Patent Publication Number: US-2021163272-A1

Title: Cable break-away safety device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a divisional of U.S. application Ser. No. 15/910,800 filed Mar. 2, 2018 for “CABLE BREAK-AWAY SAFETY DEVICE,” which in turn claims the benefit of U.S. Provisional Application No. 62/466,896, filed Mar. 3, 2017 for “CABLE BREAK-AWAY SAFETY DEVICE,” by M. Ijadi-Maghsoodi, P. J. Tucker, and M. A. Gonfiotti. 
    
    
     BACKGROUND 
     The present application relates generally to hoists. More particularly, this application relates to translating body rescue hoists for aircraft. 
     Rescue hoists deploy and retrieve a cable from a cable drum to hoist persons or cargo. The rescue hoists may be mounted to an aircraft, such as a helicopter. The cable drum rotates to spool or unspool the cable from the cable drum, with one end of the cable attached to the cable drum and the other end, which can include a hook or other device, deployed during operation. Rescue hoists require overload protection in case the hook or cable is caught or hung up on a grounded object. 
     With the cable attached to the cable drum, the cable should resist pull-out from the cable drum until the cable is overloaded. When the cable is overloaded, the cable should pull out freely from the cable drum to prevent damage to the rescue hoist, the airframe, or both. The cable is typically secured to the cable drum by inserting an end of the cable into a hole in the cable drum and then securing the cable to the cable drum with set screws. The set screws are torqued to a predetermined level to prevent the cable from pulling out of the cable drum. The capacity to resist pull-out is proportional to the torque applied to the set screws and to the coefficient of friction between the set screws and the cable. 
     SUMMARY 
     According to one aspect of the disclosure, a cable break-away device includes a shear cap having a head, an attachment portion, and a neck extending between and connecting the head and the attachment portion. The neck is configured to transmit tensile forces from a cable secured to the attachment portion and to fracture with the tensile forces equal to or exceeding a predetermined fracture set point. 
     According to another aspect of the disclosure, a rescue hoist assembly includes a rotating cable drum supported by a frame, a shear cap attached to the rotating cable drum, and a cable secured to the shear cap. The shear cap is configured to transmit tensile forces from the cable to the cable drum and to fracture with the tensile forces equal to or exceeding a predetermined fracture set point. 
     According to yet another aspect of the disclosure, a method of securing a cable to a cable drum includes securing an end of a cable within a receiving chamber of a shear cap and inserting the shear cap into a mounting slot extending into a barrel of the cable drum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevation view of an aircraft and rescue hoist. 
         FIG. 2A  is an isometric view of a cable drum and shear cap. 
         FIG. 2B  is an enlarged view of detail Z of  FIG. 2A . 
         FIG. 3A  is a cross-sectional view of a shear cap and cable. 
         FIG. 3B  is a cross-sectional view of the shear cap and cable in response to an overload event. 
         FIG. 4A  is an isometric view of a shear cap. 
         FIG. 4B  is a side elevation view of the shear cap of  FIG. 4A   
         FIG. 4C  is a cross-sectional view of the shear cap of  FIG. 4A  taken along line C-C in  FIG. 4A . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an elevation view of aircraft  10  and rescue hoist  12 . Rescue hoist  12  is mounted to aircraft  10  by support  14 . Cable  16  extends from rescue hoist  12  and is configured to raise and lower objects to and from aircraft  10 . During operation, cable  16  can become entangled with an object on the ground, such as a tree or building, which leads to excessive loads being transmitted to rescue hoist  12  and aircraft  10  through cable  16 . To prevent damage from occurring to either rescue hoist  12  or aircraft  10 , cable  16  should be able to break free from rescue hoist  12 . 
       FIG. 2A  is an isometric view of cable drum  18  and shear cap  20 .  FIG. 2B  is an enlarged view of detail Z of  FIG. 2A .  FIGS. 2A and 2B  will be discussed together. Cable drum  18  includes first flange  22 , second flange  24 , and barrel  26 . Barrel  26  includes mounting slot  28  and grooves  30 . Mounting slot  28  includes head receiving portion  32 , neck receiving portion  34 , and detent  36 . Shear cap  20  includes head  38 , neck  40 , and attachment portion  42 . Cable  16  includes retained end  44 . 
     Barrel  26  extends between and connects first flange  22  and second flange  24 . Grooves  30  extend about barrel  26  and are configured to maintain a position of cable  16  on barrel  26 . Mounting slot  28  extends into barrel  26 . Detent  36  is spring biased to project over neck receiving portion  34  of mounting slot  28 . Neck  40  extends between and connects head  38  and attachment portion  42  of shear cap  20 . Retained end  44  of cable  16  extends into and is secured within attachment portion  42 . Attachment portion  42  of shear cap  20  is swaged onto retained end  44  to secure retained end  44  within attachment portion  42 . Cable  16  extends from attachment portion  42  and wraps around barrel  26 . Cable  16  is generally disposed within grooves  30  to help ensure that cable  16  is evenly wrapped around barrel  26 . 
     With shear cap  20  installed on cable drum  18 , head  38  of shear cap  20  is disposed within head receiving portion  32  of mounting slot  28 . Neck  40  extends from head  38  and is disposed within neck receiving portion  34  of mounting slot  28 . Attachment portion  42  extends from neck  40  opposite head  38 . A diameter of head  38  is greater than a diameter of neck  40 , and as such a width of head receiving portion  32  is greater than a width of neck receiving portion  34 . Neck receiving portion  34  thus helps maintain head  38  within head receiving portion  32  of mounting slot  28  because head  38  is unable to pass through the narrower width of neck receiving portion  34 . Head receiving portion  32  is tightly toleranced to head  38 , such that head  38  is maintained within head receiving portion  32  and prevented from torqueing out of head receiving portion  32 . 
     Shear cap  20  is installed on cable drum  18  by pushing shear cap  20  into mounting slot  28 . As shear cap  20  passes over detent  36 , detent  36  depresses to allow shear cap  20  to pass into mounting slot  28  and then detent moves to a neutral position extending over neck receiving portion  34 , to thereby assist in retaining shear cap  20  within mounting slot  28 . For example, detent  36  can be of a ball and spring configuration, where the spring is depressed when shear cap  20  passes over detent  36 , and the spring then biases the ball back over neck receiving portion  34  to retain shear cap  20  in mounting slot  28 . The tight tolerance between head  38  and head receiving portion  32  ensures that shear cap  20  must lift vertically relative to mounting slot  28  to either install or uninstall shear cap  20  and cable  16 . 
     During operation, cable  16  is deployed from cable drum  18  and utilized to hoist various objects to and from aircraft  10  (shown in  FIG. 1 ). Shear cap  20  secures cable  16  to cable drum  18 . Both aircraft  10  and rescue hoist  12  have a rated load, and experiencing loads above the rated load can cause damage to both aircraft  10  and rescue hoist  12 . To prevent damage to aircraft  10  and rescue hoist  12 , cable  16  should detach from cable drum  18  when the load reaches too great a level, such as where cable  16  becomes entangled with a building, tree, or other object on the ground. During operation, tensile forces are transmitted to rescue hoist  12  and aircraft  10  from cable  16  through shear cap  20 . With head  38  secured in head receiving portion  32 , the tensile forces are transmitted to cable drum  18  through head  38 , and are transmitted to head  38  through neck  40 . Neck  40  has the smallest diameter of shear cap  20  and thus is the portion of shear cap  20  with the lowest tensile strength, and neck  40  is configured to fracture when the load on cable  16  reaches or exceeds a predetermined failure point, i.e. about three times the rated load of rescue hoist  12 . For example, where rescue hoist  12  has a rated load capacity of 273 kg (600 lb), then neck  40  is configured to fracture at loads exceeding 817 kg (1800 lb). When neck  40  fractures, cable  16  is detached from cable drum  18  and free to fall away from rescue hoist  12  and aircraft  10 . Shear cap  20  is a breakaway safety device that prevents damage to aircraft  10  and rescue hoist  12  due to excessive loads on cable  16 . It is understood that shear cap  20  can be configured to fracture at any desired load level, such that the predetermined failure set point can vary across differing applications, aircraft, and hoists. 
     Shear cap  20  provides significant advantages. Shear cap  20  slides into mounting slot  28  to secure cable  16  to cable drum  18 , providing for simple and quick installation. Shear cap  20  further simplifies the installation process by eliminating set screws and various other small components that were previously required to secure cable  16  to cable drum  18 . Shear cap  20  also provides mistake-proofing, in that shear cap  20  is configured to fracture and release cable  16  when the load on shear cap  20  reaches a predetermined failure set point. As such, shear cap  20  will not prematurely release cable  16  from cable drum  18 . Mounting slot  28  is also aligned with grooves  30 , which ensures that the first and each subsequent layer of cable  16  is levelly wound onto cable drum  18 . Shear cap  20  further eases maintenance as cable  16  can be removed and replaced with a new cable by lifting shear cap  20  out of mounting slot  28  and sliding a new shear cap attached to a replacement cable into mounting slot  28 . 
       FIG. 3A  is a cross-sectional view of shear cap  20  and cable  16 .  FIG. 3B  is a cross-sectional view of shear cap  20  and cable  16  in response to an overload event.  FIGS. 3A-3B  will be discussed together. Shear cap  20  includes head  38 , neck  40 , and attachment portion  42 . Attachment portion  42  includes base  46 , side wall  48 , distal end  50 , and retaining chamber  52 . Distal end  50  includes inner taper  54  and outer taper  56 . Head  38  includes head diameter D H  and neck  40  includes neck diameter D N . Cable  16  includes retained end  44 . 
     Neck  40  extends between and connects head  38  and attachment portion  42 . Head  38  is disposed at an end of neck  40  opposite attachment portion  42 . Base  46  of attachment portion  42  extends radially outward from neck  40 . Side wall  48  extends axially from base  46  and terminates at distal end  50 . Retaining chamber  52  is disposed within attachment portion  42  and is bounded by side wall  48  and base  46 . Retained end  44  of cable  16  extends into retaining chamber  52  through distal end  50 . Retained end  44  is preferably secured within retaining chamber  52  by swaging attachment portion  42 . 
     In  FIG. 3A , cable  16  is connected to shear cap  20 . With cable  16  deployed, tensile forces on cable  16  are transmitted to cable drum  18  (shown in  FIGS. 2A-2B ), and thus to rescue hoist  12  (best seen in  FIG. 1 ) through shear cap  20 . Neck  40  forms a mechanical fuse between attachment portion  42  and head  38 . Neck  40  is capable of transmitting tensile forces up to the predetermined set point. When the tensile forces experienced at neck  40  exceed the predetermined failure set point, neck  40  shears thereby releasing cable  16  from cable drum  18 . 
     In  FIG. 3B , shear cap  20  has experienced an overload event. When the tensile forces transmitted through neck  40  exceed the predetermined failure set point, neck  40  fractures, thereby disconnecting cable  16  from cable drum  18 . The predetermined failure set point is fixed based on the dimension and material used to construct shear cap  20 . In one embodiment, shear cap  20  is manufactured from stainless steel, such as 302 stainless steel, for example. It is understood, however, that shear cap  20  can comprise any desired material capable of tolerating tensile forces up to the predetermined failure set point while fracturing when the tensile forces exceed the tensile set point. For example, shear cap  20  can be a metal other than stainless steel, a ceramic material, or a composite material. 
       FIG. 4A  is an isometric view of shear cap  20 .  FIG. 4B  is a side elevation view of shear cap  20 .  FIG. 4C  is a cross-sectional view of shear cap  20  taken along line C-C in  FIG. 4A .  FIGS. 4A-4C  will be discussed together. Shear cap  20  includes head  38 , neck  40 , and attachment portion  42 . Attachment portion  42  includes base  46 , side wall  48 , distal end  50 , and retaining chamber  52 . Distal end  50  includes inner taper  54  and outer taper  56 . Head  38  includes head diameter D H , neck  40  includes neck diameter D N , and attachment portion  42  includes inner diameter D I  and outer diameter D O . 
     Neck  40  extends between and connects head  38  and attachment portion  42 . Head  38  is disposed at an end of neck  40  opposite attachment portion  42 . Base  46  of attachment portion  42  extends radially outward from neck  40 . Side wall  48  extends axially from base  46  and terminates at distal end  50 . Retaining chamber  52  is disposed within attachment portion  42  and is bounded by side wall  48  and base  46 . Head diameter D H  is greater than neck diameter D N . 
     Retaining chamber  52  is configured to receive retained end  44  (best seen in  FIGS. 3A and 3B ) of cable  16 . With retained end  44  disposed within retaining chamber  52 , attachment portion  42  is swaged onto retained end  44 , thereby exerting a clamping force on retained end  44  and securing retained end  44  within retaining chamber  52 . Attachment portion  42  secures cable  16  within retaining chamber  52  such that cable  16  is prevented from pulling out of attachment portion  42  during an overload event. As such, retained end  44  of cable  16  does not pull out of retaining chamber  52 . 
     Shear cap  20  transmits tensile forces from cable  16  through neck  40 . Neck  40  is configured to transmit tensile forces up to the predetermined failure set point and configured to fracture when the tensile forces exceed the predetermined failure set point. In this way, neck  40  is a mechanical fuse configured to release cable  16  from cable drum  18  (shown in  FIGS. 2A-2B ). 
     Shear cap  20  provides significant advantages. Cable  16  is directly connected to shear cap  20 , eliminating loose parts previously required to secure cable  16  to cable drum  18 . The predetermined failure set point is determined by the material and dimensions of neck  40 , and as such shear cap  20  provides an improved factor of safety for the attachment of cable  16  to cable drum  18  because shear cap  20  ensures that cable  16  will not detach from cable drum  18  before the tensile forces on cable  16  exceed the predetermined failure set point. 
     Discussion of Possible Embodiments 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A cable break-away device includes a shear cap having a head, an attachment portion, and a neck extending between and connecting the head and the attachment portion. The neck is configured to transmit tensile forces from a cable and to fracture in response to the tensile forces reaching a predetermined fracture set point. 
     The cable break-away device of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The head has a first diameter, the neck has a second diameter, and the first diameter is greater than the second diameter. 
     The attachment portion includes a base portion extending radially from the neck, a side wall extending axially from the base portion, and a retaining chamber defined by the base portion and the side wall. 
     The cable is secured within the retaining chamber. 
     The attachment portion is swaged onto the cable. 
     The shear cap comprises 302 stainless steel. 
     A rescue hoist assembly includes a rotating cable drum supported by a frame, a shear cap attached to the rotating cable drum, and a cable secured to the shear cap. The shear cap is configured to transmit tensile forces from the cable to the cable drum and to fracture in response to the tensile forces reaching a predetermined fracture set point. 
     The rescue hoist of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The rotating cable drum includes a barrel extending between and connecting a first flange and a second flange, and a mounting slot extending into the barrel. The shear cap is disposed in the mounting slot. 
     The mounting slot extends into the barrel proximate one of the first flange and the second flange. 
     The mounting slot includes a head receiving portion having a first width and a neck receiving portion having a second width. The second width is smaller than the first width. 
     The mounting slot includes a detent extending through the barrel and over the neck receiving portion. 
     The shear cap includes a head and a neck, and the second width is smaller than a first diameter of the head of the shear cap. 
     The shear cap comprises a head having a first diameter, a neck extending from the head and having a second diameter, the second diameter being smaller than the first diameter, and an attachment portion extending from the neck opposite the head. The cable is secured to the attachment portion. 
     The attachment portion includes a base extending radially from the neck, a side wall extending axially from the base and away from the neck, and a retaining chamber defined between the base and the side wall, the cable is secured within the retaining chamber. 
     The attachment portion is swaged onto the cable. 
     The shear cap comprises 302 stainless steel. 
     A method of securing a cable to a cable drum includes securing an end of a cable within a receiving chamber of a shear cap, the shear cap including a head, a neck extending from the head, and an attachment portion extending from the neck opposite the head, the attachment portion defining the receiving chamber, and inserting the shear cap into a mounting slot extending into a barrel of the cable drum. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     Inserting the end of the cable into the attachment portion of the shear cap, and swaging the attachment portion. 
     Inserting the head of the shear cap into a head receiving portion of the mounting slot, the head having a first diameter and the head receiving portion having a first width, inserting the neck of the shear cap into a neck receiving portion of the mounting slot, the neck having a second diameter and the neck receiving portion having a second width. The first diameter is greater than the second diameter, and the first width is greater than the second width. 
     The first diameter is greater than the second width. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.