Partial Elastohydrodynamic Lubrication Research Articles

A Data-Driven Approach to Estimate the Power Loss and Thermal Behaviour of Cylindrical Gearboxes under Transient Operating Conditions

This paper proposes an innovative methodology to estimate the thermal behaviour of the cylindrical gearbox system, considering, as a thermal source, the power loss calculated under transient operating conditions. The power loss of the system in transient conditions is computed through several approaches: a partial elasto-hydrodynamic lubrication model (EHL) is adopted to estimate the friction coefficients of the gears, while analytical and semiempirical models are used to compute other power loss sources. Furthermore, considering a limited set of operating condition points as a training set, a reduced-order model for the evaluation of the power loss based on a neural network is developed. Using this method, it is possible to simulate thermal behaviour with high accuracy through a thermal network approach in all steady-state and transient operating conditions, reducing computational time. The results obtained by means of the proposed method have been compared and validated with the experimental results available in the literature. This methodology has been tested with the FZG rig test gearbox but can be extended to any transmission layout to predict the overall efficiency and component temperatures with a low computational burden.

A discussion of Arana, A., Larrañaga, J., & Ulacia, I. (2019). Partial EHL friction coefficient model to predict power losses in cylindrical gears. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Vol. 233(2) 303–316

There is presently a heated debate within the field of elastohydrodynamic lubrication (EHL). Some have attributed this to a controversy regarding the shear dependence of viscosity. However, the real nature of the debate is, as it has been for more than 40 years, whether or not to correctly describe the piezoviscous effect. If real pressure dependence of viscosity were to be employed in all EHL analyses, then the true nature of shear dependence would become apparent and the debate would end.

A mixed elastohydrodynamic lubrication model based on virtual rough surface for studying the tribological effect of asperities

PurposeThe main purpose of this paper is to present the effort on developing a mixed elastohydrodynamic lubrication (EHL) model to study the tribological effect of asperities on rough surface.Design/methodology/approachThe model, with the use of the average flow Reynolds equation and the K-E elasto-plastic contact model, allows predictions of hydrodynamic pressure and contact pressure on the virtual rough surface, respectively. Then, the substrate elastic deformation is calculated by discrete convolution fast-Fourier transform (DC-FFT) method to modify the film thickness recursively. Afterwards, corresponding ball-on-disk tests are conducted and the validity of the model demonstrated. Moreover, the effects of asperity features, such as roughness, curvature radius and asperity pattern factor, on the tribological properties of EHL, are also discussed though plotting corresponding Stribeck curves and film thickness shapes.FindingsIt is demonstrated that the current model predicts very close data compared with corresponding experimental results. And it has the advantage of high accuracy comparing with other typical models. Furthermore, smaller roughness, bigger asperity radius and transverse rough surface pattern are found to have lower friction coefficients in mixed EHL models.Originality/valueThis paper contributes toward developing a mixed EHL model to investigate the effect of surface roughness, which may be helpful to better understand partial EHL.

Experimental study on thermal effect of tilted roller pairs in rolling/sliding contacts

PurposeThe aim of this study is to understand thermal effects and surface topography of roller bearings with misaligned load under combination of multifactors by an experimental method.Design/methodology/approachA series of orthogonal experiments would need to be planned and performed. A ranking of impact degree of factors on edge effect and eccentric load effect can be learned with multivariate analysis of variance by Statistical Product and Service Solutions software. Influence rules of each individual factor can also be obtained through more experiments. A roller surface phase diagram both before and after test can be observed with metallographic microscope. An axial profile data of roller can be measured by PGI 3D Profiler, then a roller generatrix contour can be achieved through filtering measured signal with empirical mode decomposition method.FindingsSlip fraction has most impact on edge effect, whereas tilting angle plays a key role in eccentric load effect. For the case of low temperature, skidding damage does not occur. Inversely, because of the high pressure in partial elastohydrodynamic lubrication caused by roller tilt, running-in occurs and micro asperity flattening is observed on a rough surface. And, the larger the tilting angle, the more obvious the micro-flattening and the greater the reduction of roller surface roughness after the test.Originality/valueA lot of theoretical studies on thermal effect of roller bearings surface morphology have been published. However, there are little on relevant experimental study, especially on thermal effect with an integration of sliding, tilting and unbalance loading.

Analysis on thermal effect on high-speed wheel/rail adhesion under interfacial contamination using a three-dimensional model with surface roughness

A three-dimensional numerical model of wheel/rail in rolling contact is established to study the adhesion characteristics under interfacial contamination considering surface roughness at high speed. The thermal partial elastohydrodynamic lubrication (EHL) theory in elliptical contact is used in the model. The numerical model is successfully solved by applying the iterative algorithm between the pressure field and temperature field. Multilevel method is used to solve modified Reynolds equation. Sweeping column method is used to solve energy and heat conduction equations. The effects of train speed, surface roughness amplitudes, roughness orientation and axle load on the adhesion coefficient under interfacial contamination are numerically investigated. A typical creepage-traction curve under oil contamination is obtained at high speed by the present model. In addition, the effects of temperature and the elastic-plastic deformation behaviour of asperities on the adhesion coefficient are discussed in the paper. Furthermore, the effect of different interfacial contaminations on wheel/rail adhesion using the present model on the adhesion coefficient is investigated. In order to validate the present model, the numerical results are compared with the experimental results that were obtained by JD-2 high-speed wheel/rail rolling contact machine under water/oil contaminations.

Numerical and experimental investigation on adhesion characteristic of wheel/rail under the third body condition

A numerical model of wheel and rail lubricated by a third body was established using the partial elasto-hydrodynamic lubrication theory and multi-grid method. The effects of rolling speed, surface roughness, contact load, wheel diameter, and viscosity of third body on adhesion coefficient are explored. The results show that the rolling speed, surface roughness, and the viscosity of third body have a significant influence on adhesion coefficient when the wheel/rail interface is lubricated under oil and water conditions. Furthermore, to verify the precision of the numerical calculating results, some experiments were carried out by means of a JD-1 wheel/rail simulation facility. The results show that there is same changing trend and almost same adhesion coefficient between the curves of numerical and experimental results. The relative difference between the numerical and experimental results is less than 10%. This numerical method can be used to explore the adhesion coefficient of wheel/rail under the third body condition.

A wear model for EHL contacts in gerotor type hydraulic motors

The heart of gerotor motors is a gear-set. The gear-set consists of an inner gear which is rotating and orbiting in contact with an outer gear. Wear in these contacts is investigated experimentally and with a numerical implementation of an Archard based wear model in combination with a load sharing concept. The model utilizes the symmetry of the motor and is based on a three-scale approach to estimate the wear on the gears. The global model calculates contact forces, relative surface velocities and contact radii in the contacts between inner and outer gear. The calculations performed on the local scale are used to collect information about the influence of the surface roughness on lubricant film thickness. The wear depth is calculated on a semi-local scale, involving only one tooth on the outer gear. In partial elastohydrodynamic lubrication, load is carried by the part of the conjunction where there is direct contact between the mating surfaces and by the lubricant pressure. In the wear model, wear only occurs as a direct consequence of contact between the mating surfaces. Experimental results are compared with the model predictions for equivalent running conditions. The wear predicted by the model agrees with the experimental results. For this reason, it is concluded that wear in the gerotor motor is dominated by the wear mechanisms which are considered in the tribological model.

Numerical analysis on wheel/rail adhesion under mixed contamination of oil and water with surface roughness

A preliminary two dimensional numerical model of wheel/rail in rolling contact is established to study the adhesion characteristics of wheel/rail with considering surface roughness under oil and water mixed contamination. A partial elastohydrodynamic lubrication (EHL) theory in line contact is applied in the model. The present numerical model is used to investigate the effects of contact pressures of wheel/rail, the volume fraction of oil and their locations in the contact zone, train speed on the adhesion coefficient under oil and water mixed contamination condition. In addition, the effects of oil contamination, water contamination and water/oil mixed contamination on the adhesion coefficient are compared. The numerical results show that the adhesion coefficient is greatly influenced by the train speed, the volume fraction of oil and their locations in the contact zone. Furthermore, in order to verify the accuracy of the numerical model, the numerical results are compared with the experimental results that were obtained by JD-1 wheel/rail simulation facility.

Tribological failure analysis of gear contacts of Exciter Sieve gear boxes

In the present paper the premature failure of gear contact encountered in Exciter Sieve gear boxes has been analyzed. The cause of gear contact failure is identified by simulating the load bearing capacity of lubricants and conducting controlled experiments on an Amsler disk-on-disk tribo tester. The results of performance behavior (i.e., load carrying capacity of lubricants, contact friction and weight loss of test specimens) of the simulated gear contacts have been reported. The theoretical and experimental results indicate presence of mixed to partial elastohydrodynamic lubrication conditions in the gear contact. To mitigate the problem of scuffing and scoring in the gear contacts, lubricating oils with extreme pressure additives and Base oil without additive have been tested and performance results are reported.

Analysis of wheel/rail adhesion under oil contamination with surface roughness

The objective of this study is to investigate the adhesion characteristics of wheel/rail under oil contamination with consideration of surface roughness using a three-dimensional model of wheel/rail in rolling contact. A partial elastohydrodynamic lubrication theory is employed in the model. An under-relaxation revision on the film thickness is used to keep the simulation procedure stable. The dependence of the wheel/rail adhesion coefficient on train speed, surface roughness amplitude, parameter of roughness orientation and axle load is studied under oil contamination. Moreover, the numerical solutions of a two-dimensional model are compared with those of the three-dimensional model. In addition, a good agreement has been found between the numerical results and the experimental results obtained by a JD-1 wheel/rail simulation facility, which consists of a small wheel roller serving as locomotive or rolling stock wheel and a large wheel roller serving as rail.

Effect of crowning on differential pinion shaft contact in the partial elasto-hydrodynamic lubrication

In this study, the PEHL analysis is conducted for the contact of the inner surface of the pinion gear and the pinion shaft to reveal the cause of adhesional failure on the inner surface of pinion gear of an automotive differential gear system. The numerical algorithm for the analysis of three-dimensional PEHL used in this study has advantage that the pressure and film distributions can be calculated from Reynolds equation for all mixed lubrication region without any specific boundary condition for the edge of solid contact region. Using the developed PEHL algorithm, we calculated the distributions of pressure and film thickness for the surfaces with bi-modal sine waviness at present and with single-modal crowning waviness we suggested. It is shown that the surface with the single-modal crowning waviness is more beneficial to the development of film than that with the bi-modal sine waviness.

Fabrication of TiO2 Nano-Oils by a Plasma Arc Nanoparticles Synthesis System

This work describes the feasibility of forming titanium oxide nano-oils using a modified plasma arc system. The high temperature that is generated by the plasma arc system is used to heat up and vaporize the bulk metal. Titanium oxide gas and particles are then induced into the collection piping by an induction system. They are then thoroughly mixed, with pre-condensed paraffin oil is mixed, and rapidly cooled in a process that contributes to grain nucleation and prevents particle size growth. Hence, nano-oils, with small spheres of titanium oxide can be obtained and finally stored in a collection tank. A friction test is performed using an ATE-77 Reciprocal Tribological Tester made by Cameron-Plint Tribology Limited, England. The viscosities of the nano-oils were measured using a DVIII +LVDV −IIIUCP rheometer in a rate-sweep mode over a shear-rate range of 200–1900. Results indicate that the nano-oils mixed with spherical titanium oxide can be made using a modified plasma arc system. The viscosity of nano-oil consistently exceeds that of the paraffin oil enlarging the partial elastohydrodynamic lubrication (EHL) area with a complete lubricating film between two move iron surfaces. The complete lubricating film provides good performance, then warranting the use of the titanium oxide nano-oils as revolutionary lubrication agent.

Experimental Analysis of Nanomechanics of Spherical Titanium Oxide Nanooils in Reducing Friction

This work explores the nanomechanics of sphere titanium oxide nanooils in reducing friction between two pieces of cast iron. A friction test is performed using an ATE-77 Reciprocal Tribological Tester made by Cameron-Plint Tribology Limited, England. The friction between two pieces of cast iron was determined 25-135 degrees C using home-made titanium oxide nanooils. In elastohydrodynamic lubrication (EHL), the lubricant is subjected to enormous pressures, there is considerable local heating, and the assumption of constant viscosity no longer holds up. The derivation of the governing equations for elastohydrodynamic lubrication, the pressure and temperature dependence of viscosity is recognized after the lubrication thin film approximation has been made. The viscosity of the nanooils consistently exceeded that of the paraffin oil enlarging the partial EHL area with a complete lubricating film between two move iron surfaces. The spherical geometry of TiO2 nanoparticles caused them to act as a rolling medium when the machine parts move which is in the solid friction area. Because they provide a rolling function, spherical titanium oxide nanoparticles have feasible tribological and lubrication applications in the mechanical industry to reduce noise, vibration and friction wear.

Shear behaviour of polyalkylmethacrylate solutions under thin film lubrication

Film-forming properties and traction were determined for the oils containing polyalkylmethacrylates (PAMAs) under a temperature of 40 °C and a rolling speed between 0.001 and 1 m/s with the disc-on-roller tester. Oil film thickness measurements were made under a pure rolling condition and traction measurements were made under the slide/roll ratio of 50 per cent. All the copolymers were synthesized in the base oil by a random copolymerization method. Difference in oil film thickness between polymer solutions became significant under the rolling speed below 0.1 m/s. Among non-functionalized homopolymers, PAMAs with branched alkyl group were superior to those with linear alkyl group in film-forming performance. In functionalized PAMAs, film-forming performance was affected by the functional group as well as the coexisting alkyl group. High-mole-concentration of functional group produced a greater oil film thickness than the corresponding low-mole-concentration PAMAs. This tendency was more marked for high-molecular-weight PAMAs. Among all the polymer solutions, high-molecular-weight PAMA with methyl group as a main component showed the thickest oil film, followed by high-molecular-weight PAMA containing branched alkyl group and dimethylaminoethyl group. In the low speeds of the traction–speed curves, most PAMA solutions showed the effect of friction reduction, whose extent depended upon the type of alkyl group and functional group. It was inferred that the friction behaviour in the partial elastohydrodynamic lubrication (EHL) regime was considerably affected by the friction in the thin film lubrication based on the mutual interaction between polymer molecules.

Study on Rolling Contact Fatigue in Hydrogen Environment at a Contact Pressure below Basic Static Load Capacity

Rolling contact fatigue tests were conducted in hydrogen and air at a contact pressure of 4.1 GPa, below 4.2 GPa, corresponding to the basic static load capacity in rolling contact bearing using the four-ball tester. The lubricating conditions employed were partial and full elastohydrodynamic lubrication (EHL). The results were compared with those at 5.6 GPa above the basic static load capacity in a previous paper (Endo, et al. (1)). Rolling fatigue occurred in hydrogen but did not occur in air regardless of lubricating conditions. In hydrogen, a crack was initiated in the subsurface under partial EHL conditions and at or in the vicinity of the surface under full EHL conditions. On the other hand, at 5.6 GPa, a crack was initiated at the surface under partial EHL conditions and in the subsurface under full EHL conditions. In a hydrogen environment, the fatigue life in a rolling contact was confirmed to be significantly shortened compared with that in air. The decrease in fatigue life and the difference in crack initiating place are ascribed to permeated hydrogen and its extent into the substrate according to lubricating conditions such as the contact pressure, the severity of direct contact, and the absence of oxide film. The results obtained suggest that in a hydrogen environment there is no fatigue limit in a rolling contact, which is thought to exist in air.

Analysis of Surface Roughness of Low Carbon Steel during Cold Rolling of Thin Strip

Surface roughness plays an important role in determining the tribological behaviour of mechanical components (e.g. gears and roller bearings etc.) under full-film and mixed (or partial) elastohydrodynamic lubrication conditions. This paper describes a detailed mechanics analysis of the surface roughness transformation of thin strip which has been cold rolled on an experimental mill. Low carbon steel strips were rolled at various speeds and reductions, and the effects of rolling parameters on surface roughness are studied. The results of surface roughness can provide important information to optimise the rolling schedule and to improve the rolled strip quality.

The Influence of the vane on the lubrication characteristics between the vane and the rolling piston of a rotary compressor

The rolling piston type rotary compressor has been widely used for refrigeration and air-conditioning systems due to its compactness and high-speed operation. The present analysis is part of a research program directed toward maximizing the advantages of refrigerant compressors. The study of lubrication characteristics in the critical sliding component is essential for the design of refrigerant compressors. Therefore, theoretical investigation of the lubrication characteristics of a rotary compressor being used for refrigeration and air-conditioning systems was investigated. The Newton-Raphson method was used for a partial elastohydrodynamic lubrication analysis between the vane and the rolling piston of a rotary compressor. The results demonstrated that the vane thickness and the center line position of the vane significantly influenced the friction force and the energy loss between the vane and the rolling piston.

Correlation Between Acoustic Emission Activity and Asperity Contact During Meshing of Spur Gears Under Partial Elastohydrodynamic Lubrication

This paper presents results of an experimental programme that suggested a correlation between levels of Acoustic Emission (AE) activity and the frictional resistance of contacting asperities of spur gears under partial elastohydrodynamic lubrication.

Effect of surface roughness on elastohydrodynamic traction. Part 2

To investigate the performance of a traction-drive toroidal continuously variable transmission, the traction characteristics under partial elastohydrodynamic lubrication contact were calculated theoretically based on roller test results. A calculation model was constructed for considering the effects of surface roughness on performance. The model incorporated a viscoelastic and elastic-plastic model using a nonlinear Maxwell model to represent the rheological behaviour of the traction fluid. The validity of the model was confirmed by its good agreement with the experimental results described in Part 1 of this paper. Various calculations were made to investigate the effect of surface roughness on traction under the operating conditions of an actual traction drive. The results indicated that the effect of surface roughness on durability could not be ignored.

Experimentally Established Correlation between Acoustic Emission Activity, Load, Speed, and Asperity Contact of Spur Gears Under Partial Elastohydrodynamic Lubrication

The application of the acoustic emission (AE) technique to condition monitoring of gears is still at a developmental stage. Understanding the source of AE activity at the gear mesh is fundamental if this technique is to be successfully employed for gear diagnostics and prognostics. This article presents results of an experimental programme that showed a correlation between AE r.m.s. activity and asperity contact under partial elastohydrodynamic lubrication. On the basis of experimental observations, it is postulated that AE can monitor and/or measure the effectiveness of a lubricant in minimizing asperity contact. It addition, it is concluded that two distinct types of AE are associated with the sliding and rolling of meshing spur gears.