Lubricating oil composition

Abstract

To provide a lubricating oil composition having excellent shear stability and temperature viscosity characteristics and also having high heat dissipation performance from the viewpoint of fuel saving and energy saving of an electric vehicle. A lubricating oil composition used for cooling of an electric motor and lubrication of a gear in an electric vehicle, the composition including: a lubricating base oil; and an ethylene-α-olefin copolymer with an ethylene molar content rate of 30 to 70 mol %, a kinematic viscosity at 100° C. of 10 to 5,000 mm 2 /s, a Hasen chromaticity of 30 or lower, a molecular weight distribution of 2.5 or less, and a B-value of 1.1 or more, the composition having a kinematic viscosity at 100° C. of 4 to 10 mm 2 /s, and the lubricating base oil including a mineral oil with a kinematic viscosity at 100° C. of 2 to 6 mm 2 /s, a viscosity index of 105 or more, and a pour point of −5° C. or lower, and/or a synthetic oil with a kinematic viscosity at 100° C. of 1 to 9 mm 2 /s, a viscosity index of 110 or more, and a pour point of −30° C. or lower.

1 . A lubricating oil composition used for cooling of an electric motor and lubrication of a gear in an electric vehicle, the composition comprising: a lubricating base oil composed of a (A) mineral oil having the following characteristics (A1) to (A3) and/or a (B) synthetic oil having the following characteristics (B1) to (B3) and an (C) ethylene-α-olefin copolymer having the following characteristics (C1) to (C5), the composition having a kinematic viscosity at 100° C. of 4 to 10 mm 2 /s:
 (A1) a kinematic viscosity at 100° C. of 2 to 6 mm 2 /s; 
 (A2) a viscosity index of 105 or more; 
 (A3) a pour point of −5° C. or lower; 
 (B1) a kinematic viscosity at 100° C. of 1 to 9 mm 2 /s; 
 (B2) a viscosity index of 110 or more; 
 (B3) a pour point of −30° C. or lower; 
 (C1) an ethylene molar content rate within a range of 30 to 70 mol %; 
 (C2) a kinematic viscosity at 100° C. of 10 to 5,000 mm 2 /s; 
 (C3) a Hasen chromaticity of 30 or lower; 
 (C4) a molecular weight distribution (Mw/Mn) of 2.5 or less in molecular weight obtained in terms of polystyrene, as measured by gel permeation chromatography (GPC); and 
 (C5) a B value represented by the following formula [1] of 1.1 or more: 
 
       
         
           
             
               
                 
                   
                     B 
                     = 
                     
                       
                         P 
                         
                           O 
                           ⁢ 
                           E 
                         
                       
                       
                         2 
                         ⁢ 
                            
                         
                           
                             P 
                             O 
                           
                           · 
                           
                             P 
                             E 
                           
                         
                       
                     
                   
                 
                 
                   
                     [ 
                     1 
                     ] 
                   
                 
               
             
           
         
       
       wherein P represents a molar fraction of ethylene component, P O  represents a molar fraction of α-olefin component, and P OE  represents a molar fraction of ethylene-α-olefin sequence in the total dyad sequence. 
     
     
         2 . The lubricating oil composition according to  claim 1 , wherein the (C) ethylene-α-olefin copolymer has any one or more of the following characteristics (C6) to (C8):
 (C6) a thermal diffusivity at 50° C. of 8.0×10∧-5 to 1.0×10∧-4 m∧2/s; 
 (C7) a volume resistivity at 50° C. and 250 V of 1.0×10∧15 to 1.0×10∧17 Ω·cm; and 
 (C8) a relative permittivity at 50C of 2.00 to 2.30. 
 
     
     
         3 . The lubricating oil composition according to  claim 1 , wherein the ethylene molar content rate of the (C)ethylene-α-olefin copolymer is within a range of 40 to 60 mol %. 
     
     
         4 . The lubricating oil composition according to  claim 1 , wherein the kinematic viscosity of the (C)ethylene-α-olefin copolymer at 100° C. is 20 to 2,500 mm 2 /s. 
     
     
         5 . The lubricating oil composition according to  claim 1 , wherein the α-olefin of the (C)ethylene-α-olefin copolymer is propylene. 
     
     
         6 . The lubricating oil composition according to  claim 1 , wherein the content of the (C)ethylene-α-olefin copolymer is 1 to 10% by mass based on the total amount of the lubricating base oil and the (C)ethylene-α-olefin copolymer of 100% by mass. 
     
     
         7 . The lubricating oil composition according to  claim 1 , wherein the electric vehicle is any of an electric automobile, a plug-in hybrid vehicle, a hybrid vehicle, or a fuel cell vehicle. 
     
     
         8 . The lubricating oil composition according to  claim 1 , wherein the electric motor equipped in the electric vehicle is an in-wheel motor. 
     
     
         9 . The lubricating oil composition according to  claim 1 , wherein the electric vehicle is either an electric wheelchair or an electric cart. 
     
     
         10 . The lubricating oil composition according to  claim 1 , wherein the electric vehicle is either an electric skateboard or an electric roller skate.