Grease composition for constant-velocity joint and constant-velocity joint filled therewith

1 . A grease composition for a constant-velocity joint, comprising:

(a) a base oil having a kinematic viscosity of 16.0 mm 2 /s or more at 100° C. and a viscosity index of 90 or more;

(b) a diurea-based thickener represented by the following formula (1)

wherein R 1 and R 1 ′ are each independently an octyl group, a dodecyl group, a hexadecyl group, an octadecyl group, or a cyclohexyl group;

(c) 0.2 to 2.0% by mass of a zinc dialkyldithiophosphate;

(d) 0.5 to 2.0% by mass of a non-oil-soluble molybdenum dialkyl dithiocarbamate;

(e) 0.5 to 3.0% by mass of an oil-soluble molybdenum dialkyl dithiocarbamate;

(f) 1.0 to 4.0% by mass of a zinc dialkyldithiocarbamate; and

(g) 0.1 to 1.5% by mass of a benzothiazole-thione or a derivative thereof, wherein a mass ratio between the component (f) and the component (g) is (f):(g)=8:1 to 3:1.

2 . The grease composition according to claim 1 , wherein the component (c) is represented by the following formula (2):

wherein R 2 is a primary or secondary alkyl group having 1 to 24 carbon atoms.

3 . The grease composition according to claim 1 , wherein the component (d) is represented by the following formula (3):

wherein R 30 is a primary or secondary alkyl group having 1 to 4 carbon atoms, m is 0 to 3, n is 1 to 4, and m+n=4.

4 . The grease composition according to claim 1 , wherein the component (e) is represented by the following formula (4):

wherein R 31 is a primary or secondary alkyl group having 5 to 24 carbon atoms, m is 0 to 3, n is 1 to 4, and m+n=4.

5 . The grease composition according to claim 1 , wherein the component (f) is represented by the following formula (5):

wherein R 4 is a primary or secondary alkyl group having 1 to 24 carbon atoms.

6 . A constant-velocity joint hermetically filled with the grease composition for a constant-velocity joint according to claim 1 .