Improving the Efficiency and Dynamic Properties of a Flow Control Unit in a Self-Locking Compact Electro-Hydraulic Cylinder Drive

The introduction of low cost electric motor and drive solutions provides the possibility to design cost competitive compact speed-variable drives as potentially feasible alternatives to conventional valve-controlled solutions. A main drawback in existing self-contained drive technology is the power consumption in stationary load carrying situations. However, the recent introduction of compact self-locking drive topologies with separate forward and return flow lines allow to significantly minimize the power consumption, but introduces another problem. Dependent on the control of the flow device, a continuous, but lower power consumption compared to non-self-locking drive topologies may be present. Furthermore, the piston motion may exhibit a time delay due to an outlet pressure build-up phase in the flow unit prior to actuation of the cylinder, limiting the application range of such a drive concept. The purpose of the study presented, is to analyze these properties through model-based methods, and to establish control functionalities allowing to minimize these unfortunate features. The resulting flow device control structure allows for a significant reduction in the actuation time delay as well as in the power consumption in stationary load carrying situations. Numerical results demonstrate the properties announced by the theoretical analysis and control design phase, hence broadening the application range of the self-locking drive topology in question.