This paper investigates energy efficiency and dynamic behavior through simulation and experiments of a compact electro-hydrostatic actuator system (EHA) consisting of an electric motor, external gear pump/motors, hydraulic accumulator, and differential cylinder. Tests were performed in a stand-alone crane in order to validate the mathematical model. The influence and importance of a good balance between pump/motors displacement and cylinder areas ratios is discussed. The overall efficiency for the performed motion is also compared considering the capability or not of energy recovery. The results obtained demonstrate the significant gain of efficiency when working in the optimal condition and it is compared to the conventional hydraulic system using proportional valves. The proposed system presents the advantages and disadvantages when utilizing components off-the-shelf taking into account the applicability in mobile and industrial stationary machines.

In this paper the fundamental principles of energy-conservative hydraulic control based on the fluid inertance principle are discussed and a detailed analysis of step-up switched-inertance control is presented. A non-loss system comprising an inertance tube and switching valve is modelled and its operational curves are presented as a reference for an ideal behaviour. Considering the load loss at both the tube and the PWM switched valve, a linear mathematical model for the step-up switched-inertance hydraulic system is presented which describes the pressure response as a function of the PWM duty cycle. Mathematical expressions of the flow rates through the tube and the supply and return ports as well as the system efficiency are also presented. A system prototype is evaluated on a test rig and the experimental data compared with the theoretical results, demonstrating the model accuracy. The proposed model simplifies the analysis process for step-up switching converters and thus their restrictions and potential can be investigated more quickly.

Electro-hydraulic position control systems are widely applied in several fields. The valve and cylinder configuration and the dimensioning of these systems is dependent on the requested transient response and the load profile. One of the primary factors in this regards is the selection of an asymmetric or symmetric cylinder, considering issues such as the area available for installation and the asymmetry of the external loading. According to the classical literature, the valve control orifice areas must be matched with the cylinder areas to ensure balanced pressure variation in the cylinder chambers. Moreover, considering that several real applications use non-matched components, it is evident that, depending on the system parameters and load characteristics, good performance can be obtained with this system configuration. Based on non-linear dynamic modelling and experimental results, the transient instants when cavitation or high pressure peaks can occur are determined. Subsequently, a set of equations establishing the relationship between the valve control orifice ratio and cylinder area ratio are derived. A method for determining the valve characteristics, based on parameters such as moved mass, external load force and cylinder asymmetry, is presented. The results obtained are also valid for speed control in open or closed loop system.