Following successful practical trials in December 2009, Stuttgarter Straßenbahnen AG (SSB) has now brought three Mercedes-Benz Citaro G BlueTec Hybrid buses into service, with a further two vehicles due to be delivered later this year.
The environmentally-friendly hybrid bus met with an excellent response from passengers during last year’s week-long practical trial, and also demonstrated significant fuel savings on the inner-city 42 route, one of the area’s most demanding routes with the most varied topography.
Today Hartmut Schick, head of Daimler Buses, handed over the three articulated hybrid buses to Wolfgang Arnold, board member of Stuttgarter Straßenbahnen, in the presence of Dr. Wolfgang Schuster, mayor of the provincial capital of Stuttgart, and Andreas Renschler, board member of Daimler AG with responsibility for Daimler Trucks and Daimler Buses. “Thanks to these new hybrid buses, Stuttgart is once again making significant steps forward on the road towards sustainable urban mobility. I am pleased that we are again able to demonstrate our leading role in this area. Stuttgart makes the ideal testing ground for new forms of transport and new technologies: what proves to be successful here usually goes on to be a bestseller elsewhere. I am extremely grateful to Daimler AG for the future development potential they are offering along with their creativity, and above all for co-operating with the city of Stuttgart in the field of mobility”, explained Dr. Wolfgang Schuster.
At the official handover, Andreas Renschler said: “We are extremely pleased that our long-standing customer from Stuttgart will be making use of the articulated hybrid buses from Mercedes-Benz and their cutting-edge technology in Stuttgart, and as such these are the first buses of this type to be brought into service in Baden-Württemberg. For decades, SSB’s bus and coach strategy has been consistently geared towards trialling or implementing new technologies, and we are all the more thrilled that we have been able to support them in this area”.
Mercedes-Benz Citaro G BlueTec Hybrid
The Citaro G BlueTec Hybrid is the only hybrid bus in existence today that can travel for stretches solely on electric power without using its diesel engine, approaching bus stops without making hardly any noise. After stopping, it continues in a similar fashion at several more stops along its route, without the usual loud engine noise one expects to hear from a bus. The drive system is provided by four electric wheel hub motors, which get their power from one of the world’s largest lithium-ion batteries to be used in a mobile application. This power is generated via braking, for example when driving downhill, and if necessary can also be produced via a generator driven by a diesel engine which is comparatively small for this class of vehicle. Experts refer to this concept as a serial hybrid drive.
Hartmut Schick is confident about the long-term success of the hybrid bus from Mercedes-Benz: “I expect ten to 15 percent of new orders for city buses to be made up of such hybrid drives by the year 2015. As always, SSB is leading the way in this area.”
High-tech packed into a proven vehicle concept
This technologically sophisticated diesel-electric hybrid concept has been installed in the proven articulated bus model of the world’s most successful urban bus family, the Mercedes-Benz Citaro series. The hybrid Citaro looks exactly like a conventional diesel bus from the outside, except for its high roof which houses the battery. Passengers will also notice no differences in the interior, which can accommodate around 134 people, with 48 seats arranged in the familiar bus operator configuration. The difference is in the driving: the bus is practically silent and there are no sudden jolts. Nevertheless, the four electric motors in the 18-meter bus accelerate it quite rapidly. Integrated close to the wheel hubs on the centre and rear axles, they have a combined output of 320 kW, which if necessary can also be supplied from the battery and the diesel engine-driven generator. The motors also go into action during braking, serving as generators that convert braking energy into the electricity used to charge the battery. When the latter requires additional power, the diesel engine automatically engages to provide it. This combustion engine is only half as large as that used in a regular diesel bus. Instead of 1000 kg, it weighs only 450 kg. It also has a displacement of only 4.8 litres as opposed to 12, and its output of 160 kW is around one third lower.
One of the world’s largest lithium-ion batteries to be used in a vehicle
The energy storage unit in the new Mercedes-Benz Citaro G BlueTec Hybrid is a lithium-ion battery whose power rating exceeds anything ever seen before for this technology. The battery system boasts a maximum output of 240 kW and, with a weight of less than 350 kg, it is also relatively light. Its biggest advantages over conventional battery systems are its higher energy density, higher storage capacity, and lower dead weight. By comparison, test buses equipped with hybrid drives 30 years ago in Stuttgart carried rechargeable lead batteries weighing 3000 kg on board.
Lithium-ion batteries became commercially available for the first time in 1991. Today they are used with practically everything that requires a lot of energy but low battery weight – e.g. cell phones, digital cameras, camcorders, and notebook computers. Their use in large vehicles like passenger cars, trucks, and buses is relatively new, however. Daimler already has experience with lithium-ion batteries in buses: more than 900 out of a total of 2850 hybrid buses already in use from Orion, a Daimler AG brand in the U.S. and the world market leader for hybrid buses, are equipped with lithium-ion batteries produced by the same company that built the batteries for the new Mercedes-Benz Citaro G BlueTec Hybrid. These batteries have an output roughly equivalent to that of around 9000 large laptop batteries.
Concept on the way to series production
This year, a whole series of cities in the so-called model regions will conduct practical tests of the Citaro G BlueTec Hybrid. The buses will demonstrate their suitability for everyday use by operating in regions with different topographies and speed profiles. Back in March 2009, 250 experts from various European transport companies had the opportunity to experience the Mercedes-Benz Citaro G BlueTec Hybrid articulated bus in action for the first time. The new bus was also completely put through its paces in internal test operations that included several weeks of successful trials at the Arctic Circle under the harshest conditions imaginable.
Source: Daimler AG