Starved Elastohydrodynamic Lubrication With Reflow in Elliptical Contacts

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Takashi Nogi ◽  
Hiroshi Shiomi ◽  
Noriko Matsuoka
Keyword(s):  
Boundary Condition ◽  
Film Thickness ◽  
Practical Importance ◽  
Reduction Rate ◽  
Elastohydrodynamic Lubrication ◽  
Test Device ◽  
Rolling Bearings ◽  
Optical Test ◽  
Ellipticity Ratio ◽  
Distance Formula

Under repeated overrollings, the elastohydrodynamic lubrication (EHL) film thickness can be much less than the fully flooded value due to the ejection of the lubricant from the track. The ejection of the lubricant is caused by the pressure flow in the inlet, and under conditions of negligible reflow, the reduction rate is predicted by the numerical analysis with a uniform inlet film thickness. However, the degree of starvation is determined by the balance of the ejection and reflow. In the previous papers for circular contacts, the reflow is taken into account using a nonuniform inlet film thickness obtained based on the Coyne–Elrod boundary condition. In this paper, the model for circular contacts is extended to elliptical contacts, which are of more practical importance in rolling bearings. The model is verified for the inlet distance and the film thickness using a roller on disk optical test device. Numerical results are fitted to an inlet distance formula, which is a function of the initial film thickness, the fully flooded central film thickness, the capillary number, and the ellipticity ratio. The inlet distance formula can be applied to the Hamrock–Dowson formulas for the starved film thickness.

Film Thickness and Rolling Resistance in Starved Elastohydrodynamic Lubrication of Point Contacts With Reflow

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Takashi Nogi
Keyword(s):  
Boundary Condition ◽  
Film Thickness ◽  
Numerical Study ◽  
Critical Role ◽  
Elastohydrodynamic Lubrication ◽  
Rolling Resistance ◽  
Point Contacts ◽  
Rolling Bearings ◽  
Wear Life ◽  
Minimum Film Thickness

Elastohydrodynamic lubrication (EHL) film thickness and rolling resistance play a critical role in determining friction, wear, life, and other tribological characteristics of rolling bearings. Although film thickness formulas are widely used and experimentally verified, accurate prediction of the film thickness is still difficult under starved conditions. This paper presents a numerical study of starved EHL point contacts using a nonuniform inlet film thickness obtained from a modified Coyne–Elrod boundary condition. An experimental verification of the numerical results is also presented. Based on the results of a parametric study, inlet distance formulas are obtained as a function of the initial film thickness, the fully flooded central film thickness, and the capillary number. By using the inlet distance formulas and the Hamrock–Dowson formulas, the central film thickness, the minimum film thickness, and the viscous rolling resistance can be calculated.

Elastohydrodynamic Film Thickness in Elliptical Contacts With Spinning and Rolling

1999 ◽  
Vol 121 (4) ◽  
pp. 686-692 ◽  
Author(s):  
Qian Zou ◽  
Changhua Huang ◽  
Shizhu Wen
Keyword(s):  
Film Thickness ◽  
Pressure Distribution ◽  
Computing Time ◽  
Elastohydrodynamic Lubrication ◽  
Low Complexity ◽  
Numerical Results ◽  
Analysis And Design ◽  
Pure Rolling ◽  
Thickness Prediction ◽  
Ellipticity Ratio

In this paper, a theoretical model for the film thickness prediction of elastohydrodynamic lubrication of elliptical contacts with spinning and rolling/sliding motions is presented, in which 1) an effective ellipticity ratio ke is introduced to present the ellipse feature instead of the normal ellipticity ratio k in case of that the entraining velocity at the center of contact ellipse is at an angle with minor axis, 2) Roelands and Dowson-Higginson’s equations are adopted to express the influence of pressure upon lubricant viscosity and density, 3) multilevel/multigrid techniques, with low complexity and good stability, are used for the purpose of reducing computing time in the complex numerical analysis. With this model the characteristics of film shape and pressure distribution of elastohydrodynamic lubrication of elliptical concentrated contacts with spinning and rolling/sliding were discussed. The results showed that the spinning motion has significant influence on the film shape and pressure distribution. Based on a large number of numerical results of elastohydrodynamic lubrication analysis of elliptical concentrated contacts with spinning and rolling/sliding, new expressions for the minimum and central film thickness prediction were regressed. Their accuracy was analyzed by comparisons with numerical results of an evaluation set and others’ expressions under pure rolling and/or sliding condition. The comparisons showed that the two new expressions have satisfactory accuracy and potential application to engineering analysis and design.

scholarly journals Grease film thickness measurement in rolling bearing contacts

2020 ◽  
pp. 135065012096127
Author(s):  
Xingnan Zhang ◽  
Romeo Glovnea
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Rolling Bearing ◽  
Thickness Measurement ◽  
Lubricant Film ◽  
Rolling Element Bearings ◽  
Lubricant Film Thickness ◽  
Rolling Bearings ◽  
Rolling Element ◽  
Film Thickness Measurement

Rolling bearings are the second most used machine components. They work in what it is called elastohydrodynamic lubrication regime. The geometry of rolling element bearings makes the direct measurement of the lubricant film thickness a challenging task. Optical interferometry is widely used in laboratory conditions for studying elastohydrodynamic lubrication however it cannot be used directly in rolling element bearings thus the only suitable methods are electrical techniques. Of these, film thickness measurement based on electrical capacitance of the contacts has been used in the past by a number of authors. One of the limitations of the capacitance method, when used in rolling bearings, is that it cannot distinguish between the contacts of every rolling element and raceway on one hand and on the other between the inner and outer ring contacts. In the present study the authors used an original test rig which can measure the film thickness for only one ball and separately for the inner and outer rings of a radial ball bearing. This paper thus shows for the first-time results of the lubricant film thickness, at the inner and outer raceways, in grease lubricated rolling bearings.

Analysis of the lubricating mechanism for tilting rollers in rolling bearings

2011 ◽  
Vol 225 (11) ◽  
pp. 1059-1070 ◽  
Author(s):  
X-L Liu ◽  
P Yang ◽  
P-R Yang
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Grid Method ◽  
Infinite Plane ◽  
Rolling Bearings ◽  
Velocity Parameter ◽  
Light Load ◽  
Minimum Film Thickness ◽  
Cylindrical Roller ◽  
Lubricating Mechanism

In practice, the tilting roller occurs widely in rolling bearings. In order to investigate the lubricating mechanism of tilting rollers in rolling bearings, a contact between a tilting cylindrical roller and an infinite plane is assumed in the present paper. Using the multi-grid method, a numerical solution has been obtained for the isothermal elastohydrodynamic lubrication of the contact. The film thickness and pressure with different tilt angles have been given. Results show that the property of the tilting roller’s lubrication is different from that of the parallel roller contact investigated in the past, and asymmetry is common both for the film thickness and the oil pressure under tilting conditions. Moreover, the larger the tilt angle, the smaller the minimum film thickness, and the more easily the local wear occurs in bearings. The effects of the maximum Hertzian pressure, velocity parameter, and length and end profile radius of the roller on the lubricating performance of the contact have been discussed. The conclusion can be made that better lubrication of tilting roller contact needs light load, high velocity parameter, short length, and larger end profile radius of the roller. Comparisons between the starved and fully flooded lubrication in the tilting roller contact have been given, and it has been found that starvation status can worsen the lubrication and reduce the life of roller bearings.

Study of Lubrication Film Formation in Ball Bearings Under Starved Conditions

2011 ◽  
Author(s):  
Petr Svoboda ◽  
Martin Vrbka ◽  
Petr Sperka ◽  
Ivan Krupka ◽  
Martin Hartl
Keyword(s):  
Film Thickness ◽  
Film Formation ◽  
Test Rig ◽  
Rolling Bearings ◽  
Lubrication Film ◽  
Entrainment Velocity ◽  
Optical Test ◽  
Rolling Elements ◽  
Machine Parts ◽  
Lubrication Conditions

Rolling elements (e.g. rolling bearings, gears, cams and followers, etc.) fall into the most frequently used and highly loaded machine parts in machinery industry. These parts must operate correctly, often over prolonged periods with sufficient performance. One of the most important parameters determining the performance and life of machine parts is a lubrication film thickness, which is generated within elastohydrodynamic lubricated (EHL) non-conformal contacts. The entrainment velocity and the lubricant viscosity have the main effect on the film thickness formation in the classic fluid film lubrication. In some engineering applications e.g. grease lubricated rolling bearings, the available lubricant is not enough to fill the gap between the two contact surfaces thereby a poor lubrication conditions occur. Insufficient supply of lubricant may result in starvation and consequently in lubrication film collapse. With decreasing amounts of lubricant, the inlet meniscus approaches the contact entrance and finally causes lubrication film breakdown because of contact starvation. This paper is focused on the study of effect of starved lubrication conditions on lubrication film formation of non-conformal contacts operated under pure rolling conditions. A new optical test rig with multiple EHL contacts was developed for experimental study of lubrication film formation in the thrust ball bearing. Nevertheless to start this research the first experiments will be performed using ball on disc optical test rig where EHL contact is realized only between one ball and disc.

Rough Air-Soft Elastohydrodynamic Lubrication

2013 ◽  
Vol 420 ◽  
pp. 30-35
Author(s):  
Khanittha Wongseedakaew ◽  
Jesda Panichakorn
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Modulus Of Elasticity ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Multilevel Methods ◽  
Inlet Temperature ◽  
Film Pressure ◽  
Air Inlet ◽  
Air Film

This paper presents the effects of rough surface air-soft elastohydrodynamic lubrication (EHL) of rollers for soft material under the effect of air molecular slip. The time independent modified Reynolds equation and elasticity equation were solved numerically using finite different method, Newton-Raphson method and multigrid multilevel methods were used to obtain the film pressure profiles and film thickness in the contact region. The effects of amplitude of surface roughness, modulus of elasticity and air inlet temperature are examined. The simulation results showed surface roughness has effect on film thickness but it little effect to air film pressure. When the amplitude of surface roughness and modulus of elasticity increased, the air film thickness decreased but air film pressure increased. However, the air inlet temperature increased when the air film thickness increased.

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.

scholarly journals A thermal resistances-based approach for thermal-elastohydrodynamic calculations in point contacts

2017 ◽  
Vol 232 (11) ◽  
pp. 2088-2102 ◽  
Author(s):  
Eduardo de la Guerra Ochoa ◽  
Javier Echávarri Otero ◽  
Enrique Chacón Tanarro ◽  
Benito del Río López
Keyword(s):  
Friction Coefficient ◽  
Film Thickness ◽  
Thermal Effects ◽  
Good Accuracy ◽  
Computational Cost ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
New Approach ◽  
Ball On Disc

This article presents a thermal resistances-based approach for solving the thermal-elastohydrodynamic lubrication problem in point contact, taking the lubricant rheology into account. The friction coefficient in the contact is estimated, along with the distribution of both film thickness and temperature. A commercial tribometer is used in order to measure the friction coefficient at a ball-on-disc point contact lubricated with a polyalphaolefin base. These data and other experimental results available in the bibliography are compared to those obtained by using the proposed methodology, and thermal effects are analysed. The new approach shows good accuracy for predicting the friction coefficient and requires less computational cost than full thermal-elastohydrodynamic simulations.

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.

Sign in / Sign up

Export Citation Format

Share Document