WO2012095656A2

WO2012095656A2 - Medical device

Info

Publication number: WO2012095656A2
Application number: PCT/GB2012/050037
Authority: WO
Inventors: Stephen James LAMB; Richard Thomas BOWN
Original assignee: Cambridge Design Research Llp
Priority date: 2011-01-10
Filing date: 2012-01-10
Publication date: 2012-07-19
Also published as: GB201100289D0; GB2487087A; WO2012095656A3

Abstract

This invention relates to powered medical devices such as portable oxygen generators. A powered portable oxygen concentrator (POC) is described comprising an oxygen concentrator and a heat engine coupled to the oxygen concentrator to power the oxygen concentrator. The oxygen concentrator comprises an inlet port for receiving air; a gas separator configured to separate waste gas from the received air and provide an oxygen enriched gas; an oxygen outlet port for venting the oxygen enriched gas; and an exhaust port for venting the waste gas.

Description

Medical device

FIELD OF THE INVENTION

This invention relates to powered medical devices such as portable oxygen concentrators. Furthermore, the invention has applications in the field of closed cycle gas engines. BACKGROUND TO THE INVENTION

Oxygen cylinders are commonly used in medical and emergency care applications to provide a rich source of pure oxygen to a person under treatment. Individuals with respiratory problems may also need to use such cylinders in a home environment and in some cases whilst mobile outside of a hospital or home environment. Paramedics out in the field similarly also need to carry such apparatus.

Oxygen concentrators, in particular Portable Oxygen Concentrators (POCs) are an alternative to compressed oxygen cylinders and allow for continuous provision of concentrated oxygen. Oxygen concentrators are used to separate nitrogen and oxygen in ambient air and are used to provide oxygen for industrial and medical purposes, such as in hospitals for critical care or as a supplementary oxygen source for frail patients. POCs are smaller and lighter than equivalent static units used in homes and hospitals. They are powered by batteries and can operate independently from mains power to provide oxygen outdoors and in remote locations. POCs can provide oxygen to patients who are critically injured or frail patients who require supplementary oxygen.

POCs typically operate by separating oxygen and nitrogen in the air using a process such as pressure swing adsorption (PSA). The POC contains nitrogen adsorptive materials, such as zeolites which adsorb nitrogen under pressure, and desorb nitrogen when the pressure is relieved. A cycle of pressurisation and depressurisation results in nitrogen adsorption (thereby leaving concentrated oxygen) during the pressurisation phase and nitrogen desorption during depressurisation stage. By appropriately controlling a valving arrangement nitrogen and oxygen are separated. The size of such POCs typically depend on the specified oxygen delivery rate needed and consequently the larger the delivery rate, the larger the device.

A POC requires a pump to pressurise the air inside a zeolite module. Since air is approximately 80% nitrogen, it must compress 10 litres of air for every 2 litres of oxygen it produces. Consequently, the flow rate and high pressure means the pump requires a lot of power and a POC has heavy batteries. A typical POC may have a 2kg battery which will operate the system for 1 -2 hours. As the delivery rate increases, power requirements also increase. When a device is static this causes no problem because the POC may be connected to the mains electricity. To provide portability, batteries must also be provided which consequently add further mass. Spare batteries may also be transported increasing the overall weight further and so solutions that allow POCs to be powered by alternative means are sought. To allow the POCs to be used more extensively and for longer periods of time, eliminating or minimising the reliance on batteries is key, particularly when used in remote locations without electricity.

There is therefore a desire for improved POCs to address the problems identified above.

An example of the prior art can be found in US2002/0121 191 .

SUMMARY OF THE INVENTION According to a first aspect of the invention there is provided an oxygen concentrator and a heat engine coupled to the oxygen concentrator to power the oxygen concentrator, the oxygen concentrator comprising: an inlet port for receiving air; a gas separator to separate nitrogen from the received air and provide an oxygen enriched gas; an oxygen outlet port for venting the oxygen enriched gas; and an exhaust port for venting the separated nitrogen. The integrated oxygen concentrator and heat engine provide a unit capable of oxygen generation without the need for oxygen cylinders, the powered oxygen concentrator delivering oxygen enriched gas to a patient by extracting oxygen from air. Powering the oxygen concentrator from a heat engine enables a variety of different fuels to be used such as diesel and petrol and further eliminates (or reduces) the need for carrying batteries to power the system. The oxygen concentrator may comprise a portable oxygen concentrator (POC).

The heat engine may be any suitable engine that transfers heat into mechanical energy, e.g. a combustion engine. The heat engine may comprise a closed cycle gas engine, and the closed cycle gas engine may comprise a chamber and a chamber inlet port coupled to the chamber, the chamber inlet port in fluid communication with the exhaust port for delivering the vented waste gas (typically nitrogen, which may be a byproduct) to the chamber. The vented gas is used to improve the operation of the closed cycle gas engine for charging / pressurising the closed cycle gas engine chamber (the crankcase in which the displacer and/or power piston reciprocate).

The heat engine may be connected to the oxygen concentrator by a power transmission element which directly transfers mechanical power generated by the heat engine to the oxygen concentrator. In contrast to known prior art arrangements such as JP2007151855 and US 2010/0307496, there is no need to generate electricity or another form of energy to power the oxygen concentrator. The advantages of such a direct transfer of power include overall reduced size, weight, complexity and cost of the apparatus. Furthermore, there is improved reliability.

The heat engine may be a piston heat engine and the oxygen concentrator may have a piston pump. The power transmission element may comprise a first connection to transfer reciprocating motion from the heat engine to a rotary member to drive said rotary member in rotation and a second connection to transfer reciprocating motion from the rotary member to the oxygen concentrator. The rotary member may be a rotary shaft or a crank or a similar mechanism. The first and second connections may be connecting rods.

Alternatively the power transmission element may comprise a common connecting rod connecting the heat engine and the oxygen concentrator to transmit power direct from the heat engine to the oxygen concentrator. The power transmission element may further comprise a control mechanism for controlling reciprocal motion of the common connecting rod to ensure that the reciprocal motion of the common connecting rod generated by the heat engine is converted into the required reciprocal motion necessary to drive the oxygen concentrator. According to a second aspect of the invention there is provided a powered portable oxygen concentrator comprising: a portable oxygen concentrator (POC) and a closed cycle gas engine coupled to the POC to power the POC, the POC comprising: an inlet port for receiving air; a gas separator configured to separate waste gas from the received air and provide an oxygen enriched gas; an oxygen outlet port for outputting the oxygen enriched gas; and an exhaust port for venting the separated waste gas; wherein the closed cycle gas engine comprises a chamber and a chamber inlet port coupled to the chamber, the chamber inlet port in fluid communication with the exhaust port for delivering the vented waste gas to the chamber.

Air is drawn in from the atmosphere and passed through a gas separator to separate oxygen from the waste gas (which is primarily nitrogen). The remaining gas is oxygen enriched and can be outputted via an oxygen outlet to deliver to a patient (or alternatively stored). The POC and closed cycle gas engine are further connected to feedback nitrogen, which for oxygen generation is a by-product, and used to improve the operation of the closed cycle gas engine for charging / pressurising the closed cycle gas engine chamber (the crankcase in which the displacer and/or power piston reciprocate).

The aim of all aspects is to provide enriched oxygen having a high level of oxygen, perhaps approximately 90 to 95% oxygen. Accordingly, a relatively high flowrate of air into the system is required to generate sufficiently enriched oxygen. Thus, it is essential that sufficient power is generated by the heat engine and that the power is efficiently transmitted to the oxygen concentrator to ensure relatively high flow rates.

The closed cycle gas engine may be a Stirling engine which comprises a regenerator to store heat from hot gas as it moves towards the cold region of the engine. Examples of prior art Stirling engines are shown in US2009/0206667 which discloses a free- piston Stirling engine that drives a linear alternator to act as an electrical power source; JP6218216 which discloses using a Stirling engine to drive a small oxygen generator to feed oxygen enriched air to a combustion engine; DE4103623 which discloses another Stirling engine variant; CA1215548 which discloses a free-piston Stirling engine driven compressor/pump using pump diaphragms; and DE102008004879 which discloses a free-piston Stirling engine that provides hydraulic energy. The various features described above and below may be combined with either of the above aspects and/or any of the aspects of the invention as now further described. In some preferred embodiments the powered oxygen concentrator/POC may further comprise a reservoir coupled to the oxygen outlet port to store the vented oxygen enriched gas. When used to provide oxygen directly to a patient this may be an oxygen mask coupled to an oxygen accumulation bag. The oxygen concentrator/POC in the above aspects may further comprise a gas pressuriser coupled to the inlet port for pressurising the received air which may be necessary if the gas separator uses a process such as pressure swing adsorption (PSA). The heat engine may drive the pressuriser for the oxygen concentrator directly or alternatively may be used to generate electricity which in turn is used to power the pressuriser.

The gas separator may comprise a nitrogen adsorptive material to adsorb nitrogen from the received air. Examples of such nitrogen adsorptive materials include zeolite and activated carbon although it will be appreciated that other forms of adsorbents may also be considered. Alternatively an oxygen adsorptive material may be used.

The gas pressuriser may be configured to alternate between a pressurising phase and a depressurising phase in the above aspects such that in the gas separator there is a pressure swing. During the pressurising phase, nitrogen is adsorbed by the nitrogen adsorptive material leaving an oxygen enriched gas, and during the depressurising phase nitrogen is desorped from the nitrogen adsorptive material. Nitrogen is naturally vented from the nitrogen adsorptive material (e.g. zeolite) during desorption at about 0.15MPa (1 .5 bar) during the depressurising phase. The pressure range used may range between 0 and 0.15MPa (1 .5bar) or alternatively from -0.075MPa (-0.75 Bar) to +0.075MPa (+0.75 Bar).

In an alternative arrangement, the gas separator may comprise an oxygen adsorptive material to adsorb oxygen from the received air in the above aspects. Where the gas separator also comprises a gas pressuriser, during the pressurising phase, oxygen may be adsorbed by the oxygen adsorptive material to leave a nitrogen rich gas which may be vented through the exhaust port. During the depressurising phase, oxygen is vented through the oxygen outlet port during desorption.

An intermediate pressuriser may be coupled to the exhaust port. This may be used to further pressurise the gas vented through the exhaust port before delivery to the closed cycle gas engine chamber to increase the power density of the closed cycle gas engine. The intermediate pressuriser may be a separate compressor or alternatively may be provided by using the opposite side of the existing gas pressuriser used to pressurise air drawn in from through the air inlet to reduce the component count in the system.

The powered oxygen concentrator/POC may further comprise a feedback controller to control the pressure of the gas fed back into the closed cycle gas engine. The controller may control the intermediate pressuriser and valves used to control routing of the gas so that the volume and pressure can be optimised for the given closed cycle gas engine and load. Furthermore, in embodiments a feedback restrictor may control delivery/flow of the vented gas to the closed cycle gas engine chamber dependent on an operating state of the closed cycle gas engine. It is preferable to restrict the feedback of nitrogen, or not pressurise the closed cycle gas engine at all during startup as the engine requires more startup energy when the crank case (chamber) is pressurised and so a feedback restrictor . Delaying feedback of gas until the closed cycle gas engine is fully running accordingly allows for easier startup. Typically this feedback restrictor would be part of the controller and control activation of the intermediate pressuriser. It may further comprise a valve to route the flow of gas to the closed cycle gas engine or alternative to vent any unused gas to the atmosphere.

The powered oxygen concentrator/POC may further comprise a reservoir coupled to the outlet port to store the output oxygen enriched gas in the above aspects. When used to provide oxygen directly to a patient this may be an oxygen mask coupled to an oxygen accumulation bag, which additionally acts as an expansion chamber for the delivered oxygen. Thus the store of oxygen may be temporary, or may be permanent if alternative storage means are used.

The powered oxygen concentrator/POC may further comprise an exhaust valve coupled to the exhaust port and an exhaust valve controller which is coupled to the exhaust valve and which is configured to selectively open and close the exhaust valve. The exhaust valve and controller may be used to control the flow and routing of gas vented through the exhaust port in the above aspects. Typically, in many embodiments such an exhaust valve would be open during the depressurising phase when nitrogen is being desorbed from the zeolites. However, in alternative embodiments when an oxygen adsorptive material is being used, the valve may be open during the pressurising stage.

The powered oxygen concentrator/POC may further comprise an oxygen outlet valve coupled to the oxygen outlet port and an oxygen outlet valve controller which is coupled to the oxygen outlet valve and which is configured to selectively open and close the oxygen outlet valve. The oxygen outlet value and controller co-operate in a similar manner to the exhaust valve and controller. The oxygen valve controller is configured to open the oxygen outlet valve when the exhaust valve controller is configured to close the exhaust valve and vice versa in the above aspects. Thus, in many embodiments, the oxygen value is configured to open during the pressurising stage when nitrogen is adsorbed by the zeolites. It will be appreciated that the opening/closing will also be reversed if an oxygen adsorptive material is alternatively used.

In some embodiments of the powered oxygen concentrator/POC the closed cycle gas engine may be mechanically coupled to the oxygen concentrator/POC to mechanically drive the oxygen concentrator/POC in the above aspects. One or both of the gas separator(s) and pressuriser may be driven mechanically. This coupling may be direct or indirect. It will be appreciated that a direct mechanical linkage (such as through a common shaft, e.g. a piston shaft) may be more mechanically efficient and help to minimise the overall weight of the system.

In alternative embodiments, the closed cycle gas engine may drive an electric generator, with the oxygen concentrator/POC powered by an electrically powered motor. In such an arrangement a small battery may also be provided which may be used to help start up the system, or may be used to temporarily store charge or help power other parts of the system. Any such battery should preferably be minimal to help reduce the overall weight of the system. A temperature differential for powering the closed cycle gas engine may be created by a heater heating a heat portion of the closed cycle gas engine. The heater may be a liquid fuel burner, such as a diesel or petrol fuel burner heater or alternatively may be a gas fuel burner. Such fuels are much more energy dense than batteries.

The gas pressuriser may be in the form of a pump (comprising a pumping piston arranged to reciprocate in a pumping chamber) which may be integrated into the closed cycle gas engine and coupled to the power piston, such as by a mechanical linkage. The pumping piston may then be driven by the reciprocating action of the power piston within the closed cycle gas engine. The pumping piston may be directly connected to the power piston or may be coupled by a mechanical linkage, such as via a flywheel component of the engine.

There is also provided a method of powering an oxygen concentrator by coupling a heat engine, in particular a closed cycle gas engine to an oxygen concentrator/POC according to the above aspects of the invention. Waste gas vented from the oxygen concentrator/POC is fed back into the closed cycle gas engine chamber via a chamber inlet port coupled to the chamber to pressurise the closed cycle gas engine chamber. According to a third aspect of the invention there is provided a self-pressurising closed cycle gas engine, comprising: a closed cycle gas engine; a gas pressuriser; and an inlet port for receiving a gas; wherein the closed cycle gas engine comprises: a chamber comprising a cooling portion and heating portion; a chamber inlet port coupled to the chamber; a displacer to displace a pressurised gas between the cooling portion and heating portion; and a power piston arranged to reciprocate within the chamber; wherein the gas pressuriser is coupled to the inlet port to pressurise the received gas and provide the pressurised gas; and wherein the gas pressuriser is in fluid communication with the chamber inlet port for delivering the pressurised gas to the chamber; and wherein the gas pressuriser is powered by the closed cycle gas engine.

The closed cycle gas engine comprises a power piston arranged to reciprocate within the chamber and is used to power a gas pressuriser which in turn feeds back a pressurised gas to the chamber (crankcase) of the closed cycle gas engine to improve the power density of the engine. By continuously, or periodically, repressurising the closed cycle gas engine it avoids the need to provide perfect seals on the closed cycle gas engine and thus any gas leakage over time is automatically topped up avoiding the need for periodic servicing of the engine.

The received gas may comprise nitrogen and the self-pressurising closed cycle engine may further comprise a nitrogen separator coupled between the gas pressuriser and chamber inlet port. The nitrogen separator is configured to substantially separate nitrogen from the received gas to provide a nitrogen enriched gas (when air is received, the gas is further enriched above the normal atmospheric concentration to substantially eliminate oxygen) so that nitrogen is fed back into the closed cycle gas engine. This reduces the problems of corrosion (e.g. preventing oxidisation of internal components and further removing the risk of oxygen inside the engine burning the lubricant) due to operating at high temperatures, increasing reliability, prolonging lifetimes and potentially allowing lighter and/or cheaper materials to be used. The nitrogen separator may comprise a nitrogen adsorptive material, such as a zeolite, to adsorb nitrogen from the received air and provide an oxygen enriched gas. Such nitrogen adsorptive materials are commonly more effective at pressure and thus the pressure in the nitrogen separator may alternate between a pressurising phase in which the received air is pressurised for adsorption of nitrogen by the nitrogen adsorptive material and a depressurising phase for desorption of nitrogen from the nitrogen adsorptive material. This process is known as pressure swing adsorption. In this aspect of the invention the oxygen enriched gas is a waste product and may be vented through an exhaust port to the atmosphere. In an alternative arrangement the nitrogen separator may comprise an oxygen adsorptive material to adsorb oxygen from the received air and provide a nitrogen enriched gas. Where the oxygen adsorptive material requires high pressure to function, the pressuriser may be configured to alternate between a pressurising phase for pressurising the received air for adsorption of oxygen by the oxygen adsorptive material and a depressurising phase for desorption of oxygen from the oxygen adsorptive material. Oxygen may again be vented via the exhaust port during the depressurising phase and the nitrogen enriched gas may be output during the pressurising phase. Nitrogen is naturally vented from the zeolite during desorption at about 0.15MPa (1 .5 bar). The enriched nitrogen gas may be further pressurised by an intermediate pressuriser before feeding in to the chamber inlet port of the closed cycle gas engine. The intermediate pressuriser may be configured as described above, i.e. as a separate secondary pressuriser or part of the gas pressuriser. A controller may further be provided to control the feedback and pressurising of the enriched nitrogen. Such control may be dependent on an operating state of the closed cycle gas engine such that the pressurising varies (the closed cycle gas engine typically starts up easier without the chamber being pressurised).

In some preferred embodiments of the self-pressurising closed cycle gas engine the pressuriser comprises a pumping piston coupled to a power piston in the closed cycle gas engine so that the pressuriser is mechanically driven by the closed cycle gas engine. In such an arrangement the pressuriser may be integrated into the same body as the closed cycle gas engine with the power piston and pumping piston coaxially arranged, or alternatively connected via a linkage. Such a linkage may be arranged to provide a constant velocity ratio between the pumping piston and power piston to increase engine design freedom and enabling easier balancing of the powering and pumping arranged. Such a pump may be used to pressurise the nitrogen before it is injected into the engine chamber.

The self-pressurising closed cycle gas engine may further comprise a moveable pressuriser manifold. The moveable pressuriser manifold is moveable between a first position in which the inlet port is coupled to a pressurising chamber within the pressuriser, and a second position in which the pressurising chamber is coupled to the nitrogen separator. Gas flow through the nitrogen separator needs to be controlled to generate oxygen and so timing the delivery and pressurising the gas to the correct level for the separator is important. In one configuration the moveable pressuriser manifold is arranged as a rotatable pressuriser manifold synchronised with the speed of the pressuriser / engine to ensure that delivery of gas and pressurising is as required. The pressuriser manifold may comprise multiple components including a combination of valves, electronic solenoids and may be linear or rotating,

A further manifold (a separator manifold), may also be used in the nitrogen separator for controlling distribution of pressurised air to the zeolite assemblies performing the nitrogen adsorption. In a first position, the separator manifold may be configured to couple the gas pressuriser to the nitrogen separator to receive the pressurised gas. In the second position the separator manifold may be configured to couple the nitrogen separator to the chamber inlet port to deliver the pressurised gas to the chamber. This may be periodically for example such that the pressure in the chamber is maintained / recharged. In an third position, the separator manifold is configured to allow oxygen to be vented via the exhaust, although in some embodiments a portion of this oxygen may be routed back to the nitrogen separator to allow the zeolites to regenerate. This manifold may comprise multiple components including a combination of valves, electronic solenoids and may be linear or rotating. Existing solutions measure the pump speed then control the manifold speed using a stepper motor which adds weight (the motor) and requires control electronics. The CCG engine may comprise a flywheel or other connection linking the pressuriser manifold to the internal pressuriser to drive the separator manifold.

The pressuriser manifold and separator manifold may also be linked. As the two manifolds may be running at different speeds, a gearing arrangement may be provided to couple both manifolds. The two manifolds may be linked via a belt, worm gear, spur gears for example. The gear ratio may then be arranged so that the separator manifold rotates at the correct speed relative to the pump. This solution removes the need for a separate motor and control electronics.

The self-pressurising closed cycle gas engine may comprise a reservoir to store a portion of the enriched nitrogen gas (such a portion may be all of the produced nitrogen up to the capacity of the reservoir). The stored nitrogen may preferably be pressurised (at the desorbed pressure or further pressurised by the intermediate pressuriser) and stored pressurised to drive the pump as a gas engine to start the closed cycle gas (CCG) engine - this can help to provide a compact and low-weight design.

A method of self-pressurising a closed cycle gas engine is also described, the method comprising receiving a gas, pressurising the gas and delivering the gas to the chamber/crankcase of the closed cycle gas engine to pressurise the chamber. According to another aspect of the invention there is provided a closed cycle gas engine with integrated pump comprising: a chamber comprising a cooling portion and a heating portion; a displacer to displace gas between the cooling portion and heating portion; a power piston arranged to reciprocate within the chamber; and a pump comprising a pumping element and a pumping chamber, wherein the pumping element is arranged to reciprocate in the pumping chamber; and wherein the power piston is coupled to the pumping element such that the pumping element is driven by the reciprocating action of the power piston. The pump may be a positive displacement pump and the pumping element may be a piston for example, or alternatively may comprise a diaphragm.

The chamber comprises a cooling and heating portion and may be arranged as a single cylinder. Alternatively the chamber may be arranged into one or more separate cylinders such that one of the cylinders comprises the heating portion and the other comprises the cooling portion.

The pumping piston and power piston may be coaxially arranged to eliminate the need for addition connecting linkages between the pistons, further in such an arrangement the pumping piston may be formed from the same body / on a common shaft as the power piston such that the pumping piston and power piston are coaxially arranged.. In other configurations there may be no coaxial arrangement. Alternatively, the pumping piston may be pivotally coupled to the power piston, which may be via a linkage. In any of the arrangements, the coupling may be configured to provide a constant velocity ration between the pumping piston and power piston so that the pumping and power pistons reciprocate in unison.

The closed cycle gas engine with integrated pump may further comprise a pump inlet port coupled to the pump for receiving a gas and a pump outlet port for outputting the pumped gas. The pump outlet port may be arrangement to be in fluid communication with the chamber within the closed cycle gas engine so that gas pumped using the integrated pump is fed into the chamber to pressurise the chamber and improve the engine performance.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which:

Figure 1 shows a first arrangement of the powered portable oxygen concentrator;

Figure 2 shows a second arrangement of the powered portable oxygen concentrator;

Figure 3 shows a sample system built according to Figure 1 or 2; Figure 4 shows how the pump and CCG engine may be integrated into a common body;

Figure 4a shows an enlarged view of the pump of Figure 4; Figure 5 shows the actions and motions of the power piston and displacer and pumping actions of the system in Figure 4;

Figure 6 shows an alternative arrangement of the pump and CCG engine integrated into a common body;

Figure 7 shows the arrangement of inlets and outlets to the integrated CCG engine and pump;

Figure 8 shows the exhaust and flywheel portion of the CCG engine;

Figure 9 shows how pressurised waste nitrogen can be used to assist cooling of the CCG engine and actions and motions of the power piston and displacer;

Figure 10 shows an alternative arrangement of the system for providing a self- pressurising CCG engine;

Figure 1 1 shows a timing diagram to describe the controlling of the valving connecting inlets/outlet connections 86 to spaces 96, 98, 100, 102 in Figure 4 and Figure 4a; Figure 12 shows a detailed view of a heat exchanger suitable for use in the embodiment in Figure 4;

Figure 13 shows an alternative arrangement of a powered oxygen concentrator powered by a heat engine, and

Figures 14a to 14c show various power transmission elements for use in the arrangement of Figure 13 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following terminology is used within this specification:

• A heat engine converts heat energy to mechanical work.

Other examples of heat engines include steam engines, diesel engines, petrol

(gasoline) engines.

• A Closed Cycle Gas engine (CCG engine) is a particular type of heat engine which exploits a temperature gradient to repeatedly expand and contract gas within a closed cycle to power a piston.

· A Stirling engine is a particular type of CCG engine which features a regenerator to store heat from the hot gas as it moves towards the cold region of the engine. This energy is then recovered as the cold gas returns to the hot region of the engine, which helps to improve the efficiency of the system. This principle was patented by Robert Stirling in 1816.

Figure 1 shows an arrangement of a powered portable oxygen concentrator (powered POC). A closed cycle gas engine (CCG engine) 14 is powered by heat source 12. This may be any of a wide variety of energy sources including petrol, diesel, oil, butane, propane, biomass decomposition or concentrated sunlight. The CCG engine converts the thermal energy into mechanical energy and drives an electric generator 16 to electrically drive pump 22 and motor 20 for portable oxygen concentrator 24. The portable oxygen concentrator 24 receives pressurised air from the atmosphere via pump 22 (and inlet 1 1 ) and separates oxygen from nitrogen in the air, e.g. by a pressure-swing adsorption (PSA) process. The generated oxygen 26 is routed to a patient 30 and the by-product nitrogen 28 may be vented via exhaust port 32 or more preferably some or all of the nitrogen may be routed back via a chamber inlet port to fill the CCG engine chamber. Filling the CCG engine chamber with nitrogen, reduces the problems of corrosion due to elimination or reduction of oxygen due to operation at high temperatures, increasing reliability, prolonging lifetimes and potentially allowing lighter and/or cheaper materials to be used. The nitrogen may also pressurize the CCG engine chamber. The nitrogen fed back may be further pressurized using either pump 22 or alternatively using an additional intermediate pump located between the nitrogen feedback/exhaust 32 of the output of the oxygen concentrator and the chamber inlet port of the CCG engine.

Figure 2 shows a variant of the embodiment of Figure 1 in which the CCG engine 14 drives pump 22 for the portable oxygen concentrator 24 mechanically and directly without need for an intermediate generator and motor. This mitigates the need for power conversion with a generator and motor and thus helps to reduce weight and increase efficiency. Figure 2 further shows a combined starter motor and generator, known as a dynostart 34 included in the system. When the system is activated, the motor of the dynostart 34 draws on a small battery 18 to start the engine 14 running. Once operational and producing power, the motor will behave in reverse and act as a generator to re-charge the battery 18 which in turn powers control electronics.

In both the above embodiments, the POC 24 functions by using a zeolite substance, sometimes called a 'molecular sieve', which traps nitrogen when pressurised above a certain pressure, typically 1 .5 Bar above ambient. At this raised pressure point, when ambient air passes through the zeolite, nitrogen is trapped and the remaining gases (the majority of which is oxygen) pass through. Other zeolites are able to trap some of the trace gases in ambient air such as argon, to increase the purity of the oxygen further. The oxygen can be supplied to a patient or used for other applications. In alternative arrangements other substances may be used to adsorb oxygen with the remaining gas being nitrogen. Consequently oxygen is provided during the desorption stage.

Typically after a few seconds, the zeolite becomes saturated with nitrogen which must be vented to atmosphere and the zeolite takes a further few seconds to recover. Accordingly, the POC 24 may typically have at least two zeolite modules, so that while a first saturated zeolite module is recovering, a separate zeolite module is producing oxygen. When the second module becomes saturated, the first has recovered and takes its place. In an alternative arrangement one zeolite module may be used and this may be pulsed to adsorb and desorb nitrogen (although it will be appreciated that multiple zeolite modules may also be pulsed in a similar way).

The waste nitrogen trapped inside the zeolite is pressurised to about 0.15MPa (1 .5 Bar) above ambient pressure. This can be vented directly to atmosphere or preferably diverted into the CCG engine. When the nitrogen is used to fill the crankcase (chamber) of the engine, the following process may be used:

1 . Close the nitrogen vent to atmosphere, routing the nitrogen to the crankcase in the CCG engine 14,

2. Open the nitrogen solenoid into the engine crankcase, 3. Release the nitrogen pressure from the zeolite capsule,

4. Allow the nitrogen pressure in the engine crankcase and zeolite capsule to

equalise,

5. Close the solenoid on the engine crankcase,

6. Open the nitrogen vent to atmosphere, 7. Repeat this cycle with each subsequent release of nitrogen to sequentially

increase the pressure of nitrogen inside the crankcase. Eventually the crankcase pressure will approach the zeolite pressure.

Using nitrogen generated by PSA to fill the working space (chamber) to a raised pressure in CCG engine provides for improved engine performance (higher power density) for a given sized engine. In CCG engines, especially those with a high power density, the working air inside the system is often replaced with nitrogen. Use of nitrogen prevents oxidisation of internal components and removes the risk of the oxygen inside the engine burning the lubricant. CCG engines which run using nitrogen often need to be re-pressurised and are more expensive to produce because the seals must prevent the nitrogen leaking. Using pressurised nitrogen to continuously, or intermittently / periodically charge the engine as herein described provides the advantages of running at pressure with nitrogen, without the sealing challenges. The nitrogen is naturally vented from the oxygen concentrator at a higher pressure, typically 0.15MPa (1 .5 Bar), which can be channelled into the CCG engine.

By adding an intermediate pump between the zeolite and engine crankcase, the pressure of the Nitrogen delivered to the crankcase can be raised further. The opposite side of the existing pump used to pressurise air for the zeolite modules could be used or a separate intermediate pump could be used to provide the additional pressurisation. Figure 3 shows a sample system whereby a POC is combined with a high efficiency oxygen delivery system. POCs can be scaled to produce whatever oxygen flow rate is desired, but using the oxygen efficiently is always preferable to reduce the size, weight and power requirements of the system. The mask 58 used to deliver the oxygen strongly influences how efficiently the oxygen is consumed and can be used to provide an oxygen reservoir. The ideal mask should accumulate oxygen while the patient is exhaling, fit snugly around patient's face to prevent leaks and deliver the stored oxygen in preference to ambient air initially. The powered POC 50 comprises the CCG engine 14 and an oxygen concentrator 24 with an oxygen outlet 52. A separator manifold 51 is used to control the routing and distribution of gasses from within the POC, controlling delivering of oxygen via the oxygen outlet 52. A portion of the oxygen generated is also fed back into the zeolite module within the POC to allow the zeolites to regenerate.

The oxygen outlet 52 is coupled to a high efficiency oxygen delivery system 60 which comprises a thin walled bag acting as a oxygen reservoir 54 encased in a protective container 56. This allows for temporary storage of oxygen, and can help regulate and reduce the pressure of oxygen delivered from the portably oxygen concentrator. The oxygen reservoir is then connected to an oxygen mask 58 which can be attached to a patient for delivery of oxygen. Figures 4 and 6 show how a pump and CCG engine may be integrated into a common body to further reduce weight. The power piston in the CCG engine and the pump piston may be linked directly (as in Figure 4) on a common shaft or linked via the timing mechanism of the engine (as in Figure 6) or via the flywheel. Powering the pump directly from the engine shaft or drive mechanism prevents a change in motion and helps improves efficiency. Figure 4 shows a CCG engine with integrated pump 70. The engine portion operates as a CCG engine (for example operating according to a Stirling cycle) and includes a crank case/chamber 87 having a cooling portion 80 and a heating portion 76 with a displacer 78 configured to reciprocate between and displace gas between the opposed ends. A power piston 82 is coupled to the displacer 78 via a crank connected to a flywheel such that the power piston also reciprocates.

In this arrangement, the heating portion is at the lower end of the engine. A burner 74 heats gas within the lower end of the crank case causing the gas to expand and drive the power piston 82. The flywheel momentum forces the crank to rotate and the displacer moves towards the hot end of the chamber which pushes the gas to the cooling portion of the engine. In the cooling portion 80, the crankcase/chamber 87 is finned so that gas is cooled within this portion of the chamber. The cooling causes the gas to contract and subsequently drives the power piston in the reverse direction, inwards within the chamber. The cycle is illustrated in more detail in Figure 5.

Figure 4a shows an enlarged view of the pump portion of Figure 4. At the upper end of the integrated engine and pump is the pump portion which comprises a pumping piston (or plunger) 94 moving in pumping chamber defined by spaces C (102) and D (100) (note that alternative forms of positive displacement pumps could also be used)Attached to the end of the displacer is a bearing arrangement to allow for smooth and vertical movement of the power piston and pumping piston (The spaces within the bearing separated by the bearing plate may also be used to providing pumping functionality). The plunger 94 is attached to the power piston and is driven upward as the gas expands during the high power part of the cycle, and pulled downwards by the power piston as the gas contracts in the other part of the cycle. The pump is arranged such that the peak power demand matches the peak power generated by the CCG engine.

The plunger attached to the power piston creates pumping regions formed by space A (96), space B (98) , space C (102) and space D (100) within which gasses to be pumped may flow in which nitrogen for pressurising the engine, or air to be pressurised for the PSA process may be pumped or pressurised. In this arrangement the stroke diameter, speed, flow rate and pressure of the pump are dictated by the stroke, power and speed of the engine. Inlet/outlet gas connections 86 on the right hand side of the integrated engine and pump are connected to individual spaces 96, 98, 100, 102 respectively. The gas valve plate / manifold 84 is mounted to the main engine shaft and comprises a valving arrangement to connect the individual inlet/outlet gas connections to spaces 96, 98, 100, 102 respectively at the appropriate stage within the pumping cycle, further details of which are shown in Figure 7 and Figure 1 1 . The gas valve plate sequences when each inlet is connected to spaces A-D with a valve arrangement timed to inject and output gasses at the relevant state within the cycle. A further connection 88 provides the gas connection to the crank case which can be used to receive nitrogen (pressurized or otherwise) from the oxygen concentrator of Figure 1 or Figure 2.

An exhaust heat exchanger 74 may be used on a CCG engine powered POC. This is sometimes included to recover energy in the hot exhaust gases. In this arrangement the heat exchanger protects the operator and would be especially valuable in a military context to reduce the heat signature of the device. A counter-flow spiral design heat exchanger may also be used for exhaust energy recovery. This has the further advantage of shielding neighbouring components from the high temperatures. Figure 5 shows the actions and motions of the power piston and displacer within the arrangement of figure 4. Also shown are the pumping phases of each of the spaces: space A (96), space B (98), space C (102) and space D (100). At the beginning of the cycle, stage 1 1 1 , the displacer is driven down by pressurized nitrogen and space C is pressurized. The next stage 1 12 is the period during which the power piston is driven down by pressurized nitrogen and which space A is pressurized. In the middle of the cycle, at stage 1 18, the displacer is driven up by pressurized nitrogen and space D is pressurized. The next stage 1 14 is the period during which the power piston is driven up by pressurized nitrogen and space B is pressurized. Finally, at the end of the cycle, stage 1 13 the displacer is again driven down by pressurized nitrogen and space C is pressurized and the cycle thus begins to repeat.

Figure 6 shows an alternative arrangement of the engine and pump integrated into a common body. In this configuration the pump is driven from a part of the closed cycle gas engine drive mechanism with an approximately constant velocity ratio to the power piston formed from swing arm 128 and link 126 (collectively providing the linkage between the power piston and pump piston). Driving the pump via a mechanism from the power piston allows the pump stroke to be different from that of the engine, increasing design freedom, reducing the space envelope of the engine and may be easier to balance than the arrangement in Figure 4. This also allows greater freedom as to where the pump cylinder is placed, providing further improvements in the packaging of the engine. In this arrangement pump piston 124 is connected to the power piston 82 via link 126 and swing arm 128. Space A (130) above the pump piston and space B (132) below the pump piston provide regions for pumping gas as the pump piston reciprocates.

The opposite side of the pump (for example space A (130) in Figure 6 forms the opposite side of the pump to the pumping region formed from space B (132)) may also be utilised for pumping to increase the flow rate capacity. Additionally, or alternatively, the opposite sides of the pump may also be used independently to generate positive and negative pressure for the PSA process and nitrogen adsorption / desorption. This principle is used on some PSA zeolite modules, where the positive and negative pressure is used alternatively instead of a positive pressure only. The unused side of a CCG engine powered pump may also be used to pressurise the crankcase. Figure 7 shows the arrangement of inlets and outlets to the integrated CCG engine and pump. The inlets and outlets comprise a connection 88 to the crank case, a nitrogen inlet 146, a high pressure nitrogen outlet 144, an air inlet 86 and a high pressure air outlet 148. Connection 88 to the crankcase receives nitrogen, preferably at higher than atmospheric pressure to fill crankcase/chamber of the CCG engine. Nitrogen inlet 146 provides an input to the pump which may be used to pressurise nitrogen which may subsequently be input to the crankcase via connection 88 for example. Alternatively, the nitrogen may additionally or alternatively be diverted to a low pressure relief valve 154 if the pressure of the nitrogen is too high for connection to the crankcase. The nitrogen inlets may be connected to one side of the pump such as space B (132) in Figure 6. The air inlet 149 may be connected to the other side of the pump such as space A (130) in Figure 6 with the corresponding high pressure air outlet 149 outputting the high pressure air 148. The high pressure air outlet may be connected to the portable oxygen concentrator in order to provide pressurized air for the pressure switch adsorption process. A solenoid valve 150 may be connected between the inlets and outlets and a POC. The solenoid valve 150 is shown in a start position. Starting the CCG engine cycle may be difficult if the pump and/or generator is active so by removing the pneumatic load and disconnecting the generator the starting resistance can be minimized.

Providing a low pressure crankcase starting mode can also be beneficial - starting the CCG engine requires more energy when the crank case and working gas is pressurised. Since the POC has a waste nitrogen supply and pump, the crank case pressure can be released so the starting resistance of the engine is minimised. Once the engine is started, then the pressure of the crank case and working gas can be increased selectively. To reduce the load on the closed cycle gas engine to provide for an easier start-up, the pump outlet can be disconnected as shown in Figure 7. The pump outlet is vented to the atmosphere during starting and warm-up to reduce the load on the engine. When the engine is running, a valve can be closed to connect the pump to its load.

Figure 8 shows the exhaust and flywheel sections of the CCG engine. The exhaust heat exchanger 188 often creates condensation as it cools the exhaust gas. The condensation can be directed to the cold region of the CCG engine using a wick 174. The airflow over this region helps to evaporate the water which helps to remove the moisture from the system and the act of evaporation helps to cool the engine. In addition, ambient air is warmed as it passes over the cooling fins 172 on the cold side of the engine. Some or all of this air can be used to burn the fuel and recover the energy in the warmer air. Duct 186 is used to bring warm air into the burner.

A geared flywheel 178 comprising a heavy rim 180 may be used to keep the engine turning during the 'dead-point' of the Stirling cycle. The mass of the flywheel can be reduced if it rotates faster. By gearing the fly wheel with a 3:1 ratio for example, the angular momentum is increased by a factor of 9 so the mass of the flywheel can be substantially reduced (for example with a lightweight pinion 182 on the engine output shaft coupled to the flywheel 178 via belt 184). The flywheel 178 may also be used as a fan, shown by the fan blades 176 on the flywheel in Figure 8. The cold piston of the engine requires airflow over the cooling fins to maintain its temperature. It is a common technique in other engines to mould fins onto the tip of the flywheel to act as a fan. This can be merged into the CCG engine design and the fins can be modified if the flywheel is geared to a higher speed.

Figure 9 shows how pressurised waste nitrogen 196 can be used to form a nitrogen flow 194 that can be expanded through a nozzle 198 towards the cold side of the engine 80. This has two effects. Firstly, the adiabatic expansion 200 of the gas drops its temperature. Secondly, the high speed gas flow entrains more air (feature 192 in Figure 9), further improving the engine cooling. The chart in Figure 9 shows the periods during which pressurised nitrogen can be injected into selected regions in the CCG engine.. Stages 204 show the periods in which the displacer in Figure 4 is kicked down by pressured nitrogen and space C (102) in Figure 4 is pressurised. Stage 202 shows the period in which the displacer in Figure 4 is kicked up by pressurised nitrogen and space D (100) is pressurised. The waste nitrogen can be routed to provide improved cooling.

The invention also has further uses in addition to provision of an improved portable oxygen concentrator, such as in combined heat and power systems, and concentrating solar power systems. In such systems capture and feedback of nitrogen is important, and the oxygen may be vented directly to the atmosphere, or for the combined heat and power system, used to enrich gas burning. Furthermore, the nitrogen adsorptive material could also be replaced with an oxygen adsorptive material (which would provide a nitrogen enriched gas, with oxygen as the desorbed gas).

There is an increasing demand for technologies which lower global carbon dioxide emissions to tackle global warming, such as heating and powering buildings. A Combined Heat and Power (CHP) system replaces a traditional boiler and generates typically 1 kW of electrical power and 10kW of heat. This is more efficient than supplying a home with electricity from a power station because of the losses in the national grid and the heat wasted during generation. The heat created by a CHP system is used by the house directly and there are no power transmission losses since the electricity is used at source.

CHPs may use CCG engines to power the generator because they are quiet and have low vibration. This is an important characteristic when CHPs are usually installed in domestic kitchens and must be discrete. Examples of such systems are provided by BAXI and WhisperTech.

To increase the power density of the CCG engines, the working gas which is trapped inside the engine is sometimes pressurised. Pressurising with nitrogen is safer than using air (which is 21 % oxygen) because it avoids problems due to oxidisation of parts or potentially burning any lubricants inside the engine. Once the engine is pressurised, the higher power density allows a smaller engine to generate a given power. Charging with nitrogen does however add some complexity. It must be pressurised during installation and needs to be well sealed to prevent the gas escaping, and consequently increases the costs of components and manufacture due to the higher tolerances needed. Any imperfect seal results in nitrogen slowly leaking from the system and results in the need to re-pressurise at service intervals. . Figure 10 shows the arrangement of a system to address this deficiency. Figure 10 shows a similar arrangement to Figures 1 and 2 but in this arrangement any oxygen generated is vented via exhaust 27. A small pump 23 is used to pressurise air for the PSA process within the oxygen concentrator. However, since the oxygen is vented, there is no longer a requirement for a specific flow rate of oxygen. Accordingly, the conversion process and produced nitrogen flow rate can be reduced to a rate suitable for maintaining pressure in the CCG engine only whilst powering the engine main load 25.

Figure 1 1 shows a timing diagram 220 describing the controlling of the valving connecting inlets/outlet connections 86 to space A (96), space B (98), space C (102) and space D (100) in Figure 4 and Figure 4a. The movement of gas to/from internal regions of the combined CCG engine and pump are controlled by a series of valves. These may be one way valves, electronic solenoids, a linear manifold or rotating manifold for example. A combination of valves is used to connect the internal spaces of the combined CCGE and pump to different gas sources. Figure 1 1 shows the engine motion and possible pumping configurations.

Considering spaces A and B configurations in plots 222, in the first configuration space A is acting as pump, with the moveable (pressuriser) manifold 84 /valving configured to receive atmospheric air via the inlet during the downward motion of the power piston (in Figure 4), the pressurising and outputting to the oxygen concentrator after the power piston reaches bottom dead centre (BDC) as the power piston moves upwards. Other configurations are also possible, and for example, space B may also be used to provide the crankcase / chamber pressure, pressurising gas in space B and delivering the gas to the crankcase during the downwards movement of the power piston, then receiving nitrogen from the POC when the power piston is moving upwards. The manifold / valving are timed to allow gas in and out at the appropriate stages within the engine and pressurising cycle. Alternatively space B may also be used in conjunction with space to provide a duplex pump receiving atmospheric air during the upward motion of the power piston and pressurising / outputting during the downward motion.

Considering spaces C and D configurations, these may be used to kick through the deadpoints of the flywheel as shown in the plots 224. Space C, for example, may be filled with pressurised nitrogen from the POC before and after the power piston reaches top dead centre, and space D may be filled with pressurised nitrogen from the POC before and after the power piston reaches bottom dead centre. At other points in the cycle the nitrogen may then be vented to the atmosphere.

Spaces A to D may also be used to assist with pneumatic starting. Plots 226 show the timing for injecting stored nitrogen into the spaces to assist with startup of the engine.

Alternatively, if electric starting is used, such as motor 16 from Figure 1 , then the manifold / valving may be arranged to open all regions to the atmosphere which will reduce the engine load.

Gas flow through the zeolite needs is controlled to generate oxygen in POC 24. This may be achieved with a rotating manifold (a 'separator' manifold) or electric solenoids or a combination of both. The speed of the rotating manifold is synchronised with the speed of the pump so that the zeolite is pressurised to the correct level. A portion of the oxygen generated is also fed back into the zeolite module within the POC to allow the zeolites to regenerate. Current known solutions measure the pump speed then control the manifold speed using a stepper motor which adds weight (the motor) and requires control electronics. The CCG engine has a flywheel 178 which is linked to the internal pump and could be used to drive the separator manifold. The flywheel and separator manifold could be linked via a belt, worm gear or spur gears for example. The flywheel, or other linkages / gearing may also be used to link manifold 84 (the pressuriser manifold) in Figure 4 to the separator manifold 51 in Figure 3. A gear ratio is used to set the separator manifold rotating at the correct speed relative to the pump and pressuriser manifold. This solution eliminates the need for a separate motor and control electronics.

Figure 12 (a and b) shows further details of the heat exchanger 188 of Figure 8 arranged as coiled metal elements. The heat exchanger and burner body 244 surrounds the engine hot end locating in region 242. A cutaway section in Figure 12b shows the internal coil 240. Figure 12a shows the inlet and exhaust ports on the heat exchanger with air inlet 232 at atmospheric pressure, a burner air supply 234 (which may be at approximately 500 degrees C or higher), burner exhaust 236 (which may be at approximately 600 degrees C or higher) and exhaust outlet 238 (which may be at approximately 70 degrees C).

CCG engines may also be used in concentrating solar power systems whereby sunlight is concentrated onto the engine and linked to an electrical generator. These engines may also be charged with nitrogen for the same reasons that CHP systems are. Consequently, they face the same challenges of nitrogen escaping and re-pressurising the engine at service intervals. Again, the invention as described herein can also be used to provide improved systems.

In an alternative arrangement, rather than storing electrical energy in a battery and starting the engine using a motor, high pressured gas produced by a pump or the PSA process may drive the pump as a gas engine to start the CCG engine which can help to provide a compact and low-weight design. In addition, the stored gas may also be used to charge the crankcase prior to starting.

The CCG engine produces a fluctuating power output with a defined peak power region. The generator, which may run off the flywheel or be linked on a common shaft with the engine, may be controlled so it only generates power during this peak power region. By reducing or removing the load from the generator during the low power region of the engine cycle, it reduces the burden on the flywheel which can be made lighter. In addition, during operation, high pressure nitrogen may be introduced into a cylinder coupled to the movement of the displacer of Figure 4, as it moves through each cycle. This would help kick the engine through its dead spot, reducing the need for a flywheel.

Figure 13 shows the combination of heat engine 100 and oxygen concentrator 102. The heat engine may be any suitable engine that transfers heat into mechanical energy, e.g. a combustion engine. The heat engine 100 is connected to the oxygen concentrator 102 by a power transmission element 104. In contrast to known prior art arrangements such as JP2007151855 and US 2010/0307496, the connection by a power transmission element allows direct transfer of mechanical power rather than via electricity, or via the medium of a moving vehicle, wheel and generator. The advantages of such a direct transfer of power include overall reduced size, weight, complexity and cost of the apparatus. Furthermore, there is improved reliability.

The oxygen concentrator 102 is similar to those described above and comprises an air pump or gas pressuriser 106 which is directly connected to and powered by the power transmission element. The pump or pressuriser 106 draws air into the concentrator through air inlet port 108 and into the gas separator 1 10. The waste nitrogen is expelled through a waste exhaust port 1 12 and vented into the open air. The enriched oxygen is collected in a reservoir 1 14 within the concentrator. When oxygen is required for inhalation by a patient through a mask 1 16, the enriched oxygen is drawn through oxygen outlet 1 18 along a connecting tube to the mask 1 16. It will be appreciated that any suitable form of delivery to a patient may be used.

There are several different ways of transmitting power direct via a power transmission element and examples are shown in Figures 14a to 14c. In each of Figure 13 to Figure

14c, a piston heat engine and a piston air pump are shown for simplicity. However, any engine could be used including rotary (e.g. wankel) engines, turbines etc.

Similarly, many forms of pumps and compressors exist and could be used, e.g. gear pumps, rotary pumps, centrifugal, scroll pumps, diaphragm pumps. The power transmission element would need to be adapted for different engines and different pumps. The key feature of the power transmission element is that there is a direct transfer of power.

Figure 14a shows a power transmission element using rotary motion to transfer power. The heat engine 100 is connected to a rotating shaft 124 via a first connecting rod 120. Similarly, the oxygen concentrator (particularly the pump within the oxygen concentrator) is connected to the rotating shaft 124 via a connecting rod. The heat engine 100 moves the first connecting rod 120 in a reciprocating motion which rotates the rotating shaft 124. The rotating shaft drives a second connecting rod 122 into reciprocating motion. The second connecting rod 122 is connected to the oxygen concentrator and hence powers the oxygen concentrator. Thus, the power transmission element comprises a rotary shaft and the connections to the heat engine and the oxygen concentrator. Figure 14b also shows a power transmission element using rotary motion to transfer power. In this case, the rotary element is a crank 128 which is connected to a first connecting rod 120 connected to the heat engine 100 and a second connecting rod 122 connected to the oxygen concentrator 102. Power is transmitted by reciprocating motion of the first connecting rod 120 to rotary motion of the crank 128 and to reciprocating motion of the second connecting rod 122. Thus, as in Figure 14b, the power transmission element comprises a rotary member connected to the heat engine and the oxygen concentrator via reciprocating connections.

Figure 14c shows a power transmission element in which the heat engine 100 and oxygen concentrator 102 are connected by a common connecting rod 130 to transmit power direct from a piston within the heat engine to a piston within the oxygen concentrator. However, it is not sufficient to simply drive the piston in the oxygen concentrator with the reciprocal motion of the common connecting rod 130 and a control mechanism for controlling the reciprocal motion is required. The control mechanism ensures that the reciprocal motion of the common connecting rod generated by the heat engine is converted into the required reciprocal motion necessary to drive the pump of the oxygen concentrator. There are many known mechanisms. For example, Figure 14c shows an example using a crank 128 and a crank connecting rod 132. However, other alternative such as a strong centrally-biased spring may be used.

As shown in Figures 14a to 14c, all three elements, namely heat engine, power transmission element and concentrator share a housing 126. However, it will be appreciated that this need not be the case and the three elements may be housed separately. No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims

CLAIMS:

1 . A powered oxygen concentrator comprising:

an oxygen concentrator and a heat engine coupled to the oxygen concentrator to power the oxygen concentrator,

the oxygen concentrator comprising:

an inlet port for receiving air;

a gas separator configured to separate waste gas from the received air and provide an oxygen enriched gas;

an oxygen outlet port for venting the oxygen enriched gas; and an exhaust port for venting the waste gas.

2. A powered oxygen concentrator as claimed in claim 1 , wherein the oxygen concentrator further comprises a gas pressuriser coupled to the inlet port for pressurising the received air.

3. A powered oxygen concentrator as claimed in claim 2, wherein the gas separator comprises a nitrogen adsorptive material to adsorb nitrogen from the received air; and

wherein the gas pressuriser is configured to alternate between a pressurising phase for pressurising the received air for adsorption of nitrogen by the nitrogen adsorptive material and a depressurising phase for desorption of nitrogen from the nitrogen adsorptive material.

4. A powered oxygen concentrator as claimed in any one of claims 1 to 3, further comprising a reservoir coupled to the oxygen outlet port to store the vented oxygen enriched gas.

5. A powered oxygen concentrator as claimed in any preceding claim, wherein the heat engine comprises a closed cycle gas engine, and

wherein the closed cycle gas engine comprises a chamber and a chamber inlet port coupled to the chamber, the chamber inlet port in fluid communication with the exhaust port for delivering the vented waste gas to the chamber.

6. A powered oxygen concentrator as claimed in claim 5, further comprising an intermediate pressuriser coupled to the exhaust port for pressurising the vented waste gas before delivering to the closed cycle gas engine chamber.

7. A powered oxygen concentrator as claimed in claim 6, wherein the gas pressuriser comprises the intermediate pressuriser.

8. A powered oxygen concentrator as claimed in claim 6 or 7, further comprising a feedback controller for controlling the pressurising of the vented waste gas by the intermediate pressuriser dependent on an operating state of the closed cycle gas engine.

9. A powered oxygen concentrator as claimed in any one of claims 5 to 8, further comprising a feedback restrictor to control delivery of the vented waste gas to the closed cycle gas engine chamber dependent on an operating state of the closed cycle gas engine.

10. A powered oxygen concentrator as claimed in claim 9, wherein the feedback restrictor comprises a valve configured to selectively route the vented waste gas to the chamber or to the atmosphere dependent on the operating state of the closed cycle gas engine.

1 1 . A powered oxygen concentrator as claimed in any one of claims 5 to 10, further comprising a reservoir coupled to the outlet port to store the output oxygen enriched gas.

12. A powered oxygen concentrator as claimed in any one of claims 5 to 1 1 , further comprising an exhaust valve coupled to the exhaust port and an exhaust valve controller coupled to the exhaust valve configured to selectively open and close the exhaust valve.

13. A powered oxygen concentrator as claimed in claim 12 when dependent on claim 3, wherein the exhaust valve is configured to open during the depressurising phase.

14. A powered oxygen concentrator as claimed in any one of claims 5 to 13, further comprising an oxygen outlet valve coupled to the oxygen outlet port and an oxygen outlet valve controller coupled to the oxygen outlet valve configured to selectively open and close the oxygen outlet valve.

15. A powered oxygen concentrator as claimed in claim 14 when dependent on claim 3, wherein the oxygen outlet valve is configured to open during the pressurising phase.

16. A powered oxygen concentrator as claimed in any one of claims 5 to 14, wherein the closed cycle gas engine is mechanically coupled to the oxygen concentrator to mechanically drive the oxygen concentrator.

17. A powered oxygen concentrator as claimed in any one of claims 5 to 15, wherein the closed cycle gas engine drives an electric generator and the POC is powered by an electrically powered motor.

18. A powered oxygen concentrator as claimed in any one of claims 5 to 17, wherein a temperature differential for powering the closed cycle gas engine is created by a heater heating a heat portion of the closed cycle gas engine.

19. A powered oxygen concentrator as claimed in claim 18, wherein the heater is a liquid fuel burner or a gas fuel burner.

20. A powered oxygen concentrator as claimed in any one of claims 5 to 19, wherein the chamber comprises a cooling portion and a heating portion; and further comprising:

a displacer to displace gas between the cooling portion and heating portion; a power piston arranged to reciprocate within the chamber; and

a pump comprising a pumping piston and a pumping chamber, wherein the pumping piston is arranged to reciprocate in the pumping chamber; and

wherein the power piston is coupled to the pumping piston such that the pumping piston is driven by the reciprocating action of the power piston.

21 . A powered oxygen concentrator as claimed in claim 20, wherein the pumping piston is directly coupled to the power piston.

22. A powered oxygen concentrator as claimed in claim 20, further comprising a flywheel, and wherein the pumping piston is coupled to the power piston via the flywheel.

23. A powered oxygen concentrator as claimed in any one of claims 5 to 22, wherein the closed cycle gas engine is a Stirling engine.

24. A powered oxygen concentrator as claimed in any preceding claim, wherein the oxygen concentrator is a portable oxygen concentrator (POC)

25. A self-pressurising closed cycle gas engine, comprising:

a closed cycle gas engine;

a gas pressuriser; and

an inlet port for receiving a gas;

wherein the closed cycle gas engine comprises:

a chamber comprising a cooling portion and heating portion; a chamber inlet port coupled to the chamber;

a displacer to displace a pressurised gas between the cooling portion and heating portion; and

a power piston arranged to reciprocate within the chamber; wherein the gas pressuriser is coupled to the inlet port to pressurise the received gas and provide the pressurised gas; and wherein the gas pressuriser is in fluid communication with the chamber inlet port for delivering the pressurised gas to the chamber; and

wherein the gas pressuriser is powered by the closed cycle gas engine.

26. A self-pressurising closed cycle gas engine as claimed in claim 25, wherein the received gas comprises nitrogen, the self-pressurising closed cycle gas engine further comprising a nitrogen separator coupled between the gas pressuriser and chamber inlet port configured to provide a nitrogen enriched gas, and wherein the delivered pressurised gas comprises the nitrogen enriched gas.

27. A self-pressurising closed cycle gas engine as claimed in claim 26, wherein the received gas is air,

wherein the nitrogen separator comprises a nitrogen adsorptive material to adsorb nitrogen from the received air and provide an oxygen enriched gas; and

wherein the gas pressuriser is configured to alternate between a pressurising phase for pressurising the received air for adsorption of nitrogen by the nitrogen adsorptive material and a depressurising phase for desorption of nitrogen from the nitrogen adsorptive material; and

further comprising an exhaust port for venting the oxygen enriched gas.

28. A self-pressurising closed cycle gas engine as claimed in claim 26, wherein the received gas is air;

wherein the nitrogen separator comprises an oxygen adsorptive material to adsorb oxygen from the received air and provide the nitrogen enriched gas; and

wherein the pressuriser is configured to alternate between a pressurising phase for pressurising the received air for adsorption of oxygen by the oxygen adsorptive material and a depressurising phase for desorption of oxygen from the oxygen adsorptive material, and

further comprising an exhaust port for venting the desorbed oxygen.

29. A self-pressurising closed cycle gas engine as claimed in any one of claims 26 to 28, further comprising an intermediate pressuriser coupled between the nitrogen separator and the chamber inlet port for further pressurising the enriched nitrogen gas.

30. A self-pressurising closed cycle gas engine as claimed in claim 29, further comprising a controller for controlling the pressurising of the enriched nitrogen gas dependent on an operating state of the closed cycle gas engine.

31 . A self-pressurising closed cycle gas engine as claimed in any one of claims 26 to 30 further wherein the pressuriser comprises a pumping piston, wherein the pumping piston is coupled to a power piston in the closed cycle gas engine.

32. A self-pressurising closed cycle gas engine as claimed in claim 31 , wherein the gas pressuriser further comprises a pressurising chamber and a moveable pressuriser manifold, wherein the moveable manifold is moveable between a first and a second position, wherein in the first position the manifold is configured to couple the inlet port to the pressurising chamber and in the second position the pressuriser manifold is configured to couple the pressurising chamber to the nitrogen separator.

33. A self-pressurising closed cycle gas engine as claimed in any one of claims 26 to 32, further comprising a separator manifold moveable between a first and a second position, wherein in the first position the separator manifold is configured to couple the gas pressuriser to the nitrogen separator to receive the pressurised gas and in the second position the separator manifold is configured to couple the nitrogen separator to the chamber inlet port to deliver the pressurised gas to the chamber.

34. A self-pressurising closed cycle gas engine as claimed in claim 33, where the separator manifold is moveable to a third position, wherein in the third position the separator manifold is configured to couple the nitrogen separator to the exhaust port to vent the oxygen enriched gas.

35. A self-pressurising closed cycle gas engine as claimed in claim 34, wherein in the third position, the separator manifold is further configured to deliver a portion of the oxygen enriched gas back to the nitrogen separator.

36. A self-pressurising closed cycle gas engine as claimed in any one of claims 28 to 35 further comprising a reservoir to store a portion of the enriched nitrogen gas.

37. A self-pressurising closed cycle gas engine as claimed in any one of claims 25 to 36, wherein the closed cycle gas engine is a Stirling engine.

38. A closed cycle gas engine with integrated pump comprising:

a chamber comprising a cooling portion and a heating portion;

a pump comprising a pumping element and a pumping chamber, wherein the pumping element is arranged to reciprocate in the pumping chamber; and

wherein the power piston is coupled to the pumping element such that the pumping element is driven by the reciprocating action of the power piston.

39. A closed cycle gas engine with integrated pump as claimed in claim 38, wherein the pumping element comprises a piston.

40. A closed cycle gas engine with integrated pump as claimed in claim 39, wherein the pumping piston and power piston are coaxially arranged.

41 . A closed cycle gas engine with integrated pump as claimed in claim 39, wherein the pumping piston is pivotally coupled to the power piston.

42. A closed cycle gas engine with integrated pump as claimed in claim 41 , wherein the pumping piston is pivotally coupled to the power piston using a linkage.

43. A closed cycle gas engine with integrated pump as claimed in any one of claims 39 to 42, wherein the power piston is coupled to the pumping piston to provide a constant velocity ratio between the pumping piston and power piston.

44. A closed cycle gas engine with integrated pump as claimed in any one of claims 38 to 42, further comprising a pump inlet port coupled to the pump for receiving a gas, and a pump outlet port for outputting the pumped gas, wherein the pump outlet port is in fluid communication within the chamber for delivering the pumped gas to the chamber.

45. A closed cycle gas engine with integrated pump as claimed in claim 38, wherein the pumping element comprises a diaphragm.