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
2002-12-12
2003-11-04
McAvoy, Ellen M. (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...
C508S469000, C508S470000
Reexamination Certificate
active
06642189
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to engine oil compositions, and more particularly to engine oil compositions which provide excellent fuel efficiency and viscosity at low temperatures and are lower in evaporation loss.
The fuel consumption reduction of automobile engines implemented since the oil crisis is still one of the important issues from the view point of resource- and environment-protection. The fuel consumption reduction of automobiles has been put into practice by reducing the body weight of an automobile, improving combustion efficiency, and reducing the occurrence of friction in an engine. The reduction of friction in engines has been implemented by improving the movable valve structures, reducing the number of piston rings, smoothing the abrasive surfaces of sliding parts, and using fuel efficient engine oils.
Among these measures for reducing fuel consumption, the use of such fuel efficient engine oils has become general in the market because of their excellent balance of cost and performance. The engine oils are blended with effective additives such as friction modifiers. However, in order to make friction modifiers exhibit their performance sufficiently, it is important to carefully select a base oil and formulate the other engine oil additives.
Japanese Laid-Open Patent Publication No. 8-302378 discloses an engine oil composition which comprises a specific base oil, an alkaline earth metal salicylate-based detergent, zinc dialkyldithiophosphate, a polybutenylsuccinimide-based ashless dispersant, a phenol-based ashless oxidation inhibitor, a molybdenumdithiocarbamate-based friction modifier, a viscosity index improver, in specific amounts, respectively.
Reducing the viscosity of an engine oil is considered to be one of the measures to provide an engine oil with good fuel efficiency. However, insufficient investigation or research has been done on a base oil or additives for a low viscosity engine oil.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to blend suitable additives to provide an engine oil composition which is reduced in viscosity compared to conventional fuel efficient engine oils and provides excellent fuel efficiency and viscosity characteristics at low temperatures with less evaporation loss.
As a result of extensive research and development, it was found that an engine oil composition which is reduced in viscosity compared to conventional fuel efficient engine oils, provides excellent fuel efficiency and viscosity characteristics at low temperatures, and is lower in evaporation loss can be obtained by blending a specific base oil with a specific amount of a polymethacrylate-based viscosity index improver.
According to one embodiment of the present invention there is provided an engine oil composition consisting essentially of (A) lubricating base oil having a kinematic viscosity at 100° C. of 3 to 6 mm
2
/s, a viscosity index of 120 or more, and a total aromatic content of 5 percent by mass or less and (B) a polymethacrylate-based viscosity index improver having a weight-average molecular weight of 180,000 or more, blended in such an amount that the composition has a kinematic viscosity at 100° C. of 4.0 to 9.3 mm
2
/s and a high temperature high shear viscosity at 150° C. of 2.4 to 2.7 mPa·s.
According to another embodiment of the present invention there is provided an engine oil composition consisting essentially of (A) a lubricating base oil having a kinematic viscosity at 100° C. of 3 to 6 mm
2
/s, a viscosity index of 120 or more, and a total aromatic content of 5 percent by mass or less and (B) a polymethacrylate-based viscosity index improver having a weight-average molecular weight of 180,000 or more, blended in such an amount that the composition has a kinematic viscosity at 100° C. of 4.0 to 9.3 mm
2
/s and a high temperature high shear viscosity at 150° C. of 2.4 to 2.7 mPa·s, and (C) a molybdenumdithiocarbamate.
DETAILED DESCRIPTION OF THE INVENTION
A lubricating base oil referred to as Component (A) in an engine oil composition according to the present invention has a kinematic viscosity at 100° C. of which the upper limit is 6 mm
2
/s, preferably 5 mm
2
/s and the lower limit is 2 mm
2
/s, preferably 3 mm
2
/s. Lubricant base oils having kinematic viscosities, in excess of the upper limit would lead to increased fluid resistance resulting in increased loss caused by wear occurring at engine parts to be lubricated, while those of less than the lower limit would lead to insufficient oil-film formation, resulting in less lubricity and increased evaporation loss.
Component (A) has necessarily a viscosity index of 120 or more. Such a viscosity index value contributes to the production of an engine oil composition having excellent low-temperature viscosity characteristics. Base oils having a viscosity index of less than 120 would lead to a necessity to bring it down to a lower viscosity, resulting in an increased evaporation loss and viscosity of the resulting engine oil.
The upper limit of aromatic content of Component (A) is 15 percent by mass, preferably 10 percent by mass, and most preferably 5 percent by mass. Base oils having an aromatic content in excess of the upper limit would fail to achieve synergistic effects with each additive to be used in the present invention. No particular limitation is imposed on the lower limit of aromatic content. However, Component (A) preferably has a total aromatic content of 2 percent by mass or more, because a Component (A) having a total aromatic content of less than 2 percent by mass would possibly not exhibit solubility to various additives.
The term “total aromatic content” used herein denotes an aromatic fraction content measured in accordance with ASTM D2549. Included in the aromatic fraction are generally alkylbenzenes, alkylnaphthalenes, anthracene, phenanthrene, alkylated products thereof, compounds in which 4 or more benzene rings are condensed, and compounds having hetero-aromatics, such as pyridines, quinolines, phenols, and naphthols.
Eligible base oils for the present invention are mineral lubricating oils, synthetic, lubricating oils, and mixtures of two or more of these oils mixed in a suitable ratio.
For instance, the base oils are exemplified by mineral lubricating oils, mixtures of mineral lubricating oils and non-aromatic-containing synthetic lubricating oils, and mixtures of aromatic-containing synthetic lubricating oils and non-aromatic-containing synthetic lubricating oils.
The term “mineral lubricating oil” used herein denotes not only a single mineral lubricating oil but also a mixture of two or more mineral lubricating oils. Therefore, when using two more mineral lubricating oils as the base oil, there may be used not only a mixture of mineral lubricating oils each having a total aromatic content of 15 percent by mass or less but also a mixture of a mineral lubricating oil having a total aromatic content of less than 15 percent by mass and a mineral lubricating oil having a total aromatic content exceeding 15 percent by mass, as long as the resulting base oil has a total aromatic content of 15 percent by mass or less.
Furthermore, when using a mixture of a mineral lubricating oil and a non-aromatic-containing synthetic lubricating oil, there may be used a mineral lubricating oil having a total aromatic content exceeding 15 percent by mass as long as the resulting base oil has a total aromatic content of 15 percent by mass or less.
Specific examples of the mineral lubricating oil are those obtained by subjecting a lubricant fraction obtained by vacuum-distilling an atmospheric residue derived from the atmospheric distillation of crude oil to one or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, and hydrorefining.
Specific examples of the aromatic-containing synthetic lubricating oil are alkylnaphthalenes and alkylbenzenes.
Specific examples of the non-aromatic-containing synthetic lubricating oil are polybutens and hydrides thereof; poly-&agr;-olefins such as 1-octene oligo
Igarashi Jinichi
Inoue Kiyoshi
Kurihara Isao
Akin Gump Strauss Hauer & Feld L.L.P.
McAvoy Ellen M.
Nippon Mitsubishi Oil Corporation
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