Termination for Alternate Polarity Resistance Welding Cable

This invention relates generally to cable terminations, and more particularly to a cable terminal assembly for flexible, duel-lead conductor cables of the "kickless" or low reactance level type.

Flexible, dual-lead conductor cables of the "kickless" or low reactance level type are well known in the art and are commonly employed as welding cables for connecting welding heads or guns to transformers providing current for resistance welding operations. Such cables are employed to reduce or eliminate the violent jerks or kicks resulting from the reaction of opposite polarity conductors to one another when high currents are impressed on the cable. Generally, these cables each comprise two leads or groups of multiple strand conductors which are alternately circumferentially disposed and helically wound along the cable length. The ends of the cables are secured to terminals for subsequent connection to the welding heads or transformers. Provisions may be made for fluid coolng of the welding cable assembly.

Although such cables successfully have eliminated or substantially reduced the problem of cable "kick", additional problems stem from the connection of the conductors of the same lead to respective terminal lug halves for subsequent connection to the welding heads and transformers. Substantially all mechanical failures in service occur in this part of the welding cable assembly. This problem is one for which many solutions have been sought as seen in the following U.S. Pat. Nos. 2,308,673; 2,702,311; 2,943,133; 3,127,467; 3,143,593; 3,163,704; 3,456,064; and 3,467,767. It therefore has been long recognized that the manner in which cable conductors are connected to the terminal is of major importance in obtaining substantial service life in view of the severe service requirements imposed on welding cables.

It is common manufacturing practice to join together the cable conductors of each cable lead and secure the same to respective, mutually insulated terminal halves or lugs by soldering, clamping or employing detachable cable conductor connectors. The conductors of the same lead usually are bent and/or twisted to obtain the proper alignment of the same for attachment to the respective terminal halves. Each multiple strand cable conductor consists of a large number of fine wires which are strained by such bending and/or twisting and their susceptibility to work-hardening or embrittlement during use is substantially increased thereby leading to premature fracturing of the wires and early failure of the cable assembly. This condition is aggravated further by the high temperatures generally encountered during welding when the cable is carrying high current.

In addition, strands of opposite polarity cross over each other at the termination creating wear points that can cause electrical short circuits. Moreover, because of this cross-over, the alternately disposed relationship of the conductors of opposite leads is disturbed, particularly at the critical failure area, thus inducing a physical reaction between the conductors in this area thereby further contributing to early deterioration of the cable.

In an early attempt to overcome the above-noted problems in welding cable assemblies, Botterhill disclosed in his U.S. Pat. No. 2,702,311 a cable terminal assembly for six conductor strand "kickless" cables comprising two three-way apertured and longitudinally spaced-apart extensions at the inner or rear ends of the mutually insulated terminal halves of a split cylindrical terminal. The rearwardmost extension of one of the terminal halves is longitudinally spaced from the forwardmost extension of the other terminal half by a neck which is received in an enlarged slot in the forwardmost extension in concentric and interlocking fashion, and the respective apertures of the two extensions are positioned alternately relative to each other when viewed from the rear end of the terminal whereby the apertures of both extensions are aligned respectively with the conductors of the cable. The ends of the conductors are then inserted into and soldered in place in the corresponding apertures of the terminal in order to achieve conductivity through the joint and to secure the cable to the terminal. Although the cable terminal assembly of this type eliminates the before mentioned residual stresses in the cable at the critical failure area and maintains the conductor strands alternately disposed, such cable terminal assembly is subject to several shortcomings. For example, the terminal halves are of complicated structure and therefore expensive to manufacture and difficult mutually to insulate. In addition, the heat generated during the soldering process may embrittle the conductor strand wires contributing to their early fracture and thus early failure of the cable. Moreover, when the conductor strands become broken or burned, repair and/or replacement of the damaged conductors is a difficult procedure and usually must be done at the cable manufacturer's facility resulting in costly repair and freight charges.

In a later attempt to overcome the noted problems, Toto in his U.S. Pat. No. 3,456,064 disclosed a cable termination assembly for a four conductor cable comprising a tubular cable conductor connector adapted to be connected to one of the terminal halves of a split terminal which is so orientated by suitably twisting its cable conductor receiving end such that it is aligned with the helix or lay of two of the conductors of the same cable lead. The remaining two conductors of the other cable lead are either separately secured to the other terminal half by separate connectors having a squared forward end and a diverging rear end which is also orientated with the lay of the respective individual conductors, or jointly secured by a single connector which is formed to include a U-shape channel which straddles the twisted connector. Although such cable termination assembly appears to reduce the residual stresses at the connection between the cable and terminal body, the copper strands are severely distorted by the twisting of the conductor terminal, and furthermore, the assembly proces is difficult and time consuming requiring complex dies for swaging the connectors to the desired shape. Moreover, there is no teaching as to how such a cable terminal assembly could effectively be employed with cables having more than four conductors.

The present invention provides a simplified low cost, easily formed cable terminal assembly which is rugged, electrically efficient and serviceable, and which provides cable conductor terminal connectors and terminal halves of a unique configuration for accomplishing the transition from terminal to cable, wherein the terminal ends of the conductors are allowed to remain substantially straight and in alignment with the position in which the respective conductors are located within the cable. In other words, the terminal ends of the conductors extend longitudinally in parallel relationship, and those of one cable lead are alternately disposed relative to those of the other cable lead substantially completely the longitudinal extent of the cable, whereby there is a consequent reduction in bending strains on the cable at the terminal end and reduction in the physical reaction between adjacent conductors of opposite polarity when current is applied to the cable.

It is therefore a principal object of this invention to provide a cable terminal assembly in which the conductors at their connecting ends remain straight and in alignment with their respective positions in which they are located within the cable.

It is another principal object to provide a cable terminal assembly wherein the collection of the conductors of the same lead for connecting the same to a common terminal element is accomplished by cable conductor terminal connectors and terminal elements of unique relative configurations, and not by bending, twisting and/or cross-over of the conductors.

It is still another principal object to provide terminal connectors for connecting cable conductors of the same lead to a common terminal element in a more economical and efficient manner than now practiced in the art.

A further important object is to provide in such terminal assembly simplified terminal lugs, easy to fabricate, easy mutually to insulate, and facilitating the connection of the cables thereto.

Yet another object is to provide a unique terminal and removable and mechanically attachable conductor terminal connectors for multiple conductor cables of the kickless type.

It is a further object to provide a cable terminal assembly which is substantially free of residual stresses stemming from its assembly.

Another further object is to provide a cable terminal assembly having provision for strain relief of that portion of the cable conductor emerging from the connectors provided therefor.

Still a further object is to provide a cable terminal assembly wherein the alternating relationship of the conductors of opposite leads in "kickless" cables is preserved at the cable to terminal transition thereby to minimize cable "kick" in such region.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.

In the drawing:

FIG. 1 is a fragmentary longitudinal view, partly in section, of the cable termination assembly of the invention;

FIG. 2 is a transverse section of the assembly of FIG. 1 taken on the line 2--2 thereof;

FIG. 3 is a transverse section of the assembly of FIG. 1 taken on the line 3--3 thereof;

FIG. 4 is a transverse section of the assembly of FIG. 1 taken on the line 4--4 thereof; and

FIG. 5 is an exploded perspective view of the assembly illustrated in FIGS. 1-4.

Referring now in greater detail to the drawing, a cable termination assembly constructed in accordance with the present invention is designated generally by reference numeral 10, and comprises a dual polarity terminal 12 and an electrical cable 14 which are described more fully below. Such termination assembly 10 may be employed at both ends of the cable 14 as is typical in a welding cable assembly which is commonly connected between a transformer and welding gun. The principles of the present invention may be employed with a cable assembly having provision for fluid-cooling of the same by passage of a coolant fluid through conduits in the cable assembly; however, the present invention will be described for the sake of clarity for a cable assembly not having such provision, it of course being understood that one skilled in the art could employ the principles of the invention with a fluid-cooled cable assembly.

For purposes of this disclosure, it is to be understood that the term "rearward", when used in connection with the cable termination assembly, refers to the direction generally inwardly of the end or towards the cable and to the right in FIG. 1, and that "forward" is sued to denote the direction generally towards the end or termination and to the left in FIG. 1.

The terminal 12 of the invention is generally of the basic, split cylinder type and comprises a pair of semi-cylindrical, elongated terminal lug elements or halves 16 and 18 essentially identical in shape and joined together along their respective inner flat faces 20 and 22 in non-conductive or insulated relation. A relatively thin, flat insulating plate 24 of rectangular shape disposed between the terminal lug halves 16 and 18 maintains the same electrically insulated from each other. When so spaced by the insulating plate 24, the terminal halves 16 and 18 may be held together against the insulating plate in any suitable manner. As best seen in FIG. 1, an elongate non-conductive, flexible sheath 26, which encases and protects the cable 14, extends around the rearward end of the terminal 12 and is secured thereto by an annular clamp 28 secured thereabout. It can be seen that the sheath and clamp maintain the terminal 12 in the described assembled relationship and maintain the same in a cylindrical shape for receipt in a corresponding cylindrical socket or clamp of a transformer or welding gun or the like. Preferably, a plurality of semi-annular, peripheral grooves 30 are provided in the semi-cylindrical outer surfaces of the terminal halves 16 and 18 at their rearward ends about which the sheath 26 extends to secure mechanically, as well as frictionally, the sheath 26 to the terminal 12, and further to ensure a fluid type seal in the event a fluid-cooled cable is employed.

Although the terminal 12 is shown and described as being of the cylindrical type, it should be understood that the forward portion of the terminal 12 may be formed in any manner to provide for electrical connection to a transformer or welding gun or the like. For example, the forward ends of the terminal halves may be in the form of flat, coextensive projections or lugs generally rectangular in transverse cross-section which have apertures through which a fastener may pass for securing the same to a transformer output lug or welding head lug in well-known manner. An example of this form of terminal can be seen in U.S. Pat. No. 3,456,064.

As best seen in FIGS. 4 and 5, the terminal halves 16 and 18 are essentially of like shape and each at their rearward end is radially recessed inwardly so as to provide a rearwardly projecting extension 32 which is integral with the respective terminal half and includes at opposite sides thereof substantially parallel, flat, longitudinally extending connector receiving surfaces 34 and 36 which are angularly disposed relative to the interfacing planar faces 20 and 22 of the respective terminal halves 16 and 18. The respective extensions are diametrically offset and the parallel circumferentially adjacent faces of opposite extensions are at different radial elevations. Each extension includes one or more fastener receiving apertures 38 which extend transversely therethrough and preferably are threaded for receiving a fastener therein that removably secures a cable conductor terminal connector to the extension in mating assembled relationship in a manner which will be more fully described below.

It should be appreciated that the terminal halves 16 and 18 may be readily formed from a single piece of solid bar stock of conductive metal by cutting the same along an axially extending, diametrical plane, the thickness of the cut being substantially equal that of the insulating plate 24. The rearward ends of the terminal halves may be undercut to provide the extensions 32 with the opposed connector receiving surfaces 34 and 36, the orientation of which is to be more fully described below.

Considering now the cable 14 in detail and referring particularly to FIGS. 1 and 2, the cable 14 comprises two leads or groups 40 and 42 of flexible conductors which are twisted in a helical manner along the cable length with conductors of opposite leads being alternately circumferentially disposed to form a kickless or low reactance level type cable as is well known in the art. For the purpose of the present invention, the cable 14 comprises six conductors of which three conductors, 40a, 40b and 40c, may be considered of positive polarity and three conductors, 42a, 42b and 42c, of negative polarity as indicated generally in FIG. 2. The conductors of opposite polarity or leads are spaced and electrically insulated from one another by an elongate, flexible, insulating member 44 of spur-like cross-section which includes a flexible core 46 and radially extending ribs 48 which extend between and separate the conductors of the respective leads 40 and 42. Accordingly, there are six such ribs. The sheath 26 encases the cables and protects and maintains the same in the described assembled relationship. If the cable 14 is to be fluid cooled, conduits may be provided in the cable through which coolant may pass thus to cool the cable. Conventionally, suitable fittings are provided in the terminal 12 to provide inlets and outlets for the coolant.

Referring again principally to FIG. 5, the terminal end portions of the cable conductors are provided with connector elements 50 and 52 for each cable lead 40 and 42 which provide for the electrical and mechanical connection to the terminal 12 as described below. The connectors 50 are secured, respectively, to the end portions of conductors 40a and 42a while connectors 52 are secured respectively to the other two conductors 40b, 40c and 42b, 42c of each lead. It should be appreciated that the single connectors 50 are diametrically spaced from one another and the double connectors 52 are substantially adjacent yet slightly spaced from one another. Moreover, it should be appreciated that the connectors 50 and 52 of opposite leads are, respectively, essentially of like shape and symmetrically disposed relative to the longitudinal axis of the terminal. For convenience, the connectors of the lead 40 will be described in greater detail below, it of course being understood that such description is equally applicable to the connectors of the lead 42.

The single conductor terminal connector 50 comprises a tubular member or sheath through which the terminal end portion of the conductor 40a extends substantially straight and substantially the entire extent of the connector 50 without the end portion of the conductor 40a having to be significantly bent and/or twisted from alignment with the conductor's circumferentially disposed location relative to the other conductors in the cable. The connector 50 has a forward portion 54 and a rearward portion 56. The forward portion 54 is substantially rectangular in cross-section and is formed with a substantially flat contact surface 58 adapted for mating engagement with the contact surface 34 of the extension 32 as seen in FIG. 4. The forward portion 54 also includes a fastener receiving aperture 60 which extends transveresly therethrough, and when aligned with aperture 38 in the surface 34, a clamping screw fastener 62 may extend through aperture 60 and be threadedly received in aperture 38 for removably securing the connector 50 to the extension 32 of the terminal element 16. The rearward portion 56 is formed to receive the cable conductor terminal end portion in substantially the shape as received from the cable and thus with mimimal deformation of the conductor.

The connector 52 similarly comprises a tubular member or sheath through which the terminal end portions of the conductors 40b and 40c extend, but the connector 52 is of sufficient width such that the end portions of both conductors 40b and 40c extend substantially straight substantially the entire extent of the connector 52 without the end portions thereof having to be significantly bent and/or twisted from alignment with the conductors' circumferentially disposed location relative to the other conductors in the cable.

Similar to connector 50, the connector 52 has a forward portion 64 and rearward portion 66. The forward portion 64 is substantially rectangular in cross-section and is formed with a substantially flat contact face 68 adapted for mating engagement with the contact surfaces 36 of the extension 32 as seen in FIG. 4. A fastener receiving aperture 70 extends transversely through the forward portion and may receive a fastener 72 which threadedly engages aperture 38 in the surface 36 removably to secure and clamp the connector 52 to the extension 32 of the corresponding terminal half 16. For a purpose which will become more apparent below, the forward portion includes a laterial recess or cut-out 74 adapted to clear the extension 32 of the opposed terminal half 18 without electrical contact therebetween when assembled. The rearward portion 66 is formed with two laterally spaced bosses 76 which are aligned with the cable conductors 40b and 40c and receive the end portions of the same in substantially the same shape as received from the cable. The connectors 52 are accordingly substantially L-shape in configuration with the parallel cables extending from the shorter thicker leg parallel to the long leg.

In similar fashion, the conductors of the lead 42 may be secured to the terminal element 18. Connector 50 is secured to conductor 42a which in turn is removably fastened to the extension 36 of the terminal element 18 at the receiving surface 34. Connector 52 is secured to conductors 42b and 42c which also are removably secured to the extension 32 of the terminal element 18 but at the receiving surface 36 thereof.

It will of course be appreciated that the cable connectors may be soldered, welded, or brazed, along with, or in lieu of, the clamping fasteners illustrated.

Each of the tubular connectors may be secured to their respective conductor end portion or portions by crimping or swaging or otherwise forming the connector around the end portion or portions. Such swaging or forming forms the strands of the conductor into a tightly bundled mass of conductor material. As the conductors are maintained in the rearward portions substantially in the same shape as received from the cable and are flattened at the forward portion giving the same the generally described rectangular sectional profile, there is some slight bending required to spread the conductors to the flattened shape. However, such slight bending is minor in comparison with the bending and twisting encountered in previously known methods and such bending is fully contained within the conductor connector which prevents any further bending or twisting thereof during flexure of the cable in use. It will also be appreciated that the swaging or forming process is relatively simple and requires inexpensive dies or tools.

As seen in FIG. 4, the forward end portions 58 and 68 of the respective connectors 50 and 52 are secured to the extensions 32 by their respective fasteners 62 and 72, and the connectors 50 and 52 are disposed so that the respective contact surfaces 58 and 68 of each are joined to the respective receiving surfaces 34 and 36 in abutting conductive relationship, and provide sufficiently large contact areas for electrical efficiency of the joint. Of course, the connectors connected to the conductors of the same lead are attached to the same terminal elements as above described. It can be seen that the forward portions 58 and 68 of the respective connectors 50 and 52 of opposite leads 40 and 42 are disposed on opposite sides of a diametrical plane extending longitudinally therebetween, and preferably the terminal elements 16 and 18 are orientated such that their respective inner faces 20 and 22 are substantially parallel with such diametrical plane. Moreover, the insulating plate preferably extends between the forward portions of the connectors of opposite leads as seen in FIG. 1. To assure sufficient clearance with the insulating plate 24 and proper fit, the forward portions of the connectors 50 may be slightly laterally offset from the rearward portions as best seen in FIG. 5 and generally shown at 78. Alternately or concurrently with such offset, the corners of the forward portions of the connectors adjacent the insulator plate 24 may include chamfers or radii also to ensure adequate clearance.

When so secured to the terminal elements, the connectors are maintained in closely packed relationship with connectors corresponding to the opposite leads being diametrically, alternately, spaced apart with such spacing being sufficient to prevent electrical short circuits between connectors of opposite leads. Normally the spacing need not be great as such cable assemblies in welding operations normally carry high currents at low voltages. There may be provided, if desired, insulation between the connectors corresponding to opposite leads.

In order to maintain the connectors closely packed at their respective rearward portions, it can be seen in FIG. 3 that there are provided recesses 80 between the spaced bosses 76 of the rearward portions 66 of the connectors 52 in which nest in spaced relationship the rearward portions 56 of the connectors 50 corresponding to the opposite leads. Preferably, the bosses 76 are somewhat triangular in shape formding therebetween a substantially V-shaped recess 80 which accommodates the relatively inverted, triangularly shaped, rearward portion 56 of the connector 50. It can thus be seen that the connectors when assembled have a combined transverse width which substantially corresponds to the diametric width of the cable 14. Accordingly, the sheath 26 will readily fit over the connectors to permit securing of the sheath to the terminal 12.

Because bending stresses may occur in the strands at the area directly adjacent the relatively unyielding connectors 50 and 52, a plastic sleeve 82 is fastened over each conductor with the forward end of each sleeve being secured in the boss or rearward portion of the corresponding connector to reduce the stresses in this area as would otherwise occur during flexure of the cable. The sleeve preferably extends a sufficient distance along the conductor and provides sufficient rigidity to the conductors so as to increase the radius of curvature of the strand while it is being bent so that the conductors are not subjected to high localized bending stresses. These sleeves 82 may be inserted over the ends of the conductors with a portion of the conductor projecting therebeyond, and the preshaped connector may be swaged or crimped to its desired profile in turn securing the cable conductor and sleeve in place. It will also be appreciated that the sleeve electrically insulates the conductors of opposite leads in the event the insulating member does not extend fully to the connectors.

There is accordingly provided an opposite polarity "kickless" cable which includes mutually insulated semi-circular lugs 16 and 18, each having a flattened projection 32 at its inner end, each providing recessed parallel flat conductor connecting surfaces 34 and 36 which are symmetrically respectively diametrically offset, so that the plane of one surface is radially offset from the plane of the circumjacent surface of the other projection. In this manner, the simplified L-shape two cable connector 52 may be employed on the one surface of one projection while the essentially straight single cable connector 50 is employed on the radially outwardly and circumferentially offset adjacent surface of the other projection, to connect the cables in the alternating nesting fashion shown.

The terminal connection of the present invention is in this manner easy to fabricate and assemble while providing a long service life.