SCIENTISTS from the Technische Universitaet Muenchen (TUM), in collaboration with BMW, have found it is possible to replace copper with aluminium as a conductor in on-board power systems.
Copper is currently the conductive material of choice, but aluminium is lighter and cheaper. In electric vehicles, where weight considerations come into play, aluminium could play an important part in optimising the intricate power supply networks which make up the core of the car.
The researchers found a number of ways to replace copper with aluminium.
Before aluminium can replace copper in power supply systems, a number of technological challenges need to be surmounted. When subject to high temperatures, aluminium can creep, thus ruling out the use of conventional connectors, as they would become loosened with time.
While the researchers considered combining aluminium cables and copper connectors, there is high electrochemical potential between the metals, resulting in corrosion concerns.
To solve the problem, scientists of the chairs for High Voltage Technology and Power Transmission and for Metal Casting and Forming, in cooperation with the respective departments of the BMW Group, developed an aluminium-based electrical connection concept in the project LEIKO.
LEIKO utilises a sheet metal cage to ensure the mechanical stability of the plug and guarantee the long-term support of the contact pressure spring. The contact elements no longer provide the necessary contact force, eliminating the problems associated with aluminium’s creep behaviour.
The researchers came up with a special wedge-shaped geometry for the aluminium contacts. This causes the creep to cause the two contacts to snuggle closer and closer together over time, thereby rendering the electrical connection better yet.
An additional consideration when substituting aluminium for copper is its lower electrical conductivity. As such, the cable cross-sections need to be about 60 percent larger for high-power on-board applications.
However, due to the pliability of aluminium, the standard values from copper cable processing, where bending radii are set based on the diameter, could also be used for the metal.
The researchers are now looking into the long-term behaviour of the coated aluminum contacts under even the rough conditions typical for motorized vehicles.
Results will be available by 2012, although the scientists claim initial results indicate material substitution will lead to significant improvements in weight, cost, and ultimately emissions.
Publication: Langer, S.; Lindemann, U.: Managing Cycles in Development Processes - Analysis and Classification of External Context Factors, in 17th International Conference on Engineering Design, M. N. Bergendahl, M. Grimheden, and L. Leifer, Eds. Stanford University, California, USA: Design Society, 2009, pp. 1-539 - 1-550