Lubricating oil composition

Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Nitrogen and heavy metal – or nitrogen and aluminum – in the...

Reexamination Certificate

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C508S371000, C508S372000, C508S374000, C508S379000, C508S391000, C508S445000, C508S501000

Reexamination Certificate

active

06723685

ABSTRACT:

The present invention relates to lubricating oil compositions. More particularly, the present invention relates to lubricating oil compositions, which exhibit simultaneously improved low temperature valve train wear performance, excellent compatibility with fluoroelastomer materials commonly used for seals in modern internal combustion engines, and improved fuel economy properties.
BACKGROUND OF THE INVENTION
Lubricating oil compositions used to lubricate internal combustion engines contain base oil of lubricating viscosity, or a mixture of such oils, and additives used to improve the performance characteristics of the oil. For example, additives are used to improve detergency, to reduce engine wear, to provide stability against heat and oxidation, to reduce oil consumption, to inhibit corrosion, to act as a dispersant, and to reduce friction loss. Some additives provide multiple benefits, such as dispersant-viscosity modifiers. Other additives, while improving one characteristic of the lubricating oil, have an adverse effect on other characteristics. Thus, to provide lubricating oil having optimal overall performance, it is necessary to characterize and understand all the effects of the various additives available, and carefully balance the additive content of the lubricant.
It has been proposed in many patents and articles (for example, U.S. Pat. Nos. 4,164,473; 4,176,073; 4,176,074; 4,192,757; 4,248,720; 4,201,683; 4,289,635; and 4,479,883) that oil-soluble molybdenum compounds are useful as lubricant additives. In particular, the addition of molybdenum compounds to oil, particularly molybdenum dithiocarbamate compounds, provides the oil with improved boundary friction characteristics and bench tests demonstrate that the coefficient of friction of oil containing such molybdenum compounds is generally lower than that of oil containing organic friction modifiers. This reduction in coefficient of friction results in improved antiwear properties and may contribute to enhanced fuel economy in gasoline or diesel fired engines, including both short- and long-term fuel economy properties (i.e., fuel economy retention properties). To provide antiwear effects, molybdenum compounds are generally added in amounts introducing from about 350 ppm up to 2,000 ppm of molybdenum into the oil. While molybdenum compounds are effective antiwear agents and may further provide fuel economy benefits, such molybdenum compounds are expensive relative to more conventional, metal-free (ashless) organic friction modifiers
U.S. Pat. No. 6,300,291 discloses a lubricating oil composition having a specified Noack volatility containing a base oil of a specified viscosity index, calcium-based detergent, zinc dihydrocarbyldithiophosphate (ZDDP) antiwear agent, a molybdenum compound and a nitrogen-containing friction modifier. The molybdenum compound was used in an amount providing the formulated lubricant with up to 350 ppm of molybdenum. The claimed materials are described as providing fuel economy benefits compared to compositions containing only molybdenum compounds.
Modern internal combustion engines include numerous gaskets and other seals formed of fluoroelastomer materials, such as Viton™. Nitrogen-containing additives are suspected of, over time, contributing to the deterioration of such materials. Therefore, it would be desirable to find a lubricating oil composition that provides improved fuel economy benefit; demonstrates excellent wear protection characteristics, is relatively low in cost, and is free of nitrogen-containing friction modifiers.
It has now been found that the addition of small amounts of one or more oil soluble molybdenum compounds, in combination with an ashless, organic nitrogen-free friction modifier, ZDDP and a calcium detergent provide low cost lubricating oils having a demonstrable fuel economy benefit; excellent wear protection characteristics, and reduced adverse effects on engine seals formed of Viton™ and similar fluoroelastomers.
The present invention also provides many additional advantages that shall become apparent as described below.
SUMMARY OF THE INVENTION
In accordance with a first aspect, the invention provides a lubricating oil composition displaying excellent low temperature valve train wear performance, improved fuel economy retention properties and compatibility with fluoroelastomer-based engine seals, which composition comprises an oil of lubricating viscosity having a viscosity index (VI) of at least 95; a calcium detergent in an amount introducing from about 0.05 to about 0.6 wt. % calcium into the composition; an amount of a metal dihydrocarbyldithiophosphate compound introducing up to 0.1 wt. % (1000 ppm) of phosphorus into the composition; at least one molybdenum compound in an amount sufficient to provide the composition with at least 10 ppm of molybdenum; and an effective amount of at least one organic, nitrogen-free, ashless friction modifier; the composition having a Noack volatility of less than 15%.
In accordance with a second aspect, the invention is directed to a method of improving the fuel economy, seal life and/or the wear characteristics of an internal combustion engine, which method comprises the steps of lubricating an internal combustion engine with a lubricating oil composition of the first aspect and operating the engine.
In accordance with a third aspect, the invention is directed to the use of a lubricating oil composition of the first aspect to improve the fuel economy, seal life and/or the wear characteristics of an internal combustion engine.
Other and further objects, advantages and features of the present invention will be understood by reference to the following.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The oil of lubricating viscosity can be at least one oil selected from the group consisting of Group I, Group II, or Group III base stocks or base oil blends of the aforementioned base stocks provided that the viscosity of the base oil or base oil blend is at least 95 and allows for the formulation of a lubricating oil composition having a Noack volatility, measured by determining the evaporative loss in mass percent of an oil after 1 hour at 250° C. according to the procedure of ASTM D5880, of less than 15%. In addition, the oil of lubricating viscosity may be one or more Group IV or Group V base stocks or combinations thereof or base oil mixtures containing one or more Group IV or Group V base stocks in combination with one or more Group I, Group II and/or Group III base stocks.
The most preferred oils for fuel economy retention, are:
(a) Base oil blends of Group III base stocks with Group I or Group II base stocks, where the combination has a viscosity index of at least 110; or
(b) Group III, IV or V base stocks or base oil blends of more than one Group III, IV or V base stocks, where the viscosity index is between about 120 to about 140.
Definitions for the base stocks and base oils in this invention are the same as those found in the American Petroleum Institute (API) publication “Engine Oil Licensing and Certification System”, Industry Services Department, Fourteenth Edition, December 1996, Addendum 1, December 1998. Said publication categorizes base stocks as follows:
a) Group I base stocks contain less than 90 percent saturates and/or greater than 0.03 percent sulfur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in Table E-1.
b) Group II base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in Table E-1.
c) Group III base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur and have a viscosity index greater than or equal to 120 using the test methods specified in Table E-1.
d) Group IV base stocks are polyalphaolefins (PAO).
e) Group V base stocks include all other base stocks not included in Group I, II, III, or IV.
TABLE E-1
Analytical Methods fo

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