Elektro-Hydraulic Compact Drives with variable Transmission

Research Task/Objectives

The aim of the research project is systemisation of structures for electro-hydraulic compact actuators with a hermetically enclosed oil circuit that allow discretely variable transmission. For applications with a distinct separation between high load and rapid traverse strokes, variable transmission means downsizing potential for the electric drive components involved. One major challenge that have to be overcome is combining compensation of fluctuation flow resulting from asymmetric cylinders with transmission switching principles. Also, smooth gear changes are mandatory for successful implementation in most applications and are therefore a requirements for the switching strategy to be developed. Proof of functionality and downsizing potential are to be given by means of experiments.

Approach

After analysing the downsizing potential for any given application as a function of the load cycle, the solution space for displacement controlled compact drives with discretely variable transmission is investigated systematically. Two switching principles are distinguished: Actuator-based switching that combines different cylinder areas to an effective cylinder area and pump-based switching that combines different pump displacements to an effective displacement volume. Solutions that allow displacement control with a single-rod cylinder in closed hydraulic circuit are combined with switching principles for layout and design of demonstrator actuators. A control strategy and valve arrangement for smooth switching is developed and validation of performance and downsizing potential for the entire functional unit is carried out on a test bed.

The presented research activities are part of the project “Electro-hydraulic compact drives with variable transmission” (Ref. No. 703490). The authors would like to thank the Fluid Power Research Fund of the VDMA for the funding and support.