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Fluid Power Systems for Mobile Applications: with a Focus on Energy Efficiency and Dynamic Characteristics
Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, The Institute of Technology.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis studies an innovative working hydraulic system design for mobile applications. The purpose is to improve the energy efficiency and the dynamic characteristics compared to load sensing systems without increasing the complexity or adding additional components.

The system analysed in this thesis is referred to as flow control. The fundamental difference compared to load sensing systems is that the pump is controlled based on the operator’s command signals rather than feedback signals from the loads. This control approach enables higher energy efficiency since the pressure difference between pump and load is given by the system resistance rather than a prescribed pump pressure margin. High power savings are possible especially at medium flow rates.

Furthermore, load sensing systems suffer from poor dynamic characteristics since the pump is operated in a closed loop control mode. This might result in an oscillatory behaviour. Flow control systems have no stability issues attached to the load pressure feedback since there is none.

Pressure compensators are key components in flow control systems. This thesis addresses the flow matching problem which occurs when using conventional compensators in combination with a flow controlled pump. Flow sharing pressure compensators solve this problem since the pump flow will be distributed between all active functions. A novel control approach where the directional valve is controlled without affecting the cylinder velocity with the objective of optimizing the damping is proposed.

In this research, both theoretical studies and practical implementations demonstrate the capability of flow control systems. Experiments show a reduced pump pressure margin and energy saving possibilities in a short loading cycle for a wheel loader application.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 59 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1595
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:liu:diva-92578Local ID: LIU-TEK-LIC-2013:29ISBN: 978-91-7519-600-8 (print)OAI: oai:DiVA.org:liu-92578DiVA: diva2:621033
Presentation
2013-05-17, ACAS, A-huset, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2013-05-22 Created: 2013-05-13 Last updated: 2013-06-25Bibliographically approved
List of papers
1. Energy Efficient Load Adapting System Without Load Sensing: Design and Evaluation
Open this publication in new window or tab >>Energy Efficient Load Adapting System Without Load Sensing: Design and Evaluation
2009 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In load sensing systems, the pump pressure is controlled in a closed loop control mode. In this paper, a system solution where the displacement of the pump is controlled directly from the operator's demand is studied. Both the stability and the response is thereby improved. It also implies a better energy efficiency since the pump pressure will be adapted according to the point of operation with no additional pressure margin needed. In some mobile applications, pressure compensation is required to avoid load interference. When using common pre compensators in a displacement controlled system, the pump and the valve will both control the flow. A better solution would be to control the flow by the pump and utilize the valve as a flow divider. This can be achieved by using flow sharing compensators. It also allows further energy savings since the maximum restriction area of the main spool at one of the loads can be utilized independent of the flow delivered by the pump. This paper addresses the problem with using common pre compensators in displacement controlled systems and analyses and compares both a traditional load sensing system and an open controlled pump solution with flow sharing compensators. Measurements on a wheel loader application equipped with the system presented in this paper shows a decreased energy consumption of 14 % for the working hydraulics compared to a load sensing system during a short loading cycle, provided that the pump is not saturated.

Place, publisher, year, edition, pages
Linköping: , 2009
Keyword
fluid power, mobile systems, LS systems, pre compensation, energy efficiency, flow sharing
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-52691 (URN)
Conference
11th Scandinavian International Conference on Fluid Power, SICFP'09, June 2-4, Linköping, Sweden
Available from: 2010-01-08 Created: 2010-01-08 Last updated: 2015-08-31Bibliographically approved
2. Dynamic Analysis of Single Pump, Flow Controlled Mobile Systems
Open this publication in new window or tab >>Dynamic Analysis of Single Pump, Flow Controlled Mobile Systems
2011 (English)In: The Twelfth Scandinavian International Conference on Fluid Power, SICFP'11: Volume 2 / [ed] Harri Sairiala & Kari T. Koskinen, 2011, 223-238 p.Conference paper, Published paper (Refereed)
Abstract [en]

Interest has increased in flow controlled systems in the field of mobile fluid power. The capital distinction between traditional load-sensing (LS) systems and flow controlled systems is that the pump is controlled based on the operator’s total flow demand rather than maintaining a certain pressure margin over the maximum load pressure. One of the main advantages of flow controlled systems is the absence of the feedback of the highest load pressure to the pump controller. In this paper, a dynamic analysis is performed where flow controlled and LS systems are compared. It is shown how instability can occur in LS systems due to the pump controller and proven that no such instability properties are present in flow controlled systems. A drawback with one type of flow controlled system is that the highest load dynamically will disturb the lighter loads. This paper shows a novel way to optimize the damping in such systems by controlling the opening position of the directional valve independently of the flow. The mentioned disturbance between the highest load to the others can thereby be reduced.

Keyword
Flow control, load sensing, dynamic analysis, stability, damping
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-68636 (URN)978-952-15-2519-3 (ISBN)
Conference
The Twelfth Scandinavian International Conference on Fluid Power, SICFP'11, May 18-20, 2011 Tampere, Finland
Available from: 2011-05-25 Created: 2011-05-25 Last updated: 2015-09-07
3. Optimized Damping in Cylinder Drives Using the Meter-out Orifice: Design and Experimental Verification
Open this publication in new window or tab >>Optimized Damping in Cylinder Drives Using the Meter-out Orifice: Design and Experimental Verification
2012 (English)In: 8th International Fluid Power Conference Dresden: "Fluid Power Drives!", 2012, Vol. 1, 579-591 p.Conference paper, Oral presentation only (Other academic)
Abstract [en]

This paper analyses the damping of a flow controlled cylinder with a mass load and an outlet orifice. By using linear models, a mathematical expression for the damping is derived. It is shown that the volumes on each side of the piston have a high impact on the damping. In case of a small volume on the inlet side, the damping becomes low. However, the most important thing is to design the outlet orifice area properly. There exists an optimal orifice dimension; both smaller and larger orifice areas give low damping independently of the size of the volumes. In this paper a design is proposed of the outlet orifice area that optimizes the damping of the system. Experimental results which confirm the theoretical expectations are also presented. The conclusions are that without an outlet orifice, the hydraulic system will not contribute with any damping at all. Furthermore, large dead volumes in the cylinder will increase the damping, but at the expense of the system’s efficiency.

Keyword
Damping, compensator, outlet orifice, efficiency
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-76878 (URN)
Conference
8th International Fluid Power Conference, March 26 - 28, 2012, Dresden
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2015-09-07

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Axin, Mikael

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