Heat Transfer and Thermal Elastic Deformation Analysis on the Piston/Cylinder Interface of Axial Piston Machines

Abstract

The piston/cylinder interface of swash plate–type axial piston machines represents one of the most critical design elements for this type of pump and motor. Oscillating pressures and inertia forces acting on the piston lead to its micro-motion, which generates an oscillating fluid film with a dynamically changing pressure distribution. Operating under oscillating high load conditions, the fluid film between the piston and cylinder has simultaneously to bear the external load and to seal the high pressure regions of the machine. The fluid film interface physical behavior is characterized by an elasto-hydrodynamic lubrication regime. Additionally, the piston reciprocating motion causes fluid film viscous shear, which contributes to a significant heat generation. Therefore, to fully comprehend the piston/cylinder interface fluid film behavior, the influences of heat transfer to the solid boundaries and the consequent solid boundaries’ thermal elastic deformation cannot be neglected. In fact, the mechanical bodies’ complex temperature distribution represents the boundary for nonisothermal fluid film flow calculations. Furthermore, the solids-induced thermal elastic deformation directly affects the fluid film thickness. To analyze the piston/cylinder interface behavior, considering the fluid-structure interaction and thermal problems, the authors developed a fully coupled simulation model. The algorithm couples different numerical domains and techniques to consider all the described physical phenomena. In this paper, the authors present in detail the computational approach implemented to study the heat transfer and thermal elastic deformation phenomena. Simulation results for the piston/cylinder interface of an existing hydrostatic unit are discussed, considering different operating conditions and focusing on the influence of the thermal aspect. Model validation is provided, comparing fluid film boundary temperature distribution predictions with measurements taken on a special test bench.

The Analysis of Secondary Motion and Lubrication Performance of Piston considering the Piston Skirt Profile

“…Therefore, the thermal deformation was increasingly introduced to relevant studies of the lubrication performance of the piston skirt. Pelosi and Ivantysynova [26] built a fully coupled simulation model for the piston/cylinder interface of axial piston machines and validated the model by comparing the prediction values with measurements of the fluid film boundary temperature distribution. The influence of the heat transfer and solids-induced thermal elastic deformation on the piston skirt-cylinder lubricating interface behavior was analyzed.…”

A novel FSI–thermal coupled TEHD model and experimental validation through indirect film thickness measurements for the lubricating interface in external gear machines

“…Pressure measurements aimed at validating an FSI-Thermal model of the piston cylinder interface in axial piston machines have been presented in [21,12,22]. More recently, temperature measurements have been used to validate the simulation results of an FSI-thermal model of the cylinder block-valve plate interface in swash plate type axial piston machines [23,24].…”

“…However, the above studies made the assumption of an isothermal fluid film and solid components, in addition to neglecting the deformation of the solids due to thermal loads. Detailed models of lubricating gaps other positive displacement machines, such as axial piston machines, have shown in the past that in addition to accounting for deformation of the solids due to pressure it is also important to account for thermal effects in lubricating gaps [11,12].…”

A novel approach to predict the steady state temperature in ports and case of swash plate type axial piston machines

“…Recent works of the author's research group have demonstrated that the fluid film behavior can be predicted with good level of accuracy only when multiphysics simulation model are introduced [1], [5], [6] for the piston / cylinder interface, [7], [8] for the slipper / swash plate interface and [9], [10], [2] for the cylinder block / valve plate interface. The three interfaces are subject to the same physical phenomena and therefore can be modeled using the same basic structure.…”