Defining the Design Space of Basic Hydraulic Drive Networks

Hydraulic systems are widely used throughout industry to actuate and control applications where large forces are required. These applications include off-highway machinery like excavators, loaders, manufacturing machinery like presses, injection molding machinery and so forth. With a continuously increasing focus on electrification and reduced energy consumption, emissions and rare earth material usage, energy efficiency, reduced component sizes and limited component numbers become increasingly important. In this endeavor, the recently introduced concept of hydraulic drive networks appears especially feasible to consider in applications with two or more hydraulic actuators to be controlled. Key features of hydraulic drives networks are the sole use of displacement units as flow control elements, absence of traditional control valves, and short-circuiting of hydraulic actuator chambers, while maintaining the possibility of individual control of each actuator. A consequence of these features is that possible ways of connecting the flow ports of displacement units to those of the actuators increases exponentially with the number of actuators to be controlled, rendering the use of traditional hydraulic system design methods obsolete. A possible way to systematically characterize and identify feasible networks is by use of graph theory. However, at this stage, no standardized approaches and definitions exist for such systems. This paper considers the concept of hydraulic drive networks in the framework of graph theory and applies the concept of tree-graphs to define the design space of feasible hydraulic drive network architectures for any number actuators constituting a number of control volumes for which flow must be controllable. Identifying and distinguishing each architecture in the design space is vital in the process of hydraulic drive network design, for being able to compare and optimize architectures based on objectives such as size, cost, efficiency and so forth.