Abstract:
Disclosed is a latch assembly that includes an in-line fuse, which prevents damage to the latch assembly and its component parts in the event that a force in excess of a predetermined force is exerted on the latch handle. The latch assembly includes a latch housing and a latch, which is mounted in the latch housing. The latch includes a latch handle having a trigger assembly adapted to retain and release the handle from a locked position. The latch handle in turn causes an arm assembly to cause the movement of a push/pull type cable assembly. The in-line fuse is pivotally mounted to the arm assembly, and positioned in-line with the push/pull cable. The in-line fuse pin includes a sacrificial section that is designed to change in the event that excessive forces are applied to the latch handle. Thus, when a latch assembly operator exerts excessive force in an attempt to move the latch into the locked position, and corrosion or an obstruction are present to prevent the locking mechanism from locking the panel, the in-line fuse pin will fail, thereby preventing damage to the latch mechanism and cable assembly. Once the in-line fuse pin fails, the latch loses resistance, alerting the operator that a problem with the latch mechanism needs to be corrected.

Description:
[0001]     This application claims the benefit of U.S. Provisional Application No. 60/490,978, filed Jul. 29, 2003. 
     
    
     BACKGROUND  
       [0002]     This disclosure relates to a latch assembly including an in-line fuse pin that is designed to be a sacrificial component which functions to prevent damage to the latch mechanism, in the event that an excessive force is exerted on a component of the latch assembly.  
         [0003]     Various types of latches join and lock a first aircraft structure, such as an aircraft panel or cowling, to a second aircraft structure. A typical latch includes a hook latch mounted to one half of an aircraft cowling that engages a keeper mounted to the other half as well as a reversal of these components. Some latches include a handle directly connected to the hook such that the latch is directly operable by a latch operator, while other latches are not directly operable by a latch operator.  
         [0004]     For example, cowling halves are sometimes secured to each other at the top of the cowling, near the hinge lines, by remote, top-mounted latches. Such top-mounted latches may be inaccessible and are not readily visible to operators on the ground. Several types of top-mounted latches attempt to solve the problem of inaccessibility by permitting remote operation. These top-mounted latches commonly include a hook latch to engage the keeper. The hook latch is connected to, and actuated by, a push/pull cable which, in turn, is connected to a handle mechanism located at the bottom of the cowling. This allows an operator to remotely open and close the top-mounted latch by the use of the handle. When the top-mounted latch is remotely opened, the hook disengages from the keeper allowing the cowling to be opened. After closing the cowling, the top-mounted latch may be remotely closed by an operator simply toggling the handle at the bottom of the cowling.  
         [0005]     Sometimes parts of the latch can become corroded. Such corrosion may cause an increase in friction in the latch. Friction or debris in the latch actuation member restricts complete closure of the cowling. Such circumstances may cause a mechanic to exert higher-than-desired loads to close the latch handle. The excessive loads placed upon the cable latch in-turn, in an effort to overcome resistance caused by the corrosion or debris, can cause excessive forces on and damage to the cable assembly. Damage to the cable assembly and/or associated latch can be costly and difficult to replace. Certain latches are designed such that a mechanic has the ability to exert excessive cable latch handle opening forces by continuing to pull on the handle after it has been fully extended in the open position. While in some cases this may release the latch mechanism, in others, expensive and time consuming repairs are required to fix the over loaded cables or latches.  
         [0006]     In view of the above, it should be appreciated that there is a need for a latch assembly including a fuse assembly that limits excessive forces from being exerted on the latch assembly, to prevent damage from occurring to underlying components. The present disclosure satisfies these and other needs and provides further related advantages.  
       SUMMARY  
       [0007]     The disclosure includes an in-line fuse device and fuse assembly for use with a latch assembly to prevent failure to the latch assembly and its component parts in the event that excessive force is exerted on the latch handle.  
         [0008]     The latch assembly includes a latch housing and a latch, which is mounted in the latch housing. The latch includes a latch handle having a trigger assembly adapted to release the handle from a locked position. The latch handle in turn causes an arm assembly to slide along a pair of side plates, directly causing the movement of a push/pull type cable assembly. The latch also includes a linkage that is moveable in and out of a locked position.  
         [0009]     The in-line fuse assembly can be pivotally mounted to the arm assembly, and generally positioned in-line with the push/pull cable. The in-line fuse pin includes a section that is designed to be a sacrificial component which functions to break or otherwise predictably and/or controllably fail in the event that excessive forces are applied to the latch handle. The in-line fuse is configured such as by, but not limited to a reduced cross-section, a tapered cross-section, or use of different materials. The fuse provides a controlled, intentionally positioned weak link in the latch assembly which can be controllably engineered to fail under predetermined conditions.  
         [0010]     Thus, when a latch operator exerts excessive force in an attempt to move the latch handle into a locked position, and corrosion or an obstruction interfere with the operation of the locking mechanism, the in-line fuse pin will, controllably operate to limit or prevent damage to the latch mechanism and cable assembly. For example, when the in-line fuse pin fails, the latch handle loses resistance, alerting the operator that a problem with the latch mechanism exists and needs to be corrected.  
         [0011]     Users desire an overload preventing fuse that will function before more costly damage occurs to difficult-to-replace latch assembly components in the load path. Such a fuse can be sacrificed to prevent damage to the latch assembly. An overload situation may arise if corrosion increases friction in the latch actuation members, causing a mechanic to exert higher-than-desired loads to close the cable latch, which in-turn could exert excessive forces on the cable assembly (the cable assembly is costly and difficult to replace). Certain latch designs are such that a mechanic may also exert excessive cable latch handle opening forces by continuing to pull on the handle after it has been fully opened. It is also possible for debris to jam the mechanism, so that a mechanic may try to overcome the obstruction by exerting excessive forces to open or close the cable latch handle.  
         [0012]     Other features and advantages of the disclosure will be set forth in part in the description which follows and the accompanying drawings, wherein the embodiments of the disclosure are described and shown, and in part will become apparent upon examination of the following detailed description taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a perspective view of a latch assembly in an open configuration;  
         [0014]      FIG. 2  is a perspective view of an arm member of the latch assembly;  
         [0015]      FIG. 3  is a side elevational view of the latch assembly in  FIG. 1 ;  
         [0016]      FIG. 4  is a partial fragmentary, perspective view of an in-line fuse pin on the latch assembly, partially disassembled;  
         [0017]      FIG. 5  is a sectional view of the in-line fuse pin assembly taken along line  5 - 5  in  FIG. 4 , fully assembled;  
         [0018]      FIG. 6  is a sectional view of the in-line fuse pin;  
         [0019]      FIG. 7  is a perspective view illustrating the top side of the latch assembly; and  
         [0020]      FIG. 8  is a perspective view illustrating the bottom side of the latch assembly. 
     
    
     DETAILED DESCRIPTION  
       [0021]     As illustrated in the drawings a latch assembly  10  includes an in-line fuse assembly  48  to prevent damage to the latch assembly  10  and related structures. As shown in the exemplary drawings, and with particular reference to  FIG. 1 , a latch assembly  10  having a latch handle  12  is movably connected, shown here as pivotally-connected, to a latch housing  13  defined by a first and a second side plate  14 ,  16 . The handle  12  is shown as a channel-shaped member that is adapted to allow a latch operator to open and close the latch assembly  10 . When in the closed position, the latch handle  12  generally covers or overlies the first and second side plates  14 ,  16 .  
         [0022]     The latch assembly  10  is adapted to be mounted to an aircraft structure such as a cowling  17  of an engine nacelle. The latch assembly  10  provides remote latching and/or releasing of a latch system  11  as shown in  FIG. 9 . The latch assembly system  11  includes the latch assembly  10  and a corresponding second latch system  21  including a hook latch  23  and keeper  25 . While the hook latch and keeper  23 ,  25  are shown, other second latching systems  21  are envisioned for use with the latch assembly system  11  as shown and described. The latch assembly system  11  also includes means for remotely operating the second latch system  21  connected to the latch assembly  10 . In this regard, one form of the remote operating means  29  is a cable assembly  94  as described in greater detail herein below. The latch assembly system  11  as shown in  FIG. 9  is shown in a general diagrammatic illustration and is not intended to be representative of the respective dimensions or sizes of the components. The illustration of  FIG. 9  is provided for illustrative purposes only and is not in any way intended in any way to limit the present application to the specific embodiments as shown or described therein.  
         [0023]     As shown in  FIGS. 1 and 3 , the latch handle  12 , includes a top wall  18 , that forms the top most surface of the latch assembly  10  and a pair of sidewalls  20  and  22  that are aligned parallel to each other, and perpendicular to the top wall  18 . The top wall  18  includes an opening  24  that is adapted to accept a trigger assembly  26 . The trigger assembly  26  includes a control  27  having a pair of engaging arms  29  which are adapted to engage a pair of bushings  44 , to retain the latch handle  12  in a closed position. When the trigger control  27  is depressed by the latch operator, the handle  12  is biased to an open position by a series of springs  30 ,  32 . The trigger assembly  26  includes a pivot pin assembly  34  that allows the trigger assembly  26  to pivot from a closed position to an open position. The trigger assembly  26  is biased to a locked position by the use of a spring  36 , such as a dual helix torsion spring as shown that is mounted on the pivot pin assembly  34 .  
         [0024]     While the description refers to a latch assembly  10  for use with an aircraft panel, it is within the scope of the present application and fully envisioned herein that the disclosure is applicable to ships, land vehicles, trains or any other vehicle or latching assembly which may be used on buildings or other non-vehicular structures. The description set forth herein should be expansively applied to any situation in which such a latch assembly and latch mechanism might be used in any number of situations. As will be described in greater detail herein, a fuse assembly  48  in combination with the latch mechanism  10  and latch assembly  11  generally prevents damage to the latch mechanism and latch assembly, and any related structures or components, as a result of a fuse  62  failing in any one of many structural modes in the event of a force greater than a predetermined limit is applied to the fuse  62 .  
         [0025]     The first and second sidewalls  20  and  22  include apertures  38  that are adapted to allow the placement of a pin  40  that retains arms  42 . The arms  42  include a first end  43  and a second end  45 . The arms  42  are pivotally connected to the latch handle  12  at a first end and are pivotally connected to a pair of bushings  44  at the second end that extend outwardly from housing  46  of fuse assembly  48 . The second end  45  of the arms  42  include bores  47  that are adapted to receive busings  44  which engage cross members of posts  53 . The bushings  44  slidably engage a pair of channels  51  in the first and second side plates  14 ,  16 . Housing  74  has posts  53  onto which rollers  44  fit (See  FIG. 5 )  
         [0026]     The latch assembly  10  further includes a trigger closure assembly  50  that retains the latch handle  12  in an open position prevent accidental closure. The trigger closure assembly  50  includes a crossbar  52  and first and second side members  59 ,  61  that are parallel with respect to each other and perpendicularly oriented to the crossbar  52 . The side members  59 ,  61  of the trigger closure assembly  50  each include an L-shaped channel  57  that extends along the length of the side members  59 ,  61 . The channels  57  include a horizontal leg  56  and a vertical leg  58 . The channels  57  are adapted to slidably accept the bushings  44 . When the latch handle  12  is pivoted to an open position, the bushings  44  are slid or rolled along the horizontal surface of the leg  56  of the channels  57  until arrival at the vertical leg  58 . Upon encountering the vertical leg  58  of the channels  57  the trigger closure assembly  50  is biased downward by a spring (not shown) located under a trigger lock  60  to lock the latch handle  12  in an open position. This arrangement prevents unintended closure of the latch handle  12 . Depressing the trigger closure assembly  50  aligns the bushings  44  with the horizontal leg  56  of the channels  54  to allow the latch handle  12  to be moved to the closed position.  
         [0027]     The fuse assembly  48 , as shown in  FIGS. 4-6 , is pivotally connected to the second end  45  of the arms  42 . The fuse assembly  48  includes the housing  46 , a fuse  62 , a retaining nut  64  and a lock nut  66 . The housing  46  of the fuse assembly  48  includes a top surface  68 , a spaced apart bottom surface  70 , a first side surface  72  and a spaced apart second side surface  74 . The side surfaces include a recessed portion  76  that includes outwardly extending posts  78  adapted to accept arms  42 . The housing  46  of the fuse assembly  48  further includes a first end surface  80  spaced apart from a second end surface  82 . The housing  46  of the fuse assembly  48  includes a bore  84  that extends from the first end surface  80  through to the second end surface  82 . The bore  84  is dimensioned to allow for the axial passage of the fuse pin  62 . The housing  46  of the fuse assembly  48  further includes a slot  86  communicating with the bore  84 . A retaining nut is positioned in the slot  86  for engaging the fuse pin  62  extending through bore  84 .  
         [0028]     A means  87  for preventing torsional stresses on the fuse  62  is provided. One form of the means for preventing torsional stresses is embodied as a flatted region positioned along the fuse  62 . A corresponding surface  91  is provided in the bore  84  for resisting rotation of the fuse  62  when adjusting the fuse  62 . The torsion resisting means  87  generally eliminates rotary or torsional stresses on the fuse  62  and generally applies stresses along a central axis  95 . It should be noted that the torsion resisting means  87  is shown as a “flatted” region but other variations and forms may be used such as a knurled section and corresponding internal knurled section, a multi-lobular region  89  and corresponding section  91  as well as other shapes and configurations which generally resist torsional forces and permit axial movement along a central axis  95 . Using some form of torsion resisting means helps to prevent torsional stresses from effecting the fuse breaking load such that torsional stresses are not imparted or are prevented from being imparted to the sacrificial area or neck area  92 .  
         [0029]     During adjustment of the tension on the fuse  62  the adjuster while retaining nut  64  is rotated to draw or release a threaded rod section  100  through the bore  84 . Once a desired tension is set in the fuse  62 , a lock nut  66  is positioned to maintain the desired adjustment. During the adjustment process, the means for resisting torsional stresses  87  generally prevents rotation or torsional movement of the fuse and facilitates application of the adjusting forces by the adjuster  64  along the central axis  95 .  
         [0030]     The fuse  62  is illustrated in the drawings as a generally elongated, rod shaped member having a first end  88  and a spaced apart second end  90  referred to herein as a fuse pin  62 . The fuse pin  62  is a sacrificial component which is configured to fail, break, or otherwise result in a change in its characteristics when excessive force is applied to the latch. Fuse  62  is one form or embodiment of a means for failing the connection between the latch assembly  10  and the cable assembly  94 . The operation of the fuse  62  renders the latch assembly  10  inoperable before damage may occur to other components in the latch assembly  10 . The fuse  62  provides a controlled, intentionally positioned weak link in the latch assembly which can be controllably engineered to fail only under predetermined conditions. The fuse  62  is easily accessible to allow for replacement upon failure. The fuse  62  is adapted to be positioned within and extending through the bore  84  of the housing  46  and is designed to fail at a sacrificial piece illustrated herein generally as a mid-section  92  of the fuse  62 , if an excessive load is placed thereupon. With reference to the sacrificial piece means that the sacrificial piece  92  is part of the whole fuse. While the sacrificial piece  92  is part of the whole fuse  62  it may be composed of a different material, a different physical portion, a portion of a continuous piece of material which has been treated in manner to produce different mechanical results or any number of embodiments which will result in the operation of the fuse  62  described herein. The reference to fuse  62  as used herein to identify a device that in some way fails or changes characteristics in the event that a force greater than a predetermined limit is applied to the latch assembly. Operation of the latch assembly, generally in the opening or closing mode whether operated manually by a latch operator or unintentionally under other circumstances. In this regard, the fuse  62  may take many different physical embodiments including a pin  62  as illustrated herein, a plate, a panel a linkage as well as any other physical embodiment which might provide the same function as the fuse  62  as described herein or any other means for failing, one embodiment being the fuse  62  shown and described herein.  
         [0031]     The first end  88  of the fuse pin  62  includes a first attachment structure shown in the form of a threaded bore  93  that is adapted to engage a threaded end  97  of a cable assembly  94 . The first end  88  may include an aperture  96  that is adapted to accept a cotter pin  98  or lock wire to help prevent the cable assembly  94  from disengaging from the fuse pin  62 . While the cotter pin  98  engaged in the aperture  96  may not be essential to the disengagement it may provide additional assistance in some situations. Generally, the torsion resisting means  87  associated with the fuse  62  prevents rotation of the fuse  62  while traveling in or positioned in the bore  84  thereby preventing rotation of the first end  88  relative to the threaded end  97  of the cable assembly  94 .  
         [0032]     The second end  90  of the fuse pin  62  includes a second attachment structure shown in the form of a threaded rod section  100  that is adapted to accept the retaining nut  64  and the lock nut  64 . The retaining nut  64  includes apertures  102  which can be engaged by a tool to adjust the tension on the fuse  48 . The lock nut  66  is positioned against second end surface  82  of the housing  46  and retains the position of the fuse pin  62  to maintain the correct adjustment of the cable assembly  94 .  
         [0033]     If more tension is required on the cable assembly  94  the retaining nut  64  is tightened to pull a greater portion of the fuse pin  62  into the housing  46 , the lock nut  66  retains the adjustment. The sacrificial piece  92  of the fuse  62  is configured to change in the event an excessive force is applied to the latch. As shown in  FIGS. 4-6 , the sacrificial piece  92  is in the form of a narrowed or necked section of a structure and dimension to separate in the event that a load is applied exceeding the capacity of the material. The fuse  62  operates when the load is applied exceeding the capacity of the material to further neck result of additional tension being applied thereto. As a result of the occurrence of the additional necking or stretching of the material, the latch cannot be further operated. Additionally, if the operator tries to close the latch elongation of the pin material will prevent closing of the latch. As a result, the fuse is operable in two modes to prevent damage to the latch assembly system.  
         [0034]     The fuse  62  can be designed to allow for various latch handle  12  loads without causing damage to the fuse  62 . The diameter of the sacrificial piece  92  of the fuse pin  62  can be increased for a higher resistance to failure and decreased for a lower resistance to failure. Alterations in the material the fuse pin  62  is fabricated from will also vary its rate of failure. Variations in the steel used will alter the load in which the fuse pin  62  will fail. Some of the materials utilized to fabricate the fuse pin  62  include annealed AISI 300-series, 15-5H900, and 13-8H950 stainless steels. For example, the diameter of the sacrificial piece  92  is sized to enable 25,000 cycles of fully-reversed load of 895.6 lb at 250° C. In this situation a 17-4 PH H900 fuse tensile stress may be limited to 152,382 psi maximum allowable stress. This may translate to a diameter of 0.0985″/0.0995″ where 1.07 is assumed K t  and where 229,000 psi is the maximum expected breaking strength of 15-5 PH H900.  
         [0035]     Cyclic life of 25,000 cycles at 250° C. is calculated as Load×K t /(pi/4×d2)=max allowable stress where K t =1.07. The load for the hypothetical case is 895.6 lb divided by the temperature reduction factor of 0.86 for 17-4PH-H900 stainless steel at 250° C. (=1,0411 lb which is the equivalent room temperature load) and maximum allowable stress=152,382 psi. Solving, the minimum diameter is d=0.0985″ minimum. Static strength maximum diameter is calculated as d maximum=d min.+0.0010=0.0995″. Maximum expected breaking strength is calculated as 229,000 psi×pi/4×d 2 =1,781 lb at room temperature.  
         [0036]     The foregoing example and other examples set forth in this description are not intended in any way to limit the scope of the present applications and appended claims. Rather, these are provided as examples to further help understand and enable the described device, method and system. These examples are intended to be expansive to be broadly interpreted without limitation.  
         [0037]     The sacrificial piece  92  of the fuse  62  as illustrated is a narrowed portion that is dimensioned to separate or deform in the event that a load is applied, exceeding a predetermined limit, such as the calculated failure stress of the material. The sacrificial piece  92  can be achieved through other mechanisms in addition to the reduced diameter section as shown. For example, while the dimension can be maintained another type of material, or a different material process can be used to produce the desired change in the fuse  62 . The failure mechanism in the fuse  62  may be in the form of complete separation failure as well as, but not limited to continued narrowing or necking of the fuse  62  material or buckling. The fuse  62  may be controllably frangible at a predetermined limit in the sacrificial piece or may be designed to promote plastic deformation.  
         [0038]     In use, the latch assembly  10  is attached to an aircraft structure and coupled to a cowling and is designed to retain the cowling or other panels on the aircraft in a closed position. When service of the aircraft or other access to the latched area is required for example when the cowling must be opened, the latch operator presses the control  27  of the trigger assembly  26  visible from the wall  18  of the latch handle  12 . Operating the trigger assembly  26  allows the springs  30  and  32  to bias the latch handle  12  to an open position. The outward movement of the latch handle  12  exerts a force on the arms  42  causing the bushings  44  to slide along the horizontal leg  56  of the channels  57 . The movement of the arms  42  causes the fuse assembly  48  to slide along the first and second side plates  14  and  16 .  
         [0039]     The movement of the fuse assembly  48  causes the fuse pin  62  to push the cable assembly  94 , which releases the latch. If corrosion is present in the cable assembly  94  or in the latch mechanism or debris is present preventing the unlatching the panel, the fuse assembly  48  will buckle to prevent the latch operator from exerting excessive forces on the system by failing if the force applied exceeds a predetermined limit. The failure of the fuse pin  62  alerts the latch operator that a problem has occurred in the system due to corrosion, debris or other malfunction that is required to be corrected. Once the problem is corrected, the fuse pin  62  may be replaced without the need for complete removal of riveted panels or other components that may take hours to repair, delaying flight.  
         [0040]     The fuse pin  62  is removed from the fuse assembly  48  by first removing the lock wire securing nut  66  and nut  64 . Next, nut  66  is removed from the threaded rod section  100  of the second end  90 . Once the lock nut  66  is removed, the retaining nut  64  can be rotated to remove the second end  90  of the fuse pin  62  from the housing  46 . Since the fuse pin  62  may be separated at the mid-section, due to its failed state, the first end  88  of the fuse pin  62  can be removed from the housing  46 . Once the fuse pin  62  is free from the housing  46 , the cotter pin or lock wire  98  is removed from the aperture  96  (if the cotter pin is used) and the first end  88  of the fuse pin  62  is rotated to disconnect the threaded bore  93  from the cable assembly  94 .  
         [0041]     The replacement fuse pin  62  is first threaded onto the cable assembly  94 . The cotter pin  98 , if used, is positioned within the aperture  96 . The fuse pin  62  is then inserted into the central bore  84  of the housing  46  until the fuse pin  62  comes into contact with and threadably engages the retaining nut  64 . The retaining nut  64  is rotated until the fuse pin  62  is properly positioned within the housing  46 , to ensure proper tension on the cable assembly  94 . Once the proper orientation of the retaining nut  64  with respect to the fuse pin  62  is achieved, the lock nut  66  is installed to prevent the position of the fuse pin  62  from changing with respect to the housing  46 . Once in position, a retaining wire(s) can be attached to the retaining nut  64  and lock nut  66  to prevent change in position.  
         [0042]     Various features of the invention have been particularly shown and described in connection with the disclosure as shown and described, however, it must be understood that these particular arrangements merely illustrate, and that the disclosure is to be given its fullest interpretation within the terms of the appended claims.