JP2014137114A - Worm wheel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synthetic resin-made worm wheel improved in strength of a tooth part by reduction of the weight and the size, and excellent in durability.SOLUTION: A worm wheel 21 comprises: an annular core metal 22 made of metal; and a plurality of synthetic resin-made tooth parts 23 integrally formed on an outer periphery of the core metal 22 and arranged in equal intervals in a circumferential direction. The synthetic resin-made tooth part 23 includes a first molded part 24 formed of a first synthetic resin material with no reinforced fiber, and a second molded part 25 integrally formed with the first molded part by a second synthetic resin material mixed with the reinforced fiber. The second molded part 25 is arranged in an inside of the first molded part 24, and extends in a radial direction of the core metal like a plate.

Description

  The present invention relates to a worm wheel.

  Conventionally, in an automobile, an electric power steering device that transmits rotation of an electric motor for generating a steering assist force to a wheel via a worm and a worm wheel type reduction device is used, and the worm wheel is made of a synthetic resin to reduce the weight. And low noise.

  Due to recent environmental requirements and cost reduction requirements, there is a need for weight reduction and miniaturization. For this reason, synthetic resin worm wheels are required to have higher strength, heat resistance, and wear resistance. For this reason, Patent Document 1 proposes a worm wheel in which the tooth portion of the worm wheel is formed of a synthetic resin material but the strength of the tooth portion is increased by inserting a metal plate therein.

JP 2009-299805 A

As in Patent Document 1, it is possible to temporarily increase the strength by inserting a metal plate into the tooth part of the worm wheel, but the thermal expansion coefficient of the synthetic resin of the tooth part and the metal plate can be increased. Due to the difference, stress concentration is likely to occur at the edges of the metal plate and synthetic resin in the usage environment, and the interface between the metal plate and synthetic resin is less likely to occur. There is a problem that peeling occurs and durability is gradually lowered over a long period of time.
The present invention has been made based on such a background, and an object of the present invention is to provide a synthetic resin worm wheel having improved durability and excellent durability.

  To achieve the above object, the present invention provides a metal-made annular cored bar, and a plurality of synthetic resin toothed parts integrally formed on the outer periphery of the cored bar and arranged equally in the circumferential direction. In the worm wheel, the tooth portion made of synthetic resin is formed of the first molded portion formed of a first synthetic resin material not containing reinforcing fibers and the second synthetic resin material containing reinforcing fibers. A second molded part formed integrally with the part, and the second molded part is disposed inside the first molded part and is formed to extend in a plate shape in the radial direction of the cored bar. This is the gist.

  According to the present invention, since the synthetic resin tooth portion is formed of a synthetic resin having a linear expansion coefficient equal to that of the second molding portion in which reinforcing fibers are blended and reinforced, the second molding portion is arranged in a plate shape. No stress concentration due to expansion and contraction, no occurrence of peeling at the interface between the first molded part and the second molded part, and as a result, the strength of the tooth part is improved and the synthetic resin is excellent in durability. A worm wheel can be provided.

  Furthermore, the gist of the invention described in claim 2 is that the flow direction of the reinforcing fibers of the second synthetic resin material is the radial direction of the core metal. In other words, the bending strength in the circumferential direction can be improved by making the flow of reinforcing fibers blended in the synthetic resin material in the radial direction of the cored bar, improving the strength of the tooth portion, and having excellent durability. Resin worm wheels can be provided.

  Furthermore, in the invention according to claim 3, the synthetic resin tooth portion is insert-molded by injecting the molten first synthetic resin material in a state where the second molded portion is inserted into a molding die. It is the summary. That is, since the first synthetic resin material and the second synthetic resin material are synthetic resins having close melting temperatures, the surface of the second molded part is caused by the contact of the molten first synthetic resin material that molds the first molded part during molding. Since it is in a molten state and melts at the edge part of the second molding part, stress concentration at the edge part is eliminated and it is easy to become familiar with each other, so there is no occurrence of peeling at the interface, resulting in improved tooth strength In addition, it is possible to provide a synthetic resin worm wheel having excellent durability.

  Synthetic resin worm wheel that improves the strength of the tooth part and has excellent durability by arranging the second molded part with high strength by blending reinforcing fibers inside the synthetic resin tooth part. Can be provided.

1 is a schematic diagram of an electric power steering device to which a worm wheel according to an embodiment of the present invention is applied. Sectional drawing of the deceleration mechanism to which the worm wheel which concerns on one Embodiment of this invention is applied The partially expanded sectional view of the worm wheel which concerns on one Embodiment of this invention. The schematic diagram which showed the flow of the reinforced fiber of the 2nd shaping | molding part of the worm wheel which concerns on one Embodiment of this invention. Sectional drawing of the shaping die for 2nd shaping | molding parts which concerns on one Embodiment of this invention Sectional drawing of the shaping | molding die for worm wheels which concerns on one Embodiment of this invention

  Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic diagram of an electric power steering apparatus to which a worm wheel of the present invention is applied. The configuration and operation of the electric power steering will be described with reference to FIG. The electric power steering apparatus 1 includes a steering mechanism 4 that steers the steered wheels 3 in conjunction with rotation of a steering wheel 2 that is rotated (steered) by a driver, and a steering assist mechanism 5 that assists steering. ing. The steering wheel 2 and the steering mechanism 4 are mechanically connected via a steering shaft 6, an intermediate shaft 7, and the like. The rotation of the steering wheel 2 is transmitted to the steering mechanism 4 via the steering shaft 6, the intermediate shaft 7, and the like.

  The steering shaft 6 includes an input shaft 8 connected to the steering wheel 2 and an output shaft 9 connected to the steering mechanism 4 via an intermediate shaft 7 or the like. The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be relatively rotatable on the same axis. When a steering torque of a certain value or more is input to the steering wheel 2, the input shaft 8 and the output shaft 9 rotate in the same direction while rotating relative to each other. The steering torque input to the steering wheel 2 is detected by the torque sensor 11 based on the relative rotational displacement amounts of the input shaft 8 and the output shaft 9. The torque detection result of the torque sensor 11 is input to an ECU 12 (Electronic Control Unit).

  The steered mechanism 4 is, for example, a rack and pinion mechanism. The steering mechanism 4 includes a pinion shaft 13 and a rack shaft 14. The pinion shaft 13 is connected to the steering wheel 2 via the steering shaft 6 and the intermediate shaft 7. The rotation of the steering wheel 2 is transmitted to the pinion shaft 13. A pinion 16 is formed at the tip of the pinion shaft 13 (the lower end in FIG. 1).

  The rack shaft 14 extends linearly along the left-right direction of the vehicle. The steered wheels 3 are coupled to both ends of the rack shaft 14 via tie rods 15 and knuckle arms (not shown), respectively. A rack 17 that meshes with the pinion 16 is formed in the middle of the rack shaft 14 in the axial direction. The rotation of the pinion shaft 13 is converted into an axial movement of the rack shaft 14 by the pinion 16 and the rack 17. The steered wheel 3 can be steered by moving the rack shaft 14 in the axial direction.

  The steering assist mechanism 5 includes an electric motor 18 and a speed reduction mechanism 19 (power transmission device). The output of the electric motor 18 is transmitted to the steering mechanism 4 via the speed reduction mechanism 19. A worm gear is used as the speed reduction mechanism 19. The speed reduction mechanism 19 includes a worm 20 as a drive gear and a worm wheel 21 as a driven gear that meshes with the worm 20.

The worm 20 is connected to a rotating shaft (not shown) of the electric motor 18 via a power transmission joint (not shown). The worm wheel 21 is coupled to the output shaft 9 of the steering shaft 6 so as to be able to rotate together. The worm 20 is rotationally driven by the electric motor 18.
When the worm 20 is rotated by the electric motor 18, the rotation of the worm 20 is transmitted to the worm wheel 21, and the worm wheel 21 and the output shaft 9 rotate together. Then, the pinion shaft 13 rotates together with the output shaft 9, and the rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. Thereby, the steered wheel 3 is steered.

  The electric motor 18 is controlled by the ECU 12 based on a torque detection result from the torque sensor 11 or a vehicle speed detection result from a vehicle speed sensor (not shown). Driving the worm 20 by the electric motor 18 can assist the driver's steering.

  FIG. 2 is a sectional view of a speed reduction mechanism to which a worm wheel is applied, and FIG. 3 is a partially enlarged sectional view of the worm wheel. Hereinafter, FIG. 2 and FIG. 3 will be referred to. As shown in FIG. 2, the worm wheel 21 is composed of a core metal 22 and a synthetic resin tooth portion 23 having a plurality of tooth tip surfaces. The synthetic resin tooth portion 23 includes a first molding portion 24 and a plurality of second molding portions 25 for reinforcing each synthetic resin tooth portion 23.

  The cored bar 22 is annular, has a relatively small diameter and cylindrical boss part 27, a disk-shaped end wall 28 extending radially outward from the outer periphery of the boss part 27, and the outer peripheral edge of the end wall 28 And a cylindrical peripheral wall 29 that coaxially surrounds the boss portion 27 and the end wall 28. The boss portion 27, the end wall 28, and the peripheral wall 29 are integrally formed of, for example, a single metal material. The output shaft 9 is fitted (for example, press-fitted) to the inner periphery of the boss portion 27, and is connected to the core metal 22 so as to be able to rotate together. Further, as shown in FIG. 3, a plurality of fitting recesses 30 are formed on the outer peripheral portion of the peripheral wall 29. The plurality of fitting recesses 30 are arranged at equal intervals in the circumferential direction of the cored bar 22 (generally in the left-right direction in FIG. 3). Each fitting recess 30 extends along a tooth trace direction P1 of a tooth surface 33b described later, and is formed from one end 29a to the other end 29b of the peripheral wall 29.

  The synthetic resin tooth portion 23 has a cylindrical shape. The synthetic resin tooth portion 23 surrounds the outer periphery of the cored bar 22. A part of the core metal 22 is embedded in the synthetic resin tooth portion 23 by insert molding. Thereby, the cored bar 22 and the synthetic resin tooth part 23 are joined.

  The synthetic resin tooth portion 23 includes an annular annular portion 32 and a plurality of tooth body portions 33 provided on the annular portion 32 at equal intervals in the circumferential direction. Each tooth main body portion 33 has tooth surfaces 33 b on both sides in the circumferential direction of the synthetic resin tooth portion 23. A part on the outer diameter side of the second molding part 25 constitutes a part of the tooth main body part 33, and a part on the inner diameter side of the second molding part 25 constitutes a part of the annular part 32. A part on the outer diameter side of the first molding part 24, that is, a part of the tooth part constitutes a part of the tooth main body part 33, and a part of the inner diameter side of the first molding part 24, that is, an annular part is an annular part. The part 32 is configured.

  The feature which concerns on this embodiment is that the intensity | strength of the synthetic resin tooth part 23 of the worm wheel 21 can be improved, without enlarging. The synthetic resin tooth portion 23 will be specifically described.

  In this embodiment, the plurality of synthetic resin teeth 23 are formed in a gear cutting step after resin molding. Each tooth body 33 is, for example, an oblique tooth (a helical tooth). Moreover, each tooth main-body part 33 may be not only an oblique tooth but a straight tooth (immediate tooth).

  As shown in FIG. 4, the 2nd shaping | molding part 25 is extended and formed in the radial direction of the metal core 22, and the tooth trace direction P1, respectively. As shown in FIG. 2, the length of each second molding portion 25 in the longitudinal direction is slightly shorter than the tooth width of the synthetic resin tooth portion 23 (the length in the tooth trace direction P1). Yes. Further, as shown in FIGS. 2 and 3, a part of each second molding portion 25 is fitted in the fitting recess 30. Thereby, each 2nd shaping | molding part 25 is positioned and hold | maintained by the metal core 22 in the circumferential direction.

  Each second molding portion 25 is fitted into the fitting recess 30 together with the core metal 22 by, for example, insert molding using the molding die shown in FIG. Thereby, the cored bar 22, the 1st shaping | molding part 24, and the some 2nd shaping | molding part 25 are fixed integrally, and each relative position is stabilized. The plurality of second molding parts 25 are arranged at equal intervals in the circumferential direction of the worm wheel 21 inside the first molding part 24. The plurality of second forming portions 25 correspond to the plurality of tooth main body portions 33, respectively.

  As shown in FIG. 2, each 2nd shaping | molding part 25 is extended along the tooth trace direction P1 of the corresponding tooth surface 33b. Each second molding portion 25 extends in the radial direction of the cored bar 22 from the fitting recess 30 of the cored bar 22 to a part of the tooth body 33. Furthermore, the tooth lateral side surface 25b of each second forming portion 25 is disposed inside the corresponding tooth portion 23 so as to face the tooth surface 23b of the corresponding tooth portion 23. The corresponding tooth lateral side surface 25b of the second forming portion 25 enters from the one end to the other end in the tooth line direction P1 into each tooth main body portion 33. Thereby, each tooth main-body part 33 is reinforced over the other end from the one end of the tooth trace direction P1. Accordingly, the entire synthetic resin tooth portion 23 is reinforced by the corresponding second molding portion 25. The amount of entry A1 (see FIGS. 2 and 3) of the second molding portion 25 into each tooth main body portion 33 is, for example, constant over the tooth trace direction P1.

  In the formation process of the second molding part 25, as shown in FIG. 5, the mold 40 for the second molding part is composed of an upper mold 40a and a lower mold 40b, and between the upper mold 40a and the lower mold 40b. A cavity that accommodates the cored bar 22, a cavity 40f that forms the second molding portion 25, a circular cavity 40d that is circular in cross section, and a cavity 40e that connects the cavity 40f and the cavity 40d are formed. In the upper mold 40a, a gate and a cavity 40c that connects the gate and the cavity 40d are formed.

  In the injection molding, molten resin is injected into the gate of the mold 40 so that the resin flows into the cavities 40d, 40e, and 40f formed by the molds 40a and 40b. The resin is filled around the outer peripheral surface of the peripheral wall 29 of the cored bar 22. At this time, the resin enters the fitting recess 30 of the cored bar 22. At that time, as shown in FIG. 4, the flow of the reinforcing fibers is oriented in layers in the cavities 40d and 40e, and is aligned in the radial direction of the cored bar 22 in the cavity 40f. Then, the 2nd shaping | molding part 25 is formed in the outer periphery of the metal core 22 through a pressure holding process and a cooling process.

  In the forming process of the first molding part 24, as shown in FIG. 6, the mold 50 for the first molding part is composed of an upper mold 50a and a lower mold 50b, and between the upper mold 50a and the lower mold 50b. A cavity for accommodating the cored bar 22 and a cavity 50d for forming the first molding portion 24 are formed. The upper mold 50a is formed with a gate and a cavity 50c that connects the gate and the cavity 50d.

  Similarly, in the injection molding of the first molding part 24, the molten resin is injected into the gate of the mold 50, whereby the resin flows into the cavities 50c and 50d formed by the molds 50a and 50b. The outer peripheral surface of the peripheral wall 29 of the cored bar 22 and the periphery of the second molding part 25 are filled with resin. Thereafter, the first molded part 24 is formed on the outer periphery of the cored bar 22 and the second molded part 25 through a pressure holding process and a cooling process.

  The present invention is not limited to the above embodiment. For example, a thermoplastic synthetic resin material such as nylon (polyamide), PPS (polyphenylene sulfide), PES (polyethersulfone), or POM (polyacetal) may be used as the material of the synthetic resin tooth portion 23 of the worm wheel 21. . Further, the second synthetic resin material, which is the material of the second molding portion 25 of the worm wheel 21, includes a general glass fiber as a reinforcing fiber, but also prevents wear of the worm meshing with the carbon fiber and the worm wheel. In some cases, potassium titanate whiskers or aramid fibers may be used.

  As described above, in the present embodiment, since the entire synthetic resin tooth portion 23 is reinforced by the plurality of second molding portions 25, a concentrated load applied to a part of the synthetic resin tooth portion 23 is applied to the synthetic resin tooth portion 23. The resin teeth 23 can be dispersed throughout. Thereby, it can suppress or prevent that stress concentrates on a part of synthetic-resin tooth part 23. FIG. Therefore, the strength of the synthetic resin tooth portion 23 of the worm wheel 21 can be further improved.

  Further, the synthetic resin tooth portion 23 has a high strength second molding portion 25 blended with reinforcing fibers and disposed in the first molding portion 24 in the radial direction of the core metal 22 to make the synthetic resin tooth portion 23 high. In addition, since the second synthetic resin material of each second molding part 25 and the first synthetic resin material of the first molding part 24 are synthetic resins having the same linear expansion coefficient, stress concentration due to thermal expansion and contraction is increased. No occurrence of peeling at the interface between the first molding part 24 and the second molding part 25, and as a result, the strength of the synthetic resin tooth part 23 is improved and the synthetic resin worm is excellent in durability. A wheel 21 can be provided.

  Moreover, the 2nd shaping | molding part 25 is a 2nd synthetic resin material which made the synthetic resin material mix | blended the reinforced fiber, and made the flow of the reinforced fiber the radial direction. That is, the bending strength in the circumferential direction can be improved by effectively reinforcing the tooth root having a large stress and making the flow of the reinforcing fiber blended in the synthetic resin material in the radial direction of the cored bar 22. It is possible to provide the synthetic resin worm wheel 21 with improved strength of the synthetic resin tooth portion 23 and excellent durability.

  Further, the synthetic resin tooth portion 23 is formed by integrally forming the second molded portion 25 on the outer periphery of the peripheral wall 29 of the metal core 22 with a second synthetic resin material in which reinforcing fibers are blended with the first synthetic resin material. Insert molding is performed by injecting a molten first synthetic resin material in a state in which the core 22 formed integrally with the outer periphery of the second molding portion 25 is inserted into the molding die. Therefore, since the first synthetic resin material and the second synthetic resin material are synthetic resins having a melting temperature close to each other, melting occurs at the interface between the first molded portion 24 and the second molded portion 25 during molding, and stress concentration occurs at the edge portion. Since it disappears and is easily compatible with each other, there is no occurrence of peeling at the interface, and as a result, the strength of the synthetic resin tooth portion 23 can be improved and the synthetic resin worm wheel 21 having excellent durability can be provided.

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device (vehicle steering device), 3 ... Steering mechanism, 18 ... Electric motor, 19 ... Deceleration mechanism (power transmission mechanism), 20 ... Worm, 21 ... Worm wheel, 22 ... Core metal, 23 ... Synthetic resin teeth 24, first molded part 25 ... second molded part 25b ... part of the second molded part 26 ... tooth part forming surface 31 ... inclined surface 33 ... tooth body part 33b ... Tooth surface, 35 ... press-fitting groove, 19 ... deceleration mechanism (power transmission mechanism), P1 ... tooth line direction

Claims (3)

In the worm wheel comprising a metal-made annular cored bar and a plurality of synthetic resin-made toothed parts integrally formed on the outer periphery of the cored bar and arranged equally in the circumferential direction, the synthetic resin-made tooth The part is a second molding molded integrally with the first molding part by a first molding part molded with a first synthetic resin material not blended with reinforcing fibers and a second synthetic resin material blended with reinforcing fibers. The worm wheel is characterized in that the second molding part is disposed in the first molding part and extends in a plate shape in the radial direction of the cored bar. The worm wheel according to claim 1, wherein a flow direction of the reinforcing fiber of the second synthetic resin material is a radial direction of the core metal. The synthetic resin tooth portion is insert-molded by injecting the molten first synthetic resin material in a state where the second molded portion is inserted into a molding die. The worm wheel according to claim 1 or claim 2.

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