Patent Publication Number: US-2023133462-A1

Title: Impeller and motor assembly

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a gases supply and gases humidification apparatus, particularly but not solely for providing respiratory assistance to patients or users who require a supply of gas for the treatment of diseases such as Obstructive Sleep Apnea (OSA), snoring, or Chronic Obstructive Pulmonary Disease (COPD) and the like. In particular, this invention relates to a compressor or blower for use in a gases supply apparatus which in use is integral with the gases supply apparatus. 
     Description of the Related Art 
     Devices or systems for providing a humidified gases flow to a patient for therapeutic purposes are well known in the art. Systems for providing therapy of this type, for example CPAP therapy, have a structure where gases at the required pressure are delivered from a blower (also known as a compressor, an assisted breathing unit, a fan unit, a flow generator or a pressure generator) to a humidifier chamber downstream from the blower. As the gases are passed through the heated, humidified air in the humidifier chamber, they become saturated with water vapour. The gases are then delivered to a user or patient downstream from the humidifier, via a gases conduit. 
     Humidified gases can be delivered to a user from a modular system that has been assembled from separate units (that is, a system where the humidifier chamber/heater and the breathing unit/blower are separate items) connected in series via conduits. A schematic view of a user  1  receiving air from a modular assisted breathing unit and humidifier system (together or separately a “breathing assistance apparatus”) is shown in  FIG.  1   . Pressurised air is provided from an assisted breathing unit or blower  2   a  via a connector conduit  10  to a humidifier chamber  4   a . Humidified, heated and pressurised gases exit the humidifier chamber  4   a  via a user conduit  3 , and are provided to the patient or user  1  via a user interface  5 . 
     It is becoming more common for integrated blower/humidifier systems to be used. A typical integrated system (“breathing assistance apparatus”) consists of a main blower or assisted breathing unit which provides a pressurised gases flow, and a humidifier unit that mates with or is otherwise rigidly connected to the blower unit. This mating occurs for example by a slide-on or push connection, so that the humidifier is held firmly in place on the main blower unit. A schematic view of the user  1  receiving air from an integrated blower/humidifier unit  6  is shown in  FIG.  2   . The system operates in the same manner as the modular system shown in  FIG.  1   , except that humidifier chamber  4   b  has been integrated with the blower unit to form the integrated unit  6 . 
     The user interface  5  shown in  FIGS.  1  and  2    is a nasal mask, covering the nose of the user  1 . However, it should be noted that in systems of these types, a mask that covers the mouth and nose, a full face mask, a nasal cannula, or any other suitable user interface could be substituted for the nasal mask shown. A mouth-only interface or oral mask could also be used. Also, the patient or user end of the conduit can be connected to a tracheostomy fitting, or an endotracheal intubation. 
     US 7,111,624 includes a detailed description of an integrated system. A ‘slide-on’ water chamber is connected to a blower unit in use. A variation of this design is a slide-on or clip-on design where the chamber is enclosed inside a portion of the integrated unit in use. An example of this type of design is shown in WO 2004/112873, which describes a blower, or flow generator  50 , and an associated humidifier  150 . 
     For these systems, the most common mode of operation is as follows: air is drawn by the blower through an inlet into the casing which surrounds and encloses at least the blower portion of the system. The blower (controlled by a microcontroller, microprocessor or similar) pressurises the air stream from the flow generator outlet and passes this into the humidifier chamber. The air stream is heated and humidified in the humidifier chamber, and exits the humidifier chamber via an outlet. A flexible hose or conduit is connected either directly or indirectly to the humidifier outlet, and the heated, humidified gases are passed to a user via the conduit. This is shown schematically in  FIG.  2   . 
     Impeller type fans or blowers are most commonly used in breathing systems of this type. An impeller blade unit is contained within an impeller housing. The impeller blade unit is connected to a drive of some form by a central spindle. A typical impeller housing is shown in  FIGS.  3  and  4   . A typical rotating impeller unit  54 , having a plurality of blades  151  and a shroud  152 , which in use is located inside the housing is shown in  FIGS.  5  and  6   . Air is drawn into the centre of the impeller unit through an aperture, and is then forced outwards from the centre of the housing towards an exit passage (usually located to one side of the housing) by the blades of the rotating impeller unit. 
     Generally, domestic users receive treatment for sleep apnea or similar. It is most common for a nasal mask, or a mask that covers both the mouth and nose, to be used. If a nasal mask is used, it is common to strap or tape the mouth closed, so that the use of the system is effective (mouth leak and the associated pressure drop are substantially reduced or eliminated). For the range of flows dictated by the user’s breathing, the CPAP device pressure generator provides a flow of gases at a substantially constant pressure. The pressure can usually be adjusted before use, or during use, either by a user, or a medical professional who sets up the system. Systems that provide variable pressure during use are also known - for example BiPAP machines that provide two levels of pressure: One for inhalation (IPAP) and a lower pressure during the exhalation phase (EPAP). Variable pressure or constant pressure systems are all “breathing assistance apparatus” 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved impeller or blower/compressor for use with a breathing assistance apparatus or an improved breathing assistance apparatus. 
     In one aspect the present invention may be said to consist in a breathing assistance apparatus comprising: a pressurised gases source comprising: a gases inlet, a gases outlet adapted to emit pressurised gases to an outlet of the breathing assistance apparatus, and a lightweight impeller on a rotatable plastic shaft. 
     Preferably the lightweight impeller is shroudless or otherwise has reduced material. 
     Preferably the breathing assistance apparatus further comprises a motor with a stator, wherein the rotatable plastic shaft is located within the stator, and the motor further comprises at least one bearing structure to support the rotatable plastic shaft within the stator, the bearing structure having one or more bearing mounts. 
     Preferably the bearing mounts provide compliant support to the rotatable shaft. 
     Preferably the motor further comprises a rotor within the stator, the plastic shaft being formed and coupled to the rotor by injection moulding. 
     In another aspect the present invention may be said to consist in A breathing assistance apparatus comprising: a motor comprising a rotatable plastic shaft located within a stator, a bearing structure to support the rotatable shaft in the stator, the bearing structure having one or more bearing mounts. 
     Preferably the bearing mounts provide compliant support to the rotatable shaft. 
     Preferably the motor further comprises a rotor within the stator, the plastic shaft being formed and coupled to the rotor by injection moulding. 
     In another aspect the present invention may be said to consist in a breathing assistance apparatus comprising: a pressurised gases source comprising: a housing, a gases inlet, a gases outlet adapted to emit pressurised gases to an outlet of the breathing assistance apparatus, a motor with a rotatable plastic shaft and at least one bearing structure to support the rotatable shaft within a stator, the bearing structure having one or more flexible and/or resilient bearing mounts to provide compliance and/or preload and/or damping for the rotatable shaft, a lightweight impeller coupled to the rotatable plastic shaft, a flexible and/or resilient motor mount that couples the stator and the housing to provide compliance and/or damping for the motor, a partition to define first and second interior regions within the housing, wherein the first and second regions are fluidly connected by a crescent shaped opening formed in or by the partition. 
     Preferably the lightweight impeller is shroudless or otherwise has reduced material. 
     Preferably the motor further comprises a rotor within the stator, the plastic shaft being formed and coupled to the rotor by injection moulding. 
     In another aspect the present invention may be said to consist in a method of manufacturing a shaft and rotor assembly for a motor comprising: inserting a rotor with a central opening into a first mould part, supporting a shaft extended through the central opening, coupling a second mould part to the first mould part to create a mould cavity around the central opening, injection moulding a plastic insert between the plastic shaft and the central opening to couple the plastic shaft to the rotor. 
     In another aspect the present invention may be said to consist in a method of manufacturing a shaft and rotor assembly for a motor comprising: inserting a rotor with a central opening into a first mould part, coupling a second mould part to the first mould part to create a mould cavity around the central opening, injection moulding a plastic shaft that extends through and couples to the central opening of the rotor. 
     Preferably the motor comprises a plastic rotatable shaft extending through an opening in a magnet rotor and being coupled thereto. 
     Also described is a breathing assistance apparatus comprising: a pressurised gases source comprising: a gases inlet, a gases outlet adapted to emit pressurised gases to an outlet of the breathing assistance apparatus, and a lightweight impeller. 
     Preferably lightweight impeller is shroudless or otherwise has reduced material. 
     Preferably lightweight impeller is formed in one piece. 
     Preferably the lightweight impeller has a radius of between 15 and 60 mm. 
     Preferably the lightweight impeller has a mass of less than 2 grams and preferably between 0.8 and 1.8 grams. 
     Preferably the lightweight impeller has a pressure to inertia to radius ratio greater than  50 :1 Pa per gram*mm, and preferably greater than 80:1 Pa per gram*mm. 
     Preferably the lightweight impeller has a moment of inertia to radius ratio less than 15 g*mm and preferably within the range of 8 to 12 g*mm. 
     Preferably the lightweight impeller has a blade sweep volume to a blade volume ratio of 16:1 or greater. 
     Preferably the impeller is a centrifugal impeller rotatable about a central axis. 
     Preferably the breathing assistance apparatus comprises a motor for driving the impeller wherein the motor is operated using field oriented control. 
     Preferably the gases source further comprises a housing having upper and lower internal surfaces that enclose the impeller, and wherein the impeller has a plurality of blades that are substantially open to the upper and lower internal surfaces of the housing by virtue of being shroudless. 
     Preferably the housing forms part of or is integrated with the breathing assistance apparatus. 
     Preferably the gases source further comprises a partition to define first and second interior regions within the housing, wherein the first and second regions are fluidly connected by an opening formed in or by the partition. 
     Preferably the opening formed in or by the partition is at least partially circumferential. 
     Preferably opening formed in or by the partition is crescent shaped. 
     Preferably the first region is defined by the housing and the partition and comprises the gases inlet. 
     Preferably the second region is defined by the housing and the partition and comprises the gases outlet. 
     Preferably the impeller has an axis of rotation, the partition extending radially from the axis of rotation. 
     Preferably the housing further comprises a volute in the second region. 
     Preferably the opening is proximate the periphery of the volute. 
     Preferably the impeller is located within the first region. 
     Preferably a distal end of the impeller blades curve in the direction of blade rotation. 
     Preferably the breathing assistance apparatus further comprises a motor, the motor comprising: a rotatable shaft located within a stator, and at least one bearing structure to support the rotatable shaft within the stator, the bearing structure having one or more bearing mounts. 
     Preferably the bearing mount provides compliant support to the rotatable shaft. 
     Preferably an outer portion of the one or more bearing mounts engages the stator and/or a stator frame and/or other structure. 
     Preferably an outer portion of the one or more bearing mounts engages the stator and/or frame of the stator. 
     Preferably the stator comprises a stator frame, an inner surface of the stator frame engages with the bearing structure. 
     Preferably the bearing structure further comprises one or more bearings supported by the bearing mounts about the axis of the rotatable shaft. 
     Preferably the pressurised gases source has a housing and the breathing apparatus further comprises a motor mount that couples the stator and the housing to provide compliant support to the motor. 
     Preferably the bearing mount and/or motor mount are flexible and/or resilient. 
     Preferably the volute has a tongue at least partially defining a transition between the volute and the gases outlet, the tongue located in the second interior region. 
     Preferably the bearing mounts have a curved annular body and when engaged with the stator and/or stator frame and/or other structure the annular body is coerced into an engaged configuration that provides preload to the one or more bearings. 
     Preferably the bearing mount is made from a material that provides resilience and/or flexibility to provide preload when in the engaged configuration. 
     Preferably the bearing mounts are made from a material that provides damping. 
     Preferably the motor is operated using field oriented control. 
     Also described is a breath assistance apparatus comprising: a motor comprising a rotatable shaft located within a stator, a bearing structure to support the rotatable shaft in the stator, the bearing structure having one or more bearing mounts. 
     Preferably the bearing mounts provide compliant support to the rotatable shaft. 
     Preferably an outer portion of the one or more bearing mounts engages the stator and/or a stator frame and/or other structure. 
     Preferably the stator comprises a stator frame, an inner surface of the stator frame engaging with the bearing structure. 
     Preferably the bearing structure further comprises one or more bearings supported by the bearing mounts about the axis of the rotatable shaft. 
     Preferably the bearing mount is flexible and/or resilient. 
     Preferably the bearing mounts have a curved annular body and when engaged with the stator and/or stator frame and/or other structure the annular body is coerced into an engaged configuration that provides preload to the one or more bearings. 
     Preferably the bearing mount is made from a material that provides resilience and/or flexibility to provide preload when in the engaged configuration. 
     Preferably the bearing mounts are made from a material that provides damping. 
     Also described is a pressurised gases source comprising: a centrifugal impeller driven by a motor within a housing, the housing having a gases inlet, a gases outlet and a partition to define first and second interior regions wherein the first and second regions are fluidly connected by an opening in the partition. 
     Preferably the first region is defined by the housing and the partition and comprises the gases inlet. 
     Preferably the second region is defined by the housing and the partition and comprises the gases outlet. 
     A pressurised gases source according to any of the above used in a breathing assistance apparatus according to any of the above. 
     Also described is a breathing assistance apparatus comprising: a pressurised gases source comprising: a housing a gases inlet, 
     a gases outlet adapted to emit pressurised gases to an outlet of the breathing assistance apparatus, a motor with a rotatable shaft and at least one bearing structure to support the rotatable shaft within a stator, the bearing structure having one or more flexible and/or resilient bearing mounts to provide compliance and/or preload and/or damping for the rotatable shaft, a lightweight impeller coupled to the rotatable shaft, a flexible and/or resilient motor mount that couples the stator and the housing to provide compliance and/or damping for the motor a partition to define first and second interior regions within the housing, wherein the first and second regions are fluidly connected by a crescent shaped opening formed in or by the partition. 
     Preferably the lightweight impeller is shroudless or otherwise has reduced material. 
     Preferably the lightweight impeller is formed in one piece. 
     Preferably the lightweight impeller has a radius of between 15 and 60 mm. 
     Preferably the lightweight impeller has a mass of less than 2 grams and preferably between 0.8 and 1.8 grams. 
     Preferably the lightweight impeller has a pressure to inertia to radius ratio greater than 50:1 Pa per gram*mm, and preferably greater than 80:1 Pa per gram ∗ mm. 
     Preferably the lightweight impeller has a moment of inertia to radius ratio less than 15 g ∗ mm and preferably within the range of 8 to 12 g ∗ mm. 
     Preferably the lightweight impeller has a blade sweep volume to a blade volume ratio of 16:1 or greater. 
     Also described is a pressurised gases source comprising: a gases inlet, a gases outlet, a motor with a shaft, and a lightweight impeller connected to the motor and rotatable to draw gases from the inlet and emit gases through the outlet, wherein the impeller is shroudless or otherwise has reduced material. 
     Preferably the impeller is a centrifugal impeller rotatable about a central axis. 
     Preferably the gases source further comprises a housing having upper and lower internal surfaces that enclose the impeller, and wherein the impeller has a plurality of blades that are substantially open to the upper and lower internal surfaces of the housing by virtue of being shroudless. 
     Preferably the housing forms part of or is integrated with a CPAP machine. 
     Preferably the gases source further comprises a partition to define first and second interior regions within the housing, wherein the first and second regions are fluidly connected by an opening formed in or by the partition. 
     Preferably the opening formed in or by the partition is at least partially circumferential. 
     Preferably the first interior region is defined by the housing and the partition and comprises the gases inlet. 
     Preferably the second interior region is defined by the housing and the partition and comprises the gases outlet. 
     Preferably the impeller has an axis of rotation, the partition extending radially from the axis of rotation. 
     Preferably the housing further comprises a volute in the second region. 
     Preferably the opening is proximate the periphery of the volute. 
     Preferably the impeller is located within the first region. 
     Preferably a distal end of the impeller blades curve in the direction of blade rotation. 
     Preferably the further comprising a motor, the motor comprising: a rotatable shaft located within a stator, and at least one bearing structure to support the rotatable shaft, the bearing structure having one or more bearing mounts engaged and axially aligned with the stator to provide compliant support to the rotatable shaft. 
     Preferably an outer portion of the one or more bearing mounts engages the stator. 
     Preferably the stator comprises a stator frame, an inner surface of the stator frame engaging with the bearing structure. 
     Preferably the bearing structure further comprises one or more bearings supported by the bearing mounts about the axis of the rotatable shaft. 
     Preferably the pressurised gases source further comprises a motor mount that couples the stator frame and the housing to provide compliant support to the motor. 
     Preferably the bearing mount is flexible and/or resilient. 
     Preferably the volute has a tongue at least partially defining a transition between the volute and the gases outlet, the tongue located in the second interior region. 
     Preferably the motor is vector controlled. 
     In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art 
     The term “comprising” as used in this specification means “consisting at least in part of”. When interpreting each statement in this specification that includes the term “comprising”, features other than that or those prefaced by the term may also be present. Related terms such as “comprise” and “comprises” are to be interpreted in the same manner. 
     It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7). 
     To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. The invention consists in the foregoing and also envisages constructions of which the following gives examples only. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred form of the present invention will now be described with reference to the accompanying drawings. 
         FIG.  1    shows a schematic view of a modular assisted breathing unit and humidifier system. 
         FIG.  2    shows a schematic view of a modular assisted breathing unit and humidifier system. 
         FIG.  3    shows a plan view of an example of a blower unit. 
         FIG.  4    shows a side view of the blower unit of  FIG.  3   . 
         FIG.  5    shows a profile view of an impeller. 
         FIG.  6    shows another profile view of an impeller. 
         FIG.  7    shows a profiled view of a gases supply unit. 
         FIG.  8    shows an exploded view of the gases supply unit of  FIG.  7   . 
         FIG.  9    shows an internal view of a gases supply unit (viewed from underneath). 
         FIG.  10    shows a profiled view of the gases supply unit of  FIG.  9   . 
         FIG.  11    shows a plan view of the top side of a blower unit of one embodiment. 
         FIG.  12    shows a plan view of the bottom side of the blower unit of  FIG.  11   . 
         FIG.  13    shows a profile view of the bottom side of the blower unit of  FIG.  12     
         FIG.  14 A  shows a plan view of the impeller with no shroud according to one embodiment. 
         FIG.  15 A  shows a profile view of the impeller of  FIG.  14   a    with no shroud. 
         FIG.  14 B  shows a plan view of the impeller with reduced shroud material according to one embodiment. 
         FIG.  15 B  shows a profile view of the impeller of  FIG.  14   b    with reduced shroud material. 
         FIG.  14 C  shows a plan view of the impeller with a web structure. 
         FIG.  15 C  shows a profile view of the impeller of  FIG.  14   c    with a web structure. 
         FIG.  16    shows an exploded view of the preferred housings and impeller of one embodiment. 
         FIG.  17    shows a plan view of the lower housing, partition and impeller of one embodiment. 
         FIG.  18    shows a profile view of the components of  FIG.  17   . 
         FIG.  19    shows a cross sectional view of the motor and impeller of one embodiment. 
         FIG.  20    shows a motor mounting structure one embodiment. 
         FIG.  21    shows the motor mounting structure with a motor and impeller of one embodiment. 
         FIG.  22 A  is a graph of average sound pressure levels of an earlier blower unit. 
         FIG.  22 B  is a graph of average sound pressure levels of the blower unit of the present invention. 
         FIG.  23    shows the motor mounting structure with a motor and impeller of a second embodiment. 
         FIG.  24    shows a stator lamination of the second embodiment. 
         FIG.  25    shows a pole face of the second embodiment. 
         FIG.  26    shows a bearing mount of the second embodiment. 
         FIG.  27    shows a cross sectional view of the motor and impeller of the second embodiment. 
         FIG.  28    shows a motor mounting structure of the second embodiment. 
         FIG.  29 A  is a pressure response graph of an earlier blower unit. 
         FIG.  29 B  is a pressure response graph of the blower unit of the present invention. 
         FIGS.  30 A,  30 B  show a metal shaft and magnet rotor assembly forming part of a motor. 
         FIG.  31    shows the metal shaft of the assembly in  FIGS.  30 A,  30 B . 
         FIG.  32    shows a plastic shaft and magnet rotor assembly forming part of another embodiment of the motor. 
         FIGS.  33 A and  33 B  show an injection moulding tool for manufacturing the plastic shaft and rotor assembly of  FIG.  32   . 
         FIG.  34    shows a flow diagram of an injection moulding process for the metal shaft/insert rotor assembly. 
         FIG.  35    shows a flow diagram of an injection moulding process for the plastic shaft rotor assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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. 
     The present invention relates to a lightweight/low inertia impeller. The lightweight nature of the impeller provides low inertia. 
     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. 
     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 US 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. 
     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. 
     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 . 
     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 . 
     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 . 
     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. 
     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 . 
     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 . 
     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 . 
     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. 
     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 . 
     The preferred form of the impeller is 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   .) 
     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. 
     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.  14   a  and  15   a   , 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.  14   b ,  15   b    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.  14   c ,  15   c    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.  14   b ,  15   b ,  14   c ,  15   c    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. 
     For example, a conventional shrouded impeller commonly used on a breathing assistance device, weighing approximately 17 grams and having inertia of 6 kg.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.mm2, responds pressure fluctuations of 10 cmH2O in approximately 100 ms.  FIG.  29 A  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.  29 B  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.  29 A . The reduced pressure fluctuation is less disruptive to a patient’s breathing process, and therefore advantageously increases patient comfort. 
     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.  14 B,  15 B,  14 C,  15 C . 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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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”). 
     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 . 
     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. 
     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. 
     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. 
     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 . 
     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 Flouro 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. 
     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. 
     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. 
     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 . 
     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 . 
     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. 
       FIG.  22 A  is a graph of the sound pressure level of a conventional fan unit tested in an anechoic chamber.  FIG.  22 B  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. 
     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)  270   a ,  270   b  covering the top and bottom of the annular portion  242  and the poles  243 . Each winding  68  is preferably assembled on the insulator  270   a ,  270   b  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  272   a  and downwards  272   b . 
     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  244   a ,  244   b  meeting at a central apex  244   c . 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  250   a ,  250   b  meeting at a central apex  250   c . This arrangement reduces cogging. The stator and/or rotor can have a skewed magentisation. 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 . 
     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  270   a /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  264   a  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  261   a . 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  268   a  are preferably chamfered  268   b ,  268   c . 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. 
       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  279   a ,  270   b . In the installed state (also called engaged state or configuration) the annular body is engaged with the stator  241  and/or stator frame  270   a ,  270   b  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  272   c ,  272   d  formed on the insulator  270   a ,  270   b . 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  270   a ,  270   b  at each pole  243 . In an alternative embodiment, the bearing mounts  260  are not coupled directly to the stator or insulator  270   a / 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. 
     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. 
     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  282   a ,  282   b  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 . 
     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. 
     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. 
     Alternative shaft and magnet rotor assemblies are shown in  FIG.  30  to  33 B , which can be used in the stator in place of the assembly shown in  FIGS.  19  or  27   . 
       FIGS.  30 A,  30 B 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  303   a  to  303   d . The central opening also comprises a profiled edge through a central cross-section providing a stepped ledge  308  (see  FIG.  30 B ). The metal shaft  300  has a knurled section  309   b  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  309   b  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.  30 A,  30 B 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 . 
       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  303   a  to  303   d . The central opening also comprises a profiled edge through a central cross-section providing a stepped ledge  308 . 
     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 acety or polypropylene, although any suitable injection moulding or other plastic could be used. 
     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   . 
       FIGS.  33 A and  33 B  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  331   a  and a second mould part/portion  331   b  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  323 . 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  321   a  of the mould is placed in position to create the mould cavity  332  with the bottom portion  321   b , 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  321   a ,  321   b  are removed leaving the assembly  320 , step  353 . The assembly  320  can then be used in the motor of  FIG.  19    or  FIG.  27   , for example. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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 
     The reliability risks associated with dissimilar materials are reduced. 
     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. 
     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. 
     The plastic shaft assembly is a press fit rather than a sliding fit so is more stable with less chance of rattles. 
     The cost relative to a metal shaft is reduced. This is because of the following. 
     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. 
     The need for grinding of the shaft after knurling to re-establish straightness is not required. 
     The handling and inserting the shaft into the mould is not required. 
     It is possible to use materials with better vibration absorption properties than steel. 
     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. 
     In general, the following advantages are provided for by the combination of one or more features as follows: 
     
       
         
           
               
               
            
               
                 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 blower 
                 Low inertia impeller (achieved through 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 balancing 
                 Low inertia impeller/lightweight 
               
               
                   
                 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 RPM 
                 Low inertia impeller 
               
               
                 Simplified manufacture, lower costs, better reliability 
                 Use of plastic shaft which becomes possible due to lightweight impeller, balancing advantages and other features 
               
            
           
         
       
     
     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.