This paper presents the multibody mathematical model of a hydraulic excavator, developed in the AMESim® environment, which is able to predict the machinery fuel consumption during the working cycles. The mathematical modelling approach is presented as well as the subsystems models. The experimental activity on the excavator is presented in detail. The excavator fuel consumption was measured according to the JCMAS standard. The working cycles were executed an appropriate number of times in order to minimize the stochastic influence of the operator on the fuel consumption. The results show the mathematical model capability in the machine fuel consumption prediction. The excavator model could be useful either to perform accurate analyses on the energy dissipation in the system, giving the possibility to introduce new system configurations and compare their performance with the standard one, or for the definition of novel system control strategies in order to achieve the fuel consumption reduction target.

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Environmental issues have become a critical topic at all levels and the Fluid Power industry is no exception. One of the most important research trends is aimed at improving efficiency through electrification, the availability of new electric motors and drive solutions is expected to promote the introduction of speed-controlled pump systems in mobile applications, nowadays dominated by conventional valve-controlled solutions. The paper will firstly present a collection of tests carried out on a lifting application, powered by an inverter-controlled electric motor moving a reversible gear pump/motor. The lowering phase is carried out in two alternative modes, the first one is the electric regenerative mode, the second one is the throttle-controlled mode. The analysis of the results will highlight different energy efficiencies of the system at different operating conditions. In particular the losses of volumetric unit, piping, throttle elements, hydraulic cylinder and electric components can change dramatically depending on operating conditions. In the second part of the paper, a lumped parameters model will be presented, using a commercial software. Firstly, the model will be able to catch the behavior of the test bench and secondarily it will be used to predict the expected performances of alternative design choices. Particular attention will be focused on low speed operation. In fact, there is more uncertainty and much less well-established knowledge on the behavior of the volumetric units at low speed, concerning the large body of work available for the nominal speed conditions. Finally an outlook will be drawn of expected advantages and limitations arising from the implementation of variable speed pumps on mobile machines. Such benefits will be presented with practical figures of merit such as the energy recovery performance, the increase of cycles and the cooling system size reduction.

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This paper presents the results of a study focused on mathematical modeling of an excavator hydraulic system, composed by: the pump gray box model, the kinematics model and the valve white box model. The kinematics model has been realized using the planar mechanical library of AMESim ® and is composed by the front excavation tool: the arm, the boom and the bucket. The valve section white box model has been validate with the comparison between the numerical and experimental result obtained during the laboratory tests. The excavator is equipped by a full flow sharing valve, that is very useful in this kind of machinery when during a digging cycle all the valve sections are used at the same time. In this paper the excavator mathematical model system will be composed by the pump, the kinematics and two valve sections. The new system will be validated with the comparison between the experimental results, obtained with two sections working at the same time, and the numerical results provided by the simulation. The experimental results will be obtained in two different working conditions: standard operation condition and flow saturation condition. This will show the mathematical model capability in the study of the interaction between all the system components and could be useful in the study of alternative control strategies towards energy efficient systems and new control system designs.