Battery and motor developments power future cars

Smarter battery management systems and hub motors are two of the main targets for a German electric car development programme, which involves collaboration between no less than 33 Fraunhofer Institutes.

The target platform is the "Frecc0" or "Fraunhofer e-concept car Type 0", which is currently under construction, based on an existing Artega GT car.

Battery challenges include the need for drivers to know how much farther they can go before they need a recharge, and the fact that cells within large battery packs do not always run down at the same rate. Additionally, if isolated cells fail or no longer work properly, this can affect the functioning of the whole battery.

To deal with these problems, it is necessary to use cross networked battery management systems as well as higher level energy management. Project manager Dr. Matthias Vetter of the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, who is coordinating this part of the plan, explained, "Within fractions of seconds, the electronics measure the line-to-line current, the single cell voltage and the temperature of each cell, and from this determine their state of charge and state of health. This way, a determination can be made for each cell on the threat of overload, excessive discharge, overheating or premature aging. It contains two strings, each with eight modules of twelve cells. For controlling, a total of 16 interlinked battery management systems are used. They communicate with an energy management system integrated into the battery pack via a CAN. The system can equalize differing charge statuses of the cells, and thus always provide maximum capacity and energy. At the same time, it can also issue forecasts."

Speaking of the wheel hub motors, Professor Matthias Busse, head of the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research IFAM revealed that, "We are developing a wheel hub motor that integrates all essential electric and electronic components, especially the power electronics and electronic control systems, into the installation space of the motor. Thus, no external electronics are necessary and the number and scope of the feed lines can be minimized. There is a marked increase in power compared to the wheel hub motors currently available on the market. Moreover, there is an innovative security and redundancy concept, which guarantees drive safety – even if the system breaks down."

As regards the effects of wheel hub motors on vehicle handling. Dr. Hermann Pleteit, IFM project manager, responded, "The motor is extremely compact. The high power and torque densities merely cause a relatively low increase in unsprung mass. But by configuring the chassis in different ways – like the muffler settings, for example - you can compensate for these effects. There is no impact on drive comfort."

Author
Tom Shelley

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