* F 600 HYGENIUS illustrates the transfer of technology from research vehicles to series production

At the Tokyo Motor Show in October 2005, DaimlerChrysler presented the first-ever research vehicle specifically designed as a fuel cell car: the F 600 HYGENIUS. While developing and constructing the unique four-seater, engineers were able to benefit from the extensive experience they had gained with cars such as the A-Class F-Cell.

The vehicle's entire drive unit, including the pressurized hydrogen storage tanks, is tucked away in the vehicle’s sandwich floor, as is the case with the 60-vehicle F-Cell fleet. This type of architecture makes possible a range of technical improvements and innovations that distinguish the F 600 HYGENIUS from a normal F-Cell vehicle.

The most important innovations in the fuel cell drive for the F 600 HYGENIUS include:

    * A newly developed fuel tank that stores hydrogen at 700 bar rather than the previous 350 bar — enabling the vehicle to hold four kilograms of hydrogen and travel a distance of more than 400 kilometers on one tank.
    * A new membrane technology for the fuel cells and a new humidification system consisting of hollow fibers. Both of these innovations allow for precise heat and water management, which means that water in liquid form no longer collects in the stack. Such water accumulations freeze in the winter and make cold starts difficult — but the F 600 HYGENIUS starts easily even at temperatures as low as minus 25 degrees Celsius.
    * A new electric drive unit on the rear axle in the form of a permanently excited synchronous motor that is both smaller and more powerful than its predecessor from the F-Cell.
    * A lithiumion battery that produces 30 kilowatts of power in continuous operation and 55 kilowatts at peak loads — twice the output of the nickel metal hydride batteries previously used.
    * New bipolar plates that are no longer made of graphite but instead consist of metal foils only 0.15 millimeters thick. The metal improves the conductivity and robustness of the fuel cells, and the thinner foils make the stack around 40 percent smaller than before.
    * A new electric turbocharger that supplies air (oxygen) to the fuel cells. This turbocharger is three times smaller and seven times lighter than the previously used screw-type compressor.

Together with other innovations, the new technology package is responsible for the improved fuel economy of the F 600 HYGENIUS, which consumes the energy equivalent of only 2.9 liters of diesel fuel per 100 kilometers. The research vehicle’s fuel cell system operates extremely efficiently: In the partial load range, it has an efficiency rating of 60 percent.

Test drives with clear objectives

Because the F 600 HYGENIUS is a fully operational research vehicle. Researchers and developers actually drive it every day in an effort to further improve its fuel cell powertrain system. In order to examine the stack's power output and fuel consumption, the engineers take the vehicle on different kinds of test drives that measure every conceivable parameter under everyday conditions. They also put the compact research vehicle on the roller test stand, which runs the car through defined driving cycles.

“After all, we want to improve the robustness and service life of the entire system — and the best way to see if we’re succeeding is to take the vehicle on test drives over long distances,” says Dr. Andreas Docter, who was responsible for the construction of the fuel cell system used in the F 600 HYGENIUS and also heads the Fuel Cell Systems Engineering department at DaimlerChrysler Research.

A further goal of the F 600 HYGENIUS test drives is to develop an optimal operating strategy for future B-Class F-Cell vehicles. The questions posed here include: Would it make sense to operate the vehicle only with the stack or only with the high-voltage battery? Under what conditions and performance demands should the booster function be activated, whereby energy for the electric motor is supplied by both the fuel cell and the battery? What are the best situations and points in time to shift the vehicle from one mode to the other? In which charge stage and driving situation should the motor be used as a generator and the battery be recharged? When searching for the answers to these questions, the engineers must take into account a variety of secondary parameters such as driving dynamics, fuel consumption and functional safety.

From the F 600 HYGENIUS to the B-Class F-Cell

The stack that will be used in the B-Class F-Cell and — as a double pack — in the successor model to the Citaro fuel cell bus will include a series of innovations from the F 600 HYGENIUS. Second-generation fuel cell vehicles will thus benefit not only from the experience already gained from fleet tests with the 60 A-Class F-Cell cars, but also from the new expertise gained from DaimlerChrysler’s most recent research vehicle.

The most important technological innovations that DaimlerChrysler will take from the F 600 HYGENIUS are:

    * The 700-bar tanks for storing hydrogen, in order to increase the full-tank range from today’s 160 kilometers to more than 400 kilometers.
    * The electric drive motor. This permanently energized synchronous motor, which stands out through its light and compact design, has a maximum power output of 85 kilowatts and achieves a maximum torque of 350 Nm.
    * The powerful lithium-ion battery, which serves as a high-voltage energy storage unit.
    * The technically simplified humidification and de-humidification system consisting of hollow fiber modules that lends second-generation stacks freeze-start capability.

Two other innovations from the F 600 HYGENIUS will be gradually introduced to new fuel cell fleets. First of all, the bipolar plates in the fuel cells will be made of metal foils in the future, allowing for more space-saving installation than today’s graphite plates. Secondly, a light electric compressor — rather than the heavy screw-type compressor — will be used to supply air to the stacks.

Challenges for the future

DaimlerChrysler researchers are already looking far beyond the launch of commercial applications for fuel cells in automobiles. They are examining new procedures and materials that may one day lead to further technical improvements. For example, the scientists are working on a wide range of new catalytic materials for fuel cells that require only small amounts of platinum and allow for a very long lifetime. In addition, they are assessing the advantages and disadvantages of wheel hub motors, which are constantly mentioned in connection with electric drive systems, and are also attempting to develop optimization strategies for such motors.

Technology transfer from research vehicles to series production

Mercedes-Benz has presented 11 research vehicles since 1981. The technologies and interior and exterior design concepts in these unique automobiles have often served as clear indicators of the direction automotive development is taking. Many of the systems first used in research vehicles and viewed as revolutionary just a few years ago are now used in production vehicles.

Such systems include Distronic — a proximity cruise control feature that was implemented for the first time in the F 100 research car in 1991 and was launched in a production vehicle in 1998 (S-Class). The F 100 was also equipped with gas-discharge lamps, which as xenon lights are now standard equipment in many vehicle models. Other examples of the successful transfer of systems from research vehicles to series production are Active Body Control (which is today found in the CL, S and SL-Class), window bags, cornering lights and voice-operated vehicle systems. The F 600 HYGENIUS and the fuel cell powertrains based on its fuel cell system will continue in this tradition and pave the way for the series production of environmentally friendly zero-emission technology.