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  Lubricating oilRelated Patent Categories: Solid Anti-friction Devices, Materials Therefor, Lubricant Or Separant Compositions For Moving Solid Surfaces, And Miscellaneous Mineral Oil Compositions, Lubricants Or Separants For Moving Solid Surfaces And Miscellaneous Mineral Oil Compositions (e.g., Water Containing, Etc.), Organic Compound Containing Boron, Nitrogen Containing (i.e., Nitrogen And Boron In The Same Compound)The Patent Description & Claims data below is from USPTO Patent Application 20060105921. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a lubricating oil composition, specifically, a lubricating oil composition which has a low viscosity and a good anti-wear characteristic, in particular, which is capable of maintaining an anti-wear characteristic for a long term. BACKGROUND ART [0002] In recent years, abatement of emission of carbon dioxide gas has been becoming a pressing need in light of an environmental problem, and an improvement in the fuel efficiency of automobiles has been becoming a more important theme than in the past. It can be considered that the following is effective for means for improving the fuel efficiency of automobiles: a decrease in stirring resistance by making the viscosity of a used lubricating oil low and a decrease in friction in boundary lubricating range by using a friction decreasing agent. This is producing an advantageous effect. [0003] About low-viscosity lubricating oil for internal combustion engines, suggested is a fuel consumption saving engine oil wherein a viscosity index improver having a high molecular weight is incorporated, or wherein a friction decreasing agent such as an organic molybdenum compound is further used (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-181664). In automatic transmissions composed of a torque converter, a wet clutch, a gear shaft bearing mechanism, an oil pump, and an oil pressure control mechanism, it is necessary to optimize the frictional property of the wet clutch; therefore, it is considered that a friction decreasing agent such as an organic molybdenum compound is not usually used and it is effective to make the viscosity of the lubricating oil therein low. Thus, an improvement in fuel efficiency is expected by decreasing the stirring resistance of the torque converter or the oil pump. However, the decrease in the viscosity of the lubricating oil directly causes a deterioration in the anti-wear characteristic thereof. It is therefore difficult to make the improvement in fuel efficiency by the decrease in the viscosity and the anti-wear characteristic compatible. Thus, the anti-wear characteristic is necessarily given priority. [0004] As a conventional oil for automobile transmissions which is capable of maintaining various performances, such as transmission driving property, for a long term, disclosed is an oil wherein one or more lubricant base oils of a synthetic oil type and/or mineral oil type, an anti-wear agent, an extreme-pressure agent, a metal detergent, an ashless dispersant, a friction modifier and others are optimally blended (see, for example, JP-A Nos. 3-39399, 7-268375, and 2000-63869). A viscosity index improver is generally selected from improvers having an average molecular weight of 1,000 to 1,000,000. As a lubricating oil into which a viscosity index improver having a low molecular weight is incorporated, there is disclosed, for example, an automatic transmission oil composition using the following together: 1 to 15% by weight of a monoolefin polymer or copolymer having a number-average molecular weight of 1,000 to 10,000, and 1 to 5% by weight of a copolymer of an ester made from a saturated aliphatic monohydric alcohol having an average molecular weight of 5,000 to 50,000 and methacrylic acid (see JP-A No. 61-9497); a semi-synthetic automatic transmission oil composition comprising 3 to 5% by weight of an ethylene/a-olefin copolymer having a number-average molecular weight of 26,000 to 40,000 (JP-A No. 1-168798); or a semi-synthetic automatic transmission oil composition comprising 27 to 34% by weight of a polymethacrylate having a number-average molecular weight of 19,000 to 23,000 (see JP-A No. 1-271494); or the like. [0005] However, none of these compositions are compositions for improving fuel efficiency. Accordingly, the kinematic viscosity thereof is high and investigation is not made at all about effect on the anti-wear characteristic of the compositions at the initial use stage thereof or after long-term use thereof, the effect being the most important theme in the case that the viscosity of the lubricating oil therein is made low. Additionally, the optimization of a viscosity index improver and other additives therein is not sufficiently investigated. Furthermore, the kinematic viscosity of automatic transmission oils which are commercially available at present is generally in the range of 30 to 50 mm.sup.2/s at 40.degree. C. It is therefore considered that there is not substantially any low-viscosity transmission oil wherein a fuel efficiency improvement and an anti-wear characteristic are compatible. DISCLOSURE OF THE INVENTION [0006] Thus, the present invention has been made in light of such a situation, and an object of the present invention is to provide a lubricating oil composition having a low viscosity and further having a sufficient anti-wear characteristic at the initial use stage thereof and after long-term use thereof, in particular, a low-viscosity lubricating oil composition suitable for automatic transmissions or continuously variable transmissions. [0007] The inventors have made eager investigations for solving the above-mentioned problems to find out that the problems can be solved by incorporating, into a lubricant base oil, a specific nitrogen-containing compound and a viscosity index improver having a specific molecular weight optimally. Thus, the present invention has been made. [0008] Accordingly, the present invention is a lubricating oil composition which is obtained by incorporating, into (A) a lubricant base oil comprising a mineral oil, a synthetic oil or a mixture thereof, (B) a nitrogen-containing compound having at least one alkyl group or alkenyl group having a number-average molecular weight of 900 or more and/or a derivative thereof in an amount of 0.01 to 0.20% by mass in terms of the content of nitrogen of the total of the composition, and (C) a viscosity index improver having a weight-average molecular weight of 40,000 or less, so as to set the viscosity index of the composition to 160 or more and set the kinematic viscosity of the composition into the range of 20 to 30 mm.sup.2/s at 40.degree. C. [0009] It is preferable that the (B) component is a nitrogen-containing compound having two alkyl groups or alkenyl groups having a number-average molecular weight of 1200 or more and/or a derivative thereof. [0010] It is also preferable that the lubricating oil composition of the invention essentially comprises, as the (B) component, a boron-modified compound of a nitrogen-containing compound having at least one alkyl group or alkenyl group having a number-average molecular weight of 900 or more in an amount of 0.002% or more by mass in terms of the content of boron of the total of the composition. [0011] It is also preferable that the boron-modified compound is a boron-modified compound of a nitrogen-containing compound having at least one alkyl group or alkenyl group having a number-average molecular weight of 1200 or more. [0012] It is also preferable that the boron-modified compound is a boron-modified compound of a nitrogen-containing compound having two alkyl groups or alkenyl groups having a number-average molecular weight of 1200 or more. [0013] It is also preferable that the boron-modified compound is a boron-modified compound of a nitrogen-containing compound having two alkyl groups or alkenyl groups having a number-average molecular weight of 1700 or more. [0014] It is also preferable that the ratio by mass of boron to nitrogen (B/N ratio) in the boron-modified compound is from 0.01 to 3. [0015] It is also preferable that the (B) component comprises a boron-modified compound of a bis type succinimide having a poly(iso)butenyl group having a number-average molecular weight of 2000 or more. [0016] It is also preferable that the (B) component comprises both of a bis type succinimide having a poly(iso)butenyl group having a number-average molecular weight of 900 or more and less than 2000 and boron-modified compounds a bis type succinimide having a poly(iso)butenyl group having a number-average molecular weight of 2000 or more. [0017] It is also preferable that the lubricating oil composition of the invention is used in an automatic transmission or a continuously variable transmission. [0018] The invention is also a method for maintaining the anti-wear characteristic of an automatic transmission or a continuously variable transmission by use of the above-mentioned low viscosity lubricating oil composition. BEST MODES FOR CARRYING OUT THE INVENTION [0019] The present invention is described in detail hereinafter. [0020] The (A) component in the invention is a lubricant base oil comprising a mineral oil, a synthetic oil, or a mixture thereof, and is not particularly limited. Any oil that is usually used as a base oil of a lubricating oil composition can be used whether the oil is a mineral oil or a synthetic oil. Continue reading... Full patent description for Lubricating oil Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Lubricating oil patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Lubricating oil or other areas of interest. ### Previous Patent Application: Performance-enhancing additives for lubricating oils Next Patent Application: Hydroxyalkyldithiocarbamate borate esters Industry Class: Solid anti-friction devices, materials therefor, lubricant or separant compositions for moving solid surfaces, and miscellaneous mineral oil compositions ### FreshPatents.com Support Thank you for viewing the Lubricating oil patent info. 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