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Applied Control Strategies for a Pump Controlled Open Circuit Solution
Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Fluid and Mechanical Engineering Systems . (Fluid och mekanisk systemteknik)
Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Fluid and Mechanical Engineering Systems . (Fluid och mekanisk systemteknik)
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 (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 For the purpose of saving energy the constant pressure pumps have, in the past, often been replaced by load-sensing pumps and load-sensing valves.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. 39-52 p.
Keyword [en]
Pump control, control strategies, energy recuperation, mode switching
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:liu:diva-16073OAI: diva2:133004
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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