Shape memory electrical connector

Abstract

An electrical connector for facilitating the connection of electrical wiring, the connector comprises a body portion 16 formed from a shape memory alloy, such as Nitinol, the body portion 16 having an

Description

Technical Field Examples of the present disclosure relate to an electrical connector for joining electrical conductors such as wires or tubes, the connector being formed from a shape memory alloy. Particular examples include a ring shaped connector formed from a shape memory alloy such as a nickel-titanium, arranged to be threaded onto an electrical conductor to which a connection is desired to be made. Background to the Invention and Prior Art Shape memory alloys such as nickel-titanium or copper-aluminium-nickel are known already in the art. Such shape memory alloys can have "one-way" memory or "two-way" memory, with changes in the shape of the alloy being instigated by heating or cooling of the alloy. In particular, "one-way" shape memory alloys provide for a starting shape, formed at high temperatures. Once the material has cooled then it will retain the starting shape, but may also be bent or deformed into other shapes, into which it will then stay. However, once the bent or deformed shape is then heated to the transition temperature of the material, the material will revert from the bent or deformed shape back to the starting shape. Example commercially available one way shape memory material is Nitinol, which is a nickel-titanium alloy. Separately from shape memory alloys, canted coil spring electrical connectors are also known in the art. As described in EP2459659A2, canted coil springs may be used to electrically connect two parts. Generally a first part is a female part such that a bore extends through the part and can receive a second part, which is a male part. The male part may be shaped similar to a pin, shaft, plug, shank or the like and may have an outer surface with a shape corresponding to the shape of the bore. The outer diameter of the pin is smaller than the inner diameter of the bore to allow insertion of the pin into the bore and removal of the pin from the bore. The inner surface of the bore includes a groove for retaining a canted coil spring. In conventional current conducting applications of canted coil springs, the pin is inserted into the bore such that the outer surface of the pin contacts the canted coil spring. The canted coil spring establishes a connection between the outer surface of the pin and the inner surface of the bore. Accordingly, the canted coil spring facilitates flow of electrical current between the two parts. Summary of Invention The present disclosure presents an electrical connector having a body portion formed from shape memory alloy such as Nitinol or the like, and which is further provided with a coil spring electrical connector around its outer surface to facilitate easy connection of an electrical conductor with a female connector. In one embodiment the body portion of the electrical connector is formed in a closed shape with an interior channel to surround the circumference of a conductor to which electrical connection is to be made, with the coil spring electrical connector formed concentrically with the closed shape around the outer surface thereof. For example, the closed shape may be an annular ring shape, for example a circular shape, or may be any other shape that is complementary to the shape of the conductor within the interior channel to which it is intended to surround and connect. An inner surface of the channel of the body portion which contacts against the conductor is provided with insulation piercing means in the form of one or more pins or a projecting edge that in use pierce through the insulation of an electrical wire to make contact with the conducting metal within. The body portion of the connector is formed into an initial shape having the interior channel of a first, smaller cross section, typically smaller than the diameter of the conductor to be connected, and is then deformed once cooled so as to expand the diameter of the interior channel. In use the body portion is then threaded over the wire to be connected, including over the insulation of the conductor i.e. it is not necessary to remove the conductor insulation. The body portion is then heated, and the shape memory effect of the alloy from which the body portion is formed causes the body portion to change shape to shrink the diameter of the interior channel. In so doing the insulation piercing means formed on the inner surface of the interior channel pierce through the conductor insulation to form an electrical connection with the electrical conductor within, whilst at the same time the shrinkage causes the body portion to grip and be fastened to the conductor. The conductor then has a male connector in the form of the body portion and the surrounding coil spring which can then be received and secured into a correspondingly shaped female connector. In view of the above, from one aspect there is provided an electrical connector for facilitating an electrical connection, the connector comprising: a body portion formed from a shape memory alloy, the body portion having an interior channel into which is received in use an electrical conductor to which the electrical connector is to be fastened, the interior channel having an enlarged diameter in a first state of the shape memory alloy such that the electrical conductor can be readily received therein; and a positionally tolerant electrical connector provided around an outer surface of at least part of the body portion; the arrangement being such that in use an electrical conductor is inserted into the interior channel of the body portion, and then a change in state of the shape memory alloy is effected in order to reduce the diameter of the interior channel such that the channel grips the electrical conductor securing it within the electrical connector and making electrical connection therewith. The electrical conductor may for example be an electrical wire, or an electrically conductive tube. Further features and aspects of the invention will be apparent from the appended claims. Brief Description of the Drawings Further features and advantages of the present invention will become apparent from the following description of an embodiment thereof, presented by way of example only, and by reference to the drawings, wherein like reference numerals refer to like parts, and wherein: Figure 1 is a perspective drawing of a first embodiment of the invention; Figure 2 is cross-sectional drawing of the first embodiment; Figure 3 is a second perspective view of the first embodiment showing the embodiment in use; Figure 4 is a first cross-sectional drawing showing the first embodiment mating with a female connector; Figure 5 is a second cross-sectional drawing showing the first embodiment mating with a first connector, with detail shown in close-up; and Figure 6 is a close up drawing of the cutting blade 20 piercing the wire electrical insulation during use of an embodiment. Description of the Embodiments Embodiments of the invention provide an electrical connector which is generally ring shaped and arranged to be threaded onto an electrical conductor to be connected. The body of the electrical connector is formed from a shape memory alloy (SMA) such a Nitinol, with the body being shaped at a high temperature above the upper transition temperature into the ring shape, having an internal channel therein having a diameter which is the same or less than the diameter of electrical conductor to which the connector is to be fastened. The body is then cooled to less than the lower transition temperature, and is then molded or deformed so as to increase the diameter of the internal channel to greater than that of the intended electrical conductor. In addition, a groove is formed around the outer edge of the ring shape, into which is fitted a canted coil spring electrical connector. The canted coil spring electrical connector is of such a size that is still under tension and hence retained within the groove when ring shaped body has returned to its original size with the reduced diameter internal channel. In this way the canted coil spring connector is retained on the exterior circumferential surface of the body at all times. In use, the molded or deformed ring body having the canted coil spring circumferentially arranged around it is threaded onto an electrical conductor to be connected, and is then heated past the transition temperature of the SMA, such that the body of the connector returns to its original shape with the internal channel of reduced diameter. However, because the electrical conductor is contained within the internal channel then the body portion tightens around the electrical conductor, securing the connector thereto. The inner surface of the interior channel can be provided with conductor insulation piercing means such as pins or a blade to pierce through any insulation on the conductor and ensure electrical contact with the conducting conductor within. Figures 1 to 5 show an embodiment of the invention is more detail. In Figure 1 a disc-shaped body portion 16 is provided, which is formed of a shape memory alloy such as Nitinol (NiTi). The disc shaped body portion is shaped like a flattened cylinder, and has an interior channel 12 formed therein, running axially through the disc from one side to the other. The outer facing surface of the disc shaped body portion is provided with a groove 14 running around the circumference, within which is contained a coil spring electrical connector 18, such as a canted coil spring electrical connector. Figure 2 illustrates a cross section of the disc-shaped body portion 16 of the electrical connector. Here the ring shaped nature of the connector is apparent, with the internal channel 12 forming a majority part of the width of the disc shaped body portion. The canted coil spring connector 18 can be seen in the groove 14 formed in the outer-facing surface of the disc shaped body portion. Canted coil springs are used as a compliant high current electrical path that can be tolerant to changes in geometry and wear of the mating electrical path. Formed on the inner surface of the internal channel and pointing radially inwards are electrical insulation piercing means, such as pins or the like, or, as also shown in Figure 2, a pointed edge or blade 20, which runs circumferentially around at least part, or around the whole, of the internal diameter 12. This blade is sized so as to penetrate through any electrical insulation that may be provided on the electrical conductor, to allow electrical connection to be made with the conductor within the conductor and the disc shaped body portion 16. Figure 3 shows the connector mounted on an electrical conductor 10. Here it can be seen that the disc shaped body portion 16 is fastened around the conductor 10, which passes through the internal diameter 12 of the body. Figures 4 and 5 then show how the connector body 16 may be used with conductor 10 to form a male type electrical connector, which can be received into the receiving orifice 42 of a female type connector 40. In particular, the receiving orifice 42 of the female connector is of slightly less diameter than the diameter of the canted coil spring, such that the coils of the coil spring 18 are compressed or displaced as the connector body 16 mounted on the conductor 10 is inserted into the receiving orifice. This ensures that there is constant outward pressure on the coils of the coil spring 18 when the male connector is received within the female orifice, thus ensuring both a good electrical connection between the conducting walls of the female orifice, and helping to retain the male connector within the orifice. As shown in Figure 5, the interior walls of the female receiving orifice 42 may be provided with indentations of depressions 52 formed therein, into which in use the coils of the canted coil spring are received to help secure the male connector in place within the female connector. The method of construction and use of the connector will now be described. As noted above the disc shaped body portion 16 is formed from a shape memory alloy, having a known transition temperature range. In particular, as is known in the art shape memory alloys having a transition temperature range, where shape transition from a cool deformed shape commences once the temperature of the alloy is fairs above a start transition temperature As, and then progresses as the temperature is increased until the complete transition back to the original shape of the body is achieved once the temperature us above a finish transition temperature Af. The shape memory alloy in this embodiment is a one-way alloy, such that the original shape is set by formation of the body portion at a temperature above the finish transition temperature i.e. when the material is in the Austenite state. In this case the body portion is formed with a narrow internal channel diameter, which is typically less than or at most equal to the diameter of the conductor to which the body is intended to be connected. When the body portion is then cooled to below the start transition temperature ie when it assumes the Martensite state the body portion is then deformed or molded into the shape shown in Figure 1, which has the internal channel 12 expanded to be of such a diameter that the conductor 10 can be easily threaded therethrough. The canted coil spring 18 is then fixed within the groove 14 in the outer surface thereof. In use the deformed or molded disc shaped body portion including the internal channel 12 sized to receive an electrical conductor therethrough is threaded onto a conductor to which connection is to be made. Once in place on the desired part of the conductor (see Figure 3) the body portion is then heated to greater than the finish transition temperature of the shape memory alloy, to cause the body portion to assume its original non-deformed state (the Austenite state) with the internal channel 12 being of the narrower diameter to then grip the electrical conductor and fasten the electrical connector thereto. During this process the pointed edge or blade 20 pierces through any insulation surrounding the conductor to contact the conductor. In so doing, the curved or angled nature of the blade as shown in Figure 2, in that the blade is formed on the surface of the interior diameter of the body 16 having a substantially triangular cross-section, either with straight or slightly curved (convex or concave) sides, with the cutting edge at the apex of the triangle and pointing radially inwards, as shown in Figure 6. This arrangement has the effect that when the cutting edge at the apex of the triangle cuts into the insulation it has the effect of progressively compressing the cut edge of the insulation as the triangular wedge shape of the blade 20 pushes into the insulation, so that a secure and typically liquid tight fit of the insulation against the sides of the triangular cutting blade is obtained. In terms of the shape memory alloy used, Nitinol may be used, or any of Fe-Mn-Si, Cu-Zn-AI or Cu-AI-Ni. The transition temperatures used should be higher than typical ambient temperatures that the connector would typically encounter in transit after manufacture but before use, to prevent premature actuation to shrink the connector back to its original shape after deformation into its use shape. Start transition temperatures above 50°C should be adequate, with a finish transition temperature of perhaps 10°C to 30°C higher. Conversely, the start and finish transition temperatures should not be so high that damage is caused to the insulation of the electrical conductor during fitting, and hence maximum finish transition temperature should be no higher than 100°C to prevent damage to PVC type electrical insulation. Some slight melting of the insulation during fitting of the connector can help with the sealing of the insulation against the cutting blade 20 to ensure a tight deal of the insulation against the blade, as discussed above. With respect to the nature of the electrical conductor, in some embodiments it might be a conducting wire, for example formed of metal or the like, and may be solid core or multi-strand. In other embodiments the electrical conductor may for example be a solid or a hollow tube, for example a gas supply tube, made for example from a conducting metal such as copper, and the connector is intended to be fitted over and grip onto the exterior surface of the tube in use. Various further modifications to the above described examples, whether by way of addition, deletion or substitution, will be apparent to the skilled person to provide additional examples, any and all of which are intended to be encompassed by the appended claims. The following numbered clauses provide further embodiments of the present disclosure: 1. An electrical connector for facilitating the connection of electrical wiring, the connector comprising: a body portion formed from a shape memory alloy, the body portion having an interior channel into which is received in use an electrical conductor to which the electrical connector is to be fastened, the interior channel having an enlarged diameter in a first state of the shape memory alloy such that the electrical conductor can be readily received therein; and a positionally tolerant electrical connector provided around an outer surface of at least part of the body portion; the arrangement being such that in use an electrical conductor is inserted into the interior channel of the body portion, and then a change in state of the shape memory alloy is effected in order to reduce the diameter of the interior channel such that the channel grips the electrical conductor securing it within the electrical connector and making electrical connection therewith. 2. The electrical connector according to clause 1, wherein the body portion is formed in the second state having the interior channel of reduced diameter, and is then shaped when in the first state to deform the body portion to provide the enlarged diameter. 3. The electrical connector according to clause 2, wherein the second state comprises the body portion being heated to a higher temperature, and the first state comprises the body portion being cooled to a lower temperature, the change in state comprising heating the body portion from the lower temperature to the higher temperature. 4. The electrical connector according to any of the preceding clauses, wherein the body portion is formed with a groove in its outer surface in which the coil spring electrical connector is disposed. 5. The electrical connector according to clause 4, wherein the groove extends circumferentially around the body portion. 6. The electrical connector according to any of the preceding clauses, wherein the body portion is substantially disc shaped having an annular configuration, the interior channel being formed along the axis of the annulus. 7. The electrical connector according to any of the preceding clauses, wherein the interior channel is provided with electrical insulation piercing means, arranged in use to pierce any electrical insulation surrounding the electrical conductor when the interior channel grips the conductor, and make contact with the electrical conductor within. 8. The electrical connector according to clause 7, wherein the electrical insulation piercing means comprises one or more sharpened protrusions on the interior face of the interior channel. 9. The electrical connector of clause 8, wherein the one or more sharpened protrusions comprise a circumferentially extending blade that extends around at least a part of the interior face of the interior channel. 10. The electrical connector according to clause 9, wherein the circumferentially extending blade extends around the whole interior circumference of the interior channel. 11. The electrical connector according to any of the preceding clauses, wherein the positionally tolerant electrical connector is a coil spring electrical connector. 12. An electrical interface comprising a male connector part and a female connector part, the female connector part having a bore into which the male connector part is received, the male connector part comprising an electrical connector according to any of the preceding clauses, the arrangement being such that in use when the male connector part is inserted into the bore of the female connector part, the positionally tolerant connector compresses against the interior walls of the bore and thereby forms a positionally tolerant electrical connection between the male and female connector parts. 13. A method of forming an electrical connector according to any of clauses 1 to 11, 5 comprising: threading the body portion having the positionally tolerant electrical connector provided thereon onto an electrical conductor, and positioning it at a connection position; and heating the body portion to effect a change in the shape memory alloy of the 10 body portion from the first state having the enlarged diameter interior channel to the second state having the reduced diameter interior channel, the interior channel thereby gripping the electrical conductor to form a connection between the conductor of the conductor and the body portion.

Claims

1. An electrical connector for facilitating the connection of electrical wiring, the connector comprising:a body portion formed from a shape memory alloy, the body portion having an interior channel into which is received in use an electrical conductor to which the electrical connector is to be fastened, the interior channel having an enlarged diameter in a first state of the shape memory alloy such that the electrical conductor can be readily received therein; anda positionally tolerant electrical connector provided around an outer surface of at least part of the body portion;the arrangement being such that in use an electrical conductor is inserted into the interior channel of the body portion, and then a change in state of the shape memory alloy is effected in order to reduce the diameter of the interior channel such that the channel grips the electrical conductor securing it within the electrical connector and making electrical connection therewith,wherein the interior channel is provided with electrical insulation piercing means, arranged in use to pierce any electrical insulation surrounding the electrical conductor when the interior channel grips the conductor, and make contact with the electrical conductor within.

2. The electrical connector according to claim 1, wherein the body portion is formed in the second state having the interior channel of reduced diameter, and is then shaped when in the first state to deform the body portion to provide the enlarged diameter.

3. The electrical connector according to claim 2, wherein the second state comprises the body portion being heated to a higher temperature, and the first state comprises the body portion being cooled to a lower temperature, the change in state comprising heating the body portion from the lower temperature to the higher temperature.

4. The electrical connector according to any of the preceding claims, wherein the body portion is formed with a groove in its outer surface in which the positionally tolerant electrical connector is disposed.

5. The electrical connector according to claim 4, wherein the groove extends circumferentially around the body portion.

6. The electrical connector according to any of the preceding claims, wherein the body portion is substantially disc shaped having an annular configuration, the interior channel being formed along the axis of the annulus.

7. The electrical connector according to any of the preceding claims, wherein the electrical insulation piercing means comprises one or more sharpened protrusions on the interior face of the interior channel.

8. The electrical connector of claim 7, wherein the one or more sharpened protrusions comprise a circumferentially extending blade that extends around at least a part of the interior face of the interior channel.

9. The electrical connector according to claim 8, wherein the circumferentially extending blade extends around the whole interior circumference of the interior channel.

10. The electrical connector according to any of the preceding claims, wherein the positionally tolerant electrical connector is a coil spring electrical connector.

11. An electrical interface comprising a male connector part and a female connector part, the female connector part having a bore into which the male connector part is received, the male connector part comprising an electrical connector according to any of the preceding claims, the arrangement being such that in use when the male connector part is inserted into the bore of the female connector part, the positionally tolerant connector compresses against the interior walls of the bore and thereby forms a positionally tolerant electrical connection between the male and female connector parts.

12. A method of forming an electrical connector according to any of claims 1 to 10, comprising:threading the body portion having the positionally tolerant electrical connector provided thereon onto an electrical conductor, and positioning it at a connection position; andheating the body portion to effect a change in the shape memory alloy of the body portion from the first state having the enlarged diameter interior channel to the second state having the reduced diameter interior channel, the interior channel thereby gripping the electrical conductor to form a connection between the conductor of the conductor and the body portion.

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