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As a result of the Kyoto Protocol [1], the European Union's legislation demands higher saving rates for the total energy consumption of technical equipment. Heavy Equipment, such as construction- and agricultural machines, contributes over 80% of the total off-road diesel fuel consumption in Germany per annum. It is therefore necessary to provide helpful solutions in order to reach this ambitious aim. The German Federal Ministry of Education and Research cooperates with machine manufacturers, component suppliers and research institutes in the area of heavy equipment. Under the project name TEAM [2] a three year project has been started, which is focused on the development and integration of new propulsion and steering systems for heavy equipment. One task within the project is finding an appropriate way of evaluating the energy efficiency of the enhanced machines, after the powertrain modifications have been applied to it.

Auxiliary power units (APUs) are used in mobile applications to provide electrical power until approx. 10 kW. It is state of the art that these generators are driven by a diesel engine at constant speed and are selected according to the expected maximal power needed. These systems have a low efficiency and consequently a high fuel consumption particularly when driven at small loads. The system can yield a higher efficiency for partial load conditions by reducing the rotary speed of the driving diesel engine. The optimum in rotary speed of the diesel engine for different loads is pre-programmed (engine mapping) in the diesel control unit. A frequency converter allows a constant frequency of the electricity output at variable speed of the generator. These higher costs for frequency converter and diesel controller demand especially for mobile applications a proof of efficiency, i.e. a proof of economics, which is shown in this paper.