Thermo-elastohydrodynamic Lubrication Research Articles

Effect of Solid Particle on Rough Thermo-Elastohydrodynamic Lubrication with Non-Newtonian Lubricant

This paper presents the performance characteristics of rough thermo-elastohydrodynamic lubrication (TEHL) with non-Newtonian liquid–solid lubricant based on a Power law viscosity model. The time independent modified Reynolds equation, elasticity equation and energy 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 and concentration of solid particles are examined. The simulation results showed surface roughness has rapidly effect on film pressure and film temperature. The effect of solid particle can be increases film thickness and decreases friction coefficient.

Thermo Elastohydrodynamic Lubrication with Liquid-Solid Lubricant

This paper presents the performance characteristics of thermo-elastohydrodynamic lubrication (TEHL) in line contact with non-Newtonian liquid–solid lubricant. The time independent Reynolds equation, energy equation, elastic equation and load carrying with solid particle equation were formulated for compressible fluid. Newton-Raphson method and multigrid technique were implemented to obtain film thickness, film pressure, film temperature, friction coefficient and load carrying with solid particle equation in the contact region at various concentrations of solid lubricant and applied loads. The simulation results showed that film thickness and film temperature increase but film pressure decreases when solid particles are added into liquid lubricant. The maximum film temperature and load carrying of solid particle increased but friction coefficient decreased when concentration of solid particle increased. For increasing applied loads, the minimum film thickness decreases but maximum film temperature and friction coefficient increase for all liquid lubricant and liquid-solid lubricants.

Theoretical Investigation of Friction Forces between Vane Tip and Cam-Ring in Oil Vane Pumps

Oil type used for oil vane pumps is an essential element affecting its performance. Trying to understand oil type effect and proper oil type selection will lead to significant enhancement of oil pump performance and increase its life time. In order to accomplish this task, a simple thermo-elasto-hydrodynamic lubrication (TEHL) model was used to calculate the friction forces between vane tip and cam-ring. Effect of oil temperature, vane relative speed, normal vane force, and oil film thickness were theoretically investigated for different oil types. Navier-Stokes and energy equations were numerically solved using finite difference technique. Viscosity and density distributions as a function of oil pressure and temperature were taken into consideration. Results show that proper oil type selection and its operating temperature are key parameters that significantly affecting the vane pump performance. The vane relative speed is quit important parameter affecting the coefficient of friction and should not be less than 5 m/s. increasing of lubricant film thickness is not necessarily enhances the friction coefficient between van tip and cam-ring. The study shows that the best type of oil for vane pump in some operating conditions is not necessarily the best choice for this pump in other operating conditions. It may be helpful for designers to select more than one oil type for the same pump according to its operating conditions.

The Impact of Axial Piston Machines Mechanical Parts Constraint Conditions on The Thermo-Elastohydrodynamic Lubrication Analysis of The Fluid Film Interfaces

The authors analyze the lubricating interfaces of axial piston machines considering thermo-elastohydrodynamic (TEHL) lubrication characteristics. The fluid film geometry in these conditions is strongly influenced by the surface elastic deformation of the solid boundaries. The surface elastic deformations derive from the high dynamic pressures developing in the fluid film, necessary to balance the external oscillating loads. Furthermore, elastic deflections of the fluid film develop from the thermal expansion of the solid bodies, caused by the heat generated due to viscous shear of the fluid film. The accurate determination of the solid boundaries elastic deformation is a key element to predict the fluid film geometry and consequently the lubricating interface performance.When solving for the static elastic deformation of a solid body, constraint conditions must be imposed to avoid rigid body motion. Constraint conditions strongly influence the elastic deformation analysis; therefore their definition must reflect and interpret the mechanical body real conditions. In an axial piston machine all the mechanical bodies defining the fluid film geometry are loosely constrained and significant linear displacements and rotations are intentionally allowed. Hence, the definition of proper constraint conditions for the solid bodies is not a trivial problem and advanced constraint conditions must be considered and implemented.In the fully-coupled numerical models of the lubricating interfaces developed by the research group of the authors, finite element analysis is used to determine the mechanical bodies' elastic deformations. The finite element analysis is coupled with finite volume models of the fluid film, to study the impact of the surface elastic deformations on the interfaces behavior. In this paper, the authors present and discuss the implementation of the inertia relief method on the finite element elastic deformation analysis of the main mechanical parts of an axial piston machine. Inertia relief allows simulating unconstrained structures in a static analysis using their inertia to resist the applied loads. Typical applications of this method include modeling an aircraft in flight, a submarine under water or a satellite in space. The impact of this method on the elastic deformation of the fluid film solid boundary surfaces is shown and compared to standard constraint conditions. In addition, the influence of the inertia relief method on the piston/cylinder interface fluid film behavior is discussed, presenting numerical results for a fully-coupled TEHL simulation over one shaft revolution of a special test pump capable of measuring the piston/cylinder axial viscous friction force. The improved accuracy of the piston/cylinder fully-coupled model including inertia relief effect is presented, comparing simulation results with friction force measurements.

Theoretical Investigation of Transient Lubrication in Spur Gear

This paper presents performance characteristics of transient thermo-elastohydrodynamic lubrication (TEHL) in line contact with Newtonian fluids. The time-dependent modified Reynolds equation, energy equation and elasticity equation with initial conditions were solved numerically using finite different method, Newton-Raphson method and multigrid multilevel method for an involutes spur gear to obtain the film pressure profiles, film thickness profiles, film temperature and friction coefficient in the contact region. In this analysis, the load is applied on either two pairs or one pair of gear teeth. The simulation results show that at approach point, the film thickness is minimized and film temperature rapidly increases. Film temperature and friction coefficient were suddenly increase when the transition from two pairs to one pair and vice versa are modeled as a step variation of load. The friction coefficient and film temperature were occurrence at pitch point. Film temperature and friction coefficient increase but film thickness decreases when applied load increases. For increasing of speeds, film thickness and film temperature increase but friction coefficient decreses.

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.

Transient Thermo-Elastohydrodynamic Lubrication of Rough Surface in Soft Material

This paper presents the effects of transient rough surface thermo-elastohydrodynamic lubrication (TEHL) of rollers for soft material with non-Newtonian fluid base on power law model. The time independent modified Reynolds equation, energy equation and elasticity equation were solved numerically using finite different method, Newton-Raphson method and multigrid multilevel method to obtain the film pressure profiles, film thickness profiles and friction coefficient in the contact region. The simulation results show surface roughness has effect on film thickness but its effect on film temperature is insignificant. The minimum film thickness decreases while the coefficient increases when the amplitude of surface roughness increases. Meanwhile, increasing applied loads causes the friction coefficient to decrease.

Effect of Solid Particle on TEHL under Line Contact with Solid-Liquid Lubricant

The two infinitely long surfaces in line contact under thermoelastohydrodynamic lubrication with solid-liquid lubricants were investigated. The time-dependent modified Reynolds equation elasticity equation and the adiabatic energy equation have been formulated and solved numerically with initial conditions using multi-grid multi-level method with full approximation technique. The characteristics of the two surfaces in line contact under thermoelastohydrodynamic lubrication were presented as; film pressure, film temperature and oil film thickness profiles. The results of solid-liquid lubricants with micro-particle and nano-particle under thermal elastohydrohynamic lubrication were compared with the case of pure liquid lubricant.

Transient mixed thermo-elastohydrodynamic lubrication in multi-speed transmissions

Noise, vibration and harshness (NVH) refinement as well as thermo-mechanical efficiency are the key design attributes of modern compact multi-speed transmissions. Therefore, unlike simple gear pair models, a full transmission model is required for a simultaneous study. The prominent NVH concern is transmission rattle, dominated by the intermittent unintended meshing of several lightly loaded unselected loose gear pairs arising from the system compactness. These gear pairs are subjected to hydrodynamic impacts. The thermo-mechanical efficiency is dominated by the engaged gears, with simultaneous meshing of teeth pairs subject to thermo-elastohydrodynamic regime of lubrication, with often quite thin films, promoting asperity interactions. Therefore, a full transmission model is presented, comprising system dynamics, lubricated contacts, asperity interactions and thermal balance. Generic multi-physics models of this type are a prerequisite for in-depth analysis of transmission efficiency and operational refinement. Hitherto, such an approach has not been reported in literature.

Non‐Newtonian transient thermoelastohydrodynamic lubrication analysis of an involute spur gear

AbstractThe lubrication design of gear is based on the assumption that the lubricant is an ideal Newtonian fluid. In fact, The Ree–Eyring fluid model is more in agreement with the lubricant rheological behaviour under medium or mild duty load. It is necessary for engineering lubrication design to study the non‐Newtonian transient thermal elastohydrodynamic lubrication (EHL) of gear. In the paper, a full numerical solution to the non‐Newtonian transient thermal EHL of gear is obtained by utilising the multi‐grid method, which has strong numerical stability, a quick convergence rate and a high degree of accuracy. Copyright © 2010 John Wiley & Sons, Ltd.

Thermoelastohydrodynamics of grease-lubricated concentrated point contacts

Isothermal and thermoelastohydrodynamic lubrication (TEHL) analyses of grease lubricated bearings are presented. A grease plug flow is formed in the conjunction that, with no shear at the boundaries with the solid surfaces, adheres to them in the region of high pressures under isothermal conditions. The elastohydrodynamic lubrication grease pressure distribution conforms fairly closely to that of its base oil alone, with the exception of inlet trail and pressure spike regions. The dependency of film thickness on speed (rolling viscosity) and load parameters for the base oil agrees with previously reported findings of the research community. For grease there are subtle differences with the base oil film thickness load and speed dependencies. However, it is clear that extrapolated oil film thickness formulae for oils can be used reasonably for the prediction of grease films, at least as a first approximation. The results presented agree well with optical interferometric measurements reported in the literature for grease-lubricated contacts at low temperatures and low surface velocities. TEHL analysis shows breakdown of the plug flow and significant reduction in film thickness, which can lead to changes in the regime of lubrication to mixed or boundary conditions.

Traction in EHL Line Contacts Using Free-Volume Pressure-Viscosity Relationship With Thermal and Shear-Thinning Effects

Abstract This paper investigates the traction behavior in heavily loaded thermo-elastohydrodynamic lubrication (EHL) line contacts using the Doolittle free-volume equation, which closely represents the experimental viscosity-pressure-temperature relationship and has recently gained attention in the field of EHL, along with Tait’s equation of state for compressibility. The well-established Carreau viscosity model has been used to describe the simple shear-thinning encountered in EHL. The simulation results have been used to develop an approximate equation for traction coefficient as a function of operating conditions and material properties. This equation successfully captures the decreasing trend with increasing slide to roll ratio caused by the thermal effect. The traction-slip characteristics are expected to be influenced by the limiting shear stress and pressure dependence of lubricant thermal conductivity, which need to be incorporated in the future.

Steadily loaded journal bearings: Quasi-3D mass–energy-conserving analysis

A finite-element approach to thermoelastohydrodynamic lubrication analysis is developed by extending a previous mass- and energy-conserving algorithm to include wall-convection boundary conditions, groove-mixing theory, and thermo-mechanical deformations. To this end, the cross-film-averaged energy equation is coupled with the heat conduction equations relevant to the bearing sleeve and the journal by fitting the temperature profile across the film thickness with a fourth-order polynomial. A finite-element condensation technique is used to reduce the unknowns in heat conduction equations in the bush and in the journal to the temperatures of the sleeve surface and journal axis, respectively. Applied to the analysis of steadily loaded journal bearings, the proposed method shows good agreement with published experimental results and incurs low computational cost.

Thermoelastohydrodynamic Analysis of Spur Gears with Consideration of Surface Roughness

Thermoelastohydrodynamic lubrication (TEHL) analysis for spur gears with consideration of surface roughness is presented. The model is based on Johnson’s load sharing concept where a portion of load is carried by fluid film and the rest by asperities. The solution algorithm consists of two parts. In the first part, the scaling factors and film thickness with consideration of thermal effect are determined. Then, simplified energy equation is solved to predict the surfaces and film temperature. Once the film temperature is known, the viscosity of the lubricant and therefore friction coefficient are calculated. The predicted results for the friction coefficient based on this algorithm are in agreement with published experimental data as well as those of EHL simulations for rough line contact. First point of contact is the point where the asperities carry a large portion of load and the lubricant has the highest temperature and the lowest thickness. Also, according to experimental investigations, the largest amount of wear in spur gears happens in the first point of contact. Effect of speed on film temperature and friction coefficient has been studied. As speed increases, more heat is generated and therefore film temperature will rise. Film temperature rise will result in reduction of lubricant viscosity and consequently decrease in friction coefficient. Surface roughness effect on friction coefficient is also studied. An increase in surface roughness will increase the asperities interaction and therefore friction coefficient will rise.

Influence of temperature on cam-tappet lubrication in an internal combustion engine

The transient thermo-elastohydrodynamic (TEHL) lubrication simulation and isothermal elastohydrodynamic (EHL) simulation were performed on the exhausting camtappet friction pair of an internal combustion engine. Although by employing the two models the center pressure, the thickness of the lubricant film and friction coefficient obtained were similar in the changing trend during a rotating cycle, the parameters make a great difference, especially for the thickness of the lubricant film; the TEHL was four times thicker than the EHL. These results show that the temperature should not be neglected in the study of the lubrication of cam-tappet pairs.

0735 熱弾性流体潤滑解析によるディーゼルエンジン用コンロッド軸受の研究(S44-2 燃料および潤滑技術(2),S44 燃料および潤滑技術)

In recent automotive engines, the bearing load has been increasing and the housing stiffess has been decreasing. Under these harsh operating conditions, an extreme temperature rise of the bearing is expected to occur in the region where the oil film thin. Consequently, the high temperature rise sometimes causes the bearing to occur damage. Thus, it is necessary to predict accurately the bearing performance in the design stage. A thermo-elastohydrodynamic lubrication (TEHL) analysis can predict reliably bearing performance. In order to clarify the validity of a theoretical TEHL model, a test was conducted on an actual diesel engine.

Theoretical Investigation in Thermoelastohydrodynamic Lubrication With Non-Newtonian Lubricants Under Sudden Load Change

The time-dependent thermal compressible elastohydrodynamic lubrication of a sliding line contact has been developed to investigate the effect of a sudden load change. The time-dependent modified Reynolds equation with non-Newtonian fluids has been formulated using a power law model. Properties of non-Newtonian dilatant fluids for solid-liquid lubricants have been studied experimentally using two common solid particles; namely, molybdenum disulfide and polytetrafluoroethylene. The simultaneous systems of modified Reynolds, elasticity, and energy equations with initial conditions were solved numerically using a multigrid multilevel technique. The performance characteristics of the thermoelastohydrodynamic line contact were presented with varying dimensionless time for the pressure distribution, temperature distribution, and oil film thickness. The transient response of the line contact between two infinitely long cylindrical surfaces was simulated under a heavy step load function. The coefficients of friction were also presented in this work at steady condition with varying particle concentration. This simulation showed a significant effect of solid particles on thermoelastohydrodynamic lubrication under heavy load conditions.

A New Model of Thermoelastohydrodynamic Lubrication in Dynamically Loaded Journal Bearings

Abstract A comprehensive method of thermoelastohydrodynamic (TEHD) lubrication analysis for dynamically loaded journal bearings is presented. An algorithm for mass conserving cavitation is included, and the effect of viscosity variation with the temperature is taken into account. The Reynolds equation in the film is solved using the finite element (FE) discretization. Thermal distortions as well as the elastic deformation of the bearing surfaces are computed using the FE method. The temperature of the lubrication film is treated as a time-dependent three-dimensional variable with a parabolic variation with respect to the film thickness. In order to compute the temperature of the film and its surrounding solid surfaces, a new heat flux conservation algorithm is proposed. An important element in this analysis is the consideration of thermal boundary layers for solids. It is known that the thermal transients on the film-solid interfaces and the dynamic loading have the same period (one cycle). However, beyond the thermal boundary layers, the time scale for thermal transient in the journal and bushing are several orders of magnitude greater than those for the oil film. The Fourier series approximates the instantaneous temperature fields in the solid boundary layers. In this way, the mean heat flux that passes into the solid can be computed and a steady-state heat conduction equation can be used to obtain thermal fields inside the solids. Finally, solving the complex problem of big-end connecting-rod bearing TEHD lubrication proves the efficiency of the algorithm. Oil film temperatures are found to vary considerably over the time and space.

Numerical analysis of lubrication in a journal bearing by a thermoelastohydrodynamic lubrication (TEHL) model

AbstractIn recent years, in high power, compact, and light weight automotive engines, the bearing load has been increasing and the housing stiffness has been decreasing. The engine bearing performance is significantly influenced by both an elastic deformation and an increase in temperature. Under these harsh operating conditions, an extreme temperature rise of the bearing is expected to occur in the thin oil-film region when the oil-film thickness is not kept thick enough within the bearing. Consequently, the high-temperature rise sometimes causes the bearing to have a seizure. Thus, it is necessary to predict accurately the bearing performance in a design stage. A thermoelastohydrodynamic lubrication (TEHL) analysis could theoretically predict the bearing performance under these harsh conditions with high reliability. In order to clarify the validity of the theoretical TEHL model, a rig test was conducted under dynamic load conditions. The test conditions simulated the connecting rod bearings in real aut...

Numerical analysis of lubrication in a journal bearing by a thermoelastohydrodynamic lubrication (TEHL) model

Numerical analysis of lubrication in a journal bearing by a thermoelastohydrodynamic lubrication (TEHL) model