Lubricating-oil composition

Abstract

By using a lubricating oil composition containing (1) a base oil comprising a base oil A having a kinematic viscosity at 100° C. of 2 mm 2 /s or more and 7 mm 2 /s or less and a viscosity index of 120 or less, (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less, and (3) a lubricating oil additive comprising a sulfur-based extreme pressure agent; and having a kinematic viscosity at 100° C. of more than 9.3 mm 2 /s and 12.5 mm 2 /s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more, a lubricating oil composition capable of making both a lowering in viscosity for fuel saving properties and fatigue resistance for improvement of fatigue life compatible with each other and also having excellent low-temperature viscosity properties is provided.

1 . A lubricating oil composition, comprising:
 (1) a base oil comprising a base oil A having a kinematic viscosity at 100° C. of 2 mm 2 /s or more and 7 mm 2 /s or less and a viscosity index of 120 or less;   (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less; and   (3) a lubricating oil additive comprising a sulfur-based extreme pressure agent,   wherein the lubricating oil composition has a kinematic viscosity at 100° C. of more than 9.3 mm 2 /s and 12.5 mm 2 /s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.   
     
     
         2 . The lubricating oil composition according to  claim 1 , which has a CCS viscosity at −25° C. of 7,000 mPa·s or less and a viscosity index of 135 or more. 
     
     
         3 . The lubricating oil composition according to  claim 1 , wherein the acrylate-based polymer and the olefin-based polymer each having a mass average molecular weight of 40,000 or less is a poly-α-olefin obtained from α-olefins having a carbon number of 8 or more and 12 or less and having a kinematic viscosity at 100° C. of 100 mm 2 /s or more and 2,000 mm 2 /s or less. 
     
     
         4 . The lubricating oil composition according to  claim 1 , wherein a central oil film thickness in the measurement of an oil film thickness in the elastohydrodynamic lubrication (EHL) state is 50 nm or more at a rolling speed of 1.6 m/s. 
     
     
         5 . The lubricating oil composition according to  claim 1 , wherein in the evaluation of fatigue life of a radial rolling bearing, a 50% failure probability (L50) is 3.0×10 6  times or more. 
     
     
         6 . The lubricating oil composition according to  claim 1 , wherein the base oil further comprises a base oil having a viscosity index of more than 120. 
     
     
         7 . The lubricating oil composition according to  claim 1 , wherein a kinematic viscosity at 100° C. after a shear test of the lubricating oil composition is 9 mm 2 /s or more. 
     
     
         8 . The lubricating oil composition according to  claim 1 , wherein the composition is suitable for internal combustion engines. 
     
     
         9 . The lubricating oil composition according to  claim 1 , wherein the composition is suitable for two-wheeled vehicle internal combustion engines. 
     
     
         10 . A production method of a lubricating oil composition, the method comprising:
 blending (1) a base oil comprising a base oil A having a kinematic viscosity at 100° C. of 2 mm 2 /s or more and 7 mm 2 /s or less and a viscosity index of 120 or less with (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less and (3) a lubricating oil additive comprising a sulfur-based extreme pressure agent, to produce a lubricating oil composition having a kinematic viscosity at 100° C. of more than 9.3 mm 2 /s and 12.5 mm 2 /s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.   
     
     
         11 . An internal combustion engine, comprising at least one member lubricated with a lubricating oil composition, wherein the lubricating oil composition comprises:
 (1) a base oil comprising a base oil A having a kinematic viscosity at 100° C. of 2 mm 2 /s or more and 7 mm 2 /s or less and a viscosity index of 120 or less;   (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less; and   (3) a lubricating oil additive comprising a sulfur-based extreme pressure agent, and   the lubricating oil composition has a kinematic viscosity at 100° C. of more than 9.3 mm 2 /s and 12.5 mm 2 /s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.