GB2602811A

GB2602811A - A stator for an electrical machine

Info

Publication number: GB2602811A
Application number: GB2100485.8A
Authority: GB
Inventors: Boubaker Nadhem; Muller Udo; Varsani Dipesh; Kirk Adrian; Goodwin Lee
Original assignee: Safran Electrical and Power SAS
Current assignee: Safran Electrical and Power SAS
Priority date: 2021-01-14
Filing date: 2021-01-14
Publication date: 2022-07-20
Also published as: GB202100485D0; WO2022153040A1; GB2602811A8

Abstract

A stator 101 for an electrical machine includes a stator core having plural teeth 110,120 extending in a direction of a longitudinal axis of the stator that define plural slots 130 to receive windings 111,121. A first winding 111 comprises at least one turn around first tooth 110 and a second winding 121 comprises at least one turn around second tooth 120 that is adjacent to the first tooth 110. A slot 130 has a first part annular region 131 in which there are more turns of the first winding 111 than there are turns of the second winding 121. A second part annular region, 132, at a different radial position to the first region 131 may have more turns of the second winding 121 than there are of the first; each part annular region extending over half of the radial extent of the slot. The number of tooth turns of each winding in one region may equal the number of turns of the other winding in the other region. The windings may be applied by a needle winding machine; in alternate full and partial layers 112, 123; from a single thread of wire; such that the slot has a fill factor greater than 25% and the width between adjacent windings is less than a width of the needle 150.

Description

A STATOR FOR AN ELECTRICAL MACHINE

Technical Field

The invention relates to a stator for an electrical machine. In particular, the invention relates to electrical machines having conductors wound around slots of a stator and novel methods of winding such conductors.

Background of the Invention

Electric aircraft propulsion systems typically comprise a fan (propeller), which is connected to an electrical machine. The electrical machine is typically formed of an assembly of magnetic circuit components, comprising a rotor and a stator. Rotation of the rotor relative to the stator causes interaction of the magnetic field generated by the rotor with windings provided on the stator, generating an induced electromotive force (EMF) and/or electrical current in a known manner. In a permanent magnet generator, the rotor's magnetic field is produced by permanent magnets, which induces an AC voltage in the stator windings as the stator windings pass through the moving magnetic field of the permanent magnet. The same electrical machine may also act as a motor by energising the stator windings to induce rotational drive of the rotor.

One method of assembly of stators for electrical machines is automated needle winding, in which conducting wire is wound around adjacent slots of the stator by a guiding head, typically referred to as a needle, carried on a machine. A key parameter in determining the performance of some types of electrical machines is the slot fill factor, which relates to the amount of electrically conductive windings (such as copper) as a proportion of the space inside a particular slot. Automated needle winding requires space in the slot for the needle to pass through, and this space cannot itself be automatically filled with windings, thereby lowering the achievable slot fill factor as compared to other winding techniques, such as manual winding by human hand.

There exists a need for improvement in winding arrangements for electrical machines.

Summary of the Invention

The inventors have identified a problem with needle winding as a method of assembling a stator for an electrical machine. While needle winding provides a fast method of manufacturing electrical machines as compared to manual winding, the resulting stators have a relatively low slot fill factor, in that the cross sectional area of a slot that is occupied by conducting windings is relatively low compared to the total cross sectional area of the slot. This is, in part, due to the space required in the slot to allow the needle to pass through in order to apply the last winding in each slot. The width of the needle requires an unobstructed space in the slot of the same width, in order to permit the needle to wind the last turns of a conductor around each stator tooth.

In view of the above, the inventors have devised an improved winding arrangement and method which enables the production of a needle wound stator having an increased slot fill factor. The stator has a stator core, which includes an array of stator teeth disposed around its circumference. The stator teeth extend in a longitudinal direction of the stator and define stator slots. Windings can be wound around the teeth and received by the slots. An adjacent pair of stator teeth includes a first tooth and a second tooth which, respectively, have a first tooth winding and a second tooth winding disposed therearound.

Each winding comprises a number of turns of conductor around its respective stator tooth.

The slot defined between the first tooth and the second tooth comprises a first part-annular winding region and may further comprise a second part-annular winding region. The first part-annular winding region may be located at a different position to the second part-annular winding region along a radius of the stator. Otherwise stated, the first part-annular winding region may be disposed at a first radial position with respect to the longitudinal axis of the stator and a second part-annular winding region may be disposed at a different radial position, with respect to the longitudinal axis of the stator, to the first part-annular winding region. In the first part-annular winding region of the slot, there are more turns around the first tooth than there are turns around the second tooth. This arrangement provides a stator that can be produced by needle winding with a relatively high slot fill factor.

According to one aspect of the present invention, there is provided a stator for an electrical machine, comprising: a stator core having a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator; the plurality of teeth comprising a first tooth and a second tooth adjacent to the first tooth, the first tooth comprising a first tooth winding wound therearound and comprising at least one first tooth turn, and the second tooth comprising a second tooth winding wound therearound comprising at least one second tooth turn; wherein at least one slot of the stator comprises a first part-annular winding region, disposed at a first radial position with respect to the longitudinal axis of the stator; and wherein the first part-annular winding region comprises a greater number of first tooth turns than second tooth turns.

The stator may comprise a second part-annular winding region. The second part-annular winding region may be disposed at a different radial position with respect to the longitudinal axis of the stator to the first part-annular winding region. The second part-annular winding region may comprise more second tooth turns than first tooth turns. The first part-annular winding region may extend along substantially half of the radial extent of the at least one slot. The second part-annular winding region may extend along substantially half of the radial extent of the slot. The second part-annular winding region may be disposed at a position radially inwards of the first part-annular winding region.

This has the advantage of providing a stator onto which windings can be wound via a needle winding method, while providing a sufficiently sized path along which a needle of a needle winding machine can pass in order to produce a stator having a high slot fill factor.

The number of first tooth turns in the first part-annular winding region may be equal to the number of second tooth turns in the second part-annular winding region. The number of second tooth turns in the first part-annular winding region may be equal to the number of first tooth turns in the second part-annular winding region. This has the advantage of providing a slot with an equal number of turns wound around the two teeth immediately adjacent to the slot. In a multi-phase electrical machine, this has the advantage of providing a stator in which windings at the edge of a first phase can have an equal number of turns to windings at the edge of a second phase in order to balance the motive or electrical power generated by the electrical machine.

According to another aspect of the present invention, there is provided a method of manufacturing a stator for an electrical machine, comprising the steps of: providing a stator core comprising a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator; using a needle winding machine to apply windings to the first and second teeth, without modification to the dimensions of the stator core, to provide: a first winding around a first tooth of the plurality of teeth; and a second winding around a second tooth of the plurality of teeth, adjacent to the first tooth, such that a slot disposed between the first and second teeth has a fill factor of more than 25%.

The fill factor may be defined as the total cross sectional area of windings in a given slot divided by the total cross sectional area of a naked slot.

The method requires that a needle winding machine is used to apply windings to the first and second teeth without modification of the dimensions of the stator core. This may remove a need to alter the dimensions of the slot during design and manufacture in order to achieve a certain slot fill factor. This has the advantage of providing a stator for an electrical machine having a relatively high slot fill factor, which can be achieved directly after the winding steps, instead of after any subsequent deformation or assembly of stator components.

A cross-sectional area of the plurality of slots may remain fixed throughout the method. The method may comprise a step of applying windings directly onto a solid finished stator, that is, a stator comprising a solid stator core formed from at least one substantially annular layer. This has the advantage of providing a method of manufacturing a stator without the additional complexity associated with changing the cross-sectional area of any slots after winding. Furthermore, this has the advantage of avoiding segmentation or stretching, thereby avoiding the need to assemble stator segments and to fix them together such as by welding. This has a further advantage of simplifying the method of manufacture and reducing the number of steps.

The needle may wind the second winding around the second tooth after winding the first winding around the first tooth. An adjacent pair of counterwound teeth may be provided using a single length of wire. This has the advantage of providing a method of manufacturing a stator wherein the number of cuts that may be made to the wire after winding is reduced. This simplifies the winding process and reduces the number of additional steps required after winding, which may speed up the method. Furthermore, this provides a more reliable winding by reducing the number of brazing or joining points. Also, this has the advantage of reducing winding losses because a continuous winding provides improved electrical resistivity.

The method may comprise the step of winding at least one full layer of wire around the first tooth and the second tooth. The method may subsequently comprise the step of winding at least one partial layer of wire around the first tooth and the second tooth. The partial layer may be a half layer.

The method may comprise the step of winding at least one full layer and at least one partial layer of wire around the first tooth. The partial layer may be a half layer of wire.

The method may subsequently comprise the step of winding at least one full layer and at least one partial layer of wire around the second tooth. The partial layer of wire may be a half layer of wire. This has the advantage of providing a method in which the turns of wire wound around a given tooth are completed before the needle progresses to another tooth.

This can reduce the overall distance travelled by a needle of the needle winding machine relative to the stator over the course of the needle winding method, which can thereby speed up the method.

The partial layer of wire wound around the first tooth may be located in a first part-annular winding region. The partial layer of wire wound around the second tooth may be located in a second part-annular winding region. The second part-annular winding region may be defined at a different radial position to the first part-annular winding region. A minimum distance between the first winding and the second winding may be configured to be less than the width of a needle of the needle winding machine. This has the advantage of providing a method of manufacture of a stator having a high slot fill factor wherein usage of the space within the slot is optimised.

Brief Description of the Drawings

Further features and advantages of the present invention will become apparent from the following description of embodiments thereof, presented by way of example only, and by reference to the drawings, wherein: Figure 1 is a cross sectional diagram illustrating a stator in accordance with an embodiment of the invention.

Figure 2 is a schematic diagram illustrating part of a stator in accordance with an embodiment of the invention.

Figures 3A to 3C are cross sectional diagrams illustrating a method of assembly of a stator in accordance with an embodiment of the invention.

Figure 4 is a schematic diagram illustrating the method of assembly of a stator in accordance with an embodiment of the invention.

Figures 5A to 5D are schematic diagrams illustrating a method of assembly of a stator in accordance with an embodiment of the invention.

Detailed Description

A stator is described herein in the context of an electrical machine such as the type employed for propulsion and/or electricity generation in an aircraft engine assembly. The electrical machine comprises a rotor configured to rotate about a longitudinal axis of the electrical machine, which may be connected to an output of the aircraft engine by a drive shaft. The electrical machine may be operated in a generator mode, wherein the electrical machine receives motive power from a prime mover of an aircraft such as a turbine, and generates electrical power. Alternatively, the electrical machine may operate in a motor mode, wherein the electrical machine receives electrical power from power electronics and provides mechanical power to drive a propeller directly or to act as a starter for a prime mover. Disposed around the rotor is a stator comprising a stator core having stator teeth projecting radially therefrom. In the spaces between adjacent pairs of stator teeth, stator slots are defined in which stator windings can be received. The stator windings interact with magnets, which may be permanent magnets, on the rotor to generate electricity and/or motive power. The stator includes at least a first tooth and a second tooth, defining a first slot in the space therebetween. The first tooth has first tooth turns wound therearound and the second tooth has second tooth turns wound therearound. The slot can be notionally partitioned into at least a first part-annular winding region and a second part-annular winding region, disposed across a different radial range to the first part-annular winding region. The radial extents of the first and second winding regions may be non-overlapping. In other words, the space between a pair of slots can be notionally divided between a first part-annulus and a second part-annulus having different radii, or radial extents. These part-annuli represent sub-sections or segments of a complete annulus which would extend around a full circumference of the stator. The windings are provided in such a way that, in the first part-annular winding region of a given slot, there are more first tooth turns than second tooth turns. In order to balance the number of first and second tooth turns in a given slot, there may be more second tooth turns than first tooth turns in the second part-annular winding region of the slot. As will be described below, this winding arrangement allows for automated needle winding to be used, while permitting a greater proportion of slot space to be occupied by windings, i.e. a greater slot fill factor can be achieved.

Figure 1 shows an electrical machine 100 in relation to which embodiments of the invention will be described. The electrical machine 100 comprises a rotor configured to rotate about a rotational axis 105 of the electrical machine 100. The electrical machine 100 further comprises a stator 101 disposed around the rotational axis 105. The stator 101 can be disposed at a position radially outwards from the rotor. The rotor is substantially cylindrical, having a substantially annular magnetic portion 102, which may comprise a plurality of permanent magnets (not shown) disposed therearound. The stator 101 comprises a stator core 103 which comprises a substantially annular component comprising a ferromagnetic material. The stator core 103 comprises a plurality of stator teeth. The stator teeth can be provided as radial projections from the stator core 103, the projections extending longitudinally in the direction of the axis 105. The stator core 103 comprises at least a first tooth 110 and a second tooth 120. A slot 130 is defined in the space between the first tooth 110 and the second tooth 120. As shown in Figure 1, the stator core 103 comprises a plurality of teeth, the spaces between which define a plurality of slots. The teeth are mechanically and magnetically connected to one another by a stator back iron 106.

Figure 2 shows an enlarged view of part of the stator 101 of Figure 1. In the illustrated arrangement, the first tooth 110 and the second tooth 120 extend radially inwards from the substantially annular stator core 103 to define a slot 130 in the space therebetween. The stator teeth 110, 120 may comprise trapezoidal projections from the stator core 103, the trapezoidal projections extending in the longitudinal direction of the stator 101. The first tooth 110 and the second tooth 120 may alternatively have a substantially rectangular cross-section, or any other appropriate cross-section. The stator teeth 110, 120 may comprise tooth tips. In the illustrated arrangement, the first tooth 110 comprises a first tooth tip 118a and a second tooth tip 118b. The second tooth 120 may comprise a first tooth tip 128a and a second tooth tip 128b. The tooth tips 118a, 118b of the first tooth 110 may be provided as ledges extending circumferentially from an end of the first tooth opposite to the end at which the first tooth 110 is fixed to the stator core 103. The first tooth tip 118a may extend in a first circumferential direction and the second tooth tip 118b may extend in a second circumferential direction, wherein the first circumferential direction is opposite to the second circumferential direction. The same description applies to the first tooth tip 128a and the second tooth tip 128b of the second tooth 120.

The first tooth 110 comprises a first winding 115 wound therearound. The first winding 115 comprises a plurality of turns. A turn is understood to refer to a single turn of conducting wire around a tooth of the stator 101. The turns of wire of the first winding 115 of the first tooth 110 will be referred to as first tooth turns. In the illustrated example, the first winding 115 comprises a primary layer 111 and a secondary layer 112. The primary layer 111 may comprise a single layer of the first winding 115 wound immediately therearound and extending as a coil of wire from a first end of the first tooth 110, at which the first tooth 110 is connected to the stator core 103, to a second end of the first tooth 110, at which the first tooth tips 118a, 118b extend therefrom. The primary layer 111 may comprise thirty-one first tooth turns. The primary layer 111 may be divided into a first sub-layer 111a and a second sub-layer 111b. The second sub-layer 111b may be wound around the first sub-layer 111a. The first sub-layer 111a of the primary layer 111 may comprise sixteen first tooth turns, while the second sub-layer 111b of the primary layer 111 may comprise fifteen first tooth turns. As in the illustrated arrangement, the first and second sub-layers 111a, 111b of the primary layer 111 extend along a majority of the full radial length of the first tooth 110. Therefore, these sub-layers may each be considered as a full layer of wire. A full layer of wire may extend along a radial length of the slot so that any remaining space in that layer is less than a full width of the wire. The primary layer 111 can be provided as a pair of concentric coils of wire wrapped around a majority of the surface area of the first tooth 110.

The slot 130 can be notionally divided into a plurality of part-annular winding regions. An annular winding region of the stator 101 is a notional annulus around the rotational axis in which windings of a certain type can be provided. In the arrangement shown, the stator 101 comprises a first annular winding region 131 and a second annular winding region 132. The first annular winding region 131 can, in the illustrated example, be envisaged as an annulus whose outer diameter coincides with a radially outer internal wall of the slot 130 and whose inner diameter coincides with an approximate halfway point along the radial length of the slot 130. The first annular winding region 131 may extend along substantially half of the radial extent of the slot 130. The second annular winding region 132 can, in the illustrated example, be envisaged as an annulus whose outer diameter coincides with the approximate halfway point along the length of the slot 130 and whose inner diameter coincides with a radially inner internal wall of the slot 130, which may be proximal to the tooth tips. The second annular winding region 132 may extend along substantially half of the radial extent of the slot 130. The second annular winding region 132 may be defined at a position radially inwards of the first annular winding region 131.

Having defined the annular winding regions 131, 132 in relation to the stator 101, it will be understood from Figure 2 that the first winding 115 comprises a primary layer 111, wound about the first tooth 110, and disposed across the first and second part-annular winding regions 131, 132, while the secondary layer 112 is disposed within just the first part-annular winding region 131. The secondary layer 112 comprises a plurality of first tooth turns in order to provide a coil of wire around the first tooth 110. As shown, the secondary layer 112 can be wound around the primary layer 111, and more specifically can be wound around the second sub-layer 111b or the primary layer 111. In this arrangement, the secondary layer 112 extends along a fraction, or less than a full extent, of the length of the slot 130. The fraction may be approximately one half. Other fractions may be envisaged in other embodiments. The secondary layer 112 may therefore be considered a partial-layer of wire, or a half layer of wire where it occupies half of a slot's radial length. The secondary layer 112 may comprise seven first tooth turns. The secondary layer 112 can be provided within the first part-annular winding region 131 such that it may be disposed at an outer radial portion of the slot 130.

The second tooth 120 comprises a second winding 125 wound therearound. The second winding 125 comprises a plurality of turns. The turns of wire of the second winding 125 of the second tooth 120 will be referred to as second tooth turns. In the illustrated example, the second winding 125 comprises a primary layer 121 and a tertiary layer 123. The primary layer 121 may comprise a single layer of the second winding 125 wound immediately therearound and extending as a coil of wire from a first end of the second tooth 120, at which the second tooth 120 is connected to the stator core 103, to a second end of the second tooth 120, at which the second tooth tips 128a, 128b extend therefrom.

The primary layer 121 may comprise thirty-one first tooth turns. The primary layer 121 may be divided into a first sub-layer 121a and a second sub-layer 121b. The second sub-layer 121b may be wound around the first sub-layer 121a. The first sub-layer 121a of the primary layer 121 may comprise sixteen second tooth turns, while the second sub-layer 121b of the primary layer 121 may comprise fifteen second tooth turns. In the illustrated arrangement, the first and second sub-layers 121a, 121b of the primary layer 121 extend along a majority of the full length of the second tooth 120. Therefore, these sub-layers may each be considered as a full layer of wire. As described above, a full layer of wire may extend along a radial length of the slot so that any remaining space in that layer is less than a full width of the wire. The primary layer 121 can be provided as a pair of concentric coils of wire wrapped around a majority of the surface area of the second tooth 120.

The second winding 125 comprises a tertiary layer 123. The tertiary layer 123 comprises a plurality of second tooth turns in order to provide a coil of wire around the second tooth 120. In the illustrated arrangement, the tertiary layer 123 is wound around the primary layer 121, and is more specifically wound around the second sub-layer 121b. The tertiary layer 123 can extend along a fraction of the length of the slot 130, wherein the fraction may be approximately one half. The tertiary layer 123 may comprise seven second tooth turns provided as a coil of wire extending along approximately half of the length of the slot 130, and may therefore be considered a half layer of wire. The tertiary layer 123 may be comprised within the second part-annular winding region 132.

By way of the arrangement described above, the first part-annular winding region 131 comprises a greater number of first tooth turns than second tooth turns. In the first annular part-winding region 131 of the slot 130, the illustrated arrangement shows that the first winding 115 comprises three layers of first tooth turns (i.e. the primary layer 111, comprising two layers, and the secondary layer 112), while the second winding 125 in the first part-annular winding region 132 comprises only two layers of second tooth turns (i.e. the primary layer 121, comprising two layers). In the illustrated arrangement, the opposite may be true of the second part-annular winding region 132. That is to say, in the second part-annular winding region 132, the second winding 125 comprises three layers of second tooth turns (i.e. the primary layer 121, comprising two layers, and the tertiary layer 123), while the first winding 115 comprises only two layers of first tooth turns (i.e. the primary layer 111, comprising two layers). Therefore, in the second part-annular winding region 132, the slot 130 may comprise a greater number of second tooth turns than first tooth turns. In other words, in the locality of the second part-annular winding region 132 there is a greater number of turns of the second winding 125 than turns of the first winding 115.

The number of first tooth turns in the first part-annular winding region 131 may be equal to the number of second tooth turns in the second part-annular winding region 132. Likewise, the number of second tooth turns in the first part-annular winding region 131 may be equal to the number of first tooth turns in the second part-annular winding region 132.

While the arrangement described above relates only to two teeth 110, 120 of the stator 101, it will be understood that the arrangement shown in Figure 2 may represent an elementary block, multiples of which could be disposed around the stator 101 in order to provide a winding arrangement of a full stator 101 with repeating units of the elementary block. Teeth of the stator 101 having winding arrangements similar to the first winding (with more tooth turns in the first part-annular winding region 131) could be arranged around the stator 101 so as to alternate with teeth having windings of the type of the second winding 125 (having more tooth turns in the second part-annular winding region 132).

A method of assembly of the stator 101 using needle winding will now be described with reference to Figures 2 and 3A to 3C. The winding arrangement described above permits a particularly advantageous needle winding method to be adopted to assemble the stator 101. Needle winding is typically performed by a specialised piece of equipment comprising a needle which can be moved in several directions and carry a wire in order to provide windings onto a stator. A needle 150 of a needle winding machine is schematically represented in Figure 2. The needle 150 may have a needle tip 151 at a distal end thereof. The wire may be held near the needle tip 151. The needle 150 is able to be moved relative to the stator 101 such that the needle 150 passes through the slot 130 in the longitudinal direction parallel to the rotational axis 105. The needle 150 may also be actuated in a radial direction of the stator 101, such that the needle 150 may be advanced into and retreated out of the slot 130 via a gap 134, which may be provided between the first tooth tips 118a, 128a of the first and second teeth 110, 120.

The needle winding machine may be further configured to provide for relative movement between the stator 101 and the needle 150 in the circumferential direction. This may be achieved, for example, by rotation of the stator 101 relative to the needle 150. In this way, a thread of wire carried by the needle 150 can be wound around a given tooth by passing through a first slot adjacent to the tooth and subsequently passing through a second slot on the other side of the tooth to produce a single turn of wire.

With reference to Figure 3A, a winding method will be described in relation to a first slot 161, which is directly adjacent to a second slot 162, which is directly adjacent to a third slot 163. The needle 150 can provide a turn of wire around the first tooth 110 by entering a first face of the second slot 162 and passing through the longitudinal extent of the slot 162 (i.e. into the page of Figure 3A), before exiting the second opposite face of the second slot 162. Then, the needle 150 can be actuated so as to enter the first slot 161 and pass through the longitudinal extent of the first slot 161 (i.e. out of the page of Figure 3A). This step of needle winding can be repeated in order to provide an entire layer of first tooth turns around the first tooth 110. In order to produce a layer (such as the primary layer 111), it will be appreciated that the needle 150, beginning from a position of full radial insertion into the slots, can be retreated radially inwardly such that the needle tip 151 is gradually moved closer to the gap 134 after each successive turn of wire has been wound around the first tooth 110.

After a first sub-layer 111a of the primary layer 111 has been provided by winding first tooth turns around the first tooth 110, a second sub-layer 111b can be provided by winding first tooth turns around the first tooth 110 while advancing the needle 150 in the opposite direction. That is to say, starting from a position in which the needle tip 151 is close to the gap 134, the needle 150 may continue to thread wire through the first slot 161 and the second slot 162 while being advanced further into the slots. Alternatively, after providing the first sub-layer 111a in the first slot 161 and second slot 162, the needle 150 may be fully inserted into one of the slots and then, once the needle tip 151 is at its furthest distance from the gap 134, the step of winding wire around the first tooth 110 can begin while retreating the needle 150 radially inwards. In either case, this can provide a second sub-layer 111b around the first sub-layer 111a.

The above describes how to provide a first winding 115 onto a first tooth 110. In some embodiments, this step will subsequently be repeated for each tooth of the stator 101. By rotation of the stator 101 about its axis 105 or otherwise, the needle 150 can be moved to a position from which it can wind wire around the second tooth 120, by threading the wire through the second slot 162 and the third slot 163. The primary layer 121 of the second tooth 120 can thus be provided using the method described above in relation to the primary layer 111 of the first tooth 110, but by instead threading the needle 150 through the second slot 162 and the third slot 163. By repeating this process for every tooth on the stator core 103, a primary layer of wire, comprising two sub-layers in the illustrated arrangement, can be provided around every tooth of the stator 101, as illustrated by Figure 3A. This step provides two coils of wire around every tooth of the stator 101, with one coil (providing the second sub-layer 111b) being wrapped around the other coil (providing the first sub-layer 111a).

Figure 3B illustrates a further step in this embodiment of the winding method, in which a secondary layer 112 of wire can be wound around the first tooth 110 after all of the primary layers have been wound around their respective stator teeth. Starting from a position in which the needle 150 is radially inserted into one of the first slot 161 or the second slot 162, such that the needle tip 151 is at the opposite end of the slot to the gap 134, the needle 150 can be wound around the first tooth 110, and therefore around the primary layer 111. In order to lay a single layer of wire, the needle 150 can be gradually retreated in the radial direction at the same time as the needle 150 is threaded through the first slot 161 and second slot 162, in a similar fashion to the above described method of winding the primary layer 111. As shown in Figure 3B, in contrast to the primary layer 111, winding of the secondary layer 112 can be stopped once it extends along approximately half the radial extend of the slots. In this way, a coil of wire having a length approximately half that of the coils defining the primary layer is provided around the first tooth 110 in the first part-annular winding region 131 (see Figure 2). This step can be repeated such that a secondary layer 112 of wire can be wound around every other tooth of the stator 101. For an array of teeth numbered sequentially around the circumference of the stator 101, a secondary layer 112 of wire can be provided around the odd (or even) numbered teeth, for example around the first tooth, third tooth, fifth tooth, and so on.

Figure 3C illustrates a yet further step in this embodiment of the winding method, in which a tertiary layer 123 of wire can be wound around the second tooth 120 after all primary and secondary layers have been wound around their respective stator teeth. Starting from a position in which the needle 150 is radially inserted partially into one of the second slot 162 or the third slot 163, such that the needle tip 151 is approximately halfway along the radial extent of the slot, the needle 150 can be wound around the second tooth 120, and therefore around the primary layer 121 thereof. In order to lay a single layer of wire, the needle 150 can be gradually retreated in the radial direction at the same time as the needle 150 is threaded through the second slot 162 and the third slot 163, in a similar fashion to the above described method of winding the secondary layer 112. As shown in Figure 3C, winding of the tertiary layer 123 can be stopped once it extends along approximately half the radial extent of the slots. In this way, a coil of wire having a length approximately half that of the coils defining the primary layer is provided around the second tooth 120. In this way, a coil of wire having a length approximately half that of the coils defining the primary layer is provided around the second tooth 120 in the second part-annular winding region 132 (see Figure 2). This step can be repeated such that a tertiary layer 123 of wire can be wound around every other tooth of the stator 101, alternating with the secondary layers 112 of wire. Therefore, if the secondary layers 112 of wire were provided around the odd numbered teeth, then the tertiary layers 123 of wire would be provided around the even numbered teeth, for example around the second tooth, fourth tooth, sixth tooth, and so on. It will be appreciated that the windings disposed around the first tooth 110 of Figure 3A make up the first winding 115 of Figure 2, while the windings disposed around the second tooth 120 of Figure 3A make up the second winding 125 of Figure 2.

Figure 4 illustrates an alternative winding method which differs from that described in relation to Figures 3A to 3C, especially with respect to the sequence in which the wires are wound onto the stator. While the embodiment shown in Figures 3A to 3C involves winding all turns of a particular type of layer (e.g. the primary layer) throughout the stator 101 before beginning to wind turns of the next type of layer (e.g. the secondary layer), the method shown in Figure 4 involves winding all applicable types of layer onto a given tooth before moving onto another tooth.

The lines and arrows in Figure 4 schematically represent a path 171 of the needle 150 carrying the wire throughout the stator 101. In certain examples, the winding sequence may be started by winding the first three teeth of the stator in the sequence: a, B°, A°. In such an example, from a starting point 170, a first winding 115 is wound around the first tooth 110 (e.g. the tooth with label a). This can be achieved by winding a primary layer 111 and, immediately after, winding a secondary layer 112 in the first part-annular winding region 131. The way in which each layer can be wound is the same as described earlier. Following the path 171, the needle 150 can be moved in a clockwise direction, with respect to the stator 101, to the next but one tooth (e.g. 130), where the previous step can be repeated to provide a winding of the same arrangement as the first winding 115. Then, the needle 150 can be moved in the anticlockwise direction to the second tooth 120 (e.g. A°). At this point, the second winding 125 can be wound around the second tooth 120.

This can be achieved by winding a primary layer 121 as described earlier and, immediately after, winding a tertiary layer 123 in the second part-annular winding region 132.

The winding sequence can comprise the steps of sequentially winding subsets of four teeth, A, B, C and D. The sequence in which the subset of four teeth is wound may be: B°, A°, D° and then C°. A first winding, being of the type having a primary layer 111 and a secondary layer 112, may be provided on the teeth labelled B and D. A second winding, being of the type having a primary layer 111 and a tertiary layer 123, may be provided on the teeth labelled A and C. In the example shown, after the starting step of winding first windings on a and B°, the needle can then be moved anticlockwise to the adjacent tooth, A°, on which a second winding 125 can be provided. Then, the needle can be moved clockwise to the next but two tooth, D°, on which a first winding can be provided. To complete winding of the subset, the needle can then be moved anticlockwise to the adjacent tooth, C°, on which a second winding can be provided. From C°, the needle can be moved to B1, from which the next subset of four teeth may be provided with windings in the same sequence: D' and then C'. From C', the sequence can continue to repeat around the stator until termination at an end point is required. The repeating sequence may terminate on any of the teeth labelled A, B, C, D. In the example shown, the repeating steps terminate after a second winding is provided on C", defined within an nt" subset A", B", cn, D. After completing the repeating steps, it may be necessary to terminate the sequence with a finishing step. In the example shown, the needle can be moved from C" clockwise to the next but one tooth, 13, where another second winding can be provided before the path terminates at point 172. Although examples are described by referring to clockwise and anticlockwise directions, the opposite directions could be used such that the clockwise direction refers generally to a first circumferential direction, and the anticlockwise direction refers generally to a second circumferential direction opposite the first circumferential direction.

The crosses shown at various points along the path 171 represent wire cuts. The wire can be cut in these positions in order to achieve the required network of connections with the power electronics (not shown) of the electrical machine. For a given pair consisting of a first winding and a second winding, a connection 174 may be retained from the original winding sequence, instead of cutting the wire at these points. A bridge 175 may be provided to electrically connect the first winding at the starting point 170 with the second winding at the end point 172. Therefore, the winding arrangement illustrated by Figures 1 and 2 can be achieved by at least two different methods: a first method, described above in relation to Figures 3A to 3C, and a second method, described above in relation to Figure 4.

Figures 5A to 5D illustrate a method of winding a first winding 115 around a first tooth 110 and a second winding 125 around a second tooth 120. In particular, Figures 5A to 5D demonstrate the way in which the advantageous winding arrangement described above can be achieved under the constraints dictated by the use of a needle winding machine. As described earlier, the slot fill factor is limited by the space required in a given slot to allow the needle 150 to pass through without being obstructed by any of the turns. Additionally, there may be further constraints on the distribution of wires of different phases throughout the slots of the stator core. For example, in a multi-phase electrical machine, windings from two different phases may occupy opposite sides of a single slot. Therefore, it may be necessary for the number of turns of each phase in that slot to be the same for each phase, in order to maintain an even distribution around the stator in the generation of electricity or motive power. The illustrated method helps to achieve a high slot fill factor while satisfying these constraints.

Figure 5A represents a snapshot in time during winding of the first winding 115. Having already wound the two sub-layers of the primary layer 111 of the first winding 115, the needle 150 is shown to be approximately halfway through the process of winding the secondary layer 112 of the first winding 115 around the first tooth 110. As described above, the needle 150 can be gradually retreated out of the slot, in a radially inwards direction, at the same time as threading wire around the first tooth 110 by successively passing longitudinally through the slots immediately adjacent to the first tooth 110. Under the first method of winding (see Figures 3A to 3C), the primary layer 121 of the second winding 125 will have already been wound around the second tooth 120 by the time winding of the secondary layer 112 begins. However, in the second method of winding (see Figure 4), no turns of the second winding 125 will have been wound by this point in time. Therefore, the primary layer 121 of the second winding 125 is shown using dashed lines, to illustrate that the method described herein is compatible with either the first method or the second method of winding. As can be seen from Figure 5A, the needle 150 is able to pass through the slot to wind the secondary layer 112 without being obstructed by the primary layer 121 of the second winding 125.

Figure 5B illustrates a snapshot in time at which the primary layer 121 of the second winding 125 is in the process of being wound around the second tooth 120. In particular, Figure 5B shows the first sub-layer 121a of the primary layer 121 having already been wound around the second tooth 120, and the second sub-layer 121b of the primary layer 121 having been partially wound around the second tooth 120. Whether in the first or second method of winding, the primary layer 111 of the first winding 115 will have already been wound by this point in time. In the first method of winding (see Figures 3A to 3C), the secondary layer 112 will not have been wound by this point in time, because all of the primary layers of all slots of the stator core are wound before moving on to another type of layer. However, in the second method of winding (see Figure 4), the secondary layer 112 will have already been wound by this point in time. The secondary layer 112 is therefore shown using dashed lines in Figure 5B. Notably, the needle 150 is able to move freely through the slot in order to wind the second sub-layer 121b without being obstructed by the presence of any secondary layer 112.

Figure 5C illustrates a snapshot in time of this winding method after which the primary layer 111 and secondary layer 112 of the first winding 115, and the primary layer 121 of the second winding 125, have been wound around their respective teeth 110, 120. This may be immediately after the secondary layer 112 has been wound, or after the primary layer 121 of the second winding 125 has been wound, depending on whether the first or second method of winding is adopted. At this point, there may be insufficient space for the needle 150 to be advanced radially into the first part-annular winding region 131, due to there being an insufficiently wide gap between the first winding 115 and the second winding 125. Instead, as shown in Figure 5C, the needle 150 is able to pass through the slot in the second part-annular winding region 132 due to the sufficiently large gap between the primary layer 111 of the first winding 115 and the primary layer 121 of the second winding 125. It will be appreciated that the slot shown in Figure 5C contains an uneven number of first tooth turns and second tooth turns. That is to say, there are more turns of wire around the first tooth 110 than there are around the second tooth 120 at this point in the winding method. As explained above, this may be prohibited by some winding arrangements. In order to balance the number of second tooth turns with the number of first tooth turns, and in order to make use of the remaining space in the slot, the tertiary layer 123 of the second winding 125 can be wound by the needle 150 starting from its position shown in Figure 5C. Notably, the needle 150 can pass through the slot without being obstructed by any of the other turns.

Figure 5D illustrates a snapshot in time during the process of winding the tertiary layer 123 of the second winding 125. As described earlier, the tertiary layer 123, which is shown in Figure 5D to be partway through its winding process, can be wound by threading the needle in a longitudinal direction successively through the slots immediately adjacent to the second tooth 120, while simultaneously being retreated out of the slot in a radially inwards direction. Once the tertiary layer 123 has been wound around the first tooth 120, there is no more space available for the needle 150 to wind any further turns of wire in that slot, and so the needle 150 can be moved to another slot to continue the winding method as illustrated by either the first or second winding methods described above.

This advantageous way of controlling the needle 150 in order to achieve the advantageous winding arrangement described above, is helped in part by the possibility of relative angular movement between the needle 150 and the stator core 103. In particular, in order to prevent the needle 150 from colliding with any other turns of wire during the winding process, the needle 150 can be shifted angularly relative to the stator core 103. This angular shift can be seen by comparing the position of the needle 150, relative to the windings, in Figures 5A and 5B. In this example, assuming the secondary layer 112 is wound before the primary layer 121, the needle 150 can be moved relative to the stator core 103 from the angular position shown in Figure 5A, in a clockwise direction, to the angular position shown in Figure 5B. It will be appreciated that this may alternatively be achieved by rotating the stator core 103 in an anticlockwise direction relative to the needle 150. This angular movement ensures that the needle 150 clears the secondary layer 112 while winding the primary layer 121 of the second winding 125. Similarly, the needle 150 can be shifted from the angular position shown in Figure 5B, in an anticlockwise direction, to the angular position shown in Figure 5C. This can ensure that the needle 150 is clear from the primary layer 121 during the process of winding the tertiary layer 123 of the second winding 125.

Conventional needle winding methods known from the prior art typically provide slot fill factors up to 25%. In contrast, the needle winding methods carried out in accordance with the present disclosure can produce a stator with an advantageous winding arrangement having a relatively high slot fill factor. The slot fill factor achieved is more than the 25% achieved by known needle winding methods. The slot fill factor achieved is preferably at least 30%, preferably at least 350/s, preferably at least 40%, preferably at least 450/s, preferably at least 50%. In some embodiments, the fill factor achieved is 38% or more. Notably, this can be achieved using a solid stator core 103 made of a continuous annulus of material, without the need to adopt either a deformable stator, nor a stator made out of separate segments or modules. In other words, windings can be applied to the first and second teeth such that a slot disposed therebetween has a fill factor of at least 30% without modification to the dimensions of the stator core. The cross sectional area of the plurality of slots can be fixed throughout the method. This is in contrast to prior needle winding methods, which can only achieve relatively high slot fill factors by including a step of changing the dimensions of a slot, or by forming the stator from a plurality of radially

connectable units.

Various modifications, whether by way of addition, deletion and/or substitution, may be made to all of the above described embodiments to provide further embodiments, any and/or all of which are intended to be encompassed by the appended claims.

Claims

Claims 1. A stator for an electrical machine, comprising: a stator core having a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator; the plurality of teeth comprising a first tooth and a second tooth adjacent to the first tooth, the first tooth comprising a first tooth winding wound therearound and comprising at least one first tooth turn, and the second tooth comprising a second tooth winding wound therearound comprising at least one second tooth turn; wherein at least one slot of the stator comprises a first part-annular winding region, disposed at a first radial position with respect to the longitudinal axis of the stator; and wherein the first part-annular winding region comprises a greater number of first tooth turns than second tooth turns.
2. The stator according to claim 1, further comprising a second part-annular winding region, disposed at a different radial position with respect to the longitudinal axis of the stator to the first part-annular winding region, and comprising more second tooth turns than first tooth turns.
3. The stator according to claim 1 or claim 2, wherein the first part-annular winding region extends along substantially half of the radial extent of the at least one slot.
4. The stator according to claim 2 or claim 3, wherein the second part-annular winding region extends along substantially half of the radial extent of the slot, at a position radially inwards of the first part-annular winding region.
5. The stator according to any preceding claim, wherein the number of first tooth turns in the first part-annular winding region is equal to the number of second tooth turns in the second part-annular winding region.
6. The stator according to any preceding claim, wherein the number of second tooth turns in the first part-annular winding region is equal to the number of first tooth turns in the second part-annular winding region.
7. A method of manufacturing a stator for an electrical machine, comprising the steps of: providing a stator core comprising a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator; using a needle winding machine to apply windings to the first and second teeth, without modification to the dimensions of the stator core, to provide: a first winding around a first tooth of the plurality of teeth; and a second winding around a second tooth of the plurality of teeth, adjacent to the first tooth, such that a slot disposed between the first and second teeth has a fill factor of more than 25%.
8. The method according to claim 7, wherein a cross sectional area of the plurality of slots remains fixed throughout the method.
9. The method according to claim 7 or claim 8, wherein the needle winds the second winding around the second tooth after winding the first winding around the first tooth, such that an adjacent pair of counterwound teeth are provided using a single thread of 20 wire.
10. The method according to claim 7 or claim 8, comprising the step of winding at least one full layer of wire around the first tooth and the second tooth, and subsequently winding at least one partial layer of wire around the first tooth and the second tooth.
11. The method according to claim 7 or claim 8, comprising the step of winding at least one full layer and at least one partial layer of wire around the first tooth, and subsequently winding at least one full layer and at least one partial layer of wire around the second tooth.
12. The method according to claim 10 or claim 11, wherein the partial layer of wire wound around the first tooth is located in a first part-annular winding region and the partial layer of wire wound around the second tooth is located in a second part-annular winding region which is defined at a different radial position to the first part-annular winding region.
13. The method according to any of claims 7 to 12, wherein a minimum distance between the first winding and the second winding is configured to be less than the width of a needle of the needling winding machine.