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trailer world Issue Two 2012

30      Issue Two 2012 hub system based on the standard axle, offering scope for fitting mini- generators to produce electricity. The focus of the system is not the pure brakingphase:instead,thegeneratorstartsupwhenthedrivertakeshis foot off the accelerator, i.e. no longer demands active power - in other words, whenever the retarder and engine brake are activated or when the driver just lets the vehicle roll. But the production of surplus energy is absolutely possible”, emphasises Rossenbach. Noticeable fuel savings At Bremen University, Prof. Dr.-Ing. Karl-Ludwig Krieger is responsible for this project. A team of re- searchers in his department for “Electrical Engineering and In- formation Technology/Electronic Vehicle Systems” is working at optimising this system. Meanwhile the financial benefit is already conceivable. “This energy recovery technology is capable of recu- perating more electricity than needed for generating light and com- pressed air and for operating the brakes and telematic systems”, says Prof. Krieger. “This energy can remain in the trailer to operate a refrigerator or additional modules; in theory it can also be made available to the towing vehicle.” Extensive simulation processes have already let the researchers in Bremen ascertain exactly how much energy can be recovered with an indication of the resulting fuel savings. A circular route from Nuremberg via Regensburg and Munich was used for ref- erence. This offers a good mixture of easy, medium and heavy country roads together with motorway and urban streets. “We wanted to find out exactly when the brakes are actually activated and when the retarder is used”, says Krieger. “It is only when the driver takes his foot off the pedal and wants to decelerate that our system actually recovers energy; in doing so, it also offers moder- ate support for deceleration.” The researchers found out that on average the system is de- ployed a good 30% of the time. The calculations were based on a configuration consisting of a trailer axle fitted with two en- ergy recovery generators and one battery for energy storage. “The evaluated driving profiles resulted in a peak value of nine kilowatt hours referred to the overall test route of 350 kilome- tres”, explains Prof. Krieger. “We could still produce a further three kilowatt hours on a permanent basis - this would almost be enough to replace the whole generator of the semitrailer truck.” Installation of the energy recovery system in additional axles would naturally generate a higher electricity yield. Supplying energy to the towing vehicle This converts into po- tential fuel savings of one to two percent. “The system performs on such a high level that it generates surplus energy that can be supplied back to the towing vehicle or, and this is currently more realistic, to the additional electric consumers in the trailer”, says Krieger. “In future, the whole truck-and-trailer combination should be viewed as a single unit with holistic energy management of towing vehicle and trailer, opening up greater potential for optimisation. This is what the future will look like.” This green innovation by BPW and Bremen University is certainly »The system performs on such a high level that it generates sur- plus energy that can be supplied back to the towing vehicle.« Prof. Dr.-Ing. Karl-Ludwig Krieger Technology

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