Enhanced energy efficiency of industrial application by direct driven hydraulic unit

Direct Driven Hydraulic (DDH) systems, which are characterized by a closed circuit type and a speed-controlled pump, offer a possibility of reaching higher energy efficiencies compared to the traditional open circuit type valve-controlled systems, and simultaneously offering high accuracy and dynamics. This study presents experimental results gained with a DDH system applied to an industrial position control application. The results include the system behavior regarding the accuracy of position control, pressures, power, and energy consumption with three different system structures: basic DDH, load- compensated DDH and load-compensated and damped DDH. It was found that compared to valve-controlled hydraulics, DDH system offered potential for significant energy savings, especially if combined with hydraulic load compensation. However, without damping, the motion involved marked vibrations in the end of the stroke. Vibrations were avoided by introducing damping, but at the cost of reduced energy efficiency.