. 1. A laminated winding stator for an axial-flux electric machine configured for use with a polyphase power source, a first stator portion including a first plurality of conductive coils; a second stator portion including a second plurality of conductive coils; each conductive coil of the first plurality of conductive coils and the second plurality of conductive coils includes at least a pair of active portions, each active portion extending in a generally radial direction substantially perpendicular to an axis of rotation of the electric machine; the first stator portion and the second stator portion are axially aligned and each include a space between adjacent active portions for housing a flux guide, the space of the first stator portion being circumferentially aligned with the space of the second stator portion; and a laminated wound stator, wherein each conductive coil of the first plurality of conductive coils is electrically connected to a corresponding conductive coil of the second plurality of conductive coils to form a set of conductive coils.

2. 10. The laminated wound stator of claim 1, wherein circumferentially aligned spaces in the first stator portion and the second stator portion are configured to accommodate a common flux guide.

3. 3. The laminated wound stator of claim 2 further comprising a flux guide positioned within each aligned space set.

4. 4. A laminated winding stator according to claim 1, wherein the active parts of each active part pair are circumferentially spaced apart, and circumferentially adjacent conductive coils overlap in the circumferential direction.

5. 5. A laminated wound stator according to claim 1, wherein the spaces include a first type of spaces, each space of the first type being a circumferential space between two adjacent active parts of two different conductive coils.

6. 6. A laminated winding stator according to claim 1, wherein each conductive coil includes a plurality of pairs of active parts connected in series with each other, adjacent pairs of active parts overlapping in the circumferential direction, and the spaces include spaces of a second type, each space of the second type being a circumferential space between two adjacent active parts of the same conductive coil but of different active part pairs of the conductive coil.

7. 7. The laminated winding stator of claim 6, wherein the pairs of active portions of each conductive coil may be integrally formed or formed by connecting in series a plurality of separate elements each including a pair of active portions.

8. 8. A laminated wound stator as claimed in claim 6 or 7, wherein, in use, current flows in the same direction along adjacent active parts separated by one of said second type of spaces.

9. A laminated wound stator according to any preceding claim, wherein, in use, current flows in opposite radial directions along the active portion of each active pair of each conductive coil.

10. A laminated winding stator according to any preceding claim, wherein the active parts of each active part pair are axially offset from each other.

11. A laminated wound stator according to any preceding claim, wherein each active portion comprises a plurality of axially and / or circumferentially stacked winding turn portions.

12. 12. A laminated winding stator according to any preceding claim, wherein the active portions of each conductive coil in each conductive coil set are circumferentially aligned with one another.

13. 12. A laminated winding stator as claimed in any preceding claim, wherein each active portion of each conductive coil in each conductive coil set is circumferentially offset from one another by an integer number of spaces.

14. 14. The laminated winding stator according to claim 1, wherein, in the case of an N-phase power supply, each conductive coil of each conductive coil set is connected to the same phase.

15. 15. The laminated winding stator of claim 14, wherein the laminated winding stator includes a plurality of poles, each pole including an integer M multiple of the N sets of conductive coils, with M sets of conductive coils per phase.

16. 16. The laminated winding stator according to claim 1, wherein, for each conductive coil set, the conductive coils of the first plurality of conductive coils are connected in series to the conductive coils of the second plurality of conductive coils by a connector.

17. 17. A laminated winding stator according to claim 16 when dependent on claim 14, the laminated winding stator further comprises a first busbar arrangement and a second busbar arrangement, the first busbar arrangement including a first busbar per phase and a star connection, and the second busbar arrangement including a second busbar per phase; For each of the N phases, each conductive coil from the first plurality of conductive coils of a first conductive coil set of a first pole is connected to the first busbar of that phase, and each conductive coil from the first plurality of conductive coils of a last conductive coil set of a last pole is connected to the star connection of the first busbar configuration; and each conductive coil from the second plurality of conductive coils is connected to the second bus bar for that phase to define a current path from the first pole to the last pole through the conductive coil set and the second bus bar for that phase.

18. 20. The laminated wound stator of claim 17, wherein for each phase, the second busbar of the second busbar arrangement includes a plurality of second busbar portions configured to serially connect each conductive coil set of that phase to form the current path from the first pole to the last pole.

19. 19. The laminated wound stator of claim 17 or 18, wherein the first busbar arrangement is axially adjacent to the first stator portion in a first direction along an axis of the laminated wound stator, and the second busbar arrangement is axially adjacent to the second stator portion in a second direction along the axis of the laminated wound stator opposite to the first direction.

20. 16. The laminated winding stator according to claim 1, wherein, for each conductive coil pair, the conductive coils of the first plurality of conductive coils are connected in parallel to the conductive coils of the second plurality of conductive coils by one or more connectors.

21. 1. An electric machine configured for use with a multi-phase power source, comprising: A laminated winding stator according to any one of claims 1 to 20; a first rotor portion disposed at a first axial end of the laminated winding stator; a second rotor portion disposed at a second axial end of the laminated winding stator; An electric machine comprising:

22. 22. The electric machine of claim 21 further comprising a third rotor portion axially disposed between the first stator portion and the second stator portion.

23. 23. An electric machine as claimed in claim 21 or 22, wherein each rotor section includes a number of poles equal to the number of poles of the laminated wound stator.

24. A conductive coil for use in a first stator portion of a laminated winding stator according to any one of claims 17 to 19, comprising at least a pair of active portions, a first terminal portion, and a second terminal portion; the first terminal portion is configured to extend axially in a first direction for connection to a first busbar arrangement; and A conductive coil, the second terminal portion configured to extend axially in a second direction for connection to a connector, the second terminal portion having an extension portion configured to extend in the second direction beyond the second stator portion.

25. A conductive coil for use in a second stator portion of a laminated winding stator according to any one of claims 17 to 19, comprising at least a pair of active portions, a first terminal portion, and a second terminal portion; the first terminal portion is configured to extend axially in a second direction for connection to a second busbar arrangement; and The second terminal portion is configured to extend axially in a second direction for connection to a connector.

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