JP2013067362A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device having a lightweight gear box for storing a reduction gear mechanism, having high reliability, and superior in dimensional stability.SOLUTION: This electric power steering device includes the gear box constituted by fastening and integrating a housing member 33A for storing the reduction gear mechanism and a cover member 33B for covering an opening part of the housing member 33A by a bolt 33C and a nut. This housing member 33A and the cover member 33B are manufactured by insert molding of a resin material of inserting metallic core metals 36A and 36B having a bolt hole 37 for inserting the bolt 33C.

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.
Accordingly, the present invention solves the above-described problems of the prior art and provides an electric power steering device in which a gear box that houses a reduction gear mechanism is lightweight, highly reliable, and excellent in dimensional stability. And

  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.

  In such an electric power steering apparatus, it is preferable that at least one of the housing member and the cover member includes an adhesive layer containing an adhesive on the surface of the cored bar. The adhesive layer includes a lower layer formed on the surface of the cored bar and an upper layer laminated on the upper side, and the lower layer contains a phenol resin adhesive or a coupling agent, and the upper layer Preferably contains a phenolic resin adhesive.

Moreover, it is preferable that at least one of the housing member and the cover member has a roughened surface of the cored bar.
Furthermore, the resin material is preferably a resin composition containing a thermoplastic resin and a fiber reinforcement. And it is preferable that the weight average fiber length of this fiber reinforcement is 0.7 mm or more and 5 mm or less, and an average fiber diameter is 1 micrometer or more and 30 micrometers or less.

  In the electric power steering device of 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. Light weight, high reliability and excellent dimensional stability.

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 gear reduction mechanism. It is an exploded view of a gear box. It is an exploded view of the gearbox of a modification.

  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 view 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, and FIG. 2 is a gear provided in the electric power steering apparatus of FIG. It is a fragmentary sectional view which shows the structure of a deceleration mechanism. FIG. 3 is an exploded view of the gear box.

  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. Since both the cores 36A and 36B have bolt holes 37, the housing member 33A and the cover member 33B can be integrated if the bolts 33C are inserted into the bolt holes 37 and tightened with nuts. .

  Here, the configuration of the reduction gear mechanism 30 will be described with reference to FIG. 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. 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.
Note that the gear box 33 in FIG. 3 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, the gear box 33 in FIG. 4 is suitable for an electric power steering apparatus mounted on a medium-sized or large-sized vehicle, in which the auxiliary torque by the electric motor is relatively large as compared with the example in FIG.

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 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 by 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 metal sleeve 38 inserted to insert the steering shaft 11 and the metal sleeve inserted to press-fit and fix the rolling bearings 34a and 34b). 39) 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.

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 an adhesive containing at least one of a phenol resin and an epoxy resin for the lower layer formed on the surfaces of the cores 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 adhesive agent 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 a polyamide resin is used as the resin component of the resin material, if a phenol resin adhesive is used as the upper layer of the adhesive layer, the metal cores 36A, 36B and The resin material is bonded very firmly by the phenol resin adhesive. 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.
The epoxy resin contained in the adhesive used in the lower layer is specifically preferably a glycidyl type, 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, titanate 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 containing a resol type phenol resin as a main component include TS1677-13 manufactured by Road Far East Co., Ltd., METALOC N-15 and METALOC N-23 manufactured by Toyo Chemical Laboratory (some amount of epoxy resin). Containing).

  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 the resin material, a resin composition containing a thermoplastic resin and a fiber reinforcing material is preferable. In consideration of durability reliability and impact resistance of the molded product, the number average molecular weight of the thermoplastic resin is preferably 15000 or more and 30000 or less, and more preferably 20000 or more and 28000 or less.
Also, the type of fiber reinforcement is not particularly limited, but organic fibers such as aramid fibers, aromatic polyimide fibers, and liquid crystal polyester fibers, glass fibers, carbon fibers, silicon carbide fibers, alumina fibers, boron fibers, Inorganic fibers such as metal fibers (metal types include stainless steel, iron, aluminum, etc.) are suitable. Among these fiber reinforcing materials, glass fibers and carbon fibers are preferable because of good reinforcing properties. Moreover, these fiber reinforcements may be used individually by 1 type, and may use 2 or more types together.

  The content of the fiber reinforcement in the resin composition is preferably 10% by mass or more and 50% by mass or less. 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 fiber reinforcing material in the resin composition is more preferably 20% by mass to 50% by mass, and more preferably 25% by mass to 45% by mass. More preferably.

  Moreover, it is preferable that the diameter (average fiber diameter) of the fiber reinforcement in a resin composition is 1 micrometer or more and 30 micrometers or less. When the average fiber diameter is less than 1 μm, the fibers may aggregate when mixed with the thermoplastic resin, and the fiber reinforcing material may not be dispersed uniformly. On the other hand, if the average fiber diameter is more than 30 μm, there may be a problem in fiber orientation and dispersion in the injection molding process. In addition, since the average fiber diameter is too large, the number of fiber reinforcements contained in the resin composition is reduced, and the portion composed only of the thermoplastic resin is increased, and the strength of the resin composition may become unstable. There is. In order to make such inconvenience less likely to occur, it is more preferable that the average fiber diameter of the fiber reinforcing material is 5 μm or more and 25 μm or less.

  Furthermore, it is preferable that the length (weight average fiber length) of the fiber reinforcement in the resin composition is 0.7 mm or more and 5 mm or less. Resin materials have lower impact resistance, creep properties, and rigidity (especially high-temperature rigidity) than metal materials, and are difficult to use over a long period of time. However, as mentioned above, the fiber reinforcement in the resin composition Long fibers are superior in impact resistance, creep characteristics, and rigidity (particularly high-temperature rigidity) and superior in durability and reliability as compared to the case of using a short fiber reinforcing material. Also, dimensional stability is excellent. Therefore, it is possible to make these performances equivalent to those of a conventional gear box that is entirely made of an aluminum alloy.

  If the weight average fiber length of the fiber reinforcement is less than 0.7 mm, impact resistance and dimensional stability may be insufficient. On the other hand, if the weight average fiber length is more than 5 mm, the fiber reinforcing material may be broken during the molding process in a normal molding method, and a special molding machine needs to be used to prevent the breakage. As a result, the manufacturing of the gear box 33 may be expensive.

  In addition, in the stage of the material (for example, pellet) before insert molding the housing member 33A and the cover member 33B, the weight average fiber length of the fiber reinforcing material in the resin composition is preferably 2 mm or more and 20 mm or less. If it is less than 2 mm, the weight average fiber length of the fiber reinforcement in the housing member 33A and the cover member 33B becomes less than 0.7 mm due to breakage in the molding process, and the above-mentioned performances may be insufficient.

  On the other hand, if it exceeds 20 mm, the length of the material such as pellets inevitably exceeds 20 mm, which may make it difficult to introduce the pellets into the molding machine. In order to make such inconvenience less likely to occur, it is more preferable that the weight average fiber length of the fiber reinforcement in the material such as pellets is 3 mm or more and 15 mm or less.

  Furthermore, although the kind of thermoplastic resin is not particularly limited, polyamide resin, polyester resin, polyacetal, polyether ether ketone (PEEK), polyphenylene sulfide resin (PPS) and the like are preferable. Specific examples of the polyamide-based resin include nylon 6, nylon 11, nylon 12, nylon 66, nylon 610, nylon 612, nylon 46, and semi-aromatic nylon having lower water absorption and moisture absorption than these aliphatic polyamides. Can be given. The type of semi-aromatic nylon is not particularly limited, but as a specific example, nylon 6T / 6I (manufactured by Mitsui Chemicals, Inc.) is a semi-aromatic nylon obtained by partially copolymerizing terephthalic acid with an adipic acid unit. Arlen), nylon 6T / 6I / 66 (Amodel manufactured by Solvay Advanced Polymers), nylon 6T (Zytel HTN manufactured by Du Pont), and nylon 9T (Genstar manufactured by Kuraray Co., Ltd.). Specific examples of the polyester resin include polyethylene terephthalate and polybutylene terephthalate.

  In order to improve the physical properties of such a resin composition, various additives may be added depending on the purpose. For example, a gear box of an electric power steering apparatus may be used under a situation where a thermal shock of, for example, about −40 ° C. to 100 ° C. is repeatedly applied. In order to further increase, a thermoplastic alloy may be blended with a soft component as an impact strength improver to form a polymer alloy.

  When the thermoplastic resin is a polyamide-based resin, any one selected from polyamide 11, polyamide 612, polyamide 610, modified polyamide 6T, polyamide 9T, and polyamide MXD6 is used as a hard segment, and at least one of a polyester component and a polyether component It is preferable that a block copolymer having a soft segment as a soft component.

Further, when the thermoplastic resin is a polyester resin, it is preferable that rubber particles selected from butadiene rubber and acrylic rubber are used as the soft component.
Furthermore, when the thermoplastic resin is a polyphenylene sulfide resin, it is preferable to use rubber particles selected from acrylic rubber, carboxyl-modified acrylonitrile butadiene rubber, and carboxyl-modified hydrogenated nitrile rubber as the soft component.

  The blending amount of the soft component is preferably 5% by mass or more and 50% by mass or less of the entire resin composition. If it is less than 5% by mass, the thermal shock resistance may be insufficient, and if it exceeds 50% by mass, various physical properties such as strength, rigidity, and heat resistance may be adversely affected. In order to make such inconvenience less likely to occur, the blending amount of the soft component in the entire resin composition is more preferably 10% by mass or more and 35% by mass or less.

Moreover, you may mix | blend antioxidant with the resin composition in order to suppress the oxidative degradation of a thermoplastic 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.

  Furthermore, a peroxide-decomposable antioxidant (secondary antioxidant) may be used in combination with the amine, phenolic, and hydroquinone antioxidants in the resin composition. 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 to 3.0% by mass with respect to the resin. However, depending on the kind of the antioxidant, there is an adverse effect on the non-blooming range or physical properties of the resin. If it does not reach the range, more amount may be added.
Furthermore, the following additives may be added to the resin composition as long as the amount does not impair the object of the present invention. For example, solid lubricant (graphite, hexagonal boron nitride, fluorine mica, tetrafluoroethylene resin powder, tungsten disulfide, molybdenum disulfide, etc.), inorganic powder, organic powder, lubricating oil, plasticizer, rubber, thermal stabilizer , UV absorber, photoprotective agent, inorganic or organic flame retardant, antistatic agent, mold release agent, fluidity improver, thermal conductivity improver, non-tackifier, crystallization accelerator, nucleator, pigment , Dye agents, light stabilizers, and other reinforcing materials may be added as appropriate.

  The method of mixing the thermoplastic resin, the fiber reinforcement, and the additive into the resin composition is not particularly limited, but additives other than the fiber reinforcement are added to the continuous fiber bundle of the fiber reinforcement. A method of cooling and pelletizing after impregnating the molten resin. The temperature of the thermoplastic resin at the time of melt impregnation is not particularly limited, and may be appropriately set to a temperature within a range where the thermoplastic resin is sufficiently melted and is not thermally deteriorated. Examples of the resin material made of a thermoplastic resin reinforced with such long fibers include Plastron (registered trademark) manufactured by Daicel Chemical Industries, Ltd. and Burton (registered trademark) manufactured by SABIC Innovative Plastics Co., Ltd. .

〔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, an aluminum alloy cored bar (the cored bar having the shape shown in FIG. 3 or 4) of the housing member and the cover member was subjected to a process such as air blasting to roughen the surface of the cored bar. 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 a resin material, a resin composition (UBE NYLON 2020GU6 manufactured by Ube Industries Co., Ltd.) composed of 30% by weight glass fiber and 70% by weight nylon 66, or 43% by weight glass fiber and 57% by weight nylon. 66 (Gramide TY-181GC manufactured by Toyobo Co., Ltd.).

  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, four types of gearboxes (Examples 1 to 4) in which the shape of the core metal and the type of the resin material are different were manufactured. Further, except that the surface of the metal core is not provided with an adhesive layer, the same gear box as in Example 3 (Example 5) and a gear box made of a resin material not provided with a metal core (Comparison) Example 1) was also produced. These gear boxes were repeatedly subjected to a thermal shock test, a heat resistance test, and a moisture absorption test. In Table 1, the resin composition comprising 30% by mass of the glass fiber and 70% by mass of nylon 66 described above is composed of the resin material A, the 43% by mass of glass fiber and 57% by mass of nylon 66 described above. This resin composition is indicated as resin material B.

  First, the repeated thermal shock test will be described. The gear box was kept in a high temperature environment of 100 ° C. for 30 minutes, and then kept in a low temperature environment of −40 ° C. for 30 minutes. Then, 2000 cycles were repeated with this temperature change as one cycle, and after the completion of 1000 cycles, 1500 cycles, and 2000 cycles, the occurrence of cracks and the fastening status of bolts and nuts were confirmed.

  And after the end of 1000 cycles, if there is no crack in the resin part of the gearbox and no bolts or nuts are loose, it has sufficient durability reliability necessary for actual use. In Table 1, it was indicated by a circle. In addition, even after 2000 cycles, if the resin part of the gearbox is not cracked and the bolts and nuts are not loose, it has extremely sufficient durability reliability. As a result of evaluation, it is indicated by ◎ in Table 1. Furthermore, after 1000 cycles, if the resin part of the gearbox has cracked or if the bolts and nuts have loosened, they are evaluated as rejected and indicated by x in Table 1. It was.

  As can be seen from Table 1, in Examples 1 to 4, cracks and loosening of the nut did not occur at all even after the end of 2000 cycles. On the other hand, in Example 5, although no cracks or loosening of the nut was observed after the end of 1000 cycles, the adhesive layer was not provided. Compared with ~ 4, cracks were confirmed in the resin part of the gearbox after 1500 cycles. On the other hand, in Comparative Example 1, loosening of the nut was confirmed after the end of 1000 cycles due to repeated thermal stress.

Next, the heat resistance test will be described. After the gearbox was left in a high temperature environment of 120 ° C. for 1000 hours, the fastening condition of the bolts and nuts was confirmed. The results are shown in Table 1.
As can be seen from Table 1, in Examples 1 to 5, no problems such as loosening of the nuts were observed in the tightened state of the bolts and nuts. On the other hand, in Comparative Example 1, it was confirmed that the nut was loosened as a result of the deterioration of the resin material.

  Next, the moisture absorption test will be described. The gear box was held for 300 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 40 μm, it is judged that the dimensional stability is very good, and in Table 1, it is indicated by “◎”, and those having a dimensional stability of 40 μm or more and less than 80 μm Judgment was good, and in Table 1, it was indicated by a circle, 80 μm or more was rejected, and in Table 1, it was indicated by a cross.

As can be seen from Table 1, since Example 5 had a cored bar, the dimensional stability was good and the level was acceptable. In Examples 1 to 4, since the cored bar and the resin material were firmly bonded with an adhesive, the dimensional stability was extremely good. On the other hand, the comparative example 1 was disqualified.
Next, the result of examining the relationship between the weight average fiber length of the fiber reinforcement and the physical properties of the resin composition will be described. First, the manufacturing method of the test piece used for physical property evaluation is demonstrated. Two kinds of the following seven kinds of commercially available materials (1) to (7) were appropriately selected and mixed to produce resin compositions of Examples 11 to 15 and Comparative Examples 11 to 14 shown in Table 2.

(1) Plastron (registered trademark) PA6-GF50-1 manufactured by Daicel Chemical Industries, Ltd .: A resin composition in which nylon 6 is reinforced with long glass fibers, and the fiber reinforcement content is 50% by mass.
(2) Plastron (registered trademark) PA66-GF50-2 manufactured by Daicel Chemical Industries, Ltd .: A resin composition in which nylon 66 is reinforced with long glass fibers, and the fiber reinforcement content is 50% by mass.
(3) Plastron (registered trademark) PA66-CF30-1 manufactured by Daicel Chemical Industries, Ltd .: A resin composition in which nylon 66 is reinforced with carbon long fibers, and the content of the fiber reinforcement is 30% by mass.

    (4) Amilan (registered trademark) CM1016G45N manufactured by Toray Industries, Inc .: A resin composition in which nylon 6 is reinforced with short glass fibers, and the fiber reinforcement content is 45% by mass.

(5) Amilan (registered trademark) CM1026 manufactured by Toray Industries, Inc .: Nylon 6 to which no fiber reinforcement is added.
(6) Leona (registered trademark) 14G50 manufactured by Asahi Kasei Co., Ltd .: A resin composition in which nylon 66 is reinforced with short glass fibers, and the fiber reinforcement content is 50% by mass.
(7) Leona (registered trademark) 1402 manufactured by Asahi Kasei Corporation: Nylon 66 to which no fiber reinforcement is added.

  For example, the resin composition of Example 11 is a material in which nylon 6 is reinforced with long glass fibers and the fiber reinforcing material content is 30% by mass, but the fiber reinforced resin composition (1 ) And a corresponding material (5) which is a base resin (a resin to which no fiber reinforcing material is added) were mixed and manufactured at a ratio such that the content of the fiber reinforcing material was 30% by mass. Specifically, the fiber reinforced resin composition and the base resin to which no fiber reinforcement was added were dry mixed at a predetermined ratio using a V blender.

The obtained pellets were molded with an in-line screw type injection molding machine, the test piece for bending test based on ISO178, the test piece for plane bending fatigue test based on ASTM D671, and the Charpy impact strength with notch based on ISO179-1. Test specimens and flat plates (length 100 mm, width 100 mm, thickness 2 mm) were prepared.
The test pieces made of the resin compositions of Examples 11 to 15 and Comparative Examples 11 to 14 thus obtained were subjected to the following various tests.

(A) Bending test In order to confirm the strength and rigidity of the resin material used in the manufacture of the gear box housing member and cover member, the bending strength and bending elastic modulus based on ISO 178 were measured using a bending test specimen based on ISO 178. It was measured. The results are shown in Table 2.
(B) Bending fatigue test In order to confirm the fatigue strength of the resin material used for manufacturing the gear box housing member and cover member, plane bending fatigue test based on ASTM D671 was performed using a test piece for plane bending fatigue test based on ASTM D671. A test was conducted. And the stress which is not damaged until it repeats stress load frequency | count 10 < ⁷ > times at the atmospheric temperature of 120 degreeC was measured. The results are shown in Table 2.

(C) Charpy impact strength test In order to confirm the impact resistance of the resin material used for manufacturing the gear box housing member and cover member, ISO 179 was used using a notched Charpy impact strength test piece based on ISO 179-1. The notched Charpy impact strength based on -1 was measured. The results are shown in Table 2.
(D) Measurement of warp deformation amount In order to confirm the warp deformation amount of the resin material used for manufacturing the gear box housing member and cover member, a flat plate (length 100 mm, width 100 mm, thickness 2 mm) was measured at a temperature of 23 ° C. and relative humidity. The amount of warp deformation after being left in a 50% atmosphere for 40 hours was measured. When the flat plate after being left in the atmosphere is placed on a flat plate and one corner of the four corners is pressed against the flat plate, the corner that is opposite to the pressed corner is caused by the warpage of the flat plate. Therefore, the height of the raised corner from the fixed surface was measured. The results are shown in Table 2.

(E) Measurement of weight average fiber length The weight average fiber length of the fiber reinforcement in each test piece was measured as follows. The test piece was put in a magnetic crucible and ashed for 60 minutes in an electric furnace set at 600 ° C. to completely volatilize the resin component. Then, a residue preparation was formed, and the weight average fiber length of the fiber reinforcement was measured using image analysis software Image Pro Plus manufactured by Media Cybernetics, USA. The results are shown in Table 2.

  As can be seen from Table 2, the resin compositions of Examples 11 to 14 containing glass fibers of long fibers having a weight average fiber length in the range of 0.7 mm or more and 5 mm or less are the conventional short fibers. Compared with the resin compositions of Comparative Examples 12 to 14 containing the glass fiber as a fiber reinforcement, the flexural modulus was almost the same, but the fatigue strength, Charpy impact strength, and warpage deformation amount of the long fiber Since the propagation of cracks was suppressed by the addition, the characteristics were excellent.

  Furthermore, the resin composition of Example 15 containing a long-fiber carbon fiber having a weight average fiber length in the range of 0.7 mm or more and 5 mm or less as a fiber reinforcement is obtained by using a conventional short-fiber carbon fiber as a fiber reinforcement. As compared with the resin composition of Comparative Example 11 contained as an additive, excellent bending strength, flexural modulus, and fatigue strength were exhibited despite the small amount of fiber reinforcement added.

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 (6)

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 electric power steering apparatus, wherein the housing member and the cover member are manufactured by insert molding of a resin material using a metal cored bar having a bolt hole through which the bolt is inserted.   The electric power steering apparatus according to claim 1, wherein at least one of the housing member and the cover member includes an adhesive layer containing an adhesive on a surface of the cored bar.   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 contains a phenol resin adhesive or a coupling agent, and the upper layer is phenol. The electric power steering apparatus according to claim 2, further comprising a resin adhesive.   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.   The electric power steering apparatus according to any one of claims 1 to 4, wherein the resin material is a resin composition containing a thermoplastic resin and a fiber reinforcing material.   6. The electric power steering apparatus according to claim 5, wherein the fiber reinforcing material has a weight average fiber length of 0.7 mm to 5 mm and an average fiber diameter of 1 μm to 30 μm.

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