Fraunhofer developing electric vehicle test platform
By Darren Quick
April 22, 2010
With the internal combustion engine dictating vehicle design for over a century, the move towards electric vehicles offers manufacturers the chance to completely rethink vehicle design. However, it also presents manufacturers with a whole new set of problems to be overcome. To facilitate the transition to electric cars, researchers at Franhofer-Gesellschaft are constructing an electrically operated demonstration vehicle, the “Frecc0,” which will serve as a scientific integration platform for automobile manufacturers and suppliers to test new electric vehicle components.
The Frecc0, which is an abbreviation for “Franhofer e-concept car Type 0,” is based on an existing car – the new Artega GT from Artega Automobil GmbH. Franhofer recognized that the move to electric vehicles will see the automotive industry no longer using certain parts for vehicles, with new ones taking their place instead. So, starting next year, automobile manufacturers and suppliers will be able to use the Frecc0 for testing new components.
Naturally, Franhofer will also use the Frecc0 to test a number of its own components under development, including a crash-proof battery system, a wheel hub motor and a battery charger.
Battery SystemExperts from eleven Franhofer institutes are working on a cross-networked battery system that lets drivers know how much farther he can get before the battery needs a recharge. Range can be relatively simple to determine for a gas-powered vehicle, but this is not so easy for a battery-powered car. This is because a lithium-ion battery system mostly consists of several hundred cells, and they do not always run down at an equal pace. And if isolated cells break down or no longer deliver the intended capacity, then the entire battery may be affected.
To counter these problems, elaborate, cross-networked battery management systems are used, as well as a higher-level energy management system. Researchers are developing such a system, which until now, has only existed in prototypes – and only for stationary battery systems.
Project manager Dr. Matthias Vetter of the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, who is coordinating the plan, explains the basic principle this way: "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 databus widely used throughout the automotive industry – a CAN (Controller Area Network). For example, 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," said Vetter.
The electronics also measure the onward and reverse flow temperatures of the attached cooling circuit. On the one hand, the pump should ensure that no overheating occurs; on the other hand, it should consume as little energy as possible itself. To do so, the system also controls the cooling circuit by means of a model-based regulator, thus optimizing energy consumption, lowering peak temperatures, and increasing reliability.
At the same time, the system takes over communication with the vehicle. For instance, it submits forecast reports on distances and threshold values, both for drive control as well as for charging operations. In addition, it monitors itself to determine if the desired power violates critical current and voltage limits. Then, at any time, the driver can read from the instrument panel how far he needs to drive until the battery has to be recharged.
In the event of an accident the higher level energy management is capable of shutting down the battery either in its entirety, or just line-by-line, through the use of its circuit breaker.
Wheel Hub MotorsWheel hub motors were invented back in the 19th century. Ferdinand Porsche used these motors to equip his “ Lohner Porsche” at the 1900 World Fair in Paris. Now manufacturers are looking to such motors to drive the next generation of electric vehicles. Since the motors, such as the Michelin Active Wheel System, are attached directly to the wheels, it opens up a wealth of opportunities for car designers when drafting the layout of a vehicle as they can dispense with the conventional engine bay.
“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,” explains Professor Matthias Busse, head of the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research IFAM.
And to those detractors that say wheel hub motors have negative effects on vehicle handling, Dr. Hermann Pleteit, IFM project manager, has this to say: “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.”
The Frecc0 will provide a platform to test how these components behave in a car as a total system, and will help automobile and automobile component manufacturers speed up their pace of innovation in relation to the next generation of electric vehicles.
The Frecc0 is part of the “Franhofer System Research for Electromobility” project and is making its debut appearance at this year’s Hannover Messe, which is running until April 22.