Hybrid bus fleet for Münster's public transport service

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Münster in Westphalia, which, since 2004, can boast the title of the world's most liveable city, officially inaugurated its first hybrid bus line on 27 August 2012. With the ceremonial handover of two Mercedes-Benz Citaro G BlueTec Hybrid vehicles to the Münster municipal transport service, represented by its manager of Münster’s public transport company Eckhard Schläfke, by Mr Ulrich Piotrowski, responsible for the market launch of hybrid and electric buses at Mercedes-Benz, the Westphalian city once again made good on its pledge to contribute to climate protection through the introduction of new bus technology. Münster is the largest city in Germany without a railbound municipal transport system. Since the closure of its tram system in 1954 and of trolley bus operations in 1968, the city's public transport system has operated exclusively using environmentally friendly buses.

Use on high-demand routes

The new hybrid buses are to be used primarily on high-demand and high-frequency routes, including a route running directly through the city centre across one of Münster's main tourist attractions, the Prinzipalmarkt. This is where the advantages of sustainable hybrid technology will be most apparent. Electrically driven and without a diesel engine, the new Mercedes-Benz Citaro G BlueTec Hybrid vehicles will glide almost noiselessly through the city's historic centre . The varied topography of Münster, the historic old city and the high utilisation of the transport routes all offer ideal conditions to reap the benefits of advanced hybrid technology.

Mercedes-Benz Citaro G BlueTec Hybrid

The Citaro G BlueTec Hybrid is the only hybrid bus to date that can cover sections of routes entirely on electric power without the help of its diesel engine and run virtually silently between stops. After halting at a stop, the hybrid bus moves on to the following stops in just the same smooth, silent way, without the usual hum from the engine. The drive power is provided by four electric wheel hub motors that draw their power from one of the world's largest lithium-ion batteries ever used in a mobile application. This power is regenerated from braking and, if required, can also be produced by a generator driven by a diesel engine that is relatively small for the vehicle class. Experts call this type of system a series hybrid drive.

High-Tec in a proven vehicle concept

This technologically sophisticated diesel-electric hybrid concept has been implemented in the proven articulated variant of the world's most successful city bus series, the Mercedes-Benz Citaro. From the outside, the hybrid Citaro looks just like a conventional diesel bus, apart from the slightly higher roof structure needed to accommodate the battery unit. The difference, however, becomes apparent once the bus starts moving. The driving characteristics of the Citaro are governed by four electric motors that accelerate the 18 metre bus extremely quickly and in almost total silence. Since there are no gears, passengers do not experience the jerking you have in vehicles with manual gearboxes. The wheel hub motors deliver a combined drive output of 320 kW, which is supplied as required by the battery or the generator running off the diesel engine. These electric motors are also used during braking, when they act as generators, converting brake energy into electric power for the battery. If the battery needs additional electricity, the diesel engine starts up automatically to generate more current. The combustion engine in the hybrid is only half the size of the engine in a standard diesel bus, weighing just 450 kg compared to 1000 kg, and with a displacement of 4.8 litres compared to 12. At 160 kW, the engine's output is roughly a third less.

A lithium-ion battery is used in the Mercedes-Benz Citaro G BlueTec Hybrid for energy storage. The battery system delivers a maximum of 240 kW and is relatively light, weighing under 350 kg. Compared to conventional battery systems, the ion technology battery has an impressive higher energy density, combined with a high storage capacity and a low own weight.

Bus environmental protection concept

Bus transportation in the city forms an important part of Münster's environmental protection concept. Although travelling by bus by itself contributes greatly to climate protection, the vehicles themselves are designed to satisfy the strictest environmental requirements. The current fleet of articulated buses already easily meet the strict Euro V emission standard. With the addition of the two Citaro G BlueTec Hybrid vehicles, the city's transport authority is keeping its promise to engage intensively with new technologies in the hybrid and electric vehicle fields.

Each year, over 35 million passengers use the city's public transport services. The public transport system operates 24 bus routes with a vehicle fleet of 174 buses.
New vehicle purchases such as the current hybrid fleet are, in line with the general policy of the Münster public services authorities, built on the principle of sustainability. Through the creation of an appealing public transport system, the municipal transport service is making a viable contribution to the environmental, economic and socially sustainable development of the city. Its high service frequency and modern bus fleet that meets the strictest environmental standards are some of the reasons why Münster's public transport system regularly features near the top of the league table in Germany-wide Emnid surveys.

Credits: Daimler AG

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