WO2024116015A1

WO2024116015A1 - A stator assembly

Info

Publication number: WO2024116015A1
Application number: PCT/IB2023/061691
Authority: WO
Inventors: Robert Walsh; Oliver STRUTT; Christopher GASKELL; Chukwuma IFEDI
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2022-11-30
Filing date: 2023-11-20
Publication date: 2024-06-06
Anticipated expiration: 2025-05-30
Also published as: GB2624912A; GB202218010D0; CN120226239A

Abstract

A stator assembly for an electric motor includes a stator core having a plurality of teeth spaced apart to define a slot, a coil wound about a tooth of the plurality of teeth, a bobbin that positions the coil relative to the tooth, and a slot liner located within the slot.

Description

A STATOR ASSEMBLY

Field of the Invention

The present invention relates to a stator assembly for an electric motor.

Background of the Invention

There is a general desire to improve electric machines, such as electric motors, in a number of ways. For example, improvements may be desired in terms of size, weight, power density, manufacturing cost, efficiency, reliability, and noise.

Summary of the Invention

According to a first aspect of the present invention there is provided a stator assembly for an electric motor, the stator assembly comprising: a stator core comprising a plurality of teeth spaced apart to define a slot; a coil wound about a tooth of the plurality of teeth; a bobbin that positions the coil relative to the tooth; and a slot liner located within the slot.

The bobbin may be used to control positioning of the coil, which may enable a relatively high fill factor, for example of greater than 55%, to be achieved for the winding of the coil about the tooth. By fill factor is meant a ratio of the cross- sectional area of the conductive material of the coil to the cross-sectional area of open space within the slot. At the same time, the slot liner may provide insulation to ensure creepage and clearance requirements are met. The combination of the bobbin and the slot liner may thereby provide both relevant insulation, whilst also enabling a relatively high fill factor to be achieved.

The slot liner may be formed of an electrically insulating material, such as a dielectric material. The coil may be located within adjacent slots either side of the tooth. The slot liner may substantially cover surfaces of the adjacent slots either side of the tooth.

The bobbin may comprise an aperture through which the tooth extends. The bobbin may be attached to the tooth by an adhesive, for example with the adhesive located within the aperture through which the tooth extends.

The bobbin may comprise a plurality of grooves, and an innermost layer of the coil may be located within the plurality of grooves. This may ensure that the winding is wound about the tooth in a pre-determined pattern, which may ensure that the coil is wound about the tooth with a relatively high fill factor, for example when compared to an arrangement in which the plurality of grooves are absent. In particular, absent the plurality of grooves the coil may move along the length of the tooth during winding, which may result in misalignment of the coil and a relatively poor fill factor.

The bobbin may comprise a retention member for retaining the coil within the slot, for example within the adjacent slots either side of the tooth. This may ensure correct location of the coil, and may ensure that the coil is retained in a predetermined winding pattern, thereby ensuring a relatively high fill factor. The bobbin may comprise a main body, and the retention member may extend outwardly from the main body along an outermost periphery of the slot, for example outwardly in opposing directions from the main body. The retention member may extend in a generally circumferential direction. This may act to inhibit radially outward motion of the coil.

The retention member may comprise a plurality of guide channels, and at least a portion of the coil may be located within the plurality of guide channels. This may ensure that the coil is retained in a pre-determined winding pattern, thereby ensuring a relatively high fill factor. The tooth may comprise an inner end, the bobbin may comprise an inner guide surface located about the inner end of the tooth, the inner guide surface may comprise a guide recess, and at least a portion of an initial turn of the coil may be located within the guide recess. This may ensure that the coil is retained in a predetermined winding pattern, thereby ensuring a relatively high fill factor. The inner end of the tooth may comprise a radially inner end of the tooth, for example an end of the tooth attached to a yoke of the stator core.

The plurality of teeth may be spaced apart to define a plurality of slots, and the slot liner may be located within adjacent slots either side of the tooth. Use of a single slot liner in adjacent slots may reduce component count relative to an arrangement where individual slot liners are required for each slot.

The slot liner may comprise an aperture through which the tooth extends. This may enable correct location of the slot liner relative to the tooth. The slot liner may comprise a base within which the aperture is located, and first and second upstanding arms located at opposing ends of the base. In such a manner the slot liner may extend across bases of the adjacent slots either side of the tooth, and respective outer side walls of the adjacent slots either side of the tooth. Adhesive may be located within the aperture of the slot liner, between the slot liner and at least one of the bobbin and the tooth. The slot liner may be in direct contact with surfaces of the adjacent slots either side of the tooth, for example such that there is no adhesive located between the slot liner and surfaces of the adjacent slots either side of the tooth.

The slot liner may be formed of a resi I iently deformable material. This may ensure that the slot liner is appropriately located with the adjacent slots either side of the tooth, for example by enabling the slot liner to contract during insertion of the slot liner into the adjacent slots, and expand to fill the respective slot once inserted. The slot liner may overhang ends of the respective adjacent slots either side of the tooth. This may facilitate meeting relevant creepage and clearance requirements.

The stator assembly may have a width no more than 100mm, for example a diameter of no more than 100mm. Use of both a slot liner and a bobbin with a stator assembly of such a size may facilitate relatively high fill factor whilst meeting relevant creepage and clearance requirements. The stator assembly may have a width, for example a diameter, of no more than 75mm, or no more than 50mm. The stator assembly may comprise a width, for example an outer diameter, of around 28mm.

The stator assembly may comprise a plurality of bobbins, each located about a tooth of the plurality of teeth such that a portion of the bobbin is located within respective adjacent slots either side of the tooth, a plurality of coils, each coil wound about a respective bobbin; and a plurality of slot liners, each slot liner located within adjacent slots either side of the respective tooth.

The stator core may comprise a yoke, and the tooth may be a separate component attached to the yoke. As the tooth is a separate component to the yoke, the bobbin assembly may be located relative to the tooth at a location remote from the yoke, thereby facilitating winding of the coil and location of the coil relative to the tooth. This may particularly be the case where the stator assembly has a relatively small diameter, where the slots may be relatively small. Use of a tooth that is a separate component to the yoke may facilitate use of a spindle winding method for winding the coil about the tooth. Spindle winding may enable a greater fill factor in comparison to other winding methods, for example in comparison to a fly winding method. Use of a separate tooth to the yoke may also provide greater flexibility in options for the overall shape of the tooth when compared to an arrangement in which the yoke and the tooth are integrally formed as a monolithic component. The tooth may be attached to the yoke via an adhesive.

The tooth may comprise a main body, and outer tooth tips extending outwardly from an outer end of the main body. Provision of tooth tips may provide more stator material than a corresponding stator assembly absent the tooth tips, and hence may provide greater efficiency for an electric motor comprising the stator assembly. The outer tooth tips may extend outwardly from the outer end of the main body in opposing directions. The outer tooth tips may extend circumferentially from the outer end of the main body.

The tooth may comprise a main body, and inner tooth tips extending outwardly from an inner end of the main body. Provision of tooth tips may provide more stator material than a corresponding stator assembly absent the tooth tips, and hence may provide greater efficiency for an electric motor comprising the stator assembly. The inner tooth tips may extend outwardly from the inner end of the main body in opposing directions. The inner tooth tips may extend circumferentially from the inner end of the main body.

The bobbin may comprise a first bobbin portion located about a first portion of the tooth, and a second bobbin portion located about a second portion of the tooth, the first and second bobbin portions comprising separate components attached to one another. Provision of first and second bobbin portions attached to one another may facilitate provision of radially outer tooth tips on the tooth, as the first and second bobbin portions can be brought together about the main body of the tooth without the need to slide the bobbin over the tooth.

The first and second bobbin portions may overlap one another at an interface between the first and second bobbin portions. Such an overlap may absorb any tolerances of manufacture of the first and second bobbin portions of the tooth. An interface between the first and second bobbin portions may be located at an axial end of the tooth. This may remove the interface to an area where variation in the interface does not impact on fill factor within the slots, thereby enabling a relatively high fill factor within the slots to be achieved. The interface may extend in a substantially radial direction. The first and second bobbin portions may each extend axially along substantially the entire length of the stator tooth. The first and second bobbin portions may each have a width corresponding substantially to half a width of the stator tooth.

The slot liner may be located between the bobbin and a portion of the tooth. This may ensure that the slot liner is positioned and held in place by the bobbin and the portion of the tooth, for example without the need for adhesive or the like.

The bobbin may comprise a first bobbin portion located at a first end of the tooth, and a second bobbin portion located at a second end of the tooth opposite to the first end of the tooth, the first and second bobbin portions comprising separate components. This may enable an arrangement where the first and second bobbin portions do not need to extend into the slot, and hence an arrangement in which increased fill factor may be achieved relative to an arrangement in which the first and second bobbin portions extend into the slot.

The tooth may comprise a recess, and the first bobbin portion may comprise a projection received within the recess. This may provide increased fill factor relative to an arrangement absent a recess, in which the first bobbin portion extends into the slot to a greater extent. The tooth may comprise a plurality of recesses, and each of the first and second bobbin portions may comprise a projection that extends into a corresponding recess.

The stator core may comprise a yoke, and the tooth may be integrally formed with the yoke. This may reduce component count compared to an arrangement where the yoke and the tooth are separate components. The bobbin may comprise an aperture, and an outer end of the tooth may comprise edges that do not overlie a periphery of the aperture. This may facilitate location of the bobbin relative to the tooth during manufacture, for example by enabling the bobbin to be slid onto the tooth using the aperture.

The bobbin may comprise a monolithic component. This may reduce component count compared to an arrangement where the yoke and the tooth are separate components.

The first and second bobbin portions may each comprise a respective first member corresponding to a shape of the yoke, and a respective second member corresponding to a shape of the tooth. This may provide increased cross- sectional area for the first and second bobbin portions to be attached to the respective first and second ends of the tooth, for example in comparison to an arrangement in which the first member is absent. The yoke may be annular in form, and the first members may be annular in form. The stator core may comprise a plurality of teeth, and the first and second bobbin portions may comprise a respective plurality of second members corresponding to the plurality of teeth. According to a second aspect of the present invention there is provided an electric motor comprising a stator assembly according to the first aspect of the present invention.

According to a third aspect of the present invention there is provided a vacuum cleaner comprising an electric motor according to the second aspect of the present invention.

According to a fourth aspect of the present invention there is provided a cleanerhead for a vacuum cleaner, the cleanerhead comprising a rotatable member, and an electric motor according to the second aspect of the present invention, the electric motor configured to cause rotation of the rotatable member.

The rotatable member may comprise an agitator, for example a brushbar, for agitating a surface to be cleaned.

According to a fifth aspect of the present invention there is provided a fan assembly comprising an electric motor according to the second aspect of the present invention.

According to a sixth aspect of the present invention there is provided a method comprising: providing a bobbin comprising a first aperture; winding a coil about the bobbin; providing a slot liner comprising a second aperture; providing a stator core comprising a plurality of teeth spaced apart to define a plurality of slots; passing a tooth of the plurality of teeth through the second aperture, such that the slot liner is located in adjacent slots either side of the tooth; and passing the tooth through the first aperture such that the bobbin is located around the tooth, and such that at least a portion of the bobbin, and at least a portion of the coil, is located within the adjacent slots either side of the tooth. According to a seventh aspect of the present invention there is provided a method comprising: providing a stator tooth; providing a slot liner comprising a first aperture; passing the stator tooth through the first aperture such that the slot liner is located at a position along the stator tooth; providing a first bobbin portion and a second bobbin portion separate to the first bobbin portion; connecting the first bobbin portion to the second bobbin portion such that the first and second bobbin portions are located about the stator tooth and retain the slot liner in position relative to the stator tooth; winding the bobbin to form a stator tooth subassembly; and affixing the stator tooth sub-assembly to a yoke of a stator core.

Optional features of aspects of the present invention may be equally applied to other aspects of the present invention, where appropriate.

Brief Description of the Drawings

Figure 1 is a first schematic view of a first embodiment of a stator assembly;

Figure 2 is a second schematic view of the stator assembly of Figure 1 ;

Figure 3 is an exploded view of a winding sub-assembly of the stator assembly of Figure 1 ;

Figure 4 is a first view of a bobbin of the winding sub-assembly of Figure 3;

Figure 5 is a second view of the bobbin of Figure 4;

Figure 6 is a view of a slot liner of the winding sub-assembly of Figure 3;

Figure 7 is a schematic view illustrating positioning of a coil of the winding subassembly of Figure 3; Figure 8 is a first schematic view of a second embodiment of a stator assembly;

Figure 9 is a second schematic view of the stator assembly of Figure 8;

Figure 10 is an exploded view of a winding sub-assembly of the stator assembly of Figure 8;

Figure 11 is a first view of a bobbin of the winding sub-assembly of Figure 10;

Figure 12 is a second view of the bobbin of Figure 11 ;

Figure 13 is a schematic view illustrating positioning of a coil of the winding subassembly of Figure 10;

Figure 14 is a schematic view of a third embodiment of a stator assembly;

Figure 15 is a schematic view of a fourth embodiment of a stator assembly;

Figure 16 is an exploded view of a winding sub-assembly of the stator assembly of Figure 15;

Figure 17 is a schematic view of an electric motor;

Figure 18 is a schematic view of a vacuum cleaner comprising the electric motor of Figure 17;

Figure 19 is a schematic view of the cleanerhead of the vacuum cleaner of Figure 18;

Figure 20 is a schematic view of a haircare appliance comprising the electric motor of Figure 17; and Figure 21 is a schematic view of a fan assembly comprising the electric motor of Figure 17.

Detailed Description of the Invention

A first embodiment of a stator assembly 10 is illustrated schematically in Figures 1 and 2, and comprises a stator core 12, and six winding sub-assemblies 14.

The stator core 12 comprises a yoke 16 and twelve teeth 18. The yoke 16 is annular in form, and the teeth 18 extend radially outwardly from the yoke 16. The yoke 16 and the teeth 18 are integrally formed. The stator core 12 is formed of a stack of laminations (not shown), each comprising a yoke portion and respective teeth portions that collectively define the yoke 16 and the teeth 18. Each tooth 18 has a substantially uniform rectangular cross-sectional shape. The teeth 18 are spaced apart to define a plurality of slots 19, with each slot being generally v- shaped in form, albeit with a curved rather than pointed innermost region.

A single winding sub-assembly 14 is shown in isolation in an exploded view in Figure 3. It will be appreciated that each winding sub-assembly 14 has the same form, and that only one winding sub-assembly is described here for sake of brevity. The winding sub-assembly 14 comprises a bobbin 20, a coil 22, and a slot liner 24.

The bobbin 20 is shown in isolation in Figures 4 and 5. The bobbin 20 comprises a main body 26, a guide surface 28, and a retention member 30.

The main body 26 is generally cuboidal in form, and has side faces 32 extending from a first end 34 of the main body 26 to a second end 35 of the main body 26. The side faces 32 comprise a plurality of longitudinal grooves 36. The longitudinal grooves 36 have a generally semi-circular cross-sectional shape, and are dimensioned to receive a portion of the coil 22 therein. A rectangular aperture 38 extends through the main body 26. The rectangular aperture 38 is shaped and dimensioned to correspond to a cross-sectional area of one of the teeth 18.

The guide surface 28 is located at the first end 34 of the main body 26, and comprises a rim that extends outwardly from the first end 34 of the main body 26. In some examples the guide surface 28 comprises a guide recess that extends longitudinally along the guide surface 28, is shaped and dimensioned to correspond to receive a portion of the coil 22 therein, in a similar manner to the longitudinal grooves 36.

The retention member 30 comprises first 40 and second 42 arms that extend outwardly from the second end 28 of the main body 26. The first 40 and second 42 arms extend outwardly by a greater extent than the guide surface 28, and are curved slightly in a direction toward the main body 26. The extent of each of the first 40 and second 42 arms corresponds to slightly more half of a width of one of the slots 19 at an outermost end of the slot 19. In some examples the first 40 and second 42 arms comprise one or more guide channels shaped and dimensioned to correspond to receive a portion of the coil 22 therein, in a similar manner to the longitudinal grooves 36.

The main body 26, the guide surface 28, and the retention member 30 are integrally formed of a plastic, electrically insulating, material, such that the bobbin 20 is a one-piece construction. Collectively, the main body 26, the guide surface 28, and the retention member 30, give the bobbin 20 a generally T-shaped cross- sectional shape, as seen in Figure 5.

The coil 22 comprises a copper wire having a circular cross-sectional shape, with the wire wound into a plurality of turns about the bobbin 20, as will be described in more detail hereinafter. The slot liner 24 is shown in isolation in Figure 6, and comprises a main portion 44, and first 46 and second 48 side portions. The main portion 44 is generally rectangular in form, and has an aperture 50 formed therein. The slot liner 24 has a length greater than a length of a corresponding one of the slots 19, and a width corresponding to a combined width of two adjacent slots 19 and a tooth 18 that sits between the two adjacent slots 19. The aperture 50 of the slot liner 24 is generally rectangular in form, and is shaped and dimensioned to generally correspond to the cross-sectional shape of a corresponding one of the teeth 18.

The first 46 and second 48 side portions extend upwardly from the main portion 44, and are each generally rectangular in form. The first 46 and second 48 side portions have a height from the main portion 44 substantially corresponding to a height of one of the teeth 18, or one of the corresponding slots 19.

The main portion 44 and the first 46 and second 48 side portions are integrally formed from a resiliently deformable, electrically insulating, material, such that the slot liner 24 is a one-piece construction.

To assemble the stator assembly 10, the coil 22 is wound about the bobbin 20 when the bobbin 20 is located remotely from the stator core 12. An innermost layer of the coil 20 sits within the longitudinal grooves 36 of the linear side surfaces 32 of the bobbin 20. The guide surface 28 and the retention member 30 act to inhibit relative movement of the coil 22 to the bobbin 20 in a direction along a height of the main body 26 of the bobbin 20. Location of the coil 22 relative to the bobbin 20 is illustrated schematically in Figure 7.

This process is repeated for each coil 22 and bobbin 20 of the stator assembly 10.

When it is desired to locate the wound bobbins onto the stator core 12, the slot liner 24 is positioned below the guide surface 28 of the bobbin 20, such that the rectangular aperture 38 of the bobbin 20 is aligned with the aperture 50 of the slot liner 24. The winding sub-assembly 14 is then slid onto one of the teeth 18, with the tooth 18 passing through the aperture 50 of the slot liner 24 and the rectangular aperture 38 of the bobbin 20. Adhesive may be located within the slots 19 either side of the tooth 18, and/or on the tooth 18 itself, to secure the winding sub-assembly 14 in place.

When the winding sub-assembly 14 is located on the tooth 18, the bobbin 20 extends about the tooth 18, and the coil 22 is located within the slots 19 either side of the tooth 18. The slot liner 24 is also located within the slots 19 either side of the tooth 18. By use of the bobbin to control positioning of the coil 22, a relatively high fill factor, for example of greater than 55%, can be achieved for the winding of the coil 22 about the tooth 18. At the same time, the slot liner 24 may provide insulation to ensure creepage and clearance requirements are met. The combination of the bobbin 20 and the slot liner 24 may thereby provide both relevant insulation, whilst also enabling a relatively high fill factor to be achieved.

The winding sub-assemblies 14 can be located on respective teeth 18, either in sequence, or indeed with all winding sub-assemblies 14 located at the same time, with winding sub-assemblies 14 located on every other tooth 18 of the stator core 12.

A second embodiment of a stator assembly 100 is illustrated schematically in Figures 8 and 9, where like reference numerals are used for sake of clarity.

The stator assembly 100 comprises a first stator core component 102, and six winding sub-assemblies 104.

The first stator core component 102 comprises a yoke 106, and six integral teeth 108. The yoke 106 is annular in form, and the integral teeth 108 extend radially outwardly from the yoke 106. The stator core 102 is formed of a stack of laminations (not shown), each comprising a yoke portion and respective teeth portions that collectively define the yoke 106 and the integral teeth 108. Each tooth 108 has a cross-sectional width that increases slightly radially outwardly from the tooth 108, and has tooth tips 110 extending circumferentially from an end of the tooth 108 opposite to the yoke 106.

A single winding sub-assembly 104 is shown in isolation in an exploded view in Figure 10. It will be appreciated that each winding sub-assembly 104 has the same form, and that only one winding sub-assembly 104 is described here for sake of brevity. The winding sub-assembly 104 comprises a second stator core component 112, a bobbin 114, a coil 22, and a slot liner 116.

The second stator core component 112 comprises a main body 120, an inner portion 122, and tooth tips 124. The second stator core component 112 may be thought of as a segmented stator tooth. The main body 120 and tooth tips 124 are shaped and dimensioned to correspond to one of the integral teeth 108. The inner portion 122 extends outwardly relative to the main body 120 at an opposite end of the second stator core component 112 to the tooth tips 124. The inner portion 122 has an extent corresponding substantially to a radially innermost spacing between adjacent ones of the integral teeth 108. The second stator core component 112 is formed by a plurality of laminations fixed together.

Collectively, the first stator core component 102 and the second stator core component 122 define a stator core.

The bobbin 114 is illustrated in isolation in Figures 11 and 12. The bobbin 114 of the second embodiment of the stator assembly 100 is substantially the same as the bobbin 10 of the first embodiment, save that the bobbin 114 is formed of first 126 and second 128 bobbin portions, that the guide surface 28 comprises a guide recess 130, and that the retention member 130 comprises guide channels 132. The bobbin 114 is split along its longitudinal axis L to define the first 126 and second 128 bobbin portions, with each of the first 126 and second 128 bobbin portions comprising respective stepped interfaces 134,136. Collectively, the first 126 and second 128 bobbin portions define the main body 26, the guide surface 28, and the retention member 30, including the rectangular aperture 36 when the first 126 and second 128 bobbin portions are connected together.

The guide surface 28 of the bobbin 114 extends longitudinally outwardly, as well as circumferentially outwardly, of the main body 26, and the guide recess 130 is formed in the portion of the guide surface 28 that extends longitudinally outwardly of the main body 26. The guide recess 130 is shaped and dimensioned to receive a portion of the coil 22, and receives an initial portion of the first turn of the coil 22 when wound about the bobbin 114.

The guide channels 132 extend only partly along the first 40 and second 42 arms of the retention member 30, and are each shaped and dimensioned to receive a portion of the coil 22.

The coil 22 of the second embodiment of the stator assembly 100 is substantially the same as the coil 22 of the first embodiment of the stator assembly 10, save for the number of turns.

The slot liner 116 of the second embodiment of the stator assembly 100 is substantially the same as the slot liner 24 of the first embodiment of the stator assembly 10, save that the first 46 and second 48 side portions are shaped to accommodate the tooth tips 110 of the integral teeth 108.

To assemble the second embodiment of the stator assembly 100, the second stator core component 112 is slid through the aperture 50 of the slot liner 24, when the second stator core component 112 is located remotely from the first stator core component 102, such that the main portion 46 of the slot liner 24 overlies the inner portion 122 of the second stator core component 112. The first 126 and second 128 bobbin portions are brought together about the main body 120 of the second stator core component 112, and are fixed together by an adhesive. The bobbin 114 holds the slot liner 24 in place relative to the second stator core component 112.

The coil 22 is then wound about the bobbin 114 remotely from the first stator core component 102. A first turn of the coil 22 lies within the guide recess 130 of the guide surface 28 of the bobbin 114, and an innermost layer of the coil 22 sits within the longitudinal grooves 36 of the linear side surfaces 32 of the bobbin 114. Turns of the coil 22 also sit within the guide channels 132 of the first 40 and second 42 arms of the retention member 30. Location of the coil 22 relative to the bobbin 114 is illustrated schematically in Figure 13.

This process is repeated for each winding sub-assembly 104 of the stator assembly 10.

When it is desired to locate the winding sub-assembly 104 relative to the first stator core component 102, the winding sub-assembly 104 is fixed, using adhesive, between a pair of adjacent integral teeth 108. The second stator core component 112, e.g. the segmented stator tooth, and the integral teeth 108 define slots of the stator assembly 100 within which the coil 22 is located.

A third embodiment of a stator assembly 200 is illustrated schematically in Figure 14.

The stator assembly 200 comprises a stator core 202, first 204 and second bobbin portions, first 206 and second 208 slot liners, and a coil 210.

The stator core 202 comprises a yoke 212, six first teeth 214, and six second teeth 216. The yoke 212 is annular in form. The first teeth 214 extend radially outwardly from the yoke 212, and radially outer ends of the first teeth 214 comprise circumferentially extending tooth tips 218. The second teeth 216 extend radially outwardly from the yoke 212, and are positioned in alternating fashion with the first teeth 214 to define slots 215.

The first 204 and second bobbin portions have the same form, with each having an annular section 220 and six tooth sections 222. The annular section 220 substantially corresponds to the shape and dimensions of the yoke 212, and the tooth sections 222 substantially correspond to the shape and dimensions of the second teeth 216. Although not illustrated, the tooth sections 222 can comprise grooves in a similar manner to the longitudinal grooves 36 of the first embodiment 10 of the stator assembly. The first 204 and second bobbin portions are fixed, via adhesive, to respective first and second axial ends of the stator core 200, such that the annular sections 220 overlie the yoke 212 and the tooth sections 222 overlie the second teeth 216.

The first 206 and second 208 slot liners are each formed from a resiliently deformable, electrically insulating, material, and are generally shaped to correspond to the shape of one of the slots 215. The first 206 and second 208 slot liners are each received in a respective slot 215.

The coil 210 comprises a copper wire having a circular cross-sectional shape, with the wire wound into a plurality of turns.

To assemble the third embodiment of the stator assembly 200, the first 204 and second bobbin portions are fixed to their respective ends of the stator core 202, and the first 206 and second 208 slot liners are located in respective adjacent slots 215 either side of one of the second teeth 216. The coil 210 is wound remotely from the stator core 202, and subsequently slotted over the second tooth 216 such that the coil 210 sits within the first 206 and second 208 slot liners. It will be appreciated that further slot liners and coils are utilised for each for the remaining slots and second teeth 216 to form the full stator assembly 200.

A fourth embodiment of a stator assembly 300 is illustrated schematically in Figure 15.

The stator assembly 300 comprises a first stator core component 302, and six winding sub-assemblies 304.

The first stator core component 302 comprises a yoke 306, and six integral teeth 308. The yoke 306 is annular in form, and the integral teeth 308 extend radially outwardly from the yoke 306. Each integral tooth 308 has tooth tips 310 extending circumferentially from an end of the tooth 308 opposite to the yoke 306, and undercuts 313 at the interface with the yoke 306. Only one pair of undercuts 313 is illustrated in Figure 15. Other forms of attachment mechanism that do not utilise the undercuts 313 are also envisaged.

A single winding sub-assembly 304 is shown in isolation in an exploded view in Figure 16. It will be appreciated that each winding sub-assembly 304 has the same form, and that only one winding sub-assembly 304 is described here for sake of brevity. The winding sub-assembly 304 comprises a second stator core component 312, first 314 and second 315 bobbin portions, a coil 316, and first 318 and second 319 slot liners.

The second stator core component 312 comprises a main body 320, an inner portion 322, and tooth tips 324. The second stator core component 312 may be thought of as a segmented stator tooth. The main body 320 and tooth tips 324 are shaped and dimensioned to correspond to one of the integral teeth 308. The main body 320 comprises recesses 325. The inner portion 322 extends outwardly relative to the main body 320 at an opposite end of the second stator core component 312 to the tooth tips 324. The inner portion 322 has an extent corresponding substantially to a radially innermost spacing between adjacent ones of the integral teeth 308, and ends of the inner portion 322 are shaped and dimensioned to be received within corresponding undercuts 313.

Collectively, the first stator core component 302 and the second stator core component 322 define a stator core.

The first 314 and second 315 bobbin portions have substantially the same form, with each having a main body 326, an inner member 328, an outer member 330, and projections 332. The main body 326 is shaped to correspond to the main body 320 of the second stator core component 312, the inner member 328 is shaped to correspond to the inner portion 322 of the second stator core component 312, and the outer member 330 is shaped to correspond to the tooth tips 324 of the second stator core component 312. Edges of the main body 326 that extend between the inner member 328 and the outer member 330 comprise grooves 332 for receiving a portion of the coil 316. The projections 332 extend orthogonally from the main body 326, and are shaped and dimensioned to be received within corresponding ones of the recesses 325 of the second stator core component 312.

The coil 316 of the fourth embodiment of the stator assembly 300 is substantially the same as the coil 22 of the first embodiment of the stator assembly 10, save for the number of turns.

The first 318 and second 319 slot liners are formed of a resiliently deformable, electrically insulating, material, and define generally v-shaped channels. To assemble the fourth embodiment of the stator assembly 300, the first 314 and second 315 bobbin portions are fixed to respective ends of the second stator core component 312, with the projections 332 of the first 314 and second 315 bobbin portions located within the recesses 325 of the second stator core component 312. The first 318 and second 319 slot liners are fixed to opposing sides of the second stator core component 312, and the coil 316 is wound about the main body 320 of the second stator core component 312 such that the coil 316 lies within the first 318 and second 319 slot liners.

This process is repeated for each winding sub-assembly 304 of the stator assembly 300.

When it is desired to locate the winding sub-assembly 304 relative to the first stator core component 302, the winding sub-assembly 304 is slid axially such that the inner portion 322 of the second stator core component 312 slots into the undercuts 313 of adjacent integral teeth 308 of the first stator core component 302. Adhesive can also be used to fix the winding sub-assembly 304 in place. This process is repeated for each winding sub-assembly 304 of the stator assembly 300.

Common to each of the first 10, second 100, third 200, and fourth 300, embodiments of the stator assembly, is use of both a bobbin and a slot liner. By use of the bobbin to control positioning of the coil, a relatively high fill factor, for example of greater than 55%, can be achieved for the winding of the coil about the tooth. At the same time, the slot liner may provide insulation to ensure creepage and clearance requirements are met. The combination of the bobbin and the slot liner may thereby provide both relevant insulation, whilst also enabling a relatively high fill factor to be achieved.

An electric motor 400 comprising any of the first 10, second 100, third 200, and fourth 300, embodiments of the stator assembly, and a rotor assembly 402 is illustrated schematically in Figure 17. The rotor assembly 402 is an outer rotor assembly 402 comprising a plurality of permanent magnets (not shown). In use, a voltage is applied to the coils of the stator assembly 10, 100,200,300 to generate a magnetic field, which in turn interacts with the permanent magnets to rotate the rotor assembly 402 relative to the stator assembly 10,100,200,300. Further details of the electric motor 400 are not pertinent, and so will not be described here for sake of brevity. Although illustrated here as an outer rotor motor, it will be appreciated that inner rotor motors that utilise the teachings discussed herein are also envisaged.

A vacuum cleaner 500 comprising the electric motor 400 is illustrated schematically in Figure 18. The vacuum cleaner 500 comprises a main unit 502, a wand 504, and a cleanerhead 506.

The cleanerhead 506 is illustrated schematically in Figure 19, and comprises a housing 508, a brushbar 510, and the electric motor 400. The electric motor 400 is located within the brushbar 510, and is used to drive motion of the brushbar 510 within the housing 508 in use. Further details of the cleanerhead 506 are not pertinent, and so will not be described here for sake of brevity.

A haircare appliance 600 comprising the electric motor 400 is illustrated schematically in Figure 20. Here the electric motor 400 generates an airflow through the haircare appliance 600 in use.

A fan assembly 700 comprising the electric motor 400 is illustrated schematically in Figure 21 . Here the electric motor 400 generates an airflow through the fan assembly 700 in use.

Whilst particular examples and embodiments have thus far been described, it should be understood that these are illustrative only and that various modifications may be made without departing from the scope of the invention as defined by the claims.

Claims

1 . A stator assembly for an electric motor, the stator assembly comprising: a stator core comprising a plurality of teeth spaced apart to define a slot; a coil wound about a tooth of the plurality of teeth; a bobbin that positions the coil relative to the tooth; and a slot liner located within the slot.

2. A stator assembly as claimed in Claim 1 , wherein the bobbin comprises a plurality of grooves, and an innermost layer of the coil is located within the plurality of grooves.

3. A stator assembly as claimed in Claim 1 or Claim 2, wherein the bobbin comprises a retention member for retaining the coil within the slot.

4. A stator assembly as claimed in Claim 3, wherein the retention member comprise a plurality of guide channels, and at least a portion of the coil is located within the plurality of guide channels.

5. A stator assembly as claimed in any preceding claim, wherein the tooth comprises an inner end, the bobbin comprises an inner guide surface located about the inner end of the tooth, the inner guide surface comprises a guide recess, and at least a portion of an initial turn of the coil is located within the guide recess.

6. A stator assembly as claimed in any preceding claim, wherein the plurality of teeth are spaced apart to define a plurality of slots, and the slot liner is located within adjacent slots either side of the tooth.

7. A stator assembly as claimed in Claim 6, wherein the slot liner comprises an aperture through which the tooth extends.

8. A stator assembly as claimed in any preceding claim, wherein the slot liner is formed of a resil iently deformable material.

9. A stator assembly as claimed in any preceding claim, wherein the slot liner overhangs ends of the respective adjacent slots either side of the tooth.

10. A stator assembly as claimed in any preceding claim, wherein the stator assembly has a width of no more than 100mm.

11. A stator assembly as claimed in any preceding claim, wherein the stator core comprises a yoke, and the tooth is a separate component attached to the yoke.

12. A stator assembly as claimed in any preceding claim, wherein the tooth comprises a main body, and outer tooth tips extending outwardly from an outer end of the main body.

13. A stator assembly as claimed in any preceding claim wherein the tooth comprises a main body, and inner tooth tips extending outwardly from an inner end of the main body.

14. A stator assembly as claimed in any preceding claim, wherein the bobbin comprises a first bobbin portion located about a first portion of the tooth, and a second bobbin portion located about a second portion of the tooth, the first and second bobbin portions comprising separate components attached to one another.

15. A stator assembly as claimed in Claim 14, wherein the first and second bobbin portions overlap one another at an interface between the first and second bobbin portions.

16. A stator assembly as claimed in Claim 14 or Claim 15, wherein an interface between the first and second bobbin portions is located at an axial end of the tooth.

17. A stator assembly as claimed in any preceding claim, wherein the slot liner is located between the bobbin and a portion of the tooth.

18. A stator assembly as claimed in any of Claims 1 to 13, wherein the bobbin comprises a first bobbin portion located at a first end of the tooth, and a second bobbin portion located at a second end of the tooth opposite to the first end of the tooth, the first and second bobbin portions comprising separate components.

19. A stator assembly according to Claim 18, wherein the tooth comprises a recess, and the first bobbin portion comprises a projection received within the recess.

20. A stator assembly as claimed in any of Claims 1 to 10, wherein the stator core comprises a yoke, and the tooth is integrally formed with the yoke.

21 . A stator assembly as claimed in Claim 20, wherein the bobbin comprises an aperture, and an outer end of the tooth comprises edges that do not overlie a periphery of the aperture.

22. A stator assembly as claimed in Claim 20 or Claim 21 , wherein the bobbin comprises a monolithic component.

23. A stator assembly as claimed in Claim 20, wherein the bobbin comprises a first bobbin portion located at a first end of the tooth, and a second bobbin portion located at a second end of the tooth opposite to the first end of the tooth, the first and second bobbin portions comprising separate components.

24. A stator assembly as claimed in Claim 23, wherein the first and second bobbin portions each comprise a respective first member corresponding to a shape of the yoke, and a respective second member corresponding to a shape of the tooth.

25. An electric motor comprising a stator assembly as claimed in any preceding claim.

26. A vacuum cleaner comprising an electric motor as claimed in Claim 25.

27. A cleanerhead for a vacuum cleaner, the cleanerhead comprising a rotatable member, and an electric motor as claimed in Claim 25, the electric motor configured to cause rotation of the rotatable member.

28. A fan assembly comprising an electric motor as claimed in Claim 25.

29. A method comprising: providing a bobbin comprising a first aperture; winding a coil about the bobbin; providing a slot liner comprising a second aperture; providing a stator core comprising a plurality of teeth spaced apart to define a plurality of slots; passing a tooth of the plurality of teeth through the second aperture, such that the slot liner is located in adjacent slots either side of the tooth; and passing the tooth through the first aperture such that the bobbin is located around the tooth, and such that at least a portion of the bobbin, and at least a portion of the coil, is located within the adjacent slots either side of the tooth.

30. A method comprising: providing a stator tooth; providing a slot liner comprising a first aperture; passing the stator tooth through the first aperture such that the slot liner is located at a position along the stator tooth; providing a first bobbin portion and a second bobbin portion separate to the first bobbin portion; connecting the first bobbin portion to the second bobbin portion such that the first and second bobbin portions are located about the stator tooth and retain the slot liner in position relative to the stator tooth; winding the bobbin to form a stator tooth sub-assembly; and affixing the stator tooth sub-assembly to a yoke of a stator core.