For these components, coatings and surface finish are extremely important. Making surfaces
smoother has provided significant benefits, but costs increase exponentially with increasing
surface quality. Information is needed on adequate smoothness. There is a need to develop
affordable, lead-free coatings for crankshaft bearings and durable, wear-resistant coatings for
rings and cylinder liners.
It is anticipated that in order to meet stringent diesel engine emission requirements, fuel injection
pressures will increase significantly, and flexible fuel metering/controlling devices will be
needed. At the same time, the million-mile warranty goal will require improved system
component and material durability. Higher fuel pressures will require new developments to
prevent abrasive "jet" wear, eliminate seizure and galling of plungers, and increase the fatigue
strength of components.
Fruitful areas for research include:
Advanced low-friction, wear-resistant coatings for plungers and valve seats.
Hydraulic modeling for fluid cavitation and fuel spray pattern.
Affordable high-fatigue-strength materials.
Increasing power density is the current primary concern of bearing manufacturers. As with any
component, transmitting more power through a smaller package results in higher stresses, which
can lead to fatigue failures.
In recent years, significant improvements in power density, without sacrificing fatigue life, have
been made with the following three approaches:
Improving the materials, primarily cleanliness of steels.
Improving machining to produce more accurate motion geometries.
Improving the surface texture by making surfaces much smoother.
It is felt that those techniques have been taken as far as possible, and any further increase in load-
bearing capacity will require special surface treatments probably coatings to prevent surface
failures. Designing a coating system for a bearing is not simple. In addition to overcoming the
significant problems of adhesion, wear resistance, and cost, it may be necessary to have different
coatings on different parts of the bearing depending upon whether the relative motion is rolling,
sliding, or a combination of both.
There also are opportunities to improve bearing performance by optimizing the lubrication
system through improved base fluids and additives. Modifying the lubricant also can be
complicated. In one instance, a special additive to reduce wear resulted in a 50% decrease in
fatigue life. In other words, all aspects of bearing performance must be considered when
choosing and developing a lubricant.