GB2624878A

GB2624878A - A brushless permanent magnet motor

Info

Publication number: GB2624878A
Application number: GB2217909.7A
Authority: GB
Inventors: Glyn Salmon Pierre
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2022-11-29
Filing date: 2022-11-29
Publication date: 2024-06-05
Also published as: WO2024115990A1; GB202217909D0

Abstract

A brushless permanent magnet motor (10, Fig. 1) comprising a rotor (14, Fig. 4) having an impeller or impellor (54, Fig. 4) to induce an airflow, a stator (12, Fig. 3), and a frame (16, Fig. 1) housing the rotor and stator. The frame has a main body (64, Fig. 7) and a separate end cap 68 on the upstream end of the motor, which is shaped aerodynamically to keep the air flow attached to the main body. The end cap 68 may have a parabolic profile with a radius of curvature is at least 0.3 times the width of the cap. The motor may have cavities to contain rotor and stator components, perhaps separated from one another by e.g. an o-ring (62, Fig. 7), and each may have inlets 84 (and 78, Fig. 1) at an upstream end and outlets (86, Fig. 7 and 80, Fig. 1) at a downstream end. Airflow through the cavities (94 and 96, Figs. 9 and 10) may be kept separate, perhaps by spacing the inlets and outlets around the periphery of the housing. The motor may run at between 10,000 and 500,000rpm, and be used in a vacuum cleaner.

Description

A BRUSHLESS PERMANENT MAGNET MOTOR

Field of the Invention

The present invention relates to a brushless permanent magnet motor.

Background of the Invention

There is a general desire to improve electric machines, such as brushless permanent magnet motors. For example, improvements may be desired in terms of cooling the brushless permanent magnet motors.

Summary of the Invention

According to a first aspect of the present invention there is provided a brushless permanent magnet motor comprising a rotor assembly rotatable to generate an airflow, a stator assembly, and a frame within which the rotor assembly and stator assembly are housed, the frame comprising an end cap and a main body, wherein the end cap and the main body are separate components, and the end cap is configured to cause a portion of the airflow to be attached to a portion of the main body which overlies the stator assembly.

The stator assembly may be cooled by the passage of the portion of the airflow over the portion of the main body. For example, the portion of the airflow may convectively cool the portion of the main body, which may in turn conductively cool the stator assembly. As a result of the portion of the airflow being attached to the portion of the main body, greater heat transfer between the main body and the portion of the airflow may occur, which may increase the cooling of the stator assembly, compared to an arrangement where the portion of the airflow were detached from the portion of the main body. Cooling the stator assembly may increase the life of the stator assembly. Additionally, forming the end cap and the main body as separate components may increase the ease of assembly of the motor when compared with an arrangement in which the main body and the end cap were integrally formed. For example, the stator assembly and the rotor assembly may be inserted into the main body, and then the end cap attached to the main body. Moreover, forming the end cap and the main body as separate components may enable greater control over the process of forming the end cap (such as moulding) than if the end cap and main body were integrally formed. Greater control over the process may enable greater control of the geometry of the end cap which may lead to increased attachment of the airflow. Optionally, the end cap is upstream of the main body.

Optionally the end cap is configured to cause the portion of the airflow to attach to the end cap. The portion of the airflow may remain attached to the frame as the portion of the airflow travels downstream from the end cap and over the main body. Thereby, attaching the portion of the airflow to the end cap provides a mechanism for causing the portion of the airflow to be attached to the portion of the main body which overlies the stator assembly. Additionally, attaching the portion of the airflow to the end cap may enable the portion of the airflow to be attached along a greater proportion of the frame, and thereby facilitate greater cooling, than if the portion of the airflow were attached at a point further down the frame.

Optionally, a ratio of a radius of curvature of the end cap to a maximum width of the end cap is no less than 0.30. Ratios of no less than 0.30 may facilitate the attachment of the portion of the airflow to the end cap and thereby to the portion of the main body.

Optionally, the maximum width of the end cap is measured along an axis which is perpendicular to a central longitudinal axis of the brushless permanent magnet motor.

Optionally, a plane extends along a central longitudinal axis of the brushless permanent magnet motor, and the end cap is shaped such that, when viewed in the plane, the end cap has a parabolic profile The inventors have identified that a parabolic profile may facilitate the attachment of the portion of the airflow to the end cap and thereby to the portion of the main body.

Optionally, when the frame is assembled, a maximum width of a portion of the end cap which abuts the main body is substantially the same as a maximum width of a further portion of the main body which abuts the end cap This may facilitate the attachment of the portion of the airflow to the portion of the main body which overlies the stator assembly by reducing the likelihood of the portion of the airflow becoming detached from the frame as the portion of the airflow moves from the end cap to the main body.

Conversely, if the widths were significantly different, a step may be provided between the end cap and the main body which may result in the airflow detaching from the frame. Optionally, the maximum width of the portion of the end cap which abuts the main body and the maximum width of the further portion of the main body which abuts the end cap is measured along an axis which is perpendicular to a central longitudinal axis of the brushless permanent magnet motor.

Optionally, the main body comprises a stator assembly cavity within which the stator assembly is at least partially located, the main body comprises a stator assembly cavity inlet for allowing a further portion of the airflow to enter the stator assembly cavity, and the end cap is configured to cause the further portion of the airflow to be attached to the main body upstream of the stator assembly cavity inlet. As a result, the further portion of the airflow may be directed over the stator assembly within the stator assembly cavity, which may increase cooling of the stator assembly when compared to an arrangement without the stator assembly cavity and the stator assembly cavity inlet. Additionally, by the further portion of the airflow being attached to the main body upstream of the stator assembly cavity inlet, the flow rate of the further portion of the airflow into the stator assembly cavity inlet may be increased compared to an arrangement where the further portion were detached upstream of the stator assembly cavity inlet. Thereby, the cooling of the stator assembly may be further increased. Optionally, the end cap is configured to cause the further portion of the airflow to attach to the end cap to cause the further portion of the airflow to be attached to the main body upstream of the stator assembly cavity inlet.

Optionally, the end cap comprises an inlet for allowing an additional portion of the airflow to enter the frame, and an outlet for allowing the additional portion of the airflow to exit the frame. As a result, the inlet and the outlet may be used to direct the additional portion of the airflow to provide cooling to components of the motor which are located within the frame. For example, the rotor assembly may comprise a component which is located between the inlet and the outlet such that the additional portion of the airflow passes over, and cools, the component. Cooling components of the motor may increase the life of the motor and/or enable the motor to operate at a higher speed when compared to not cooling components of the motor.

Optionally, the end cap comprises a cavity located between the inlet and the outlet, and a component of the rotor assembly extends into the cavity. As a result, the component and thereby the rotor assembly may be cooled by the additional portion of the airflow as it flows through the cavity. For example, the component may be convectively cooled by the additional portion of the airflow, and other components of the rotor assembly may be conductively cooled by the component. Additionally, the component may act as a centrifugal pump to increase the flow rate of the additional portion of the airflow through the cavity and thereby increase the cooling of the motor.

Optionally, a minimum clearance between the component and the end cap is no less than 0.17 mm. As a result, the additional portion of the airflow may have a greater flow rate than if the minimum clearance were less than 0.17mm. As a result, the cooling of the rotor assembly may be increased compared to a configuration in which the clearance was less than 0.17mm.

Optionally, an outer diameter of the component is no less than 2.3 mm. As a result, the component may impart a greater velocity to the additional portion of the airflow, which may increase the amount of centrifugal pumping performed by the component and thereby increasing the flow rate of the additional portion of the airflow to a greater extent than a component having a diameter which is less than 2.3 mm.

Optionally, the main body comprises a stator assembly cavity within which the stator assembly is at least partially located, and the brushless permanent magnet motor comprises a seal configured to inhibit the additional portion of the airflow from flowing from the cavity to the stator assembly cavity. Providing the seal may prevent the additional portion of the airflow which has already been used for cooling the rotor assembly, and may therefore be heated, from being used within the stator assembly cavity to cool the stator assembly. Thereby, another portion of the airflow (such as the further portion of the airflow) which may be cooler than the portion of the airflow which has passed through the cavity (for example, due to not being previously used to cool the rotor assembly), may be used to cool the stator assembly within the stator assembly cavity. This may increase the cooling of the stator assembly compared to an arrangement without the seal.

Optionally, the end cap is located upstream of the stator assembly, and the rotor assembly comprises a bearing located upstream of the stator assembly. As a result, the inlet and the outlet may be used to direct the additional portion of the airflow to cool the bearing. For example, the additional portion of the airflow may be directed over a component of the motor which is connected to the bearing to conductively cool the bearing. Thereby, cooling of the bearing may be increased compared to an arrangement without an inlet and an outlet. Increasing the cooling of the bearing may be particularly advantageous because the life of the bearing may be especially sensitive to excessive temperatures, when compared to other components of the motor (such as a shaft of the rotor assembly). Thereby increasing the cooling of the bearing may have a greater impact on the life of the motor compared to cooling other, less temperature sensitive components of the motors.

Optionally, the end cap is configured to cause the portion of the airflow to attach to the end cap upstream of the outlet and downstream of the inlet. The additional portion of the airflow entering the inlet may decelerate which may result in the pressure of the additional portion of the airflow at the inlet increasing relative to the pressure of the portion of the airflow which is attached to the end cap. Therefore, by attaching the portion of the airflow to the end cap upstream of the outlet and downstream of the inlet, and thereby providing the attached portion of the airflow at the outlet but not the inlet, a pressure difference between the inlet and outlet may be created. This pressure difference may increase the flow rate of the additional portion of the airflow through the cavity and thereby may increase the cooling of the rotor assembly compared to an end which was not so configured. For example, if the portion of the airflow attached downstream of the inlet, a region of stationary air may be provided at the outlet which may have substantially the same pressure as the additional airflow at the inlet and thereby a smaller or no pressure difference may be created.

Optionally, the main body comprises a stator assembly cavity within which the stator assembly is at least partially located, the main body comprises a stator assembly cavity inlet for allowing a further portion of the airflow to enter the stator assembly cavity, and the outlet is offset from the stator assembly cavity inlet about a periphery of the main body and in an axial direction. As a result, cooling of the stator assembly may be increased compared to an arrangement in which the outlet and the stator assembly cavity inlet were not offset. As described above, the additional portion of the airflow may be directed by the inlet and the outlet to cool components within the frame. Therefore, the additional portion of the airflow exiting from the outlet may be heated. If the outlet were not offset with the stator assembly cavity inlet, the previously heated additional portion of the airflow emitted from the outlet may enter the stator assembly cavity inlet and be less effective at cooling the stator assembly than airflow which had not previously been directed to cool components within the frame. Optionally, the axial direction is parallel with a central longitudinal axis of the brushless permanent magnet motor.

Optionally, the rotor assembly comprises an impeller located downstream of the stator assembly. As a result, greater cooling of the motor may occur than if the impeller were upstream of the stator assembly because the impeller may heat the airflow as the impeller works on the airflow, which may reduce the effectiveness of the airflow at cooling the motor.

Optionally, the rotor assembly and stator assembly are configured to rotate the rotor assembly in use at an operational speed of no less than 10,000 revolutions per minute The flow rate of the airflow may be proportional to the operational speed. Thereby, having an operational speed of no less than 10,000 revolutions per minute (rpm) may increase the flow rate of the airflow, and thereby the cooling provided by the airflow, compared to an operational speed of less than 10,000 RPM.

Optionally, the rotor assembly and stator assembly are configured to rotate the rotor assembly in use at an operational speed, and the operational speed is no greater than 500,000 revolutions per minute. The amount of heat generated within the motor may be proportional to the operational speed. For example, a greater operational speed may result in a greater amount of heat being generated. Therefore, having an operational speed of no greater than 500,000 rpm may reduce the amount of heat generated and thereby increase the life of the components of the motor compared to an operational speed of less than 500,000 rpm. Optionally, the operational speed is no greater than, 400,000 rpm, 300,000 rpm, 200,000 rpm, or 150,000 rpm.

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

Brief Description of the Drawings

Figure 1 is a side view of a brushless permanent magnet motor; Figure 2 is a perspective view of the brushless permanent magnet motor, Figure 3 is a perspective view of a stator assembly of the brushless permanent magnet motor; Figure 4 is a perspective view of a rotor assembly of the brushless permanent magnet 25 motor, Figure 5 is a cross-sectional view through the brushless permanent magnet motor with the stator assembly and rotor assembly removed; Figure 6a isa perspective view of a top of an end cap of the brushless permanent magnet motor; Figure 6b is a perspective view of a bottom of the end cap of the brushless permanent magnet motor; Figure 7 is an enlarged cross section of an upstream end of the brushless permanent magnet motor; Figure 8 is a first cross-sectional view through the brushless permanent magnet motor, Figure 9 is a second cross-sectional view through the brushless permanent magnet motor; Figure 10 is a third cross-sectional view through the brushless permanent magnet motor; Figure 11 is an enlarged cross section of an upstream end of the brushless permanent magnet motor; and Figure 12 is a perspective view of a vacuum cleaner incorporating the brushless permanent magnet motor.

Detailed Description of the Invention

A brushless permanent magnet motor according to the present invention, generally designated 10, is illustrated in Figures 1 and 2, with components of the brushless permanent magnet motor 10 shown in Figures 3 and 4.

The brushless permanent magnet motor 10 comprises a stator assembly 12, a rotor assembly 14, a frame 16, and a diffuser 18.

The stator assembly 12 is illustrated in isolation in Figure 3, and comprises four stator core sub-assemblies 20 and a termination assembly 22.

The stator core sub-assembly 20 comprises a stator core (not shown), a bobbin 24, and a winding 26. The stator core has a generally C-shaped form and may be referred to as a c-core. The bobbin 24 is over moulded to the stator core, and comprises first 28 and second 30 connection portions. The first 28 and second 30 connection portions are complementarily shaped, such that adjacent bobbins 24 in the stator assembly 12 can be connected to one another by axially sliding the relevant connection portions 28,30 together. The winding 26 is wound about the bobbin 24.

The termination assembly 22 comprises a first, upper, terminal 32, a second, lower, terminal 34, a first termination tab 36, and a second termination tab 38. Each of the first 32 and second 34 terminals is generally annular in form, with the first terminal 32 overlying the second terminal 34. The windings 26 of the stator core sub-assemblies 20 are connected to the first 32 and second 34 terminals. The first 36 and second 38 termination tabs project upwards from the termination assembly 22 and are each connected to one of the first terminal 32 and the second terminal 34. The termination tabs 36,38 are used to provide power to the terminals 32,34.

The rotor assembly 14 is shown in isolation in Figure 4. The rotor assembly 14 comprises a shaft 40, a permanent magnet 42, first 44 and second 46 bearings, first 48, second 50 and third 52 balancing rings, and an impeller 54.

The shaft 40 is elongate in form, having an upstream end 56 and a downstream end 58, with upstream and downstream referring generally to a direction of airflow over the brushless permanent magnet motor 10 in use. The permanent magnet 42 is mounted generally centrally along the shaft 40. The first balancing ring 48 is mounted to the shaft at the upstream end 56, with the first bearing 44 mounted to the shaft 40 adjacent to the first balancing ring 48. The second balancing ring 50 is mounted to the shaft 40 between the first bearing 44 and the permanent magnet 42. The impeller 54 is mounted to the downstream end 58 of the shaft 40. The second bearing 46 is mounted to the shaft 40 adjacent to the impeller 54, with the third balancing ring 52 mounted to the shaft 40 between the second bearing 46 and the permanent magnet 42. The outer diameter of the first balancing ring 48 is no less than 2.3 mm.

The rotor assembly 14 comprises a pre-load spring 60 for applying a pre-load to the first bearing 44, and a seal in the form of an o-ring 62 located about the first bearing 44 The frame 16 can be seen in Figures 1, 2 and 5, and comprises a main body 64, a shroud 66, and an end cap 68.

The main body 64 is generally cylindrical in form with four protrusions 70 The main body 64 defines first 70 and second 72 bearing seats for the respective first 44 and second I0 46 bearings. The main body 64 also defines a channel 74 within which the rotor assembly 14 is located and into which the stator assembly 12 extends. Each of the protrusions 70 overlies a stator core sub-assembly 16.

The main body 64 of the frame 16 comprises a plurality of cooling inlets 78, and a plurality of cooling outlets 80. The plurality of cooling inlets 78 are located in a region below the first bearing seat 70, and are spaced about the periphery of the main body 64. The plurality of cooling inlets 78 are shaped to direct airflow flowing over the main body 64 in use into the channel 74, which provides a cooling effect to the stator assembly 12 and components of the rotor assembly 14 located between the cooling inlets 78 and outlets 80, such as the permanent magnet 42. The plurality of cooling outlets 80 are located in a region of the second bearing seat 72, and are spaced about the periphery of the main body 64. The plurality of cooling outlets 80 are shaped to direct airflow flowing through the channel 74, outwardly from the frame 16, before the airflow passes through the impeller 54.

A downstream end of the main body 64 of the frame 16 defines a labyrinth seal with the impeller 54.

The shroud 66 is axially spaced from the main body 64, and has a central aperture that overlies the impeller 54, such that airflow can interact with the impeller 54 in use.

As shown in Figures 6a, 6b, and 7, the end cap 68 is hollow and forms an upstream end of the frame 16. The end cap 68 comprises a cavity 82, an inlet 84, outlets 86, termination pockets 88, fingers 90, and adhesive slots 92 The end cap 68 has a parabolic profile. The parabolic profile is such that the end cap 68 is substantially perpendicular to the central longitudinal axis at an apex of the profile and substantially parallel with the central longitudinal axis at the ends of the parabolic profile.

A ratio of a radius of curvature of the end cap 68 to a maximum width of the end cap 68 I] is no less than 030. The maximum width occurs at a portion of the end cap 68 which abuts and connects to the main body 64 The cavity 82 extends between the inlet 84 and the outlets 86. The inlet 84 is circular in shape and is centred on the apex of the parabolic profile. The outlets 86 are located at either end of the parabolic profile and on opposite sides of the end cap 68. In this example, the outlets 86 are rectangular in shape, however, other shapes of outlet 86 may be used. The end cap 68 comprises two outlets 86. However, in other examples, the end cap 68 may comprise a single outlet 86 or three or more outlets 86.

The termination pockets 88 are holes in the end cap 68 through which the termination tabs 36,38 extend. The fingers 90 project in a downstream direction away from the inlet 84, are resiliently deformable, and, when not mounted to the brushless permanent magnet motor 10, the plurality of fingers 90 splay slightly outwardly from the main body 64. The fingers 90 engage an inside of the channel 74 to mount the end cap 68 to the main body 64. The adhesive slots 92 are located in the downstream face of the end cap 68 and contain adhesive which secures the end cap 68 to the main body 64.

A cross-section through the brushless permanent magnet motor 10 is shown in Figure 8.

As can be seen, the rotor assembly 14 sits within the frame 16, with the first bearing 44 located at the first bearing seat 70, the second bearing 46 located at the second bearing seat 72, and the permanent magnet 42 aligned with the stator cores of the stator assembly 12. The impeller 54 is thereby located on a downstream side of the stator assembly 12, and the first bearing 44 is located on an upstream side of the stator assembly 12 The end cap 68 is connected to an upstream end of the main body 64, and thereby is located on an upstream side of the stator assembly 12.

As can be seen in Figure 7 the o-ring 62 sits between the first bearing 44 and the main body 64 and acts as a seal to inhibit the passage of airflow. Thereby the o-ring 62 separates the channel 74 into an upper portion and a lower portion. In the lower portion, the second balancing ring 50, permanent magnet 42, third balancing ring 52, part of the stator assembly 12, and second bearing 46 are located. In the upper portion, part of the first bearing 44, part of the shaft 40 and the first balancing ring 48 are located. The end cap 68 is connected to the upstream end of the main body 64 such that the cavity 82 of the end cap 68 and the upper portion of the channel 74 form a single cavity.

The first balancing ring 48 and part of the shaft 40 extend into the cavity 82 of the end cap 68 such that there is a minimum clearance between an inside of the end cap 68 and the first balancing ring 48 of no less than 0.17 mm. The maximum width of the portion of the end cap 68 which abuts and connects to the upstream end of the main body 64 is substantially the same as a maximum width of the upstream end of the main body 64. The maximum width of the portion of the end cap 68 is 21.3 mm and the maximum width of the upstream end of the main body 64 is 21.3 mm.

As shown in Figures 1 and 2, the outlets 86 of the end cap 68 are offset from the cooling inlets 78 about the periphery of the main body 64 and in an axial direction (i e., a direction parallel with the central longitudinal axis of the brushless permanent magnet motor 10) The diffuser 18 is located downstream of the impeller 54. The diffuser 18 is attached to the shroud 66 and comprises a plurality of vanes for turning airflow as it passes through the diffuser 18 from the impeller 54 in use. Although depicted as a multi-stage diffuser, i.e. 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 windings 24 of the stator assembly 12 to generate a magnetic field that interacts with the permanent magnet 42 to cause rotation of the rotor assembly 14. After an initial acceleration phase, the rotor assembly 14 rotates at a steady state speed, called an operational speed, of between 10,000 rpm and 500,000 rpm. Rotation of the rotor assembly 14 causes rotation of the impeller 54 which generates an airflow through the brushless permanent magnet motor 10.

Referring now to Figure 9, due to the shape of the end cap 68, a first portion 94 of the airflow attaches to the end cap 68 downstream of the inlet 84 and upstream of the outlets 86. The first portion 94 of the airflow then remains attached to the frame 16 as the first portion 94 of the airflow flows from the end cap 68 to the main body 64 and around the protrusions 70. Heat generated by the stator assembly 12 is transferred to the first portion 94 of the airflow via the protrusions 70. The first portion 94 of the airflow then continues downstream until it enters the shroud 66 and interacts with the impeller 54 before leaving the brushless permanent magnet motor 10 via the diffuser 18.

Referring now to Figure 10 due to the shape of the end cap 68, a second portion 96 of the airflow attaches to the end cap 68 downstream of the inlet 84 and upstream of the outlets 86. The second portion 96 of airflow is offset from the first portion 94 of the airflow around the periphery of the end cap 68 such that as the second portion 96 of the airflow flows down the frame 16 (remaining attached to the frame 16) the second portion 96 of the airflow flows into the cooling inlets 78 and into the frame 16. The second portion 96 of the airflow then flows along the channel 74. Heat generated by the stator assembly 12 and permanent magnet 42 is transferred to the second portion 96 of the airflow. The second airflow then exits the frame 16 through the cooling outlets 80. The second portion 96 of the airflow then continues downstream until it enters the shroud 66 and interacts with the impeller 54 before leaving the brushless permanent magnet motor 10 via the diffuser 18 Referring now to Figure 11, a third portion 98 of the airflow enters the cavity 82 of the end cap 68 via the inlet 84. The third portion 98 of the airflow then flows over the first balancing ring 48 which, due to the rotation of the first balancing ring 48, accelerates the third portion 98 of the airflow. The third portion 98 of the airflow then exits the cavity 82 of the end cap 68 via the outlets 86. As described above, the upper portion of the channel 74 and the cavity 82 of the end cap 68 form a single cavity. As a result, some of the third portion 98 of the airflow flows over the first bearing before exiting the cavity 82 of the end cap 68 via the outlets 86.

Once the third portion 98 of the airflow has exited the outlets 86 of the end cap 68, the third portion 98 of the airflow flows along the main body 64 and through the impeller 54. Due to the outlets 86 of the end cap 68 being offset about the periphery of the frame 16 from the cooling inlets 78, the heated third portion 98 of the airflow exits the outlets 86 and enters the shroud 66 without entering the cooling inlets 78.

As a result of the end cap 68 being configured to cause the first portion 94 of the airflow to be attached to the protrusions 70 which overlie the stator assembly 12, the stator assembly 12 may be cooled by the passage of the first portion 94 of the airflow over the protrusions 70. For example, the first portion 94 of the airflow may convectively cool the protrusions 70, which may in turn conductively cool the stator assembly 12. As a result of the first portion 94 of the airflow being attached to the protrusions 70, greater heat transfer between the main body 64 and the first portion 94 of the airflow may occur, which may increase the cooling of the stator assembly 12, compared to an arrangement where the first portion 94 of the airflow were detached from the protrusions 70. Cooling the stator assembly 12 may increase the life of the stator assembly 12. Forming the end cap 68 and the main body 64 as separate components may increase the ease of assembly of the brushless permanent magnet motor 10 when compared with an arrangement in which the main body 64 and the end cap 68 were integrally formed. For example, the stator assembly 12 and the rotor assembly 14 may be inserted into the main body 64, and then the end cap 68 attached to the main body 64. Moreover, forming the end cap 68 and the main body 64 as separate components may enable greater control over the process of forming the end cap 68 (such as moulding) than if the end cap 68 and main body 64 were integrally formed. Greater control over the process may enable greater control of the geometry of the end cap 68 which may lead to increased attachment of the airflow.

As a result of the end cap 68 comprising the inlet 84 and the outlets 86, the inlet 84 and the outlets 86 may be used to direct the third portion 98 of the airflow to provide cooling to components of the motor which are located within the frame 16 and on the upstream side of the stator assembly 12 (i.e., remote from the impeller 54). For example, the first balancing ring 48 and a portion of the shaft 40 are located between the inlet 84 and the outlets 86 and may be cooled by the passage of the third portion 98 of the airflow. Cooling the first balancing ring 48 and shaft 40 may also conductively cool other components of the rotor assembly 14 such as the first bearing 44. Cooling components of the brushless permanent magnet motor 10 may increase the life of the brushless permanent magnet motor 10 and/or enable the brushless permanent magnet motor 10 to operate at a higher speed when compared to not cooling components of the brushless permanent magnet motor 10.

In the above example, the main body 64 comprises protrusions 70 which overlie the stator assembly 12. However, in other examples, the main body 64 may have other shapes such that the protrusions 70 may be omitted and other portions of the main body 64 overlie the stator assembly 12. Therefore, in a more general sense it may be said that a portion of the main body 64 overlies the stator assembly 12, and the end cap 68 is configured to cause a portion of the airflow to be attached to the portion of the main body 64 which overlies the stator assembly 12.

In the above example, the first balancing ring 48 extends into the cavity 82 of the end cap 68. However, other components of the rotor assembly 14 may instead extend into the cavity 82 of the end cap 68, for example, the first balancing ring 48 may be omitted, and the shaft 40 of the rotor assembly 14 extend into the cavity 82 of the end cap 68 without the first balancing ring 48 The brushless permanent magnet motor 10 described herein may find particular utility in fields where small form factor yet high power density is desirable. As an example, a vacuum cleaner 100 comprising the bnishless permanent magnet motor 10 is illustrated schematically in Figure 12.

Although described herein with a combination of features, it will be appreciated that embodiments of the brushless motor 10 where only some of the above-mentioned features are implemented are also envisaged. I6

Claims

Claims 1. A brushless permanent magnet motor comprising: a rotor assembly rotatable to generate an airflow; a stator assembly; and a frame within which the rotor assembly and stator assembly are housed, the frame comprising an end cap and a main body, wherein: the end cap and the main body are separate components; and the end cap is configured to cause a portion of the airflow to be attached to a portion of the main body which overlies the stator assembly.
2. A brushless permanent magnet motor as claimed in claim 1, wherein the end cap is configured to cause the portion of the airflow to attach to the end cap 3. A brushless permanent magnet motor as claimed in claim 2, wherein a ratio of a radius of curvature of the end cap to a maximum width of the end cap is no less than 0.30.4. A brushless permanent magnet motor as claimed in claim 2 or claim 3, wherein: a plane extends along a central longitudinal axis of the brushless permanent 20 magnet motor; and the end cap is shaped such that, when viewed in the plane, the end cap has a parabolic profile.5. A brushless permanent magnet motor as claimed in any one of claims 2 to 4, 25 wherein, when the frame is assembled, a maximum width of a portion of the end cap which abuts the main body is substantially the same as a maximum width of a further portion of the main body which abuts the end cap.6. A brushless permanent magnet motor as claimed in any preceding claim, wherein: the main body comprises a stator assembly cavity within which the stator assembly is at least partially located; the main body comprises a stator assembly cavity inlet for allowing a further portion of the airflow to enter the stator assembly cavity; and the end cap is configured to cause the further portion of the airflow to be attached to the main body upstream of the stator assembly cavity inlet.7. A brushless permanent magnet motor as claimed in any preceding claim, wherein the end cap comprises an inlet for allowing an additional portion of the airflow to enter the frame, and an outlet for allowing the additional portion of the airflow to exit the frame.8. A brushless permanent magnet motor as claimed in claim 7, wherein: the end cap comprises a cavity located between the inlet and the outlet; and a component of the rotor assembly extends into the cavity.9. A brushless permanent magnet motor as claimed in claim 8, wherein a minimum Is clearance between the component and the end cap is no less than 0.17 mm.10. A brushless permanent magnet motor as claimed in claim 8 or claim 9, wherein an outer diameter of the component is no less than 2.3 mm.10. A brushless permanent magnet motor as claimed in any one of claims 8 to 10, wherein: the main body comprises a stator assembly cavity within which the stator assembly is at least partially located; and the brushless permanent magnet motor comprises a seal configured to inhibit the additional portion of the airflow from flowing from the cavity to the stator assembly cavity.12. A brushless permanent magnet motor as claimed in any one of claims 7 to 11, wherein: the end cap is located upstream of the stator assembly; and the rotor assembly comprises a bearing located upstream of the stator assembly.13. A brushless permanent magnet motor as claimed in any one of claims 7 to 12, wherein the end cap is configured to cause the portion of the airflow to attach to the end cap upstream of the outlet and downstream of the inlet.14. A brushless permanent magnet motor as claimed in any one of claims 7 to 13, wherein: the main body comprises a stator assembly cavity within which the stator assembly is at least partially located; the main body comprises a stator assembly cavity inlet for allowing a further portion of the airflow to enter the stator assembly cavity; and the outlet is offset from the stator assembly cavity inlet about a periphery of the main body and in an axial direction.15. A brushless permanent magnet motor as claimed in any preceding claims, wherein the rotor assembly comprises an impeller located downstream of the stator assembly.16. A brushless permanent magnet motor as claimed in any preceding claim, wherein the rotor assembly and stator assembly are configured to rotate the rotor assembly in use at an operational speed of no less than 10,000 revolutions per minute.17. A brushless permanent magnet motor as claimed in any preceding claim, wherein: the rotor assembly and stator assembly are configured to rotate the rotor assembly in use at an operational speed; and the operational speed is no greater than 500,000 revolutions per minute.18. A vacuum cleaner comprising a brushless permanent magnet motor as claimed in any preceding claim.