Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions. Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved micro-wedge flow. The results show good agreement between numerical predictions and experimental measurements using a precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for given conditions, dependent on the intended application under laboratory conditions. The translation of the same into practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain. This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue than that obtained under ideal laboratory conditions.

The piston ring/cylinder liner conjunction can experience various regimes of lubrication during piston strokes inside the engine cylinder. In the current engines, the nature of lubrication usually remains hydrodynamic at mid-stroke, while a mixed regime of lubrication may be experienced at and near reversals. The direct contact between the tips of some of the asperities of opposing surfaces leads to mixed (partial) regime of lubrication. A model proposed by Greenwood and Tripp can be used to predict asperity-level contribution to the total piston friction. At the same time, Reynolds equation can be employed to predict the portion of load carried by the lubricant trapped between the asperities. Friction between the asperity tips is usually proportional to the load that they support, stated in terms of a proportionality factor, that is, coefficient of friction. The surfaces are usually furnished with hard wear-resistant coatings and in parts by solid lubricants. Both the piston rings and cylinder liner surfaces are usually coated. These coatings change the friction characteristics of the counterfaces because of their surface topography as well as material mechanical properties. Atomic force microscope is used to obtain surface topographical parameters in contact tapping mode. The corresponding surface topographical parameters are obtained from representative regional areas of the contacting solid surfaces, using a Talysurf. The combination of topography and coating characteristics are used to develop the necessary parameters for a boundary friction model. A numerical model of the top compression ring to cylinder liner is developed based on mixed-hydrodynamic regime of lubrication. The results for friction and the effect of coating on the power loss and wear of the conjunction are discussed in this article.

Real cylinder bores are out-of-round and axially asymmetrical. The top compression ring, nominally an incomplete circle, is subjected to ring tension and cyclic combustion force in order to conform to the bore surface. The bounding surfaces are rough and their conjunction is subject to a transient tribological state. Therefore, the ring–bore conjunction is only partially conforming for most of the engine cycle. The conjunction may be viewed as a problem of scale, depending on the analysis carried out at a certain bore order (out-of-roundness). Therefore, the contact may be viewed as a multi-lobed rough conjunction, where the regime of lubrication may vary from hydrodynamics to mix with dominant asperity friction at piston reversals. Measured bores and ring profiles are used to predict conjunctional power loss and percentage fuel energy consumed. Furthermore, lubricant’s flow through the ring is predicted throughout the engine cycle. These measures are key industrial design drivers for fuel efficiency and reduction of emissions. The results show that the effect of bore out-of-roundness can be even more significant than the surface topography.

Piston–cylinder interactions account for a significant portion of frictional losses in an internal-combustion engine. This is mainly as the result of significant changes in the operating conditions (the load, the speed and the temperature) as well as the contact geometry and the encountered topography during a typical engine cycle. These changes alter the regime of lubrication which underlies the mechanisms of friction generation. The multi-variate interactive nature of the problem requires quite complex analyses which do not fully replicate the actual in-situ conditions. Therefore, there is a need for direct measurement of cyclic friction under controlled conditions. The paper describes the use of a novel floating-liner arrangement which is capable of direct measurement of friction, its transitory mechanisms, as well as determination of the regime of lubrication.

The paper describes a combined tribodynamics analysis (dynamics and contact tribology) of cylindrical roller bearings of a heavy duty truck transmission under high applied loads. The dynamic analysis provides the transient variations in contact load. It also determines the vibration spectrum of the bearing as well as that of contact dynamics. It is shown that with sufficient preloading and/or interference fitting a widely spread loaded region results, which reduces bearing-induced vibration. The transient tribological analysis, including thermal analysis with a novel and realistic lubricant inlet boundary condition demonstrates that non-Newtonian mixed elastohydrodynamic regime of lubrication is prevalent, but with reduced friction compared with unrealistic dry Coulombic friction, which is often assumed in literature.

There are increasing pressures upon the automotive industry to reduce harmful emissions as well as meeting the key objective of enhanced fuel efficiency, while improving or retaining the engine output power. The losses in an internal combustion (IC) engine can be divided into thermal and parasitic as well as due to gas leakage because of untoward compression ring motions. Frictional losses are particularly of concern at low engine speeds, assuming a greater share of the overall losses. Piston–cylinder system accounts for nearly half of all the frictional losses. Loss of sealing functionality of the ring pack can also contribute significantly to power losses as well as exacerbating harmful emissions. The dynamics of compression ring is inexorably linked to its tribological performance, a link which has not been made in many reported analyses. A fundamental understanding of the interplay between the top compression ring three-dimensional elastodynamic behavior, its sealing function and contribution to the overall frictional losses is long overdue. This paper provides a comprehensive integrated transient elastotribodynamic analysis of the compression ring to cylinder liner and its retaining piston groove lands' conjunctions, an approach not hitherto reported in the literature. The methodology presented aims to aid the piston ring design evaluation processes. Realistic engine running conditions are used which constitute international drive cycle testing conditions.