GB2626583A

GB2626583A - An electric motor

Info

Publication number: GB2626583A
Application number: GB2301191.9A
Authority: GB
Inventors: Alexander Morley Harry; James Gaskell Christopher; Glyn Salmon Pierre; Sivagnanasundaram Subenuka; Serafimov Palatov Kaloyan; Celik Tuncay; Charlton Clothier Andrew
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2023-01-27
Filing date: 2023-01-27
Publication date: 2024-07-31
Also published as: GB202301191D0; WO2024157210A1

Abstract

An electric motor includes a stator assembly 12, a frame 16, and a rotor assembly 14 rotatably mounted to the frame. The rotor assembly includes an impeller 64 for generating an airflow through the electric motor, the frame is overmoulded onto the stator assembly, and the frame defines a plurality of diffuser vanes 94 located downstream of the impeller. The frame may be formed of a material having a coefficient of thermal conductivity of at least 4 W/mK and a dielectric strength of at least 15kV/mm. The electric motor may be used in a vacuum cleaner or a haircare appliance.

Description

AN ELECTRIC MOTOR

Field of the Invention

The present invention relates to an electric motor.

Background of the Invention

There is a general desire to improve electric machines, such as electric motors, 10 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 an electric motor comprising: a stator assembly; a frame; and a rotor assembly rotatably mounted to the frame; wherein the rotor assembly comprises an impeller for generating an airflow through the electric motor, the frame is overmoulded onto the stator assembly, and the frame defines a plurality of diffuser vanes located downstream of the impeller.

As the frame is overmoulded onto the stator assembly and the frame defines a plurality of diffuser vanes located downstream of the impeller, the frame may provide a number of different functions, including providing structural support for components of the electric motor, providing a thermal transfer path away from the stator assembly via the diffuser vanes, and providing a portion to which further components of the electric motor may be mounted. Providing a thermal transfer path from the stator assembly via the diffuser vanes may avoid a need to directly cool the stator assembly with airflow generated by the impeller, which may lead to increased aerodynamic and/or acoustic performance relative to an arrangement in which the stator assembly is directly cooled by airflow generated by the impeller.

Overmoulding the frame to the stator assembly may reduce tolerances relative to 5 an arrangement where the frame and the stator assembly are separate components fixedly attached to one another via adhesive or the like, and may enabled increased levels of concentricity between the frame and the stator assembly. Overmoulding the frame to the stator assembly may also aid with inhibition of relative movement between the frame and the stator assembly during 10 manufacture.

The stator assembly may comprise an electrical connection to a power source, and the frame may encapsulate the stator assembly such that the electrical connection is the only component of the stator assembly that is exposed through the frame. Encapsulating the stator assembly in such a manner may improve heat conduction from the stator assembly to the diffuser vanes, which may enable the electric motor to run at higher power than an arrangement absent the encapsulation. Such encapsulation may further aid with inhibiting relative movement between the stator assembly and the frame.

The electrical connection may comprise a plurality of electrical terminals that extend outwardly from the frame, for example outwardly in a direction parallel to a rotational axis of the rotor assembly.

The frame may comprise an inner portion that encapsulates the stator assembly, and an annular outer portion spaced from the inner portion to define an air passage, and the plurality of diffuser vanes may extend between the inner portion and the annular outer portion within the air passage. As the diffuser vanes are located within the air passage, airflow generated by the impeller in use may pass over the diffuser vanes, thereby removing heat from the stator assembly from the electric motor.

The inner portion, the outer annular portion, and the plurality of diffuser vanes, may be integrally formed, for example integrally formed as part of the same overmoulding process.

The plurality of diffuser vanes may each comprise a root thickness of at least 1mm at the inner portion. This may provide improved thermal conduction relative to diffuser vanes having a root thickness of less than 1mm at the inner portion. The plurality of diffuser vanes may each comprise a root thickness of at least 1.2mm, or at least 1.4mm, at the inner portion.

The plurality of diffuser vanes may each comprise a ratio of a root thickness at the inner portion to a shroud thickness at the outer portion of between in the region of 2:1 to 3:1.

The plurality of diffuser vanes may each comprise a cross-sectional shape comprising a root edge at the inner portion, a shroud edge at the outer portion, and first and second side edges extending between respective ends of the root edge and the shroud edge, wherein the first and second side edges are concave.

This may provide an increased surface area relative to an arrangement with straight side edges, which may provide for improved thermal transfer, whilst having minimal impact on aero-acoustic performance.

The annular outer portion may have an outer diameter of no more than 50mm, for example no more than 45mm, no more than 40mm, no more than 35mm, or no more than 30 mm. Thermal management in such a size of electric motor may be important to enable a desired power output to be achieved, and, as the stator assembly is heat source in use, overmoulding the frame to the stator assembly such that the frame also defines diffuser vanes may aid with such thermal management. The annular outer portion may have an outer diameter of around 28.5mm.

The inner portion may comprise an outer diameter of no more than 30mm, for example no more than 25mm, or no more than 20mm. The inner portion may comprise an outer diameter of around 19.4mm. The air passage may have a width, for example a width in a radial direction, of at least 5mm, for example at least 6mm. The air passage may have a width of no more than 7mm.

The electric motor may comprise a maximal axial length, for example a length in a direction parallel to the rotational axis of the rotor assembly, of less than 60mm, or less than 50mm. The electric motor may comprise a maximal axial length of around 46.5mm.

The electric motor may be configured to generate air flow at a rate of between 5 L/s and 25 Lis in use, for example between 9 L/s and 22 L/s in use.

The stator assembly may comprise a stator core component, and each of the plurality of diffuser vanes may extend along the frame for an axial length of at least 50% of a length of the stator core component. This may provide a path of thermal conduction along at least 50% of the length of the stator core component, which may aid with removal of heat generated by the stator assembly in use. Each of the plurality of diffuser vanes may extend along the frame for an axial length of at least 60%, at least 70%, at least 80%, or at least 90%, of the length of the stator core component. The axial length may comprise a length in a direction parallel to the rotational axis of the rotor assembly, for example in a direction parallel to a longitudinal axis of a shaft of the rotor assembly. The stator core component may comprise a stack of laminations of electrical steel.

Each of the plurality of diffuser vanes may extend along the frame for an axial length of between 5mm and 20mm, for example between 8mm and 16mm. Each of the plurality of diffuser vanes may extend along the frame for an axial length of around 12mm.

The stator assembly may comprise a coil having an upstream end and a downstream end, each of the plurality of diffuser vanes may comprise a respective leading edge and a respective trailing edge, and distances between the respective trailing edges and the downstream end of the coil, measured in directions parallel to a rotational axis of the rotor assembly, may be no more than 30% of a distance measured between the upstream end and the downstream end of the coil in a direction parallel to the rotational axis of the rotor assembly. Thus the trailing edges of the plurality of diffuser vanes may enable removal of heat from the downstream end of the coil, which is the portion of the coil furthest removed from the impeller. Upstream and downstream may be used to indicate directionality relative to a direction of airflow through the electric motor in use. Distances between the respective trailing edges and the downstream end of the coil, measured in directions parallel to the rotational axis of the rotor assembly, may be no more than 20%, or no more than 10%, of the distance measured between the upstream end and the downstream end of the coil in the direction parallel to the rotational axis of the rotor assembly.

The respective leading edges of the plurality of diffuser vanes may be located 20 within a distance from the upstream end of the coil, and the distance may be between 35% to 50% of the distance between the upstream end of the coil and the downstream end of the coil.

The plurality of diffuser vanes may each have a blade sweep of around 0 degrees.

The plurality of diffuser vanes may comprise at least 7 diffuser vanes, at least 9 diffuser vanes, at least 11 diffuser vanes, or at least 13 diffuser vanes. The plurality of diffuser vanes may comprise exactly 13 diffuser vanes, for example no more than 13 diffuser vanes and no less than 13 diffuser vanes.

The frame may be formed of a material having a coefficient of thermal conductivity of at least 4 W/mK. This may provide efficient heat transfer away from the stator assembly, via the plurality of diffuser vanes, in use. The frame may be formed of a material having a coefficient of thermal conductivity of at least 5 W/m K. The frame may be formed of a material having a dielectric strength of at least 15kV/mm. This may enable a relatively small sized stator assembly whilst also meeting creepage and clearance requirements. This may enable a higher voltage to be utilised in the stator assembly, compared to where a material of lower dielectric strength is used, which may enable the electric motor to operate with increased efficiency and/or increased power density.

The frame may define a bearing seat, and the rotor assembly may comprise a bearing assembly located at the bearing seat to rotatably mount the rotor assembly to the frame. Thus the frame may provide structural support for the bearing assembly, alongside providing a thermal heat sink path away from the stator assembly via the diffuser vanes.

The frame may define a further bearing seat spaced apart from the bearing seat, and the rotor assembly may comprise a further bearing assembly located at the further bearing seat to rotatable mount the rotor assembly to the frame.

The electric motor may comprise a housing component attached to the frame upstream of the diffuser vanes, and the housing component may comprise a further plurality of diffuser vanes. As the housing component is attached to the frame, for example with the housing component being a separate component to the frame, increased flexibility of design for at least one of the plurality of diffuser vanes and the further plurality of diffuser vanes may be provided. For example, moulding two rows of diffuser vanes in an overmoulding process may place restrictions on the geometry achievable for the vanes in light of tooling requirements. By utilising a housing component separate to the frame, a wider range of geometries may be achievable for the plurality of diffuser vanes and the further plurality of diffuser vanes than would be the case if the plurality of diffuser vanes and the further plurality of diffuser vanes were formed as part of a same moulding process. For example, the plurality of diffuser vanes may be optimised for thermal transfer of heat away from the stator assembly, whilst the further plurality of diffuser vanes may be optimised for aero-acoustic performance.

The further plurality of diffuser vanes may comprise diffuser vanes of a different shape and/or size to the diffuser vanes of the plurality of diffuser vanes.

The housing component may comprise a further inner portion, and a further annular outer portion spaced from the further inner portion to define a further air passage, and the further plurality of diffuser vanes may extend between the further inner portion and the further annular outer portion within the further air passage. Collectively, the air passage and the further air passage may define an air channel through the electric motor. The further plurality of diffuser vanes may be located upstream of the plurality of diffuser vanes within the air channel.

The further plurality of diffuser vanes may be located radially outwardly of, and may at least partially axially overlap, a portion of the stator assembly. As the housing component is mounted to the frame, and the further plurality of diffuser vanes at least partially axially overlap a portion of the stator assembly, the housing component may define a heat transfer pathway away from the stator assembly, which may enable increased cooling of the stator assembly relative to an arrangement in which the housing component is not present. The housing component may at least partially axially overlap a bearing assembly of the rotor assembly.

The frame may be formed of a thermosetting epoxy resin with 80% -95% thermally conductive ceramic filler.

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

According to a third aspect of the present invention there is provided a haircare appliance comprising an electric motor according to the first aspect of the present invention.

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

Brief Description of the Drawings

Figure 1 is a schematic perspective view of an electric motor; Figure 2 is a schematic cross-sectional view of the electric motor of Figure 1; Figure 3 is a schematic perspective view of a stator assembly of the electric motor of Figure 1; Figure 4 is a schematic exploded view of the stator assembly of Figure 3; Figure 5 is a schematic perspective view of a stator core assembly of the stator assembly of Figure 3; Figure 6 is a schematic exploded view of the stator core assembly of Figure 5; Figure 7 is a schematic cross-sectional view of a rotor assembly of the electric motor of Figure 1; Figure 8 is a schematic cross-sectional view of a shaft of the rotor assembly of Figure 7; Figure 9 is a first schematic cross-sectional view of a frame of the electric motor of Figure 1; Figure 10 is a second schematic cross-sectional view of a frame of the electric motor of Figure 1; Figure 11 is a schematic view of a diffuser blade of the frame of Figure 9; and Figure 12 is a second schematic perspective view of the electric motor of Figure 1.

Detailed Description of the Invention

An electric motor 10 is illustrated schematically in Figures 1 and 2.

The electric motor 10 comprises a stator assembly 12, a rotor assembly 14, a 20 frame 16, a housing component 18, and a shroud 20.

The stator assembly 12 is illustrated schematically in Figures 3 and 4, and comprises first 22, second 24 and third 26 stator core assemblies, and first 28 and second 30 busbar assemblies.

The first stator core assembly is shown in Figures 5 and 6. Each of the first 22, second 24, and third 26 stator core assemblies has substantially the same form, and so the second 24 and third 26 stator core assemblies will not be described in detail here for the sake of brevity. It will be appreciated that like reference numerals for features of the first stator core assembly 22 may be used for corresponding features of the second 24 and third 26 stator core assemblies.

The first stator core assembly 22 comprises a stator core segment 32, a bobbin 34, first 36, second 38, and third 40 termination connections, and first 42 and second 44 coils.

The stator core segment 32 is formed of a stack of steel laminations (not shown), and is generally arcuate in form, with a height greater than its length and width. The stator core segment 32 spans an arc length of substantially 120 degrees. Circumferential end faces of the stator core segment 32 are generally planar in form.

The bobbin 34 is formed of a plastics material, and is overmoulded onto the stator core segment 32. The bobbin 34 comprises connection recesses 46, a window 48, and connection features 50. The connection recesses 46 are generally cylindrical in form, and are shaped and dimensioned to receive the respective first through third termination connections 36-40. The window 48 is generally elongate and rectangular in cross-section, and provides line-of-sight to a radially outer face of the stator core segment 32. The window 48 enables an appropriate magnet to hold the stator core segment 32 in place during assembly of the first stator core assembly 22. The connection features 50 comprise appropriate projections and/or recesses that interact with corresponding recesses and/or projections of the second 24 and third 26 stator core assemblies to hold the stator core assemblies 22,24,26 relative to one another.

The first through third termination connections 36-40 have substantially the same form, and are generally elongate pins with a square cross-sectional shape, formed from an electrically conductive material. The first 36 and second 38 termination connections are inserted into respective connection recesses 46 with a push-fit, and extend axially outwardly from a first end 52 of the first stator core assembly 22. The third termination connection 40 is inserted into a respective connection recess 46 and extends axially outwardly from a second end 54 of the first stator core assembly 22 opposite to the first end 52 of the first stator core assembly 22.

The first 42 and second 44 coils are formed from turns of copper wire, and are wound about the bobbin 34 such that the first 42 and second 44 coils overlie radially inner and radially outer surfaces of the stator core segment 32. The stator assembly 12 is a slotless stator assembly. The first 42 and second 44 coils are represented in block form, such that individual turns are not visible, in the figures for the sake of clarity. The first 42 and second 44 coils are formed from a single piece of copper wire, such that the first 42 and second 44 coils are wound using a continuous winding process. For example, the first coil 42 being at the first termination connection 36, is wound about the bobbin 34, and hence the stator core segment 32, and tied off at the third termination connection 40. The second coil 42 then starts at the third termination connection 40, is wound about the bobbin 34, and hence the stator core segment 32, and tied off at the second termination connection 38. The first 42 and second 44 coils are wound in opposite directions, with one of the first 42 and second 44 coils being right-hand wound, and the other of the second 44 and first 42 coils being left-hand wound.

Collectively, the first 22, second 24 and third 26 stator core assemblies, when connected together, define an annulus having a central bore 56 for receiving a rotor assembly, with the stator assembly 12 having a diameter of no more than 40mm. When connected together the generally circumferential faces of the stator core segments 32 are substantially in contact with one another, such that a generally annular stator core is formed by the stator core segments 32. The first 36 and second 38 termination connections of each stator core assembly 22,24,26 form a first subset of termination connections located at a first end 58 of the stator assembly 12, and the third termination connections 40 form a second subset of termination connections located at a second end 60 of the stator assembly 12.

The first 36 and second 38 termination connections are evenly spaced about a circumference of the first end 58 of the stator assembly 12, whilst the third termination connections 40 are evenly spaced about a circumference of the second end 60 of the stator assembly 12.

The first busbar assembly 28 is located at the first end 58 of the stator assembly 10, and forms connections with the first 36 and second 38 termination connections of the stator core assemblies 22,24,26. Further details of the first busbar assembly 28 are not pertinent to the present invention, and so will not be described here for sake of brevity, save to say that the first busbar assembly 28 comprises three electrical connections 59.

The second busbar assembly 30 is located at the second end 50 of the stator assembly 10, and connects all of the third termination connections 40 together.

Further details of the second busbar assembly 30 are not pertinent to the present invention, and so will not be described here for sake of brevity.

The coils 42,44 and the first 28 and second 30 busbar assemblies define a three-phase parallel star connection, with the first 36 and second 38 termination connections acting as live connections, and the third termination connections 40 acting as neutral connections.

The rotor assembly 14 is shown in Figure 7.

The rotor assembly 14 comprises a shaft 62, an impeller 64, first 66 and second 68 bearing assemblies, first 70 and second 72 balance rings, and a permanent magnet 74.

The shaft 62 is illustrated in isolation in the schematic cross-section of Figure 8.

The shaft 62 comprises a first portion 76, a second portion 78 adjacent to the first portion 76, a first transition region 80 between the first 76 and second 78 portions, a third portion 82 adjacent to the second portion 78, and a second transition region 84 between the second 78 and third 82 portions. In such a manner the second portion 78 is considered to be intermediate the first 76 and third 82 portions. The first portion 76 defines a first end 86 of the shaft 62, and the third portion 82 defines a second end 88 of the shaft 62 opposite to the first end 86.

The shaft 62 is a monolithic stainless steel component, such that the first 76, second 78 and third 82 portions are integrally formed. The shaft 62 has a relative magnetic permeability of around 20. In some alternative examples, the first 80 and/or second 84 transition regions may be omitted.

The impeller 64 is a mixed flow impeller and is press-fit to the first portion 76 such that the impeller 64 is located at the first end 86 of the shaft 62. Axial and/or radial flow impellers are also envisaged. The impeller 64 is injection moulded using a PEEK material.

The first bearing assembly 66 comprises a ball bearing assembly, and is press-fit to the first portion 76 of the shaft 62 such that the first bearing assembly 66 lies partly within a hollow interior of the impeller 64. The first bearing assembly 66 has an outer diameter greater than outer diameters of each of the second bearing assembly 68, the first 70 and second 72 balance rings, and the permanent magnet 74.

The second bearing assembly 68 comprises a ball bearing assembly, and is press-fit to the third portion 82 of the shaft 62 such that the second bearing assembly 68 is located at the second end 88 of the shaft 62. The first 66 and second 68 bearing assemblies are located at points on the respective first 76 and third 82 portions of the shaft 62 such that the stride between the first 66 and second 68 bearing assemblies is around 30mm.

The first balance ring 70 is press-fit to the first portion 76 of the shaft 62, and the second balance ring 72 is press-fit to the third portion 82 of the shaft 62. The second bearing assembly 68 is located closer to the second end 82 of the shaft 62 than the second balance ring 72. The second balance ring 72 has a smaller mass than the first balance ring 70.

The permanent magnet 74 is a two-pole sintered magnet, and is mounted to the second portion 78 of the shaft 62 via an adhesive.

The frame 16 is shown in cross-section in Figure 9, and comprises an inner portion 90, an outer portion 92, and a plurality of diffuser vanes 94.

The inner portion 90 is generally elongate in form, and is tapered inwardly at both ends. The inner portion 90 comprises an internal channel having a first portion 96, a second portion 98, a third portion 100, and a fourth portion 102. The first 96 and fourth 102 portions have diameters substantially corresponding to outer diameters of the first 66 and second 68 bearing assemblies respectively. The first 96 and fourth 102 portions act as bearing seats for the first 66 and second 68 bearing assemblies when the rotor assembly 14 is positioned relative to the frame 16. The second portion 98 is dimensioned so that the first balance ring 70 is received within the second portion 98 when the rotor assembly 14 is positioned relative to the frame 16, and the third portion 100 is dimensioned so that the permanent magnet 74 is received within the third portion 100 when the rotor assembly 14 is positioned relative to the frame 16. The inner portion 90 has an outer diameter of around 19.4mm.

The outer portion 92 is annular in form and has a diameter greater than the inner portion 90 such that the outer portion 92 is concentrically arranged with the inner portion 90. The outer portion has a diameter of around 28mm. The outer portion 92 has a smaller axial length than the inner portion 90, such that the outer portion 92 only overlies a section of the inner portion 90. Collectively the inner portion and the outer portion 92 define an air passage 93. The air passage 93 has a width of around 6.85mm.

The diffuser vanes 94 extend between the inner portion 90 and the outer portion 92, and each diffuser vane 94 has a leading edge 104 and a trailing edge 106. A distance D between the leading edge 104 and the trailing edge 106, measured parallel to a rotational axis of the rotor assembly R within the frame 16, is around 12mm.

A single diffuser blade 84 is illustrated in isolation in Figure 11. A cross-sectional shape of the diffuser blade 84 comprises a root edge 95, a shroud edge 97, a first side edge 99, and a second side edge 101. The root edge 95 has a length of around 1.4mm, and the shroud edge 97 has a length of around 0.5mm. This gives a ratio of root edge length to shroud edge length of around 2.8:1. The first 99 and second 101 side edges are concave in form.

There are thirteen diffuser vanes 84 in total, and each has a blade sweep of around zero degrees.

The frame 16 is formed via an overmoulding process, with the frame 16 overmoulded onto the stator assembly 12, with the combination of the frame 16 and the stator assembly 12 seen in Figure 9. The inner portion 90, the outer portion 92, and the plurality of diffuser vanes 94 are thus integrally formed, such that the frame 16 is a monolithic component. The material used to form the frame has a coefficient of thermal conductivity of at least 4 W/mK, and a dielectric strength of at least 15kV/mm. An appropriate material is a thermosetting epoxy resin with 80% -95% thermally conductive ceramic filler.

The inner portion 90 encapsulates the stator assembly 12, with only the three electrical connections 59 extending outwardly from the frame 16. The frame 16 is formed about the stator assembly 12 such that the diffuser vanes 94 partially overlap with the stator assembly 12 in an axial direction. The leading edges 104 are located at a distance E from an upstream end 108 of the coils 42,44 that is within 50% of an axial length of the coils 42,44 from the upstream end 108 of the coils 42,44, with the distance E measured in a direction parallel to the rotational axis R of the rotor assembly 14. The trailing edges 106 are located at a distance F from a downstream end 110 of the coils 42,44 that is within 10% of the axial length of the coils 42,44 from the downstream end 110 of the coils 42,44, with the distance F measured in a direction parallel to the rotational axis R of the rotor assembly 14. In such a manner the diffuser vanes 94 extend along an axial length that is at least 50% of an axial length of the stator core segments 32.

The housing component 18 can be seen in Figure 12, and comprises an inner member 112, an outer member 114, and a plurality of further diffuser vanes 116. The inner member 114 is generally annular in form, and has an inner diameter corresponding to an outer diameter of the inner portion 90 frame 16, in a region of the frame 16 upstream of the outer portion 92 of the frame 16. The inner member 114 is attached to the inner portion 90 of the frame 16 via adhesive. The outer member 116 is annular in form, and arranged generally concentrically with the inner member 114 to define a further air passage 118. Collectively, the further air passage 118 and the air passage 93 define an air channel through the electric motor 10.

The further diffuser vanes 116 extend between the inner member 112 and the outer member 114, and each further diffuser vane 116 has a leading edge 120 and a trailing edge 122. The trailing edges 122 axially overlap with locations of the upstream ends 108 of the coils 42,44.

The housing component 18 is formed as part of a moulding process separate to the overmoulding process that forms the frame 16. The inner member 112, the outer member 114, and the further diffuser vanes 116 are integrally formed such that the housing component 18 is a monolithic component. The material of the housing component 18 is different to the material of the frame, and is a 20% GF-reinforced PC/ABS.

The shroud 20 is generally frustoconical and hollow in form, and has an open end 124 that defines an inlet of the electric motor 10. The shroud 20 is mounted to the housing component 18 via adhesive.

In use, a voltage is applied to the coils 42,44 of the stator assembly 12 such that a magnetic field is created by the stator assembly 12. The magnetic field created by the stator assembly 12 interacts with the permanent magnet 74 of the rotor assembly 14 to rotate the rotor assembly 14 relative to the stator assembly 12.

Rotation of the rotor assembly 14 generates an airflow through the air channel via the impeller 64. The airflow rate is in the region of 9 Lis to 22 Lis, depending on a mode of operation f the electric motor 10.

As the voltage is applied to the coils 42,44, heat is generated by the stator assembly 12. As the stator assembly 12 is encapsulated by the frame 16, and the plurality of diffuser vanes 94 are located within the air channel, the plurality of diffuser vanes 94 effectively act as heat sinks for removing heat generated by the stator assembly 12 from the electric motor 10. Providing a thermal transfer path from the stator assembly 12 via the plurality of diffuser vanes 94 may avoid a need to directly cool the stator assembly 12 with airflow generated by the impeller 64, which may lead to increased aerodynamic and/or acoustic performance relative to an arrangement in which the stator assembly 12 is directly cooled by airflow generated by the impeller 64.

As the frame 16 is overmoulded onto the stator assembly 12, the frame provides structural support for the first 66 and second 68 bearing assemblies, and provides a portion to which the housing component 18 is mounted. Overmoulding the frame 16 to the stator assembly 12 may also reduce tolerances relative to an arrangement where the frame 16 and the stator assembly 12 are separate components fixedly attached to one another via adhesive or the like, and may enabled increased levels of concentricity between the frame 16 and the stator assembly 12.

Whilst particular examples and embodiments have thus far been described, it 5 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

Claims 1. An electric motor comprising: a stator assembly; a frame; and a rotor assembly rotatably mounted to the frame; wherein the rotor assembly comprises an impeller for generating an airflow through the electric motor, the frame is overmoulded onto the stator assembly, and the frame defines a plurality of diffuser vanes located downstream of the impeller.
2. An electric motor as claimed in Claim 1, wherein the stator assembly comprises an electrical connection to a power source, and the frame encapsulates the stator assembly such that the electrical connection is the only component of the stator assembly that is exposed through the frame.
3. An electric motor as claimed in Claim 1 or Claim 2, wherein the frame comprises an inner portion that encapsulates the stator assembly, and an annular outer portion spaced from the inner portion to define an air passage, and the plurality of diffuser vanes extend between the inner portion and the annular outer portion within the air passage.
4. An electric motor as claimed in Claim 3, wherein the plurality of diffuser vanes each comprise a root thickness of at least 1mm at the inner portion.
5. An electric motor as claimed in Claim 3 or Claim 4, wherein the annular outer portion has an outer diameter of no more than 50mm.
6. An electric motor as claimed in any of Claims 3 to 5, wherein the plurality of diffuser vanes each comprise a cross-sectional shape comprising a root edge at the inner portion, a shroud edge at the outer portion, and first and second side edges extending between respective ends of the root edge and the shroud edge, and the first and second side edges are concave.
7. An electric motor as claimed in any preceding claim, wherein the stator assembly comprises a stator core component, and each of the plurality of diffuser vanes extends along the frame for an axial length of at least 50% of a length of the stator core component.
8. An electric motor as claimed in any preceding claim, wherein the stator assembly comprises a coil having an upstream end and a downstream end, each of the plurality of diffuser vanes comprises a respective leading edge and a respective trailing edge, and distances between the respective trailing edges and the downstream end of the coil, measured in directions parallel to a rotational axis of the rotor assembly, are no more than 30% of a distance measured between the upstream end and the downstream end of the coil in a direction parallel to the rotational axis of the rotor assembly.
9. An electric motor as claimed in any preceding claim, wherein the frame is formed of a material having a coefficient of thermal conductivity of at least 4 20 W/m K.
10. An electric motor as claimed in any preceding claim, wherein the frame is formed of a material having a dielectric strength of at least 15kV/mm.
11. An electric motor as claimed in any preceding claim, wherein the frame defines a bearing seat, and the rotor assembly comprises a bearing assembly located at the bearing seat to rotatably mount the rotor assembly to the frame.
12. An electric motor as claimed in any preceding claim, wherein the electric motor comprises a housing component attached to the frame upstream of the diffuser vanes, and the housing component comprises a further plurality of diffuser vanes.
13. An electric motor as claimed in Claim 12, wherein the further plurality of diffuser vanes are located radially outwardly of, and at least partially axially overlap, a portion of the stator assembly.
14. An electric motor as claimed in any preceding claim, wherein the frame is formed of thermosetting epoxy resin with 80% -95% thermally conductive ceramic filler.
15. A vacuum cleaner comprising an electric motor as claimed in any preceding claim.
16. A haircare appliance comprising an electric motor as claimed in any of Claims 1 to 14.