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 mm 2 /s, and composed of base oil having the viscosity of 2.5-4.5 mm 2 /s, and base oil having the viscosity of 10-40 mm 2 /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 mm 2 /s.

1 . A lubricant composition for automatic transmissions comprising: 
 (A) a lubricant base oil having a kinematic viscosity at 100° C. of 3.7 to 4.1 mm 2 /s, and consisting of:    lubricant base oil (A1) having a kinematic viscosity at 100° C. of 2.5 to 4.5 mm 2 /s, and    lubricant base oil (A2) having a kinematic viscosity at 100° C. of 10 to 40 mm 2 /s;    (B) a poly(meth)acrylate viscosity index improver having a weight average molecular weight of 15000 to 30000 at 1 to 20 mass % of the total amount of the composition;    (C) an imide friction modifier having a hydrocarbon group with 8 to 30 carbon atoms at 2 to 4 mass % of the total amount of the composition;    (D) a phosphorus extreme pressure agent at 0.01 to 0.04 mass % of the total amount of the composition in terms of phosphorus; and    (E) an ashless dispersant having at least one alkyl or alkenyl group of a number average molecular weight of not lower than 2000 at 0.01 to 0.04 mass % of the total amount of the composition in terms of nitrogen;    wherein said composition has a kinematic viscosity at 100 °C. of 5.6 to 5.8 mm 2 /s.    
   
   
       2 . A method for lubricating an automatic transmission comprising the step of lubricating an automatic transmission with a lubricant composition comprising: 
 (A) a lubricant base oil having a kinematic viscosity at 100° C. of 3.7 to 4.1 mm 2 /s, and consisting of:    lubricant base oil (A1) having a kinematic viscosity at 100° C. of 2.5 to 4.5 mm 2 /s, and    lubricant base oil (A2) having a kinematic viscosity at 100° C. of 10 to 40 mm 2 /s;    (B) a poly(meth)acrylate viscosity index improver having a weight average molecular weight of 15000 to 30000 at 1 to 20 mass % of the total amount of the composition;    (C) an imide friction modifier having a hydrocarbon group with 8 to 30 carbon atoms at 2 to 4 mass of the total amount of the composition;    (D) a phosphorus extreme pressure agent at 0.01 to 0.04 mass % of the total amount of the composition in terms of phosphorus; and    (E) an ashless dispersant having at least one alkyl or alkenyl group of a number average molecular weight of not lower than 2000 at 0.01 to 0.04 mass % of the total amount of the composition in terms of nitrogen;    wherein said composition has a kinematic viscosity at 100° C. of 5.6 to 5.8 mm 2 /s.