28 May 2007
DaimlerChrysler announced it will unveil the first prototype of the diesel-electric hybrid Mercedes-Benz Citaro to the general public this year. The prototype employs diesel-electric series hybrid technology which will allow emission-free operation in battery-only mode. The system will be installed in a Citaro G articulated bus. 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.
In the Citaro series hybrid, 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 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 is 320 kW.
When drawing into, standing at and accelerating away from bus stops, the hybrid bus can operate in electric-only mode, which is virtually emission-free and also much quieter.
The Citaro hybrid is powered by a 4.8 liter engine, instead of the large 12 liter six-in-line engine normally used in the articulated model. Since the diesel engine is not required to produce peak outputs, it is able to operate 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 tailored to frequent steady-state operation, for optimal emissions performance and fuel efficiency.
DaimlerChrysler’s North American bus subsidiary Orion has been supplying series hybrid buses since 2003, with about 1000 buses on the road and 500 more on order. The Orion VII Hybrid was developed by Orion in cooperation with BAE Systems. DaimlerChrysler’s commercial vehicle subsidiary Fuso has launched the Aero-Star hybrid bus model in Japan.