Ball screw grease composition for rack-assisted electric power steering
A ball screw grease composition for a rack-assisted electric power steering contains a thickener, a base oil, and at least one compound selected from the group consisting of a Ca sulfonates, fatty acids, and triglycerides, wherein the kinematic viscosity of the base oil at 40° C. is 4-100 mm 2 /s, and the worked penetration of the composition is 265-385.
1 . A method for lubricating a ball screw part of rack-assisted electric power steering, comprising:
applying a grease composition to the ball screw part of rack-assisted electric power steering,
wherein the grease composition comprises:
a thickener;
a base oil; and
at least one compound selected from the group consisting of a Ca sulfonate, and a triglyceride, wherein
the thickener is represented by formula (I):
R 1 —NHCONH—R 2 —NHCONH—R 3 (I)
wherein R 1 and R 3 may be the same or different, and each represent a straight chain saturated alkyl group having 8 to 20 carbon atoms or a cyclohexyl group, and R 2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms,
the base oil contains poly-α-olefin,
a kinematic viscosity at 40° C. of the base oil is 4 to 100 mm 2 /s, and
a worked penetration of the composition is 265 to 385.
2 . The method according to claim 1 , wherein the compound is a Ca sulfonate having a base number of 350 mgKOH/g or less.
3 . The method according to claim 1 , wherein the compound is neutral calcium dinonylnaphthalenesulfonate.
4 . The method according to claim 1 , wherein the compound is a triglyceride in which an aliphatic moiety of the triglyceride is a linear or branched, saturated or unsaturated fatty acid having 7 to 26 carbon atoms.
5 . The method according to claim 1 , wherein the compound is hydrogenated castor oil.
6 . The method according to claim 1 , wherein each of R 1 and R 3 is a straight chain saturated alkyl group having 8 carbon atoms and R 2 is a group derived from diphenylmethane-4,4′-diisocyanate.
7 . The method according to claim 1 , wherein the content of the poly-α-olefin is 50% by mass or more based on the total mass of the base oil.
8 . The method according to claim 1 , wherein the content of the base oil is 80 to 91% by mass based on the total mass of the composition.
9 . The method according to claim 1 , wherein the content of the compound is 1 to 10% by mass based on the total mass of the composition.
10 . The method according to claim 1 , wherein the grease composition further comprises other additives selected from the group consisting of an antioxidant, an inorganic passivator, a rust preventive, an oiliness improver, an antiwear agent, an extreme pressure agent, and a solid lubricant.
11 . The method according to claim 1 , wherein the worked penetration of the composition is 285 to 340.
12 . The method according to claim 1 , wherein all elements constituting the ball screw are steel.
13 . A method for suppressing torque variation at a ball screw part of rack-assisted electric power steering, comprising:
applying a grease composition to the ball screw part of rack-assisted electric power steering,
wherein the grease composition comprises:
a thickener,
a base oil; and
at least one compound selected from the group consisting of a Ca sulfonate, and a triglyceride, wherein
the thickener is represented by formula (I):
R 1 —NHCONH—R 2 —NHCONH—R 3 (I)
wherein R 1 and R 3 may be the same or different, and each represent a straight chain saturated alkyl group having 8 to 20 carbon atoms or a cyclohexyl group, and R 2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms,
the base oil contains poly-α-olefin,
a kinematic viscosity at 40° C. of the base oil is 4 to 100 mm 2 /s, and
a worked penetration of the composition is 265 to 385.