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Mobile Working Hydraulic System Dynamics
Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with innovative working hydraulic systems for mobile machines. Flow control systems are studied as an alternative to load sensing. The fundamental difference 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 and there is no load pressure feedback causing stability issues. Experimental results show a reduced pump pressure margin and energy saving potential for a wheel loader application.

The damping contribution from the inlet and outlet orifice in directional valves is studied. Design rules are developed and verified by experiments.

A novel system architecture is proposed where flow control, load sensing and open-centre are merged into a generalized system description. The proposed system is configurable and the operator can realize the characteristics of any of the standard systems without compromising energy efficiency. This can be done non-discretely on-the-fly. Experiments show that it is possible to avoid unnecessary energy losses while improving system response and increasing stability margins compared to load sensing. Static and dynamic differences between different control modes are also demonstrated experimentally.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. , 85 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1697
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:liu:diva-121070DOI: 10.3384/diss.diva-121070ISBN: 978-91-7685-971-1 (print)OAI: oai:DiVA.org:liu-121070DiVA: diva2:851607
Public defence
2015-10-02, A35, A-huset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-09-07 Created: 2015-09-04 Last updated: 2015-09-08Bibliographically approved
List of papers
1. Flow versus pressure control of pumps in mobile hydraulic systems
Open this publication in new window or tab >>Flow versus pressure control of pumps in mobile hydraulic systems
2014 (English)In: Proceedings of the Institution of mechanical engineers. Part I, journal of systems and control engineering, ISSN 0959-6518, E-ISSN 2041-3041, Vol. 228, no 4, 245-256 p.Article in journal (Refereed) Published
Abstract [en]

This work studies an innovative working hydraulic system design for mobile applications, 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. 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. This allows the pump to be designed to meet the response requirements without considering system stability. Pressure compensators are key components in flow control systems. This study addresses the flow matching problem which occurs when using traditional 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. Simulation results and measurements on a wheel loader application demonstrate the energy-saving potentials and the dynamic improvements for the flow control system.

Place, publisher, year, edition, pages
Sage Publications, 2014
Keyword
Hydraulics, flow control, load-sensing, mobile systems, energy efficiency, dynamic characteristics, compensators
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-105796 (URN)10.1177/0959651813512820 (DOI)000333799100005 ()
Available from: 2014-04-07 Created: 2014-04-07 Last updated: 2017-12-05Bibliographically 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
4. A Hybrid of Pressure and Flow Control in Mobile Hydraulic Systems
Open this publication in new window or tab >>A Hybrid of Pressure and Flow Control in Mobile Hydraulic Systems
2014 (English)In: 9th InternationalFluid Power Conference (IFK). Vol. 1. Aachen, Germany, 24-26 March 2014 / [ed] Hubertus Murrenhoff, 2014, 190-201 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a hybrid pump controller approach for mobile hydraulic systems, influenced by both pressure and flow. The controller is tuneable to be able to set the order of importance of the pressure and flow controller, respectively. It is thus possible to realize a load sensing system, a flow control system or a mix of the two. Using a low load pressure feedback gain and a high flow control gain, a system emerges with high energy efficiency, fast system response, high stability margins and no flow matching issues. In this paper, both theoretical studies and practical implementations demonstrate the capability of a hybrid pump control approach.

Keyword
Mobile hydraulics, pressure control, flow control, energy efficiency, dynamics
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-105794 (URN)978-3-9816480-0-3 (ISBN)
Conference
9th International Fluid Power Conference (IFK), 24-26 March 2014, Aachen, Germany
Available from: 2014-04-07 Created: 2014-04-07 Last updated: 2015-09-07Bibliographically approved
5. Energy Efficient Fluid Power System for Mobile Machines with Open-centre Characteristics
Open this publication in new window or tab >>Energy Efficient Fluid Power System for Mobile Machines with Open-centre Characteristics
2014 (English)In: 9th JFPS International Symposium on Fluid Power. Matsue, Japan, 28-31 October 2014, The Japan Fluid Power System Society , 2014, 452-459 p.Conference paper, Published paper (Other academic)
Abstract [en]

This paper presents a flexible and energy efficient system solution which mimics the behaviour of an open-centre system. An electro-hydraulic variable displacement pump and closed-centre valves are used. Instead of having a flow in the open-centre gallery, that flow is calculated using a pressure sensor and a valve model. The variable pump is then controlled in order to only deliver the flow that would go to the actual loads. It is also possible for the operator to decide how much load dependency there should be. The extreme case is not having any load dependency at all, resulting in a system where the pump displacement setting is controlled according to the sum of all requested load flows. It is thus possible to realize a system design with open-centre characteristics, a flow control system or something in between. Each operator can thereby get their optimal control characteristic while having high energy efficiency.

Place, publisher, year, edition, pages
The Japan Fluid Power System Society, 2014
Keyword
Mobile hydraulics, energy efficiency, dynamics, damping
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-111819 (URN)4-931070-10-8 (ISBN)
Conference
9th JFPS International Symposium on Fluid Power, Shimane, Japan, 28-31 October 2014
Available from: 2014-11-04 Created: 2014-11-04 Last updated: 2016-05-17Bibliographically approved
6. A Flexible Working Hydraulic System for Mobile Machines
Open this publication in new window or tab >>A Flexible Working Hydraulic System for Mobile Machines
2016 (English)In: International Journal of Fluid Power, ISSN 1439-9776, Vol. 17, no 2, 79-89 p.Article in journal (Other academic) Published
Abstract [en]

This paper proposes a novel working hydraulic system architecture for mobile machines. Load sensing, flow control and open-centre are merged into a generalized system description. The proposed system is configurable and the operator can realize the characteristics of any of the standard systems without compromising energy efficiency. This can be done non-discretely on-the-fly. One electrically controlled variable displacement pump supplies the system and conventional closed-centre spool valves are used. The pump control strategies are explained in detail. Experimental results demonstrate one solution to the flow matching problem and the static and dynamic differences between different control modes.

Place, publisher, year, edition, pages
Taylor & Francis, 2016
Keyword
Mobile hydraulics, dynamics, energy efficiency, pump controller
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-121068 (URN)10.1080/14399776.2016.1141635 (DOI)
Available from: 2015-09-04 Created: 2015-09-04 Last updated: 2017-12-04Bibliographically approved

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Axin, Mikael

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