Patent Publication Number: US-2022220972-A1

Title: Blower with bearing tube

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/504,531, filed Jul. 8, 2019, which is a continuation of U.S. patent application Ser. No. 14/136,399, filed Dec. 20, 2013, now U.S. Pat. No. 10,396,640, which is a continuation of U.S. patent application Ser. No. 12/155,528, filed Jun. 5, 2008, now U.S. Pat. No. 8,636,479, which claims the benefit of U.S. Provisional Application Nos. 60/924,909, filed Jun. 5, 2007, 60/996,001, filed Oct. 24, 2007, and 61/064,477, filed Mar. 7, 2008, each of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a blower for generating a pressure differential (e.g., air at positive or negative (vacuum) pressure). In an embodiment, the blower may be used in a positive airway pressure (PAP) device or flow generator used for the delivery of respiratory therapy to a patient. Examples of such therapies are Continuous Positive Airway Pressure (CPAP) treatment, Non-Invasive Positive Pressure Ventilation (NIPPV), and Variable Positive Airway Pressure (VPAP). The therapy is used for treatment of various respiratory conditions including Sleep Disordered Breathing (SDB) and more particularly Obstructive Sleep Apnea (OSA). However, the blower may be used in other applications (e.g., vacuum applications (medical or otherwise)). 
     BACKGROUND OF THE INVENTION 
     Blowers generally include two main parts: a rotating part, namely an impeller and shaft; and a stationary part that defines a fluid flow path, typically a chamber such as a volute. 
     Bearings are usually employed in pairs and in coaxial arrangements to support the rotating part, e.g., shaft. Ideally, the two bearings are located by a stationary member that constrains the two bearings in perfect axial alignment. Real world designs are less than perfect and, therefore, compromise bearing performance. 
     A widely employed bearing suspension mode involves holding each bearing within a separate housing structure and fitting those housing structures together to approximate a coaxial bearing arrangement. 
     There are two main classes of constraints on the packaging of bearings. One constraint relates to the practical limits of manufacturing precision, and another constraint relates to the need to attach and efficiently package items that must rotate. 
     With respect to the first constraint, although the precision of part forming technologies improves continuously, the state of the art is far from perfect. Furthermore, increased precision usually translates to greater expense, often dissuading a manufacturer from embracing the state of the art processes. 
     The second constraint is driven by the need to place items (such as a rotor/stator) between bearing pairs. This typically leads to the use of a two part housing construction. A consequence of multipart housings is that they accumulate unwanted tolerance build-up at each faying or joint surface, and, as such, each component part must be precisely shaped so that the accumulated dimensional errors remain within acceptable range. 
     Thus, a need has developed in the art for an improved arrangement that does not suffer from the above-mentioned drawbacks. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention relates to a blower including a stationary portion including an inlet and an outlet, a rotating portion provided to the stationary portion (e.g., in close proximity to, but not touching), and a motor (e.g., electric motor) adapted to drive the rotating portion. The inlet and outlet are co-axially aligned. The stationary portion includes a housing, a stator component provided to the housing, and a tube providing an interior surface. The rotating portion includes one or more bearings that are provided along the interior surface of the tube to support a rotor within the tube (e.g., bearings connect the rotating portion to the stationary portion). In an alternative embodiment, the stator component may include stator vanes, and the stator vanes may be a separate part to the tube. In an embodiment, the blower is structured to supply air at positive pressure. In an embodiment, the stator component and/or tube may be constructed of a plastic material. 
     Another aspect of the invention relates to a PAP device for generating a supply of pressurized gas to be provided to a patient for treatment. The PAP device includes an outer casing, a blower, and a support system provided between the blower and the outer casing. The support system includes an annular seal provided to an outer surface of the blower and adapted to engage the outer casing to support the blower within the casing and separate an inlet side of the blower from an outlet side of the blower. In an alternative embodiment, the annular seal may be overmolded to the blower or may be a separate part that is adapted to be attached to the blower. 
     Another aspect of the invention relates to a method for forming windings of a stator assembly in a blower. The method includes providing a stationary portion for the blower including a tube adapted to support a rotor, and using the tube as a mandrel to form the windings of the stator assembly. 
     Another aspect of the invention relates to a blower including a stationary portion including an inlet and an outlet, a rotating portion provided to the stationary portion, and a motor adapted to drive the rotating portion. The stationary portion includes a housing and a stator component provided to the housing. The stator component includes a portion adapted to support a rotor of the rotating portion and a cage that surrounds the portion. In an embodiment, the blower is structured to supply air at positive pressure. In an embodiment, the stator component may be constructed of a plastic material. In an embodiment, the portion includes a tube and the motor includes a stator assembly that is provided along an exterior surface of the tube. In an alternative embodiment, the portion includes a metal bearing support having first and second parts adapted to support first and second bearings that support the rotor. 
     Another aspect of the invention relates to a blower including a stationary portion including an inlet and an outlet, a rotating portion provided to the stationary portion, a motor adapted to drive the rotating portion and including a stator assembly with windings, and a detection system to detect faults in the motor by monitoring resistance of the windings and/or current draw and then providing a signal to indicate detected faults in the motor. In an embodiment, the blower is structured to supply air at positive pressure. 
     Another aspect of the invention relates to a stator (e.g., one or two or more part magnetic core) for a stator assembly. The stator includes an inner portion including a plurality of stator teeth and a ring-shaped outer portion structured to receive the inner portion. The outer portion includes a plurality of recesses along its inner circumference adapted to receive respective teeth of the inner portion. 
     Another aspect of the invention relates to a blower including a stationary portion including an inlet and an outlet, a rotating portion provided to the stationary portion, and a motor adapted to drive the rotating portion. The inlet and outlet are co-axially aligned. The stationary portion includes a housing and a metal bearing support provided to the housing. The metal bearing support includes first and second parts and the rotating portion includes first and second bearings that are supported by the respective first and second parts to support a rotor within the metal bearing support. In an embodiment, the blower is structured to supply air at positive pressure. 
     Other aspects, features, and advantages of this invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of this invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings facilitate an understanding of the various embodiments of this invention. In such drawings: 
         FIG. 1-1  is a cross-sectional view of a blower according to an embodiment of the present invention; 
         FIG. 1-2  is a perspective view of a stator vane/cover component of the blower shown in  FIG. 1-1 ; 
         FIG. 1-3  is a perspective view of a vaned shield of the blower shown in  FIG. 1-1 ; 
         FIG. 1-4  is a top view of the blower shown in  FIG. 1-1  with a blower housing cover removed; 
         FIG. 2  is a cross-sectional view of a blower according to another embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of a blower according to another embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of a blower according to another embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of a support system for a blower according to an embodiment of the present invention; 
         FIG. 6-1  is a partial cross-sectional view of a sealing arrangement for a blower according to an embodiment of the present invention; 
         FIG. 6-2  is a partial cross-sectional view of a sealing arrangement for a blower according to another embodiment of the present invention; 
         FIG. 7-1  is a perspective view of a blower according to another embodiment of the invention; 
         FIG. 7-2  is a side view of the blower shown in  FIG. 7-1 ; 
         FIG. 7-3  is a cross-sectional view of the blower shown in  FIG. 7-1 ; 
         FIG. 7-4  is an enlarged portion of the cross-sectional view shown in  FIG. 7-3 ; 
         FIG. 7-4B  is an enlarged portion of a blower in cross-section according to another embodiment of the present invention; 
         FIG. 7-5  is another cross-sectional view of the blower shown in  FIG. 7-1 ; 
         FIG. 7-6  is an enlarged portion of the cross-sectional view shown in  FIG. 7-5 ; 
         FIG. 7-7  is a side view of the blower shown in  FIG. 7-1  with a housing removed; 
         FIG. 7-8  is a top perspective view of a stator component of the blower shown in  FIG. 7-1 ; 
         FIG. 7-9  is a bottom perspective view of the stator component shown in  FIG. 7-8 ; 
         FIG. 7-10  is a cross-sectional view of the stator component shown in  FIG. 7-8 ; 
         FIG. 7-11  is a top perspective view of a first shield of the blower shown in  FIG. 7-1 ; 
         FIG. 7-12  is a top view of the first shield shown in  FIG. 7-11 ; 
         FIG. 7-13  is a top perspective view of a second shield of the blower shown in  FIG. 7-1 ; 
         FIG. 8  is a cross-sectional view of a blower according to another embodiment of the present invention; 
         FIGS. 9-1 to 9-2  are cross-sectional views of a blower according to another embodiment of the present invention; 
         FIGS. 10-1 to 10-3  are various views of a stator according to an embodiment of the present invention; 
         FIG. 11  is a plan view of a stator according to another embodiment of the present invention; 
         FIG. 12-1  is a perspective view of a blower according to another embodiment of the invention; 
         FIG. 12-2  is a cross-sectional view of the blower shown in  FIG. 12-1 ; 
         FIG. 12-3  is a perspective view of a stator of the blower shown in  FIG. 12-1 ; 
         FIG. 13-1  is a perspective view of a blower according to another embodiment of the invention; and 
         FIG. 13-2  is a cross-sectional view of the blower shown in  FIG. 13-1 . 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS 
     The following description is provided in relation to several embodiments which may share common characteristics and features. It is to be understood that one or more features of any one embodiment may be combinable with one or more features of the other embodiments. In addition, any single feature or combination of features in any of the embodiments may constitute additional embodiments. 
     In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear. Aspects of the invention will be described herein in its application to non-invasive ventilation (NIVV) treatment apparatus (e.g., positive airway pressure (PAP) devices or flow generators), such as CPAP (e.g., in the range of 4-28 cmH 2 O, at flow rates of up to 180 L/min (measured at the mask)), variable pressure therapy (e.g., low range of 2-6 cmH 2 O and high range of 6-30 cmH 2 O), mechanical ventilation and assisted respiration, but it is to be understood that the features of the invention will have application to other fields of application where blowers are used, such as vacuum cleaners, cooling equipment in computers and HVAC devices such as those found in buildings and vehicles. That is, the blowers described herein may have application in both positive pressure and negative pressure applications. 
     Also, while each blower embodiment below is described as including two stages, it should be appreciated that each embodiment may a single stage design or other multiple stage designs, e.g., three, four, or more stages. 
     In this specification, the words “air pump” and “blower” may be used interchangeably. In this specification, the phrase “stationary part” may be taken to include “volute”. The term “air” may be taken to include breathable gases, for example air with supplemental oxygen. It is also acknowledged that the blowers described herein may be designed to pump fluids other than air. 
     1. Blower with Bearing Tube 
       FIGS. 1-1 to 1-4  illustrate a blower  10  according to an embodiment of the present invention. As illustrated, the blower  10  includes two stages with two corresponding impellers  50 ,  52 . In this embodiment, one impeller  50  is positioned on one side of the motor  40  and the other impeller  52  is positioned on the other side of the motor  40 . However, other suitable impeller arrangements are possible, e.g., two impellers positioned on the same side of the motor. Also, the blower  10  may include a single stage design or other multiple stage designs, e.g., two or more impellers. 
     1.1 General Description 
     A stationary portion of the blower  10  includes a housing  20  with first and second housing parts  22 ,  24 , a stator component  30  including stator vanes  32 , and first and second shields  60 ,  70 . A rotating portion of the blower  10  includes a rotatable shaft or rotor  80  adapted to be driven by motor  40  and first and second impellers  50 ,  52  provided to end portions of the shaft  80 . The motor  40  includes a magnet  42  (e.g., two pole magnet) provided to shaft  80  and a stator assembly  44  to cause spinning movement of the shaft  80  via the magnet  42 . In an embodiment, the motor may be operated without the use of rotor position sensors, e.g., no Hall sensors on printed circuit board (PCB), which may reduce the number of wires, e.g., 3 wires. 
     The stator assembly  44  includes windings  46  and a stator or stator lamination stack  48  (e.g., slotless or toothless) provided to the windings  46 . Further details of coil winding is disclosed in U.S. Provisional Application No. 60/877,373, filed Dec. 28, 2006, which is incorporated herein by reference in its entirety. 
     The blower  10  is generally cylindrical and has an inlet  26  provided by the first housing part  22  at one end and an outlet  28  provided by the second housing part  24  at the other end. The blower  10  is operable to draw a supply of gas into the housing  20  through the inlet  26  and provide a pressurized flow of gas at the outlet  28 . 
     The blower  10  has axial symmetry with both the inlet  26  and outlet  28  aligned with an axis  15  of the blower  10 . In use, gas enters the blower  10  axially at one end and leaves the blower  10  axially at the other end. Such arrangement may provide relatively low noise in use, e.g., due to axial symmetry and/or low volute turbulence. Exemplary embodiments of such blowers are disclosed in PCT Application No. PCT/AU2007/000719, filed May 24, 2007, which is incorporated herein by reference in its entirety. 
     In an embodiment, the blower  10  may be relatively compact and have an overall diameter D of about 50-60 mm, e.g., 53 mm, and an overall length L of about 45-55 mm, e.g., 52 mm. However, other suitable sizes are possible. 
     1.2 Stator Component 
     As shown in  FIGS. 1-1 and 1-2 , the stator component  30  includes a base  34 , an annular flange  36  extending from the base  34 , a tube or bearing tube  38 , and a plurality of stator vanes  32 . In the illustrated embodiment, the stator component  30  is integrally formed (e.g., injection molded of plastic material) as a one-piece structure. However, the stator component  30  may be constructed in other suitable manners. 
     As best shown in  FIG. 1-1 , the annular flange  36  is sandwiched between the first and second housing parts  22 ,  24  to support the stator component  30  within the housing  20 . 
     The plurality of stator vanes  32 , e.g., between 2 and 100 stator vanes, are structured to direct airflow towards an orifice  35  in the base  34 . In the illustrated embodiment, the stator component  30  has six stator vanes  32 . Each vane  32  is substantially identical and has a generally spiral shape. In addition, each vane  32  includes an inner portion  37  (adjacent the tube  38 ) and an outer portion  39 . As best shown in  FIG. 1-2 , the inner portion  37  is recessed (e.g., reduced in height) with respect to the outer portion  39 . However, the stator component may have other suitable structure to condition the airflow between stages. 
     1.2.1 Bearing Alignment and Retention 
     The interior surface  90  of the tube  38  is structured to retain and align the bearings  100 ,  102  that rotatably support the shaft  80 . In addition, the tube  38  encloses the magnet  42  on the shaft  80 , which is aligned in close proximity to the stator assembly  44  provided along an exterior surface  92  of the tube  38 . In the illustrated embodiment, the tube  38  has at least a portion that is sufficiently “magnetically transparent” to allow a magnetic field to pass through it, which allows the stator assembly  44  to act on the magnet  42  positioned within the tube  38  without significant loss of flux density and/or increased heat, if any. In an embodiment, such “magnetic transparency” may be provided by one or more of the tube&#39;s material properties, e.g., non-electrically conductive, non-magnetic, and/or thermally conductive. For example, the tube may include one or more of the following: anisotropic materials, composite (e.g., base polymers (e.g., LCP and PPS) with either ceramic fillers, graphite fillers, and/or other fillers), heterogeneous fill, insert molding, plating, ion implantation, etc. Alternatively, or in addition, such “magnetic transparency” may be provided by the tube&#39;s structural properties, e.g., one or more perforations, slits, etc. in the tube. It should be appreciated that the tube may include one or more of these properties and/or a sufficient degree of these properties to provide sufficient “magnetic transparency.” Further details of a magnetically transparent tube are disclosed in U.S. Provisional Application Nos. 60/853,778, filed Oct. 24, 2006, and 60/929,558, filed Jul. 3, 2007, each of which is incorporated herein by reference in its entirety. 
     In the illustrated embodiment, the tube has a circular cross-sectional configuration along its length. However, it should be appreciated that the tube may have other suitable shapes, e.g., square, polygonal, conical, etc. Also, the tube may include one or more parts, e.g., multi-part construction. In addition, the tube may have different material properties along its length or circumference, e.g., different levels or regions of “magnetic transparency”, “non-electrical conductivity”, and/or “thermal conductivity.” 
     In the illustrated embodiment, the tube  38  is structured such that mixed bearing sizes may be used. As shown in  FIG. 1-1 , the upper end of the tube  38  is structured to support bearing  100  and the lower end of the tube  38  is structured to support bearing  102  having a smaller size or diameter than bearing  100 . 
     Specifically, the upper end of the tube  38  includes an annular surface  90 ( 1 ) defining a diameter d1 and adapted to support bearing  100 . The lower end of the tube  38  includes an annular surface  90 ( 2 ) defining a smaller diameter d2 and adapted to support bearing  102 . As illustrated, the one-piece tube  38  provides accurate bore-to-bore alignment which provides accurate bearing-to-bearing alignment. 
     In an embodiment, the tube may be manufactured such that upper and lower ends of the tube are adapted to support bearings of the same size. However, a tube structured to support mixed bearing sizes may facilitate a line of draw molding process. Also, the tube may be structured to support one or more bearings, and the bearings may include other suitable configurations, e.g., fluid bearings. Further, in an embodiment, the tube may be structured such that the upper end of the tube is structured to support a bearing having a smaller size or diameter than the bearing supported at the lower end of the tube (e.g., blower with a larger inlet diameter to the second impeller). 
     A sloped surface  90 ( 3 ) may be provided between surfaces  90 ( 1 ) and  90 ( 2 ) to guide the shaft  80  (with bearings  100 ,  102  provided to respective end portions) into the lower end of the tube  38 . For example, the smaller bearing side of the shaft  80  may be inserted into or “dropped into” the tube  38  through the upper end of the tube  38 . As the smaller bearing  102  approaches the lower end, the sloped surface  90 ( 3 ) will guide the bearing  102  into engagement with surface  90 ( 2 ) having a reduced diameter. Thus, the bearing  102  is self-guided into its operative position. 
     In the illustrated embodiment, the lower end of the tube  38  includes a flange  94  that provides a stop or support for the bearing  102  at the lower end. The upper end of the tube  38  is adapted to engage the shield or rotor cap  60 , which provides a stop for the bearing  100  at the upper end and hence retains the shaft  80  within the tube  38 . 
     Washers  104  and a spring or biasing element  106  may be provided between the bearing  102  and the rotor magnet  42  to maintain alignment of the rotor magnet  42  with the stator assembly  44  and/or provide a pre-load to the inner race of bearing  102 . 
     In an embodiment, end portions of the shaft  80  may include one or more bonding grooves for securing the bearings  100 ,  102  in an operative position, and an intermediate portion of the shaft  80  may include one or more bonding grooves (e.g., helical bonding grooves) for securing the magnet  42  in an operative position. The bonding grooves may be provided to selected portions of the shaft (e.g., ends and middle of the shaft) or the bonding grooves may extend along the entire length of the shaft. In another embodiment, an intermediate portion of the shaft may include threads (e.g., extending outwardly from the exterior surface of the shaft) for securing the magnet in an operative position. 
     1.2.2 Stator Assembly Alignment and Retention 
     The stator assembly  44  is provided along the exterior surface  92  of the tube  38 . In addition, the stator component  30  and first shield  60  cooperate to support and maintain the stator assembly  44  in an operative position. 
     As illustrated, the windings  46  of the stator assembly  44  are encased or supported by the recessed, inner portion  37  of the stator vanes  32 , and the stack  48  of the stator assembly  44  is encased or supported by the outer portion  39  of the stator vanes  32 . In addition, the shield  60  includes an annular flange  64  that encloses an upper portion of the windings  46  and engages an upper side  47  or an exterior surface  49  of the stack  48  (e.g., left side of  FIG. 1-1  shows flange  64  engaging upper side  47  of stack  48  and right side of  FIG. 1-1  shows flange  64  engaging exterior surface  49  of stack  48 ). The elongated portions of the annular flange  64  (i.e., the portions engaging exterior surface  49  of the stack  48 ) are provided to accommodate tabs that engage the housing as described in greater detail below. Thus, the stator component  30  and shield  60  cooperate to enclose and sandwich the stator assembly  44 . 
     In the illustrated embodiment, the exterior surface  49  of the stack  48  and/or the annular flange  64  engaging the stack  48  is exposed to the flow of gas. This arrangement allows forced-convection cooling of the stack  48  as gas flows through the housing  20  in use. In addition, this arrangement may assist in heating the gas or patient air. 
     Further, the windings  46  of the stator assembly  44  are exposed to the flow of gas to allow cooling and assist in heating the gas or patient air. 
     In an embodiment, the stator component  30  and shield  60  may be thermally conductive (e.g., add graphite or other filler to polymer material) to help with heat conduction. 
     1.3 Shields 
     The first or upper shield  60  includes a disk portion  62  and the annular flange  64  extending from the outer edge of the disk portion  62  and adapted to engage the stator assembly  44  as described above. The outer edge of the disk portion  62  substantially aligns with or extends radially beyond the outer edge of the impeller  50 . The shield  60  provides a narrow annular gap  110  between the annular flange  64  and the side wall of the housing part  22 , which is sufficient to direct gas into the stator component  30 . 
     The disk portion  62  includes an opening  66  that allows the shaft  80  to extend therethrough. An annular flange or projection  68  is provided along the opening  66  that is structured to engage the upper end of the tube  38  of the stator component  30 , e.g., with a friction fit. 
     Also, the annular flange  64  includes one or more tabs  65  that are adapted to engage within respective slots  23  defined between the first housing part  22  and the stator component  30  (e.g., see  FIGS. 1-1 and 1-4 ). As shown in  FIG. 1-4 , the shield  60  includes three tabs  65  that are received in respective slots  23  defined between the first housing part  22  and the stator component  30 . However, any suitable number of slots/tabs may be provided. Also, it should be appreciated that the slots/tabs may be optional and the shield  60  may be supported within the housing in other suitable manners. 
     The second or lower shield  70  includes a plurality of stator vanes  72 , e.g., between 2 and 100 stator vanes, to direct airflow towards the outlet  28 . In the illustrated embodiment, the shield  70  has 7 stator vanes. Each vane  72  is substantially identical and has a generally spiral shape. In addition, each vane  72  includes an inner portion  73  (adjacent the hub  74 ) and an outer portion  75 . As best shown in  FIGS. 1-1 and 1-3 , the outer portion  75  is recessed (e.g., reduced in height) with respect to the inner portion  73 , and a contoured edge  76  extends between the inner and outer portions  73 ,  75 . 
     In the illustrated embodiment, the stator vanes  72  support the shield  70  within the second housing part  24  adjacent the outlet  28 . As illustrated, the contoured edge  76  of the shield  70  engages the edge of the outlet  28  to align the shield  70  with the outlet  28 . The hub  74  and inner portion  73  of the vanes  72  extend at least partially through the outlet  28  and the outer portion  75  of the vanes  72  engage the lower wall of the second housing part  24 . The hub  74  at the central portion of the shield  70  is shaped to direct the air flow down towards the outlet  28 . 
     1.3.1 Alternative Airflow Path 
     In an embodiment, the shield  60  may include an inlet conduit  84  and an outlet conduit  86  (as indicated in dashed lines in  FIG. 1-1 ) to provide pressure balance across the bearings  100 ,  102 . Specifically, the inlet and outlet conduits  84 ,  86  provide a short circuit of pressure around the tube  38  and hence the bearings  100 ,  102  to avoid such drying out or displacement of the bearings&#39;  100 ,  102  lubricant (e.g., air flow through the tube and through the interior of the bearings can dry out grease in the bearings and carry away heat from the bearings). That is, the inlet conduit  84  allows air to flow into the space between the shield  60  and the tube  38 , and the outlet conduit  86  allows air to flow out of the space. Such arrangement allows any pressure differential to bleed through the inlet and outlet conduits  84 ,  86 , rather than travel through the tube  38  as described above. 
     In an alternative embodiment, as shown in  FIG. 2 , grooves  184 ,  186  may be provided along the shaft  80  to provide a short circuit of airflow or pressure around each of the bearings  100 ,  102  to avoid drying out of the bearings. As illustrated, the grooves  184 ,  186  are provided adjacent respective bearings  100 ,  102  and allow air to flow through the grooves  184 ,  186  rather than through respective bearings  100 ,  102 , e.g., when air flows through the tube  38  due to pressure differential inside tube  38 . In an embodiment, one or more grooves may extend along the length of the shaft, rather than along selected portions as illustrated. Alternatively, the grooves  184 ,  186  may be on the tube  38  adjacent the outside diameter of respective bearings  100 ,  102 . 
     1.4 Impellers 
     In the illustrated embodiment, each impeller  50 ,  52  includes a plurality of continuously curved or straight blades  54  sandwiched between a pair of disk-like shrouds  55 ,  56 . The shrouds may help to reduce tonal noise in use. The lower shroud  56  incorporates the hub or bushing  58  that is adapted to receive the shaft  80 . Also, each impeller  50 ,  52  includes a tapered configuration wherein the blades  54  taper towards the outer edge. Further details of impellers are disclosed in PCT Application No. PCT/AU2006/001617, filed Oct. 27, 2006, which is incorporated herein by reference in its entirety. 
     In an embodiment, each impeller may be constructed of glass reinforced polycarbonate. In another embodiment, each impeller may be constructed of glass reinforced liquid crystal polymer (LCP), e.g., Ticona Vectra-E130i. Glass reinforced LCP may improve acoustic dampening, especially with respect to reducing the tonal acoustic noise by reducing the impeller resonating. However, other suitable materials are possible. 
     1.5 Fluid Flow Path 
     In the first stage, air enters the blower  10  at the inlet  26  and passes into the first impeller  50  where it is accelerated tangentially and directed radially outward. It is noted that suction is developed at the inlet to draw air into the blower. Air then flows in a spiral manner with a large tangential velocity component and also an axial component passing through the gap  110  defined by the outer edge of the shield  60  and the side wall of housing part  22 . As noted above, air may bleed through the shield  60  (through the inlet and outlet conduits  84 ,  86 ) to provide pressure balance in use. Air then enters the stator vanes  32  formed in the stator component  30  and is directed radially inwardly towards orifice  35 , and thereafter onto the second stage. 
     In the second stage, air passes into the second impeller  52  where it is accelerated tangentially and directed radially outward. Air then flows in a spiral manner with a large tangential velocity component and also an axial component passing through the gap  112  defined by the outer edge of the shield  70  and the side wall of housing part  24 . Air then enters the stator vanes  72  formed in the shield  70  and is directed towards the outlet  28 . 
     In the illustrated embodiment, the airflow enters and exits each stage within the blower in a substantially axial direction. Consequently, the air enters the blower axially at one end, and leaves the blower axially at the other end. The axially symmetric blower provides balance, which leads to lower levels of blade pass tone, and lower levels of turbulence noise. 
     2. Blower with Mixed Flow Upper Impeller 
       FIG. 3  illustrates a blower  210  according to another embodiment of the present invention. The blower  210  is substantially similar to the blower  10  described above. In contrast, the upper impeller  250  has a mixed flow configuration and corresponding portions of the first housing part  222  and first shield  260  are tapered to match the mixed flow configuration of the upper impeller  250 . 
     As illustrated, each of the blades  254  of the impeller includes an end portion  257  that tapers toward the outer edge. In addition, the end portion  257  of each blade  254  is bent, angled, or sloped downwardly with respect to the hub  258 . For example, a longitudinal axis L of each end portion  257  may be bent or angled at an angle α with respect to an axis H of the hub  258 . Such angle α may be about 90°-160°, e.g., 125°. However, other suitable angles are possible depending on application. 
     The upper wall  225  of the first housing part  222  is tapered to match the mixed flow configuration of the impeller  250 , and the upper wall  267  of the shield  260  is tapered to match the mixed flow configuration of the impeller  250 . 
     3. Blower with Alternative Stationary Portion 
       FIG. 4  illustrates a blower  310  according to another embodiment of the present invention. Similar to the blowers  10 ,  210  described above, the blower  310  includes two stages with one impeller  350  positioned on one side of the motor  340  and one impeller  352  positioned on the other side of the motor  340 . Also, the blower  310  has axial symmetry with both the inlet  326  and outlet  328  aligned with an axis  315  of the blower  310 . In contrast, the blower  310  provides an alternative arrangement of the stationary portion. 
     3.1 General Description 
     A stationary portion of the blower  310  includes a housing  320  with first and second housing parts  322 ,  324 , a stator component  330  including stator vanes  332 , and first and second shields  360 ,  370 . A rotating portion of the blower  310  includes a rotatable shaft or rotor  380  adapted to be driven by motor  340  and first and second impellers  350 ,  352  provided to end portions of the shaft  380 . The motor  340  includes a magnet  342  provided to shaft  380  and a stator assembly  344  to cause spinning movement of the shaft  380  via the magnet  342 . 
     In an embodiment, as shown in  FIG. 4 , the blower  310  may be relatively compact and have an overall diameter D of about 50-60 mm, e.g., 53 mm, and an overall length L of about 45-55 mm, e.g., 52 mm. Each impeller  350 ,  352  may have a diameter of about 40-45 mm, e.g., 42 mm. However, other suitable sizes are possible. 
     3.2 Stator Component 
     As shown in  FIG. 4 , the stator component  330  includes a base  334 , an annular flange  336  extending from the base  334  to support the stator component  330  within the housing  320 , a tube  338  to retain and align the bearings  300 ,  302  that rotatably support the shaft  380 , and a plurality of stator vanes  332 . Similar to the above embodiments, the stator component  330  may be integrally formed (e.g., injection molded) as a one-piece structure. 
     In the illustrated embodiment, each vane  332  includes an outer portion  339  that is sufficiently long so that it can support and maintain the stator assembly  344  in an operative position. As illustrated, the outer portion  339  of each vane  332  provides an interior surface  315  that engages an exterior surface  345  of the stator assembly  344 . In an embodiment, opposing vanes may define a diameter d of about 30-35 mm, e.g., 34 mm, for securing the stator assembly  344  in position. However, other suitable sizes are possible, e.g., depending on the size of the stator assembly. 
     In addition, the free end of the outer portion  339  of each vane  332  is adapted to engage the shield  360  so that it can support and maintain the shield  360  in an operative position. 
     3.3 Shields 
     The first or upper shield  360  includes an inner annular flange  367  and an outer annular flange  369 . The inner annular flange  367  is structured to engage the upper end of the tube  338  of the stator component  330 , e.g., with a friction fit, and the outer annular flange  369  is structured to engage the outer portion  339  of the vanes  332 , e.g., with a friction fit. 
     The second or lower shield  370  is supported and maintained by the second housing part  324  in an operative position. The hub  374  at the central portion of the shield  370  is shaped to direct the air flow down towards the outlet  328 . 
     3.4 Housing 
     In the illustrated embodiment, the second housing part  324  of the housing  320  includes a plurality of stator vanes  325 , e.g., between 2 and 100 (e.g., about 5-15) stator vanes, to direct airflow towards the outlet  328 . As illustrated, the stator vanes  325  support the shield  370  within the second housing part  324  adjacent the outlet  328 . Also, at least one of the stator vanes  325  includes a projection  327  adapted to extend through an opening  377  provided in the shield  370  to align and secure the shield  370  in position. 
     4. Support System for Blower 
     Each of the blowers  10 ,  210 ,  310  described above may be supported within an outer casing or chassis (e.g., forming a portion of a NIVV device such as a PAP device or flow generator). In an embodiment, each blower may be supported within the outer casing by a support system that is structured to provide support and provide a seal between the inlet and the outlet sides of the blower. 
     In an embodiment, as shown in  FIG. 5 , the outer casing  400  includes a base  402  and a cover  404  provided to the base  402 . The support system  405  includes a side  406  support and a bottom support  408  to support the blower (e.g., blower  10 ). 
     As illustrated, the side support  406  is in the form of an annular ring (e.g., made of Silicone or TPE) that is provided to the blower housing (e.g., housing  20 ) and includes an end portion  407  adapted to engage within a respective slot  403  defined between the base  402  and cover  404 . The bottom support  408  is in the form of multiple flexible feet or flexible pegs, e.g., 3 feet, that are adapted to engage the base wall of base  402 . The annular ring  406  (also referred to as a divider seal or a soft girdle/seal) suspends/supports the blower  10  in the chassis and divides or seals the inlet side of the blower from the outlet side of the blower (i.e., divide or separate low and high pressure sides), e.g., to avoid the need for a connection tube that directs flow towards the outlet of the outer casing  400 . The feet  408  may act as a backup seal between the inlet and outlet sides of the blower or a backup support for the blower, e.g., in case the ring  406  creeps in old age. 
     As illustrated, a relatively small outlet muffler volume V1 is provided on the outlet side of the blower and a relatively small inlet muffler volume is provided on the inlet side of the blower V2. 
     In an embodiment, the annular ring  406  and feet  408  may be overmolded onto the outside of the first housing part  22  of the blower  10  (i.e., the first stage cover of the blower). As illustrated, an overmolded feeder  409  may interconnect the overmolded ring  406  with each of the overmolded feet  408 . For example, the first housing part  22  (along with the second housing part  24 ) may be constructed of a relatively rigid plastic material, e.g, polycarbonate (PC) or acrylonitrile butadiene styrene (ABS), and the overmolded ring  406 , feet  408 , and feeders  409  may be constructed of an elastomeric material, e.g., Versollan™. Alternative, the ring, feet, and/or feeders may be separate molded pieces that are attached in an operative position. 
     The support system  405  provides an arrangement that avoids the need for inlet and outlet seals adjacent the inlet and outlet of the blower. In addition, the support system  405  is constructed of an elastomeric material that isolates (e.g., vibration isolated) and/or serves as a suspension between the blower  10  and the outer casing  400 , e.g., without using springs. In an embodiment, additional supports (e.g., feet or pegs) may be provided to the top and/or sides of the blower so that the outer casing and the blower supported therein may be oriented in any direction, e.g., casing may be positioned on its side rather than vertically. 
     5. Sealing Arrangement for Blower Housing 
     Each of the blowers  10 ,  210 ,  310  described above may include a sealing arrangement between the housing parts of the housing, e.g., to prevent leak or loss of pressure. 
     In an embodiment, as shown in  FIG. 6-1 , the end portion of the first housing part  522  of the blower (i.e., the first stage cover of the blower) includes a stepped configuration with first and second steps  527 ( 1 ),  527 ( 2 ). Each of the steps  527 ( 1 ),  527 ( 2 ) is provided with a sealing structure, i.e., first and second seals  597 ( 1 ),  597 ( 2 ) respectively. In an embodiment, the seals  597 ( 1 ),  597 ( 2 ) may be overmolded with the first housing part  522  in a manner as described above, e.g., elastomeric seals  597 ( 1 ),  597 ( 2 ) overmolded to relatively rigid plastic first housing part  522 . 
     The end portion of the second housing part  524  of the blower includes a similar stepped configuration as the first housing part  522 , e.g., first and second steps  529 ( 1 ),  529 ( 2 ). 
     As illustrated, when the first and second housing parts  522 ,  524  are coupled to one another, the first seal  597 ( 1 ) of the first housing part  522  engages the first step  529 ( 1 ) of the second housing part  524  to provide a seal between housing parts  522 ,  524 . Also, the second step  527 ( 2 ) of the first housing part  522  and the second step  529 ( 2 ) of the second housing part  524  cooperate to define a slot adapted to receive and support the edge  531  of stator component  530  including stator vanes  532  (e.g., similar to stator component  30 ). The second seal  597 ( 2 ) provides a seal between the stator component  530  and the housing parts  522 ,  524 . 
     In addition, multiple snap-fit members  516 , e.g.,  3  snap-fit members, are provided to the end portion of the first housing part  522  that are adapted to engage a respective shoulder  518  provided to the second housing part  524  with a snap-fit. The snap-fit members  516  secure the first and second housing parts  522 ,  524  to one another and maintain the seal. However, it should be appreciated that the first and second housing parts may be secured to one another in other suitable manners, e.g., welding, adhesive (e.g., gluing), heat staking, fasteners (e.g., screws), etc. 
       FIG. 6-1  also illustrates an overmolded ring  406  and feeder  409  provided to the first housing part  522 , and the ring  406  engaged within the slot between the base  402  and cover  404  of an outer casing as described above. In addition,  FIG. 6-1  illustrates impeller  554  between stator component  530  and the outlet of the blower. 
     In an alternative embodiment, as shown in  FIG. 6-2 , the edge  531  of the stator component  530  may include a relatively rigid protrusion  533  (e.g., v-shaped protrusion) adapted to engage the second seal  597 ( 2 ), e.g., to improve grip and sealing. Also, the second seal  597 ( 2 ) may have a more block-like configuration, rather than a bead-like configuration as shown in  FIG. 6-1 . 
     6. Alternative Blower Embodiment 
       FIGS. 7-1 to 7-13  illustrate a blower  610  according to another embodiment of the present invention. Similar to the blowers  10 ,  210 ,  310  described above, the blower  610  includes two stages with one impeller  650  positioned on one side of the motor  640  and one impeller  652  positioned on the other side of the motor  640 . Also, the blower  610  has axial symmetry with both the inlet  626  and outlet  628  aligned with an axis  615  of the blower  610 . 
     6.1 General Description 
     A stationary portion of the blower  610  includes a housing  620  with first and second housing parts  622 ,  624 , a stator component  630 , and first and second shields  660 ,  670 . A rotating portion of the blower  610  includes a rotatable shaft or rotor  680  adapted to be driven by motor  640  and first and second impellers  650 ,  652  (e.g., mixed flow) provided to end portions of the shaft  680 . The motor  640  includes a magnet  642  provided to shaft  680  and a stator assembly  644  to cause spinning movement of the shaft  680  via the magnet  642 . 
     The stator assembly  644  includes windings  646  and a stator or stator lamination stack  648  (e.g., slotless or toothless) provided to the windings  646 . In an embodiment, the resistance of the windings  646  and/or current draw (e.g., at start-up) may be monitored to determine temperature, which may be used to indicate faults in the motor (e.g., bearing fault detection, bearing end of life failure or rubbing condition, software fault in the electronic drive systems). For example, after the motor has stopped but still remains warm, the resistance of the windings may be measured (e.g., via a circuit in the blower). It is noted that resistance of the windings changes with temperature in a known way. If the resistance was such that it implied a much hotter than usual temperature, the device would go into a fault mode, e.g., and prompt the user to have the blower serviced. Several blower faults tend to lead to unusually high temperatures, e.g., bearing end of life failures or software faults in electronic drive systems. 
     The inlet  626  is provided by the first housing part  622  (also referred to as a first stage cover) at one end and the outlet  628  is provided by the second housing part  624  (also referred to as a final stage cover) at the other end. 
     6.2 Stator Component 
     As best shown in  FIGS. 7-7 to 7-10 , the stator component  630  includes an annular base portion  634 , a shield portion  636 , a tube or bearing tube  638  extending from the shield portion  636 , and a plurality of spaced apart side walls  632  extending between the base portion  634  and the shield portion  636 . As illustrated, the stator component  630  forms a cylindrical “cage” and the spaced apart side walls  632  define openings  633  into the “cage”. The stator component  630  may be integrally formed (e.g., injection molded) as a one-piece structure. However, the stator component  630  may be constructed in other suitable manners and/or may be made in separate parts. 
     As best shown in  FIGS. 7-3 to 7-5 , the base portion  634  is sandwiched between the first and second housing parts  622 ,  624  to support the stator component  630  within the housing  620 . In addition, the second housing part  624  may include a protrusion  695  (e.g., v-shaped protrusion as best shown in  FIG. 7-4 ) adapted to engage the first housing part  622 , e.g., to improve grip and sealing. 
     In an alternative embodiment, as shown in  FIG. 7-4B , the first housing part  622  may include a connecting portion  622 ( 1 ) structured to overlap and/or overhang a connecting portion  624 ( 1 ) of the second housing part  624 . Similar to the above embodiment, the base portion  634  of the stator component  630  is sandwiched between the first and second housing parts  622 ,  624 . In addition, the second housing part  624  may include a protrusion  696  for sealing against the first housing part  622 . 
     The outer edge of the shield portion  636  substantially aligns with or extends radially beyond the outer edge of the impeller  650 . The shield portion  636  provides a narrow annular gap  710  between its outer edge and the side wall of the housing part  622 , which is sufficient to direct gas into the stator component  630 . The shield portion  636  includes an opening  666  that allows access to the interior of the tube  638 . 
     6.2.1 Bearing Alignment and Retention 
     Similar to the above embodiments, the tube  638  is structured to retain and align bearings  600 ,  602  (e.g., of mixed bearing sizes) that rotatably support the shaft  680 . In addition, the tube  638  is sufficiently “magnetically transparent”, which allows the stator assembly  644  to act on the magnet  642  positioned within the tube  638  without significant loss of flux density and/or increased heat, if any. 
     Also, the tube  638  may be constructed of an acoustically damped material to damp vibrations caused by rotor operation, e.g., polypropylene, nylon (reinforced), liquid crystal polymer (LCP) with ceramic loading (conduct heat), polyphenylene sulfide (PPS) with graphite fill, polyetheretherketone (PEEK). If ball bearings are utilized, the number of balls within the bearings may be optimized to minimize vibrations. 
     A cap portion  668  is provided to the shield portion  636  along the opening  666 . The cap portion  668  provides a stop for the bearing  600  and hence retains the shaft  680  within the tube  638 . In addition, the cap portion  668  may act as a spacer for the impeller  650 . 
     Washers  604  and a spring or biasing element  606  may be provided between the bearing  602  and the rotor magnet  642  and a spacer  607  may be provided between the bearing  600  and the rotor magnet  642 , e.g., to maintain alignment/spacing of the rotor magnet  642  with the stator assembly  644 , act as wear stop, and/or provide a pre-load. Also, the spacer  607  (e.g., constructed of metallic ferrite) adjacent the bearing  600  acts as a magnetic shunt or flux shield to direct magnetic field towards the windings  646  and away from the bearing  600 , e.g., to avoid heating bearing. It should be appreciated that such a spacer or shield may also be provided adjacent the bearing  602 . The flux shield may be an optional component, but may increase bearing/lube life due to reduced eddy current losses in the bearing outer races and balls. 
     As shown in  FIG. 7-3 , the spring  606  provides an inner race pre-load (IRP), e.g., about 1.25 lb spring load, on the bearing  602 . Specifically, the bearing  602  includes an inner race  602 ( 1 ), an outer race  602 ( 2 ), and ball bearings  602 ( 3 ) provided between the inner and outer races (e.g., there may be a clearance between the ball bearings and the races). The inner and outer races  602 ( 1 ),  602 ( 2 ) provide surfaces upon which the ball bearings  602 ( 3 ) run. Also, the bearing may include a spacer element between the inner and outer races to maintain spacing between the ball bearings (e.g., cylinder with openings to receive respective ball bearings). In the illustrated embodiment, the spring  606  is constructed and arranged to engage the inner race  602 ( 1 ) of the bearing  602  to provide a spring load to the bearing, which brings the ball bearings into contact with the races (i.e., load transmitted from the inner race to the ball bearings, and from the ball bearings to the outer race). 
     In an alternative embodiment, the spring may be constructed and arranged to provide an outer race pre-load (ORP) on the bearing, e.g., see  FIGS. 8 and 9-1 to 9-2  described below. 
     6.2.2 Alternative Airflow Path 
     Similar to the embodiment described above, the shield portion  636  and cap portion  668  cooperate to provide by-pass passages or conduits  686  (as shown in  FIGS. 7-6 and 7-8 ) to provide pressure balance across the bearings  600 ,  602 . Specifically, the by-pass passages  686  provide a short circuit of pressure around the tube  638  and hence the bearings  600 ,  602 . 
     In an embodiment, a tight tolerance (i.e., a small gap) is provided between the inner diameter of the cap portion  668  and the shaft  680  which increases the impedance between the cap portion  668  and the shaft  680 . Hence, air can flow with less resistance through the by-pass passage or bleed hole  686  (e.g., tight tolerance may also apply to the by-pass arrangement shown in  FIG. 1-1 ). 
     Without a by-pass, air may flow through the bearings, upwards from the high pressure side to the low pressure side. The by-pass passage connects the high pressure zone to a point above the top bearing. This means high pressure exists more or less equally across the pair of bearings. Therefore, there is little flow through the bearings, and the grease neither dries out nor gets displaced, thereby improving bearing longevity. 
     6.2.3 Stator Assembly Alignment and Retention 
     The stator assembly  644  is provided along the exterior surface of the tube  638 . In addition, the stator component  630  and first shield  660  cooperate to support and maintain the stator assembly  644  in an operative position, as described in greater detail below. 
     6.3 First Shield 
     As best shown in  FIGS. 7-11 to 7-12 , the first shield  660  includes a base  661  and a plurality of stator vanes  663  provided to the base  661 . The first shield  660  is attached to the stator component  630 , e.g., by engaging pins  665  on the first shield  660  with respective openings  635  provided in the base portion  634  of the stator component  630  (e.g., pins heat staked into position). However, the first shield  660  may be attached to the stator component  630  in other suitable manners. 
     The plurality of stator vanes  663 , e.g., between 2 and 100 stator vanes, are structured to direct airflow towards an orifice  667  in the base  661 . In the illustrated embodiment, the stator component  630  has six stator vanes  663 . Each vane  663  is substantially identical and has a generally spiral shape. In addition, each vane  663  includes an inner portion  637  (adjacent the orifice  667 ) and an outer portion  639 . As best shown in  FIG. 7-11 , the inner portion  637  is recessed (e.g., reduced in height) with respect to the outer portion  639 . 
     As best shown in  FIGS. 7-3 and 7-5 , the windings  646  of the stator assembly  644  are engaged or supported by the recessed, inner portion  637  of the stator vanes  663 , and the stack  648  of the stator assembly  644  is engaged or supported by the outer portion  639  of the stator vanes  663 . 
     In addition, the exterior surface  649  of the stack  648  (e.g., see  FIGS. 7-3 and 7-5 ) includes a toothed configuration that is adapted to engage or interlock with spaced-apart teeth  651  provided by interior surfaces of the spaced apart side walls  632  (e.g., see  FIG. 7-9 ). Remaining portions of the toothed configuration of the stack  648  at least partially protrude through the openings  633  in the stator component  630 , e.g., flush with exterior surfaces of the side walls  632  (see  FIGS. 7-5 and 7-7 ). Thus, the stator component  630  and first shield  660  cooperate to retain or secure the stator assembly  644  in an operative position. 
     As shown in  FIGS. 7-1 to 7-3 and 7-7 , wires  698  (e.g., three wires for a three phase motor) extend from the windings  646  to outside the housing  620  to conduct current from an external source to the windings  646 . As illustrated, slots  631  are provided through the stator component  630  (see  FIG. 7-9 ) and slots  621  are provided through the housing  620  (see  FIG. 7-3 ) to accommodate passage of respective wires  698  from the windings  646  to outside the housing  620 . 
     In the illustrated embodiment, the stack  648  and windings  646  are exposed to the flow of gas, e.g., via the openings  633  in the stator component  630 , as shown in  FIGS. 7-3, 7-5, and 7-7 . This arrangement allows forced-convection cooling of the stack  648 /windings  646  as gas flows through the stator component  630  in use. In addition, this arrangement may assist in heating the patient air. 
     6.4 Second Shield 
     As shown in  FIG. 7-13 , the second shield  670  includes a plurality of stator vanes  672 , e.g., between 2 and 100 stator vanes, to direct airflow towards the outlet  628 . In the illustrated embodiment, the shield  670  has 7 stator vanes. Each vane  672  is substantially identical and has a generally spiral shape. In addition, each vane  672  includes an inner portion  673  (adjacent the hub  674 ) and an outer portion  675 . As best shown in  FIGS. 7-3 and 7-5 , the outer portion  675  is recessed (e.g., reduced in height) with respect to the inner portion  673 , and a contoured edge  676  extends between the inner and outer portions  673 ,  675 . 
     In the illustrated embodiment, the stator vanes  672  support the shield  670  within the second housing part  624  adjacent the outlet  628 . As illustrated, the contoured edge  676  of the shield  670  engages the edge of the outlet  628  to align the shield  670  with the outlet  628  (see  FIG. 7-3 ). The hub  674  and inner portion  673  of the vanes  672  extend at least partially through the outlet  628  and the outer portion  675  of the vanes  672  engage the lower wall of the second housing part  624 , as best shown in  FIG. 7-3 . The hub  674  at the central portion of the shield  670  is shaped to direct the air flow down towards the outlet  628 . 
     In addition, the second shield  670  includes pins  677  that are adapted to engage with respective openings  678  provided in lower wall of the second housing part  624 , e.g., pins heat staked into position, as shown in  FIG. 7-3 . However, the second shield  670  may be attached to the second housing part  624  in other suitable manners. 
     The second shield  670  (also referred to as a final stage disc) includes a disc or shield to cover the stator vanes  672  in order to keep any discontinuities away from the blades of the impeller  652 . However, other structure may be provided to keep any discontinuities away from the impeller blades. For example, the stator vanes  672  may be integrated into the second housing part  624 , and the impeller  652  may include a lower shroud to act as a rotating shroud or shield between the impeller blades and stator vanes  672 . 
     6.5 Fluid Flow Path 
     In the first stage, air enters the blower  610  at the inlet  626  and passes into the first impeller  650  where it is accelerated tangentially and directed radially outward. It is noted that suction is developed at the inlet to draw air into the blower. Air then flows in a spiral manner with a large tangential velocity component and also an axial component passing through the gap  710  defined by the outer edge of the shield portion  636  and the side wall of housing part  622 . Air then enters the stator component  630  via the openings  633  in the stator component  630 , and flows into the stator vanes  663  of the first shield  660  where it is directed radially inwardly towards orifice  667 , and thereafter onto the second stage. 
     In the second stage, air passes into the second impeller  652  where it is accelerated tangentially and directed radially outward. Air then flows in a spiral manner with a large tangential velocity component and also an axial component passing through the gap  712  defined by the outer edge of the second shield  670  and the side wall of housing part  624 . Air then enters the stator vanes  672  formed in the shield  670  and is directed towards the outlet  628 . 
     6.5.1 Alternative Structure to Direct Flow 
     In the above-described embodiments, the blowers include stator vanes to direct airflow towards a second stage and towards the outlet. Such stator vanes help to straighten the flow and remove the “swirl” caused by the impellers. In alternative embodiments, the stator vanes may be replaced with alternative structure to direct or straighten flow. For example, a grid, mesh (e.g., woven), honeycomb-like structure, and/or extrusion (e.g., helical) may be provided to direct flow in use. 
     Also, in an alternative embodiment, multiple tangential feeds may be provided to the axial outlet  628  to direct flow tangentially from the outlet. 
     7. Tube as a Mandrel 
     In an embodiment, the tube of the stator component may be used as a mandrel to help form the windings of the stator assembly. The tube may be structured and shaped to facilitate its use as a mandrel. For example, the cylindrical and tapered construction of the tube may facilitate its use as a mandrel. The shape may be polygonal, e.g., rectangle, triangle, square, pentagon, hexagon, etc. In addition, the tube may include one or more structural components, such as splines, to aid with separation of the windings from the mandrel. 
     8. Interstage Seal 
       FIG. 8  illustrates a blower according to another embodiment of the present invention. The blower is similar to blower  610  described above and indicated with similar reference numerals. In contrast, the first shield  660  (i.e., the interstage “de-swirl” vane) includes a lip region or flange  660 ( 1 ) adapted to engage or seal against the second housing part  624 . Specifically, the lip region  660 ( 1 ) of the first shield  660  is structured to engage the base portion  634  of the stator component  630 , and the lip region  660 ( 1 ) and base portion  634  are supported and/or sandwiched between the first and second housing parts  622 ,  624  to support the first shield  660  and the stator component  630  within the housing  620 . Moreover, the lip region/base portion arrangement is structured to provide an interstage seal to prevent air leakage from the second stage back into the first stage in use. In addition, the connecting portion  622 ( 1 ) of the first housing part  622  is structured to overlap and/or overhang the connecting portion  624 ( 1 ) of the second housing part  624 . 
     However, an interstage seal may be provided in other suitable manners. For example, a gasket or gooey sealant may be used at the interfaces of the shield  660 , stator component  630 , and housing parts  622 ,  624 . In another embodiment, one or more of the interface surfaces may be overmolded with a soft silicone or TPE. 
     9. Blower with Metal Bearing Support 
       FIGS. 9-1 to 9-2  illustrate a blower  810  according to another embodiment of the present invention. Similar to the blowers described above, the blower  810  includes two stages with one impeller  850  positioned on one side of the motor  840  and one impeller  852  positioned on the other side of the motor  840 . Also, the blower  810  has axial symmetry with both the inlet  826  and outlet  828  aligned with an axis  815  of the blower  810 . 
     In contrast to the blowers described above, the bearings  800 ,  802  that support shaft  880  are retained by a metal housing assembly (rather than a plastic tube), as described in greater detail below. It is noted that the metal housing assembly includes a “cage”-like adaptor that supports the metal housing assembly within the blower housing and allows gas to flow into the first shield and onto the second stage in a similar manner to the “cage” like stator component described above. 
     9.1 General Description 
     A stationary portion of the blower  810  includes a housing  820  with first and second housing parts  822 ,  824 , a metal housing assembly  830 , and first and second shields  860 ,  870 . A rotating portion of the blower  810  includes a rotatable shaft or rotor  880  adapted to be driven by motor  840  and first and second impellers  850 ,  852  provided to end portions of the shaft  880 . The motor  840  includes a magnet  842  provided to shaft  880  and a stator assembly  844  to cause spinning movement of the shaft  880  via the magnet  842 . 
     9.2 Metal Housing Assembly 
     The housing assembly  830  is constructed of a metallic material and includes a main housing  832 , an end bell  834 , and an adaptor  836  (e.g., secured to one another by one or more fasteners  838 ). As illustrated, the main housing  832  provides a recess for supporting bearing  800  and the end bell  834  provides a recess for supporting bearing  802 . The main housing and end bell are structured to support bearings of the same size. However, the main housing and end bell may be structured to support mixed bearing sizes. 
     The metal bearing support provided by the housing assembly  830  improves heat transfer from the bearings in use. Also, the main housing  832 , end bell  834 , and adaptor  836  (e.g., constructed of aluminum) may be machined bar stock. In an embodiment, the end bell and adaptor may be aluminum die cast pieces for high volume production. 
     As best shown in  FIG. 9-2 , the adaptor  836  forms a cylindrical “cage” that defines openings  833  into the cage. 
     9.3 Stator Assembly Alignment and Retention 
     The main housing  832  and end bell  834  cooperate to support and maintain the stator assembly  844  in an operative position. 
     9.4 Interstage Seal 
     Similar to the  FIG. 8  embodiment described above, a lip region  860 ( 1 ) of the first shield  860  is structured to engage the base  836 ( 1 ) of the adaptor  836 , and the lip region  860 ( 1 ) and base  836 ( 1 ) are supported and/or sandwiched between the first and second housing parts  822 ,  824  to support the first shield  860  and housing assembly  830  within the housing  820 . In addition, the lip region/base arrangement is structured to provide an interstage seal to prevent air leakage from the second stage back into the first stage in use. 
     9.5 Outer Race Preload (ORP) 
     In the illustrated embodiment, a spacer or flux shield  804  is provided between each bearing  800 ,  802  and the rotor magnet  842 . In addition, a spring or biasing element  806  is provided between the bearing  802  and the end cap  834 . 
     The spring  806  (e.g., crest-to-crest spring) provides an outer race preload (ORP) (outer race preload also shown in  FIG. 8 ) on the bearing  802  (instead of an inner race preload such as that shown in  FIG. 7-3 ). Specifically, the spring  806  is constructed and arranged to engage the outer race  802 ( 2 ) of the bearing  802  to provide a spring load to the bearing, which brings the ball bearings into contact with the races (i.e., load transmitted from the outer race  802 ( 2 ) to the ball bearings  802 ( 3 ), and from the ball bearings  802 ( 3 ) to the inner race  802 ( 1 )). 
     In an embodiment, the ORP arrangement may reduce or eliminate corrosion of the second stage bearing  802  (e.g., at the inner race) over the life of the blower. 
     9.6 Fluid Flow Path 
     In the first stage, air enters the blower  810  at the inlet  826  and passes into the first impeller  850  where it is accelerated tangentially and directed radially outward. It is noted that suction is developed at the inlet to draw air into the blower. Air then flows in a spiral manner with a large tangential velocity component and also an axial component passing through the gap  910  defined by the outer edge of the housing assembly  830  and the side wall of housing part  822 . Air then flows into the stator vanes  863  of the first shield  860  via the openings  833  in the adaptor  836  where it is directed radially inwardly onto the second stage. 
     In the second stage, air passes into the second impeller  852  where it is accelerated tangentially and directed radially outward. Air then flows in a spiral manner with a large tangential velocity component and also an axial component passing through the gap  912  defined by the outer edge of the second shield  870  and the side wall of housing part  824 . Air then enters the stator vanes  872  formed in the shield  870  and is directed towards the outlet  828 . 
     10. Closed Slot External Winding 
       FIGS. 10-1 to 10-3  illustrate a stator  948  for a stator assembly according to an embodiment of the present invention. The stator  948  includes an outer portion  948 ( 1 ) ( FIG. 10-1 ) and an inner portion  948 ( 2 ) ( FIG. 10-2 ) structured to be received within the outer portion  948 ( 1 ).  FIG. 10-3  shows the stator  948  with the assembled outer and inner portions  948 ( 1 ),  948 ( 2 ). 
     The inner portion  948 ( 2 ) has a plurality of stator teeth  949 , e.g., six stator teeth, on which stator coils or windings are wound. The outer portion  948 ( 1 ) is ring shaped and includes a plurality of recesses  950  along its inner circumference adapted to receive respective teeth of the inner portion  948 ( 2 ). When assembled, the stator  948  provides a closed slot arrangement. 
     The outer circumference of the outer portion  948 ( 1 ) includes a toothed configuration that is adapted to engage or interlock with the stator component (e.g. for use in blower  610  similar to the arrangement described above in relation to  FIGS. 7-7 and 7-9 ). In addition, one or more slots  951  may be provided in the outer circumference of the outer portion  948 ( 1 ) to accommodate passage of respective wires from the windings. 
     This “closed-slot” stator-core arrangement facilitates the insertion of magnet wire because magnet wire can be inserted from the outside via a generously wide slot opening. That opening becomes closed when the outer portion  948 ( 1 ) is provided to the toothed inner portion  948 ( 2 ). In its final assembled form, there is no opening of the slot, and as such, there is little magnetic detent (or magnetic cogging effect) produced by the interaction of the rotor&#39;s salient poles and the stator. It is a cost-effective, low cogging configuration. 
     In the illustrated embodiment, each tooth  949  of the inner portion  948 ( 2 ) has a generally T-shaped arrangement with substantially square edges. In an alternative embodiment, as shown in  FIG. 11 , the end portion of each tooth  949  (and corresponding recesses  950  in the outer portion  948 ( 1 )) may be more rounded. 
     In yet another embodiment, the stator assembly may include an ironless and slotless stator (i.e., using air as the flux return path, rather than using iron to concentrate the flux). 
     11. Blower with Slotted Stator 
       FIGS. 12-1 to 12-3  illustrate a blower  1010  according to another embodiment of the present invention. Similar to the blowers described above, the blower  1010  includes two stages with one impeller  1050  positioned on one side of the motor  1040  and one impeller  1052  positioned on the other side of the motor  1040 . Also, the blower  1010  has axial symmetry with both the inlet  1026  and outlet  1028  aligned with an axis of the blower  1010 . 
     In this embodiment, the stator  1048  of the stator assembly includes a slotted configuration. As best shown in  FIG. 12-3 , the stator or lamination stack  1048  includes a ring-shaped main body  1048 ( 1 ) and a plurality of stator teeth  1048 ( 2 ), e.g., six stator teeth, extending radially inwardly from the main body  1048 ( 1 ). The stator coils or windings  1046  are wound on respective teeth  1048 ( 2 ) as shown in  FIG. 12-2 . The windings can be inserted from the inside via respective slot openings (spacing between teeth). 
     Similar to arrangements described above, the outer circumference of the main body  1048 ( 1 ) includes a toothed configuration that is adapted to engage or interlock with the stator component  1030 . In addition, one or more slots  1051  may be provided in the outer circumference of the main body  1048 ( 1 ) to accommodate passage of respective wires from the windings  1046 . 
     The remaining portions of the blower are similar to arrangements described above, e.g., housing  1020  with first and second housing parts  1022 ,  1024 , “cage”-like stator component  1030  with bearing tube  1038 , and first and second shields  1060 ,  1070 . 
     12. Blower with Coreless Motor 
       FIGS. 13-1 to 13-2  illustrate a blower  1110  according to another embodiment of the present invention. Similar to the blowers described above, the blower  1110  includes two stages with one impeller  1150  positioned on one side of the motor  1140  and one impeller  1152  positioned on the other side of the motor  1140 . Also, the blower  1110  has axial symmetry with both the inlet  1126  and outlet  1128  aligned with an axis of the blower  1110 . 
     In this embodiment, the blower  1110  includes a coreless motor in which the windings or magnet wire are wound directly on the stator component thereby eliminating a stator or lamination stack. For example, as best shown in  FIG. 13-2 , windings or magnet wire  1146  may be wound directly on the bearing tube  1138  of the stator component  1130 . In an embodiment, the windings may be at least partially supported by side walls of the stator component. 
     The remaining portions of the blower are similar to arrangements described above, e.g., housing  1120  with first and second housing parts  1122 ,  1124 , “cage”-like stator component  1130 , and first and second shields  1160 ,  1170 . In the illustrated embodiment, the first housing part  1122  may include one or more guide structures  1123  for guiding magnet wire outside the housing, e.g., binding post for looping wire. 
     13. Alternative Embodiments for Assembly 
     In an embodiment, the bearings supporting the shaft may be bonded to respective ends of the bearing tube by a plasma treatment stage. For example, with respect to the embodiment of blower  610 , plasma may be used to treat the plastic surface of the first stage bearing seat of bearing tube  638  that engages the outer race of bearing  600 . The plasma treatment allows the adhesive of choice (e.g., a Loctite cyanoacrylate compound) to wet nicely when applied. This wetting action has been shown to increase the bondline strength and also reduce the variation in that process (as determined by shear strength). The bondline holds the rotor assembly within the tube and stator assembly. 
     In an alternative embodiment, liquid primers may be used to treat the bearing seat before the adhesive (e.g., a Loctite cyanoacrylate compound) is applied. Also, an alternative to cyanoacrylate compound as an adhesive with the plasma/primers may be epoxy. 
     In an embodiment, the first and second housing parts of the housing may be bonded together with ultrasonic welding using a shear joint. 
     Also, in an embodiment, combinations of rigid and softer materials may be molded in a two-shot process (e.g., co-molding) to improve sealing in various positions through the blower. 
     In order to have the lead wires being the same length as they exit the blower housing, a “binding post” or “cleat” may be positioned on the outside of the housing. One or more wires may be looped around that binding post so that the lengths of the wires can be equalized. 
     In an embodiment, a labyrinth seal may be provided to allow the pressure to equalize between the outboard side of the first-stage bearing and the outboard side of the second-stage bearing to the extent that it is possible with minimal recirculating flow beneath the first-stage impeller (e.g., see  FIGS. 7-3 and 7-6 ). 
     While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment. Furthermore, each individual component of any given assembly, one or more portions of an individual component of any given assembly, and various combinations of components from one or more embodiments may include one or more ornamental design features. In addition, while the invention has particular application to patients who suffer from OSA, it is to be appreciated that patients who suffer from other illnesses (e.g., congestive heart failure, diabetes, morbid obesity, stroke, bariatric surgery, etc.) can derive benefit from the above teachings. Moreover, the above teachings have applicability with patients and non-patients alike in non-medical applications.