There could hardly be a greater span between history and future than at the present time in Dresden. Anyone riding past Dresden’s most beautiful monuments and squares along bus route 62 can experience this at first hand as he or she will be sitting in a hybrid-drive Citaro – a Mercedes‑Benz brand articulated bus.
The first two of a total order of eight Mercedes‑Benz Citaro G BlueTec Hybrid were handed over to Managing Director Reiner Zieschank, representing the Dresden Transport Company, by Konstantinos Tsiknas, head of Mercedes‑Benz Omnibuses Germany, on the Theatre Square on May 2011.
Operating on exacting routes
In future, the hybrid buses will mainly be used for the popular 60-routes with their frequent regular services, thus making the most of the undoubtable advantages of their sustainable hybrid technology. Such a situation with changing topography, proximity to the inner city as well as the opportunity to make full use of their loading capacity is ideal for proving just how suitable the vehicles are for coping with practical conditions. The number of hybrid vehicles even allows a complete route to be covered without “mixing” the vehicles. Whole sections of the route can then be operated using only electricity.
Mercedes‑Benz Citaro G BlueTec Hybrid
The Citaro G BlueTec Hybrid is the only hybrid bus in operation up to now which can cover whole sections of the route running on just electricity without the diesel engine, making it virtually silent when approaching bus stops. And it can carry on driving to a number of stops without the expected rumbling of the engine. The bus is propelled by four wheel-hub electric motors which are supplied with electricity by one of the world’s largest lithium-ion batteries in use for mobile operations. The electricity is produced when the bus uses its brakes and if necessary a generator can also be used which is driven by a diesel engine which is comparatively small for this type of vehicle. When referring to this concept, experts talk of a serial hybrid drive.
High tech in a time-tried vehicle concept
This technologically demanding diesel-electric hybrid concept has been realised in the time-tried articulated bus of the world’s most successful range of city buses: the Citaro. From the outside there is no visible difference to a conventional diesel bus, apart from the raised roof to provide space for the battery. The difference is only apparent when driving. Virtually silent and with no jolting, but very swiftly, the four electric motors accelerate the 18 metre long bus. They are fitted close to the wheel hubs on the centre and rear axles and together they supply 320 kW of driving power which is taken as required from the battery or the generator run by the diesel engine. The electric motors are, however, also used for braking. This means that they also act as generators in a similar way to the well-known dynamos on bicycles by transforming the braking energy into electric current for the battery. If the battery should need additional electricity, then the diesel engine starts up automatically to generate more current. In comparison with a conventional diesel bus, the combustion engine is only half as large with 450 kg instead of 1000 kg and a cubic capacity of only 4.8 l instead of twelve. Its performance is about 160 kW, that is about a third lower.
Worldwide one of largest lithium-ion batteries in a vehicle
In the new Mercedes‑Benz Citaro Blue Tec Hybrid, the energy needed is stored in a high-performance lithium-ion battery of a size not used up to now. The battery system supplies a maxium of 240 kW and is comparatively light with a weight less than 350 kg. Very important advantages when compared with a conventional battery system are also the great density of the energy combined with a greater storage capacity and relatively low own weight. In comparison: Thirty years ago, test buses with hybrid drive in Stuttgart were carrying lead-accumulators weighing 3000 kg.
Lithium-ion batteries have only been commercially available on the market since 1991. Nowadays they are used practically everywhere where there is a high demand for power but a low weight is important: cell phones, digital cameras, camcorders, notebooks etc. In large vehicles such as cars, trucks and buses they are still relatively new. Daimler already has experience with lithium-ion batteries in buses. More than 1000 of the 3000 hybrid buses from Orion, a Daimler AG brand in the USA and international market leader for hybrid buses, are already running on lithium-ion batteries from the same manufacturer supplying the battery system for the new Mercedes‑Benz Citaro G BlueTec Hybrid. This provides a battery performance which corresponds to that of about 9000 large laptop accumulators.
Sustainable mobility in Dresden
Over 400,000 passengers a day use the vehicles of the Dresden Transport Company. Funiculars and ferries are also part of the transport provided in the capital city of Saxony as well as buses and trams, and the people of Dresden and tourists make the most of their flexibility. With its bus fleet of 145 vehicles, the Transport Company runs 29 bus routes.
As is true of the entire company policy of the Dresden Transport AG, acquiring new vehicles such as the current hybrid fleet takes the principle of sustainability into account. By creating an attractive local transport system, the Transport Company wants to make its own contribution to an ecological, cost-effective and socially compatible development of the city. With its workforce of 1703 as well as 94 trainees, the Transport Company is one of the most important employers in Dresden.
Source: Daimler AG