Press Kit: History of fuel cell development at Mercedes-Benz
Stuttgart
Jun 25, 2007
Into the future with NECAR and NEBUS
NECAR 1, 1994: Laboratory-like van
On April 13, 1994, Daimler-Benz invited the international press to come to Eselsberg hill in Ulm, Germany, site of Ulm University and the new Daimler-Benz Research Center. The arriving journalists knew that something special was in the air since Edzard Reuter, chairman of the Board of Management of the integrated technology group, was scheduled to open the press conference and not, as originally expected, the host of the Ulm facility, Prof. Hartmut Weule, Board of Management member responsible for Research.
They were not disappointed because, to their astonishment, what Reuter and Weule introduced to them was not the new Research Center but the first vehicle in Europe featuring fuel cells capable of operating under workaday conditions. The vehicle was christened NECAR (New Electric Car). To distinguish it from subsequently introduced, further developed vehicles, it was eventually named NECAR 1.
NECAR 1, a Mercedes-Benz MB 100 van model, had already run up several thousand miles by the time of its presentation, operating on German roads with its revolutionary electric drive trouble-free since December 1993.
The research vehicle was more like a mobile laboratory than an automobile suited for daily use. The 800 kilograms (1,800 lbs) of the quite compact, though still voluminous, fuel cell power generation system, with hydrogen as fuel, including electronic controls, compressor, cooling system and hydrogen tank, plus a number of measuring instruments, filled the entire cargo space.
The output of the total twelve fuel cell stacks from Ballard Power Systems Inc., Canada, was 50 kilowatts (kW). The tank held 150 liters (40 gallons) of compressed gas (300 bars), adequate for a range of about 130 km (80 miles). The electric motor developed 30 kW/41 hp, giving NECAR 1 a top speed of 90 km/h (56 mph).
With this vehicle, Daimler-Benz proved to a worldwide audience beyond all doubt the basic suitability of the fuel cell technology as an electric vehicle propulsion system and, at the same time, highlighted its biggest advantages: its energy converting efficiency, appreciably higher than that of all drive systems previously used for automobiles employing internal combustion engines; its highest levels of environmental friendliness; and the fact that it used resources sparingly.
The range and speed of NECAR 1, though still modest, encouraged all interested parties. The next objectives were to reduce the size of the system, put more efficiency into it and, of course, take weight out of it. In addition, future fuel-cell-powered vehicles from Daimler-Benz had to permit operation on methanol, a liquid fuel that can be handled almost like gasoline.
Prof. Weule could be proud of what had been achieved in only three years. After all, he was the man who had unflaggingly been pushing ahead the development of the fuel cell vehicle drive since 1991.
NECAR 2, 1996: V-Class, six-seater
A Mercedes-Benz V-Class, a multipurpose vehicle with up to three rows of seats, which was just in the making at the time, was chosen as component carrier for the next research vehicle. On May 14, 1996, Daimler-Benz presented to the public the world’s first passenger car with fuel cell drive – NECAR 2. The V-Class – officially, the model did not begin selling until September – featured a 45-kW/62-hp electric motor under the short hood and an integrated 50-kilowatt fuel cell power plant.
The two hydrogen tanks, each holding 140 liters (37 gallons), were located under a dome on the roof which emphasized the body lines. The maximum speed was 110 km/h (68 mph) and the range a good 250 kilometers (155 miles). The six seats were available to the occupants with no restrictions.
In place of the twelve fuel cell stacks of NECAR 1, total output 50 kW, NECAR 2 now had only two stacks consisting of 150 cells each but the same overall output. First and foremost, this was achieved with completely newly developed fuel cells with more effective power output and higher operational reliability. The waste air from the fuel cells was used for energy recovery and optimal air supply to the fuel cells.
All in all, the fuel cell system in NECAR 2, reduced in size and volume, weighed only about 270 kilograms (600 lbs) or one third of its predecessor. The scaling down of the system and the enhancement of efficiency were accomplished. The future of the fuel-cell-powered vehicle had been brought a little closer.
The Group,” said Daimler-Benz Research Chief Prof. Weule on the occasion of the presentation of NECAR 2, “continues traveling in the fast lane worldwide with this revolutionary technology. No other company in the automotive industry in Europe, the U.S.A. or the Far East has attained our level in research activities regarding the fuel cell.”
The presentation of NECAR 2 caused a sensation throughout the world: “The Times” called NECAR 2 “a breakthrough in exhaust-free driving.” “Reuters” called it a “a giant step forward for Daimler and Ballard, who have reduced the cells to less than one fifth of their original mass without sacrificing power.” The specialized “Hydrogen & Fuel Cell Letter” pointed out that the U.S. Energy Department’s timetable did not provide for a fuel cell energy system before 1998, a concept car before 2000, or a prototype before 2004. The Letter estimated that “Daimler’s announced schedule is at least four years ahead of the U.S. plans.”
NEBUS, 1997: Environmentally compatible city bus
Thought was first given to a bus with a fuel cell drive in March 1994, even prior to the presentation of NECAR 1. On May 26, 1997, Daimler-Benz finally presented the NEBUS (New Electric Bus) in Stuttgart. It was the product of the collaboration of Daimler-Benz Research, EvoBus GmbH, the Group’s Competence Center for Emission-free Commercial Vehicles (KEN) and Zahnradfabrik Friedrichshafen.
The basis of the NEBUS was the Mercedes-Benz O 405 OH standard city bus. It used hydrogen as source of energy and was therefore a genuine “Zero Emission Vehicle”. Thanks to electric drive it was extremely quiet; one could merely hear the low hum of the wheel hub motors, the air compressor and the tire noises. The practical bus, licensed by the German Technical Inspection Association, was 2.50 meters (8ft 2 in) wide, 3.50 meters (11 ft 6 in) tall and 12 meters (39 ft 4 in) long, had a curb weight of 14 tons and accommodated 34 seated and 24 standing passengers. The entrances were only about 34 centimeters (13 inches) above the ground. This low-floor design was made possible by the wheel hub drive developed by ZF Friedrichshafen in which electric motors close to the wheels directly transmitted the current from the fuel cells to the wheels.
During braking, the wheel hub motors acted as “engine brakes,” producing excess current in the process which was converted into heat on the roof in water-cooled brake resistors and escaped into the atmosphere. The transmission and drive shaft required by a diesel bus were dispensed with.
NEBUS had a range of 250 kilometers (155 miles) on one tank filling, easily enough to handle the average daily distance covered by a regular service bus, 140 to 170 kilometers (87 to 106 miles). Its top speed was around 80 km/h (50 mph).
Owing to the powerful wheel hub motors, shifting was unnecessary; the bus’s gentle, continuously variable acceleration scored well with passengers. The reaction time of the fuel cells was very dynamic: when the accelerator was depressed, the power was available in less than one second and proved to be entirely comparable to that of a good diesel engine. Air-cooled 75 kW/102 hp three-phase asynchronous motors were fitted – one each on the right and left of the rear axle. The total output of 150 kW/204 hp matched that of a good diesel drive. There were additional supply systems and reserves for the on-board electric power supply with power steering, compressed air, brakes and door controls.
Ten stacks with 150 fuel cells each fitted in the rear of the NEBUS delivered a total output of 250 kilowatts and 720 volts of electricity. 21 kilograms (46.25 lbs) of hydrogen were stored in seven roof-mounted fiberglass-wrapped pressurized aluminum tanks at a pressure of 300 bars.
The NEBUS was about 3.5 tons heavier than a conventional diesel bus and had a relatively high center of gravity. To prevent the roof load of some 1,900 kilograms (4,185 lbs) from amplifying any pitch and roll especially during cornering, specially developed sensor-controlled adaptive shock absorbers suppressed these tendencies by adjusting the tension and compression stages of the shock absorbers to the different loads and permitting only slight tilt, much to the benefit of the passengers and their safety.
The on-board electric system featured three distinct voltage levels: 600 volts for driving and for the ZF axle with the wheel hub motors; 380 volts for the power steering pump and the air compressor, and finally 24 volts for the vehicle power supply and the reserve power steering pump. Another environment-friendly detail were the solar roof hatches with the aid of which the electric current generated by solar cells was converted to operate the air-conditioning and ventilation ducts independently of the rest of the electric system.
The NEBUS proved its workaday suitability in real-world operation in Mannheim; further demonstrations in various locations around the world followed.
In 1998 the Daimler-Benz partner Ballard Power Systems Inc. delivered three American “P3” prototype buses with fuel cell drive as test vehicles to the Chicago Transit Authority and three to BC Transit, Vancouver.
NECAR 3, 1997: A-Class with methanol reformer in the trunk
At a Board of Management meeting in April 1996 Dr. Dieter Zetsche, head of Development at the time, emphatically spoke out in favor of getting the next fuel cell concept car – it was planned to build a Mercedes-Benz A-Class to run on methanol – on its wheels as quickly as possible, even if the methanol reformer that was undergoing development was not yet minimized in volume to an extent that it could be fitted into the sandwich floor of the A-Class.
With this car, Prof. Weule saw his vision of 1991 fulfilled: within five years, he had imagined traveling in a vehicle that uses easy-to-handle methanol as a fuel, which is reformed into hydrogen on board the vehicle.
September 10, 1997, thus rang in a new era of alternative vehicle propulsion systems with the showing of the NECAR 3 in Frankfurt am Main, a car based on the A-Class, the compact Mercedes-Benz with the double floor and the modest length of 3.60 meters (11 ft 10 in). The pioneering innovation in this car was the world’s first fuel cell system incorporating the on-board production of hydrogen. Methanol served as fuel; the hydrogen needed to operate the fuel cell was generated from it with the aid of a reformer.
The reformer – a complex in-house development of Daimler-Benz, still in its early stages –used in the NECAR 3 had the character of a laboratory model. It needed a great deal of space in the rear passenger compartment and definitely required further reduction in size. The “rest” of the fuel cell system was already working “underfloor.” When the gas pedal – a gas pedal it was, indeed – was depressed, the system responded, delivering 90 percent of its maximum output in just two seconds – a fuel cell car with the dynamic power of an automobile with combustion engine.
This sedan was the first of a new generation of fuel cell cars equally suitable for use in heavily populated downtown areas as they were for long-distance journeys, because refueling with methanol – every filling station could offer this fuel in future – would be a familiar exercise for the owner of such a vehicle.
As in NECAR 2, in NECAR 3 two stacks with 150 fuel cells each sufficed to generate 50 kilowatts output. They worked at a temperature of about 80°C (176°F). The water produced during operation of the fuel cells was reused to reform the methanol into hydrogen.
A tank filling of 38 liters (10 gallons) of methanol provided a range of easily 300 kilometers (186 miles), and the electric motor developing 45 kW/61 hp permitted a top speed – intentionally limited – of 120 km/h (almost 75 mph).
NECAR 4, 1999: Emission-free driving pleasure
NECAR 4, also based on the Mercedes-Benz A-Class, was a “ZEV,” a Zero Emission Vehicle with pure hydrogen operation, and was presented to the world on March 17, 1999, in Washington, D.C., by Jürgen E. Schrempp and Robert J. Eaton, then CEOs of DaimlerChrysler.
Outstanding features were the space for five passengers plus luggage, the range of over 450 kilometers (280 miles), and the driving pleasure afforded by a top speed of 145 km/h (90 mph). In short: emotions instead of emissions.
The two stacks in NECAR 4 each consisted of 160 individual, tightly packed fuel cells which together attained an output of 70 kilowatts, about 40 percent more than the predecessor, NECAR 3. They fitted together into a suitcase-sized box and thus all found room in the underfloor of the A-Class.
The fine touches to the cell components resulted in a clear-cut improvement in power generation and current intensity, which was now around 340 amperes – in contrast to the 260 amperes of NECAR 3 – with no impairment of efficiency. In this case efficiency means: of the chemical energy contained in the hydrogen, as much as 80 percent is converted into electric energy at part load, and still a good 50 percent at full load.
In NECAR 4 the electric motor and transmission also were of new design: the transversely installed asynchronous motor in the nose of the A-Class with an output of 55 kW/75 hp embodied a new design principle in which the motor enclosed the drive axle. The transmission was integrated in the right side of the motor to save space. From there one half-shaft led directly to the right front wheel; the other ran through the motor to the left wheel. Moreover, this motor attained its maximum torque as early as the car moved off, a decisive characteristic for very dynamic driving performance.
The cold liquid hydrogen (-253°C or -423°F) was located in the rear in a cylindrical tank of 100 liters (26.5 gallons) or five kilograms (11 lbs) capacity; it extended slightly into the trunk from below. To maintain the extremely low temperature, it was made up of two steel capsules, one inside the other, so that it looked like an oversized thermos flask.
But since the fuel cells required gaseous hydrogen to operate, the ice-cold liquid fuel passed into the gaseous state on the way to them. This was achieved by means of two heating elements integrated in the tank; they ensured that the stacks were supplied with hydrogen gas immediately upon starting and allowed them to supply electricity instantaneously. The result was starting behavior which easily compared with that of conventional vehicles.
NECAR 4 was a vehicle which was very well suited for fleet use, for delivery services, and for taxis operating in a defined region. The quiet and emission-free vehicles can return to their fleet headquarters and be supplied again with new energy at a central hydrogen filling station. Refueling hardly takes any longer than for a gasoline- or diesel-engined vehicle.
NECAR 4a (advanced) 2000: Practical testing with hydrogen
The NECAR 4a version served practical testing. Introduced on November 1, 2000, NECAR 4a became the basis, already prepared for small series, of further planned A-Class cars of the same design, intended to undergo intensive field and road tests in California until 2003 under everyday conditions in the California Fuel Cell Partnership.
In contrast to the NECAR 4 introduced in 1999, the “California” NECAR 4 operated on compressed hydrogen. It also attained a top speed of 145 km/h (90 mph), but additionally featured better driving dynamics owing to the optimized 55 kW/75 hp electric motor.
In the compact fuel cell system, the core of which was now made up only of a single Ballard Mark 900 stack with 75 kilowatts output, the volume could be halved and the weight reduced by another third. The three hydrogen tanks in the underfloor, with a volume of 140 liters (37 gallons) each, were pressurized to 350 bars. The approximately two kilograms of hydrogen sufficed for a range of 200 kilometers (over 120 miles). The use of components of lightweight design both in the passenger compartment and the body additionally reduced weight.
NECAR 5, 2000: A milestone on the way to production standards
NECAR 5, after NECAR 4a actually the sixth version in the line of NECAR concept cars, was presented on November 7, 2000, in Berlin by Jürgen E. Schrempp, then Chairman of the Board of Management of DaimlerChrysler, in the presence of then German Chancellor Gerhard Schröder.
NECAR 5 was the world’s most advanced fuel cell car and the mature successor to NECAR 3, with which the Group first demonstrated in 1997 that hydrogen for the fuel cell can be obtained from methanol with the aid of a reformer on board the vehicle.
The still quite voluminous reformer of NECAR 3 was halved in size in only three years, and its weight was reduced appreciably. So for the first time, NECAR 5 housed the entire fuel cell system including reformer in the sandwich floor of the Mercedes-Benz A-Class, whose interior now belonged entirely to the passengers and their luggage. The top speed was over 145 km/h (90 mph), and the car was capable of covering a distance of more than 400 kilometers (250 miles) before refueling – thanks to the 45-liter (12-gallon) tank.
Also due to measures designed to reduce body weight, NECAR 5 was about 300 kilograms (660 lbs) lighter altogether than its direct predecessor, NECAR 3. Driving dynamics and acceleration benefited from this, as they did from the more powerful 55 kW/75 hp electric motor and the higher output of the fuel cell, whose sole stack module delivered 75 kilowatts as in NECAR 4a. This module, together with the sensors, the humidifiers and the electronics, fitted into a vibration- and shock-resistant container with compact dimensions (80 x 40 x 25 centimeters or 32 x 16 x 10 inches).
The Ballard Mark 900 stack was already designed for large-scale production. Owing to a newly developed coolant on ethylene-glycol basis, the drive system was now frost-resistant and ready to start even in icy winter weather. Like the diesel engine of former days, the system required a warm-up time before reaching working temperature.
1,111-kilometer record run with NECAR 5
For the Mercedes-Benz research cars of the NECAR series it has always been: drive, drive, drive – as much and as far and as long as possible. To demonstrate the performance of NECAR 5, the car was put through a first long-distance test in December 2001 on highways No. 1 and 101 in California. It ended with a new record: 1,111 kilometers (690 miles) in two days. During this record run the car managed about 13 hours of daily operation with no problems worth mentioning. It was the longest test drive of a methanol-powered fuel cell vehicle until then. Thus, the propulsion technology of NECAR 5, with fuel refilled the conventional way, fulfilled the hopes placed in it on its first major attempt. Further long-distance trials were scheduled in which the main concern was coping with difficult topographic and climatic conditions.
 
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