Lubrication and Friction

One of the major costs incurred by railway companies is the maintenance of turnouts. This situation occurs because the large dynamic forces between the wheels of a train and the rails of a turnout cause excessive wear, rolling contact fatigue and rapid degradation of other components. A thorough understanding of the dynamic interaction between a train and a turnout could lead to a better design of the vehicle and track structures, deeper insight into the damage mechanisms and subsequently to smarter maintenance planning.

In this study, a review of the available literature on lubrication techniques during machining processes was conducted. Factors such as workpiece material, tool material and machining conditions were observed to be vital to the performance of any of the techniques. The performance and drawback of each technique were highlighted based on the machining conditions. It concludes by making a case for minimum quantity lubrication (MQL) method using vegetable oil-based lubricant in different machining processes, as a way of addressing the environmental health issues and cost associated with the application of lubricant in machining processes.

In this paper are presented the power losses and sources of their occurrence in worm gear boxes. These are the losses that occur in the coupling of worm teeth and worm gear, losses in bearings, seals and oil churning power losses in the transmission. When the operation of worm gearing is characterized by line contact of coupled elements which is accompanied by significant sliding, the highest value have the power losses in the worm and worm gear coupling compared to other losses in gearing. Among other things, in the paper also presents the expressions that are used for calculation of individual power losses and efficiency of the gearing. The size of the losses primarily depends on the type of coupled material and geometry of worm pair, circumferential velocity (input rotational speed), the type and viscosity of lubricating oil, load, worm shape, and temperature and so on. The paper also deals with the influence of different factors on power losses and efficiency. As the efficiency of the worm pair is significantly lower compared to other types of gear pairs, the appropriate combination of geometric parameters and materials of worm and worm gear, lubrication and working conditions can significantly affect its increase.

This paper deals with the tribological performance of carbon nanoparticles dispersed in polyalphaolefin PAO6 oil. Stribeck curves are obtained under various operating conditions, using a fully instrumented pin-on-disc tribometer under controlled conditions. A detailed multi-physics thermal fluid flow model with Lagrangian low concentration discrete solid phase and Eulerian multi-phase fluid with cavitation represented by modified Rayleigh-Plesset and vapour transport equation is presented. The numerical predictions under identical conditions to the experiments show good conformance with the measurements, and provide a fundamental understanding of the role of nanoparticles. Results show improved heat transfer from the contact with the presence of nanoparticles even at low levels of concentration. The analysis shows that this leads to higher lubricant viscosity, load carrying capacity and reduced friction. Furthermore, a resulting small region of cavitation at low volume fraction does not unduly affect the enhanced heat transfer of nanoparticles. This combined experimentation and detailed numerical analysis has not hitherto been reported in literature.

A systematic approach is required in order to determine the frictional characteristics of a contacting pair in the presence of a tribofilm. Despite the clear benefits in functionality and in reducing wear, the generation of ZDDP-based tribofilms often lead to increased frictional losses. Such an increase is also observed in the tribometric tests reported here, as well as in open literature. This paper investigates the underlying mechanics for the rise in friction using an integrated methodology, based upon Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). The use of an analytical contact mechanics model demonstrates that the pressure coefficient of boundary shear strength, measured using lateral force microscopy, provides an explanation for the observed increase in measured friction at micro-scale.

A tribo-dynamics model, predicting the conjunctional inefficiency and dynamic response of automotive hypoid gear pairs is presented. A dynamics model is coupled with an analytical friction model (viscous and boundary). The temperature rise at the centre of the conjunction is accounted for through use of thermal network model and Time Temperature Superposition (TTS) method, as well as the time varying geometry of the meshing gear teeth. Newtonian and non-Newtonian lubricant shear behaviour are both considered Surface topography measurements of a run-in pinions are obtained. Inefficiency calculations are performed for typical automotive drive cycle snapshots. Precisely measured lubricant shear characterstics for lubricants different blended viscosity modifiers and evolving surface topography are used in the study of transmission inefficiency. The integrated thermal-tribodynamic analysis is shown to distinguish between different viscosity modifier types, an approach not hitherto reported in literature.

The effects of mechanical factors viz. applied load and temperature on the tribological performance of 5% palm oil methyl ester (POME) blended lubricant were studied using a steel-cast iron pair. Wear and frictional measurements were made using a stationary steel ball and a reciprocating cast iron plate in a modified universal wear and friction testing machine. The test conditions were contact pressure, 400 MPa; mean contact velocity, 0.34 m/s; reciprocating stroke, 80 mm; loads, 100-1100 N (fixed temperature); and temperature, 40-140°C (fixed load). Wear scar surfaces were investigated using scanning electron microscopy (SEM) to understand the wear mechanisms involved. Analysis of post bench test lubricating oils was performed using an ISL viscometer and TAN/TBN analyzers to investigate the lubricating oil degradation properties. Results showed that at lower loads (up to 500 N) and temperatures (up to 100°C), the wear rates under 5% POME lubricant are lower, whereas at higher loads and temperatures, the wear rates are higher. The friction behavior of POME as an additive in commercial lubricant indicates the prevalence of the boundary lubrication regime. The viscosity test results showed that 5% POME can improve the viscosity index (VI) properties of mineral-based lubricant up to 500 N load. However, in this investigation, corrosive wear and pits on the damaged surface are the dominant wear mode at higher temperature. (C) 2000 Elsevier Science S.A. All rights reserved. The effects of mechanical factors viz. applied load and temperature on the tribological performance of 5% palm oil methyl ester (POME) blended lubricant were studied using a steel-cast iron pair. Wear and frictional measurements were made using a stationary steel ball and a reciprocating cast iron plate in a modified universal wear and friction testing machine. The test conditions were contact pressure, 400 MPa; mean contact velocity, 0.34 m/s; reciprocating stroke, 80 mm; loads, 100-1100 N (fixed temperature); and temperature, 40-140 °C (fixed load). Wear scar surfaces were investigated using scanning electron microscopy (SEM) to understand the wear mechanisms involved. Analysis of post bench test lubricating oils was performed using an ISL viscometer and TAN/TBN analyzers to investigate the lubricating oil degradation properties. Results showed that at lower loads (up to 500 N) and temperatures (up to 100 °C), the wear rates under 5% POME lubricant are lower, whereas at higher loads and temperatures, the wear rates are higher. The friction behavior of POME as an additive in commercial lubricant indicates the prevalence of the boundary lubrication regime. The viscosity test results showed that 5% POME can improve the viscosity index (VI) properties of mineral-based lubricant up to 500 N load. However, in this investigation, corrosive wear and pits on the damaged surface are the dominant wear mode at higher temperature.

http://ac.els-cdn.com/S0043164800003197/1-s2.0-S0043164800003197-main.pdf?_tid=76eb2d7a-a9c6-11e3-81cf-00000aab0f02&acdnat=1394615741_dd76d6d488369b9225becace1fbc4e09
http://www.sciencedirect.com/science/article/pii/S0043164800003197

Improved fuel efficiency and reduced emissions are key drivers for modern drivetrain systems. Therefore, in recent years, dry sumps with air-oil mist lubrication have been used for efficient transmission design in order to reduce the churning losses. With dry sumps appropriate cooling measures should be implemented to dissipate the generated contact heat in an efficient manner. This paper integrates a tribological model with three dimensional thermofluid analysis in order to predict the heat generated in the lubricated meshing gear contacts and its dissipation rate by an impinging oil jet in air-oil mist environment. Such an approach has not hitherto been reported in literature. The results show that the generated heat under realistic conditions cannot be entirely dissipated by the impinging oil jet in the air-oil mist transmission casing. Numerical results are used to derive extrapolated regressed equations for heat transfer purposes for time-efficient analysis. These conform well with the detailed numerical results.

Cylinder liner temperature affects frictional losses. Optimum liner temperature improves energy efficiency and reduces emissions. Liner temperature is hardly affected by viscous shear of lubricant. This implies optimum conditions would be independent of engine speed. a b s t r a c t Despite extensive research into alternative methods, the internal combustion engine is expected to remain as the primary source of vehicular propulsion for the foreseeable future. There are still significant opportunities for improving fuel efficiency, thus directly reducing the harmful emissions. Consequently, mitigation of thermal and frictional losses has gradually become a priority. The piston-cylinder system accounts for the major share of all the losses as well as emissions. Therefore, the need for an integrated approach, particularly of a predictive nature is essential. This paper addresses this issue, particularly the role of cylinder liner temperature, which affects both thermal and frictional performance of the piston-cylinder system. The study focuses on the top compression ring whose critical sealing function makes it a major source of frictional power loss and a critical component in guarding against further blow-by of harmful gasses. Such an integrated approach has not hitherto been reported in literature. The study shows that the cylinder liner temperature is critical in mitigating power loss as well as reducing Hydrocarbon (HC) and Nitrogen Oxide (NOx) emissions from the compression ring – cylinder liner conjunction. The results imply the existence of an optimum range for liner working temperature, independent of engine speed (at least in the studied cases) to minimise frictional losses. Combined with the study of NOx and HC emissions, the control of liner temperature can help to mitigate frictional power loss and reduce emissions.

It is necessary to develop an analytical solution in order to combine predictions with measured tribolog-ical parameters and fundamentally understand the mechanism of lubrication in a typical region of engine cycle, using tribometric studies. This paper deals with the development of such a representative approach. An analytical, rather than a numerical approach is expounded, as it is shown to suffice for the purpose of precise time-efficient predictions, which conform well to the measurements. The effect of surface topography, material and operating conditions are ascertained for the representative case of top compression ring—cylinder liner contact at the top dead centre reversal in transition from the compression to power stroke. Stainless steel uncoated surface used as press fit cylinder liners for niche original equipment manufacturer applications are compared with those furnished with a Nickel-Silicon Carbide wear-resistant coating of choice in high performance motorsport.

Tribological characteristics (weight wear, friction moment and roughness) were determined and compared for sliding friction couple steel C45/leaded brass C330 at the running-in period in motor oil SAE 30 and oil SAE 30 with 1% and 2% complex ester. The used complex ester consisted of adipic acid, polyethylene gly-col-200 and 2-ethylhexanol. The anti-wear performance of complex esters was tested on a SMC-2 tribotester of the roller-sector type. Intensive running-in for the oils containing friction modifier occurred till the end of the 1st hour while that process for the oil SAE 30 continued up to the 4th hour. Wear of the couple with friction modifier of complex ester was over 2 times lower than the blank oil. Running-in moment and roughness of the friction couple in the model system with modifier were lower and more favourable than the blank oil. A significant part of the friction modifiers is the ashless antifriction additives, free of sulphur and phosphorus 1. The group of the ashless friction modifiers includes esters of aliphatic acids and polyvalent alcohols, amides, amines, etc 2,3. Many patents cite oil formulations containing ashless friction modifiers 4 , derivates of glycerol in combination with other additives, which exhibit synergistic effect and their use leads to fuel economy. Esters of dicarboxylic acids (sebacic, adipic, etc.)

Frictional losses are one of the main causes of reduced energy efficiency in all machines and mechanisms. In particular, there is mounting pressure upon manufacturers of all forms of vehicle to comply with increasingly stringent legislation and directives with regard to harmful emissions. Therefore, reduction of friction has become an imperative issue. The traditional approach of dealing with surface material and lubricant formulation in isolation has been replaced by a lubricant–surface system approach. This paper presents multi-scale experimentation from nano/meso-scale lateral force microscopy of ultra-thin surface adsorbed films through to micro-scale precision sliding tribometry to investigate lubricant–surface friction optimisation within the mixed regime of lubrication, using lubricants with different organic and inorganic friction modifying species. These affect the parameters of the system, commonly used as input to models for mixed and boundary regimes of lubrication. Therefore, the precise measurement of these parameters at different physical scales is important. The study also makes use of detailed numerical predictions at micro-scale through combined solution of the average Reynolds equation as well as interaction of wetted asperities in mixed and boundary regimes of lubrication. Good agreement is found between the predictions and measurements at micro-scale tribometric interactions. Furthermore, the same trends are observed in testing across the physical scales.

A tribo-dynamics model of a differential hypoid gear pair is presented, integrated with lubricated contact of meshing teeth pair with lubricants of varying rheological properties. Particular attention is paid to the effect of lubricant formulation and gear geometry on the system efficiency. The  influence of gear torsional dynamic response is taken into account in a 4-Degree of Freedom (DoF) model. The contact geometry and kinematics of the hypoid gear pair are estimated, using Tooth Contact Analysis (TCA). Two fully formulated gear lubricants of the same viscosity grade (SAE 75W-90) blended with the same additive pack, but with different types and concentration of viscosity modifier (VM) are considered. Conjunctional friction is predicted for viscous shear of fully characterised lubricants as well as boundary interaction of rough surfaces. The results show loss of friction resulting in resonant response of the gear pair with impact of meshing teeth exhibiting non-linear jump phenomenon. The predictions also show that lubricants with higher pressure – viscosity (PV) coefficients tend to exhibit increased power loss.

V tomto příspěvku provedeme matematickou analýzu vlivu velikosti dílčího úběru na houževnatost taženého drátu z perlitické oceli. Běžně používanou mírou houževnatosti drátu pro kordy do pneumatik je počet ohybů do lomu. Tento ukazatel je velmi citlivý na jakékoliv projevy nehomogenity mikrostruktury a tím i mechanických vlastností po průřezu drátu. K iniciaci trhliny při zkoušce střídavým ohýbáním dochází vždy na povrchu drátu, případně těsně pod ním. Použití nevhodných technologických parametrů vede k tomu, že povrchové vrstvy drátu bývají vystaveny výrazně vyšší deformaci, tím roste riziko vzniku mikrotrhlin v cementitických lamelách perlitu, což následně vyústí v dramatický pokles počtu ohybů do lomu. Pomocí matematického modelování na bázi metody konečných prvků provedeme analýzu vlivu počtu tahů (resp. vlivu velikosti dílčí deformace Q d ) a součinitele tření na homogenitu pole intenzity deformace při tažení ocelového drátu pro kordy do pneumatik. Po analýze výsledků se potvrdilo, že nižší součinitel tření při tažení a menší počet tahů vedou jednoznačně k lepší houževnatosti finálního drátu vyjádřenou počtem ohybů do lomu. Vliv počtu tahů je při tom výraznější. Při použití vyššího součinitele tření se rozdíl velikosti intenzity deformace ve středu a na povrchu drátu zvětšil o 30 %. Snížení počtu tahů vedlo k vyrovnání deformačního pole v taženém drátu. Rozdíl velikosti intenzity deformace ve středu a na povrchu drátu klesl o 40%, navíc došlo k celkovému snížení intenzity deformace v drátě po tažení.

One of the main problems in the plastic deformation of materials is the determination of the coefficient of friction as well as the subsequent application of the simulation for comparative analysis. However forecasting process and matching between simulation and experimental data is still a problem. Causes of this are factors such as roughness, mechanical properties of the material, chemical composition, etc. which strongly influence the behavior of the material in the simulation of the process. In this study, an approach is proposed to determine the changeable coefficient of friction in the deformation process experimentally, taking into account implicitly the influence of surface roughness on the friction curves. For the comparative analysis between experiment and simulation of the process, the experimental data for objective assessment was introduced. Nevertheless, there are differences between experiment and simulation, which is most evident in high loads, using lubricants differing from more than 12 units for graphite lubricant, with more than 6 units with oil and with dry friction with 8 units.

The study of textured surface performance is one of the highly researched topics in recent times. This is mainly due to the advantages that such surfaces can potentially provide in practice, in mitigating adverse tribological conditions, such as friction and wear. However, considering the complexities found in practice, a methodological analysis and evaluation procedure is essential in order to gain an understanding of the benefits from utilising such features in a given contact. The current study provides a combined analytical and experimental approach towards an enhanced understanding of the behaviour of textured surfaces relative to their untextured counterparts. The developed analytical models are invaluable in providing an insight into the relationship between the many parameters involved in defining even simple surface texture feature geometry and the expected outcomes in practice, when corroborated with experimental results. The current study reports on such an endeavour. With the studied texture configuration, the results have shown the possibility of reducing friction by as much as 25%.

This paper presents a wear process analysis of piston‐cylinder set in internal combustion engines.Piston mechanism is a very important factor in the proper lubrication of the engine, but also a potential cause of increased consumption of oil. There are very important kinematic ‐ tribological properties of piston mechanisms in this regard. From the point of reliability and functionality, critical parts of this circuit are the piston rings. Wear is most pronounced in the first piston ring, since it is exposed to the highest pressure and temperature, as well as the direct impact of fuel and combustion products. The intensity of wear of piston ‐ cylinder set depends on many factors, but the most influential ones are: construction, materials used for the production of the parts of this assembly, production technology and conditions of use.

Recently, much effort has been focused on research and development of new types of lubricating oil additives to reduce wear and friction in the tribological systems. It has been noted that the use of additives to improve the lubricating capacity and durability of oil plays an important role in the wear and friction process of materials, Due to the environmental problems, many researchers are embarking on the viability of the vegetable-based lubricants, In this article a critical review has been made on vegetable-based lubricant additives with specific properties and application. This article explains the advantages and manufacturing processes of vegetable-based oils, which will give a better understanding of using biodegradable lubricating oil additives. A case study on palm oil methyl ester as an additive has been presented in this paper.

http://www.emeraldinsight.com/journals.htm?issn=0036-8792&volume=55&issue=3&articleid=874623&show=pdf

The paper presents transient thermal-mixed-hydrodynamics of piston compression ring–cylinder liner conjunction for a 4-cylinder 4-stroke gasoline engine during a part of the New European Drive Cycle (NEDC). Analyses are carried out with and without cylinder de-activation technology in order to investigate its effect upon the generated tribological conditions. In particular, the effect of cylinder deactivation upon frictional power loss is studied. The predictions show that overall power losses in the piston–ring cylinder system worsen by as much as 10% because of the increased combustion pressures and liner temperatures in the active cylinders of an engine operating under cylinder deactivation. This finding shows the down-side of this progressively employed technology, which otherwise is effective in terms of combustion efficiency with additional benefits for operation of catalytic converters. The expounded approach has not hitherto been reported in literature.

The paper describes the theoretical study concerning the effect of lubricant inertia forces and deformability of the bearing elastic layer on the performance of a plain journal bearing. The problem is investigated for a Newtonian lubricant under isothermal and isoviscous conditions. The analysis considers the generalized Reynolds equation governing the flow of lubricant in the clearance space and the linear elasticity equation governing the displacement field in the bearing shell. An iterative numerical procedure with successive over-relaxation is used to pressure distribution within the lubricated conjunction. Bearing performance characteristics have been presented for typically selected values of generalized Reynolds number Re* and elasticity parameters of the elastic liner. It has been observed that the combined effect of fluid inertia forces and bearing flexibility affects the performance characteristics of a dynamically loaded journal bearing.

The vortex generators are in the form of a rectangular wing is used in present study.. These vortex generators can be mounted on the fin surfaces by either welding, punching or embossing. These vortex generators induce stream wise longitudinal vortices. These vortices disrupt the growth of the thermal boundary layer and serves to bring about heat transfer enhancement between the fluid and the fin surfaces. The geometrical configuration considered in this study is representative of a plate-fin heat exchanger. Air is taken as the working fluid. The flow regime is assumed to be turbulent because, usually the fin spacing is small and the mean velocity is such that the Reynolds numbers of interest are below the critical Reynolds number. The constant heat flux boundary condition is used. This research work gives a performance data for a rectangular wing in a plate-fin heat exchanger. In order to evaluate the performance, bulk temperature and average Nusselt number are calculated. The heat transfer enhancement is observed with the use of vortex generator. It is observed that the heat transfer increases with the increase in the angle of attack and Reynolds number. The experiments are also performed varying the geometrical size and the angle of attack. For a fixed area, increase in the length gives more heat transfer enhancement then an increase in the height of the wing. Vortex generators with aspect ratios of A = 1, 1.33, 2 are studied at attack angles of 20°,30°and 40°.  The results indicate that the stream wise vortices generated by a wing can enhance local Nusselt numbers by more than 200% in a developing channel flow. Under some conditions, the average Nusselt number nearly doubled for a heat transfer area that was 37 to 63 times the wing area.

Keywords— Heat transfer Enhancement, Friction factor, delta wing, turbulator

The paper presents direct measurement of in-cylinder friction from a single cylinder motocross race engine under motored conditions and compares the same with a new analytical predictive method. These conditions are encountered in piston-cylinder system with the application of cylinder deactivation (CDA) technology, which is a growing trend. The analytical method takes into account the various regions within instantaneous contact of compression ring-cylinder liner, including lubricant film rupture, cavitation zone and the subsequent lubricant film reformation. The analysis also includes the effect of boundary friction and lubricant rheology. The predictions and direct measurements of cyclic friction show good agreement and indicate dominance of viscous friction under the investigated engine running conditions. In particular, it is shown that the compression ring contribution to in-cycle friction is most pronounced in the region of high cylinder pressures because of combined Poiseuille friction and some boundary solid interactions. The combined experimental-analytical approach has not hitherto been reported in literature.

IC engines contribute to global warming through extensive use of fossil fuel energy and emission of combustion by-products. Innovative technologies such as cylinder de-activation (CDA), after-exhaust heat treatment, surface texturing and coatings are proposed to improve fuel economy and reduce emissions of the vehicle fleet. Therefore, study of coating technology through a comprehensive multi-physics analytical model of engine top compression ring is important to ascertain ways of promoting energy savings. This paper presents a multi-scale, multi-physics model of the compression ring-cylinder bore conjunction, using three alternative bore surfaces. The model comprises ring dynamics, contact tribology, heat transfer and gas blow-by. Tribological and thermal properties of advanced coatings, such as Nickel Nanocomposite (NNC) and diamond-like carbon (DLC) are compared with an uncoated steel bore surface as the base line configuration. Such a comprehensive analysis has not hitherto been reported in open literature, particularly with original contributions made through inclusion of salient properties of alternative bore materials for high performance race engines. Power loss and FMEP are evaluated in a dynamometric test, representative of the Worldwide harmonised Light vehicles Test Cycle (WLTC). The NNC coating shows promising tribological improvements. The DLC coating is detrimental in terms of frictional power loss and FMEP, although it can effectively improve sealing of the combustion chamber. The differences in power loss of nominated bore surfaces are represented as fuel mass and CO emissions, using theoretical and empirical relations. For the first time the paper shows that advanced coatings can potentially mitigate the adverse environmental impacts of spark ignition (SI) engines, with significant repercussions when applied to the global gasoline-powered vehicle fleet.