Lubricating oils used in passenger cars and heavy duty diesel engines have changed over the years. Today's engines are designed to run hotter and harder than in the past. Various additives have been added to lubricant formulations in order to reduce wear between moving parts. One particularly common antiwear additive is a zinc dialkyl dithiophosphate (“ZnDDP”). While such zinc compounds are particularly useful as antiwear agents, such zinc compounds may have one or more of the following disadvantages: increased levels of sulfur and/or phosphorus in the finished lubricant.
Future generations of passenger car motor oils and heavy duty diesel engine oils require lower levels of phosphorus and sulfur in the finished oil in order to protect pollution control devices as it is well known that sulfur and phosphorus containing additives may poison or otherwise reduce the effectiveness of pollution control devices. For example, current GF-4 motor oil specifications require a finished oil to contain less than 0.08 wt % and 0.7 wt % phosphorus and sulfur, respectively, and PC-10 motor oil specifications, the next generation heavy duty diesel engine oil, requires oils to contain less than 0.12 wt % and 0.4 wt % phosphorus and sulfur, respectively, and 1.0 wt % sulfated ash. Certain antiwear additives known in the industry contain phosphorus and sulfur at levels which reduce the effectiveness of pollution control devices.
Therefore, a need exists for lubricant additives and compositions that provide enhanced antiwear properties and which are more compatible with pollution control devices used for automotive and diesel engines. A need also exists for such lubricant additives and compositions which are more compatible with such pollution control devices without adversely affecting oil solubility, corrosion, and/or darkening the color of the finished lubricant. Such additives may contain phosphorus and/or sulfur or may be substantially devoid of phosphorus and/or sulfur.
In one embodiment herein is presented a lubricated surface including a lubricant composition including a base oil of lubricating viscosity, at least one metal salt of phosphorothioic acid, and an amount of at least one hydrocarbon soluble titanium compound effective to provide an increase in antiwear properties of the lubricant composition wherein a ratio of titanium metal to phosphorus in the antiwear agent ranges from about 0.3:1 to about 1.5:1.
In another embodiment, there is provided a vehicle having moving parts and containing a lubricant for lubricating the moving parts. The lubricant includes an oil of lubricating viscosity, a friction modifier, and an antiwear agent comprising an amount of at least one hydrocarbon soluble titanium compound and an amount of at least one metal salt of phosphorothioic acid. A ratio of titanium metal to phosphorus in the antiwear agent ranges from about 0.3:1 to about 1.5:1. The antiwear agent provides a antiwear film thickness that is greater than a film thickness provided by the titanium compound or phosphorus compound alone.
In yet another embodiment there is provided a fully formulated lubricant composition including a base oil component of lubricating viscosity, and an antiwear agent comprising an amount of hydrocarbon soluble titanium-containing compound and an amount of at least one metal salt of phosphorothioic acid. A ratio of titanium metal to phosphorus in the antiwear agent ranges from about 0.3:1 to about 1.5:1.
A further embodiment of the disclosure provides a method for increasing an antiwear film thickness adjacent to a lubricated surface. The method includes contacting the surface with a lubricant composition comprising a base oil of lubricating viscosity and an amount of an antiwear agent comprising a hydrocarbon soluble titanium compound and a metal salt of phosphorothioic acid. The antiwear agent has a titanium metal to phosphorus ratio that provides a synergistic increase in the antiwear film thickness compared to an antiwear film thickness provided by a lubricant composition containing only one of the titanium compound and the metal salt of phosphorothioic acid.
As set forth briefly above, embodiments of the disclosure provide a combination of a hydrocarbon soluble titanium compound and a hydrocarbon soluble phosphoric acid metal salt that may significantly improve the antiwear properties of a lubricant composition and may enable a decrease in the amount of phosphorus and sulfur additives required for equivalent antiwear improving characteristics. The additive may be mixed with an oleaginous fluid that is applied to a surface between moving parts. In other applications, the additive may be provided in a fully formulated lubricant composition. The additive is particularly directed to meeting the currently proposed GF-4 standards for passenger car motor oils and PC-10 standards for heavy duty diesel engine oils, as well as future passenger car and diesel engine oil specifications and standards.
The compositions and methods described herein are particularly suitable for increasing a lubrication boundary layer between lubricated surfaces that is synergistically thicker than a boundary layer formed by a lubricant composition that is devoid of either the titanium compound or the phosphorus compound. Other features and advantages of the compositions and methods described herein may be evident by reference to the following detailed description which is intended to exemplify aspects of the embodiments without intending to limit the embodiments described herein.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the embodiments disclosed and claimed.