Multiconductor Stranded Remote-control Cable

Abstract

Multiconductor cable comprising a plurality of metal wires of high unit tensile strength, at least two wires fulfilling wholly or in part the function of an electrical conductor, a core withstanding the mechanical forces to which the cable is subjected when it is unwound, certain of the multiple wires being grouped to form a multi-strand single-channel conductor in which the mechanical strength and the electrical resistance are locally distributed at distinct location, said cable receiving a plastic protective coating obtained by extrusion or impregnation.

Description

The present invention relates to a stranded remote-control cable having a plurality of high tensile steel or alloy conductors, and more particularly to a remote-control cable in which the useful section of a conductor thereof is apportioned among a plurality of wires in order to improve the overall mechanical strength of the cable without affecting its lightness.

The transmission over wires of remote-control commands issuing from a fixed or mobile object such as an air, sea or land vehicle or a missile, offers, among other advantages by comparison with wireless transmission means, that of being impervious to jamming.

Wires used for this technique must satisfy many requirements arising from a variety of electrical, mechanical, climatic, ageing and environmental difficulties.

Various trends have emerged, and techniques have gradually evolved from the single conductor to the composite conductor.

Initially cables consisted of a single light alloy (alumag) conductor wire with a diameter from 0.15mm to 0.22mm, protected by a film of alumina deposited by anodic oxidation and sealed by dipping in special baths such as potassium bichromate baths. The danger of breakage of these wires as a result of the motions of command-guided missiles and the precariousness of the protection provided by the anodic surface treatment of the wire led operators to use steel wires with a diameter from 0.15mm. to 0.22mm, provided with external protection such as enamel or a cotton covering. The missile was accordingly connected to the guidance station, usually by means of at least two wires of this kind, each several thousand meters long. The wires were wound to form two spools carried by the missile, and each of these two-single-strand wires provided both the electric circuit and the mechanical strength required for the link. Thus, in the aeronautical field, this so-called "two-spool" technique was applied to the first generation of wire-guided missiles (the SS-10. SS-11 and SS-12 family of missiles). These wires had a diameter of 0.15 mm, 0.20mm and 0.22 mm, and were enamelled and had a final diameter included between 0.21mm and 0.30 mm.

As the performance requirements imposed in the art became more stringent, new solutions were evolved that gave satisfaction in varying degrees. With the increasing effort in aeronautical engineering to achieve, among other things, greater strength coupled with smaller size and weight, the "single-spool" solution with a single interconnecting wire was adopted for missile guidance. This resulted in the design of two conductor remote-control cables.

The electric circuit, which must do as little mechanical work as possible, invariably comprises two enamelled copper conductors which may or may not be cloth-covered.

The necessary mechanical strength is obtained by adding a textile structure of polyester, regenerated cellulose or silicone to the two conductors. The textile threads may either run parallel to the conductors or be stranded in with the latter.

Such stranding makes for a more even structure and has the advantage of reducing capacitive effects.

An arrangement of the conductors to form parallel wires allows the conductors to be centered within the cable in order to better protect them during the unwinding process.

The assembly is then covered in order to ensure better overall cohesion. It may be further covered with a suitably adapted plastic covering, obtained either by ordinary coating or by through-impregnation (in vacuum or not), this latter application significantly improving electrical conductivity in the event of immersion in water.

Although this new technique resulted in very notable improvements, it was insufficiently reliable because of the low resistance to the effects of contact or environment, which was in turn due to the "cascade" type structure.

The present invention accordingly provides a new cable obtained by stranding a plurality of metal wires made of very-high-tensile steel or special alloys, for example, that perform wholly or partly the function of conductors and offer the various advantages already available in the prior art, but with less danger of rupturing.

Further particulars and advantages will emerge from the description which follows of several non-imitative exemplary embodiments of the invention, given with reference to the accompanying drawings, in which:

FIG. 1 is an overall view of a stranded cable according to the invention;

FIG. 2 is a section taken through the line II--II OF FIG. 1, and

FIGS. 3 to 5 are sectional views corresponding to FIG. 1, showing alternative embodiments.

Reference to FIG. 1 shows a cable 10 comprising a plurality of conducting wires 1 to 6 stranded about a core 7. The wires 1, 2, 3 of one group thereof are crossed by the same current, the return path of which is provided by the other group of wires 4, 5, 6 of the pair of conductors of single-channel cable 10.

The stranded cable 10 is encased in a coating or cover 8, or in both (a covering and an outer coating).

The wires 1 to 6 have a steel core and are coated with possibly electrolytic copper over the annular portion 9.

An insulating envelope 11, obtained by enamelling for example, is provided over the copper.

The core wire 7 is made of steel and its main function is to withstand the mechanical forces to which the cable is subjected as it is unwound.

Reference is next had to FIG. 3 for a similar arrangement of two pairs of conductors 12, 13 and 14, 15, respectively, wherein three aligned wires 16, 17 and 18 provide the overall mechanical strength therebetween, the complete cable being encased at 19 in a textile cover and coating.

It was found that a multiconductor cable according to this invention is satisfactory for transmitting commands to a command-guided missile even in the absence of copper. FIG. 4 shows four conductors arranged in two groups 20, 21 and 22, 23, respectively, these conductors being made of steel and covered with insulation 11.

Whereas the single wires of the prior art were wires of 0.15 to 0.22 mm gauge, the clustered wires of the conductor pairs according to this invention are wires with diameters of less than 0.05 to 0.1 mm, the unit electrical resistance of which is almost the same and the overall mechanical strength of which is considerably greater for substantially the same total cable weight.

The core 24 in the center of the wires is a textile core.

Reference is lastly had to the alternative embodiment of FIG. 5, which shows seven clustered steel conductors 25, insulated by enamelling and covering, the entire assembly being through-impregnated in vacuum subsequent to stranding, in accordance with conventional techniques.

The conducting wires 1 to 6 and 12 to 15 help to increase the mechanical strength of the cable stranded about the cores 7 and 16 to 18. These wires are galvanized, coppered or otherwise protected against corrosion. The wires 20 to 23 and 25 alone assure the electrical conductivity and the mechanical strength of the cable. Preferably, they are made of very-high-tensile steel of good conductivity.

The wires are stranded sufficiently tightly in helical fashion, with a pitch of a few millimeters, over variable lengths that may extend to several thousand meters. This tightly wound configuration ensures cable homogeneity, so that in the event of rupture of one of the conductors the cable as a whole should retain its structural stability.

The stranded cable thereby obtained is possibly covered subsequently, in which case it is impregnated with a plastic which is thermosetting or thermoplastic whereby to obtain a structure possessing the required attributes of tightness, flexibility, electrical strength and overall gauge of the finished cable.

A few examples of stranded cables according to this invention are given below

EXAMPLE 1

The cable includes three parallel steel wires 0.1mm in diameter, with a tensile strength included between 250 and 300 kg/mm.sup.2 that assures in particular the mechanical strength of the cable.

These three single wires extend parallel to one another in the same plane and receive, on either side of said plane, parallel to themselves, two wires with a steel core of identical grade (of 0.05mm diameter), which are copper-coated (outer diameter: 0.07mm) and covered externally with an insulating coating (outer diameter: 0.1mm), after possible covering of said wires.

Subsequent to the precedingly described stranding operation, this set of seven wires is covered and impregnated to the final outer diameter (0.35 mm to 0.40 mm approximately). The cable obtained thus possesses the required mechanical characteristics:

Weight: .ltoreq.0.380 g/m

Resistance: 4.5 .OMEGA. /m

Mechanical strength: > 8 daN

Yield strength: 2 percent

EXAMPLE 2

A single 0.1 mm diameter steel wire assures the mechanical strength primarily and is surrounded by six 0.05 mm diameter coppered and insulated steel core wires. Subsequent to stranding, the covering and the top impregnation coating are effected in the manner described precedingly. Such a cable has the following physical characteristics:

Mechanical strength: >8 da N

Weight: .ltoreq. 0.360 g/meter

Resistance: .apprxeq. 5 .OMEGA./m

EXAMPLE 3

The cable comprises in this case four single insulated steel wires arranged parallel to a textile core which contributes to the overall mechanical strength and which is made of polyester, cellulose or silicone. Subsequent to stranding, the entire assembly is covered and impregnation-coated.

It goes without saying that changes may be made in the embodiment hereinbefore described for exemplary purposes, without departing from the scope of the invention as set forth in the appended claims.

Claims

We claim:

1. A remote-control multiconductor cable for command-guided missiles comprising

a steel core means to withstand the mechanical forces to which the cable is subjected when it is unwound,

at least two electrical conductor wire means wound helically about said core means to form a multi-strand single channel conductor with mechanical strength and electrical resistance locally distributed at distinct locations,

each said electrical conductor wire means being a steel wire means having a diameter substantially in the range of 0.05mm to 0.1mm and having a copper coating thereon and further coated with an insulating deposit

whereby the electrical resistivity of said electrical conductor wire means is relatively lower and the mechanical strength and yield strength of the cable as a whole is relatively higher than that of a single wire of identical cross-section.

2. A cable according to claim 1, characterized in that the stranding is effected at a sufficiently close pitch of the order of a few millimeters, whereby cable homogeneity is obtained by the tightness of the winding and the cable retains its structural stability in the event of rupturing of a strand.

3. A cable according to claim 1, characterized in that said cable has a covering and a plastic protective coating.

4. A cable according to claim 3, characterized in that the protective plastic is selected from the group consisting of polyvinyl chloride, nylon and silicone.

5. The remote-control cable according to claim 1 further characterized by the cable including said core means and said electrical conductor wire means having a weight of not more than .380 grams per meter.