U.S. patent application number 12/458072 was filed with the patent office on 2010-01-07 for apparatus for supplying breathable gas.
This patent application is currently assigned to ResMed Limited. Invention is credited to Stanley Clark, Muditha Pradeep Dantanarayana, Ian Malcolm Smith, Alexander Virr, Nicola Frances Wickham, Peter John Deacon Wickham.
Application Number | 20100000535 12/458072 |
Document ID | / |
Family ID | 3806664 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000535 |
Kind Code |
A1 |
Wickham; Peter John Deacon ;
et al. |
January 7, 2010 |
Apparatus for supplying breathable gas
Abstract
An apparatus for supplying breathable gas includes a main
housing, a sub-housing removably connected to the main housing, and
a vent valve assembly provided to the sub-housing. The sub-housing
has a gas flow path between a gas inlet and a gas outlet. The vent
valve assembly includes a gas venting conduit in fluid
communication with the gas flow path. The gas venting conduit is
adapted to be selectively restricted by a cam abutting an exterior
of the gas venting conduit, whereby a position of the cam is
variable to vary gas passing through the gas venting conduit which
varies a flow rate of gas leaving the gas outlet.
Inventors: |
Wickham; Peter John Deacon;
(Five Dock, AU) ; Virr; Alexander; (Balmain,
AU) ; Smith; Ian Malcolm; (Westleigh, AU) ;
Dantanarayana; Muditha Pradeep; (Cherrybrook, AU) ;
Clark; Stanley; (Holgate, AU) ; Wickham; Nicola
Frances; (Five Dock, AU) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
ResMed Limited
Bella Vista
AU
|
Family ID: |
3806664 |
Appl. No.: |
12/458072 |
Filed: |
June 30, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10984893 |
Nov 10, 2004 |
7571725 |
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12458072 |
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10414297 |
Apr 16, 2003 |
6899100 |
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10984893 |
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09931909 |
Aug 20, 2001 |
6629528 |
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10414297 |
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09268758 |
Mar 16, 1999 |
6302105 |
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09931909 |
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Current U.S.
Class: |
128/205.24 |
Current CPC
Class: |
A61M 2205/125 20130101;
A61M 2016/0021 20130101; A61M 16/205 20140204; A61M 16/107
20140204; A61M 16/204 20140204; A61M 2205/42 20130101; A61M
2016/0039 20130101; A61M 16/0066 20130101; A61M 16/0057 20130101;
A61M 16/20 20130101 |
Class at
Publication: |
128/205.24 |
International
Class: |
A61M 16/20 20060101
A61M016/20; A61M 16/00 20060101 A61M016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 1998 |
AU |
PP2401 |
Claims
1-15. (canceled)
16. An apparatus for supplying breathable gas, the apparatus
comprising: a main housing; a sub-housing removably connected to
the main housing, the sub-housing having a gas flow path between a
gas inlet and a gas outlet; and a vent valve assembly provided to
the sub-housing, the vent valve assembly including a gas venting
conduit in fluid communication with the gas flow path, the gas
venting conduit adapted to be selectively restricted by a cam
operatively communicated with the gas venting conduit, whereby a
position of the cam is variable to vary gas passing through the gas
venting conduit which varies a flow rate of gas leaving the gas
outlet.
17. An apparatus as claimed in claim 16, wherein the gas venting
conduit includes a flexible portion adapted to be selectively
restricted by the cam.
18. An apparatus as claimed in claim 17, wherein the cam is
controlled by a motor.
19. An apparatus as claimed in claim 18, wherein the gas venting
conduit and flexible portion are removable from the main housing
along with the sub-housing while the cam and motor remain with the
main housing.
20. An apparatus as claimed in claim 18, wherein the cam and motor
are associated with the main housing and are isolated or not in
fluid communication with the gas flow path.
21. An apparatus as claimed in claim 16, wherein the gas venting
conduit is removable from the main housing along with the
sub-housing to allow cleaning, sterilizing, disinfecting, and/or
replacement along with the sub-housing.
22. An apparatus as claimed in claim 16, further comprising an
impeller within the sub-housing in fluid communication between the
gas inlet and the gas outlet.
23. An apparatus as claimed in claim 22, wherein the impeller is
adapted to releasably engage a motive power source within the main
housing.
24. An apparatus for supplying breathable gas, the apparatus
comprising: a main housing; a sub-housing removably connected to
the main housing, the sub-housing having a gas flow path between a
gas inlet and a gas outlet; and a vent valve assembly including a
gas venting conduit and a cam adapted to selectively restrict the
gas venting conduit, the gas venting conduit being provided to the
sub-housing and in fluid communication with the gas flow path and
the cam being provided to the main housing and isolated or not in
fluid communication with the gas flow path, wherein the gas venting
conduit is removable from the main housing along with the
sub-housing while the cam remains with the main housing.
25. An apparatus as claimed in claim 24, wherein the gas venting
conduit includes a flexible portion adapted to be selectively
restricted by the cam.
26. An apparatus as claimed in claim 25, wherein the cam is
controlled by a motor.
27. An apparatus for supplying breathable gas, the apparatus
comprising: a Y-shaped conduit including a first conduit portion in
communication with a supply of pressurized gas, a second conduit
portion in communication with a patient, and a third conduit
portion in communication with atmosphere; a first vent valve
assembly including a first flexible portion provided to the first
conduit portion; a second vent valve assembly including a second
flexible portion provided to the third conduit portion; and first
and second cams adapted to selectively restrict respective first
and second flexible portions, wherein the first and second cams are
linked so that one of the flexible portions is restricted while the
other of the flexible portions is enlarged which controls the
pressure of gas supplied to the patient.
28. An apparatus as claimed in claim 27, wherein the cams are
controlled by a motor.
29. An apparatus as claimed in claim 27, wherein the first flexible
portion is restricted and the second flexible portion is enlarged
to lower the pressure of gas supplied to the patient.
30. An apparatus as claimed in claim 27, wherein the first flexible
portion is enlarged and the second flexible portion is restricted
to raise the pressure of gas supplied to the patient.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an apparatus for supplying
breathable gas to a human used in, for example, the Continuous
Positive Airway Pressure (CPAP) treatment of Obstructive Sleep
Apnea (OSA), other respiratory. diseases/disorders such as
emphysema or the application of assisted ventilation.
BACKGROUND OF THE INVENTION
[0002] CPAP treatment of Obstructive Sleep Apnea (OSA) involves the
delivery of a breathable gas (generally air) pressurised above
atmospheric pressure to a patient's airways via a conduit and a
mask. CPAP pressures of 4 cm H.sub.2O to 22 cm H.sub.2O are
typically used for treatment of OSA, depending on patient
requirements. Treatment pressures for assisted ventilation can
range of up to 32 cm H.sub.2O and beyond, again depending on
patient requirements.
[0003] For either the treatment of OSA or the application of
assisted ventilation or similar, the pressure of the gas delivered
to patients can be constant level, bi-level (in synchronism with
patient breathing) or auto setting in level. Throughout this
specification reference to CPAP is intended to incorporate a
reference to any one of, or combinations of, these forms of
pressurised gas supply.
[0004] A disadvantage of existing CPAP gas supply apparatus,
especially those used in hospitals and the like, is the danger of
biological contamination and disease/virus/bacteria transfer. More
particularly, there can be a significant reverse flow during heavy
expiration and/or coughing and biological material exhaled by a
patient can be deposited in the gas supply apparatus and
transferred to another patient who uses the same machine. Further,
a patient continually using the same machine can be re-infected by
a prior condition.
[0005] Hitherto, CPAP apparatus have basically comprised a closed
outer casing surrounding internal components. Components inside,
and constituting part of, the gas flow path include the gas inlet,
inlet filter, impeller, outlet muffler and gas outlet. Components
outside the gas flow path include control electronics, power
regulators and motor. As a result, present CPAP apparatus have a
gas flow path that is extremely difficult to clean/sterilise
without the time consuming dismantling and removal of all the "gas
flow path" components. Further, without disassembly, common
sterilisation procedures such as autoclaving will damage the
circuit boards and other electrical components.
[0006] An attempt to solve the above problem involves incorporating
a bacteriological filter into the gas flow path adjacent the gas
outlet to prevent biological material being forced back into the
machine and any such material leaving the machine and being inhaled
by the patient. However, these filters are expensive and add a
significant resistance to the air path. requiring larger and
noisier fans and motors. A more restricted air path also represents
a major difficulty. to administering bi-level CPAP treatment due to
the higher inspiratory air flow requirements of patients with
advanced respiratory disease. Moreover, it is difficult to produce
a biological filter which can trap very small biological particles
such as viruses and spores that is still able to pass the required
amount of air with an acceptable pressure drop, as decreasing
filter pore size decreases hydraulic permeability.
[0007] It is an object of the present invention to substantially
overcome or at least ameliorate one or more of the above prior art
deficiencies.
SUMMARY OF THE INVENTION
[0008] Accordingly, in a first aspect, the present invention
provides an apparatus for supplying breathable gas, the apparatus
including: [0009] a main housing; [0010] a sub-housing having a gas
flow path between a gas inlet and a gas outlet; [0011] a motive
power source within the main housing; [0012] an impeller within the
sub-housing in fluid communication between the gas inlet and the
gas outlet, the impeller adapted to releaseably engage the motive
power source external the gas flow path, [0013] wherein the
sub-housing is releasably connectable to said main housing.
[0014] Preferably, the sub-housing includes one or more of an inlet
filter, outlet muffler, gas flow rate sensing means, gas pressure
sensing means or gas supply vent valve assembly.
[0015] Desirably, the motive power source is an electric motor.
[0016] Desirably also, the main housing includes one or more of a
power supply and control system for the motor.
[0017] The motor preferably includes an output shaft terminating in
an engaging formation adapted to releasably engage a complimentary
engaging formation provided on the impeller.
[0018] The main housing preferably also includes a removable or
pivotable lid adapted to restrain the sub-housing adjacent the main
housing. In a preferred form, the lid includes acoustic shielding
to reduce the emission of noise generated by the impeller and
motor.
[0019] In a preferred embodiment, the gas flow rate sensing means
includes a flexible flap in the gas flow path, the flap disposed
between a light source and a linear image sensor respectively
disposed either side of the flap and external to the gas flow path,
whereby the amount of light incident on the image sensor is
proportional to the deflection of the flap which is proportional to
the gas flow rate.
[0020] In another preferred embodiment, the gas pressure sensing
means includes a flexible membrane having one side in fluid
communication with the gas flow path and an opposite side abutting
a force probe coupled to a force transducer, whereby the
displacement of the probe and transducer is proportional to the
displacement of the membrane which is proportional to the gas
pressure.
[0021] In yet another preferred embodiment, the gas vent valve
assembly includes a gas venting conduit in fluid communication with
the gas-flow path, the gas venting conduit adapted to be
selectively restricted by a cam abutting the gas venting conduit
exterior, whereby varying the cam position varies gas passing
through the gas venting conduit which varies the flow rate of
remaining gas leaving the gas outlet.
[0022] Preferably, the motor power source includes a disk having
magnets thereon and the impeller includes magnets mounted thereon,
the disk magnets and the impeller magnets being adapted to
attract.
[0023] Alternatively, the motive power source includes a disk
having magnets thereon and the impeller includes a magnetically
attractable plate mounted thereon, the disk magnets and the plate
being adapted to attract.
[0024] In another embodiment, the motive power source includes a
disk having magnets thereon and the impeller includes a non-ferrous
metal plate, or a plate formed from a non magnetically attractable
material having non-ferrous metal therein, mounted thereon.
[0025] In a further embodiment, the impeller includes a shaft
having ferrite or other magnetic material mounted thereon and the
main housing includes electric motor windings adapted to surround
the ferrite or other magnetic material.
[0026] In a second aspect, the present invention discloses a method
of cleaning, sterilising or disinfecting the gas flow path of the
breathable gas supply apparatus of the first aspect, said method
comprising the steps of: [0027] (a) removing the sub-housing from
the main housing, and [0028] (b) cleaning, sterilising,
disinfecting or replacing the sub-housing; and [0029] (c)
connecting the sub-housing to the main housing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Preferred embodiments of the invention will now be described
by way of example only, with reference to the accompanying drawings
in which:
[0031] FIG. 1 is a cross sectional side view of a first embodiment
of an apparatus according to the invention in an assembled
state;
[0032] FIG. 2 is a side view of the apparatus shown in FIG. 1 in a
disassembled state;
[0033] FIG. 3 is a sectional side view of a gas flow rate sensing
mean which can be incorporated into the apparatus of FIG. 1;
[0034] FIG. 4 is a side view of a gas pressure sensing means which
can be incorporated into the apparatus of FIG. 1;
[0035] FIG. 5 is a side view of a portion of a gas vent valve
assembly which can be incorporated into the apparatus of FIG.
1;
[0036] FIG. 6 is a top view of another gas vent valve assembly
which can be incorporated into the apparatus of FIG. 1;
[0037] FIG. 7 is a schematic sectional side view of a second
embodiment of an apparatus according to an invention in an
assembled state;
[0038] FIG. 8 is a schematic cross sectional side view of an
alternative form of sub-housing which can be used with the main
housing shown in FIG. 7;
[0039] FIG. 9 is a top view of an impeller housing and motor
assembly adapted for use with an apparatus according to the
invention;
[0040] FIG. 10 is a cross sectional side view of the assembly shown
in FIG. 9 along line 10-10 of FIG. 9;
[0041] FIG. 11 is an exploded view of the housing shown in FIG.
10;
[0042] FIG. 12 is a schematic top view of a first magnet
arrangement used in the embodiment shown in FIG. 7;
[0043] FIG. 13 is a schematic top view of a second magnet
arrangement used in the embodiment shown in FIG. 7;
[0044] FIG. 14 is a schematic top view of a third magnet
arrangement used in the embodiment shown in FIG. 7;
[0045] FIG. 15 is a schematic cross sectional side view of the
magnet arrangement shown in FIG. 14;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] Referring firstly to FIG. 1, there is shown an apparatus 10
for supplying breathable gas in accordance with a first embodiment
of the invention. The apparatus 10 includes a main housing 12 and a
sub-housing 14. The sub-housing 14 has a gas inlet 16 and a gas
outlet 18 which is connected to a face mask (not shown) by a
flexible conduit 20 to supply a breathable gas (eg. air) to a
patient.
[0047] The main housing 12 includes a motive power source in the
form of an electric motor 22 which receives power from an
electrical power source 24. An electronic control system 26
controls the power source 24 to thus control the speed of the motor
22.
[0048] The inlet 16 and the outlet 18 represent the beginning and
end respectively of a gas flow path through the sub-housing 14. The
passage of gas along the flow path is represented by arrows 28. The
sub-housing 14 also includes an impeller 30 disposed in the flow
path in fluid communication between the inlet 16 and outlet 18 and
partitions 32 which form a housing around the impeller 30 and an
expansion chamber-type outlet muffler 31.
[0049] The impeller 30 includes a female engagement formation in
the form of slotted cylinder 34 which is adapted to -releasably
engage to the male engagement formation on the end of motor shaft
36 in the form of projections 38 (only one shown). It is important
to note that the engagement between the impeller 30 and the motor
shaft 36 is external the gas flow path. Other engaging arrangements
such as splines, dogs, clips, non contact magnetic couplings or the
like can also be used.
[0050] The main housing 12 includes a hinged lid 40 which is
adapted to releasably clamp the sub-housing 14 to the main housing
12. The lid 40 can include acoustic shielding to reduce the
emission of noise generated by the impeller 30 and the motor
22.
[0051] FIG. 2 shows the lid 40 in an open position in which the
motor shaft 36 is disengaged from the impeller 30 allowing the
sub-housing 14 to be removed from the main housing 12.
[0052] The removability of the sub-housing 14 represents a major
improvement over prior art devices as the sub-housing 14 contains
most of the "gas flow path" components of the breathable gas supply
apparatus 10 that can come into contact with airborne particles
from atmosphere or from the patient being treated and it can easily
be removed, disposed and replaced with a clean, sterile or
disinfected sub-housing 14. Alternatively, the sub-housing 14 can
be removed, cleaned, sterilised or disinfected and then
reinstalled.
[0053] The protruding portion of the shaft 36 may also contact
airborne particles and removing the sub-housing 14 provides easy
access to this component. for cleaning, sterilising or
disinfecting.
[0054] In a preferred form, the sub-housing 14 is moulded from
plastics material such as polypropylene, polycarbonate, acrylic,
aluminium, polyurethane foam (such as 1SF-1350 type manufactured by
URETEC) or other like high temperature resistant biocompatible
materials which can be easily cleaned, sterilised or disinfected
using common procedures such as autoclaving.
[0055] Depending on the requirements of the breathable gas supply
apparatus 10, the sub-housing 14 can also include an inlet filter
42 (see FIG. 1).
[0056] In some breathable gas supply apparatus, such as those used
for bi-level CPAP, it is desirable to measure the flow rate of gas
delivered to the patient. An embodiment of a gas flow rate sensing
means 44 suitable for use with the removable sub-housing 14 is
shown in FIG. 3 and includes a flexible flap 46 disposed in the gas
flow path between a light source 48 and a linear image sensor 50.
The greater the gas flow passing the flap 46 causes proportionally
greater deflection of the flap 46 and thus a proportionally greater
amount of occluding of light from the light source 48 that falls on
the linear image sensor 50. In this way, the output of the sensor
50 can be calibrated to be indicative of flap deflection and thus
gas flow rate.
[0057] With this arrangement, only the flexible plastic flap 46 is
within the flow path and is therefore cleaned etc or replaced along
with the sub-housing 14. The expensive and delicate light source 48
and sensor 50 are external of gas flow path, free from
contamination risk and remain fixed to the main housing 12.
[0058] In some breathable gas supply apparatus, it is also
necessary or desirable to be able to measure the pressure of the
gas delivered to the patient. An embodiment of a pressure sensing
arrangement suitable for use with the removable sub-housing 14 is
shown in FIG. 4 and includes a flexible membrane 60 having one side
62 in fluid communication with the flow path and an opposite side
64 abutting a force probe 66 coupled to a force transducer 68.
Increases and decreases in gas pressure cause the membrane 60 to
expand and contract respectively and displace the force probe 66
thereby altering the output of the transducer 68. Thus, it is
possible to calibrate a relationship between gas pressure and
transducer output.
[0059] As with the gas flow rate sensing means 44, this embodiment
is suitable for use with the removable sub-housing 14 as the
membrane remains fixed to the sub-housing 14 and may be easily
cleaned, sterilised or disinfected or replaced along with the
sub-housing 14. The probe 66 and transducer 68 are external the
flow path, free from contamination risk and remain fixed to the
main housing 12.
[0060] Bi-level CPAP is usually administered by either altering the
impeller motor speed in synchronism with patient breathing or using
a vent valve assembly to control the ratio of gas vented to
atmosphere to gas delivered to the patient. FIG. 5 shows an
embodiment of a gas vent valve assembly 70 suitable for use with
the removable sub-housing 14. The vent valve assembly 70 includes
gas venting conduit 72 in fluid communication with the gas outlet
18 shown in FIG. 1 and having a flexible portion 74. A pivotable
cam 76 controlled by a motor 78 is used to selectively restrict the
internal cross section of the flexible portion 74 and thereby
control the proportion of gas vented to atmosphere from the system
to regulate the pressure of remaining gas supplied to the patient.
As with the embodiments of FIGS. 3 and 4, the venting conduit 72
and flexible portion 74 can be removed, cleaned and replaced with
the sub-housing 14, whilst the cam 76 and motor 78 remain external
the flow path and fixed to main housing 12.
[0061] FIG. 6 shows another embodiment of a gas vent valve
assembly, suitable for use with the removable sub-housing 14, which
controls the pressure of gas supplied to the patient with two
pivotable cams 76A and 76B which restrict respective flexible
portions 74A and 74B. The cams 76A, 76B form part of two vent valve
assemblies 70A and 70B of a similar nature to the assembly 70 shown
in FIG. 5. The. cams 76A, 76B are linked so that upon rotation by
motor 78 one flexible portion is progressively restricted while the
other is progressively enlarged and vice-versa.
[0062] In the embodiment shown, the cams 76A, 76B are installed
adjacent a Y shaped conduit 80 which comprises three conduit
portions 82, 84 and 86 which are in fluid communication with the
impeller 30, outlet 18 and atmosphere respectively. If a low gas
supply pressure to the patient is desired, the valve assemblies
70A, 70B are used to simultaneously restrict the gas flow in the
conduit portion 82 from the flow generator while increasing the gas
flow to the atmosphere through conduit portion 86. If a high gas
supply pressure to the patient is desired, the pivotable cams 76A
and 76B are turned in the opposite direction to simultaneously
restrict the venting of gas to the atmosphere through conduit
portion 86 and increase the gas supplied to the patient through
conduit portion 84.
[0063] The embodiment of FIG. 6 provides an apparatus for supplying
breathable gas that uses relatively less power and causes less wear
on the flow generator motor and bearings. The gas flow vented to
atmosphere is also reduced which thereby reduces the associated
noise of the gas passing through the vent to atmosphere.
[0064] FIG. 7 shows an apparatus 90 for supplying breathable gas in
accordance with a second embodiment of the invention. Similar to
the first embodiment, the apparatus 90 includes a main housing 92
and a sub-housing 94.
[0065] The sub-housing 94 has an inlet chamber 96 and an outlet
chamber 98 within which is located an impeller 100. The impeller
100 is mounted on the bottom end of a shaft 102. The top end of the
shaft 102 is retained in a bearing assembly 103 mounted to the
inlet chamber 96. The impeller 100 also includes a number of
magnets 104 mounted near its periphery. Six equiangularly spaced
magnets are used in the preferred embodiment.
[0066] The main housing 92 includes a motive power source in the
form of an electric motor 106. A disk 108 is attached to the output
shaft 110 of the motor 106. Magnets 112 are mounted near the
periphery of the disk 108 in general alignment with the magnets 104
provided on the impeller 100. The magnets 104 and 112 are
configured to attract each other.
[0067] Energising the motor 106 causes the disk 108 to rotate. The
attraction between the magnets 104 and 112 causes the impeller 100
to rotate also. The rotation of the impeller 100 draws air through
upper openings 114 in the inlet chamber 96, through to a lower
opening 116 and into the impeller 100. Pressurised air is then
forced through outlet 118 of the outlet chamber 98, as indicated by
arrows 120. The outlet 118 of the sub-housing 94 is connected to a
face mask (not shown) by a flexible conduit (not shown) to supply
the air (or other breathable gas) to a patient.
[0068] As with the first embodiment, the sub-housing 94, which
contains all. of the components that can come into contact with
particles from atmosphere or from the patient being treated, can be
easily and quickly removed from the main housing 92 by overcoming
the attraction between the magnets 104 and 112. As with the first
embodiment, this allows the sub-housing 94 to be easily removed and
disposed and replaced with a new clean, sterile or disinfected
sub-housing 94 or removed, cleaned, sterilised or disinfected and
then reinstalled.
[0069] FIGS. 12, 13, and 14 and 15 respectively show three
preferred arrangements of the magnets 112 on the disk 108. In FIG.
12, the magnets 112 have their poles aligned in one direction
(North being shown). In FIG. 13, the magnets 112 are arranged with
adjacent magnets 112 having alternating poles. In FIGS. 14 and 15,
the magnets 104, 112 have alternating poles grouped in pairs by
magnetic bridges 122. The magnets 104 on the impeller 100 are
arranged with opposite (ie. attracting) polarity to those of the
disk 108.
[0070] FIG. 8 shows an alternative form of a sub-housing 130 that
can also be used with the main housing 92 shown in FIG. 7. The
sub-housing 130 is very similar to the sub-housing 94. and like
reference numerals have been used to denote like features. However,
in the sub-housing 130, the impeller 100 includes a plate 132 on
its underside rather than the magnets 104 shown in the embodiment
of FIG. 7.
[0071] In one form, the plate 132 is made from a material that is
attracted to magnets, for example steel. As with the embodiment
shown in FIG. 7, when the disk 108 rotates the attraction between
the magnets 112 and the plate 132 causes rotation in the impeller
100 also.
[0072] In another form, the plate 132 is made of a non-ferrous
metal, for example Aluminium. In this form, when the disk 108
rotates the magnets 112 produce a magnetic field which passes
through the plate 132 and causes eddy currents in, and rotation of,
the plate 132 and thus the impeller 100 also. Alternatively, the
plate 132 can be formed from a non magnetically attractive
material, for example a polymer, having a non-ferrous metal, such
as Aluminium, therein.
[0073] FIGS. 9 to 11 show an impeller housing and motor assembly
140 suitable for use in an apparatus for supplying breathable gas
in accordance with another embodiment of the invention. In this
embodiment, the assembly 140 includes an upper part 142 which
constitutes a sub-housing and a lower part 144 which constitutes a
main housing. The upper part 142 includes an inlet 146, an outlet
147 and an impeller 148 mounted therein.
[0074] As best shown in FIG. 11, the impeller 148 includes a hollow
shaft 150 to which is mounted ferrite material 152. The lower part
144 includes a shaft 154 which is adapted to be received within the
interior of the hollow shaft 150 to form a bearing. The lower part
144 also includes motor windings 156 that surround the ferrite
material 152. Energising the motor windings 156 creates a magnetic
field which causes the ferrite material 152, and thus the impeller
148, to rotate and draw air from the inlet 146 to the outlet 147
for supplying gas to the patient by the means previously
described.
[0075] Similar to the earlier embodiments, the upper part 142 and
the impeller 148 can be removed for cleaning, sterilising,
disinfecting or replacement without dismantling the rest of the
apparatus to which the lower part 144 is attached. Removing the
upper part 142 and the impeller 148 also provides easy access to
external surfaces 158 of the lower part 144 for cleaning,
sterilising or disinfecting.
[0076] In a variation (not shown) of the embodiment shown in FIGS.
9 to 11, gas is bled from the impeller 148 into the interface
between the hollow shaft 150 and the shaft 154 to float the
impeller 148 (in the manner of an air bearing) and thus reduce
noise.
[0077] Although the invention has been described with reference to
the preferred. embodiments, it would be appreciated by those
skilled in the art that the invention may be embodied in many other
forms.
* * * * *