GB2343152A - Inflatable structure including elastic member to limit maximum inflation pressure - Google Patents

Abstract

An inflatable structure such as a life jacket or life raft is formed from an air tight cover 16, a chemical gas generator 5 and an elastic member that deforms during initial inflation to limit the maximum pressure within the airtight cover 16. The gas produced by a chemical gas generator is initially at a high temperature and takes up its maximum volume. Subsequently the gas cools and contracts to its operational volume. In order to prevent damage to the air tight cover 16 the elastic member expands during initial inflation and then contracts as the gas cools thereby limiting the maximum pressure within the structure and preventing over-inflation. The elastic member may comprise part of the airtight cover 16 itself or may comprise an internal elastic baffle 22 (see figure 7) or an external elastic member (see figures 11 and 12).

Description

TITLE : An inflatable structure.

TECHNICAL FIELD: The present invention relates to inflatable structures, including a device for inflating 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, supporting objects. In the operating condition the cover is given an increased rigidity and a functional form. The structure includes at least one gas generator, generating a pressuri2ed gas, having a temperature exceeding the temperature of the environment, and means for 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 hot and therefore over time will cool. (Generally the gas produced will be hotter than the surrounding air temperature or water temperature at any one time) Therefore over a period of time the volume will be reduced.

Gas generator reactions (burning) are essentially an exothermic reaction-typically a gas generating chemical has some 3-4 Megajoules per kg of thermal energy. When the gas is released this heat energy is released and consequently the gas is hot. However, gas released from a compressed gas cylinder is very cold and consequently even if the air temperature is cold, the gas will be warmed and will then expand. To compensate for this, large inflatable structures such as liferafts etc., are fitted with pressure relief valves so that at higher air temperatures the excess gas is vented to atmosphere. Therefore the pressure relief valves on these structures using compressed gas will compensate for the excess gas filling the structure. Small inflatable structures such as lifejackets can accommodate excess pressure because they have a higher burst pressure and therefore a higher safe working pressure than the larger structures. They also are not so critical in terms of maintaining rigidity-As a consequence, they do not need pressure relief valves.

Inflatable structures are typically made out of a woven fabric coated with a gas holding layer and have only minimal stretch or reduced elasticity. These larger structures need to maintain a given operating pressure in order to maintain rigidity within the structure and therefore support the survivors as well as providing the floatation buoyancy. In the case of lifejackets the"degree of rigidity"is less important.

A gas generator will typically produce hot gas which may be in the order of +200 C when it initially fills the structure. Some gas generators can produce cooler gas and particularly in the case of"augmented"systems which also use compressed gas, the gas produced can be relatively cool. However, generally the gas will be warmer at some stage than the external air temperature. Over a period of time the gas will then cool to the eventual operating temperature of the structure which will be nearer to the external air or water temperature where the structure is inflated. Lifesaving inflatables are generally expected to operate in an air temperature range of-30 C to +60 C.

Therefore over a period of time, the gas temperature could ultimately be reduced down to-30 C. As volume is directly proportional to temperature, then to ultimately produce, a certain volume of gas where the ultimate temperature would be-30 C then this would require an additional volume of nearly the same amount as the initial volume for example.

Inflatables such as liferafts are designed to operate at a working pressure and at no time should the ultimate gas pressure exceed two times this working pressure. It is typically expected that the burst pressure is expected to be at least three times the working pressure. Therefore if an additional volume of gas of the same amount was discharged into the structure, this would cause the structure to burst.

However, immediately after discharge, the gas filling the structure is rapidly cooling as the heat is transferred to the atmosphere away from the inflatable structure. This will obviously be faster the colder the air or water temperature surrounding the structure is. Consequently, with the use of prior art equipment the inflated volume will be reduced and the inflated structure will partly loose its supporting function. Alternatively, an overfil- ling of a prior art structure will involve a great risk that the structure bursts.

DISCI. OSURE OF THE PRESENT INVENTION : The object of the present invention is to overcome the problem of the excess volume and increased temperature of the gas.

Said object is achieved by means of the inflatable structure according to the present invention, which is charac- terized therein, that said structure includes at least one elastic member provided to allow changes of the volume of the body in order to maintain a chosen operational pressure in said operational condition of said body BRIEF DESCRIPTION OF THE DRAWINGS : The present invention will be further described by way of examples as shown in the accompanying drawings in which Fig. 1 shows by way of a diagram pressure as a function of time during gas generation and inflating an inflatable body according to the present invention, Fig. 2 and 3 show a first example of an inflatable structure according to the present inven tion in the form of a life-jacket at the end of the stage of inflating and in the operational condition respectively, Fig. 4 shows a second example of an inflatable structure according to the present inven- tion in the form of a life-raft at the end of the stage of inflating, Fig. 5 shows the life-raft during a firs time pe riod of its operational condition after the stage of inflating, Fig. 6 shows the life-raft during a second time period of the operational condition, Fig. 7 and 8 show schematically an example of a tubular body forming an inflatable structure or a part thereof according to the present invention at the end of the stage of in flating, Fig. 9 and 10 show the inflatable structure according to fig. 7 and 8 in its continuous operational condition, Fig. 11 shows a further example of a tubular body at the end of the stage of inflating, whereas Fig. 12 shows the tubular body according to fig.

11 in its continuous operational condi tion.

PREFERRED EMBODIMENTS : The overall principle according to the present invention is to create an inflatable structure such that all or part of the inflatable structure can expand in volume also at the end of the stage of inflating, thereby limiting the maximum pressure within the structure-thus preventing the problem of the structure bursting when being overfilled with gas or alternatively collapsing due to loss of volume.

The present principle is schematically illustrated in fig.

1 in comparison with prior art structures. In the diagram a curve 1 represents a structure having a non-elastic cover of a body forming the inflatable structure or part thereof.

This curve shows a progressive increase of pressure by time during inflation of the structure, which results in bursting if the pressure within the structure exceeds the maximum allowed pressure-A second curve 2 illustrates the increase of pressure by time in an inflatable structure according to the present invention. This curve 2 shows an increase of pressure by time during a first period of inflating. At the end of inflating the structure at time t,, an operational pressure is reached and will not be exceeded due to the fact that the structure expands in volume. Due to elastic properties of the structure according to the present invention the operational pressure will substantially be maintained also when the volume will be reduced due to the fact that the structure can retract elastically.

Fig. 2 and 3 show a first example of an inflatable structure according to the present invention in the form of a life-jacket 3 comprising one or more inflatable bodies 4- The structure also includes at least one gas generator 5, mounted in the body, able to inflate the body after actuation by means of a controller not shown. The gas generation occurs chemically by ignition of a compound of chemicals which normally have an unstable valency, involving that gas molecules are rapidly released. The gas generator includes means for discharging the gas rapidly into a closed chamber 6. In a folded uninflated condition of the structure the body 4 and the chamber 6 have a minimum volume and have in the inflated condition a suitable volume for full function.

The structure according to fig. 2 and 3 is of a type which does not require any rigidity in the structure and simply provides an amount of buoyancy needed to support floata tion. For this purpose the life-jacket 3 has a cover 7 enclosing the inflatable chamber 6, said cover having a wall which is made by a gas holding elastic material to accommodate a change in volume. Fig. 2 shows the jacket at the end of the stage of inflation during which the body 4 of the structure has an oversize, i. e. a volume exceeding the ultimate volume. This is possible due to the elasticity of the wall of the cover 7. The discharged gas has as a result of the chemical process a very high temperature during the inflation, which clearly exceeds the temperature in the environment outside the structure 4, which can be in the interval of for example-30 C-+40 C. Due to dissipation of heat energy to the environment the temperature within the body 4 will be reduced to the level of the environment or somewhat higher, due to the heat energy from the body of the wearing person. This results in a reduction of volume which is apparent from fig. 3 which shows the inflatable jacket in its continuous operational condition, i. e. a time period after inflating the structure, still having a fully functional form due to retraction of the elastic cover 7. The structure is fully able to carry a person floating on a water surface.

The cover 7 according to the present invention must be made of a material having good elastic properties, for example an elastic fabric. In the case of a tubular structure the volume is directly proportional to the diameter of the tube and therefore a 100% increase in volume would require some 40% increase in the diameter of the tube.

In other applications where it is important that the supporting part of a structure retains a degree of rigidity -e. g. the inflatable main tubular part of a liferaft, then this part of the structure cannot be elastic otherwise it would loose its rigidity and would collapse too easily and, as a result, fail to support the occupants. However some other parts of the liferaft which are inflatable do not need to retain rigidity to the same extent and in this case these parts of the liferaft could be made to expand or contrat without affecting the structural rigidity of the main tube. The inflatable chambers which are parts of the liferaft expanding and contracting could be for example, the inflatable arch tube that supports the protectinc canopy for the occupants, or the inflatable floor whict acts as an insulation for the occupants against the effectue of the cold water underneath see fig. 4-6, which explaine this.

Fig. 4-6 show a liferaft 8 schematically as a crosssectional view having a main supporting structure in the form of a tubular body extending in a closed ring anc having at least one gas generator 5 for decharging hot ga : into the inflatable structure and primarily into the inflatable main supporting structure, i. e. the tubulaj inflatable body 9. This body 9 of the main supportinc structure has in this type of application a cover 10 whict is flexible, but substantially non-elastic in order t ( maintain a structural rigidity. Also the bottom floor 11 is a part of the main supporting structure and should be mad ( of a non-elastic, but flexible material in order to be able to be folded in a stored condition. However the bottor floor 11 supports inflatable bodies 12 which can have wall : 13 which are elastic and enabling the bodies to change volume. Fig. 4-6 further show the inflatable arch tube 14 or tubes that support the protecting canopy 15 for the occupants. The arch tube 14 belongs also preferably to the elastic part of the structure, i. e is formed as a hollov body 15 having a cover 16 made by an elastic material enabling a volume increase without exceeding a predetermined operational pressure. The dashed lines 17 show the extension of the inside elastic walls in the operationa : condition when the volume is reduced which also is shown il fig. 6. In the shown example the chambers 18,19 of the canopy and/ox floor or indeed the other expanding structures are connected to the main supporting structure by one-way pressure relief valves 20. These valves allow gas only to pass in one direction and only at a predetermined pressure. This then means that the passage of gas between the chambers will depend on the pressure differential at a predetermined pressure. This then means that if one compartment is punctured e. g. the inflatable floor and loses its gas and therefore its pressure and volume, then the gas in the main supporting structure will not be lost.

The material of the canopy 15 is preferably of non-elastic but can alternatively be made of elastic material. Fig. 5 shows the structure in a first time period of the operational condition, in which some temperature and volume reduction has taken place.

In another application as shown in figs. 7-10 the inflatable body 21 or structure, for example a tube, is made with a division or"baffle"layer 22, which could be made from or could include an elastic material. The baffle layer 22 extends transversely through the body 21 between opposite walls. This tube would then be made such that at maximum pressure the division of the elastic material is fully stretched, see figs 7 and 8, but loss of volume results in the elastic material being reduced in length but pressure is still maintained-albeit at a reduced volume, see figs.

9 and 10.

In the example as shown i figs. 7-10 the baffle 22 can either be open enabling gas to fill the whole body 21 from one or several gas generators 5 at merely one side of the baffle, alternatively, if the baffle 22 is closed, gas generators must be arranged on either side of the baffle.

In the example as shown in figs. 11 and 12 two bodies 23, 24, which can have a cover 25 of a non-elastic material, are connected with each other by means of at least two elastic members 26,27 which in the end of the stage of inflating are expanded allowing the bodies 23,24 to have their maximum volume, in the example having substantially circular shape. In an operational condition, the volume has been reduced in the bodies, 23, 24, as shown in fig. 12, normally due to the fact that gas has gained a reduced temperature. However sufficient supporting function is maintained due to retraction of the elastic members 26,27, still maintaining the outer shape of the two bodies 23,24.

In this example the bodies have separate chambers 28,29, each having at least one gas generator 5.

The controlled gas generation 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 T'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 surface.

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 modified within the scope of the accompanying claims. For example the elastic material can be part of the elastic wall or member. For example a part of the surface can be elastic or it can be an elastic layer combined with extendable non-elastic layers. The elastic members as shown in figs. 7-12 can be non-closed members, for example elastic bars instead of sheet material. The elasticity is normally two-dimensional, but can alternatively be one-dimensional or three-dimensional. The inflatable structure has such elastic properties that the chosen operational pressure can be maintained substantially unchanged within such a range of volume changes which occurs in an inflatable structure, due to temperature changes between the maximum temperature during inflation and minimum temperature in the operational condition.

Claims (5)

1. CLAIMS : 1-An inflatable structure (3), including at least one body (4), including a flexible, closed cover (7), at least one device for inflating the body 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 functional form, said device including at least one gas generator (5), generating a pressurized gas, having a temperature exceeding the temperature of the environment and means for discharging the gas into at least one chamber (6), enclosed 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 structure includes at least one elastic member (7) provided to allow changes of the volume of the body in order to maintain a chosen operational pressure in said operational condition of said body.
2. 2. An inflatable structure 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 said elastic member being a sheet member, forming the cover (7) of the body or a part thereof.
3. 3. An inflatable structure 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 inflat- able structure comprises two or several bodies (9,12,15), of which at least one body (9) has a cover which is made of a non-elastic material and at least one further body (13, 14) which is made of an elastic material, allowing change of volume of said further body or bodies in the operational condition of the structure.
4. 4. An inflatable structure 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 said elastic member is a baffle (22) extending inside the body (21) between opposite walls.
5. 5. An inflatable structure 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 said elastic member (7) has elastic properties adapted to maintain said chosen operational pressure within a range of temperature changes between the maximum temperature during inflation and minimum temperature in the operational condition.