DaimlerChrysler is developing a series-hybrid version of its Citaro bus, which the company has also used as a platform for its fuel cell bus work. DaimlerChrysler will introduce the system, which will be installed in a Citaro G articulated bus, in the second half of this year. Pilot operation begins early in 2008, and series production is scheduled for 2009.
The Citaro series hybrid uses a downsized diesel engine as the genset to provide power for a lithium-ion battery pack located on the roof. The Citaro hybrid will use four electric wheel hub motors on the center and rear axles of the vehicle, with total output of 320 kW.
When drawing into, standing at and accelerating away from bus stops, the hybrid bus can operate in electric-only mode. DaimlerChrysler anticipates that the hybrid will offer 20% to 30% lower fuel consumption than conventional diesel Citaros.
With diesel-electric hybrid vehicles from Orion in North America, Mercedes-Benz in Europe and Mitsubishi Fuso in Asia, DaimlerChrysler does not only have the longest, but also the most extensive experience with alternative drive systems for commercial vehicles. Therefore the new hybrid drive Citaro is an important step towards cost efficient and zero-emission driving.—Andreas Renschler, the DaimlerChrysler Board of Management Member responsible for the Truck Group and Buses
The hybrid uses a 4.8-liter diesel rather than the 12-liter unit in a conventional articulated model. The torque curve of the hybrid-bus engine is tailored to the frequent steady-state operation of a series hybrid application, resulting in optimal emissions performance and fuel efficiency.
The smaller engine weighs approximately 450 kg, compared to the 1,000 kg of the 12-liter unit. The hybrid-drive Citaro also dispenses with a conventional automatic transmission, resulting in further weight savings and improved efficiency. 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.
DaimlerChrysler is positioning the hybrid-drive Citaro as a logical step on the way to a fuel-cell-powered urban regular-service bus of the future. In principle, the diesel engine genset would simply need to be replaced by fuel cells. This is also the approach GM is highlighting in its E-Flex family with the series hybrid Volt and the fuel-cell Volt.
DaimlerChrysler’s North American bus subsidiary produces the series-hybrid Orion bus. Since 2003, Orion has won contracts to supply numerous US and Canadian cities, from New York to San Francisco, with a total of some 1,500 Orion VII Hybrid low--floor urban regular-service buses, around 1,000 of which are already on the road. On top of this, there are also options on a further 525 vehicles.
BAE Systems, the provider of the hybrid drive in the Orion, recently announced that it will introduce a lithium-ion battery pack with cells from A123Systems for the HybriDrive beginning next year. (Earlier post.)
Likewise active in the field of series hybrid-drive urban buses is DaimlerChrysler’s Japanese commercial vehicle subsidiary Fuso, with the low-floor Aero-Star model.