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  Lubricant composition for automatic transmissionUSPTO Application #: 20070270320Title: Lubricant composition for automatic transmission Abstract: The invention provides a lubricant composition for automatic transmissions excellent in sustainability of anti-shudder property, low-temperature viscosity characteristics, and oxidation stability, and excellent and well-balanced in durability of friction characteristics, energy-conserving performance, and anti-fatigue performance on gears. The composition contains a base oil having a kinematic viscosity at 100° C. of 3.7-4.1 mm2/s, and composed of base oil having the viscosity of 2.5-4.5 mm2/s, and base oil having the viscosity of 10-40 mm2/s; 1-20 mass % poly(meth)acrylate viscosity index improver having Mw of 15000-300.00; 2-4 mass % imide friction modifier having a C8-C30 hydrocarbon group; 0.01-0.04 mass % phosphorus extreme pressure agent in terms of phosphorus; and 0.01-0.04 mass % ashless dispersant having at least one alkyl or alkenyl group of a number average molecular weight of ≧2000 in terms of nitrogen, all with respect to the total amount of the composition, and has the viscosity of 5.6-5.8 mm2/s. (end of abstract) Agent: Sughrue Mion, PLLC - Washington, DC, US Inventors: Masaaki Itou, Yasuhiro Murakami, Yoshie Arakawa, Makoto Maeda, Takahiro Sugiyama USPTO Applicaton #: 20070270320 - Class: 508469000 (USPTO) Related 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 -c(=o)o- Compound, Specified Compound Wherein The Single Bonded Oxygen Is Bonded Oxygen Is Bonded Directly To An Additional Carbon, Which Carbon May Be Single Bonded To Any Atom But May Be Multiple Bonded Only To Carbon (i.e., Specified Carboxylic Acid Ester), Plural -c(=o)o- Groups Attached Directly Or Indirectly To Each Other By Nonionic Bonding (e.g., Estolides Of Hydroxy Carboxylic Acids, Etc.), Polymer Of Alpha, Beta-olefinically Unsaturated Carboxylate Monomer (e.g., Polymethylmethacrylate, Etc.) The Patent Description & Claims data below is from USPTO Patent Application 20070270320. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF ART [0001] The present invention relates to a lubricant composition for automatic transmissions, in particular, to a lubricant composition for automatic transmissions, particularly for vehicles, which prolongs fatigue life of gears irrespective of its low viscosity, and which is excellent and well-balanced in sustainability of anti-shudder property, low-temperature viscosity characteristics, oxidation stability, and durability of friction characteristics. BACKGROUND ART [0002] There is recently a pressing need for saving energy consumption of vehicles, or energy conservation, in order to address environmental issues, for example, by reduction of CO.sub.2 emission. Engines and automatic transmissions are strongly demanded to contribute to energy-saving, and lubricants therefor are desired to have lower agitation resistance and friction resistance. [0003] One means for making automatic transmissions energy-conserving is to lower the viscosity of a lubricant used therein. By lowering the viscosity of lubricants used in a vehicle automatic transmission for example, which has a torque converter, a wet clutch, gear-bearing mechanisms, an oil pump, and a hydraulic control mechanism, the agitation resistance and friction resistance in these parts are reduced, which results in improvement in power transmission efficiency and thus in vehicle fuel efficiency. [0004] However, the lowered viscosity of lubricants used in these parts may remarkably shorten their fatigue life, causing seizure or the like to result in troubles in the transmission. In particular, when a phosphorus extreme pressure agent is used for improving extreme pressure property of a low-viscosity lubricant, fatigue life of gears is remarkably impaired, so that it is usually hard to lower the viscosity of such lubricant. On the other hand, a sulfur extreme pressure agent may improve fatigue life of gears, but impairs oxidation stability, so that a large amount of antioxidants is required. [0005] As a conventional automatic transmission fluid for vehicles capable of maintaining various performances, such as transmission characteristics, for a prolonged period of time, there are reported optimized blends of synthetic and/or mineral lubricant base oils, anti-wear agent, extreme pressure agent, metal detergent, ashless dispersant, friction modifier, viscosity index improver, and the like (JP-3-39399-A, JP-7-268375-A, JP-2000-63869-A, and JP-2001-262176-A). [0006] These compositions, however, are not intended to improve fuel efficiency, and thus have a high kinematic viscosity. No discussion is made in these publications regarding the effect of reduction in lubricant viscosity on fatigue life of gears. Sufficient discussion has not been made on a composition that may solve such a problem. There are recently proposed automatic transmission fluids having a lowered viscosity, for example, in JP-2004-169025-A, JP-2004-155924-A, and JP-2004-155873-A. These lubricants have excellent sustainability of anti-shudder property, low-temperature viscosity characteristics, and oxidation stability, but are yet to be improved in excellence and balance of durability of friction characteristics, contribution to energy conservation, and anti-fatigue performance on gears. SUMMARY OF THE INVENTION [0007] It is an object of the present invention to provide a lubricant composition for automatic transmissions which has excellent sustainability of anti-shudder property, low-temperature viscosity characteristics, and oxidation stability, and is excellent and well-balanced in durability of friction characteristics, energy-conserving performance, and anti-fatigue performance on gears, in particular a lubricant composition for automatic transmissions, particularly suitable for vehicle automatic transmissions, having both energy-conserving performance and anti-fatigue performance on gears. [0008] The present inventors have made intensive studies for solving the above problems to find out that a low-viscosity lubricant composition for automatic transmissions wherein particular base oils and particular additives are combined, may solve the above problems, thereby completing the present invention. [0009] According to the present invention, there is provided a lubricant composition for automatic transmissions comprising: [0010] (A) a lubricant base oil having a kinematic viscosity at 100.degree. C. of 3.7 to 4.1 mm.sup.2/s, and consisting of lubricant base oil (A1) having a kinematic viscosity at 100.degree. C. of 2.5 to 4.5 mm.sup.2/s and lubricant base oil (A2) having a kinematic viscosity at 100.degree. C. of 10 to 40 mm.sup.2/s; [0011] (B) a poly(meth)acrylate viscosity index improver having a weight average molecular weight of 15000 to 30000 (sometimes referred to as component (B) hereinbelow) at 1 to 20 mass % of the total amount of the composition; [0012] (C) an imide friction modifier having a hydrocarbon group with 8 to 30 carbon atoms (sometimes referred to as component (C) hereinbelow) at 2 to 4 mass % of the total amount of the composition; [0013] (D) a phosphorus extreme pressure agent (sometimes referred to as component (D) hereinbelow) at 0.01 to 0.04 mass % of the total amount of the composition in terms of phosphorus; [0014] (E) an ashless dispersant having at least one alkyl or alkenyl group of a number average molecular weight of not lower than 2000 (sometimes referred to as component (E) hereinbelow) at 0.01 to 0.04 mass % of the total amount of the composition in terms of nitrogen; [0015] wherein said composition has a kinematic viscosity at 100.degree. C. of 5.6 to 5.8 mm.sup.2/s (sometimes referred to as the present composition hereinbelow). [0016] The present composition is capable of prolonging fatigue life of gears irrespective of its low viscosity, has excellent sustainability of anti-shudder property, low-temperature viscosity characteristics, and oxidation stability, and is excellent and well-balanced in durability of friction characteristics, energy-conserving performance, and anti-fatigue performance on gears. The present composition is particularly suitable for vehicle automatic transmissions, has both energy-conserving performance and anti-fatigue performance on gears, and is capable of achieving energy conservation of vehicles. PREFERRED EMBODIMENTS OR THE INVENTION [0017] The present invention will now be explained in detail. [0018] The present composition is characterized in that the particular lubricant base oil (A) and particular components (B) to (E) are contained at a good balance, and the kinematic viscosity at 100.degree. C. is in the range of 5.6 to 5.8 mm.sup.2/s. [0019] Having the particular composition and the kinematic viscosity in the particular range mentioned above, the present composition is capable of prolonging fatigue life of gears irrespective of its low viscosity, and is excellent and well-balanced in sustainability of anti-shudder property, low-temperature viscosity characteristics, oxidation stability, and durability of friction characteristics. [0020] If the kinematic viscosity at 100.degree. C. of the present composition is higher than 5.8 mm.sup.2/s, the energy-conserving performance given by reduction of agitation resistance and excellent low-temperature viscosity characteristics cannot be achieved sufficiently. If the kinematic viscosity is lower than 5.6 mm.sup.2/s, fatigue life of gears cannot be prolonged sufficiently Continue reading... Full patent description for Lubricant composition for automatic transmission Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Lubricant composition for automatic transmission 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. 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