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Control of Hybrid Hydromechanical Transmissions
Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with control aspects of complex hybrid hydromechanical transmissions for heavy mobile working machines. Control problems are identified and solved to facilitate the implementation and use of these systems.

Fuel prices and environmental concerns have increased the interest in hybrid hydromechanical transmissions for heavy mobile working machines. Hybridisation, the introduction of a secondary energy source in the transmission, offers attractive improvements in terms of both fuel efficiency and performance. These improvements are, in turn, enabled by software control. A complex transmission architecture has several components that need to interact in a stable manner. In addition, optimal utilisation of the added energy source is required to maximise fuel savings. Meanwhile, there is a strong trend towards automation, where many of the operator’s difficult control tasks need to be managed by computers. Sophisticated control strategies are therefore needed, along with a deeper understanding of dynamic properties.

Previous research on the control of hybrid hydromechanical transmissions has primarily focussed on on-road applications. The working conditions of heavy working machines place different requirements on the transmission, which is also reflected in the control strategy.

This thesis highlights the importance of fast response of the variable displacement pump/motors used in hybrid hydromechanical transmissions. Their central position in the interface between hydraulics and mechanics makes their dynamic performance a limiting factor both for the stability of the transmission control loops and in the realisation of smooth mode shifts in multiplemode transmissions. Dynamic models and control strategies for displacement actuators are derived and validated in simulation and experiments. A linear model for dynamic analysis of a general hybrid hydromechanical transmission for heavy working machines is derived and a powertrain control strategy based on decoupled control is proposed. The strategy is verified in simulations and experiments in hardware-in-the-loop simulations, and may be used in a working machine with or without a human operator.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. , p. 106
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1992
National Category
Control Engineering Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:liu:diva-159771DOI: 10.3384/diss.diva-159771ISBN: 9789176850510 (print)OAI: oai:DiVA.org:liu-159771DiVA, id: diva2:1344487
Public defence
2019-09-20, ACAS, Building A, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2019-08-21 Created: 2019-08-21 Last updated: 2019-09-05Bibliographically approved
List of papers
1. Mode Shifting in Hybrid Hydromechanical Transmissions
Open this publication in new window or tab >>Mode Shifting in Hybrid Hydromechanical Transmissions
2015 (English)In: ASME/BATH 2015 Symposium on Fluid Power and Motion Control, ASME Press, 2015, p. 13-Conference paper, Published paper (Refereed)
Abstract [en]

Demands for low cost sustainable solutions have increased the use of and interest in complex hydromechanical transmissions for heavy off-road vehicles. In transmissions with multiplemodes, an important condition is to maintain the tractive force during the mode shifting event. For hybrid hydromechanical transmissions, with a direct connection to a hydraulic accumulator, the impressed system pressure caused by the hydraulic accumulator has not yet been observed to interfere with this condition. In this paper, a black box model approach is used to modify the hydraulic system after obtaining knowledge regarding how it is affected by a mode shift. A comparative study is carried out where a full vehicle model of a mobile working machine is simulated with two different hydraulic systems. The results show that different system solutions imply different demands on the included components, and that the mode shifting event is not a negligible factor in heavy hydraulic hybrid vehicles.

Place, publisher, year, edition, pages
ASME Press, 2015
Keywords
Mode shifting, hydromechanical transmissions, fluid power, heavy construction machinery
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-126556 (URN)10.1115/FPMC2015-9583 (DOI)000373970500045 ()978-0-7918-5723-6 (ISBN)
Conference
ASME/BATH 2015 Symposium on Fluid Power and Motion Control, Chicago, Illinois, USA, October 12–14, 2015
Projects
Research on Hydromechanical Transmissions and Hybrid Motion systems, RHYTHM
Funder
Swedish Energy Agency, P39367-1
Available from: 2016-03-30 Created: 2016-03-30 Last updated: 2019-08-21
2. Modelling of the Swash Plate Control Actuator in an Axial Piston Pump for a Hardware-In-the-Loop Simulation Test Rig
Open this publication in new window or tab >>Modelling of the Swash Plate Control Actuator in an Axial Piston Pump for a Hardware-In-the-Loop Simulation Test Rig
2016 (English)In: Proceedings of the 9th FPNI Ph.D. Symposium on Fluid Power, FPNI2016, ASME Press, 2016, article id UNSP V001T01A044Conference paper, Published paper (Refereed)
Abstract [en]

Hydraulic hybrid system solutions are promising in the quest for energy efficiency in heavy construction machines. Hardware-in-the-loop simulations, where hardware is included in software simulations in real time, may be used to facilitate the development process of these systems without the need to build expensive prototypes. In this paper, the displacement actuator of a prototype pump used in a hardware-in-the-loop simulation test rig is modelled and validated against hardware, in order to draw conclusions regarding its dynamic behaviour in a future control design. The results show that the dynamic response of the modelled displacement actuator is mainly determined by the system pressure as well as the response and geometry of the control valve.

Place, publisher, year, edition, pages
ASME Press, 2016
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-133328 (URN)10.1115/FPNI2016-1570 (DOI)000398986900044 ()978-0-7918-5047-3 (ISBN)
Conference
The 9th FPNI Ph.D. Symposium on Fluid Power
Projects
Research on Hydromechanical Transmissions and Hybrid Motion systems, RHYTHM
Funder
Swedish Energy Agency, P39367-1
Note

The authors would like to thank the Swedish Energy Agency for contributing funds for the research project. Thanks also go to Bosch Rexroth for providing the prototype machines.

Available from: 2016-12-20 Created: 2016-12-20 Last updated: 2019-08-21
3. Displacement Control Strategies of an In-Line Axial-Piston Unit
Open this publication in new window or tab >>Displacement Control Strategies of an In-Line Axial-Piston Unit
2017 (English)In: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden / [ed] Petter Krus, Liselott Ericson and Magnus Sethson, Linköping: Linköping University Electronic Press, 2017, Vol. 144, p. 244-253Conference paper, Published paper (Refereed)
Abstract [en]

The need for efficient propulsion in heavy vehicles has led to an increased interest in hybrid solutions. Hydraulic hybrids rely on variable hydraulic pumps/motors to continuously convert between hydraulic and mechanical power. This process is carried out via the implementation of secondary control which, in turn, is dependent on a fast displacement controller response. This paper reports on a study of a prototype axial piston pump of the in-line type, in which the displacement is measured with a sensor and controlled using a software-based controller. A pole placement control approach is used, in which a simple model of the pump is used to parametrise the controller using desired resonance and damping of the closed loop controller as input. The controller’s performance is tested in simulations and hardware tests on the prototype unit. The results show that the pole placement approach combined with a lead-compensator controller architecture is flexible, easy to implement and is able to deliver a fast response with high damping. The results will in the future be used in further research on full-vehicle control of heavy hydraulic hybrids.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017
Series
Linköping Electronic Conference Proceedings, ISSN 1650-3686, E-ISSN 1650-3740 ; 144
Keywords
Hydraulic hybrids, displacement control, pole placement
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-139854 (URN)10.3384/ecp17144244 (DOI)9789176853696 (ISBN)
Conference
The 15th Scandinavian International Conference on Fluid Power, SICFP’17, June 7-9, 2017, Linköping, Sweden
Available from: 2017-08-17 Created: 2017-08-17 Last updated: 2019-08-21Bibliographically approved
4. A General Approach to Low-Level Control of Heavy Complex Hybrid Hydromechanical Transmissions
Open this publication in new window or tab >>A General Approach to Low-Level Control of Heavy Complex Hybrid Hydromechanical Transmissions
2018 (English)In: BATH/ASME 2018 Symposium on Fluid Power and Motion Control, 2018Conference paper, Published paper (Refereed)
Abstract [en]

This paper focuses on the low-level control of heavy complex hydraulic hybrids, taking stability and the dynamic properties of the included components into account. A linear model which can describe a high number of hybrid configurations in a straightforward manner is derived and used for the development of a general multiple input multiple output (MIMO) decoupling control strategy. This strategy is tested in non-linear simulations of an example vehicle and stability requirements for the low-level actuators are derived. The results show that static decoupling may be used to simplify the control problem to three individual loops controlling pressure, output speed and engine speed. In particular, the pressure and output speed loops rely on fast displacement controllers for stability. In addition, it was found that the decoupling is facilitated if the hydrostatic units have equal response. The low-level control of heavy complex hydraulic hybrids may thus imply other demands on actuators than what is traditionally assumed.

Keywords
Control, Multiple input multiple output control, heavy hydraulic hybrids, hydromechanical transmissions
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-154306 (URN)10.1115/FPMC2018-8877 (DOI)000460491500042 ()2-s2.0-85058056485 (Scopus ID)978-0-7918-5196-8 (ISBN)
Conference
BATH/ASME 2018 Symposium on Fluid Power and Motion Control, Bath, United Kingdom, September 12-14, 2018
Funder
Swedish Energy Agency, P39367-2
Note

Funding agencies: Swedish Energy Agency

Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2019-08-21Bibliographically approved
5. Low-Level Control of Hybrid Hydromechanical Transmissions for Heavy Mobile Working Machines
Open this publication in new window or tab >>Low-Level Control of Hybrid Hydromechanical Transmissions for Heavy Mobile Working Machines
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 9, article id 1683Article in journal (Refereed) Published
Abstract [en]

Fuel efficiency has become an increasingly important property of heavy mobile working machines. As a result, Hybrid Hydromechanical Transmissions (HMTs) are often considered for the propulsion of these vehicles. The introduction of hybrid HMTs does, however, come with a number of control-related challenges. To date, a great focus in the literature has been on high-level control aspects, concerning optimal utilization of the energy storage medium. In contrast, the main topic of this article is low-level control, with the focus on dynamic response and the ability to realize requested power flows accurately. A static decoupled Multiple-Input-Multiple-Output (MIMO) control strategy, based on a linear model of a general hybrid HMT, is proposed. The strategy is compared to a baseline approach in Hardware-In-the-Loop (HWIL) simulations of a reference wheel loader for two drive cycles. It was found that an important benefit of the decoupled control approach is that the static error caused by the system’s cross-couplings is minimized without introducing integrating elements. This feature, combined with the strategy’s general nature, motivates its use for multiple-mode transmissions in which the transmission configuration changes between the modes. 

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
hydromechanical transmissions, hybridization, control, construction machinery; decoupled control, hardware-in-the-loop
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-157504 (URN)10.3390/en12091683 (DOI)000469761700099 ()
Funder
Swedish Energy Agency, P39367-2
Note

Funding agencies: Swedish Energy Agency (Energimyndigheten) [P39367-2]

Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-08-21Bibliographically approved

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Larsson, L. Viktor

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