Grease composition for hub unit bearing employing an angular contact ball bearing and hub unit bearing

A grease composition for a hub unit bearing employing an angular contact ball bearing, comprising:

• (a) as a thickener a mixture of diurea compounds represented by formulas (I), (II) and (III):
• R1—NHCONH—R2—NHCONH—R1 (I)
• R1—NHCONH—R2—NHCONH—R3 (II)
• R3—NHCONH—R2—NHCONH—R3 (III)
• wherein Rl is cyclohexyl group, R2 is —C6 H4 —CH2 —C6 H4 , and R3 is a straight-chain or branched alkyl group having 18 carbon atoms;
• the molar ratio of the cyclohexyl groups with respect to the total number of moles of the cyclohexyl groups and straight-chain or branched alkyl groups having 18 carbon atoms being 85 to 95 % in the thickener;
• (b) a base oil selected from the group consisting of a mineral oil, a synthetic hydrocarbon oil and a mixture thereof;
• (c) a molybdenum dialkyldithiocarbamate;
• (d) a calcium sulfonate;
• and
• (e) an antioxidant selected from the group consisting of antioxidants having at least one functional group selected from amine functional groups, phenol functional groups, and quinoline functional groups,
• wherein the base oil has a kinetic viscosity of 70 to 400 mm2/s at 40° C.,
• wherein the thickener (a) is contained in an amount of 3 to 20 mass % based on the total mass of the grease composition,
• wherein the molybdenum dialkyldithiocarbamate (c) is contained in an amount of 1 to 5 mass % based on the total mass of the composition, and
• wherein the calcium sulfonate (d) is contained in an amount of 1 to 5 mass % based on the total mass of the composition.