A compressor assembly

Abstract

A compressor assembly 14a for providing suction in a vacuum cleaner. The compressor assembly comprises an impeller 15 for generating an airflow 26, and a diffuser 21 downstream of the impeller. The di

Description

BACKGROUND Some appliances include compressors to generate a flow of fluid (e.g. air). One example is 5 a vacuum cleaner, which typically includes a compressor to create suction, allowing dust and debris to be drawn from a surface into the vacuum cleaner. Other examples of appliances that can include a compressor are fans (such as floor fans) and hair care appliances such as hair dryers (in which the compressor may generate a flow of air that can be heated to style a user’s hair). 10 SUMMARY In a first aspect there is disclosed a compressor assembly for providing suction in a vacuum cleaner, the compressor assembly comprising: an impeller for generating an airflow; a motor for driving rotation of the impeller; a diffuser downstream of the impeller, the diffuser comprising an airflow duct at least partly defining an airflow passage for 15 receipt of an airflow generated by the impeller, the airflow passage being annular so as to surround an internal core; and a noise-reduction cavity fluidly interconnecting first and second regions of the airflow passage located on opposite sides of the internal core (e.g. diametrically opposite sides of the internal core). The impeller is located between the noise-reduction cavity and the motor. 20 Providing a noise-reduction cavity interconnecting first and second regions of an airflow passage can aid in reducing the amount of noise emitted by the vacuum cleaner. In some compressor assemblies a high amplitude acoustic tone can be generated at the rotational frequency of the impeller (e.g. a rotational frequency of a motor of the compressor assembly). In some cases this tone can be caused by mechanical unbalance of 25 the rotational parts of the compressor assembly causing vibrations that result in acoustic radiation through the structure of the compressor assembly. However, in other arrangements this high amplitude acoustic tone has alternatively or additionally been found to be in the form of airborne noise In such arrangements, airborne noise (instead of the above-described structural noise) is 30 generated at a frequency that matches the rotational speed of the impeller. This airborne 09 02 26 noise can propagate from the compressor assembly (and indeed, a vacuum cleaner of which the compressor assembly may form part of) via an airflow path and through an outlet of the compressor assembly (or vacuum cleaner). As a result, such noise can be audible to a user of a vacuum cleaner including the compressor assembly. 5 Without being bound to any particular theory, it appears that such airborne noise is generated as a result of the formation of a pair of positive and negative pressure regions (or high and low pressure regions) on diametrically opposite sides of the impeller (effectively creating a dipole acoustic response). These positive and negative pressure regions rotate with the impeller. 10 One solution to addressing such noise may be to provide a diffuser with an airflow passage that is sufficiently long so as to allow the pressure regions to cancel. However, this can significantly increase the size of the compressor assembly, which can impact the overall size of the vacuum cleaner in which the compressor assembly may be installed. Instead, by providing a cavity that interconnects first and second regions on opposite sides 15 of the passage, the positive and negative pressure regions are able to mix with one another. This effectively allows the positive and negative pressure regions to at least partly cancel one another out before they are able to propagate from the compressor assembly. This can provide a reduction in noise without needing to significantly increase the size of the compressor assembly (and in some cases not requiring any increase of the compressor 20 assembly size). Reducing such noise increases the comfort for a user using an appliance including the compressor assembly. Similarly, by reducing the noise that is propagated from the compressor assembly a faster or more powerful motor may be used for a given level of noise, which can provide increase performance without detriment to user experience. 25 Optional features of the first aspect will now be set out. These are applicable singly or in any combination with any aspect. The noise-reduction cavity may form part of (e.g. may be at least partly defined within) the diffuser. 09 02 26 The noise-reduction cavity may be located within the internal core surrounded by the airflow passage. The noise-reduction cavity may be located partly within the internal core or fully within the internal core. Thus, the annular airflow passage may surround the internal core (e.g. circumferentially surround the internal core). 5 By utilising space within the internal core, the inclusion of the noise-reduction cavity may have minimal impact on the overall size of the compressor assembly. That is, in such an arrangement the noise-reduction cavity may utilise space that would otherwise be unutilised. Accordingly, such an arrangement may aid in providing a compact compressor assembly. 10 The noise-reduction cavity may be external to the internal core surrounded by the airflow passage. The noise-reduction cavity may be fully external to the internal core or partly external to the internal core. The noise-reduction cavity may be axially offset from the internal core. The noise-reduction cavity may be provided at an axial end of the compressor assembly. In such arrangements (i.e. with an external noise-reduction cavity) 15 the noise-reduction cavity may not be surrounded by the annular airflow passage. Providing the noise-reduction cavity external to the internal core may aid in assembly of the compressor assembly, especially in circumstances where the noise-reduction cavity is to be retrofitted to an existing design. That is such an arrangement may allow improved access for such installation (compared to installation, for example, within the internal 20 core). The internal core may have a substantially circular cross-sectional shape (i.e. taken in a plane perpendicular to a rotational axis of the impeller). The internal core may be substantially cylindrical. The internal core may have a width (e.g. diameter) of between 5 mm and 150 mm, or e.g. 25 between 10 mm and 100 mm, or e.g. between 15 mm and 85 mm. The first and second regions may be spaced by a distance of between 5 mm and 150 mm, or e.g. between 10 mm and 100 mm, or e.g. between 15 mm and 85 mm. The internal core may have a height (e.g. taken in a direction parallel to a rotational axis of the impeller) of less than 20 mm, or e.g. less than 15 mm. 09 02 26 The airflow passage may be substantially fully defined by the diffuser. In other embodiments, part of the airflow passage may e.g. be upstream of the diffuser. For example, part of the airflow passage may extend between the impeller and the diffuser. The airflow passage may comprise an annular inlet. The airflow passage may comprise an 5 annular outlet. The airflow passage may comprise an inlet oriented for receipt of airflow in an axial direction. The airflow passage may comprise an inlet oriented for receipt of airflow in a radial direction (e.g. may face radially inwardly). The airflow passage may comprise an axial portion extending parallel to a rotational axis of the impeller. The first and second interconnected regions (e.g. diametrically opposing 10 regions) of the airflow passage may form part of the axial portion of the airflow passage. In other words, the annular airflow passage may open to the noise-reduction cavity at locations along the axial portion of the airflow passage. The airflow passage may comprise a radial portion extending radially with respect to a rotational axis of the impeller. The radial portion may be for flow of air in a radially 15 outward direction. The radial portion may be immediately downstream of the impeller (i.e. may be adjacent the impeller). The radial portion may be at an upstream end of the diffuser. The first and second interconnected regions of the airflow passage may form part of the radial portion of the airflow passage. In other words, the airflow passage may open to the noise-reduction cavity at the radial portion of the airflow passage. 20 The term “radial” as used herein (unless otherwise specified) refers to a direction that is substantially perpendicular to a central axis of the annular airflow passage (e.g. substantially perpendicular to a rotational axis of the impeller). Likewise, the term “axial” as used herein (unless otherwise specified) refers to a direction that is substantially parallel to a central axis of the annular airflow passage (e.g. substantially parallel to a rotational 25 axis of the impeller). In some embodiments, the first and second interconnected regions may be located at a portion of the airflow passage that is upstream of the diffuser (e.g. between the impeller and the diffuser). That is, the noise-reduction cavity may open to airflow passage at locations that are upstream of the diffuser (e.g. between the impeller and the diffuser). 09 02 26 The first and second interconnected regions may be arranged for receipt only of air that has passed through the impeller (i.e. may not be arranged for receipt of air upstream of the impeller). The noise-reduction cavity may be fully open between the first and second regions of the 5 airflow passage. That is, a linear reference line extending between the first and second regions may be uninterrupted (e.g. by a structure of the compressor assembly). In other embodiments, the noise-reduction cavity may not be fully open between the first and second regions of the airflow passage. For example, a structure of the compressor assembly may be positioned between the first and second regions (e.g. a linear reference 10 line extending between the first and second regions may be interrupted by a structure of the impeller). The noise-reduction cavity may have a substantially annular cross-sectional shape (taken perpendicular to a rotational axis of the impeller). The cavity may have a substantially cylindrical or tubular shape. 15 The duct may comprise an annular inlet. The duct may comprise an annular outlet. An inlet of the duct may be oriented to receive an airflow flowing in an axial direction (i.e. may face in a direction along a rotational axis of the impeller). An inlet of the duct may be oriented to receive an airflow flowing in a radial direction (e.g. may face radially inward). The duct may comprise first and second spaced apart walls defining the airflow passage 20 therebetween. One or both of the first and second walls may comprise a tubular portion. In any axial portions of the duct (i.e. defining axial portions of the airflow passage) the first and second walls may be spaced radially from one another. In any radial portions of the duct (i.e. defining radial portions of the airflow passage), the first and second walls may be spaced axially from one another. 25 The first wall of the duct may separate the noise-reduction cavity from the airflow passage. For example, a first side of the first wall may at least partly define the airflow passage and a second opposite side of the first wall may at least partly define the noise-reduction cavity. The first wall may be an inner wall (e.g. radially inward wall) of the airflow duct and the 09 02 26 second wall may be an outer wall (e.g. radially outward wall) of the airflow duct (e.g. at least in an axial portion of the airflow passage / duct). The noise-reduction cavity may be fluidly connected to the airflow passage by one or more openings formed in the duct. The one or more openings may be formed in the first wall of 5 the duct (i.e. the one or more openings may be formed in the first and second regions of the airflow passage). Each opening may be in the form of an aperture such as e.g. a slot or hole. The one or more openings may comprise an annular opening that may extend (e.g. circumferentially) around the internal core. The one or more openings may comprise a plurality of openings 10 (e.g. an array or row of openings) that are circumferentially spaced from one another around the internal core (e.g. so as to extend circumferentially around the internal core). The annular opening or the plurality of openings may extend substantially fully (circumferentially) around the internal core. By providing an opening (or a plurality of openings) that extend around the internal core, 15 as the positive and negative pressure regions rotate around the annular airflow passage they continue to be interconnected by the noise-reduction cavity (and thus can continue to mix and cancel one another out). Thus, such an arrangement can further reduce airborne noise propagating from the compressor assembly. Each of the one or more openings may have a width taken in a direction along the airflow 20 passage (e.g. in a radial direction for a radial portion of the airflow passage or in an axial direction for an axial portion of the airflow passage). The width of at least one opening (e.g. each opening) may be smaller than a distance between first and second walls (i.e. across the airflow passage) taken at the location of the at least one opening. This may minimise disruption to air flowing along the airflow 25 passage. The width of the at least one opening may be, for example, between 0.5 mm and 5 mm, or e.g. between 1 mm and 3 mm. 09 02 26 In some embodiments a porous media may define or extend across the opening (e.g. a filter media, such as PTFE filter media). The impeller may include a hub from which blades may extend (e.g. generally radially). The impeller may be a mixed flow impeller. The impeller may be an axial flow impeller. 5 The impeller may be a radial flow impeller. Thus, the impeller may be configured to receive a substantially axial airflow (i.e. substantially parallel to a rotational axis of the impeller) and may be configured to discharge the airflow in a non-axial direction (e.g. at an angle to the rotational axis, such as substantially perpendicular to the rotational axis). The impeller may be configured to 10 discharge air in a substantially radial direction. The compressor assembly may comprise a shroud. The shroud may substantially circumferentially surround the impeller. The shroud may be configured to guide air moved by the impeller to the airflow passage of the diffuser. The shroud may have a frustoconical shape. 15 The shroud may at least partly define an annular outlet, e.g. for radial discharge of air into the diffuser. The shroud may at least partly define an axial outlet e.g. for axial discharge of air into the diffuser. The compressor assembly may be suitable for providing suction within a vacuum cleaner (i.e. allowing the vacuum cleaner to draw dust and debris from a surface). The compressor 20 assembly may be configured to operate at a speed of at least 50,000 rpm (i.e. the motor may be configured to rotate the impeller at such a rotational speed). The impeller and / or the motor may be positioned within the internal core. The impeller may be positioned at least partly within a part of an axial portion of the airflow passage. That is, the axial portion of the airflow passage may surround the impeller. Thus, the 25 airflow passage may extend from the impeller and then in a direction towards the impeller (e.g. towards the motor of the compressor assembly). 09 02 26 In other embodiments the airflow passage may extend from the impeller and away (e.g. axially away) from the impeller. In such embodiments, the impeller may not be located within the internal core. (i.e. may be external to the internal core). The first wall the duct (e.g. the wall in which the one or more openings are formed) of may 5 be a hub-side wall extending from the hub of the impeller. In other words, the hub-side wall may comprise a surface that is substantially contiguous with a surface of the hub (i.e. other than clearance providing for rotation of the hub). That is, air may flow along a surface of the hub onto a surface of the hub-side wall of the duct. In some embodiments, the hub-side wall may be an outer wall of the duct (e.g. when the 10 noise-reduction cavity is external to the internal core). In some embodiments, the hub-side wall may be an inner wall of the duct (e.g. when the noise-reduction cavity is within the internal core). The second wall of the duct may be a shroud-side wall extending from a shroud of the compressor assembly. In other words, the shroud-side wall may comprise a surface that is 15 substantially contiguous with a surface of the shroud. That is, air may flow along a surface of the shroud onto a surface of the shroud-side wall of the duct. In some embodiments, the shroud-side wall may be an outer wall of the duct (e.g. when the noise-reduction cavity is within the internal core). In some embodiments, the shroud-side wall may be an inner wall of the duct (e.g. when the noise-reduction cavity is external to 20 the internal core). The noise-reduction cavity may be on a hub side of the compressor assembly. The noisereduction cavity may be adjacent to or proximate to the hub of the impeller. The hub of the impeller may be closer than the shroud or motor to the noise-reduction cavity. The noise-reduction cavity may be located at an axial end of the compressor assembly that is 25 distal from the shroud or motor (i.e. closer to the hub than the shroud or motor). The noise-reduction cavity may be located at an axial end of the compressor assembly that is distal from the shroud or motor. Thus, the impeller may be located between the noisereduction cavity and the shroud. 09 02 26 The duct may comprise one or more vanes (e.g. within the airflow passage). The one or more vanes may be configured to direct airflow within the airflow passage. For example, the one or more vanes may be configured to direct airflow within the airflow passage along a helical airflow path. 5 The first and second regions (e.g. and the one or more openings) may be upstream of the one or more vanes, or may be downstream of the one or more vanes. In some embodiments, the duct may comprise a plurality of rows of vanes, the rows spaced along the airflow passage. The first and second regions (e.g. and the one or more openings) may be positioned between two rows of the plurality of rows of vanes. 10 In a second aspect there is disclosed a vacuum cleaner comprising a compressor assembly according to the first aspect. The vacuum cleaner may comprise a cleaning head, a main body and may include a tube (e.g. wand) connecting the cleaning head to the body. The compressor assembly may form part of the main body. In further aspects, the compressor assembly of the first aspect may be for an appliance 15 other than a vacuum cleaner. Thus, in a third aspect there may be provide a compressor assembly for providing an airflow in an appliance, the compressor assembly comprising: an impeller for generating an airflow; a diffuser downstream of the impeller, the diffuser comprising an airflow duct at least partly defining an airflow passage for receipt of an airflow generated by the impeller, the airflow passage being annular so as to surround an 20 internal core; and a noise-reduction cavity fluidly interconnecting first and second regions of the airflow passage located on opposite sides of the internal core (e.g. diametrically opposite sides of the internal core). The appliance may be, for example, a fan (e.g. a floor fan) or other air treatment appliance (the compressor assembly may be configured for supplying a flow of air into a space). The 25 appliance may be a hair care appliance, such as a hair dryer (the compressor assembly may be configured for supplying a flow of air for styling hair). The compressor assembly of the second aspect may be otherwise as described above with respect to the first aspect (e.g. may include one or more of the optional features of the first aspect described above). 09 02 26 In a fourth aspect, there is provided a fan comprising a compressor assembly according to the third aspect. In a fifth aspect, there is provided a hair care appliance comprising a compressor assembly according to the third aspect. 5 In a sixth aspect there is disclosed a diffuser for a vacuum cleaner comprising: an airflow duct defining an airflow passage for receipt of an airflow generated by an impeller, the airflow passage being annular so as to surround an internal core; and a noise-reduction cavity fluidly interconnecting first and second regions of the airflow passage located on opposite sides of the internal core (e.g. diametrically opposite sides of the internal core). 10 The diffuser may be as otherwise described above with respect to the first aspect. Thus, for example, the diffuser may comprise one or more of the optional features of the diffuser of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS Figure lisa perspective view of a vacuum cleaner; 15 Figure 2A is section view of a compressor assembly according to a first embodiment; Figure 2B is a perspective view of the compressor assembly of the first embodiment; Figure 3 is a schematic view showing an internal core of the compressor assembly of Figure 2A; Figure 4 is a schematic view showing positive and negative pressure regions in an airflow 20 passage; Figure 5 is a section view of a compressor assembly according to a second embodiment; Figure 6 is a section view of a compressor assembly according to a third embodiment; and Figure 7 is a perspective section view of a diffuser according to a fourth embodiment. DETAILED DESCRIPTION 25 Figure 1 illustrates a vacuum cleaner 10 including a main body 11 and a cleaning head 12 connected to the main body 11 by an elongate tube 13 (i.e. a wand). The main body 11 includes a compressor assembly (not visible) for providing suction, such that air (along with dust and debris) can be drawn into and through the main body 11 via the cleaning head 12 and the elongate tube 13. 09 02 26 Figures 2A and 2B illustrate an exemplary compressor assembly 14a that can be provided as part of the main body 11 of the vacuum cleaner 10 for moving air through the vacuum cleaner 10 (i.e. to provide suction so that the vacuum cleaner 10 can function to pick up dust and debris from a surface). For completeness it is noted there are minor differences 5 between the compressor assemblies 14a illustrated in Figures 2A and 2B as a result of the schematic nature of Figure 2A. The compressor assembly 14a comprises mixed flow impeller 15 for generating an airflow (the impeller 15 is omitted in Figure 2B for clarity). The impeller 15 includes a hub 17 and a plurality of blades 18 extending radially from the hub 17. The compressor assembly 14a 10 also includes a motor 19 for driving the impeller 15 to rotate about a rotational axis 20 to draw air into and discharge air from the impeller 15. In particular, the motor 19 is configured to rotate the impeller 15 at a speed of at least 50,000 rpm. To guide air through the impeller 15, the compressor assembly 14a further includes a shroud 35 (providing an outer housing for the impeller 15). The shroud 35 has a hollow 15 frustoconical shape and circumferentially surrounds the impeller 15. Air thus flows through the impeller 15 between the hub 17 and an inner surface 36 of the shroud 35. The compressor assembly 14a further includes a diffuser 21 for receipt of airflow 26 from the impeller 15 and for directing the airflow towards an outlet of the vacuum cleaner 10 (i.e. for discharge into the external environment). 20 The diffuser 21 includes an annular airflow duct 22, which defines an annular airflow passage 23 for receipt of an airflow generated by the impeller 15. The annular shape of the airflow passage 23 means that it surrounds an internal core 24. For clarity, the internal core 24 is illustrated schematically in Figure 3 (in which much of the detail of Figure 2A is removed). The diffuser 21 further includes (or defines) a generally frustoconical noise-25 reduction cavity 25 fluidly interconnecting first 27 and second 28 regions of the airflow passage 23 located on opposite sides of the internal core 24 (e.g. diametrically opposite sides of the internal core 24). In this case, the noise-reduction cavity 25 is located within the internal core 24 of the airflow passage 23. 09 02 26 The airflow passage 23 of the illustrated compressor assembly 14a includes a tubular upstream axial portion 32 and a tubular downstream axial portion 33 that are connected by a (curved U-shaped) radial portion 34. Thus, the airflow 26 exits the impeller 15, flows along the upstream axial portion 32 in a first direction (away from the impeller 15), is 5 turned approximately 180 degrees in the radial portion 34, and then flows in a second direction (opposite the first direction) along the downstream axial portion 33 back towards the impeller 15. Accordingly, the downstream axial portion 33 circumferentially surrounds the impeller 15. The airflow 26 may then be discharged from the compressor assembly 14a (and from the vacuum cleaner 10). 10 Although not shown, the airflow duct 22 can includes a plurality of vanes (within the airflow passage 23) arranged obliquely so as to guide the airflow 26 in a helical motion along the airflow duct 23. Such vanes may be arranged in circumferentially extending rows spaced along the airflow passage 22. The airflow duct 22 includes first 37 and second 38 spaced apart walls (which define the 15 airflow passage 23 therebetween). Each of the first 37 and second 38 spaced apart walls of the duct 22 has a generally tubular shape (i.e. surrounding the impeller 15 and the internal core 24). In the illustrated embodiment the first wall 37 can be referred to as a “hub-side” wall because it extends from (close to) the hub 17 of the impeller 15. The second wall 38 can be referred to as a “shroud-side” wall because it extends from the shroud 35 of the 20 impeller 15. The first wall 37 includes an opening 39 in the form of a circumferential slot that provides fluid communication between the airflow passage 23 and the noise-reduction cavity 25. Accordingly, an entirety of the circumference of the airflow passage 23, at the location of the opening 39, is open to the noise-reduction cavity 25. Thus, the opening 39 (along with 25 the noise-reduction cavity 25) interconnects opposite sides of the airflow passage 23 (i.e. on opposite sides of the internal core 24). To minimise disruption to airflow, the width of the opening (i.e. the vertical dimension of the opening 39 as illustrated) is smaller than a width of the airflow passage 23 (i.e. the distance between the first 37 and second 38 walls of the airflow duct 22). 09 02 26 In addition to being bounded by the first wall 37 of the airflow duct 22, the noise-reduction cavity 25 is also bounded by (i.e. defined between) opposite first 40 and second 41 cavity walls. The first cavity wall 40 is adjacent the impeller 15. The second cavity wall 41 forms an external wall of the compressor assembly 14a and extends across the internal core 5 24 defined by the airflow passage 23 (i.e. so as to extend across a central void of the duct 22). As has already been discussed above, the provision of such a noise-reduction cavity 25 can help reduce the amount of airborne noise propagating along the airflow passage 23. One source of such airborne noise is differences in air pressure, initially surrounding the 10 impeller 15 and subsequently propagating along the airflow passage 23 (i.e. creating airborne noise). These air pressure differences are illustrated in Figure 4. As shown in Figure 4, the noise can be generated by a negative (or low) pressure region 29 and a positive (or high) pressure region 30 that are located on diametrically opposite sides of the airflow passage 23. These negative 29 and positive 30 pressure regions rotate about 15 the internal core 20 with rotation of the impeller 15, generating airborne noise that can propagate along the airflow passage 23 and ultimately to the external environment (i.e. via the airflow passage 23). The noise-reducing cavity 25 (i.e. of Figures 2A and 2B) prevents (or at least reduces) such propagation of airborne noise by fluidly connecting the negative 29 and positive 30 20 pressure regions within the airflow passage 23, allowing them to mix and cancel out. In this way, the compressor assembly 14a can operate with reduced noise. Figure 5 illustrates a compressor assembly 14b that is a variation of the compressor assembly 14a shown in Figures 2A and 2B. It should be appreciated that this variation is substantially the same as that previously discussed except for any differences set out below 25 (for this reason the same reference numerals are used). The compressor assembly 14b of Figure 5 differs from that of Figures 2A and 2B in that the noise-reduction cavity 25 is defined between a cavity wall 41 (extending across a central void defined by the duct 22) and an internal space of the impeller 15. The first 27 and second 28 regions of the airflow passage 23 interconnected by the noise-reduction 09 02 26 cavity 25 are immediately downstream of the impeller 15 (and upstream of the duct 22). Likewise, fluid communication between the airflow passage 23 and the noise-reduction cavity 25 is provided by an opening 39 in the form of a gap that is defined between the first duct wall 37 and the impeller 15 (in particular the hub 17 of the impeller 15). Accordingly, 5 the positive and negative pressure regions that may form in the airflow passage 23 (as discussed above) are able to mix via the noise-reduction cavity 25 to cancel one another out. Figure 6 illustrates a compressor assembly 14c that provides yet another variation. Again, it should be appreciated that this variation is substantially the same as those previously 10 discussed except for differences set out below (again, the same reference numerals are used). The impeller 15 of this compressor assembly 14c is configured to discharge the airflow 26 in a radial direction (i.e. perpendicular to the rotational axis 20 of the impeller 15). Accordingly, immediately downstream of the impeller 15, the airflow passage 23 includes 15 a radial portion 34. Downstream of the radial portion 34 is an axial portion 33, which (as per the previous compressor assemblies 14a, 14b) extends back towards the impeller 15 so as to circumferentially surround the impeller 15. Unlike the previously described variations, the noise-reduction cavity 25 (which has an annular shape) of the compressor assembly 14c of Figure 6 is external to the internal core 20 24 defined by the airflow passage 23. In other words, the noise-reduction cavity 25 is not surrounded by the annual airflow passage 23. Instead, the noise-reduction cavity 25 is positioned externally so as to be at an axial end of the compressor assembly 14c. The noise-reduction cavity 25 is bounded by the first (hub-side) wall 37 of the duct 22 and a cavity wall 41 that also forms an external wall of the compressor assembly 14c. 25 The first 27 and second 28 regions of the airflow passage interconnected by the noisereduction cavity 25 are within the radial portions 34 of the airflow passage 23. Openings 39 provide fluid communication between the first 27 and second 28 interconnected regions to allow mixing of the positive and negative pressure regions that may form during use. In this embodiment, the openings 39 are in the form of a plurality of slots that extend (and are 30 spaced) circumferentially around the internal core 24. 02 26 Figure 7 illustrates a diffuser 21d that is a further variation of the above discussed arrangements. Again, it should be appreciated that this variation is substantially the same as those previously discussed except for differences set out below (for this reason, the same reference numerals are used). 5 As may be appreciated, the diffuser 21 d is configured for use with an impeller of the type that discharges an airflow 26 in a radially outward direction. In particular, the airflow passage 23 of the diffuser 21d includes a radial portion 34 that provides an annular inlet 43 so as to be immediately downstream of the impeller (when present). In contrast to previously discussed arrangements, downstream of the radial portion 34, the airflow 10 passage 23 includes an axial portion 33 which extends away from the impeller (when present). The cylindrical noise-reduction cavity 25 is positioned within (i.e. so as to be circumferentially surrounded by) this axial portion 33 of the airflow passage 23. Openings 39 in the form of circumferentially extending slots, are formed in the first (hub-side) wall 27 so as to surround the noise-reduction cavity 25. These provide a fluid connection 15 between the airflow passage 23 and the noise-reduction cavity 25 to facilitate reduction in airborne noise propagation as has already been discussed above. 09 02 26

Claims

1. A compressor assembly for providing suction in a vacuum cleaner, the compressor assembly comprising:5 an impeller for generating an airflow;a motor for driving rotation of the impeller;a diffuser downstream of the impeller, the diffuser comprising an airflow duct at least partly defining an airflow passage for receipt of an airflow generated by the impeller, the airflow passage being annular so as to surround an internal core; and10 a noise-reduction cavity fluidly interconnecting first and second regions of theairflow passage located on opposite sides of the internal core;wherein the impeller is located between the noise-reduction cavity and the motor.

2. The compressor assembly according to claim 1 wherein the noise-reduction cavity is 15 located within the internal core surrounded by the airflow passage.

3. The compressor assembly according to claim 2 wherein the airflow passage comprises an axial portion extending parallel to a rotational axis of the impeller.20 4. The compressor assembly according to claim 3 wherein the first and secondinterconnected regions of the airflow passage form part of the axial portion of the airflow passage.

5. The compressor assembly according to claim 1 wherein the noise-reduction cavity is 25 external to the internal core surrounded by the airflow passage.

6. The compressor assembly according to any one of the preceding claims wherein the airflow passage comprises a radial portion extending radially with respect to a rotational axis of the impeller.3009 02 267. The compressor assembly according to claim 6 wherein the first and second interconnected regions of the airflow passage form part of the radial portion of the airflow passage.5 8. The compressor assembly according to any one of the preceding claims wherein the ductcomprises first and second spaced apart walls defining the airflow passage therebetween.

9. The compressor assembly according to claim 8 wherein the noise-reduction cavity is fluidly connected to the airflow passage by one or more openings formed in the first wall 10 of the duct.

10. The compressor assembly according to claim 9 wherein the first wall of the duct is a hub-side wall extending from a hub of the impeller.15 11. The compressor assembly according to claim 9 or 10 wherein the second wall of theduct is a shroud-side wall extending from a shroud of the impeller.

12. The compressor assembly according to any one of claims 9 to 11 wherein at least one of the one or more openings has a width that is smaller than a distance between first and 20 second walls taken at the location of the at least one opening.

13. The compressor assembly according to any one of claims 9 to 12 wherein the one or more openings comprise an annular opening or an annular array of openings extending circumferentially around the internal core.2514. The compressor assembly according to claim 13 wherein the one or more openings extend substantially fully around the internal core.

15. The compressor assembly according to any one of the preceding claims wherein the 30 motor is configured to rotate the impeller at a rotational speed of at least 50,000 rpm.

16. A vacuum cleaner comprising the compressor assembly according to any one of the preceding claims.CXICXI

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