JP2006044306A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prolong the lifetime by suppressing the wear of resin gear teeth and establish a higher output while the whole device is maintained compactly by reducing the frictional loss of a reduction gear mechanism and a rack-and-pinion type motion converting mechanism. <P>SOLUTION: The electric power steering device includes the reduction gear mechanism having a follower gear structured so that a resin part consisting of a resin compound and furnished at the peripheral surface with gear teeth is formed rigidly at the periphery of a core pipe of metal, while a driving gear is made of metal, wherein the surface roughness on the tooth flank is 0.15 μm or less by the arithmetic mean roughness Ra, and at least between the follower gear and the driving gear, a base oil and a grease compound are interposed; the base oil containing at least one of the poly-α-olefin oil and mineral oils in a content of 80 mass% or more, and the grease compound containing as additives a specific oily agent and a specific nonpolar solid lubricant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering device that transmits an 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 cored bar is made of a resin composition and has gear teeth on the outer peripheral surface. The present invention relates to an increase in output of an electric power steering apparatus that has a driven gear integrally formed with a formed resin portion and a rack and pinion type motion conversion mechanism.

  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.

  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, as shown in FIG. 3, the worm 12 is made of metal, and the resin portion 3 made of resin and formed with gear teeth 10 on the outer peripheral surface is bonded to the worm wheel 11 on the outer periphery of the metal core tube 1. Noise countermeasures are carried out by using an integrated agent 8.

  The resin part 3 is made of, for example, a material in which a reinforcing material such as glass fiber or carbon fiber is mixed with a base resin such as polyamide 6, polyamide 66, polyacetal, polyether ether ketone (PEEK), or polyphenylene sulfide (PPS). In addition, MC (monomer cast) nylon, polyamide 6, polyamide 66, etc. that do not contain a reinforcing material are used. Among these, in consideration of dimensional stability and cost, MC nylon not containing a reinforcing material, polyamide 6, glass 66 containing polyamide, polyamide 46, and the like are mainly used.

  In the reduction gear mechanism, grease is applied to the tooth surfaces of the gear teeth 10 of the worm wheel 11 and the tooth surfaces of the worm 12 to suppress the wear. For the purpose of suppressing, a grease composition containing a polyolefin wax has been proposed (see Patent Document 1). However, in recent years, the electric power steering device avoids an increase in the contact surface pressure between the worm 12 and the worm wheel 11 in order to cope with application to a large vehicle or downsizing of the device for securing a living space in the vehicle. Therefore, further wear reduction is required. At the same time, there is an increasing demand for suppressing friction loss of input power.

Furthermore, in an electric power steering apparatus equipped with a rack and pinion type motion conversion mechanism (not shown), grease is generally lubricated, but this rack and pinion is used to reduce the size and increase the efficiency of the apparatus. Similarly, there is an increasing demand for a lubricating grease for a motor-type motion conversion mechanism that suppresses friction loss of input power.
JP-A-9-194867

  The present invention has been made in view of such a situation, and in an electric power steering apparatus having a resin worm wheel and further having a rack and pinion type motion conversion mechanism, the resin gear teeth of the worm wheel are provided. The purpose is to increase the output while reducing the friction loss of the reduction gear mechanism and the rack and pinion type motion conversion mechanism and keeping the entire device compact. .

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 the metal core tube.
The driving gear is made of metal, the surface roughness of the sliding surface of the gear tooth with the gear tooth of the driven gear is 0.15 μm or less in terms of arithmetic average roughness Ra, and
A base oil containing at least one selected from poly-α-olefin oil and mineral oil at a ratio of 80% by mass or more between at least the driven gear and the drive gear, and (a) a derivative of montanic acid as an additive At least one selected from wax, fatty acid amide wax, ester wax, ketone wax, oxidized polyolefin wax, and (b) polytetrafluoroethylene, polyvinylidene fluoride, ethylene tetrafluoride-hexafluoropropylene copolymer resin, tetrafluoride An electric power steering device characterized by interposing a grease composition containing at least one selected from ethylene-ethylene copolymer resin, polyvinyl fluoride, polyethylene, polystyrene, polymethyl methacrylate, and polyethylene terephthalate.
(2) The sum of the contents of the component (a) and the component (b) is 8% by mass or less with respect to the total amount of grease, and the content of the component (a) is 1. 4 to 3.5% by mass, the content of the component (b) is equal to or more than the content of the component (a) and 3% by mass or more based on the total amount of grease. The electric power steering apparatus according to (1) above.
(3) The drive gear is subjected to palsonite treatment, and the resin portion of the driven gear contains 25 to 35 mass% of glass fiber with a diameter of 5 to 9 μm in the polyamide resin based on the total amount of the resin. The electric power steering apparatus according to the above (1) or (2).
(4) The thickener of the grease composition is at least one selected from lithium soap, barium composite soap, diurea compound represented by chemical formula (I) or chemical formula (II), and base oil kinematic viscosity is The electric power steering device according to any one of (1) to (3) above, wherein the electric power steering device is 30 to 150 mm ² / s at 40 ° C.

(In the formula, R1 and R2 are linear alkyl groups having 8 to 16 carbon atoms, which may be the same or different.)
(5) A ratio including a rack and pinion type motion conversion mechanism, a kinematic viscosity at 40 ° C. of 30 to 150 mm ² / s, and at least one selected from mineral oil and polyα-olefin oil is a ratio of 80% by mass or more. Grease containing at least one selected from base oils, lithium soaps as thickeners, molybdenum dithiocarbides and molybdenum dithiophosphates as friction reducers in a proportion of 0.5 to 6.5% by mass based on the total amount of grease The electric power steering device according to any one of (1) to (4) above, which is lubricated with a composition.

  According to the present invention, there is provided a compact and high-power electric power steering apparatus that has a long life with little wear on the gear teeth of the worm wheel, and further has a low friction loss of the reduction gear mechanism and the rack and pinion type motion conversion mechanism. The

  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. As shown in FIG. 3, the reduction gear mechanism includes a worm wheel 11 having a resin portion 3 and a metal worm 12.

  The worm 12 is made of, for example, a metal such as S45C material or SUJ2 material, and in order to ensure high power transmission efficiency, the sliding surface (hereinafter referred to as “tooth surface”) of the gear tooth worm wheel 11 with the gear tooth 10. Is calculated to have an arithmetic average roughness Ra of 0.15 μm or less, preferably 0.12 μm or less. In the present invention, as will be described later, the components (a) and (b) are added to reduce wear. When the arithmetic average roughness Ra exceeds 0.15 μm, the wear reduction effect by these components is exceeded. The increase of the frictional force due to catching of the irregularities on the tooth surface of the worm 12 becomes obvious.

  Moreover, in order to suppress the damage by the glass fiber contained in the resin part 3 of the worm wheel 11, it is preferable that the worm 12 is subjected to heat treatment, nitriding treatment or the like to increase the surface hardness, and is subjected to pulsonite treatment. Particularly preferred.

  The worm wheel 11 is not limited except that the worm wheel 11 is provided with the resin portion 3, but to describe a preferred embodiment, the resin portion 3 is made of MC nylon or polyamide 6, polyamide 66, polyamide 46 containing glass fibers. It is preferably formed from a resin composition. The molecular weight of the polyamide resin is a range that can be injection-molded in the state of containing glass fiber, specifically, the number average molecular weight is 13,000 to 28000, and considering the fatigue resistance and moldability, the number average molecular weight is 18000 to 26000. More preferred. When the number average molecular weight is less than 13,000, the molecular weight is too low, the fatigue resistance is poor, and the practicality is low. On the other hand, if the number average molecular weight exceeds 28000, it is not preferred that glass fiber is contained at a content described later, because the melt viscosity becomes too high to accurately mold the resin part 3.

  In the polyamide resin composition, the glass fiber preferably has a diameter of 5 to 13 μm, and the content thereof is preferably 10 to 40% by mass of the total amount of the resin composition. Considering the wear resistance and dimensional stability of the resin part 3, it is particularly preferable to contain 25 to 35% by mass of a glass fiber having a diameter of 5 to 9 μm. This is because it is indispensable that the glass fibers are finely and uniformly dispersed throughout the resin part 3 in order to maintain the abrasion resistance and dimensional stability of the resin part 3 at a high level. When glass fibers having a diameter of less than 5 μm are used, mechanical strength such as impact resistance of the resin part 3 tends to be lowered, and the manufacturing cost is increased and the practicality is lowered. On the other hand, when the diameter of the glass fiber exceeds 9 μm, the wear resistance becomes inferior, particularly when the diameter exceeds 13 μm. In addition, using glass fibers having a diameter of 5 to 9 μm means that a larger number of glass fibers are dispersed in the resin even when the glass fiber is thicker than this, even if the same content is used. The load resistance of the resin part 3 is increased, so that it can withstand use at higher surface pressure. When the glass fiber content is less than 25% by mass, the mechanical strength of the resin part 3 and the effect of suppressing dimensional changes due to water absorption are reduced, and particularly when the glass fiber content is less than 10% by mass. On the other hand, if the glass fiber content exceeds 35% by mass, the worm 12 is likely to be damaged, wear of the worm 12 is promoted, and the durability of the reduction gear mechanism 20 may be insufficient, particularly 40% by mass. It becomes remarkable when exceeding.

  The fiber length of the glass fiber is preferably 100 to 900 μm, particularly preferably 300 to 600 μm. If the fiber length is less than 100 μm, the reinforcing effect and the effect of suppressing dimensional change due to water absorption are small, and if it exceeds 900 μm, the reinforcing effect and the effect of suppressing dimensional change due to water absorption increase, but the resin part 3 breaks when molded. Or deterioration of the molding accuracy due to a decrease in orientation is assumed, which is not preferable.

  Moreover, a part of glass fiber may be replaced with other reinforcing materials such as a fibrous material such as carbon fiber and a whisker-like material such as potassium titanate whisker, and a colorant or the like may be added.

  Furthermore, in order to prevent deterioration due to heat during molding and use, MC-based nylon and polyamide resin compositions are each added with an iodide-based heat stabilizer and an amine-based antioxidant, either alone or in combination. May be.

  In order to form the resin part 3, the melt of the above MC nylon or polyamide resin composition may be filled into a mold in which the core tube 1 is disposed and cured. And the gear tooth 10 is formed in the outer peripheral surface of the resin part 3 by cutting, and the worm wheel 11 is obtained.

  For the purpose of bonding the core tube 1 and the resin portion 3 more firmly, and since the polyamide resin has high water absorption, it is also preferable to provide the adhesive layer 8 for the purpose of further suppressing dimensional changes due to water absorption. In order to form the adhesive layer 8, for example, there is a method in which a silane coupling agent is applied to the outer peripheral surface of the core tube, the resin portion 3 is heated and pressed, and then high-frequency heating is performed. Silane coupling has an alkoxy group, which is a hydrolyzable group, at one end of the molecular structure. This alkoxy group is hydrolyzed to change into a hydroxyl group, which undergoes dehydration condensation with a hydroxyl group on the metal surface. A covalent bond having a strong binding force is formed. Further, the other end has an organic functional group, and this organic functional group is bonded to an amide bond in the molecular structure of the polyamide resin. And the metal core 1 and the resin part 3 join firmly by these coupling | bonding. The organic functional group of the silane coupling agent is preferably an amino group or an epoxy group because of its reactivity with the amide group. As the silane coupling agent having such an organic functional group, γ-glycidoxypropyltri Methoxysilane, β (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β- (aminoethyl) -γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, etc. Is mentioned. In particular, those having an epoxy group as the organic functional group are more preferable because of their high reactivity with amide bonds.

  Further, when high-frequency heating is performed, a strong adhesive layer 8 is formed, and only the inner peripheral surface (interface) of the resin portion 3 in contact with the outer peripheral surface of the core tube is melted to remove residual stress generated by press-fitting. It can be done together. In addition, adhesive force increases more by making the core pipe temperature at the time of high frequency heating into 200-450 degreeC. The heating atmosphere may be in the air, but it is preferable to perform the heating in an inert gas atmosphere such as argon gas because the oxidative deterioration of the resin portion 3 is suppressed.

  In addition to the configuration shown in FIG. 3, for example, a spur gear shown in FIG. 4, a helical gear shown in FIG. 5, a bevel gear shown in FIG. 6, a hypoid gear shown in FIG. It is. In the same manner as above, each drive gear is made of metal, preferably pulsonite treated, the tooth surface is further processed with an arithmetic average roughness Ra of 0.15 μm, and the driven gear has an adhesive layer 8 on the core tube 1. Thus, the resin portion 3 made of the same resin composition is integrated, and gear teeth 10 are formed on the outer periphery of the resin portion 3.

  A grease composition for lubrication is interposed between the gears of the worm wheel 11 and the worm 12 configured as described above. The base oil of the grease composition is selected from poly-alpha olefin oil and mineral oil with low polarity in consideration of chemical action on MC nylon and polyamide resin forming the resin part 3 and rubber material forming the damper 130. At least one kind is contained in a proportion of 80% by mass or more. The mineral oil is preferably refined by appropriately combining vacuum distillation, oil removal, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing, clay refining, hydrorefining, and the like. Although there is no restriction | limiting in the lubricating oil which can be used together, For example, since mineral oil and poly alpha olefin oil are nonpolar and have low wettability with respect to a polyamide resin, in order to improve this, lubricating oil with polarity can be used.

The base oil preferably has a kinematic viscosity at 40 ° C. of 30 to 150 mm ² / s. If the kinematic viscosity is less than 30 mm ² / s (40 ° C.), the oil film forming ability is inferior, and the durability of the resin gear teeth 10 of the worm wheel 11 may be reduced. On the other hand, if the kinematic viscosity exceeds 150 mm ² / s (40 ° C.), the low temperature characteristics deteriorate, and there is a possibility that the viscosity increase or solidification will occur in a low temperature environment and the power transmission efficiency of the reduction gear mechanism will be reduced.

  Thickeners include metallic soaps such as lithium soap and lithium composite soap, inorganic thickeners such as diurea, and organic thickeners such as polytetrafluoroethylene. From the viewpoint of low friction, lithium soap, barium composite soap, and a diurea compound represented by chemical formula (I) or chemical formula (II) are preferable.

  In chemical formula (I) or chemical formula (II), R1 and R2 are linear alkyl groups having 8 to 16 carbon atoms, which may be the same or different.

  The grease composition also includes (a) at least one selected from montanic acid derivative waxes, fatty acid amide waxes, ester waxes, ketone waxes and oxidized polyolefin waxes as essential additives, and (b) polytetrafluoroethylene. , Polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer resin, tetrafluoroethylene-ethylene copolymer resin, polyvinyl fluoride, polyethylene, polystyrene, polymethyl methacrylate, polyethylene terephthalate and Are added in combination. Among the components (b), polytetrafluoroethylene and polyethylene are preferable.

  The component (b) is a nonpolar solid lubricant, and mixing this with grease suppresses heat generation on the sliding surface between the resin gear teeth 10 of the worm wheel 11 and the gear teeth of the metal worm 12. Thus, the effect of extending the durable life of the resin gear teeth 10 can be obtained. In order to obtain such an effect, the component (b) is preferably added in an amount of 3% by mass or more based on the total amount of grease. However, since the component (b) has a thickening action, if the amount added is too large, the grease may harden in a low temperature environment and deteriorate the slidability. For example, the power transmission efficiency is large at −40 ° C. Since it falls, it is preferable to make an upper limit into 8 mass%.

  In addition, since the component (b) is not tied to the sliding surface with any strong bonding force, it is difficult to exert its friction reducing ability when sliding under high load or high speed. In the reduction gear mechanism of an electric power steering device, the gear teeth have a complicated shape and are driven under various conditions depending on the driving state of the automobile. As a result, the frictional resistance of the sliding surface goes up and down violently. Although the mechanism for generating this stick-slip is not clear, both gear teeth intermittently come into direct contact with each other over part or all of the sliding surface between the metal gear teeth of the worm 12 and the resin gear teeth 10 of the worm wheel 11. It is thought to be the cause.

  The oily agent as component (a) has an action of suppressing the occurrence of stick slip. The oil-based agent adsorbs on the metal surface of the sliding part to form a monolayer to several molecule layered thin film, reducing the surface tension of the metal surface, increasing the wettability of metal to oil, and the probability of rupture of the oil film Decrease. Therefore, even when the lubricating oil film breaks under a lubricating condition exceeding the load bearing capacity of the component (b), this (between the metal gear teeth of the worm 12 and the resin gear teeth 10 of the worm wheel 11 ( The direct contact between the two surfaces is prevented by the thin film due to the component a), and the increase in frictional resistance is suppressed.

  In addition, various types of resin / rubber materials including a rubber damper 130 are used around the reduction gear mechanism 20. For this reason, alcohols and fatty acid derivatives, among those conventionally used as oiliness agents, often affect the physical properties of resins and rubber materials. On the other hand, the component (a) listed above has a small influence on the resin / rubber material because a polar group exists in a part of the polymer structure. The component (a) is preferable because it has a surface tension as small as that of the component (b) but also has a function as a solid lubricant (cleaving with low friction on the sliding surface).

  Further, as schematically shown in FIG. 8, the component (a) and the component (b) are sheared on the sliding surfaces of the resin gear teeth 10 of the worm wheel 11 and the metal gear teeth of the worm 12. However, the degree of friction changes depending on the existence ratio. Accordingly, the addition amount of the component (a) should be an amount sufficient to suppress stick-slip, and at the same time, it should be an amount that does not inhibit the low frictional ability of the component (b). It is preferable to set it as 1.4-3.5 mass% with respect to.

  For the above reasons, in the present invention, the total amount of component (a) and component (b) is 8% by mass or less based on the total amount of grease, and the content of component (a) is based on the total amount of grease. 1.4 to 3.5% by mass, and added so that the content of component (b) is equal to or greater than the content of component (a) and 3% by mass or more based on the total amount of grease. It is preferable.

  Moreover, you may add another additive to a grease composition as needed. For example, any of known antioxidants, rust inhibitors, metal corrosion inhibitors, oiliness agents, antiwear agents, extreme pressure agents, solid lubricants and the like can be applied and added.

The electric power steering device of the present invention may include a rack and pinion type motion conversion mechanism. Although there is no restriction | limiting in the structure and structure of a rack and pinion type | formula motion conversion mechanism, Kinematic viscosity in 40 degreeC is 30-150 mm < ² > / s, and at least 1 sort (s) chosen from mineral oil and poly alpha olefin oil is 80 mass% or more. A base oil contained in a proportion, lithium soap as a thickener, and at least one selected from molybdenum dithiocarbide and molybdenum dithiophosphate as a friction reducing agent in a proportion of 0.5 to 6.5% by mass with respect to the total amount of grease. Lubricated with a grease composition.

The mineral oil is preferably the same refined mineral oil as described above. If the kinematic viscosity of the base oil is less than 30 mm ² / s (40 ° C.), the oil film forming ability is poor and the durability may be reduced. If the base oil exceeds 150 mm ² / s (40 ° C.), the low temperature characteristics deteriorate and the temperature is low. There is a risk of increased viscosity or solidification in the environment and reduced power transmission efficiency. Lithium soap is a preferred thickener from the viewpoint of low friction, and low friction is further improved by the combined use with molybdenum dithiocarbide or molybdenum dithiophosphate. Therefore, when the content of molybdenum dithiocarbide and molybdenum dithiophosphate is less than 0.5% by mass of the total amount of grease, it does not sufficiently contribute to the improvement of low friction. Moreover, even if it adds exceeding 6.5 mass%, the improvement of the effect corresponding to an increment will not be acquired, but it may become uneconomical and may cause corrosion depending on an environment.

  Moreover, you may add another additive to a grease composition as needed. For example, any of known antioxidants, rust inhibitors, metal corrosion inhibitors, oiliness agents, antiwear agents, extreme pressure agents, solid lubricants and the like can be applied and added.

  The electric power steering apparatus according to the present invention is configured as described above, but the surface roughness of the tooth surface of the worm 12 in the reduction gear mechanism is set to an arithmetic average roughness Ra of 0.15 μm or less, and the grease has a high friction reducing effect. By lubricating with the composition, as shown in the examples described later, the wear becomes long with a low wear, and the power transmission efficiency exceeding 85% is obtained, and the output becomes high while maintaining the compactness of the apparatus. .

  Hereinafter, the present invention will be described more specifically with reference to test examples, but the present invention is not limited thereto.

(Test-1: Verification of arithmetic mean roughness)
A cross-knurled, degreased outer diameter 45 mm, width 13 mm S45C core tube is placed in a mold fitted with a sprue and a disk gate, and polyamide 6 containing 30% by mass of glass fiber is injection molded. A worm wheel plank material having an outer diameter of 60 mm and a width of 13 mm was formed, and then the outer periphery of the resin portion was cut to form gear teeth to produce a worm wheel shown in FIG. Further, worms made of S45C material, subjected to pulsonite treatment, and having different tooth surface arithmetic average roughness Ra were prepared. In addition, arithmetic mean roughness Ra is a value of the sliding part of a tooth surface, and was measured along the sliding direction.

Further, a polyalphaolefin oil having a base oil kinematic viscosity at 40 ° C. of 60 mm ² / s is used as a base oil, and a diurea compound represented by the chemical formula (I) (mixed in a weight ratio of 1: 1 with an amine having 8 to 18 carbon atoms). The test grease was prepared by changing the amount of polytetrafluoroethylene (PTFE) added to a base grease using a thickener as a thickener. In addition, all the test greases were unified to a blending consistency of 280.

The above worm wheel and worm are incorporated into the actual reduction gear mechanism of the electric power steering apparatus, and the test grease is applied evenly to the gear tooth surface of the worm wheel and the gear tooth surface of the worm to maintain the ambient temperature at 80 ° C. Steering was performed at a rotational speed of 50 min ^−1, the output power with respect to the input power was measured, and the power transmission efficiency in the reduction gear mechanism was obtained.

  The results are shown in a graph in FIG. 9, and it can be determined that the addition amount of PTFE is preferably 3% by mass or more. Moreover, it can be judged that the arithmetic average roughness Ra of the tooth surface of the worm is 0.15 μm or less, because an efficiency of 85% or more can be realized. When the arithmetic average roughness Ra of the tooth surface is 0.12 μm or less, the efficiency of 90% or more can be achieved, which is more preferable.

(Test-2: (b) Verification of component types)
A test grease was prepared by adding PTFE, polyethylene (PE), and polymethyl methacrylate (PMM) at a ratio of 3% by mass to the same base grease as in Test-1. The blending consistency was also unified at 280. Further, gear teeth made of S45C material subjected to pulsonite treatment and having tooth surface arithmetic average roughness Ra of 0.12 μm were prepared as worms. And the power transmission efficiency was calculated | required similarly.

  The results are shown in a graph in FIG. 10, and it is understood that polyethylene and PTFE are particularly preferable as the component (b), and both have substantially the same performance.

(Test-3: Verification of addition amount of component (a) and component (b))
To the same base grease as in test 1, polyethylene and montanic acid partially saponified ester wax (“Lycowax OP” manufactured by Clariant) were added at a constant 7 mass%, and the mixing ratio was changed. A test grease was prepared. The worm was made of a gear tooth made of S45C treated with pulsonite and having an arithmetic average roughness Ra of 0.12 μm. And the power transmission efficiency was calculated | required similarly. The results are shown in a graph in FIG.

  In addition, the steering input shaft continues to rotate 360 degrees alternately left and right, the operating torque of the input shaft is continuously measured, and when abnormal fluctuation is recognized, it is determined that stick slip has occurred. The number of sliding was determined. The results are shown in a graph in FIG. 12, where the horizontal axis represents the amount of montanic acid partially saponified ester wax added, and the vertical axis represents no addition of montanic acid partially saponified ester wax (ie, 100% polyethylene). The relative value (sliding frequency ratio) with respect to was shown.

  From FIG. 11 and FIG. 12, in order to increase the power transmission efficiency without causing stick-slip, the component (a) is contained in an amount of 1.4 to 3.5% by mass with respect to the total amount of grease, and (b It can be seen that the amount of the component) should be equal to or greater than the amount of the component (a).

(Test-4: Verification of base oil composition)
A polyol ester oil (30 mm ² / s @ 40 ° C.) and a polyalphaolefin oil (30 mm ² / s @ 40 ° C.) are mixed at different mixing ratios, and the above diurea is added to the test grease. Prepared. Then, a cylindrical plate made of ethylene acrylic rubber (diameter 10 mm, thickness 5 mm) was immersed in the test grease, and left in a constant temperature bath at 100 ° C. for 100 hours. Then, the cylindrical plate was taken out and the dimensional change in thickness was measured.

  The results are shown in a graph in FIG. 13, and when the poly α-olefin oil is 80% by mass or more with respect to the total amount of the base oil, the dimensional change rate is 0.3% or less, which is almost negligible. .

(Test-5: Verification of rack and pinion type motion conversion mechanism grease)
For diurea-mineral oil-based grease or lithium soap-mineral oil-based grease, input power and output power were measured using a rack and pinion mechanism having a structure shown in FIG. 14, and power transmission efficiency was measured. In addition, the penetration degree was both 250, and the base oil kinematic viscosity was 40 mm at 65 mm ² / s. The results are shown in FIG. 15, and it can be seen that lithium soap-mineral oil grease is more advantageous in terms of power transmission efficiency.

  Therefore, 3% by mass of molybdenum dithiocarbide (MoDTC) or molybdenum dithiophosphate (MoDTP) was added as an additive to the above lithium soap-mineral oil grease, and the same measurement was performed. The results are also shown in FIG. 15, and it can be seen that these two types of additives are effective in improving the power transmission efficiency.

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 deceleration mechanism. It is a perspective view which shows an example of a worm wheel and a worm. It is a perspective view which shows the other example (spur gear) of a reduction gear mechanism. It is a perspective view which shows the further another example (helical gear) of a reduction gear mechanism. It is a perspective view which shows the further another example (bevel gear) of a reduction gear mechanism. It is a perspective view which shows the further another example (high void gear) of a reduction gear mechanism. It is a schematic diagram for demonstrating the state of (a) component and (b) component in the sliding surface of a worm wheel and a worm. It is a graph which shows the result obtained by Test-1. It is a graph which shows the result obtained by Test-2. It is a graph which shows the result obtained by test-3. It is a graph which shows the result obtained by test-3. It is a graph which shows the result obtained by Test-4. It is the elements on larger scale which show the rack and pinion type | formula motion conversion mechanism used by Test-5. It is a graph which shows the result obtained by test-5.

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 Recess 15 Lubricant containing polymer 50 Steering column 70 Steering shaft 90 Bearing 91 Bearing 100 Electric motor 110 Rolling bearing 120 Housing 130 Damper

Claims (5)

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 the metal core tube.
The driving gear is made of metal, the surface roughness of the sliding surface of the gear tooth with the gear tooth of the driven gear is 0.15 μm or less in terms of arithmetic average roughness Ra, and
A base oil containing at least one selected from poly-α-olefin oil and mineral oil at a ratio of 80% by mass or more between at least the driven gear and the drive gear, and (a) a derivative of montanic acid as an additive At least one selected from wax, fatty acid amide wax, ester wax, ketone wax, oxidized polyolefin wax, and (b) polytetrafluoroethylene, polyvinylidene fluoride, ethylene tetrafluoride-hexafluoropropylene copolymer resin, tetrafluoride An electric power steering device characterized by interposing a grease composition containing at least one selected from ethylene-ethylene copolymer resin, polyvinyl fluoride, polyethylene, polystyrene, polymethyl methacrylate, and polyethylene terephthalate.   The sum of the contents of the component (a) and the component (b) is 8% by mass or less with respect to the total amount of grease, and the content of the component (a) is 1.4 to 3 with respect to the total amount of grease. The content of the component (b) is 0.5% by mass or more and the content of the component (a) is equal to or more than 3% by mass with respect to the total amount of grease. The electric power steering apparatus as described.   2. The drive gear is subjected to palsonite treatment, and the resin portion of the driven gear contains 25 to 35 mass% of glass fiber having a diameter of 5 to 9 μm in a polyamide resin with respect to the total amount of the resin. Or the electric power steering apparatus of 2. The thickener of the grease composition is at least one selected from lithium soap, barium composite soap, diurea compound represented by chemical formula (I) or chemical formula (II), and base oil kinematic viscosity at 40 ° C. The electric power steering device according to claim 1, wherein the electric power steering device is 30 to 150 mm ² / s.

(In the formula, R1 and R2 are linear alkyl groups having 8 to 16 carbon atoms, which may be the same or different.) It includes a rack and pinion type motion conversion mechanism, has a kinematic viscosity at 40 ° C. of 30 to 150 mm ² / s, and contains at least one selected from mineral oil and poly α-olefin oil in a proportion of 80% by mass or more. A grease composition comprising a base oil, lithium soap as a thickener, and at least one selected from molybdenum dithiocarbide and molybdenum dithiophosphate as a friction reducing agent in a proportion of 0.5 to 6.5% by mass based on the total amount of grease. The electric power steering apparatus according to any one of claims 1 to 4, wherein the electric power steering apparatus is lubricated.

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