BRUSHLESS MOTOR

A brushless motor having a stator assembly, a rotor assembly rotatable relative to the stator assembly, and a frame within which the stator assembly and the rotor assembly are housed. The rotor assembly includes a shaft, first and second bearings attached to the shaft, and a permanent magnet attached to the shaft between the first and second bearings. The rotor assembly includes an impeller attached to the shaft, with the first bearing located further away from the impeller than the second bearing. The rotor assembly includes an o-ring mounted between the first bearing and the frame.

FIELD OF THE INVENTION

The present invention relates to a brushless motor.

BACKGROUND OF THE INVENTION

There is a general desire to improve electric machines, such as brushless 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 brushless motor comprising a stator assembly, a rotor assembly rotatable relative to the stator assembly, and a frame within which the stator assembly and the rotor assembly are housed, wherein the rotor assembly comprises a shaft, first and second bearings attached to the shaft, a permanent magnet attached to the shaft between the first and second bearings, an impeller attached to the shaft, the first bearing located further away from the impeller than the second bearing, and an o-ring mounted between the first bearing and the frame.

The brushless motor according to the first aspect of the present invention may be beneficial as the o-ring may at least partially vibrationally isolate the first bearing from the frame, and this may inhibit vibrations, and hence noise, from being transferred between the first bearing and the frame in use.

The o-ring may comprise a resiliently deformable member having a generally toroidal form, for example such that the o-ring extends annularly about the first bearing. The o-ring may be in contact with each of the first bearing and the frame.

The o-ring may be mounted between the first bearing and the frame such that the o-ring is able to move axially relative to the frame without deformation of the o-ring, for example able to roll axially in a direction parallel to a central longitudinal axis of the shaft. This may provide an arrangement with relatively low axial stiffness compared to, for example, an arrangement in which the o-ring is not able to move axially relative to the frame in a similar manner. Axial movement of the o-ring may also facilitate pre-loading of the first bearing, for example pre-loading of an outer race of the first bearing.

The o-ring may be mounted between the first bearing and the frame such that the o-ring is substantially uncompressed. This may provide relatively easy axial movement of the o-ring relative to the frame compared to, for example, an arrangement where the o-ring is mounted between the first bearing and the frame such that the o-ring is compressed.

The o-ring may comprise a substantially circular cross-sectional shape when mounted between the first bearing and the frame. This may provide easier axial movement of the o-ring compared to, for example, an o-ring comprising a polygonal cross-sectional shape.

The o-ring may comprise a radial stiffness in the region of 1.0×106N/m to 4.0×106N/m, for example around 2.5×106N/m. Provision of an o-ring with a relatively high radial stiffness may provide a rotor assembly with a relatively high radial stiffness. This may enable the rotor assembly to comprise a sub-critical rotor assembly, which may allow the brushless motor to operate at a speed range below the resonant frequencies of the rotor assembly.

The o-ring may comprise a material having a Shore A hardness in the region of 65-90, for example a Shore A hardness in the region of 75. Such a Shore A hardness may provide an o-ring that is relatively resistant to compression in normal use, enabling the rotor assembly to comprise a sub-critical rotor assembly, whilst also enabling compression of the o-ring in the event of abnormal use, for example where the brushless motor is subject to forces due to being dropped in use. The o-ring may comprise an elastomeric material.

The o-ring may contact the frame over a region that is substantially smooth, and the o-ring may be able to move axially over the region of the frame. This may enable greater axial movement of the o-ring relative to the frame compared to, for example, an arrangement where the o-ring is disposed in a groove or channel formed in the frame. A region of the frame radially adjacent to the o-ring may be substantially smooth, for example substantially free of recesses and/or projections.

The o-ring may contact an outer surface of the first bearing over a region that is substantially smooth, and the o-ring may be able to move axially over the region of the outer surface. This may enable greater axial movement of the o-ring relative to the first bearing compared to, for example, an arrangement where the o-ring is disposed in a groove or channel formed on an outer surface of the first bearing. A region of an outer surface of the first bearing radially adjacent to the o-ring may be substantially smooth, for example substantially free of recesses and/or projections.

The frame may comprise a channel having a first portion with a first diameter, a second portion with a second diameter less than the first diameter, and a step defining a transition from the first portion to the second portion, the step defining an axial stop for inhibiting axial movement of the o-ring. This may inhibit axial motion of the o-ring in at least one axial direction in use. The first bearing may be partially located within the first portion and partially located within the second portion, for example with around half of a length of the first bearing located in the first portion and around half of the length of the first bearing located in the second portion. The o-ring may be located substantially centrally on the first bearing, for example at a location approximately halfway along the length of the first bearing.

The step may define an axial stop for inhibiting axial movement of the o-ring in a direction toward the impeller. This may inhibit axial motion of the o-ring toward the impeller in use.

The rotor assembly may comprise a pre-load spring for applying a load to an outer race of the first bearing. This may ensure correct alignment of the outer race and an inner race of the first bearing in use. The o-ring and the pre-load spring may enable relative axial movement of the outer face of the first bearing to the frame.

The o-ring may comprise a thermal conductivity of at least 3 W/mK. This may provide for heat transfer from the bearing to the frame in use.

The brushless motor may comprise a stopper for inhibiting radial motion of the rotor assembly relative to the frame. Use of an o-ring may enable radial movement of the first bearing in the event of forces experienced during abnormal use of the brushless motor, for example when the brushless motor or a device in which the brushless motor is installed is dropped, whilst provision of the stopper may prevent excessive radial motion of the rotor assembly relative to the frame. The stopper may inhibit the first bearing from contacting the frame. The stopper may inhibit the permanent magnet from contacting one or more pole faces of stator cores of the stator assembly in use, for example by virtue of the stopper inhibiting radial motion of the rotor assembly relative to the frame.

The stopper may comprise an end cap positioned to at least partially overlie the first bearing, and at least a portion of the end cap may be located between the first bearing and the frame. Providing the stopper as an end cap may provide for easier manufacture of the stopper compared to, for example, an arrangement where the stopper is integrally formed with the frame.

A first distance, for example a first radial distance, between the portion of the end cap located between the first bearing and the frame may be less than a second distance, for example a second radial distance, between the permanent magnet and the stator assembly. This may enable the stopper to inhibit the permanent magnet contacting the stator assembly, for example pole tips of stator cores of the stator assembly, in the event of radial movement of the rotor assembly in use.

The end cap may comprise a main body and a finger extending from the main body, the finger located between the first bearing and the frame. This may inhibit radial motion of the rotor assembly relative to the frame whilst also requiring less material for the end cap than, for example, a corresponding arrangement where the main body of the end cap is located between the bearing and the frame.

The finger may be resiliently deformable relative to the main body. This may enable the end cap to inhibit radial motion of the rotor assembly relative to the frame, whilst also accounting for tolerances that occur during manufacture. For example, a resiliently deformable finger may be deformable during positioning of the end cap relative to the frame such that tolerances introduced during manufacture of the frame may be accounted for.

The end cap may comprise a plurality of fingers extending from the main body, the plurality of fingers located between the first bearing and the frame. Using a plurality of fingers may enable radial motion of the rotor assembly relative to the frame to be inhibited at a number of locations, whilst still using less material than, for example, a monolithic member located between the first bearing and the frame about the entire periphery of the first bearing.

The plurality of fingers may be evenly spaced about a periphery of the end cap. This may allow for inhibition of radial motion of the rotor assembly relative to the frame about a periphery of the first bearing.

Each of the plurality of fingers may be resiliently deformable relative to the main body. This may facilitate positioning of the fingers between the frame and the first bearing, whilst also accounting for tolerances introduced during manufacture of the frame.

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

DETAILED DESCRIPTION OF THE INVENTION

A brushless permanent magnet motor according to the present invention, generally designated1, is illustrated inFIG.1, with components of the brushless permanent magnet motor illustrated inFIGS.2to7. Although described here in relation to a brushless permanent magnet motor, it will be appreciated by a person skilled in the art that at least some of the teachings disclosed herein may be applicable to other types of brushless motor.

The brushless permanent magnet motor comprises a stator assembly10, a rotor assembly12, and a frame14.

The stator assembly10is illustrated in isolation inFIG.2, and comprises four stator core sub-assemblies16and a termination assembly18. The four stator core sub-assemblies are shown connected inFIG.3, with the termination assembly18shown in isolation inFIG.4. An individual stator core sub-assembly16can be seen inFIGS.5and6, and it will be appreciated that each stator core sub-assembly16has substantially the same structure.

The stator core sub-assembly16comprises a stator core20, a bobbin22, and a winding24wound about the bobbin22. The stator core20has a back26, and first28and second30arms extending from the back26. The stator core20has a generally C-shaped form, and may be referred to as a c-core. The first28and second30arms each comprise a respective first portion32,34and a respective second portion36,38. Each first portion32,34extends substantially orthogonally from the back26, and each second portion36,38is angled at around 28 degrees relative to the respective first portion32,34. Each second portion36,38is around 2 times the length of the respective first portion32,34.

The second portions36,38are angled inwardly toward one another, and collectively the back26and the first28and second30arms define a winding channel40within which the winding24is located. Given the relative orientations of the back26and the first28and second30arms, the winding channel40has a generally trapezoidal cross-sectional area, as seen inFIG.6. It has been found that provision of a generally trapezoidal winding channel40may enable a winding pattern of the winding24that achieves a relatively high fill factor, whilst angling the second portions36,38of the first28and second30arms inwardly toward one another may reduce a height of the stator core20.

The stator core20comprises pole faces42,44disposed at ends of the respective second portions36,38, with the pole faces42,44extending to either side of the respective second portions36,38. The pole faces42,44are spaced apart from one another to define a slot gap46, with the slot gap46defining a point of entry into the winding channel40. The pole faces42,44are asymmetric to provide saliency, and are curved with each pole face42,44having a different center of curvature. The asymmetry of the pole faces42,44results in different distances from each pole face42,44to a centre line B of the slot gap46. Each pole face42,44is asymmetric relative to the other pole face44,42, but each individual pole face42,44is also asymmetric about a center line of that pole face.

To maximise flux linkage between the stator core20and the rotor assembly12in use, it may be desirable for the pole faces42,44to be as wide as possible. However, increasing the width of the pole faces42,44in an inward direction may reduce a width of the slot gap46, making winding of the stator core20difficult. Increasing the width of the pole faces42,44in an outward direction may increase flux leakage between adjacent stator cores20in the stator assembly10. To provide a compromise between these competing factors, a ratio of the combined width of the pole faces42,44to the width of the slot gap46is in the region of 3:1 to 7:1.

The stator core20is formed of a plurality of laminations, each having the form previously described. A protrusion48is located on an outer surface of each second portion36,38, with the protrusions48being used to weld the laminations together to form the stator core20. In other examples, the laminations are glued together rather than welded. The protrusions48may be located out of a main flux loop of the stator assembly10in use, which may minimise stator iron loss. The protrusions48are located at a same distance along each respective second portion36,38, which may minimise induced voltage potential between the two points so as to minimise losses. The back26is asymmetric about the centre line B of the slot gap, which enables correct orientation of the stator core20during manufacture.

The bobbin22is overmoulded to the stator core20, such that the bobbin22overlies inner and outer surfaces of the back26, inner surfaces of the first portions32,34of the first28and second30arms, and inner and outer surfaces of the second portions36,28of the first28and second30arms. The bobbin22thereby lines the winding channel40, and allows the winding24to be wound about the back26of the stator core20. Overmoulding the bobbin22to the stator core20enables the bobbin to have a wall thickness in the region of 0.4 mm in the winding channel40, which may maximise the available cross-sectional area to be filled with the winding24.

The bobbin22is overmoulded to the stator core20such that shoulders of the stator core20, i.e. portions of the stator core the bridge the back26and the first portions32,34of the first28and second30arms, are exposed, and such that the pole faces42,44are exposed, for reasons that will be discussed hereafter.

A region of the bobbin22on an outer surface of the second portion36of the first arm28defines a first connection portion50, and a region of the bobbin22on an outer surface of the second portion38of the second arm30defines a second connection portion52. The first connection portion50comprises a rounded projection that extends partially along the length of the bobbin22, and the second connection portion52comprises a rounded recess that extends partially along the length of the bobbin22. The first50and second52connection portions are complementarily shaped, such that adjacent bobbins22in the stator assembly10can be connected to one another by axially sliding the relevant connection portions50,52together. The connection portions50,52allows relative axial movement of connected bobbins22, whilst inhibiting circumferential and radial separation of the bobbins22. The connection portions50,52enable individual stator core sub-assemblies16to be connected together during manufacture, as will be described hereinafter.

As seen in the cross-sectional view ofFIG.6, the bobbin22comprises a winding guide56located in a region of an outer surface of the back26. The winding guide56serves to guide the winding24during winding of the stator core22.

When wound, as seen in the cross-sectional view ofFIG.6, the winding24has a generally trapezoidal form within the winding channel40. This may provide a relatively high fill factor. The winding24is asymmetric about the back26, with the portion of the winding24that overlies an outer surface of the back26defining a different cross-sectional shape to the portion of the winding24located within the winding channel40. This may enable a relatively high fill factor within the winding channel24, whilst still providing flexibility for connection to terminals of the termination assembly18.

The termination assembly18comprises a first, upper, terminal58, a second, lower, terminal60, and a sleeve62. Each of the first58and second60terminals is generally annular in form, with the first terminal58overlying the second terminal60. The sleeve62is overmoulded to the first58and second60terminals such that the relative positions of the first58and second60terminals are maintained. The sleeve62comprises a plurality of apertures64which enable the windings24of the stator core sub-assemblies16to be connected to the first58and second60terminals. The sleeve62further comprises a plurality of locating features66for locating the sleeve62relative to the bobbins22during manufacture, and wire guides68formed on the locating features66. The locating features66are each located adjacent to a corresponding aperture64.

The shaft70is elongate in form, having an inlet end86and an outlet end88, with inlet and outlet referring generally to a direction of airflow through the brushless permanent magnet motor1in use. The permanent magnet72is mounted generally centrally along the shaft70. The first balancing ring78is mounted to the shaft70at the inlet end86, with the first bearing74mounted to the shaft70adjacent to the first balancing ring78. The second balancing ring80is mounted to the shaft70between the first bearing74and the permanent magnet72.

The impeller84is mounted to the outlet end88of the shaft70. The second bearing76is mounted to the shaft70adjacent to the impeller84, with the third balancing ring82mounted to the shaft70between the second bearing76and the permanent magnet72. The second bearing76comprises annular grooves77for receiving adhesive.

The rotor assembly12further comprises a pre-load spring90for applying a pre-load to the first bearing74, an annular washer91in contact with the pre-load spring90and the outer race of the first bearing74, and an o-ring92located about the first bearing74, as will be discussed in more detail hereinafter.

The frame14can be seen inFIGS.1,8and9, and comprises a main body94, a shroud96, and a plurality of struts98extending between the main body94and the shroud96. The main body94is generally cylindrical in form, defines first100and second102bearing seats for the respective first74and second76bearings, and defines a channel104within which the rotor assembly12is received. The shroud96is radially spaced from the main body94, and has a central aperture that overlies the impeller84, such that airflow can interact with the impeller84in use.

To manufacture the frame14, the frame14is overmoulded to the stator assembly10in an overmoulding process. Given the form of the wound stator core sub-assemblies16, the overmoulding of the frame14results in the main body94of the frame14having protrusions110which overlie the windings24located on the backs26of the stator cores22. The protrusions110are formed such that the shoulders of the stator cores22are not covered by the frame14. This allows the shoulders of the stator cores22to be exposed to airflow through the brushless permanent magnet motor1in use, which may provide a cooling effect for the stator cores22. The frame14is also overmoulded such that the pole faces42,44of the stator cores22are exposed to the interior of the channel. Collectively, at least 10% but no more than 30% of each stator core is not covered by the frame14.

The protrusions110define regions of increased radius relative to the regions of the main body94that lie between adjacent stator core sub-assemblies. This reduces a volume of material required for the frame14compared to a frame that has a constant radius, and may provide improved heat transfer may removing unnecessary frame material.

To aid with heat transfer away from the rotor assembly12and the stator assembly10in use, the frame14is formed from a material having a through-plane thermal conductivity, of at least 1.5 W/mK. To provide strength to the brushless permanent magnet motor1, the frame comprises a Young's modulus in the region of 10-45 GPa, for example in the region of 25 GPa.

To further aid with heat transfer away from the windings24, the frame14comprises a plurality of turbulators112formed on the protrusions110. Each turbulator112is a projection upstanding from a protrusion110, with the turbulators112formed as part of the same overmoulding process that defines the rest of the frame14. It will be appreciated that in alternative embodiments the turbulators112may be formed as separate components to the remainder of the frame14, and attached to the frame14in any appropriate manner, such as via an adhesive or the like.

The turbulators112are arranged in pairs along the length of each protrusion110. Each turbulator112is angled at around 60 degrees relative to an axis parallel to a central longitudinal axis of the brushless permanent magnet motor1, i.e. an axis parallel to the shaft70. Collectively a pair of turbulators112defines a general chevron-like shape, with the chevron-like shape pointing toward the impeller84. In alternative embodiments, not illustrated here, each turbulator112may itself comprise a chevron-shape.

There may be a compromise to be reached in terms of allowing the turbulators112to generate vortices in the region of the protrusions110to aid with transfer of heat away from the windings24of the stator assembly10in use, versus avoiding choking airflow through the brushless permanent magnet motor1in use. A pitch to height ratio of each turbulator in the region of 10:1 has been found to be an effective compromise, with a height of each turbulator in the region of 0.6 mm, for example around 0.58 mm.

The form of turbulator112described above may be effective at generating vortices in the region of the protrusions110, which overlie the windings24on the backs26of the stator cores22, with such vortices aiding with transfer of heat away from the windings24of the stator assembly10in use.

The struts98extend from the protrusions to the shroud96, such that the struts98also overlie the windings24on the backs26of the stator cores22. The struts98may thereby act as heat sinks for the windings24, with airflow moving over the struts98in use to carry heat away from the struts98. A leading end of each strut98is substantially aligned with a leading edge of a winding24that the strut overlies to ensure that the strut98is aligned with the appropriate heat source, i.e. winding24. The leading end of each strut is aerodynamically shaped, in a curved manner, to promote desirable airflow characteristics through the brushless permanent magnet motor1in use.

The main body94of the frame14comprises a plurality of inlet cooling apertures114, a plurality of outlet cooling apertures116, and an adhesive injection aperture (not shown). The plurality of inlet cooling apertures114are located in a region below the first bearing seat100, and are spaced about the periphery of the main body94. The plurality of inlet cooling apertures114are shaped to direct airflow flowing through the brushless permanent magnet motor1in use into the channel104, which provides a cooling effect for the rotor assembly12. The main body94of the frame14further comprises a plurality of inlet guide grooves or channels115formed in the outer surfaces of the main body94, with each of these inlet guide grooves115being arranged to guide airflow flowing through the brushless permanent magnet motor1in use into a respective inlet cooling aperture114. Each of the plurality of inlet guide grooves115extend axially, in a direction parallel to a central longitudinal axis of the brushless permanent magnet motor1, from the upstream end of the main body94of the frame14to the respective inlet cooling apertures114.

The plurality of outlet cooling apertures116are located in a region of the second bearing seat102, and are spaced about the periphery of the main body94. The plurality of outlet cooling apertures116are shaped to direct airflow flowing through the channel104, outwardly from the frame14, before the airflow passes through the impeller84. The adhesive injection aperture allows insertion of adhesive into the annular grooves77of the second bearing76through the frame14.

An outlet end of the main body94of the frame defines a labyrinth seal with the impeller84.

A cross-section through the brushless permanent magnet motor1is shown inFIGS.8and9. As can be seen, the rotor assembly12sits within the frame14, with the first bearing74located at the first bearing seat100, the second bearing76located at the second bearing seat102, and the permanent magnet72aligned with the stator cores22of the stator assembly10. The second bearing76is secured to the second bearing seat102by adhesive located in the annular grooves77formed on the outer race of the second bearing76.

The channel104of the frame comprises first120and second122portions of different diameters in the region of the first bearing74, with the first120and second122portions collectively defining the first bearing seat100.

The o-ring92is located substantially centrally along the axial length of the first bearing74. The o-ring92sits between the first bearing74and the frame14in the first portion120of the channel104such that the o-ring92is substantially uncompressed, and has a substantially circular cross-sectional profile. The o-ring has a shore A hardness of around 75, and has a radial stiffness in the region of 1.0×106N/m to 4.0×106N/m, for example around 2.5×106N/m. Providing the o-ring92with a relatively high radial stiffness may in turn provide the rotor assembly12with a relatively high radial stiffness. This allows the rotor assembly12to operate as a sub-critical rotor assembly, and allows the brushless permanent magnet motor1to operate in a speed range below all resonant frequencies of the rotor assembly12. The o-ring92has a thermal conductivity of at least 3 W/mK, which may aid with heat transfer away from the first bearing74in use.

The low compression of the o-ring92between the first bearing74and the frame14in the first portion120of the channel104, along with the substantially circular cross-sectional profile of the o-ring92, enables the o-ring92to roll axially, in a direction parallel to a central longitudinal axis of the brushless permanent magnet motor1. This may facilitate pre-loading of the first bearing74by the pre-load spring90via the annular washer91. A step change between the first120and second122portions of the channel104defines an axial stop for inhibiting motion of the o-ring92toward the impeller84.

A third portion124of the channel104has a reduced diameter relative to the first120and second122portions of the channel104, with the permanent magnet72sitting within the third portion124of the channel104. A step change between the second122and third124portions of the channel104defines a seat for the pre-load spring90. A fourth portion126of the channel104has an increased diameter relative to the third portion of the channel104, with the fourth portion126of the channel104defining the second bearing seat102.

Whilst the o-ring92is relatively stiff, the o-ring92is still deformable in the event that the brushless permanent magnet motor1experiences forces during abnormal use, for example as a result of the brushless permanent magnet motor1or a product in which the motor is installed being dropped. A distance between the first bearing74and a wall of the channel104in the first portion120is greater than a distance between the first bearing74and a wall of the channel104in the second portion122. Similarly, the distance between the first bearing74and a wall of the channel104in the second portion122is greater than a distance between the permanent magnet72and a wall of the channel104in the third portion124, and greater than a distance between the permanent magnet72and the pole faces42,44in the third portion124. As a result, when the o-ring92is compressed during abnormal use, there is a risk that the permanent magnet72will contact the pole faces42,44or the wall of the channel104in the third portion124, which can cause damage to the permanent magnet72.

To avoid this happening, the brushless permanent magnet motor1has an end cap128, which is shown in isolation inFIG.10.

The end cap128comprises a main body130, a plurality of fingers132extending from the main body130, and a plurality of flanges133extending from the main body128. The main body130is generally cylindrical in form, and hollow. The main body130overlies the inlet end86of the shaft70and the first balancing ring78when the brushless permanent magnet motor1is assembled. The plurality of fingers132are resiliently deformable, and, when not mounted to the brushless permanent magnet motor1, the plurality of fingers132splay slightly outwardly from the main body128. The plurality of fingers132extend from the main body128in a first direction, and the plurality of flanges133extend from the main body128in a second direction substantially orthogonal to the first direction. The plurality of flanges133engage the main body94of the frame14to prevent over-insertion of the end cap128into the frame14.

An enlarged view of the end cap128located at the inlet end86of the shaft70is shown inFIG.11.

The end cap128is located in the first portion120of the channel104such that the fingers132contact the wall of the first portion120of the channel104to retain the end cap128within the first portion120. The plurality of fingers132are located between the first bearing74and the wall of the first portion120of the channel104, with the plurality of fingers132spaced from the first bearing74. A distance between the first bearing74and the plurality of fingers132is less than the distance between the permanent magnet72and a wall of the channel104in the third portion124, and less than the distance between the permanent magnet72and the pole faces42,44in the third portion124.

Thus in the event that the o-ring92is deformed when the brushless permanent magnet motor1experiences forces during abnormal use, the first bearing74contacts at least some of the plurality of fingers132before the permanent magnet72is able to contact the pole faces42,44or the wall of the channel104in the third portion124. Thus the plurality of fingers132may act as a stopper to inhibit radial motion of the first bearing74.

As depicted here, the end cap128comprises an aperture135through which the shaft70extends. In alternative embodiments, the end cap128may not comprise the aperture135, which may facilitate creation of a sealed bearing cartridge. Similarly, the plurality of inlet cooling apertures114and the plurality of outlet cooling apertures116may be omitted where a sealed bearing cartridge is desirable. A sealed bearing cartridge may inhibit airflow from entering the region of the frame14in which the bearings74,76are housed in use, which may reduce emissions.

The brushless permanent magnet motor1further comprises a diffuser134located downstream of the impeller84. The diffuser134is attached to the shroud96and comprises a plurality of vanes136for turning airflow as it passes through the diffuser134from the impeller84in use. Although depicted as a multi-stage diffuser, ie a diffuser with more than one row of vanes, it will be appreciated that other forms of diffuser, such as a single stage diffuser, are also envisaged.

In use, current is passed through the windings24of the stator assembly10to generate a magnetic field that interacts with the permanent magnet72to cause rotation of the rotor assembly12, and hence rotation of the impeller84. This causes air to be drawn into the brushless permanent magnet motor1, where air interacts with the impeller84before exiting the brushless permanent magnet motor1via the diffuser134.

Steps involved in manufacture of the brushless permanent magnet motor1will now be reiterated.

Each stator core sub-assembly16is assembled individually, with the bobbin22overmoulded to the stator core20, and the winding24wound about the bobbin22. Individual stator core sub-assemblies16are connected to one another via the first50and second52connection portions of the respective bobbins22.

The sleeve62is overmoulded to the first58and second60terminals to define the termination assembly18, and the windings24are fused to the first58and second60terminals. Collectively, the stator core sub-assemblies16and the termination assembly18define the stator assembly10. The sleeve62and the bobbins22are formed from different materials, and are overmoulded to their respective components in separate overmoulding processes.

The frame14is overmoulded to the stator assembly10in a separate overmoulding process to each of those of the bobbins22and the sleeve62, and the frame14is formed from the same material as the sleeve62.

The rotor assembly12is inserted into the frame14, and the end cap128is located over the inlet end86of the shaft70.

A first method200of manufacturing the brushless permanent magnet motor1is illustrated in the flow diagram ofFIG.12.

The method200comprises obtaining202the plurality of stator core sub-assemblies16, connecting204adjacent stator core sub-assemblies16to form the stator assembly10, and overmoulding206the stator assembly10to define the frame14within which the stator assembly10is housed.

By overmoulding the stator assembly10to define the frame14, the need for the stator core sub-assemblies16to be individually adhered to the frame14may be removed, and this may provide a manufacturing process with fewer steps than a manufacturing process in which the stator core sub-assemblies16are individually adhered to the frame14. Overmoulding the frame14to the stator assembly10may, in some examples, provide increased thermal transfer from the stator core sub-assemblies16to the frame14compared to embodiments where stator core sub-assemblies16are adhered to the frame14.

Overmoulding the frame14to the stator assembly10may provide a brushless permanent magnet motor1having a greater overall stiffness than, for example, a brushless permanent magnet motor in which the stator core sub-assemblies are individually adhered to the frame. Overmoulding the frame14to the stator assembly10may also facilitate manufacture of a brushless motor having a generally sealed bearing cartridge compared to, for example, an arrangement where the frame has apertures into which individual stator core sub-assemblies are mounted. A sealed bearing cartridge may inhibit airflow from entering the region of the frame14in which the bearings74,76are housed in use, which may reduce emissions.

A second method300of manufacturing the brushless permanent magnet motor1is illustrated in the flow diagram ofFIG.13.

The method300comprises obtaining302the plurality of stator core sub-assemblies16, and overmoulding304the plurality of stator core sub-assemblies16to define the frame14such that at least a portion of the back26and the first28and second30arms of each stator core20is exposed through the frame14.

As above, by overmoulding the stator core sub-assemblies16to define the frame14, the need for the stator core sub-assemblies16to be individually adhered to the frame14may be removed, and this may provide a manufacturing process with fewer steps than a manufacturing process in which the stator core sub-assemblies16are individually adhered to the frame14. Overmoulding the frame14to the stator core sub-assemblies16may, in some examples, provide increased thermal transfer from the stator core sub-assemblies16to the frame14compared to embodiments where stator core sub-assemblies16are adhered to the frame14.

Overmoulding the frame14to the stator core sub-assemblies16may provide a brushless permanent magnet motor1having a greater overall stiffness than, for example, a brushless permanent magnet motor in which the stator core sub-assemblies are individually adhered to the frame.

However, overmoulding of the stator core sub-assemblies16may remove the stator core sub-assemblies16from a region of airflow through the brushless permanent magnet motor1in use, which may result in the stator cores22and/or the windings24experiencing increased temperatures in use. By overmoulding the frame14to stator core sub-assemblies16such that at least a portion of the back26and the first28and second30arms of each stator core22is exposed through the frame14, at least a portion of each stator core22may be exposed to airflow through the brushless permanent magnet motor1in use, which may provide a cooling effect, thereby reducing any increases in temperature experienced as a result of the overmoulding of the stator core sub-assemblies16.

The brushless permanent magnet motor1described herein may find particular utility in fields where small factor yet high power density is desirable. As an example, a vacuum cleaner comprising the brushless permanent magnet motor is illustrated schematically inFIG.14.

Although described herein with a combination of features, it will be appreciated that embodiments of the brushless motor1where only some of the above-mentioned features are implemented are also envisaged. For example, the turbulators112may still find utility in an arrangement in which the shoulders of the stator cores22are not exposed by the frame14.