JP2013112052A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device, in which a gear box housing a reduction gear mechanism is light in weight, high in reliability, and having superior dimension stability and heat resistance.SOLUTION: An electric power steering device includes a gear box 33. The gear box includes a housing member 33A housing a reduction gear mechanism 30 and a cover member 33B covering an opening of the housing member 33A, and is formed by tightly securing and integrating them with a bolt 33C and a nut. The housing member 33A and the cover member 33B are produced by insertion-molding of resin material. In the insertion molding, a metallic core metal 36B having a bolt hole, through which a bolt 33C is inserted, is inserted into the resin material. The resin material contains polyamide resin with a glass-transmission temperature of ≥80°C.

Description

  The present invention relates to an electric power steering apparatus.

The electric power steering device, when a steering torque is input to a steering shaft via a steering wheel by a driver of an automobile, steers the output of the electric motor as an auxiliary torque for assisting the steering torque via a reduction gear mechanism. It is a device that transmits to the shaft to assist the driver's steering.
In the column-type electric power steering device, a gear box that houses the reduction gear mechanism, that is, a substantially cylindrical housing member that houses the reduction gear mechanism, and a bolt or the like attached to the housing member. The cover member that covers the opening is made of a metal material such as an aluminum alloy.

On the other hand, in recent years, automobiles have been reduced in weight because there has been a demand for energy saving and energy saving of automobiles and reduction of carbon dioxide emissions. Therefore, the electric power steering device is also required to be further reduced in weight, and the reduction in the weight of the gear box made of metal has been studied.
In order to reduce the weight of gearboxes made of metal, it is only necessary to use a material with a lower specific gravity, that is, a resin material. However, simply changing the material may not ensure the same quality as conventional products. There is. Particularly problematic is a method of fixing metal parts to a resin structure.

  For example, when the housing member and the cover member are fastened with bolts, or the bearings supporting the steering shaft and the worm shaft are directly press-fitted into the gear box and fixed as in the conventional case, the bolt axial force or bearing pressure input As a result, the resin material may be deteriorated. As a result, the axial force of the bolt and the pressure input of the bearing gradually decrease, and in the worst case, the bolt and the bearing may fall out of the gear box.

  A technique for improving such a reliability problem is proposed in Patent Document 1. The electric power steering apparatus disclosed in Patent Document 1 is reduced in weight by forming a housing composed of a sensor housing that houses a steering state detection sensor and a gear housing that houses a reduction gear mechanism, all from a resin material. It has been. At this time, the sensor housing and the gear housing are each composed of a resin having a laser energy permeability (polyamide resin) and a resin having a laser energy absorption property (polyamide resin to which carbon powder is added). It is integrated by irradiating a laser to heat-weld the joint surface.

JP 2009-298246 A JP-A-2005-231308

However, it is considered that it is difficult to realize highly reliable bonding unless a technique such as that disclosed in Patent Document 2 is applied to the bonding method called laser welding.
Further, in the technique disclosed in Patent Document 1, a resin sensor housing and a gear housing are molded, and then a bearing that supports the steering shaft is press-fitted and fixed in the housing. Deteriorated, the pressure input gradually decreases, and in the worst case, the bearing may fall out of the housing. Therefore, there is room for improvement in reliability.

Furthermore, since the sensor housing and the gear housing are all made of a polyamide resin material, deformation due to water absorption tends to occur, and there is room for improvement in terms of dimensional stability. Furthermore, it cannot be said that heat resistance (for example, high-temperature rigidity) is sufficient.
Accordingly, the present invention provides an electric power steering apparatus that solves the above-described problems of the prior art and that has a lightweight, highly reliable gear box that accommodates a reduction gear mechanism and that has excellent dimensional stability and heat resistance. This is the issue.

  In order to solve the above problems, an aspect of the present invention has the following configuration. That is, an electric power steering apparatus according to an aspect of the present invention includes an electric motor that outputs an auxiliary torque that assists the steering torque in accordance with a steering torque input to a steering shaft, and the auxiliary torque that decelerates the auxiliary torque. An electric power steering apparatus comprising: a reduction gear mechanism that transmits to a steering shaft, the housing member having a housing member that houses the reduction gear mechanism, and a cover member that covers an opening of the housing member. And a gear box in which the cover member is fastened and integrated by a bolt, and the housing member and the cover member are made of a resin material insert having a metal core having a bolt hole through which the bolt is inserted. It is manufactured by molding, and the resin material has a glass transition temperature of 80 ° C. or higher. Characterized in that it contains a certain polyamide resin.

  In such an electric power steering apparatus, the resin material comprises a semi-aromatic polyamide resin having a glass transition temperature of 80 ° C. or higher and a number average molecular weight of 15000 or more and 30000 or less, and at least one of organic fiber and inorganic fiber. It is preferable that the ratio of the fibrous reinforcing material contained in the fiber reinforced resin composition is 20% by mass or more and 50% by mass or less.

In addition, at least one of the housing member and the cover member includes an adhesive layer containing an adhesive on the surface of the core metal, and the adhesive layer includes a lower layer formed on the surface of the core metal; And an upper layer laminated on the upper side, the lower layer preferably contains a phenol resin adhesive or a coupling agent, and the upper layer preferably contains a phenol resin adhesive.
Furthermore, it is preferable that at least one of the housing member and the cover member has a roughened surface of the cored bar.

  In the electric power steering apparatus according to the present invention, the housing member and the cover member are manufactured by insert molding of a resin material using a metal cored bar as an insert, and are fastened and integrated by a bolt. Contains a polyamide resin having a glass transition temperature of 80 ° C. or higher, so that the gear box is lightweight, highly reliable, and excellent in dimensional stability and heat resistance.

It is a figure showing a schematic structure of an electric power steering device concerning one embodiment of the present invention. It is a fragmentary sectional view which shows the structure of a reduction gear mechanism. It is a fragmentary sectional view which shows the structure of a reduction gear mechanism. It is a figure of the cover member of a gear box. It is a figure of the housing member of a gear box. It is a fragmentary sectional view showing composition of a reduction gear mechanism with which an electric power steering device of a modification is provided. It is a figure of the cover member of the gear box with which the electric power steering device of FIG. 6 is provided. It is a figure of the housing member of the gear box with which the electric power steering device of FIG. 6 is provided.

  An embodiment of an electric power steering apparatus according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a column-type electric power steering apparatus for an automobile, which is an embodiment of the electric power steering apparatus according to the present invention. 2 and 3 are partial cross-sectional views showing the configuration of the reduction gear mechanism included in the electric power steering apparatus of FIG. 1, and FIG. 2 is a partial cross-sectional view cut along a plane orthogonal to the steering shaft. 3 is a partial cross-sectional view taken along a plane parallel to the steering shaft. Further, FIG. 4 is a view of the cover member of the gear box as viewed from the upper end side in the axial direction of the steering shaft, and FIG. 5 is a view of the housing member of the gear box as viewed from the upper end portion in the axial direction of the steering shaft. is there. In addition, the grid | lattice-like hatching in each figure has shown that this part is a part comprised with resin.

  The electric power steering apparatus of FIG. 1 includes a steering shaft 11 to which a steering torque input to a steering wheel 10 by a driver of an automobile is transmitted. The steering shaft 11 is composed of an upper shaft 11a and a lower shaft 11b connected by a torsion bar (not shown), and is supported inside the steering shaft housing 12 so as to be rotatable around an axis. The steering shaft housing 12 is fixed at a predetermined position in the vehicle interior in a posture in which the lower portion is inclined toward the front of the vehicle. The steering wheel 10 is fixed to the upper end of the upper shaft 11 a protruding from the steering shaft housing 12.

  A rack and pinion mechanism 20 that converts the rotation of the steering shaft 11 into the motion of left and right steered wheels (not shown) is a rack 21 that is movable in the axial direction and a rack that is supported obliquely with respect to the axis of the rack 21. A pinion 22 having teeth that mesh with the teeth of 21 and a cylindrical rack housing 23 that supports the rack 21 and the pinion 22. The rack and pinion mechanism 20 is arranged substantially horizontally in the engine room at the front of the vehicle so that the longitudinal direction thereof is along the width direction of the vehicle.

Since the upper end portion of the pinion 22 and the lower end portion of the lower shaft 11 b of the steering shaft 11 are connected via two universal joints 25 and 26, the rotation of the steering shaft 11 is rack 21 by the rack and pinion mechanism 20. The left and right sliding motions are converted and steered wheels (not shown) connected to both ends of the rack 21 are steered.
A steering assist mechanism that supplies auxiliary torque for assisting the steering torque to the lower shaft 11b is connected to the lower shaft 11b of the steering shaft 11. The steering assist mechanism includes a reduction gear mechanism 30 configured by, for example, a worm gear connected to the lower shaft 11b, and an electric motor 13 that outputs an auxiliary torque and supplies the auxiliary torque to the reduction gear mechanism 30.

  The reduction gear mechanism 30 is accommodated in a gear box 33 provided continuously to the steering shaft housing 12. More specifically, the reduction gear mechanism 30 is accommodated in a substantially cylindrical housing member 33A, and the opening of the housing member 33A is covered with a cover member 33B. The housing member 33A and the cover member 33B are fastened and integrated by a bolt 33C.

  Each of the housing member 33A and the cover member 33B is manufactured by insert molding of a resin material using metal cores 36A and 36B as inserts. This resin material is a material containing a polyamide resin having a glass transition temperature of 80 ° C. or higher. Since both the core bars 36A and 36B have bolt holes 37, the housing member 33A and the cover member 33B can be integrated by inserting the bolts 33C into the both bolt holes 37 and tightening them with nuts. it can.

Here, the configuration of the reduction gear mechanism 30 will be described with reference to FIGS. The reduction gear mechanism 30 includes a worm wheel 31 fitted to the outer periphery of the lower shaft 11 b and a worm 32 that meshes with the worm wheel 31. Worm shafts 32 a and 32 b are integrally formed at both ends of the worm 32, and these worm shafts 32 a and 32 b are rotatably supported by rolling bearings 34 a and 34 b that are press-fitted and fixed to the gear box 33, respectively. . In addition, the electric motor 13 is attached to the gear box 33 by means such as bolt fastening, for example, and the drive shaft 13a and the worm shaft 32b of the electric motor 13 are spline-coupled or serrated-coupled, for example.
Since the worm wheel 31 is connected to the lower shaft 11b, the rotation (auxiliary torque) of the electric motor 13 is transmitted to the lower shaft 11b while being decelerated via the worm 32 and the worm wheel 31.

  When steering torque (rotational force) is input to the steering wheel 10 by the driver, the steering shaft 11 rotates. This steering torque is detected by a torsion bar. Based on the detected steering torque, the output of the electric motor 13 (rotational force assisting steering) is controlled. The output (auxiliary torque) of the electric motor 13 is supplied to the lower shaft 11b of the steering shaft 11 while being decelerated by the reduction gear mechanism 30, and is combined with the steering torque. As the steering shaft 11 rotates, the pinion 22 rotates, and the rotation of the pinion 22 is converted into a sliding motion in the horizontal direction of the rack 21 by the rack and pinion mechanism 20, and the steered wheels are driven to steer the automobile. Is done.

  Here, the gear box 33 will be described in more detail with reference to FIGS. As described above, both the housing member 33A and the cover member 33B are manufactured by insert molding of a resin material using metal core bars 36A and 36B as inserts. Part or whole is covered with a resin material.

  The gear box 33 in FIGS. 2 to 5 is suitable for an electric power steering device mounted on a light vehicle or a small vehicle having a displacement of 1500 cc or less, in which the auxiliary torque by the electric motor is relatively small. On the other hand, in the gear box 33 of FIGS. 6 to 8, since the core bars 36A and 36B are provided with the arm 40 for reinforcement, the auxiliary torque by the electric motor is relatively large as compared with the examples of FIGS. -It is suitable for an electric power steering device mounted on a large vehicle. FIG. 6 is a partial cross-sectional view showing the configuration of the reduction gear mechanism 30, which is a cross-sectional view cut along a plane parallel to the steering shaft 11. 7 is a view of the cover member 33B of the gear box 33 as viewed from the upper end side in the axial direction of the steering shaft 11. FIG. 8 shows the housing member 33A of the gear box 33 in the upper end portion in the axial direction of the steering shaft 11. It is the figure seen from the side.

  The housing member 33A and the cover member 33B that constitute the gear box 33 are lighter than conventional gear boxes that are entirely made of a metal material because portions other than the core bars 36A and 36B are made of a resin material. Therefore, it is excellent in dimensional stability as compared with a conventional gear box that is entirely made of a resin material. Further, since the resin material contains a polyamide resin having a glass transition temperature of 80 ° C. or higher, the gear box 33 is excellent in heat resistance (for example, high-temperature rigidity).

  Furthermore, since the core metal 36A of the housing member 33A and the core metal 36B of the cover member 33B have bolt holes 37 through which the bolts 33C are inserted, the housing member 33A and the cover member 33B can be fixed with the bolts 33C. it can. Therefore, the bonding strength between both 33A and 33B is high. Further, there is no possibility that the resin material is deteriorated by the axial force of the bolt 33C. Therefore, there is almost no possibility that the axial force of the bolt 33C will drop and the bolt 33C will fall off the gear box 33, and the reliability is high.

  In addition, when the peripheral part of the bolt hole 37 of the metal cores 36A and 36B is covered with the resin material by insert molding, there is a concern that the axial force of the bolt 33C may be reduced due to the deterioration of the resin material in this part. Therefore, it is preferable to ensure a sufficient allowance for the surface of the core bars 36A and 36B so that the peripheral portion of the bolt hole 37 is not covered with the resin material. In addition, a sealing member such as an O-ring is attached to the peripheral portion of the bolt hole 37 of the cored bars 36A and 36B in order to prevent a lubricant such as grease enclosed in the gear box 33 from leaking to the outside. A groove may be provided.

  Further, according to the insert molding method, the rolling bearings 34a and 34b (or the rolling bearings 35a and 35b inserted to pass through the steering shaft 11 and the bearing metal sleeve 38, and the rolling bearings 34a and 34b are press-fitted and fixed. For this purpose, the metal sleeve 39) to be inserted can be integrated with the resin structure simultaneously with the injection molding of the resin material. That is, according to the insert molding method, integration of the resin portion and the metal part (insert) is achieved simultaneously with the injection molding. Therefore, there is no need to press-fit metal parts after molding the resin material, so that the manufacturing process can be simplified. Further, if the insert molding method is used, the rolling bearings 34a and 34b are fixed without being press-fitted into the housing member 33A, so that there is no possibility that the resin material is deteriorated due to the pressure input. Therefore, there is almost no possibility that the rolling bearings 34a and 34b fall off from the gear box 33, and the reliability is high. The axial width of the sleeves 38 and 39 is preferably larger than the axial width of the rolling bearings 34b and 35a.

  Furthermore, according to the insert molding method, the gear box 33 can be manufactured at a lower cost than a conventional gear box which is entirely made of an aluminum alloy. This is because, when a conventional gear box made entirely of an aluminum alloy is manufactured, a secondary processing step of the aluminum alloy is required, but this step is not required according to the insert molding method.

  When performing the insert molding method, it is preferable to previously provide an adhesive layer containing an adhesive on the surfaces of the core bars 36A and 36B. That is, it is preferable to perform the insert molding method using the core bars 36A and 36B whose surfaces are covered with the adhesive layer as inserts. By doing so, the cored bars 36A and 36B and the resin material are firmly bonded by the adhesive, so that the dimensional stability of the housing member 33A and the cover member 33B is good. The method for providing the adhesive layer is not particularly limited, and examples thereof include application and spraying of a solution containing the adhesive or the adhesive itself.

Below, the metal material which comprises the metal cores 36A and 36B, the resin material used for insert molding, and an adhesive agent are demonstrated in detail.
There are no particular limitations on the type of metal material constituting the cored bar 36A, 36B. For example, carbon steel for mechanical structure such as S53C, bearing steel such as SUJ2, cold rolled steel plate (SPCC), SUS430, SUS410. Etc. Stainless steel can be used. However, light metals such as aluminum, aluminum alloy, and magnesium alloy are preferable from the viewpoint of weight reduction.

  In order to improve the adhesion between the core bars 36A and 36B and the resin material, it is preferable to roughen the surfaces of the core bars 36A and 36B. If the core bars 36A and 36B whose surfaces are roughened are used, the adhesive force due to the adhesive can be increased when the adhesive layer is provided on the core bars 36A and 36B, and the core can be provided even when the adhesive layer is not provided. The adhesion between the gold 36A and 36B and the resin material can be improved. A method for roughening the surfaces of the core bars 36A and 36B is not particularly limited, but a shot blasting method or a chemical etching method is preferable.

  Next, the adhesive layer will be described. The adhesive layer may be a single layer, but may be a laminate of a plurality of adhesive layers. When laminating a plurality of adhesive layers, it is preferable to use a phenol resin-based adhesive containing a phenol resin for the lower layer formed on the surfaces of the cored bars 36A and 36B. Moreover, you may use a coupling agent as a primer instead of an adhesive agent. And it is preferable to use the phenol resin adhesive containing a phenol resin for the upper layer laminated | stacked on the upper side of a lower layer.

Since the polyamide resin and the phenol resin have good compatibility, when the phenol resin adhesive is used as the upper layer of the adhesive layer, the core metals 36A and 36B and the resin material are bonded very firmly by the phenol resin adhesive. Is done. Therefore, a sufficiently strong adhesive force can be obtained without roughening the surfaces of the core bars 36A and 36B. However, as a matter of course, the adhesive force is higher when the surfaces of the core bars 36A and 36B are roughened.
The phenol resin contained in the adhesive used for the lower layer is specifically preferably a resol type phenol resin, and can be obtained by reacting phenols with formaldehyde in the presence of a basic catalyst.

  Further, the adhesive used in the lower layer may contain an epoxy resin, specifically, a glycidyl type is preferable, and is obtained from epichlorohydrin and an active hydrogen compound. Examples of the active hydrogen compound include phenol derivatives, glycols, organic acids, amines, and the like, and a phenol derivative is preferable in consideration of storage stability as an adhesive and cost. A specific example of the adhesive used for the lower layer is XPJ-60 manufactured by Road Far East.

  Furthermore, the type of coupling agent used as a primer instead of the adhesive is not particularly limited, but silane, chromium, titanium, and aluminate coupling agents are preferred. However, currently silane coupling agents are the mainstream. The silane coupling agent has a silanol group bonded to the metal cores 36A and 36B at one end of the molecule, and an organic functional group capable of binding to the resin material (or upper layer) at the other end of the molecule. Yes.

  In the present invention, aminosilane coupling agents are particularly preferred among silane coupling agents because of their high reactivity with various resin materials. Examples of aminosilane-based force coupling agents include N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, and γ-aminopropyltriethoxysilane. Is preferred. Specific examples of the aminosilane-based force pulling agent include KBP-40 and KBP-43 manufactured by Shin-Etsu Silicone Co., Ltd.

  When forming the lower layer, an organic solvent in which the adhesive is dissolved to a concentration of 0.5 to 20% by mass in an organic solvent such as isopropyl alcohol, methyl ethyl ketone, or methyl isobutyl ketone, or a mixed solvent thereof. A solution can be used. When a coupling agent is used instead of the adhesive, the coupling agent is diluted with water, alcohol, or a mixed solvent of water and alcohol so that the concentration is 0.1 to 2.0% by mass. Can be used.

Then, an organic solvent solution of the adhesive or a diluting solution of the coupling agent is arranged on the surface of the core metal by dipping, spraying, coating (brush coating) or the like, and a film shape having a thickness of 0.5 to 5 μm Then, after drying at room temperature, for example, by drying and curing at 150 to 250 ° C. for 5 to 30 minutes, the lower layer is baked onto the cored bar.
On the other hand, as the adhesive used for the upper layer, it is preferable to use an organic solvent solution obtained by dissolving an adhesive composition mainly composed of a resol type phenol resin in an organic solvent at a solid content concentration of 5 to 40% by mass. . Examples of the adhesive composition mainly composed of a resol type phenolic resin include TS1677-13 manufactured by Road Far East, Metallock N-15 and Metalolc N-23 manufactured by Toyo Chemical Research Laboratories. Of the epoxy resin).

  And after arranging this organic solvent solution on the surface of the cored bar by a method such as dipping, spraying, coating (brush coating), etc., to form a film with a thickness of 0.5-5 μm and drying at room temperature, For example, when dried and cured at 100 to 150 ° C. for several minutes to 30 minutes, the upper layer is baked onto the core metal in a semi-cured state that is not washed away by the high-temperature and high-pressure molten resin at the time of insert molding. Then, the upper layer is completely cured by heat from the molten resin at the time of insert molding and further by subsequent secondary heating (for example, heat treatment at 150 ° C. for 2 hours).

  Next, the resin material will be described. As described above, a polyamide resin having a glass transition temperature of 80 ° C. or higher is used as the resin material, but a semi-aromatic polyamide resin having a glass transition temperature of 80 ° C. or higher and a number average molecular weight of 15000 or higher and 30000 or lower. And a fiber reinforced resin composition containing a fibrous reinforcing material composed of at least one of an organic fiber and an inorganic fiber is preferable. In consideration of durability reliability and impact resistance of the molded product, the number average molecular weight of the semi-aromatic polyamide resin is more preferably 15000 or more and 30000 or less, and further preferably 20000 or more and 28000 or less.

  The semi-aromatic polyamide resin is a polyamide resin obtained by polymerizing an aromatic monomer and an aliphatic monomer. For example, a polymer of an aromatic dicarboxylic acid and an aliphatic diamine and a polymer of an aromatic diamine and an aliphatic dicarboxylic acid can be given. Since the semi-aromatic polyamide resin has a benzene ring in the molecular structure, various physical properties such as heat resistance are superior to the aliphatic polyamide resin.

  When the glass transition temperature of the semi-aromatic polyamide resin is 80 ° C. or higher, which is higher than the temperature at which the gear box 33 is normally used, there is almost no decrease in rigidity at high temperatures (for example, 80 ° C.), and creep at high temperatures. Deformation is suppressed to a level that can be ignored in practice. For example, since nylon 6 and nylon 66 have a glass transition temperature of about 60 ° C., rigidity is lowered at a high temperature (for example, 80 ° C.).

  The type of the semi-aromatic polyamide resin is not particularly limited, but as a specific example, nylon 6T / 6I, which is a semi-aromatic nylon obtained by partially copolymerizing terephthalic acid with an adipic acid unit (Mitsui Chemicals, Inc.) Arlen), nylon 6T / 6I / 6-6 (Amodel, manufactured by Solvay Advanced Polymers), nylon 6T (Zytel HTN, manufactured by Du Pont), and nylon 9T (Genstar, manufactured by Kuraray Co., Ltd.).

These semi-aromatic polyamide resins have lower water absorption than, for example, nylon 6 or nylon 66. Therefore, the gear box 33 has excellent dimensional stability (small dimensional change due to water absorption) and environmental reliability (small strength reduction due to water absorption).
The type of fibrous reinforcing material is not particularly limited, but organic fibers such as aramid fibers, glass fibers, carbon fibers, metal fibers (metal types include stainless steel, iron, aluminum, etc.), etc. Inorganic fibers are preferred. Or you may use together an organic fiber and an inorganic fiber.

  As for content of the fibrous reinforcement in a fiber reinforced resin composition, 10-50 mass% is preferable. If it is less than 10% by mass, the mechanical strength and dimensional stability of the resin material may be insufficient, and if it exceeds 50% by mass, the toughness and thermal shock resistance of the resin material may be insufficient. There is. In order to make such inconvenience less likely to occur, the content of the fibrous reinforcing material in the fiber reinforced resin composition is more preferably 20 to 50% by mass, and further preferably 25 to 45% by mass. preferable.

  In order to improve the physical properties, various additives may be added to such a fiber reinforced resin composition depending on the purpose. For example, a crystal nucleating agent may be added to increase the crystallinity of the polyamide resin. The kind of crystal nucleating agent is not particularly limited, and examples thereof include inorganic fine particles such as talc and silica, and metal oxides such as magnesium oxide and aluminum oxide. The addition amount of the crystal nucleating agent is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.03% by mass or more and 3% by mass or less of the fiber reinforced resin composition.

Moreover, you may mix | blend antioxidant with a fiber reinforced resin composition in order to suppress the oxidative degradation of a polyamide resin. The kind of antioxidant is not particularly limited, and examples thereof include amine antioxidants, phenolic antioxidants, and hydroquinone antioxidants.
Examples of amine antioxidants include amine / ketone antioxidants represented by 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and diallylamine series represented by p, p'-dicumyldiphenylamine. Examples thereof include antioxidants and p-phenylenediamine-based antioxidants represented by N, N′-diphenyl-p-phenylenediamine.

Examples of phenolic antioxidants include monophenolic antioxidants represented by 2,6-di-t-butyl-4-methylphenol, and 2,2′-methylenebis (4-methyl-6-t-butylphenol). ) And other polyphenolic antioxidants.
Examples of hydroquinone antioxidants include 2,5-di-t-butylhydroquinone.

  Further, in the fiber reinforced resin composition, a peroxide-decomposable antioxidant (secondary antioxidant) may be used in combination with the amine-based, phenol-based, and hydroquinone-based antioxidants. Examples of the secondary antioxidant include sulfur-based secondary antioxidants such as 2-mercaptobenzimidazole and phosphorus-based secondary antioxidants such as tris (nonylated phenyl) phosphite.

The blending amount of the antioxidant as described above is preferably about 0.1% by mass or more and 3.0% by mass or less with respect to the polyamide resin. If it is in a range that does not adversely affect the physical properties, an amount larger than that may be blended.
Furthermore, you may add suitably a light stabilizer, an antistatic agent, a plasticizer, an inorganic or organic flame retardant, other reinforcing materials, etc. to a fiber reinforced resin composition as needed.

〔Example〕
The present invention will be described more specifically with reference to the following examples. A method for manufacturing the gear box of the electric power steering apparatus will be described below.
First, the surface of the metal core was roughened by applying air blasting or the like to the aluminum alloy core metal (the metal core shown in FIGS. 4 and 5) of the housing member and the cover member. Next, after applying a phenol resin adhesive (which may be a primer) to the surface of the roughened cored bar, it is air-dried at room temperature, and then processed at a high temperature of 150 to 250 ° C. and completely baked. By curing, the lower layer of the adhesive layer was formed.

Furthermore, after applying the phenolic resin adhesive for the upper layer on the lower layer, it is air-dried at room temperature, followed by heat treatment, and the upper layer adhesive is baked in a semi-cured state, whereby the upper layer of the adhesive layer Formed.
The metal core obtained in this way, the metal sleeve for inserting the steering shaft and the metal sleeve for press-fitting and fixing the rolling bearing supporting the worm shaft are set in the mold as inserts, Insert molding of the resin material was performed.

  As the resin material, Arlen A335 manufactured by Mitsui Chemicals, Inc., which is a resin composition comprising 35% by mass of glass fibers and 65% by mass of semi-aromatic nylon (indicated as “resin material A” in Table 1), Amodel AS-1145HS (referred to as “resin material B” in Table 1) made by Solvay Advanced Polymers, which is a resin composition comprising 45% by mass of glass fiber and 55% by mass of semi-aromatic nylon, 45% by mass Zytel HTN 51G45HSL (designated as “resin material C” in Table 1) manufactured by DuPont, which is a resin composition composed of 55% by mass of nylon 66 and 55% by mass of nylon, 35% by mass of glass fiber and 65% by mass of Genesta G1300A manufactured by Kuraray Co., Ltd., which is a resin composition comprising semi-aromatic nylon (indicated as “resin material D” in Table 1) Gramide T663G30 (referred to as “resin material E” in Table 1) manufactured by Toyobo Co., Ltd., which is a resin composition comprising 30% by weight glass fiber and 70% by weight nylon 66, or 30% by weight glass UBE NYLON 1015GU6 (referred to as “resin material F” in Table 1) manufactured by Ube Industries, Ltd., which is a resin composition composed of fibers and 70 mass% nylon 6, was used.

The housing member and the cover member obtained by insert molding were fastened and integrated with bolts and nuts to complete the gear box.
As shown in Table 1, six types of gear boxes (Examples 1 to 4 and Comparative Examples 1 and 2) having different types of resin materials were manufactured. These gear boxes were subjected to a falling weight impact test and a moisture absorption test.

First, the falling weight impact test (before water absorption treatment) will be described. Under each temperature environment of −40 ° C., 25 ° C., and 80 ° C., a weight of about 50 g was dropped freely from a height of 75 cm on the gear box, and the degree of damage generated on the surface of the gear box was confirmed.
When the depth of the indentation on the surface of the gear box was 150 μm or less, it was evaluated as acceptable, and in Table 1, it was indicated by a circle. Further, when the depth of the indentation on the surface of the gear box exceeded 150 μm, or when a crack or a crack occurred, it was evaluated as rejected and shown in Table 1 as x.

  As can be seen from Table 1, since the gearboxes of Examples 1 to 4 are made of a resin material containing a polyamide resin having excellent high-temperature rigidity with a glass transition temperature of 80 ° C. or higher, the glass transition temperature is low. Compared with Comparative Examples 1 and 2, which are made of a resin material containing a polyamide resin, the damage was small not only at −40 ° C. and 25 ° C. but also at a high temperature environment of 80 ° C.

Next, a falling weight impact test after the water absorption treatment will be described. After the gearbox is held for 300 hours in an environment of temperature 80 ° C and humidity 90% RH to absorb water, a drop weight impact test similar to that described above is performed in a temperature environment of 25 ° C to cause damage to the gearbox surface. The degree of was confirmed. Note that the acceptance criteria are the same as those in the falling weight impact test described above.
As can be seen from Table 1, the gearboxes of Examples 1 to 4 are made of a resin material containing a low water-absorbing semi-aromatic polyamide resin. Therefore, the gear box is a resin material containing a polyamide resin having a high water absorption rate. The damage was small compared to the comparative examples 1 and 2 that were configured.

Next, the moisture absorption test will be described. The gear box was held for 500 hours in an environment of temperature 80 ° C. and humidity 90% RH to absorb moisture, and then the outer diameter of the gear box was measured. And when the amount of change in the outer diameter before and after moisture absorption is less than 30 μm, it is judged that the dimensional stability is good, and it is accepted, and in Table 1, it is indicated by ○, and those with 30 μm or more are rejected. In FIG.
As can be seen from Table 1, since the gearboxes of Examples 1 to 4 are composed of a resin material containing a low water absorption semi-aromatic polyamide resin, the dimensional stability was good. On the other hand, the gear boxes of Comparative Examples 1 and 2 were rejected because they were made of a resin material containing a polyamide resin having a high water absorption rate.

11 Steering shaft 13 Electric motor 30 Reduction gear mechanism 33 Gear box 33A Housing member 33B Cover member 33C Bolt 36A, 36B Core metal 37 Bolt hole

Claims (4)

An electric power steering system comprising: an electric motor that outputs an auxiliary torque that assists the steering torque according to a steering torque input to the steering shaft; and a reduction gear mechanism that decelerates the auxiliary torque and transmits the auxiliary torque to the steering shaft. A device,
A housing member that accommodates the reduction gear mechanism; and a cover member that covers an opening of the housing member; and a gear box in which the housing member and the cover member are fastened and integrated by a bolt,
The housing member and the cover member are manufactured by insert molding of a resin material with a metal cored bar having a bolt hole through which the bolt is inserted,
The electric power steering apparatus, wherein the resin material contains a polyamide resin having a glass transition temperature of 80 ° C. or higher.   The resin material is a fiber containing a semi-aromatic polyamide resin having a glass transition temperature of 80 ° C. or higher and a number average molecular weight of 15000 or more and 30000 or less, and a fibrous reinforcing material made of at least one of organic fibers and inorganic fibers. 2. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is a reinforced resin composition, and a ratio of the fibrous reinforcing material included in the fiber reinforced resin composition is 20% by mass or more and 50% by mass or less.   At least one of the housing member and the cover member includes an adhesive layer containing an adhesive on the surface of the core metal, and the adhesive layer includes a lower layer formed on the surface of the core metal, An upper layer laminated on the upper side, the lower layer contains a phenol resin adhesive or a coupling agent, and the upper layer contains a phenol resin adhesive. The electric power steering apparatus as described.   The electric power steering apparatus according to any one of claims 1 to 3, wherein at least one of the housing member and the cover member has a roughened surface of the cored bar.

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