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

Abstract

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.

A Comparison Study of a Novel Self-Contained Electro-Hydraulic Cylinder versus a Conventional Valve-Controlled Actuator—Part 1: Motion Control

“…As demonstrated in this reference, additional damping is necessary to achieve smooth operations since the combination of a pressure-compensated control valve and a counterbalance valve [20] are used to identify the gain margin and the phase cross over frequency. This is a necessary step to derive the PI-controller gains in Table 2 that are based on Equations (15) and (16).…”

“…Current commercial solutions of the SCC technology are limited and typically tailor-made [8], especially the ones developed for load-carrying applications that are required to contain passive load-holding devices, according to the safety regulations (e.g., ISO 17096 and DNVGL-ST-0378). Then, the research emphasis is primarily on different electro-hydraulic configurations [10][11][12][13], for low-power servo applications [14][15][16][17]. There is, therefore, a lack of experimental studies comparing state-of-the-art, valve-controlled technology for load-carrying applications to self-contained hydraulic cylinders in the technical literature, both in terms of motion performance and energy efficiency.…”

A Method for Smoothly Disengaging the Load-Holding Valves of Energy-Efficient Electro-Hydraulic Systems

“…Proposing self-sufficient, electro-hydraulic assemblies with a sealed reservoir, arranged in closed-circuit configuration, and with a wired connection to the electric grid facilitates the commissioning enormously. Solutions with a single positive-displacement pump/motor [9]- [16], and alternatives with two units were investigated [7], [17]- [19]. These different versions were mainly proposed to manage the differential flow dictated by asymmetric cylinders, that can be compensated in multiple ways [20].…”

“…These different versions were mainly proposed to manage the differential flow dictated by asymmetric cylinders, that can be compensated in multiple ways [20]. However, only a very few solutions specifically address the load-holding capability [14], [15], [16], [18], [19]. In these throttleless architectures, energy can be recovered in case of overrunning loads so that there is only the need for passive load-holding (i.e., maintaining a given piston position without consuming any power).…”

A Comparison Study of a Novel Self-Contained Electro-Hydraulic Cylinder versus a Conventional Valve-Controlled Actuator—Part 2: Energy Efficiency

“…SCCs can in fact enhance energy efficiency, modular design, plug-and-play installation, and reduced maintenance [12]. Current commercial solutions of the SCC technology are limited and typically tailor-made, whereas the research emphasis is primarily on different electro-hydraulic configurations [13][14][15][16], energy-efficiency [17][18][19][20][21], thermal analysis [22][23][24], and low-power servo applications [25]. According to the survey presented in [10], compact and self-contained solutions comprising passive load-holding devices, able to operate in four quadrants, and suitable for power levels above 5 kW are missing, both on the market and four quadrants, and suitable for power levels above 5 kW are missing, both on the market and in the technical literature.…”