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 shortcircuiting
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.