Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Heavy metal or aluminum in an organic phosphorus compound...
Reexamination Certificate
1997-12-09
2003-08-12
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Heavy metal or aluminum in an organic phosphorus compound...
C508S485000, C208S018000
Reexamination Certificate
active
06605573
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a lubricating oil composition for internal combustion engines, and more specifically to an ester-blended lubricating oil composition for internal combustion engines, which makes use of a blended base stock composed of an ester and a poly (&agr;-olefin) and/or a highly-refined mineral oil and allows a molybdenum-containing friction modifier to show its effects to maximum extent.
DESCRIPTION OF THE PRIOR ART
For a lubricating oil for internal combustion engines of automotive vehicles or the like, which may hereinafter be called the “engine oil”, diversified performance is required such as cooling of an inside of an engine, cleaning and dispersion of combustion products, and also prevention of rusting and corrosion in addition to lubrication of piston rings and a cylinder lining, bearings for a crankshaft and connecting rod, and a valve-operating mechanism including cams and valve lifters.
Moreover, keeping in step with the recent move toward internal combustion engines of higher performance and higher output for automotive vehicles, sliding parts are exposed to ever increasing more severe friction and abrasion conditions at high temperatures, leading to a demand for a lubricating oil capable of withstanding such extremely severe conditions. With a view to meeting this demand, synthetic lubricating oils making use of highly-refined mineral oils and ester base stocks and/or synthetic hydrocarbon base stocks excellent in oxidation stability, cleaning and dispersing properties and the like have been proposed as substitutes for conventional mineral oils. To cope with energy and environmental problems, however, it is indispensable for an engine oil to have fuel consumption saving ability. It has therefore become extremely important for such engine oil to also have a small friction loss in an internal combustion engine. For the reduction of frictional loss, friction modifiers hence are being increasingly used. Organomolybdenum compounds, for example, molybdenum dialkyldithiocarbamates (MoDTC), oxymolybdenum diethylate amides and the like have been proposed [see Japanese Patent Publication (Kokoku) No. SHO 49-6392, Japanese Patent Application Laid-Open (Kokai) No. SHO 54-113604, Japanese Patent Application Laid-Open (Kokai) No. HEI 6-100879, etc.].
However, molybdenum-base friction modifiers carry with them the problems that they show extremely low friction reducing effects when used in combination with ester-blended base stocks and that the effects of molybdenum-base friction modifiers are substantially reduced in the presence of a phosphorus component such as a zinc dithiophosphate, especially in the presence of such a phosphorus component at a high concentration.
As has been explained above, there is a significant obstacle involved with the use of ester-blended base stocks as lubricating oils for internal combustion engines, said lubricating oils being required to have friction reducing effects, although they are excellent in oxidation stability, cleaning and dispersion ability and the like.
An object of the present invention is therefore to provide a fuel-consumption-saving, synthetic lubricating oil composition of a low coefficient of friction, which allows a molybdenum-base friction modifier to show its friction reducing effects to maximum extent in an ester-blended base stock.
SUMMARY OF THE INVENTION
In view of the status of developments of fuel-consumption-saving lubricating oils as described above, the present inventors have proceeded with an extensive investigation. As a result, it has been found that use of a synthetic ester base stock of particular properties as a component of a lubricating oil composition makes it possible to highly exhibit the friction reducing effects of a molybdenum-base friction modifier. Based on this finding, the present invention has now been completed.
The present invention relates to a lubricating oil composition for internal combustion engines, said composition containing an ester-blended base stock, an organomolybdenum compound and a zinc dithiophosphate, wherein said ester-blended base stock comprises:
an ester having a kinematic viscosity of from 8 cSt to 35 cSt at 100° C. and a saponification value of 200 mg-KOH/g or lower; and
a poly (&agr;-olefin) and/or a highly-refined mineral oil.
Preferably, the present invention relates to a lubricating oil composition for internal combustion engines, comprising:
a base stock composed of a blend of:
at least one ester selected from the group consisting of diesters and polyol esters, each of which has a kinematic viscosity of from about 8 cSt to 35 cSt at 100° C. and a saponification value of from 80 mg-KOH/g to 200 mg-KOH/g, and a poly (&agr;-olefin) obtained by low-degree polymerization of an &agr;-olefin and/or a highly-refined mineral oil having a sulfur content of 5 ppm or lower and an aromatic hydrocarbon content of 1 wt % or lower; and based on the whole weight of said lubricating oil composition,
100 ppm to 1,000 ppm, in terms of molybdenum, of a molybdenum dithiocarbamate; and
800 ppm to 1,800 ppm, in terms of phosphorus, of a zinc dithiophosphate.
More preferably, the present invention relates to a lubricating oil composition for internal combustion engines, comprising:
a blended base stock composed of:
10 wt % to 30 wt % of an ester base stock having a kinematic viscosity of from 8 cSt to 35 cSt at 100° C. and a saponification value of from 80 mg-KOH/g to 200 mg-KOH/g, and
90 wt % to 70 wt % of a poly (&agr;-olefin) base stock or a highly-refined mineral base stock;
100 ppm to 1,000 ppm, in terms of molybdenum, of a molybdenum dithiocarbamate; and
800 ppm to 1,800 ppm, in terms of phosphorus, of a zinc dithiophosphate.
DETAILED DESCRIPTION OF THE INVENTION
Unique features of the present invention reside in the use of (i) an organic acid ester as a base stock in the lubricating oil composition for internal combustion engines and further in the selection and use, as the organic acid ester, of an organic ester having (ii) a saponification value of 200 mg-KOH/g or lower and (iii) a kinematic viscosity of at least 8 cSt at 100° C. The present inventors have found for the first time that the use of an organic acid ester having a saponification value and a viscosity in these ranges as a base stock in a lubricating oil composition for internal combustion engines makes it possible to fully exhibit the performance of a molybdenum-base friction modifier.
The ester useful as a component of the lubrication oil composition according to the present invention for internal combustion engines is selected from organic acid esters, for example, from the group consisting of diesters including dimer acid esters, polyol esters and complex esters, said esters having a kinematic viscosity of from 8 cSt to 35 cSt at 100° C. and a saponification value of 200 mg-KOH/g or lower.
Preferred examples of diesters usable in the lubricating oil composition of the present invention for internal combustion engines are diesters in which the total number of carbon atoms is 38 or greater. No particular limitation is imposed on the diesters, insofar as their total carbon numbers as defined above are 38 or greater and they are available through esterification reactions between dibasic acids and alcohols. Those obtained by bonding between aliphatic dibasic acids having 4 to 40 carbon atoms and alcohols having 4 to 24 carbon atoms can be used. Preferred examples of aliphatic dibasic acids having 4 to 40 carbon atoms can include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanoic diacid, dodecanoic diacid, tridecanoic diacid, and dimer acids. Dimer acids are typically identified in the trade as dicarboxylic acids usually containing about 36 carbons. Among alcohols having 4 to 24 carbon atoms, preferred examples can include n-butanol, isobutanol, n-pentanol, isopentanol, n-hexanol, 2-ethylbutanol, cyclohexanol, n-heptanol, isoheptanol, methylcyclohexanol, n-octanol, dimethylhexanol, 2-ethylhexanol, 2,4,4-trimethylpentanol
Kanbara Makoto
Koganei Katsuya
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