The Minimum Film Thickness in Lubricated Line Contacts during a Reversal of Entrainment—Piezoviscous Behaviour

1992 ◽  
Vol 206 (6) ◽  
pp. 417-424 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Lubrication Theory ◽  
Rate Of Change ◽  
Operating Conditions ◽  
Entrainment Velocity ◽  
Residual Film ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Important Exception

In many line contacts the operating conditions, such as load, entrainment velocity and contact radii, vary with time. Generally, the results from standard elastohydrodynamic lubrication theory, derived for constant conditions, can be used to obtain a quasi-steady prediction of film thickness that is sufficiently accurate for design purposes. An important exception to this is where the entrainment direction changes because, under those conditions, the quasi-steady approach predicts that there will be no clearance between the surfaces while in practice a residual film will persist. A previous paper showed that the minimum film thickness during entrainment reversal depends primarily on the rate of change of entrainment velocity. Limit expressions for the minimum clearance in the four regimes of lubrication were obtained. The present paper is part of a programme to develop a minimum film thickness chart for entrainment reversal and deals with the transition between the rigid-piezoviscous and the elastic-piezoviscous regimes.

The Minimum Film Thickness in Lubricated Line Contacts during a Reversal of Entrainment—General Solution and the Development of a Design Chart

1994 ◽  
Vol 208 (1) ◽  
pp. 53-64 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Rate Of Change ◽  
Operating Conditions ◽  
Radius Of Curvature ◽  
Velocity Change ◽  
Surface Separation ◽  
Residual Film ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Interpolation Procedure

In most line contacts the load, effective radius of curvature and entraining velocity change with time. Generally this is ignored when calculating the film thickness and a quasi-steady solution is obtained. Under most conditions the errors introduced by this are either small or are not critical. However, when the entraining velocity reverses, as, for example, in some designs of cams, the quasi-steady approach predicts that the film thickness will be zero. In practice a residual film persists and can provide adequate surface separation. Previous papers by the author have shown that the minimum film thickness at entrainment reversal depends on the rate of change of the entraining velocity. Expressions for the film thickness in the four regimes of lubrication—rigid isoviscous, rigid piezoviscous, elastic isoviscous and elastic piezoviscous—were obtained and the variations of the film thickness in the transitions between adjacent regimes examined. The present paper examines the region where more than two regimes overlap. The values of film thickness obtained are then used to develop an interpolation procedure for the accurate calculation of the minimumfilm thickness under all operating conditions.

The Minimum Film Thickness in Lubricated Line Contacts during a Reversal of Entrainment—Isoviscous Behaviour

1992 ◽  
Vol 206 (5) ◽  
pp. 337-345 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Transition Zone ◽  
Static Analysis ◽  
Rate Of Change ◽  
Entrainment Velocity ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Static Approach ◽  
The One

In most line contacts, the film thickness can be adequately determined using a quasi-static analysis. The one exception appears to occur when the direction of entrainment changes. Here, the quasi-static approach predicts that the film will fall to zero while, in practice, there will always be a finite clearance between the surfaces. It was shown in a previous paper that this minimum clearance depends upon the rate of change of entrainment velocity, and limit expressions for the film thicknesses in the four regimes of lubrication were developed. The present paper examines the transition between the rigid-isoviscous and the elastic-isoviscous regimes and determines how the minimum film thickness behaves in this transition zone.

Roughness Amplitude Reduction Under Non-Newtonian EHL Conditions

2005 ◽  
Author(s):  
A. D. Chapkov ◽  
C. H. Venner ◽  
A. A. Lubrecht
Keyword(s):  
Film Thickness ◽  
Pressure Fluctuations ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Quantitative Prediction ◽  
Point Contacts ◽  
Minimum Film Thickness ◽  
Roughness Amplitude ◽  
Average Film Thickness ◽  
Ehl Contact

The influence of surface roughness on the performance of bearings and gears operating under ElastoHydrodynamic Lubrication (EHL) conditions has become increasingly important over the last decade, as the average film thickness decreased due to various influences. Surface features can reduce the minimum film thickness and thus increase the wear. They can also increase the temperature and the pressure fluctuations, which directly affects the component life. In order to describe the roughness geometry inside an EHL contact, the amplitude reduction of harmonic waviness has been studied over the last ten years. This theory currently allows a quantitative prediction of the waviness amplitude and includes the influence of wavelength and contact operating conditions. However, the model assumes a Newtonian behaviour of the lubricant. The current paper makes a first contribution to the extension of the roughness amplitude reduction for EHL point contacts including non-Newtonian effects.

The Elastohydrodynamic Lubrication of Elliptical Point Contacts Operating in the Isoviscous Region

1995 ◽  
Vol 209 (4) ◽  
pp. 225-234 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Radius Ratio ◽  
Point Contacts ◽  
Reasonable Estimate ◽  
Wide Range ◽  
Minimum Film Thickness

The elastohydrodynamic lubrication of point contacts is examined and results for the minimum film thickness are presented for a wide range of radius ratios and operating conditions. The results are compared with the predictions of the appropriate regime formulae. Although these formulae give a reasonable estimate of the contact's behaviour, the actual clearances are often substantially different, particularly close to the regime boundaries. Interpolation equations for seven values of radius ratio are given and these should be sufficient to allow the minimum clearance to be estimated for most isoviscous point contacts.

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 Minimum Film Thickness in Line Contacts During Reversal of Entrainment

1993 ◽  
Vol 115 (1) ◽  
pp. 191-199 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Steady State ◽  
Film Thickness ◽  
Rate Of Change ◽  
Radius Of Curvature ◽  
Operating Cycle ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Involute Gears ◽  
Shaft Seals ◽  
Steady State Predictions

In contacts, such as cams, non-involute gears and shaft seals, where the direction of entrainment reverses during the operating cycle, the minimum film thickness is typically found just after the reversal. This paper shows that this minimum film thickness is determined by the rate of change of the entraining velocity and by the fluid and surface properties. For line contacts, four regimes of lubrication are found—as for the steady-state situation—and expressions for the film thickness in each regime are developed. This enables an outline design chart for the minimum film thickness to be constructed. It is shown that this information, together with the steady-state predictions is sufficient to determine the variation of film thickness with time in most situations where load, radius of curvature, and entraining velocity vary.

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.

Investigation of the Failure of Heavily Loaded Journal Bearings

1994 ◽  
Vol 208 (3) ◽  
pp. 167-171
Author(s):  
D Ashman
Keyword(s):  
Film Thickness ◽  
Reynolds Equation ◽  
Journal Bearing ◽  
Elastohydrodynamic Lubrication ◽  
Failure Criteria ◽  
Operating Conditions ◽  
Minimum Film Thickness ◽  
Hydrodynamic Solution ◽  
Metrological Study ◽  
Theoretical Minimum

This paper gives details of a combined theoretical and experimental investigation of a plain journal bearing under heavily loaded conditions together with a metrological study of the bearing geometry. It was found that under high loading conditions a simplified analytical expression relating the Sommerfeld number to the non-dimensional minimum film thickness, using a hydrodynamic solution of the isoviscous form of the Reynolds equation, could be developed. An alternative theoretical solution based on elastohydrodynamic lubrication was also considered. In addition, experimental work determined a variety of operating conditions that produced metal-to-metal contact. These operating conditions were then compared with the theoretical minimum film thickness calculations and bearing manufacturing data. This process was used to determine combined failure criteria based on operating conditions and machining capability.

Thermal Elastohydrodynamic Lubrication of Axially Crowned Rollers

2021 ◽  
pp. 1-21
Author(s):  
Wassim Habchi
Keyword(s):  
Film Thickness ◽  
Design Parameter ◽  
Numerical Study ◽  
Elastohydrodynamic Lubrication ◽  
Negative Influence ◽  
Reference Case ◽  
Critical Design ◽  
Lubrication Performance ◽  
Minimum Film Thickness ◽  
Line Contacts

Abstract This work presents a comprehensive numerical study of thermal elastohydrodynamic lubrication performance in axially crowned rollers, based on a full-system finite element approach. Axial crowning has always been introduced to finite line contacts, as a mean for improving film thickness. Its influence on friction has often been overlooked though. The current work reveals that axial crowning has a negative influence on friction, increasing it significantly with respect to the reference case of straight rollers. It is shown that, with increased crowning height (or reduced crowning radius), minimum film thickness is increased, but so is friction. Therefore, film thickness enhancement comes at the expense of a deterioration in friction. Besides, achieving sufficient enhancements in minimum film thickness would require using relatively low crowning radii, which would lead to a substantial increase in friction. The frictional increase is traced back to an overall increase in contact pressures and effective contact area within the lubricating conjunction. It is also shown that, when film thickness is the most critical design parameter, the best compromise between enhanced film thickness and deteriorated friction would be to combine axial crowning with roller-end profiling. However, when friction is the most critical design parameter, a simple roller-end profiling would offer the best compromise.

Thermal Non-Newtonian Elastohydrodynamic Lubrication of Rolling Line Contacts

1991 ◽  
Vol 113 (3) ◽  
pp. 481-491 ◽  
Author(s):  
H. Salehizadeh ◽  
N. Saka
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Shear Stresses ◽  
Hertz Contact ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Pressure Spike ◽  
Heavy Loads

The two-dimensional thermal elastohydrodynamic equations were numerically solved for a Ree-Eyring type lubricant under pure rolling conditions. Profiles of lubricant pressure, film thickness, and temperature were obtained for medium to heavy loads and moderate to high rolling speeds. The pressure results generally show a small secondary peak near the outlet, but at the highest load considered no pressure spike is obtained and the pressure profile is almost Hertzian. The film thickness results show an increase in minimum film thickness with increasing rolling speeds, but at a lesser rate than those predicted for a Newtonian fluid under isothermal conditions. It is found that unless the lubricant becomes non-Newtonian in the inlet region, the reduction in minimum film thickness at high rolling speeds is completely due to thermal effect. The lubricant temperature profile and the amount of heat generated and dissipated in the contact region were also calculated. The lubricant temperature reaches a maximum just before the entrance to the Hertz contact region. Both shear and compression heating are found to be important in raising the lubricant temperature in the inlet. As the lubricant enters the Hertz contact zone, the temperature first drops rapidly, because of the rapid heat conduction to the rollers, and then remains almost constant for most of the Hertz contact. Near the exit where the pressure gradients are large, the lubricant temperature drops rapidly below the ambient because of lubricant expansion. The lubricant then heats up rapidly before leaving the contact area as a result of heat generated by shear stresses.

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