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On Energy Efficient Mobile Hydraulic Systems: with Focus on Linear Actuation
Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
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: urn:nbn:se:liu:diva-142326DOI: 10.3384/diss.diva-142326ISBN: 9789176855119 (print)OAI: oai:DiVA.org:liu-142326DiVA: diva2:1152750
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
List of papers
1. 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
2. Modelling and Control of a Complementary Energy Recuperation System for Mobile Working Machines
Open this publication in new window or tab >>Modelling and Control of a Complementary Energy Recuperation System for Mobile Working Machines
2013 (English)In: / [ed] Petter Krus, Magnus Sethson, Liselott Ericson, Linköping University Electronic Press, 2013, 21-30 p.Conference paper, Published paper (Refereed)
Abstract [en]

The concept of hybrid technologies for mobile working machines has gained increased attention in recent years. This paper deals with a parallel hybrid system for energy recuperation based on a two-machine hydraulic transformer. The system can be connected hydraulically to an existing hydraulic circuit as a complementary add-on system. The linear analysis of the system visualises the control difficulties coming from a low inertia, slow control dynamics of the machines and the non-linear stick-slip friction during low speeds. A control strategy based on linear control methods is proposed and evaluated in a hardware test bench. It is shown that an acceptable performance can be achieved even with fairly simple models. Additionally, a start-up procedure is proposed to start the transformer from zero speed

Place, publisher, year, edition, pages
Linköping University Electronic Press, 2013
Series
Linköping Electronic Conference Proceedings, ISSN 1650-3686 (print), 1650-3740 (online) ; 092
Keyword
Parallel hybrid, Energy recuperation, Hydraulic transformer
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-100142 (URN)10.3384/ecp1392a3 (DOI)978-91-7519-572-8 (ISBN)
Conference
13th Scandinavian International Conference on Fluid Power, June 3-5, 2013, Linköping, Sweden
Available from: 2013-10-29 Created: 2013-10-29 Last updated: 2017-10-26Bibliographically approved
3. Towards Resistance-free Hydraulics in Construction Machinery
Open this publication in new window or tab >>Towards Resistance-free Hydraulics in Construction Machinery
2012 (English)In: 8th International Fluid Power Conference, Dresden: Dresdner Verein zur Förderung der Fluidtechnik , 2012, Vol. 2, 123-138 p.Conference paper, Published paper (Refereed)
Abstract [en]

The topic of resistance-free motion control refers to solutions that minimize or completely eliminate the need for proportional valves, hence avoiding the throttling losses associated with metering. Previous research by the authors shows how a secondary control system could be used to improve energy efficiency in construction machines. The proposed solution uses hydraulic transformers, powered by a common pressure rail system driving both the linear work implements and the rotary drives of a propulsion system in a wheel loader. An emphasis in this paper is on the sizing aspects of transformer-based system design. The solution under special observation enables the use of smaller transformers utilizing the differential cylinder as a two-stage gearbox by means of “short-circuiting” its two cylinder chambers. The results and outlook from this study touch on how state-of-the-art secondary control systems could improve the energy efficiency of future construction machinery and suggest potential areas of improvement.

Place, publisher, year, edition, pages
Dresden: Dresdner Verein zur Förderung der Fluidtechnik, 2012
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-132927 (URN)
Conference
8th International Fluid Power Conference, Dresden, March 26-28, 2012
Funder
Swedish Energy Agency, P32064-1
Available from: 2016-12-01 Created: 2016-12-01 Last updated: 2017-10-26Bibliographically approved
4. A novel hydromechanical hybrid motion system for construction machines
Open this publication in new window or tab >>A novel hydromechanical hybrid motion system for construction machines
2017 (English)In: International Journal of Fluid Power, ISSN 1439-9776, Vol. 18, no 1, 17-28 p.Article in journal (Refereed) Published
Abstract [en]

This paper deals with a novel type of hybrid motion system for construction machines based on a common pressure rail shared between a hydromechanical power-split transmission and secondary controlled work hydraulics. A construction machine with driveline and work functions is a complex coupled motion system and the design of an effective hybrid system needs to take both subsystems into account. Studies on energy efficient hybrid systems for construction machines have hitherto principally focused on one subsystem at a time - work hydraulics or driveline. The paper demonstrates a use case with a specific transmission concept proposal for a medium-sized wheel loader. The system is modelled and simulated using an optimal energy management strategy based on dynamic programming. The results show the benefits of a throttle-free bidirectional link between the machine's subsystems and the energy storage, while taking advantage of the complex power flows of the power-split transmission.

Place, publisher, year, edition, pages
Abingdon, UK: Taylor & Francis, 2017
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-142329 (URN)10.1080/14399776.2016.1210423 (DOI)
Available from: 2017-10-26 Created: 2017-10-26 Last updated: 2017-11-09Bibliographically approved

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