Transmission lubricating oil composition

1. A lubricating oil composition, comprising:

(A) a base oil comprising (A-1) a synthetic oil having a kinematic viscosity at 100° C. of 1.0 to 10.0 mm 2 /s;

(B) a viscosity index improver having a mass average molecular weight of 10,000 to 50,000;

(C-1) a polyamide, which is a reaction product between a polyamine compound and a carboxylic acid compound, wherein the carboxylic acid compound is a monovalent fatty acid having a carbon number from 8 to 24; and

(C-2) a polyol ester which is a partial ester of a polyol and a fatty acid having 12 to 24 carbon atoms,

wherein a total amount of the component (C-1) and the component (C-2) is from 0.01 to 5.0% by mass on the basis of a total amount of the composition.

2. The composition of claim 1 , wherein the component (A-1) is a poly-α-olefin, a hydrogenated product of a poly-α-olefin, or both.

3. The composition of claim 1 , wherein the component (A-1) is present in an amount from 1.0 to 10.0% by mass on the basis of a total amount of the composition.

4. The composition of claim 1 , wherein the component (B) is a poly(meth)acrylate.

5. The composition of claim 1 , wherein the component (B) is present in an amount from 1.0 to 20.0% by mass on the basis of a total amount of the composition.

6. The composition of claim 1 , having a kinematic viscosity at 100° C. of 3 to 15 mm 2 /s.

7. The composition of claim 1 , having a viscosity index of 100 or more.

8. The composition of claim 1 , having a volume resistivity of 1.0×10 7 Mu or more.

9. The composition of claim 1 , having a Brookfield viscosity at −40° C. of 30,000 mPas or less.

10. The composition of claim 1 , wherein the polyamine compound is an aliphatic polyamine having a total carbon number of 6 to 30, and

wherein the carbon number of the hydrocarbon group of the carboxylic acid is from 12 to 24.

11. The composition of claim 10 , wherein the aliphatic polyamine has a total carbon number of 16 to 24, and

wherein the carbon number of the hydrocarbon group of the carboxylic acid compound is from 18 to 22.

12. The composition of claim 1 , wherein the base oil further comprises a mineral oil having a kinematic viscosity at 100° C. of 1.5 to 6 mm 2 /s,

wherein the composition comprises from 60.0 to 90.0% by mass of the mineral oil on the basis of a total amount of the composition and from 1.0 to 10.0% by mass of the synthetic oil (A-1) on the basis of a total amount of the composition.

13. The composition of claim 11 , wherein the component (B) is present in an amount from 3.0 to 15.0% by mass on the basis of a total amount of the composition.

14. The composition of claim 1 , further comprising:

a friction modifier which is neither the polyamide (C-1) nor the polyol ester (C-2), and

a pour point depressant which is neither the polyamide (C-1) nor the polyol ester (C-2).

15. The composition of claim 1 , wherein the polyol of the polyol ester (C-2) comprises trimethylolethane, ditrimethylolethane, trimethylolpropane, ditrimethylolpropane, glycerin, pentaerythritol, dipentaerythritol, tripentaerythritol, or sorbitol, and

wherein the carboxylic acid of the polyol ester (C-2) comprises stearic acid or oleic acid.

16. The composition of claim 1 , wherein the base oil further comprises a mineral oil having a kinematic viscosity at 100° C. of 1.5 to 6 mm 2 /s, and

wherein the composition comprises from 60.0 to 90.0% by mass of the mineral oil on the basis of a total amount of the composition and from 2.0 to 5.0% by mass of the synthetic oil (A-1) on the basis of a total amount of the composition,

with a balance comprising further synthetic oil.

17. The composition of claim 1 , having a kinematic viscosity at 100° C. of 3 to 15 mm 2 /s, and

having a viscosity index of 150 or more.

18. The composition of claim 1 , wherein the total amount of the component (C-1) and the component (C-2) is from 0.01 to 1.0% by mass on the basis of a total amount of the composition.