Key technology for key buses – hybrid makes its mark in Offenburg city centre

Key technology for key buses – hybrid makes its mark in Offenburg city centre
24.
September 2012
Stuttgart/Offenburg
  • Two Citaro G BlueTec Hybrid buses go to Offenburg
  • Added comfort with transmission-free four-wheel drive
  • Electric, emission-free and virtually noiseless over urban routes of up to 10 km in length
  • Hybrid drive makes electric driving in the pedestrian zone possible
Stuttgart/Offenburg – The city buses in Offenburg are known locally as "Key buses". In a reflection of the motto that "Key buses open up the whole town to you", the bus has gained the wholehearted acceptance of the local population and these days forms the backbone of Offenburg's local public transport system. State-of-the-art and, since very early on, extremely environmentally compatible regular-service buses provide an extensive network that covers the whole city region and even extends into the "Cappuccino Mile", as the city's central pedestrian shopping area is known. On 17 September 2012 the, to date, cleanest buses to feature in the history of Offenburg were presented to the general public: two Mercedes-Benz Citaro G BlueTec Hybrid models. In the presence of the Minister of Transport for the state of Baden-Württemberg, Winfried Hermann, and the Mayor of the City of Offenburg, Edith Schreiner, the vehicles were handed over by Tammo Voigt, Head of Public Transport Fleet Sales in the Mercedes-Benz Bus and Coach unit, to Johannes Müller, representing the Board of Management of the local operating company, the "Südwestdeutschen Aktienverkehrs-gesellschaft" (SWEG, or South-West German Transport Operating Company). "As the local transport company for Offenburg we take very seriously our commitment to planning and operating in a way that is environmentally responsible. We are proud to be able to integrate fully such significant and key technology into our regular transport operations", commented Johannes Müller.
Along the "Cappuccino Mile" without a murmur
The Citaro G BlueTec Hybrid is the only hybrid bus to date capable of covering distances of up to ten kilometers on electric power alone, and thus emission-free and virtually noiseless. It will therefore be a significant enhancement on its proposed routes through Offenburg's pedestrian zone, known locally as the "Cappuccino Mile". Tourists enjoying the sunshine outside the cafés along the street will in future no longer be disturbed by the engine noise they might have expected. "Such are the advantages of this sustainable technology", as Tammo Voigt knows. "The close network of bus stops, the idiosyncracies of an old town and the broad level of acceptance enjoyed by the routes represent the ideal conditions for hybrid drive as a technology of the future. The people of Offenburg will now be able to travel through these sensitive areas virtually without a sound and absolutely emission-free."
High tech made to measure
The hybrid concept used by Mercedes-Benz is what as known as a serial hybrid drive system. The vehicle is driven by four electric wheel hub motors, which draw their power whilst on the move from a lithium-ion battery. This power is accumulated during braking but can also, if necessary, be generated via a a generator powered by a small diesel engine. This unit, however, is only half the size of the type normally found in a conventional diesel bus, weighing just 450 kg rather than 1000 kg and with a displacement of 4.8 litres as opposed to 12 litres. Its output, at 160 kW, is around a third lower.
Externally, the Citaro G BlueTec Hybrid differs very little from a conventional diesel bus, with the exception of the slightly higher roof structure to accommodate the battery. The battery system delivers a maximum output of 240 kW and, at less than 350 kg, is also comparatively light. The energy storage units it uses make up one of the most powerful lithium-ion batteries in the world. Compared with conventional battery systems, the accumulators used here impress with a high storage capacity in relation to their own weight.
Local public transport of the future is quiet and comfortable
The 18-metre-long Mercedes-Benz accelerates briskly, yet almost silently. Without the usual sensation of changing gear – the hybrid bus doesn't have a transmission – passengers do not experience the jerking, load changes or shifts of gear that you get with a manual gearbox. The wheel hub motors deliver a combined output of 320 kW. Depending on the system status, the energy they require is drawn either from the battery or from the generator that is powered by the diesel engine. If the battery indicates that extra power is needed, the diesel engine automatically kicks in to provide the additional energy. The electric motors are also used for braking. In this case they function as generators themselves, converting braking energy into electric power for the battery.
SWEG – keeping the south west of Germany moving
Modern and regional, to put it in a nutshell, is the way the "Südwestdeutsche Aktienverkehrsgesellschaft", or SWEG, sees itself. The reach of the company's public transport as well as goods transport services extends from Weil am Rhein and Lörrach in the south of Baden-Württemberg and up to Bad Mergentheim in the north east, whereby more than 500 out of a total of 750 employees work in the bus division. A state-of-the-art fleet is made up of 300 company-owned buses and coaches, plus 50 hired vehicles. Many of these vehicles already meet the most stringent emission standard currently around, EEV (Enhanced Environmentally Friendly Vehicle).
Last year the SWEG, with its ten transport operators and five subsidiary companies, was responsible for the impressive figure of 61.8 million passenger journeys.
As is the case across the transport operating area as a whole, buses in particular play a significant role in Offenburg. The long-standing positive image enjoyed by buses has ensured their widespread acceptance among the community. In fact, buses are just as much an accepted part of the city scene as are its historic half-timbered houses.

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    Tammo Voigt, Head of Public Transport Fleet Sales in the Mercedes-Benz Bus and Coach unit, presents the two Mercedes-Benz Citaro G BlueTec Hybrid buses to Johannes Müller, Board Member of the Südwestdeutschen Aktienverkehrs-gesellschaft (SWEG – South West German Transport Operating Company) in the presence of the Minister of Transport for the German state of Baden-Württemberg, Winfried Becker, and the Mayor of the City of Offenburg, Edith Schreiner. From left to right: Tammo Voigt, Head of Public Transport Fleet Sales in the Mercedes-Benz Bus and Coach unit, Winfried Becker, Minister of Transport for Baden-Württemberg, Edith Schreiner, Mayor of Offenburg, and Johannes Müller, Member of the Board of Management of the "Südwestdeutschen Aktienverkehrs-gesellschaft" (SWEG).
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