Lubricating oil composition, lubricating method, and transmission
Provided are a lubricating oil composition containing a synthetic oil (1) having a kinematic viscosity at 100° C. of 2.5 mm 2 /s or less, and a polymethacrylate (2) having a monovalent functional group containing an oxygen atom in the molecule while having a specific structural unit, which satisfies both high viscosity index and high shear stability, and a lubrication method and a transmission using the lubricating oil composition.
1. A lubricating oil composition, comprising:
a synthetic oil having a kinematic viscosity at 100° C. of less than 2.3 mm 2 /s ; and
a polymethacrylate having a in the molecule,
wherein the polymethacrylate has a structural unit of formula (I),
wherein R 1 is a divalent aliphatic hydrocarbon group having 24 to 40 carbon hydroxyl group atoms, and X 1 is a, and the polymethacrylate has a mass average molecular weight in a range of 20,000 to 70,000, and a content in a range of 5% by mass to 15% by mass based on the total amount of the lubricating oil composition.
2. The lubricating oil composition according to claim 1 , wherein the mass average molecular weight of the polymethacrylate is in a range of in a range of 25,000 to 70,000.
3. The lubricating oil composition according to claim 1 , wherein the content of the polymethacrylate is in a range of 5% by mass to 13% by mass based on the total amount of the lubricating oil composition.
4. The lubricating oil composition according to claim 1 , wherein the lubricating oil composition is formulated to have a kinematic viscosity at 100° C. in a range of 4 mm 2 /s to 7 mm 2 /s.
5. The lubricating oil composition according to claim 1 , wherein the lubricating oil composition is formulated to have a viscosity index of 260 or more.
6. The lubricating oil composition according to claim 1 , wherein the lubricating oil composition is formulated to have a rate of change in kinematic viscosity at 40° C. of 5% or less, as calculated with respect to an ultrasonically-treated composition obtained by irradiating the lubricating oil composition with ultrasonic waves for 60 minutes according to JASO M347-95 and an untreated lubricating oil composition, their kinematic viscosity at 40° C. (v 1 , v 0 ) being measured according to JIS K2283:2000, and the rate of reduction ((v 0 −v 1 )/v 0 ×100) is a rate of change in kinematic viscosity at 40° C.
7. The lubricating oil composition according to claim 1 , wherein the lubricating oil composition is formulated to have a kinematic viscosity at 100° C. in a range of 4 mm 2 /s to 7 mm 2 /s and a viscosity index of 260 or more.
8. A lubrication method, comprising: applying the lubricating oil composition of claim 1 to a device.
9. The lubrication method according to claim 8 , wherein the device is a transmission.
10. A transmission, comprising:
a transmission device; and
the lubricating oil composition of claim 1 .
11. The lubricating oil composition according to claim 1 , wherein the kinematic viscosity of the synthetic oil at 100° C. is 2.2 mm 2 /s or less.
12. The lubricating oil composition according to claim 1 , wherein the mass average molecular weight of the polymethacrylate is in a range of 25,000 to 55,000.
13. The lubricating oil composition according to claim 2 , wherein the content of the polymethacrylate is in a range of 5% by mass to 13% by mass based on the total amount of the lubricating oil composition.
14. The lubricating oil composition according to claim 2 , wherein the lubricating oil composition is formulated to have a kinematic viscosity at 100° C. in a range of 4 mm 2 /s to 7 mm 2 /s.
15. The lubricating oil composition according to claim 2 , wherein the lubricating oil composition is formulated to have a viscosity index of 260 or more.
16. The lubricating oil composition according to claim 2 , wherein the lubricating oil composition is formulated to have a rate of change in kinematic viscosity at 40° C. of 5% or less, as calculated with respect to an ultrasonically-treated composition obtained by irradiating the lubricating oil composition with ultrasonic waves for 60 minutes according to JASO M347-95 and an untreated lubricating oil composition, their kinematic viscosity at 40° C. (v 1 , v 0 ) being measured according to JIS K2283:2000, and where a rate of reduction ((v 0 −v 1 )/v 0 ×100) is a rate of change in kinematic viscosity at 40° C.
17. The lubricating oil composition according to claim 2 , wherein the lubricating oil composition is formulated to have a kinematic viscosity at 100° C. in a range of 4 mm 2 /s to 7 mm 2 /s and a viscosity index of 260 or more.
18. The lubricating oil composition according to claim 1 , wherein the polymethacrylate further includes a structural unit of formula (II),
where R 2 is a divalent aliphatic hydrocarbon group having 1 to 40 carbon atoms, and X 2 is a monovalent functional group.
19. The lubricating oil composition according to claim 1 , further comprising:
a disperant.
20. The lubricating oil composition according to claim 3 , wherein the lubricating oil composition is formulated to have a kinematic viscosity at 100° C. in a range of 4 mm 2 /s to 7 mm 2 /s.