Multilevel solution for thermal elastohydrodynamic lubrication of rolling/sliding circular contacts

This paper describes a comprehensive model of Elastohydrodynamic piston lubrication, incorporated the crown lands into solution domain to characterize the effect of crown-liner interactions on piston motion. Elastohydrodynamic Lubrication (EHL) analysis of a piston skirt-liner conjunction is in general a useful methodology for design analysis of pistons. The diameters of piston crown lands are much less than those of skirt and liner for typical piston designs. Therefore crown lands normally do not interact with liner under usual operating conditions and hence most of the researchers exclude crown lands from the EHL analysis and mainly focus on piston skirt. However, under some of the engine operating conditions piston crown lands play important role in the secondary dynamics and tribology aspects of pistons. During the thermodynamic cycle when piston is hot and cylinder liner is relatively colder, piston thermal expansion leads to crown-liner interaction, which necessitates EHL, asperity contact and wear considerations of piston crown along with piston skirt. The simulation methodology for piston EHL analysis uses a mass-conserving algorithm for the finite volume method solution of Reynolds equation, which is coupled to elasticity relations and Greenwood-Tripp asperity contact model. Elrod’s mass conserving algorithm enables to model and analyze partially lubricated piston-liner interface by the input of oil supply and moreover rigorously handles cavitated zones, and takes into account piston ring grooves, piston cut-outs and unlubricated areas due to piston geometry. Results are presented from parametric studies that show comparisons between the analyses of the models with piston skirt lubrication only and piston lubrication, which incorporates the crown lands to the EHL domain.

This article presents the results of a series of thermal elastohydrodynamic lubrication (EHL) analyses of a set of disc experiments carried out by Patching et al. The authors have previously calculated the heat partition at each load stage fromthe experimental data, and the present work seeks to compare the heat partition developed in a thermal EHL analysis of the lubricant film with that calculated from the experiments. These EHL analyses show that the heat partition depends on the non-Newtonian formulation used. Only when the dissipation takes place by wall slip occurring at the faster moving surface do the heat partition results approach those determined from the experimental results. It is concluded that this combination of experimental heat partition results with associated EHL analysis can prove to be a much more discerning test of rheological behaviour in EHL contacts than is provided by measurement of traction.

As the traction drive works under the high traction oil, in small slip ratio, and sometime accompanied with skew, the surface fatigue failures of the traction drive rollers are different to that of gears and bearings. In this research, fatigue tests of traction rollers are performed under the conditions of different load, slip ratio and skew angle. The effects of running condition on the fatigue lives of traction rollers are clarified considering the surface crack growth and wear. A higher slip ratio will make a lower fatigue life, but skew will lead to a higher fatigue strength because of the severe surface wear, which diminishes tile surface crack length, and the mechanics condition, which makes surface crack grow difficultly. For evaluation of the effects of such as slip ratio and skew on the fatigue strength of traction rollers, a new method is put forward in which the relationship between the surface temperature index and fatigue life is used instead of S-N curve.

Train idling in traction and skidding in braking pose significant risks to operational safety. The traction and braking performance of rail vehicles is constrained by the wheel–rail adhesion state. Optimizing the target acceleration/deceleration design values and adhesion control strategies based on wheel–rail adhesion characteristics can enhance adhesion utilization and ensure train operational safety. Current research has primarily investigated wheel–rail adhesion characteristics with third bodies under either traction or braking conditions separately, without systematic comparative analysis of their differences. This limitation hinders further optimization of adhesion control strategies for both traction and braking. To systematically investigate and compare potential differences in wheelrail adhesion characteristics between traction and braking under conditions of third-body contamination, this article performed wheel–rail adhesion characteristic tests under various conditions. These conditions included different speeds (20–80 km/h), axle loads (11–17 t), and progressively increasing maximum slip ratios (with the maximum slip ratio incrementally raised until the adhesion improvement point emerged) with water and antiwear fluid as third bodies. The results indicate a significant discrepancy in the slip ratio conditions required for adhesion improvement on the adhesion coefficient–slip ratio curve between traction and braking conditions: A higher slip ratio is required for adhesion improvement under traction conditions compared to braking conditions. Ultimately, this article elucidates and validates the underlying mechanisms by which distinct wheel–rail contact temperatures under traction and braking conditions give rise to differences in adhesion characteristics.

In order to improve the steering performance of vehicles on low adhesion roads, this paper proposed a drift control method by coordinating the steering angle and the rear wheel slip ratio. Because lateral force of rear wheels is saturated with high longitudinal slip ratio under the drift condition, a vehicle dynamic model considering the coupling of the rear wheels’ longitudinal and lateral force is established. In view of the fact that the lateral tire force is affected by the nonlinearity of sideslip angle and slip ratio, the vehicle dynamic model is complex and makes it difficult for controller design. Due to this, a description method of the nonlinear relationship is presented for simple which introduces a virtual control quantity representing the influence of slip ratio on lateral tire forces based on the function of tire force with sideslip angle and slip ratio. Then, a sliding mode control method is proposed to ensure the stability of the closed-loop system and an off-line two-dimensional map is constructed to convert the virtual control quantity into the actual control quantity. The simulation results in the high-precision vehicle dynamics simulation software show that even if the initial state is far from the equilibrium point of drift, the drift controller also can ensure the stability of the closed-loop system and achieve a good drift performance.

A numerical solution to the elastohydrodynamic lubrication (EHL) problem of two coated elastic bodies in line contact is introduced. The non-Newtonian behavior of the lubricant is incorporated into EHL analysis using Eyring's nonlinear viscous model. The surface elastic deformations are computed from full elasticity analysis of layered elastic half-space. The iterative Newton–Raphson technique is used in the numerical solution. Subsurface stresses are calculated using two different techniques, the numerical integral scheme based on Fourier transformation and the finite element method. The effects of surface coating (material and thickness) on the pressure profile and subsurface stresses are presented and discussed. Copyright © 2006 John Wiley & Sons, Ltd.

Elastohydrodynamic lubrication analysis of a functionally graded layered bearing surface, with particular reference to 'cushion form bearings' for artificial knee joints.

ABSTRACTThe pure squeeze thin film elastohydrodynamic lubrication motion of circular contacts with effects of surface forces and surface roughness taken into account is explored under constant load conditions. The coupled transient stochastic Reynolds, elasticity deformation, the load balance, surface forces (hydrodynamic, solvation and van der Waals pressure) and lubricant rheology equations were solved simultaneously by using the finite difference method and the Gauss–Seidel iteration method. The simulation results reveal that the differences between radial type roughness and circular type roughness problems are apparent as the film thickness is thinner than 5 nm. The oscillation phenomena in pressure and film thickness come mainly from the action of solvation forces. The effects of surface forces become significant as the film thickness becomes thinner. The film thickness with circular type roughness is thicker than that with radial type roughness. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents the results of a transient analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with a non-Newtonian lubricant under oscillatory motion. Effects of the transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using the multigrid, multilevel method with full approximation technique. The film thickness and the pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally. For an increase in the applied load on the cylinders or a decrease in the lubricant viscosity, there is a reduction in the minimum film thickness, as expected. The predicted film thickness for smooth surfaces is slightly higher than the film thickness obtained experimentally, owing primarily to cavitation that occurred in the experiments. The lubricant film under oscillatory motion becomes very thin near the ends of the contact when the velocity goes to zero as the motion direction changes, but a squeeze film effect keeps the fluid film thickness from decreasing to zero. This is especially true for surfaces of low elastic modulus. Harmonic surface roughness and the viscosity and power law index of the non-Newtonian lubricant all have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion.

Application of modified iterative method to simulate rainfall infiltration in unsaturated soils

The objective of the present paper is to clarify the effect of slip condition, ie. slip ratio, outer surface velocity, and lubrication oil temperature on the contact fatigue strength for pitting (pitting strength) of the carburized steel. Rolling contact fatigue (RCF) tests were conducted on 26mm diameter specimens made of carburized steel under oil lubrication. Then, slip ratio, outer surface velocity, and lubrication oil temperature as the slip condition were changed on the RCF tests. As a result, pitting strength decreased with the increase of slip ratio, the decrease of outer surface velocity, and the decrease of lubrication oil temperature. Furthermore, relationships between the above-mentioned three parameters, friction coefficient, and contact surface temperature were evaluated. Then slip ratio, outer surface velocity, and lubrication oil temperature influenced to friction coefficient and contact surface temperature. The friction coefficient slightly decreased when contact surface temperature increased. Lastly, it was found that the friction coefficient was main parameter which directly determines the pitting strength.

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.

In this paper, the pure squeeze thin film elastohydrodynamic lubrication (TFEHL) motion of circular contacts with electric double layer (EDL) is explored under constant load condition. The coupled transient modified Reynolds, elasticity deformation, the load balance, and lubricant rheology equations were solved simultaneously by using the finite difference method and the Gauss-Seidel iteration method. The simulation results reveal that the effect of electric double layer produces an obvious increase in the film thickness and apparent viscosity. The greater the Zeta-potential, the greater the apparent viscosity, and the greater the film thickness.

Analytical and numerical calculations for thermal elastohydrodynamic lubrication problems of helical W-N gears

This article analyses the generation of ‘optimal’ grids for lubrication problems including hydrodynamic and elastohydrodynamic lubrication. It does this by using existing numerical solutions on (very) fine and regular grids, and studying the coarse grids generated by algebraic multigrid. This article analyses two hydrodynamic lubrication applications, the circular hydrodynamic lubrication contact and the rough surface lubrication. The latter subject is currently attracting a large interest from both industry and university. A third elastohydrodynamic lubrication application highlights the strong coupling in the high-pressure zone.