Rotor assembly

Abstract

A rotor assembly for a brushless permanent magnet motor includes a shaft including a first portion having a first diameter, a second portion having a second diameter, and a third portion having a third diameter. The rotor assembly includes a first bearing assembly mounted to a first portion of the shaft, a permanent magnet mounted to a second portion of the shaft, and a second bearing assembly mounted to a third portion of the shaft. The second portion is intermediate the first portion and the third portion, the second diameter is smaller than the first diameter, and the third diameter is smaller than the first diameter and the second diameter.

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, a rotor assembly for a brushless permanent magnet motor is provided, the rotor assembly comprising: a shaft comprising a first portion having a first diameter, a second portion having a second diameter, and a third portion having a third diameter; a first bearing assembly mounted to the first portion of the shaft; a permanent magnet mounted to the second portion of the shaft; and a second bearing assembly mounted to the third portion of the shaft; wherein the second portion is located between the first portion and the third portion, the second diameter is smaller than the first diameter, and the third diameter is smaller than the first diameter and the second diameter.

[0004] The rotor assembly according to the first aspect of the present invention can effectively decouple the inner diameter of the permanent magnet from the inner diameters of the first and second bearing assemblies, and decouple the inner diameters of the first and second bearing assemblies from each other, thereby achieving greater flexibility compared to, for example, a shaft having a constant diameter along its length, which would require the permanent magnet and the first and second bearing assemblies to have substantially similar inner diameters. In other words, in the rotor assembly of the present invention, the inner diameter of the permanent magnet can be specified independently of the inner diameters of the first and second bearing assemblies, and the inner diameters of the bearing assemblies can be specified independently of each other.

[0005] For example, it may be desirable to provide a relatively large bearing assembly at one end of the shaft to provide appropriate loading of the rotor assembly. However, if the inner diameter of the permanent magnets needs to be the same as the inner diameter of such a relatively large bearing assembly, the packaging volume of the permanent magnets may need to be increased radially or axially to achieve the same volume of magnetic material compared to using a shaft with a smaller diameter portion on which the permanent magnets are mounted, as in the case of the present invention. Therefore, the rotor assembly of the present invention can allow the packaging volume of the permanent magnets to be reduced while still providing the same volume of magnetic material.

[0006] The use of such a relatively large first bearing assembly, such as the first bearing assembly of the rotor assembly, can enable the use of a relatively small second bearing assembly, such as the second bearing assembly of the rotor assembly. If a shaft having two diameters is used, one for accommodating the relatively large bearing assembly and one for accommodating the relatively small bearing assembly, the permanent magnet will need to include an inner diameter corresponding to either of these diameters. This can impose constraints on the diameter of the bearing assembly in order to accommodate sufficient magnetic material for the permanent magnet in the manner previously described. The rotor assembly of the first aspect of the present invention can alleviate these factors.

[0007] Furthermore, the rotor assembly according to the first aspect of the invention may provide improved rotor dynamics, such as the frequency response of the rotor assembly, compared to, for example, a similar rotor assembly having a shaft of constant diameter. For example, it may be desirable for a critical operating mode of the rotor assembly to occur outside the speed range over which the brushless permanent magnet motor comprising the rotor assembly is intended to operate in normal use. The frequency response of the rotor assembly may depend on the stiffness of the shaft. Therefore, for a constant diameter shaft, the options for modifying the stiffness of the shaft to change the frequency response may be limited. It has previously been proposed to use special shaft materials, such as ceramic materials, as a means of changing the frequency response to shift the critical operating mode outside the speed range over which the brushless permanent magnet motor comprising the rotor assembly is intended to operate in normal use. However, such special materials may be expensive and difficult to manufacture and / or machine to the desired dimensions.

[0008] By providing a shaft having portions of different diameters, the rotor assembly of the present invention can be used to provide a stiffness variation sufficient to shift the critical operating mode outside the speed range in which the brushless permanent magnet motor including the rotor assembly is intended to operate in normal use, without resorting to exotic materials. This can reduce the cost and / or complexity of the rotor assembly's manufacturing process while also ensuring adequate frequency response.

[0009] The rotor assembly of the first aspect of the present invention can also enable the use of relatively inexpensive manufacturing methods to form the shaft. For example, it may be desirable to provide a surface roughness to the shaft to facilitate mounting the first and second bearing assemblies and the permanent magnets thereon. It has been found that a shaft having three sections with different diameters is particularly well-suited for centerless precision grinding processes, for example, where the first and third sections are precision ground simultaneously, while a different surface roughness is applied to the second section.

[0010] The second portion may include a surface roughness different from at least one (e.g., both) of the first and third portions. At least one of the first and third portions may include a surface roughness in the range of 0.1 Ra to 0.3 Ra. The second portion may include a surface roughness in the range of 0.3 Ra to 0.5 Ra.

[0011] The shaft may comprise a relative magnetic permeability in the range of 20 to 100, for example about 20. The shaft may comprise a ferromagnetic material, for example steel. The shaft may comprise stainless steel.

[0012] The first portion may include a first end of the shaft.The third portion may include a second end of the shaft opposite the first end of the shaft.

[0013] The first diameter may be in the range of 1% to 20% greater than the second diameter, for example approximately 11% greater than the second diameter.

[0014] The first diameter may be in the range of 35% to 100% greater than the third diameter, for example approximately 66% greater than the third diameter.

[0015] The second diameter may be in the range of 10% to 75% greater than the third diameter, for example approximately 50% greater than the third diameter.

[0016] The first diameter may be in the range of 3.0 mm to 7.0 mm, for example, approximately 5.0 mm. The second diameter may be in the range of 2.5 mm to 6.5 mm, for example, approximately 4.5 mm. The third diameter may be in the range of 1.0 mm to 5.0 mm, for example, approximately 3.0 mm.

[0017] The length of the first portion can be at least one different from the length of the second portion and the length of the third portion. Varying the length of the portion in this manner can increase flexibility in customizing the rotor dynamics in the manner previously described, for example, compared to a shaft of constant diameter and / or compared to a shaft having portions of varying diameters but the same length. The length of the first portion can be at least one greater than the length of the second portion and the length of the third portion. This can facilitate mounting more components on the first portion of the shaft, for example, at one end of the shaft compared to a second, opposite end.

[0018] The length of the first section can be in the range of 10% to 75% greater than the length of the second section. The length of the first section can be in the range of 25% to 200% greater than the length of the third section. Varying the length of the sections in this manner can provide increased flexibility in tailoring the rotor dynamics in the manner previously described, for example, compared to a shaft of constant diameter and / or compared to a shaft with sections of different diameters but the same length. The length of the second section can be greater than the length of the third section. For a given shaft length and a given first section length, this can maximize the amount of shaft to which the permanent magnets can be mounted.

[0019] The length of the second portion may be in the range of 10% to 75% greater than the length of the third portion.

[0020] The shaft may comprise an overall length in the range of 25 mm to 75 mm, for example, approximately 50 mm. The first portion may comprise a length in the range of 15 mm to 35 mm, for example, in the range of 25 mm. The second portion may comprise a length in the range of 10 mm to 20 mm, for example, in the range of 15 mm. The third portion may comprise a length in the range of 5 mm to 15 mm, for example, in the range of 10 mm.

[0021] The permanent magnet may comprise a length at least as long as a length of the second portion.The permanent magnet may comprise a length in the range of 10 mm to 22 mm, for example in the range of 8 mm.

[0022] The distance between the first bearing assembly and the second bearing assembly, for example a step between the center points of the first bearing assembly and the second bearing assembly, may be in the range of 15 mm to 45 mm, for example in the range of 30 mm.

[0023] The shaft may include a transition region between the first portion and the second portion, the transition region including a fourth diameter that is smaller than the first diameter and the second diameter. Such a transition region may facilitate manufacture of the rotor assembly, for example by providing a passageway that provides easy access between the permanent magnets and the second portion of the shaft during assembly, such that adhesive may be injected into the passageway.

[0024] One or more of the first, second and third portions may include a tapered end portion. This may facilitate passing components over the relevant portion of the shaft during assembly.

[0025] The rotor assembly may include an impeller mounted to the first portion, the impeller being mounted further away from the second portion than the first bearing assembly. Mounting the impeller to the first portion of the shaft, for example at the end of the first portion of the shaft having the largest diameter, may enable a relatively large bearing to be positioned proximate the impeller, which may provide improved rotor dynamics compared to a smaller bearing assembly positioned proximate the impeller.

[0026] The shaft may include a fourth portion having a fourth diameter that is smaller than the first diameter, the first portion being intermediate the fourth portion and the second portion, and the rotor assembly may include an impeller mounted to the fourth portion. This may allow for greater flexibility in the aerodynamic design of the impeller, compared to, for example, an embodiment in which the impeller and the first bearing assembly are mounted to a portion of the shaft having a constant diameter. For example, mounting the impeller to a shaft portion having a smaller diameter than the shaft portion to which the first bearing assembly is mounted may allow for a smaller impeller hub diameter at the impeller inlet. This may result in a greater variation in the average radius from the impeller inlet to the impeller outlet, which may result in a greater pressure rise.

[0027] Mounting the impeller on a shaft portion having a smaller diameter than the shaft portion on which the first bearing assembly is mounted may also reduce the mass of the shaft in the region of the impeller, which may result in improved rotor dynamics, for example due to the lower mass of the cantilever on the unsupported portion of the shaft.

[0028] The first bearing assembly can be larger than the second bearing assembly. For example, the first bearing assembly can include at least one of: a larger outer diameter than the second bearing assembly, a larger inner diameter of the bearing assembly, and, if the first bearing assembly and the second bearing assembly include ball bearings, a larger ball size than the second bearing assembly.

[0029] The impeller may be mounted directly to the shaft, for example press-fitted to the shaft.

[0030] The first bearing assembly and / or the second bearing assembly can be mounted directly to the shaft. For example, at least one of the first bearing assembly and the second bearing assembly can be press-fitted to the respective first and third portions of the shaft. This can provide improved rotor dynamics compared to, for example, a rotor assembly in which the bearing assembly is indirectly mounted to the shaft with one or more intermediate components therebetween.

[0031] The permanent magnets may be mounted to the shaft via an adhesive. This may reduce the risk of compromising the structural integrity of the permanent magnets compared to, for example, a rotor assembly where the magnets are press-fit onto the shaft.

[0032] The permanent magnet may comprise an outer diameter substantially corresponding to the outer diameter of the second bearing assembly.This may facilitate insertion of the rotor assembly into an associated housing of the brushless permanent magnet electric machine.

[0033] The permanent magnet may include a two-pole permanent magnet.

[0034] The rotor assembly can include at least one balancing ring, such as a balancing ring mounted to the first portion between the first bearing assembly and the permanent magnets, and / or a balancing ring mounted to the third portion between the second bearing assembly and the permanent magnets. For example, such balancing rings can achieve improved rotor dynamics compared to a rotor assembly without such balancing rings.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] According to a fifth aspect of the present invention, a shaft of a rotor assembly for a brushless permanent magnet motor is provided, the shaft comprising a first portion having a first diameter, a second portion having a second diameter different from the first diameter, and a third portion having a third diameter different from the first diameter and the second diameter, wherein the second portion is located between the first portion and the third portion, the second diameter is smaller than the first diameter, and the third diameter is smaller than the first diameter and the second diameter.

[0040] 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

[0041] Figure 1 is a schematic cross-sectional view of a rotor assembly;

[0042] Figure 2 yes Figure 1 a schematic cross-sectional view of a shaft of a rotor assembly;

[0043] Figure 3 yes Figure 1 A schematic perspective view of a first balancing ring of a rotor assembly;

[0044] Figure 4 It shows Figure 1 A flowchart of the steps for assembling a rotor assembly;

[0045] Figure 5 is included Figure 1 Schematic diagram of a brushless permanent magnet motor having a rotor assembly;

[0046] Figure 6 is included Figure 5 Schematic diagram of a vacuum cleaner with a brushless permanent magnet motor;

[0047] Figure 7 is included Figure 1 Schematic diagram of a hair care appliance with a brushless permanent magnet motor;

[0048] Figure 8 is used for Figure 1 Schematic diagram of an alternative shaft and balance ring of a rotor assembly;

[0049] Figure 9 is used for Figure 1 Schematic diagram of an alternative shaft and impeller of a rotor assembly. DETAILED DESCRIPTION

[0050] Figure 1The 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.

[0051] 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 intermediate 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.

[0052] The first portion 24 has a first shaft diameter A within a range of 5.0 mm and a length within a range of 25 mm. The first shaft diameter A defines the maximum diameter of the shaft 12. The ends of the first portion 24 taper slightly inward from the first shaft diameter A. The second portion 26 has a second shaft diameter B within a range of 4.5 mm and a length within a range of 15 mm. The end of the second portion 26 closest to the third portion 28 tapers slightly inward from the second shaft diameter B. The third portion 28 has a third shaft diameter C within a range of 3.0 mm and a length within a range of 10 mm. The end of the third portion 28 distal from the second portion 26 tapers slightly inward from the third shaft diameter C. The first transition region 25 has a fourth shaft diameter D, which is smaller than the first and second shaft diameters A and B, but larger than the third shaft diameter C. The second transition region 27 has a fifth shaft diameter E, which is smaller than the third shaft diameter C.

[0053] 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.

[0054] 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. Second portion 26 has a length approximately 50% greater than the length of third portion 28.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 step between the first and second bearing assemblies 16, 18 is approximately 30 mm.

[0060] The first balance ring 20 is Figure 3 1 . The first gimbal 20 has a base 36 and an upright wall 38. The base 36 is generally annular and solid, having a central bore 40. The central bore 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 bore 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 castellated 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.

[0061] The second gimbal 22 is generally 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 located closer to the second end 32 of the shaft 12 than the second gimbal 22. The second gimbal 22 has a lower mass than the first gimbal 20.

[0062] 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.

[0063] 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.

[0064] 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, such adhesive may be largely hidden 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 it.

[0065] Therefore, it may be necessary to use an alternative process for curing the adhesive, such as a thermal curing process. However, the thermal curing process may take significantly longer than the UV curing process. This may result in a window period during which the permanent magnets 23 are not firmly held in place relative to the shaft 12, and during this window period, 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.

[0066] 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.

[0067] 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.

[0068] exist Figure 4 The method 100 according to the above is shown in a flow chart of FIG.

[0069] Method 100 includes providing a shaft 102, and providing a rotor assembly component and a permanent magnet 104, at least one of which includes a through hole. The method includes mounting the rotor assembly component to the shaft 106; and positioning the permanent magnet relative to the shaft 108 such that the permanent magnet contacts the rotor assembly component at an interface and the through hole is located at the interface.

[0070] It will be appreciated 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.

[0071] 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.

[0072] In particular, this can effectively decouple the inner diameter of the permanent magnet 23 from the inner diameters of the first and second bearing assemblies 16, 18, and decouple the inner diameters of the first and second bearing assemblies 16, 18 from each other, thereby achieving greater flexibility compared to, for example, a shaft having a constant diameter along its length, which would require the permanent magnet and the first and second bearing assemblies 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 diameters of the first and second bearing assemblies 16, 18, and the inner diameters of the bearing assemblies 16, 18 can be specified independently of each other.

[0073] 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.

[0074] For example, the first shaft diameter A can be in the range of 1% to 20% larger than the second shaft diameter B, can be in the range of 35% to 100% larger than the third shaft diameter C, and can be in the range of 3.0 mm to 7.0 mm. The second shaft diameter B can be in the range of 10% to 75% larger than the third shaft diameter C, and can be in the range of 2.5 mm to 6.5 mm. The third shaft diameter C can be in the range of 1.0 mm to 5.0 mm.

[0075] In use, the rotor assembly 10 is mated with the stator assembly 200 to form a brushless permanent magnet motor 202, such as Figure 6 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 .

[0076] exist Figure 6 A vacuum cleaner 300 including a brushless permanent magnet motor 202 is schematically shown in FIG.

[0077] exist Figure 7 A hair care appliance 400 comprising a brushless permanent magnet motor 202 is schematically shown in FIG.

[0078] 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.

[0079] exist Figure 9 Another 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 9The 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.

[0080] 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

Claims

1. A rotor assembly for a brushless permanent magnet motor, the rotor assembly comprising: a shaft comprising a first portion having a first diameter, a second portion having a second diameter, and a third portion having a third diameter; a first bearing assembly mounted to the first portion of the shaft; a permanent magnet mounted to the second portion of the shaft; and a second bearing assembly mounted to the third portion of the shaft; The second portion is located between the first portion and the third portion, the second diameter is smaller than the first diameter, and the third diameter is smaller than the first diameter and the second diameter.

2. The rotor assembly according to claim 1, wherein: The first diameter is in a range of 1% to 20% greater than the second diameter.

3. The rotor assembly according to claim 1 or 2, wherein: The first diameter is in a range of 35% to 100% greater than the third diameter.

4. A rotor assembly according to any one of the preceding claims, wherein: The second diameter is in a range of 10% to 75% greater than the third diameter.

5. A rotor assembly according to any one of the preceding claims, wherein: The length of the first portion is at least one of different from the length of the second portion and different from the length of the third portion.

6. A rotor assembly according to any one of the preceding claims, wherein: The length of the first portion is at least one of greater than the length of the second portion and greater than the length of the third portion.

7. A rotor assembly according to any one of the preceding claims, wherein: The length of the first portion is in a range of 10% to 75% greater than the length of the second portion.

8. A rotor assembly according to any one of the preceding claims, wherein: The length of the first portion is in a range of 25% to 200% greater than the length of the third portion.

9. A rotor assembly according to any one of the preceding claims, wherein: The length of the second portion is different from the length of the third portion.

10. A rotor assembly according to any one of the preceding claims, wherein: The length of the second portion is greater than the length of the third portion.

11. A rotor assembly according to any one of the preceding claims, wherein: The length of the second portion is in a range of 10% to 75% greater than the length of the third portion.

12. A rotor assembly according to any one of the preceding claims, wherein: The shaft includes a transition region intermediate the first portion and the second portion, the transition region including a fourth diameter that is smaller than the first diameter and the second diameter.

13. A rotor assembly according to any one of the preceding claims, wherein: One or more of the first portion, the second portion, and the third portion include a tapered end.

14. A rotor assembly according to any one of the preceding claims, wherein: The rotor assembly includes an impeller mounted to the first portion, the impeller being mounted further from the second portion than the first bearing assembly.

15. The rotor assembly according to any one of claims 1 to 13, wherein: The shaft includes a fourth portion having a fourth diameter smaller than the first diameter, the first portion is located intermediate the fourth portion and the second portion, and the rotor assembly includes an impeller mounted to the fourth portion.

16. A rotor assembly according to any one of the preceding claims, wherein: At least one of the first bearing assembly and the second bearing assembly is press-fitted to the respective first and third portions of the shaft.

17. A rotor assembly according to any one of the preceding claims, wherein: The first bearing assembly is larger than the second bearing assembly.

18. A rotor assembly according to any one of the preceding claims, wherein: The permanent magnet includes an outer diameter substantially corresponding to an outer diameter of the second bearing assembly.

19. A brushless permanent magnet electric machine comprising a rotor assembly according to any one of the preceding claims.

20. A vacuum cleaner comprising the brushless permanent magnet motor according to claim 19.

21. A hair care appliance comprising the brushless permanent magnet motor according to claim 19.

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