THE IMPACT OF AXIAL PISTON MACHINES MECHANICAL PARTS CONSTRAINT CONDITIONS ON THE THERMO-ELASTOHYDRODYNAMIC LUBRICATION ANALYSIS OF THE FLUID FILM INTERFACES

Authors

  • Matteo Pelosi Purdue University, Department of Agricultural and Biological Engineering & School of Mechanical Engineering, 225 S. University St., West Lafayette, Indiana 47907, USA
  • Monika Ivantysynova Purdue University, Department of Agricultural and Biological Engineering & School of Mechanical Engineering, 225 S. University St., West Lafayette, Indiana 47907, USA

Keywords:

thermo-elastohydrodynamic lubrication, axial piston machine, inertia relief, piston/cylinder interface, constraint conditions

Abstract

The authors analyze the lubricating interfaces of axial piston machines considering thermo-elastohydrodynamic (TEHL) lubrication characteristics. The fluid film geometry in these conditions is strongly influenced by the surface elastic deformation of the solid boundaries. The surface elastic deformations derive from the high dynamic pressures developing in the fluid film, necessary to balance the external oscillating loads. Furthermore, elastic deflections of the fluid film develop from the thermal expansion of the solid bodies, caused by the heat generated due to viscous shear of the fluid film. The accurate determination of the solid boundaries elastic deformation is a key element to predict the fluid film geometry and consequently the lubricating interface performance. When solving for the static elastic deformation of a solid body, constraint conditions must be imposed to avoid rigid body motion. Constraint conditions strongly influence the elastic deformation analysis; therefore their definition must reflect and interpret the mechanical body real conditions. In an axial piston machine all the mechanical bodies defining the fluid film geometry are loosely constrained and significant linear displacements and rotations are intentionally allowed. Hence, the definition of proper constraint conditions for the solid bodies is not a trivial problem and advanced constraint conditions must be considered and implemented. In the fully-coupled numerical models of the lubricating interfaces developed by the research group of the authors, finite element analysis is used to determine the mechanical bodies’ elastic deformations. The finite element analysis is coupled with finite volume models of the fluid film, to study the impact of the surface elastic deformations on the interfaces behavior. In this paper, the authors present and discuss the implementation of the inertia relief method on the finite element elastic deformation analysis of the main mechanical parts of an axial piston machine. Inertia relief allows simulating unconstrained structures in a static analysis using their inertia to resist the applied loads. Typical applications of this method include modeling an aircraft in flight, a submarine under water or a satellite in space. The impact of this method on the elastic deformation of the fluid film solid boundary surfaces is shown and compared to standard constraint conditions. In addition, the influence of the inertia relief method on the piston/cylinder interface fluid film behavior is discussed, presenting numerical results for a fully-coupled TEHL simulation over one shaft revolution of a special test pump capable of measuring the piston/cylinder axial viscous friction force. The improved accuracy of the piston/ cylinder fully-coupled model including inertia relief effect is presented, comparing simulation results with friction force measurements.

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Author Biographies

Matteo Pelosi, Purdue University, Department of Agricultural and Biological Engineering & School of Mechanical Engineering, 225 S. University St., West Lafayette, Indiana 47907, USA

Matteo Pelosi Born on December 29th 1982 in Parma (Italy). He received his B.Sc. and M.Sc. in Mechanical Engineering from University of Parma (Italy) in 2005 and 2007 respectively. In February 2012 he obtained his Ph.D. degree in Fluid Power from Purdue University (USA). The design and modelling of hydraulic systems has been his main research area, both at a system and a component level. His Ph.D. research focused on discovering the physical behavior of hydrostatic piston machines fluid film interfaces, through the generation of advanced fluid-structure interaction and thermal numerical models. Starting from March 2012, he joined Öhlins Racing AB (Sweden).

Monika Ivantysynova, Purdue University, Department of Agricultural and Biological Engineering & School of Mechanical Engineering, 225 S. University St., West Lafayette, Indiana 47907, USA

Monika Ivantysynova Born on December 11th 1955 in Polenz (Germany). She received her MSc. Degree in Mechanical Engineering and her PhD. Degree in Fluid Power from the Slovak Technical University of Bratislava, Czechoslovakia. After 7 years in fluid power industry she returned to university. In April 1996 she received a Professorship in fluid power & control at the University of Duisburg (Germany). From 1999 until August 2004 she was Professor of Mechatronic Systems at the Technical University of Hamburg-Harburg. Since August 2004 she is Professor at Purdue University, USA. Her main research areas are energy saving actuator technology and model based optimization of displacement machines as well as modeling, simulation and testing of fluid power systems. Besides the book “Hydrostatic Pumps and Motors” published in German and English, she has published more than 80 papers in technical journals and at international conferences.

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Published

2018-12-30

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