Abstract:
A low resistance pathway includes a flexible member, a surface interfacing the flexible member, a sealing feature, and a fastener. The sealing feature forms an interior edge of at least one of the flexible member and the surface. The fastener compresses the flexible member to contact the surface.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to sealing components, and more particularly to the electrical bonding of components in a manner that provides for a low electrical resistance pathway between components utilizing only a localized portion of the components. 
         [0002]    Many applications, including aerospace applications, have requirements that a low resistance pathway exist between interfacing components. This is especially true in explosive environments. These requirements are instituted to reduce the potential for an electrical short to ground between the components that could result in the generation of an electrical arc in the explosive environment. 
         [0003]    Achieving a low resistance electrical bond provides protection for two classes of electromagnetic phenomena that can cause functional upsets in equipment, cause structural damage due to damage from concentrated energy absorption, or be potentially hazardous to personnel. Different regulatory requirements govern different equipment depending upon the application in which the equipment is used. For example, two classes of electrical bonding are applicable to composite structures; Class R and Class S. Class R electrical bonding pertains to equipment containing electrical circuits which may produce radio frequencies, either desired or undesired, and requires that the equipment be designed such that a continuous low impedance bonding path is formed from the equipment, enclosure, or housing to an aircraft structure. Class R electrical bonding also requires that this be accomplished through clean metal-to-metal, prepared metal-to-composite, or composite-to-composite contact of mounting plates, racks, brackets, or other component mating surface(s). Class S electrical bonding applies to all conductive components of an aircraft that are subject to frictional charging and do not otherwise have a bonding requirements, and states that they shall be bonded to the aircraft structure with a total path resistance of 1 ohm or less. Class R electrical bonding states that the bonding paths shall be accomplished through mechanical contact of components and shall be configured to include the minimum number of interfaces consistent with accepted design practice for that type of equipment. 
         [0004]    Previously, one method of achieving the low resistance bonding requirement was to use the entire split line between interfacing components. A fillet of sealant was applied around the entire interface between the components and one or more bonding straps were attached to the assembled components to provide a path to ground. However, this method of achieving low resistance bonding added weight to the component assembly as a result of the sealant and fasteners used for the bonding strap(s). Additionally, the method introduced complexity into the manufacture and repair of the components as the entire interface between the components was used to achieve a solid and durable bond. 
       SUMMARY 
       [0005]    A low resistance pathway includes a flexible member, a surface interfacing the flexible member, a sealing feature, and a fastener. The sealing feature forms an interior edge of at least one of the flexible member and the surface. The fastener compresses the flexible member to contact the surface. 
         [0006]    In another aspect, a housing assembly includes a first component, a second component, and a low resistance pathway. The second component and the first component are configured to interface along a split line. Together the first component and the second component form the low resistance pathway along a portion of the split line. The low resistance pathway is sealed from a remainder of the first component and the second component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of an assembly including a split line between separated first and second components. 
           [0008]      FIG. 2  is an exploded view of a low resistance pathway formed between the first component and the second component showing a fastener, a washer, a tab, a sealant groove, and an interface surface. 
           [0009]      FIG. 2A  is a perspective view of the low resistance pathway of  FIG. 2  showing the application of a sealant to parts of the low resistance pathway including a fillet and a groove. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    As will be described subsequently, the invention includes a low resistance pathway comprising portions of a first component and a second component. Low resistance pathway includes a flexible member such as a tab, which is held in contact with an interface surface of the adjacent component by a fastener to achieve a low bonding resistance therebetween. In the embodiment described, a portion of low resistance pathway is isolated from the remainder of assembly by one or more sealing feature(s) such as a groove. The groove is filled with sealant along its length to create a seal between the bonding interface and the remainder of first and second components. Sealing feature(s) and sealant seal low resistance pathway from environmental factors that could cause corrosion which would increase the resistance of the low resistance pathway between the first and second components. Low resistance pathway is additionally sealed from the environment surrounding assembly using a fillet of sealant extending along the edge(s) of low resistance pathway. Thus, low resistance pathway provides a localized bonding interface with low resistance between first component and second component. Isolating the low resistance pathway to a localized portion of the first and second component reduces costs by eliminating the need for larger amounts of sealant and one or more fasteners for a bonding strap associated with the prior art. Additionally, low resistance pathway can reduce the costs associated with manufacture and repair of assembly. 
         [0011]      FIG. 1  shows a perspective view of an assembly  10  with a split line  12  between a first component  14  and a second component  16 . In  FIG. 1 , assembly  10  is disassembled to illustrate portions of assembly  10  including a mounting flange  18 , apertures  20 A and  20 B, a sleeve  22 , and a low resistance pathway  24 . 
         [0012]    In the embodiment shown in  FIG. 1 , assembly  10  comprises a housing assembly for a component such as a motor, pump, or valve. Although described in reference to an aerospace industry application, the inventive concepts described are not limited to the aerospace industry and are applicable to industries where it is desirable to reduce the potential for an electrical short to ground failure mode. 
         [0013]    As shown in  FIG. 1 , assembly  10  is disassembled along split line  12  to provide access to internal components (not shown). In addition to housing various components, first component  14  has mounting flange  18  that extends circumferentially around first component  14  and projects radially outward therefrom. In the embodiment shown, mounting flange  18  has multiple apertures  20 A spaced therearound. 
         [0014]    Similar to first component  14 , sleeve  22  extends from second component  16 . Sleeve  22  extends circumferentially around second component  16  and projects axially outward therefrom. Sleeve  22  is sized to fit over the outer circumference of first component  14  when first component  14  and second component  16  are assembled. 
         [0015]    In the embodiment shown, sleeve  22  has multiple apertures  20 B spaced therearound. When second component  16  is assembled on first component  14 , apertures  20 A and  20 B are aligned and receive fasteners (not shown) therein to secure first component  14  to second component  16 . 
         [0016]    When assembled, portions of first component  14  and second component  16  (and mounting flange  18  and sleeve  22 ) interface and abut one another along split line  12 . In the embodiment shown, split line  12  comprises surfaces of mounting flange  18  and sleeve  22 . Although not shown in  FIG. 1 , a gasket or similar feature can be disposed along split line  12  to create a seal between first component  14  and second component  16 . 
         [0017]    As shown in  FIG. 1 , low resistance pathway  24  is segregated from the remainder of assembly  10  and comprises a small portion of mounting flange  18  and sleeve  22 . In the embodiment shown, low resistance pathway  24  takes up only a portion of assembly  10  and not the entire split line  12  as associated with the prior art. The size and number of bonding assemblies per component assembly will vary from embodiment to embodiment in order to achieve the desired resistance. Resistance of assembly  10  can be calculated utilizing commercially available software such as software available from ANSYS, Inc. of Canonsburg, Pa. 
         [0018]    By utilizing localized low resistance pathway  24 , the weight and cost of the assembly  10  can be reduced by eliminating the need for larger amounts of sealant and one or more fasteners associated with the prior art. Additionally, low resistance pathway  24  can reduce the costs associated with manufacture and repair of assembly  10 . 
         [0019]      FIGS. 2 and 2A  show low resistance pathway  24  formed between the first components  14  and second component  16 .  FIG. 2  shows an exploded view of low resistance pathway  24  and  FIG. 2A  shows the application of a sealant  26  to parts of the low resistance pathway  24 . In addition to sealant  26 , low resistance pathway  24  includes a sealing feature  28  such as a groove, a tab  30 , an interface surface  32 , a tab fastener  34 , a washer  36 , and a fillet  38 . Additionally,  FIG. 2A  illustrates a split line fastener  40  in close proximity to low resistance pathway  24 . 
         [0020]    Second component  16  has multiple apertures  20 B spaced therearound. Similarly, first component  14  has multiple apertures  20 A spaced therearound. When second component  16  is assembled on first component  14 , (as shown in  FIG. 2B ) apertures  20 A and  20 B are aligned and receive fasteners  40  therein to secure first component  14  to second component  16 . 
         [0021]    In the embodiment shown, low resistance pathway  24  is disposed at the outer circumference of assembly  10 . In other embodiments, low resistance pathway  24  can be disposed at other locations along split line  12  such as an inner circumference. As shown in  FIG. 2A , sealant  26  is disposed around the periphery of low resistance pathway  24  and is disposed in sealing feature  28 . The amount (thickness, width, and height) of sealant  26  applied will vary with environment and application and should be sufficient to provide for a durable environmentally resistant bond. The type of sealant  26  can vary depending upon the application environment to which assembly  10  is exposed. In one embodiment, sealant  26  comprises a fire resistant silicone sealant such as DAPCO® 2100 primerless silicone sealant manufactured by Cytec Industries Inc. of Woodland Park, N.J. DAPCO 2100 has fire resistance up to 3500° F. (1925° C.) and it has a fluid resistance to phosphate ester fluids. 
         [0022]    Sealing feature  28  comprises a machined groove that extends uninterrupted from a first edge of low resistance pathway  24  to a second edge of low resistance pathway  24 . Sealing feature  28  allows sealant  26  to be disposed along an internal edge of low resistance pathway  24 . As previously discussed sealing feature  28  is filled with sealant as shown in  FIG. 2A  to form a seal between low resistance pathway  24  and the remainder of assembly  10  and between the external environment and low resistance pathway  24 . The size of sealing feature  28  will vary with environment and application and should be sufficient to provide for a durable environmentally resistant bond. Although shown as a single groove along second component  16 , sealing feature  28  can comprise other structures capable of aiding to form a seal such as multiple grooves, tongue and groove, or the like. Sealing feature  28  can be disposed on first component  14 , second component  16 , or both first and second components  14  and  16  as desired. 
         [0023]    Sealing feature  28  is disposed below an inner portion of tab  30 . Tab  30  comprises a thin flexible member with reduced stiffness compared to other portions of mounting flange  18  ( FIG. 1 ). Thus, tab  30  deflects under the clamping force applied by tab fastener  34  to contact interface surface  32  of second component  16 . By allowing tab  30  to flex under the clamping force applied by tab fastener  34 , (through washer  36 ) flexible tab  30  allows the majority of the housing clamping pressure and vibration loads to be carried by split line fasteners  40  (only one is shown in  FIGS. 2 and 2A ) connecting first component  14  to second component  16 . Contact between tab  30  and interface surface  32  and between tab fastener  34  and second component  16  provides a low resistance pathway between first component  14  and second component  16 . 
         [0024]    As shown in  FIG. 2A , tab  30  has a smaller size than interface surface  32  such that interface surface  32  extends past the outer edge of tab  30  to form a ledge feature  37  between the tab  30  and interface surface  32  when first component  14  is mounted to second component  16 . This ledge surface allows sealant  26  to be placed around the edge of tab  30  (and along the edge of interface surface  32 ) to form fillet  38 . Fillet  38  of sealant  26  provides a durable seal from the environment surrounding assembly  10 . Thus, fillet  38  and sealing feature  28  allow sealant  26  to be disposed entirely around tab fastener  34  to isolate tab fastener  34  from the remainder of assembly  10  and external environment. 
         [0025]    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.