Enhancement of thermal effect in zero entrainment velocity contact under low surface velocity

2016 ◽  
Vol 230 (12) ◽  
pp. 1554-1561 ◽  
Author(s):  
Binbin Zhang ◽  
Jing Wang
Keyword(s):  
Mathematical Model ◽  
Film Thickness ◽  
Thermal Effect ◽  
Viscosity Index ◽  
Elastohydrodynamic Lubrication ◽  
Surface Velocity ◽  
Surface Waviness ◽  
Entrainment Velocity ◽  
Smooth Contact ◽  
Wedge Effect

In the current study, in order to obtain a thick film thickness under zero entrainment velocity at low surface velocity, the effects of ambient viscosity, pressure–viscosity index of the lubricant, and the surface waviness are investigated numerically based on a thermal elastohydrodynamic lubrication mathematical model. The increasing ambient viscosity and modest waviness can deepen the dimple by a stronger “temperature-viscosity wedge” effect. With the combined effect of ambient viscosity, pressure–viscosity index, and surface waviness, a small centralized dimple in smooth contact evolves into a big classical one together with the disappearance of the former thin droopy film thickness.

Thermal Elastohydrodynamic Lubrication of an Optimized Cam–Tappet Pair in Smooth Contact

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
W. Wu ◽  
J. Wang ◽  
C. H. Venner
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Temperature Profiles ◽  
Cam Mechanism ◽  
Basic Segment ◽  
Order Polynomial ◽  
Isothermal Analysis ◽  
Base Circle ◽  
Smooth Contact ◽  
Oil Characteristics

A high-order polynomial gas distribution cam mechanism is investigated theoretically from the viewpoint of thermal elastohydrodynamic lubrication (EHL). First, a cam with a larger base circle radius is employed, which results in slide–roll ratio 2.0 < S < 9.0 when the two surfaces move oppositely. The pressure, film thickness, and temperature profiles at a number of angular positions of the cam are presented, together with the isothermal results. The comparison between thermal and isothermal oil characteristics is also shown. It is revealed that the isothermal analysis partly overestimates the actual film thickness and it also misses some essential local phenomena. Second, a cam with a smaller base circle radius is studied, which leads to drastic variations in the slide–roll ratio which encounters four times’ occurrences of infinity in one working period. The pressure, film thickness, and temperature profiles at some angular cam positions together with the oil characteristics are given, showing much dramatic variations. A very small film thickness is observed at the contact of the tappet with the start of the cam basic segment, which suggests a possible risk of direct contact of both surfaces.

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.

Thermal Elastohydrodynamic Lubrication Analysis for Point Contact Transmission

2009 ◽  
Author(s):  
Hai-zhou Huang ◽  
Xi-chuan Niu ◽  
Xiao-yang Yuan
Keyword(s):  
Film Thickness ◽  
Numerical Solutions ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Surface Velocity ◽  
Squeeze Film ◽  
Elastic Displacement ◽  
Circular Arc ◽  
Tooth Width ◽  
Contact Transmission

To investigate the thermal EHL (elastohydrodynamic lubrication) in point contact transmission, a model considering the two-dimensional surface velocity of tooth face and the running-in is proposed. The numerical solutions for pressure, temperature and film thickness distribution in the contact zone are obtained by solving equations including the Reynolds, Energy and the elastic displacement with variable dimension meshing method. The model was used to study the point contact transmission of the circular arc gear in a windlass. The main results show that it is pure rolling along the direction of tooth width, and the rolling speed plays a leading role in improving the lubricating performance and transmission efficiency of circular arc gear. The squeeze film effect makes the pressure peak tend to be gentle and the film thickness increase slightly.

Influence of lubrication starvation and surface waviness on the oil film stiffness of elastohydrodynamic lubrication line contact

2016 ◽  
Vol 24 (5) ◽  
pp. 924-936 ◽  
Author(s):  
Yuanyuan Zhang ◽  
Huaiju Liu ◽  
Caichao Zhu ◽  
Chaosheng Song ◽  
Zufeng Li
Keyword(s):  
Film Thickness ◽  
Contact Stiffness ◽  
Elastohydrodynamic Lubrication ◽  
Force Balance ◽  
Line Contact ◽  
Surface Waviness ◽  
Regular Surface ◽  
Normal Contact ◽  
Oil Film ◽  
Film Stiffness

Stiffness properties of interfacial engineering surfaces are of great importance to the dynamic performance of relevant mechanical systems. Normal contact stiffness and oil film stiffness of line contact problems are studied in this work analytically and numerically. The Hertzian contact theory and the Yang–Sun method are applied to predict the contact stiffness, while the empirical elastohydrodynamic lubrication (EHL) film thickness method and the complete numerical EHL model are used to predict the oil film stiffness. The numerical model mainly consists of the Reynolds equation; the film thickness equation, in which the regular surface roughness is taken into consideration; the force balance equation; and the viscosity-pressure equation. The effects of the normal load, rolling speed, regular surface waviness, and starved lubrication level on the oil film stiffness are investigated.

The Thermal Elastohydrodynamic Lubrication Analysis of Seawater-Lubricated Thordon Bearing

2011 ◽  
Vol 396-398 ◽  
pp. 2507-2510 ◽  
Author(s):  
Li Jing Zhang ◽  
You Qiang Wang
Keyword(s):  
Numerical Simulation ◽  
Film Thickness ◽  
Thermal Effect ◽  
Thermal Condition ◽  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Shaft Diameter ◽  
Pressure Peak

Based on Reynolds equation, the numerical simulation of thermal elstohydronamic lubrication for seawater-lubricated thordon bearing was carried out, the effects of the load, the speed and the shaft diameter on the pressure and the film thickness were discussed. The results show that thermal effect has little effect on the pressure, but the film thickness under the thermal condition is smaller than isothermal. The pressure peak is increased and the film thickness is decreased greatly with the increase of load. The pressure peak is decreased and the film thickness is increased greatly with the increase of speed.

An Anomalous Elastohydrodynamic Lubrication Film: Inlet Dimple

2005 ◽  
Vol 127 (2) ◽  
pp. 425-434 ◽  
Author(s):  
F. Guo ◽  
P. L. Wong
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Lubrication Film ◽  
Entrainment Velocity ◽  
Limiting Shear Stress ◽  
The Individual ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Wall Slippage

This paper presents a deliberately designed elastohydrodynamical lubrication (EHL) experiment for the study of the individual effect of the limiting shear stress and wall slippage. Very slow entrainment speeds were employed to avoid influential shear heating and oils of high viscosities were chosen to ensure that the conjunction was under typical EHL. An anomalous EHL film, characterized by a dimple at the inlet region, was obtained. Literature revealed that this inlet dimple was reported in some numerical studies taking into consideration the limiting-shear-stress characteristics of the lubricant and wall slippage. It was found that even under the same kinematic conditions, different types of film shape would be generated by simple disc sliding and simple ball sliding. Simple disc sliding produces an inlet dimple with a comparatively thick inlet film thickness, which droops rapidly toward the outlet region. For simple ball sliding, there is also an inlet dimple but the central film thickness is rather uniform. However, by prerunning the conjunction at a zero entrainment velocity (at the same linear speeds but in opposite directions) before the sliding experiment, the slope of the central film of simple disc sliding becomes smaller. It is probably due to the modification of solid-liquid interface, i.e., the slippage level, by the highly pressurized and stressed prerunning conditions. With a prescribed prerunning, which can produce very similar films at simple disc sliding and simple ball sliding, variation of film thickness was studied and it was found that the inlet dimple film has obvious dependence on entrainment speeds, but was not sensitive to loads. The present experimental results can be considered as direct evidence for those numerical findings of the inlet dimple. Tentatively, an effective viscosity wedge is proposed to account for the formation of the inlet dimple.

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.

Approximating EHL Film Thickness Profiles Under Transient Conditions

2002 ◽  
Vol 124 (3) ◽  
pp. 443-447 ◽  
Author(s):  
S. Messe´ ◽  
A. A. Lubrecht
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Analytical Approximation ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Numerical Techniques ◽  
Transient Conditions ◽  
Entrainment Velocity ◽  
Thickness Profile ◽  
Ehl Contact

In ElastoHydrodynamic Lubrication (EHL), transient processes are much more common than stationary ones. Predicting the film thickness under steady state conditions has become straight forward. Using numerical methods, the effect of transient conditions on the film thickness profile can be computed. However, those analyses are very time consuming even using advanced numerical techniques. As such, they are inadequate for industrial applications as design and development. This paper shows that under certain assumptions, an approximate formula of the transient film thickness profile can be derived under transient operating conditions. The variations can occur in the geometry, the load or the hydrodynamic velocity. The theory can handle all variations separately, or even a combination of several parameters varying simultaneously. The analytical approximation obtained is rather good apart from the constriction at the contact edge(s). This approach can be applied to any set of time dependent conditions (load, speed, geometry). As an example an EHL contact is studied in which reversal of the entrainment velocity occurs.

The Contribution of a Sliding Velocity to EHL Film Thickness Distribution

2012 ◽  
Author(s):  
Milan Omasta ◽  
Ivan Krupka ◽  
Martin Hartl
Keyword(s):  
Film Thickness ◽  
Thickness Distribution ◽  
Central Area ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Sliding Velocity ◽  
Contact Conditions ◽  
Entrainment Velocity ◽  
Pure Rolling ◽  
Circular Contact

In general contact conditions, the surface velocities are variously oriented, thus the entrainment and sliding velocity act at different directions. The effects of magnitude and direction of the sliding velocity in elastohydrodynamic lubrication (EHL) circular contact have been investigated. Film thickness distribution has been obtained using thin-film colorimetric interferometry. It has been found that direction of sliding velocity with respect to entrainment velocity play a role in film thickness distribution, particularly at high slide-to-roll ratios. A superposition of the effects of a pure rolling and of an opposite sliding has been considered. The pure rolling condition creates typical horse-shoe shaped film, whereas under the opposite sliding condition (i.e. zero entrainment velocity) conical depression in the central area of Hertzian contact called “dimple” has been observed.

Influence of Different Viscosity Lubricant to Finite Line Contacts on Elastohydrodynamic Lubrication (EHL) under Oscillating

2012 ◽  
Vol 538-541 ◽  
pp. 1939-1944
Author(s):  
Yan Fei Wang ◽  
Tong Shu Hua ◽  
Hao Yang Sun
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Oil Film ◽  
Entrainment Velocity ◽  
Finite Line Contact ◽  
Line Contacts ◽  
Finite Line ◽  
Contact Roller ◽  
Two Parameters ◽  
Experimental Rig

To make further researches into the elastohydrodynamic lubrication properties of a finite line contact roller, oscillating experiments were carried out on made overload experimental rig for oil film measurement using optical interference technique. Film thickness and shape were measured in two kinds of viscosity polyisobutylene. This study indicates that both lubricant viscosity and roller entrainment velocity play an important role on EHL of finite line contacts. On motion, the more increase in viscosity or speed, the thicker the oil film thickness, simultaneity edge effect is distinctly intensified and film thickness increases less on roller end, difference of the film thickness is increased between roller end and the central. Above two parameters are significant for logarithmic profile roller in crowning design.

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