Promote and demand
The Rhein-Ruhr transport association (VRR), of which WSW mobil GmbH is also a member, launched a promotional programme for buses with hybrid technology in 2009. Today approximately 70 hybrid buses belonging to VRR transport companies have been subsidised with the help of the programme for "Innovative projects for the improvement of local public transport". The objective is to pool the findings and experience gained with regard to the new technology as part of a research programme and put them at the disposal of other transport companies and vehicle manufacturers. Ulrich Piotrowski is responsible for the market launch of hybrid and electric buses at Mercedes‑Benz. He believes that: "Wuppertal is just perfect for using the Citaro G BlueTec Hybrid. The demanding topography provides sufficient opportunity for energy recuperation via the brakes, but, if necessary, can also clearly demonstrate deficits thanks to the challenging routes. The experience gained during daily operations is invaluable to the further development of vehicles."
Mercedes-Benz Citaro G BlueTec Hybrid
When topographical conditions are ideal, the Citaro G BlueTec Hybrid can drive up to 10 kilometres using exclusively electric power without the help of the diesel engine. Four electric wheel hub motors which draw their power from lithium ion batteries provide the drive. Electric current is generated when the brakes are applied and, if required, can also be obtained via a generator which is driven by a small diesel engine. Experts speak of a serial hybrid in this context.
Needs-based equipment
The technically sophisticated diesel-electric hybrid concept has been realised in the well-established articulated version of the successful Mercedes-Benz Citaro urban bus family. The light blue vehicle hardly differs from the rest of the WSW Citaro fleet. The bright and friendly interior is characterised by large windows. The traffic red grab rails are a contrast to the blue seat covers. A video surveillance system with five cameras improves safety and avoids damage through vandalism. The climate control in the passenger compartment and at the driver's workplace can be regulated independently of one another via the overhead air-conditioning system. The air-conditioning concept, just like the fire alarm system and the automatic fire extinguishing system in the engine compartment, is standard WSW equipment.
Two 48.26 cm TFT monitors in the front and rear sections display the names of bus stops. When connected to the IBIS on-board computer, information regarding route progress and the name of the next bus stop are displayed. The IBIS is not only responsible for the control of the passenger information systems, but also for traffic signal preemption in Wuppertal. The control centre can directly transmit acoustic and visual information to one or all of the vehicles on the service route. The exact position of the vehicle is determined, evaluated and transmitted to the passenger information boards located at the bus stops using GPS. Passengers at the bus stops are thus informed in real time about exact arrival and departure times.
HighTec in urban buses
Four electric motors influence the driving characteristics of the Citaro. They accelerate the 18 meter long bus quickly and almost silently. As no transmission is used, passengers notice no jerking typical of gear changes. The drive output of the wheel hub motors is 320 kW, supplied as required by the battery and the diesel engine driven generator. These electric motors are also used for braking the vehicle. They then function like generators and convert the brake energy into electric current for the battery. If the battery indicates that it requires more power, the diesel engine automatically starts in order to generate additional energy. In comparison to a bus that runs on diesel only, the combustion engine is only half the size, weighs only 450 kg instead of 1000 kg and its engine capacity is 4.8 litres as opposed to 12 litres. At 160 kW, its output is about one third lower.
The energy storage unit used in the Mercedes‑Benz Citaro G BlueTec Hybrid is a lithium ion battery. The battery system supplies a maximum of 240 kW and, weighing less than 350 kg, is comparably light. Compared to conventional battery systems, batteries with ion technology impress with a higher energy density in conjunction with a greater storage capacity and lower weight.
WSW mobil GmbH
At present the 100 percent subsidiary of the Wuppertal Stadtwerke GmbH employs around 740 employees. In 2010, 89.6 million passengers used the WSW mobil GmbH services. The bus fleet comprises approximately 300 regular service buses. Together the 65 service routes are 633.7 km long, whereby the service stretches from Wuppertal and Solingen via Remscheid to as far away as parts of the Ennepe-Ruhr district.
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