Pre-cut molded body for power transmission resin gears, and power transmission resin gears

Abstract

To provide a gear cutting preform of a resin gear for power transmission in which a void in the injection molding can be prevented and a forming cycle can be shortened, and provide the resin gear for power transmission.SOLUTION: A preform 1 is provided before providing a gear tooth of a resin gear for power transmission. The preform comprises a cored bar 2 and an annular resin part 3 for covering up an outer circumference of the cored bar 2. The annular resin part 3 comprises an annular inside resin component 4, and an annular outside resin component 5 being the material different from the annular inside resin component 4. The annular inside resin component 4 covers up the outer circumference of the cored bar 2. The annular outside resin component 5 covers the outer circumference of the annular inside resin component 4. In the outer circumferential surface of the annular outside resin component 5, a recessed groove 6 providing a cutting margin is present in the position for providing the tooth groove of the gear tooth. In the axial side face B of the annular outside resin component 5, an axial thinned part 5A is present in the position between the tooth grooves adjacent in the circumferential direction of the resin gear for power transmission.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a resin gear for power transmission comprising a core metal and an annular resin part.

Background Art

[0002] In order to meet the needs such as weight reduction and quietness, there is a resin gear for power transmission comprising a core metal and an annular resin part covering the outer periphery thereof (for example, see paragraph of Patent Document 1).

[0003] Reference).

[0003] The worm wheel of Patent Document 1 has a helical gear shape in order to avoid the appearance of voids on the tooth surface, and a blank having a tooth width and a tooth thickness uniformly formed over the entire tooth width direction is mold-formed. That is, first, with a metal core bush, which is the core metal, disposed as an insert work in an injection mold, a blank 10 having the above shape with a machining allowance for cutting not made too thick is injection-molded. Next, a resin worm wheel finished to have a tooth surface shape of a predetermined worm wheel is manufactured by subjecting the blank 10 to cutting on both the tooth part 11 and the tooth root 12 (see FIGS. 3 and 5 of Patent Document 1).

[0004] On the other hand, there is one in which the annular resin part is molded in two steps (for example, see Patent Document 2). That is, the worm wheel of Patent Document 2 molds a connecting part 14 of a thermoplastic resin on the outer periphery of an inner part 12 which is the core metal, and then molds an outer part 16 of a thermoplastic resin on the outer periphery of the connecting part 14 (see FIG. 1 of Patent Document 3). There is a flash on the axial surface of the connecting part 14.

[0005] On the other hand, in a resin gear for power transmission in which the core metal is absent and the whole is made of a synthetic resin, in order to accurately transmit power while suppressing the generation of noise, there is one in which the end in the axial direction of the helical teeth is recessed (for example, see Patent Document 3). That is, the helical gear of Patent Document 3 provides a recess 21 and a thin part 22 at the end of the helical teeth 20, and the elastic deformation of the thin part 22 relaxes the impact at the time of collision between the ends of the helical teeth 20 (see FIG. 4 of Patent Document 3).

Prior Art Documents

[0006] [Patent Document 1] Patent No. 4423815 [Patent Document 2] German Patent Application Publication No. 102012102780 Specification [Patent Document 3] Japanese Patent Publication No. 2008-115886 [Overview of the project] [Problems that the invention aims to solve]

[0007] Conventional resin gears for power transmission require gear cutting to create the gear teeth after molding. This necessitates increasing the thickness of the resin in the gear cutting area, resulting in thick-walled molded products. In the injection molding process of thick-walled molded products, it is necessary to increase the holding pressure and lengthen the holding pressure process to suppress voids, which are defects in thick-walled molded products. Furthermore, because the solidification rate is slow, the cooling process from the completion of the holding pressure process to the start of mold opening also needs to be lengthened. Consequently, the molding cycle becomes long in the injection molding of thick-walled molded products.

[0008] The present invention aims to provide a pre-cut molded body for a resin gear for power transmission, and a resin gear for power transmission, which can suppress voids in injection molding and shorten the molding cycle. [Means for solving the problem]

[0009] A molded body of a power transmission resin gear before gear cutting according to a first aspect of the present invention is a molded body of a power transmission resin gear before the teeth are provided, and consists of a core metal and an annular resin portion covering the outer circumference of the core metal. The outer surface of the annular resin portion has at least one recessed groove with a cutting allowance at the position where the tooth grooves of the teeth are provided. The axial end face of the annular resin portion has axial material removal at the position between adjacent tooth grooves in the circumferential direction of the power transmission resin gear. Furthermore, the radial position of the axial material removal is at least 2 mm radially inward from the outer diameter of the annular resin portion, and radially inward from the innermost part of the groove. ru.

[0010] A pre-cut molded body for a power transmission resin gear according to a second aspect of the present invention is a pre-cut molded body for a power transmission resin gear according to a first aspect, wherein the annular resin portion comprises an annular inner resin member and an annular outer resin member made of a different material from the annular inner resin member. The annular inner resin member covers the outer circumference of the core metal, and the annular outer resin member covers the outer circumference of the annular inner resin member. The annular outer resin member has the groove on its outer circumferential surface, and the annular outer resin member has the axial material removal on its axial end face.

[0011] According to the pre-cutting molded body of a resin gear for power transmission according to the first aspect of the present invention, and the pre-cutting molded body of a resin gear for power transmission according to the second aspect of the present invention, axial material removal occurs at the position between adjacent tooth grooves in the circumferential direction of the resin gear for power transmission. Furthermore, the radial position of the axial material removal is at least 2 mm radially inward from the outer diameter of the annular resin portion, and radially inward from the innermost part of the groove. Therefore, since the thickness of the resin in the area where teeth are set during gear cutting does not increase, there is no need to increase the holding pressure in the holding pressure process to suppress voids, which are defects in thick-walled molded products, and there is no need to lengthen the holding pressure process time. Moreover, since the solidification rate is not as slow as that of thick-walled molded products, there is no need to lengthen the cooling process time from the completion of the holding pressure process to the start of mold opening. Therefore, the molding cycle can be shortened. Furthermore, because of the aforementioned axial material removal, the weight of the molded body of the resin gear for power transmission before gear cutting can be reduced.

[0012] A pre-cut molded body for a resin gear for power transmission according to a third aspect of the present invention is a pre-cut molded body for a resin gear for power transmission according to a first aspect, wherein the groove extends around the entire circumference at the position where the tooth grooves of the teeth are provided.

[0013] According to the molded body of a resin gear for power transmission before gear cutting according to the third aspect of the present invention, since there is a recessed groove around the entire circumference at the position where the tooth grooves of the resin gear for power transmission are to be made, the amount of resin used for molding is reduced, and thus material costs can be reduced.

[0014] The pre - formed body of the resin gear for power transmission according to the fourth aspect of the present invention is the pre - formed body of the resin gear for power transmission according to the first aspect, wherein the axial undercut is at both end faces in the axial direction of the annular resin part.

[0015] According to the pre - formed body of the resin gear for power transmission according to the fourth aspect of the present invention, since the axial undercut is at both end faces in the axial direction of the annular resin part, it is difficult to deform due to molding shrinkage, so the shape accuracy of the pre - formed body of the resin gear for power transmission does not deteriorate.

[0016] The resin gear for power transmission according to the fifth aspect of the present invention is provided with tooth grooves on the entire circumference of the teeth based on the position of the concave groove in any of the pre - formed bodies of the resin gear for power transmission according to the first aspect to the fourth aspect.

[0017] According to the resin gear for power transmission according to the fifth aspect of the present invention, the same effects as those of the pre - formed body of the resin gear for power transmission according to the first aspect to the fourth aspect are achieved.

Effect of the Invention

[0018] As described above, according to the pre - formed body of the resin gear for power transmission and the resin gear for power transmission according to the present invention, voids in injection molding can be suppressed and the molding cycle can be shortened.

Brief Description of the Drawings

[0019] [Figure 1] It is a perspective view of the resin gear for power transmission according to an embodiment of the present invention. [Figure 2] It is a longitudinal sectional side view of the resin gear for power transmission. [Figure 3] It is an enlarged front view of the main part of the resin gear for power transmission. [Figure 4] It is a perspective view of the pre - formed body of the resin gear for power transmission according to an embodiment of the present invention. [Figure 5]It is a perspective view of the pre - tooth - cutting formed body shown in FIG. 4 as seen from the back side. [Figure 6] It is a longitudinal sectional side view of the pre - tooth - cutting formed body. [Figure 7] It is an enlarged front view of the main part of the pre - tooth - cutting formed body. [Figure 8] It is a perspective view showing a modified example of the pre - tooth - cutting formed body.

Embodiments for Carrying out the Invention

[0020] Next, embodiments of the present invention will be described in detail based on the accompanying drawings.

[0021] In this specification, the direction of the rotation axis of the resin gear A for power transmission is referred to as the "axial direction", and the "radial direction" and "circumferential direction" are defined based on the axis center (reference symbol O in FIG. 2) of the rotation axis. The view seen from the axial direction is taken as the front view.

[0022] <Resin Gear for Power Transmission> As shown in the perspective view of FIG. 1 and the longitudinal sectional side view of FIG. 2, the resin gear A for power transmission is composed of a metal core 2 and an annular resin part 3 covering the outer periphery thereof. Teeth T are formed at equal intervals in the circumferential direction on the outer peripheral surface of the annular resin part 3. The resin gear A for power transmission is used, for example, as a worm wheel of a worm gear used in an electric power steering.

[0023] (Core) The core 2 is, for example, an annular sleeve as shown in FIGS. 1 and 2, but it may have a shaft portion instead of an annular sleeve.

[0024] (Annular Resin Part) The annular resin portion 3 consists of an annular inner resin member 4 and an annular outer resin member 5. The annular inner resin member 4 covers the outer circumference of the core metal 2, and the annular outer resin member 5 covers the outer circumference of the annular inner resin member 4. One end face of the annular inner resin member 4 in the axial direction is provided with material removal grooves 4A arranged equally in the circumferential direction, as shown in Figures 2, 5, and 6. Therefore, the annular outer resin member 5 covers the outer circumference of the annular inner resin member 4 more narrowly on the end face side where the material removal grooves 4A are located, up to the area in front of the material removal grooves 4A, while the other end face side in the axial direction of the annular inner resin member 4 covers a wider area radially inward than the end face side.

[0025] The annular inner resin member 4 is made of synthetic resin reinforced with a reinforcing material such as glass fiber, while the annular outer resin member 5 is made of synthetic resin not reinforced with the aforementioned reinforcing material. In other words, the annular inner resin member 4 and the annular outer resin member 5 are made of different materials. "Different materials" includes not only cases where the polymers are different, but also cases where the polymers are the same but the reinforcing material content is different.

[0026] The annular resin portion 3 does not necessarily have to consist of an annular inner resin member 4 and an annular outer resin member 5. In other words, the annular resin portion 3 may be a single piece made of synthetic resin that does not contain reinforcing materials such as glass fibers.

[0027] (Meat theft from the area) As shown in the longitudinal cross-sectional side view of Figure 2, the annular outer resin member 5 of the annular resin part 3 has axial material removals 5A and 5B on both axial end faces B and C. As shown in the enlarged front view of the main part of Figure 3, the axial material removals 5A and 5B are located between adjacent tooth grooves G, G in the circumferential direction of the power transmission resin gear A, and are spaced apart in the circumferential direction and arranged equally in the circumferential direction.

[0028] <Pre-cut molded body for power transmission resin gears> The pre-measuring molded body 1 of the resin gear A for power transmission, shown in the perspective views of Figures 4 and 5, the longitudinal cross-sectional side view of Figure 6, and the enlarged front view of the main part of Figure 7, is a molded body of the resin gear A for power transmission before teeth T (Figure 1) are provided.

[0029] On the outer circumferential surface of the annular outer resin member 5 of the annular resin part 3, there is a recessed groove 6 with a cutting allowance provided at the position where the tooth grooves G (Figure 1) of the teeth T of the power transmission resin gear A are to be provided.

[0030] (Meat theft from the area) The annular outer resin member 5 of the annular resin part 3 has axial material removal grooves 5A and 5B spaced apart in the circumferential direction and arranged at equal intervals in the circumferential direction. As shown in Figures 6 and 7, the axial material removal grooves 5A and 5B are located between adjacent grooves 6, 6 in the circumferential direction, that is, between adjacent tooth grooves G, G of the power transmission resin gear A (Figure 3) in the circumferential direction.

[0031] As shown in Figure 6, the axial material removal 5A is formed by a shallow recess where the annular outer resin member 5 covers the surface of the annular inner resin member 4, a deeper recess located radially outward from the shallow recess, and a curved surface connecting the shallow recess and the deep recess. As shown in Figure 6, the axial material removal 5B is formed by a deep recess located on the opposite side in the axial direction from the deep recess of the axial material removal 5A.

[0032] For example, referring to Figure 7, the radial positions of the axial material removals 5A and 5B are set to be at least 2 mm radially inward from the outer diameter of the annular outer resin member 5, and radially inward from the innermost part of the groove 6. Furthermore, since the tooth roots and their vicinity are the areas where the greatest strength is required in the resin gear A for power transmission, the tooth root width (Wa + Wb) in the parts where the axial material removals 5A and 5B shown in Figures 2 and 6 are set is set to (W / 4) ≤ (Wa + Wb) ≤ (W / 3) with respect to the axial width W of the outer diameter of the annular outer resin member 5, and Wa and Wb are distributed to the center in the width direction of width W (the dashed line Wo in Figures 2 and 6), with Wa ≥ (W / 8) and Wb ≥ (W / 8). This makes it possible to achieve both tooth root strength and moldability in injection molding, which is the challenge of the present invention.

[0033] Although the axial material removal may be formed on one end face in the axial direction of the annular outer resin member 5, forming it on both axial ends of the annular outer resin member 5 makes it less susceptible to deformation due to molding shrinkage, thus preventing deterioration of the shape accuracy of the molded body 1 before gear cutting.

[0034] When forming axial material removal on one axial end face of the annular outer resin member 5, refer to Figures 2 and 6 and set Wa and Wb as follows: If there is no material removal 5a on the Wa side but there is material removal 5b on the Wb side, then (W / 8)≦Wb≦(W / 6), and if there is no material removal 5b on the Wb side but there is material removal 5a on the Wa side, then (W / 8)≦Wa≦(W / 6). This makes it possible to achieve both tooth root strength and moldability in injection molding, which is the problem of the present invention.

[0035] As shown in Figure 3, when viewing the resin gear A for power transmission from the front (either the axial end or the other end), it is desirable that the wall thickness between the outer diameter side of the axial material removal 5A, 5B and the tooth groove G be at least 2 mm and no more than 3 mm at its minimum. By setting it in this way, it is possible to maintain the strength of the tooth T in the approximately circumferential direction while ensuring moldability in injection molding, which is the problem of the present invention, in relation to the recessed groove 6 with a machining allowance.

[0036] (Injection molding of annular inner resin component) As described above, the annular inner resin member 4 of the annular resin portion 3 is made of synthetic resin reinforced with a reinforcing material such as glass fiber, and the binder synthetic resin is a thermoplastic resin or a thermosetting resin.

[0037] As shown in the perspective view of Figure 5, the annular inner resin member 4 has axial material removals 4A arranged equally in the circumferential direction and spaced apart at the circumferential direction on one end face in the axial direction. The annular inner resin member 4 is injection molded by setting the round shaft of a disc-shaped insert core (not shown) fitted into the inner diameter hole 2A of the mandrel 2 in an injection molding die. The axial material removals 4A are formed by axially projecting protrusions provided on the insert core.

[0038] By providing the axial material removal 4A in the annular inner resin member 4, the weight of the molded body 1 before gear cutting can be reduced. Furthermore, the volume of the annular inner resin member 4 is reduced, shortening the solidification time and thus shortening the molding cycle.

[0039] (Injection molding of annular outer resin component) As described above, the annular outer resin member 5 of the annular resin portion 3 is made of synthetic resin that is not reinforced with reinforcing materials such as glass fibers, and the synthetic resin is a thermoplastic resin.

[0040] The injection molding of the annular outer resin member 5 is performed by setting the insert core, mandrel 2, and annular inner resin member 4 in an injection molding die. The injection molding of the annular outer resin member 5 forms the axial material removal 5A and 5B on the axial end face, and the recessed groove 6 on the outer circumferential surface.

[0041] In the pre-gear cutting molded body 1 with the above configuration, there are axial material removals 5A and 5B between adjacent tooth grooves G, G in the circumferential direction of the power transmission resin gear A. Therefore, the thickness of the resin in the area where teeth are made during gear cutting does not increase, so there is no need to increase the holding pressure in the holding pressure process to suppress voids, which are defects in thick-walled molded products, and there is no need to lengthen the holding pressure process time. Furthermore, since the solidification rate is not as slow as that of thick-walled molded products, there is no need to lengthen the cooling process time from the completion of the holding pressure process to the start of mold opening. Therefore, the molding cycle can be shortened. Moreover, because of the axial material removals 5A and 5B, the pre-gear cutting molded body 1 can be made lighter.

[0042] <Gear cutting process> When performing gear cutting on the pre-cut molded body 1 shown in Figures 4 and 7 to complete a resin gear A for power transmission with teeth T as shown in Figures 1 and 3, the tooth grooves G of the tooth groove T are provided around the entire circumference, using the position of the recessed groove 6 on the outer surface of the pre-cut molded body 1 as a reference. By cutting the tooth groove G using the position of the recessed groove 6 as a reference, the axial material removal 5A, 5B and the tooth groove G do not interfere with each other.

[0043] The groove 6 provided on the outer circumferential surface of the annular outer resin member 5 of the annular resin part 3 only needs to serve as a reference when cutting the gear groove G, so it may be provided in only one place as shown in the perspective view of Figure 8; in other words, at least one groove 6 is sufficient. However, providing the groove 6 around the entire circumference as shown in Figure 4 reduces the amount of resin used for molding, thus reducing material costs.

[0044] The embodiments described above are all illustrative and not limiting. Various improvements and modifications can be made without departing from the scope of the present invention. [Explanation of symbols]

[0045] 1. Molded body of resin gear for power transmission before gear cutting. 2. Core 2A inner diameter hole 3. Annular resin part 4. Annular inner resin member 4A Axial meat stealing 5. Annular outer resin member 5A, 5B Axial material removal 6. Grooves A Resin gear for power transmission End faces in the B and C axes G tooth groove O axis center T tooth W Axial width of the outer diameter portion of the annular outer resin member Wo centered in width

Claims

1. A molded body before the teeth of a resin gear for power transmission are attached, It consists of a core metal and an annular resin part that covers the outer circumference of the core metal, On the outer surface of the annular resin portion, there is at least one recessed groove with a cutting allowance at the position where the tooth grooves of the teeth are to be provided. The axial end face of the annular resin portion has axial material removal at positions between adjacent tooth grooves in the circumferential direction of the power transmission resin gear. The radial position of the axial material removal is at least 2 mm radially inward from the outer diameter of the annular resin portion, and radially inward from the innermost part of the groove. A molded body of a resin gear for power transmission before gear cutting.

2. The annular resin portion consists of an annular inner resin member and an annular outer resin member made of a different material from the annular inner resin member. The annular inner resin member covers the outer circumference of the core metal, The annular outer resin member covers the outer circumference of the annular inner resin member, The annular outer resin member has the aforementioned groove on its outer surface, The annular outer resin member has the axial material removal on its axial end face. A molded body of a resin gear for power transmission according to claim 1, before gear cutting.

3. The aforementioned groove extends around the entire circumference at the position where the tooth groove of the tooth is provided. A molded body of a resin gear for power transmission according to claim 1, before gear cutting.

4. The aforementioned axial material removal is located on both axial end faces of the annular resin portion. A molded body of a resin gear for power transmission according to claim 1, before gear cutting.

5. A resin gear for power transmission, wherein the tooth grooves of the teeth are provided around the entire circumference with reference to the position of the recessed groove in the molded body before tooth cutting according to any one of claims 1 to 4.

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