document: BACKGROUND 
         [0001]    The present invention relates generally to support structures, and more particularly to a mounting link between an engine structure and an attached structure such as an auxiliary gearbox. 
           [0002]    Aircraft gas turbine auxiliary gearboxes are expected to withstand a variety of loads, from routine vibrational loads to sudden or extreme shocks caused by hard landings. The most extreme loads come from so-called “blade-off” events, when blades of the engine detach due to impacts or the like, causing severe shocks and often major damage to the working engines. Blade-off event loads are extremely unpredictable, but can be more than an order of magnitude stronger than any other sudden or extreme shock gas turbine engines are expected to experience, such as impacts due to hard landings. Extreme loads can cause damage to the gearbox itself, as well as to attached peripheral systems driven by the gearbox. In addition, extreme loads that damage or disconnect parts of the gearbox from the engine can result in potentially dangerous oil leakages. For all of these reasons conventional gearboxes and gearbox connections are constructed to rigidly withstand all anticipated loads. Often, conventional gearboxes and gearbox connections may require additional material or be heavier to withstand such extreme loads. 
         BRIEF SUMMARY 
         [0003]    According to an embodiment, a link assembly between an engine and a gearbox includes a male link coupled to the engine or the gearbox, a female link coupled to the engine or the gearbox, wherein the female link receives the male link to allow translation of the male link relative to the female link and to form a radial interface, wherein the radial interface dampens translation of the male link relative to the female link, and a pin releasably coupled to the male link and the female link to selectively retain the male link and the female link. 
           [0004]    According to an embodiment, a gearbox assembly to attach to an engine includes a gearbox, and a link assembly to couple the engine to the gearbox, the link assembly including a male link coupled to the engine or the gearbox, a female link coupled to the engine or the gearbox, wherein the female link receives the male link to allow translation of the male link relative to the female link and to form a radial interface, wherein the radial interface dampens translation of the male link relative to the female link, and a pin releasably coupled to the male link and the female link to selectively retain the male link and the female link. 
           [0005]    Technical function of the embodiments described above includes that the female link receives the male link to allow translation of the male link relative to the female link and to form a radial interface, wherein the radial interface dampens translation of the male link relative to the female link, and a pin releasably coupled to the male link and the female link to selectively retain the male link and the female link. 
           [0006]    Other aspects, features, and techniques of the embodiments will become more apparent from the following description taken in conjunction with the drawings. 
       
      
       
         BRIEF DESCRIPTION OF THE DRAWINGS 
           [0007]    The subject matter is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the embodiments are apparent from the following detailed description taken in conjunction with the accompanying drawings in which like elements are numbered alike in the FIGURES: 
             [0008]      FIG. 1  is a perspective view of one embodiment of an auxiliary gearbox for a gas turbine engine; 
             [0009]      FIG. 2  is a perspective view of one embodiment of a mounting link for use with the auxiliary gearbox of  FIG. 1 ; and 
             [0010]      FIG. 3  is a perspective cross-sectional view of the mounting link of  FIG. 2 . 
         
      
      
       DETAILED DESCRIPTION 
         [0011]    Referring to the drawings,  FIG. 1  is a perspective view of a gearbox assembly  10 , which includes a gearbox  12  and supporting elements sufficient to secure the gearbox  12  with respect to the engine  100 . The engine  100  is depicted only schematically, and can, for example, be an aircraft gas turbine engine with a structural engine case, or another engine component to which the gearbox  12  is secured. The gearbox assembly  10  includes driveshaft connection  14 , peripheral load connections  16  and  18 , seal  20 , and mounting links  22 ,  24 , and  26 . The gearbox  12  can, for example, be an auxiliary gearbox disposed to transmit torque from the engine  100  to a variety of peripheral loads not directly related to operation of the engine  100  or to propulsion (e.g. to a generator or air circulation system). 
           [0012]    A driveshaft connection  14  attaches to a shaft of the engine  100  for torque transmission. The peripheral load connections  16  and  18  are two illustrative auxiliary driveshaft connection points for attachment of peripheral loads to the gearbox  12 . Peripheral loads can include any systems driven by, but not included within, the engine  100 , including but not limited to air circulation systems and electrical generators. Although only two peripheral load connections  16  and  18  are depicted in  FIG. 1 , the gearbox  12  can more generally support any number and location of peripheral load connections. 
           [0013]    Seal  20  and mounting links  22 ,  24 , and  26  collectively constrain the gearbox  12  with respect to the gas turbine engine structure  100  in all six translational and rotational degrees of freedom, without over constraining the gearbox  12 . The seal  20  can for example, be a spigot-type annular seal that constrains the gearbox  12  in two degrees of freedom corresponding to the normal basis of the reference plane on which the seal  20  lies. In the depicted embodiment, mounting links  22  and  26  each provide a single independent degree of constraint, while the mounting link  24  provides two more independent degrees of constraint. More generally, the collection of all linkages connecting the gearbox  12  to the engine  100  including the seal  20 , as well as provides a total of six independent constraints on the translational and rotational freedom of the gearbox  12  with respect to the engine  100 . In alternative embodiments, these constraints can be distributed about more or fewer separate linkages. The independence of these constraints prevents overconstraint (e.g. two links constraining the same degree of freedom) that would necessitate tighter tolerances and could increase damage done to the gearbox and/or the linkages in the event of severe impacts. The locations and number of degrees of freedom constrained by each linkage may vary across different embodiments, so long as the collection of all linkages constrains all six degrees of freedom without significantly overconstraining any. 
           [0014]    Referring to  FIGS. 2 and 3 , the mounting link  26  is shown. In the illustrated embodiment, the mounting link  26  includes a female link  30 , a male link  32 , and a pin  35 . The mounting link  26  can be utilized as a medium to long link to connect the engine  100  to an associated structure, such as the gearbox  12 , as shown in  FIG. 1 . The mounting link  26  can rigidly constrain one degree of freedom between the engine  100  and the gearbox  12 . In the illustrated embodiment, extreme loads may break the rigid constraint of the mounting link  26  by shearing the pin  44  to allow a permitted range of motion. In the illustrated embodiment, the interface between the female link  30  and the male link  32  can dampen the relative motion within the permitted range of motion. Referring to  FIG. 1 , the increased and damped mobility of the gearbox  12  relative to the engine  100  allows the mounting link  26  to absorb extreme shocks without either detaching the gearbox  12  from the engine  100  or transmitting potentially destructive loads from the engine  100  to the gearbox  12 . 
           [0015]    Referring back to  FIGS. 2 and 3 , in the illustrated embodiment, the female link  30  includes a link mounting end  31  and a link interface end  36 . The female link  30  can be formed with any suitable geometry and formed from any suitable material. In the illustrated embodiment, the link mounting end  31  can include a feature to attach or otherwise couple to a component such as the engine  100  or the gearbox  12  as shown in  FIG. 1 . In the illustrated embodiment, the link mounting end  31  includes a hole to allow a bolt or feature of a component to pass through to attach the female link  30  to the component. In the illustrated embodiment, the opposite end of the female link  30  is the link interface end  36 . The link interface end  36  includes a cavity to receive the male link  32 . The male link  32  can translate relative to the female link  30  after the pin  44  is broken or otherwise released. 
           [0016]    In the illustrated embodiment, the male link  32  includes a link mounting end  33  and a link interface end  34 . The male link  32  can be formed with any suitable geometry and formed from any suitable material. In the illustrated embodiment, the link mounting end  33  can include a feature to attach or otherwise couple to a component such as the engine  100  or the gearbox  12  as shown in  FIG. 1 . In the illustrated embodiment, the male link  32  is attached to the corresponding component that female link  30  is not attached to link two components. For example, the female link  30  may be attached to the engine  100  while the male link  32  is attached to the gearbox  12 . In the illustrated embodiment, the link mounting end  33  includes a hole to allow a bolt or feature of a component to pass through to attach the male link  32  to the component. In the illustrated embodiment, the opposite end of the male link  32  is the link interface end  34 . The link interface end  34  is received by the female link  30  in the link interface end  36  of the female link  30 . The male link  32  can translate relative to the female link  30  after the pin  44  is broken or otherwise released. 
           [0017]    In the illustrated embodiment, the pin  44  selectively prevents the relative translation of the female link  30  and the male link  32 . In the illustrated embodiment, the pin  44  passes through a through hole  37  of the female link  30  and a through hole  38  of the male link  32  to engage and retain the female link  30  and the male link  32 . In certain embodiments, the through hole  37  of the female link  30  and the through hole  38  of the male link  32  are axially aligned. In the illustrated embodiment, the through hole  37  and the through hole  38  are disposed near the link interface end  36  of the female link  30  and link interface end  34  of the male link  32 . In the illustrated embodiment, the pin  44  can be in an interference fit with the female link  30  and the male link  32 . In the illustrated embodiment, the mounting link  26  can further include a plug  40 . The plug  40  can axially retain the pin  44 . The plug  40  can be disposed or otherwise fit within the through hole  37  in addition to the pin  40  to prevent the unintentional removal of the pin  44 . 
           [0018]    In the illustrated embodiment, the pin  44  can serve as a fusible link. In certain embodiments, the pin  44  can shear when a sufficiently strong shock or heavy load is applied. In certain embodiments, a shear plane can be predefined to provide a designated area to allow the pin  44  to shear. In certain embodiments, the pin  44  can be formed of a less durable material than the female link  30  and the male link  32  to facilitate the desired shear characteristics. 
           [0019]    In the illustrated embodiment, the pin  44  is designed to shear at a known load magnitude corresponding to the maximum structural capability of the gearbox assembly  12 , the unfused mount components, and the engine mounting structure  100 , as shown in  FIG. 1 . This can be accomplished by selecting an appropriately durable diameter and material for the pin  44 , and/or by priming the pin  44  for shear with suitably shaped shear initiation points. In general, the pin  44  must be at least strong enough to withstand peak non-destructive impact loads such as low cycle loads from hard landings and other non-routine but expected shocks. These loads can, for example, reach 10-15 Gs. In at least some embodiments, the pin  44  will not break until loads at least 10-25 times higher than expected low cycle loads are experienced. Very few loads experienced during aircraft engine operation reach these levels, but shocks due to blade-off events can be high enough to shear the pin  44 . 
           [0020]    After an event that can cause the pin  44  to shear, fuse, or otherwise release, the female link  30  and the male link  32  are allowed to translate relative to each other. In the illustrated embodiment, the female link  30  and the male link  32  can translate generally axially. Advantageously, mounting link  26  limits or prevents damage that could otherwise be done to gearbox  12  and its attached peripherals by transmitting such extreme loads, while simultaneously helping to prevent gearbox  12  from detaching from engine  100  ( FIG. 1 ). 
           [0021]    In the illustrated embodiment, the female link  30  and the male link  32  are in contact at the radial interface  35  between the link interface end  36  and the link interface end  34 . As the female link  30  and the male link  32  translate, the frictional radial interface  35  between the female link  30  and the male link  32  provides coulomb damping to dissipate energy created by the translation. In the illustrated embodiment, the amount of coulomb damping provided by the radial interface is determined by the coefficient of friction, the geometry, and the contact areas of the female link  30  and the male link  32 . In certain embodiments, the materials of the female link  30  and the male link  32  are selected to provide the desired level of coulomb damping. In certain embodiments, the damping force provided by the radial interface  35  is greater than the force required to shear the pin  44 . In other embodiments, the damping force provided by the radial interface  35  is less than the force required to shear the pin  44 . 
           [0022]    In the illustrated embodiment, the snap ring  42  can be utilized to limit the relative travel of the male link  32  within the female link  30 . In the illustrated embodiment, the snap ring  42  can be installed after the male link  32  is disposed within the female link  30  to retain the male link  32  at the end of the travel range to prevent the mounting link  26  from separating after the pin  44  is sheared. 
           [0023]    Advantageously, the use of the pin  44  and the coulomb damping provided by the radial interface  35  obviates the need for all linkages and peripheral connections to be capable of surviving the extreme loads produced during fan blade-off events, which would otherwise either be entirely infeasible, or would dramatically increase the weight and mass of material required to adequately reinforce associated systems. Fan blade-off events necessitate maintenance to repair or replace damaged engine components, and the pin  44  can be replaced with an intact pin  44  during maintenance following any shock sufficient to break the pin  44 . 
           [0024]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments. While the description of the present embodiments has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications, variations, alterations, substitutions or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the embodiments. Additionally, while various embodiments have been described, it is to be understood that aspects may include only some of the described embodiments. Accordingly, the embodiments are not to be seen as limited by the foregoing description, but are only limited by the scope of the appended claims.
summary: A link assembly between an engine and a gearbox includes a male link coupled to the engine or the gearbox, a female link coupled to the engine or the gearbox, wherein the female link receives the male link to allow translation of the male link relative to the female link and to form a radial interface, wherein the radial interface dampens translation of the male link relative to the female link, and a pin releasably coupled to the male link and the female link to selectively retain the male link and the female link.