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TU München and BMW collaborating on work to replace copper with aluminum as a conductor in on-board power systems

7 February 2011

Leiko
Lab version of the LEIKO aluminum power plug. Click to enlarge.

Scientists from the Technische Universität München (TUM) are collaborating with engineers from BMW to develop the means to replace copper with aluminum as a conductor in on-board power systems.

Currently copper is the conductive material of choice; however, in comparison to aluminum copper is heavy and expensive. With electric power and electronics playing an ever-increasing role in all kinds of vehicles—and in particular for fully electric vehicles—the switch to the cheaper and lighter aluminum could be an attractive option.

LEIKO. Before the lighter and less expensive aluminum can replace copper in power supply systems, a number of technological challenges need to be surmounted. When temperatures are high, as one example, 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. Additionally, joining copper to aluminum is rather demanding with the current state of technology.

TUM 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 the aluminum-based LEIKO concept is to counteract these difficulties.

A sheet metal cage (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 application of precious metal plating made it possible to relocate the formation of corrosion-prone local elements to less critical locations in the system.

On-board cables. 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 aluminum 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.

Aging. 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.

—Professor Udo Lindemann from the Institute of Product Development at TUM

The projects find their theoretical counterparts in the Collaborative Research Center (SFB) 768, Managing Cycles in Innovation Processes, funded by the German Research Foundation (DFG). This 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.

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.

Resources

  • 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

February 7, 2011 in Power Electronics, Vehicle Systems | Permalink | Comments (9) | TrackBack (0)

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Comments

Gotta ask. What happens with copper-clad, square cross-section aluminum? What is the endurance of coils wound with Al?

Copperclad aluminium conductors work quite well, both for signals and power in electronics. It is now the time to start the use of sodium again in buried power cables to free up more copper and aluminium for above ground uses. Plastic insulations are now superior to all past insulation and preserve the sodium well.

Copper has advantages in motors and transformers. ..HG..

Aluminum was tried for residential wiring in the 1970s. It turned out to be a disaster. Lots of fires due to high resistance joints.

How many kg of copper are there in a normal car?

HG, Sodium, really??? No matter what the metallic sodium is clad in, that would be a really bad idea. A home mechanic just clipping a wire could be disastrous, maybe not immediately, but a little bit later when there is enough moisture, then you have a fire, then a bigger fire. I can see sodium in a nuclear reactor where at least the people operating it have some sense, but in the car or a home, hardly.

A very special aluminium alloy is required to replace copper but is it not impossible to do.

Coke Machine: I believe Harvey is suggesting sodium for high-voltage utility power lines, not anything in or to the home.

Whatever handling problems sodium presents, it is never going to be scarce on this planet.

EP, True, but wherever it is used I would prefer there be a lot of smart people around, not the everyday person who is going to dig up the line accidentally with a backhoe. Why even bother with Sodium despite it's abundance, as aluminium, which is almost as abundant is more conductive, and a lot less reactive.

Having seen what happens when an aluminum cable gets a hole in the insulation and corrodes through, a sodium-filled tube might be easier to manage. You can refill the sodium if you get minor leakage, so the MTBF may well be higher. That also allows service to be scheduled, rather than having to be performed upon failure.

You do have issues with backhoes, but a poly or teflon jacket with Kevlar reinforcement isn't going to be significantly more vulnerable than aluminum and the electrical pyrotechnics involved in breaking a HV line will not be exacerbated too much by a bit of sodium.

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