trailer world issue Two 2010

Issue Two 2010 13 Future II contact partner for operational stability and system reliability in Electromobility System Research at the Fraunhofer Institute, sees en- ergy density as one of the crucial criteria, at least in the medium term. “The energy den- sity of diesel fuel is about a hundred times higher than that of batteries.” This means that one litre of diesel fuel stores the same amount of energy as “one hundred litres of battery”. Electromobility System Research is therefore at present only looking into city cars and lo- cal public transport buses where this problem is of minor significance in view of the short cycles of use. At the most, for the research expert, envisaging a parallel hybrid drive with an electric motor integrated in the drive train is no more than a hypothetical future scenario for classic long-distance transport; under certain topographical conditions this may take on the function of the retarder and be responsible for recuperation, acting as a booster when starting up or on steep inclines and thus generating significant fuel savings so that it may possibly be an interesting aspect for the companies involved. Drawbacks: loss of payload and space One of the main counter arguments con- cerns the loss of payload. A fuel cell drive system in a 40-tonne truck-trailer com- bination with a reasonable range would mean added weight of at least 3 tonnes, or approximately one third of the weight of a well-equipped towing truck, while the bat- teries for an E-truck would be even heavier. Then there’s the problem of where to store the necessary H2. Hydrogen is kept in sev- eral tubular tanks at a pressure of 350 or 700 bar. The massive tubes take up many times the volume of an 800 l diesel tank. Serial hybrid drive as a possible alternative, with a compact stationary motor in the truck as power source with interconnected batter- ies and drive provided by electric in-wheel motors, has no significant advantages in a 40-tonne truck compared to current con- figurations. Furthermore, limited range, handling problems and the lack of an H2 infrastruc- ture are at least medium-term arguments against using any kind of in-wheel electric motors in heavy trucks, putting the special case of hydro-drive on one side for the time being. This refers to hydraulic in-wheel mo- tors on the front axle that function as trac- tion aids and turn a truck with conventional rear-wheel drive into a 4-wheel truck at low speeds on medium-duty ground. MAN has brought this concept to the market for cus- tomers particularly on construction sites. Hybrid drives and the possibly related use of in-wheel motors constitute at the most a practical alternative for short- and medium- distance distribution traffic with a high share of stop-and-go. Classic long-distance truck trains on the other hand will probably have to manage without Porsche’s innovative con- cept for several decades to come. (rk) »Electric drives in the form of hybrid technology are conceiva- ble in trucks.« Dr.-Ing. Michael Jöckel, Fraunhofer-Institute Structure of an in-wheel motor Stator bracket In-wheel motor rotor Rotor bracket Brake rotor and brake caliper In-wheel motor stator

trailer world issue Two 2010

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