Compressor

Abstract

A compressor has a rotor assembly having an impeller for generating an airflow through the compressor, a stator core assembly for causing rotation of the impeller, and a diffuser assembly for acting on the airflow generated by the impeller. The diffuser assembly has a first diffuser stage and a second diffuser stage. The first and second diffuser stages are separate components connected to one another by a fastener.

Claims

1. A compressor comprising a rotor assembly having an impeller for generating an airflow through the compressor, a stator core assembly for causing rotation of the impeller, and a diffuser assembly for acting on the airflow generated by the impeller, wherein the diffuser assembly comprises a first diffuser stage and a second diffuser stage, the first and second diffuser stages comprising separate components connected to one another by a fastener; wherein the first diffuser stage comprises a first hub, a first outer wall, and a first plurality of diffuser blades extending between the first hub and the first outer wall, and the second diffuser stage comprises a second hub, a second outer wall, and a second plurality of diffuser blades extending between the second hub and the second outer wall; and wherein the fastener extends between the first and second hubs at a location remote from an outer diameter of the first and the second hubs, such that the fastener is removed from the common flow path.

2. The compressor of claim 1, wherein the first and second diffuser stages are formed by separate moulding processes.

3. The compressor of claim 1, wherein the first and second hubs and the first and second outer walls comprise a cylindrical global form.

4. The compressor of claim 1, wherein at least one of the first or second hub is hollow, and the other of the second or first hub, comprises a locating projection which extends into the hollow interior of the first or second hub.

5. The compressor of claim 1, wherein the second diffuser stage comprises an outer diameter smaller than an outer diameter of the first diffuser stage.

6. The compressor of claim 1, wherein the first diffuser stage comprises a first anti-rotation projection and/or recess for engaging a corresponding second anti-rotation recess and/or projection of the second diffuser stage.

7. The compressor of claim 1, wherein the second diffuser stage comprises a greater number of diffuser blades than the first diffuser stage.

8. The compressor of claim 1, wherein diffuser blade inlet angles vary between the first and second diffuser stages.

9. The compressor of claim 1, wherein diffuser blade outlet angles vary between the first and second diffuser stages.

10. The compressor of claim 1, wherein the first diffuser stage comprises a diffuser blade outlet angle which is smaller than a diffuser blade inlet angle of the second diffuser stage.

11. The compressor of claim 1, wherein the second diffuser stage comprises a stagger angle which is smaller than a stagger angle of the first diffuser stage.

12. The compressor of claim 1, wherein a maximum diffuser blade thickness of the first diffuser stage is greater than a maximum diffuser blade thickness of the second diffuser stage.

13. The compressor of claim 1, wherein the second diffuser stage comprises a diffuser blade chord length smaller than a diffuser blade chord length of the first diffuser stage.

14. The compressor of claim 1, wherein the second diffuser stage comprises a greater diffuser blade solidity than the first diffuser stage.

15. The compressor of claim 1, wherein the impeller comprises a mixed flow impeller.

16. The compressor of claim 1, wherein the diffuser assembly comprises a third diffuser stage, the second diffuser stage is located downstream of the first diffuser stage, and the third diffuser stage is located downstream of the second diffuser stage.

17. A vacuum cleaner comprising the compressor of claim 1.

18. A diffuser assembly for a compressor, the diffuser assembly comprising a first diffuser stage and a second diffuser stage, wherein the first and second diffuser stages comprise separate components connected to one another by a fastener; wherein the first diffuser stage comprises a first hub, a first outer wall, and a first plurality of diffuser blades extending between the first hub and the first outer wall, and the second diffuser stage comprises a second hub, a second outer wall, and a second plurality of diffuser blades extending between the second hub and the second outer wall; and wherein the fastener extends between the first and second hubs at a location remote from an outer diameter of the first and the second hubs, such that the fastener is removed from the common flow path.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) In order to better understand the present invention, and to show more clearly how the invention may be put into effect, the invention will now be described, by way of example, with reference to the following drawings:

(2) FIG. 1 is an exploded perspective view of a compressor according to aspects of the present invention;

(3) FIG. 2 is an exploded perspective view of a rotor assembly of the compressor of FIG. 1;

(4) FIG. 3 is an exploded perspective view of a stator core assembly of the compressor of FIG. 1;

(5) FIG. 4 is a cross-sectional view of the compressor of FIG. 1 taken along a central longitudinal axis of the compressor of FIG. 1;

(6) FIG. 5A is a front perspective view of a first diffuser stage of a diffuser assembly of the compressor of FIG. 1;

(7) FIG. 5B is a rear perspective view of a first diffuser stage of a diffuser assembly of the compressor of FIG. 1;

(8) FIG. 6A is a front perspective view of a second diffuser stage of a diffuser assembly of the compressor of FIG. 1;

(9) FIG. 6B is a rear perspective view of a second diffuser stage of a diffuser assembly of the compressor of FIG. 1;

(10) FIG. 7A is a front perspective view of a third diffuser stage of a diffuser assembly of the compressor of FIG. 1;

(11) FIG. 7B is a rear perspective view of a third diffuser stage of a diffuser assembly of the compressor of FIG. 1;

(12) FIG. 8 is a first table indicating parameters of blades of the diffuser stages of FIGS. 5A-B through 7A-B;

(13) FIG. 9 is a second table indicating parameters of blades of the diffuser stages of FIGS. 5A-B through 7A-B;

(14) FIG. 10A is a first cross-sectional view of a diffuser assembly of the compressor of FIG. 1, taken along a central longitudinal axis of the compressor of FIG. 1;

(15) FIG. 10B is a schematic perspective view showing assembly of the diffuser assembly of the compressor of FIG. 10A;

(16) FIG. 11A is a front view of the diffuser assembly of FIG. 1 with a section removed;

(17) FIG. 11B is a second cross-sectional view of a diffuser assembly of the compressor of FIG. 1, corresponding to the section removed in FIG. 11A;

(18) FIG. 12A is a schematic cross-sectional view through blade assemblies of first, second and third diffuser stages of the compressor of FIG. 1, taken at a hub of the corresponding diffuser stage;

(19) FIG. 12B is a schematic cross-sectional view through blade assemblies of first, second and third diffuser stages of the compressor of FIG. 1, taken at a mid-point along the radial distance of the blade;

(20) FIG. 12C is a schematic cross-sectional view through blade assemblies of first, second and third diffuser stages of the compressor of FIG. 1, taken at an outer wall of the corresponding diffuser stage;

(21) FIG. 13 is a schematic diagram indicating blade parameters for diffuser stages of the compressor of FIG. 1;

(22) FIG. 14 is a plot of pressure rise against flow rate for the compressor of FIG. 1;

(23) FIG. 15 is a plot of suction power against flow rate for the compressor of FIG. 1;

(24) FIG. 16 is a perspective view of a vacuum cleaner comprising the compressor of FIG. 1;

(25) FIG. 17 is an exploded perspective view of a diffuser assembly for use with the compressor of FIG. 1;

(26) FIG. 18 is a first table indicating parameters of blades of the diffuser stages of FIG. 17; and

(27) FIG. 19 is a second table indicating parameters of blades of the diffuser stages of FIG. 17.

DETAILED DESCRIPTION OF THE DISCLOSURE

(28) FIG. 1 shows an exploded perspective view of a compressor 10 according to an embodiment of the present invention. Certain components, such as control electronics and an external housing, are not shown for clarity. The compressor 10 includes a rotor assembly 12, a frame 14 and four stator core assemblies 16, 18, 20 and 22. When the compressor 10 is assembled, the rotor assembly 12 is located within and mounted to the frame 14, and the stator core assemblies 16, 18, 20, 22 are located in respective slots in the frame 14. For example, the stator core assembly 16 is located within slot 24 in the frame 14. The frame 14 may be a one-piece construction, for example moulded as a single object, and includes an impeller shroud 26 that covers the impeller 42 as shown in FIG. 4. The compressor 10 also includes a diffuser assembly 28.

(29) FIG. 2 shows an exploded perspective view of the rotor assembly 12. The rotor assembly 12 comprises a shaft 30 on which is mounted a rotor core permanent magnet 32, a first balancing ring 34 and a second balancing ring 36. When the rotor assembly 12 is assembled, a pair of bearings 38, 40 are mounted on the shaft 30 on either side of the core 32 and balancing rings 34, 36. An impeller 42 is mounted at one end of the shaft 30, and a sensor magnet 44 is mounted at the other end.

(30) FIG. 3 shows an exploded perspective view of a stator core assembly 50. The stator core assembly 50 may be any one of the stator core assemblies 16, 18, 20, 22 shown in FIG. 1. The stator core assembly 50 comprises a C-shaped stator core 52, a first C-shaped bobbin portion 54 and a second C-shaped bobbin portion 56.

(31) The stator core 52 comprises a back 58, a first arm 60 and a second arm 62. Each of the arms 60, 62 includes a respective protrusion 64, 66 on the outer surface of the stator core 52. The protrusions 64, 66 extend along the axial length of the stator core 52.

(32) The first bobbin portion 54 includes arms that define a first slot 68. Similarly, the second bobbin portion 56 includes arms that define a second slot 70. The bobbin portions 54, 56 slide onto the stator core 52 such that, when assembled, the slots 68, 70 accommodate the back of the stator core 52. The bobbin portions 54, 56 have a generally H-shaped cross-section such that a stator winding (shown in FIG. 1) may be wound around the bobbin portions in the assembled stator core assembly, and hence around the back of the stator core 52.

(33) FIG. 4 shows a cross-section of the assembled compressor 10 through a plane that includes the axis of rotation of the rotor assembly 12. It can be seen that the bearings 38, 40 of the rotor assembly 12 are mounted directly to and within the frame 14. The stator core assemblies 16, 20 are also shown inserted into their respective slots in the frame 14. It can be seen that on each stator core assembly 16,18,20,22 the bobbin portions 54, 56 enclose the back 58 of the stator core 52.

(34) The diffuser assembly 28 is shown in isolation in FIGS. 10A-B and 11A-B, and comprises a first diffuser stage 100, a second diffuser stage 200 and a third diffuser stage 300. Each diffuser stage 100,200,300 is a separate component, moulded separately in separate injection moulding processes, with the diffuser stages 100,200,300 being joined together by three screws 108.

(35) The first diffuser stage 100 is located downstream of the impeller 42, but upstream of the second diffuser stage 200. The second diffuser stage 200 is located downstream of the first diffuser stage 100, but upstream of the third diffuser stage 300. The third diffuser stage 300 is located downstream of the second diffuser stage 200. This arrangement of the diffuser stages 100,200,300 can be seen in FIGS. 4 and 10A-B. The first diffuser stage 100 may be referred to as an upstream-most diffuser stage, and the third diffuser stage 300 may be referred to as a downstream-most diffuser stage.

(36) The first 100, second 200, and third 300 diffuser stages can be seen in isolation in FIGS. 5A-B, 6A-B and 7A-B respectively.

(37) The first diffuser stage 100 comprises a first hub 110, a first outer wall 112, and a first plurality of blades 114. The first diffuser stage 100 has a length of 14.9085 mm in an axial direction, for example a direction parallel to a central longitudinal axis of the compressor 10. The first hub 110 is substantially cylindrical in form, and is substantially hollow, with a closed upstream end 116 and an open downstream end 118. The first hub 110 has an outer diameter corresponding substantially to an outer diameter of the impeller 42, as can be seen from FIG. 4.

(38) Located within the hollow interior of the first hub 110 are three screw receiving spigots 120, and a primary set of anti-rotation projections 122. The three screw receiving spigots 120 are each shaped and dimensioned to receive a corresponding screw 108, and are spaced evenly about the first hub 110, for example spaced at 120° intervals. The primary set of anti-rotation projections 122 are shaped and dimensioned to be received within corresponding secondary anti-rotation recesses 216 of a second hub 202 of the second diffuser stage 104.

(39) The first outer wall 112 is substantially cylindrical in form, and extends annularly about the first hub 110. The first plurality of blades 114 extend between the first hub 110 and the first outer wall 112, and define a first plurality of flow passageways 124 between adjacent blades 114. In the embodiment shown in FIGS. 5A and 5B, the first plurality of blades 114 comprises 11 blades. The geometry of the first plurality of blades 114 will be described further below, with reference to FIGS. 8 and 9.

(40) The second diffuser stage 200 comprises a second hub 202, a second outer wall 204, and a second plurality of blades 206. The second diffuser stage 200 has a length of 7.69 mm in an axial direction, for example a direction parallel to a central longitudinal axis of the compressor 10. The second hub 202 is substantially cylindrical in form, and is substantially hollow, with a closed upstream end 208 and an open downstream end 210.

(41) The second hub 202 comprises an annular wall 212 upstanding from the upstream end 208. The annular wall 212 extends about substantially the entire circumference of the second hub 202. The annular wall 212 is spaced inwardly from the circumference of the second hub 202 such that the second hub 202 comprises a shoulder 214 for engaging the first hub 110. The annular wall 212 is shaped and dimensioned to be received within the hollow interior of the first hub 110, ie within the open downstream end 118.

(42) The annular wall 212 comprises secondary anti-rotation recesses 216 which are shaped and dimensioned to receive corresponding primary anti-rotation projections 122 of the first hub 110. The second hub 202 comprises three screw receiving through-holes 218 which are spaced evenly about the second hub 202, for example spaced at 120° intervals. The three screw receiving through-holes 218 are each shaped and dimensioned to receive a corresponding screw 108. The secondary anti-rotation recesses 216 may be used to properly align the first 100 and second 200 diffuser stages, such that the screw receiving spigots 120 are aligned with the screw receiving through-holes 218.

(43) The second hub 202 has an outer diameter corresponding substantially to an outer diameter of the first hub 110, as can be seen from FIGS. 10A-B. The second outer wall 204 has an outer diameter slightly less than the first outer wall 112, as can be seen in FIG. 10A, for example.

(44) The screw receiving through holes 218 extend through the entirety of the second hub 202, and secondary screw receiving spigots 220 are formed about the through holes 218 in the hollow portion of the second hub 202, for example formed on the open downstream end 210 of the second hub 202. A secondary anti-rotation projection 222 is located in the hollow portion of the second hub 202, and is shaped and dimensioned to be received in a tertiary anti-rotation recess 316 of the third diffuser stage 300.

(45) The second outer wall 204 is substantially cylindrical in form, and extends annularly about the second hub 202. The second plurality of blades 206 extend between the second hub 202 and the second outer wall 204, and define a second plurality of flow passageways 224 between adjacent blades 206. In the embodiment shown in FIGS. 6A and 6B, the second plurality of blades 206 comprises 19 blades. The geometry of the second plurality of blades 206 will be described further below, with reference to FIGS. 8 and 9.

(46) The third diffuser stage 300 comprises a third hub 302, a third outer wall 304, and a third plurality of blades 306. The third diffuser stage 300 has a length of 5.88 mm in an axial direction, for example a direction parallel to a central longitudinal axis of the compressor 10. The third hub 302 is substantially cylindrical in form, and is substantially hollow, with a closed upstream end 308 and an open downstream end 310.

(47) The closed upstream end 308 is defined by a cylindrical projection 312, and a shoulder 314, such that the global form of the third diffuser stage corresponds substantially to that of a boater hat, as can be seen from FIG. 7A.

(48) The cylindrical projection 312 is shaped and dimensioned to be received within the hollow interior of the second hub 202, ie within the open downstream end 210 of the second hub 202. The cylindrical projection comprises a tertiary anti-rotation recess 316 for receiving the secondary anti-rotation projection 222 of the second diffuser stage 200. The shoulder 314 is shaped and dimensioned to engage the second hub 202, and the shoulder 314 has an outer diameter corresponding substantially to an outer diameter of the second hub 202.

(49) The third hub 302 comprises three screw receiving through-holes 318 which are spaced evenly about the third hub 302, for example spaced at 120° intervals. The three screw receiving through-holes 318 are each shaped and dimensioned to receive a corresponding screw 108. The tertiary anti-rotation recess 316 may be used to properly align the second 200 and third 300 diffuser stages, such that the screw receiving through-holes 218 of the second hub 200 are aligned with the screw receiving through-holes 318 of the third hub 300.

(50) The third hub 302 has an outer diameter corresponding substantially to an outer diameter of the first hub 110 and an outer diameter of the second hub 203, as can be seen from FIGS. 10A-B.

(51) The screw receiving through holes 318 extend through the entirety of the third hub 302, and tertiary screw receiving spigots 320 are formed about the through holes 318 in the hollow portion of the third hub 302, for example formed on the open downstream end 310 of the third hub 302. End faces of the tertiary screw receiving spigots 320 interface with heads of screws 108 when the diffuser assembly 28 is assembled.

(52) The third outer wall 304 is substantially cylindrical in form, and extends annularly about the third hub 302. The third plurality of blades 306 extend between the third hub 302 and the third outer wall 304, and define a third plurality of flow passageways 324 between adjacent blades 306. In the embodiment shown in FIGS. 7A and 7B, the third plurality of blades 306 comprises 25 blades. The geometry of the third plurality of blades 306 will be described further below, with reference to FIGS. 8 and 9.

(53) As mentioned above, each diffuser stage 100,200,300 is a separate component, for example moulded separately in separate injection moulding processes, with the diffuser stages 100,200,300 being joined together by three screws 108, as shown in FIG. 10B. Cross-sections through the diffuser assembly 28 comprising the first 100, second 200, and third 300 diffuser stages are shown in FIGS. 10A-B and 11A-B.

(54) Once the diffuser assembly 28 is in an assembled configuration, the first 124, second 224, and third 324 pluralities of flow passageways, defined by the first 114, second 206, and third 306 pluralities of blades respectively, together form a common flow path, denoted by arrow A in FIGS. 10A-B, through the diffuser assembly 28. The first 124, second 224, and third 324 pluralities of flow passageways each diverge slightly along their length, as seen in FIG. 10A, and this may provide a reduced speed of airflow through the flow passageways 124,224,324, which may provide acoustic benefits.

(55) The first 100, second 200 and third 300 diffuser stages are formed as separate components, and are formed from a plastic material. This enables the use of a wider range of blade geometries for the first 114, second 206, and third 306 pluralities of blades than would be possible if, for example, the diffuser assembly 28 was formed as a single component, using a single moulding process.

(56) As can be seen from FIGS. 8, 9 and 12A-C, the first 114, second 206 and third 306 pluralities of blades 114 each have a cross-sectional shape which varies in a radial direction, with each of the blades 114, 206, 306 having a different geometry at their respective hubs 110,202,302, outer walls 112,204,304, and mid points between the hubs 110,202,302 and outer walls 112,204,304. The different cross-sectional areas can be identified in FIGS. 12A, 12B, and 12C, where FIG. 12A corresponds to cross-sectional shape at the hubs 110,202,302, FIG. 12C corresponds to cross-sectional shape at the outer walls 112,204,304 and FIG. 12B corresponds to cross-sectional at a mid-point between respective hubs 110,202,302 and outer walls 112,204,304.

(57) As can further be seen from FIGS. 8 and 9, other geometrical properties and parameters of the blades 114,206,306 vary both between sets of blades, and in a radial direction along each blade of a set of blades 114,206,306 between respective hubs 110,202,302 and outer walls 112,204,304.

(58) The first plurality of blades 114 have a stagger angle of 57.4° at the first hub 110, a stagger angle of 54.0° at a mid-point, and a stagger angle of 53.7° at the first outer wall 112. Stagger angle here is measured as an angle between a line parallel to a central longitudinal axis of the compressor 10 and a chord of the diffuser blade, as shown by γ in FIG. 13.

(59) The first plurality of blades 114 have a blade inlet angle of 64.3° at the first hub 110, a blade inlet angle of 64.3° at a mid-point, and a blade inlet angle of 64.2° at the first outer wall 112. Blade inlet angle is here measured as an angle between a line parallel to a central longitudinal axis of the compressor 10 and a line tangential to a camber curve of a diffuser blade at the leading edge of the diffuser blade, as shown by β1 in FIG. 13.

(60) The first plurality of blades 114 have a blade outlet angle of 26.2° at the first hub 110, a blade outlet angle of 26.5° at a mid-point, and a blade outlet angle of 26.2° at the first outer wall 112. Blade outlet angle is here measured as an angle between a line parallel to a central longitudinal axis of the compressor and a line tangential to a camber curve of a diffuser blade at the trailing edge of the diffuser blade, as shown by β2 in FIG. 13. As shown in FIG. 13, the blade outlet angle β2 is a negative blade outlet angle, and the tangential line is inclined in an opposite direction to the tangential line which encloses the angle β1. It will be appreciated that, although not shown in FIG. 13, for a positive blade outlet angle β2, the tangential line at the trailing edge of the diffuser blade is inclined in the same direction as the tangential line at the leading edge of the diffuser blade.

(61) The first plurality of blades 114 have a maximum blade thickness of 0.0012 m, with the maximum thickness located at 41.74% of chord length from the leading edge.

(62) The first plurality of blades 114 have a chord length of 0.0128 m at the first hub 110, a chord length of 0.01270 m at a mid-point, and a chord length of 0.01261 m at the first outer wall 112.

(63) The first plurality of blades 114 have an axial chord length of 0.007455 m at the first hub 110, an axial chord length of 0.007461 m at a mid-point, and an axial chord length of 0.007466 m at the first outer wall 112.

(64) The first plurality of blades 114 have a solidity of 1.3 at the first hub 110, a solidity of 1.2 at a mid-point, and a solidity of 1.08 at the first outer wall 112.

(65) The first plurality of blades 114 have an axial solidity of 0.76 at the first hub 110, an axial solidity of 0.6922 at a mid-point, and an axial solidity of 0.64 at the first outer wall 112.

(66) The first plurality of blades 114 have a sweep of −7° at the leading edge, and a sweep of 0° at the trailing edge. The first plurality of blades 114 have a lean of −8° at the first hub 110, and a lean of 8° at the first outer wall 112.

(67) The second plurality of blades 206 have a stagger angle of 39.8° at the second hub 202, a stagger angle of 33.4° at a mid-point, and a stagger angle of 34.3° at the second outer wall 204.

(68) The second plurality of blades 206 have a blade inlet angle of 48.5° at the second hub 202, a blade inlet angle of 48.5° at a mid-point, and a blade inlet angle of 47.4° at the second outer wall 204.

(69) The second plurality of blades 206 have a blade outlet angle of 25.2° at the second hub 202, a blade outlet angle of 18.6° at a mid-point, and a blade outlet angle of 20.9° at the second outer wall 204.

(70) The second plurality of blades 206 have a maximum blade thickness of 0.00063 m, with the maximum thickness located at 34.14% of chord length from the leading edge.

(71) The second plurality of blades 206 have a chord length of 0.0091 m at the second hub 202, a chord length of 0.0084 m at a mid-point, and a chord length of 0.0085 m at the second outer wall 204.

(72) The second plurality of blades 206 have an axial chord length of 0.00698 m at the second hub 202, an axial chord length of 0.00698 m at a mid-point, and an axial chord length of 0.00698 m at the second outer wall 204.

(73) The second plurality of blades 206 have a solidity of 1.6 at the second hub 202, a solidity of 1.3 at a mid-point, and a solidity of 1.2 at the second outer wall 204.

(74) The second plurality of blades 206 have an axial solidity of 1.2 at the second hub 202, an axial solidity of 1.1 at a mid-point, and an axial solidity of 1.0 at the second outer wall 204.

(75) The second plurality of blades 206 have a sweep of 0° at the leading edge, and a sweep of 0° at the trailing edge. The second plurality of blades 206 have a lean of 1.8° at the second hub 202, and a lean of 0.1° at the second outer wall 204.

(76) The third plurality of blades 306 have a stagger angle of 19° at the third hub 302, a stagger angle of 21.4° at a mid-point, and a stagger angle of 19.7° at the third outer wall 304.

(77) The third plurality of blades 306 have a blade inlet angle of 24.9° at the third hub 302, a blade inlet angle of 27.2° at a mid-point, and a blade inlet angle of 26.6° at the third outer wall 304.

(78) The third plurality of blades 306 have a blade outlet angle of −5.9° at the third hub 302, a blade outlet angle of 0.4° at a mid-point, and a blade outlet angle of −5.3° at the third outer wall 304.

(79) The third plurality of blades 306 have a maximum blade thickness of 0.00035 m, with the maximum thickness located at 39.00% of chord length from the leading edge.

(80) The third plurality of blades 306 have a chord length of 0.0037 m at the third hub 302, a chord length of 0.0038 m at a mid-point, and a chord length of 0.0037 m at the third outer wall 304.

(81) The third plurality of blades 306 have an axial chord length of 0.0035 m at the third hub 302, an axial chord length of 0.0035 m at a mid-point, and an axial chord length of 0.0035 m at the third outer wall 304.

(82) The third plurality of blades 306 have a solidity of 1.1 at the third hub 302, a solidity of 1.0 at a mid-point, and a solidity of 0.9 at the third outer wall 304.

(83) The third plurality of blades 306 have an axial solidity of 1.1 at the third hub 302, an axial solidity of 0.97 at a mid-point, and an axial solidity of 0.88 at the third outer wall 304.

(84) The third plurality of blades 306 have a sweep of 0° at the leading edge, and a sweep of 0° at the trailing edge. The third plurality of blades 306 have a lean of −0.2° at the third hub 302, and a lean of 0.5° at the third outer wall 304.

(85) The inventors of the present application have found that utilising a diffuser assembly 28 comprising first 100, second 200, and third 300 diffuser stages having the blade geometries discussed above may be beneficial relative to use of only a first diffuser stage 100 having the blade geometries discussed above.

(86) In particular, and as can be seen from FIGS. 14 and 15, a compressor utilising diffuser assembly 28, indicated by line 400, as opposed to a compressor utilising solely diffuser stage 100, indicated by line 402, can achieve both a greater pressure raise and an increase in suction power (airwatts) for a given flow rate. The additional diffuser stages 200,300 which provide this improved performance are enabled by forming the diffuser stages 100,200,300 as separate components, and attaching the diffuser stages 100,200,300 with the screws 108.

(87) A vacuum cleaner 500 comprising a compressor 10 according to an aspect of the present invention is shown in FIG. 16. The vacuum cleaner 500 benefits from the increase in suction power (air watts) discussed above.

(88) A second embodiment of a diffuser assembly 600 for use with the compressor 10 is shown in FIG. 17, and comprises first 700, second 800, and third 900 diffuser stages.

(89) The general structure of the first 700, second 800 and third 900 diffuser stages of the second diffuser assembly 600 is substantially the same as the structure of the corresponding first 100, second 200 and third 300 diffuser stages of the first diffuser assembly 28, and hence only the differences will be described for the sake of brevity.

(90) Each of the first 700, second 800, and third 900 diffuser stages comprises a hub 702,802,902, an outer wall 704,804,904, and a plurality of diffuser blades 706,806,906 extending between the hub 702,802,902 and the outer wall 704,804,904. Each of the first 700, second 800, and third 900 diffuser stages comprises a single corresponding screw receiving formation 708,808,908 for receiving a screw 108. The screw receiving formations 708,808,908 are located centrally on corresponding hubs of the first 700, second 800, and third 900 diffuser stages.

(91) The first 700, second 800 and third 900 diffuser stages of the second diffuser assembly 600 also differ from the first 100, second 200 and third 300 diffuser stages of the first diffuser assembly 28 in their diffuser blade geometry. The blade geometries of the first 700, second 800 and third 900 diffuser stages are described below, with reference to FIGS. 18 and 19.

(92) The first plurality of blades 706 have a stagger angle of 60.2° at the first hub 702, and a stagger angle of 58.2° at the first outer wall 704. The first plurality of blades 706 have a blade inlet angle of 70.8° at the first hub 702, and a blade inlet angle of 72.6° at the first outer wall 704. The first plurality of blades 706 have a blade outlet angle of 46.7° at the first hub 702, and a blade outlet angle of 39.3° at the first outer wall 704.

(93) The first plurality of blades 706 have a maximum blade thickness of 0.000876 m at the first hub 702, with the maximum thickness located at 35.0% of chord length from the leading edge. The first plurality of blades 706 have a maximum blade thickness of 0.000875 m at the first outer wall 704, with the maximum thickness located at 33.7% of chord length from the leading edge.

(94) The first plurality of blades 706 have a chord length of 0.0196 m at the first hub 702, and a chord length of 0.0171 m at the first outer wall 704. The first plurality of blades 706 have an axial chord length of 0.0097 m at the first hub 702, and an axial chord length of 0.0090 m at the first outer wall 708. The first plurality of blades 706 have a solidity of 1.8 at the first hub 702, and a solidity of 1.3 at the first outer wall 704. The first plurality of blades 706 have an axial solidity of 0.9 at the first hub 702, and an axial solidity of 0.7 at the first outer wall 704.

(95) The first plurality of blades 114 have a sweep of 25°. The first plurality of blades 114 have a lean of 1.6° at the first hub 702, and a lean of 1.6° at the first outer wall 704.

(96) The second plurality of blades 806 have a stagger angle of 33.0° at the second hub 802, and a stagger angle of 27.2° at the second outer wall 804. The second plurality of blades 806 have a blade inlet angle of 54.9° at the second hub 802, and a blade inlet angle of 49.9° at the second outer wall 804. The second plurality of blades 806 have a blade outlet angle of 14.4° at the second hub 802, and a blade outlet angle of 8.4° at the second outer wall 804.

(97) The second plurality of blades 806 have a maximum blade thickness of 0.000642 m at the second hub 802, with the maximum thickness located at 37.6% of chord length from the leading edge. The second plurality of blades 806 have a maximum blade thickness of 0.000640 m at the second outer wall 804, with the maximum thickness located at 36.3% of chord length from the leading edge.

(98) The second plurality of blades 806 have a chord length of 0.0083 m at the second hub 802, and a chord length of 0.0078 m at the second outer wall 804. The second plurality of blades 806 have an axial chord length of 0.0070 m at the second hub 802, and an axial chord length of 0.0070 m at the second outer wall 804. The second plurality of blades 806 have a solidity of 1.6 at the second hub 802, and a solidity of 1.3 at the second outer wall 804. The second plurality of blades 806 have an axial solidity of 1.4 at the second hub 802, and an axial solidity of 1.1 at the second outer wall 804.

(99) The second plurality of blades 806 have a sweep of 0°. The second plurality of blades 806 have a lean of −0.1° at the second hub 802, and a lean of −0.1° at the second outer wall 804.

(100) The third plurality of blades 906 have a stagger angle of 17.0° at the third hub 902, and a stagger angle of 17.0° at the third outer wall 904. The third plurality of blades 906 have a blade inlet angle of 24.6° at the third hub 902, and a blade inlet angle of 24.3° at the third outer wall 904. The third plurality of blades 906 have a blade outlet angle of 6.5° at the third hub 902, and a blade outlet angle of 6.8° at the third outer wall 904.

(101) The third plurality of blades 906 have a maximum blade thickness of 0.000642 m at the third hub 902, with the maximum thickness located at 37.6% of chord length from the leading edge. The third plurality of blades 906 have a maximum blade thickness of 0.000638 m at the third outer wall 904, with the maximum thickness located at 36.3% of chord length from the leading edge.

(102) The third plurality of blades 906 have a chord length of 0.0063 m at the third hub 902, and a chord length of 0.0063 m at the third outer wall 904. The third plurality of blades 906 have an axial chord length of 0.0060 m at the third hub 902, and an axial chord length of 0.0060 m at the third outer wall 904. The third plurality of blades 906 have a solidity of 1.2 at the third hub 902, and a solidity of 1.0 at the third outer wall 904. The third plurality of blades 906 have an axial solidity of 1.2 at the third hub 902, and an axial solidity of 1.0 at the third outer wall 904.

(103) The third plurality of blades 906 have a sweep of 0°. The third plurality of blades 906 have a lean of −0.1° at the third hub 902, and a lean of −0.1° at the third outer wall 904.

(104) The first diffuser stage 700 comprises 11 blades 706, and has an axial length of 13 mm. The second diffuser stage 800 comprises 23 blades 806, and has an axial length of 8 mm. The third diffuser stage 900 comprises 23 blades 906, and has an axial length of 7 mm.

(105) As indicated above, forming the first 700, second 800, and third 900 diffuser stages as separate components enables the use of a wider range of blade geometries, which may provide performance benefits, for example in terms pressure recovery and acoustics.