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A mechanical model of an axial piston machine
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

A mechanical model of an axial piston-type machine with a so-called wobble plate and Z-shaft mechanism is presented. The overall aim is to design and construct an oil-free piston expander demonstrator as a first step to realizing an advanced and compact small-scale steam engine system. The benefits of a small steam engine are negligible NOx emissions (due to continuous, low-temperature combustion), no gearbox needed, fuel flexibility (e.g., can run on biofuel and solar), high part-load efficiency, and low noise. Piston expanders, compared with turbines or clearance-sealed rotary displacement machines, have higher mechanical losses but lower leakage losses, much better part-load efficiency, and for many applications a more favourable (i.e., lower) speed. A piston expander is thus feasible for directly propelling small systems in the vehicular power range. An axial piston machine with minimized contact pressures and sliding velocities, and with properly selected construction materials for steam/water lubrication, should enable completely oil-free operation. An oil-free piston machine also has potential for other applications, for example, as a refrigerant (e.g., CO2) expander in a low-temperature Rankine cycle or as a refrigerant compressor.

 

An analytical rigid-body kinematics and inverse dynamics model of the machine is presented. The kinematical analysis generates the resulting motion of the integral parts of the machine, fully parameterized. Inverse dynamics is applied when the system motion is completely known, and the method yields required external and internal forces and torques. The analytical model made use of the “Sophia” plug-in developed by Lesser for the simple derivation of rotational matrices relating different coordinate systems and for vector differentiation. Numerical solutions were computed in MATLAB. The results indicate a large load bearing in the conical contact surface between the mechanism’s wobble plate and engine block. The lateral force between piston and cylinder is small compared with that of a comparable machine with a conventional crank mechanism.

 

This study aims to predict contact loads and sliding velocities in the component interfaces. Such data are needed for bearing and component dimensioning and for selecting materials and coatings. Predicted contact loads together with contact geometries can also be used as input for tribological rig testing. Results from the model have been used to dimension the integral parts, bearings and materials of a physical demonstrator of the super-critical steam expander application as well as in component design and concept studies.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , 56 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2009:16
Keyword [en]
Multi-body mechanical model, axial piston, Z-shaft, wobble plate, Sophia
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-10948ISBN: 978-91-7415-408-5 (print)OAI: oai:DiVA.org:kth-10948DiVA: diva2:233028
Presentation
2009-08-16, B242, Brinellvägen 83, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2009-08-28 Created: 2009-08-27 Last updated: 2010-10-18Bibliographically approved
List of papers
1. Axial piston machine kinematics
Open this publication in new window or tab >>Axial piston machine kinematics
2007 (English)In: OST Proceedings, 2007, Tallinn, Estonia, 2007Conference paper, Published paper (Refereed)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-25332 (URN)
Conference
OST-07 Symposium on Machine Design, Tallin, 2007
Note
QC 20101018Available from: 2010-10-18 Created: 2010-10-18 Last updated: 2010-10-18Bibliographically approved
2. Describing a mechanical model of a novel axial piston type steam expander
Open this publication in new window or tab >>Describing a mechanical model of a novel axial piston type steam expander
2008 (English)In: Proceedings NordDesign 2008, Tallinn, Estonia / [ed] L.Roosimölder, 2008Conference paper, Published paper (Refereed)
Keyword
Constraint mechanics, vector analysis, joint interfaces, multi-body, mechanical work
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-25335 (URN)
Conference
NordDesign 2008, August 2008, Tallinn, Estonia
Note
QC 20101018Available from: 2010-10-18 Created: 2010-10-18 Last updated: 2010-10-18Bibliographically approved
3. A dynamical model of an axial piston machine
Open this publication in new window or tab >>A dynamical model of an axial piston machine
2009 (English)In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:kth:diva-25339 (URN)
Note
QS 20120315Available from: 2010-10-18 Created: 2010-10-18 Last updated: 2017-12-12Bibliographically approved

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