WO2017039497A1

WO2017039497A1 - Fan-driven respiratory assistance apparatus with reversed fan-motor assembly

Info

Publication number: WO2017039497A1
Application number: PCT/SE2015/050915
Authority: WO
Inventors: Carl-Erik Troili
Original assignee: Maquet Critical Care Ab
Priority date: 2015-08-31
Filing date: 2015-08-31
Publication date: 2017-03-09

Abstract

The present invention relates to a fan-driven respiratory assistance apparatus (1) comprising a fan (3) for pressurising gas to be delivered to a patient (11), and a motor arrangement (5) for driving said fan. The fan comprises a gas inlet opening (2), a gas outlet opening (4), and an impeller (12) for generating a flow of gas from the gas inlet opening to the gas outlet opening, via said impeller. The motor arrangement (5) comprises a motor (8) for rotating the impeller (12) so as to generate said flow of gas. The impeller (12) and the motor arrangement (5) are arranged in relation to each other such that the direction of flow into the impeller (12) is directed away from the motor arrangement (5).

Description

FAN-DRIVEN RESPIRATORY ASSISTANCE APPARATUS WITH REVERSED FAN -MOTOR ASSEMBLY

TECHNICAL FIELD

The present invention relates to the field of fan-driven respiratory assistance apparatuses, such as fan-driven ventilators. In particular, the present invention relates to a fan-motor assembly for a fan-driven respiratory assistance apparatus for delivery of pressurized gas to a patient.

BACKGROUND

In fan-driven ventilators for delivery of pressurised gas to patients, the fan (sometimes referred to as blower or turbine) and the fan motor are normally axially aligned along the motor axis with the fan being mounted on top of the motor and the drive shaft of the motor protruding upwards into the housing of the fan in order to drive the rotation of an impeller, mounted within said housing.

The impeller is typically located immediately downstream a gas inlet opening of the fan housing, normally positioned on the upper side of the fan housing, and the rotation of the impeller causes surrounding gas to be drawn into said gas inlet opening and into the impeller. The gas flowing into the impeller is typically directed into a volute in which flow is converted into pressure. The pressurised gas may then be supplied to the patient or a gas regulating module of the respiratory assistance apparatus via a gas outlet opening of the fan housing. This type of fan-motor assemblies for fan-driven ventilators has been found to suffer from several drawbacks. For example, the elevated pressure in the motor-facing part of the fan causes dust contained in the gas to penetrate into the motor housing, severely reducing the lifetime of motor components in general and the drive shaft bearing in particular.

Furthermore, if the gas that is drawn into the fan is an oxygen-enriched gas, such as a mixture of air and oxygen, oxygen too may penetrate the motor housing. Besides the risk of motor fire if penetrating into the motor compartment, oxygen has an aging effect on the lubricant of the drive shaft bearing, thus further reducing the lifetime of the bearing.

Yet further, the relatively high pressure swings occurring in the high-pressure environment of the motor-facing part of the fan may blow away the lubricant of the drive shaft bearing, further reducing its lifetime.

Yet another problem associated with fan-motor assemblies for fan-driven ventilators according to prior art is how to provide efficient cooling of the motor and motor components. Heat causes the lubricant, the motor and motor components to age faster.

WO2008059341 presents a solution to the problem of efficient cooling of the motor by provision of a motor-fan assembly wherein the housing of the fan extends around the motor such that air that is drawn into the fan is first guided through an air channel delimited by the fan housing and the motor housing. Thereby, the air serves to cool the motor housing prior to flowing into the volute of the fan.

This problem is also addressed by WO2012139681 disclosing a motor-fan assembly in which the high-pressure gas having passed through the impeller and volute of the fan is used for cooling the motor. Although presenting suggestions on how to achieve more efficient cooling of the motor, the motor-fan assemblies disclosed in WO2008059341 and WO2012139681 fail to solve the above mentioned problems of oxygen- occasioned motor fires and dust, oxygen and pressure swing-related aging and wearing-out of the drive shaft bearing.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve or at least mitigate one or more of the above mentioned problems associated with fan-driven respiratory assistance apparatuses according to prior art.

A particular object of the invention is to increase the lifetime of the fan motor and/or the drive shaft bearing of a fan-driven ventilator. This and other objects are achieved according to the present invention by a fan-driven respiratory assistance apparatus, such as a ventilator, comprising a fan for pressurising gas to be delivered to a patient, and a motor arrangement for driving said fan. The fan comprises a gas inlet opening, a gas outlet opening, and an impeller for generating a flow of gas from the gas inlet opening to the gas outlet opening, via said impeller. The motor arrangement comprises a motor for rotating the impeller of the fan so as to generate said flow of gas. The impeller and the motor arrangement are arranged in relation to each other such that the direction of the gas flowing into the impeller is directed away from the motor arrangement.

In other words, the present invention comprises a fan-driven respiratory assistance apparatus comprising a fan for pressurising gas to be delivered to a patient, and a motor arrangement for driving said fan. The fan comprises a gas inlet opening, a gas outlet opening, and an impeller for generating a flow of gas from the gas inlet opening to the gas outlet opening, via said impeller. The motor arrangement comprises a motor for rotating the impeller so as to generate said flow of gas. The gas inlet opening of the fan faces the motor arrangement.

In fan-driven ventilators according to prior art, the fan is typically mounted on top of the motor arrangement and gas is drawn into the impeller from above, meaning that the direction of the gas flow into the impeller is directed towards the motor arrangement. Besides the fact that the flow of gas into the impeller is directed towards the motor arrangement, this conventional fan- motor assembly design creates an elevated pressure in the part of the fan located adjacent to the motor arrangement, causing the above discussed problems.

By reversing the orientation of the impeller in relation to the motor arrangement, as proposed by the present invention, the motor arrangement becomes located adjacent to a low-pressure part of the fan instead of a high- pressure part of the fan, thereby preventing dust particles in the gas that is drawn into the gas inlet opening of the fan to be pushed into the motor or other dust-sensitive components of the motor arrangement. Furthermore, if the gas passing through the fan contains oxygen, the proposed solution minimizes the risk of pushing oxygen into the motor arrangement. Thereby, the proposed respiratory assistance apparatus is more suitable than conventional fan-driven ventilators for use in ventilation systems in which oxygen is added to the gas mixture upstream the fan.

Yet another advantage of the motor arrangement being positioned adjacent to the low-pressure part of the fan instead of the high-pressure part of the fan is the reduction of pressure swings in the immediate surroundings of the motor arrangement. Pressure swings in the low-pressure part of the fan, upstream the impeller, is substantially lower than pressure swings occurring downstream the impeller, normally by a factor of at least 10 and often by a factor of 20 to 30. High pressure swings may have undesired effects on the motor and motor components, e.g. the effect of blowing away lubricant from the drive shaft bearing of the motor arrangement, thereby substantially reducing the product lifetime. By avoiding that the motor and the drive shaft bearing are exposed to large pressure swings, the proposed solution increases the lifetime of the motor arrangement substantially.

Preferably, the gas inlet opening of the fan is arranged on a side of the fan facing the motor arrangement, such that gas is drawn into the gas inlet opening from in between the fan and the motor arrangement. This causes at least a part of the motor arrangement facing the fan to be subjected to the flow of surrounding gas that is drawn towards the gas inlet opening of the fan by the rotation of the impeller. Thus, at least the part of the motor arrangement facing the fan is arranged in fluid communication with the flow of gas that is drawn into the gas inlet opening of the fan. In this way, the relatively cold gas surrounding the fan-motor assembly is caused to make thermal contact with at least said part of the motor arrangement prior to or after flowing into the gas inlet opening of the fan, and so serves to cool this part of the motor arrangement and the components thereof.

In some fan-driven ventilators according to prior art, the pressurised gas leaving the gas outlet opening of the fan is used for cooling the motor arrangement and the components thereof. However, the pressurised gas having passed through the fan is warmer than the surrounding non- pressurised gas that is drawn into the gas inlet opening of the fan. Consequently, another advantage of positioning the motor arrangement adjacent to the low-pressure part of the fan is that non-pressurised gas that is drawn into the fan can be used for more efficient cooling of the motor arrangement.

The motor arrangement further comprises a drive shaft connecting the motor with the impeller of the fan, and at least one drive shaft bearing in which the drive shaft is journaled, arranged on the fan-facing side of the motor. The drive shaft bearing arrangement is a critical component of fan-driven ventilators and is often worn out rather quickly in fan-driven ventilators according to prior art, in which they are exposed to high pressures and large pressure swings. In the proposed respiratory assistance apparatus, the drive shaft bearing is arranged adjacent to the low-pressure part of the fan, thus reducing the pressure and the pressure swings in the immediate surroundings thereof.

Thus, by preventing pressure swings from removing the lubricant of the bearing, preventing dust and oxygen from penetrating the bearing, and allowing the relatively cold gas that is drawn into the fan to cool the motor arrangement and hence also the bearing comprised therein, the proposed invention substantially increases the lifetime of the drive shaft bearing of the motor arrangement.

The motor arrangement typically comprises a motor housing, typically housing at least the motor and said drive shaft bearing. Preferably, at least a part of the motor housing comprising the drive shaft bearing is arranged in fluid communication with gas that is drawn into the gas inlet opening. This means that said part of the motor housing is arranged in fluid communication with the flow of gas flowing towards the impeller of the fan such that thermal contact is made between said part of the motor housing and said flow of gas, upstream the impeller. Said thermal contact may be made prior to and/or after entrance of said flow of gas into the gas inlet opening of the fan. Preferably, at least said part of the motor housing is made of a thermally conducting material, such as aluminium, titanium, copper, silver, gold or other materials having good thermal conductivity, in order for the relatively cold flow of surrounding gas flowing towards the impeller to efficiently cool the drive shaft bearing and/or other components enclosed by the motor housing.

Like in typical fan-driven ventilators according to prior art, the fan of the respiratory assistance apparatus may be axially aligned with the motor and preferably arranged on top of the motor housing, i.e. located above and adjacent to the motor arrangement. The drive shaft connecting the motor with the impeller of the fan may protrude upwards from the motor housing into the fan. Preferably, the gas inlet opening of the fan is arranged on the side of the fan facing the motor arrangement such that the drive shaft runs through the gas inlet opening of the fan.

In one embodiment, the part of the motor housing facing the fan is substantially cone-shaped with the top of the cone pointing towards the gas inlet opening of the fan, thereby causing a gap having a wedge-shaped cross section to be formed between the motor housing and the fan. The gas inlet opening of the fan is arranged such that surrounding gas is drawn into said gap, in which it makes thermal contact with the walls of the cone-shaped motor housing, and further into the fan via the gas inlet opening.

The cone-shape of the motor housing allows for a compact design of the fan- motor assembly while permitting sufficiently high flows of gas into the fan during operation thereof. Furthermore, the drive shaft bearing is preferably arranged within the cone-shaped part of the motor housing such that surrounding gas that is drawn into the gas inlet opening of the fan will serve to cool the drive shaft bearing as it makes thermal contact with the cone- shaped motor housing.

Preferably, to further increase this cooling effect, a part and at least the top of the cone-shaped motor housing may be arranged to protrude into the air inlet opening of the fan, exposing a larger area of the motor housing to the relatively cold gas flowing into the fan. In one embodiment, the gas inlet opening of the fan is arranged on the side of the fan facing the motor housing, a part of the cone-shaped motor housing protruding into said gas inlet opening such that gas is drawn into the fan via an opening surrounding at least a part of the motor housing, and preferably the part of the motor housing in which the drive shaft bearing is located. In some embodiments, the respiratory assistance apparatus may be provided with at least one gas channel running through the motor housing for further improving cooling of the internal motor arrangement components. The at least one gas channel may be configured such that the flow of gas that is drawn into the air inlet opening of the fan during operation of the respiratory apparatus passes through the air channel and makes thermal contact with at least one internal motor arrangement component (i.e. a component inside the motor housing) prior to being drawn into the air inlet opening of the fan. For example, both the fan-proximate end of the motor housing facing the gas inlet opening of the fan and the opposite, fan-distant end of the motor housing can be provided with one or more through-holes arranged in fluid communication with each other via one or more air channels running through the motor arrangement. Gas will then be drawn into the motor arrangement via the through holes of the distant end of the motor housing and make thermal contact with internal motor components before being drawn out of the through holes in the proximate end of the motor housing and into the gas inlet opening of the fan. Such an air channel may be configured to pass by the drive shaft bearing of the motor arrangement to further improve cooling thereof, thus further extending the bearing lifetime. It should be noted, however, that guiding the gas that is to be pressurised through the motor arrangement before entrance into the gas inlet opening of the fan may undesirably increase the temperature of the gas that is delivered to the patient.

Furthermore, the fan typically comprises a gas duct connecting the gas inlet opening and the gas outlet opening, which gas duct is delimited by a fan housing. The impeller is arranged within said gas duct, preferably close to the gas inlet opening. Preferably, the gas inlet opening is aligned with the impeller along the direction of the motor axis such that gas flowing into the gas inlet opening flows towards the impeller along a substantially straight path. Downstream the impeller, the gas duct may have any shape and/or comprise any means known in the art for converting the kinetic energy of the gas flow caused by the rotation of the impeller into pressure. For example, at least parts of the gas duct may constitute a volute, a radial diffuser and/or an axial diffuser for converting flow to pressure.

In one embodiment, the fan is a centrifugal fan and a part of the gas duct is a volute into which the gas flow from the impeller is directed. The impeller is arranged in the centre of the volute and configured to cause a centrifugal flow of gas through the volute, which centrifugal flow is converted into pressure by the volute. Preferably, as discussed above, the gas inlet opening of the fan is arranged on a side of the fan facing an end of the motor arrangement from which the drive shaft protrudes. The drive shaft protrudes out from the motor housing, into the gas inlet opening of the fan and further onto the impeller in the centre of the volute. Upon rotation of the impeller, surrounding gas is drawn into a gap between the motor arrangement and the fan, into the gas inlet opening of the fan and further into the impeller in a direction which is substantially parallel to the drive shaft axis and which is directed away from the motor arrangement. The substantially axial flow of gas is redirected by the impeller and forced into the volute, extending radially in a direction substantially perpendicular to the drive shaft axis (and the motor axis). In a peripheral part of the volute (or downstream a radial or axial diffuser, optionally used in combination with the volute), pressurised gas for delivery to the patient is provided via the gas outlet opening of the fan.

The reversed orientation of the fan in relation to the motor arrangement according to the principles of the present invention has shown not to impede the performance of the fan-driven respiratory assistance apparatus compared to conventional fan-driven ventilators. Thus, the proposed invention provides a fan-driven respiratory assistance apparatus, such as a ventilator, having maintained performance as compared to conventional fan-driven ventilators, while the lifetime of the motor arrangement and the possibility of adding oxygen upstream the fan are substantially improved.

More advantageous aspects and effects of the breathing assistance apparatus of the invention will be described in the detailed description following hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description provided hereinafter and the accompanying drawings which are given by way of illustration only. In the different drawings, same reference numerals correspond to the same element.

Fig. 1 illustrates a fan-driven respiratory assistance apparatus according to one embodiment of the present disclosure; Fig. 2 illustrates a fan-motor assembly according to one embodiment of the present disclosure.

Fig. 3Aillustrates a fan-driven respiratory assistance apparatus according to another exemplary embodiment of the present disclosure,

Fig. 3B illustrates a fan-driven respiratory assistance apparatus according to one embodiment of the present disclosure;

Fig. 3C illustrates a fan-driven respiratory assistance apparatus according to one embodiment of the present disclosure, and

DETAILED DESCRIPTION

Fig. 1 illustrates an exemplary embodiment of a fan-driven respiratory assistance apparatus 1 arranged to ventilate a patient 1 1 . The apparatus 1 comprises a fan-motor assembly 15 including a fan 3 and a motor arrangement 5, a control unit 20, an inspiratory module 7 and an expiratory module 9.

The fan 3 of said fan-motor assembly 15 comprises a gas inlet opening (shown and described below with reference to Fig. 2) through which gas is drawn into the fan 3, and a gas outlet (also shown and described below with reference to Fig. 2) through which pressurised gas is delivered. During operation of the fan-motor assembly 15, surrounding gas in the vicinity of said gas inlet opening is drawn into the fan 3. The fan-motor assembly 15 may be arranged within a housing 16. In this case, the housing 16 may comprise at least one air inlet (not shown) through which surrounding air can flow into the housing 16 and further into the fan 3 to be pressurised.

In this exemplary embodiment, the fan-motor assembly 15 is configured to deliver pressurised gas to the inspiratory module 7 of the respiratory assistance apparatus 1 . The inspiratory module 7 is configured to regulate the flow and/or pressure of the gas to the patient 1 1 based on current settings of the respiratory assistance apparatus 1 and/or sensor data obtained by various sensors (not disclosed). When used together with an inspiratory module 7 capable of regulating the flow and/or pressure delivered to the patient 1 1 , the fan-motor assembly 15 may be configured to deliver an essentially constant pressure. The essentially constant pressure produced by the fan may be predefined or selectable by an operator via a user interface (not disclosed) of the respiratory assistance apparatus 1 . The inspiratory module 7 may comprise at least one controllable valve 23 for regulating the pressure and/or flow of gas delivered to the patient 1 1 .

The respiratory assistance apparatus 1 further comprises an expiratory module 9 arranged to receive exhaled gas from the patient 1 1 and to pass the received expiration gas onto a scavenging system (not shown) or surrounding air, Furthermore, the expiratory module 9 typically comprises at least one valve (not disclosed) for regulating an expiratory pressure applied to the patient 1 1 during expiration.

The respiratory assistance apparatus 1 further comprises a control unit 20. Said control unit 20 is arranged to control the operation of the fan-motor assembly 15 by controlling the speed of the motor driving the fan 3. The control unit 20 may also be arranged to control said inspiratory module 7, e.g. by controlling said at least one valve for regulating the flow and/or pressure of breathing gas delivered to the patient 1 1 . The control unit 20 may further be arranged to control the operation of the expiratory module 9, e.g. by controlling said at least one valve for regulating expiratory pressure applied to the patient 1 1 during expiration.

The fan-driven respiratory assistance apparatus 1 may further comprise a housing 17 enclosing the components of said apparatus 1 . Said housing 17 may comprise an air inlet (not disclosed) through which gas can enter the housing 17. Said air inlet preferably comprises a particle filter (not disclosed). The interior of the housing 17, or a part thereof, may serve as a volume from which gas is drawn into said fan 3. In some embodiments where a fan-motor assembly housing 16 exist, said housing 16 may form said volume from which gas is drawn into said fan. The gas is then drawn from the interior of the housing 17 into said fan 3, via an air inlet of the fan-motor assembly housing 16, if such housing 16 exist. In other embodiments, the fan-motor assembly 15 or parts thereof may be arranged external to the housing 17 of the respiratory assistance apparatus 1 . In particular, a part of the housing 16 of the fan-motor assembly in which the above-mentioned air inlet is arranged may be located external to the housing 17 of the respiratory assistance apparatus 1 , such that air is drawn into the housing 16 of the fan-motor assembly from outside the housing 17 of the respiratory assistance apparatus. The gas that is drawn into and pressurised by the fan 3 of the fan-motor assembly 15 is typically air but may also be other gases or gas mixtures, such as oxygen-enriched air. To this end, according to one aspect of the present disclosure, an oxygen source 13 may be connected to the fan-driven respiratory assistance apparatus 1 . The oxygen source 13 may be connected to the respiratory assistance apparatus 1 so as to add oxygen to the gas which is to be delivered to the patient 1 1 upstream said fan-motor assembly 15. The amount of oxygen added to the gas upstream said fan-motor assembly 15 may be controlled by a valve 24. The oxygen may be delivered to a volume within the housing 17 from which gas is drawn into said fan 3. The oxygen may alternatively be delivered to a close vicinity of said fan, within said housing 16 via a gas inlet (not shown). The control unit 20 may be arranged to control the amount of oxygen added to the gas upstream said fan-motor assembly 15 by controlling said at least one valve 24.

Fig. 2 illustrates the fan-motor assembly 15 of Fig. 1 and Fig. 3a-3c according to the invention in more detail. The fan-motor assembly 15 comprises a fan 3 and motor arrangement 5. Said fan 3 comprises a housing 18 defining a gas duct through which a gas inlet opening 2 and a gas outlet 4 of the fan 3 are fluidly connected to each other. The gas inlet opening 2 and the gas outlet 4 are openings in said fan housing 18.

An impeller 12 is arranged within said gas duct, downstream said gas inlet opening 2 and upstream said gas outlet 4. The impeller 12 is preferably axially aligned with the gas inlet opening 2 along a centre axis of the fan 3, which centre axis coincides with a motor axis A of the motor arrangement 5, such that gas flowing into the gas duct of the fan 3 via the gas inlet opening 2 can flow into the impeller 12 along a flow path being substantially parallel with said centre axis and motor axis A, and directed away from the motor arrangement 5, as illustrated by arrows in the drawing. Consequently, the gas inlet opening 2 of the fan 3 is arranged on a side of the fan 3 facing the motor arrangement 5 and located between the motor arrangement 5 and the impeller 12 of the fan 3.

The impeller 12 is arranged to rotate around an axis of rotation, coinciding with the centre axis of the fan and the motor axis A of the motor arrangement 5. Said impeller 12 comprises impeller blades and a hub portion from which said blades protrudes radially. The impeller blades are arranged in a direction perpendicular to the axis of rotation of the impeller 12. The rotation of the impeller blades serves to redirect the gas flow flowing into the impeller by approximately 90°, into a part of the gas duct forming a volute of the fan 3, i.e. a curved funnel that increases in cross sectional area as it approaches the gas outlet 4. Thereby, the substantially axial gas flow flowing into the impeller 12 is converted into a radial, centrifugal flow through the windings of the volute, in which gas flow is converted to pressure.

The impeller 12 is arranged in a part of the fan 3 that is distant to the motor arrangement 5. In the exemplary embodiment illustrated in Fig. 2 in which the fan 3 is mounted on top of the motor arrangement 5, this part of the fan constitutes an upper part of the fan. The opposite part of the fan 3 that is located proximate to the motor arrangement 5, i.e. the lower part of the fan 3 forms a low-pressure part or low-pressure end of the fan 3 as gas flowing through said part of the fan is low-pressure gas which has not yet been pressurised. Said impeller 12 comprises pressure increasing vanes (not disclosed) which increases the pressure of the gas downstream said impeller 12 as the impeller 12 rotates.

The gas duct 16 of the fan 3 comprises three parts; a first part 16a upstream said impeller 12, a second part 16b housing said impeller 12, and a third part 16c downstream said impeller 12. The first part 16a of the gas duct forms a gas inlet channel conveying gas from the gas inlet opening 2 towards the impeller 12. The second part 16b of the gas duct forms an impeller compartment in which the gas flow is accelerated and redirected into the third part 16c of the gas duct. The third part 16c of the gas duct is the funnel of the volute in which pressure is gradually built up, allowing pressurised gas to be delivered to the patient 1 1 via the gas outlet 4 coupled to the end of said funnel, schematically illustrated as a dashed circle 4 in Fig. 2. The third part 16c of the gas duct is the funnel of the volute in which pressure is gradually built up, allowing pressurised gas to be delivered to the patient 1 1 via the gas outlet 4 located in the end of said funnel.

The impeller 12 is connected to a motor 8 of the motor arrangement 5 via a drive shaft 14. The drive shaft 14 couples the impeller 12 to a rotor (not shown) of the motor 8 and so causes the impeller to rotate with the speed of the motor 8. The drive shaft 14 is aligned with the motor axis A and protrudes through the motor arrangement 5, through the first part 16a of the gas duct of the fan 3, and onto the impeller 12 at which it is connected to the hub portion to cause the impeller 12 to rotate along with the drive shaft 14. The drive shaft 14 is journaled in at least one bearing 6, herein referred to as a drive shaft bearing of the motor arrangement 5. The drive shaft bearing 6 is positioned on the fan-facing side of the motor 8, and thereby proximate to the low-pressure part of the fan facing the motor arrangement 5.

The motor arrangement 5 is enclosed in a motor housing 22. The motor housing 22 is formed of an upper part 22a and a lower part 22b. The drive shaft bearing 6 is positioned within the upper part of the motor housing 22a.

The fan 3 is arranged adjacent to the motor arrangement 5 along the motor axis A. The gas inlet opening 2 of the fan 3, typically circular in shape, is provided on the side of the fan facing the motor arrangement 5 and encloses the drive shaft 14.

In this exemplary embodiment, the upper part 22a of the motor housing 22 is shaped as a cone protruding into the gas inlet opening 2 of the fan 3 as disclosed in figure 2. When the impeller 12 rotates, gas is drawn from the vicinity of the gas inlet opening 2 and transported to the outlet 4 of the fan 3 via said first part 16a of the gas duct, said second part 16b of the gas duct comprising the impeller 12 and said third part 16c of the gas duct forming said volute. Due to the orientation of the fan 3, i.e. the positions of the impeller 12 and the gas inlet opening 2 in relation to the motor arrangement 5, the direction of the gas flow in the first part 16a of the gas duct, upstream the impeller 12, is essentially vertical. Hence, the direction of the gas flow into the impeller 12 is directed away from the motor arrangement 5 and the upper part 22a of the motor housing 22 enclosing the drive shaft bearing 6, as illustrated with arrows in figure 2. Hence, as the impeller 12 rotates, the gas and possibly dust and/or oxygen contained in the gas drawn into the fan 3 is directed away from the upper part 22a of the motor housing, towards the impeller 12. This direction of the flow of gas has the effect that dust and possibly a high level of oxygen in said gas will not enter into the motor housing 22, and hence will not affect the bearing 6 situated in the upper part 22a of the motor housing 22 or the motor 8 situated in the lower part 22b of the motor housing 22. Hence, the orientation of the fan 3 and motor arrangement 5 according to the invention prolongs the lifetime of the motor 8 and the drive shaft bearing 6. Furthermore, as the impeller 12 rotates, the gas that is drawn into the gas inlet opening 2 and into the first part 16a of the gas duct flows past the upper part 22a of the motor housing 22 which causes a cooling effect of at least said upper part of the motor housing 22a. The conical shape and placement of the upper part 22a of the motor housing 22 in relation to the gas inlet opening 2 causes a large area of the upper part 22a of the motor housing 22 to be exposed to the flow of gas created by the rotating impeller12, causing efficient cooling of the upper part 22a of the motor housing 22. In addition, at least the upper part 22a of the motor housing 22 may be constructed in a material having high thermal conductivity, such as steel or aluminium, in order to increase the cooling effect of the flow of gas on the upper part 22a of the motor housing 22. Since said upper part of the motor housing 22a encloses the bearing 6, said bearing will be cooled by said flow of gas, further prolonging the lifetime of said bearing 6. To improve the cooling effect even further, the upper part 22a of the motor housing 22 might be equipped with cooling fins or a similar construction enlarging the surface of the cone. Fig. 3A illustrates another exemplary embodiment of a fan-driven respiratory assistance apparatus 1 according to the present disclosure, arranged to ventilate a patient 1 1 . In this embodiment, the oxygen source 13 is arranged to ad oxygen to the gas downstream the fan-motor assembly 15, i.e. oxygen is added to the pressurised gas (typically air) delivered by the fan 3. For example, oxygen may be added in said inspiratory module 7. The inspiratory module 7 may comprise a mixing chamber 18 arranged to form a desired mixture of gas and oxygen to be delivered to the patient 1 1 . The composition of the gas mixture may be set by an operator via a user interface (not disclosed) of the respiratory assistance apparatus 1 . The amount of oxygen added to said mixing chamber 18 may be controlled by a valve 24. The control unit 20 may be arranged to control the amount of oxygen added to the gas downstream said fan-motor assembly 15 by controlling said valve 24.

Fig. 3B illustrates another exemplary embodiment of a fan-driven respiratory assistance apparatus 1 according to the present disclosure, arranged to ventilate a patient 1 1 . In this embodiment, the respiratory assistance apparatus 1 does not comprise an inspiratory module 7 for regulating the pressure and/or flow of the breathing gas delivered to the patient. Instead, the control unit 20 is configured to control the operation of the fan-motor assembly 15 to regulate the pressure and/or flow of breathing gas delivered to the patient 1 1 . To this end, the control unit 20 may control the speed of a motor of the motor arrangement 5, which motor controls the rotational velocity of an impeller of the fan, as will be discussed in greater detail below. The rotational velocity of the impeller in turn determines the pressure of the pressurised gas delivered by the fan-motor assembly 15. Thereby, the fan- motor assembly 15 can be controlled to deliver pressure controlled ventilation of the patient 1 1 . The motor speed of the motor arrangement 5 may be controlled by the control unit 20 to deliver a substantially constant pressure to the patient 1 1 (CPAP) or to deliver a variable pressure to the patient 1 1 based on current settings of the respiratory assistance apparatus 1 and/or sensor data obtained by various sensors (not disclosed). An oxygen source 13 may be connected to the respiratory assistance apparatus 1 so as to add oxygen to the gas which is to be delivered to the patient 1 1 upstream said fan-motor assembly 15. According to one aspect, a constant flow of oxygen is directed into the housing 17, from which gas is drawn into said fan 3. According to another aspect, a constant flow of oxygen is directed into a close vicinity of said fan 3, within the housing 16, from which gas is drawn into said fan 3. According to another exemplary embodiment of present disclosure, a valve (not disclosed) is arranged to control the flow of oxygen added to the gas upstream the fan 3. Fig. 3C illustrates another exemplary embodiment of a fan-driven respiratory assistance apparatus 1 according to the present disclosure, arranged to ventilate a patient 1 1 . In this embodiment, the respiratory assistance apparatus 1 does not comprise an inspiratory module 7 for regulating the pressure and/or flow of the breathing gas delivered by the fan. Instead, the control unit 20 is configured to control the operation of the fan-motor assembly 15 to regulate the pressure and/or flow of breathing gas delivered to the patient 1 1 . To this end, the control unit 20 may control the speed of a motor of the motor arrangement 5, which motor controls the rotational velocity of an impeller of the fan, as will be discussed in greater detail below. The rotational velocity of the impeller in turn determines the pressure of the pressurised gas delivered by the fan-motor assembly 15. Thereby, the fan- motor assembly 15 can be controlled to deliver pressure controlled ventilation of the patient 1 1 . The motor speed of the motor arrangement 5 may be controlled by the control unit 20 to deliver a substantially constant pressure to the patient 1 1 (CPAP) or to deliver a variable pressure to the patient 1 1 based on current settings of the respiratory assistance apparatus 1 and/or sensor data obtained by various sensors (not disclosed). An oxygen source 13 may be connected to the respiratory assistance apparatus 1 so as to add oxygen to the gas which is to be delivered to the patient 1 1 downstream said fan-motor assembly 15. Said oxygen is added to a gas mixing chamber 18 in which a desired gas mix is created. According to one aspect, a constant flow of oxygen is directed into the gas mixing chamber 18. According to another exemplary embodiment of present disclosure, the amount of oxygen added to said mixing chamber 18 may be controlled by a valve 24. The control unit 20 may be arranged to control the amount of oxygen added to the gas downstream said fan-motor assembly 15 by controlling said valve 24.

Claims

A fan-driven respiratory assistance apparatus (1 ) comprising a fan

(3) for pressurising gas to be delivered to a patient (1 1 ), and a motor arrangement (5) for driving said fan,

the fan comprising a gas inlet opening (2), a gas outlet opening

(4), and an impeller (12) for generating a flow of gas from the gas inlet opening to the gas outlet opening, via said impeller,

the motor arrangement comprising a motor (8) for rotating the impeller so as to generate said flow of gas,

characterised in that the impeller (12) and the motor arrangement (5) are arranged in relation to each other such that the direction of flow into the impeller is directed away from the motor arrangement.

Respiratory assistance apparatus (1 ) according to claim 1 , wherein the gas inlet opening (2) of the fan (3) is facing the motor arrangement (5) such that gas is drawn into the gas inlet opening from in between the fan and the motor arrangement.

Respiratory assistance apparatus (1 ) according to claim 1 or 2, wherein the motor arrangement (5) comprises a drive shaft (14) connecting the motor (8) with the impeller (12) of the fan, and at least one drive shaft bearing (6) located between the motor and the impeller of the fan.

Respiratory assistance apparatus (1 ) according to claim 3, wherein the motor arrangement (5) further comprises a motor housing (22), a part (22a) of which houses said drive shaft bearing (6), said part of the motor housing being arranged in fluid communication with gas that is drawn into the gas inlet opening (2) of the fan.

5. Respiratory assistance apparatus (1 ) according to claim 4, wherein said part (22a) of the motor housing (22) faces the gas inlet opening (2) of the fan (3).

6. Respiratory assistance apparatus (1 ) according to claim 5, wherein said part (22a) of the motor housing is substantially cone-shaped with the top of the cone pointing towards the gas inlet opening (2).

7. Respiratory assistance apparatus (1 ) according to claim 6, wherein said cone-shaped part (22a) of the motor housing (22) protrudes at least partly into the gas inlet opening (2).

8. Respiratory assistance apparatus (1 ) according to any of the

preceding claims, wherein said motor arrangement (5) and the fan (3) are axially aligned along the motor axis (A), said gas inlet opening (2) being arranged centrally on the side of the fan facing the motor arrangement such that the motor axis runs through the centre of the gas inlet opening.

9. Respiratory assistance apparatus (1 ) according to any of the

preceding claims, further comprising means for adding oxygen to the gas that is drawn into the gas inlet opening (2) of the fan, upstream said gas inlet opening.

10. Respiratory assistance apparatus (1 ) according to any of the

preceding claims, wherein the motor arrangement (5) is provided with at least one gas channel configured such that at least some gas that is drawn into the gas inlet opening (2) of the fan (3) makes thermal contact with at least one internal component of the motor arrangement prior to being drawn into said gas inlet opening. Respiratory assistance apparatus (1 ) according to any of the preceding claims, wherein the fan (3) comprises a gas duct connecting said gas inlet opening (2) with said gas outlet opening (4), at least a part of said gas duct constituting a volute, a radial diffuser and/or an axial diffuser for converting said flow of gas into pressure.