A Coupled Elastohydrodynamic Lubrication Model for Radial Piston Motors Incorporating Piston Tilt and Deformation
DOI:
https://doi.org/10.13052/ijfp1439-9776.2711Keywords:
Radial piston motors, elastohydrodynamic lubrication, deformation, power lossAbstract
This study presents a coupled Elastohydrodynamic Lubrication (EHL) simulation model for a multi-lobe radial piston motor and its experimental validation under high-load and low-speed conditions. These operating regimes pose challenges such as severe wear and excessive power loss due to complex lubricating interfaces, which are difficult to characterize experimentally. To address this, the model solves a density-based Reynolds equation incorporating multi-body dynamics, throttling losses, and elastic deformations of components. Simulation results reveal that lubrication regimes and asperity contact pressures depend strongly on chamber pressure and motor speed. The roller–bushing interface operates under mixed lubrication, while the piston–cylinder interface exhibits boundary lubrication during high-load conditions due to severe asperity contact. Piston tilt and asymmetric deformation significantly affect film thickness and pressure distribution of lubricating interfaces. Incorporating a friction model based on experimental data enabled a realistic analysis of power loss, identifying the upper piston–cylinder interface and throttling loss as major contributors. The model provides a detailed framework for simulating and analyzing tribological behaviors in radial piston motors and can be used to evaluate the effects of design parameters such as clearance, geometry, and material properties.
Downloads
References
H. Olsson, J. Ukonsaari, Wear testing and specification of hydraulic fluid in industrial applications, Tribology International, 36(11): 835–841, 2003, https://doi.org/10.1016/S0301-679X(03)00101-4.
C. Zhang, H. Tan, Y. Fang, X. Zhang, Y. Yang, Y. Duan, M. Han, S. Cui, B. Xu, J. Zhang, Deformation pre-compensated optimization design of cam ring for low pulsation hydraulic motors, Journal of Zhejiang University SCIENCE A, 24(2) 130–145, 2023, https://doi.org/10.1631/jzus.A2200552.
U. Pettersson, S. Jacobson, Textured surfaces for improved lubrication at high pressure and low sliding speed of roller/piston in hydraulic motors, Tribology International, 40(2): 355–359, 2007, https://doi.org/10.1016/j.triboint.2005.11.024.
R. Lewis, Friction in a hydraulic motor piston/cam roller contact lined with PTFE impregnated cloth, Wear, 266(7–8): 888–892, 2009, https://doi.org/10.1016/j.wear.2008.12.009.
D. Nilsson, B. Prakash, Investigation into the seizure of hydraulic motors, Tribology International, 43(1–2): 92–99, 2010, https://doi.org/10.1016/j.triboint.2009.05.001.
L. Dahlén, H. Olsson, Analysis of two sliding contacts inside a radial piston hydraulic motor, Proceedings of the JFPS International Symposium on Fluid Power 2002, (5–2): 537–542, 2002, https://doi.org/10.5739/isfp.2002.537.
P. Isaksson, D. Nilsson, R. Larsson, Elasto-hydrodynamic simulation of complex geometries in hydraulic motors, Tribology International, 42(10): 1418–1423, 2009, https://doi.org/10.1016/j.triboint.2009.05.018.
P. Isaksson, D. Nilsson, R. Larsson, and A. Almqvist, The influence of surface roughness on friction in a flexible hybrid bearing, Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 225(10):975–985, 2011, https://doi.org/10.1177/13506501114172.
X. Zhang, J. Zhang, B. Xu, Z. Yang, Q. Zhao, H. Zhang, The effect of slotted hole on minimum oil film thickness of piston in radial piston hydraulic motor, Proceedings of the ASME/BATH 2021 Symposium on Fluid Power and Motion Control, 2021, https://doi.org/10.1115/FPMC2021-69937.
C. Zhang, X. Zhang, P. Dong, H. Zhang, Z. Zheng, J. Zhang, B. Xu, Composite thermal oil film lubrication model for hybrid journal bearings, Tribology International 194, 2024, https://doi.org/10.1016/j.triboint.2024.109556.
C. Li, T. Jiang, C. Liu, H. Xu, G. Shi, Investigation of the leakage in the flow distribution pair of radial piston hydraulic motors through CFD analysis and experiments, Flow Measurement and Instrumentation, 96, 2024, https://doi.org/10.1016/j.flowmeasinst.2024.102555.
T. Ransegnola, L. Shang, Andrea Vacca, A study of piston and slipper spin in swashplate type axial piston machines, Tribology International, 167, 2022, https://doi.org/10.1016/j.triboint.2021.107420.
S. Sarode, L. Shang, Andrea Vacca, Numerical investigation of the influence of part geometric tolerances on piston/cylinder interface performance, International Journal of Fluid Power, 23_3, 343–362, 2022, https://doi.org/10.13052/ijfp1439-9776.2334.
S. Mukherjee, L. Shang, A. Vacca, Numerical analysis and experimental validation of the coupled thermal effects in swashplate type axial piston machines, Mechanical Systems and Signal Processing, 220, 2024, https://doi.org/10.1016/j.ymssp.2024.111673.
A. Pawar, Andrea Vacca, Manuel Rigosi, Comparative analysis of external gear machine performance considering deformation and thermal effects, International Journal of Fluid Power, 25_3, 465–492, 2024, https://doi.org/10.13052/ijfp1439-9776.2543.
R. Ivantysyn, J. Weber, Advancing thermal monitoring in axial piston pumps: simulation, measurement, and boundary condition analysis for efficiency enhancement, International Journal of Fluid Power, 25_4, 547–590, 2024, https://doi.org/10.13052/ijfp1439-9776.2546.
T. Ransegnola, A strongly coupled simulation model of positive displacement machines for design and optimization, Doctoral Thesis, Purdue University, 2020.
N. Patir and H. S. Cheng, An average flow model for determining effects of three-dimensional roughness on partial hydrodynamic lubrication, Journal of Tribology, 100(1): 12–17, 1978, https://doi.org/10.1115/1.3453103.
N. Patir and H. S. Cheng, Application of Average Flow Model to Lubrication Between Rough Sliding Surfaces, Journal of Tribology, 101(2):220–229, 1979, https://doi.org/10.1115/1.3453329.
W. Chengwei and Z. Linqing, An average Reynolds equation for partial film lubrication with contact factor, Journal of Tribology, 111(1):188–191, 1989, https://doi.org/10.1115/1.3261872.
Si C. Lee and N. Ren, Behavior of elastic-plastic rough surface contact as affected by surface topography, load, and material hardness, Tribology Transactions, 39(1):67–74, 1996, https://doi.org/10.1080/10402009608983503.
M. Pelosi and M. Ivantysynova, The impact of axial piston machines mechanical parts constrain conditions on the thermo-elastohydrodynamic lubrication analysis of the fluid film interfaces, Internation Journal of Fluid Power, 14(3):35–51, 2013, https://doi.org/10.1080/14399776.2013.10801412.
E. Buckingham, On physically similar systems: Illustrations of the use of dimensional equations, Phys. Rev., vol. 4, no. 4 1914, https://doi.org/10.1103/PhysRev.4.345.
M. D. Hersey, The laws of lubrication of horizontal journal bearings, J. Wash. Acad. Sci. 4, 542, 1914.
B.J Hamrock, S.R. Schmid, and B.O. Jacobson, Fundamentals of Fluid Film Lubrication (2nd ed.). CRC Press. 2004.
