Pump-controlled hydraulic circuits for single-rod actuators: New designs and performance evaluation
Loading...
Date
2020
Authors
Imam, Ahmed
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
This thesis investigates the challenges in designing pump-controlled single-rod actuators and proposes new solutions for them. Three different concepts to overcome the reported performance problems are proposed. By applying the new concepts, eight different new designs are introduced, among which, five are experimentally evaluated. These designs show good performance, efficiency and energy recuperation ability as compared to previously reported circuits.
Hydraulic actuation systems are favored in many applications due to their fast response, high power-to-weight ratio, and stability under variable loading conditions. Efficiency, however, is the main disadvantage of conventional valve-controlled hydraulic actuators, which is typically around 25%. Pump-controlled hydraulic actuation systems are more efficient than valve-controlled ones, as they eliminate the energy losses due to flow throttling in valves and require less cooling effort. The existing common pump-controlled circuits for single-rod actuators experience a performance problem at specific operating conditions. More specifically, circuits encounter oscillatory performance at low loading conditions.
In this thesis, a detailed analysis to identify the low performance operating regions of a commonly-used single-rod hydraulic pump-controlled circuit that utilizes two pilot operated check valves is performed. Factors affecting these regions are discussed. The analysis is repeated to evaluate performance of circuits with closed-center and open-center shuttle valves. Findings are also validated by experimental results. Based on these findings, three different concepts to improve circuit performance, specially, in the oscillatory zone are proposed. The proposed concepts are: selective throttling over flow, selective oil leakage, and shifting of critical zone into lower loading margin. Building upon these concepts, eight different new circuits are designed. Simulation studies verify the enhanced performance of the proposed circuits as compared to the benchmark design. Five of the eight proposed circuits that utilize available off-the-shelf industrial components are prototyped and tested using a newly constructed test rig. The test rig has been designed to facilitate the implementation of different circuits and for various loading conditions. It is shown that the proposed designs do not require additional electronic control components, which is desirable in industrial applications. Furthermore, energy studies demonstrated superior efficiency of the proposed circuits compared to the valve-controlled counterparts
Description
Keywords
Pump-Controlled Hydraulic Circuits, Single-Rod Actuators, efficiency