Commuter comfort on a new basis
Trailblazer for alternative drive systems
Continuous expansion into an extended family of buses
In the late 1970s, the standard regular-service urban bus
Mercedes-Benz O 305 and its sisters, the O 305 G and O 307, had reached a tremendous level of maturity. On the other hand, the time had come to develop a successor. The premier comfort feature of urban buses, with passengers frequently boarding and alighting after short trips, is a low bus floor and convenient entrance. This not only applies to passengers whose mobility is impeded; for all other passengers too it means rapid and safe entry and exit.
“S 80” was the prototype of a new generation of Mercedes-Benz urban buses which went into trial operation in 1980. Its technology and equipment were defined by a committee of the Association of Public Transport Companies (VÖV, today the Association of German Transport Operators (VDV), in which operators and manufacturers jointly worked out a uniform concept for standardized buses in a specifications book. However, the new buses were ahead of their time: The low-profile tires caused problems because they got too hot. As a result, not only was tire mileage reduced, but brake service life too.
Based on this experience, the demands on the new standard regular-service urban bus were reduced. The tires were made bigger, but two steps instead of the previous three of the first generation made entering the new buses much more comfortable. The look of the new Mercedes-Benz O 405 standard regular-service urban bus of 1983 was close to that of the S 80. Characteristic features: the cubically designed 11.5 meter long body with generous glazing and the big destination indicator box over the windshield, plus a striking U-shaped bumper which enclosed the rectangular headlamps. Headroom and the lines of sight were considerably enlarged; inside, the O 405 seemed much more spacious than its predecessor. An improved heating and ventilation system gave the interior the right temperature. Initially, engine output started at 150 kW (204 hp) delivered by a horizontally installed in-line six-cylinder at the rear of the bus.
NAW contributes a special midi version
One year later the compact midibus Mercedes-Benz O 402, optically a shortened
O 405, rounded off the urban bus range at its lower end with 50 seats for passengers. The chassis came from the Swiss affiliate NAW Nutzfahrzeuggesellschaft Arbon & Wetzikon, successor to the tradition-steeped Swiss commercial vehicle makers Saurer and FBW. Also in 1985, an Italian bodybuilder produced the compact Mercedes-Benz
O 301 touring coach for Daimler-Benz on the basis of the NAW chassis. It closed the gap between the O 309 and the O 303. However, neither midibus was destined to have a long life.
1985 was a vintage year for innovations in the regular-service buses with the star. The O 405 got a big brother, the articulated pusher bus O 405 G. As it did with the previous bus series, Daimler-Benz presented a standard rural-service bus, just under 12 meters in length, designating it the O 407. Visually and technically a derivative of the urban bus O 405, it differed from the O 405 among others things in having a one-piece windshield and a higher floor with a luggage compartment underneath as well as a single-wing door at the front. One hundred years after the invention of the automobile by Gottlieb Daimler and Carl Benz, the company’s buses, with the O 303 and O 405 as mainstay, presented themselves in the very best shape.
First articulated bus with a diesel-electric drive
Further variants of the Mercedes-Benz O 405 debuted just a year later. They included the O 405 T trolleybus and, as test object, the O 405 GTD dual-powered bus, an articulated bus with a diesel-electric drive. Innovative power was demonstrated again in 1989. At the Frankfurt International Motor Show two new buses simultaneously celebrated premieres. The low-floor urban bus O 405 N featuring front and central entrances with no stairs and a low floor all the way to the rear axle rang in a new era of comfort in public transit. Between regular-service bus and touring coach, Daimler-Benz positioned the O 408. This combination service bus was suitable for regular service and excursion use and consequently was a bus for daily operation around the clock. It was based on the O 407 and had that bus’s angular face and massive U-shaped bumper, but also had a large, curved, undivided windshield with the destination indicator box inside. Also, the side windows extended up to the roof. There was a fully glazed single-wing door at the front and a double door in the middle. Excursion seats with high backrests, on raised platforms, and luggage racks identified the O 408 as suitable for excursions. A powertrain with up to 220 kW (299 hp) and a six-speed transmission also showed this to be an excursion bus. For regular service use,
184 kW (250 hp) and five speeds would make do if necessary.
Daimler-Benz completed the range of regular-service buses in 1992 with the low-floor articulated bus O 405 GN and two years later with another low-floor bus, the O 405 NÜ for rural service.
In the 1990s the topic of alternative drive systems again gained importance. At the beginning of the decade tests were conducted with hydrogen drive. In 1994 Daimler-Benz presented Europe’s first natural gas-powered low-floor urban bus, the
O 405 GNG articulated. Parallel to this there was the O 405 NG solo urban bus and the rural-service bus O 405 ÜNG. A total of 15 gas-fired buses were tested in practical operation nationwide at transit companies.
Typical for the gas-powered buses was a box-like hump on the roof. It contained the gas cylinders, whose contents were compressed to a pressure of 200 bar. The specially designed steel cylinders wrapped in aramid fiber can even withstand 500 bar. The engine was based on the horizontal in-line six-cylinder OM 447 hA, a conventional turbocharged diesel engine that was converted to a spark-ignition engine. The power was regulated by means of a throttle valve. The big advantage of the natural gas-powered vehicles: they did more than twice as well as required by the future Euro 2 emission standard, two years before this standard went into effect. The range of the new natural gas-fired buses was about 300 kilometers.
That same year the prototype of the O 405 GNTD dual-powered articulated bus premiered: this low-floor articulated bus had a diesel engine and an electric wheel hub drive. It could also be designed as a trolleybus. The diesel engine was fitted in an unusual position in this dual-powered bus: transversely, at the rear. This way it made room for a door with a low-floor entrance behind the rear axle. The unaccustomed position was possible because the GNTD made do without a transmission and differential: The energy produced by the diesel engine via a generator (or, alternatively, fed in from the electricity grid) was transmitted to two each air-cooled wheel hub motors on the center and rear axles. Together these motors developed 300 kW and simultaneously serve as generator brake and thus as a service brake.
Numerous new developments shared the limelight at the 1996 International Commercial Vehicle Show in Hanover. At a mature age, the O 405 the gradually was developing into a large family. There was the O 405 NÜL, a long, two-axle version of the low-floor rural-service bus, with two axles and a length of 13.4 meters. It showed what was possible, anticipating future permissible dimensions. A step in the opposite direction was the short urban bus O 405 NK: at 10.4 meters overall length it could be classed as a midi. And it already could be had with a natural gas-fired engine. For buses which operate on biodiesel, Mercedes-Benz made 500 oxidation catalysts available as part of a large-scale test. A combination bus for rural service and excursion work supplemented the O 405/407 family and took the place of the rather stern looking O 408: The O 550 Integro was the first new bus from the still young EvoBus combine. And it was the first bus from Mercedes-Benz that bore a name.
The fuel cell premieres in the regular-service bus
In 1997 the new developments continued to appear in quick succession. NEBUS was the name of a Mercedes-Benz O 405 with a novel type of drive system: it was the world’s first fuel cell-powered bus suited for regular service. It pointed new ways to an environmentally friendly future. The NEBUS emitted no exhaust gases; only water issued from the exhaust pipe. NEBUS stands for “New Electric Bus,” but could also mean “No Emission Bus.” The fuel of the revolutionary vehicle was hydrogen which was stored in cylinders on the roof, the same as in the gas buses. The rear end of the bus accommodated ten fuel cell stacks, each with a power output of 25 kW. In an electrochemical reaction they converted hydrogen into electricity, which in turn drove the wheel hub motors. The new bus was extremely quiet in operation; acceleration was very dynamic. The local exhaust emissions consisted exclusively of harmless water vapor.
NEBUS was both climax and end of the development of the O 405, whose exceedingly successful career gradually was coming to a close after more than a dozen years. Born as a second-generation standard bus, the O 405 had gone through an almost incredible evolution: it embarked upon a second career as a low-floor bus, and in the process even surpassed the initially planned S 80 for passenger friendliness. Numerous variants grew out of its original specifications book; with different drive systems, including even the fuel cell, it pointed a way far into the future.
The great success of the O 405 can best be measured in figures: around 12,000 solo buses, more than 3700 articulated buses, about 5000 rural-service units including the O 407 and O 408 add up to the impressive figure of 20,488 regular-service buses from a single family. With that the O 405 set a tremendously high standard by which its successor would be measured. But the successor stands a chance of outdoing even the O 405, for in the Citaro, in 1997 Mercedes-Benz presented a revolutionary concept for regular-service buses.