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Control Strategy for Energy Efficient Fluid Power Actuators: Utilizing Individual Metering
Linköping University, Department of Management and Engineering, Fluid and Mechanical Engineering Systems . Linköping University, The Institute of Technology.ORCID iD: 0000-0002-6371-1390
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a solution enabling lower losses in hydraulic actuator systems. A mobile fluid power system often contains several different actuators supplied with a single load sensing pump. One of the main advantages is the need of only one system pump. This makes the fluid power system compact and cost-effective.

A hydraulic load often consists of two ports, e.g. motors and cylinders. Such loads have traditionally been controlled by a valve that controls these ports by one single control signal, namely the position of the spool in a control valve. In this kind of valve, the inlet (meter-in) and outlet (meter-out) orifices are mechanically connected. The mechanical connection makes the system robust and easy to control, at the same time as the system lacks flexibility. Some of the main drawbacks are

The fixed relation between the inlet and outlet orifices in most applications produce too much throttling at the outlet orifice under most operating conditions. This makes the system inefficient.

The flow directions are fixed for a given spool position; therefore, no energy recuperation and/or regeneration ability is available.

In this thesis a novel system idea enabling, for example, recuperation and regeneration is presented. Recuperation is when flow is taken from a tank, pressurized by external loads, and then fed back into the pump line. Regeneration is when either cylinder chambers (or motor ports) are connected to the pump line. Only one system pump is needed. Pressure compensated (load independent), bidirectional, poppet valves are proposed and utilized.

The novel system presented in this thesis needs only a position sensor on each compensator spool. This simple sensor is also suitable for identification of mode switches, e.g. between normal, differential and regenerative modes. Patent pending.

The balance of where to put the functionality (hardware and/or software) makes it possible to manoeuvre the system with maintained speed control in the case of sensor failure. The main reason is that the novel system does not need pressure transducers for flow determination. Some features of the novel system:

Mode switches The mode switches are accomplished without knowledge about the pressures in the system

Throttle losses With the new system approach, choice of control and measure signals, the throttle losses at the control valves are reduced

Smooth mode switches The system will switch to regenerative mode automatically in a smooth manner when possible

Use energy stored in the loads The load, e.g. a cylinder, is able to be used as a motor when possible, enabling the system to recuperate overrun loads

The system and its components are described together with the control algorithms that enable energy efficient operation. Measurements from a real application are also presented in the thesis.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2007. , 60 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1341
Keyword [en]
Fluid power, mode switch, energy efficient, independent metering, split spool, poppet
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:liu:diva-12540Local ID: LIU-TEK-LIC-2007:50ISBN: 978-91-85895-06-9 (print)OAI: oai:DiVA.org:liu-12540DiVA: diva2:443
Presentation
2007-12-20, A35, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-09-12 Created: 2008-09-12 Last updated: 2015-08-31Bibliographically approved
List of papers
1. Study on Individual Pressure Control in Energy Efficient Cylinder Drives
Open this publication in new window or tab >>Study on Individual Pressure Control in Energy Efficient Cylinder Drives
2006 (English)In: 4th FPNI-Ph.D. Symphosium, FPNI’06, Sarasota, United States, 13th–17th June, 2006, M. Ivantysynova (ed.), 2006, 77-99 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper deals with energy efficient mobile valves with cylinder loads. In recent years, the need for energy efficient fluid power systems has increased. The reason is the increasing price of oil as well as tougher environmental regulations. One way of achieving an energy efficient directional valve is to use individually controlled meter-in and meter-out orifices and transfer functionality from hardware to the software controller. This type of solution makes it possible to keep metering losses low. Energy recovery is also made possible since both speed and lowest cylinder chamber pressure can be controlled. The challenge in such a controller is to decouple the chamber pressures in the MIMO (multi-input-multi-output) hydraulic system into independent SISO (single-input-single-output) systems. In this paper, a decoupling based on a linear analysis of the physical system has been implemented and tested in a cylinder position control application. The controller is evaluated in terms of performance and robustness. In the near future, this project will continue with other approaches as well, as there are several interesting control approaches available.

 

Keyword
Fluid power, separate metering, decouped control
National Category
Information Science
Identifiers
urn:nbn:se:liu:diva-12537 (URN)1-42430-499-7 (ISBN)
Note
Volume 1, No. 4Available from: 2008-09-12 Created: 2008-09-12 Last updated: 2015-08-31
2. The Dynamic Properties of a Poppet Type Hydraulic Flow Amplifier
Open this publication in new window or tab >>The Dynamic Properties of a Poppet Type Hydraulic Flow Amplifier
2007 (English)In: 10th Scandinavian International Conference on Fluid Power, SICFP´07 / [ed] J. Vilenius and K. T. Koskinen, Tampere, Finland: Tampere University of Technology , 2007, 161-178 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper examines the dynamic properties of a two-stage flow control valve of the "Valvistor" brand. There are several benefits to this: the valve ha a high closed loop bandwidth, the design allows big flow capacities etc. An attractive feature of this two-stage valve is that the pilot flow contributes to the total flow giving higher steady state flow efficiency. This paper presents an analythical model of this particular type of valve. A simplified model with relevant approximations is also presented. Measurements on the valve were made to validate the valve model. The paper also includes a further discussion about the pros and cons of the valve in open and closed loop applications.

Place, publisher, year, edition, pages
Tampere, Finland: Tampere University of Technology, 2007
Keyword
Fluid power, Valvistor, dynamic model
National Category
Information Science
Identifiers
urn:nbn:se:liu:diva-12538 (URN)
Conference
10th Scandinavian International Conference on Fluid Power, SICFP´07, 21st–23rd May, Tampere, Finland
Available from: 2008-09-12 Created: 2008-09-12 Last updated: 2015-08-31
3. A Novel Valve Concept Including the Valvistor Poppet Valve
Open this publication in new window or tab >>A Novel Valve Concept Including the Valvistor Poppet Valve
2007 (English)In: The Tenth Scandinavian International Conference on Fluid Power / [ed] J. Vilenius and K. T. Koskinen, Tampere, Finland: Tampere University of Technology , 2007, 355-364 p.Conference paper, Published paper (Refereed)
Abstract [en]

These days, energy efficient mobile fluid power systems are of great interest. A mobile system containing several different cylinder drives supplied with a single load sensing pump (LS-pump) has a number of advantages as well as disadvantages. One fo the main advantages is the need of only one system pump. This makes the fluid power system compact and cost-effective. A challenge is to keep the hydraulic losses at a low level, especially losses at smaller loads. This paper introduces a fail-safe proportional valve element that is based on the Valvistor poppet valve. Due to the demands of flexibility the poppet valve is bi-directional. The valve has an innovative hydro-mechanic layout that makes it fail-safe, unwanted lowering loads, for example, never occur. The new valve includes simple sensors that are suitable for identificaiton of mode switches, e g between normal, differential and regenerative modes. It is also possible to manoevre the system with maintained velocity control in case of sensor failure. In a less complex system the concept has benefits as well. For example in systems where fail-safe bi-directional on/off valves are needed, then without mode sensing capabilities.

Place, publisher, year, edition, pages
Tampere, Finland: Tampere University of Technology, 2007
Keyword
Fluid power, poppet valve, Valvistor, bi-directional, fail-safe
National Category
Information Science
Identifiers
urn:nbn:se:liu:diva-12539 (URN)
Conference
10th Scandinavian International Conference on Fluid Power, SICFP´07, 21st–23rd May, Tampere, Finland
Available from: 2008-09-12 Created: 2008-09-12 Last updated: 2015-08-31

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Eriksson, Björn

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