Mercedes F 600 HYGENIUS In Depth

Press Release

Technology: The latest from the future

• Drive: fuel cell drive made more efficient and practicable than ever
• Body concept: compact-class car offering luxury-class comfort
• Seats: new concept for excellent child safety and a healthy posture
• Dashboard: virtual displays to reduce the strain on the eyes

"The future of the automobile" - this Mercedes slogan takes concrete form in the F 600 HYGENIUS. The research vehicle with its advanced fuel cell drive gives a look forwards to the future of motoring as envisioned by Mercedes-Benz: a future that is completely emission-free and based on a new energy source that is not dependent in any way on the earth's resources of crude oil.

It has only been eleven years since the world's very first fuel cell-powered vehicle took to the roads - a very short time indeed in view of the immense research and development challenge associated with turning this pioneering drive system into automotive reality. Premiered in 1994, NECAR 1 (New Electric Car) was a small van, packed to the roof with some 800 kilograms of componentry that made up the fuel cell power plant. Top speed was 90 km/h and the operating range just 130 kilometres. Today, over 100 Mercedes fuel cell models are being put through their paces in day-to-day operation by customers around the world: "F-Cell" passenger cars built on the platform of the A-Class, small vans and urban buses. They have already covered some 1.5 million kilometres between them and continue to supply vital data on a daily basis that is channelled into the continued advancement of this technology.

This wealth of practical experience and the expertise of a team made up of some 150 scientists and automotive engineers fuelled the development of the new improved fuel cell drive unit in the F 600 HYGENIUS, which represents a major milestone en route to bringing this technology up to series-production standard.

The powerplant aboard the F 600 HYGENIUS, which generates electrical power, heat and pure water from the chemical reaction between hydrogen and oxygen (air), comprises four stacks made up of a total of 400 individual fuel cells. Inside the cells, the chemical elements flow through the fine channels of the bipolar plates: hydrogen on the positively charged side (the anode) and air on the negatively charged side (the cathode). The bipolar plates are separated by a wafer-thin plastic film coated with a noble metal catalyst that allows only the positively charged hydrogen ions (protons) to migrate to the cathode where they react with the air to form water. The film is impermeable for the negatively charged electrons which migrate to the cathode via an external connection instead: this causes the electric current to flow that is used to power the F 600 HYGENIUS.

Several key details of this emission-free process have been optimised by the experts at Mercedes. The bipolar plates are now made from metal plates measuring just 0.15 millimetres thick instead of the graphite material used previously. This improves conductivity and strength at the same time as reducing the amount of space required: as a result, the stacks have been made around 40 per cent smaller compared to the system in the A-Class "F-Cell".

With a view to reducing the drive system's size and weight, while also boosting its power and efficiency, Mercedes-Benz developed a new electric turbocharger to feed air to the fuel cell. This replaces the previous screw-type supercharger which was some three times larger, seven times heavier and considerably noisier.

Intelligent water management enables starts at temperatures as low as -25°C

The only by-product resulting from the chemical reaction between hydrogen and air in the fuel cell is water. This water has an important function to fulfil as it keeps the plastic film between anode and cathode moist, which is essential to maintaining its proton conductivity. Previously, the water produced by the fuel cell was caught in the discharge air and injected in fluid form into the supply air - with the major drawback that the fuel cells froze at sub-zero temperatures.

The improved system used in the F 600 HYGENIUS is notable for its newly developed plastic film that requires far less moisture. This allows the engineers to fit a far simpler humidifying device comprising hollow-fibre bundles that are permeable to water vapour but impermeable to air. After being compressed in the turbocharger, the fresh air flows through the humidifier and absorbs just as much moisture as is needed for the proton exchange at the plastic films. The permanent airflow also helps to "dispose of" the water produced by the reaction and keep the cells free of liquid water. The discharge air is also directed through the hollow-fibre modules where some of the water vapour absorbed in the stack is dissipated to the compressed supply air.

Moist air instead of water, breathable dehumidifiers instead of condensers and pumps - this intelligent principle for water management in the fuel cell represents a major breakthrough as far as cold-start capabilities are concerned. The newly devised gas-to-gas humidifier and the new improved plastic film mean there is no liquid water left in the stacks when the driver switches off the drive unit at the end of the journey. Consequently, there is no risk of the system freezing up in winter; far from it in fact, with the fuel cell drive springing to life even at arctic temperatures as low as - 25° Celsius.

Efficiency climbs to 60 per cent, fuel consumption drops to 2.9 litres

Quite apart from representing a further major step towards full production maturity, these innovations and others make a very healthy difference to the drive system's energy efficiency. Fitted in the F 600 HYGENIUS, the fuel cell system achieves an efficiency factor of around 60 per cent even at partial throttle, making it far more economical than conventional combustion engines which only attain their maximum efficiency of 45 per cent at full throttle.

Expressed in terms of diesel fuel, the latest research vehicle from Mercedes consumes the equivalent of just 2.9 litres per 100 kilometres.

Booster effect for snappy acceleration

Such exemplary economy is also the result of an intelligent energy management system which adapts the drive concept to the driving situation as it changes. Consequently, the F 600 HYGENIUS works in a similar way to a hybrid car:

• During normal driving (at a constant speed), the electric motor is supplied with energy from the fuel cell directly. This puts a maximum of 66 kW/90 hp on tap, with any surplus energy being used to charge the high-voltage battery.
• When accelerating from standstill or overtaking, the high-voltage battery cuts in to supply energy to the electric drive unit as well. This booster effect increases the maximum power available to 85 kW/115 hp.
• When parking or manoeuvring, the battery acts as the sole source of energy with a peak output of 55 kW/75 hp.
• During vehicle braking, the electric motor automatically switches function to act as a generator which charges the battery. This intelligent system of recuperation allows drive energy to be recovered.

700-bar hydrogen reservoir extends range to 400 kilometres

The entire fuel cell system fits underneath the occupant cell of the F 600 HYGENIUS, including a newly developed tank which can store up to four kilograms of hydrogen at a pressure of 700 bar. Both the reservoir capacity and the storage pressure have therefore been approximately doubled compared to the A Class "F Cell" vehicles, extending the maximum operating range to over 400 kilometres.

For the first time in a fuel cell vehicle, Mercedes-Benz is using a high-power lithium-ion battery to store electrical energy. This delivers an output of 30 kW in continuous operation and up to 55 kW at maximum throttle, more than double the power output of the former nickel-metal hydride batteries.

The electric motor fitted to the research vehicle's rear axle has been developed in house, drawing on all of the Stuttgart engineers' experience with the fuel cell drive. Unlike the asynchronous motors fitted in the past, the new unit is a permanently excited synchronous motor whose constant power output of 60 kW/82 hp delivers 250 Newton metres of pulling power, far more than a comparable combustion engine is capable of. The rear-mounted electric motor can even deliver brief power spurts of up to 85 kW/ 115 hp with torque peaking at 350 Newton metres. Here is a summary of the data for the energy and drive system at the heart of the F 600 HYGENIUS:

Fuel cell paves the way for new forms of clean energy supply

The fuel cell points the ways forwards into a future with a guaranteed energy source. Hydrogen is the most commonly occurring of all chemical elements and is renewable, meaning that its manufacture has no implications for the environment. Fuel cells convert hydrogen into electrical energy extremely efficiently in a process that produces neither pollutants nor the greenhouse gas carbon dioxide. To put it in a nutshell: hydrogen is the fuel which, in the opinion of the experts, holds the greatest potential for the future.

For Mercedes-Benz, hydrogen-powered fuel cell vehicles represent the culmination of a five-stage plan targeting mobility that is both free from dependency on crude oil and free from emissions. Consequently, the Stuttgart-based manufacturer is investing heavily in this technology and has undertaken to make it marketable some time between 2012 and 2015. The fuel cell will do more than just put an end to the reliance of motor vehicles on crude oil resources: the new F 600 HYGENIUS, for instance, also presents motorists with new possibilities for energy usage which would previously have been inconceivable.

• At the weekends - when camping or picnicking - the fuel cell can power the coffee percolator, refrigerator, electric grill, television or party lights.
• During the working week, tradesmen are simply able to connect machines and tools up to the fuel cell vehicle's 110/220V power socket, while business executives can take their computer, printer and fax machine with them on business trips and work anywhere they need to.

Passengers even reap the benefit of the fuel cell's power en route: drinks placed in the cup holders between the front seats can be kept chilled or hot using energy from the powerplant.

In theory, the electrical output of the fuel cell in the F 600 HYGENIUS (66 kW) would be sufficient to supply power to several detached houses. This is an interesting concept which merits further investigation.