Thermal Elastohydrodynamic Lubrication Research Articles

Numerical solution of thermal EHL line contact with bio-based oil as lubricant

ABSTRACT The paper presents the numerical solution of line contact thermal elastohydrodynamic lubrication (EHL) with bio-based lubricant. The model comprises Reynolds equation, film thickness, load balance and energy equations with appropriate boundary conditions by incorporating viscosity–pressure–temperature and density–pressure–temperature relations. Second-order finite difference scheme is used for the discretised form and their equation. The multigrid method with full approximation scheme is used to solve the Reynolds equation along with multilevel multi-integration method for film thickness equation. The pressure, film thickness and temperature distributions for two rolling velocities and various loads with a bio-based lubricant are presented in detail. The present findings yield a reduction in the minimum film thickness for high speed. Details of pressure spike as a function of relevant parameters are given. The results are compared with earlier findings based on different methods.

Effect of bearing materials on journal bearings under TEHL with lubricant based on Carreau model

ABSTRACTThis work presents a transient analysis of journal bearings under thermal elastohydrodynamic lubrication (TEHL) based on the Carreau model. The effects of the elastic modulus of the bearing liner have been investigated using numerical simulations. A time-dependent modified Reynolds equation and an adiabatic energy equation based on the Carreau model have been formulated and numerically solved to examine the performance of the journal bearings. The results show that the minimum film thickness and the friction coefficient both increase with decreasing bearing liner elastic modulus. In contrast, the dimensionless load carrying capacity, dimensionless maximum film temperature, and dimensionless maximum film pressure all decrease with decreasing bearing liner elastic modulus. The stability regions tend to decrease in size for journal bearings under TEHL, especially for journal bearings composed of soft materials.

A Newtonian thermal elastohydrodynamic lubrication model for ferrofluid‐lubricated involute spur gear pair

AbstractAn elastohydrodynamic model of ferrofluid‐lubricated involute spur gears was established, and transient thermal elastohydrodynamic lubrication (EHL) analysis was conducted using multigrid method and multigrid integral method. The transient lubricant film thickness, pressure, and friction coefficient characteristics of the spur gears were compared under different carrier fluid ferrofluids. Ester‐based H01 ferrofluid was selected to further examine the lubricant film elastohydrodynamic characteristics of the involute spur gears under different loads and speeds. The results indicated that the film thickness and the inlet area pressure were the largest when hydrocarbon‐based E02 ferrofluid was used for lubrication and were the smallest when ester‐based ferrofluid H01 was used for lubrication. When ester‐based H01 ferrofluid was used, the film thickness, the inlet area pressure, and the second pressure peak increased with the increase of speed, and the second pressure peak shifted toward the inlet area. The friction coefficient and the maximum temperature gradually decreased with the increase of speed, and the second pressure peak, the friction coefficient, and the maximum temperature gradually increased with the increase of load, while the film thickness gradually decreased.

Tribological and thermal properties of a crowned gear pair with high-speed and heavy-load in thermal micro-elastohydrodynamic lubrication

The oil film stiffness, temperature rise of oil film, flash temperature and frictional loss ratio of a crowned gear pair with non-Newtonian transient thermal elastohydrodynamic lubrication of rough surfaces in high-speed and heavy-load operating conditions are investigated. The pressure, film thickness, coefficient of friction and temperature rise are calculated along the action line of spur gears to verify the validity of full numerical solution. Subsequently, the effects of high-speed, heavy-load and roughness on those tribological and thermal properties of a crowned gear drive are discussed. The results show that in high-speed, heavy-load and rough surface contact, the crown modification is in favor of stability improvement of gear drive due to smoother curve of oil film stiffness. The temperature rise of the oil film and flash temperature on tooth surface are quite high which are prone to result in gear scuffing. Moreover, small flash temperature and frictional loss ratio occur in the domains near the start of active profile and the tip due to the effect of crown modification.

Thermal elastohydrodynamic lubrication characteristics of double involute gears at the graded position of tooth waist

Abstract According to the meshing characteristics of double involute gears, a method for calculating its contact line length and equivalent curvature radius is proposed. Based on the EHL theory, established a thermal EHL calculation model for double involute gears at the graded position of tooth waist considering the characteristics of non-Newtonian fluid. The thermal EHL characteristics between the graded position of the tooth root and top are different. The variation of the tooth waist order parameters can influence the lubrication performance at the graded position of the tooth waist, and compared with the isothermal solutions, the influence of thermal effect on the EHL characteristics is unremarkable at this location.

Thermal elastohydrodynamic lubrication analysis of helical gear pair under starved lubrication condition

AbstractIn the present study, thermal starved elastohydrodynamic lubrication (EHL) model is developed for a helical gear pair. The influences of inlet oil‐supply layer, input speed, lubricant viscosity, and surface roughness on the lubrication behaviour are investigated. The minimum film thickness, temperature rise of teeth surfaces and oil film, and the friction coefficient are predicted along the line of action (LOA). Results show that the effects of inlet oil‐supply layer, input speed, and lubrication viscosity on the tribological performance are remarkable. Under the starved lubrication, the influence of inlet oil supply on the temperature rise is insignificant. Meanwhile, the effect of surface roughness has been discussed. It reveals that the roughness texture along the entrainment velocity direction has significant influence on the lubrication characteristics. The results provide the tribological guidance for design of a helical gear pair in engineering.

Size effect on thermal elastohydrodynamic lubrication of industrial chain bush-pin hinge pair

PurposeThe purpose of this paper is to use elastohydrodynamic lubrication (EHL) theory to study the variation of the equivalent curvature radius “R” on the change of oil film thickness, pressure, temperature rise and friction coefficient in the contact zone between bush-pin in industrial chain drive.Design/methodology/approachIn this paper, the contact between bush and pin is simplified as infinitely long line contact. The lubrication state is studied by numerical simulation using steady-state line contact thermal EHL. The two constitutive equations, namely, Newton fluid and Ree–Eyring fluid are used in the calculations.FindingsIt is found that with the increase of equivalent curvature radius, the thickness of oil film decreases and the temperature rise increases. Under the same condition, the friction coefficient of Newton fluid is higher than that of Ree–Eyring fluid. When the load increases, the oil film thickness decreases, the temperature rise increases and the friction coefficient decreases; and the film thickness increases with the increase of the entraining speed under the condition “R < 1,000 mm”.Research limitations/implicationsThe infinite line contact assumption is only an approximation. For example, the distances between the two inner plates are 5.72 mm, by considering the two parts assembled into the inner plates, the total length of the bush is less than 6 mm. The diameter of the pin and the bore diameter of the bush are 3.28 and 3.33 mm. However, the infinite line contact is also helpful in understanding the general variation of oil film characteristics and provides a reference for the future study of finite line contact of chain problems.Originality/valueThe change of the equivalent radius R on the variation of the oil film in the contact of the bush and the pin in industrial chain drive was investigated. The size effect influences the lubrication characteristic greatly in the bush-pin pair.

Effects of spinning on the mixed thermal elastohydrodynamic lubrication and fatigue life in point contacts

This paper presents a numerical study on the fatigue life for the non-Newtonian mixed thermal elastohydrodynamic lubrication (TEHL) of elliptical contacts with spinning. Sinusoidal surface is used to consider the effect of surface roughness, and the influences of spinning on the mixed TEHL characteristics and fatigue life are investigated. The results show that the temperature, friction coefficient and power loss increase monotonously with the increase of spinning. The spinning motion with moderate velocity is beneficial for improve the lubrication characteristics and fatigue life. However, the fatigue life can be reduced significantly by spinning under severe mixed lubrication conditions. The effects of spinning become weak or even negligible in the full-film lubrication state.

A Thermal Elastohydrodynamic Lubrication Model for Crowned Rollers and Its Application on Apex Seal–Housing Interfaces

This paper presents a thermal elastohydrodynamic lubrication (EHL) model for analyzing crowned roller lubrication performances under the influence of frictional heating. In this thermal EHL model, the Reynolds equation is solved to obtain the film thickness and pressure results while the energy equation and temperature integration equation are evaluated for the temperature rise in the lubricant and at the surfaces. The discrete convolution fast Fourier transform (DC-FFT) method is utilized to calculate the influence coefficients for both the elastic deformation and the temperature integration equations. The influences of the slide-to-roll ratio (SRR), load, crowning radius, and roller length on the roller lubrication and temperature rise are investigated. The results indicate that the thermal effect becomes significant for the cases with high SRRs or heavy loads. The proposed thermal EHL model is used to study the thermal-tribology behavior of an apex seal–housing interface in a rotary engine, and to assist the design of the apex seal crown geometry. A simplified crown design equation is obtained from the analysis results, validated through comparison with the optimal results calculated using the current crowned-roller thermo-EHL (TEHL) model.

Thermal EHL Characteristics Investigation on Axle Box Bearings of Railway Vehicle Based on Slicing Method

Lubrication failures of axle box bearings can lead to accidents, such as bearing burnout and hot axle cutting. Presently, the modeling of the vehicle‐track system dynamics rarely considers the nonlinear contact load of axle box bearings, and this leads to imperfection in the vehicle‐track system dynamics calculation. And then, the load distribution and lubrication characteristics of axle box bearings are difficult to obtain. Therefore, in this paper, we fully consider the time‐varying nonlinear contact load of bearings and track irregularity in establishing the bearing‐wheel‐rail system coupling‐dynamics model. The dynamic response of axle box bearings is obtained by taking the vertical, strong impact‐time‐varying load on the carrying saddles as the external excitation. The load‐balance equation of dynamic pressure lubrication is then obtained, according to the slicing method of bearing rollers. Finally, the elastohydrodynamic lubrication (EHL) model of axle box bearings is established considering thermal and scale effects. The results show that the central film thickness under thermal EHL was decreased by 13.61% compared with that under isothermal EHL. As the velocity of the contact pair increases, the thickness difference between thermal and isothermal EHL became larger. Thermal effects should be considered in the EHL model, in order to truly reflect the characteristics of EHL under a high speed.

Efficient running-in of gears and improved prediction of the tooth flank load carrying capacity

PurposeThe purpose of this paper is to determine parameters for an efficient running-in of gears and an improved method for the prediction of the tooth flank load carrying capacity.Design/methodology/approachIn this contribution, a model for the calculation of the pitting life of involute spur gears is introduced, which is based on an extension of the life model according to Ioannides and Harris for rough surfaces. To achieve the most realistic thermal elastohydrodynamic lubrication simulation and stress calculation possible, measured real surfaces and elastic-plastic material properties of the area close to the surface are used. Special attention is paid to the compatibility of the fatigue life calculation for heterogeneous rough surfaces and their consistent consideration in the lifespan calculation.FindingsA non-destructive running-in for twin-disc pairings can be performed using suitable operating parameters, which subsequently can be transferred to tooth flank tests. Using the extended life model according to Ioannides and Harris, an enhanced prediction of the tooth flank load carrying capacity is possible.Originality/valueThe developed extended life model includes a new numerical approach for calculating the tooth flank load carrying capacity. It has the potential to reliably support and hence to accelerate the design process of gears.

Temperature Estimations in Elastohydrodynamic Contacts of Tribochemical Processes: A Comparative Study Using Modeling by Mechanical/Wear Process Mechanisms and Chemical Kinetic Modeling

Abstract This article deals with the subject of thermal Elastohydrodynamic Lubrication (EHL) and how temperatures can be estimated in elastohydrodynamic contacts. An attempt has been made to explain why it is essential to study temperature effects in EHL, and the process of thermal EHL modeling has been elucidated by solving a simple thermal EHL model. The temperatures obtained from this simple model seem to agree well with published literature. A comprehensive literature review of the numerous studies in thermal EHL modeling with particular emphasis on recent developments in this field has been presented. The second part of this comprehensive study includes a comparison between temperatures in the EHL contact as obtained by mechanical models and a chemical model, which will be discussed. The contact temperature required to consume the lubricant by oxidation during a microsample wear test is determined by a chemical kinetic model. Finally, the discrepancy between the temperatures obtained by both the chemical kinetic model and the mechanical model is discussed, presenting various plausible explanations to account for the temperature difference.

Parametric Studies of Mechanical Power Loss for Helical Gear Pair Using a Thermal Elastohydrodynamic Lubrication Model

In this study, a comprehensive mechanical efficiency model based on the thermal elastohydrodynamic lubrication (TEHL) is developed for a helical gear pair. The tribological performance of the helical gear pair is evaluated in terms of the average film thickness, friction coefficient, mechanical power loss, mechanical efficiency, etc. The influence of basic design parameters, working conditions, thermal effect, and surface roughness are studied under various transmission ratios. Results show that the contribution of thermal effect on the tribological performance is remarkable. Meanwhile, the rolling power loss constitutes an important portion of the total mechanical power loss, especially around the meshing position where the pitch point is located in the middle of contact line and the full elastohydrodynamic lubrication (EHL) state with the friction coefficient less than 0.005. The proper increase of normal pressure angle and number of tooth can improve the tribological performance. The influence of helix angle on the mechanical efficiency is less significant. A positive addendum modification coefficient for pinion and a negative addendum modification coefficient for wheel are good for improving the mechanical efficiency. The results provide the tribological guidance for design of a helical gear pair in engineering.

Thermal elastohydrodynamic lubrication analysis of deep groove ball bearing

PurposeThe purpose of this study is to investigate the thermal elastohydrodynamic lubrication (TEHL) analysis of a deep groove ball bearing.Design/methodology/approachThe TEHL model for the groove ball is first established, into which the elastic deformation is incorporated. In doing so, the elastic deformation is solved with the fast Fourier transform (FFT). And the bearing temperature rise is solved by the point heat source integration method. Then, effects of the applied load, relative velocity and the slide-roll ratio on the TEHL of the bearing are analyzed.FindingsThere exist the large pressure peaks at two edges of the raceway along its width direction and the increment in the relative velocity between the roller and the raceway, or one in the slide-roll ratio arguments the temperature rise.Originality/valueThis study conducts a detailed discussion of the TEHL analysis of deep groove ball bearing and gives a beneficial reference to the design and application of this kind of bearings.

Effects of Texture Orientation on the Mixed Thermal Elastohydrodynamic Lubrication and Fatigue Life in Point Contacts

Predicting the mixed thermal lubrication performance and fatigue life of point contact components becomes more and more important with the increasing demand for the load capacity of machinery. To achieve this, a deterministic mixed thermal elastohydrodynamic lubrication (TEHL) model in point contacts considering surface roughness is developed in this study. This model is capable of determining the pressure and temperature under different lubrication regimes from mixed to full-film lubrication. Then, the established model is extended to the subsurface stress and fatigue life predictions. Numerical simulations are conducted to analyze the lubrication characteristics and fatigue life for the three-dimensional (3D) sinusoidal surfaces with variable directions. Results show that increasing entraining velocity contributes to the reduction of pressure fluctuation and prolongation of fatigue life. However, the resulting temperature increases with the entraining velocity. As for the influence of lubricant viscosity, increasing it prolongs the fatigue life, especially under mixed TEHL conditions. What's more, the effect of rough surface texture feature on fatigue life has a close relationship with the lubrication regime.

Thermal insulation effect on EHL of coated cam/tappet contact during start up

PurposeThis paper aims to investigate the lubrication performance of cam/tappet contact during start up. Especially, the thermal insulation effects of coating on the lubrication performance during cold start up process and warm start up process are studied.Design/methodology/approachA numerical model for the analysis of thermal elastohydrodynamic lubrication of coated cam/tappet contact is presented. In this model, the Reynolds equation and the energy equations are discretized by the finite difference method and solved jointly.FindingsDuring start up, the contact force at cam nose-to-tappet contact decreases with increasing time, while the absolute entrainment velocity has the upward trend. The minimum film thickness, maximum average temperature and friction power loss increase with increasing time, while the coefficient of friction decreases during start up. Because of the thermal insulation effect, the coating can significantly increase the degree of temperature rise. Compared with the uncoated case, the coated cam/tappet results in a lower friction power loss. Generally, the friction power loss in the cold start up process is much higher than that in the warm start up process.Originality/valueBy this study, the lubrication performance and the kinematics and the dynamics of the cam/tappet during start up process are investigated. Meanwhile, the thermal insulation effect of coating is also illustrated. The difference of lubrication performance between cold start up process and warm start up process is analyzed. The results and thermal elastohydrodynamic lubrication method presented in this study can be a guidance in the design of the coated cam/tappet.

Research on the sliding friction associated spur-face gear meshing efficiency based on the loaded tooth contact analysis.

In order to solve the problem of Meshing Efficiency of spur-face gear sliding friction, a method for calculating the Meshing Efficiency of Spur-Face gear is proposed based on Elastohydrodynamic lubrication (EHL) theory. Through the Tooth Contact Analysis (TCA) and Loaded Tooth Contact Analysis technique (LTCA) method, the meshing process of the Spur-Face gear was simulated. The calculation model of Sliding friction coefficient was established by using non Newtonian quasi steady thermal Elastohydrodynamic lubrication (TEHL) theory, and the calculation model of Meshing Efficiency of Spur-Face gear was established. The influence of input torque and rotational speed on Meshing Efficiency is analyzed. The results show that Sliding friction coefficient is an important factor affecting the Meshing Efficiency of gears. Sliding friction coefficient is not the same at different positions of the tooth surface. Sliding friction coefficient is affected by input speed and input torque. This method provides a theoretical basis for further optimization calculation of Spur-Face gear.

Thermal Elastohydrodynamic Lubrication of Ceramic Materials

ABSTRACTThe effect of thermal conductivity on point elastohydrodynamic lubrication (EHL) contacts was discussed with representative engineering ceramics and steel by a non-Newtonian thermal EHL analysis. Through this investigation, fundamentals of EHL characteristics of contact surfaces composed of different thermal conductivities were generally revealed and a combination of optimum ceramic materials has been proposed. Furthermore, when the contacting materials are the same, it has been pointed out that the equivalent elastic modulus should be rather small and the thermal conductivity of the contact material should be high to obtain a thick overall film thickness and low film pressure.

A New Method for Eyring Shear-Thinning Models in Elliptical Contacts Thermal Elastohydrodynamic Lubrication

A new method for solving the shear stress and the effective viscosity of Eyring shear-thinning fluid in thermal elastohydrodynamic lubrication (EHL) was proposed and applied to two models. Model 1 is the thermal EHL model with one-direction velocity, and model 2 is the spinning thermal EHL model in which the velocity varies with coordinates. Comparisons between the new and the existing method were carried out. Results show that only replacing the shear strain rate of model 1 with that of model 2, the shear stress and the effective viscosity of model 2 for Eyring shear-thinning fluid can be obtained. For model 1, results obtained with the two methods are the same. The new method can be qualified and applied into model 2. It is proved that the new method has higher efficiency for shear-thinning fluid than the existing method. Therefore, the new method is more efficient and can be used for spinning Eyring shear-thinning thermal EHL.

Non-Newtonian thermal elastohydrodynamic simulation of helical gears considering modification and misalignment

Abstract Elastohydrodynamic lubrication (EHL) is significant for gear tribology design. This paper introduces a novel non-Newtonian thermal EHL model for helical gears with modifications and misalignments. An asymmetric spherical roller contact model is proposed for the contact between the modified tooth surfaces incorporating misalignments. In conjunction with a load distribution model, the geometric parameters of EHL model are derived from unloaded meshing simulation and kinematic analysis. In addition to a pressure-temperature iteration method, several specific numerical techniques are applied for the severe convergence due to edge contact. The effects of modifications and misalignments on tribological behavior are investigated. Results indicate that the edge contact at both ends of mesh leads to high pressure and temperature, as well as thin film thickness. The double-crowning improves lubrication performance and provides a superior tolerance for misalignments.