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
2001-11-26
2002-12-31
Howard, Jacqueline V. (Department: 1764)
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...
C508S371000, C508S372000, C508S375000, C508S391000
Reexamination Certificate
active
06500786
ABSTRACT:
The present invention relates to lubricating oil compositions. More particularly, the present invention relates to lubricating oil compositions, which exhibit improved low temperature valve train wear performance with reduced phosphorus content.
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, reduce engine wear, to provide stability against heat and oxidation, to reduce oil consumption, to inhibit corrosion, to act as a dispersant, and reduce friction loss. Some additives provide multiple benefits, such as a dispersant/viscosity modifier. Other additives, while improving one characteristic of the lubricating oil, have an adverse effect on other characteristics. Thus, to provide a 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.
To provide improved low temperature valve train wear performance, conventional lubricants are formulated with an antiwear additive. Metal hydrocarbyl dithiophosphates, particularly zinc dialkyldithiophosphates (ZDDP), are the primary antiwear additive used in lubricating oils for internal combustion engines. ZDDP provides excellent wear protection at a comparatively low cost and also functions as an antioxidant. However, there is some evidence that phosphorus in lubricants can shorten the effective life of automotive emission catalysts. Accordingly, industry has limited the amount of phosphorus that lubricants can contain. The current industry category (ILSAC GF-3) mandates a lubricant phosphorus limit of 1000 ppm. It is possible that the next category of service fill oils in the United States will mandate even more stringent limits, such as a maximum phosphorus content of no more than 600 ppm, or even 500 ppm.
Concurrently, there has been a move to higher quality (including hydrocracked and synthetic) base oils which have lower sulfur content, lower wax content and reduced volatility. These oils, due to a higher natural viscosity index, provide improved lubricant performance and low temperature characteristics.
To meet these emerging requirements, it would therefore be advantageous to provide lubricating oils, particularly lubricating oils formulated with base oils having relatively high viscosity indices and low volatilities for improved fuel economy, that also provide excellent low temperature valve train wear performance with reduced amounts of phosphorus-containing antiwear additives.
U.S. Pat. Nos. 5,346,635 and 5,439,605 describe lubricating oils completely free of phosphorus-containing antiwear additives containing a complex blend of ashless friction reducers, ashless antiwear/extreme pressure additives, antioxidants, metal detergents and polymeric viscosity modifiers and flow improvers, which compositions purportedly provide acceptable properties. These compositions may also contain a molybdenum-containing additive, as a friction modifier.
Each of WO 96/37,582 and EP 0 855 437 describe lubricating oil formulations that contain, in addition to other specified and required additives, an amount of ZDDP that may provide 600 ppm or less of phosphorus, together with a molybdenum-based friction modifier.
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, molybdenum compounds provide enhanced fuel economy in gasoline or diesel fueled engines (spark- and compression-ignited engines, respectively), including both short and long term fuel economy (i.e., fuel economy retention properties).
It has now been found that by adding even a small amount of these molybdenum compounds to a lubricating oil, excellent low temperature valve train wear performance can be achieved with reduced levels of ZDDP. Thus, lubricating oils providing excellent low temperature valve train wear performance can be formulated with reduced levels of phosphorus can be provided.
The present invention also provides many additional advantages that shall become apparent as described below.
SUMMARY OF THE INVENTION
In accordance with first aspect of the invention, there is provided a lubricating oil composition providing excellent low temperature valve train wear performance, which composition comprises at least one oil of lubricating viscosity, at least one molybdenum compound in an amount sufficient to provide the composition with at least 50 ppm by mass, of molybdenum; a phosphorus-free antioxidant and a metal-free friction modifier, which composition contains an amount of ZDDP that contributes no more than 600 ppm of phosphorus to the lubricating oil composition.
In accordance with a second aspect of the invention, there is provided a lubricating oil composition as described in the first aspect of the invention, wherein the oil of lubricating viscosity has a viscosity of between about 4.0 mm
2
/sec and 5.5 mm
2
/sec at 100° C. and/or the lubricating oil composition (the fully formulated oil) has a NOACK volatility of no more than 15 wt. %.
In accordance with a third aspect of the invention, there is provided a lubricating oil composition as described in the first aspect of the invention, wherein the antioxidant is present in an amount effective to achieve a MHT-4 TEOST result of no more than 45 mg. of deposit.
In accordance with a fourth aspect of the invention, there is provided a lubricating oil composition as described in the first aspect of the invention, wherein the metal-free friction modifier is present in an amount effective to achieve a pass in a Sequence VIB fuel economy test.
In accordance with a fifth aspect of the invention, there is provided a lubricating oil composition as described in the first aspect of the invention, which further contains an overbased metallic detergent.
In accordance with another aspect of the invention, described is the use of a molybdenum compound to provide improved low temperature valve train wear performance to a lubricating oil composition containing a metal hydrocarbyl dithiophosphate in an amount introducing no more than 600 ppm of phosphorus into the composition, a metal-free friction modifier and a phosphorus-free antioxidant.
Other and further aspects, objects, advantages and features of the present invention will be understood by reference to the following specification.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The lubricating compositions of the present invention contain an oil of lubricating viscosity, an amount of a metal hydrocarbyl dithiophosphate, particularly ZDDP, and an amount of a molybdenum compound sufficient to provide the composition with at least 50 ppm by mass of molybdenum. An amount of about 50 ppm to 350 ppm by mass of molybdenum from a molybdenum compound has been found to be effective as an auxiliary antiwear agent in combination with reduced levels of ZDDP. Specifically, a molybdenum compound, in an amount providing from 50 ppm to 200 ppm by mass has been found to be sufficient to provide antiwear characteristics to formulations containing ZDDP in amounts introducing from about 500 to 600 ppm by mass into the composition.
With reduced amounts of ZDDP, molybdenum compounds have been found to provide insufficient fuel economy/friction modifying characteristics and compositions containing, in combination, a molybdenum compound and a reduced amount of ZDDP may not provide a reliable pass of a Sequence VIB fuel economy test. Metal-free friction modifiers have been found to provide excellent fuel economy results in systems containing reduced amounts of ZDDP.
Molybdenum compounds are expensive compared to ZDDP. In the total absence of ZDDP, far more of the molybdenum compound (e.g., an amount providing about 8
Hartley Rolfe J.
Waddoups Malcolm
Howard Jacqueline V.
Infineum International Ltd.
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