Abstract:
An apparatus for connecting a plurality of conductors in a cable to a corresponding mating includes a plurality of crimp contacts, a plastic nose insert, an elastomeric nose and a pair of plastic body housings that attach together in a clamshell fashion and in which the conductors are contained and attached. A strain relief assembly is provided that is used to urge the apparatus into a position of mating and which automatically increases the strain relief that is provided whenever slack develops by the use of a plurality of fingers and tapered ratcheting teeth. Various methods of reducing shear intermediate the pair of body housings are disclosed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention:  
           [0002]    The present invention, in general, relates to electrical connectors and, more particularly, to electrical connectors that are used to supply electrical power to an aircraft and which are field-replaceable.  
           [0003]    In order to energize the electrical systems of an aircraft without running a generator on-board the aircraft, an electrical cable is used to supply 400 Hz electrical power to the aircraft. Typically, the electrical power that is supplied is three phase and is at approximately 200 volts (AC).  
           [0004]    The mating interface on the plug on the end of the cable which mates to the aircraft is standardized by adherence to U.S. Military Specification MIL-C7974.  
           [0005]    Switches are sometimes installed in the connector plug and are used to actuate a device to extend or retract additional lengths of cable off of a spool or to cycle power to the aircraft through the cable at appropriate times. For example, it is not appropriate to supply electrical power the moment an electrical connection is made because this can damage the electrical contacts.  
           [0006]    Similarly, it is not appropriate to use physical disengagement of the connector as a means of withdrawing electrical power from the aircraft. As is well known in the electrical arts, this will cause arcing to occur and will in turn damage the electrical contacts.  
           [0007]    A plurality of switches (typically up to four switches) and a plurality of lights (to indicate switch function, power status, or other) may optionally be included in these and various types of connectors.  
           [0008]    To cycle power, “on” and “off” switches are used to energize and de-energize a relay at the source of electrical power on the ground. The “on” switch can then be depressed to energize power to the aircraft only after the connector is properly mated to the aircraft and, conversely, the “off” switch can be depressed to de-energize electrical power before any attempt is made to remove the connector from the aircraft.  
           [0009]    The on and off switches are optional in these types of connectors. The use of a recessed contact is also generally used in these types of connectors to prevent the application of electrical power to the aircraft until a sufficiency of mating amongst the contacts that actually supply electrical power to the aircraft has first been accomplished.  
           [0010]    However, the defect to this purely mechanical approach to regulating the application of electrical power to the aircraft is that if a person abruptly jerks the connector apart from the aircraft, there remains the potential for damage to occur to the contacts as a result of the subsequent arcing that is likely to occur.  
           [0011]    The other common types of switches are typically labeled “in” and “out”. When the “in” switch is depressed, the spool will wind in such a direction so as to retract the cable and when the “out” switch is depressed, the spool will unwind and spool out additional cable to reach the aircraft. A cable hoist is often used in place of a spool, with the same effects.  
           [0012]    Often, the plug that is disposed at the end of the electrical cable is molded (i.e., it is made of a type of rubber) and it is permanently attached to the cable by the manufacturer. Therefore, it cannot be replaced in the field. A molded plug that is durable and can be replaced in the field is desirable.  
           [0013]    It is far more likely that defects will arise in or proximate the connector than elsewhere in the cable itself. Obviously, if a defect should arise in the connector, it is advantageous to be able to replace the connector instead of the entire cable. Such a connector is known in the arts as one that is “field attachable” or “field replaceable”.  
           [0014]    It is known according to the present state of the art to utilize a replaceable contact section, sometimes called a “nose”, as is disclosed in U.S. Pat. No. 4,758,175 and which is incorporated by reference herein. This permits the end user to replace this portion of the connector when needed due to abrasion or other types of damage that may occur.  
           [0015]    The preceeding type of nose is typically attached to a another component, a nose insert that is surrounded by a split two-part plastic body housing which is filled with epoxy that is allowed to flow into the housing through the switch hole(s). There are problems associated with this approach.  
           [0016]    The first is that the two-part plastic body housing does not provide an adequate seal to prevent epoxy from leaking out. While not posing a problem in performance, this is undesirable from an aesthetic point of view.  
           [0017]    Also, the plastic that the body housing is made of tends itself to loosen and wear over the course of time. As such, it may develop slack. A strain relief is typically added as well and it serves to limit the bend radius.  
           [0018]    A maintenance schedule may be established to periodically tighten any clamps or screws and to take up slack that may develop (due to a general loosening or wear).  
           [0019]    However, there is no way to really know if any established maintenance schedule is correct. If maintenance is done too often, there is an excess of labor. If it is not done often enough, the result is ineffective strain relief and premature wear and failure. Without adequate strain relief when removing the cable from the aircraft, the person may be pulling on the individual conductors, rather than on the jacket and connector. This can cause premature wear and conductor failure to occur.  
           [0020]    Also, due to size constraints, the plastic body housing is thin and the two halves may move in shear with respect to one-another. The two halves may also tend to separate and, as mentioned hereinabove, epoxy may tend to leak out before it has fully set.  
           [0021]    The epoxy potting is necessary in order to meet the required specifications and also to provide the durability that is needed. These connectors may, for example, be dropped, dragged, or run over by machinery that is being operated nearby (e.g., ramp tractors). Therefore, the connectors must be resistant to crushing and also to other types of severe loading that they may experience.  
           [0022]    Also, when these connectors are inserted (or withdrawn), a great deal of force is typically required, a force that is normally measured in the “tens” of pounds. The force to insert the connector into the aircraft can even approach or exceed one-hundred pounds of force. Field personnel expect this and it is not an issue other than to note that these connectors are subject to substantial forces that occur during their insertion and removal.  
           [0023]    The aforementioned problems and requirements for connecting power to an aircraft tend to be extreme and therefore are poised to maximally benefit from the instant disclosure. However, the invention is applicable, as desired, for use in various applications other than those involving aircraft. In general, wherever a durable field replaceable type of a connector is required, the benefits and uses as disclosed herein, apply.  
           [0024]    Accordingly there exists today a need for a field attachable electrical connector &amp; self-tightening method of strain relief that helps to reduce the aforementioned problems.  
           [0025]    Clearly, such an apparatus would provide a useful and desirable device and method.  
           [0026]    2. Description of Prior Art:  
           [0027]    Electrical connectors are, in general, known. While the structural arrangements of the known types of devices, at first appearance, may have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0028]    It is an object of the present invention to provide a field attachable electrical connector that can be replaced in the field.  
           [0029]    It is also an important object of the invention to provide a field attachable electrical connector that is durable.  
           [0030]    Another object of the invention is to provide a field attachable electrical connector that includes means for resisting motion between two halves of a body housing in shear.  
           [0031]    Still another object of the invention is to provide a field attachable electrical connector that includes means for resisting separation from occurring between two halves of a body housing.  
           [0032]    Still yet another object of the invention is to provide a field attachable electrical connector that provides a method for adjusting the amount of strain relief automatically during normal use.  
           [0033]    Yet another important object of the invention is to provide a field attachable electrical connector &amp; self-tightening method of strain relief that uses the force that is required to insert the connector into the aircraft to automatically take up (i.e., compensate) for any slack that may have occurred over time and use.  
           [0034]    Still yet another important object of the invention is to provide a field attachable electrical connector &amp; self-tightening method of strain relief that is adapted to satisfy the requirements of U.S. Military Specification “MIL-C-7974”.  
           [0035]    Briefly, a field attachable electrical connector &amp; self-tightening method of strain relief that is constructed in accordance with the principles of the present invention has a split plastic body housing consisting of two halves that includes a pair of retaining grooves on each of the two halves, the retaining grooves being adapted to fill with epoxy and to retain the two halves adjacent to each other. A plurality of pins on one of the halves fits into a plurality of holes on the remaining one of the halves when the two halves are adjoined, thereby reducing shear. The body housing is adapted to contain a plastic nose insert, an elastomeric nose, a plurality of crimp contacts, a plurality of switches and lights, and the necessary wiring. When the two halves are properly oriented adjacent to each other, a distal end of each of the two halves that is disposed opposite to that where the elastomeric nose is disposed includes a ratcheting cable retention system. The ratcheting cable retention system provides automatic adjustment of a strain relief that passes over the cable. The strain relief is pressed over a plurality of fingers that are attached to the two halves of the body housing. The strain relief thereby serves to retain the distal ends adjacent to each other. Furthermore, the strain relief cooperates with a tapered ratcheting system on the fingers so that when the connector is pushed into the aircraft the strain relief is grasped and is used to push the connector into mating with the aircraft. Any slack that may have developed over time between the fingers and the cable that is disposed under the fingers is automatically removed by the strain relief being urged closer to the two body halves, thereby tightening the fingers against the cable. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]    [0036]FIG. 1 is an exploded view in perspective of the field attachable electrical connector &amp; self-tightening method of strain relief.  
         [0037]    [0037]FIG. 2 is an enlarged cross sectional view taken along the line  2 - 2  in FIG. 1, except that the two halves of the body housing are shown together in this view.  
         [0038]    [0038]FIG. 3 is an enlarged cross-sectional view of a portion of one of the fingers as shown in FIG. 1 with typical dimensions.  
         [0039]    [0039]FIG. 4 is a partial cross-sectional view of the strain relief of FIG. 1.  
         [0040]    [0040]FIG. 5 is a partial cross-sectional view of the compression ring of FIG. 4 with typical dimensions.  
         [0041]    [0041]FIG. 6 is an enlarged cross-sectional view of “Detail A” of FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]    Referring on occasion to all of the FIGURE drawings and now in particular to FIG. 4 is shown, a field attachable electrical connector &amp; self-tightening method of strain relief, identified in general by the reference numeral  10 .  
         [0043]    A first half of a body housing  12  mates with a second half of a body housing  14 . The first and second halves of the body housing  12 ,  14  are typically formed of a suitable plastic.  
         [0044]    The first and second halves of the body housing  12 ,  14  are preferably identical in construction (to minimize the number of different component parts) and, as shown, are rotated 180 degrees about a center longitudinal axis.  
         [0045]    A nose insert  16  is also typically formed of a suitable plastic. The nose insert  16  partially fits into a first end  18  of nose  20  as shown by arrow  21 . The nose  20  is preferably formed of an elastomer, such as rubber.  
         [0046]    A plurality of crimp contacts  22  (only one is shown) of various sizes are used. The crimp contacts  22  are normally formed of copper.  
         [0047]    Each of the crimp contacts  22  are normally crimped onto an end of each appropriate conductor by a standard crimping operation, as is well known in the arts. Then they are each inserted into the back of the nose insert  16 , as shown by arrow  24 .  
         [0048]    The elastomeric nose  20  is secured to the nose insert  16  by sealing screws (not shown) that enter in through certain of the holes on a side opposite the first end  18  of the nose  20 . The sealing screws then engage threads in the bottom of each of the crimp contacts  22 .  
         [0049]    The sealing screws each include an elastomeric seal under the screw head and therefore also provide a water barrier as well as securing the nose  20  to the nose insert  16 .  
         [0050]    The first half of the body housing  12  includes a plurality of first pins  26  that protrude from one end thereof and which each enter into one of a plurality of first holes  28  on the second half of the body housing  14 .  
         [0051]    The second half of the body housing  14 , on a side opposite that of where the first holes  28  are disposed, includes a plurality of second pins  30 . The second pins  30  are similarly to the first pins  26 . The second pins  30  each enter into one of a plurality of second holes  32  that are included on the first half of the body housing  12 .  
         [0052]    When the first and second halves  12 ,  14  are assembled together, the first and second pins  26 ,  30  and the first and second holes  28 ,  32  cooperate to provide resistance to shear from occurring between the two halves  12 ,  14  as well as providing a tight fit and proper alignment of each of the halves  12 ,  14  along a perimeter thereof with respect to each other.  
         [0053]    The first and second halves  12 ,  14  are assembled in a “clamshell” configuration around a cable (not shown). The cable includes a cable jacket which surrounds the cable (i.e., wire) conductors.  
         [0054]    The cable and cable jacket pass through a strain relief assembly  34 . The strain relief assembly  34  is described in greater detail hereinafter. The conductors of the cable are each attached to one of the crimp contacts  22 , as was described hereinabove.  
         [0055]    Certain of the conductors that are provided in the cable are attached to lights and switches (not shown) that were described hereinabove in the “BACKGROUND OF THE INVENTION” section.  
         [0056]    The lights and switches are each attached to the first and second halves  12 ,  14  through a plurality of accessory mounting holes  36 . The accessory mounting holes  36  may include “knockouts” that are removed, as desired, to accommodate any of the lights and switches.  
         [0057]    The nose insert  16  includes a pair of protrusions  38  on each side thereof (only one side is shown) that align with a pair of corresponding recesses  40  on the first and second halves  12 ,  14 .  
         [0058]    Each of the pair of protrusions  38  includes a threaded insert that is adapted to receive a mounting screw (not shown) that passes through a hole provided in each of the corresponding recesses  40 . The mounting screws secure the first and second halves  12 ,  14  to the nose insert  16  and also retain the first and second halves  12 ,  14  adjacent to each other.  
         [0059]    Both of the pairs of protrusions  38 , the recesses  40 , and the mounting screws cooperate together thereby serving to provide resistance to shear proximate the nose insert  16 .  
         [0060]    Referring now also to FIG. 2, a retaining groove  42  is disposed on each end of each of the first and second halves  12 ,  14 . A larger groove  44  is provided on each end of the nose insert  16 .  
         [0061]    After the connector  10  is assembled, an epoxy potting compound  46  is poured in through one or more of the accessory mounting holes  36  and is allowed to harden (typically overnight) before the connector  10  is used.  
         [0062]    The epoxy potting compound  46  passes around a pair of arcuate terminations  48  (i.e., lips) in each of the retaining grooves  42  and forms a generally “C” shaped cross section of the epoxy potting compound  46  that, when hardened, resists separation of the two halves  12 ,  14  in this area.  
         [0063]    During assembly of the connector  10 , the strain relief assembly  34  is slid in a first direction along a longitudinal axis of the cable. The strain relief assembly  34  is urged in the first direction over the cable and it is forced over a plurality of fingers  50 , to which it is secured by a plurality of first ratcheting teeth  52  on the fingers and a plurality of corresponding second ratcheting teeth  54  on a circular metallic insert  56  that is molded into the strain relief assembly  34 .  
         [0064]    Accordingly, the strain relief assembly  34  is adapted for longitudinal movement in the first direction but is prevented from longitudinal movement in a direction that is opposite that of the first direction. See also FIG. 3 through FIG. 6 inclusive.  
         [0065]    The metallic insert  56  is preferably formed of an aluminum alloy and it preferably includes a diamond knurl finish  58 .  
         [0066]    A contoured and tapered casing  60  is formed of an elastomer (i.e., rubber) and is molded around the metallic insert  56 . As the cross-sectional view of FIG. 4 shows, the metallic insert  56  is solidly embedded in the casing  60  and would resist any longitudinal displacement with respect to the casing  60 . The diamond knurl finish  58  further serves to secure the metallic insert  56  to the casing  60 .  
         [0067]    The casing  60  provides a gradual bend radius which protects the cable from being bent at too sharp of an angle proximate the connector  10 .  
         [0068]    The casing  60  also allows for a comfortable grip and it is used to push the connector  10  into a mating position with a corresponding connector half (not shown) that is typically disposed on an aircraft frame (not shown).  
         [0069]    During initial assembly of the connector  10 , the casing  60  is forced over the fingers  50  with a sufficient force so as to cause each of the fingers to bend in toward the cable.  
         [0070]    Each of the fingers  50  includes on an inside radius thereof, a plurality of gripping teeth  62 . When the casing  60  is urged toward the connector  10 , the metallic insert  56  is forced over the fingers  50 .  
         [0071]    As the decreasing taper of the second ratcheting teeth  54  of the metallic insert  56  are forced over the first ratcheting teeth  52  of the fingers  50 , the overall outside diameter of the plurality of fingers  50  is progressively reduced.  
         [0072]    The gripping teeth  62 , in turn, are urged to increasingly bite into the cable jacket thereby serving to secure the connector  10  to the cable and providing improved strain relief functioning. When sufficient force is applied to the casing  60  the gripping teeth  62  will be urged into optimum contact with the cable jacket.  
         [0073]    When the casing  60  is then used to urge (i.e., push) the connector  10  into the aircraft, the force that is applied to the casing  60  is evenly distributed through the connector  10  and the cable jacket. This prevents the application of an excessive force directly to the individual wire conductors that could result in premature failure of the connector  10  or the cable within the connector  10 .  
         [0074]    Over the course of time and use, it is possible for a mechanically attached strain relief to loosen. Each time the connector  10  is inserted into the aircraft, considerable force is applied to the casing  60  which again tends to urge the casing  60  further toward (and over) the fingers  50 .  
         [0075]    If sufficient slack has developed so that maintenance (i.e., tightening) of the strain relief assembly  34  is required, this is accomplished automatically and at precisely the proper time when it is needed.  
         [0076]    This occurs, substantially unnoticed, in that when adjustment is required, the force that is applied to the casing  60  when the connector  10  is being inserted into the aircraft will cause the second ratcheting teeth  54  on the inside of the metallic insert  56  to pass over one, or possibly two, more of the first ratcheting teeth  52  of the fingers  52 . This, in turn, further urges the gripping teeth  62  to bite (clamp) down onto the cable jacket.  
         [0077]    Accordingly, the need to periodically tighten (i.e., maintain) the strain relief assembly  34  is eliminated as a separate task because it is automatically accomplished whenever it is required simply during normal use (i.e., insertion) of the connector  10 . Optimum levels of strain relief are always provided without the need for additional maintenance.  
         [0078]    Over the useful life of the connector  10 , only a small amount of displacement (in the first direction) of the strain relief assembly  34  will occur or is needed to ensure a proper level of strain relief.  
         [0079]    Replacement of the field attachable electrical connector  10  is accomplished by cutting the old connector  10  off of the cable and stripping the conductors (as is well known in the arts) of the cable and by repeating the assembly process as described hereinabove with a new connector  10 .  
         [0080]    Lastly, a new quantity of the epoxy potting compound  46  is then poured into the new connector  10  to fill the voids and recesses therein and it is allowed to harden prior to using the new connector  10 .  
         [0081]    The invention has been shown, described, and illustrated in substantial detail with reference to the presently preferred embodiment. It will be understood by those skilled in this art that other and further changes and modifications may be made without departing from the spirit and scope of the invention which is defined by the claims appended hereto.