It’s a prototype of a diesel-electric hybrid bus from DaimlerChrysler! The company plans to unveil this bus, the Citaro, to the general public sometime this year. The bus has a sophisticated hybrid system, that allows the bus to run in emission-free battery-only mode. Rather than providing continuous driving power, the diesel engine in the Citaro series hybrid operates as a generator to produce electrical power when required. The electrical power is stored in maintenance-free lithium-ion batteries mounted on the roof of the Citaro. They are charged not only by the diesel generator but also by energy recuperation from braking.
The actual drive power to the wheels of the Citaro hybrid is provided by four electric wheel hub motors on the center and rear axles of the vehicle. The total wheel hub motor output of 320 kW is ample for an articulated bus even under strenuous operating conditions.
When drawing into, standing at and accelerating away from bus stops, the hybrid bus can operate in electric-only mode, which is not only virtually emission-free but also much quieter.
A big advantage of the clever series hybrid technology used in the Citaro is downsizing: instead of the large 12-liter six-in-line engine normally used in the articulated model, the hybrid bus is fitted with a compact unit with a displacement of 4.8 liters. This reduces the weight of the engine from approximately 1,000 kg to approximately 450 kg.
Since the diesel engine of the Citaro hybrid does not drive the vehicle directly, it is not required to produce peak outputs and is therefore able to operate very economically and with low environmental impact over a narrow rpm range at or close to its peak efficiency. The torque curve of the hybrid-bus engine is therefore tailored to frequent steady-state operation, for optimal emissions performance and fuel efficiency.
The hybrid-drive Citaro is able to dispense with a conventional automatic transmission. This results in improved efficiency and weight savings. The downsizing of the drivetrain components means that the weight penalty of the Citaro hybrid bus over a conventional diesel-powered articulated bus is only around one tonne.
Following the unveiling of the prototype in the second half of 2007, pilot operation will begin early next year. The series production is scheduled for 2009.
Via PureGreenCars and DaimlerChrysler