Abstract:
An inflation device for an aircraft emergency evacuation slide or other inflatable device produces a greater number of moles of gas than the number of moles of gas stored. This is accomplished by selecting the stored inflation gas to be one of a family of gases capable of undergoing a thermal decomposition, such as nitrous oxide, such that two moles of nitrous oxide are decomposed to form two moles of diatomic nitrogen and a mole of diatomic oxygen. Because the universal gas constant is the same for all gases, the three moles of nitrogen and oxygen produced by the decomposition of two moles of nitrous oxide occupy 50% more volume than the two moles of nitrous oxide would have occupied at the same temperature and pressure. By decomposing the stored nitrous oxide, the inflator is capable of inflating a device that is 50% larger than would be possible using un-decomposed gas.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to emergency evacuation equipment for aircraft. In particular, this invention relates to a device for inflating an inflatable aircraft emergency evacuation slide or other inflatable device.  
           [0002]    The requirement for reliably evacuating airline passengers in the event of an emergency is well known. Emergencies at take-off and landing often demand swift removal of the passengers from the aircraft because of the potential from injuries from fire, explosion, or sinking in water. A conventional method of quickly evacuating a large number of passengers from an aircraft is to provide multiple emergency exits, each of which is equipped with an inflatable evacuation slide. Current state-of-the-art emergency evacuation slide systems comprise an inflatable evacuation slide which is stored in an uninflated, folded state together with a source of inflation gas. The source of inflation gas typically comprises a gas generator, stored compressed gas, or a combination thereof. Compressed stored gas inflators typically require the storage of a relatively large volume of gas at a relatively high pressure. As a result of high gas storage pressures, the walls of the storage vessel must be relatively thick for increased strength. The combination of large volume and thick walls results in relatively heavy and bulky inflator designs. Additionally, where only a compressed gas is used to inflate the evacuation slide, a large drop in temperature occurs as the compressed gas expands, often causing ice to form, which can block the flow of gas. Pyrotechnic gas generators have an advantage in that they are small, lightweight, and produce a high volume of gas. The high temperature gas produced by a gas generator alone, however, causes numerous problems including sagging of the evacuation slide as the inflation gas cools and, in some cases, melting or scorching of the fabric out of which the inflation slide is fabricated. Because of the disadvantages associated with pure stored gas and pure pyrotechnic inflation devices, current state of the art emergency evacuation slide systems typically comprise a hybrid inflator, which utilizes a stored compressed gas together with a pyrotechnic gas generator. The pyrotechnic gas generator augments the stored compressed gas by providing additional gas as well as heat to counteract the effects of the expansion-induced cooling of the compressed gas as it expands out of the pressure vessel. Despite these advances, convention hybrid evacuation slide inflators are still heavy and bulky. On one modem commercial aircraft, the weight of the pressure vessel alone is almost 35 pounds and weight of the gas charge over 16 pounds. Accordingly, the need still exists to further reduce the size and weight of emergency evacuation slide inflators and thereby improve the payload volume, weight, and fuel economy of the aircraft on which they are mounted.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention comprises an inflation device for an aircraft emergency evacuation slide or other inflatable device wherein the number moles of gas produced by the inflator is greater than the number of moles of gas stored. According to one embodiment of the present invention, this is accomplished by selecting the stored inflation gas to be one of a family of gases capable of undergoing a thermal decomposition. As used herein, a gas capable of undergoing a decomposition reaction refers to a gas the molecules of which may be disassociated from a single molecular species into two or more molecular species. “Thermal decomposition” is a decomposition reaction that is initiated and sustained by subjecting the gas to an elevated temperature.  
           [0004]    In an illustrative embodiment, two moles of nitrous oxide are decomposed to form two moles of diatomic nitrogen and a mole of diatomic oxygen. Because the universal gas constant is the same for all gases, the three moles of nitrogen and oxygen produced by the decomposition of two moles of nitrous oxide occupy 50% more volume than the two moles of nitrous oxide would have occupied at the same temperature and pressure. Therefore, by decomposing the stored nitrous oxide, the illustrative evacuation slide inflator is capable of inflating an aircraft evacuation slide that is 50% larger than would be possible using undecomposed nitrous oxide. Since nitrous oxide has the same molecular weight was carbon dioxide (the most commonly used aircraft evacuation slide inflation gas), all else being equal, an aircraft evacuation slide inflator utilizing decomposing nitrous oxide will result in a weight savings of at least ⅓as compared with the weight of the inflation gas of a conventional carbon dioxide hybrid inflator. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0005]    The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which:  
         [0006]    [0006]FIG. 1 is a simplified, partially crossed sectioned plan view of an aircraft evacuation slide inflator incorporating principals of the present invention;  
         [0007]    [0007]FIG. 2 is a simplified, partially crossed sectioned plan view of another alternative embodiment of an evacuation slide inflator incorporating features of the present invention.  
         [0008]    [0008]FIG. 3 is a simplified, partially crossed sectioned plan view of yet another alternative embodiment of an evacuation slide inflator incorporating features of the present invention.  
         [0009]    [0009]FIG. 4 is a simplified, partially crossed sectioned plan view of yet another alternative embodiment of an evacuation slide inflator incorporating features of the present invention.  
         [0010]    [0010]FIG. 5 is a simplified, partially crossed sectioned plan view of an alternative embodiment of an evacuation slide inflator incorporating features of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0011]    The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detail description and the drawing figures, specific illustrative examples are shown and herein described in detailed. It should be understood, however, that the drawing figures and the drawing description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make/use the invention claimed herein and for setting forth the best mode for carrying out the invention.  
         [0012]    [0012]FIG. 1 is a simplified partially sectioned plan view of an aircraft emergency evacuation slide inflator  10 . As will be described in greater detail below, the inflator  10  generates an inflation gas by decomposing a stored source gas material into at least two inflation gas species. The inflator  10  comprises a pressure vessel  12  containing a source gas mixture  14  that includes at least one gas source material that is capable of undergoing a thermal decomposition to form decomposition species used to inflate an associated aircraft evacuation slide or other inflatable device. A wide variety of gas source materials that undergo decomposition to form gaseous products are available. Such gas source materials include peroxide and peroxide derivatives such as methyl hyperoxide, and mixtures of methyl hyperoxide and methanol, hydrogen peroxide, alkyl hydroperoxides, propionyl and butyryl peroxide as well as mixtures thereof and nitrous oxide, (N 2 O). Preferably the decomposable gas source material is nontoxic and noncorrosive in both the pre and post decomposition states; is relatively stable at ambient temperatures thus permitting and facilitating storage in a compressed gas or liquid phase; and liquefies at a relatively modest pressure at ambient temperatures.  
         [0013]    In view of the manufacturability, storage and handling concerns, the preferred decomposable gas source material for use in practice of the present invention is nitrous oxide. In accordance with the chemical reactions (1) identified below, upon the decomposition of nitrous oxide, the decomposition products from one mole of nitrous oxide (N 2 O) are two moles of diatomic nitrogen (N 2 ) and one mole of diatomic oxygen (O 2 ); 
         2N 2 O=2N 2 +O 2   (1) 
         [0014]    Nitrous oxide, although classified as an oxidizer, in practice is generally nontoxic and noncorrosive and is relatively inert up to temperatures of about 200° C. Further, nitrous oxide, as compared to gases such as oxygen, nitrogen, and argon, liquefies relatively easily at ambient temperatures. Finally, nitrous oxide has the same molecular weight as carbon dioxide, which is the gas most commonly used in state of the art hybrid air bag inflators. Therefore, use of an equal amount of nitrous oxide entails no additional weight in inflation gas over conventional carbon dioxide inflators.  
         [0015]    As used in the present invention the decomposable gas source material can be stored in a gaseous, liquid or multi-phase form (i.e., partially gaseous and partially liquid mixture). The premium on size generally placed on aircraft payload volume dictates a preference for smaller size evacuation slide inflators. Since the density of the gas source material is significantly greater in a liquid, rather than gaseous state, storage of source gas materials primarily in a liquid state will typically be preferred.  
         [0016]    Pressure vessel  12  is closed by means of a reactor  16  placed in the area of the exit aperture  18  of pressure vessel  12 . Reactor  16  comprises a housing  20  having a bore  22 , which defines a gas channel though housing  20 . Bore  22  is initially obstructed by means of a propellant mixture  24  filling the gas channel defined by bore  22 . Housing  20  is preferably composed of ceramic or other material having high temperature stability and low thermal conductivity and which is resistant to attack by atomic oxygen at elevated temperatures. Pyrotechnic composition  24  may be any conventional propellant that combusts rapidly producing heat and gaseous combustion products with little or not particulates. Such energizers include cyclotrimethylene trinitramine (RDX); cyclotetramethylene tetranitramine (HMX); pentaerythritol tetranitrate (PETN), hexanitrohexaazaisowurtzitane (CL 20 ), thermite, UPCO  7021  or similar energizers.  
         [0017]    The base end  26  of housing  20  includes an opening  28  into which is inserted in a sealing relationship an initiator  30 . It should be noted that to facilitate the sealing relationship between initiator  30  and pressure vessel  12 , base end  28  may comprise a separate metal disk to which initiator  30  may be welded or crimped in order to provide a suitable hermetic seal. Initiator  30  may be of any suitable type including pyrotechnic, bridgewire, spark-discharge, exploding foil, or laser igniter, capable of producing sufficient heat input to initiate the combustion of pyrotechnic composition  24 . A plenum  42  or other suitable undercut in the wall of pressure vessel  12  provides a suitable transition between bore  22  and inlet  32  of pressure regulator  34 .  
         [0018]    Pressure regulator  34  may be of a conventional design, such as a sliding spool regulator. Regulator  34  is adapted to regulate the pressure at inlet  32  down to a lower pressure at outlet  36  such that the gas pressure at inlet  36  of aspirator  38  is within the design pressure bandwidth for maximum efficiency of aspirator  38 .  
         [0019]    Aspirator  38  comprises a venturi (not shown). As compressed gas flows through inlet  36  of aspirator  38  the venturi produces a low pressure area that causes the aspirator to ingest about four times as much gas as is supplied by the inflator alone. This ingestion of air continues until the back pressure in aspirator outlet  40  exceeds a threshold pressure, indicating the inflatable device (not shown) is nearing full inflation, at which time the aspirator check valve or flapper doors close to prevent loss of inflation gas through the aspirator. Aspirators suitable use in the present invention include that disclosed in U.S. Pat. No. 4,368,009 to Heimovics, et al. the specification of which is incorporated herein by reference to the extent necessary to supplement this disclosure.  
         [0020]    In operation, such as upon sensing the opening of an aircraft emergency evacuation door in the armed condition, an electrical signal is sent to the initiator  30 . The initiator  30  functions and initiates combustion of the pyrotechnic composition  24 . Pyrotechnic composition  24  heats housing  20  in the area of bore  22  to a temperature above the decomposition temperature for the stored nitrous oxide (about 1200° F./650° C.). Simultaneously, consumption of the initiator  30  and pyrotechnic composition  24  opens the gas channel defined by bore  22  to begin the flow of source gas mixture  14  into pressure regulator  34  and ultimately into the inflatable device. As the source gas mixture  14  flows through bore  22 , however, the elevated temperature of housing  20  in the region of bore  22  causes the thermal decomposition of the nitrous oxide in the source gas mixture. Because the thermal disassociation of nitrous oxide is also exothermic the associated release of energy maintains the temperature of housing  20  in the region of bore  22  above the threshold temperature for the thermal decomposition of the nitrous oxide. Thus, the decomposition reaction is sustained for as long as the source gas mixture is flowing through housing  20  at a sufficient rate to compensate for the heat loss through housing  20 .  
         [0021]    As noted herein before, the thermal decomposition of nitrous oxide results in a 1.5:1 increase in the gas available for inflating the inflatable devices (2 moles of nitrous oxide being decomposed into a total of 3 moles of nitrogen and oxygen). Thus, an inflator in accordance with the present invention provides high inflation capacity with a minimum amount of stored gas. Additionally, by reacting the nitrous oxide source gas mixture only as it passes out of pressure vessel  12  the possibility of overpressurizing pressure vessel  12  by disassociating the nitrous oxide in the source gas mixture while it is still confined is minimized. Thus, pressure vessel  12  can be of lighter weight construction than would be necessary if, for example, the source gas mixture were decomposed while still in pressure vessel  12  as in certain prior art automobile airbag inflators.  
         [0022]    In circumstances where the gas flow rate is sufficiently high and/or the thermal conductivity of housing  20  sufficiently low, it may be advantageous to include a diluent gas such as carbon dioxide to control the rate of heating of housing  20  and to insure that the decomposable constituent of the source gas mixture decomposes only as it is passing through housing  20  and not while still in pressure vessel  12 . Carbon dioxide is a preferred diluent because it has a high thermal capacity (66 calories/gram latent heat of vaporization) and liquefies relatively easily at ambient temperatures and thus may be stored in a small volume. A mixture in the range of from 50/50 nitrous oxide/carbon dioxide to 20/80 nitrous oxide/carbon dioxide; preferably 40/60 nitrous oxide/carbon dioxide; and most preferably about 30% nitrous oxide and 70% carbon dioxide is preferred in the present invention as ratios in the range of 30% nitrous oxide 70% carbon dioxide will not reliably sustain the nitrous oxide decomposition outside the reactor  16  because of the heat absorbed by the carbon dioxide.  
         [0023]    [0023]FIG. 2 depicts an alternative embodiment of an inflator  210  incorporating features of the present invention. Inflator  210  comprises a pressure vessel  212  containing a source gas mixture  214  which is capable of undergoing a thermal decomposition to form at least two separate gaseous species for filling an inflatable device. Pressure vessel  212  is closed by means of a reactor  216  composed of a suitable material having low thermal conductivity and high temperature strength, such as a ceramic, placed in the area of exit aperture  218 . Reactor  216  comprises a central bore  222  and a plurality of peripheral bores  224  and  226  therethrough. Peripheral bores  224  and  226  are in fluid communication with plenum  242  leading to inlet  232  of regulator/valve  234 .  
         [0024]    As with the embodiment of FIG. 1, central bore  222  is initially obstructed by pyrotechnic composition  228  filling the gas channel defined by central bore  222 . Base end  230  of reactor  216  includes an initiator  232  for initiating the combustion of pyrotechnic composition  228  in central bore  222  of reactor  216 .  
         [0025]    Because of the wide range of ambient temperatures over which aircraft emergency evacuation slides must operate (typically −65° F. to +165° F.) an inflator capable of producing enough disassociated nitrous oxide to fully inflate an evacuation slide at −65° F. will produce substantially more than enough gas to fully inflate the same aircraft slide at +165° F. In fact, the substantial excess gas may lead to over-pressurization of the evacuation slide. To prevent over-pressurization caused by the excess inflation gas, conventional designs must incorporate multiple pressure relief valves to vent the excess pressure, thereby adding extra weight to the evacuation slide system. Accordingly, to avoid the problems associated with potential high temperature over-pressurization of the evacuation slide, the embodiment of FIG. 2 is capable of delaying the onset of the gas disassociation, thereby reducing the total number of moles of gas produced for filling the inflatable device.  
         [0026]    In operation, such as upon the sensing the opening of an aircraft emergency exit, an electrical signal is sent to regulator valve  234  which immediately begins the flow of source gas mixture  214  through outlet  236  to the aspirator (not shown) for ultimate inflation of the inflation device. A pressure transducer  246  senses when the pressure level inside pressure vessel  212  has dropped below a predetermined threshold. Upon sensing the reduced pressure in pressure vessel  212 , pressure transducer  246  enables an electrical signal to reach initiator  232 . Upon functioning of initiator  232 , pyrotechnic composition  224  combusts and heats reactor  216  to a temperature above the decomposition temperature of the nitrous oxide constituent of the source gas mixture. Since the portion of the source gas mixture that has already passed through reactor  216  is undecomposed, the total gas output of inflator  210  is a mixture of nitrous oxide, nitrogen, oxygen and the carbon dioxide diluent rather than pure nitrogen, oxygen and diluent carbon dioxide as in the embodiment of FIG. 1. The total number of moles of gas, and therefore the total gas pressure produced by inflator  210  is reduced in proportion to the quantity of nitrous oxide that is unreacted. Thus, the embodiment of FIG. 2 includes the additional capability of controlling the total inflation pressure by regulating the total number of moles of gas used to inflate the inflatable device.  
         [0027]    [0027]FIG. 3 depicts an additional alternative embodiment of inflator  310  incorporating features of the present invention. Inflator  310  comprises a pressure vessel  312  containing a source gas mixture  314  comprising at least one source gas material capable of undergoing thermal decomposition. Reactor  316 , however, is located on the low pressure side of the regulator/valve  334 . As with the embodiments of FIGS. 1 and 2, reactor  316  comprises a housing  320  composed of a suitable high temperature, low thermal conductivity material such as ceramic, which includes a central bore  322  and one or more peripheral bores (not shown) therethrough. A pyrotechnic composition  324  and an initiator  326  initially obstruct central bore  322 .  
         [0028]    In operation, such as upon sensing the opening of an emergency exit door, an electrical signal is sent to regulator valve  334  which begins the flow of source gas mixture  314 . Simultaneously or after an appropriate delay, initiator  326  receives a signal. Upon functioning, initiator  326  ignites pyrotechnic composition  324 , which heats reactor  316  to a temperature above the decomposition temperature of the nitrous oxide constituent of source gas material  314 . Placing the reactor  316  on the low-pressure side of regulator/valve  334  facilitates control of the disassociation reaction. This is because the gas flow rate, and therefore the disassociation rate and heat input caused by the exothermic nature of the disassociation are occurring at relative steady state flow rates, as regulated by regulator valve  334 .  
         [0029]    [0029]FIG. 4 depicts another alternative embodiment of an inflator  410  incorporating features of the present invention. Inflator  410  comprises a pressure vessel  412  having contained therein a source gas material  414  including a gas species capable of undergoing thermal decomposition to form two or more gaseous species for inflation of an inflatable device. A reactor  416  comprises a housing  418  made of a suitable material having a bore  420  therethrough. A series of inductive windings made of a suitable high conductivity material such as copper are wound around housing  418 .  
         [0030]    In operation, such as upon the sensing of an emergency exit door being opened, an electrical signal is sent to regulator/valve  434  which opens to begin the flow of source gas material to being inflation of the inflatable device. Simultaneously, or after a suitable delay, an alternating high amperage current is sent to windings  422  which cause inductive heating of housing  418  to a temperature above the disassociation temperature of the nitrous oxide constituent of source gas material  414 . Depending on the ratio of carbon dioxide diluent to nitrous oxide, once initiated, the decomposition reaction may be self-sustaining due to the exothermic nature of the decomposition of nitrous oxide. Alternatively, the ratio of nitrous oxide to diluent may be chosen such that additional energy in the form of inductive heating from windings  422  are necessary to sustain the decomposition reaction. Thus, the embodiment of FIG. 4 is capable of starting and stopping the disassociation reaction, thus providing additional control over not only the total number of moles of gas produced but the inflation profile as well.  
         [0031]    [0031]FIG. 5 depicts another alternative embodiment of an inflator  510  incorporating features of the present invention. Inflator  510  comprises a pressure vessel  512  having contained therein a source gas material  514  including a gas species capable of undergoing thermal decomposition to form two or more gaseous species for inflation of an inflatable device. A reactor  516  comprises a housing  518  made of a suitable material having a bore  520  therethrough. A series of resistance windings made of a suitable high resistance, high temperature material such as FeCrAlY are wound around housing  518 .  
         [0032]    In operation, such as upon the sensing of an emergency exit door being opened, an electrical signal is sent to regulator/valve  534  which opens to begin the flow of source gas material to being inflation of the inflatable device. Simultaneously, or after a suitable delay, a current is sent to windings  522  which heat housing  518  to a temperature above the disassociation temperature of the nitrous oxide constituent of source gas material  514 . Depending on the ratio of carbon dioxide diluent to nitrous oxide, once initiated, the decomposition reaction may be self-sustaining due to the exothermic nature of the decomposition of nitrous oxide. Alternatively, the ratio of nitrous oxide to diluent may be chosen such that additional energy in the form of from windings  522  are necessary to sustain the decomposition reaction thus enabling the disassociation reaction to be started and stopped.  
         [0033]    Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention shall be limited only to the extent required by the appended claims and the rules and principals of applicable law.