A gasless reservoir solution for electro-hydraulic compact drives with two prime movers

Søren Ketelsen, Damiano Padovani, Morten Kjeld Ebbesen, Torben Ole Andersen, Lasse Schmidt

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

2 Scopus citations

Abstract

Due to an increased focus on improving the energy efficiency and compactness of hydraulic linear actuators, the electrohydraulic compact drive (ECD) has received increased attention lately. In this study the ECD consists of variable-speed electric motors and fixed-displacement pumps, which are directly connected to the cylinder, thus controlling the linear motion in a throttleless manner. Furthermore, ECDs are self-contained systems, i.e. based on a fully enclosed oil circuit, in order to avoid external contamination and air to enter the system and to increase system compactness. Conventionally a low-pressure gasloaded accumulator is used as an oil reservoir to compensate for the flow imbalance occurring whenever utilizing single-rod cylinders in closed systems. The accumulator pressure is to be kept relatively low to stay within the required limits governed by the permitted pump housing's pressure. Generally, this pressure is not allowed to exceed 1-3 bar. To avoid violating this limitation, the gas volume must be significantly larger than the actual oil volume, which needs to be stored in the accumulator. This requirement decreases the obtainable compactness of the ECD, especially for systems with a large cylinder stroke. Furthermore, the accumulator represents a potential of gas leakage, which ultimately could result in the ECD being non-functional. This paper presents a gasless reservoir solution, improving the system compactness and avoiding the risk of gas leakage. The proposed solution is based on a bootstrap reservoir which is charged by the lowest cylinder chamber pressure. This strategy is feasible for the class of ECDs that is capable of controlling the lowest cylinder chamber pressure alongside the cylinder motion. An ECD consisting of two electric prime movers is considered as a case study. It is shown how the gasless reservoir may be integrated into the system, and an analysis of how this affects the operating range and the dynamic couplings of the system is presented. This leads to the derivation of a control strategy for the Multi-Input-Multi-Output (MIMO) system based on state decoupling, by defining virtual inputs to control virtual outputs. A numerical study suggests that the reservoir volume may be reduced by approximately 50% for the given system dimensions. The proposed control strategy shows good position tracking performance while also being able to control the reservoir pressure within the predefined limits of 1 to 3 bar.

Original languageEnglish
Title of host publicationBATH/ASME 2020 Symposium on Fluid Power and Motion Control, FPMC 2020
PublisherAmerican Society of Mechanical Engineers
ISBN (Electronic)9780791883754
DOIs
StatePublished - 2020
Externally publishedYes
EventBATH/ASME 2020 Symposium on Fluid Power and Motion Control, FPMC 2020 - Virtual, Online
Duration: 9 Sep 202011 Sep 2020

Publication series

NameBATH/ASME 2020 Symposium on Fluid Power and Motion Control, FPMC 2020

Conference

ConferenceBATH/ASME 2020 Symposium on Fluid Power and Motion Control, FPMC 2020
CityVirtual, Online
Period9/09/2011/09/20

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