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Saving Energy in Construction Machinery using Displacement Control Hydraulics: Concept Realization and Validation
Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Fluid and Mechanical Engineering Systems . (Flumes)
2008 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the sector of mobile hydraulics, valve controlled systems are predominant. In these systems the load force and speed are adjusted by control valves. In machines where multiple drives are used in parallel at extremely varying loads the energy efficiency of such systems is often compromised over large working regions. Most valve controlled systems also lack the possibility to recuperate potential energy.

A different category of hydraulic systems, called displacement controlled hydraulics are based on the manipulation of the hydraulic flow using the relative displacement of the hydraulic machines as the final control element. This type of hydrostatic power transfer, yields a resistance free velocity control, ideally leading to lossless load actuation.

This thesis concerns the introduction of a new type of displacement controlled hydraulic system, adapted for construction machinery. The system decouples the hydraulic functions using one dedicated hydraulic machine for each drive. These machines are of open circuit type, capable of over center operation which enables energy recuperation. The system also comprises four separate valves that by means of switching allow the cylinder to be controlled over all four load quadrants. Depending on the selected valve hardware, the system may also include features available in a conventional valve controlled system, such as meter-out flow control. The system supports both symmetrical and asymmetrical cylinders. However, using the asymmetrical type the load may be controlled in two distinct states of operation. This yields an increased region of operation, which is otherwise generally stated as a drawback in displacement controlled systems. It also allows the selection between different control modes, where one of the modes is always more efficient than another.

In this research both theoretical studies and a practical implementation demonstrate the energy related benefits of the new concept. The target application of this study is a medium-size wheel loader. Measurement results using the wheel loader in a short truck loading cycle show a 10% percent reduction in fuel consumption. According to the theoretical investigation, this corresponds to a 20% reduction in energy consumption for the hydraulicsystem itself.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2008. , 117 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1372
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:liu:diva-15588Local ID: LIU-TEK-LIC-2008:30ISBN: 978-91-7393-860-0 (print)OAI: oai:DiVA.org:liu-15588DiVA: diva2:126676
Presentation
A35, A-huset, Campus Valla, Linköpings universitet, Linköping, Sweden (English)
Opponent
Supervisors
Available from: 2009-01-07 Created: 2008-11-19 Last updated: 2009-04-30Bibliographically approved
List of papers
1. Mode Switching and Energy Recuperation in Open-Circuit Pump Control
Open this publication in new window or tab >>Mode Switching and Energy Recuperation in Open-Circuit Pump Control
2007 (English)In: The 10th Scandinavian International Conference on Fluid Power, Tampere, Finland, Tampere, Finland: Tampere University of Technology , 2007, 197-209 p.Conference paper, Published paper (Refereed)
Abstract [en]

Today´s mobile machines most often contain hydraulic valve controlled drives in an open loop circuit. For the purpose of saving energy, the constant pressure pumps have in the past frequently been replaced by load-sensing pumps and load-sensing valves. However, considering applications where the load is helped by the gravitational force, even these hydraulic systems often suffer from poor efficiency. In this article, a novel pump-controlled hydraulic system is studied where energy recuperation from lowering motions is posssible. The pumps are fully displaceable in both directions, working as motors when lowering loads. The amount of recuperated energy is highly dependent of the chosen control strategy, the hydromechanical properties as well as the target application. Furthermore, the article describes how valve design becomes an important feature in an attempt to reach high efficiency and machine operability.

Place, publisher, year, edition, pages
Tampere, Finland: Tampere University of Technology, 2007
Keyword
Pump control open circuit energy efficiency energy recuperation
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-16075 (URN)
Available from: 2009-01-07 Created: 2009-01-07 Last updated: 2009-04-30Bibliographically approved
2. Applied Control Strategies for a Pump Controlled Open Circuit Solution
Open this publication in new window or tab >>Applied Control Strategies for a Pump Controlled Open Circuit Solution
2008 (English)In: Proceedings of the 6:th IFK: International Fluid Power Conference, Dresden, Germany, Dresden: Dresdner Verein zur Förderung der Fluidtechnik e.V. , 2008, 39-52 p.Conference paper, Published paper (Other academic)
Abstract [en]

Today’s mobile machines most often contain hydraulic valve controlled drives in an open loop-circuit. For the purpose of saving energy the constant pressure pumps have, in the past, often been replaced by load-sensing pumps and load-sensing valves. In mobile applications these load-sensing solutions have significantly reduced the energy consumption. However, in applications with unequal drive pressure levels the load sensing systems still result in energy losses, referred to as metering losses. Throttling losses associated to load lowering have also been paid more attention to in the energy debates. By instead adopting direct pump displacement control, with the capability of energy recuperation in lowering motions, many of these losses can be avoided. In this article the author has studied a hydraulic system configuration where each actuator/supply system comprises a variable displacement pump/motor working in an open-circuit together with four separate electrically controlled valves. The four valves render a solution versatile in control, as the cylinder chambers can be connected to pump and/or tank as well as be closed at any time. The pump is electrically controlled and is used either in pressure control mode or flow control mode depending on the state of operation. Along with the hardware described above, the open-circuit solution requires a number of electronic sensors as well as a microprocessor control system, hence the system is a mechatronic system. In contrast to a conventional hydraulic system the control objectives in this concept are not strictly defined by the hardware configuration, but instead many of its critical parameters can be adjusted in software, thus an increased flexibility in system design is obtained. Consequently, defining the desired system properties becomes even more important. Furthermore system robustness must be considered to a greater extent, due to the increased number of sensors and components. The main focus in this paper is to show how machine operability and performance depends on a set of chosen control strategies, what can be achieved as to energy efficiency and driver comfort and at what cost. Additionally the trade-off between energy efficiency and comfort is discussed. In previous work the author has investigated the influence on energy efficiency by lowering loads in different modes of operation, in respect to how the valves are controlled. In this article strategies to decide which mode of operation is the most energy efficient are considered, and how transitions between these modes can be handled by pressure matching prior to opening valves. As the open circuit solution does not support energy storage over time, methods to manage recuperated excess energy is investigated in order to prevent the primary mover from speeding up. The author will also discuss some application specific challenges where a wheel loader has been equipped with the open-circuit solution. For instance, how to handle interference between drives due to the mechanical coupling in the lifting framework and how to handle load actuation over gravity center.

Place, publisher, year, edition, pages
Dresden: Dresdner Verein zur Förderung der Fluidtechnik e.V., 2008
Keyword
Pump control, control strategies, energy recuperation, mode switching
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-16073 (URN)
Available from: 2009-01-07 Created: 2009-01-07 Last updated: 2017-10-26Bibliographically approved
3. Evaluating a Pump Controlled Open Circuit Solution
Open this publication in new window or tab >>Evaluating a Pump Controlled Open Circuit Solution
2008 (English)In: International Exposition for Power Transmission, Nevada, USA: Proceedings of the 51:st IFPE, Nevada, USA: Omnipress , 2008, 681-694 p.Conference paper, Published paper (Other academic)
Abstract [en]

Today’s mobile machines most often contain hydraulic valve controlled drives in an open loop-circuit. For the purpose of saving energy the constant pressure pumps have, in the past, often been replaced by load-sensing pumps and load-sensing valves. In mobile applications these load-sensing solutions have significantly reduced the energy consumption. However, in applications with unequal drive pressure levels the load sensing systems still result in energy losses, referred to as metering losses. Throttling losses associated to load lowering have also been paid more attention to in the energy debates. By instead adopting direct pump displacement control, with the capability of energy recuperation in lowering motions, many of these losses can be avoided. In this article the author has studied a hydraulic system configuration where each actuator/supply system comprises an electrically controlled variable displacement pump/motor working in an open-circuit together with four separate electrically controlled valves. The four valves render a solution versatile in control, as the cylinder chambers can be connected to pump and/or tank as well as be closed at any time. Depending on how the valves are controlled different modes of operation are achieved, which in turn yields different total energy efficiency depending on the present working point. In this study the performance, operability and energy consumption is evaluated in a wheel loader that is first looked upon with its original load sensing hydraulic system and then modified with a completely new pump controlled hydraulic system. Measurements published in this article demonstrate the advantages and drawbacks of pump control in an open circuit compared to a load sensing system. Performance is evaluated by looking at productivity, loading capacity and duty cycle time of a typical loading cycle. Operability is evaluated by looking at response times, load oscillations and driver comfort. Theoretical calculations of energy efficiency including metering and throttling losses over the valves as well as pump efficiency, line losses and losses in the recuperation phase are evaluated and validated. The fuel consumption of the pump-controlled wheel loader is measured and put side by side to measurements of the same machine equipped with a load-sensing hydraulic system.

Place, publisher, year, edition, pages
Nevada, USA: Omnipress, 2008
Keyword
Pump control, energy recuperation, mode switching
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-16074 (URN)
Available from: 2009-01-07 Created: 2009-01-07 Last updated: 2009-04-30Bibliographically approved

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Heybroek, Kim

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