Abstract:
An inflation valve for use with an inflatable emergency evacuation slide includes a thermally actuated gas relief valve having an exhaust port the effective size of which increases with increasing temperature. The exhaust port is metered by a valve member. The valve member position is controlled by a thermal actuator that lengthens with increasing temperature. At high ambient temperatures, the valve member moves to uncover the exhaust port thereby increasing the effective size of the port so that a large percentage of the inflation gas is vented. At low ambient temperatures the valve member moves to cover the exhaust port, thereby decreasing effective size of the exhaust port so that little or no inflation gas is vented.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to emergency evacuation equipment for aircraft, in particular to an inflation device for inflating an inflatable aircraft evacuation slide or other inflatable device. 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 passengers from the aircraft because of the potential for 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 that is stored in a folded, uninflated 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. Pyrotechnic gas generators have an advantage in that they are small, lightweight, and produce a high volume of gas, however, the high temperature gas produced by a gas generator alone can cause 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. 
   Use of stored compressed gas by itself, although simple, implicates a weight penalty that must be paid for carrying a pressure vessel having sufficient capacity (in terms of volume and pressure) to inflate the evacuation slide over the wide operational temperature range specified for such slides. Additionally, where only a compressed gas is used to inflate the evacuation slide, a large drop in temperature occurs as the gases expand, often causing ice to form, which can block the flow of gas. Accordingly, 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 effects of the expansion-induced cooling of the compressed gas as it expands out of the pressure vessel. 
   To further augment the volume of gas delivered to the evacuation slide, many evacuation systems utilize aspirators such as that disclosed in U.S. Pat. No. 4,368,009 to Heimovics, et al. As the compressed gas flows through the aspirator, a venturi draws additional air into the aspirator to pump about two to three times as much gas into the evacuation slide as is supplied by the gas source alone. 
   Despite these advances, there still exists problems due to the wide ambient temperature range over which these inflation systems are required to operate, typically from −65° F. to +160° F. The amount of gas available must be enough to pressurize the evacuation slide at the coldest temperature. Because of the relationship between pressure and temperature within a fixed volume, however, as the ambient temperature rises above the minimum, the pressure within the pressure vessel rises proportionately. Accordingly, at higher temperatures, the inflation system produces substantially more gas than is necessary to inflate the evacuation slide. To prevent overpressurization and possible rupturing of the inflatable evacuation slide, provisions must be made to vent the excess inflation gas. 
   A conventional method of venting the excess inflation gas is to provide several pressure relief valves in the inflatable slide itself. Pressure relief valves, however, add significant weight to the inflatable evacuation slide and add substantial volume to the inflatable slide in its uninflated, stored condition. According to U.S. Pat. No. 6,240,951 to Yori and assigned to the assignee of the present invention, excess inflation gas may be vented by means of a regulator valve that includes an active waste gate, which vents excess gas as the pressure in the outlet port of the regulator valve rises. Although the valve of Yori accomplishes the function of venting excess inflation gas it does so at the cost of substantial complexity and cost. 
   Accordingly, what is needed is a simple and inexpensive control valve for an aircraft emergency evacuation slide that reliably vents excess inflation gas thereby eliminating or reducing the number of pressure relief valves required in the slide itself. 
   SUMMARY OF THE INVENTION 
   The present invention comprises a control valve that includes a thermally actuated gas relief valve having an exhaust port the effective size of which increases with increasing temperature. According to an embodiment of the invention, the control valve comprises an inlet port in fluid communication with the pressure vessel containing the stored inflation gas, a primary valve member closing the inlet port, a primary outlet port in fluid communication with the inflatable evacuation slide and a chamber leading from the inlet port to the primary outlet port. The thermally actuated gas relief valve is in fluid communication with the chamber leading from the primary valve member to the primary outlet port. 
   In operation, in the event of an aircraft emergency exit door being opened in the “armed” condition, the primary valve member is opened allowing inflation gas to flow into the chamber. Depending on the ambient temperature conditions, a portion of the gas entering the chamber is vented through the thermally actuated gas relief valve. At high ambient temperatures, the effective size of the exhaust port of the thermally actuated gas relief valve is large and a large percentage of the inflation gas is vented. At low ambient temperatures the effective size of the exhaust port of the thermally actuated gas relief valve is small or closed and, therefore, little or no inflation gas is vented through the thermally actuated gas relief valve. Because ambient temperature is an effective proxy for gas pressure within a closed container, the thermally actuated gas relief valve exhausts excess pressure when there is excess inflation gas in the system without exhausting inflation gas at colder temperatures which would result in an under-inflation condition. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     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: 
       FIG. 1  is an exploded perspective view showing an inflation system incorporating features of the present invention; 
       FIG. 2  is a cross-sectional view of a control valve for use in the evacuation slide system of  FIG. 1 ; and 
       FIG. 3  is a cross-sectional view of the thermally actuated valve portion of the control valve of  FIG. 2 ; and 
       FIG. 4 . is an exploded view of the thermally actuated valve of  FIG. 3   
   

   DETAILED DESCRIPTION 
   The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed 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 and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention. 
   With reference to  FIG. 1 , an inflatable aircraft evacuation slide system  10  incorporating features of the present invention comprises a pressure vessel  12  containing pressurized inflation gas, a control valve  14  and an inflatable evacuation slide  16  stored in an uninflated condition within in a packboard compartment  18 . Packboard compartment  18  is secured within a recess  20  in the outer hull of aircraft  22  and covered by a cover panel  24 . Pressure vessel  12  further includes a pyrotechnic gas generator (not shown) that heats and augments the stored inflation gas within pressure vessel  12 . In normal operation, the opening of the aircraft emergency evacuation exit door in the armed condition causes a signal to be sent to control valve  14  causing control valve  14  to open allowing inflation gas to flow from pressure vessel  12  into inflation line  26  to operate the locks allowing cover panel  24  to fall away and to inflate inflatable evacuation slide  16 . Simultaneously, the gas generator is initiated to augment and heat the stored inflation gas flowing out of pressure vessel  12 . As noted hereinbefore, when evacuation slide system  10  is initiated at an elevated temperature, substantial excess inflation gas is produced due to the combined thermal effects of the ambient temperature and the pyrotechnic gas generator. Accordingly, in addition to functioning as the primary valve between the source of inflation gas and the inflatable evacuation slide, control valve  14  further acts to vent the appropriate portion of the excess inflation gas as more fully described hereinafter. 
   With reference to  FIG. 2 , control valve  14  comprises a valve body  30  attached to the outlet  32  of pressure vessel  12 . Valve body  30  includes a first chamber  34  that is in fluid communication with vessel  12  via an inlet filter  36 . First chamber  34  is sealed from a second chamber  38  by means of a primary valve  40  composed of a ball member  42  that is seated against a valve seat  44 . First chamber  34  has an overpressure exhaust vent that is sealed by means of an overpressure burst disk  46 . Overpressure burst disk  46  ruptures in the event pressure in first chamber  34  exceeds a predetermined safe pressure and vents the overpressure to the atmosphere through a neutral thrust diffuser  48 . Second chamber  38  is separated from a third chamber  50  by means of a secondary valve member which in the illustrative embodiment comprises a burst disk  52 . 
   With additional reference to  FIGS. 3 and 4 , control valve  14  further comprises a thermally actuated gas relief valve assembly  60  that is attached to an outlet fitting  56 . Outlet fitting  56 , in turn, is attached to the outlet port  54  of vale body  30 . Thermally actuated gas relief valve  60  comprises a housing  62 , a valve member  64  and a thermal actuator  66 . Housing  62  has an inlet port  68  in fluid communication with chamber  50  and an exhaust port  70  that depending on the position of valve member  64 , is fully obstructed, partially obstructed, or unobstructed by valve member  64 . A burp seal  72 , typically a conventional O-ring, prevents dirt and moisture from entering exhaust port  70  while providing little or no resistance to gas flowing out through exhaust port  70 . Thermal actuator  66  is positioned within a sleeve  74 , which is held within a cylinder housing  76 . Cylinder housing  76 , in turn, is threaded into housing  62  with an O-ring seal  78 . A spring  80 , biases valve member  64  toward the fully closed position. The spring bias is resisted by thermal actuator  66  which presses on a piston  82  that rides in the bore of sleeve  74 . The precise location of valve member  64  is adjusted during assembly by insertion of an appropriate number of shims  84 , which are sandwiched between the end of thermal actuator  66  and a cap  86  that is threaded onto cylinder housing  76 . Cap  86  is sealed with a conventional O-ring seal  78 . 
   Thermal actuator  66  is formed of a material having a high thermal coefficient of expansion, preferably from 0.0001-0.001 inch/inch degree Fahrenheit, more preferably from 0.0002-0.0004 inch/inch degree Fahrenheit and most preferably about 0.0003 inch/inch degree Fahrenheit. In the illustrative embodiment, the thermal actuator  66  is a solid cylinder of silicone rubber 150GS124 available from Smithers Scientific Services, Inc. of Akron, Ohio. Silicone rubber 150GS124 has a thermal coefficient of expansion of 0.00028 inch/inch degree Fahrenheit. In the illustrative embodiment, the thermal actuator is 2.5 inches long and, therefore, over a temperature range of −65° F. to +160° F. the thermal actuator is capable of moving the valve member 0.160 inches from a fully closed position to a fully opened position. 
   In normal operation, when the aircraft emergency evacuation exit is opened in the armed condition an electro-explosive device (not shown) opens primary valve  40  by rotating ball member  42  off its seat  44 , allowing pressure to flow from first chamber  34  into second chamber  38 . Rising pressure in second chamber  38  causes burst disk  52  to rupture allowing inflation gas to flow from second chamber  38  into third chamber  50 . The majority of the inflation gas enters inflation line  26  to immediately operate the locks to release cover panel  24  and begin inflation of inflatable evacuation slide  16 , however, depending on the position of valve member  64  a portion of the inflation gas is vented through exhaust port. In high ambient temperature conditions (i.e., +160° F.) thermal actuator  66  has expanded to its maximum length of 2.55 inches which leaves exhaust port  70  of thermally actuated gas relief valve assembly  60  in its fully unobstructed condition. This allows the maximum portion of inflation gases entering chamber  50  to be vented. Because at high ambient temperature conditions, substantially more than enough inflation gas is available to fill the emergency evacuation slide, maximum venting conditions enable the slide to be fully inflated without rupturing. Conversely, in cold temperature conditions (i.e., −65° F.) thermal actuator  66  has decreased in length by 0.160 inches and, therefore, no inflation gas is exhausted through exhaust port  70 . Accordingly, 100% of the inflation gas generated at −65° F. is directed into the inflatable emergency evacuation slide to ensure the slide is fully inflated at the cold temperature condition. Since thermal actuator  66  is essentially an analog device that expands linearly with respect to temperature, at any given ambient temperature between −65° F. and +160° F. thermal actuator  66  will extend to a length that is proportional to the temperature difference between −65° F. and +160° F. In doing so, a linearly proportional volume of gas is exhausted through exhaust port  70  resulting in the ideal volume of gas being directed into the emergency evacuation slide for the given ambient conditions. 
   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. For example, although in the illustrative embodiment control valve  14  comprises valve body  30 , fitting  56  and housing  62 , a unitary valve body incorporating the primary valve and gas relief valve functions is considered within the scope of the present invention. Similarly, although the evacuation slide system  10  shown in the illustrative embodiment is an over-wing slide, the inflation system of the present invention is equally applicable to door exit slides as well as other applications in which the volume of gas needs to be varied with temperature such as rafts, pontoons and the like. Accordingly, it is intended that the invention should be limited only to extent required by the appended claims and the rules and principals of applicable law.