Recent demands to reduce pollutant emissions and improve energy efficiency have driven the implementation of hybrid solutions in mobile machinery. This paper presents the results of a numerical and experimental analysis conducted on a hydraulic hybrid excavator (HHE). The machinery under study is a middle size excavator, whose standard version was modified with the introduction of an energy recovery system (ERS). The proposed ERS layout was designed to recover the potential energy of the boom, using a hydraulic accumulator as a storage device. The recovered energy is utilized through the pilot pump of the machinery which operates as a motor, thus reducing the torque required from the internal combustion engine (ICE). The analysis reported in this paper validates the HHE model by comparing numerical and experimental data in terms of hydraulic and mechanical variables and fuel consumption. The mathematical model shows its capability to reproduce the realistic operating conditions of the realized prototype, tested on the field. A detailed energy analysis comparison between the standard and the hybrid excavator models was carried out to evaluate the energy flows along the system, showing advantages, weaknesses and possibilities to further improve the machinery efficiency. Finally, the fuel consumption estimated by the model and that measured during the experiments are presented to highlight the fuel saving percentages. The HHE model is an important starting point for the development of other energy saving solutions.

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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There is an increasing demand in the field of construction equipment to simultaneously develop both a construction equipment system and a control strategy, especially when a short commissioning period is desired. Moreover, the manufacturer's engineering teams must satisfy the needs of operators in different geographical locations. Therefore, there is a need for a powerful software development tool, able to reproduce the behaviour of complex mechanical systems, such as large manipulators, mobile cranes and excavators, in transient conditions and with low calculation times, with the ultimate aim of realizing a "control-oriented" model able to perform real time simulations in a hardware in the loop (HiL) or software in the loop (SiL) environment. This approach can lead to great time savings, as it allows testing and debugging the control unit simultaneously with the development of the actual physical system to be controlled. In contrast, the development of a reliable multi-system model can be a valuable instrument in performing full system optimization, given the ability to simulate the interaction between various components (hydraulics, engine, and kinematics) under actual operating conditions. The ultimate aim of this research is to realize a customized control strategy, able to guarantee performance improvements (e.g. fuel consumption reduction) for the specific application. The complexity in modelling these systems is attributed to the inherently nonlinear hydraulic drive used to achieve precise motion and power control.The hydraulic systems are characterized by a superior power density in comparison with electrical or mechanical systems, but hydraulic systems are less efficient due to the energy conversions involved. In order to reduce the energy losses, new system layouts are proposed [1] to [3], but typically the systems are designed for satisfying the load requirements controlling the fluid flow generated by the pumps. Variable displacement pumps are essential for controlling the flow; in axial piston pumps, the displacement can be varied by tilting the swash plate, which can be achieved fast enough to meet the dynamic demands due to multiple loads. The swash plate angular position is controlled by means of an actuator working in feedback with the load; these types of pumps are known as load-sensing pumps. The load signals from the actuators are transferred to the pump regulators through the load-sensing line. A load-sensing, flow-sharing valve block was used for the application considered; flow sharing is a useful feature when the global flow rate required by the various elements exceeds the pump's maximum flow rate, especially in excavators where several simultaneous motions are required.A literature review shows that pump models could be conceived in a number of ways, either for analysing specific aspects in greater detail [4]