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The development of modern engines involves the use of new materials such as diamond-like carbon (DLC) coatings. As these coatings possess different mechanical and physical characteristics to steel, investigation of their friction and wear properties when rubbing against a steel counterpart in a lubricated environment is needed. Specific tests were used to assess the tribological behaviour of these new surfaces (specifically an undoped DLC and a chromium-doped DLC coating). Chemical analyses were also performed in order to evaluate the reactivity of the formulated oil on the various surfaces. The results of the present work clearly show that there was no evidence of tribochemical reaction on DLC coatings. Anti-wear additives were still reacting on the steel counterpart for the undoped DLC case, resulting in better wear properties for the coating. The addition of a metal to the amorphous carbon matrix led to an improvement in wear but inhibited/removed the anti-wear film on the steel counterpart. [ABSTRACT FROM AUTHOR]

The issues associated with tribological scaling are discussed, focusing on specific examples from (a) journal bearing lubrication, (b) piston ring lubrication, (c) elastohydrodynamic line contact lubrication, and (d) fluid scaling.It is demonstrated that in general it is possible, for two dissimilar lubricated contacts, to define dimensionless parameters (such as, for example, a Sommerfeld parameter and an eccentricity ratio) such that if they have the same value for one of these parameters, then the other dimensionless parameter will also be the same. However, other parameters of interest, such as friction, wear, and lubricant temperature rise, will in general be different. Therefore for a complete tribological understanding of a contact, the best approach is to attempt to reproduce the geometries, kinematics, and operating conditions as closely as possible. [ABSTRACT FROM AUTHOR]

Government legislation, customer requirement, and pressure from the original equipment manufacturers (OEM) continually pushes the issue of increased vehicle fuel economy to the forefront. Lubricant manufacturers responded by creating low viscosity lubricants with complex additive packages capable of reducing total engine friction while maintaining the useful life of the engine. An important component in the lubricant additive package is the friction modifier, whose job is to reduce the sliding friction of components operating in the boundary lubrication regime. It is widely agreed that 40-60 per cent of mechanical friction can be attributed to the piston/ring/cylinder wall interface, much of which is as a result of the compression ring whose lubrication is kept purposely minimal to control exhaust emissions. A logical progression to research suggests utilizing fuel to administer friction modifier directly to the top ring zone of the engine, the area where its effects are most beneficial. This article describes a series of tests conducted using a Plint TE-77 reciprocating tribometer to investigate the synergy of lubricant and fuel containing friction modifier at the top ring zone. A computational model has been modified and utilized to further investigate the potential impact of administering friction modifier at the top ring zone via the fuel. [ABSTRACT FROM AUTHOR]

With tightening emission regulations, increased expected fuel economy, and longer drain intervals impacting on lubricant formulation, greater understanding of how oil degrades in an automotive engine is becoming ever more important. Equally significant is the effect that this degraded lubricant has on the tribological operation of the engine, particularly its overall internal friction and component wear. In a previous paper, four tests to degrade oil in a single cylinder engine were reported [1]. These tests were set up such that the lubricating oil was degraded in the ring pack before returning to the sump, where it was sampled and chemical and rheological analysis undertaken. This paper reports the extension of this work using the same Hydra engine and describes how oil has additionally been extracted from the rear of the top piston ring during engine operation. This extracted oil has then been subjected to similar analysis as the sump oil samples in the previous tests, along with additional analysis to look at the tribological properties of the oil using tribometers. The results clearly show significant differences in the rheological, tribological, and chemical properties of the fresh oil and used sump oil samples when compared with the top ring zone (TRZ) oil samples, particularly the effect of load on the levels of volatiles present in the TRZ samples and their effect on traction and friction coefficient values during tribological testing. [ABSTRACT FROM AUTHOR]

A review is undertaken of the important trends in engine lubricant performance tests that have taken place over the last 10–15 years. Lubricant formulations are driven by industry standard specifications, original equipment manufacturer requirements, and consumer needs. A review is given of the important specifications and associated performance tests, and how these have impacted on lubricant development. The key trends are, firstly, the need for improved fuel economy, secondly, the need for improved oxidation stability, thirdly, the need for improved handling of contaminants (e.g. soot), and, fourthly, the recent move to lubricants containing low levels of sulphur, phosphorus, and sulphated ash, for after-treatment device compatibility reasons. [ABSTRACT FROM AUTHOR]

Presents a letter to the editor about the simplification of the short bearing approximation.

There is currently a strong focus on producing increasingly fuel-efficient vehicles, both to help meet CO[sub 2] emissions reductions targets arising from the Kyoto Agreement on climate change, and, in certain countries, to avoid large government-imposed financial penalties. This paper reviews the role that lubricants can play in reducing a vehicle's fuel consumption. The paper reviews the lubricant factors that affect fuel consumption. The paper also reviews a number of engine friction models, which help to give insight into the relative importance of the different engine components to total engine friction. The paper reviews how these models compare with results from the European and US passenger car standard fuel economy engine tests now in place. The paper also reviews the issues surrounding engine durability with the lower-viscosity fuel economy lubricants that are now being developed. The majority of the paper is concerned with fuel economy in passenger car vehicles, but there is also some discussion of the issues surrounding improved fuel economy in heavy-duty diesel trucks. [ABSTRACT FROM AUTHOR]

For short journal bearings (defined as those where L/D <0.5, where L is the length and D is the diameter), such as those used in modern automotive engines, the `short bearing approximation' is an attractive fast tool for bearing designers to use as a first approximation. The essence of the approximation is that the pressure variation across the width of the bearing is much greater than that around the circumference of the bearing. With this approximation, it is possible to neglect certain terms in the Reynolds equation, and an analytical expression for the pressure variation around the bearing can be written down. By integrating the pressure around the bearing, an analytical expression relating the load, W, to the eccentricity ratio, , may be obtained. The standard `short bearing approximation' assumes that the lubricant is Newtonian, and so any variation in the lubricant viscosity with the shear rate is neglected In this paper, an isothermal analysis is made which uses the short bearing approximation but allows for the possibility of lubricant shear thinning. The variation in the lubricant viscosity with the shear rate is assumed to be as described by the Cross equation, which has previously been shown to give a good fit to measured flow curves. A detailed description of the analysis is given, together with results obtained when the model was applied to a modern automotive con-rod bearing. (Note that the effects of pressure on lubricant viscosity have been neglected.). [ABSTRACT FROM AUTHOR]

The sensitivity of engine friction to lubricant viscometry has been determined for a modern fuel-efficient engine, the Mercedes Benz M111 2.0litre gasoline engine, under both cold starting and fully warmed-up conditions. The study has taken into account realistic lubricant viscometric parameters such as the lubricant viscosity variation with shear rate and temperature. Results are reported for the variation of engine friction with different monograde and multigrade lubricants, including the distribution of friction losses between valve train, piston assembly and bearings with the differ ent lubricant types. The work also enabled estimates to be made of the proportion of hydrodynamic and boundary friction in the engine, since the vast majority of boundary lubrication occurs in the valve train. Knowledge of the ratio of boundary to hydrodynamic lubrication was found to be important since the two key lubricant parameters that can be varied are (a) viscosity and (b) the introduction of a friction modifier additive. The viscosity of the lubricant will affect the hydrodynamically lubricated parts of the engine whereas the presence of a friction modifier will reduce boundary friction in the engine. Brief comparisons are made of the lubricant sensitivity of the Mercedes Benz M111 engine with other important fuel-efficient engines (such as the Ford Sequence VI and Ford Sequence VI A engines). [ABSTRACT FROM AUTHOR]