DaimlerChrysler is developing a hybrid version of its Citaro bus, with pilot operation to begin next year and full-scale production planned for 2009.
The Citaro hybrid uses a downsized diesel engine to provide power for a lithium-ion battery pack on the roof. When drawing into, standing at, or accelerating away from bus stops, the hybrid bus operates in electric-only mode. DaimlerChrysler says the hybrid will offer 20-30 percent lower fuel consumption than conventional diesel Citaros.
The hybrid will use four electric wheel hub motors on the center and rear axles of the vehicle, with a total output of 320 kWs of power.The hybrid uses a 4.8-liter diesel engine rather than the large 12-liter unit in a conventional articulated model. The torque curve (the pulling power of the engine) of the hybrid-bus engine has been especially tailored to the hybrid application, resulting in low emissions and good fuel economy.
The smaller engine weighs 450 kg, compared to the 1,000 kg of the 12-liter unit and 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 bus service bus of the near future. In principle, the diesel engine would simply need to be replaced by fuel cells. This is also the approach GM is going for in its E-Flex family - the series hybrid Volt and the fuel-cell Volt passenger vehicles.
DaimlerChrysler’s North American bus subsidiary produces the hybrid Orion bus, which has proved very successful. Since 2003, Orion has won contracts to supply 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.