Impeller and motor assembly

Abstract

A breathing assistance apparatus has a pressurised gases source featuring a lightweight impeller with a plastic shaft. The impeller is shroudless. The plastic shaft is supported within the stator by a bearing structure. The resilient motor mount couples the stator and the housing and provides compliance and/or damping for the motor.

Claims

1. A breathing assistance apparatus comprising: a pressurised gases source comprising: a housing, a gases inlet, a gases outlet configured to emit pressurised gases, and a motor comprising: a rotor comprising a central opening, the central opening comprising a central portion with an indent, a rotatable shaft arranged to extend through the central opening, a one-piece plastic insert in contact with the rotatable shaft and the indent of the central opening, thereby directly coupling the rotatable shaft to the rotor, and at least one bearing structure that supports the rotatable shaft within a stator.

2. The breathing assistance apparatus according to claim 1, wherein the at least one bearing structure comprises one or more flexible and/or resilient bearing mounts that provides compliance and/or preload and/or damping for the rotatable shaft.

3. The breathing assistance apparatus according to claim 1, further comprising a lightweight impeller coupled to the rotatable shaft.

4. The breathing assistance apparatus according to claim 1, further comprising a flexible and/or resilient motor mount that couples the stator and the housing to provide compliance and/or damping for the motor.

5. The breathing assistance apparatus according to claim 1, wherein the pressurised gases source further comprises a partition to define first and second interior regions within the housing, wherein the first and second interior regions are fluidly connected by a crescent shaped opening formed in or by the partition.

6. The breathing assistance apparatus according to claim 1, wherein the indent spans a full vertical thickness of the rotor immediately adjacent to the indent.

7. The breathing assistance apparatus according to claim 1, wherein the one-piece plastic insert prevents relative motion between the rotor and the rotatable shaft.

8. The breathing assistance apparatus according to claim 1, wherein the central portion of the central opening comprises four indents.

9. The breathing assistance apparatus according to claim 8, wherein each indent of the four indents is equidistant from adjacent indents.

10. The breathing assistance apparatus according to claim 1, wherein the indent is substantially rectangular.

11. The breathing assistance apparatus according to claim 1, wherein the rotatable shaft is metal.

12. The breathing assistance apparatus according to claim 1, wherein the rotatable shaft comprises a relatively rough section that engages with the one-piece plastic insert.

13. The breathing assistance apparatus according to claim 12, wherein the relatively rough section is a knurled section.

14. The breathing assistance apparatus according to claim 1, wherein the rotatable shaft comprises a hexagonal cross-section.

15. The breathing assistance apparatus according to claim 1, wherein the one-piece plastic insert has a radially outermost surface that is between an outer surface of the rotatable shaft and an outermost surface of the rotor.

16. A breathing assistance apparatus comprising: a pressurised gases source comprising: a housing; a gases inlet, a gases outlet adapted to emit pressurised gases, and a motor comprising: a rotor comprising a central opening, the central opening comprising a central portion with an indent, a rotatable plastic shaft being formed with an integrated portion that is arranged to engage with the indent, thereby coupling the rotatable plastic shaft to the rotor, and at least one bearing structure that supports the rotatable plastic shaft within a stator.

17. The breathing assistance apparatus according to claim 16, wherein the at least one bearing structure comprises one or more flexible and/or resilient bearing mounts that provides compliance and/or preload and/or damping for the rotatable plastic shaft.

18. The breathing assistance apparatus according to claim 16, further comprising a lightweight impeller coupled to the rotatable plastic shaft.

19. The breathing assistance apparatus according to claim 18, wherein the lightweight impeller is shroudless.

20. The breathing assistance apparatus according to claim 16, further comprising a flexible and/or resilient motor mount that couples the stator and the housing to provide compliance and/or damping for the motor.

21. The breathing assistance apparatus according to claim 16, wherein the pressurised gases source further comprises a partition to define first and second interior regions within the housing, wherein the first and second interior regions are fluidly connected by a crescent shaped opening formed in or by the partition.

22. The breathing assistance apparatus according to claim 16, wherein the indent spans a full vertical thickness of the rotor immediately adjacent to the indent.

23. The breathing assistance apparatus according to claim 16, wherein the rotatable plastic shaft prevents relative motion between the rotor and the rotatable plastic shaft.

24. The breathing assistance apparatus according to claim 16, wherein the central portion of the central opening comprises four indents.

25. The breathing assistance apparatus according to claim 24, wherein each indent of the four indents is equidistant from adjacent indents.

26. The breathing assistance apparatus according to claim 16, wherein the indent is substantially rectangular.

27. The breathing assistance apparatus according to claim 16, wherein the rotatable plastic shaft comprises a hexagonal cross-section.

28. The breathing assistance apparatus according to claim 16, wherein an outermost surface of the rotatable plastic shaft is radially inward of an outermost surface of the rotor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A preferred form of the present invention will now be described with reference to the accompanying drawings.

(2) FIG. 1 shows a schematic view of a modular assisted breathing unit and humidifier system.

(3) FIG. 2 shows a schematic view of a modular assisted breathing unit and humidifier system.

(4) FIG. 3 shows a plan view of an example of a blower unit.

(5) FIG. 4 shows a side view of the blower unit of FIG. 3.

(6) FIG. 5 shows a profile view of an impeller.

(7) FIG. 6 shows another profile view of an impeller.

(8) FIG. 7 shows a profiled view of a gases supply unit.

(9) FIG. 8 shows an exploded view of the gases supply unit of FIG. 7.

(10) FIG. 9 shows an internal view of a gases supply unit (viewed from underneath).

(11) FIG. 10 shows a profiled view of the gases supply unit of FIG. 9.

(12) FIG. 11 shows a plan view of the top side of a blower unit of one embodiment.

(13) FIG. 12 shows a plan view of the bottom side of the blower unit of FIG. 11.

(14) FIG. 13 shows a profile view of the bottom side of the blower unit of FIG. 12

(15) FIG. 14A shows a plan view of the impeller with no shroud according to one embodiment.

(16) FIG. 15A shows a profile view of the impeller of FIG. 14a with no shroud.

(17) FIG. 14B shows a plan view of the impeller with reduced shroud material according to one embodiment.

(18) FIG. 15B shows a profile view of the impeller of FIG. 14b with reduced shroud material.

(19) FIG. 14C shows a plan view of the impeller with a web structure.

(20) FIG. 15C shows a profile view of the impeller of FIG. 14c with a web structure.

(21) FIG. 16 shows an exploded view of the preferred housings and impeller of one embodiment.

(22) FIG. 17 shows a plan view of the lower housing, partition and impeller of one embodiment.

(23) FIG. 18 shows a profile view of the components of FIG. 17.

(24) FIG. 19 shows a cross sectional view of the motor and impeller of one embodiment.

(25) FIG. 20 shows a motor mounting structure one embodiment.

(26) FIG. 21 shows the motor mounting structure with a motor and impeller of one embodiment.

(27) FIG. 22A is a graph of average sound pressure levels of an earlier blower unit.

(28) FIG. 22B is a graph of average sound pressure levels of the blower unit of the present invention.

(29) FIG. 23 shows the motor mounting structure with a motor and impeller of a second embodiment.

(30) FIG. 24 shows a stator lamination of the second embodiment.

(31) FIG. 25 shows a pole face of the second embodiment.

(32) FIG. 26 shows a bearing mount of the second embodiment.

(33) FIG. 27 shows a cross sectional view of the motor and impeller of the second embodiment.

(34) FIG. 28 shows a motor mounting structure of the second embodiment.

(35) FIG. 29A is a pressure response graph of an earlier blower unit.

(36) FIG. 29B is a pressure response graph of the blower unit of the present invention.

(37) FIGS. 30A, 30B show a metal shaft and magnet rotor assembly forming part of a motor.

(38) FIG. 31 shows the metal shaft of the assembly in FIGS. 30A, 30B.

(39) FIG. 32 shows a plastic shaft and magnet rotor assembly forming part of another embodiment of the motor.

(40) FIGS. 33A and 33B show an injection moulding tool for manufacturing the plastic shaft and rotor assembly of FIG. 32.

(41) FIG. 34 shows a flow diagram of an injection moulding process for the metal shaft/insert rotor assembly.

(42) FIG. 35 shows a flow diagram of an injection moulding process for the plastic shaft rotor assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(43) The present invention will be described with reference to a breathing assistance apparatus/system where the humidifier chamber is integrated with the gases supply unit (also referred to as a respirator unit or blower unit). However, it should be noted that the system is equally applicable to a modular system.

(44) The present invention relates to a lightweight/low inertia impeller. The lightweight nature of the impeller provides low inertia.

(45) An example of an integrated gases supply unit 7 with which embodies the present invention is shown in FIG. 7—this is one example and should not be limiting. The integrated unit 7 comprises two main parts: a gases supply unit or blower unit 8 and a humidifier unit 9. Humidification unit 9 is partially enclosed within the external shell 80 of the blower unit 8 in use, except for the top of the humidification unit 9. It also comprises an internal controller 14 such as a microcontroller, microprocessor or similar for controlling the blower unit and other operations, such as that shown schematically in dotted lines. It is not necessary to describe the structure and operation of the humidification unit 9 in detail in order to fully describe the present invention.

(46) The body of the gases supply unit 8 has the form of a generally rectangular block with substantially vertical side and rear walls, and a front face that is angled slightly rearwards (all the walls can be angled inwards slightly if required). In the preferred embodiment, the walls, base and top surface are all manufactured and connected as far as possible to minimise the occurrence of seams, and any necessary seams are sealed. As shown in FIG. 7, the gases supply unit 8 includes a control knob 11, located on the lower section of the front face of the gases supply unit 8, with a control display 12 located directly above the knob 11. A patient outlet 30 is shown passing out of the rear wall of the gases supply unit 8. In the preferred embodiment, the free end of the outlet 30 faces upwards for ease of connection. The patient outlet 30 is adapted to allow both pneumatic and electrical connection to one end of a conduit—e.g. conduit 3—running between the integrated unit 7 and a patient interface—e.g. interface 5. An example of the type of connector that can be used and the type of dual connection that can be made is described in U.S. Pat. No. 6,953,354. It should be noted that for the purposes of reading this specification, the patient interface can be thought of as including both the interface 5 and the conduit 3 where it would be appropriate to read it in this manner.

(47) The internal structure and components of the gases supply unit 8 will now be described with reference to FIGS. 8, 9 and 10. The gases supply unit 8 includes an enclosing external shell 80 which forms part of, and encloses, the gases supply unit 8. The shell 80 includes internal air passages for ducting air passing through the gases supply unit 8, and also internal recesses, cavities or slots into which components of the gases supply unit 8 is located in use. The shell 80 of the gases supply unit 8 is further adapted to include an open-topped compartment 13. In use, humidifier chamber 9 is located within the compartment 13. Blower unit 8 includes a heater base or heater plate, located at the bottom of the compartment 13. A humidifier inlet aperture 15 and humidifier outlet aperture 16 are located on the wall of the compartment 13, towards the top of the compartment 13. In the preferred embodiment, the inlet and outlet apertures 15, 16 are aligned so as to mate with inlet and outlet humidifier ports 17, 18 located on the humidifier chamber 9, when the system is in use. It should be noted that other forms of humidifier inlet are possible. For example, a conduit running between the gases supply unit 8 and e.g. the lid of the humidifier chamber 9. Also, if the humidifier chamber is a separate item (that is, not rigidly connected to the gases supply unit in use), the humidifier inlet aperture 15 will not be connected directly to the humidifier chamber, but will be connected instead to one end of a conduit or similar leading from the humidifier inlet aperture on the gases supply unit, to the humidifier chamber.

(48) Air from atmosphere is drawn into the shell of the gases supply unit 8 through an atmospheric inlet vent 19. This vent 19 can be located wherever is convenient on the external surface of the shell of the gases supply unit 8. In the preferred embodiment, as shown in FIG. 9 (viewing the housing from underneath), the inlet vent 19 is located on the rear face of the shell of the gases supply unit 8, on the right hand side of the rear face (right hand side when looking forwards). In the preferred embodiment, air is drawn in through the inlet vent 19 by means of a fan unit 20 which forms part of the gases supply unit 8, and which is located inside the enclosing external shell of the gases supply unit 8. The fan unit 20 provides a pressurised gases stream for the gases supply unit and therefore the assisted breathing system. The fan unit 20 will be described in more detail below. The air is drawn into the fan unit 20 indirectly, via a curved inlet path 22 formed through the shell of the gases supply unit 8. Path C runs from the inlet vent 19 up over the power supply cavity and though the venturi (shown in dotted lines) past into curved path 22 (including absorber foam channel and through a thermistor flow sensor) to an aperture 23 formed in the gases supply unit shell 80, the aperture 23 passing into a recess/plenum 21 which is formed in the gases supply unit shell 80, in which the fan unit 20 is located. The air then passes into the inlet 27.

(49) The gases stream passes through the fan unit 20 to the humidifier inlet aperture 15 as follows: the shell of the gases supply unit 8 includes a chamber or outlet duct 26 which forms at least part of an outlet air path to allow gaseous communication between the fan unit 20 and the humidifier inlet aperture 15. In the preferred embodiment, the outlet duct 26 runs up between the right hand side wall of the gases supply unit 8 (from behind looking forwards) and the front wall, up to the humidifier inlet aperture 15. As shown in FIGS. 9 and 10, air exiting the fan unit 20 enters the duct 26.

(50) In use, air exits the shell of the gases supply unit or blower 8 via the humidifier inlet aperture 15 and enters the humidifier chamber 9. In the preferred form, the humidifier inlet aperture 15 forms an outlet at the end of the duct 26. The gases are humidified and heated in the chamber 9, before passing out of the chamber 9 through the humidifier outlet aperture 16, which is directly or indirectly connected to the patient outlet 30 (it should be noted that the outlet of the humidifier chamber 9 could also be completely separate from the gases supply unit 8). The heated humidified gas is then passed to the user 1 via conduit 3. The patient outlet 30 is adapted to enable pneumatic attachment of the patient conduit 3, and in the preferred embodiment, outlet 30 is also adapted to enable electrical connection via an electrical connector. A combined electrical and pneumatic connection can be useful for example if the conduit 3 is to be heated. Electrical heating of a conduit such as conduit 3 can prevent or minimise the occurrence of condensation within the conduit 3. It should also be noted that the outlet connection does not have to be via the shell of the integrated unit 7. If required, the connection for the conduit 3 could be located directly on an outlet from humidifier chamber 9.

(51) The blower unit 8 in use is set to a user-specified pressure level and/or the pressure level can be automatically controlled. The flow rate for the preferred embodiment will vary during use, depending on the users breathing. The power to fan unit 20 can be altered, to change the speed at which the impeller 24 is rotating, and therefore the pressure.

(52) The structure of the fan unit 20 according to one embodiment shall now be described, with particular reference to FIGS. 11, 12 and 13. The fan unit 20 is located in recess 21 of the shell of the gases supply unit 8 in use, as described above with reference to FIGS. 9 and 10. In the preferred form, the fan unit 20 comprises a rotating impeller located inside a casing having the form of a snail or scroll casing 25.

(53) It can be seen that the fan unit 20 appears generally circular in plan view, as shown in FIGS. 11 and 12. The fan casing 25 includes an inlet aperture 27. In the preferred form, inlet aperture 27 is a circular hole located in approximately the centre of the casing 25 and passing from the outside of the casing to the inside. Air from the inlet path 22 (see FIG. 10) enters the fan casing 25 via the inlet aperture 27. It should be noted that where it would be appropriate to include the aperture 23 and at least part of the recess 21 as part of the air inlet path, the specification should be read as including these elements. The preferred form of the casing 25 of the fan unit 20 also includes an outlet passage 28.

(54) In the preferred form, the outlet passage 28 is a short passage formed as an integral part of the casing 25 and aligned substantially tangentially to the circumference to the remainder of the generally circular casing 25. A fan casing outlet aperture or exit aperture 29 (see e.g. FIG. 13) is located at the outer end of the passage 28. It should be noted that the fan casing exit aperture 29 could be located wherever is convenient on the passage 28 (i.e. it does not have to be at the end of the passage, it could be through the passage wall partway along its length, for example). Exit aperture 29 opens into the duct 26. The outlet passage 28 forms part of the air path from the fan to the humidifier inlet aperture 15.

(55) The fan casing 25 encloses the fan in use, except for the inlet aperture 27 and the exit aperture 29 of the passage 28. In the preferred embodiment, rotation of the fan unit 20 is driven by a motor, the fan or impeller unit being adapted for connection to the motor. Air or gases are drawn through inlet aperture 27 in the centre of the casing 25, into the centre of the impeller unit 24, and are then forced outwards as a gases stream through the exit aperture 29 of the outlet passage 28 by the impeller blades 31 as the impeller unit 24 rotates.

(56) In the preferred form, the fan outlet passage or exit passage 28 has a generally rectangular cross-section, and the exit passage 28 is aligned substantially tangentially to the casing 25. However, the cross-section of the fan outlet passage 28 could be any suitable shape, such as oval, rectangular or circular. The fan outlet passage 28 could also be arranged at any suitable angle to the impeller unit, for example facing radially outwards, or at any suitable angle between tangential and radial. The fan outlet passage 28 causes the gases forced outwards by the impeller unit 24 to coalesce as a fluidic gases stream, and dictates the direction in which the gases stream flows. The overall path or overall direction of the gases flow will be along the passage from the fan towards the fan casing exit aperture 29.

(57) The preferred form of the impeller shown in FIGS. 14 and 15. The impeller 24 has a plurality of blades 31 extending outward from a central hub 32. The impeller is a centrifugal impeller. The hub 32 defines the axis about which the impeller rotates. Preferably the hub 32 has an aperture or recess on the underside to allow engagement with a motor shaft which facilitates impeller rotation. However, other engagement mechanisms, such as over moulding of the hub with a shaft, could be used. When the impeller is rotated, air enters the impeller blades in the region proximate the hub 32, travels radially outward and exits the blades proximate the blade tips 33. The impeller is preferably made in one piece (“one piece construction”), as opposed to moulded in multiple parts and joined. This is possible when there is no shroud—or at most one shroud. This reduces misalignment of components that might lead to imbalance or other disadvantages. In the preferred embodiment there is no shroud (in contrast with for example the shroud 152 shown in FIGS. 5 and 6.)

(58) The blades 31 preferably provide a substantially flat surface, from the hub 32 to the blade tip, and incident the direction of rotation to thereby centrifuge gases. Preferably the tips of the impeller blade tips 33 partially curve in the direction of impeller rotation (“arrow “A”). That is, the blade tips 33 are forward swept. Forward swept blade tips help to impart stronger rotational forces on the gases flowing through the impeller than straight or backswept blades. The forward swept blade tips help to produce a high pressure annulus between beyond tip of each blade. The inner portion 31 of the impeller blade may be somewhat backswept. A backswept blade allows for some recirculation of gases on the blade surface itself. The backswept inner blade portion may be beneficial to increase pressure generation and allow for stable low and reverse gases flow.

(59) The impeller is constructed to be lightweight. Preferably, this is by making the impeller shroudless, or at least partially shroudless, thereby removing weight. To achieve a lightweight impeller, as shown in FIGS. 14a and 15a, each of the blades 31 of the preferred impeller 24 are open between the blades (that is, the upper and lower “faces” or “planes” of the impeller are open to the internal surfaces of the housing of the fan unit 20) thereby defining a shroudless centrifugal impeller. By omitting a shroud on both the upper and/or lower faces of the impeller blades, the weight of the impeller 24 can be substantially reduced. The weight of the impeller can also be reduced in other ways, in addition to or alternatively to omitting the shroud. For example, a lightweight material can be used. Also, thin blades with minimal material and large gaps between blades could be implemented to reduce weight. Alternatively, a shroud 35 with some of the material removed, such as shown in FIGS. 14b, 15b could be used. A scalloped shaped 36 shroud is provided whereby some of the material between blades 31 is removed. Any suitable amount of material could be removed. A shroud channels air from the impellers. Where significant material is removed, the resulting structure may in fact no longer carry out this function of a shroud but rather just provide support for impeller blades 31. In this case, the impeller 24 may still be considered shroudless, despite having some structure between impeller blades 31. In yet a further embodiment shown in FIGS. 14c, 15c the structure between the impeller blades is a webbing that is disposed centrally between impellers. Such as structure does not function as a shroud. The reduced material structure or webbing 36 can be of any shape (not just scalloped) or extent, of which FIGS. 14b, 15b, 14c, 15c show two examples. A lightweight impeller 24 provides benefits such as manufacturing cost, low rotational inertia and is balanced or requires little effort to rotationally balance once manufactured. An impeller with low rotational inertia can be quickly accelerated and decelerated. A lightweight, shroudless impeller is therefore suited for quickly responding to fluctuating pressure requirements, such as the normal inhalation and exhalation cycle of a patient connected to the breathing assistance device in which the impeller operates.

(60) For example, a conventional shrouded impeller commonly used on a breathing assistance device, weighing approximately 17 grams and having inertia of 6 kg.Math.mm2, can respond to pressure fluctuations of 10 cmH2O in approximately 2 seconds. By contrast, the preferred impeller, weighing approximately 1.7 grams and inertia of 0.5 kg.Math.mm2, responds pressure fluctuations of 10 cmH2O in approximately 100 ms. FIG. 29A shows a graph of pressure verses time for the earlier impeller weighing 17 grams. The impeller is operated to attempt to maintain a constant pressure of 4 cmH2O during the normal inhalation and exhalation cycle of a patient. In comparison, FIG. 29B shows a graph of pressure verses time for the preferred impeller 24. It can be seen that the decrease in mass and rotational inertia over the earlier impeller exhibits much less pressure fluctuation that the impeller of FIG. 29A. The reduced pressure fluctuation is less disruptive to a patient's breathing process, and therefore advantageously increases patient comfort.

(61) As mentioned, the lightweight can be achieved by omitting a shroud. However, it is not necessary to omit the entire shroud—rather just sufficient shroud to bring the weight of the impeller to a suitable level—such as shown in FIGS. 14B, 15B, 14C, 15C. Therefore, lightweight can be achieved by having as much open space (area or volume) between the blades as possible. The open space can be defined in terms of the blade volume to blade sweep volume ratio/percentage. That is, the blades sweep a volume X when rotating and the blades themselves have a combined volume Y (which is the volume of each blade combined). Alternatively, from a plan perspective, the open space can be defined in terms of the blade area to the blade sweep area. The ratios should be kept as low as possible. In one embodiment, for example the swept volume of the impeller is approximately 19,000 mm3, where the blades constitute a volume of approximately 1,200 mm3. The ratio of swept volume to blade volume is therefore approximately 16:1, thereby defining an impeller that is lightweight compared to the smaller, more densely designed and heavier impellers used earlier.

(62) The lightweight impeller can have a weight for example of less than 2 grams and preferably between 0.8 and 1.8 grams, or more preferably, between 1.2 and 1.7 grams, or even more preferably 1.7 grams. These are just examples or a preferred embodiment and the impeller need not be this weight, but some other weight that renders it lightweight.

(63) Alternatively, a lightweight impeller can be designed to remove as much of the shroud as necessary to bring the moment of inertia to radius ratio down to preferably less than 15 gram*mm, and more preferably between 8-12 gram*mm and in one possible embodiment approximately 11 gram*mm. For example, in one possible embodiment, such an impeller can have a radius of 35 mm, a circumference of 219 mm, and at 15,000 rpm a moment of inertia of 344.22, a tip speed of 54.98 m/s, a pressure of 1,800 Pa and a tip speed to inertia to radius ratio of 3.5 or more and for example 5.59. More generally, a lightweight impeller could have dimensions/parameters within the following ranges (note these ranges are indicative—not limiting): radius: 15 mm-60 mm; and/or weight: less than 2 grams.

(64) A pressure ratio to inertia to radius ratio of greater than 50:1 Pascals per gram*mm and preferably 80:1 Pa per gram*mm or more at 1,000 Pa.

(65) Lightweight impellers enable larger radius impellers to be used. Yet larger radius impellers can be used than those mentioned above. Larger radius impellers provide greater tip speed and pressure. The construction of the impeller allows for greater radius impellers because the lightweight nature of the impeller is such that even with larger impellers, the inertia is still low enough to provide the required response and pressures.

(66) The lightweight nature of the impeller can be achieved through removing mass through any suitable means, such as removing the shroud and/or material from the impeller and/or using lighter materials. One possible manner in which to reduce impeller mass is to reduce the number of blades.

(67) The impeller generates a high pressure annulus between the tip and inner face of the housing. The backward facing impeller with a forward sweep at the tip also allows for recirculation on the blade itself, which helps with increased pressure generation and stable flow and reverse flows.

(68) The fan unit 20 as shown in FIGS. 11 and 12 and described above is shown in exploded form in FIG. 16. The blower has an upper housing layer 50 and a lower housing layer 51 that assemble to encapsulate a partitioning layer 52 and the impeller 24. The blades of the impeller are open to the internal surfaces of the upper and lower housing layers. The partition layer 52 and the inner surface of the upper layer 50 are profiled to substantially enclose the impeller blades when the layers are assembled. This forms a first interior region (“upper region”). The upper housing layer 50 has the aperture 27 that defines the gases entry into the blower. The lower housing layer defines a volute 53 where gases are collected before emission from the blower. Preferably the volute 53 also has a sealing inner wall 56. The wall 56 defines a space internal to the lower housing that may be used to house a motor. The lower housing layer 51 and the partition 52 form a second interior region (“lower region”).

(69) The outlet passage 28 of the fan unit 20 is connected to the volute 53 via an aperture 54. The aperture 54 and the volute wall 53 define a tongue 55 whereby gases circulating in the volute 53 are diverged into the outlet passage 28.

(70) The partition layer 52 is generally circular and substantially divides the upper housing 50 from the lower housing 51 thereby defining the upper and lower gases flow (interior) regions of the blower. To allow gases to flow from the upper region to the lower region an aperture (opening) 57 is located at, or close to the outer edge of the partition. The aperture 57 is shown more clearly in FIGS. 17 and 18. The aperture 57 is most preferably an opening formed by a cut-away in the partition layer 52, or some other configuration/shape of the housing 51 such that the combination/arrangement of the partition layer 52 and the housing 51 creates an aperture/opening between the two. However, the aperture 57 may also comprise a flow path formed separately to the partition layer, such as a bulge or fluid channel formed in the walls of the upper 50 and lower housings 51. The cut-away could form a circumferential aperture 57 between the housing 51 and partition 52, for example. The curvature/centre of radius of the circumferential aperture 57 is preferable offset from the centre of radius of the partition 52 or otherwise has a curvature that differs from that of the circumference of the partition 52 resulting in an eccentric or otherwise offset circumferential aperture 57 around the circumference of the partition 52 as shown in the Figures. This produces an aperture 57 with a crescent (“smile”) shaped opening that spans a leading edge 58 to a trailing edge 59. However, the aperture may be of any shape with a gradual opening and closing relative to the plane of impeller rotation. The aperture allows for gradual supply of pressure and flow from the high static pressure source at the top of the blower. The angle of the aperture opening and closing is tuned to allow for reverse flow to return through the system in a stable fashion. It also contributes to the blade pass noise reduction by not having a sharp break in geometry. The aperture provides addition tongues, as well as that on the outlet. The gradual opening and closing of the aperture (“tapers”) provides tongues. The maximum velocity at the outlet (e.g. 10 m/s) is less than that at the tapers (e.g. 60 m/s). The gradual opening and closing with blades passing at that speed manages blade pass noise. The width and length of the aperture 57 controls the velocity in the lower (volute) section of the housing. A wider and longer aperture increases velocity in the volute, for example.

(71) During operation of the blower, the impeller 24 is rotated in direction A—see FIG. 17. The rotation of the impeller 24 draws gases through the inlet 27 and through the blades 31 toward the outer wall of the upper housing layer 50. During operation, air B can also be drawn through the stator/rotor from the other side of the housing—see e.g. FIG. 13. The air B drawn through can cool the motor. The shroudless impeller 24 enables air to be drawn through the motor in this manner thus providing cooling. The forward swept blade tips 31 impart strong rotational forces to the gases circulating in the upper region of the blower housing to thereby create high circulating gas speeds. Gases in the upper region will naturally flow through the aperture 57 to the lower region due to pressure differential between regions. When the gases in the upper region, having a high velocity and low pressure, enter the lower region, specifically the volute 53, the gas velocity drops and the pressure increases. Typically the volute 53 has a greater volume than the upper region to help facilitate a gases pressure increase.

(72) By dividing the blower internal space into two separate regions a number of advantages can be realised. In a conventional blower, high velocity gases leaving the impeller are incident to the edge, or tongue, that defines a physical boundary where gases are split from the volute to enter the outlet passage. High velocity gas flow at incident the tongue is turbulent and inefficient to blower performance. The turbulence caused by the tongue reduces also introduces a source of noise. In contrast, dividing the housing of the preferred blower into the upper and lower regions reduces the impact caused by the tongue. The upper region allows the gases to circulate at a high speed. The gradual radial opening and closing of the preferred partition 57 provides a fluid path to the lower region that is free from (or has reduced) aerodynamically turbulent edges. When circulating gases have entered the lower region, the enlarged volume of the volute encourages the gases to slow and increase pressure. The reduced gases velocity reduces the impact of turbulence normally caused by the tongue 55 to a low or negligible level. The blower unit is therefore able to operate across a wide pressure and flow range with substantially reduced noise output when compared to other blowers. A wider and longer aperture 57 increases the flow rate of the lower region relative to the upper region. Therefore, the size of the aperture is selected according to the desired flow rate and pressure range of the blower unit.

(73) The motor used to drive the impeller 24 is shown in cross section in FIG. 19. Preferably the motor is a brushless DC motor operated using sensorless vector control (also termed “field oriented control”) controlled by a microcontroller, microprocessor or similar controller 14 (such as shown in FIG. 7), for example, via the connector 131 mounted to a PCB 130. The control can be tuned to suit a low inertia impeller. The central hub 32 of the impeller 31 is engaged with a shaft 60 that extends from the motor 61. Mounted to the shaft is a plurality of, preferably small, magnetic segments to form a rotor 62. In one embodiment the magnet is 20 mm in diameter, but more generally the diameter could be less than 20 mm and preferably between 10 mm to 15 mm. The magnet volume is less than 1600 mm3 and can be between 500 mm3 and 1600 mm3. Surrounding the rotor 62 is a laminated stator having a plurality of poles 63 and windings 68. The stator is mounted to the PCB or other substrate 130 and the windings coupled to the connector 131. The windings are selectively energised by the microcontroller 14 via the connector 131 to facilitate rotation of the rotor, and therefore the shaft 60 and impeller 31, about the central axis defined by the centreline of the shaft 60.

(74) The shaft 60 is held within the motor by a bearing structure. Preferably the bearing structure has one or more bearings 64 and one or more bearing mounts 65. The bearing mounts 65 as shown engage with the bearings on an inner surface and with the stator on an outer surface. The preferred engagement of the mount to the bearings and the stator is frictional. To promote a frictional engagement, the bearing mounts 65 are made of a soft, yet resilient and/or flexible material such as silicone rubber or other elastomeric material. The material can be low creep, temperature stable, low compression set with a high tan delta (highly viscous), highly damped. Examples comprise: Dough Moulding Rubbers like—NBR, Nitrile and Fluoro silicone; Thermo Plastic Elastomers (TPE's) like Santoprene by Exxon; Thermo Plastic Urethanes like Dynaplast by GLS Corporation; Heat Cured. Casting Urethanes like 10T90 by National Urethanes; and multiple other cold cast rubbery compounds like RTV (Room Temperature curing Vulcanites) by Dow Corning, Whacker and others. In another embodiment, bushings (rubber or otherwise) could be used instead of bearings.

(75) Such materials allow the mounts 65 to compress when installed, then expand into their chosen location to be held in place by engagement expanded dimension with a restriction. The mounts 65 are optionally restrained by an overhang 66 formed as part of an electrical insulator/isolator or other frame structure (“stator frame”) on the stator. Similarly, the bearings may be restrained by an overhang 67 formed as part of the bearing mount. Either or both of the overhangs may be discretely positioned about the inner and outer annulus of the bearing mounts, or alternatively, extends around the circumference of the mount to define a recess in which the mount is located.

(76) The bearing mounts provide compliance to the rotatable shaft 60. As rotatable objects, such as the rotor 62, shaft 60 and impeller 31 usually suffer from some degree of rotational imbalance, the bearing mounts are able to isolate inherent rotation induced vibration from the motor rotor. It has been found that combination of the lightweight, shroudless impeller having a low rotational inertia, as described above, together with the given compliance of the bearing mounts enables the rotor 62, shaft 60 and impeller 31 to be manufactured and any post manufacture balancing process for the rotating components entirely omitted. These advantages benefit manufacturing costs and time. The lightweight nature of the impeller allows any imbalances to be compensated by the bearing mounts. A lightweight impeller also allows faster speed response of the impeller to changing conditions. Any unwanted fluctuations in pressure due the lack of shroud can be compensated for by quickly changing the impeller speed to return pressure to the desired level.

(77) It should be noted that while FIG. 19 shows the bearing mounts 65 mounted within the motor stator, they may equally be housed externally to the motor. For example, the mounts 65 may instead be mounted within journals formed within the blower housings, or the gases supply unit 7. In such circumstances where the bearing mounts are located within the gases supply unit 7, it may also be advantageous to omit discrete structures for the blower housing 50, 51, instead mounding the inner surfaces of the housings directly to the internal structure of the gases supply unit 7.

(78) To provide further vibration damping of the rotational components of the blower, the motor and impeller, can optionally be mounted on a compliant mounting device. FIG. 20 shows one embodiment of such a mounting device 70. In accordance with the preferred embodiment of the invention the mount is most preferably made from a soft, flexible yet resilient material such as silicone rubber. The mounting device 70 has an internal recess 71 in which the stator is relieved. Preferably the internal recess is smaller than the outer surface of the motor to encourage an interference fit between these components. FIG. 21 shows the motor 61 positioned within the mounting recess 71.

(79) A plurality of projections 72 encircles the upper and lower surfaces of the mount 70. Each projection 72 preferably has a base recessed into the body of the mount to effectively increase the length whereby the projections are free to bend. The end of projection extends past the upper and lower surfaces of the mount to provide supporting leverage to the mount and motor assembly. During operation of the motor, vibration caused by any imbalance of the rotational components is absorbed by each of the projections by allowing the body of the mount 70 to move relative to the surface on which the projections 72 are supported.

(80) FIG. 22A is a graph of the sound pressure level of a conventional fan unit tested in an anechoic chamber. FIG. 22B is a graph of the sound pressure lever of a fan unit according to the present invention. It can be seen that the lightweight and shroudless impeller 24, the flexible bearing mounts 65 and flexible motor mount 70 contribute to a significantly reduced noise output across the tested spectral range of 50 Hz to 10 kHz.

(81) A further embodiment of the motor and impeller assembly is shown in FIGS. 23 to 28. Many aspects of this embodiment are the same as those in the previous embodiment. Features described in relation to the previous embodiment not described in this embodiment can be assumed to exist in this embodiment where appropriate. Like features will use the same reference numerals as the previous embodiment. The motor used to drive the impeller 24 is shown in cross-section in FIG. 27. Preferably the motor is a brushless DC motor operated using sensorless vector control (“field oriented control”) controlled by a microcontroller, microprocessor or similar controller 14 (such as shown in FIG. 7), for example, via a connector 231 mounted to a PCB/substrate 230 (such as shown in FIG. 23). The control can be tuned to suit a low inertia impeller. Referring to FIGS. 23, 24 and 27, the central hub 32 of the impeller 24 is engaged with a shaft 60 that extends from the motor 61. Mounted to the shaft is a plurality of, preferably small, magnetic segments to form a rotor 62. Surrounding the rotor 62 is a laminated stator 241 having an annular outer portion 242 and a plurality of poles 243 and windings 68. The stator is mounted to the PCB or other substrate 230 and the windings 68 coupled to the connector 231. The stator 241 has an electrical insulator/isolator (forming a stator frame) 270a, 270b covering the top and bottom of the annular portion 242 and the poles 243. Each winding 68 is preferably assembled on the insulator 270a, 270b over each pole 243. Protrusions for engagement and retainment are provided around the circumference 271 extending upwards and at the end of the poles extending upwards 272a and downwards 272b.

(82) Referring to the plan view of one of the laminations 240 in FIG. 24, each lamination comprises an annular outer portion 242 and a pole portion 243 extending radially inwards. The edge 244 of each pole portion 243 includes a wave shape. The wave shape comprises two concave portions 244a. 244b meeting at a central apex 244c. Referring to FIG. 25, when a plurality of the laminations 240 are stacked to create the stator 241, each pole 243 has an inner radial face 250 with a wave shape as shown in FIG. 25, The face 250 comprises two concave portions 250a, 250b meeting at a central apex 250c. This arrangement reduces cogging. The stator and/or rotor can have a skewed magnetization. The windings are selectively energised using the controller 14 via the connector 231 to facilitate rotation of the rotor, and therefore the shaft 60 and impeller 31, about the central axis defined by the centreline of the shaft 60.

(83) The shaft 60 is held within the motor by a bearing structure. Preferably the bearing structure has one or more bearings 64 and one or more bearing mounts 260 (see FIG. 26). The bearing mounts 260 as shown engage with the bearings 64 on an inner surface 261 and with the stator 241/insulator 270a/270b on an outer surface as shown in FIG. 27. The bearing mount 260 comprises a main annular body 265 that curves from a low point at a central aperture 263 to a higher point at the outer circumference 262. The outer circumference comprises an engaging lip 264, preferably with a chamfer 264a on the intersection of the outer circumference 262 with the main annular body 265. The intersection of the inner aperture 263 with the inner circumference 261 of the main body 265 also preferably has a chamfer 261a. An annular wall/boss 266 extends upwardly from the main annular body 265 at the inner aperture 263. The top portion 267 of the annular wall 266 has an overhanging engagement lip 268. The intersection of the lip 268 with the annular wall 266 and with the overhanging lip side wall 268a are preferably chamfered 268b, 268c. The preferred engagement of the bearing mount 260 to the bearings 64 and the stator 241 is frictional. To promote a frictional engagement, the bearing mounts 260 are made of a soft, yet resilient and/or flexible material such as silicone rubber or other elastomeric material. The material can be low creep, temperature stable, low compression set with a high tan delta (highly viscous), highly damped. Possible materials were described in relation to the previous embodiment. Such materials allow the mounts 260 to compress when installed, then expand into their chosen location to be held in place by engagement expanded dimension with a restriction. They also provide compliance.

(84) FIG. 27 shows the bearing mounts in solid lines in the uninstalled/unassembled state, with an upward curvature. The dotted lines show the bearing mounts 260 in the installed/assembled state, clipped in to the stator/insulator 279a, 270b. In the installed state (also called engaged state or configuration) the annular body is engaged with the stator 241 and/or stator frame 270a, 270b and the annular body 265 is coerced from the curved state (shown in solid lines) into an engaged (flat) configuration (shown in dotted lines) that provides preload to the one or more bearings by action of the bearing mount providing bias provided by the resilient/flexible body acting on the stator and/or stator frame and the bearings. The mounts 260 are optionally restrained by an overhang 272c, 272d formed on the insulator 270a, 270b. Similarly, the bearings 64 may be restrained by an overhang 268 formed as part of the boss 266 on the bearing mount 260. Either or both of the overhangs may be discretely positioned about the inner and outer annulus of the bearing mounts, or alternatively, extends around the circumference of the mount to define a recess in which the mount is located. The impeller/shaft/rotor is assembled into the stator 241 by assembling the bearings 64 on the shaft 60, assembling the bearing mounts 260 on the bearings 64 and manipulating the bearing mounts 260 (by hand, jig or other means) so they engage with the stator insulator 270a, 270b at each pole 243. In an alternative embodiment, the bearing mounts 260 are not coupled directly to the stator or insulator 270a/241 but rather are coupled to another structure such as a housing. Any coupling arrangement with any suitable structure can be provided which provides the required functions as set out below.

(85) The bearing mounts 260 provide compliance to the rotatable shaft 60. As rotatable objects, such as the rotor 62, shaft 60 and impeller 24 usually suffer from some degree of rotational imbalance, the bearing mounts are able to isolate inherent rotation induced vibration from the motor rotor. It has been found that combination of the lightweight, shroudless impeller having a low rotational inertia, as described above, together with the given compliance of the bearing mounts enables the rotor 62, shaft 60 and impeller 24 to be manufactured and any post manufacture balancing process for the rotating components entirely omitted. These advantages benefit manufacturing costs and time. The lightweight nature of the impeller 24 allows any imbalances/misalignment to be compensated by the bearing mounts 260 the arrangement is self aligning due to the bearing mount compliance (due to resilience and/or flexibility, for example). The bearing mount construction, including the geometry and material, also provides axial preload on the bearings, e.g. of up to 7 Newtons. The annular nature of the bearing provides consistent/even preload around the bearing 64. The resilient/flexible curved annular body allows the bearing to be installed in place and provide the preload. The annular nature of the bearing mount 260 provides for even preload around the bearing, while the low creep construction material maintains preload. The material of the bearing mounts 260 is also preferably a viscoelastic damping material that provides damping, which reduces the likelihood of resonance during operation of the motor. Such a viscoelastic material can also provide the required resilience/flexibility to provide the preload. An example of such a material is a Thermo Plastic Urethane like Dynaplast by GLS Corporation. Other materials resilient and/or flexible materials mentioned above for the bearing mount 260 could be adapted to provide the required damping by adding mica. A lightweight impeller also allows faster speed response of the impeller to changing conditions. Any unwanted fluctuations in pressure due the lack of shroud can be compensated for by quickly changing the impeller speed to return pressure to the desired level. The bearing mounts also provide vibration isolation.

(86) To provide further vibration damping of the rotational components of the blower, the motor and impeller, can optionally be mounted on a compliant mounting device (motor mount) 280. FIGS. 23, 27 and 28 shows one embodiment of such a mounting device 280. In accordance with the preferred embodiment of the invention the mount is most preferably made from a soft, flexible yet resilient material such as silicone rubber. The mounting device 280 has an annular body 282 with upper and lower engaging lips 282a, 282b that define an internal recess 281 in which the stator 241 is disposed. Preferably the internal recess 281 is smaller than the outer surface of the stator to encourage an interference fit between these components. FIG. 27 shows the motor positioned within the mounting recess 281.

(87) A plurality of projections 283 encircles the upper and lower surfaces of the mount 280. The end of projection extends past the upper and lower surfaces of the mount to provide supporting leverage to the mount and motor assembly. During operation of the motor, vibration caused by any imbalance of the rotational components is absorbed by each of the projections by allowing the body of the mount 280 to move relative to the surface on which the projections 283 are supported.

(88) The description above describes embodiments of a blower comprising a lightweight impeller assembly. FIGS. 19 and 27 show embodiments with a metal (e.g. steel) shaft 60 assembled on a magnet rotor 62. The metal shaft is press fit into an aperture in the magnet rotor. This requires fine tolerance control to ensure a good tight fit to reduce slipping. However, the fit should not be so tight as to risk cracking the magnet rotor.

(89) Alternative shaft and magnet rotor assemblies are shown in FIGS. 30 to 33B, which can be used in the stator in place of the assembly shown in FIG. 19 or 27.

(90) FIGS. 30A, 30B and 31 show a possible alternative rotor assembly of the embodiments described above. The assembly comprises a metal shaft 300 (see FIG. 31) and a magnet rotor 301. The magnet rotor 301 has a central opening 302. The central opening 302 comprises a central portion with indents 303a to 303d. The central opening also comprises a profiled edge through a central cross-section providing a stepped ledge 308 (see FIG. 30B), The metal shaft 300 has a knurled section 309b in its exterior and extends through the central opening 302. A plastic insert 303 is injection moulded between the shaft 300 and the magnet rotor 301 in the central opening 302. The plastic insert 303 is overmoulded onto the stepped ledge 308 of the magnet rotor. This provides an insert 303 with a similar exterior shape to the central opening 302. An interlocking (cog dog) is formed between the shaft 300 and overmoulded (insert) material 303, so that the metal shaft knurled section 309b engages with the overmoulded insert 303 to couple the shaft 300 to the magnet rotor 301. The assembly 304 can be used in the embodiments described above such as an FIGS. 19 and 27, wherein the shaft 60 and magnet rotor 62 of those embodiments are replaced with the metal shaft 300/plastic insert 303/magnet rotor 301 assembly 304 as described in FIGS. 30A, 30B and 31. The assembly can be created as shown in FIG. 34. The rotor is placed in a mould, step 340, the shaft is introduced, step 341, the other mould half is introduced, step 342, the insert is injection moulded between the shaft/rotor, step 343, and then the mould removed, step 344.

(91) FIG. 32 shows plan, elevation and isometric views of a magnet rotor and shaft assembly 320 according to another alternative embodiment. The assembly 320 comprises a rotor 301 formed from a magnet material. The magnet rotor 301 has a central opening 302. The central opening 302 comprises a central portion with indents 303a to 303d. The central opening also comprises a profiled edge through a central cross-section providing a stepped ledge 308.

(92) The assembly 320 also comprises a plastic shaft 321 that extends through the centre of the insert opening 310 and is overmoulded onto the magnet rotor 301 as will described below. When overmoulded, the shaft comprises an integral overmould magnet insert portion 323. The shaft 321 can be formed to comprise a hex 322 or other location profile for press fit coupling with the impeller 24. The plastic shaft 321 comprises any suitable plastic or combination thereof, such as acetyl or polypropylene, although any suitable injection moulding or other plastic could be used.

(93) The assembly 320 can be used in the embodiments described above such as an FIGS. 19 and 27, wherein the shaft 60 and magnet rotor 62 of those embodiments are replaced with the plastic shaft 321/magnet rotor 301 assembly 320 as described in FIG. 32.

(94) FIGS. 33A and 33B show an injection moulding tool that can be used to manufacture the shaft/rotor assembly 320, and FIG. 35 is a flow diagram of a method of manufacture. The tool 320 is an open and close two-part mould tool comprising a first mould part portion 331a and a second mould part/portion 331b that come together to form a mould/cavity 332 comprising a magnet jig 333. The mould comprises a cavity to form the shaft 321, hex fit shape 322 and overmould portion 23. During manufacture of the assembly 320, a magnet rotor 301 with an opening 302 as described above is introduced into the mould and placed in position in one half of the mould forming the jig 333, step 350. The top portion 321a of the mould is placed in position to create the mould cavity 332 with the bottom portion 321b, step 351. An injection moulding process starts, step 352, to injection mould plastic to create the shaft 321 overmoulded onto the magnet rotor 301. The injection moulding process overmoulds plastic over the stepped ledge 308 portion of the rotor magnet 301 to create the insert portion 323. Once the injection moulding process is complete, the mould portions 321a, 321b are removed leaving the assembly 320, step 353. The assembly 320 can then be used in the motor of FIGS. 19 or FIG. 27, for example.

(95) Previously, it has not been possible to use a plastic shaft/rotor assembly in the motor of a blower of a CPAP machine or similar. A plastic shaft is not sufficiently strong to withstand the forces involved in such motors. However, in the lightweight impeller embodiments described above, the forces are such that a plastic shaft rotor becomes a possibility. The lightweight and low inertia nature of the rotor along with the compliant bearing mount and other features that reduce unbalancing forces and other forces enable the use of a plastic shaft. Both the plastic rotor assembly and the method of manufacture provide advantages over existing metal shaft rotors.

(96) The combination of various features of the present invention provide advantages, which can be achieved using a single impeller. Using a lightweight/low inertia impeller (e.g. by removing some or all of the shroud and/or reducing blade material) reduces imbalance of the impeller due to manufacturing tolerances. Previously, after manufacture and during assembly of a blower, it has been necessary to remove/add material to the impeller to improve balancing. The lightweight nature of the impeller means that any small imbalance can be tolerated without requiring rectification. Coupled to this, where the imbalance is not small enough, the resilient/flexible bearing structure mounts 65 and/or stator mount can compensate for any imbalance in the impeller. As the impeller is lightweight enough, any imbalance is of a small enough magnitude to be compensated for by the bearing structure mounts 65, without the need for altering the weight of the impeller during assembly.

(97) The lightweight construction also allows for a larger diameter impeller, which in turn provides higher tip speed for a particular RPM. This allows for lower RPM operation of the blower while still achieving the required pressure (which is dependent on tip speed). Having a lower RPM reduces vibration to an acceptable level, or to a level that can be compensated for by the bearing structure and/or stator mount. The lightweight construction of the impeller as mentioned previously enables the larger impeller as it provides lower inertia that achieves the required pressures/response. That is, lower torque is required to speed up and slow down the impeller to reach the required tip speeds/pressures. This improves dynamic performance (response). In addition to this, small magnets in the motor (combined with the bearing structure) remove the need for balancing during assembly, improve dynamic performance.

(98) The resilient/flexible bearing structure allows for self-alignment, compliance, damping and preload of the impeller and shaft assembly. This makes assembly easier, and in combination with the lightweight/low inertia impeller reduce or negates the need for balancing modifications during assembly, as mentioned previously. The bearing structure provides for relaxed tolerances during manufacture as it compensates for larger tolerances. The bearing structure also isolates and/or damps vibrations, also allowing high RPM speeds of the impeller where necessary. The stator frame/motor mount also provides vibration isolation.

(99) The partition that separates the blower into first and second regions separates out the high velocity region to reduce noise. This allows for and maintains a constant high velocity of flow while diffusing the velocity to pressure.

(100) The use of a plastic shaft also provides a number of benefits over a metal (e.g. steel) shaft, including (but not limited to) the following

(101) The reliability risks associated with dissimilar materials are reduced.

(102) The knurled interface between the cog/dog insert and the shaft does not have to be monitored for cracking, slipping, run out, shrinkage, fluid ingress/corrosion.

(103) The impeller to shaft interface is improved and carries similar reduced reliability risks. It is less prone to cracking because of similar thermal expansion (due to plastic on plastic press fitting). There is reduced chance of slipping because of the opportunity to add some keying feature like a hex or grooves.

(104) The plastic shaft assembly is a press fit rather than a sliding fit so is more stable with less chance of rattles.

(105) The cost relative to a metal shaft is reduced. This is because of the following.

(106) Manufacturing the shaft to the tolerance for a sliding fit is not required because the plasticity of the plastic shaft allows for much wider tolerance or inaccuracy to press fit the bearings.

(107) The need for grinding of the shaft after knurling to re-establish straightness is not required.

(108) The handling and inserting the shaft into the mould is not required.

(109) It is possible to use materials with better vibration absorption properties than steel.

(110) Ease of assembly can be improved by reducing the length of the bearing press fit engagement by reducing shaft diameter with a hex, undercutting the impeller side of the shaft.

(111) In general, the following advantages are provided for by the combination of one or more features as follows:

(112) TABLE-US-00001 Advantage Features providing advantage Low noise impeller Low RPM (due to large diameter impeller) Partition to provide two regions, one containing the impeller Low cogging torque Sensorless vector drive/field oriented control Fast responding Low inertia impeller (achieved through blower shroudless/lightweight construction) Small magnet with diameter less than 20 mm Sensorless vector drive Lower cost No balancing required during assembly Small volume magnet Simple bearing mount One piece impeller Assembly without Low inertia impeller/lightweight balancing Flexible/resilient bearing structure Motor mount/stator frame isolator Low RPM impeller Small magnet with diameter less than 20 mm One piece impeller Large diameter impeller/ Low inertia impeller Low RPM Simplified manufacture, lower Use of plastic shaft which becomes costs, better reliability possible due to lightweight impeller, balancing advantages and other features

(113) Although the present invention has been described in terms of a certain embodiment, other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. For instance, various components may be repositioned as desired. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow.