Some friends of mine actually
built out an electrical vehicle some years back and in the process gained a lot
of knowhow. One tidbit was that the
cable harness made from copper grabbed sixty pounds of weight right away. Thus an EV does need to shed as much copper
as possible. Aluminum is an obvious
alternative. It is also likely to be
easy to make safe in an automobile which was its problem in house wiring in
which long term creep caused increasing resistance and failure.
I suspect that EVs will use aluminum
extensively for the heavy duty current load once the manufacturers get used to
doing so.
I also suspect that good design
will minimize even that quite easily.
Aluminum to replace copper as a conductor in on-board power systems
February 7, 2011
This CAD drawing shows an innovative electrical connector based on
aluminum conductors instead of copper. It's part of a project to remove
obstacles to using this lighter, less expensive material in electric cars and
other vehicles. Credit: Copyright TU Muenchen
Electric power and electronics are playing an ever-increasing role in
all kinds of vehicles. Currently copper is the conductive material of choice.
But in comparison to aluminum copper is heavy and expensive. In particular for
fully electric vehicles the switch to the cheaper and lighter aluminum would be
an interesting option. That is why the optimization of intricate power supply
networks is now in the focus of engineering research. Scientists from the
Technische Universitaet Muenchen (TUM, Germany
At first glance it is not at all clear why copper is still used as conductor in modern
electric or semi-electric vehicles – when aluminum is lighter and significantly
less costly. However, before aluminum can replace copper inpower supply systems,
a number of technological challenges need to be surmounted. When temperatures
are high – and there are many places in a car where that is the case – aluminum
displays a distinct creep behavior. Conventional connectors could thus not be
used, as they would become loose with time.
One possible alternative – the use of aluminum-based elements in cables
and copper-based elements in connection areas – also entails problems. Because
there is a high electrochemical potential between a copper contact and an
aluminum cable, this kind of wiring would be very prone to corrosion. Besides,
joining copper to aluminum is rather demanding with the current state of
technology. In order to counteract the aforementioned difficulties, 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 innovative aluminum-based electrical connection concept in
the project LEIKO.
A sheet metal cage, which is an electromagnetic compatibility
requirement anyway, enhances the mechanical stability of the plug and
guarantees the long-term support of the contact pressure spring. Because the
necessary contact force is no longer provided by the contact elements
themselves, the originally problematic creep behavior of aluminum turns into a
contact stabilizing, and thus, positive property. This, in turn, also
guarantees a constant contact force over a lifetime of ten years.
To this end the researchers came up with a special wedge-shaped
geometry for the aluminum contacts. The aluminum creep now leads to the two
contacts snuggling closer and closer together over time, thereby rendering the
electrical connection better yet. Moreover, the consistent use of aluminum
alloys and the ingenious application of precious metal plating made it possible
to relocate the formation of corrosion-prone local elements to less critical
locations in the system.
A further problem with substituting aluminum for copper is its lower
electrical conductivity. In the case of high-power on-board systems in
particular, the cable cross-sections, which are about 60 per cent larger, need
to be taken into account in the construction of cable ducts and feed-throughs.
One positive thing the scientists discovered was that because aluminum is very
pliable, the standard values from copper cable processing, where bending radii
are set based on the diameter, could also be used for aluminum.
In order to determine the long-term behavior of the coated aluminum
contacts under even the rough conditions typical for motorized vehicles, the
project partners, together with leading suppliers, have successfully initiated
a further research project. Funded by the Bavarian Research Foundation (BFS),
this project will deliver evidence on the aging behavior and thus the
suitability of the concept by 2012.
Initial results indicate that the material substitution will lead to
significant improvements in weight, cost, and ultimately emissions. "We
expect the high-voltage on-board systems of most electric vehicles to
be based on aluminum by 2020. Aluminum will find its way into low-voltage
on-board systems as well, because the price of copper will rise significantly
with increasing demand," says Professor Udo Lindemann from the Institute
of Product Development at the TU Muenchen.
The project finds its theoretical counterpart in the Collaborative Research
Center
Another aspect of the research conducted within SFB 768 is a student
project to develop an electrically driven go-cart. In order to experience the
manifold challenges of innovation management first-hand, the students started
with a standard base structure and went through the entire development process
for all subsystems of the vehicle. The results of the LEIKO project are also
integrated into the student project – the entire high-voltage on-board system
is implemented in aluminum.
The results are to be incorporated in the TUM electro vehicle MUTE,
which will be presented at the IAA 2011.
More information: 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
Provided by Technische Universitaet Muenchen
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