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Evaluating a Pump Controlled Open Circuit Solution
Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Fluid and Mechanical Engineering Systems .
Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Fluid and Mechanical Engineering Systems .
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 (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 For the purpose of saving energy the constant pressure pumps have, in the past, often been replaced by load-sensing pumps and load-sensing valves.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. 681-694 p.
Keyword [en]
Pump control, energy recuperation, mode switching
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:liu:diva-16074OAI: diva2:133008
Available from: 2009-01-07 Created: 2009-01-07 Last updated: 2009-04-30Bibliographically approved
In thesis
1. Saving Energy in Construction Machinery using Displacement Control Hydraulics: Concept Realization and Validation
Open this publication in new window or tab >>Saving Energy in Construction Machinery using Displacement Control Hydraulics: Concept Realization and Validation
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.
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1372
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:liu:diva-15588 (URN)LIU-TEK-LIC-2008:30 (Local ID)978-91-7393-860-0 (ISBN)LIU-TEK-LIC-2008:30 (Archive number)LIU-TEK-LIC-2008:30 (OAI)
A35, A-huset, Campus Valla, Linköpings universitet, Linköping, Sweden (English)
Available from: 2009-01-07 Created: 2008-11-19 Last updated: 2009-04-30Bibliographically approved

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