The Lubrication Regime at Pin-Pulley Interface in Chain CVTs

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
G. Carbone ◽  
M. Scaraggi ◽  
L. Soria
Keyword(s):  
Pressure Distribution ◽  
High Pressures ◽  
Elastohydrodynamic Lubrication ◽  
Asperity Contact ◽  
Normal Stress Distribution ◽  
Lubrication Regime ◽  
Starting Point ◽  
High Fatigue ◽  
Variable Transmission ◽  
Pressure Peak

This paper deals with the strongly nonstationary squeeze of an oil film at the interface between the chain pin and pulley in chain belt continuously variable transmission. We concentrate on the squeeze motion as it occurs as soon as the pin enters the pulley groove. The duration time to complete the squeeze process compared with the running time the pin takes to cover the entire arc of contact is fundamental to understand whether direct asperity-asperity contact occurs between the two approaching surfaces to clarify what actually is the lubrication regime (elastohydrodynamic lubrication (EHL), mixed, or boundary) and to verify if the Hertzian pressure distribution at the interface can properly describe the actual normal stress distribution. The Hertzian pressure solution is usually taken as a starting point to design the geometry of the pin surface; therefore, it is of utmost importance for the designers to know whether their hypothesis is correct or not. Taking into account that the traveling time, the pin spends in contact with the pulley groove, is of about 0.01 s, we show that rms surface roughness less than 0.1 μm, corresponding to values adopted in such systems, guarantees a fully lubricated EHL regime at the interface. Therefore, direct asperity-asperity contact between the two approaching surfaces is avoided. We also show that the Hertzian solution does not properly represent the actual pressure distribution at the pin-pulley interface. Indeed, after few microseconds a noncentral annular pressure peak is formed, which moves toward the center of the pin with rapidly decreasing speed. The pressure peak can grow up to values of several gigapascals. Such very high pressures may cause local overloads and high fatigue stresses that must be taken into account to correctly estimate the durability of the system.

Numerical Modeling of Mixed Lubrication and Flash Temperature in EHL Elliptical Contacts

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Neelesh Deolalikar ◽  
Farshid Sadeghi ◽  
Sean Marble
Keyword(s):  
Surface Deformation ◽  
Elastohydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Asperity Contact ◽  
Lubrication Regime ◽  
Predicting Performance ◽  
Pure Rolling ◽  
Rolling Element ◽  
Contact Pressures ◽  
Film Lubrication

Highly loaded ball and rolling element bearings are often required to operate in the mixed elastohydrodynamic lubrication regime in which surface asperity contact occurs simultaneously during the lubrication process. Predicting performance (i.e., pressure, temperature) of components operating in this regime is important as the high asperity contact pressures can significantly reduce the fatigue life of the interacting components. In this study, a deterministic mixed lubrication model was developed to determine the pressure and temperature of mixed lubricated circular and elliptic contacts for measured and simulated surfaces operating under pure rolling and rolling/sliding condition. In this model, we simultaneously solve for lubricant and asperity contact pressures. The model allows investigation of the condition and transition from boundary to full-film lubrication. The variation of contact area and load ratios is examined for various velocities and slide-to-roll ratios. The mixed lubricated model is also used to predict the transient flash temperatures occurring in contacts due to asperity contact interactions and friction. In order to significantly reduce the computational efforts associated with surface deformation and temperature calculation, the fast Fourier transform algorithm is implemented.

A numerical method to investigate the mixed lubrication performances of journal-thrust coupled bearings

2019 ◽  
Vol 71 (9) ◽  
pp. 1099-1107
Author(s):  
Guo Xiang Guo Xiang ◽  
Yanfeng Han ◽  
Renxiang Chen ◽  
Jiaxu Wang Jiaxu Wang ◽  
Ni Xiaokang
Keyword(s):  
Thrust Bearing ◽  
Load Capacity ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Mixed Lubrication ◽  
Hydrodynamic Effect ◽  
Asperity Contact ◽  
Content Type ◽  
Lubrication Regime ◽  
Coupled Effect

Purpose This paper aims to present a numerical model to investigate the mixed lubrication performances of journal-thrust coupled bearings (or coupled bearings). Design/methodology/approach The coupled hydrodynamic effect (or coupled effect) between the journal and the thrust bearing is considered by ensuring the continuity of the hydrodynamic pressure and the flow field at the common boundary. The mixed lubrication performances of the coupled bearing are comparatively studied for the cases of considering and not considering coupled effect. Findings The simulated results show that the hydrodynamic pressure distributions for both the journal and thrust bearing are modified due to the coupled effect. The decreased load capacity of the journal bearing and the increased load capacity of the thrust bearing can be observed when the coupled effect is considered. And the coupled effect can facilitate in reducing the asperity contact load for both the journal and thrust bearing. Additionally, the interaction between the mixed lubrication behaviors, especially for the friction coefficient, of the journal and the thrust bearing is significant in the elastohydrodynamic lubrication regime, while it becomes weak in the mixed lubrication regime. Originality/value The developed model can reveal the mutual effects of the mixed lubrication behavior between the journal and the thrust bearing.

Influence of Surface Texture on Micro EHL in Boundary Regime Sliding

2012 ◽  
Author(s):  
Robert Erck ◽  
Oyelayo O. Ajayi ◽  
Cinta Lorenzo-Martin ◽  
George R. Fenske
Keyword(s):  
Thin Film ◽  
Coefficient Of Friction ◽  
Elastohydrodynamic Lubrication ◽  
Asperity Contact ◽  
Disc Surface ◽  
Lubrication Regime ◽  
Uncoated Steel ◽  
Constant Friction ◽  
The Coefficient Of Friction ◽  
Hydrogenated Amorphous

A hard steel ball was slid against textured coated and uncoated steel disks that had strongly directionally ground surfaces. The friction coefficient during ball-on-disk rotating low-speed lubricated sliding was continuously measured. The coefficient of friction rose from ≈ 0.12, which is typical for boundary lubrication regime, to as high as 0.45 whenever the ball was sliding parallel to the grinding ridges on the disc surface. The persistence of this “spike” in the friction was observed to be correlated with the hardness of the disc surface and the nature of the coating. We propose that the frictional spike is due to loss of micro-elastohydrodynamic lubrication, combined with side leakage, leading to intimate asperity-asperity contact. As a result, the coefficient of friction is close to that which is obtained there is no or minimal lubrication. This conclusion is supported by enhanced and persistent frictional spikes in tests conducted with discs coated with a very hard nitride thin film, and constant friction for a disk coated with hydrogenated amorphous carbon, which has low coefficient of friction when there is no/minimal lubrication.

Mixed Lubrication Analyses by a Macro-Micro Approach and a Full-Scale Mixed EHL Model

2004 ◽  
Vol 126 (1) ◽  
pp. 81-91 ◽  
Author(s):  
Q. Jane Wang ◽  
Dong Zhu ◽  
Herbert S. Cheng ◽  
Tonghui Yu ◽  
Xiaofei Jiang ◽  
...  
Keyword(s):  
Pressure Distribution ◽  
Numerical Experiments ◽  
Flow Model ◽  
Elastohydrodynamic Lubrication ◽  
Full Scale ◽  
Asperity Contact ◽  
Average Pressure ◽  
Average Flow ◽  
Simplified Approach ◽  
Average Flow Model

This paper presents an improvement of a simplified approach, namely, the macro-micro approach, used to model the mixed elastohydrodynamic lubrication problems in counterformal contacts, and its comparison with Zhu and Hu’s full-scale mixed-EHL model. In this approach, Patir and Cheng’s average flow model is employed to obtain the distribution of piecewise average pressure. A contact-embedment method that incorporates the detail of asperity contact pressure into the overall pressure distribution is utilized to reveal the severity of surface interaction. Numerical experiments are conducted, and the results are compared with those obtained by means of the full-scale mixed-EHL. The regime of the application of this macro-micro approach is explored.

Rolling and Sliding Contact Stress Parameters in Elastohydrodynamic Lubrication

1967 ◽  
Vol 34 (2) ◽  
pp. 471-477 ◽  
Author(s):  
R. A. Schoeppel ◽  
R. M. Evan-Iwanowski
Keyword(s):  
Pressure Distribution ◽  
Contact Stress ◽  
Contact Area ◽  
Elastohydrodynamic Lubrication ◽  
Considerable Change ◽  
Rolling Contact ◽  
Shear Stresses ◽  
High Speeds ◽  
Pressure Peak ◽  
Distribution Studies

The fatigue life at high operating speeds of machine components, such as bearings, gears, and cams, depends upon the shape and magnitude of the elastohydrodynamic pressure distribution. Studies show that two bodies in rolling contact at high speeds indicate a significant departure from the usual Hertzian pressure distribution present at low rolling speeds. The contact stress distribution for an elastohydrodynamic pressure distribution in an infinitely large plate is determined in this paper. The pressure peak on the outlet side of the contact area and the long pressure sweep on the inlet side of the contact area create a pressure distribution which is asymmetrical. The pressure peak has a significant effect on the normal and shear stresses. Superimposing contact stresses due to sliding indicates a considerable change in the stresses resulting from sliding direction.

A New Deterministic Model for Mixed Lubricated Point Contact With High Accuracy

2020 ◽  
pp. 1-33
Author(s):  
Shuowen Zhang ◽  
Chenhui Zhang
Keyword(s):  
High Performance ◽  
Deterministic Model ◽  
Contact Region ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Stribeck Curve ◽  
Asperity Contact ◽  
Lubrication Regime ◽  
Pressure Boundary Condition

Abstract Mixed lubrication is a major lubrication regime in the presence of surface roughness. A deterministic model is established to solve mixed lubricated point contact in this paper, using a new method to solve asperity contact region in mixed lubrication. Treatment of pressure boundary condition between elastohydrodynamic lubrication region and asperity contact region is discussed. The new model is capable of calculating typical Stribeck curve and analyzing transition of lubrication regime, from full film lubrication to boundary lubrication. Moreover, final result of the model is independent of pressure initialization. High performance in accuracy and convergence has been achieved, which is of great importance for further lubrication modelling with consideration of nano-scale roughness, intermolecular and surface forces.

Performance of Spur Gears Considering Surface Roughness and Shear Thinning Lubricant

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
S. Akbarzadeh ◽  
M. M. Khonsari
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Asperity Contact ◽  
Spur Gears ◽  
Lubricant Film Thickness ◽  
Lubrication Regime ◽  
Effect Of Surface

A model is developed for predicting the performance of spur gears with provision for surface roughness. For each point along the line of action, the contact of pinion and gear is replaced by that of two cylinders. The radii of cylinders, transmitted load, and contact stress are calculated, and lubricant film thickness is obtained using the load-sharing concept of Johnson et al. (1972, “A Simple Theory of Asperity Contact in Elastohydrodynamic Lubrication,” Wear, 19, pp. 91–108) To validate the analysis, the predicted film thickness and the friction coefficient are compared to published theoretical and experimental data. The model is capable of predicting the performance of gears with non-Newtonian lubricants—such as that of shear thinning lubricants—often used in gears. For this purpose, a correction factor for shear thinning film thickness introduced by Bair (2005, “Shear Thinning Correction for Rolling/Sliding Electrohydrodynamic Film Thickness,” Proc. Inst. Mech. Eng., Part J: J. Eng. Tribol., 219, pp. 1–6) has been employed. The results of a series of simulations presenting the effect of surface roughness on the friction coefficient are presented and discussed. The results help to establish the lubrication regime along the line of action of spur gears.

Feet Plantar Pressure Distribution Among Female School Teachers

2020 ◽  
Author(s):  
Ayuni Nabilah Alias ◽  
Karmegam Karuppiah ◽  
Vivien How ◽  
Velu Perumal
Keyword(s):  
Pressure Distribution ◽  
Pressure Measurement ◽  
Plantar Pressure ◽  
Significant Finding ◽  
School Teachers ◽  
Plantar Pressure Distribution ◽  
Starting Point ◽  
The Right

Abstract Background: Plantar pressure distribution has been recognized as a significant finding to associate with various feet conditions. Objectives: To determine the feet plantar pressure distribution among female school teachers; Methods: This research consisted of 124 female school teachers. Respondents was asked to walk at a regular pace for 10 seconds from a fixed starting point while using footwear pressure insole device and pressure measurement was recorded.; Results: The findings show that lateral heel exerted the most pressure in the right and left foot (94 kPa vs 85 kPa). The second highest average of plantar pressure distribution for right foot among female school teachers was medial forefoot (67 kPa), followed by central forefoot (55 kPa), lateral forefoot (52 kPa) and lateral midfoot with 49 kPa. For the left foot, the second highest for average of plantar pressure distribution was medial forefoot (58 kPa), followed by lateral forefoot (48 kPa), and central forefoot (47 kPa) and lateral midfoot (33 kPa). The result was significant differences as the right foot often exerted greater pressure on any part of the foot than the left foot; Conclusions: The pressure plantar distribution of foot reflects the conditions of school teachers with various posture and movement.

scholarly journals Numerical Simulation of the Hydraulic Performances and Flow Pattern of Swallow-Tailed Flip Bucket

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Lifang Zhang ◽  
Jianmin Zhang ◽  
Yakun Guo ◽  
Yong Peng
Keyword(s):  
Pressure Distribution ◽  
Flow Pattern ◽  
Width Ratio ◽  
Unit Discharge ◽  
Plunge Pool ◽  
Strip Shape ◽  
Pressure Peak ◽  
The Impact ◽  
Discharge Distribution ◽  
Opening Width

In this study, the evolution process of the swallow-tailed flip bucket water nappe entering into the plunge pool is simulated by using the standard k-ε turbulence model and the volume-of-fluid method. The effects of the upstream opening width ratio and downstream bucket angle on the flow pattern, the unit discharge distribution, and the impact pressure distribution are studied. Based on the numerical results, the inner and outer jet trajectories are proposed by using the data. Results show that the longitudinal stretching length decreases with the increase of the upstream opening width ratio and increases with the increase of the downstream bucket angle. The water nappe enters the plunge pool in a long strip shape. Thus, the unit discharge distribution of water nappe entry is consistent with the pressure distribution at the plunge pool bottom. The upstream opening width ratio and downstream bucket angle should be chosen as their intermediate values in order to have a uniform discharge distribution and to reduce the pressure peak at the plunge pool floor, which is effectively to avoid instability and destruction of plunge pool floor.

scholarly journals Effects of bushing profiles on the elastohydrodynamic lubrication performance of the journal bearing under steady operating conditions

2019 ◽  
Vol 20 (2) ◽  
pp. 207 ◽  
Author(s):  
Chongpei Liu ◽  
Bin Zhao ◽  
Wanyou Li ◽  
Xiqun Lu
Keyword(s):  
Journal Bearing ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Parabolic Profile ◽  
Leakage Flow Rate ◽  
Lubrication Performance ◽  
Load Carrying ◽  
Edge Wear ◽  
Flow Rate Change

The bushing profiles have important effects on the performance of journal bearing. In this article, the effects of plain profile, double conical profile, and double parabolic profile on the elastohydrodynamic lubrication of the journal bearing under steady operating conditions are investigated. The journal misalignment and asperity contact between journal and bushing surface are considered, while the modification of the bushing profiles due to running-in is neglected. Finite element method is used for the elastic deformation of bushing surface, while the numerical solution is established by using finite difference method and overrelaxation iterative method. The numerical results reveal that the double parabolic profile with appropriate size can significantly increase the minimum film thickness and reduce the asperity contact pressure and friction, while the maximum film pressure, load-carrying capacity, and leakage flow rate change slightly under steady operating conditions. This study may help to reduce the edge wear and prolong the service life of the journal bearing.

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