Siemens researchers are working with French company Segula Matra Technologies to develop a drive system for an electric single seater race car designed for Formulec, a new world racing series. Testing the prototype under racing conditions will provide insights that will help promote the development of electric cars for everyday use.
Before the drive can start its test run, the Siemens-Matra team has to optimally set up, adjust, and connect the vehicle's test rig. A trial is then carefully monitored in the test rig.
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Hockenheimring, Circuit de Monaco, and Silverstone are names that evoke images of the fascinating and glamorous world of motor sports. On the other hand, a small production hall at Siemens' research center in the south of Munich, is quite another matter. At first glance, all you see are a few computers and a pallet holding several metal boxes. Nonetheless, the researchers who work here on a test rig run by Siemens Corporate Technology (CT), might one day end up thoroughly transforming auto racing worldwide.
The researchers are developing a drive system for an electric race car named Electric Formula EF01 that is to take part in the new Formulec race series scheduled to start in 2011. Formulec is comparable to the GP2 race series, which is considered to be the last step before Formula 1. Drivers such as Nico Rosberg and Lewis Hamilton had their first successes in this series.
The concept for the new series was developed by the Alternative Energies Commission of the International Automobile Association (FIA) and was drawn up in close contact with advisors to FIA's President. Formulec is planning the new electric car racing series and French company Segula Matra Technologies has commissioned several firms to develop the required components.
As part of this Electric Formula EF01 project, Siemens CT is responsible for the powertrain, which encompasses the electric motor; the inverter, which converts the direct current from the battery into three-phase alternating current; and associated control units. “We had basically already developed electric motor building blocks for different applications such as trains, machine tools, and cars,” says Prof. Gernot Spiegelberg, who is responsible for electric mobility at Siemens CT. “However, this race car needs a motor that is not only powerful, but light and compact.”
Excellent Efficiency. And that's exactly what Spiegelberg's team is developing. CT researchers are optimizing existing drives and designing a twin-motor drive system for the EF01 project. “We coupled two engines to achieve twice the output,” says Spiegelberg, pointing at one of several metal boxes. The box contains the two motors, each of which has a peak output of 125 kW. However, the power input is limited by the battery, which is why a total of 180 kW (the equivalent of 245 hp) is actually available for driving purposes. With that level of output, the two-motor drive system can propel the race car at speeds of up to 250 km/h.
Karl-Josef Kuhn, a member of Spiegelberg's team and the manager of the electric mobility projects at the test rigs, adds, “What's crucial, however, is of course the mechanical output power, and by that I mean what actually makes it to the wheels after subtracting any losses along the way.” The Electric Formula EF01 system has an output power of 176 kW, corresponding to an efficiency of 98 %.
“That is an extremely good value,” says Kuhn. Normally, electric cars have an efficiency of 95 % at best. By contrast, conventional combustion engines have a thermodynamic efficiency of only about 30 %the remaining energy is lost as waste heat. If you examine the entire functional chain from the source of energy to its consumption (the “well-to-wheel” value), electric cars using renewable energies achieve a value of over 70 %, whereas the value for combustion engines just barely exceeds 20 %.
100 km/h in Three Seconds. Pioneering feats were also achieved for another powertrain parameter, in that the gears for the twin motor are changed by means of a central two-speed transmission. This is unusual because electric cars have a high torque across the entire rpm range. As a result, electric vehicles designed for road use can generally get moving and accelerate to their top speeds without needing gear changes or even a transmission.
“In principle, the Electric Formula EF01 car could also take part in most races in second gear,” says Kuhn. However, on racetracks with very tight curves, such as the Circuit de Monaco, drivers have to temporarily reduce the vehicle's speed so much that it is advisable to change gears by means of a rocker switch in order to achieve optimum racing conditions.
In first gear, the EF01 twin motor accelerates the car from 0 to 100 km/h in three seconds, while in second gear it can achieve speeds of up to 250 km/h. To keep the interruption of the tractive force at the wheels as short as possible, the car's specifications stipulated that gear changes must take place particularly quickly. And indeed, shifting takes place in an eye-popping 150 ms in the Electric Formula car. Dr. Tilo Moser, manager of the Segula Matra project and its research team are especially proud of this parameter. “A highly precise control system is needed in order to achieve this value for our clutchless transmission,” says Kuhn. “This, in turn, required us to optimize the control software.” No other manufacturer that has tried to develop transmissions for electric motors has achieved a similarly effective solution so far.