Rotor damper

Abstract

A motor 10, such as for use in a vacuum cleaner, comprises a rotor assembly 15 comprising a shaft 110, a motor body 30, a bearing assembly 120 configured to support rotation of the shaft about a longi

Description

BACKGROUND There is a general desire to improve motors, and in particular damping systems for motors. For example, improvements may be desired in terms of size, weight, power density, manufacturing cost, efficiency, reliability, and noise. Implementation of damping in highspeed rotating machinery is a desirable feature from a reliability and dynamics perspective. SUMMARY A first aspect of the invention provides a motor comprising a motor body, a rotor assembly comprising a shaft and an impeller, a bearing assembly, and a non-contact damper. The bearing assembly is mounted to the motor body and configured to support rotation of the shaft about a longitudinal rotational axis of the shaft. The bearing assembly is mounted to the shaft at a first position along the shaft. The non-contact damper is proximate the shaft at a second position spaced longitudinally from the first position, and configured to damp shaft vibrations having a displacement at least partially perpendicular to the longitudinal rotational axis. The impeller is mounted to the shaft at a third position, longitudinally separated from the first position and the second position and between the first position and the second position along the shaft. The non-contact damper is soft-mounted to a portion of the motor body to allow displacement of the non-contact damper at least partially perpendicular to the longitudinal rotational axis. The non-contact damper is configured to damp shaft vibrations having at least a partial perpendicular component relative to the longitudinal rotational axis of the shaft, which can be considered transverse vibrations of the shaft. Such vibrations can occur as the motor is accelerated to an operating range and can have an increased amplitude when the rotational speed of the rotor assembly passes through a critical speed, which can be considered to correspond with a resonant, or in other words modal, frequency of the rotor assembly of the motor. These vibrations result in stresses on the shaft which can result in mechanical failure of the shaft, shortening an operational lifespan of the shaft and motor. These vibrations can also result in unwanted impact of the shaft or rotor assembly with static components of the motor, risking damage to the shaft, rotor assembly and / or static components of the motor. This further reduces the operational lifespan of the motor or constituent components. The non-contact damper can reduce an overall vibrational displacement of the shaft compared with a motor provided without a damper. Reducing vibrations in the shaft can reduce stresses experienced by the shaft, and prevent or reduce mechanical failure of the shaft, which can prolong the operational lifespan of the shaft, for example. Reducing overall displacement of the shaft can prevent or reduce a risk of a portion of the rotor assembly contacting a static part of the motor, which can otherwise result in damage to the motor and a reduced operational lifespan of the motor, for example. By providing a non-contact damper at a position spaced longitudinally from the position of the bearing assembly, a bearing support stiffness of the bearing assembly can remain relatively high compared with, for example, providing the damper at the bearing assembly, such as integrating the damper into the bearing assembly. Resonant frequencies of the rotor assembly can thereby be controlled to ensure critical speeds of the motor do not fall within the operating range of the motor, for example. By soft-mounting the non-contact damper to the portion of the motor body to allow at least partial displacement perpendicular to the longitudinal rotation axis, no or less additional stiffness can be added to the motor compared with hard-mounting the non-contact damper, for example. In examples, soft-mounting the non-contact damper can be considered to minimise the stiffness of the non-contact damper. This can prevent undesirably changing the motor’s modal response, which can impact performance of the motor by, for example, shifting a critical speed of the motor into the operating range of the motor. Soft-mounting the non-contact damper can provide a further source of damping of the shaft, to enhance the damping provided by the non-contact damper. This can further reduce displacement of the shaft, for example. By soft-mounting the non-contact damper, the non-contact damper can move at least partially perpendicular to the longitudinal rotational axis. In this way, the non-contact damper can at least partially track movement of the shaft or rotor assembly away from the longitudinal rotational axis, which might occur as the rotor assembly passes through a critical speed, for example, and transverse vibrations are induced. Similarly, where such vibrations result in contact of the shaft or rotor assembly with the non-contact damper, the impact can be absorbed and lessened compared with a hard-mounted, non-contact damper. This can reduce a risk of damage to the shaft or rotor assembly and thereby improve an operational lifespan of the motor. Because the motor can more effectively damp vibrations of the rotor assembly, the motor can be more robust to accelerating through a critical speed, which can allow the motor to be routinely operated at higher running speeds compared with motors which must be run at sub-critical speeds, for example. This can improve the performance of the motor. The non-contact damper may be coupled to a mechanical damper. The mechanical damper may be separated from the shaft and configured to contribute to the damping of the shaft. The overall damping of the non-contact damper can be enhanced by the mechanical damper, such that an overall displacement of the shaft can be reduced relative to the noncontact damper without a mechanical damper, for example. This can reduce an amount of damping required by the non-contact damper alone which can allow a non-contact damper which is easier to manufacture to be used, for example. Damping of the rotor assembly can be achieved by contributions of the non-contact damper, the mechanical damper coupled to the non-contact damper, and the soft-mounting of the non-contact damper to the motor body. The mechanical damper may be separated from, or in other words not in contact with, the shaft, ensuring modal response of the motor is not, or only minimally, changed. This can ensure the operating range of the motor remains between the critical speeds of the motor, for example, and that a target operating speed is sufficiently far away from a critical speed of the motor. The mechanical damper may comprise a viscoelastic material, which can produce a damping effect over a relatively wide range of frequencies and can be manufactured straightforwardly. The mechanical damper may comprise a wire mesh damper. A wire mesh damper can be used across a relatively wide range of temperatures. In examples, the wire mesh damper may be formed from metal. Such a wire mesh damper can exhibit low mechanical hysteresis such that it provides a relatively uniform damping effect across its operational lifespan, and can be resistant to corrosion. The non-contact damper may be a hydrodynamic damper. The hydrodynamic damper may function by a squeeze-film damping effect, for example. A hydrodynamic damper can be suitable for non-magnetic constructions, for example, and can function passively without requiring a source of power, avoiding an associated risk of loss of power. The hydrodynamic damper may comprise protruding or recessed surface features. Such surface features can enhance a damping effect of the hydrodynamic damper. The shaft may, also or alternatively, comprise protruding or recessed surface features proximate the hydrodynamic damper. Such surface features on the shaft can further enhance a damping effect of the hydrodynamic damper. The non-contact damper may be a magnetic damper. The magnetic damper can provide magnetic levitation of the shaft to prevent impact of the shaft or rotor assembly with surrounding components, including the magnetic damper. In examples, the magnetic damper may allow for active damping control which can allow for damping properties of the non-contact damper to be modified as the motor speeds up or slows down during startup and shutdown, for example. This can further improve damping performance as the rotor assembly passes through critical speeds. The non-contact damper may be soft-mounted to the portion of the motor body by a viscoelastic material. In examples, the viscoelastic material is a rubber O-ring, and can be straightforwardly installed and removed. Such an O-ring with appropriate mechanical properties can be selected and the non-contact damper tuned as required. The non-contact damper may be soft-mounted to the portion of the motor body by a spring. In examples, the spring is a leaf-spring. In yet further examples, a metal mesh may be used to soft-mount the non-contact damper to the portion of the motor body. A portion of the non-contact damper may be arranged non-parallel to the shaft, such that a portion of an axial load on the shaft, and hence bearing assembly, is reduced. This can reduce a risk of damage to the bearing assembly and improve an operational lifespan of the bearing assembly, for example. The rotor assembly comprises an impeller mounted to the shaft. In that case, the impeller is mounted at a third position, longitudinally separated from the first position and the second position. The impeller may be operable, when rotated as part of the rotor assembly, to move a fluid such as air. The third position may be between the first position and the second position. That is, the impeller may be mounted between position of the bearing assembly and the position of the non-contact damper. In such a case, the non-contact damper may be positioned near an end of the shaft furthest from the bearing assembly. The end of the shaft furthest from the bearing assembly can be where greatest displacement of the shaft occurs, and so providing the non-contact damper at this position may be relatively more effective at reducing displacement of shaft compared with, for example, providing a damper at or integrating the damper with the bearing assembly. The motor may further comprise a housing in which the rotary assembly is disposed. The housing may contain a fluid, such as air, and accordingly act to constrain, or guide, flow of the fluid around or through the motor. For example, rotation of the impeller may produce movement of a fluid, such as air, surrounding the rotor assembly, which the housing of the motor can help guide. The movement of air, for example, can be used to cool a stator of the motor which can further improve the ability of the motor to operate at a higher running speed. The housing may comprise a flow guide, the shaft passing through the flow guide. The flow guide can be considered a tapered portion of the housing in which a width, perpendicular to the rotational axis of the shaft, decreases with respect to position along the rotational axis. A flow guide can smooth flow of the fluid, such as to an inlet of the impeller, to improve impeller performance and further enhance a cooling effect of air drawn over the stator, as mentioned above. The non-contact damper can mitigate changes to the rotor dynamics, such as the critical speeds or vibrational displacement of the rotor assembly, which might arise from the flow guide. The non-contact damper may be positioned in the flow guide. This can effectively utilise space within the motor by arranging both the flow guide and the non-contact damper along a same length of the shaft, which can allow for a relatively compact motor compared with providing these elements separately along the length of the shaft, for example. The portion of the motor body the non-contact damper may be soft-mounted to may be a portion of the flow guide of the housing. In this way, the non-contact damper can be provided as part of the housing and may not require, for example, modification of the rotor assembly, the motor body, or other parts of the motor. In this sense, the non-contact damper can be provided in a modular fashion. According to a second aspect, a vibrational damping element for damping a shaft of a rotor assembly of a motor is provided. The vibrational damping element comprises a noncontact damper configured to, when proximate to a shaft rotating about a longitudinal rotational axis, induce damping in shaft vibrations having a displacement at least partially perpendicular to the longitudinal rotational axis. The non-contact damper is soft-mounted to a portion of the motor body to allow, relative to the shaft, displacement of the noncontact damper at least partially perpendicular to the longitudinal rotational axis. Advantages as described for the first aspect are equally realised by the second aspect, where appropriate. Such a vibrational damping element may be provided in a modular fashion and installed into existing motors without requiring modification of the motor or constituent rotor assembly, for example. For example, the vibrational damping element may form part of a housing of the motor. Being provided in a modular fashion can allow the vibrational damping element to be straightforwardly installed, removed, modified, and / or repaired, for example. According to a further aspect of the invention, there is provided a vacuum cleaner comprising a motor according to the first aspect of the invention or a vibrational damping element according to the second aspect. Optional features of aspects of the present invention may be equally applied to other aspects of the present invention, where appropriate. BRIEF DESCRIPTION OF THE DRAWINGS Figure lisa schematic cross-sectional view of a motor. Figure 2 is a schematic cross-sectional view of the motor of Figure 1 contained within a housing. Figure 3 is a schematic cross-sectional view of the non-contact damper of Figure 1. Figure 4 is a schematic cross-sectional view of a third non-contact damper. Figure 5a and 5b illustrate schematic perspective views of further non-contact dampers. Figure 6 is a schematic cross-sectional view of a second motor. Figure 7 is a schematic cross-sectional view of a third motor. Figure 8 is a schematic illustration of a vacuum cleaner comprising the motor of Figure 1. DETAILED DESCRIPTION A motor, generally designated 10, is shown schematically in Figure 1. The motor 10 comprises a motor body 30, a stator assembly 150, a rotor assembly 15, a bearing assembly 120, and a vibrational damping element 101. The rotor assembly 15 comprises a shaft 110. The shaft 110 is generally cylindrical, having a circular cross section and a length perpendicular to the cross-section. The length defines a longitudinal rotational axis as indicated by the arrow A. As described hereafter, a length of the shaft 110 can be considered to be in a direction parallel with the longitudinal rotational axis A, and a longitudinal position can be considered to be a position with respect to the longitudinal rotational axis A. The rotor assembly 15 comprises an impeller 140 mounted to the shaft 110. In the example of Figure 1, the impeller 140 is mounted to a third position 111c at a distal end of the shaft 110, but in general the position of the impeller 140 may be mounted to alternative points of the shaft, for example as illustrated in Figure 7. The bearing assembly 120 is located at a first position Illa which is longitudinally spaced from the impeller 140. In this example, a first portion of the bearing assembly 120 is mounted to the motor body 30 and a second portion is mounted to the shaft 110. The first portion mounted to the motor body 30 is an outer race and the second portion mounted to the shaft 110 is an inner race, and ball bearings are provided between the inner race and the outer race in order to support rotation of shaft 110 and hence the rotor assembly 15 about the longitudinal rotational axis A. In other examples, other types of bearing which allow for rotation of the rotor assembly 15 about the longitudinal rotational axis A may be used, such as roller bearings or air bearings, for example. The stator assembly 150 is located at a position adjacent to the bearing assembly 120, in this example such that the bearing assembly 120 is between the stator assembly 150 and the impeller 140. In general, the stator assembly 150 is operable to produce rotational motion of the rotor assembly 150. In this example, the stator assembly 150 comprises one or more coils, or windings, which can generate a magnetic field when energised. A permanent magnet on the shaft (not shown) interacts with the magnetic field and results in rotational motion of the shaft relative to the stator assembly 150 and motor body 30. It will be appreciated that the precise configuration of the stator assembly 150 is immaterial to the present disclosure, and that the rotational motion of the rotor assembly 150 can be brought about in a variety of manners. The motor body 30 can generally be considered to act as a support for the stator assembly 150, a portion of the bearing assembly 120, and the vibrational damping element 101. In general, components attached to the motor body 30 can be considered to be static relative to the rotor assembly 15 in that said components and motor body 30 do not rotate with the rotor assembly 15. The motor body 30 may not be a monolithic structure and may comprise separate portions which each remain static relative to the rotor assembly 15. The motor 10 is operable to rotate the rotor assembly 15 about the longitudinal rotational axis A, thereby generating rotational motion of the impeller 140. Fluid contacted by the impeller 140, such as air or water, is accelerated by the rotational motion of the impeller 140. In one example, the motor 10 can be used in a vacuum cleaner, illustrated later by Figure 8. The vibrational damping element 101, in this example, is located at a second position 111b with respect to the length of the shaft 110 which is between the bearing assembly 120 at the first position Illa and the impeller 140 at the third position 111c. In other examples, such as that illustrated by Figure 6, the impeller 140 can be provided between the bearing assembly 120 and the vibrational damping element 101, such that the third position 111c is longitudinally between the first position Illa and the second position 111b. The vibrational damping element 101 comprises a non-contact damper 103 proximate the shaft 110. The non-contact damper 103 is, in this example, a hydrodynamic damper which operates on a squeeze-film air damping principal. Accordingly, in this example, the noncontact damper 103 forms a hollow cylinder disposed around the shaft and through which the shaft 110 is provided. The non-contact damper 103 comprises a surface which runs, in this example, parallel to an outer surface of the shaft, the two surfaces separated by, in this example, a one-millimetre channel. The non-contact damper 103 therefore spans circumferentially around the shaft 110, such that the surface of the non-contact damper 103 encircles the shaft 110. In other examples, however, the non-contact damper may span around only a portion of the circumference of the shaft, or may be formed of a plurality of sections which each span around a respective portion of the circumference of the shaft. The non-contact damper 103 comprises surface features 104 which, in this example, comprise a regularly-spaced array of substantially uniform protrusions, where substantially uniform means they are identically shaped within manufacturing tolerances. The shaft also comprises surface features 113 along the length of the shaft proximate the non-contact damper, or in other words at and near to the second position 111b. The shaft surface features 113 comprises a regularly-spaced array of substantially uniform recesses. The surface features 104, 113 are configured to enhance the squeeze-film air damping provided by the non-contact damper 103. Particular examples of the surface features 104, 113 are described later with reference to views in Figures 3, 5a, and 5b. The non-contact damper 103 is soft-mounted by a soft-mounting element 105 to the motor body 30. The skilled person will appreciate that “soft-mounting” refers to a mounting which has a low radial mechanical stiffness relative to the bearing assembly, for example, such that the soft-mounting element 105 is compressible or stretchable. Accordingly, in examples, the soft-mounting element 105 has a radial mechanical stiffness coefficient which is at least an order of magnitude lower than that of the bearing assembly. In the example of Figure 1, the soft-mounting element 105 is formed from a viscoelastic material, such as a rubber O-ring, but in other examples may be a spring formed from a metal, for example. The soft-mounting element 105 is disposed between the motor body 30 and the non-contact damper 103 such that the non-contact damper 103 is separated from the motor body 30 by the soft-mounting element 105. The non-contact damper 103 in this example further comprises a mechanical damper 107. In the example of Figure 1, the mechanical damper 107 is disposed between the noncontact damper 103 and the soft-mounting element 105, such that the mechanical damper 107 and soft-mounting element 105 can be considered to be positioned in series between the non-contact damper 103 and the motor body 30. In other examples, the nonmechanical damper 107 can be placed adjacent to the soft-mounting element 105, such that the mechanical damper 107 and soft-mounting element 105 can be considered to be position in parallel between the non-contact damper 103 and the motor body 30. In general, the mechanical damper 107 is coupled to the non-contact damper and positioned such that the mechanical damper 107 is separated from, or in other words not in contact with, the shaft 110. The mechanical damper 107 comprises viscoelastic material, but in other examples other mechanical dampers could be used, for example a wire mesh damper which may be formed from metal. In use, the motor 10 can accelerate the rotor assembly 15 from having zero rotational speed up to an operating speed, which is a rotational speed at which the motor is desired to be used. For example, the operating speed might be 130,000 revolutions per minute. In accelerating to the operating speed, the rotor assembly 15 will be accelerated through speeds which correspond to a resonant, or modal or natural, frequency of the rotor assembly 15. Such speeds are hereafter referred to as critical speeds. For example, a critical speed for a given rotor assembly might be 60,000 revolutions per minute. At such critical speeds, the rotor assembly, in particular the shaft, can undergo significant transverse vibrations, which are displacements away from longitudinal rotational axis A of the rotor assembly 15. The direction of transverse shaft vibrations is indicated by arrow X in Figure 1. These shaft vibrations are, in general, at least partially perpendicular to the longitudinal rotational axis A. As described herein, damping of the shaft can be understood to more generally apply to damping of the entire rotor assembly 15, and likewise displacement of the shaft 110 can be understood to more generally apply to displacement of components of the rotor assembly, such as the impeller 140. The shaft vibrations can result in increased stresses through the shaft 110, which can weaken the shaft and lead to mechanical failure of the shaft, for example through prolonged use of the motor 10. Additionally or alternatively, displacement away from the longitudinal rotational axis A associated with the shaft vibrations can result in contact of the shaft 110 or rotor assembly 15 more generally with the surrounding motor body 30, or components affixed to the motor body. This contact risks damage to the shaft 110, rotor assembly 15, motor body 30 or components attached thereto, which may render the motor 10 unusable. The non-contact damper 103 is configured as a squeeze-film air damper. A thin layer of air, contained within the channel between the shaft 110 and the non-contact damper 103, acts to damp vibration of the shaft 110, thereby providing a first source of damping of the rotor assembly 15. Accordingly, whilst the channel in this example is one millimetre, it will be appreciated that in other examples the channel for such a squeeze-film air damper may be different according to the design of the squeeze-film air damper, such as more than a tenth of a millimetre, or less than three millimetres, for example. The non-contact damper 103, in being soft-mounted to the motor body 30, can undergo displacement towards or away from the motor body 30. Accordingly, the non-contact damper 103 can undergo displacement at least partially perpendicular to the longitudinal rotational axis A. As the shaft 110 vibrates and undergoes displacement at least partially perpendicular to the longitudinal rotational axis A, the non-contact damper 30 is able to at least partially track the motion of the shaft 110. That is, if the shaft 110 undergoes a vibration which displaces the shaft 110 towards the motor body 30, the non-contact damper 103 will also undergo a displacement towards the motor body 30 in the same direction, maintaining a channel between the non-contact damper 103 and the shaft 110. This can reduce the risk of impact of the shaft 110 with the non-contact damper 103. Furthermore, should such an impact occur, the soft-mounting element 105 is able to absorb at least a portion of the impact force, reducing risk of damage resulting from impact of the shaft 110 with the non-contact damper 103. Additionally, the soft-mounting element 105 is able to provide a second source of damping of the shaft 110 and rotor assembly 15 by functioning as a mechanical damper. The mechanical damper 107 further contributes to damping of the shaft 110 and the rotor assembly 15, and in effect acts as a third source of damping of the rotor assembly 15. The mechanical damper 107 can be used to further enhance or tune the damping provided by the non-contact damper 103. For example, a reduction in the maximum displacement of shaft vibrations may be greater when the mechanical damper 107 is provided compared with the non-contact damper 103 without the mechanical damper 107, or compared to a motor with no vibration damping element 101 at all. This can be useful where the noncontact damper 103 does not produce enough damping alone to effectively damp the rotor assembly 15 and prevent collision of the rotor assembly 15 with the motor body 30, for example. The vibrational damping element 101 is positioned away from the bearing assembly 120, which means a stiffness of the bearing assembly 120 is unaffected or only minimally affected compared with, for example, integrating the vibrational damping element 101 with the bearing assembly 120. Additionally, a modal response of the motor, such as the resonant frequencies, can remain unaffected or only minimally affected. This can allow, for example, the vibrational damping element 101 to be implemented, where suitable, across different motors with known modal responses and without requiring subsequent modification of the motors. The skilled person will appreciate that the vibrational damping element 101 is equally applicable in motors with additional, or alternatively configured, bearing assemblies, such as a bearing assembly provided either side of the stator assembly 150. In Figure 2, the motor 10 is illustrated disposed in a motor housing 180. The motor housing 180 is a hollow shell which circumferentially encapsulates the motor 10, and specifically the rotor assembly 15. The motor housing 180 has a flow guide 182 through which the rotor assembly 15 passes. The flow guide 182 is located between the bearing assembly 120 and the impeller 140. In the flow guide 182, a diameter of the motor housing 180, as considered perpendicular to the longitudinal rotational axis A of the rotor assembly 15, is reduced relative to the diameter of the motor housing 180 either side of the flow guide 182. In other words, the flow guide 182 is a tapered section of the motor housing 180 in which the diameter of the motor housing 182 is reduced. The flow guide 182 may alternatively be described as a neck region of the motor housing 180. The vibrational damping element 101 in this example is positioned in the flow guide 182 of the motor housing 182. In this example, the vibrational damping element 101 is physically separate from the motor housing 182 and is attached to the motor body 30, but in other examples may be attached to the motor housing 182 by support elements, for example. In some examples, the vibrational damping element 101 is directly attached to the flow guide of the motor housing 180 and is not directly attached to the same portion of the motor body 30 as the bearing assembly 120, for example. In use, for fluid-moving motors that drive impellers, the motor housing 180 acts to contain and guide fluid which is proximate the motor 10. For example, air can be guided through the motor housing 180 due to rotation of the impeller 140, as indicated by arrows F which indicate a portion of airflow within the motor housing. This can enhance flow of the air through the motor 10, for example. Enhancing the flow of air can refer to, for example, an increased flow rate of the air, or a decreased turbulence of the air, or arranging for a specific flow pattern of the air, for example. The flow guide 182 can further enhance the flow of air, or more generally fluid, guided by the motor housing 180, by, for example, concentrating the air, achieving a higher flow speed and or reducing turbulence of the air before it contacts the impeller 140. In this way, the flow guide 182 is effectively positioned as, and can function as, an inlet guide to the impeller 140. For example, the motor housing 180 can be configured to produce a specific flow of air to cool the motor 15, enabling higher operating powers, for example. In some examples, whilst the motor housing 180 may comprise such a flow guide to produce particular air flow, for example, introduction of the flow guide may also alter the modal response of the motor 15, or in other words change the resonant frequencies of the motor 15, and / or worsen vibrations which occur at critical speeds of the motor 15. For example, introduction of a flow guide might effectively lengthen the rotor assembly 15 by requiring space to be provided between the bearing assembly 120 and the impeller 140. The spatial footprint of the motor 10 is therefore increased. In positioning the vibrational damping element 101 in the flow guide 182, enhanced shaft vibrations which might arise from introduction of such a flow guide and the corresponding changes to air flow can be mitigated whilst not requiring a further increase of length to accommodate the vibrational damping element. In other words, space introduced to accommodate the flow guide 182 of the motor housing 180 is more efficiently utilised by also introducing the vibrational damping element 101 into the same area, whilst effectively mitigating negative effects on rotor dynamics brought about by the flow guide 182. This can produce a more compact motor compared with, for example, lengthening the shaft 110 to accommodate the vibrational damping element 101 at another position of the shaft 110. Figure 4 schematically illustrates a further example of the vibrational damping element 101 in cross sectional view. In this example, the non-contact damper 103 comprises slots 105a, or grooves, on a surface facing the motor body 30. The slots are semi-circular in profile and receive the soft-mounting element 105. In this way, a portion of the soft-mounting element 105 protrudes into the non-contact damper 103, which can allow for, for example, lateral forces on the non-contact damper 103 to be more effectively absorbed by the soft-mounting element 105. Figure 3, 5a and 5b illustrate the surface features 104, 113 in further detail. Figure 3 schematically illustrates the shaft 110 comprising the surface features 113 and the non-contact damper 103 comprising the surfaces features 104 in cross-sectional view. As can be seen in Figure 3, whilst the channel between the non-contact damper 103 and the shaft 110 is approximately one millimetre on average, the surface features 104, 113 give the channel non-parallel sides and so the width of the channel varies along its length, relative to the longitudinal rotational axis. Figure 5a schematically illustrates the shaft 110 comprising the surface features 113 and the non-contact damper 103 in a perspective view. In the example of Figure 5a, the noncontact damper 103 lacks surface features, and instead comprises a relatively smooth surface. The surface features 113 comprise an array of recesses in the surface of the shaft 110. In this example, each recess is approximately hexagonal in shape, as considered in the plane of the surface of the shaft 110, and the array is approximately ordered as a hexagonal lattice. Figure 5b schematically illustrates the shaft 110 and the non-contact damper 103 comprising the surface features 104 in a perspective view. In the example of Figure 5b, the shaft 110 lacks surface features, and instead comprises a relatively smooth surface. Similarly to the example of Figure 5a, the surface features 104 comprise an array of recesses in the surface of the non-contact damper 103. Each recess is approximately hexagonal in shape, as considered in the plane of the surface of the non-contact damper 103, and the array is approximately ordered as a hexagonal lattice. The skilled person will appreciate that the non-contact damper 103 and shaft 110 may, in other examples, comprise other structural configurations and arrangements of surface features. The surface features 104, 113 may be recesses or protrusions which are circular, square, rectangular, or any other geometry, for example. The surface features 104, 113 may be organised in a non-regular configuration, such as having a higher number density at a first portion of the shaft 110 or non-contact damper 103 and a lower number density at a second portion of the shaft 110 or non-contact damper 103, where number density refers to a number of surface features 104, 113 per surface area. In some examples, positions of protrusions of a first surface may be aligned to correspond with respective positions of recesses in a second surface, wherein the first surface is one of the shaft 110 or non-contact damper 103 and the second surface is the other of the shaft 110 or non-contact damper 103. In other examples, the surface features 104, 113 may comprise grooves, ridges, or trenches, which might circumferentially span the shaft 110 or non-contact damper 103, for example. Figure 6 schematically illustrates the motor 10 comprising a second example of a vibrational damping element 201 with a corresponding second example of a shaft 210. Features of the vibrational damping element 201 can be considered to be substantially similar to vibrational damping element 101 of Figure 1, and differences will be described hereafter. In vibrational damping element 201, a non-contact damper 203 is provided. The noncontact damper 203 has a conical internal profile, such that a surface facing the shaft 210 is non-parallel to the longitudinal axis of the shaft 210. In other words, the non-contact damper 203 is angled relative to the longitudinal axis of the shaft 110. The non-contact damper surface 203 is angled slightly towards the impeller 140. The shaft 210 comprises a complementary conical shape at a portion proximate the noncontact damper 203, such that an external surface of the shaft 210 facing the non-contact damper 203 remains parallel to the surface of the non-contact damper 203 and the channel between the non-contact damper and the shaft remains is constant. The external surface of the shaft 210, proximate the non-contact damper 203, is thereby non-parallel to the longitudinal axis of the shaft 210. In this configuration, the non-contact damper 203, which is non-parallel with the longitudinal axis of the shaft 210, can also damp displacements which are parallel with the longitudinal axis of the shaft, as well as damp those which are perpendicular to the longitudinal axis of the shaft. This can allow the vibrational damping element 201 to effectively reduce an axial load, indicated by arrow B, on the shaft 110 and rotor assembly 15, and hence reduce stresses induced in the bearing assembly 120, whilst still providing damping of transverse vibrations of the shaft 110. Axial loads on the shaft 110 can result from rotation the impeller 140, for example. This can improve reliability of the components by reducing risk of damage, for example. Figure 7 schematically illustrates a second example of a motor 20 in cross-sectional view. The motor 20 comprises a rotor assembly 25 in which the impeller 140 is mounted at a position 211c which is not the distal end of the shaft 110. Instead, the vibrational damping element 201 is positioned at the distal end of the shaft 110 at a position 211b, and the impeller 140 is mounted between the vibrational damping element 201 and the bearing assembly 120, with respect to the length of the shaft 110. Performance of the vibrational damping element 201 may be enhanced by being positioned at the far end of the shaft 110, in that maximum transverse displacements of the shaft 110 and rotor assembly 25 may occur at a position furthest from the bearing assembly 120, thereby rendering the vibrational damping element 201 more effective. The configuration of motor 20, and in particular the specific positioning of the vibrational damping element 201, can be useful where there is insufficient room between the bearing assembly 120 and the impeller 140 in which to fit the vibrational damping element 101. For example, it may be desired to install the vibrational damping element 101 to an existing motor without modification of the motor components or layout, and an existing distal end of the shaft may be received by the vibrational damping element 101 in order to damp vibrations of the motor. Figure 8 schematically illustrates a vacuum cleaner 1000 comprising the motor 10. The vacuum cleaner 1000, in comprising the motor 10 equipped with the vibrational damping element 101, is able to accelerate through critical speeds of the motor 10 with reduced vibration felt by the user and reduced risk of damage to the motor components, rendering the motor 10 more robust. This can improve a lifespan of the motor 10 and hence the vacuum cleaner 1000. Being able to reliably accelerate through critical speeds of the motor 10 allows the motor to operate at supercritical speeds, which can improve suction power of the vacuum cleaner 1000, for example. The reduced vibration felt by the user can improve handling of the device, such as allowing the device to be used more accurately or precisely. It will be appreciated that other appliances comprising the motor 10 are envisaged. For example, a haircare appliance in the form of a hairdryer may comprise the motor 10. The vacuum cleaner 1000 or any other appliance may comprise the motor 10 as described in Figures 1, 2 or any other motor. The above examples are to be understood as illustrative examples. Further embodiments are envisaged. For example, the non-contact damper 103 described above is a hydrodynamic damper which functions based on a squeeze-film air damping effect. In other examples, a magnetic non-contact damper may be additionally or alternatively provided. In such examples, the shaft may be magnetically levitated by magnets of the magnetic non-contact damper, and damping achieved by eddy currents induced in the shaft. The magnetic noncontact damper can achieve similar benefits as described for the hydrodynamic non-contact damper. The vibrational damping element may be provided as a modular component in that it is not integrated with the rest of the motor. Instead, for example, it may be installed onto existing motors at an unoccupied portion of the shaft of the motor, that is, a portion of the shaft with sufficient surrounding space for the vibrational damping element to be installed. In some examples, the vibrational damping element may be integrated into a motor 12 09 25 housing, for example at the flow guide of the housing, again allowing an existing motor to have the vibrational damping element installed without necessarily requiring modification of the motor itself. It will be appreciated that as the motor housing is static relative to the rotor assembly, in being attached to the motor housing the vibrational damping element is 5 static relative to the rotor assembly, and as such the motor housing can be considered to form a portion of the motor body, even if structurally separate from the stator assembly or bearing assembly, for example. The motor described above comprised a single bearing assembly. In other examples, one 10 or more bearing assemblies may be provided at different positions along the shaft. The motor described above comprises an impeller. In other examples, the motor may alternatively or additionally comprise other components such a propellor, a wheel, or a gear. The person skilled in the art will appreciate the damping provided by the vibrational 15 damping element applies irrespective of the particular components attached to the rotor assembly. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in 20 combination with one or more features of any other of the embodiments, or any combination of any other embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

1. A motor comprising:a rotor assembly comprising a shaft and an impeller mounted to the shaft,a motor body,a bearing assembly mounted to the motor body and configured to support rotation of the shaft about a longitudinal rotational axis of the shaft, the bearing assembly mounted to the shaft at a first position along the shaft; anda non-contact damper proximate the shaft at a second position spaced longitudinally from the first position and configured to damp shaft vibrations having a displacement at least partially perpendicular to the longitudinal rotational axis, whereinthe impeller mounted is to the shaft at a third position, longitudinally separated from the first position and the second position and between the first position and the second position along the shaft, andthe non-contact damper is soft-mounted to a portion of the motor body to allow displacement of the non-contact damper at least partially perpendicular to the longitudinal rotational axis.

2. The motor of claim 1, wherein the non-contact damper is coupled to a mechanical damper, the mechanical damper separated from the shaft and configured to contribute to the damping of the shaft.

3. The motor of claim 2, wherein the mechanical damper comprises a viscoelastic material.

4. The motor of claim 2 or 3, wherein the mechanical damper comprises a wire mesh damper.

5. The motor of any previous claim, wherein the non-contact damper is a hydrodynamic damper.

6. The motor of claim 5, wherein the hydrodynamic damper comprises protruding or recessed surface features.

7. The motor of claim 5 or claim 6, wherein the shaft comprises protruding orrecessed surface features proximate the hydrodynamic damper.

8. The motor of any of claim 1 to 4, wherein the non-contact damper is a magnetic damper.

9. The motor of any previous claim, wherein the non-contact damper is soft-mounted to the portion of the motor body by a viscoelastic material.

10. The motor of any of claim 1 to 8, wherein the non-contact damper is soft-mounted to the portion of the motor body by a spring.

11. The motor of any previous claim, wherein at least a portion of the non-contact damper is arranged non-parallel to the shaft and configured to reduce an axial load on the shaft.

12. The motor of any previous claim, further comprising a housing in which the rotary assembly is disposed.

13. The motor of claim 12, wherein the housing comprises a flow guide, the shaft passing through the flow guide.

14. The motor of claim 13, wherein the non-contact damper is positioned in the flow guide.

15. The motor of claim 14, wherein the portion of the motor body the non-contact damper is soft-mounted to is a portion of the flow guide of the housing.

16. A vacuum cleaner comprising the motor of any previous claim.2 09 25

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