Elastohydrodynamic Lubrication Analysis Research Articles

Effect of Thermal Conductivity on Maximum Film Pressure in Point EHL Contact of Ceramics with Transverse Surface Roughness

Abstract Based on a fully flooded non-Newtonian transient thermal elastohydrodynamic lubrication analysis of representative engineering ceramics and a steel with different thermal conductivities and different surface roughness, it is clarified that material combinations leading to a reduction in the maximum film pressure can be found using the thermal conductivities of the contacting materials and the smooth surface temperatures of the same contacting materials. The results will make a significant contribution to the design of machine elements involving contact between materials of different thermal conductivity and surface roughness.

Analysis of isothermal elastohydrodynamic lubrication on the rough surface of a new type of trident universal joint

Analysis of isothermal elastohydrodynamic lubrication on the rough surface of a new type of trident universal joint

Implementation of a New Smart-Lubricant Model Using Generalized Newtonian Approach in Soft Elastohydrodynamic Lubrication

Abstract This is an inceptive attempt to replace the classical Bingham fluid model with a continuous double Newtonian power-law-based constitutive equation for smart lubricants like magneto-rheological, electro-rheological, and ferro-fluids. The implementation of Bingham model in hydrodynamic (HD) and elastohydrodynamic (EHD) lubrication analyses is highly challenging and inconvenient due to its inherent discontinuity. Therefore, the present work demonstrates the use of an already existing rheological model with an appropriate set of parameters to describe the flow behavior of smart lubricants in a soft-EHD lubrication algorithm based on the generalized Newtonian approach. The formation of both floating and adherent cores validates the proposed model. An extensive parametric study is also performed to explore the effects of operating speed, load, and slide-to-roll ratio on the soft-EHL characteristics. The results are very promising, showing that it's possible to customize smart lubricants to match specific operating conditions. This is achieved by adjusting the yield stress value accordingly, allowing for the desired variation in lubrication characteristics.

Modeling and analysis of elastohydrodynamic lubrication of orthogonal face gear with installation errors

Installation error is one of the most prominent factors affecting the lubrication of face gear. To analyze the lubrication performance of the face gear with installation errors, the installation error model of the orthogonal face gear transmission system is established. Then, the contact path, equivalent curvature radius, load distribution and entrainment velocity are studied using the face gear loaded tooth contact analysis (LTCA). On this basis, the lubrication governing equations of the face gear are established according to the elastohydrodynamic lubrication (EHL) theory. In addition, the oil film thickness, oil film pressure and coefficient of friction in the process of face gear drives are calculated using the method of progressive mesh densification (PMD). Finally, the effects of axis intersection angle error, axis intersection error and axial displacement error on lubrication characteristics are analyzed. The results reveal that when the axial intersection angle error and axial displacement error are negative and the axial intersection error is positive, the minimum oil film thickness of the face gear tooth surface is less than that without error. When the error values are the same, the minimum oil film thickness and coefficient of friction have larger changes with the axial displacement error than with the axis intersection error, and the contact path has a bigger movement range.

Thermal mixed elastohydrodynamic lubrication modeling and analysis of the lubricated non-conformal contacts with non-Gaussian surface roughness and coating

The lubricated non-conformal contact generally works under the mixed-EHL regime. Optimizing the surface topography or selecting the right coating is an effective way to improve its performance. This paper presented an improved mixed-TEHL model for the lubricated non-conformal contacts with the effects of roughness and coating in consideration. The effect of coating was solved analytically by employing the Papkovich–Neuber potentials. It was found that the properties of coatings, especially their elastic modulus, significantly affect the pressure and stress distribution. In comparison to other roughness parameters, standard deviation and kurtosis have a significant impact. As expected, the present model can provide an efficient analysis of the tribological behavior and the stress distribution of the lubricated non-conformal contacts.

Tribological Analysis of Steels in Fuel Environments: Impact of Alloy Content and Hardness

The performance and durability of high-pressure fuel systems in combustion engines are critical for consistent operation under extreme conditions. High-pressure fuel systems are traditionally lubricated with fuel that is compressed and delivered to the combustion chamber. However, lubrication with fuel presents significant challenges in these systems when used with low-viscosity fuels, leading to increased wear rates, especially in reciprocating contacts. This study delved into the tribological performance of steels of varying alloy content (annealed and hardened variants of AISI-52100, CF2, and D2) against alumina and hard 52100 counterbody materials in ethanol and decane environments. Friction and wear behaviors were evaluated, highlighting the influence of material interactions and environmental factors. Elastohydrodynamic lubrication analysis of the tested systems indicated that ethanol and decane form lubricating films of nanometer-scale thickness, confirming the boundary lubrication regimes of the performed tests. In summary, the tribological behavior trends were similar for alumina and 52100 counterbodies. Even though soft 52100 steel demonstrated low friction, its wear was the largest for both tested environments and counterface materials. Among all the tested materials, hard D2 experienced the lowest wear. 52100 and D2 steels showed opposite friction change behavior when comparing hard and soft samples, with lower friction observed for softer 52100 steel and harder D2 steel. Meanwhile, the wear was lower for harder candidates than for softer ones independent of the environment and counterbody material. Raman spectroscopy analysis of the formed wear tracks indicated the formation of carbon films with larger intensities of characteristic carbon peaks observed for more wear-resistant materials. These results suggest the synergistic effect of hardness and tribochemical activity in reducing the wear of materials.

Elastohydrodynamic lubrication analysis with eccentric errors for planetary roller screw mechanism

The lubrication characteristics of planetary roller screw mechanism (PRSM) with eccentric errors are investigated in this work. And the formulas of entrainment velocities with eccentric errors are derived. The film thickness and pressure distributions of screw-roller (SR) and nut-roller (NR) thread pairs are analyzed. It finds that the film thickness of SR thread pair is larger than that of NR thread pair. Moreover, the effects of eccentric errors on comprehensive meshing radius, entrainment velocities and lubrication characteristics of SR and NR thread pairs are discussed. The results show that the eccentric errors have significant effects on lubrication characteristics of PRSM.

Thermal elastohydrodynamic lubrication analysis of the oil film temperature in tapered roller bearings

Tapered roller bearings often experience thermal deformation and stress concentration due to high temperature during prolonged operation. However, the traditional model for calculating bearing heat does not consider the thermal elastohydrodynamic behavior of the lubricant. To address this issue, this paper proposes a finite line contact model based on thermal elastohydrodynamic lubrication analysis for calculating the temperature distribution of the lubricant within tapered roller bearings. The temperature of the lubricant is solved using the column-by-column technique. The results show that the temperature distributions along the thickness of the oil film are symmetrical, with the highest temperature occurring at the middle layer. Furthermore, the temperature at the middle layer increases with both the bearing speed and the concentrated load. These findings provide a theoretical framework for calculating the temperature distribution of lubricated bearings, offering valuable insights for practical applications.

Thermoelastohydrodynamic Mixed Lubrication of Combined Rod Seals Operating at High Pressures and Speeds: Mathematical Modeling and Numerical Analysis

Abstract Thermoelastohydrodynamic (TEHD) mixed lubrication characteristics of a step-combined rod seal under high-pressure and high-speed conditions are analyzed in this article. A novel TEHD mixed lubrication model for combined rod seals is innovatively established from the perspective of “seal-film-rod” system for the first time. Parameterized studies are conducted to evaluate the thermal effect on seal behavior with the comparison of isothermal elastohydrodynamic (EHD) lubrication analysis. Numerical results show that the interface friction heat is quite remarkable and mainly concentrated on the sealing lip, especially in high pressure and speed cases. With the increasing sealed pressure or rod speed, the temperature rise becomes more obvious and has a more significant impact on the sealing performance. The excessively rising temperature will even exceed the melting point of the sealing material, causing thermal damage.

Elastohydrodynamic Rotational Lubrication Analysis on the Multi-Body Dynamic Properties of Journal-Bearing Systems

This research aims to investigate the properties of elastohydrodynamic rotational lubrication analysis on journal-bearing systems. To simulate elastohydrodynamic lubrication on journal-bearing systems, the Elasto-Hydro-Dynamic (EHD) solver is combined with the Multi-Body Dynamic (MBD) solver to create MBD virtual environment with lubricant. The hydrodynamic lubricant is governed by using the Reynolds equation, whereas the elastic contact is governed using Greenwood and Tripp theories. The simulation is performed by changing the operating conditions such as the speed, load, and clearance between two surfaces. One can find these parameters’ effects such as film thickness, hydrodynamic pressure, and friction. The result shows that the friction induced by shaft speed is similar to the Stribeck curve on mixed lubrication regime. Consequently, the clearance, speed, and load will not only affect the friction but also affect the hydrodynamic pressure and film thickness.

Lubrication Performance of Misaligned Journal Bearings with Flexible Structure under Shock Load Conditions

Bearings might be damaged due to shock loads caused by disturbances, in addition to static loads. In this study, a flexible structure was applied to enhance the lubrication characteristics of misaligned journal bearings subjected to impact loads. When an impact load is added to the bearing, a misaligned journal bearing has a high possibility of metal-to-metal contact. It might also lead to failure. Misalignment can occur at any time during bearing operation. A flexible structure is applied to the end of the bearing as a way to improve lubrication performance in a system where impact loads might be applied. The bearing’s lubrication performance was numerically assessed under unsteady-state conditions. An elastohydrodynamic lubrication analysis was conducted, taking into account elastic deformation. The lubrication characteristics of misaligned journal bearings were compared with the dimensionless minimum film thickness. The flexible structure and elastic modulus of the bearing were investigated so that it could support the load without contact according to the change in the maximum magnitude of the impact load. When subjected to oil film pressure, this flexible structure underwent elastic deformation, resulting in enlargement of the oil film. A misaligned journal bearing with a suitable flexible structure provided stable lubrication without metal-to-metal contact, even under shock load conditions. The flexible structure was incorporated into the high-load-bearing region of the journal bearing as a groove. Therefore, the application of a flexible structure in misaligned journal bearings can effectively enhance lubrication performance in misaligned conditions and under shock loads.

Deterministic surface roughness effects on elastic material contact with shear thinning fluid media

Abstract The formation of lubrication films is described using the hydrodynamic lubrication theory, which is based on the Reynolds equation that includes shear thinning behaviors of lubricant. Contacting surfaces are considered to undergo elastic deformation owing to concentrated contact pressures that exceed 1.0 GPa in most engineering applications. Under the contact condition of a high load on a relatively small contact area, elastic deformation of contacting bodies directly influences the formation of the lubricated film. Elastohydrodynamic lubrication (EHL) analysis is applied to correctly analyze the lubricated contact. Under an EHL contact, the scale of the lubrication film thickness is frequently less than that of the surface roughness that results from either the manufacturing or running-in processes. In this work, surface roughness is considered in detail, and two-dimensional surface roughness is measured as that characterizing general engineering surface roughness. The deterministic method regarding the surface roughness is considered for computing EHL film formation under several contact conditions such as load, contact velocity, and elasticity of contacting materials.

Effect of temperature rise on a tandem of ball-bearings with an O-configuration in motorized spindle under oil-air lubrication

Accurately predicting the thermal behavior of motorized spindles is a critical task in manufacturing industry. In this study, a thermo-mechanical-solid coupling-behavior on the motorized spindle in working condition was investigated and analyzed. Firstly, the bearing mechanical analysis of the motorized spindle under assembly constraints was discussed and a new coupling model was founded. Concurrently, the impacts of oil film thickness and the spacing rings on the displacement were considered into this model. Secondly, for the deformation of bearing, combined with Jones-Harris's quasi-static force–deformation bearing model, a mathematical model about a tandem of ball-bearings was built. And in this model, a new analytical method was proposed to decouple the deformation generated by thermal and centrifugal forces from the Hertz contact deformation, making the deformation analysis clear and orderly. Thirdly, from the perspective of heat generation mechanism and principle, based on the above bearing model, the elastohydrodynamic lubrication analysis on the bearing was executed, the thermal network model of bearing with multiple heat sources was set up, and the bearing node's scheme was optimized. Eventually, the effects of parameters such as speed, cooling water flow, and air flow on temperature rise and bearing parameters were calculated and analyzed, and the theoretical results were examined by tests, which provides some reference and guidance for the structural design of precision spindle.

A New Type of Misaligned Journal Bearing with Flexible Structure

A flexible structure is applied to improve the lubrication performance of a misaligned journal bearing. The journal bearing is a representative sliding bearing, and there is damage due to metal-to-metal contact as a result of misalignment. Since misalignment is an unavoidable phenomenon, a journal bearing with a flexible structure was proposed as a way to improve it. The lubrication characteristics of the bearing were evaluated numerically under a steady-state condition. EHL (elastohydrodynamic lubrication) analysis considering elastic deformation was performed. The lubrication performance was compared in accordance with variation of the geometry of the flexible structure and evaluated based on the minimum film thickness. Moreover, the results of the journal bearing with a flexible structure were compared with those of the journal bearing without the flexible structure. The flexible structure was then applied in the form of a groove to the area supporting high load on the journal bearing; it was elastically deformed by the generated oil film pressure, which helps obscure a larger oil film. Through numerical analysis, it was found that the journal bearing with a flexible structure can improve the lubrication performance in the misaligned condition.

Non‐spherical shape optimization of artificial hip joint based on elastohydrodynamic lubrication analysis

AbstractStructural optimization design is a promising way to further promote the lubrication performance of the artificial hip joint (AHJ). In this work, a non‐spherical shape optimization design strategy for the femoral head is firstly proposed. The generatrix, the line rotated about an axis that generates the bearing surface of the femoral head, is characterized based on a third‐order Bezier curve. The performance of the AHJ under steady‐state condition is analyzed by solving the governing equations of the elastohydrodynamic lubrication problem, and the minimum lubricating film thickness of the AHJ is maximized by adjusting the positions of four control points of the Bezier curve based on the simulated annealing method. The results show that, when compared with the standard spherical femoral head, the optimized non‐spherical femoral head can significantly improve the minimum thickness and reduce the maximum pressure of the lubricating film of the AHJ. Through the analysis of the optimization process, the results further reveal that the shape of the femoral head has a direct impact on the thickness distribution of the lubricating film. This research will provide guidance and theoretical support for novel design of AHJs.

Thermal Elastohydrodynamic Lubrication of Herringbone Gear Considering the Effect of Oil Gas Mixture

AbstractIn order to analyze the dynamic behavior of the oil film in the herringbone gear meshing area under oil injection lubrication conditions more accurately, this paper proposed a thermal elastohydrodynamic lubrication (TEHL) analysis method, by combining the traditional TEHL calculation method with two-phase flow theory. First, ansys/cfx 18.1 was used to determine the air content of the lubricating oil in the meshing zone under the injection condition. Then, considering the influence of air content on the rheological properties of lubricating oil, the traditional TEHL model was improved. On this basis, the influence of injection angle α1 on the oil fraction and the lubrication characteristics of the oil film were analyzed. This research can provide a feasible method for the analysis of the lubrication characteristics of herringbone gear.

Elastohydrodynamic lubrication analysis of tapered roller bearing considering effect of free ends

The EHL model of tapered roller bearing considering free ends is established and the effect of force on the large end is also considered. The free ends are constructed through the overlapping method, and the distribution of pressure and film thickness are obtained with the unified Reynolds equation. The effect of force and distance between two neighboring free ends are investigated, based on which the proper contact case is selected. The EHL of tapered roller bearing with different fillets and Lundberg profile are discussed. The results show the length and radius of roller fillet and the modification of Lundberg profile roller should be carefully selected to improve lubrication performance with low pressure, large minimal film thickness and low stress concentration.

Tribology and dynamic characteristics of textured journal-thrust coupled bearing considering thermal and pressure coupled effects

The journal-thrust coupled bearing in diesel engine operates under complex load and high working temperature. Under extreme working conditions, it supports the crankshaft and prevents its axial movement through the lubrication of journal and thrust parts. This study is mainly aimed to establish the thermal elastohydrodynamic (TEHD) lubrication analysis model for textured journal-thrust coupled bearing, which considered the thermal and pressure coupled effects in the lubrication process by proposing the flow, pressure and thermal continuity conditions between the journal and thrust parts. A specific coupled bearing testing equipment was set up and the experimental results validated the correctness of the TEHD lubrication model. Necessity of considering thermal and pressure coupled effect was confirmed through comparison of different models. Apart from that, parametric analyses were conducted to explore the influences of thermal and pressure coupled effects on lubrication performances and dynamic characteristics under different eccentricity ratio of journal part, geometry film thickness of thrust part and surface topography (mainly realized by texture distribution of thrust part).

Elasto-hydrodynamic lubrication analysis of a porous misaligned crankshaft bearing operating with nanolubricants

In this paper, the combined effects of the characteristic size and concentration of inorganic fullerene-like tungsten disulphide nanoparticles (IF-WS2 NPs) or molybdenum disulphide nanoparticles (IF-MoS2 NPs) on the nonlinear dynamic behaviour of a gasoline engine crankshaft bearing subject to an arbitrary force torsor (effective applied force and moment vector) are theoretically and numerically investigated using the V. K. Stokes micro-continuum theory. These NPs are the most common additives for lubrication purposes due to their excellent tribological characteristics along with their effect on reducing friction and wear. It is assumed that the journal (crankshaft) currently made of a forged steel is rigid and the main bearing consists of a thin poroelastic liner made of low elastic modulus materials like Babbitt metals fixed in a stiff housing as defined by ASTM B23-00. The Krieger-Dougherty law is included in the proposed EHD model to account for the viscosity variation with respect to the volume fraction of nanoparticles dispersed in the base lubricant. On the other hand, the characteristic size of nanomaterials is introduced by a new material entity, denoted l, which is responsible for a couple-stress property. The Reynolds equation is derived in transient conditions and modified to account for the size of nanoparticles and the bearing-liner permeability property. For an arbitrary force torsor, the hydrodynamic pressure distribution, the squeeze film velocities, and the misalignment angular velocities are determined simultaneously by solving the discretized Reynolds equation and the equilibrium equations with the damped Newton-Raphson iterative method at each crank angle step. The crankshaft center trajectories in three sections of the main journal axis as well as the misalignment angles are deduced from the squeeze film velocities and the misalignment angular velocities by means of a Runge-Kutta scheme. According to the obtained results, the combined effects of the size and concentration of fullerene-like nanoparticles on the dynamic behavior of a compliant dynamically loaded crankshaft bearing operating with dynamic misalignment are significant and cannot be overlooked.

Calculation and influence analysis of tooth surface friction coefficient of planetary gear system in mixed lubrication condition

Based on the gearing theory, the calculation formulas of comprehensive curvature radius, relative sliding speed and tooth surface contact stress of internal and external meshing gear pair of the planetary gear system are deduced in this paper. Combined with load sharing theory and thermal elastohydrodynamic lubrication analysis method, the oil film thickness, film bearing ratio and friction coefficient are solved and the effects of roughness and input power on the friction coefficient are studied. The results show that with the increase of tooth surface roughness, the film bearing ratio decreases and friction coefficient increases; As the input power increases, the film temperature increases, the oil viscosity and film thickness decreases, which causes the tooth surface friction coefficient increases.