GB2617064A

GB2617064A - Electric motor

Info

Publication number: GB2617064A
Application number: GB2204249.3A
Authority: GB
Inventors: John Isaacs Andrew
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2022-03-25
Filing date: 2022-03-25
Publication date: 2023-10-04
Also published as: WO2023180730A1; GB202204249D0

Abstract

Heat dissipating arrangement for electric motors 100, comprising a rotor assembly 20 comprising a plurality of rotor fins 50 longitudinally adjacent the rotor magnets 27 and a stator assembly 30 comprising a plurality of stator fins 40 longitudinally adjacent the stator 32, wherein the rotor and stator fins overlap. There may be a gap between rotor and stator vanes that is filled with a thermally conductive fluid. The stator assembly may comprise a bobbin 34 that carries the stator and stator fins, the bobbin conducts heat from the stator to the fins. Stator and rotor fins may have nested concentric fins of increasing radius, the concentric fins of the rotor fit in a gap between concentric fins of the stator (140, 150, Fig.5). The length of the stator and rotor fins may decrease as the radial distance increases. The motor may be a sealed. The motor may be placed in an agitator of a vacuum cleaner, the motor rotating the agitator which acts as a heatsink. The motor may be used as a vacuum cleaner compressor, the rotor comprising an impellor (128, Fig.5) that carries the rotor fins 150. The compressor may comprise a thermally insulating diffuser (102, Fig.5).

Description

ELECTRIC MOTOR

TECHNICAL FIELD

The present invention relates to an electric motor, a cleaner head for a vacuum cleaner, a compressor for a vacuum cleaner and a vacuum cleaner.

BACKGROUND

In an electric motor there are losses in the rotor and stator which are apparent as waste heat. If the motor is not to overheat rapidly, its heat output must be dissipated, or rejected.

The power capability of the electric motor can be limited by the ability of conductors in the windings of the stator to carry current without overheating and melting.

In known applications, heat output from electric motors is dissipated by active cooling, whereby additional energy is used to cool the windings. Examples of active cooling include forcing air over the motor by operating fans or blowers, forcing liquid over or near to the motor, and using thermoelectric coolers.

In the application of an electric motor in a vacuum cleaner, for example, active cooling can negatively impact the performance of the vacuum cleaner. For example, power may be required to operate the active cooling, which may reduce a speed at which the electric motor can safely operate and/or the battery life of the vacuum cleaner. For example, a portion of airflow generated during operation of the vacuum cleaner may be diverted from providing suction on a surface to be cleaned so that it instead flows over the electric motor.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided an electric motor comprising a rotor assembly that rotates about a longitudinal rotational axis of the electric motor, and a stator assembly comprising a stator and a plurality of stator fins that extend substantially parallel to the longitudinal rotational axis and away from the stator towards the rotor assembly. The rotor assembly comprises a plurality of rotor fins that extend substantially parallel to the longitudinal rotational axis and towards the stator, such that portions of the rotor fins overlap longitudinally with portions of the stator fins.

The overlapping stator fins and rotor fins increase a surface area of the stator assembly that is adjacent to the rotor assembly in a space-efficient manner. In turn, this increases the capacity for heat transfer away from the stator and can reduce the need for or even obviate active cooling. In some examples, heat transfer from the stator fins to the rotor fins is primarily by heat transfer from the overlapping stator and rotor fins.

In any event, reduction or avoidance of active cooling means that the motor can run faster, draw more current (for instance, increasing torque) and/or use less energy (for instance, battery energy) in operation.

In traditional air-cooled electric motors, airflow to cool the electric motor is generated during use of the electric motor and is not generated when the electric motor is not in use.

As such, the temperature of the electric motor typically peaks, at a temperature that is greater than a desirably operating temperature of the electric motor, at a certain period of time after the electric motor is switched off, before slowly cooling to an ambient temperature.

A benefit of an arrangement according to the first aspect is that heat continues to dissipate away from the stator even when the motor us not in use. Accordingly, a temperature of the motor does not increase after the electric motor is switched off, or peaks at a lower temperature, and cools to an ambient temperature faster than the aforementioned air-cooled electric motors Each of the stator fins and the rotor fins have a proximal end connected to the respective stator assembly or rotor assembly and a distal end further from the respective stator assembly or rotor assembly than the proximal end The distal ends of the stator fins are closer to the rotor assembly than the distal ends of the rotor fins, and the distal ends of the rotor fins are closer to the stator than the distal ends of the stator fins.

At least a portion of the plurality of stator fins may overlap the stator in a direction radially outward from the longitudinal axis. This may help to reduce an overall diameter of the stator assembly. For example, at least 50% of the plurality of stator fins may overlap the stator in a direction radially outward from the longitudinal axis. For example, all of the plurality of stator fins are radially inward of an outer perimeter of the stator. In such an example, the overall diameter of the stator assembly is defined by the diameter of the stator rather than the plurality of stator fins such that the provision of the stator fins does not impact the overall diameter of the electric motor. Similarly, at least a portion of the plurality of rotor fins may overlap the stator in a direction radially outward from the longitudinal axis.

Some or all of the plurality of stator fins may not overlap with the stator in a direction parallel to the longitudinal rotational axis. For example, the stator fins may be separated from the stator in a direction parallel to the longitudinal rotational axis. This may help to reduce an overall diameter of the stator assembly and, in turn, the electric motor. Similarly, the plurality of rotor fins may not overlap with the stator in a direction parallel to the longitudinal rotational axis.

Each of the plurality of stator fins may overlap a respective adjacent rotor fin by at least 75% of a length of the stator fin. For example, the plurality of stator fins may overlap a respective adjacent rotor fin by 90% of a length of the stator fins. This may provide a relatively large surface area of the stator assembly that is adjacent to the rotor assembly to encourage heat transfer from the stator fins to the rotor fins during use of the electric motor.

A length of the plurality of stator fins and/or rotor fins may decrease as a function of a distance of a respective stator or rotor fin from the longitudinal rotational axis That is, stator and/or rotor fins that are closer to the longitudinal rotational axis may be longer than stator and/or rotor fins that are further away from the longitudinal rotational axis.

This may reduce, during use of the electric motor and thus rotation of the rotor fins about the longitudinal rotational axis, the effect of any forces caused by misalignment of the stator or rotor assemblies relative to one another and/or relative to the longitudinal rotational axis.

A thickness of each of the plurality of stator fins and/or rotor fins may be in the region of 0.2mm -0.6mm. For the same overall size motor, thinner stator and rotor fins allow more fins to be overlapped, increasing the surface area for heat transfer between the stator and rotor fins.

The electric motor may be arranged to rotate the rotor assembly relative to the stator assembly at a rotation speed such that laminar flow of a fluid between adjacent stator and rotor fins is generated. This may be advantageous in ensuring conduction is the dominant cause of heat transfer between adjacent fins.

The electric motor may be arranged to rotate the rotor assembly relative to the stator assembly at a rotational speed such that non-laminar flow of a fluid between adjacent stator and rotor fins is generated. This may be advantageous in ensuring convection is the dominant cause of the heat transfer between adjacent fins.

Each of the stator fins of the plurality of stator fins may be substantially equally spaced from an adjacent rotor fin of the plurality of rotor fins. This may help to provide more even heat transfer between the stator fins and the rotor fins. This may also help to provide more even flow of a fluid, for example air, between the adjacent fins.

A distance between an adjacent stator fin and rotor fin may be in the region of 0.3mm -Imm, for example approximately 0.5mm. Such a distance may conform to relevant standard requirements for electric motors. Reducing a distance between the adjacent stator and rotor fins can increase a rate of heat conduction from the stator fin to the rotor fin.

The stator fins and the rotor fins may comprise a material having a thermal conductivity of at least 50 W/mK. This may help to increase a rate of heat dissipation compared to agitators comprising materials of a lower thermal conductivity. For example, the fins may comprise, or be formed from aluminium.

A gap between the pluralities of fins is at least partially filled with a fluid, the fluid having a greater thermal conductivity than air. For example, the fluid may be a liquid comprising an oil or a thermal grease. The fluid may increase a rate of heat transfer from the stator fins to the rotor fins.

The stator assembly may comprise bobbin on which the stator is mounted, and, during use of the electric motor, the bobbin may be configured to conduct the heat from the stator to the plurality of stator fins. This may provide effective heat transfer from the stator to the rotor fins. The bobbin may comprise an electrically insulating material.

The bobbin and the plurality of stator fins may be unitary, or form a single part, for example may be monolithic. This may aid in heat dissipation from the bobbin to the stator fins. This may also reduce a part count of the electric motor, which may reduce the cost, complexity, and assembly time of the electric motor.

The plurality of stator fins may be in the form a plurality of nested concentric stator rings of increasing radius and centred about the longitudinal rotational axis, with a concentric stator gap between neighbouring concentric stator fins. This may provide a space efficient arrangement, wherein the rotor fins are positioned in radial gaps between adjacent concentric stator fins. The plurality of rotor fins may be in the form a plurality of nested concentric rotor rings of increasing radius and centred about the longitudinal rotational axis, with a concentric rotor gap between neighbouring concentric rotor fins.

Portions of the concentric rotor fins may overlap longitudinally with portions of the concentric stator fins such that the portions of respective concentric rotor fins are located in a respective concentric stator gap and the portions of respective concentric stator fins are located in a respective concentric rotor gap. This may provide a space efficient arrangement in which a relatively large surface area of the concentric stator fins is positioned adjacent to a relatively large surface area of the concentric rotor fins.

One or more concentric stator or rotor ring may be formed from a solid annulus. This may help to reduce friction between adjacent fins. One or more concentric stator or rotor rings may be formed from a plurality of protrusions arranged relative to one another in a ring, for example two or more arc sections that generally form a ring. This may provide a greater surface area for increased heat transfer from the stator fins to the rotor fins.

One or more voids surrounding the stator may be at least partially filled with a material having a greater thermal conductivity than air. This may reduce an amount of air, which is a relatively poor conductor of heat, within the stator assembly to provide more effective heat transfer from the stator to the stator fins. The material may be electrically insulating.

For example, the material may comprise a thermally conductive paste, such as an epoxy resin.

The electric motor may be a sealed motor. This provides the advantage that ambient air surrounding the electric motor cannot enter the stator and/or rotor assembly and thus reduce an amount of heat transfer to the rotor fins. This may also provide the advantage that any liquids contained in the electric motor are less likely to escape, or leak, from the electric motor which may reduce maintenance requirements of the motor and/or increase a lifespan of the motor.

According to a second aspect of the present invention, there is provided a cleaner head, or nozzle, for a vacuum cleaner. The cleaner head comprises an electric motor according to the first aspect of the present invention, and a heat sink in the form of an agitator, or brushbar, surrounding the electric motor, wherein the rotor assembly is connected to the agitator such that torque generated by the electric motor is transmitted to the agitator.

The cleaner head according to the second aspect of the present invention may be advantageous as the inventors of the present application have determined that providing a cleaner head as claimed can prevent the electric motor exceeding a predetermined maximum temperature during use of the vacuum cleaner. This may help the vacuum cleaner meet predefined safety standards.

Such a cleaner head can reduce or obviate a need for a portion of airflow generated by the vacuum cleaner to be diverted to travel over and/or through the electric motor to dissipate heat generated at the stator during use of the electric motor. This, in turn, can increase the suction performance of the vacuum cleaner for the same amount of airflow compared to a cleaner head that does not comprise an electric motor according to the first aspect of the invention. Rotation of the agitator during use of the electric motor can increase a rate of heat dissipation through convection of heat to the air surrounding the agitator Providing the agitator as a heat sink can increase a rate of heat dissipation from the stator.

Further, there is no requirement to provide a separate heat sink, or a smaller heat sink can be employed. This may allow the overall size, weight, complexity and/or cost of the cleaner head to be reduced.

The agitator may comprise a material having, a thermal conductivity of at least 10 W/mK.

For example, the agitator may comprise aluminium, such as an aluminium body from which a plurality of brush elements extend. For example, the agitator may comprise a composite plastic. This may help to increase a rate of heat dissipation compared to agitators comprising materials of a lower thermal conductivity.

The electric motor may be configured to operate at a rotational speed in the region between 1,000 rpm and 6,000 rpm. Speeds in this range may be suitable for operation of the agitator to pick-up dirt from a surface during operation of the vacuum cleaner. Speeds in this range may be suitable for maintaining laminar flow of a fluid located between adjacent stator and rotor fins.

According to a third aspect of the present invention, there is provided a compressor for a vacuum cleaner. The compressor comprises an electric motor according to the first aspect of the present invention. The rotor assembly of the electric motor comprises an axle surrounded by the stator assembly and an impeller connected to the axle such that torque generated by the electric motor is transmitted to the impeller via the axle. The plurality of rotor fins extend from the impeller towards the stator. In effect, the impellor acts as a heat sink for the electric motor.

Such a compressor can prevent the electric motor exceeding a predetermined maximum temperature during use of the vacuum cleaner. This may help the vacuum cleaner meet predefined safety standards and/or allow the motor to operate at faster speeds.

Typically, the flowrate through an impeller of a vacuum cleaner decreases as a restriction in the vacuum cleaner increases, for example as the vacuum cleaner is used on a carpet a filter loads with dust. For air-cooled compressors, as flowrate decreases, the rotational speed of the impeller increases to help maintain suction performance. The maximum rotational speed of the impeller is limited by flow rate because a portion of the flow rate is used to cool the electric motor. The compressor according to the third aspect of the present invention may be advantageous as the inventors of the present application have determined that providing a compressor as claimed can negate, or reduce, a need for airflow, such as a portion of airflow generated by rotation of the impeller, to travel over and/or through the electric motor to dissipate heat generated at the stator during use of the electric motor. As such, a compressor according to the invention can help to decouple the relationship between flowrate and maximum rotational speed of the impeller.

Providing the impeller as a heat sink can increase a rate of heat dissipation from the stator. Further, there is no requirement to provide a separate heat sink, or a smaller heat sink can be employed. This may allow the overall size, weight, complexity and/or cost of the vacuum cleaner to be reduced. Rotation of the impeller during use of the electric motor can increase a rate of heat dissipation through convection of heat to the airflow generated by the impeller.

The electric motor may be configured to operate at a rotational speed in the region between 40,000 rpm and 180,000 rpm. Speeds in this range may be suitable for operation of the impeller to generate sufficient airflow for operation of the vacuum cleaner. Speeds in this range may be suitable for generating turbulent flow of a fluid located between adjacent stator and rotor fins.

The compressor may comprise a diffuser downstream of the impeller. The diffuser may substantially surround the stator assembly. The diffuser defines an air pathway for guiding airflow generated by the impeller, and a mounting structure for supporting the electric motor in a fixed position relative to the diffuser. This provides a space-efficient arrangement.

The diffuser may comprise, or be formed from, a thermally insulating material, for example rubber. This may help to prevent heat dissipation from the stator via the diffuser, which may in turn reduce heating of the airflow as is passes through the air pathway. This may encourage heat dissipation via the stator fins, rotor fins and impeller.

According to a fourth aspect of the present invention, there is provided a vacuum cleaner.

The vacuum cleaner comprises a cleaner head according to the second aspect of the present invention. Additionally, or alternatively, the vacuum cleaner comprises a compressor according to the third aspect of the present invention.

The vacuum cleaner according to the fourth aspect of the present invention may be advantageous as the inventors of the present application have determined that providing a cleaner head and/or compressor comprising an electric motor according to the first aspect of the present invention may provide increased suction performance, compared to a similar vacuum cleaner that does not comprise the electric motor, because none, or a reduced amount, of the airflow generated during operation of the vacuum cleaner need be diverted to flow over and/or through the electric motor(s).

BRIEF DESCRIPTION OF THE DRAWINGS

Examples will now be described, with reference to the accompanying drawings, in which: Figure I is a perspective view of an electric motor according to an example, Figure 2 is an exploded perspective view of the electric motor of Figure 1; Figure 3 is an exploded cross-sectional side view of the electric motor of Figure 1; Figure 4 is a cross-sectional side view of the electric motor of Figure 1; Figure 5 is a cross-sectional view of a compressor according to an example; Figure 6 is a perspective view of a vacuum cleaner head according to an example; and Figure 7 is a cross-sectional front view of the cleaner head of Figure 6.

DETAILED DESCRIPTION

An electric motor according to the present teaching may be suitable for use in a variety of applications and is arranged to provide a relatively large surface area for heat transfer away from a stator of the electric motor, as compared to conventional electric motors.

As used herein, the term "stator" is generally used to describe a structure comprising a plurality of windings connected to an electric supply through which, in use of the motor, an electric current is passed in order to generate magnetic fields to cause relative rotational movement between the stator and rotor.

As used herein, the term 'rotor assembly" is generally used to describe a rotor comprising one or more magnets, the magnets arranged to interact with the magnetic fields generated by the stator to cause relative rotational movement between the stator and the rotor.

Figures 1 to 4 show different views of one example of an electric motor 10 according to the present teaching.

The electric motor 10 comprises a rotor assembly 20, a stator assembly 30 and an input 14 through which the electric current is passed to a stator 32 of the stator assembly 30. In use of the electric motor 10, the rotor assembly 20 rotates about stator assembly 30 and about a longitudinal rotational axis 12 of the electric motor 10. During use of the electric motor 10, heat is generated at the stator 32 and must be dissipated to prevent overheating of the electric motor 10, which may cause, for example, damage to the stator 32 and/or the input 14.

The stator 32 is mounted on a bobbin 34. The bobbin 34 is configured to conduct heat away from the stator 32. In the example shown, the bobbin comprises a central bore 36 arranged to receive an axle 22 extending from the rotor assembly 20 along the longitudinal rotational axis 12. The axle is supported, in this example, by two bearings 38 located in the central bore 36.

When assembled as illustrated in Figure 1, an outer wall 24 of the rotor assembly 20 surrounds the stator 32 about the longitudinal rotational axis 12. In this example, a plurality of magnets 27 are located on an inner surface 26 of the outer wall 24 and adjacent to an outer perimeter of the stator 32. Accordingly, in use of the example electric motor 10, the stator is fixed to an apparatus in which the motor 10 is comprised and the magnets 27 interact with magnetic fields generated by the stator 32, causing the magnets 27 to rotate around the outer perimeter of the stator 32 to rotate the rotor assembly 20 about the longitudinal rotational axis 12.

The stator assembly 30 comprises a plurality of stator fins 40 that extend substantially parallel to the longitudinal rotational axis 12. The rotor assembly 20 comprises a plurality of corresponding rotor fins 50 that also extend substantially parallel to the longitudinal rotational axis 12. The stator and rotor fins 40, 50 increase the surface area of the respective stator and rotor assemblies 30, 20. When the electric motor 10 is assembled, the stator fins 40 extend away from the stator 32 towards the rotor assembly 20 and the rotor fins 50 extend towards the stator 32, as best shown in Figure 4. Accordingly, portions of the rotor fins 50 overlap, mesh, or interleave longitudinally with portions of the stator fins 40. In this way, a relatively large surface area of the stator assembly overlaps with, or is proximal to, a relatively large surface area of the rotor assembly to provide an increased rate of heat transfer from the stator assembly 30 to the rotor assembly 20. Accordingly, this assists in keeping components of the electric motor 10, such as the stator 32 and the bearings 38, below a maximum temperature threshold during use of the electric motor 10.

The stator fins 40 are connected to the bobbin 34 such that, during use of the electric motor 10, heat is transferred from the bobbin 34 to the stator fins 40 and on to the rotor fins 50.

According to the particular example shown, all or at least a majority of the plurality of stator fins 40 and rotor fins 50 are spaced radially outwardly from the longitudinal rotational axis 12 by no more than a maximal radial dimension of the stator 32. This is achieved by arranging the stator fins 40 longitudinally alongside the stator 32, and the rotor fins 50 longitudinally alongside the magnets 27 of the rotor assembly 20. In this manner, an overlap of the stator fins 40 and rotor fins 50 occurs longitudinally spaced from the assembled stator/rotor magnet arrangement. A particularly radially-space-efficient electric motor 10 can thereby be formed, albeit with a slightly greater longitudinal length, since maximum diameters of the stator fins 40 and the rotor fins 50 is substantially equal to the maximum diameter of the stator 32. It will be appreciated that, in other examples, a portion of the stator fins 40 and/or the rotor fins 50 may be positioned radially outward of the stator 32, which may increase a total surface area of the stator fins 40 and/or the rotor fins 50.

In the example shown, the stator fins 40 do not overlap with the stator 32 in a direction parallel to the longitudinal rotational axis 12. The stator fins 40 are adjacent to the stator 32 along the longitudinal rotational axis 12 and positioned between the stator 32 and the rotor fins 50.

In the example shown, the stator fins 40 and the rotor fins 50 are of substantially equal length in a direction parallel to the longitudinal rotational axis 12, helping to maximise a surface area of the stator fins 40 that is adjacent to the rotor fins 50 for a given overall size of the electric motor 10. It will be appreciated that, in other examples, for example in the electric motor 110 described hereinafter with respect to Figure 5, this need not be the case.

In the example shown, the stator fins 40 and the rotor fins 50 are of substantially uniform thickness along their length. That is, parallel to the longitudinal axis 12. The thickness is 0.5mm in this example. It will be appreciated that, in other examples, some or all of the stator fins 40 and rotor fins 50 have a non-uniform thickness along their length. In an example, the stator fins 40 taper in thickness as they extend away from the stator 32 and the rotor fins 50 taper in thickness as they extend towards the stator 32.

In the example shown, the stator fins 40 and the rotor fins 50 comprise hollow cylindrical, or tubular, elements of varying radii that are concentric about the longitudinal rotational axis 12. The radii are selected so that the stator fins 40 and the rotor fins 50, when the motor 10 is assembled, are interleaved with one another, or nested, without touching one another. In the present example, each of the stator fins 40 overlap one another along the longitudinal rotational axis 12 and are equally spaced from a neighbouring stator fin 40 by a concentric stator gap 42. Further, each of the rotor fins 50 overlap one another along the longitudinal rotational axis 12 and are equally spaced from a neighbouring rotor fin 50 by a concentric rotor gap 52. When the electric motor 10 is assembled, as best shown in Figure 4, portions of the rotor fins 50 overlap longitudinally with portions of the stator fins 40. In this way, the portions of respective rotor fins 50 are located in a respective concentric stator gap 42 and the portions of respective stator fins 40 are located in a respective concentric rotor gap 52. It will be appreciated that the stator fins 40 and rotor fins 50 may have any other suitable profile, as long as they are arranged such that they do not collide during rotation of the rotor assembly 20 relative to the stator assembly 30. For example, rather than having a solid-walled cylindrical form, a fin may have gaps, spaces or voids around its periphery or comprise multiple, spaced apart elements around its periphery. Deployment of gaps, spaces or voids may be beneficial for promoting movement of fluid between the fins, and/or increase heat transfer between the fins in other ways. In any event, other forms of fin are conceivable.

In this example, a distance between a stator fin 40 and an adjacent rotor fin 50 located in the respecting concentric stator gap 42 is approximately 0.5mm.

According to the particular example shown, each of the stator fins 40 overlap a respective adjacent rotor fin 50 by approximately 90% of a length of the stator fin 40. It will be appreciated that in other examples, a percentage of overlap may be higher or lower than 90%, but generally a greater percentage of overlap results in a faster rate of heat transfer from the stator fins 40 to the rotor fins 50.

In this example, the stator fins 40 and the rotor fins 50 are formed of aluminium with a thermal conductivity of 140 W/mK.

Although not shown in this example, in some examples, the gaps 42, 52 between the stator and rotor fins 40, 50 are filled with a fluid other than air. The fluid ideally has a greater thermal conductivity than air, for example, oil, which may assist heat transfer from the stator fins 40 to the rotor fins 50 without unduly increasing friction between the fins 40, 50 Although not shown in this example, in some examples, one or more voids surrounding the stator 32 are at least partially filled with a material having a greater thermal conductivity than air, such as oil. This may assist heat transfer from the stator 32 to the stator fins 40 Although not shown in this example, in some examples, the electric motor 10 is a sealed motor and comprises a seal to prevent ingress of fluid into the stator and rotor assemblies 30, 20. This can increase the number of applications for which the electric motor 10 is suitable, for example the electric motor 10 may be submergible.

Figure 5 shows a compressor 100 according to the teaching herein. The compressor 100 comprises an electric motor 110 that is somewhat similar to the electric motor 10 described with reference to Figures 1-4. Corresponding components of the electric motor have the same reference numeral as the electric motor 10, but increased by 100, and will not be described again for conciseness. Whilst the magnets 27 of the electric motor 10 are radially outward of the stator 32, in this example, the magnets 127 are positioned radially inwardly of the stator 132.

In this example, the compressor 100 is a compressor for a vacuum cleaner and configured to generate an airflow sufficient to provide adequate pick-up performance by the vacuum cleaner. In other examples, the compressor 100 may be a compressor for another type of device, for example a hair styling device or a fan assembly.

In this example, the rotor assembly 120 comprises a plurality of magnets 127 located on the axle 122 and adjacent to an inner perimeter of the stator 132 such that, in use of the motor, the magnets 127 interact with magnetic fields generated by the stator 132 and rotate around the inner perimeter of the stator 132 to rotate the axle 122, and thus the rotor assembly 120, about the longitudinal rotational axis 112. The rotor assembly 120 comprises an impeller 128 connected to the axle U2 such that torque generated by the electric motor 110 is transmitted to the impeller 128 via the axle 122. The impeller 128 has a generally conical form, tapering down from left to right (as shown in Figure 5).

The plurality of rotor fins 150 extend from the impeller U8 substantially parallel to the longitudinal rotational axis 112, rearwardly away from the impeller 128 and towards the stator 132. The plurality of stator fins 140 extend substantially parallel to the longitudinal rotational axis 112 and away from the stator 132 towards the impeller 128. In this example, the rotor fins 150 and the stator fins 140 overlap by around 90% of their length, in a corresponding manner to the stator and rotor fins 40, 50 described with reference to Figures 1-4, such that heat is transferred from the stator fins 140 to the rotor fins 150 in use of the electric motor 110.

The impeller 128 is formed from a suitable material, in this example aluminium, to assist in heat transfer away from the stator 132 via the rotor fins 150. Accordingly, the impeller 128 is configured to act as a heat sink for the electric motor 110. In this example, the impeller 128 is formed as a single part with the rotor fins 150 but in other examples, the impeller 128 and the rotor fins 150 are fabricated as separate parts that are thermally coupled.

As with the electric motor 10 described with reference to Figures 1-4, the stator fins 140 and the rotor fins 150 are cylindrical, concentric and nested/interleaved, having increasing radius and centred about the longitudinal rotational axis 112. The stator fins 140 and the rotor fins 150 have a length in a direction parallel to the longitudinal rotational axis 112. In this example, the length of the stator fins 140 and the rotor fins 150 decreases, generally linearly as the distance from the longitudinal rotational axis 112 increases. This helps to provide a more space-efficient and lighter electric motor 110, while accommodating the tapered shape of the impeller 128. This may also help to reduce rotational instability of the rotor assembly 120 by keeping the longer, and thus heavier, fins closer to the longitudinal rotati onal axis 112.

In this example, in use, the electric motor 110 is configured to rotate the impeller 128 at a speed of around 120,000rpm. At such rotational speeds, the relative velocity between the stator fins 140 and the respective adjacent rotor fins 150 is such that substantially turbulent flow is generated in the gaps between the fins 140, 150 and the primary mechanism of heat transfer from the stator fins 140 to the rotor fins 150 is by convection.

The compressor 100 of this example comprises a diffuser 102 downstream of the impeller 128. The arrows shown in Figure 5 depict a direction of airflow A generated by the impeller 128. The diffuser 102 defines an air pathway 104 for guiding the airflow A generated by the impeller 128 around the electric motor 110. The diffuser 102 surrounds the stator assembly 130 along a portion of its length and comprises a mounting structure 106 for supporting the electric motor 110 in a fixed position relative to the diffuser 102. This provides a particularly space-efficient configuration.

The diffuser 102 is at least partially formed from rubber, a thermally insulating material, to help prevent heat transfer from the stator 132 to the airflow A and instead promote heat transfer towards the stator fins 140. In some examples, although not shown in Figure 5, the diffuser 102 is at least partially formed from a material with a thermal conductivity of at least of at least 50 W/mK and configured to conduct heat away from the stator 132.

Figures 6 and 7 show different views of a cleaner head 200 for a vacuum cleaner according to an example. The cleaner head 200 comprises the electric motor 10 as described with reference to Figures 1-4, an outer housing 202 defining a chamber 204 having an inlet aperture located in a side of the chamber that contacts, in use, a surface to be cleaned and an outlet 208, and an agitator 210 rotatably fixed in the chamber 204. The outlet 208 couples to a wand 1 of the vacuum cleaner.

In use of the vacuum cleaner, the cleaner head 200 is passed over a surface to be cleaned and an airflow is drawn from the inlet aperture, which faces the surface to the cleaned, over the agitator 210 and to the outlet 208 to pick up dust, dirt and other particulates from the surface. The agitator 210 comprises a main body 212 and protrusions 214 extending outwardly of the main body 212, the protrusions 214 configured to contact the surface to assist in the pickup of dust, dirt and other particulates from the surface.

The agitator 210 surrounds the electric motor 10. The form of the motor 10, facilitated by the arrangement of the stator and rotor fins 40, 50, provides a particularly space-efficient configuration. The electric motor 10 is configured to rotate the agitator 210 within the chamber 204 to assist in the pickup of dust, dirt and other particulates from the surface. The stator assembly 30 is fixed to the outer housing 202 via a connection between the bobbin 34 and a support structure 206 extending from a leftmost end (as viewed in Figure 7) of the outer housing 202 into the agitator 210, and the rotor assembly 20 is fixedly connected to the main body 212 of the agitator 210, such that torque generated by the electric motor is transmitted to the agitator 210.

In use of the electric motor 10, heat is transferred from the rotor fins 50 to the main body 212 of the agitator 210 via a thermal coupling between the rotor 20, more specifically the rotor fins 50, and the main body 212. The main body 212 is comprises a material having a thermal conductivity suitable for assisting in heat transfer away from the stator 32 via the rotor fins 50 so that the agitator 210 is configured to act as a heat sink. In this example, the main body 212 of the agitator 210 is formed from aluminium with a thermal conductivity of 140 W/mK. In this example, a thermal, graphite pad (not shown) is positioned between the rotor 20 and the main body 212 to encourage heat transfer. In other examples, the rotor 20 and the main body 212 form a single body, or a thermal paste is positioned between the rotor 20 and the main body 212.

In use, the electric motor 10 is configured to rotate the agitator 210 at a speed of around 4,000rpm. At such rotational speeds, the relative velocity between the stator fins 40 and the respective adjacent rotor fins 50 is such that substantially laminar flow is generated in the gaps 42, 52 between the fins 40, 50 and the primary mechanism of heat transfer from the stator fins 40 to the rotor fins 50 is by conduction. In examples other than those shown in the drawings, the stator and/or rotor fins 50, 40 comprise turbulence-inducing features configured to generate or increase turbulent flow in the gaps 42, 52 and thereby increase heat transfer from the stator fins 40 to the rotor fins 50.

Another example of the invention includes a vacuum cleaner comprising the compressor 100 shown in Figure 5 and the cleaner head 200 shown in Figures 6 and 7.

The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, some or all of the stator and/or rotor fins may comprise one or more slots to increase turbulent airflow in the gaps between the fins. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

CLAIMSAn electric motor, comprising; a rotor assembly that rotates about a longitudinal rotational axis of the electric motor; and a stator assembly comprising: a stator; and a plurality of stator fins that extend substantially parallel to the longitudinal rotational axis and away from the stator towards the rotor assembly, wherein the rotor assembly comprises a plurality of rotor fins that extend substantially parallel to the longitudinal rotational axis and towards the stator, such that portions of the rotor fins overlap longitudinally with portions of the stator fins.
2. The electric motor according to claim 1, wherein at least a portion of the plurality of stator fins overlap the stator in a direction radially outwardly from the longitudinal rotational axis.
3. The electric motor according to claim 1 or claim 2, wherein some or all of the plurality of stator fins do not overlap with the stator in a direction parallel to the longitudinal rotational axis.
4. The electric motor according to any preceding claim, wherein each of the plurality of stator fins overlap a respective adjacent rotor fin by at least 75% of a length of the stator fin.
5. The electric motor according to any preceding claim, wherein each of the stator fins of the plurality of stator fins are substantially equally spaced from an adjacent rotor fin of the plurality of rotor fins.
6. The electric motor according to any preceding claim, wherein a gap between the pluralities of fins is at least partially filled with a fluid, the fluid having a greater thermal conductivity than air.
7. The electric motor according to any preceding claim, wherein the stator assembly comprises a bobbin on which the stator is mounted, and, during use of the electric motor, the bobbin is configured to conduct the heat from the stator to the plurality of stator fins
8. The electric motor according to any preceding claim, wherein the plurality of stator fins comprises nested concentric stator fins of increasing radius and centred about the longitudinal rotational axis, with a concentric stator gap between neighbouring concentric stator fins, and the plurality of rotor fins comprise nested concentric rotor fins of increasing radius and centred about the longitudinal rotational axis, with a concentric rotor gap between neighbouring concentric rotor fins, wherein portions of the concentric rotor fins overlap longitudinally with portions of the concentric stator fins such that the portions of respective concentric rotor fins are located in a respective concentric stator gap and the portions of respective concentric stator fins are located in a respective concentric rotor gap.
9. The electric motor according to any preceding claim, wherein a length of the stator fins and the rotor fins in a direction parallel to the longitudinal rotational axis decreases as a function of a distance of a respective stator or rotor fin from the longitudinal rotational axis.
10 The electric motor according to any preceding claim, wherein one or more voids within the stator assembly are at least partially filled with a material having a greater thermal conductivity than air.
11. The electric motor according to any preceding claim, wherein the electric motor is a sealed motor.
12. A cleaner head for a vacuum cleaner, the cleaner head comprising: an electric motor according to any preceding claim, and a heat sink in the form of an agitator surrounding the electric motor, wherein the rotor assembly is connected to the agitator such that torque generated by the electric motor is transmitted to the agitator.
13. A compressor for a vacuum cleaner, the compressor comprising: an electric motor according to any preceding claim, the rotor assembly comprising: an axle surrounded by the stator assembly and an impeller connected to the axle such that torque generated by the electric motor is transmitted to the impeller via the axle, wherein the plurality of rotor fins extend from the impeller towards the stator.
14. The compressor according to claim 13, comprising a diffuser downstream of the impeller and surrounding the stator assembly, the diffuser defining: an air pathway for guiding airflow generated by the impeller, and a mounting structure for supporting the electric motor in a fixed position relative to the diffuser, wherein the diffuser is formed from a thermally insulating material.
15. A vacuum cleaner comprising a cleaner head according to claim 12 and/or a compressor according to claim 13 or claim 14.