Abstract:
An ignition lead that includes at least one terminal assembly having a replaceable terminal contact that provides a simple means of replacing worn contacts without removal and replacement of the entire ignition lead. The terminal assembly includes the replaceable contact which threads onto a contact body located within a tubular insulator. A retaining ring attaches to the contact to hold the insulator in place over the contact body. The contact can include a groove that extends around the contact to receive the retaining ring. Replacement of the contact involves removing the retaining ring from the groove in the contact, sliding the insulator off the terminal assembly, unthreading the worn contact, threading on a replacement contact, reassembling the insulator onto the assembly, and then securing the insulator in place by snapping the retaining ring back into the groove on the replacement contact.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of U.S. Provisional Patent Application No. 60/472,606 filed May 22, 2003, the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to ignition leads used with igniters in reciprocating and gas turbine engines and, more particularly, to the terminal contacts used on such ignition leads. 
     BACKGROUND OF THE INVENTION 
     An ignition lead is a high voltage cable (typically 2–25 kV) used to deliver high voltage ignition pulses from an ignition system to some type of ignition device, which in turn uses the ignition pulses to generate sparks for igniting a fuel/air mixture. Due to the high voltage involved, electrical contacts of the ignition lead are susceptible to damage and often wear out before the other ignition lead components. Two such contacts are the terminal contacts located at each end of the ignition lead, one of which is a first terminal contact connecting a component of the ignition system, such as an exciter circuit, to the insulated center wire of the ignition lead, and the other of which is a second terminal contact connecting the center wire to an ignition device, such as a spark plug or igniter. With many ignition lead designs, if either of these terminal contacts become worn out, a time consuming and costly maintenance procedure is required to replace them. 
     Conventional ignition lead terminal contacts are not replaceable. Thus, when the contact wears out, the entire terminal assembly, or worse yet, the entire ignition lead may need to be replaced. This is particularly costly in applications having ignition leads of great length, sometimes exceeding twenty-five feet or more. Moreover, the time required by a skilled mechanic to replace an entire ignition lead, particularly in a gas turbine application, can be as much as four hours in some instances. 
     Replaceable terminal contact assemblies for ignition leads are known in the art, an example of which is built by Champion Aerospace Inc. of Liberty, S.C., for ARP670 type 2f termination. This replaceable contact assembly  10  is shown in  FIG. 1  and generally includes a contact body  12  and a replaceable tubular connector  14 . Contact body  12  is a generally cylindrical metallic component having a blind hole  20  extending into an upper axial end and a threaded male portion  22  extending from a lower axial end. The blind hole is designed to permanently receive the stranded center wire  24  of the ignition lead by crimping the contact body around the wire and firmly retaining it in place (as demonstrated by the illustrated deformation of contact body  12 ). The exterior threads of male portion  22  are threaded into replaceable tubular connector  14 , which generally includes a longitudinal bore  30  having a threaded female portion  32  located at its upper axial end and an opening  34  located at its lower axial end. The threads of male portion  22  are sized to fit those of female portion  32  such that the replaceable tubular connector  14  can be threadingly attached and removed from the permanently attached contact body  12 . Opening  34  is sized to receive an electrode of an igniter such that the high voltage pulse passing through contact assembly  10  is transmitted to the igniter. Other components, such as an insulator  36  and various connection pieces, are also seen in the drawing and are well known in the art. According to this design, when the terminal contact needs replacement, the tubular connector  14  is simply unthreaded from the contact body and a new connector is installed. 
     It is a general object of the invention to provide a replaceable contact assembly that can be used not only for ARP670 type 2f termination, but also for a wide variety of other types of ignition lead termination including, for example, other ARP670 termination designs. 
     SUMMARY OF THE INVENTION 
     The present invention provides an ignition lead and a replaceable terminal contact therefor, as well as a method of manufacturing the ignition lead and replacing the terminal contact. The ignition lead includes at least one terminal assembly having a replaceable contact that is threaded or otherwise removably attached to a contact body located within a tubular insulator. A retaining component attaches to the replaceable contact to hold the insulator in place over the contact body. The terminal contact itself includes a connecting feature, such as threads at one end of the contact, to permit it to be secured to the contact body, and the contact can include a groove that extends at least partially around the contact at a location intermediate the two ends of the contact. Replacement of the contact involves removing the retaining component, sliding the insulator off the terminal assembly, disconnecting the worn contact, removably attaching a replacement contact, reassembling the insulator (or a replacement one) onto the assembly, and the securing the insulator in place by reattaching the retaining component (or a replacement one) onto the replacement contact. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred exemplary embodiment of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein: 
         FIG. 1  is a cutaway view of a prior art replaceable ignition lead terminal assembly; 
         FIG. 2  is a cutaway view of a preferred embodiment of an ignition lead terminal assembly of the present invention; 
         FIG. 3  is a sectional view along lines  3 — 3  showing the retaining ring of the ignition lead terminal assembly of  FIG. 2 , and; 
         FIG. 4  is a top-down view of an alternative embodiment of a retaining ring that may be used in the ignition lead terminal assembly of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The terminal assembly described herein utilizes a replaceable contact for one or more terminal ends of the center wire of an ignition lead. For a standard ignition lead having two ends each with a connector, the replaceable terminal design described below can be used at one or both of the connectors. The ignition lead can be used with various ignition circuit components such as an exciter circuit or an ignition device such as a spark plug or an igniter; however, these are but a few of the components that could be used in connection with the ignition lead described herein. Furthermore, the terminal assembly can be used in conjunction with a wide array of engines, but is particularly advantageous when used with either an aircraft reciprocating or gas turbine engine. Because the present invention is primarily concerned with the contact portion of the disclosed terminal assembly, no description is provided for the other components seen in the figures, or for the other portions of the ignition lead not shown in the figures. Such other components and portions of the ignition lead are known to those skilled in the art. 
     Referring now to  FIG. 2 , an embodiment of the present invention is shown in the form of an ignition lead  40  that includes an insulated center wire  42  and a terminal assembly  44 . Center wire  42  can be solid core or stranded wire, and includes a bare terminal end  46 . Terminal assembly  44  includes a connector  48  along with a tubular insulator  50  that provides electrical isolation between the connector  48  and the terminal contact components. These components include a contact body  52  securely attached to the center wire  46 , a replaceable contact  54  threaded onto the contact body  52 , and a retaining component  56  which maintains the insulator  50  in place over the terminal contact components. 
     Contact body  52  is a generally cylindrical, electrically conductive metallic component designed to couple center wire  46  of the ignition lead  40  to the replaceable contact  54 . Contact body  52  can be made from 303 stainless steel or any other suitable material. The contact body generally includes a first blind bore  62  at an upper axial end and a second blind bore  64  at a lower axial end. The upper blind bore  62  is designed to receive the bare end  46  of the center wire and permanently attaches over the exposed end  46  by brazing, crimping, or any other suitable means. By “permanently” it is meant that the components are secured by any means of connection that is not intended to be removable, such as by crimping, soldering, brazing, or conductive adhesive. This is to be contrasted with the term “removably” which, as used herein, means that the components are secured together in a manner that permits subsequent separation of the components without damaging or substantially deforming them. This can include the threaded connection of the illustrated embodiment as well as snap fit connections or mating connections that utilize a third component to maintain the parts together. 
     This permanent connection of the center wire  46  and contact body  52  forms a secure mechanical and electrical connection. At the opposite axial end of the contact body  52  is the lower blind bore  64 . This bore is provided with internal (female) threads for connecting to replaceable contact  54 . It is worth noting that the contact body shown here is simply a preferred embodiment that has been provided for exemplary purposes and to which numerous modifications could be made. For instance, instead of having two blind bores  62  and  64 , each of which only extends inwardly by a certain axial length, there could be a single longitudinal bore that extends the entire axial length of the contact body such that it accommodates both the center wire  46  and replaceable contact portion  54 . Furthermore, rather than providing a contact body with a female portion and a replaceable contact with a male portion, the contact body could be equipped with a downwardly extending male portion and, in turn, the replaceable contact would have the female portion. These are just a few of the modifications that can be utilized without departing from the scope of the present invention. 
     Replaceable contact  54  is an electrically conductive component designed to couple contact body  52  to an ignition device or other circuitry such that the contact  54  may be easily replaced. Preferably, the replaceable contact is a plug-like component generally including a threaded axial end  70 , a circumferential groove  72  and a contact surface  74 . As previously discussed, threaded axial end  70  is a male portion designed to thread into female portion  64  such that the two components are firmly, yet removably attached to one another. These threads on contact  54  are a connecting feature of that component which permits it to be removably attached to the contact body  52 , and it will be understood that snap connections and other types of connecting features can be used without departing from the scope of the invention. The circumferential groove  72  extends around the outer surface of the replaceable contact portion at a location intermediate the two ends  70 ,  74  of the contact. This groove  72  is sized to receive retaining component  56 . Thus, the exact shape and size of the groove is largely dependent upon the particular retaining component used. Contact surface  74  is the surface to or from which the high voltage ignition pulse either enters or leaves the ignition lead, depending on whether terminal assembly  44  is being used to couple the ignition lead to an ignition circuit or an ignition device, respectively. This surface is susceptible to pitting, corrosion and other consequences of high voltage use, and is typically the portion of the ignition lead that wears out first and needs replacement. Preferably, this contact  54  is made from Inconel™ 600. If desired, precious metal inserts or other arc resistant or Corona resistant materials can be used to improve the operation and/or functionality of the terminal assembly  44 . Again, the specific embodiment of replaceable contact  54  shown here has been provided as an example with numerous other variations being possible. For example, the threaded end  70  or the entire replaceable contact  54  could be plated to help prevent thread seizure or to affect other attributes of the contact. Contact surface  74  could be convex, concave, pointed, or have one of numerous other contours. Furthermore, the circumferential groove need not extend entirely around the outer surface of the contact, but could vary from that shown in order to accommodate retaining rings of numerous designs, shapes and sizes, as will now be discussed. 
     In the illustrated embodiments, retaining component  56  comprises a retaining ring, or snap ring, that snaps into groove  72 . The retaining ring  56  is formed from a resilient metallic material such as PH 15-7MO which is known in the art, and it attaches to the replaceable contact  54  such that it maintains the cylindrical insulator  50  in place. According to the embodiment shown in  FIG. 3 , the retaining component  56  is an E-ring that includes an opening  100 , end tangs  102  and  104 , and a center tang  106 . During installation of the retaining component, end tangs  102  and  104  are spread, preferably by manual force, such that opening  100  is made large enough to fit around the replaceable contact  54  and firmly seat within groove  72 . Once installed in groove  72 , the end tangs  102 ,  104  and center tang  106  are the only portions of the E-ring that contact the outer surface of the replaceable contact  54 , which, as seen in  FIG. 3 , has a circular cross-section. The E-ring embodiment of  FIG. 3  is but one example of the type of retaining component that could be used. Alternative retaining components, such as gapped, continuous, and other standard retaining rings offered by ring manufacturers such as Smalley Steel Ring Co., could also be used with the terminal assembly  44 . For instance,  FIG. 4  shows an alternative retaining component embodiment that is in the form of a C-ring. This C-ring embodiment operates largely the same as that of  FIG. 3 , but includes an opening  82  and end tangs  84 ,  86 . As indicated in the Figure, the C-ring does not include a center tang. Both the E-ring and C-ring embodiments of the retaining component  56  are free to rotate within groove  72 . 
     The function of the retaining ring  56  is to captively hold the insulator in place over the otherwise exposed high voltage components; namely, the bare end  46  of the center wire, the contact body  52 , and the upper portion of contact  54 . The insulator is retained in place between the retaining ring  56  and a portion of the terminal assembly  44 . More specifically, the connector  48  includes a hex  90  and coupler  92  that secures the hex  90  to the insulated center wire  42 , while permitting rotation of the hex  90  so that the terminal assembly  44  can be threaded onto a mating component, be it an ignition device or a mating socket connector. Housed within the coupler  92  is a spring  94  and a washer  96 . The spring  94  extends about the center wire  42  between a back wall  98  of the coupler and the washer  96 . This spring is, but need not be, under compression so that it presses washer  96  and, thus insulator  50 , axially toward retaining ring  56 . When the terminal assembly  44  is coupled to an ignition device, such as an igniter or spark plug, this axial force against the retainer ring causes replaceable contact  54  to firmly press against the terminal contact of the ignition device with which the terminal assembly is coupled; a significant contact-to-contact load is desirable. As will be appreciated by those skilled in the art, when connector  48  is tightened onto an ignition device or other mating socket connector, spring  94  is forced into greater compression which helps retain the insulator  50  tightly in place and improves the contact-to-contact load mentioned above. To hold the spring  94  and washer  96  in place during removal of the contact  54  and insulator  50 , a spring retainer  88  is used to snap into the coupler  92 . Spring retainer can be made from copper alloy C11000. The other components of connector  48  can be made of suitable materials that will be known to those skilled in the art. 
     Having described in detail the construction of the terminal assembly  44  for ignition lead  42 , it will be appreciated that the ignition lead can be manufactured using a suitable assembly process, such as the following. First, the connector  48  with all of its components is assembled onto the end of the insulated center wire  42 . Then, the contact body  52  is permanently attached to the bare end  46  of the center wire. The terminal contact  54  is then threaded onto the contact body. The insulator  50  is then placed over the contact body  52  and is secured in place by attaching the retaining ring  56  to the terminal contact. This last step can be done by snapping the retaining ring  56  into the groove  72 , although it will be appreciated that other retaining components that attach to the contact  54  in other ways (so that no groove  72  is needed), can be used in lieu of retaining ring  56 . 
     During replacement, a worn out contact  54  is removed from the terminal assembly  44  and a new one is installed. The first step in the replacement of a worn out contact  54  is to remove the retaining ring  56 . Depending on the particular design of the retaining ring, removal can typically be accomplished with a pair of pliers or similar tool. In the both the E-ring and C-ring embodiments of  FIGS. 3 and 4 , respectively, a mechanic can grasp one or more of the end tangs  102 ,  104 ,  84 ,  86  with a pair of needle-nosed pliers or similar tool, and spread them apart so that the ring  56  can be pulled off of the worn out terminal contact  54 . With the retaining ring removed, the tubular insulator  50  may simply be slid off of the terminal assembly  44 , thereby exposing the contact body  52  and replaceable contact  54 . With the exterior surface of both of these components exposed, the mechanic can grasp each of them with a tool, such as a wrench, and unscrew the replaceable contact  54  from the contact body  52 . A new replacement contact  54  is then threaded onto contact body  52  and torqued to a desired value. Subsequently, the original insulator or a replacement one is slid back over top of terminal assembly  44 , against the downward spring bias of spring  94 , and pushed upwards such that the retaining ring  56  may again be installed within the circumferential groove. Either the original retaining ring  56  or a replacement one can be used. A significant advantage of this arrangement is that the total replacement time for a worn contact can be as short as fifteen minutes, although the actual replacement time can of course be dependent on a variety of factors. 
     It will thus be apparent that there has been provide in accordance with the present invention an ignition lead and replaceable terminal contact therefor which achieves the aims and advantages specified herein. It will, of course, be understood that the foregoing description is of a preferred exemplary embodiment of the invention and that the invention is not limited to the specific embodiment shown. Various changes and modifications will become apparent to those skilled in the art. For example, although the contact body  52  is shown herein as being directly connected to the center wire  46 , it will be appreciated that it can be connected to the center wire indirectly, such as via one or more other electrically conductive components. All such changes and modifications are intended to be within the scope of the present invention. 
     As used in this specification and appended claims, the terms “for example,” “for instance,” and “such as,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that necessarily requires a different interpretation.