IE913162A1 - An electric cable constituted by copper wires - Google Patents

Abstract

The invention relates to an electrical cable whose core consists of an assembly of copper wires, the assembly comprising tinned-copper wires and bare copper wires. Application to the manufacture of cables for the automobile industry.

Description

The present invention relates to electric cables in which the core is constituted by a set of copper wires. It applies in particular to the electric cabled used in the motor vehicle industry.

The cables used in the motor vehicle industry are mostly made by using a copper core constituted by a geometrical or non-geometrical assembly of bare copper wires. The electrical network of a motor vehicle is made up from such cables, with the network being in the form of a harness containing nearly all of the electrical cabling of the vehicle and being designed to facilitate installation during manufacture. in certain limiting cases, cores are used that are made from wires of copper coated in a layer of solder.

Before the harness is made up, these cables are cut to the desired length, stripped, and connected to connectors.

In most cases, the connections to connectors are made by crimping the connectors onto the cable cores or by displacing cable insulation.

The majority of connectors used are coated with solder on their faces that are to come into contact with the wires of the cable core.

Connectors are a major source of faults in the motor vehicle industry and numerous studies and much research has been performed for making connections more reliable.

A large portion of the faults used to lie in the connections between connectors. Progress has been achieved with connections of this type and these faults are now greatly reduced.

Another portion of these faults can be attributed to the connections between cables and connectors.

Cost considerations lead the motor vehicle industry to use connectors that are crimped onto stripped cables or that make connection by displacing cable insulation. Unfortunately, the effectiveness of such connections can be degraded over time in the presence of moisture, particularly if electrical couples exist between the conductors that are to be associated.

Problems of the same type are also to be found in other branches of industry, for example, in the manufacture of household appliances.

The studies which have been performed to date show that 5 using cable cores of bare copper and using these types of connection gives rise to failure rates that can be reduced no further merely by optimizing crimping parameters or by improving connectors.

After performing a certain number of studies, the 10 Applicant has observed that using tinned wires to make up cable cores, in particular for motor vehicles, provides a very perceptible improvement in the performance and the reliability of connections. However, such cables are more expensive than cables having bare copper wires, and this is not acceptable for many motor vehicle manufacturers. Firstly this is a field of activity where there is a high level of competition, and seoondly the current trend is to increase the number of electrical or electronic circuits in motor vehicles, thereby increasing electric cable length. in order to mitigate these drawbacks, it is proposed to make electric cable cores by assembling together both bare copper wires and tinned copper wires.

The invention thus provides an electric cable whose core is constituted by an assembly of copper wires, wherein said assembly comprises both tinned copper wires and bare copper wires.

The Applicant has observed that manufacturing cables from copper wires coated with a layer of solder provides the following advantages when crimping onto a tinned connector and relative to cable cores made of copper that is not coated in solder: better mechanical strength of cable-to-cable connector connections over a wider range of crimping adjustments; reduced mean contact resistance in the cable-to-cable 35 connection in the initial state; reduced mean contact resistance of the connection after current cycling or after rapid temperature changes,* and a very great reduction in the dispersion of electrical contact resistance values after current cycling or rapid changes in temperature.

These advantages are maintained when using non-crimped 5 connectors, e.g. insulation displacement or other connectors.

In accordance with the invention, assembling a mixture of bare copper wires and tinned copper wires has the purpose of eliminating or reducing copper-on-copper contacts that generate failures, while nevertheless obtaining an advantageous cost price.

Various different proportions of tinned wires to bare wires may be used in a cable core. The higher the proportion of tinned wires, the better the mechanical and electrical performance. In practice, a compromise needs to be made in the application of such cables between cost price and the quality desired for the connections.

In theory, the proportion of tinned copper wires within the core of a cable may lie between only one tinned wire per core to all of the wires in the core minus one.

The thickness of the layer of solder as a function of wire diameter may be the same as for cables in which the core is entirely made up of tinned copper wires. In fact, the thickness of the solder on the copper wires is of little importance, it may equally well be thick or thin.

The tinned wires may be disposed within the cable core either geometrically or non-geometrioally.

Nevertheless, it is advantageous to make up the core so as to reduce the number of contacts between bare wires. This may be done by having a regular distribution of tinned wires amongst the bare wires in the cable core. It is also possible to use a technique that is known per se for cores made of twisted wires.

There is no particular problem in manufacturing electrical cables of the invention. To form a cable core, it suffices merely to replace some of the reels containing bare copper wire with the desired proportion of reels containing tinned copper wire.

For example, for a 19-wire core of hexagonal configuration, tinned wires may be used for the inner layer of the core i.e. for the six wires around the central strand.

When the core has no stable geometrical configuration (as 5 applies to stranded cores), the tinned wires are preferably placed in the center of the core.

Claims (2)

1/ An electrical of copper wires, copper wires and cable whose core is constituted by an assembly wherein said assembly comprises both tinned bare copper wires.

2. / An electrical cable according to claim 1, in which the tinned copper wires are regularly distributed amongst the bare copper wires. 10 3/ An electrical cable according to claim 1 or 2, wherein the core is made up of twisted wires.