Presumably on the basis of the positive results from the first hybrid bus deployed in the Munich administrative district, the Munich Regional Transport vehicle fleet now also includes a Mercedes-Benz Citaro G BlueTec Hybrid Omnibus. The handover of the vehicle for its intended use took place on 22 September 2011, when Ulrich Piotrowski, the Market Launch Manager for Mercedes-Benz hybrid and electric buses, presented a symbolic key to Jörg Schuchtmann, the Operations Manager of Busservice Watzinger GmbH & Co. KG.
The Citaro is part of a new pilot project in the “Munich District Energy Vision” initiative, aimed at reducing the district’s energy consumption by 60 percent by the year 2050, and meeting the 40-percent demand with renewable forms of energy. Passenger public transport is also one of the modules in the overall emissions balance, so this too is an area for research and incentives. On the basis of favourable past experience, the Munich administrative district has now decided to subsidise more hybrid buses and carry out a long-term test on them. According to Ulrich Piotrowski: “In terms of exhaust emissions and noise reduction, hybrid as an eco-friendly drive technology stands out as the best option at the moment, because of its practical advantages and high level of electrification.”
Deployment on a particularly difficult route
The Mercedes-Benz Citaro G BlueTec Hybrid will be used on one of the operator’s most important routes, number 266, running between the Planegg suburban railway station and the Grosshadern hospital. This route will be an effective showcase for the benefits of the new sustainable technology. “A dense network of bus stops, the central business district nearby and high passenger use provide ideal conditions to test and raise the public profile of the pioneering technology of these vehicles. The hybrid bus will now allow an almost noiseless and emissions-free service in the vicinity of the hospital,” said a delighted Jörg Schuchtmann.
Mercedes-Benz Citaro G BlueTec Hybrid
The Citaro G BlueTec Hybrid is at present the only hybrid bus with capability to complete a distance of up to ten kilometres on electricity only, given ideal topographical conditions. In this case, the familiar rumble of the diesel engine is not heard at all. The bus pulls up silently at the bus stop, and continues in the same fashion for several more stops along the route. The drive system consists of four electric hub motors, which draw their current from one of the world’s largest in-vehicle lithium-ion batteries.
This current is generated from braking manoeuvres, or also where necessary via a generator driven by the diesel engine, which is a comparatively small unit for this vehicle class. Experts refer to this as “serial hybrid drive” technology. Diesel fuel savings, and the associated reduction in CO2 emissions, are around 20 percent.
High tech in a proven vehicle design
This sophisticated diesel-electric hybrid design concept has been implemented in the proven articulated version of the most successful city bus family worldwide, the Mercedes-Benz Citaro. From the outside, it is difficult to tell the vehicle apart from a conventional diesel bus, except for the higher roof structure to accommodate the battery. But travelling in the bus is a very different experience: the four electric motors rapidly accelerate the 18-metre-long bus virtually silently, and with no jerks or jolting (because there is no transmission). The motors are fitted close to the wheel hubs on the middle and rear axles, together providing total drive power of 320 kW, supplied where necessary from both the battery and the generator operated by the diesel engine. These electric motors are also used for braking purposes, operating as generators, or like the dynamo device familiar to cyclists, to convert the energy braking into electrical current for the battery. The diesel engine is automatically activated to provide supplementary current whenever additional demand is indicated by the battery. In comparison with a straight diesel bus, the internal combustion engine is only half the size in total, weighing just 450 kg instead of 1000 kg, and with a displacement of only 4.8 litres as compared with 12 litres. Output is approximately one third lower, at 160 kW.
One of the world’s largest in-vehicle lithium-ion batteries
The energy storage device used in the new Mercedes-Benz Citaro G BlueTec Hybrid is a lithium-ion battery that is the first to provide a power rating of this order of magnitude. The battery system delivers a maximum of 240 kW, and it is also relatively light, weighing less than 350 kg. Key advantages over conventional battery systems include a higher energy density, higher storage capacity and low weight. By way of comparison, the hybrid buses on trial in Stuttgart three decades ago had lead batteries on board, weighing as much as 3000 kg.
Lithium-ion batteries first became commercially available in 1991. This technology is now used in almost all situations where there is a high energy demand and low weight: mobile telephones, digital cameras, camcorders, notebooks, etc. They have been used only relatively recently in large vehicles such as passenger cars, trucks and buses. Daimler already has experience with the use of lithium-ion batteries in buses. Over 1000 of the 3000 Orion hybrid buses are now running on lithium-ion batteries produced by the same manufacturer. Orion is a Daimler AG brand in the USA and a world leader in hybrid buses. It also supplies the battery system for the new Mercedes-Benz Citaro G BlueTec Hybrid. The output delivered by this system is equivalent to that of around 9000 large laptop batteries.
Busservice Watzinger GmbH & Co. KG
The Watzinger bus company has a total workforce of 347 employees, making it one of Bavaria’s largest. The company has depots in Munich, Bad Abbach, Siegenburg and Regensburg, and transports a total of approximately 18.7 million passengers each year. Its fleet of 159 state-of-the-art buses cover a total distance of 8.4 million kilometres per year.
Source: Daimler AG
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