On the way to electromobility: STOAG procures two hybrid buses

STOAG is taking another important step towards environmental protection. With the acquisition of two hybrid buses from MAN, she is participating in a funding program for innovative technology in the Rhein-Ruhr transport association. A total of 30 million euros has been made available by the VRR since 2009 to test the everyday suitability of the environmentally friendly buses and to make the knowledge and experience with the new technology from the VRR area available to other transport companies and vehicle manufacturers.

The hybrid technology in public service buses represents an important intermediate step on the way to the purely electrically operated bus. At just under 355.000 euros per vehicle, the hybrid buses are 100.00 euros more expensive than conventional buses, but are subsidized with 255 euros per bus. "Environmentally friendly, energy-saving, innovative" is what it says on the rear of the two solo buses, which are quite different from the other STOAG buses just by their appearance. The higher roof structure in which the capacitors are located is unmistakable.  

Hybrid technology: efficient and environmentally friendly

Hybrid technology can increase the efficiency of the vehicle drive while at the same time reducing exhaust emissions. The word hybrid means "of two different origins". A “hybrid vehicle” refers to a vehicle that is operated by two different types of drive or energy sources. The diesel hybrid bus combines a diesel engine with a fuel tank and an electric machine with a power storage unit in the form of an accumulator. This combination has decisive advantages: fuel consumption and CO₂-Emissions are significantly reduced compared to the conventional diesel engine. A distinction is made between parallel hybrid drive, in which the wheels can be driven by an internal combustion engine, an electric motor or both together, and serial hybrid drive, in which an internal combustion engine drives a generator that supplies the electricity to drive the wheels .

While conventional buses convert their mechanical energy into heat when braking, so that it is lost, the Lion's City Hybrid from MAN recovers the braking energy and uses it for the drive. The automatic start-stop system can also reduce fuel consumption and emissions. After all, city buses spend between 25 and 40 percent of their service life at a standstill or in front of red lights. 

Serial drive offers advantages

STOAG opted for buses with serial hybrid technology. This drive technology is particularly suitable for buses that often stop and start again, as is the rule in city traffic. The combustion engine has no mechanical connection to the drive axle. The MAN Lion's City Hybrid is powered by two electric drive motors. These work as generators during braking and convert the braking energy into electrical energy. This is stored in so-called ultracaps, which are located on the roof of the buses. With this energy, the bus can accelerate emission-free and quietly and - depending on the topography - cover a distance of up to 200 meters purely electrically. If the energy storage device is empty, the environmentally friendly diesel engine in the rear of the bus switches on automatically in order to produce the electricity for the electric drive motors on board with the help of a generator. The diesel engine with an output of 184 kW (250 PS) meets the voluntary EEV emissions standard and has a regulated CRT particle filter that filters up to 99 percent of the soot particles from the exhaust gas flow.

Up to 30 percent less CO? and up to 40 percent less nitrogen oxides compared to conventional buses with Euro 5 engines and EEV emissions standards can be achieved according to the manufacturer. The fuel savings should be between 10 and 20 percent. The purely electric starting of the hybrid buses enables low-noise and low-emission driving off at the bus stop or at the traffic lights. The hybrid buses thus make an important contribution to reducing fine dust and carbon dioxide pollution as well as noise pollution.  

A new driving experience

Technology enthusiasts can see how the hybrid drive works on a monitor in the vehicle. The driving experience in a hybrid bus is similar to that in a tram - as soon as the diesel engine switches off during the journey and the bus is exclusively powered by an electric drive, this gives the impression of a whirring tram: an extremely comfortable driving experience. The electric drive works measurably quieter both inside and outside the bus. STOAG is also breaking new ground when it comes to interior design: stainless steel rods and anthracite-colored covers characterize the image and ensure a bright and friendly atmosphere. The third door and the stationary engine lead to a changed room layout in the rear area of ​​the bus. The driver is constantly informed about the state of charge and the operational readiness of the system. The display on the dashboard shows all the data necessary for efficient, gentle and economical drivers: the charge status and the current energy recovery.