Daimler Delivers Citaro Hybrid Buses in Stuttgart

Following successful practical trials in December 2009, Stuttgarter Straßenbahnen AG (SSB) has commissioned three Mercedes-Benz Citaro G BlueTec Hybrid buses, with a further two vehicles due to be delivered later this year.

The Citaro G BlueTec Hybrid is the only hybrid bus in existence today that can travel for stretches solely on electric power without using its diesel engine.

The Citaro hybrid bus is driven by electric wheel hub motors that obtain their electricity from one of the world’s largest lithium-ion batteries ever to be used for a mobile application. The electricity is generated through braking during downhill driving, for example. If necessary, it can also be produced by a generator driven by a diesel engine that is relatively small for the Citaro’s vehicle class.

The 18-meter bus is driven by four electric motors which are integrated directly into the wheel hubs on the center and rear axles, with a combined output of 320 kW.

The motors also go into action during braking, serving as generators that convert braking energy into the electricity used to charge the battery. When the latter requires additional power, the diesel engine automatically engages to provide it. This combustion engine is only half as large as that used in a normal diesel bus. Instead of 1,000 kg, it weighs only 450 kg. It also has only 4.8 liters displacement as opposed to 12, and its output of 160 kW is around one-third lower.

The energy storage unit in the new Mercedes-Benz Citaro G BlueTec Hybrid is a lithium-ion battery with a maximum output of 240 kW and a weight of less than 350 kg. By comparison, test buses equipped with hybrid drives 30 years ago in Stuttgart carried rechargeable lead batteries weighing 3,000 kg on board.