Lubrication and Friction

Abstract

This chapter describes in brief the basic lubrication and friction processes at the major engine components. It 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, 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. The remainder of the friction comes from the crankshaft, connecting rod, and camshaft bearings, and the valvetrain oscillating parts. The bearings are in predominantly hydrodynamic lubrication, in contrast to the valvetrain oscillating components, which are characterized to be mostly in the mixed/boundary lubrication regimes. Lubricating oil composition is discussed in the final section. It is generally believed that the bulk oil viscosity, with proper viscosity and (boundary) friction modification, could be controlled to lower component friction, in conjunction with antiwear additives. Effects of lubricant‐derived ash on diesel particulate filter ( DPF ) restriction are significant, with large differences observed among lubricant‐derived ash originating from different metallic‐based additives—such as among calcium, magnesium, or zinc compounds—at the same mass accumulation.