EP0635901B1 - Process for connecting an electric cable to a terminal element and correspondant terminal element - Google Patents

Description

The invention relates to a method for connecting an electric cable to an end element such as a connector contact. The invention also relates to an end element which can be used for implementing this method.

The invention applies mainly to the connection of electrical cables comprising a core of a light metal such as aluminum, coated with an insulating sheath. However, it can also be used for the connection of cables whose core is made of any other material such as copper, in particular when a tightness of the connection is desired and / or when it is desired that the connection be made of non-aggressive for the cable.

In industries such as the aeronautical industry using long lengths of electric cables and for which financial and / or weight savings are desired, certain cables with a large copper core have been replaced in recent years by cables with aluminum core. In fact, despite the need to use cables with an aluminum core of larger cross section to compensate for a lower conductivity compared to that of copper, the mass balance shows a gain of around 50%.

To benefit more widely from the weight saving obtained by the use of cables with aluminum core, it would be logical to also replace the cables with copper core of smaller section by aluminum core cables. This particularly concerns cables with a copper core going from gauge 10 (4.9 mm ² in cross section) to gauge 24 (0.2 mm ² in cross section).

However, if the difference in tensile strength between the two materials does not pose a particular problem for cables with a section greater than 5 mm ² , it becomes critical for cables with a smaller section. Indeed, the forces exerted on the cables, in particular during the making of the cabling, may then be detrimental to the electrical continuity of the circuits, therefore to the safety of aircraft.

Another problem concerns the sensitivity of aluminum to chemical attack. This sensitivity means that the connection between the aluminum cable and the copper contact must be sealed, in order to isolate the aluminum from the ambient environment, which is not necessary when using a copper cable.

However, given the larger diameter of the cables with an aluminum core compared to cables with a copper core with equivalent resistivity, any increase in the diameter of the contacts to ensure the tightness and the tensile strength of the connection makes it difficult, even impossible, the use of the standardized tools necessary for fitting and unlocking the contacts, if the most common standardized connectors are used, for unlocking the contacts from the rear.

Furthermore, an increase in diameter of the cavities which are formed on the standardized connectors for receiving the standardized contacts is difficult to envisage without a modification of the location of the cavities, due to the proximity of these on the existing connectors. However, a modification of the positions of the cavities would be tantamount to rendering obsolete all the standard connectors currently used.

Finally, a change in connection technology to use contacts with front unlocking would require major modifications and the creation of new connectors, which is obviously not desirable.

In document GB-A-977 466, it has been proposed to connect an electric cable to an end element such as an electrical contact by introducing the end of the cable into a blind bore, of uniform diameter, machined in an area of connection, of the end element. The external surface of this connection zone is initially a frustoconical surface whose diameter increases towards the open end of the bore. The end element is made of a ductile metal, so that a radial compaction force exerted on the connection zone has the effect of giving the external surface of this zone a cylindrical shape, of uniform diameter. A mechanical connection opposing the separation of the end element and the cable is thus produced.

However, the solution described in this document GB-A-977 466 is not applicable to a cable with an aluminum core of cross section less than 5 mm ² , given the low tensile strength of such a cable. .

In addition, and whatever the nature of the metal from which the cable is made, the solution described in document GB-A-977 466 does not allow a sealed connection to be made.

The main object of the invention is a method for connecting an electric cable such as a cable with an aluminum core of small cross section on a end element such as an electrical contact ensuring a stable and reliable electrical connection, satisfactory mechanical strength as well as a seal against the external environment, without complicating the implementation, without rendering the standardized connectors currently used and preserving as much as possible the use of existing tools.

• on introduit le câble dans l'alésage borgne ; et
• on compacte radialement la partie arrière de raccordement pour donner à la surface extérieure une forme cylindrique ;

caractérisé par le fait

• qu'on utilise un câble comportant une âme revêtue d'une gaine isolante ;
• qu'on dénude le câble sur une longueur inférieure à celle de l'alésage borgne ;
• qu'on introduit le câble dans un alésage borgne étagé formé d'au moins deux tronçons cylindriques ayant chacun une extrémité d'entrée chanfreinée, de telle sorte qu'une partie non dénudée du câble soit reçue dans un tronçon d'entrée de l'alésage, la partie tronconique de la surface extérieure étant située autour du tronçon d'entrée et d'au moins un autre tronçon de l'alésage ; et
• qu'on compacte radialement la zone de raccordement de l'élément d'extrémité par tréfilage, en exerçant une traction sur cet élément, de façon à faire passer la zone de raccordement dans une filière calibrée.

According to the invention, this result is obtained by means of a method of connecting an electric cable to an end element, a rear connection part of which has a blind bore and an external surface having at least one frustoconical part, the diameter increases towards an open end of the bore, in which:

• the cable is introduced into the blind bore; and
• the rear connection part is radially compacted to give the external surface a cylindrical shape;

characterized by the fact

• that a cable is used comprising a core coated with an insulating sheath;
• that the cable is stripped over a length less than that of the blind bore;
• that the cable is introduced into a stepped blind bore formed by at least two cylindrical sections each having a chamfered entry end, so that a non-stripped portion of the cable is received in an entry section of the bore, the frustoconical part of the outer surface being situated around the inlet section and at least one other section of the bore; and
• that the connection area of the end element is radially compacted by drawing, by exerting traction on this element, so as to pass the connection area through a calibrated die.

Thanks to these characteristics, the mechanical connection between the end element and the cable core is completed by a mechanical connection between the end element and the insulating sheath. Since the latter is generally made of plastic material with high mechanical and electrical performance, the mechanical strength is improved and makes it possible in particular to envisage the connection of a cable of small section with a light metal core. In addition, the connection thus produced is waterproof and is not aggressive for the cable.

In a preferred embodiment of the invention, an end element is used which has at least one inspection hole which opens into a bottom section of the blind bore and a transparent sealing sleeve is placed in this section of bottom, before introducing the cable into the bore.

The inspection hole makes it possible in particular to treat the interior of the blind bore, before placing the transparent sealing sleeve there. Thanks to the transparency of the sleeve, it also makes it possible to check the correct positioning of the cable core when the connection has been made. The transparent sleeve then preserves the tightness of the connection.

Advantageously, and in particular when using a cable whose core is made of light metal, an interface ring is also placed, made of an electrically conductive material such as silver, in an intermediate section of the bore, after having installed the transparent sealing sleeve in the bottom section and before introducing the cable into the bore. This interface ring is intended to improve the electrical contact between the cable core and the end element as well as to compensate for the difference in expansion between the materials constituting these two parts. To facilitate the introduction of the cable into the bore while avoiding the need for polarization, the interface ring is chamfered inwards at its two ends.

The invention also relates to an end element which can be used during the implementation of the connection method defined above.

More specifically, an end element is proposed mounted, by radial compaction, on the end of an electric cable, this element comprising a front part and a rear connection part, the latter comprising a blind bore, receiving one end. of the cable, and an outer surface having at least one frustoconical part whose diameter increases towards an open end of the bore, characterized in that, the end element being designed to be mounted on the end of a cable comprising a core coated with an insulating sheath, stripped over a length less than that of the blind bore, the latter is stepped and formed of at least two cylindrical sections each having a chamfered inlet end, a section of entry of the bore receiving a non-stripped part of the cable, the frustoconical part of the external surface being situated around the entry section and at least one at tre section of the bore, and the front part has a shoulder facing the rear connection part, capable of serving as an anchorage for a traction device, for the radial compaction of the rear connection part by drawing.

When the blind bore formed in the connection zone of the end element comprises an inlet section, an intermediate section and a bottom section, the external surface of this bore comprises a cylindrical section which surrounds the bottom section of the bore and a frustoconical section which surrounds the intermediate section and the inlet section of the bore.

• la figure 1 est une vue en coupe longitudinale partielle d'un élément d'extrémité tel qu'un contact électrique prévu pour être raccordé à l'extrémité d'un câble électrique ; et
• les figures 2A à 2H sont des vues en coupe longitudinale illustrant schématiquement les principales étapes de mise en oeuvre du procédé de raccordement selon l'invention.

A preferred embodiment of the invention will now be described, by way of nonlimiting example, with reference to the appended drawings, in which:

• Figure 1 is a partial longitudinal sectional view of an end element such as an electrical contact intended to be connected to the end of an electrical cable; and
• FIGS. 2A to 2H are views in longitudinal section schematically illustrating the main steps in implementing the connection method according to the invention.

In Figure 1, there is shown an end element 10 such as an electrical contact, before its connection to the end of an electrical cable 12 formed of a core 14 and an insulating sheath 16. The core 14 of cable 12 can be made of any metal, although the invention advantageously applies to the case where this core is made of a light metal such as aluminum. The insulating sheath 16 is made of a plastic material with high mechanical and electrical performance. It covers the core 14 of the cable 12, with the exception of its end which is stripped over a predetermined length L.

The end element 10 is made of an electrically conductive material and having good cold deformation capabilities, such as a copper alloy.

The end element 10 has a symmetry of revolution about a longitudinal axis and comprises a standardized front part 10a, strictly identical to the front part of the existing contacts, as well as a rear connection part 10b, the shape of which is modified in accordance with the invention.

In the case where the end element is constituted by an electrical contact as illustrated in FIG. 1, the front part 10a is identical to that of the standard male contacts. However, this front part 10a can take various shapes and dimensions depending on the application envisaged. These forms can in particular be those of a female contact or a tip. For a reason which will appear later, it is important to observe that the front part 10a of the end element 10 has a flange 18 which defines a shoulder 20 facing the rear connection part 10b.

The rear connection part 10b of the end element 10, which begins immediately behind the shoulder 20, has an external surface which successively defines, from this shoulder, a cylindrical part 22, of uniform diameter, and a tapered portion 24, the diameter of which increases from the cylindrical portion 22 to the rear end of the element 10. As illustrated in FIG. 1, the length of the tapered portion 24 is substantially double the length of the cylindrical part 22.

In addition, a stepped blind bore 26 is formed coaxially in the rear connection part 10b of the end element 10 and extends to the inside of the flange 18. Starting from the bottom, this bore 26 comprises a cylindrical bottom section 26a, of relatively small diameter, an intermediate cylindrical section 26b, the diameter of which is slightly greater than that of the bottom section 26a and a cylindrical inlet section 26c, the diameter of which is slightly greater than that of the section intermediate 26b. At their inlet end, each of the cylindrical sections 26a, 26b and 26c has a chamfer 28a, 28b and 28c respectively.

Apart from its end which is situated inside the flange 18, the bottom section 26a of the bore 26 is located entirely inside the cylindrical part 22 of the external surface of the rear connection part 10b. The intermediate section 26b of the bore 26, the length of which is slightly greater than that of the bottom section 26a, is mainly located inside the frustoconical part 24 of the outer surface of the rear connection part 10b and is extends slightly inside the cylindrical part 22. Finally, the inlet section 26c of the bore 26 is completely located inside the frustoconical part 24 and has a length less than that of the cylindrical sections 26a and 26b .

Furthermore, it should be noted that the length L of the stripped part of the cable 12 is predetermined so as to be slightly greater than the abutment length of the sections 26a and 26b of the bore 26, but substantially less than the total length of this bore 26.

The bottom section 26a of the bore 26 has a calibrated diameter equal to the diameter of the core 14 of the cable 12, increased by a slight clearance and by two thicknesses of a transparent sealing sleeve 30 intended to be mounted slightly by force in this bottom section 26a. The transparent sealing sleeve 30 can in particular be manufactured from a tubular sheath made of extruded plastic, sectioned at regular intervals. It has a completely symmetrical shape, so that it can be mounted in the bottom section 26a of the bore 26 without having to resort to a long and costly polarization.

A manhole 32 is drilled radially in the rear connection part 10b of the end element 10, so as to lead to the cylindrical part 22 of the external surface of this rear part 10b and in the bottom section 26a of the bore 26. This inspection hole 32 facilitates the treatment of the surface of the blind bore 26, that is to say the possible deposit of protective coatings on this surface as well as its rinsing. It also makes it possible to visually check the presence of the core 14 of the cable 12 when the connection has been made.

The intermediate cylindrical section 26b of the blind bore 26 has a calibrated diameter equal to the diameter of the core 14 of the cable 12, increased by a very slight clearance and by two thicknesses of an interface ring 34. The ring d interface 34 is designed to be mounted slightly by force in the intermediate section 26b of the bore 26. It is machined from a highly conductive material making it possible to improve the contact between the core 14 of the cable 12 (for example aluminum) and the end element 10 (for example made of copper alloy). The interface ring 34 also makes it possible to compensate for the difference in expansion between the materials constituting these two parts (coefficient of expansion of approximately 17 for a copper alloy and approximately 23 for an aluminum alloy). To best fulfill these two functions, the interface ring 34 is advantageously made of silver. In fact, the conductivity of the silver is satisfactory and its coefficient of expansion is approximately 19. In addition, it is a metal which is easy to machine and relatively malleable.

It should be noted that the presence of the interface ring 34 can sometimes be avoided. This is particularly the case when the core 14 of the cable 12 is also made of a copper alloy. This is also the case when this interface ring can be replaced by a metallic deposit fulfilling the same function inside the bore 26.

To facilitate the introduction of the cable 14, the interface ring 34 has at each of its ends an internal chamfer 36. This symmetrical configuration of the interface ring 34 makes it possible to avoid having to resort to a long and costly polarization during assembly.

The various stages of the connection of the electric cable 12 to the end element 10 will now be described with reference to Figures 2A to 2H successively.

Firstly, a number of surface treatments are carried out on the end element 10, according to usual techniques. These surface treatments generally include copper plating of all the interior and exterior surfaces of the element 10, facilitating the adhesion of the other deposits. Nickel plating can also be carried out on the front part 10a of the element 10. It is also possible to carry out either a thin gilding on all the interior and exterior surfaces of the element 10, or a thick selective gilding on the front part 10a of this element. Finally, as already indicated, a deposit of money can be made inside the bore 26, in particular when it is desired to dispense with the interface ring 34.

The inspection hole 32 makes it possible to escape the air contained in the bore 26 during the electrolytic deposition and facilitates the various rinses.

Then and as illustrated in FIG. 2A, the transparent sealing sleeve 30 is mounted slightly by force in the bottom section 26a of the bore 26. This operation is facilitated by the presence of the chamfer 28a at the entry of this section 26a. When it is finished, the transparent sealing sleeve 30 extends over the entire length of the bottom section 26a and thus seals the inspection hole 32 (FIG. 2B).

The interface ring 34 is in turn mounted slightly by force in the intermediate section 26b of the bore 26. This operation is facilitated by the chamfer 28b which is located at the entrance to the section 26b. When it is finished, the interface ring 34 occupies the entire length of the intermediate section 26b.

Is then introduced into the bore 26, equipped with the sleeve 30 and the ring 34, the partially stripped end of the cable 12, as illustrated in Figure 2B. Since the length L of the stripped part of the cable 12 is less than the total length of the bore 26 and barely greater than the cumulative length of the sections 26a and 26b of this bore, the end of the non-stripped portion of the cable 12 is located inside the inlet section 26c of the bore 26, near the chamfer 28b, when the end of the cable 10 is in abutment in the bottom of this bore. It should be noted that the introduction of the cable 10 is facilitated, for its core 14, by the chamfer 36 formed at the entrance to the interface ring 34 and, for its sheath 16, by the chamfer 28c formed at the entry of the entry section 26c of the bore 26. The penetration of the end of the core 14 into the transparent sealing sleeve 30 does not pose any particular problem, since the inside diameter of this sleeve is slightly greater than the inside diameter of the interface ring 34. It is visually checked, through the inspection hole 32, through the transparent sleeve 30.

As also illustrated in FIG. 2C, the introduction of the end of the cable 12 into the end element 10 is preceded or followed by the positioning of the end element 10 in a crimping tool illustrated very schematically. This crimping tool comprises a pliers 38 and a calibrated die 40.

The clamp 38 is formed of at least two jaws which enclose the end element 10 around the cylindrical part 22 of its outer surface, so as to be able to bear on the shoulder 20, as illustrated in FIG. 2D .

The die 40 is also formed of at least two half-shells which are closed on the cylindrical part 22 of the external surface of the end element 10, when the clamp 38 is closed as illustrated in FIG. 2D.

The rear connection part 10b of the end element 10 is then radially compacted by wire drawing, as illustrated in FIGS. 2E and 2F. As the arrows F illustrate in these figures, this drawing or crimping operation is carried out by exerting a tensile force on the end element 10, along its axis, by means of the clamp 38, so as to make pass over its entire length the rear connection part 10b through the calibrated die 40. This operation has the consequence of transforming the external surface of the rear connection part 10b into a cylindrical surface, the uniform diameter of which is substantially equal to the diameter initial of the cylindrical part 22.

The intermediate section 26b and the inlet section 26c of the bore 26 are thus given shapes frustoconical whose diameter decreases towards the open end of the bore 26. The deformation of the intermediate section 26b of the bore results in a similar deformation of the interface ring 34.

Consequently, and as illustrated in FIG. 2G, when this drawing operation is finished, there is a mechanical connection both between the end element 10 and the core 14 of the cable 12 and between the element d end 10 and the sheath 16 of this cable. This mechanical connection is opposed to any accidental tearing of the end element and ensures sufficient mechanical strength when the core 14 of the cable 12 is of small diameter and formed of a light metal such as aluminum. In addition, the mechanical connection obtained between the end element 10 and the sheath 16 of the cable 12 seals the connection, together with the transparent sealing sleeve 30 in line with the inspection hole 32 (FIG. 2H).

A connection is thus made which is particularly suitable for the use of a cable with an aluminum core but whose tightness and non-aggressive nature make it possible to envisage its application in the case of a cable whose core is made in all other material including copper.

Claims (10)

1. Process for the connection of an electric cable (12) to an end member (10), whose rear connection portion (10b) has a blind hole (26) and an outer surface having at least one truncated cone-shaped portion (24), whose diameter increases towards an open end of the hole, in which: the cable (12) is introduced into the blind hole (26) and the rear connection portion (10b) is radially compacted to give the outer surface a cylindrical shape, characterized in that:

   - use is made of a cable (12) having a core (14) covered with an insulating sheath (16),

   - the cable is bared over a length smaller than that of the blind hole (26),

   - the cable is introduced into a stepped blind hole (26) formed from at least two cylindrical sections (26a, 26b, 26c), each having a chamfered entrance end (28a, 28b, 28c), so that an unbared portion of the cable is received in an entrance section (26e) of the hole, the truncated cone-shaped portion (24) of the outer surface being located around the entrance section (26c) and at least one other section of the hole (26) and

   - radial compaction takes place of the rear connection portion of the end member (10) by wiredrawing, whilst exerting a tension on said member, so as to pass the rear connection portion into a calibrated die (40).
2. Process according to claim 1, characterized in that use is made of an end member (10) having at least one inspection hole (32) issuing into a bottom section (26a) of the blind hole and, before introducing the cable (12) into said blind hole, a transparent sealling sleeve (30) is placed in the bottom section.
3. Process according to claim 2, characterized in that use is made of the inspection hole (32) for facilitating the treatment of the interior of the blind hole (26), prior to the positioning there of the transparent sealing sleeve (30).
4. Process according to either of the claims 2 and 3, characterized in that, after placing the transparent sealing sleeve (30) in the bottom section (26a) and before introducing the cable (12) into the blind hole (26), an interface ring (34) made from an electrically conductive material is placed in an intermediate section (26b) of the blind hole.
5. Process according to claim 4, characterized in that use is made of an interface ring (34), chamfered towards the inside at its ends.
6. End member fitted, by radial compacting, onto the end of an electric cable (12), said member having a front portion (10a) and a rear connection portion (10b), the latter having a blind hole (26) receiving one end of the cable, and an outer surface having at least one truncated cone-shaped portion (24), whose diameter increases towards an open end of the blind hole, characterized in that the end member is to be fitted onto the end of a cable (12) having a core (14) covered with an insulating sheath (16) and bared over a length smaller than that of the blind hole (26), the latter being stepped and formed from at least two cylindrical sections (26a, 26b, 26e) of the hole receiving an unbared portion of the cable, the truncated cone-shaped portion (24) of the outer surface being located around the entrance section and at least one other section of the hole, and the front portion (10a) has a shoulder (20) turned towards the rear connection portion (10b) and able to serve as an anchoring means for the tension device for the radial compacting of the rear connection portion by wiredrawing.
7. End member according to claim 6, characterized in that at least one inspection hole (32) issues into a bottom section (26a) of the blind hole and a transparent sealing sleeve (30) is placed in said bottom section.
8. End member according to claim 7, characterized in that the blind hole also has an intermediate section (26b) in which is placed an interface ring (34) made from an electrically conductive material.
9. End member according to claim 8, characterized in that the ends of the interface ring (34) are chamfered towards the inside and the internal diameter of said ring is slightly smaller than the internal diameter of the transparent sealing sleeve (30).
10. End member according to either of the claims 8 and 9, characterized in that the outer surface has a cylindrical portion (22) mainly surrounding the bottom section (26a) of the hole and a truncated cone-shaped portion (24) mainly surrounding the intermediate section and entrance section of the hole.

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