JP2006160072A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grease-lubricated electric power steering device having a resin-made worm wheel which is capable of enhancing the durability and responsiveness thereof. <P>SOLUTION: In the electric power steering device, the assist output by an electric motor is transmitted to a steering mechanism of a vehicle via a reduction gear mechanism. In a driven gear of the reduction gear mechanism, a resin part consisting of a resin composition with gear teeth formed on an outer circumferential surface is integrated with the outer circumference of a metallic core tube. The driven gear is lubricated with the grease composition containing wax having the acid value of 6-30 mgKOH/g and the dropping point of 72-104°C at the rate of 2-12 mass% of the entire amount of the grease. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering device that transmits auxiliary output from an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism, and in particular, the outer periphery of a metal core tube is made of a resin composition and has gear teeth on the outer peripheral surface. The present invention relates to an electric power steering apparatus including a driven gear integrally formed with a formed resin portion and grease-lubricated.

  An electric power steering apparatus incorporated in an automobile is configured as shown in FIGS. 1 and 2, for example. As shown in the figure, a steering shaft 70 is inserted into a hollow steering column 50 and is rotatably supported by rolling bearings 90 and 91 housed in a housing 120. The steering shaft 70 is a hollow shaft and accommodates a torsion bar 80. On the output shaft 60 side, the worm wheel 11 is provided on the outer peripheral surface of the steering shaft 70, and the worm 12 is engaged with the worm wheel 11. A reduction gear mechanism composed of the worm wheel 11 and the worm 12 is connected to an electric motor and housed in a housing 120. Here, the worm 12 is connected to the rotating shaft of the electric motor 100 and corresponds to a drive gear, while the worm wheel 11 corresponds to a driven gear.

  The worm 12 is supported by a rolling bearing 110 such as a pair of ball bearings and connected to the electric motor 100, and the space between the pair of rolling bearings 110 of the housing 120 is usually in the worm 12 and the worm wheel. 11 is filled with grease for lubrication between both gear teeth. Furthermore, preload is applied to the rolling bearing 110, and when a minute kickback input is input from the tire side, the worm 12 is moved in the axial direction to prevent the electric motor 100 from rotating, and only the kickback is applied to the handle side. In order to convey this information, a rubber damper 130 is attached to the worm side of the rolling bearing 110. As the rubber used, acrylic rubber represented by ethylene acrylic rubber having a small compression set is generally used.

  In the above reduction gear mechanism, when both the worm wheel 11 and the worm 12 are made of metal, there is a problem that unpleasant sounds such as rattling noises and vibration sounds are generated when the handle is operated. Therefore, for example, as shown in FIG. 3, as the worm wheel 11, a resin portion 3 made of a resin and having gear teeth 10 formed on the outer peripheral surface is used on the outer periphery of the metal core tube 1 with an adhesive 8. Noise countermeasures are taken using the integrated system.

  For example, polyamide 6, polyamide 66, polyacetal, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), polyamideimide, and other base resins are blended with the resin portion 3 in a reinforcing material such as glass fiber or carbon fiber. In addition to the above materials, MC (monomer cast) nylon, polyamide 6, polyamide 66, polyamide imide and the like which do not contain a reinforcing material are used. Of these, MC nylon, polyamide imide, polyamide 6 containing glass fiber, polyamide 66, polyamide 46, etc., which do not contain reinforcing materials, are the mainstream in consideration of dimensional stability and cost.

  Further, grease is filled for lubrication between the gear teeth of the worm wheel 11 and the worm 12, and conventionally, as this grease, grease for resin lubrication containing a fatty acid containing a hydroxyl group or a fatty acid ester of a polyhydric alcohol is used. A composition is known (see, for example, Patent Document 1). However, although this resin-lubricating grease composition is excellent in that torque fluctuations are suppressed even after long-term use and there is no sense of incompatibility in handling operations even after long-term operation, Since the lubrication location is heavily loaded and the use conditions become severe and the static friction force increases, so-called catching is likely to occur particularly when the handle is turned slowly, resulting in problems such as a shortened durability life.

  In order to solve such problems, a grease composition containing a polyolefin wax having an average molecular weight of 900 to 10000 in a proportion of 0.5 to 40% by mass (see, for example, Patent Document 2), synthetic hydrocarbon oil and urea A grease composition containing a compound and further added with a montan wax (see, for example, Patent Document 3), and a grease composition containing 0.1 to 30% by mass of polyethylene oxide wax (see, for example, Patent Document 4) ) Etc. are also proposed.

JP-A-8-209167 JP-A-9-194867 JP 2002-371290 A JP 2003-3185 A

  However, although each of the above grease compositions has an effect of improving the wear resistance of the resin portion, there is a continuing demand for further improvement of durability, and in order to improve responsiveness, a reduction gear mechanism is used. The demand for improved torque transmission efficiency is also high. Therefore, an object of the present invention is to improve the durability and responsiveness of an electric power steering apparatus that includes a resin worm wheel and is grease-lubricated.

In order to achieve the above object, the present invention provides the following electric power steering apparatus.
(1) An electric power steering device that transmits auxiliary output from an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism,
The driven gear of the reduction gear mechanism is integrally provided with a resin portion made of a resin composition and having gear teeth formed on the outer peripheral surface thereof on the outer periphery of a metal core tube, and an acid value of 6 to 30 mgKOH / g. An electric power steering apparatus characterized by being lubricated with a grease composition containing wax having a dropping point of 72 to 104 ° C. in a proportion of 2 to 12% by mass of the total amount of grease.
(2) The wax is at least one selected from ester wax and partially saponified ester wax, and the thickener of the grease composition is at least one selected from metal soap and metal composite soap. The electric power steering device according to (1) above.
(3) The base oil of the grease composition contains at least one selected from synthetic hydrocarbon oil and mineral oil in an amount of 70% by mass or more of the total amount of the base oil, and the thickener is selected from lithium soap and lithium composite soap. The electric power steering apparatus according to the above (1) or (2), wherein the electric power steering apparatus is at least one kind.
(4) The electric power steering device according to any one of (1) to (3), wherein the resin forming the resin portion is a polyamide resin or a polyamideimide resin.

  In the electric power steering device of the present invention, the resin worm wheel of the reduction gear mechanism and the metal worm are lubricated with a grease composition containing a specific wax. Wear is suppressed, durability is increased, torque transmission efficiency is increased, and a long-life and high-performance electric power steering apparatus is provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In the present invention, the configuration of the electric power steering device itself is not limited, and for example, the electric power steering device shown in FIGS. 1 and 2 can be exemplified. Further, as shown in FIG. 3, the reduction gear mechanism is also a worm wheel in which a resin portion 3 made of a resin composition and having gear teeth 10 formed on the outer peripheral end face thereof is integrated on the outer periphery of a metal core tube 1. 11 and a metal worm 12. In the worm wheel 11, the metal core tube 1 and the resin portion 3 may be bonded together with an adhesive 8. As the adhesive 8, for example, a silane coupling agent, a titanate coupling agent, or a triazine thiol compound is used. be able to.

  The resin component of the resin portion 3 can be an ABS resin or a PC resin, but is preferably a polyamide resin or a polyamideimide resin because of excellent heat resistance and mechanical strength. Among the polyamide resins, considering water absorption and fatigue resistance, polyamide 6, polyamide 66, polyamide 46, polyamide 610, polyamide 612, polyamide 12, polyamide 11, polyamide MXD6, polyamide 6I6T, modified polyamide 6T, etc. are preferable. Among them, polyamide 6, polyamide 66, and polyamide 46 are particularly preferable because of excellent fatigue resistance. Further, these polyamide resins may be mixed with other resins having compatibility with the polyamide resin. Examples thereof include polyolefins modified with an acid such as maleic anhydride (for example, polyethylene, polypropylene, ethylene-α-olefin copolymer, propylene-α-olefin copolymer, etc.).

  Even if these resins are used alone, they exhibit a certain level of durability, work against the wear of the metal worm 12 that is the counterpart material of the worm wheel 11, and sufficiently function as a reduction gear. However, since the gear teeth 10 may be damaged or worn when used under more severe use conditions, it is preferable to add a reinforcing material in order to further improve the reliability.

  As the reinforcing material, glass fiber, carbon fiber, potassium titanate whisker, aluminum borate whisker and the like are preferable, and those treated with a silane coupling agent are more preferable in consideration of adhesiveness with the above-mentioned resins. Moreover, these reinforcing materials can be used in combination of multiple types. Considering the impact strength, it is preferable to mix a fibrous material such as glass fiber or carbon fiber, and considering the damage of the worm 12, it is preferable to combine the whisker-like material with the fibrous material. The mixing ratio in the case of using the mixture varies depending on the types of the fibrous material and the whisker-like material, and is appropriately selected in consideration of impact strength, damage to the worm 12, and the like. These reinforcing materials are preferably blended in a proportion of 5 to 40% by weight, particularly 10 to 30% by weight. When the blending amount of the reinforcing material is less than 5% by weight, the mechanical strength is hardly improved, which is not preferable. When the blending amount of the reinforcing material exceeds 40% by weight, the worm 12 is likely to be damaged, wear of the worm 12 is promoted, and durability as a reduction gear may be insufficient.

  Furthermore, in order to prevent deterioration due to heat during molding and use, an iodide-based heat stabilizer and an amine-based antioxidant may be added to the resin either alone or in combination.

  In the electric power steering apparatus schematically configured as described above, the space between the pair of rolling bearings 110 of the housing 120 is used for lubrication between the gear teeth of the worm 12 and the worm wheel 11 as in the prior art. The following grease composition is filled.

  The base oil of the grease composition is 70% by mass or more, preferably 90% by mass or more of the total amount of the base oil, and is at least one selected from synthetic hydrocarbon oils such as low-polarity poly α-olefin oils and mineral oils. The mineral oil is preferably refined by appropriately combining vacuum distillation, solvent removal, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing, white clay purification, hydroxylation purification, and the like. Since such a base oil has low polarity, swelling of the resin part of the worm wheel can be suppressed. Similarly, a decrease in strength and a decrease in elasticity of the rubber damper 130 can be suppressed.

  The base oil may contain a lubricating oil having polarity as long as it is less than 30% by mass, preferably less than 10% by mass. Polyamide resin or polyamide-imide resin used suitably for the resin part of the worm wheel has low wettability with low-polarity lubricating oil, so improving the film formability of the oil film by blending a small amount of high-polarity lubricating oil Can be made. The lubricating oil having polarity is not particularly limited, and various ester oils such as diester oil, polyol ester oil, and aromatic ester oil, and various aromatic ether oils such as polyphenyl ether and alkyl diphenyl ether are preferable.

Further, the kinematic viscosity of the base oil is preferably 18 mm ² / s (40 ° C.) or more. If the kinematic viscosity of the base oil is less than 18 mm ² / s (40 ° C.), a sufficient oil film thickness cannot be ensured on the sliding surface, and both transmission efficiency and wear resistance deteriorate. The upper limit of the kinematic viscosity is 150 mm ² / s (40 ° C.), and if it exceeds this, the low-temperature fluidity becomes inferior.

  In the present invention, since the friction characteristics of the thickener significantly affect the friction characteristics of the grease composition, metal soap, metal composite soap or urea compound exhibiting low friction is used. In the grease composition used in the present invention, since wax is blended to reduce friction, the sliding surface has a portion where wax is present, a portion where a thickener is present, a portion where base oil is present, metal and resin. And the portion in direct contact with each other are considered to be mixed, and the sum of the frictional forces in these portions becomes the frictional force applied between the worm 12 and the worm wheel 11. Therefore, even if the friction is reduced in the portion where the wax is present, the friction does not become a certain value or less if the friction force of the thickener is large. Therefore, in order to make the friction lower, at least one of metal soap, metal composite soap, and urea compound is used as a thickener.

  Examples of the metal soap include lithium soap, calcium soap, sodium soap, aluminum soap, lithium complex soap, calcium complex soap, sodium complex soap, barium complex soap, aluminum soap, among others, lithium soap and lithium complex soap, especially 12-hydroxy lithium stearate or lithium stearate is preferable because of low friction.

  Examples of the urea compound include diurea compounds, triurea compounds, tetraurea compounds, polyurea compounds, urea / urethane compounds, diurethane compounds, and mixtures thereof. Among them, the following [I] or [II] is represented. Aliphatic diurea is preferred because of particularly low friction. In the formula, R1 and R2 are linear alkyl groups having 7 to 19 carbon atoms, which may be the same or different.

  The amount of the thickener is not limited as long as the grease can be formed with the base oil, but is preferably 5 to 25% by mass of the total amount of grease. When there is too much thickener than 25 mass%, grease may become hard too much and grease may not spread over a sliding part. On the other hand, if the thickener is less than 5% by mass, the grease becomes too soft and there is a risk of spilling out. Further, the blending degree is preferably 200 to 350.

  In the grease composition, a wax having an acid value of 6 to 30 mgKOH / g and a dropping point of 72 to 104 ° C. is blended as an additive that exhibits friction reduction and wear suppression effects in sliding between resin and metal. Is done. The dropping point is a temperature defined by ASTM D 3954. There are two possible mechanisms for reducing the friction of the sliding portion with wax. For one, the wax reduces friction by cleaving, shearing, and deforming at low stress on the friction surface—that is, it functions as a solid lubricant. The other is explained as follows. The regulation of the acid value of the wax in the present invention corresponds to the regulation of the amount of carboxyl groups (—COOH) in the wax. The wax having a carboxyl group is adsorbed on the metal surface to form a low-friction film, and this film functions as an oily agent. In addition, a similar coating is formed on the polyamide resin or the polyamideimide resin, which is the base resin of the resin portion, derived from hydrogen bonding as described below. As a result, direct contact between the polyamide resin and the metal is avoided, friction between the worm and the worm wheel is reduced, and torque transmission with high efficiency becomes possible. Therefore, when the acid value is less than 6 mgKOH / g, it is difficult to form a coating derived from this carboxyl group, and the friction reducing effect is not sufficiently exhibited. On the other hand, when the acid value is higher than 30 mgKOH / g, chemical attack on the resin becomes obvious and the resin portion is worn.

  On the other hand, for example, a polyethylene wax as described in Patent Document 2 does not have a carboxyl group and attracts the resin surface only by a relatively weak intermolecular force, so that an oil film is formed when the peripheral speed is increased. It becomes difficult.

  In addition, as the atmospheric temperature increases, the oil film of the base oil formed on the sliding portion becomes thinner, and it becomes easier to run out of oil. Since the wax melts by heating and becomes a highly viscous liquid having lubricity, by adding the wax to the grease composition, a new lubricating film is formed by the wax when the temperature rises, and the oil film of the base oil breaks. Will come to compensate. In order to effectively exhibit such a grease replenishing action, it is desirable that the wax melts at a temperature at which the base oil starts to run out of oil film. In the present invention, the maximum ambient temperature of the reduction gear mechanism (general column) In consideration of the assist type electric power sheering apparatus of about 60 ° C., wax having a dropping point of 72 to 104 ° C. is used. In the case of a wax having a dropping point exceeding 104 ° C., the grease does not melt even at a temperature at which the base oil runs out of oil, so that no grease replenishing action is exhibited. In addition, the wax having a dropping point of less than 72 ° C. melts even in a low temperature range where melting is unnecessary, so that the depletion of the wax is accelerated, resulting in a decrease in durability.

  The type of wax is not limited as long as it satisfies the above acid value and dropping point, but ester wax and partially saponified ester wax are preferable. In addition, these ester waxes and partially saponified ester waxes have a remarkable grease replenishing action particularly when metal soap or metal composite soap is used as a thickener. This is because the wax has an acid value, so that a reaction occurs between the melted wax and the thickener, so that the fatty acid constituting the metal soap or the metal composite soap is partially liberated and the thickener has a thickening property. This is due to a synergistic effect with the phenomenon that the oil content in the grease increases as described above, and the lubricant is quickly replenished to the sliding portion.

  The blending amount of the wax is preferably 2 to 12% by mass with respect to the total amount of grease. If the blending amount is less than 2% by mass of the total amount of grease, the effect of reducing wear cannot be obtained. If the blending amount exceeds 12% by mass, the grease becomes too hard and sufficient lubricating performance cannot be exhibited. A more preferable blending amount is 2.5 to 11% by mass of the total amount of grease.

  The grease composition may contain additives such as an antioxidant, a rust inhibitor, a metal corrosion inhibitor, an oil agent, an antiwear agent, an extreme pressure agent, and a solid lubricant as necessary. Any of these may be known ones. However, since the additive acts competitively with the wax, it is necessary to consider the addition amount so as not to reduce the effect of reducing the wear of the wax.

  The present invention will be further described below with reference to test examples, but the present invention is not limited thereby.

(Test-1)
A base grease having a blending degree of 300 formed by blending lithium stearate as a thickener with a poly α-olefin oil having a kinematic viscosity at 40 ° C. of 47 mm ² / s, both of which are ester wax or partially saponified by Clariant "Licowax KST (acid value 5 mgKOH / g or less, dropping point 56 to 63 ° C)", "Licowax F (acid value 6 to 10 mgKOH / g, dropping point 77 to 83 ° C)", "Licowax E (acid) 15-20 mg KOH / g, dropping point 79-85 ° C.) ”,“ Licolub WE40 (acid value 13-26 mg KOH / g, dropping point 73-79 ° C.) ”,“ Licolub WE 4 (acid value 20-30 mg KOH / g, dropping) Point 78-85 ° C.) ”,“ Licowax KPE (acid number 25-35 mg KOH / g, dropping point 79-85 ° C.) ”,“ Licowax O (acid number 10-15 mg KOH / g, dropping point 98-105 ° C.) ”, " Licowax OP (acid value 9-14 mg KOH / g, dropping point 96-102 ° C.) ”,“ Licowax KPS (acid 30-40 mg KOH / g, dropping point 80-85 ° C.) ”,“ Licowax OM (acid value 20-30 mg KOH / g, dropping point 86 to 93 ° C.) ”and“ Licowax BJ (acid number 17 to 25 mg KOH / g, dropping point 72 to 78 ° C.) ”were formulated so as to be 7% by mass of the total amount of grease to prepare a test grease. did.

  And as a parameter | index of the transmission efficiency of a reduction gear mechanism, the friction coefficient between resin-metals was measured about each test grease using the friction tester shown in FIG. In this friction tester, a test grease is applied to a test plate made of polyamide 66 containing 30% by mass of glass fiber (adjusted to arithmetic mean roughness Ra of 1.0), and SUJ2 made of 10 mm in diameter, The horizontal stress caused by friction is detected with a load cell at a maximum contact pressure of 170 MPa, a rocking distance of 30 mm, a frequency of 16 Hz, and an ambient temperature of 60 ° C., and the coefficient of friction is calculated from the output voltage. Calculated. A coefficient of friction of 0.064 or less was accepted.

(Test-2)
Further, the wear resistance performance of each of the above test greases was evaluated. First, a cross-knurled, degreased outer diameter 43 mm, width 13 mm S45C core tube is placed in a mold fitted with a sprue and a disk gate, and polyamide 66 containing 30% by weight of glass fiber (Ube Industries) (UBE Nylon 2020GU6 manufactured by Co., Ltd., containing copper additive) is injection molded into a worm wheel blank with an outer diameter of 60 mm and a width of 13 mm, and then the outer periphery of the resin part is cut to form gear teeth. A worm wheel shown in FIG. 3 was produced. Then, it is built into the electric power steering device of an actual automobile together with the worm made of S45C, and each test grease is evenly applied to the gear teeth of the worm wheel and the tooth portion of the worm, and the snake is operated at the ambient temperature of 60 ° C. 1.5 m / s) was repeated, and the amount of wear of the gear teeth of the worm wheel was measured after snaked 100,000 times. The amount of wear was an increase in backlash of 3 ° or less.

  The results of Test-1 and Test-2 are shown in FIG. 5 as a graph. When either one of the coefficient of friction or the amount of wear is rejected, the mark is blacked out. As shown in the figure, all compositions satisfying both the coefficient of friction and the amount of wear are in a region surrounded by a square having an acid value of 6 to 30 mg KOH and a dropping point of 72 to 104 ° C., and the wax specified in the present invention is added. It can be seen that the wear resistance is improved.

(Test-3)
Add the amount of “Licolub WE40” made by Clariant to base grease with a blending degree of 300, which is a blend of lithium stearate as a thickener with poly α-olefin oil having a kinematic viscosity at 40 ° C. of 47 mm ² / s. Test greases were prepared by adding different amounts. The test grease was measured for backlash increase and low temperature starting torque at −40 ° C. according to JIS K2220 5.14. The backlash increase amount is 3 ° C. or less as in the case of Test-2. Also, in cold regions, the reduction gear mechanism of the electric power steering device may be exposed to about -40 ° C. Therefore, it is assumed that the low temperature starting torque is measured at -40 ° C and the torque to be transmitted is consumed. 20 N · cm or less was regarded as a pass as a standard for reducing the amount of slag.

  The results are shown in a graph in FIG. 6, and it can be seen that by adding 2 to 12% by mass of the wax with respect to the total amount of grease, good wear resistance can be imparted and high torque transmission efficiency can be obtained even at low temperatures. The wax addition amount is more preferably 2.5 to 11% by mass.

(Test-4)
Test greases were prepared with the formulations shown in Table 1. The lithium composite soap was prepared so that lithium 12-hydroxystearate was 75% by mass of the total amount, and lithium azelate was 25% by mass of the total amount, and the aliphatic diurea was R1 in the above formula [I]. , R2 is a compound having a linear octyl group. As the wax, Clariant polyethylene wax “Licowax PE 520” or Clariant ester wax “Licolub WE 40” was used. And about the test grease, it carried out similarly to Test-1 and Test-2, and measured the friction coefficient and the backlash increase amount. The determination criteria are the same. The results are also shown in Table 1.

From Table 1, it can be seen that even if polyethylene wax (Comparative Example 1) or a base oil having a kinematic viscosity of less than 18 mm ² / s (Comparative Example 2) is used, it does not contribute to the reduction of the frictional force.

(Test-5)
A polyol ester having kinematic viscosity of 30 mm 2 / ^s at 40 ° C., the mixed oil kinematic viscosity were mixed by changing the mixing ratio of the poly-α- olefin oil of 30 mm 2 / ^s at 40 ° C., by blending a diurea test A grease was prepared. Then, an ethylene acrylic rubber disk having a diameter of 10 mm and a thickness of 5 mm was immersed in the test grease, and left in a constant temperature bath at 100 ° C. for 100 hours. The thickness of the disk was measured after immersion, and the amount of change (dimensional change rate) from before immersion was determined.

  The results are shown in graph form in FIG. 7. When the ester oil, which is a polar oil, is mixed, the dimensional change rate is 0.3% or less and almost negligible if the mass of the base oil is 30 mass% or less. It turns out that it can be suppressed.

It is a partial section lineblock diagram showing an example of an electric power steering device. It is AA sectional drawing of FIG. 1, and is a schematic block diagram which shows the connection part periphery of an electric motor and a reduction gear mechanism. It is a perspective view which shows an example of a worm wheel and a worm. It is a schematic diagram which shows the structure of a friction tester. It is a graph which shows the relationship between the acid value and dropping point which were obtained in the Example. It is the graph which occupies the relationship of the wax addition amount and backlash increase amount which were obtained in the Example. It is a graph which shows the relationship between the amount of ester oil in base oil and the dimensional change rate of acrylic rubber which were obtained in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core pipe 3 Resin part 8 Adhesive 10 Gear tooth 11 Worm wheel 12 Worm 13 Tooth part 14 Recessed 15 Lubricant containing polymer 50 Stelling column 70 Steering shaft 80 Torsion bar 90 Bearing 91 Bearing 100 Electric motor 110 Rolling bearing 120 Housing 130 Damper

Claims (4)

An electric power steering device that transmits auxiliary output by an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism,
The driven gear of the reduction gear mechanism is integrally provided with a resin portion made of a resin composition and having gear teeth formed on the outer peripheral surface thereof on the outer periphery of a metal core tube, and an acid value of 6 to 30 mgKOH / g. An electric power steering apparatus characterized by being lubricated with a grease composition containing wax having a dropping point of 72 to 104 ° C. in a proportion of 2 to 12% by mass of the total amount of grease.   The wax is at least one selected from an ester wax and a partially saponified ester wax, and the thickener of the grease composition is at least one selected from a metal soap and a metal composite soap. The electric power steering device according to Item 1.   The base oil of the grease composition contains at least one selected from synthetic hydrocarbon oil and mineral oil in an amount of 70% by mass or more of the total amount of the base oil, and the thickener is at least one selected from lithium soap and lithium composite soap. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is an electric power steering apparatus.   The electric power steering device according to any one of claims 1 to 3, wherein the resin forming the resin portion is a polyamide resin or a polyamideimide resin.

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