JP2016137796A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device in which a gear box storing a gear speed reduction mechanism is light-weighted and has excellent impact resistance, creep characteristics, rigidity and dimensional stability.SOLUTION: The electric power steering device comprises a gear box 33 in which a housing member 33A storing a gear speed reduction mechanism 30 and a cover member 33B covering an opening part of the housing member 33A are fastened to be integrated with a bolt 33C and a nut. The housing member and the cover member are formed by press-molding a resin material having a metallic core grid with a bolt hole, through which is inserted the bolt, inserted thereinto. The resin material is a resin composition containing a fiber reinforced material having an average fiber length of 0.5 mm or more and thermoplastic resin, where a ratio of the fiber reinforced material contained in the resin composition is 10 wt.% or more and 60 wt.% or less.SELECTED DRAWING: Figure 3

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 a gear box made of metal has been studied.

  In order to reduce the weight of a gear box made of metal, it is only necessary to use a material with a lower specific gravity, that is, a resin material. However, it is difficult to ensure the same quality as conventional products simply by changing the material. It is thought that there is. Of particular concern is that resin materials have lower impact resistance, creep properties, and rigidity than metal materials. Further, in the case of replacement of a metal material with a resin material, it is not easy to ensure dimensional stability equivalent to that made of metal with a resin structure.

  As this type of conventional technology, for example, the technology described in Patent Document 1 is known. 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.

  However, in Patent Document 1, the sensor housing and the gear housing are all formed of a polyamide-based resin material or a polyamide-based resin filled with reinforcing fibers. However, in order to perform laser welding, the fiber content must be reduced. Therefore, physical properties such as high-temperature strength, impact resistance, creep characteristics, and rigidity are considered difficult to withstand long-term use. In addition, for these sensor housings and gear housings, suitable resin materials are described in consideration of the moldability of injection molding, but in the case of injection molding, the length of the reinforcing fiber is increased in consideration of moldability. Is not preferred. Because of such restrictions, it is not always easy to maintain physical properties such as impact resistance and rigidity equivalent to those of metal materials.

JP 2009-298246 A

  The present invention solves the above-mentioned 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 and has excellent impact resistance, creep characteristics, rigidity, and dimensional stability. The purpose is to provide.

In order to achieve the above object, an electric power steering apparatus according to the present invention is configured as follows.
An electric power steering system comprising: an electric motor that outputs an auxiliary torque that assists the steering torque in accordance with 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 houses the reduction gear mechanism, and a cover member that covers an opening of the housing member are provided with a gear box that is fastened and integrated by a bolt,
The housing member and the cover member are formed by press molding of a resin material with a metal cored bar having a bolt hole through which the bolt is inserted,
The resin material is a resin composition containing a fiber reinforcing material having an average fiber length of 0.5 mm or more and a thermoplastic resin, and the ratio of the fiber reinforcing material contained in the resin composition is 10% by weight. An electric power steering device that is 60% by weight or less.

  In the electric power steering device of the present invention, the housing member and the cover member are formed by press molding of a resin material using a metal cored bar as an insert, and are fastened and integrated by a bolt. Is a fiber reinforced resin composition containing a reinforced fiber having an average fiber length of 0.5 mm or more and a thermoplastic resin, so that the gear box is lightweight and has impact resistance, creep characteristics, rigidity, 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 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 explanatory drawing of the manufacturing method of a cover member.

  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 racked 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.

  Both the housing member 33A and the cover member 33B are manufactured by insert molding of a resin material using metal cores 36A and 36B (see FIG. 3) as inserts. As will be described in detail later, this resin material is composed of a resin composition containing a thermoplastic resin and a fiber reinforcing material.

  In manufacturing the cover member 33B, first, an aqueous solution 33Bx in which thermoplastic resin fibers and glass fibers are dispersed in water as shown in FIG. 6A is created. Next, as shown in FIG. 6B, the aqueous solution 33Bx is injected into the papermaking mold D from the position indicated by the arrow X. At this time, the pre-molded body 33By is formed by dehydration as indicated by an arrow W. Next, the core metal 36B and the resin material are integrated by press molding the pre-molded body 33By. That is, the core metal 36B is disposed in a mold (not shown), and the pre-molded body 33By described above is disposed in the concave portion of the core metal 36B, then the mold is closed and pressurized, and heated at 350 ° C. for 30 seconds. To do. Similarly, the metal core 36A and the resin material are integrated by the press molding using the metal core 36A as an insert in the housing member 33A.

  As is apparent from FIG. 3, the housing member 33A and the cover member 33B are not particularly thick and have a substantially uniform thickness as a whole. This is because, as described above, the core metal 36B and the resin material are integrated by press molding, so that the fiber reinforcing material is uniformly distributed in the thermoplastic resin and the rigidity and the like are improved. This is because it is unnecessary.

  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 32a and 32b are integrally formed at both ends of the worm 32, and these worm shafts 32a and 32b are rotatably supported by rolling bearings 34a and 34b 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. In the gear box 33 shown in FIGS. 2 to 5, since the core bars 36A and 36B are provided with the arm 40 for reinforcement, the electric power steering mounted on the middle / large-sized vehicle in which the auxiliary torque by the electric motor is relatively large. It is suitable for the apparatus.

  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. It is. Moreover, it is excellent in impact resistance, rigidity, and dimensional stability as compared with a conventional gear box that is entirely made of a resin material.

  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 surfaces of the core bars 36A and 36B so that the peripheral portion of the bolt hole 37 is not covered with the resin material. Further, 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 sealed in the gear box 33 from leaking to the outside. A groove may be provided.

  Further, according to the insert molding, the rolling bearings 34a and 34b (or the rolling bearings 35a and 35b and the bearing metal arm 40 inserted to insert the steering shaft 11 and the rolling bearings 34a and 34b are press-fitted and fixed. For this purpose, the inserted metal sleeve 39) can be integrated with the resin structure simultaneously with the press molding of the resin material. That is, according to the insert molding, the integration of the resin portion and the metal part (insert) is achieved simultaneously with the press 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 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.

  When performing insert molding, 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 insert molding using the core bars 36A and 36B whose surfaces are covered with an adhesive layer as inserts. By doing so, the core 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 becomes 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.

  Although the kind of metal material which comprises the core metal 36A, 36B is not particularly limited, 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 by 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 core 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 phenol derivatives are preferable in view 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.

  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, 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).

  As the resin material, a resin composition containing a thermoplastic resin and a fiber reinforcing material is preferable. That is, a resin composition in which a fiber reinforcing material such as glass fiber or carbon fiber is blended with a thermoplastic resin is preferable.

  The thermoplastic resin is not particularly limited, but specific examples include polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 612, polyamide 46, and an absorbent material compared to these polyamides. Nylon 6T / 6I (Arlen made by Mitsui Chemicals, Inc.), nylon 6T / 6I / 6-6 (Solvay Advanced Polymers, Inc.), a so-called semi-aromatic nylon obtained by partially copolymerizing terephthalic acid with adipic acid units. Amodel), nylon 6T (ZytelHTN manufactured by DuPont), and nylon 9T (Genstar manufactured by Kuraray Co., Ltd.) are preferable.

  The fiber reinforcement is not particularly limited, but specific examples include glass fiber, carbon fiber, metal fiber, aramid fiber, aromatic polyimide fiber, liquid crystal polyester fiber, silicon carbide fiber, alumina fiber, boron fiber, and the like. Can be illustrated. Of these, glass fiber and carbon fiber are preferable because of their good reinforcement.

  The fiber reinforcing material preferably has an average fiber length of 0.5 mm or more. When the average fiber length is less than 0.5 mm, impact resistance and dimensional stability are not so improved. As for the compounding quantity in the resin composition of a fiber reinforcement, 10 to 60 weight% is preferable. When the blending amount of the fiber reinforcement is less than 10% by weight, the mechanical strength is hardly improved, which is not preferable. On the other hand, when the blending amount exceeds 60% by weight, the toughness of the material is impaired, and for example, the thermal shock resistance may be insufficient.

〔Example〕
The method for manufacturing the gear box of the electric power steering apparatus of the present invention will be described below with reference to examples.

  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 core member thus obtained was placed in a mold, and a housing member and a cover member were produced by insert molding in which a pre-molded body was press-molded.

  In producing the housing member and the cover member, first, an aqueous solution in which thermoplastic resin fibers and glass fibers were dispersed in water was poured into a papermaking mold to form a pre-molded body. Next, a cored bar was placed in the mold, and the pre-molded body was placed at a predetermined position with respect to the cored bar. Then, the mold was closed and pressurized, and heated at 350 ° C. for 30 seconds.

  According to the present Example, the tensile strength was comparable with the conventional aluminum die-cast housing member and cover member. This is presumably because the average fiber length of the fiber reinforcing material can be increased by press molding, and the fiber reinforcing material is dispersed with little unevenness. Moreover, since it is formed from the resin composition, the weight can be reduced to 80% of the conventional product.

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 (1)

  An electric power steering system comprising: an electric motor that outputs an auxiliary torque that assists the steering torque in accordance with 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. An apparatus comprising: a gear box in which a housing member that accommodates the reduction gear mechanism and a cover member that covers an opening of the housing member are fastened together by bolts, and the housing member and the cover member are The resin material is formed by press molding of a resin material with a metal core having a bolt hole through which the bolt is inserted, and the resin material has a fiber reinforcing material having an average fiber length of 0.5 mm or more, A resin composition containing a thermoplastic resin, and the proportion of the fiber reinforcement contained in the resin composition is 10 wt% or more 6 An electric power steering apparatus characterized by% by weight or less.

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