Minimum Oil Film Thickness Research Articles

Inspection of Hydrodynamic Lubrication in Infinitely Long Journal Bearing with Oscillating Journal Velocity

Unsteady transient analysis is carried out for hydro-dynamically lubricated journal bearing with infinitely long approximation. The performance characteristics are investigated by oscillating the journal velocity as a ‘sine’ function of the angle for which the journal rotates with an angular speed. Results comprising of Minimum lubricant film thickness, Dynamic pressure and load, Wall shear stress, Eccentricity, Temperature distribution and heat flux with respect to time are presented in the analysis graphically with the aid of ORIGION PRO 8. The journal bearing is analyzed in ANSYS 14.0 ‘Transient Thermal’ package. The journal is modeled as a “moving wall” with an absolute rotational speed of 3000 rpm. Appropriate equations and numerical solutions (Simpson’s 1/3rd integration rule and Newton-Raphson method) are developed using ‘C programming’ for solving the Reynolds compressible differential equation. The numerical procedure is fully automated and the scheme converges rapidly. Design parameters are included in the computation taking into account turbulence and gravity. After carrying out all the above discussed scrutiny, it was observed that minimum oil film thickness is a function of oscillating velocity, pressure is inversely proportional to the minimum oil film thickness, and eccentricity and wall shear stress are also a function of the oscillating journal velocity. While the value of coefficient of friction and coefficient of friction variable are found to be maximum at the maximum velocity, thus leading to its dependency on the oscillating journal velocity. Also, variation of temperature distribution and heat flux with respect to time leads to converging of the results. Validating McKee’s investigation leads to completion of the venture

On the running-in behavior of rough surface of piston rings in mixed lubrication regime

Purpose – The purpose of this paper is to study the real-time change of surface roughness at different small regions of piston rings during running-in process. Meanwhile, the effects of real-time change of the rough surface topography on the lubrication and friction of piston rings are investigated. Design/methodology/approach – An uneven wear model has been developed to research the running-in behavior at the different small regions of piston rings. The model is verified by comparing the simulation results with the experimental results on a reciprocating friction and wear test rig. Findings – This research shows that the wear process of piston ring surface is uneven during running-in. At most time of the operating cycle except the vicinity of top dead center and bottom dead center, the minimum oil film thickness ratio increases while the friction force and power loss decrease after the running-in period. Originality/value – Through this research, the running-in behavior of piston rings is investigated in detail. The interaction between the running-in and the lubrication and friction of piston rings is understood more deeply.

Analysis of piston-pin lubrication considering the effects of structure deformation and cavitation

Running conditions for piston pin boss bearing have become very severe due to the high combustion pressure and piston temperature increase over the past ten years. The aim of this paper was to analyze the friction and lubrication characteristic of piston pin boss bearings and a connecting rod small end bearing. This paper provided a comprehensive analysis of piston pin based on a multi-body dynamic model which considers the oil film cavitation and structure deformation. Effects of different lubrication models, pin structures, and thermal deformation on the lubrication were discussed. The lubrication characteristics and performance parameters including oil film pressure distribution, asperity contact pressure, the minimum oil film thickness, the maximum oil film pressure, and friction power loss were listed. The results showed that the minimum oil film thickness was very different and the maximum oil film pressure was nearly the same. A parabola profile of pin bore can reduce the wear to some extent, and a flare profile intensified wear in some places and caused the wear to be concentrated on a smaller area. Reducing the inner diameters will reduce the wear of the pin boss. However, in a realistic design of the pin, avoiding high inertial force of the piston system and satisfying the demand for reliability of the pin, increasing the inner diameters and reliability is a ‘trade off’ problem. A suitable design of the hollow diameter is very important. The results can provide guidance for the design of the pin boss bearing.

Analysis of thermoelastohydrodynamic performance of journal misaligned engine main bearings

To understand the engine main bearings’ working condition is important in order to improve the performance of engine. However, thermal effects and thermal effect deformations of engine main bearings are rarely considered simultaneously in most studies. A typical finite element model is selected and the effect of thermoelastohydrodynamic(TEHD) reaction on engine main bearings is investigated. The calculated method of main bearing’s thermal hydrodynamic reaction and journal misalignment effect is finite difference method, and its deformation reaction is calculated by using finite element method. The oil film pressure is solved numerically with Reynolds boundary conditions when various bearing characteristics are calculated. The whole model considers a temperature-pressure-viscosity relationship for the lubricant, surface roughness effect, and also an angular misalignment between the journal and the bearing. Numerical simulations of operation of a typical I6 diesel engine main bearing is conducted and importance of several contributing factors in mixed lubrication is discussed. The performance characteristics of journal misaligned main bearings under elastohydrodynamic(EHD) and TEHD loads of an I6 diesel engine are received, and then the journal center orbit movement, minimum oil film thickness and maximum oil film pressure of main bearings are estimated over a wide range of engine operation. The model is verified through the comparison with other present models. The TEHD performance of engine main bearings with various effects under the influences of journal misalignment is revealed, this is helpful to understand EHD and TEHD effect of misaligned engine main bearings.

Relationship between Supplied Oil Flow Rates and Oil Film Thicknesses under Starved Elastohydrodynamic Lubrication

Many studies have already considered starved lubrication. However, there have been no reports on the oil film thicknesses under steady starved EHL (elastohydrodynamic lubrication), where the ultra-low volume of oil supplied per unit time is uniform. The present study examined the relationship between the supplied oil flow rate and oil film thickness under steady starved lubrication. A ball-on-disk testing machine was used in experiments to measure the oil film thickness by means of optical interferometry. A microsyringe pump was used to accurately control the supplied oil flow rate. The supplied oil flow rate was kept constant, and the minimum oil film thickness was measured for 1 h after the start of the tests to determine the relationship between the supplied oil flow rate and oil film thickness.

Research on the Static and Dynamic Characteristics of Misaligned Journal Bearing Considering the Turbulent and Thermohydrodynamic Effects

Journal misalignment usually exists in journal bearings that affect nearly all the bearings static and dynamic characteristics including minimum oil film thickness, maximum oil film pressure, maximum oil film temperature, oil film stiffness, and damping. The main point in this study is to provide a comprehensive analysis on the oil film pressure, oil film temperature, oil film thickness, load-carrying capacity, oil film stiffness, and damping of journal bearing with different misalignment ratios and appropriately considering the turbulent and thermo effects based on solving the generalized Reynolds equation and energy equation. The results indicate that the oil thermo effects have a significant effect on the lubrication of misaligned journal bearings under large eccentricity ratio. The turbulent will obviously affect the lubrication of misaligned journal bearings when the eccentricity or misalignment ratio is large. In the present design of the journal bearing, the load and speed become higher and higher, and the eccentricity and misalignment ratio are usually large in the operating conditions. Therefore, it is necessary to take the effects of journal misalignment, turbulent, and thermal effect into account in the design and analysis of journal bearings.

An EHD-mixed lubrication analysis of main bearings for diesel engine based on coupling between flexible whole engine block and crankshaft

Purpose – The purpose of this paper is to develop a good calculation model to accurately predict the lubrication characteristic of main bearings of diesel engine and improve the service life. Design/methodology/approach – Based on the coupling of the whole flexible engine block and the flexible crankshaft reduced by the Component Mode Synthesis (CMS) method, considering mass-conserving boundary conditions, the average flow model equation and Greenwood/Tripp asperity contact theory, an elastohydrodynamic (EHD)-mixed lubrication model of the main bearings for the diesel engine is developed and researched with the finite volume method and the finite element method. Findings – Obviously, the mixed lubrication of bearings is normal, while full hydrodynamic lubrication is transient. The results show that under the whole flexible block model, maximum oil film pressure, maximum asperity contact pressure and radial shell deformation decrease, while minimum oil film thickness increases. Oil flow over edge decreases, and so does friction loss. Therefore, coordination deformation ability of whole engine block is favorable to mean load. In the whole block model, friction contact happens on both upper shell and lower shell positions. In addition, average oil film fill ratio at the key position becomes smaller in the whole engine block model, and consequently increases the chances of cavitations erosion more. So, wearing resistance of both upper and lower shells and anti-cavitations erosion ability must be enhanced simultaneously. Originality/value – Based on the coupling of the whole flexible engine block and the flexible crankshaft reduced by the CMS method, considering mass-conserving boundary conditions, the average flow model equation and Greenwood/Tripp asperity contact theory, an EHD-mixed lubrication model of the main bearings for the diesel engine is built, which can predict the lubrication of journal bearings more accurately.

The Effect of Elastic Deformation on the Load-Carrying Capacity of Textured Sliding Surfaces

In order to study the differences in load-carrying capacity of surface-textured soft materials and stiff materials, a theoretical hydrodynamic model considering elastic deformation is developed for numerical simulation analysis. Minimum oil film thickness at a certain load is computed as an index to evaluate the load-carrying capacity of textured sliding surfaces made of soft materials and stiff materials. The results show that the elastic modulus affects greatly on the load-carrying capacity. In the case of the surface texture with a dimple aspect of 0.05, textured soft materials has a higher load-carrying capacity than that of the stiff materials. In the case of the surface texture with a dimple aspect of 0.01 and only under high loads, textured stiff materials provides a better load-carrying capacity than that of the soft materials.

Tribilogical performances of connecting rod and by using orthogonal experiment, regression method and response surface methodology

Dynamic lubrication analysis of connecting rod is a very complex problem. Some factors have great effect on lubrication, such as clearance, oil viscosity, oil supplying hole, bearing elastic modulus, surface roughness, oil supplying pressure and engine speed and bearing width. In this paper, ten indexes are used as the input parameters to evaluate the bearing performances: minimum oil film thickness (MOFT), friction loss, the maximum oil film pressure (MOFP) and average of the oil leakages (OLK). Two orthogonal experiments are combined to identify the factors dominating the bearing behavior. The stepwise regression is used to establish the regression model without insignificant variables, and two most important variables are used as the input to carry out the surface response analysis for each model. At last, the support vector machine (SVM) is used to identify the asperity contact. Compared with SVM model, the particle swarm optimization-support vector machines (PSO–SVM) can predict the asperity contact more precise, especially to the samples near dividing line. In future work, more soft computing methods with statistical characteristic are used to the tribology analyses.

歯面の摩擦力を考慮した動力伝達用歯車のマイクロピッチング発生機構の検証

To reduce weight and improve efficiency of the power transmission, the gears must be miniaturized and lubricant viscosity must be lower. However, these changes will bring about augment of contact pressure and severe lubricating condition. These conditions might occur micro pitting. Accordingly, designing method for micro pitting is required to reduce weight and improve efficiency of the transmission. For designing micro pitting, the calculated flash temperature is used. On the other hand according to ISO/TR, micro pitting can be designed using ratio of sum of arithmetic average roughness and elastic hydraulic lubrication (EHL) minimum oil film thickness. However, in the designing method using flash temperature, it cannot take into account surface roughness and EHL oil film thickness. And if using designing method shown ISO/TR, the limit of each gear has to be measured. So, new theory about gear surface failure was focused. This theory says that false mode of the gear tooth surface is influenced by the frictional force. Based on this theory coefficient of friction was calculated using Matsumoto's formulae and frictional force was compared with micro pitting pattern on gear tooth surface. Results obtained are shown as follows. (1) The pattern of the area micro pitting was occurred is corresponded with the pattern of the area calculated frictional force is higher. (2) The result shown (1) gives that the occurrence of micro pitting has correlation with the frictional force on the tooth surface. (3) The reason why micro pitting is not necessarily grown into pitting is expected that caused load distribution change due to wear of tooth surface.

Analysis of hydrodynamic loads on performance characteristics of engine main bearings

This article aims to present a numerical study of the behavior of engine main bearings under dynamic load. The coupling performance characteristics of oil film between crankshaft and engine block are analyzed. The film pressure is solved numerically with Reynolds boundary conditions when various bearing characteristics are calculated. Hydrodynamic lubrication is analyzed with finite difference method for solving the Reynolds equation for thermo effect. The other models, such as engine block and crankshaft-connecting rod system, are processed by utilizing the finite element method. Above this system, model applied in this paper is simulated by employing multi-body dynamic method to capture the dynamic characteristics of engine dynamic simulation. Through the methods mentioned above, the performance characteristics of engine main bearings under hydrodynamic loads in a six-cylinder in-line diesel engine were received. And the orbit movement, minimum oil film thickness, and power loss in the bearing were estimated over the wide range of engine operation.

Numerical Study of Thermohydrodynamic Characteristics of Oil Tilting-Pad Journal Bearings with a Self-Pumping Fluid Flow Circulation

A thermohydrodynamic numerical code is developed for analyzing the steadily loaded finite tilting-pad journal bearings for vertical hydropower plants. The Reynolds equation and the two-dimensional energy equation in fluid film lubrication are solved by the central difference technique with a successive overrelaxation scheme and the backward difference with an iterative technique, respectively. In the simulation, the lubricant viscosity is changed with the temperature variation (in both axial and sliding directions) and the pad deformation is brought up in calculations. Oil circulation is considered as a self-pumping fluid flow through pad side leakage via a circumferential groove. Self-lubricating approach is guaranteed the oil cooling procedure and bearing performance in hydropower plants. The effects of pad number, preload factor, pivot position, and shaft rotational speed on the bearing performance are illustrated. Power friction loss, maximum oil film temperature, circulated oil fluid flow, minimum oil film thickness, and pad tilting angle are the most important results.

Mixed Lubrication and Friction Power Loss of Piston Ring Pack

With consideration of asperity contact, the minimum oil film thickness and friction power loss are calculated by simultaneous solution of the dynamics, blow-by and lubrication of piston ring pack. Take the piston ring pack in the first cylinder from the free end of a six-cylinder diesel engine for example, results show that the asperity contact takes place at all of the compression rings and oil ring; the minimum oil film thickness is 1.04μm at the top ring; the total friction loss power is 0.94kW, the top ring accounts for 37.2%, the second ring accounts for 33.0%, the oil ring accounts for 29.8%.

Parameter variation and data mining of oil-film bearings: a stochastic study on the Reynolds’s equation of lubrication

The modeling and simulation process of oil-film bearing dynamics constitutes a rather essential task integrated in the workflow of various mechanical products. Specifically, in the turbo charger industry, the correct capture and understanding of the associated nonlinear rotating dynamics is of utmost importance, since the system’s efficiency and lifetime span depends on it. The root cause of the nonlinear rotordynamic effects is the oil-film concentrated in the rotor’s journal bearings. Its behavior is highly coupled with both the system’s geometric and dynamic configuration. The dynamics of the oil-film are described by the well-known Navier–Stokes equation, which under a series of assumptions and simplifications results to the, so-called, Reynolds equation. In this paper, the Reynolds equation is numerically solved based on a finite difference scheme and several parameter variation studies are conducted in an effort to pinpoint the most influential parameters—journal bearing geometric dimensions, oil-film properties and rotor-velocity-driven inputs—with respect to designated responses—friction, oil-film pressure force, minimum oil-film thickness and boundary oil-flow—all of which are regarded as important in terms of the aforementioned system’s efficiency and lifetime span. Based on multivariate analysis algorithms, correlation outcomes and global sensitivity results are presented. In an effort to capture possible nonlinear phenomena, which might not be possible via linear data mining tools, the Spearman rank-order coefficient and self-organizing maps methodology are applied.

Influence of carbon black in engine oil on wear of H-free diamond-like carbon coatings

Wear tests were conducted on hydrogen-free DLC coatings lubricated with engine oil containing carbon black (CB) in order to clarify their wear resistance. The influence of CB on accelerating wear was noticeable in the region where the minimum oil film thickness was less than the averaged secondary particle diameter of CB aggregates. According to a Raman spectroscopic analysis, the amount of DLC coating wear when lubricated in oil without CB tended to increase with increasing oil temperature and with an increasing Id/Ig ratio in the coating surface layer. In contrast, the Id/Ig ratio of the DLC coatings tested in oil containing CB tended to decrease, though the amount of DLC coating wear increased, which indicated a different wear mechanism.

Swing Characteristic of Pads in Four-pad Tilting Pad Bearing

The swing characteristic of pads on four-pad tilting pad bearing is studied systematically with the guide bearing for helim circulator in fourth generation nuclear power units HTR as object. Theoretical derivation reveals that dimensionless pad pendulum angle depends on structural parameters, preload and eccentricity, but independent of viscosity of lubrication oil film, shaft rotating speed and clearance. Numerical analysis shows that: pad pendulum angle is determined by pad circumferential position relative to the load, preload and eccentricity. When the structural parameters of tilting pad bearing are constant, pendulum angle curve of pad facing the load was depend on preload, its pendulum angle increases first and then decreases with the eccentricity ratio increase while the preload less than 0.5, when the preload is greater than 0.5 its pendulum angle decreases gradually with the eccentricity ratio increase; pendulum angle curve of pad side of the load increases or decreases with the eccentricity ratio increase when the preload is smaller, and remains constant first and then decreases with the eccentricity ratio increase when the preload is greater. Pad pendulum angle has great influence on minimum oil film thickness; its value maybe negative thus leads to the minimum oil film thickness greater than fixed pad. The study results provides basis for safety operation analysis of the helim circulator.

Numerical Analysis of High Power Marine Diesel Engine Main Bearing Load and Lubricating Properties

The main bearing is one of the primary friction pairs of a diesel engine. The lubrication condition affects the performance of the marine diesel engine directly. Continuous working time of main bearings is longer, load is higher and working condition is even worse especially in low medium speed marine diesel engine, making it difficult to form good dynamic pressure lubrication.Therefore, this paper takes a high-power marine diesel G32 with 9 cylinders as an example, calculates and analyzes the load, the orbit of main shaft center and the minimum thickness of oil film in each main bearing, providing the basis to estimate each main bearing’s lubricating condition, predicting each main bearing’s performance precisely and judging whether there exists abnormal working conditions in each main bearing.

Study on thermoelastohydrodynamic performance of bearing with surface roughness considering shaft deformation under load in shaft‐bearing system

PurposeCurrent lubrication analyses of misaligned journal bearings are generally performed under some given preconditions. The purpose of this paper is to calculate the lubrication characteristics of a journal bearing with journal misalignment caused by shaft deformation under load, considering the surface roughness, thermal effect and (thermal and elastic) deformation of bearing surface simultaneously.Design/methodology/approachThe lubrication of bearing was analyzed by average flow model based generalized Reynolds equation. The deformation of bearing surface under pressure or heat of oil film was calculated by compliance matrix method. The compliance matrix was established by finite element analysis. The temperature distributions of oil film and bearing were calculated by energy equation and heat conduction equation.FindingsWhen the thermal deformation of bearing and journal surface is considered, the radius clearance affects not only the value of the maximum oil film pressure and minimum oil film thickness, but also the distribution of oil film pressure and thickness of misaligned bearing. The effect of thermal deformation of bearing on the performance of misaligned bearing is larger than that of elastic deformation of bearing. Whether or not the surface roughness affects the performance of misaligned bearing and the affecting level depends greatly on the condition of deformation of bearing surface.Originality/valueThe surface roughness, thermal effect and (thermal and elastic) deformation of bearing surface were considered simultaneously in the thermoelastohydrodynamic lubrication analysis of bearing with journal misalignment caused by shaft deformation under load. The results of this paper are helpful to the design of the bearing.

Numerical Analysis and Study of Crankshaft System Hydrodynamic Lubrication and Dynamic Coupling System

Using finite element method and multi-body dynamics method, this study established an engine digitalized virtual prototype embraced tribological characteristics in virtual prototype and MATLAB platform, and introduced Elastohydrodynamics theory into the system, wrote program with difference equation method, and solved the Reynolds Equation through shafting-bearing self-feedback control system, obtained the crankshaft main bearing reaction force which considered the system's oil film dynamic lubricating friction behaviour, and also obtained data of main bearing's load capacity, path of axle center and the minimum thickness of oil film. Though analysis, it is found that engine crankshaft system's oil film dynamic lubricating friction has certain impact on system's dynamic characteristics, where using hydrodynamic lubrication coupling multi-body dynamic system for simulation could better reflect the engine's actual working conditions, therefore the oil film dynamic lubricating friction behaviour of the system should be considered in dynamic simulation calculations.

Effect of Design Parameters on the Reduction of Top Piston Ring Friction

In order to reduce ring-liner interface friction power loss, this paper focuses on the structure parameters of the top ring, and investigates how the value of those parameters will influence top ring-liner friction power loss and the minimum thickness of oil film at top ring-liner interface. A mixed lubrication model is developed to simulate the effect of varying design parameters on ring-liner friction. Case study shows that ring-liner friction power loss will be reduced with decreased axial ring height and barrel height. This study provides a theoretical basis for design the top ring with reduced friction power loss at ring-liner interface.