Rotor assembly

Abstract

A rotor assembly for a brushless permanent magnet motor includes a shaft, a permanent magnet mounted to the shaft, and a rotor assembly component mounted to the shaft and in contact with the permanent magnet at an interface between the rotor assembly component and the permanent magnet. At least one of the rotor assembly component and the permanent magnet includes a through hole at the interface.

Description

Technical Field

[0001] The present invention relates to a rotor assembly for a brushless permanent magnet motor and a brushless permanent magnet motor comprising the rotor assembly. Background Art

[0002] It is often desirable to improve electric motors, such as brushless motors, in a variety of ways. For example, improvements may be desired in size, weight, power density, manufacturing cost, efficiency, reliability, and noise. Summary of the Invention

[0003] According to a first aspect of the present invention, there is provided a rotor assembly for a brushless permanent magnet motor, the rotor assembly comprising: a shaft; permanent magnets mounted to the shaft; and a rotor assembly component mounted to the shaft and in contact with the permanent magnets at an interface between the rotor assembly component and the permanent magnets; wherein at least one of the rotor assembly component and the permanent magnets comprises a through hole at the interface.

[0004] By placing the rotor assembly components in contact with the permanent magnets, the ease of manufacture of the rotor assembly can be increased compared to, for example, an arrangement in which no rotor assembly components are in contact with the permanent magnets. For example, the contact of the permanent magnets with the rotor assembly components can be used to properly axially position the permanent magnets relative to the shaft during the assembly process and can alleviate the need for appropriate tooling to hold the permanent magnets in their desired axial positions during assembly.

[0005] By providing through-holes at the interface between the rotor assembly and the permanent magnets, the ease of assembly of the rotor assembly can be increased and / or the cost of assembly of the rotor assembly can be reduced, compared to, for example, an arrangement without such through-holes. For example, it may be desirable to use an adhesive to bond the permanent magnets to the shaft. Such through-holes can allow excess adhesive to drain away from the passage between the permanent magnets and the shaft, whereas without such through-holes, there would be no such leakage path for the adhesive.

[0006] Furthermore, it may be desirable to have the inner diameter of the permanent magnet be as concentric as possible with the shaft. In the event that adhesive is applied between the permanent magnet and the shaft, the adhesive is largely obscured by the permanent magnet. This can inhibit the use of certain types of curing processes, such as ultraviolet (UV) curing, to cure the adhesive, as there is no guarantee that the UV light will reach all of the adhesive and, therefore, fully cure it.

[0007] Therefore, it may be necessary to use an alternative process for curing the adhesive, such as a thermal curing process. However, thermal curing processes can take significantly longer than UV curing processes. This can result in a window in which the permanent magnets are not securely held in place relative to the shaft, and misalignment of the permanent magnets relative to the shaft can occur during this window. Proper alignment of the permanent magnets and the shaft is important for reliable operation of the brushless permanent magnet motor, including the rotor assembly.

[0008] By providing through holes at the interface between the rotor assembly components and the permanent magnets, a line of sight path can be provided so that a relatively fast-curing UV adhesive can be used to secure the permanent magnets relative to the shaft, while a longer thermal cure process is used to fully secure the permanent magnets to the shaft.

[0009] It will be appreciated that the through-holes may be filled with adhesive in the assembled rotor assembly, but when adhesive is not present, such through-holes may provide a line of sight to the shaft.

[0010] The through-hole may comprise a cut-out in an end portion of at least one of the rotor assembly component and the permanent magnet, for example such that at least one of the rotor assembly component and the permanent magnet comprises a toothed end portion.

[0011] At least one of the rotor assembly component and the permanent magnet may include a plurality of through-holes located at the interface. By providing a plurality of through-holes, increased adhesive drainage paths and / or increased line of sight may be provided at different locations around the perimeter of the interface compared to an arrangement having a single through-hole.

[0012] The plurality of through holes may be evenly spaced around at least one of the rotor assembly component and the permanent magnet. This may provide increased security in positioning the permanent magnet to the shaft during the assembly process relative to an arrangement having unevenly spaced through holes.

[0013] At least one of the rotor assembly component and the permanent magnet may include at least three through-holes located at the interface.Providing at least three through-holes may provide a relatively good compromise between structural integrity and providing a leakage path / line of sight.

[0014] At least one of the rotor assembly component and the permanent magnet may include exactly three through-holes located at the interface.

[0015] The rotor assembly components may include through-holes. This may provide increased structural integrity and ease of manufacture compared to arrangements where the permanent magnets include through-holes, and this increased structural integrity may enable the permanent magnets to withstand higher rotational speeds and / or higher temperatures in use with reduced risk of failure. Furthermore, this may provide an increased volume of magnetic material for a given packaging volume compared to arrangements where the permanent magnets include through-holes.

[0016] The shaft may include a first portion to which the rotor assembly components are mounted, a second portion to which the permanent magnets are mounted, and a transition region between the first portion and the second portion, the first portion having a first diameter, the second portion having a second diameter smaller than the first diameter, the transition region having a third diameter smaller than the first diameter and the second diameter, and the through-hole may overlap the transition region. Such a transition region may facilitate manufacture of the rotor assembly, for example by providing easy access to a passage between the permanent magnets and the second portion of the shaft during assembly, such that adhesive may be injected into the passage.

[0017] The through hole may overlap the transition region and the first portion.

[0018] The rotor assembly component may include a bore including a first region having a first diameter and a second region having a second diameter smaller than the first diameter, and the first region may be located at an interface. Providing a region of increased diameter at the interface may define an area in which adhesive used to bond the permanent magnet to the shaft may accumulate. Providing an area in which adhesive may accumulate may promote bonding of the adhesive to the rotor assembly component, which may inhibit separation of the adhesive from the rotor assembly component when the rotor assembly rotates in use.

[0019] The rotor assembly components may include one or more of a gimbal, an impeller, and a bearing assembly. The rotor assembly component may be a gimbal. The gimbal is typically provided so that material can be removed from the gimbal to achieve desired rotor dynamics. This can facilitate providing a through hole without affecting the gimbal's primary function.

[0020] The rotor assembly may include a bearing assembly mounted to the shaft, and the gimbal may be located between the bearing assembly and the permanent magnets. This may space the bearing assembly, which may typically include ferromagnetic components, from the permanent magnets while also promoting desired rotor dynamics performance.

[0021] The rotor assembly may include another bearing assembly mounted to the shaft on an opposite side of the permanent magnet from the bearing assembly. Providing bearing assemblies on both sides of the shaft may provide improved performance relative to corresponding arrangements having, for example, only one bearing assembly or two bearing assemblies located on the same side of the permanent magnet.

[0022] The rotor assembly may include a further balancing ring mounted to the shaft between the further bearing assembly and the permanent magnets.Providing a further balancing ring may provide increased flexibility in rotor dynamics performance compared to an arrangement having only one balancing ring.

[0023] The further gimbal may comprise a smaller mass than the gimbal.Providing such an asymmetric gimbal arrangement may provide increased flexibility in motor construction compared to arrangements having only one gimbal or two identical gimbals.

[0024] The rotor assembly may comprise an impeller mounted to a shaft, and the balancing ring may be located between the impeller and the permanent magnets. This may provide improved rotor dynamics compared to an arrangement where, for example, the permanent magnets are located between the impeller and the balancing ring.

[0025] According to a second aspect of the present invention, there is provided a brushless permanent magnet motor comprising a rotor assembly according to the first aspect of the present invention.

[0026] A brushless permanent magnet motor may include a stator assembly including one or more coils that, when energized, generate a magnetic field that interacts with permanent magnets to rotate a shaft relative to the stator assembly.

[0027] According to a third aspect of the present invention, there is provided a vacuum cleaner comprising the brushless permanent magnet motor according to the second aspect of the present invention.

[0028] According to a fourth aspect of the present invention, there is provided a hair care appliance comprising the brushless permanent magnet motor according to the second aspect of the present invention.

[0029] According to a fifth aspect of the present invention, there is provided a method of manufacturing a rotor assembly for a brushless permanent magnet motor, the method comprising providing a shaft, providing a rotor assembly component and a permanent magnet, at least one of the rotor assembly component and the permanent magnet comprising a through hole, mounting the rotor assembly component to the shaft, and positioning the permanent magnet relative to the shaft such that the permanent magnet contacts the rotor assembly component at an interface, and the through hole is located at the interface.

[0030] The method may include providing an adhesive between the permanent magnet and the shaft such that the adhesive is visible through the through-hole, and curing the adhesive using a light-curing process to bond the permanent magnet to the shaft.

[0031] The method may include further curing the adhesive using a thermal curing process.

[0032] Where appropriate, optional features of one aspect of the invention may be equally applied to other aspects of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic cross-sectional view of a rotor assembly;

[0034] Figure 2 yes Figure 1 a schematic cross-sectional view of a shaft of a rotor assembly;

[0035] Figure 3 yes Figure 1 A schematic perspective view of a first balancing ring of a rotor assembly;

[0036] Figure 4 It shows Figure 1 A flowchart of the steps for assembling a rotor assembly;

[0037] Figure 5 is included Figure 1 Schematic diagram of a brushless permanent magnet motor having a rotor assembly;

[0038] Figure 6 is included Figure 5 Schematic diagram of a vacuum cleaner with a brushless permanent magnet motor;

[0039] Figure 7 is included Figure 1 Schematic diagram of a hair care appliance with a brushless permanent magnet motor;

[0040] Figure 8 is used for Figure 1 Schematic diagram of an alternative shaft and gimbal for a rotor assembly; and

[0041] Figure 9 is used for Figure 1 Schematic diagram of an alternative shaft and impeller of a rotor assembly. DETAILED DESCRIPTION

[0042] Figure 1 The rotor assembly 10 is schematically shown in FIG. The rotor assembly 10 includes a shaft 12, an impeller 14, a first bearing assembly 16 and a second bearing assembly 18, a first balance ring 20 and a second balance ring 22, and a permanent magnet 23.

[0043] Axis 12 Figure 2 1. The shaft 12 is shown separately in a schematic cross-section. The shaft 12 includes a first portion 24, a second portion 26 adjacent to the first portion 24, a first transition region 25 between the first portion 24 and the second portion 26, a third portion 28 adjacent to the second portion 26, and a second transition region 27 between the second portion 26 and the third portion 28. In this manner, the second portion 26 is considered to be between the first portion 24 and the third portion 28. The first portion 24 defines a first end 30 of the shaft 12, and the third portion 28 defines a second end 32 of the shaft 12 opposite the first end 30. The shaft is a one-piece stainless steel component such that the first portion 24, the second portion 26, and the third portion 28 are integrally formed. The shaft 12 has a relative magnetic permeability of approximately 20. In some alternative examples, the first transition region 25 and / or the second transition region 27 may be omitted.

[0044] First portion 24 has a first shaft diameter A of approximately 5.0 mm and a length of approximately 25 mm. First shaft diameter A defines the maximum diameter of shaft 12. The ends of first portion 24 taper slightly inward from first shaft diameter A. Second portion 26 has a second shaft diameter B of approximately 4.5 mm and a length of approximately 15 mm. The end of second portion 26 closest to third portion 28 tapers slightly inward from second shaft diameter B. Third portion 28 has a third shaft diameter C of approximately 3.0 mm and a length of approximately 10 mm. The end of third portion 28 distal from second portion 26 tapers slightly inward from third shaft diameter C. First transition region 25 has a fourth shaft diameter D, which is smaller than first shaft diameter A and second shaft diameter B, but larger than third shaft diameter C. Second transition region 27 has a fifth shaft diameter E, which is smaller than third shaft diameter C.

[0045] Thus, the first portion 24 has a first shaft diameter A that is greater than the second shaft diameter B of the second portion 26 and greater than the third shaft diameter C of the third portion 28. Specifically, the first shaft diameter A is approximately 11% greater than the second shaft diameter B and approximately 66% greater than the third shaft diameter C. The second shaft diameter B is approximately 50% greater than the third shaft diameter C.

[0046] The length of first portion 24 is approximately 66% greater than the length of second portion 26, and the length of first portion 24 is approximately 150% greater than the length of third portion 28. The length of second portion 26 is approximately 50% greater than the length of third portion 28.

[0047] The first and second portions 24, 28 of the shaft 12 are precision ground to a surface roughness in the range of 0.1 to 0.3 Ra. The second portion 26 of the shaft 12 is precision ground to a surface roughness greater than the surface roughness of the first and second portions 24, 28 of the shaft 12, typically having a surface roughness in the range of 0.3 to 0.5 Ra.

[0048] The impeller 14 is a mixed flow impeller and is press fit to the first portion 24 such that the impeller 14 is located at the first end 30 of the shaft 12. Axial flow and / or radial flow impellers are also contemplated. The impeller 14 is injection molded using PEEK material.

[0049] The first bearing assembly 16 comprises a ball bearing assembly and is press-fitted to the first portion 24 of the shaft 12 such that the first bearing assembly 16 is partially located within the hollow interior of the impeller 14. The first bearing assembly 14 thus has an inner diameter that substantially corresponds to the first shaft diameter A. The outer diameter of the first bearing assembly 16 is greater than the outer diameter of each of the second bearing assembly 18, the first and second gimbals 20, 22, and the permanent magnet 23.

[0050] The second bearing assembly 18 comprises a ball bearing assembly and is press-fitted to the third portion 28 of the shaft 12 such that the second bearing assembly 18 is located at the second end 32 of the shaft 12. The second bearing assembly 18 thus has an inner diameter that substantially corresponds to the third shaft diameter C. The outer diameter of the second bearing assembly 18 substantially corresponds to the outer diameter of the second gimbal 22 and the permanent magnet 23, but is smaller than the outer diameter of the first gimbal 20.

[0051] The first and second bearing assemblies 16, 18 are located at points on the respective first and third portions 24, 28 of the shaft 12 such that the span between the first and second bearing assemblies 16, 18 is approximately 30 mm.

[0052] The first balance ring 20 is Figure 3 The first gimbal 20 is shown separately in FIG. The first gimbal 20 has a base 36 and an upright wall 38. The base 36 is substantially annular and solid, having a central aperture 40. The central aperture 40 has a diameter substantially corresponding to the first shaft diameter A of the first portion 24 of the shaft 12, such that the first gimbal 20 is press-fitted to the first portion 24 of the shaft 12 when assembled. The upright wall 38 is integrally formed with the base 36 from a plastic material, such that the first gimbal 20 is a single-piece component. The upright wall 38 projects annularly from the base 36 around the central aperture 40 and has three through-holes 42, which may also be referred to as cutouts, evenly spaced around the perimeter of the upright wall 38, giving the upright wall 38 a generally toothed form. When mounted to the shaft 12, the through-holes 42 span the first portion 24 and the transition region 25 of the shaft 12.

[0053] The second gimbal 22 is substantially annular and solid and is formed of a plastic material. The second gimbal 22 is press-fitted to the third portion 28 of the shaft 12, with the second bearing assembly 18 positioned closer to the second end 32 of the shaft 12 than the second gimbal 22. The second gimbal 22 has a smaller mass than the first gimbal 20.

[0054] The permanent magnet 23 is a two-pole sintered magnet that is mounted to the second portion 26 of the shaft 12 via an adhesive. When the permanent magnet 23 is mounted to the second portion 26 of the shaft 12, the permanent magnet 23 contacts the upright wall 38 of the first gimbal 20 at the interface 44. The interface 44 is formed by Figure 1 The dotted line in FIG.

[0055] To assemble the rotor assembly 10, the impeller 14 is initially press-fitted onto the first portion 24 of the shaft 12. The first bearing assembly 16 is then also press-fitted onto the first portion 24 of the shaft 12, with the first bearing assembly 16 inserted from the second end 32 of the shaft 12. The first gimbal 20 is then also press-fitted onto the first portion 24 of the shaft 12, with the first bearing assembly 16 inserted from the second end 32 of the shaft 12.

[0056] The permanent magnet 23 is then bonded to the second portion 26 of the shaft 12 via an adhesive. It may be desirable to have the inner diameter of the permanent magnet 23 as concentric as possible with the shaft 12. In the event that adhesive is applied between the permanent magnet 23 and the shaft 12, this adhesive is largely obscured by the permanent magnet 23. This may inhibit the use of certain types of curing processes, such as ultraviolet (UV) curing processes, to cure the adhesive, as there is no guarantee that the UV light will reach all of the adhesive and, therefore, fully cure.

[0057] Therefore, it may be necessary to use an alternative process for curing the adhesive, such as a thermal curing process. However, a thermal curing process may take significantly longer than a UV curing process. This may result in a window in which the permanent magnets 23 are not securely held in place relative to the shaft 12, and in which misalignment of the permanent magnets relative to the shaft may occur. Proper alignment of the permanent magnets 23 and the shaft 12 may be important for reliable operation of the brushless permanent magnet motor including the rotor assembly 10.

[0058] The form of the first gimbal 20 and the contact between the first gimbal 20 and the permanent magnet 23 at the interface 44 can facilitate proper alignment of the permanent magnet 23 and the shaft 12 during manufacture of the rotor assembly 10. Specifically, the permanent magnet 23 can be slid along the shaft 12 from the second end 32 of the shaft 12 until the end of the permanent magnet 12 contacts the upstanding wall 38 of the first gimbal 20. By placing the first gimbal 20 in contact with the permanent magnet 23, proper axial positioning of the permanent magnet 23 relative to the shaft 12 can be achieved during assembly.

[0059] Furthermore, because the through-holes 42 are located at the interface 44 between the rotor assembly components and the permanent magnets, a line-of-sight path can be provided so that a relatively fast-curing UV curing process can be used to bond the permanent magnets 23 relative to the shaft 12, while a longer thermal curing process can then be used to fully cure the adhesive to secure the permanent magnets 23 to the shaft 12. It should be understood that in the final assembled rotor assembly 10, the through-holes 42 can be at least partially filled with an adhesive, such as a positioning adhesive.

[0060] exist Figure 4 The method 100 according to the above is shown in a flow chart of FIG.

[0061] Method 100 includes providing 102 a shaft, and providing 104 a rotor assembly component and a permanent magnet, at least one of the rotor assembly component and the permanent magnet including a through hole. The method includes: mounting 106 the rotor assembly component to the shaft; and positioning 108 the permanent magnet relative to the shaft such that the permanent magnet contacts the rotor assembly component at an interface, and the through hole is located at the interface.

[0062] It should be understood that the method 100 is described herein more generally with respect to rotor assembly components, and that other components (such as the first bearing assembly 16 or the impeller 14, or indeed the permanent magnets 23 themselves) may be shaped to provide through-holes, and that other components (such as the first bearing assembly 16 or the impeller 14) may be placed in contact with the permanent magnets 23 to ensure proper axial alignment.

[0063] Another benefit associated with rotor assembly 10 stems from the form of shaft 12, and in particular, first portion 24 having a first shaft diameter A that is greater than second shaft diameter B of second portion 26 and greater than third shaft diameter C of third portion 28, with second shaft diameter B being greater than third shaft diameter C.

[0064] In particular, this can effectively decouple the inner diameter of the permanent magnet 23 from the inner diameter of the first bearing assembly 16 and the second bearing assembly 18, and decouple the inner diameters of the first bearing assembly 16 and the second bearing assembly 18 from each other, thereby achieving greater flexibility compared to, for example, a shaft having a constant diameter along its length, in which the permanent magnet and the first and second bearing assemblies are required to have substantially similar inner diameters. In other words, in the rotor assembly 10, the inner diameter of the permanent magnet 23 can be specified independently of the inner diameter of the first bearing assembly 16 and the second bearing assembly 18, and the inner diameters of the bearing assemblies 16, 18 can be specified independently of each other.

[0065] While specific dimensions of the first portion 24 , the second portion 26 , and the third portion 28 of the shaft 12 have been shown in the specific examples above, alternative shaft dimensions and ratios are also contemplated.

[0066] For example, the first shaft diameter A may be approximately 1% to 20% larger than the second shaft diameter B and approximately 35% to 100% larger than the third shaft diameter C, and may be in the range of 3.0 mm to 7.0 mm. The second shaft diameter B may be approximately 10% to 75% larger than the third shaft diameter C and may be in the range of 2.5 mm to 6.5 mm. The third shaft diameter C may be in the range of 1.0 mm to 5.0 mm.

[0067] In use, the rotor assembly 10 is mated with the stator assembly 200 to form a brushless permanent magnet motor 202, such as Figure 5 The stator assembly 200 includes three coils 204 and when the three coils 204 are driven with an appropriate voltage, the stator assembly 200 generates a magnetic field that interacts with the permanent magnets 23 to rotate the rotor assembly 10 .

[0068] exist Figure 6 A vacuum cleaner 300 including a brushless permanent magnet motor 202 is schematically shown in FIG.

[0069] exist Figure 7 A hair care appliance 400 including a brushless permanent magnet motor 202 is schematically shown in FIG.

[0070] exist Figure 8 An alternative shaft 500 and a first balancing ring 502 are schematically shown in FIG. 5 , wherein the same reference numerals are used for clarity. Figure 8 The shaft 500 and Figure 1 and Figure 2 The difference of axis 12 is that Figure 8 The shaft 500 omits the first transition region 25 . Figure 8 The first gimbal 502 has a hole having a first region 504 and a second region 506 of different diameters. The first region 504 has a larger diameter than the second region 506 and defines an area in which adhesive for bonding the permanent magnets 23 to the shaft 500 can accumulate. Providing an area in which the adhesive can accumulate can facilitate bonding of the adhesive to the first gimbal 502, which can inhibit the adhesive from detaching from the first gimbal 502 when the rotor assembly rotates in use.

[0071] exist Figure 9 A further alternative shaft 600 and impeller 14 are schematically shown in FIG, wherein the same reference numerals are used for clarity. Figure 9 The shaft 600 and Figure 1 and Figure 2 The difference of axis 12 is that Figure 9 The shaft 600 has a fourth portion 602 having a sixth shaft diameter F that is smaller than the first shaft diameter A. The impeller 14 is mounted to the fourth portion 602. Figure 1 and Figure 2 This may allow for greater flexibility in the aerodynamic design of the impeller 14 compared to the embodiment of FIG.

[0072] It should be understood that Figure 1 and Figure 2 Other features of the rotor assembly 10 may be related to Figure 8 and Figure 9 Used together with the embodiments of

[0073] While specific examples and embodiments have been described thus far, it should be understood that these are illustrative only and that various modifications may be made without departing from the scope of the invention as defined by the following claims.

Claims

1. A rotor assembly for a brushless permanent magnet motor, the rotor assembly comprising: axis; a permanent magnet mounted to the shaft; and a rotor assembly component mounted to the shaft and in contact with the permanent magnet at an interface therebetween; Wherein, at least one of the rotor assembly component and the permanent magnet includes a through hole located at the interface.

2. The rotor assembly according to claim 1, wherein: At least one of the rotor assembly component and the permanent magnet includes a plurality of through-holes at the interface.

3. The rotor assembly according to claim 2, wherein: The plurality of through-holes are evenly spaced around at least one of the rotor assembly component and the permanent magnet.

4. A rotor assembly according to any one of the preceding claims, wherein: At least one of the rotor assembly component and the permanent magnet includes at least three through-holes located at the interface.

5. A rotor assembly according to any one of the preceding claims, wherein: The rotor assembly component includes the through-hole.

6. A rotor assembly according to any one of the preceding claims, wherein: The shaft includes a first portion, a second portion, and a transition region between the first portion and the second portion, the rotor assembly component being mounted to the first portion, the first portion having a first diameter, the permanent magnet being mounted to the second portion, the second portion having a second diameter smaller than the first diameter, the transition region having a third diameter smaller than the first diameter and the second diameter, and wherein the through hole overlaps the transition region.

7. A rotor assembly according to any one of the preceding claims, wherein: The rotor assembly component includes a bore having a first region having a first diameter and a second region having a second diameter smaller than the first diameter, and the first region is located at the interface.

8. A rotor assembly according to any one of the preceding claims, wherein: The rotor assembly components include one or more of a gimbal, an impeller, and a bearing assembly.

9. A rotor assembly according to any one of the preceding claims, wherein: The rotor assembly component is a balancing ring.

10. The rotor assembly according to claim 9, wherein: The rotor assembly includes a bearing assembly mounted to the shaft, and the gimbal is located between the bearing assembly and the permanent magnet.

11. The rotor assembly according to claim 10, wherein: The rotor assembly includes another bearing assembly mounted to the shaft on an opposite side of the permanent magnet from the bearing assembly.

12. The rotor assembly according to claim 11, wherein: The rotor assembly includes a further balancing ring mounted to the shaft between the further bearing assembly and the permanent magnet.

13. The rotor assembly according to claim 12, wherein: The further gimbal comprises a smaller mass than the gimbal.

14. A rotor assembly according to any one of claims 9 to 13, wherein: The rotor assembly includes an impeller mounted to the shaft, and the balance ring is located between the impeller and the permanent magnet.

15. A brushless permanent magnet electric machine comprising a rotor assembly according to any one of the preceding claims. 16 . A vacuum cleaner comprising the brushless permanent magnet motor according to claim 15 .

17. A hair care appliance comprising the brushless permanent magnet motor according to claim 15.

18. A method of manufacturing a rotor assembly for a brushless permanent magnet motor, the method comprising: Provide shaft; providing a rotor assembly component and a permanent magnet, at least one of the rotor assembly component and the permanent magnet comprising a through hole; mounting the rotor assembly components to the shaft; and The permanent magnet is positioned relative to the shaft such that the permanent magnet contacts the rotor assembly component at an interface, and the through-hole is located at the interface.

19. The method according to claim 18, wherein The method includes providing an adhesive between the permanent magnet and the shaft such that the adhesive is visible through the through-hole, and curing the adhesive using a photo-curing process to bond the permanent magnet to the shaft.

20. The method according to claim 19, wherein The method includes further curing the adhesive using a thermal curing process.

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