Technology trend on boundary lubrication additives as like as anti-wear agents and friction modifiers for automotive engine oil application is summarized. ZnDTP has been still main additive in automotive engine oil formulation as cost effective one providing both wear protection and oxidation inhibition. Phosphorus content in motorcycle engine oil will be reduced to cope with future tighter exhaust emission regulation as same as passenger car engine oil. Newly developed organic friction modifiers showed superior fuel economy improvement performance for passenger car gasoline engine oil compared with exiting FMs. MoDTC application in heavy duty diesel engine oil maybe gradually proceeding because soot contamination into engine oil have been reducing in recent heavy duty diesel engine to meet emission regulation.

A tribo-layer derived from additives in lubricant is available to enhance low friction property or becoming high wear proof when a mating surfaces were suffered insufficient lubrication. Recently, not only steel metals but also carbonaceous coatings are reported as new findings and problems that tribo-layer by additives built on a carbonaceous coating surface and acceleration of its wear. It is assumed that a hardness of such tribo-layer has an effect of materials wear amount, therefore, precise hardness of a tribo-layer without hardness of underlying material is necessary. This paper reviews a hardness of topmost surface measurement method that is so-called “nano-scratch”by using atomic force microscope.

This article focused on the recent technologies of lubricant additives for extending the rolling contact fatigue life. The rolling contact fatigue life depends on the lubricant film thickness, the friction force, and the contact stress. In order to extend the rolling contact fatigue life, thicken the lubricant film thickness, reduce the friction force, and relax the contact stress are effective. Polymer additives are effective for thickening the lubricant film and reducing friction force. Boundary lubricity additives form the low friction layer and some kind of boundary film lead to contact stress relaxation.

As the number of hybrid vehicles where oil temperature is lower than conventional ones equipped with internal combustion engines increases, friction reduction by engine oils under lower temperature conditions as well as under high temperature is required. Therefore, new friction modifier (FM) technologies need to be developed. Molybdenum dithiocarbamate (MoDTC) has widely been used for fuel economy engine oils because of its excellent performance for reducing friction, especially at high temperatures. However, the technology cannot simply be applied to hybrid vehicles because it is ineffective at low temperatures. Research of combined use of adsorption type FMs, which works well at low temperatures, with MoDTC to reduce friction under both high and low temperatures were reviewed. In general, the combined use of both FMs brings antagonism because of the competitive adsorption. However, the polymer type adsorption FM (PFM) can reduce friction while keeping low friction properties of MoDTC. It is suggested that the combined use of MoDTC and PFM can be the solution to reduce friction under a wide temperature range.

Lubricating oils are closely related to the development of mechanical technology. They play a major role as one of the important means for achieving miniaturization of equipment and improvement of energy efficiency. Recently, the viscosity of lubricating oils such as engine oils, hydraulic oils and metalworking oils have been reduced from the viewpoint of improving fuel efficiency and processing accuracy. Therefore, the requirement for lublicanting oil performance becomes higher. In particular, improvement of wear prevention, which is a function to prevent physical damage to the machines, can be said to be one of the important issues that lubricating oil must overcome in order to respond to the development of mechanical technology. Many antiwear agents contain phosphorus, sulfur, and metal components. However, in diesel engine oil, for example, ash from metal components can promote clogging of the Diesel particulate filter (DPF). In addition, the phosphorus / sulfur component may poison the catalyst of the exhaust gas treatment equipment and reduce the exhaust gas treatment capacity. Against this background, in recent years, the development of anti-wear agents that don't contain phosphorus, sulfur, or metal components has been promoted. In this paper, we introduce ashless antiwear agents that have been attracting attention in recent years as additives for lubricating oils.

Since nano-carbon materials with well-controlled structure have gone into industrial production, an application as lubricant additive is coming closer to reality. They are primarily used as boundary lubrication additives due to their fitness to a narrow gap between sliding surfaces under boundary lubrication condition. More environmentally friendly formulation of lubricants can be possible with the carbon materials by reduced use of molybdenum, zinc, sulfur, phosphorus in additives. The key to maximizing their effect is to fully solubilize/disperse in the lubricant oil and to avoid aggregation. Their performance can largely depend on lubrication conditions determining oil film thickness, such as oil viscosity, load, and so on. Synergistic or antagonistic effects should be considered in combination use with other conventional boundary lubrication additives. The application of nano-carbon additives is illustrated with examples of fullerenes, nanodiamonds, and onion-like carbons. Possible lubrication mechanism is discussed based on simulation and experimental studies.

Solving the problem of global warming has become an important issue in modern society. Further improvement in fuel efficiency of automobiles is indispensable for reducing carbon dioxide emissions which causes global warming. The polymer type oil film forming agent is effective under severe friction conditions from the elastohydrodynamic lubrication region to the boundary lubrication region, and greatly contributes to the improvement of the fuel economy performance of automobile gear oil. In this paper, the functions and effects of polymer-type oil film forming agents will be explained using automobile gear oil.

It is necessary to further improve the thermal efficiency of internal combustion engine to reduce CO₂ emissions. For a piston, it is important to understand the lubrication characteristics in order to reduce the friction of a piston skirt. In this paper, the clarification of the relationship between the oil film thickness and the frictional force is carried out to explain the friction-generating mechanism on a piston skirt during the operation of an engine mechanism.

Carbonaceous hard coatings have promising tribological properties, such as low friction, high hardness and high wear resistance. In particular, CN_x (Carbon Nitride) coating and a-C:H (hydrogenated amorphous carbon) coating show ultra low friction coefficient (µ < 0.01) in dry nitrogen gas. However, the mechanism of ultra low friction has not clarified. We have developed the in-situ measurement method on friction area during sliding to clarify the ultra low friction mechanism of carbonaceous hard coating. In this research, we demonstrated in-situ measurement of surface energy on friction area during friction by manufacturing friction tester in ESEM (Environmental Scanning Electron Microscope) chamber. Moreover, we estimated the effect of surface energy on friction property of carbonaceous hard coatings. We used UV irradiation to prepare the carbonaceous hard coatings, which have different surface energy. From the results, friction coefficient of carbonaceous hard coating decreased with surface energy, however the approximate line which showed the relationship between friction coefficient and surface energy did not pass through the origin. It suggested that friction occurred beneath the sliding surface in coatings or transferred layers not on the surface. Moreover, surface energy of carbonaceous hard coatings approached the value of graphite when carbonaceous hard coatings showed low friction. It suggested that structure of carbonaceous hard coatings had become graphite-like structure.