Lubricating oil composition for automatic transmission

Abstract

A lubricating oil composition for automatic transmission comprises a base oil having a pour point of −25° C. or lower and a kinematic viscosity of 2 to 7 mm 2 /s at 100° C., (A) a over-based calcium sulfonate having a total base number of 300 to 500 mg KOH/g, (B) a succinimide having boron atom and/or a succinimide having no boron atom, which are substituted with a hydrocarbon group (an alkyl groups or alkenyl groups having an average molecular weight of 1,000 to 3,500), and, and (C) a phosphorous acid ester-based compound, each in a specific amount. The composition has a great statical friction coefficient (μs), an excellent transmission torque capacity and a friction characteristic having a μ ratio of 1 or smaller, exhibiting excellent resistance to transmission shock on clutching.

1 . A lubricating oil composition for automatic transmission which comprises a base oil having a pour point of −25° C. or lower and a kinematic viscosity of 2 to 7 mm 2 /s at a temperature of 100° C., (A) a over-based calcium sulfonate having a total base number of 300 to 500 mg KOH/g in an amount in a range of 2,000 to 3,500 ppm by mass as calcium, (B) at least one of a succinimide substituted with a hydrocarbon group and having no boron atom and a succinimide substituted with a hydrocarbon group and having boron atom, the succinimides having an alkyl group or an alkenyl group having an average molecular weight of 1,000 to 3,500, in an amount such that an amount of nitrogen is in a range of 100 to 500 ppm by mass and an amount of boron is in a range of 0 to 300 ppm by mass, and (C) a phosphorous acid ester-based compound in an amount in a range of 100 to 300 ppm by mass as phosphorus, each amount being based on an entire amount of the composition.  
     
     
         2 . A lubricating oil composition for automatic transmission according to  claim 1 , wherein the base oil is a paraffinic highly purified based oil having a value of % C A  of 0.1% by mass or smaller.  
     
     
         3 . A lubricating oil composition for automatic transmission according to any one claims  1  and  2 , wherein the phosphorous acid ester-based compound of component (C) is an acidic phosphorous acid ester.