Abstract:
A pressure activated latch includes a latch housing, a fluid inlet, a fluid outlet, an internal biasing member and a sliding latch pin that is configured to engage a latch tab that is substantially adjacent to the latch housing. The latch pin is slidable between a first position in which the latch pin prevents fluid communication between the fluid inlet and the fluid outlet and engages the latch tab and a second position in which the latch pin is disengaged from the latch tab and fluid communication is permitted between the fluid inlet and the fluid outlet. The internal biasing member is configured to apply a force upon the latch pin to bias it into the first position.

Description:
FIELD OF THE INVENTION 
   The present invention is directed to a pressure activated latch, and more particularly to a pressure activated latch for an emergency life raft on an aircraft. 
   BACKGROUND OF THE INVENTION 
   Emergency flotation devices are required on many aircraft to provide emergency assistance to passengers in the event the aircraft experiences an emergency situation and is forced down in water. Emergency flotation devices generally include systems designed to float the aircraft, systems for emergency life rafts and life vests for individual occupants. 
   One example of an airplane flotation system is shown in U.S. Pat. No. 1,776,865. The system includes inflatable bags located in a forward portion of an airplane and is manually operated by a pilot. The bags are stored in a non-inflated state within closed compartments. The system utilizes pressure cylinders to sequentially unlock doors of the compartments and inflate the inflatable bags. During operation the pilot activates the pressure cylinder by releasing pressurized gas. After inflation, the pilot is required to pull a cord that places the pressure cylinder into an intermediate position to block further fluid flow between the pressurized fluid. A first disadvantage of the system is that it does not provide for a valve that remains closed until a predetermined pressure is applied. As a result, any increase in pressure may cause the doors to unlock and the inflatable bags to inflate even when undesired. Another disadvantage is that it requires manual operation by the pilot even after the initial activation of the system. 
   U.S. Pat. No. 2,264,321 to Manson, describes a life-saving device that includes an inflatable life raft that is arranged in a compartment on the side of a vehicle such as an airplane. The compartment is closed by a pair of hinged doors that are spring-loaded to urge them into an opened position. The doors are held closed by pins that extend through meshing lugs that are included on the doors. A pull cord is secured to the pins and a valve on an inflating-gas container so that pulling on the cord sequentially removes the pins from the lugs and operates the valve to permit the flow of gas from the container to the raft. The cord fully disengages from the gas container after the valve is operated. A first disadvantage of the system is that the pins may be disengaged without a complete activation of the system. In addition, the pull cord may become bound which may result in the pin disengaging without activation of the gas container. A further disadvantage is that there is that the gas container valve does not include a mechanism to close the gas path between the gas container and the raft after the raft is inflated. 
   In view of the above, there exists a need for a pressure activated latch for an emergency flotation system that provides sequential unlatching and inflation, that will unlatch when subjected to a pressure above a predetermined threshold pressure and that will automatically prevent fluid communication between the pressurized fluid source and the inflatable after inflation. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, it is an object of the present invention to provide a pressure activated latch for an emergency flotation system that provides sequential unlatching of an emergency door and inflation of a flotation device. 
   It is another object of the invention to provide a pressure activated latch for use in an emergency flotation system that is internally biased so that it remains closed until a predetermined pressure is applied. 
   It is another object of the invention to provide a pressure activated latch for an emergency flotation system that returns to a closed position after a flotation device has been adequately inflated. 
   In the preferred embodiment of the invention, a pressure activated latch includes a latch housing, a fluid inlet, a fluid outlet, a latch pin and an internal biasing element. The latch pin includes an interface portion that extends out of the latch housing and is designed to engage a latch tab included on an emergency flotation system door. The latch pin also includes a sealing portion that creates a slidable fluid seal within the latch housing. The internal biasing element creates a biasing force that is chosen so the latch pin is biased to engage a latching tab while still providing a seal between the fluid inlet and fluid outlet. 
   The latch is configured so that when a pressurized fluid is injected into the fluid inlet it causes the latch pin to slide within housing thereby sequentially unlocking the emergency door and inflating the inflatable device. After the inflatable device is inflated, the pressure at the inlet and out let equalize and the internal biasing element returns the pin to the original biased position where the sealing portion is again located between the fluid inlet and the fluid outlet and prevents fluid communication therebetween. 
   These and other features and advantages of the present invention will be appreciated from review of the following detailed description of the invention, along with the accompanying figures in which like reference numerals refer to like parts throughout. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a side panel of an aircraft having a baggage compartment door in a closed configuration; 
       FIG. 2  is a perspective view of a side panel of an aircraft having a baggage compartment door in an open configuration and including an emergency life raft kit; 
       FIG. 3  is an enlarged detail view of a portion A, shown in  FIG. 2 , of the emergency life raft kit including a pressure activated latch in accordance with the principles of the present invention; 
       FIG. 4  is an exploded view of the pressure activated latch of  FIG. 3 ; 
       FIG. 5  is a side view of the pressure activated latch of  FIG. 3  in a latched configuration; 
       FIG. 6  is a cross-sectional view of the pressure activated latch taken along line B-B of  FIG. 5 ; 
       FIG. 7  is a side view of the pressure activated latch in an unlatched configuration; 
       FIG. 8  is a cross-sectional view of the pressure activated latch taken along line C-C of  FIG. 7 ; 
       FIG. 9  is a schematic of an embodiment of an emergency flotation system incorporating the pressure activated latch in accordance with the present invention; 
       FIG. 10  is a schematic of another embodiment of an emergency flotation system incorporating the pressure activated latch in accordance with the present invention; and 
       FIG. 11  is a cross-sectional view of another embodiment of the pressure activated latch in a latched configuration. 
   

   DETAILED DESCRIPTION 
   In the following paragraphs, the present invention will be described in detail by way of example with reference to the attached drawings. Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention. As used herein, the “present invention” refers to any one of the embodiments of the invention described herein, and any equivalents. Furthermore, reference to various feature(s) of the “present invention” throughout this document does not mean that all claimed embodiments or methods must include the referenced feature(s). 
   Referring to  FIGS. 1 , a panel  10  on the fuselage of an aircraft, such as a helicopter, includes a baggage compartment door  12  that provides access to a baggage compartment. An emergency life raft kit  14  is incorporated into baggage compartment door  12 . Life raft kit  14  (not shown in  FIG. 1 ) is located in door  12  because it is easily accessible for installation and maintenance by releasing a baggage compartment door latch  16  and opening door  12 . However, it should be appreciated that emergency life raft kit  14  may be located anywhere on the aircraft including a dedicated life raft storage compartment. 
   Life raft kit  14  generally includes a storage compartment  18 , a life raft (not shown), a pressurized fluid source (not shown) and a pressure activated latching assembly  19  that includes one or more latches  28 . Storage compartment  18  includes an emergency door  20  that may be opened to expose the life raft contained therein. Compartment  18  is fixed to an inner surface  22  of compartment door  12  and extends through compartment door  12  so that emergency door  20  is exposed at the outer surface of panel  10 . Preferably, compartment  18  is mounted to compartment door  12  so that an outer surface  24  of emergency door  20  is flush with, or recessed from, an outer surface  26  of compartment door  12 . Latching assembly  19  may also be fixed to inner surface  22  of compartment door  12 . It should be appreciated that compartment  18  and latching assembly  19  may be fixed to compartment door  12  by any technique known in the art. For example, mounting flanges  21  may be provided on each of the components and mechanical fasteners may be used to fix mounting flanges  21  to compartment door  12 . 
   As will be described in greater detail below, advantages of latching assembly  19  over known latching assemblies for emergency flotation devices include that latches  28  passively control the sequential unlatching of emergency door  20  and inflation of the life raft in addition to being internally biased to a position where there is no fluid communication between the fluid source and the life raft. In addition, those advantages are available in a small, self-contained, easily serviceable latch. Referring to  FIGS. 2 and 3 , latching assembly  19  generally includes two latches  28  and a plurality of pressure lines  30 ,  31 ,  32  that fluidly couple latches  28  and the life raft to the pressurized fluid source. In particular pressure line  30  extends between the pressurized fluid source and a first latch  28 . In the present embodiment, the pressurized fluid source is not located on compartment door  12  so at least a portion of fluid line  30  is configured to extend across the interface of the storage compartment and compartment door  12 . The end of pressure line  30 , opposite to the pressurized fluid source, terminates at an inlet  34  of first latch  28 . Pressure line  31  is coupled to an outlet  36  of first latch  28  and extends to an inlet  34  of second latch  28 . Finally, pressure line  32  extends from outlet  36  of second latch  28  to the life raft that is housed in compartment  18  in a deflated state. 
   Emergency door  20  includes a latch tab  38  that corresponds to each latch  28  and a latch pin  40  included in each latch  28  interfaces with a latch tab aperture  42  in each latch tab  38  to selectively lock emergency door  20  in a closed position. Latch pin  40  is configured to be biased toward a latched configuration (i.e., toward latch tab  38  into aperture  42 ) by an internal biasing member. During operation, latch pin  40  may be forced into an unlatched configuration (i.e., away from latch tab  38  and out of aperture  42 ) by a fluid pressure increase within the respective latch  28  caused by a release of pressurized fluid from the pressurized fluid source into pressure lines  30  and  31 . 
   Referring to  FIGS. 4-6 , the structure of each latch  28  will be described. Latch  28  includes latch pin  40  that extends longitudinally through a latch housing  46 . Latch pin  40  is slidably received within a bore  44  of housing  46  so that latch pin  40  is movable between an extended, latched configuration (shown in  FIGS. 5 and 6 ) and a retracted, unlatched configuration (shown in  FIGS. 7 and 8 ), as will be discussed in greater detail below. 
   Bore  44  includes a proximal portion  48  that has a first diameter D 1  that approximates the diameter of a sealing surface  50  of an enlarged sealing portion  51  of latch pin  40 . The interface between sealing surface  50  and the internal surface of proximal portion  48  of bore  44  provides a fluid seal that prevents pressurized fluid from flowing past enlarged portion  51  during operation. A distal portion  52  of bore  44  has a second diameter D 2  that approximates the diameter of a sealing surface  53  of an interface portion  54  of latch pin  40 . Interface portion  54  extends through distal portion  52  of bore  44  out of latch housing  46 . The interface between sealing surface  53  and distal portion  52  provides a sliding seal so that pressurized fluid injected into latch housing  46  is prevented from escaping from latch housing  46 . It should be appreciated that one or more sealing members may also be provided at the sliding interfaces. For example, one or more O-rings  100  or compressible collars may be provided for the seals at sealing surfaces  50  and  53 , as shown in  FIG. 11 . 
   A biasing force is exerted on latch pin  40  by an internal biasing element, such as biasing spring  56 . Spring  56  is located proximal to latch pin  40  within proximal portion  48  of bore  44 . A distal end  58  of spring  56  interfaces with a spring interface surface  60  that is located on enlarged portion  51  of latch pin  40 . A cover  62  is coupled to the proximal end of latch housing  46  with mechanical fasteners  63  and optional washers  65  and prevents spring  56  from translating out of bore  44  when latch pin  40  is moved proximally. Cover  62  also provides a spring interface surface  64  that interfaces with a proximal end  66  of spring  56  so that spring  56  may be compressed between spring interface surface  64  of cover  62  and spring interface surface  60  of latch pin  40 , to place a biasing force upon latch pin  40 . It should be appreciated that the internal biasing member may be any device that is located internal to latch  28  that is capable of placing a biasing force on latch pin  40 . For example, the internal biasing member may be any type of spring such as a helical spring or, as shown in  FIG. 11 , belville spring washers  102 . Alternatively, the internal biasing member may be a magnet oriented to bias the latch pin  40  into the latched configuration. 
   The translation of latch pin  40  within bore  44  is limited in both the proximal and distal directions by travel limit stops. In the present embodiment, the travel of latch pin  40  is limited by travel limit stops that are included on latch pin  40 . In particular, travel of latch pin  40  in the proximal direction is limited by a first travel limit stop (first step portion  70 ) and travel in the distal direction is limited by a second travel limit stop (second step portion  71 ). First step portion  70  is located proximal of enlarged portion  51  and forms a proximal end  72  of latch pin  40 . Step portion  70  has an outer diameter D 3  that is smaller than diameter D 1  of enlarged portion  51  of latch pin  40  and the difference in diameters D 1  and D 3  creates spring interface surface  60  described above. The length of step portion  70  is chosen so that proximal end  72  contacts cover  62  when latch pin  40  is translated to a desired proximal-most position corresponding to the unlatched configuration. It should be appreciated, however, that spring  56  may be chosen so that the translation of latch pin  40  is limited by compression of spring  56  rather than contact between proximal end  72  of latch pin  40  and cover  62 . 
   Second step portion  71  of latch pin  40  is located between enlarged portion  51  and interface portion  54  and includes a diameter D 4  that is smaller than diameter D 1  but larger than diameter D 2 . The difference between diameters D 2  and D 4  creates a shoulder  74  that is too large to translate into distal portion  52  of bore  44 . As a result, the travel of latch pin  40  is limited by contact between shoulder  74  and a shoulder  75  that is located at the interface of proximal portion  48  and distal portion  52  of bore  44 . 
   Latch inlet  34  and latch outlet  36  are provided through latch housing  46  and into bore  44 . Inlet  34  is located near a distal end of bore  44  so that pressurized fluid may be injected into bore  44  to translate latch pin  40  proximally. As mentioned above, diameter D 3  of step portion  71  differs from diameter D 1  and creates an empty space  76  around step portion  71  when latch pin  40  is in a distal-most position. The length and diameter of step portion  71  and the location of inlet  34  are chosen so that inlet  78  is in fluid communication with empty space  76  when latch pin  40  is located in the distal-most position. Outlet  36  is located proximal of inlet  34  so that when latch pin  40  is located in the distal-most position enlarged portion  51  is located between inlet  34  and outlet  36  and prevents fluid communication between inlet  34  and outlet  36 . The location of outlet  36  is also chosen so that when latch pin  40  is in a proximal-most position, enlarged portion  51  is located further proximal from outlet  36 , thereby allowing fluid communication between inlet  34  and outlet  36  via bore  44 . 
   Fluid connection ports  82  may be provided at each inlet  34  and outlet  36  so that fluid lines  30 , 31 , 32  may be conveniently coupled to respective latch assemblies  28 . Each port  82  includes a threaded surface  83  that is configured to be received by a threaded surface in a respective inlet  34  or outlet  36 . Preferably, an O-ring  84  is provided with each port  82  to seal port  82  to the respective inlet  34  or outlet  36 . Ports  82  may be any fluid connection port known in the art that provide a sealable interface with a fluid line. For example, fluid connection ports  82  may be compression fittings. 
   During operation, latch  28  transforms from a latched configuration, shown in  FIGS. 5 and 6 , to an unlatched configuration, shown in  FIGS. 7 and 8 . As described above, that transformation allows emergency door  20  to open so that an inflatable flotation device, such as an emergency life raft, may be ejected from compartment  18  when it is inflated. During normal operation of an aircraft, there is no pressurized fluid injected into pressure lines  30 ,  31 ,  32  or bore  44  and latch  28  is maintained in the latched configuration by spring  56  and the distal travel of latch pin  40  is limited by contact between shoulder  74  of latch pin  40  and shoulder  75  of bore  44 . Additionally, interface portion  54  of latch pin  40  extends out of latch housing  46  and is received by latch tab aperture  42  of an adjacent latch tab  38 . Fluid communication between inlet  34  and outlet  36  also is prevented by the sealing interface of enlarged portion  51  of latch pin  40  with bore  44  between inlet  34  and outlet  36 . 
   During an emergency event, pressurized fluid is released from the pressurized fluid source and enters latch  28  through inlet  34 . The pressurized fluid passes through inlet  34  and enters space  76  and increases the fluid pressure within space  76 . The increased pressure within space  76  applies a force to a face  78  of latch pin  40  that is directed proximally. The pressure of the fluid and the spring constant of spring  56  are chosen so that the force applied to face  78  when the pressurized fluid is released is sufficient to overcome the spring force created by  56  and to move latch pin  40  proximally, thereby placing latch  28  in the unlatched configuration. 
   When latch  28  is in the unlatched configuration, as shown in  FIGS. 7 and 8 , latch pin  40  is located in a proximal position that results in interface portion  54  disengaging from aperture  42  of latch tab  38 , thereby releasing emergency door  20 . In addition, as latch pin  40  moves proximally, enlarged portion  51  is moved proximal of outlet  36 , thereby placing inlet  34  in fluid communication with outlet  36 . The pressurized fluid that is injected into bore  44  is then able to flow past latch pin  40 , through outlet  36  and further to an additional series connected latch  28  or an inflatable device. Latch pin  40  may be moved proximally until it reaches a proximal-most position in which the travel of latch pin  40  is limited by contact between proximal end  72  of latch pin  40  and cover  62 . 
   It should be appreciated that the components of latch  28  and latch tab  38  are dimensioned so that interface portion  54  disengages aperture  42  of latch tab  38  completely before enlarged portion  51  has moved sufficiently to allow communication between inlet  34  and outlet  36 . As a result, latch  28  inherently controls the sequence of the release of emergency door  20  and the inflation of an inflatable device that is downstream. 
   In addition, the biasing force applied by spring  56  assures that latch  28  automatically ends fluid communication between inlet  34  and outlet  36  when the pressure within bore  44  has dropped to a predetermined value after the inflatable device is inflated. As a result, latch  28  automatically ends fluid communication between the pressurized fluid source and the inflatable device after sufficient inflation. 
   Referring to  FIGS. 9 and 10 , schematics of alternative embodiments of an emergency flotation system  90  will be described. As generally described above, emergency flotation system  90  includes a pressurized fluid source, such as an inflation reservoir  92  that stores a pressurized gas, such as air or nitrogen, for selectively inflating an inflatable device  94 , such as a life raft. A pressure line  30  fluidly links inflation reservoir  92  with latching assembly  19  through a valve  96 . Valve  96  is normally closed so that fluid communication between inflation reservoir  92  and latching assembly  19  is prevented. In an emergency, the system may be activated by an electronic switch in the cockpit or a manual lever  98 . Activation of switch or lever  98  allows pressurized fluid to be injected into latching assembly  19 , which activates one or more latches  28 , and into inflatable device  94 . It should be appreciated that latches  28  may be connected either in series (shown in  FIG. 9 ) or parallel (shown in  FIG. 10 ) with inflation reservoir  92  as desired. 
   A series connection between latches  28  provides sequential unlatching of the plurality of latches which is followed by inflation of inflatable device  94 . A series connection may be used to reduce the length of pressure line required for the system. A parallel connection between latches  28  and inflation reservoir  92  allows the plurality of latches to be unlatched simultaneously with the inflation of inflatable device  94  thereafter. In a parallel system, an inlet of each latch  28  is directly coupled to inflation reservoir  92  through pressure line  30  and an outlet of each latch is directly coupled to inflatable device  94 . In the parallel system a pressure line  31  between an outlet of the first latch  28  and an inlet of the second latch  28  would not be required. 
   One skilled in the art will appreciate that the present invention can be practiced by other than the various embodiments and preferred embodiments, which are presented in this description for purposes of illustration and not of limitation, and the present invention is limited only by the claims that follow. It is noted that equivalents for the particular embodiments discussed in this description may practice the invention as well.