WO1993017467A1

WO1993017467A1 - Electrical connector

Info

Publication number: WO1993017467A1
Application number: PCT/GB1993/000325
Authority: WO
Inventors: Jacques Delalle
Original assignee: Raychem S.A.; Raychem Limited
Priority date: 1992-02-20
Filing date: 1993-02-16
Publication date: 1993-09-02
Also published as: GB9203591D0

Abstract

A device for forming an electrical connection to one or more elongate electrical conductors comprises an electrically insulating sleeve (1) and a metallic connecting element (2) located within the sleeve. The connecting element has a tapering internal surface which has a screw thread so that a tempory electrical connection can be formed by twisting the device about the conductor or conductors. The screw thread is periodically interrupted along its length so as to cause it to rasp the elongate electrical conductor or conductors as the device is twisted. The connecting element may, for example, be formed by coiling a piece of wire of polygonal cross section into a tapering coil, and the interruptions may comprise substantially 'V' shaped indentations (8).

Description

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This invention relates to electrical connectors, and especially to connectors for forming solder joints between conductors in electrical harnesses, cables and the like.

Electrical harnesses, for example as manufactured in the automotive industry, are often quite complex. In some instances they are manufactured by forming two or more sub-assemblies of wires, terminals, connectors and any other components, and then forming electrical connection(s) between the sub-assemblies. In such a case the assembly of the harness may be controlled by computer permitting, with the aid of a monitor, the assembly operator to see schematically the lay up and to check correct build-up of the assembly at each stage of the harness manufacture. In order to enable this control process to operate the ends of the conductors of the sub-assemblies are connected, eg. by means of spring contacts, and an electrical current or signal is passed through the assembly in order to obtain verification that the harness is correct. It is only after such verification is obtained that the clips are removed and a permanent electrical connection is formed.

International patent application No. PCT/GB91/01016 describes an electrical connector which comprises an internally screw-threaded connecting element heated in a heat-shrinkable sleeve that contains a quantity of solder. The conductors can be stripped of insulation and inserted in the connector which is then twisted on the conductors to form a temporary electrical connection, for example for testing the harness. The device may then be heated, for example by means of a hot-air gun. or infrared lamp, to melt the solder and form a permanent electrical connection.

Although the connection is simple to use and will form an excellent sealed solder connection it requires the ends of the conductors to be stripped of insulation which can. be difficult for certain conductors, for example for conductors insulated with enamel.

According to the present invention, there is provided a device for forming an electrical connection to one or more elongate electrical conductors, which comprises an electrically insulating sleeve, a metallic connecting element located within the sleeve, the connecting element having a tapering internal surface which has a screw thread so that a temporary electrical connection can be formed by twisting the device about the conductor or conductors, wherein the screw thread is periodically interrupted along its length so as to cause it to rasp the elongate electrical conductor or conductors as the device is twisted.

By means of the device according to the invention it is possible to form an excellent connection to an enamel insulated conductor either alone or in conjunction with one or more other enamel insulated or otherwise insulated conductors without the need to strip the enamel insulation from the conductors.

Normally the device will include a quantity of solder for forming a permanent electrical connection between the or each conductor and the connecting element.

According to another aspect, the invention provides a method of forming an electrical connection between one or more elongate electrical conductors and a device comprising an electrically insulating sleeve, a metallic connecting element located within the sleeve, and a quantity of solder for forming a permanent internal surface which has a screw thread that is periodically interrupted along its length, the method comprising:

(i) inserting one or more elongate electrical conductors into the device so that the end(s) thereof are located within the connecting element;

(ii) twisting the device about the conductors) to form a temporary electrical connection thereto; and

(iii) heating the device to fuse the solder and form a permanent electrical connection to the conductor(s);

wherein the interrupted screw thread rasps the conductor(s) when the device is twisted and so removes part of the electrical insulation therefrom.

At least in the broadest aspect of the invention the connecting element may generally have any form although it is preferred for it to be formed by coiling a piece of wire into a tapering coil so that the windings form the screw thread. Preferably the internal surface of the connecting element is at least partly conical, for example it may be conical or frusto-conical. If the connecting element is formed from a wire, it can grip the bundle of conductors introduced therein due to the resilience of the wire and the fact that it will be enlarged radially to some extent by the introduction of the bundle. However, in one advantageous form of device it has been radially expanded from its relaxed state during manufacture of the device and to be retained in its expanded state so that it will radially contract, or attempt radially to contract, when the permanent connection is formed. Thus, for example, the spring may be held out against its resilient recovery forces by the sleeve or by the solder, so that softening of the sleeve or melting of the solder will allow the spring to recover. For example, a boss may be formed on the internal surface of the sleeve or on the internal surface of the solder which will disappear when the device is heated. The degree of expansion need not be great, for example it might be not more than 5% or even not more than 2%, since it may be desirable that the coil remains in contact with the solder element when the device is heated.

The wire may be formed with a circular cross-section, although it is preferred for the wire to have a relatively sharp ridge along its length, eg. formed by cold drawing or cold rolling, which, when the wire has been coiled, is directed toward the interior of the coil in order to form the screw thread. In particular it is advantageous for the wire to be formed with a polygonal, and especially a square, cross-section. The wire may be formed from an appropriate metal or metal alloy, but preferably is formed from copper, and especially from copper having substantially the same purity as that conventionally employed from electrical conductors.

Other configurations of connecting element may, however, be employed. For example it may be formed from a solid block of metal that has been tapped with a screw thread.

In the case of connecting elements that are formed from a coil of wire, the wire may be provided with a number of indentations which interrupt the screw thread formed when the wire is coiled. These may be formed, for example, by means of a toothed roller or any other method that will produce a sharp cutting edge. The indentations are preferably substantially "V" shaped when viewed from the side of the wire and have a depth in the range of from 0.1 to 0.5 mm especially from 0.15 to 0.2 mm. However, other shapes and sizes of indentations may instead be employed depending on the type of wire, for example "U" shaped or rectangular grooves. The grooves may be located next to one another so that they "touch" or they may be separated from one another by a greater or lesser extent.

The device may be made in a variety of forms. It may be in the form of a stub splice having one open end for receiving a bundle of - 5 -

conductors and one closed end, or in the form of an in-line splice in which a double connecting element can receive conductors from both ends. Such device are described in international patent application No. WO92/00616. The device may include a terminal hug that extends from the sleeve as described in British patent application No. 9118841.7 or it may be configured to allow a conductor, eg. a coaxial cable, to extend through the device as described in British patent application No. 9125923.4. The disclosures of the International and British applications are incorporated herein by reference.

Usually the sleeve will be dimensionally recoverable, and especially dimensionally heat-recoverable, that is to say the article has a dimensional configuration that may be made substantially to change when subjected to heat treatment.

Usually these articles recover, on heating, towards an original shape from which they have previously been deformed but the term

"heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed.

In their most common form, such articles comprise a heat- shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in US Patents 2,027,962; 3,086,242 and 3,597,372. As is made clear in, for example, US Patent 2,027,962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form but, in other applications, a preformed dimensionally heat-stable article is deformed to a dimensionally heat- unstable form in a separate state.

In the production of heat-recoverable articles, the polymeric material may be cross-linked at any stage in the production of the article that will enhance the desired dimensional recoverability. One manner of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point or, for amorphous materials the softening point, as the case may be, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use, since the deformed state of the article is heat-unstable, application of heat will cause the article to assume its original heat-stable shape.

Any material to which the property of dimensional recoverability may be imparted may be used to form the sleeve. Preferred materials include low, medium or high density polyethylene, ethylene copolymers, eg. with alpha olefins such as 1- butene or 1-hexene, or vinyl acetate, polyamides or fluoropolymers, eg. polytetrafluoro ethylene, vinylidine fluoride or ethylene- tetrafluoroethylene copolymer.

As mentioned above, the device normally includes a quantity of solder, ie. a quantity of soft solder as distinct from brazing material, for forming a permanent solder connection. The solder may, for example, simply be in the form of an Snβ3Pb37 eutectic composition which will melt as the device is heated and the sleeve recovers, or more than one solder composition having differing melting points may be employed, as described in International Application No. WO88/09068. In this form of device, melting of the higher melting point component, eg. Snge.sAgs.s eutectic will provide a visual indication that the device has been heated sufficiently to melt the lower melting point composition and to form a satisfactory solder joint. If desired the lower melting point solder may be a non-eutectic composition and, for example as described in International Application No. PCT/GB90/00234, the higher and lower melting point solder compositions may together form a eutectic composition. For example, a non-eutectic Sn6oPb o lower melting point component may be employed with a higher melting point component formed from pure tin in relative amounts that an Snβ3Pb37 eutectic is formed. The disclosures of these two patent applications are incorporated herein by reference. An advantage of employing a two component solder, and especially a tin, Sn6oPb4o combination is that it reduces the possibility of "wicking" that is to say, travel of the solder along the conductors and away from the joint area due to capillary action by the stranded conductors, which can be caused by prolonged heating of the device.

The solder may be positioned anywhere where it will be able to flow into the connecting element to form a solder joint. The solder may be employed in the form of a ring or in any other form for example a ball, and may be disposed symmetrically about the sleeve axis or offset from it. The solder element may, for instance, be located at the smaller diameter end of the connecting element in which case it may be in the form of a ball or plug, or it may be located in the region of a large diameter end of the connecting element, for example in the form of a ring. Preferably the solder is in the from of an element that surrounds the connecting element, especially where the connecting element is in the form of a coil so that the fused solder can flow through the windings of the coil to the interior thereof. More than one quantity of solder may be employed, for example where the connecting element has more than one tapering internal surface for forming a splice.

Two forms of device in accordance with the present invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a sectional view along the axis of one form of device according to the invention;

Figure 2 is a sectional view along the axis of another form of device according to the invention; Figure 3 is a side view showing part of the wire forming the connecting element of a device according to the invention in greater detail;

Figure 4 is a section taken along the line I-I of Figure 3;

Figure 5 is a sectional view of yet another form of device according to the invention; and

Figure 6 is a view of the device of Figure 5 located on a length of coaxial cable.

Referring to the accompanying drawings, Figure 1 shows a device for forming a stub splice in a bundle of electrical wires, which comprises a heat-shrinkable sleeve 1 formed from polyvinylidine fluoride, a connecting element 2 formed by coiling a hard tempered copper wire into a tapering helix, a ring 3 of a fluxed Snβ₃Pb₃₇ eutectic solder, a thermoplastic sealing ring 4 formed from uncrosslinked low density polyethylene and a thermoplastic spherical seal 5. The wire has a square cross-section and has been coiled so that a pair of flat faces 6 and 7 extending along the copper wire are oriented toward the interior of the connecting element 2, and a number of V shaped grooves 8 have also been formed in the wire (only the grooves in a portion of the connecting element having been shown).

In order to form a stub splice between a number of wires they are simply inserted into the open end of the sleeve 1 after stripping insulation from the ends of the wires where appropriate, and the device is twisted through an angle of about 90° to screw the connecting element 2 onto the wire ends. A permanent electrical connection is then formed by heating the device, for example by means of a hot-air gun or infrared lamp, in order to shrink the sleeve 1 onto the conductors, fuse the solder ring 3 and fuse the sealant ring 4 onto the wire insulation. If any of the wires have an enamel coating as electrical insulation; for example enamel coated solid copper wires, the insulation need not be stripped from the end of the wire since the V- shaped grooves 8 will rasp against the insulation and cut through it to the copper conductor.

Figure 2 shows another form of device according to the invention that operates in the same principle as that shown in Figure 1. The device comprises the a polyvinylidine fluoride heat-shrinkable sleeve 1, a connecting element 2 formed as a coil of hard tempered copper wire, a ring 3 of solder and a thermoplastic sealing ring 4, substantially as described with reference to Figure 1 with the exception that the solder ring 3 is formed as a composite solder ring having a quantity 3' of a fluxed Snβ₃Pb₃₇ eutectic alloy and a small temperature indicating ring 3" of higher melting point Sn97.sAG₂.5 solder as described in US patent No. 5,086,967, the disclosure of which incorporated herein by reference. As in Figure 1, the copper wire forming the connecting element originally has a square cross-section, and the device includes a terminal comprising a lug portion 10 and a hollow shank 11 into the end of which the connecting element 2 can be screwed. This form of device enables the wire bundle that is terminated by the device to be mechanically connected to another external conductor. As with the device shown in Figure 1 in the inner surface of the wire forming the connecting element 2 is provided with a number of V-shaped grooves 8 that will rasp any enamel wire insulation when the device is rotated about the wire bundle and form an electrical connection to the underlying conductor.

Figures 3 and 4 show a section of the wire forming the connecting element 2 of the device shown in Figure 2 in greater detail. In this case the connecting element is formed from a wire having a square cross-section with flats of dimension between 0.3 and 0.8 mm. A number of V-shaped grooves or indentations 8 have been formed in the wire, the groove faces 12 forming an angle of approximately 90° with the faces of adjacent grooves. Each groove has a depth of about 0.15 to 0.20 mm. The grooves may be separated from one another by a short distance or they may, as shown, be arranged as closely together as possible so that the groove faces 12 and the internal side faces 6 and 7 of the wire meet a a series of points.

Figures 5 and 6 show a form of device according to the invention of the form described in British patent application No. 9125913.4 for connecting one or more ground leads to the shield of a coaxial cable. This form of device comprises a heat-recoverable polvinylidine fluoride sleeve 1 that contains a generally diabolo shaped connecting element 2, a wrap of fluxed Snβ₃Pb₃₇ eutectic solder 3, and a pair of fusible polyethylene sealing rings 4' and 4", one sealing ring being located at each end of the connecting element 2. As described above, the connecting element has been formed from by coiling a copper wire that has a square cross-section and a number of V shaped grooves 8 along one edge of the wire (only the grooves in a portion of the connecting element having been shown).

In use a central portion of the outer jacket 20 of a coaxial cable 21 is removed in order to expose a portion of the braid 22 forming the screen. One or more enamel insulated solid conductor ground leads 23 can be inserted into one open end of the connecting element 2 and the element 2 can then be twisted about the coaxial cable 21 and the ground lead in order to grip the ground lead and to scrape away part of the enamel insulation. When the device is heated the sleeve 1 will recover and the solder 3 and sealing rings 4' and 4" will melt to form a permanent sealed electrical connection.

The connecting element 2 is capable of expanding at its waist if necessary in order to fit over coaxial cables of a range of diameters, the maximum diameter being determined by the size of the chamber formed by the central section 25 of heat-recoverable sleeve 1. Provision of the solder 3 in the form of wrap will allow the solder to accommodate any increase in size of the connecting element. If the connecting element 2 has to increase in size in order to fit over the coaxial cable, any resilience in the element will facilitate scratching of the teeth formed by the grooves 8 on the ground lead 23.

Claims

Claims:

1. A device for forming an electrical connection to one or more elongate electrical conductors, which comprises an electrically insulating sleeve, and a metallic connecting element located within the sleeve, the connecting element having a tapering internal surface which has a screw thread so that a temporary electrical connection can be formed by twisting the device about the conductor or conductors, wherein the screw thread is periodically interrupted along its length so as to cause it to rasp the elongate electrical conductor or conductors as the device is twisted.

2. A device as claimed in claim 1, wherein the connecting element is formed by coiling a piece of wire into a tapering coil.

3. A device as claimed in claim 2, wherein the wire has a relatively sharp ridge along its length which is directed toward the interior of the coil in order to form the screw thread.

4. A device as claimed in claim 3, wherein the wire has a polygonal cross-section.

5. A device as claimed in any one of claims 2 to 4, wherein the wire has a number of indentations along its length which interrupt the screw thread.

6. A device as claimed in claim 5, wherein the indentations have a depth in the range of from 0.1 to 0.3 mm.

7. A device as claimed in claim 5 or claim 6, wherein the indentations are substantially "V" shaped.

8. A device as claimed in any one of claims 1 to 7, wherein the connecting element is connected to a terminal lug that extends from one end of the insulating sleeve.

9. A device as claimed in any one of claims 1 to 7, wherein the connecting element has two open ends to enable one or more electrical conductors to be inserted therein from each open end and/or to allow an elongate conductor to extend through the device.

10. A device as claimed in any one of claims 1 to 9, wherein the sleeve is dimensionally heat-recoverable.

11. A device as claimed in any one of claims 1 to 10, which includes a quantity of solder for forming a permanent electrical connection between the or each conductor and the connecting element.

12. A method of forming an electrical connection between one or more elongate electrical conductors and a device comprising an electrically insulating sleeve, a metallic connecting element located within the sleeve, and a quantity of solder for forming a permanent internal surface which has a screw thread that is periodically interrupted along its length, the method comprising:

(iii) heating the device to fuse the solder and form a permanent electrical connection to the conductors); wherein the interrupted screw thread rasps the conductors) when the device is twisted and so removes part of the electrical insulation therefrom.

13. A method as claimed in claim 12, wherein the or at least one of the electrical conductors has a layer of enamel insulation.

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