Automotive Intelligence - the web for automotive professionals and car enthusiasts
April 01, 2009
Given appropriate public sector support for hybrid technology, market insiders expect a potential annual demand for at least 300 hybrid buses in western Europe, which would enable diesel fuel consumption, CO2 emissions and pollutant emissions in the cities to be drastically reduced. In North America the Daimler bus brand Orion already has 1700 hybrid buses in day-to-day operation, which makes it the world market leader for hybrid technology in commercial vehicles.
Mercedes-Benz Citaro G BlueTec Hybrid
The Mercedes-Benz Citaro G BlueTec Hybrid has a technologically very sophisticated, serial hybrid drive system which allows emission-free driving under battery power alone over short distances. The drive system is installed in an articulated Citaro G bus, and drives the centre and rear axles by means of four wheel hub motors – a combination that makes this articulated hybrid bus unique.
The diesel engine in the serial hybrid bus does not act as a primary drive unit, but rather drives the generator to produce electric power as required. This energy is stored by maintenance-free lithium-ion batteries mounted on the roof. The batteries are not only fed by the diesel generator, but also with energy recuperated during braking.
The energy generated by recuperation when braking on the approach to bus-stops or traffic lights is used both to supply the vehicle at standstill and when moving off. This means that the hybrid bus is able to operate purely under electric power, and therefore practically without emissions, when stationary and under acceleration – with a significant reduction in noise as well.
Power is transferred to the wheels of the Citaro G BlueTec Hybrid by four electric wheel hub motors on the centre and rear axles. Even under heavy operating conditions, the 320 kW total output of the wheel hub motors is ample for an articulated bus.
Downsizing is among the greatest advantages of the serial hybrid system in the Citaro: instead of the large, 12-litre six-cylinder in-line engine normally employed in an articulated bus, a more compact unit with a displacement of 4.8 litres is used. As a result the engine weight is reduced from around 1000 kg to just 450 kg or so.
World's first lithium-ion battery in this output category
The lithium-ion battery used in the articulated Citaro G BlueTec Hybrid is in an output category of its own. The battery system generates 180 kW and is comparatively light in weight at under 350 kg. Major advantages over conventionnal battery systems include a higher energy density combined with a high storage capacity and a low battery weight.
Changes in the automobile industry are increasing the demand for clean, efficient and economical vehicles. According to forecasts, the market volume for powerful lithium-ion batteries is set to exceed the 10 bill. euro mark over the next decade, with the market for battery materials exceeding 4 bill. euros. In Germany alone, the government envisages at least one million electric cars populating the roads in the cities by 2020.
(Mar 30, 2009)