Effects of the thermal conductivity of contact materials on elastohydrodynamic lubrication characteristics

2010 ◽  
Vol 224 (12) ◽  
pp. 2577-2587 ◽  
Author(s):  
M Kaneta ◽  
P Yang
Keyword(s):  
Thermal Conductivity ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Fluid Film ◽  
Contact Materials ◽  
Entrainment Velocity ◽  
Pressure Distributions ◽  
Traction Coefficient ◽  
Lubrication Characteristics ◽  
Lubricant Viscosity

Isothermal elastohydrodynamic lubrication (EHL) theory has brought the improvement in function, performance, and durability of machine elements with concentrated contacts. The main reason is that the theory can evaluate the lubrication characteristics, such as film thickness and pressure distributions, from the shape and size of contacting materials, lubricant viscosity at the entrance to the EHL conjunction, entrainment velocity, equivalent elastic modulus, and applied load. However, in order to estimate the film thickness and pressure distributions more accurately and to make clear the traction behaviour based on lubricant rheology, it is necessary to establish thermal EHL theory, which incorporates heat generation in the fluid film and heat transfer in the machine system on the foundation of isothermal EHL theory. The thermal conductivity of contact materials controls temperature in the fluid film and consequently the lubricant viscosity. Therefore, the EHL characteristics are affected remarkably by the thermal conductivity of contact materials. In this article, the effects of the thermal conductivity of contacting materials on the film thickness, pressure, and traction coefficient are described.

Experimental Investigation for Finite Line Contact Edge Effect of Elastohydrodynamic Lubrication

2012 ◽  
Vol 538-541 ◽  
pp. 1945-1951 ◽  
Author(s):  
Yu Xue ◽  
Tong Shu Hua ◽  
Hao Yang Sun
Keyword(s):  
Experimental Investigation ◽  
Film Thickness ◽  
Contact Area ◽  
Elastohydrodynamic Lubrication ◽  
Line Contact ◽  
Heavy Load ◽  
Entrainment Velocity ◽  
Finite Line Contact ◽  
Finite Line ◽  
Lubricant Viscosity

To reveal the principle of the close effect about the EHL finite roller, contraposing the log-convex roller, the finite line contact EHL film shape and thickness were observed through self-made heavy-load optical EHL experimental device. Experiments were carried out under several different pressure and viscosity, and three groups of interference pictures were obtained under three different entrainment velocities. As the load increased, both the length and width of the roller contact area added, and the width of the contact zone in the end was larger than that in the centre, the close effect was more obvious; when the entrainment velocity and lubricant viscosity increased, the film thickness in the central roller became thicker while the increase in the roller end was little, the high film thickness difference enhanced the close effect. The entrainment velocity, load and lubricant viscosity all have great effect on the EHL characteristics of the finite roller.

Effects of Thermal Properties of Contact Materials and Slide-Roll Ratio in Elastohydrodynamic Lubrication

2021 ◽  
pp. 1-34
Author(s):  
Motohiro Kaneta ◽  
Kenji Matsuda ◽  
Hiroshi Nishikawa
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Film Thickness ◽  
Thermal Inertia ◽  
Elastohydrodynamic Lubrication ◽  
Mechanical And Thermal Properties ◽  
Contact Materials ◽  
The Difference ◽  
Thermal Ehl

Abstract The effects of thermal conductivity, heat capacity, thermal inertia and slide-roll ratio on point elastohydrodynamic lubrication (EHL) are discussed with engineering ceramics and steel by a non-Newtonian thermal EHL analysis. When the thermal conductivities of contacting materials are significantly different, the film thickness is greatly affected by which material has the higher velocity. However, the film thickness is dominated by the heat capacity when the difference in thermal conductivity is not large. In contact of materials with the same mechanical and thermal properties, the central film thickness and friction coefficient are influenced by the thermal inertia.

A Theoretical Analysis of the Mixed Elastohydrodynamic Lubrication in Elliptical Contacts With an Arbitrary Entrainment Angle

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Wei Pu ◽  
Jiaxu Wang ◽  
Ying Zhang ◽  
Dong Zhu
Keyword(s):  
Film Thickness ◽  
Numerical Simulations ◽  
Model Development ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Thin Film Lubrication ◽  
Entrainment Velocity ◽  
Asperity Contacts ◽  
Thickness Prediction ◽  
Lubrication Characteristics

Numerical simulations of the elastohydrodynamic lubrication (EHL) have been conducted by many researchers, in which the entrainment velocity is usually parallel to one of the axes of Hertzian contact ellipse. However, in some engineering applications, such as the counterformal contacts in spiral bevel and hypoid gears, entraining velocity vector may have an oblique angle that could possibly influence the lubrication characteristics significantly. Also, a vast majority of gears operate in mixed EHL mode in which the rough surface asperity contacts and lubricant films coexist. These gears are key elements widely used for transmitting significant power in various types of vehicles and engineering machinery. Therefore, model development for the mixed EHL in elliptical contacts with an arbitrary entrainment angle is of great importance. In the present paper, a recently developed mixed EHL model is modified to consider the effect of arbitrary entraining velocity angle, and the model is validated by comparing its results with available experimental data and previous numerical analyses found in literature. Based on this, numerical simulations are conducted to systematically study the influence of entrainment angle on lubricant film thickness in wide ranges of speed, load, and contact ellipticity. The obtained results cover the entire lubrication spectrum from thick-film and thin-film lubrication all the way down to mixed and boundary lubrication. In addition, minimum film thickness prediction formula is also developed through curve-fitting of the numerical results.

Influence of Surface Waviness on the Thermal Elastohydrodynamic Lubrication of an Eccentric-Tappet Pair

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
J. Wang ◽  
C. H. Venner ◽  
A. A. Lubrecht
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Surface Waviness ◽  
Film Pressure ◽  
Oil Film ◽  
Working Cycle ◽  
Temperature Oscillations ◽  
Minimum Film Thickness ◽  
Traction Coefficient ◽  
Oil Film Pressure

The effect of single-sided and double-sided harmonic surface waviness on the film thickness, pressure, and temperature oscillations in an elastohydrodynamically lubricated eccentric-tappet pair has been investigated in relation to the eccentricity and the waviness wavelength. The results show that, during one working cycle, the waviness causes significant fluctuations of the oil film, pressure, and temperature, as well as a reduction in minimum film thickness. Smaller wavelength causes more dramatic variations in oil film. The fluctuations of the pressure, film thickness, temperature, and traction coefficient caused by double-sided waviness are nearly the same compared with the single-sided waviness, but the variations are less intense.

Two Dimensional Modified Reynolds Equation Including Pressure Dependent Viscosity Effect

2012 ◽  
Author(s):  
Jung Gu Lee ◽  
Alan Palazzolo
Keyword(s):  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Fluid Film ◽  
Maximum Pressure ◽  
Elastic Solids ◽  
Pressure Distributions ◽  
Pressure Dependent Viscosity ◽  
Modified Reynolds Equation ◽  
Dependent Viscosity ◽  
Modified Equation

The Reynolds equation plays an important role for predicting pressure distributions for fluid film bearing analysis, One of the assumptions on the Reynolds equation is that the viscosity is independent of pressure. This assumption is still valid for most fluid film bearing applications, in which the maximum pressure is less than 1 GPa. However, in elastohydrodynamic lubrication (EHL) where the lubricant is subjected to extremely high pressure, this assumption should be reconsidered. The 2D modified Reynolds equation is derived in this study including pressure-dependent viscosity, The solutions of 2D modified Reynolds equation is compared with that of the classical Reynolds equation for the ball bearing case (elastic solids). The pressure distribution obtained from modified equation is slightly higher pressures than the classical Reynolds equations.

Thermal Non-Newtonian Elastohydrodynamic Lubrication of Line Contacts Under Simple Sliding Conditions

1992 ◽  
Vol 114 (2) ◽  
pp. 317-327 ◽  
Author(s):  
Shao Wang ◽  
T. F. Conry ◽  
C. Cusano
Keyword(s):  
Film Thickness ◽  
Surface Temperature ◽  
Thermal Effects ◽  
Elastohydrodynamic Lubrication ◽  
Reduction Factor ◽  
Simple Formulation ◽  
Maximum Surface ◽  
Line Contacts ◽  
Traction Coefficient ◽  
Maximum Surface Temperature

A computationally simple formulation for the stationary surface temperature is developed to examine the thermal non-Newtonian EHD problem for line contacts under simple sliding conditions. Numerical results obtained are used to develop a formula for a thermal and non-Newtonian (Ree-Eyring) film thickness reduction factor. Results for the maximum surface temperature and traction coefficient are also presented. The thermal effects on film thickness and traction are found to be more pronounced for simple sliding than for combined sliding and rolling conditions.

The elastohydrodynamic lubrication of piston rings

1983 ◽  
Vol 386 (1791) ◽  
pp. 409-430 ◽  
Keyword(s):  
Film Thickness ◽  
Combustion Chamber ◽  
Diesel Engines ◽  
Elastohydrodynamic Lubrication ◽  
Cylinder Liner ◽  
Piston Rings ◽  
Lubrication Regimes ◽  
Piston Seal ◽  
Cylinder Liners ◽  
Lubricant Viscosity

The piston seal that separates the hostile environment of the combustion chamber from the crankcase that contains the lubricant is an essential machine element in reciprocating engines. The sealing force pressing the piston rings against the cylinder liner varies with the combustion chamber pressure to form an effective self-adjusting mechanism. The conjunctions between piston rings and cylinder liners are thus subjected to cyclic variations of load, entraining velocity and effective lubricant temperature as the piston reciprocates within the cylinder. Recent theoretical and experimental studies have confirmed that piston rings enjoy hydrodynamic lubrication throughout most of the engine cycle, but that a transition to mixed or boundary lubrication can be expected near top dead centre. The purpose of the present paper is to examine the suggestion that elastohydrodynamic lubrication might contribute to the tribological performance of the piston seal, particularly near top dead centre. The mode of lubrication in eight four-stroke and six two-stroke diesel engines is assessed in terms of the dimensionless viscosity and elasticity parameters proposed by Johnson (1970), and the associated map of lubrication régimes. The survey indicates unequivocally that elastohydrodynamic action can be expected during part of the stroke in all the engines considered. In the second part of the paper a detailed examination of the influence of elastohydrodynamic action in one particular engine is presented to confirm the general findings recorded in the study of lubrication régimes. Current analysis of the lubrication of rigid piston rings already takes account of the variation of surface temperature along the cylinder liner and its influence upon lubricant viscosity. It is shown that, when the enhancing influence of pressure upon viscosity is added to the analysis of rigid piston rings, the predicted cyclic minimum film thickness is more than doubled. Full elastohydrodynamic action, involving both local distortion of the elastic solids and the influence of pressure upon viscosity, results in a fourfold increase in film thickness. It is further shown that it is necessary to take account of the variation of squeeze-film velocity throughout the lubricated conjunction at each crank angle if reliable predictions of film shape and thickness are to be achieved. It is thus concluded that the wave of elastic deformation, which ripples up and down the cylinder liners many times each second in diesel engines, together with the associated local elastic deformations on the piston rings themselves, combine with the influence of pressure upon lubricant viscosity to enhance the minimum oil film thickness in the piston seal by elastohydrodynamic action.

A Quantitative Solution for the Full Shear-Thinning EHL Point Contact Problem Including Traction

2007 ◽  
Author(s):  
Yuchuan Liu ◽  
Q. Jane Wang ◽  
Scott Bair ◽  
Philippe Vergne
Keyword(s):  
Film Thickness ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
High Viscosity ◽  
Viscosity Models ◽  
Pure Rolling ◽  
Volume Viscosity ◽  
Traction Coefficient ◽  
Simulation And Experiment

We present a realistic elastohydrodynamic lubrication (EHL) simulation in point contact using a Carreau-like model for the shear-thinning response and the Doolittle-Tait free-volume viscosity model for the piezoviscous response. The liquid is a high viscosity polyalphaolefin which possesses a relatively low threshold for shear-thinning. As a result, the measured EHL film thickness is about one-half of the Newtonian prediction. We derived and numerically solved the two-dimensional generalized Reynolds equation for the modified Carreau model based on Greenwood [1]. Departing from many previous solutions, the viscosity models used for the pressure and shear dependence were obtained entirely from viscometer measurements. Truly remarkable agreement is found in the comparisons of simulation and experiment for traction coefficient and for film thickness in both pure rolling and sliding cases. This agreement validates the use of a generalized Newtonian model in EHL.

Occurrence of High Pressure Spike in Unidirectional Start–Stop–Start Point Contacts

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
P. Sperka ◽  
J. Wang ◽  
I. Krupka ◽  
M. Hartl ◽  
M. Kaneta
Keyword(s):  
High Pressure ◽  
Film Thickness ◽  
Rolling Contact Fatigue ◽  
Contact Fatigue ◽  
Elastohydrodynamic Lubrication ◽  
Rolling Contact ◽  
Point Contacts ◽  
Pressure Distributions ◽  
Machine Element ◽  
Pressure Spike

The transient film thickness and pressure distributions in point elastohydrodynamic lubrication (EHL) contacts during start–stop–start motion are discussed based on experimental and numerical analyses. When the machine element starts to move after the stopping, where the oil is entrapped between two surfaces, the pressure at the exit area increases very much. The pressure increase depends markedly on the overall film thickness before the stopping of the motion, but is hardly controlled by the acceleration after the stopping. It can be considered that this phenomenon affects the rolling contact fatigue damage.

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