Electrical-interconnection assemblies and methods of forming interconnections therein
This invention relates to electrical interconnection assemblies, and to methods of forming interconnections therein. 
     The invention is particularly, though not exclusively, applicable to the establishment of interconnections between the thin conductors of a thermocouple and the thicker conductors necessary for connecting the thermocouple to an external temperature-measuring circuit. 
     Difficulty has been experienced in the past in establishing electrical interconnection between electrical conductors of significantly differing diameter, especially where very thin conductors are involved and it is necessary for the interconnection to withstand stresses caused by vibration and temperature changes, such as, for example, those experienced within a gas-turbine engine. 
     It is an object of the present invention to provide an interconnection assembly including an electrical interconnection and a mechanical support for the conductors so that the electrical connection is as far as possible not required to support the weight of the conductors nor to withstand shock forces transmitted through them. 
     According to one aspect of the present invention there is provided an arrangement including an electrical interconnection between two electrical conductors, in which the conductors extend from opposite directions into, and are retained by, a support member, wherein one of the conductors turns back on itself through the support member to emerge from the same direction as the other conductor and the interconnection is established by connection together of said other conductor and the emergent portion of said one conductor. 
     With such an arrangement, both conductors may be readily secured firmly within the support member, so that the electrical connection between the conductors can be to a large degree isolated from any movement of those conductors occuring away from the support member. The likelihood of degradation, or ultimately, fracture, of the electrical interconnection can accordingly be reduced using the arrangement of the invention. 
     The two conductors may be of the same diameter as one another, but the invention is of especial advantage when the diameters differ significantly from one another. In the latter case, the rigid mechanical support provided by the support member for the thicker conductor reduces to a significant extent flexing that may be transmitted through this conductor to the electrical connection from outside. Such flexing, which may arise from vibration, could be detrimental to the interconnection and cause fracture of the thinner conductor. 
     According to a further aspect of the present invention there is provided a method of forming an electrical interconnection between two electrical conductors, wherein a first conductor is passed from one direction through a support member and is retained therein with one end emergent therefrom, and electrical connection is established between this end and an end of a second conductor that is carried by the support member, the said second conductor extending through the support member from the opposite direction to said one direction and then turning back on itself through the support member to its said end. 
     With such a method the formed electrical interconnection tends to be isolated from the remainder of the two conductors so that connections may be made to them elsewhere with reduced risk of damage to the said electrical interconnection. 
    
    
     A thermocouple probe, which is for use in an aircraft gas-turbine engine and which includes an electrical interconnection, and a method of forming such interconnection, all in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a sectional side elevation of the thermocouple probe; 
     FIG. 2 is a section on the line II--II of FIG. 1, to an enlarged scale; 
     FIG. 3 is an enlarged perspective view of one end of the probe of FIG. 1, before final encapsulation of the probe; and 
     FIG. 4 is an enlarged sectional view of the probe taken on the line IV--IV of FIG. 1. 
    
    
     Referring to FIGS. 1 and 2, the thermocouple probe has an outer tubular shell 1 and a flange 2 by which it is bolted to a wall 3 of the jet-pipe of a gas-turbine aircraft engine. The shell 1 projects through the wall 3 and at its far end encloses a thermocouple 4 which receives hot combustion gases via an aperture 5 that faces upstream of the gas flow in the jet-pipe. 
     The thermocouple 4 is formed by two metal-encased junctions 6, one of which is provided by the welding together of wires 7 and 8, and the other (not shown) by the welding together of wires 9 and 10. The wires 7 and 9, which are of a nickel-chrome alloy, and the wires 8 and 10, which are of a nickel-aluminum alloy, are the inner conductors of a mineral-insulated cable 11 that extends within the shell 1 along the length of the probe from the thermocouple 4 for establishing external electrical connection with the junctions 6. The inner conductors 7 to 10 of the cable 11 are insulated from one another and from the metal cable-sheath 12 by compacted magnesium oxide powder 13. 
     The cable 11 extends along the probe in a helical path against the inner surface of the shell 1, with its metal sheath 12 brazed along substantially the whole of its length to this surface. At the near-end of the probe, outside the jet-pipe, the cable 11 is retained through a metal washer 14 for connection via a set of leads or further conductors 15 to 18 (of which only conductors 15 and 16 are shown in FIG. 1) to an external measuring circuit (not shown). The cable 11 and the conductors 15 to 18 extend from opposite directions into, and are retained by a ceramic cylindrical block 19 retained within the near-end of the probe, such that mechanical forces on the electrical connections between the conductors 7 to 10 and 15 to 18 are minimized. 
     Referring to FIGS. 3 and 4, the conductors 15 to 18 enter the outer face 20 of the block 19 through individual ones of four equi-spaced holes, and where they emerge from the inner face 21 of the block 19 within the shell 1, are bent back on themselves to pass again through the block 19 via four adjacent holes. The conductors 15 to 18 emerge from the outer face 20 of the block 19 to leave short emergent end portions 22 to 25 projections from that face. The cable 11, on the other hand, extends axially through the block 19 from within the shell 1, its outer sheath 12 and the insulating material 13 terminating flush with the face 20. The conductors 7 to 10 extend from the sheath 12 and are twisted around respective ones of the projecting ends 22 to 25 of the conductors 15 to 18. The conductors 7 to 10 are spot-welded in place so as to ensure that the good electrical connections established individually with the conductors 15 to 18 are maintained. Insulating sleeves 26 are fitted on the conductors 15 to 18 where they enter the face 20 to ensure that connection with the conductors 7 to 10 is confined to the re-emergent ends 22 to 25. 
     The conductors 15 to 18 and the cable 11 fit tightly into the block 19 so that the welded interconnections are not loaded by the weights of the conductors and cable. This is particularly important in this application of the invention, since the conductors 15 to 18 are 0.040 inch in diameter and the conductors 7 to 10 of the cable 11 are 0.011 inch in diameter. Unless there is good mechanical support for interconnections of wires of such different diameters there is a high probability that the finer wires will break in due course. 
     During manufacture of the probe, the cable 11 is first secured within the shell 1 and through the washer 14, by brazing. An electrically-insulating washer 27 is fitted over the cable 11 against the washer 14 within the shell 1 to insulate the conductors 15 to 18 from the washer 14 when the block 19 is fitted. 
     The conductors 15 to 18 bent into &#34;U&#34;-shapes are threaded through the block 19 from the face 21. The open end of the shell 1 around the cable 11 is then filled with a thermosetting adhesive 28, and the block 19 pushed into the shell 1 with the face 21 leading, over the cable 11 and onto the washer 27. Excess adhesive is removed, and the probe heated to cure the adhesive and to secure the block 19 to the shell 1. 
     The inner conductors 7 to 10 of the cable 11 are now twisted and welded to the respective ends 22 and 25 of the conductors 15 to 18. The insulating sleeves 26 are also now fitted onto the conductors 15 to 18. 
     A further sleeve 29 is pushed tightly over the block 19 and into abutment with the end of the shell 1, to shroud the conductor ends 22 to 25. The space within the sleeve 29 is filled with thermosetting adhesive 30 (see FIG. 1), which seeps into any gaps that may still exist around the conductors 15 to 18 and the cable 11 and in the block 19. This adhesive is then cured so as to secure the fragile thermocouple-conductors 7 to 10 firmly with the block 19. Additionally the comparatively-robust conductors 15 to 18 are in this way further secured to the block 19 to inhibit transfer to their electrical interconnection with the conductors 7 to 10, of externally applied forces. 
     In the embodiment described, the block 19 is wholly of electrically-insulative material, but it may alternatively be of an electrically-conductive material, if conductors 15 to 18 are electrically insulated where they pass through it.