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On Fluid Power Pump and Motor Design: Tools for Noise Reduction
Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, The Institute of Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Noise and vibration are two of the main drawbacks with fluid power  systems. The increasing requirements concerning working environment as well as machines' impact on surroundings put components and systems to harder tests. The surrounding machines, e.g. combustion engines, have made considerable progress regarding the radiated noise. This allows the fluid power system's noise to become more prominent. Noise from fluid power systems has been a research topic for several decades and much improvement has been achieved. However, considerable potential for improvement still remains.

In addition to the legislation governing working environment, the machines tend to be used as more multi-quadrant machines, which require more flexible noise reduction features. One of the main benefits with fluid power is the high power density. To increase this value even more, the system's working pressure increases, which correlates with increased noise level.

The main source of noise is considered to be the pump and motor unit in the fluid power system. The noise can be divided into two parts: fluid-borne noise and structure-borne noise. The fluid borne noise derives from flow pulsation which is subsequently spread through pipeline systems to other parts of the fluid power systems. The flow pulsation is created due to the finite stiffness of oil and the limited number of pumping elements. The structure-borne noise generates directly from pulsating forces in the machine. The pulsating forces are mainly created by the pressure differences between high and low pressure ports.

Effective and accurate tools are needed when designing a quiet pump/motor unit. In this thesis simulation based optimisation is used with different objective functions including flow pulsation and pulsating forces as well as audible noise. The audible noise is predicted from transfer functions derived from measurements. Two kinds of noise reduction approaches are investigated; cross-angle in multi-quadrant machines and non-uniform placement of pistons. The simulation model used is experimentaly validated by source flow measurements. Also, source flow measurements with the source admittance method are investigated.

In addition, non-linear flow through a valve plate restrictor is investigated and the steady state restrictor equation is proposed to be extended by internal mass term.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 130 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1417
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-73981ISBN: 978-91-7519-994-8 (print)OAI: oai:DiVA.org:liu-73981DiVA: diva2:479598
Public defence
2012-01-20, Sal A35, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-01-18 Created: 2012-01-18 Last updated: 2012-01-18Bibliographically approved
List of papers
1. Flow pulsation reduction for variable displacement motors using cross-angle
Open this publication in new window or tab >>Flow pulsation reduction for variable displacement motors using cross-angle
2007 (English)In: Power Transmission and Motion Control (PTMC 2007) / [ed] D. N. Johnston, and A. Plummer, Essex: Hadleys Ltd , 2007, 103-116 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper considers using the cross-angle in variable displacement hydraulic machines. The cross-angle is a fixed displacement angle around the axis perpendicular to the normal displacement direction. The cross-angle changes the angles to the pistons top and bottom dead centres as a function of the fraction of displacement in such a way that the valve plate timing is varied and different pre-compression and decompression angles are obtained. A non-gradient optimisation technique, the Complex method, is used together with a comprehensive simulation model in order to find the optimal cross-angle for a variable displacement hydraulic motor. The paper shows that the cross-angle can be used to reduce noise in variable displacement motors. One issue that makes the motor application more difficult is the increased dependence between outlet and inlet flow ripple which is not found in pump applications. Furthermore, the paper discusses how to use the cross-angle for machines which can work both as a motor and a pump.

Place, publisher, year, edition, pages
Essex: Hadleys Ltd, 2007
Keyword
Cross-angle flow pulsations noise hydraulic pump hydraulic motor
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-40965 (URN)54778 (Local ID)978-0-86197-140-4 (ISBN)54778 (Archive number)54778 (OAI)
Conference
Power Transmission and Motion Control (PTMC 2007), 12-14 September, Bath, UK
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-11-08
2. On optimal design of hydrostatic machines
Open this publication in new window or tab >>On optimal design of hydrostatic machines
2008 (English)In: Proceedings of the 6th International Fluid Power Conference, IFK, Vol WS, 2008, 273-286 p.Conference paper, Published paper (Refereed)
Abstract [en]

Noise is a well known challenge for hydraulic systems and hydrostatic machines is one of the largest noise contributors in a hydraulic system. The noise from the machine originates from flow pulsations in the discharge and suction ports, as well as pulsations in piston forces and bending moments. To the design a quite hydraulic machine is a difficult task where many different objectives need to be considered. This paper presents a generic method for how optimization based on simulation models could be used to design quieter hydraulic machines. In order to stay competitive on a global market an efficient product development process is essential for all manufacturing industries. By using simulation-s tools in the design process, the product can be analysed before the actual product is manufactured. Furthermore, in order to find an optimal design of the machine with respect to noise, a comprehensive dynamic simulation model is needed. The model contains all important noise contributors. In the paper, the simulation models are used together with a non-gradient optimization method in order to find the best possible design. A vital part when using optimization to support design is always to formulate the objective function. As mentioned above, noise is generated from different sources and all these sources need to be considered when the objective function is formulated. For example a design that minimizes flow pulsations in the suction port will surely perform badly in some other objective. Therefore noise minimization could be looked upon as a typical multi-objective optimization problem. It is also not evident how the different objective should be ranked because the observed noise level is strongly depending on the system in which the machine is to be used. The paper also considers whether the objective function should be formulated in time or frequency domain. Traditionally, simulation of machine performance is conducted in the time domain, but the human ear hears noise in the frequency domain and perceives high and low frequencies differently. Furthermore, transformation from piston forces into emitted noise is much higher at high-frequency content than low-frequency content. This makes it natural to formulate the objective function in frequency domain, which raises the question of how the different harmonic should be ranked. In the paper a number of different approaches to formulate the objective function is presented and evaluated. The objectives considered are flow pulsation in both discharge and suction ports, as well as pulsation in piston forces and bending moments. Furthermore, the objectives are studied in both time and frequency domain. The design application is a variable hydraulic machine of bent axis type with nine pistons, which is operated both as a pump and a motor. However, the methods presented in the paper could be applied to other types of hydraulic machines as well. 

Keyword
Fluid power, pump, motor, noise, optimisation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-42260 (URN)62133 (Local ID)62133 (Archive number)62133 (OAI)
Conference
6th International Fluid Power Conference, March 31-April 2, Dresden, Germany
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2012-01-18Bibliographically approved
3. Optimisation of Structure Borne Noise and Fluid Borne Noise from Fluid Power Pumps and Motors
Open this publication in new window or tab >>Optimisation of Structure Borne Noise and Fluid Borne Noise from Fluid Power Pumps and Motors
2009 (English)In: Proc. of the 11th Scandinavian Fluid Power Conference, 2009Conference paper, Published paper (Other academic)
Abstract [en]

Structure borne noise in a machine rises from piston force and bending moments among others. This noise arises directly from the pump shell. In this study, a transfer function methodology is employed for mapping simulated internal pump dynamics, such as piston forces and bending moments, on to structure borne noise. Using these transfer functions, it is possible to predict how, for instance, changed valve plate timing affects simulated piston forces and bending moments and in turn how that will affect audible noise. Hence, it is possible to design an objective function that directly reflects audible noise. The transfer functions are experimentally obtained and are valid for a specific machine shell and to some minor extent the room’s acoustical properties. Also, fluid borne noise is important to consider when designing a quiet machine. Fluid borne noise arises mainly from flow pulsation created inside the machine.

Simulation of the internal pump dynamics, and optimisations, are carried out using a pump model developed in the simulation tool HOPSAN. The design application is a hydraulic machine of bent axis type with seven pistons. The theory outlined and the method proposed in the paper can also be applied to other types of hydraulic machines. The paper shows how both structure borne noise and fluid borne noise can be considered using multi-objective optimisation. The paper shows how different noise reduction features affect the sound pressure level and the flow pulsation. The paper also compare the pump and motor case.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-73977 (URN)
Conference
The 11th Scandinavian Fluid Power Conference, June 2-4, Linköping, Sweden
Available from: 2012-01-18 Created: 2012-01-18 Last updated: 2012-01-26Bibliographically approved
4. Noise reduction by means of non-uniform placement of pistons in a fluid power machine
Open this publication in new window or tab >>Noise reduction by means of non-uniform placement of pistons in a fluid power machine
2010 (English)Manuscript (preprint) (Other academic)
Abstract [en]

In conventional machines, the pulsations are periodic and originate from the uniform placement of a given number of pistons. This paper discusses the possibilities to introduce non-uniform placement of the pistons. The pulsations periodicity is thus changed, which can have a major impact on the noise level and how the noise is experienced. A number of approaches are presented, evaluated and ranked and the usefulness of the modifications is assessed. This study employs a transfer function methodology to map simulated internal pump dynamics, such as piston forces and bending moments, to audible noise. Using these transfer functions, it is possible for instance to predict how changed valve plate timing affects simulated piston forces and bending moments and in turn how this will affect audible noise. Copyright © 2009 by ASME.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-73978 (URN)
Conference
2nd Annual Dynamic Systems and Control Conference October 12-14, Hollywood, CA, USA
Available from: 2012-01-18 Created: 2012-01-18 Last updated: 2012-01-18Bibliographically approved
5. Measurement of Free Air in the Oil Close to a Hydraulic Pump
Open this publication in new window or tab >>Measurement of Free Air in the Oil Close to a Hydraulic Pump
2009 (English)In: JFPS International Journal of Fluid Power System, ISSN 1881-5286, Vol. 2, no 2, 39-44 p.Article in journal (Refereed) Published
Abstract [en]

Noise is a well-known challenge in hydraulic systems and hydrostatic pumps are one of the largest noise contributors in a hydraulic system. The existing noise reduction features, such as pressure relief groove and pre-compression filter volume, are more or less dependent on the working condition. It is essential to know the amount of free air when designing a quiet pump; however, it is not evident how much free air the oil contains. The free air content is different if the suction port is boost pressured or self-priming. The amount of free air in a well-designed system can be as low as 0.5% while in others up to 10%.This paper uses the three-transducer method to measure the amount of free air in the oil. The oil's compressibility can be measured for different working conditions and the free air content can then be calculated. The pre-study is performed with an extensive simulation model. Various noise reduction features' sensitivity to free air content is considered.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-63018 (URN)
Available from: 2010-12-09 Created: 2010-12-09 Last updated: 2012-01-18Bibliographically approved
6. Unsteady Flow through Valve Plate Restrictor in a Hydraulic Pump/Motor Unit
Open this publication in new window or tab >>Unsteady Flow through Valve Plate Restrictor in a Hydraulic Pump/Motor Unit
2010 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Noise is a well known challenge in hydraulic systems. Hydrostatic machines are among the largest noise contributors in a hydraulic system.The noise from the machine originates from flow pulsations at the discharge and suction ports, as well as pulsations in piston forces and bending moments.

This article investigates the dynamic behaviour of unsteady flow through a valve plate in an axial piston pump. The proposed extension of the steady state restrictor equation includes a dynamic internal mass term and a resistance. The results from 1D model are validated with a 3D CFD model. Different valve plates’ configurations and pump sizes are easily simulated with the two simulation models. The simulation results show very good comparison with experimental tests. The proposed method is verified with a hydraulic pump application but it can probably also apply for original restrictors too.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-73980 (URN)
Conference
2nd Annual Dynamic Systems and Control Conference October 12-14, Hollywood, CA, USA
Available from: 2012-01-18 Created: 2012-01-18 Last updated: 2012-01-18Bibliographically approved

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