Competence

Signal cables based on copper alloys for applications
in the automotive sector

Environmental protection and the husbanding of resources more and more take center stage in vehicle development with a special focus on minimizing weight and fuel consumption while enhancing safety and comfort. The growing use of electronic assistance systems constitutes a major step in this direction, which entails an increasing demand for signal cables. At the same time, the space accorded to cable harnesses is declining because of optimized safety systems. Signal cables made out of alternative materials may render an important contribution to overcoming this predicament.


Signal cables to-date

As far as electrical conductivity goes, signal cables in vehicles do not have to meet extraordinary requirements, whereas mechanical aspects are of a much greater significance. Signal cables should feature a tensile strength of no less than 70 N. In order to attain this value, a bare copper strand would have to have a cross-section of at least 0.35 mm². Falling below this threshold could give rise to various risks, such as the plug disconnecting from the conductor during a repair.

One possible attempt at improvement might lie in using copper strands in hard condition. So far copper has always been used in soft condition, although hard copper has a much higher tensile strength. Unfortunately hard copper re-crystallizes at room temperature already – thus turning soft again, which in other words means that the hard condition cannot be maintained.

Image: De-fortification of hard-drawn ETP copper stored at 60 °C (1)

By adding on small portions of other materials, the re-crystallization temperature of copper can be drastically increased so that temperatures prevalent in vehicles will not cause the material to soften up. Silver, tin and magnesium are particularly fit for this purpose.


Alternative materials

LEONI Histral® H
LEONI Histral® H

Due to their mechanical and electrical properties, the following three alloys lend themselves excellently for being used as signal cables in vehicles.

All the above materials comply with the OEM delivery specifications. By now, the relevant conductors have obtained their OEM approval. As a corollary, a copper strand with a cross-section of 0.35 mm² may now be replaced with 

  • a strand made from LEONI Histral® H79 (CuAg) featuring a cross-section of 0.17 mm²
  • a strand made from LEONI LEONI Histral® H72 (CuSn) or LEONI Histral® H77 (CuMg) featuring a cross-section of 0.13 mm² 

The fact that all these alloys have a higher resistance than copper does not bear any significance for signal cables in vehicles.


Advantages of signal cables made from LEONI Histral® alloys

Space efficiency

Owing to the cross-section having been reduced from 0.35 mm² auf 0.17 mm² resp. 0.13 mm² a lot less space will be needed. So the same number of cables can be processed using up less space or the same space can hold a lot more cables than before.

Weight efficiency

Another aspect associated with improved space efficiency is a significant economization in weight. On average, a medium-sized car has about 800 signal cables built into it, weighing some 6 to 7 kilograms. This could lead to a weight reduction of approximately 35 % to 75 % in the event of an all-out substitution of traditional materials.

Higher mechanical strength

The alternative materials outlined above can be processed in hard condition. Thus a tensile strength of some 90 N can be reached, which naturally entails a longer flex life as well. This criterion is of particular importance on the Japanese market with its much more stringent requirements than in Europe relative to sensor cables taking care of driver assistance systems.

ABS cables are exposed to strong vibrations and manoeuvers throughout the entire service life of a vehicle. Traditionally, fine strands with a cross-section of 0.75 mm² have been used for this application. A substitution by alloys would allow for cutting down the cross-section to 0.25 mm².

Price stability

Lower cross-sections will also cause the amount of copper consumed per 1 km of cable to go down. As a consequence, rather volatile metal prices fluctuating continuously will give way to more stable prices charged for fabrication adder. Thus, our customers are going to profit from better long-term visibility through prices that are easier to calculate and less susceptible to fluctuations.

Process stability

LEONI Histral® H72 (CuSn), H77 (CuMg) and H79 (CuAg) represent a safe option with regard to their sourcing and processing. Histral® materials reliably stay within the tolerances of the applicable norms. On the other hand, the tolerance levels applied for analyzing purposes are geared towards specific applications.

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Further information

Cables made of alternative materials at LEONI

Die wichtigsten Bordnetz-Trends (German) 
Published Sept 2014 in "Elektronik automotive Sonderheft Bordnetz"

For source information

(1) Magazine METALL, Trends in conductor materials for signal cables in cars, Nov 2009

LEONI


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