Victor W. Wong, Simon C. Tung - Overview of automotive engine friction and reduction trends - Effects of surface, material, and lubricant-additive technologies

Article. — Friction. — 2016. — Volume 4. — P. 1-28Abstract: In this paper, the fundamentals of friction specific to the environments of engine components tribology are reviewed, together with discussions on the impact of developing vehicle powertrain technologies, surface and material technologies, as well as lubricant and additive technologies on promises of continuing friction and wear reduction trends. This paper focsuses on friction reduction in mainly automotive engines, however.
The paper starts with a clarification of the common descriptors of mechanical losses and friction in the engine, followed by the topic of lubrication fundamentals such as lubrication regimes. Then the lubrication of the contacting surfaces in each of the major engine subsystems is discussed in turn. These subsystems include the piston assembly: ring-pack/liner, piston-skirt/liner, and piston-pin/connecting-rod contacts; connecting rod and crankshaft bearings; and the valvetrain subsystem. The relative contributions to total friction from the various subsystems are discussed, with the piston-assembly contributing to about half of the total friction. Lastly, besides new hardware and material science changes, several advanced additives such as advanced friction modifiers, antiwear additive chemistries, low viscosity lubricants, and the introduction of new VI Improvers all represent possible tribological solutions to the challenge of meeting more stringent energy efficiency requirements and environmental legislation. The final section of this paper will discuss the future trends of engine friction reduction and wear control by surface modification such as friction-reducing coatings or surface textures in engine components. In brief, the paper reviews the characteristics of component friction in the environment of the internal combustion engine and the relevant design considerations, addresses the impact of emerging technologies on engine friction and the tribological changes and requirements, especially on lubricant and additives, and lastly discusses the interactions between lubricant-additive formulations and material surface engineering, and their effects on friction, wear and engine durability. The increasing importance and interplay between synergistic advancements in component design, material and surface engineering, and advanced lubricant-additive formulation will be fully illustrated.