Laboratory version of the aluminum power plug as it is used at the e-cart.
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), in collaboration with BMW engineers, have now found out what tricks make
it possible to replace copper with aluminum.
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 in power
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.
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
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.
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
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% 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.
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
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.
projects find its theoretical counterpart in the Collaborative Research Center
(SFB) 768, Managing Cycles in Innovation Processes, funded by the German
Research Foundation (DFG). It aims to bundle competencies from computer
science, engineering, economics, and the social sciences in order to look into
challenges at the interfaces of innovation processes along with partners from
industry. The goal of this research is to use an interdisciplinary perspective
to develop industry-relevant solutions in dealing with dynamic changes in
company environments, as well as in company internal process landscapes.
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
results are to be incorporated in the TUM electro vehicle MUTE, which will be
presented at the IAA 2011.