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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, 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 For the purpose of saving energy the constant pressure pumps have, in the past, often been replaced by load-sensing pumps and load-sensing valves.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. 39-52 p.
Keyword [en]
Pump control, control strategies, energy recuperation, mode switching
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:liu:diva-16073OAI: oai:DiVA.org:liu-16073DiVA: diva2:133004
Available from: 2009-01-07 Created: 2009-01-07 Last updated: 2017-10-26Bibliographically 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.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1372
National Category
Fluid Mechanics and Acoustics
Identifiers
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)
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
2. On Energy Efficient Mobile Hydraulic Systems: with Focus on Linear Actuation
Open this publication in new window or tab >>On Energy Efficient Mobile Hydraulic Systems: with Focus on Linear Actuation
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this dissertation, energy efficient hydraulic systems are studied. The research focuses on solutions for linear actuators in mobile applications, with emphasis on construction machines. Alongside the aspect of energy efficiency, the thesis deals with competing aspects in hydraulic system design found in the development of construction machines. Simulation models and controls for different concepts are developed, taking the whole machine into account. In line with this work, several proof of concept demonstrators are developed.

First, pump controlled systems are studied and a novel concept based on an open-circuit pump configuration is conceived. Special consideration is paid to multi-mode capabilities that allow for a broadened operating range and potential downsizing of components. Simulation models and controls are developed and the system is experimentally validated in a wheel loader application.

Second, the possibility for energy recuperation in valve controlled systems is investigated. In such solutions, a hydraulic motor, added to the meter-out port, is used for energy recovery during load lowering and in multi-function operation. Recuperated energy is either be used momentarily or is stored in a hydraulic accumulator. The proposed solution means an incremental improvement to conventional systems, which is sometimes attractive to machine manufacturers due to fewer uncertainties in reliability, safety and development cost. The energy recovery system is studied on a conceptual level where several alternative systems are proposed and a concept based on a two-machine hydraulic pressure transformer is selected for a deeper control study followed by experimental validation.

Third, so-called `common pressure rail' systems are suggested. This technique is well established for rotary drives, at least for the industrial sector. However, in applying this technique to mobile hydraulics, feasible solutions for linear actuators are needed. In this dissertation, two approaches to this problem are presented. The first one is the hydraulic pressure transformer, studied in simulation as the key-component of a `series hybrid' topology for wheel loaders. In the second approach variable displacement linear actuators (VDLA) based on a 4-chamber cylinder and multi-mode control is applied. In a theoretical study a model predictive control approach is suggested and new insights to the trade-off between controllability and energy efficiency of a multi-chamber cylinder are presented. Finally, a fullscale hydraulic hybrid system based on secondary controlled hydraulic motors and VDLAs is designed and experimentally validated on a large excavator.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. 82 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1857
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:liu:diva-142326 (URN)10.3384/diss.diva-142326 (DOI)9789176855119 (ISBN)
Public defence
2017-11-17, C3, C-huset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Energy AgencyVINNOVA
Available from: 2017-10-26 Created: 2017-10-26 Last updated: 2017-11-09Bibliographically approved

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Heybroek, KimPalmberg, Jan-Ove

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