Grease composition for electric power steering device, and electric power steering device
Provided are both a grease composition for an electric power steering device and an electric power steering device. The grease composition can keep a sufficiently low coefficient of friction in a sliding area between a steel and a resin over a long period, is less susceptible to being removed from the sliding area, does not cause break down of an oil film, and thus can minimize the occurrence of stick-slips. A grease composition for an electric power steering device, containing a synthetic hydrocarbon oil which exhibits a density of 0.75 to 0.95 g/cm 3 at 15° C., a saturated aliphatic amide compound, boron nitride, a glycerin fatty acid partial ester, and a metal soap-based thickener; and an electric power steering device using the grease composition.
1. A grease composition for electric power steering devices, consisting of:
a synthetic hydrocarbon oil having a density of 0.75 to 0.95 g/cm 3 at 15° C.,
a saturated aliphatic amide compound,
boron nitride,
a glycerin fatty acid partial ester, and
a metal soap-based thickener,
wherein the saturated aliphatic amide compound is selected from the group consisting of compounds represented by the following formulae (1), (2), and (3):
R 1 —CO—NH—R 2 (1)
R 3 —CO—NH-A 1 -NH—CO—R 4 (2)
R 5 —NH—CO-A 2 -CO—NH—R 6 (3),
wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 each independently represents an aliphatic hydrocarbon group of 5 to 25 carbon atoms, and R 2 may alternatively represent a hydrogen atom, and
wherein A 1 and A 2 represent bivalent saturated aliphatic hydrocarbon groups of 1 to 10 carbon atoms.
2. The grease composition for electric power steering devices according to claim 1 , wherein the synthetic hydrocarbon oil is a poly-α-olefin, and is contained in 50 to 95 mass % with respect to the total amount of the grease composition.
3. The grease composition for electric power steering devices according to claim 1 , wherein the saturated aliphatic amide compound is contained in 5 to 20 mass % with respect to the total amount of the grease composition.
4. The grease composition for electric power steering devices according to claim 1 , wherein the boron nitride is contained in 0.2 to 5 mass % with respect to the total amount of the grease composition.
5. The grease composition for electric power steering devices according to claim 1 , wherein the glycerin fatty acid partial ester is contained in 0.1 to 5 mass % with respect to the total amount of the grease composition.
6. The grease composition for electric power steering devices according to claim 1 , wherein the metal soap-based thickener is contained in 2 to 15 mass % with respect to the total amount of the grease composition.
7. An electric power steering device comprising:
a steering mechanism for turning wheels in response to a steering operation of a steering wheel,
a motor that provides a steering force to the steering mechanism,
a worm gear that transmits torque of the motor to the steering mechanism, the worm gear being configured from a worm wheel formed of a resin material, and a worm shaft formed of a metallic material, with a grease composition applied to a meshing surface of the worm wheel and the worm shaft,
wherein the grease composition consists of a synthetic hydrocarbon oil having a density of 0.75 to 0.95 g/cm 3 at 15° C., a saturated aliphatic amide compound, boron nitride, a glycerin fatty acid partial ester, and a metal soap-based thickener,
wherein the saturated aliphatic amide compound is selected from the group consisting of compounds represented by the following formulae (1), (2), and (3):
R 1 —CO—NH—R 2 (1)
R 3 —CO—NH-A 1 -NH—CO—R 4 (2)
R 5 —NH—CO-A 2 -CO—NH—R 6 (3),
wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 each independently represents an aliphatic hydrocarbon group of 5 to 25 carbon atoms, and R 2 may alternatively represent a hydrogen atom, and
wherein A 1 and A 2 represent bivalent saturated aliphatic hydrocarbon groups of 1 to 10 carbon atoms.
8. The grease composition according to claim 1 , wherein the boron nitride is a hexagonal atmospheric phase powder having a particle diameter of 1 to 10 μm.
9. A method for lubricating an electric power steering device that includes a resin sliding member and a metallic sliding member, comprising applying a grease composition that consists of:
a synthetic hydrocarbon oil having a density of 0.75 to 0.95 g/cm 3 at 15° C.;
boron nitride;
a glycerin fatty acid partial ester;
a metal soap-based thickener; and
a saturated aliphatic amide compound selected from the group consisting of compounds represented by the following formulae (1), (2), and (3):
R 1 —CO—NH—R 2 (1)
R 3 —CO—NH-A 1 -NH—CO—R 4 (2)
R 5 —NH—CO-A 2 -CO—NH—R 6 (3),
wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 each independently represents an aliphatic hydrocarbon group of 5 to 25 carbon atoms, and R 2 may alternatively represent a hydrogen atom, and
wherein A 1 and A 2 represent bivalent saturated aliphatic hydrocarbon groups of 1 to 10 carbon atoms.
10. A grease composition for electric power steering devices, consisting of:
a synthetic hydrocarbon oil having a density of 0.75 to 0.95 g/cm 3 at 15° C.,
a saturated aliphatic amide compound,
boron nitride,
a glycerin fatty acid partial ester,
a metal soap-based thickener, and
at least one antioxidant,
wherein the saturated aliphatic amide compound is selected from the group consisting of compounds represented by the following formulae (1), (2), and (3):
R 1 —CO—NH—R 2 (1)
R 3 —CO—NH-A 1 -NH—CO—R 4 (2)
R 5 —NH—CO-A 2 -CO—NH—R 6 (3),
wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 each independently represents an aliphatic hydrocarbon group of 5 to 25 carbon atoms, and R 2 may alternatively represent a hydrogen atom, and
wherein A 1 and A 2 represent bivalent saturated aliphatic hydrocarbon groups of 1 to 10 carbon atoms.
11. An electric power steering device comprising:
a steering mechanism for turning wheels in response to a steering operation of a steering wheel,
a motor that provides steering force to the steering mechanism,
a worm gear that transmits & torque of the motor to the steering mechanism, the worm gear being configured from a worm wheel formed of a resin material, and a worm shaft formed of a metallic material, with a grease composition applied to a meshing surface of the worm wheel and the worm shaft,
wherein the grease composition consists of
a synthetic hydrocarbon oil having a density of 0.75 to 0.95 g/cm 3 at 15° C.,
a saturated aliphatic amide compound,
boron nitride,
a glycerin fatty acid partial ester,
a metal soap-based thickener, and
at least one antioxidant,
wherein the saturated aliphatic amide compound is selected from the group consisting of compounds represented by the following formulae (1), (2), and (3):
R 1 —CO—NH—R 2 (1)
R 3 —CO—NH-A 1 -NH—CO—R 4 (2)
R 5 —NH—CO-A 2 -CO—NH—R 6 (3),
wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 each independently represents an aliphatic hydrocarbon group of 5 to 25 carbon atoms, and R 2 may alternatively represent a hydrogen atom, and
wherein A 1 and A 2 represent bivalent saturated aliphatic hydrocarbon groups of 1 to 10 carbon atoms.