GB2343151A - Inflatable structure with gas generator and protective diffuser - Google Patents

Abstract

An inflatable structure such as a life jacket or life raft is formed from an air tight cover 3, a chemical gas generator 1 and a protective flexible diffuser 11 enclosing the gas generator 1. The use of chemical gas generators to inflate structures is advantageous over conventional compressed gas in that the generators are smaller, lighter and provide faster inflation. However the gas they produce is at a high temperature and this high temperature gas could potentially damage the inflatable structure. The provision of a flexible diffuser 11 allows the generated gas to be distributed and cooled before coming into contact with the air tight cover 3 thereby minimising the risk of damage. By making the diffuser 11 flexible allows the size of the structure when uninflated to be kept to a minimum.

Description

TITLE: A device for inflating inflatable structures.

TECHNICAL FIELD: The present invention relates to a device for inflating inflatable structures, including at least one body, consisting of a flexible, closed cover, for the purpose of converting the body between a stored condition, in which said cover encloses a minimum of volume, and a continuous operating condition, the result of which is to support objects. In the operating condition the cover is given an increased rigidity and a predetermined form. The method and device include initiating a chemical process in a gas generator, generating a pressurized gas, having a temperature exceeding the temperature of the environment, and discharging the gas into at least one chamber, closed by said flexible cover, creating a gas pressure exceeding the pressure in the environment outside the cover.

PRIOR ART: The concept of using the gas produced from the reaction process of a chemical gas generator in order to inflate marine safety and survival equipment is prior known. Inventions which either use the gas generant to produce all the gas or where it is used in conjunction with a compressed gas inflation system show the typical prior art.

Traditionally inflatable structures for marine safety and survival have been inflated using compressed gas stored in metal cylinders. The gas is released when required by opening a valve which can be automatically or manually actuated. The gas fills the inflatable structure through high pressure hoses and valves and the structure is often in a number of separate chambers. The hoses and valves route the gas into the inflatable chambers. using a chemical which produces a particular volume of gas when it burns is an alternative system of inflation which is prior known per se. Such chemicals normally have an unstable valency which means that gas molecules are rapidly released when a compound is ignited. Such compounds are typically Sodium Azide based or Nitro-Cellulose based Recent developments are using less toxic materials including organic gas generators. These chemicals do not have toxic residue such as free sodium. Development of such chemicals has recently been advanced with the greater use of gas generators in order to inflate driver and passenger restraint bags (air bags) in automobiles and in other restraint applications.

The advantages of using a chemical gas generator as opposed to traditional compressed gas, are as follows : 1. Gas generator systems are generally lighter by comparison.

2. Gas generator systems are generally smaller by compa rison.

3. Gas generator systems are generally faster when filling an inflatable structure, are not liable to freezing and the speed of inflation is not detrimen- tally affected by external air and water temperatures.

4. Gas generator systems generally produce hot or warm gas rather than gas entering the inflatable structure well below freezing temperature, as is the case with compressed gas. This is particularly important for human survival and the prevention of hypothermia.

5. Gas generator systems generally have fewer parts e. g. valves and high pressure hoses and are therefore cheaper to produce and to assemble into the inflatable structure. However, there are problems with using gas generators to inflate such equipment. One of these is that the volume of gas produced to fill the structure when initially produced is very hot. Generally the gas produced will be hotter than the surrounding air temperature or water temperature at any one time. Gas generators typically produce gas in the order of +1000 C to +2000 C (this contrasts to gas entering an inflatable chamber from a compressed gas system which is typically in the order of-70 C).

This hot gas presents a problem as the heat can damage or indeed"burn"the inflatable material by overheating it.

This of course would cause the inflatable structure to burst and could also burn a person who might be in contact with it. Typically in the use of automobile"airbags" (driver and passenger restraint systems), manufacturers have tried to reduce the heat output and produce"cool"or "cooler"type systems. Some of these are systems which combine together a gas generator with a compressed gas cylinder. This is described in patent applications, or they use heat filters or heat absorbers. Typically such heat absorbing chemicals are Inorganic Oxides such as Aluminium oxide. Others use metal bicarbonates etc which decompose at high temperature. This decomposition is endothermic and therefore reduces the gas temperature. In some cases this endothermic reaction can also provide additional gas, see e. g. Patent Specification DE 223310.

In such cases as described above, the"coolants"are contained in some rigid structure which surrounds or is in line with the gas generator material (or alternatively is mixed with a gas generator compound). In the case of where the coolants surround or are in line with the gas generator, the hot gas passes through the heat absorbing medium. However even with coolants the gas temperature is still hot and the temperature of the surface of the gas generator itself is normally extremely hot.

Such additions to the gas generating system increase both the weight and size of the system.

DISCLOSURE OF INVENTION : The object of the present invention is to overcome the problem with the risk of damaging inflatable structures as a result of the increased temperature and/or pressure of the emitted gas by means of a device having a minimum of size and weight.

Said object is achieved by means of the device according to the present invention by surrounding the gas generator with a flexible envelope forming a diffuser which allows gas to pass through it but diffuses the gas such that the temperature and/or pressure of the gas as it exits from the diffuser has achieved a reduced value.

BRIEF DESCRIPTION OF DRAWINGS: The present invention will be further described by way of examples as shown in the accompanying drawings in which Figs. 1-5 shows different stages during inflation of an inflatable structure using a diffuser according to the present invention, Fig 6 shows a diagram over the temperature inside the inflatable structure during inflation as a function of time without and with diffuser respectively, Figs. 7 and 8 show a first example of a diffuser, having a heat reflective surface, Figs. 9 and 10 show two examples of a diffuser being made of a heat absorbing material, Fig. 11 shows a diagram over the temperature as a function of time in a diffuser according to a further example in which a Phase Change Material, and Figs. 12-14 show an inflatable structure having a diffuser acting as a pressure diffuser.

PREFERRED EMBODIMENTS : The device according to the present invention is schemati- cally shown in figs. 1-5 and includes a gas generator 1, mounted in an inflatable body 2 for the purpose of inflating the body in order to give the body its intended function of use to form an inflated structure. The body is normally stored in a package, normally folded in order to demand a minimum of space. The body consists of a flexible closed cover 3 of for example a woven fabric, coated with a gas holding layer. The cover has normally limited elasticity. The cover encloses a closed chamber 4 which in the folded, uninflated condition has a minimum volume and which in inflated condition has a predetermined ultimate operational volume for full function. Consequently it is very important for the body to achieve and maintain its ultimate volume, especially in case of emergency equipment.

The gas generator 1 uses preferably an initiator or actuator which for example is an electronic initiator, including a battery and a micro controller. The initiator is for example connected to a small cap which contains a compound of chemicals which normally have an unstable valency, involving that gas molecules are rapidly released when the compound is ignited. Such a compound is for example Sodium Azid based or Nitro-cellulose based. Other compounds such as compounds for gas generators for restraints bags (airbags) in automobiles can be used in principe. The cap is provided with means for discharging the gas in the form of for example one or more nozzles 5 directed inwardly to the chamber 4 to be inflated.

In order to control the gas generation the generator includes one or more sensors or other control means, such as a clock connected by means of one or more sensor or control inputs 6. The sensor or sensors can be a temperature sensor sensing the internal gas temperature after release or discharge into the chamber 4. Said temperature sensor can be combined with a further temperature sensor sensing the external temperature of the environment, i. e. surrounding water of gas, such as air or atmosphere. A further or alternative sensor can be a pressure sensor sensing the internal pressure of the discharged gas in the chamber 4. Instead of said sensors the gas generator 1 can be controlled by time separately or in combination with the above sensors.

According to the present invention the problem of the emitted gas being at a high temperature is solved by surrounding the gas generator 1 with a diffuser 7 in the form of a flexible envelope which allows gas to pass through it but diffuses the heat such that the temperature of the gas as it exits from the diffuser is cooler. whilst the gas is expanding the heat is being dissipated and the temperature is therefore constantly reduced relative to the distance from the gas generator. The diffuser forms a barrier or protective shield, which consequently is gaspermeable.

Fig. 1 shows the inflatable structure in a folded storing condition in which the body 3 with its cover 3 is folded. The structure is shown more schematically for the matter of clarity but in practice the structure can form a very flat package with the cover in a close contact with the envelope 7 and the gas generator 1. Due to the flexibility of the diffuser envelope 7, it can be stored in a folded condi tion, either folded randomly, i. e. in an unstructured order, or in predetermined foldings, so that the envelope encloses the gas generator 1 very closely. The envelope either encloses the gas generator 1 completely together with the cover 3 of the body 2 or, is attached to the periphery of the gas generator in a sealing manner. Preferably the gas generator has a circular periphery and is substantially cylindric with its nozzle 5 or nozzles directed inwardly to an inner chamber 8, enclosed by the envelope 7. This inner chamber 8 has a minimum volume in the stored position of the inflatable structure. The nozzle 5 is consequently directed to an inwardly faced surface 9 of the envelope.

When the inflatable structure is to be inflated the gas generator 1 is activated through the control input 6. The gas generator begins to burn with a flame temperature in the size of +1. 500 C. The gas generator 1 as a whole, including its housing 9 will rapidly be subjected to a rise of temperature, radiating heat energy to the environment.

However, by means of the envelope 7, heat energy will be absorbed or reflected or a combination thereof, protecting the cover 3 from damaging heat.

As a next stage, illustrated in fig. 3, hot gas is created and is charged through the nozzle 5 or nozzles inwardly to the body 2 of the inflatable structure. However, due to the presence of the diffuser envelope 7 the internal temperature of the envelope will primarily be raised and filled with gas whilst the hot gas is directed to the inwardly faced surface 10 of the envelope 7 enclosing the internal chamber 8 when it is filled by the hot gas. Consequently the cover 3 of the body 2 will not be hit by the rapidly outstreaming gas, which will be well protected from heat.

Next stage is shown in fig. 4, in which the diffuser envelope 7 has reached full volume of gas whilst allowing gas to pass through the wall 11 of the envelope 7 in a diffused manner due to pressure difference between both sides of the wall 11, i. e. on the inside of the inner surface 10 of the wall 11 and on the outside of its outer surface 10'. Directly upon filling the inner chamber, heat also will dissipate to the chamber 4 of the body and the gas will pass through the wall 11, distributed over a large part of the area of the envelope in many directions. The delayed and diffused transport of the gas from the envelope to the chamber of the body will result in a highly reduced temperature of the gas when contacting the cover 3 of the body. At a certain stage according to fig. 4 the temperature of the gas within the envelope 7 can be for example +400C and the temperature in the chamber 4 of the body has for example been reduced to +200 C.

Fig. 5 shows the final stage in which the inflatable structure is full. inflated, i. e. has full volume and has reached peak temperature and pressure in the chamber 4 of the body 2, for example 200 C whereas the temperature of the chamber 8 of the envelope 7 has been reduced to the same temperature. Due to dissipation through the cover 3 of the body 2 to the environment the temperature will be rapidly reduced as a result of the fact that the environment in all situations always has a lower temperature.

The diagram of fig. 6 shows a comparison between temperature in a structure without diffuser and with diffuser. The temperature will be measured within the chamber 4 of the cover 3 outside the envelope 7 for example in an area near the cover. The curve 12 shows that the temperature rapidly reaches a peak at a high level, which can damage the cover 3 of the body whilst the curve 13 shows the change of temperature by time using diffuser according to the present invention resulting in a slow increase of temperature to a maximum which in the shown example is a third of the peak temperature without diffuser.

The flexible gas diffuser will typically be constructed from a heat resistant material forming the flexible wall l.

11. Typically it might for example be a woven fabric which is constructed from a heat material fibre such as carbon fibre or some other heat resistant fibre, it would additionally for example have an inner surface 11 coated with a heat reflecting material such as aluminium, see figs. 7 and 8. Such types of fabric are available for applications such as protective suits used in fire fighting. The material would either be porous by construction or would be made to be porous by perforating the material with very many fine holes. In this way the emitted hot gas is not localise onto one small area (hot spot) but is spread more evenly and will additionally be at a lower temperature than without the diffuser for a given area immediately adjacent to the diffuser.

Typically the flexible material might also be a heat absorbing material. Here, for example the material might include compounds which are heat absorbent-such as metallic oxides, which could be impregnated or held in the material, see fig 9. Alternatively, see figs. 9 and 10, layers 14, 15 of porous material might enclose heat absorbing compounds 16 in powder or granular form between the two layers of fabric. Also in these examples the wall 11 of the envelope 7 allows gas to pass through, whilst the heat is absorbed by the heat absorbent material.

Especially advantageous in a flexible gas diffuser would be the use of a"Phase-Change Material"PCM's absorb and hold considerable heat. Typically they are for example waxes etc which, when they change phase by melting, when the temperature exceeds their melting point. The material changes from a solid to a liquid, able to absorb considerable heat through latent heat diffusion. Typically waxes can absorb between 40 and 60 calories/g. Fabrics can be impregnated with such materials by coating the fabrics (e. g. U. S.

Patent No. 4,871,615) or by creating micro-encapsulated PCM spheres of material which can then be included in the material or fabric (e. g. U. S. Patent No. 5,366,801).

Alternatively, such micro-encapsulated PCM's could be held d between layers of material. where the stored heat energy is of a reversible type (i. e. in the case of PCM'S) the heat is stored and then given out on cooling, i. e. the latent heat given out as the PCM returns from liquid to solid~ In this case, this output of heat can be used to warm the wearer of a lifejacket or the occupants of a liferaft over a period of time, see fig. 11. The material of the inflatable structure itself could include reversible heat store materials such as micro-encapsulated PCM's and thus further increase the overall reversible heat storage capability of the inflatable structure.

The flexible diffuser can further also act as a filter in that the residues from the burning of the gas generant such as carbon or other burnt materials and other particles do not contaminate the inside of the inflatable structure.

Additionally it is expected that in certain applications after use the flexible gas diffuser can be dispose of complete with the residue of the burning, along with the used gas generator attached to it.

As illustrated in figs, 12-14 the flexible gas diffuser 7 can also act as a pressure dif f user ln some cases it is advantageous for a gas generator to burn very rapidly and to produce all its gas very quickly. Such advantages are the fact that the burning when it is quicker may be cleaner i. e. less bi-products such as solid residue and additionally the burning may be also more reliable. However inflatable structures may not be designed to withstand such an "explosive"pressure front from the gas generator. In this case an inflatable structure designed to achieve safe working pressure in 5 seconds might be inflated by the gas generator in 0.5 seconds. In this case it would cause localise over pressure in certain areas and cause the structure to burst. However the flexible gas diffuser can act as a high pressure reservoir-such that all hot gas is retained and held by the diffuser in a period of 0. 5 seconds but then is released more slowly from the diffuser into the structure over a longer period of time-say 5 seconds. This therefore fills the inflatable structure more slowly and in a more controlled way as shown in figs. 1214, illustrating in fig. 12 an initial stage, after 0.5 seconds, an intermediate stage, after 2.0 seconds, during which gas passes through the diffuser 7, and a final stage, during which the body is filled to its final volume and pressure- The device according to the present invention can be used in different applications for by way of example marine and aeronautical safety and survival equipment including for example the following: -Inflatable liferafts for single person use (single seat liferafts) -Inflatable liferafts for multi person use up to 150 persons (multi seater liferafts) -Inflatable lifejackets (US-"life preserver") gas inflated only -Inflatable lifejackets-composite that is, combination of gas and inherently buoyant foam -Marine inflatable evacuation slide systems-for evacu- ation on ships and often used in conjunction with large inflatable Liferafts.

-Aeronautical inflatable slide systems-for evacuation of aircraft onto land or water -Emergency buoyancy systems and self righting systems (marine applications). Inflatable bag used to provide emergency buoyancy for a vessel e. g. : 1 If it is damaged and is sinking and therefore provides sufficient buoyancy to prevent sinking.

2 If it turns over and capsizes. Here buoyancy can be provided which inflates under water and which then turns the vessel upright again (used for both motor vessels or for sailing vessels such as catamarans).

3 Emergency buoyancy systems and self-righting systems aeronautical use. Here inflatable buoyancy can provide emergency buoyancy to an aircraft (typically a rotor wing aircraft) if it ditches but can also provide a buoyancy to prevent the aircraft"capsizing".

4 Inflatable boats which can be rapidly inflated so as to be used at the site of an emergency-often these can be"air-dropped"from an aircraft either by parachute or by a"low level"drop.

5 inflatable emergency indicating buoys which are released from a sinking vessel or a vessel in distress in order to indicate the position on the water surfac .

6 Emergency Lifting Bags. These are large inflatable bags used to lift an aircraft if its undercarriage has collapsed following a crash landing.

7 Emergency inflatable buildings used to house equipment or people in an emergency relief application. The present invention is not limited to the example as described above with reference to the accompanying drawings, but can be modifie within the scope of the accompanying claims.

Claims (9)

1. CLAIMS: 1. A device for inflating inflatable structures, including at least one body, including a flexible, closed cover (3), for the purpose of converting the body between a stored condition, in which said cover encloses a minimum of volume, and a continuous operating condition, supporting objects in which operating condition the cover is given an increased rigidity and a predetermined form, said device including -means for initiating a chemical process in at least one gas generator (1), generating a pressurized gas, having a temperature exceeding the temperature of the environment -means (5) for discharging the gas into at least one chamber (4), enclose by said flexible cover, creating a gas pressure exceeding the pressure in the environment outside the cover c h a r a c t e r i z e d t h e r e i n, that -said device includes a flexible diffuser (7) in the form of an envelope, which is positioned within said chamber (4) and encloses the means (5) for discharging the gas, and that -said diffuser forms a flexible barrier which in the stored condition has a minimum of size and, during said discharge is expanded delaying and distributing passage of gas through the wall (11) of the envelope for the purpose of protecting the cover (3) of the body (2).
2. 2. A device according to claim 1, c h a r a c t e r i z e d t h e r e i n, that the flexible wall (11) of the diffuser (7) is porous, including a number of passages extending through the wall from an inner surface (10) faced to the gas generator (1) and to another surface (10') faced to the cover (3).
3. 3. A device according to claim 2, c h a r a c t e r i z e d t h e r e i n, that at least part of the wall (11) is perforated, forming said passages.
4. 4. A device according to claim 2, c h a r a c t e r i z e d t h e r e i n, that the flexible wall (11) is made of a porous material.
5. 5. A device according to claim 2, c h a r a c t e r i z e d t h e r e i n, that the inner surface (10) of the flexible wall (11) is heat reflective.
6. 6. A device according to claim 2, c h a r a c t e r i z e d t h e r e i n, that the flexible wall (11) is heat absorbing.
7. 7. A device according to claim 1, c h a r a c t e r i z e d t h e r e i n, that the flexible diffuser (7) acts as a heat reducing diffuser.
8. 8. A device according to claim 1 or 7, c h a r a c t e r i z e d t h e r e i n, that the flexible diffuser (7) acts as a pressure diffuser, delaying by means of the wall (1) equalization of pressure between each sides of the wall.
9. 9. A device according to claim 1, characterized therein, thatthe inflat- able structure is an emergency equipment.