How long will oil reserves last? Are there better alternative drive systems to the internal combustion engine? Discussion of such questions has continued with varying intensity since the invention of the car itself, determined by economic, political and technological factors. For this reason the search for alternative drives was also an issue in the days of Benz & Cie. and Daimler-Motoren-Gesellschaft. And it remains a topic of great relevance for Mercedes-Benz vehicles today. In particular, experimentation is currently focusing on innovative engines and drive systems, on fuels – and on revolutionary principles such as the fuel cell.
Hybrid drives (from 1969)
Mixed drive systems, in particular the combination of electric motor and internal combustion engine, are another option for automobiles of the future in addition to the fuel cell. Since 1969, Mercedes-Benz has been doing research in this area without interruption. But the tradition of hybrid drives goes a long way farther back in brand history: as early as in 1907 Daimler Motoren-Gesellschaft in Vienna Neustadt introduced a Mercedes-Mixte developed by Ferdinand Porsche. Various passenger cars and commercial vehicles followed as hybrid models. But use of the mixed drive came to an end in the first quarter of the 20th century.
In 1969, the OE 302 hybrid bus marked the beginning of new research. During the following years (the first time in a car in 1982) more than 20 concept and research cars with hybrid drives emerged in all vehicle categories from the smart HyPer small car to the Atego truck. In 2005 Mercedes-Benz unveiled an S-Class with hybrid drive at the North American International Auto Show in Detroit. Then, at the 2005 Frankfurt International Motor Show (IAA), two more concept cars based on the new S-Class W 221 were placed on display: the DIRECT HYBRID with gasoline engine and electric motor and the BLUETEC HYBRID, in which a diesel engine works together with the electric unit. The electric motor of both these concept cars develops 8.2 hp (6 kW) and serves as a starter and acceleration booster; moreover, the motor can be used as a generator to transform kinetic energy into electric power.
The accelerated development of hybrid drive systems plays a major role in the systematic further development of conventional gasoline and diesel engines through the use of new, environmentally compatible fuels and the development of alternative drive concepts capable of series production. Hybrid drives in concept and research cars meanwhile have attained fuel savings of up to 20 percent in the New European Driving Cycle (NEDC). Extensive tests in particular with the F 500 Mind research car of 2003 mainly underscore the potential savings in urban traffic, which is characterized by frequent slowing down and moving off and low speeds. Modern hybrids can make very good use of the synergies of the different drive units under such conditions: the electric motor with its high torque moves the vehicle from a standing start and at low speeds, whereas the internal combustion engine powers the car in its optimum performance range. For peak output such as required for accelerating on autobahns, both units work together.
In developing the latest generation of hybrids Mercedes-Benz focuses attention on a powerful and compact drive, a combination of a power split hybrid concept, an intelligent synthesis of serial (separate generation and delivery of power by sequentially arranged units) and parallel (both drives can be used individually or together) hybrid. The patented two-mode hybrid, unlike previously known single-mode systems, operates with appreciably smaller electric motors, which makes the system more compact. But above all the two-mode hybrid covers two operating ranges, obtaining the best possible power output while reducing fuel consumption. DaimlerChrysler is cooperating with General Motors (GM) to develop this two-mode hybrid in an alliance of equal partners which BMW also is joining under a Memorandum of Understanding. In this cooperation, Mercedes-Benz is concentrating on developing rear-wheel-drive and four-wheel-drive cars of the luxury class.
Fuel cell systems as automotive power units (from 1994)
As an electrochemical energy converter the fuel cell is considered to be the most promising of all the alternative automotive energy sources, having a high efficiency, zero emissions when used with hydrogen and very low emissions when operated with methanol. It also has a very wide range of applications as an energy source for example in fuel cell cars, satellites, space stations, emergency backup generators and power stations. The world’s first fuel cell powered vehicle, with which Daimler-Benz researchers proved the suitability of the fuel cell as an automotive power source in 1994, was named NECAR 1, New Electric Car Number 1. The test vehicle, a Mercedes van, was practically a mobile laboratory: the cargo area was completely filled by the very large 800-kilogram fuel cell system with its small hydrogen tank. In 1996 it was already replaced by NECAR 2, a Mercedes-Benz V-Class with an integral fuel cell power unit beneath its short hood. The six seats were fully available to the occupants. The hydrogen tanks were installed on the roof. Top speed: 110 kilometers per hour, operating range: approximately 250 kilometers. 1997 saw the introduction of NECAR 3 on the basis of the Mercedes-Benz
A-Class. The car was fueled with methanol and the hydrogen was for the first time generated with the help of an onboard reformer. The latter immediately converts fuel into hydrogen when the gas pedal is depressed, however it still required a great deal of space in the luggage compartment. The remainder of the system was accommodated in the sandwich floor. The 38-liter tank capacity was sufficient for approximately 400 kilometers.
NECAR 4 was a Zero Emission Vehicle (ZEV) operated purely with hydrogen, based on an A-Class with space for five occupants and their luggage. The liquid hydrogen was located in the rear, in a cylindrical tank. Operating range: up to 450 kilometers, top speed: 145 kilometers. As NECAR 4 had no exhaust emissions whatsoever, the car met the future standards for California as early as in 1999. Number 4 was a decisive step towards series production maturity. A variant of NECAR 4 equipped with even more efficient technology and three compressed-hydrogen tanks in the rear participated in practical trials in California, where intensive field and driving tests under day-to-day conditions were carried out with a total of 15 vehicles until 2003. In NECAR 5, which was presented on November 7, 2000, the entire fuel cell system including the methanol reformer was placed in the sandwich floor of the Mercedes-Benz A-Class. The interior is entirely at the disposal of occupants and luggage. As a result of numerous weight-reducing measures NECAR 5 is approximately 300 kilograms lighter than its direct predecessor, NECAR 3. This benefits both handling dynamics and acceleration. The top speed is over 150 kilometers per hour.
NECAR 5, finally, is a major step towards a fuel cell car suitable for private transport. For the first time in the automobile history, the liquid hydrogen carrier, methanol, provides an automotive fuel which does not come from fossil materials and can furthermore be produced from renewable resources. Fuel cells utilize the energy in the fuel almost twice as efficiently as a gasoline engine. They will therefore safeguard sustainable individual mobility in the future, based on renewable and environmentally highly compatible energy sources.
With the NEBUS, the New Electric Bus which came onto the scene in mid-1997, fuel cell technology also entered the commercial vehicle sector. The hydrogen was stored in seven fiberglass-clad aluminum tanks mounted on the roof. One filling was sufficient for 250 kilometers, the daily mileage of a regular service bus. In 2003 the first 30 fuel cell powered urban buses took up service in major cities in Europe. They were later joined by further buses all over the world. Development’s current “top-of-the-line model” is the Mercedes-Benz Citaro fuel cell bus with an output of more than 200 kW (147 kW) and an operating range of 200 kilometers.
Mercedes-Benz demonstrated the latest developments in fuel cell technology with the F 600 HYGENIUS research car at the 39th Tokyo Motor Show in 2005. The new fuel cell is 40 percent smaller than previous systems, but at the same time much more efficient and powerful: the system develops 85 kW (115 hp) and has maximum torque of 350 Newton meters. This gives it 30 percent better performance than earlier versions, and yet the new fuel cell consumes 16 percent less energy – among other things owing to the electric motor’s ability to recover drive energy during braking and feed it into the lithium-ion battery. Called recuperation, this process is also employed in the current hybrid vehicles from Mercedes-Benz. In terms of diesel fuel, the consumption of the F 600 HYGENIUS is 2.9 liters per 100 kilometers (81 mpg). Progress is now taking tangible shape: at the 2007 Frankfurt Motor show, Mercedes-Benz announced a production version of the B-Class with fuel cell drive for the year 2010.