In the last decades, digital hydraulics has emerged as a new alternative for the development of more efficient hydraulic systems, where the effects of throttling losses and internal leakages are minimized through the use of conventional hydraulic components associated in parallel or through switching hydraulics. In the aviation industry, hydraulic systems are commonly applied to control highly relevant systems, such as landing gear and flight control surfaces. In this context, digital hydraulics can be used as an alternative solution to improve the energy efficiency of aircraft hydraulic systems. Based on that, this paper aims to present three new hydraulic actuators for application on aircraft flight control surfaces using digital hydraulics. The actuators are being studied by the Laboratory of Hydraulic and Pneumatic Systems - LASHIP of the Federal University of Santa Catarina - UFSC and are called Digital Hydraulic Actuator - DHA, Digital Electro Hydrostatic Actuator - DEHA and Variable Speed Digital Electro Hydrostatic Actuator - VSDEHA. The simulation results show that the actuators developed can be 23 times more efficient than conventional servo-hydraulic actuators, with equivalent dynamic characteristics, demonstrating the potential for application of these new actuators in aeronautical systems.
Hydraulic actuation systems have a broad range of applications covering almost all areas of manufacturing and production and also the service industry. However, it is usual for systems to have low energy efficiency. In recent decades, due to global environmental concerns, research in the field of digital hydraulics to develop more efficient hydraulic systems has increased. In this paper, an analysis of the possible combinations of chambers in a multi-chamber cylinder is presented. A mathematical expression is derived to verify the total number of combinations of chambers that it is possible to achieve for a cylinder with four or more chambers and that result in different constant velocities without cavitation occurring. In addition, a digital hydraulic pump is considered as a supply unit and, since it has discrete output flow rates, an analytical method to combine the pump with a multi-chamber cylinder is developed resulting on a total number of cylinder velocities with a required resolution. For application in a positioning system, design guidelines for an actuator using a cylinder with four chambers and a digital hydraulic pump with three fixed displacement units are presented in which an optimization algorithm for the calculation of the cylinder areas and the volumetric displacement of the pumps is applied. The proposed approaches were applied to design a proof-of-concept and the experimental values presented very good accuracy when compared with the results obtained with the model. Closed-loop position control responses shows that the system can achieve the required setting time with a smooth movement and steady state error around 1 mm.
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