Resin gear for power transmission, and method for manufacturing a resin gear for power transmission

Abstract

To provide a resin gear for power transmission that can suppress deformation caused by forced extraction without requiring a special tooth shape. [Solution] This is a resin gear 1 for power transmission in which gear teeth 10 are provided on the outer circumferential surface of an annular resin part 3. The annular resin part 3 consists of an annular inner resin member 4 that covers the outer circumference of the core metal 2 and an annular outer resin member 5 that covers the outer circumference of the annular inner resin member 4. The annular inner resin member 4 has a plurality of axial material removal portions 6 that are spaced apart in the circumferential direction. The annular outer resin member 5 has a filling portion 8 that fills the axial material removal portions 6 and an axial surface cover portion 9 that covers the filling portion 8 and is located radially inward RI of the side portion 10C of the teeth 10.

Description

Technical Field

[0001] The present invention relates to a resin gear for power transmission composed of 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 worm wheel used in combination with a worm of a worm gear reducer, for example, which is a resin gear for power transmission composed of a core metal and an annular resin part covering the outer periphery thereof (see, for example, Patent Documents 1 to 3).

[0003] When forming the teeth of the worm wheel formed on the outer peripheral surface of the annular resin part by injection molding, the teeth have an undercut shape with respect to the mold for forming the teeth. Therefore, when taking out the worm wheel, which is a molded product, from the mold, forced ejection is required, so the teeth of the worm wheel taken out from the mold are deformed.

[0004] In Patent Document 1, a mold structure is adopted in which a large number of slide cores for forming tooth grooves are arranged radially around the core, and the slide cores are supported so as to be able to advance and retreat in the radial direction. Thereby, forced ejection is avoided.

[0005] In Patent Document 2, the tooth bottom at half of the tooth width of the teeth on the side far from the mold parting surface of the mold whose mold opening and closing direction is the axial direction is formed into a special tooth shape parallel to the axial direction. Thereby, forced ejection is avoided.

[0006] In Patent Document 3, the shape of the teeth on the side far from the mold parting surface of the mold whose mold opening and closing direction is the axial direction is formed into a special tooth shape with a smaller undercut amount. Thereby, forced ejection is enabled.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] When a mold structure including the slide core, as described in Patent Document 1, is adopted, the difficulty of mold manufacturing is high, the mold becomes large, mold costs increase, and productivity decreases. Furthermore, there is a concern that the quality of the molded product will deteriorate due to burrs that form on the dividing surface of the slide core.

[0009] When using the special tooth profile described in Patent Document 2, it is necessary to change the design specifications of the worm wheel's tooth profile. Furthermore, as the tooth thickness of the worm wheel decreases and the contact surface with the worm that meshes with it decreases, the strength of the worm wheel is reduced.

[0010] When creating the special tooth profile as described in Patent Document 3, it is necessary to change the design specifications of the worm wheel's tooth profile. Furthermore, because forced extraction is performed, deformation of the molded product cannot be suppressed.

[0011] The present invention aims to provide a resin gear for power transmission that can suppress deformation due to forced extraction without requiring a special tooth shape. [Means for solving the problem]

[0012] A resin gear for power transmission according to a first aspect of the present invention is a resin gear for power transmission in which gear teeth are provided on the outer circumferential surface of an annular resin portion. The annular resin portion consists of an annular inner resin member that covers the outer circumference of a core metal and an annular outer resin member that covers the outer circumference of the annular inner resin member. The annular inner resin member has a plurality of axial material removal portions that are spaced apart in the circumferential direction. The annular outer resin member has a filling portion that fills the axial material removal portions and an axial surface cover portion that covers the filling portion and is located radially inward on the side of the teeth.

[0013] A resin gear for power transmission according to a second aspect of the present invention is a resin gear for power transmission according to a first aspect, wherein the teeth have a root shape that follows the outer circumference shape of the worm, and the tooth surface is a curved surface with an arc shape, and is a worm wheel used as a worm reducer in combination with the worm.

[0014] A resin gear for power transmission according to a third aspect of the present invention is a resin gear for power transmission according to a first or second aspect, wherein a plurality of axial protrusions are spaced apart in the circumferential direction on the outer circumferential surface of the annular inner resin member, which is radially inward of the teeth on the outer circumferential surface of the annular outer resin member, and the axial material removal portion is radially inward of the axial protrusions.

[0015] A method for manufacturing a resin gear for power transmission according to a fourth aspect of the present invention is a method for manufacturing a resin gear for power transmission in which gear teeth are provided on the outer circumferential surface of an annular resin portion. The annular resin portion consists of an annular inner resin member that covers the outer circumference of a mandrel and an annular outer resin member that covers the outer circumference of the annular inner resin member. The annular inner resin member has a plurality of axial material removal portions that are spaced apart in the circumferential direction. The annular outer resin member has a filling portion that fills the axial material removal portions and an axial surface cover portion that covers the filling portion and is located radially inward on the side of the teeth.

[0016] The manufacturing method comprises a primary molding step and a secondary molding step. In the primary molding step, the core is set in a primary molding die with the mold opening direction axial, and molten primary molding resin is injected into the cavity of the primary molding die to injection mold the annular inner resin member, thereby producing a primary molded body consisting of the core and the annular inner resin member. In the secondary molding step, the primary molded body is set in a secondary molding die with the mold opening direction axial, and molten secondary molding resin is injected into the cavity of the secondary molding die to injection mold the annular outer resin member on which the teeth are provided. The filling portion and the axial surface cover portion of the annular outer resin member are located on the mold splitting surface side of the secondary molding die.

[0017] In the resin gear for power transmission and the method for manufacturing the resin gear for power transmission according to the present invention as described above, the annular resin portion of the resin gear for power transmission comprises an annular inner resin member that covers the outer circumference of the mandrel and an annular outer resin member that covers the outer circumference of the annular inner resin member. The annular inner resin member has a plurality of axial material removal portions that are spaced apart in the circumferential direction. The annular outer resin member has a filling portion that is filled in the axial material removal portions of the annular inner resin member and an axial surface cover portion that covers the filling portion and is located radially inward on the side of the tooth.

[0018] When forming the power transmission resin gear by setting the primary molded body, consisting of the core metal and the annular inner resin member, into a secondary molding die, the filling portion and the axial surface cover portion are located on the mold splitting surface side of the secondary molding die. When demolding the molded product from the secondary molding die, the amount of radial outward deformation of the teeth is reduced by the axial material removal portion of the annular inner resin member, located radially inward on the side of the teeth, and the filling portion and axial surface cover portion of the annular outer resin member. Furthermore, the teeth on the outer circumferential surface of the annular outer resin member, which have been deformed radially outward due to forced demolding, are returned radially inward after demolding by the molding shrinkage of the axial surface cover portion that covers the filling portion, located radially inward on the side of the teeth, thus further reducing the amount of deformation due to forced demolding. [Effects of the Invention]

[0019] According to the resin gear for power transmission and the method for manufacturing the resin gear for power transmission of the present invention, deformation due to forced extraction can be suppressed without creating a special tooth shape, thanks to the axial material removal portion of the annular inner resin member and the filling portion of the annular outer resin member that is filled in the axial material removal portion and the axial surface cover portion that covers the filling portion and is located radially inward on the side of the tooth. [Brief explanation of the drawing]

[0020] [Figure 1] This is a perspective view of a resin gear for power transmission according to an embodiment of the present invention. [Figure 2]It is a front view of the resin gear for power transmission. [Figure 3] It is a longitudinal sectional view of the resin gear for power transmission. [Figure 4] It is a perspective view of the primary molded body according to an embodiment of the present invention. [Figure 5] It is a front view of the primary molded body. [Figure 6] It is a perspective view of the mandrel according to an embodiment of the present invention. [Figure 7A] It is a longitudinal sectional view showing a state where an annular outer resin member is injection-molded in the secondary molding process, and the fixed-side mold etc. are omitted. [Figure 7B] It is a longitudinal sectional view showing a state in the middle of taking out the molded product from the secondary molding die after injection molding and cooling and solidifying in the secondary molding process. [Figure 7C] It is a longitudinal sectional view of the molded product taken out from the secondary molding die. [Figure 8] It is a first modification example of the axial undercut portion of the annular inner resin member. [Figure 9] It is a second modification example of the axial undercut portion of the annular inner resin member. [Figure 10] It is a third modification example of the axial undercut portion of the annular inner resin member. [Figure 11] It is a fourth modification example of the axial undercut portion of the annular inner resin member.

Embodiments for Carrying Out the Invention

[0021] Next, embodiments of the present invention will be described in detail based on the accompanying drawings.

[0022] In this specification, the direction parallel to the axis of the rotation axis of the resin gear 1 for power transmission (reference symbol O in FIGS. 2-3) is referred to as the "axial direction" (reference symbol J), and based on the axis, the "radial direction" and the "circumferential direction" (reference symbol C) are defined. The radial direction approaching the axis is the "radially inward" (reference symbol RI), and the radial direction moving away from the axis is the "radially outward" (reference symbol RO). The view seen from the axial direction is the front view.

[0023] [Resin gears for power transmission] As shown in Figure 1-3, the power transmission resin gear 1 consists of a metal core 2 and an annular resin part 3 covering its outer circumference. Teeth 10 are formed on the outer surface of the annular resin part 3 at equal intervals C in the circumferential direction.

[0024] In this embodiment, the resin gear 1 for power transmission is a worm wheel W that meshes with a worm. As shown in Figures 1 and 3, the tooth 10 has a tooth root 10A that is arc-shaped and follows the outer circumference of the worm, and a tooth surface 10B that is an arc-shaped curved surface. A worm gear reducer consisting of a worm wheel W and a worm is used, for example, in electric power steering.

[0025] (Core metal) The core metal 2 is, for example, an annular sleeve as shown in Figure 1-3, but it may also be a shaft portion rather than an annular sleeve.

[0026] (Annular resin part) As shown in Figure 1-3, 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. The annular inner resin member 4 is made of synthetic resin reinforced with a reinforcing material such as glass fiber. The annular outer resin member 5 is made of synthetic resin not reinforced with the aforementioned reinforcing material, but may also be made of synthetic resin reinforced with the aforementioned reinforcing material.

[0027] (Affordable Meat Theft Club) As shown in Figure 2-5, the annular inner resin member 4 has a plurality of axial material removal portions 6 arranged spaced apart in the circumferential direction C on one surface in the axial direction J. As shown in Figure 3, the annular inner resin member 4 has a plurality of axial material removal portions 7 arranged spaced apart in the circumferential direction C on the other surface in the axial direction J.

[0028] As shown in Figure 2, the axial material removal portion 6 is located radially inward RI of the tooth 10 of the resin gear 1 for power transmission. Similarly, the axial material removal portion 7 shown in Figure 3 is also located radially inward RI of the tooth 10.

[0029] (Filling section and axial surface cover section) As shown in Figure 1-3, the annular outer resin member 5 has a filling portion 8 that fills the axial material removal portion 6, and an axial surface cover portion 9 that covers the filling portion 8 and is located radially inward RI of the side portion 10C of the tooth 10. The axial thickness T of the axial surface cover portion 9 shown in Figure 3 is 1 mm or more (T ≥ 1 mm). If the thickness T is less than 1 mm (T < 1 mm), there is a concern that the flow of resin to the axial material removal portion 6 during injection molding of the annular outer resin member 5 will be poor, resulting in insufficient molding of the filling portion 8.

[0030] (Gate remains) As shown in Figure 1-3, the resin gear 1 for power transmission has gate marks G2 that occur when the annular outer resin member 5, which includes the teeth 10, is injection molded, and these gate marks G2 are located on one surface in the axial direction J, i.e., on the surface where the axial surface cover portion 9 is located.

[0031] [Manufacturing method for resin gears for power transmission] The manufacturing method for the resin gear 1 for power transmission consists of a primary molding step and a secondary molding step. In the primary molding step, a core metal 2 is used as an insert workpiece, and an annular inner resin member 4 is injection molded to manufacture a primary molded body A. In the secondary molding step, the primary molded body A is used as an insert workpiece, and an annular outer resin member 5 is injection molded to manufacture the resin gear 1 for power transmission.

[0032] (Primary molded body) As shown in Figure 4-5, the primary molded body A consists of a core metal 2 and an annular inner resin member 4. The outer surface of the annular inner resin member 4 has axial protrusions 11 formed at equal intervals C in the circumferential direction, and there are axial material removal portions 6 and 7 radially inward RI of the axial protrusions 11.

[0033] (Primary molding process) With the core metal 2 shown in Figure 6 set in a primary molding die whose opening and closing direction is axial J, primary molding molten resin is injected into the cavity of the primary molding die from the gate of the primary molding die to injection mold the annular inner resin member 4, thereby manufacturing a primary molded body A consisting of the core metal 2 and the annular inner resin member 4.

[0034] The gate of the primary molding die is, for example, a pin gate. This eliminates the need for a gate processing step, as the molded product can be separated from the runner by opening the primary molding die. As shown in Figure 4-5, the gate mark G1 that occurs when the annular inner resin member 4 of the primary molded body A is injection molded is located on one surface side in the axial direction J where the axial material removal portion 6 is located.

[0035] In the primary molded body A, axial protrusions 12 are formed on the outer surface of the core metal 2 at equal intervals C in the circumferential direction, as shown in Figure 6, so that the annular inner resin member 4 is prevented from rotating relative to the core metal 2.

[0036] The axial protrusions 11 on the outer surface of the primary molded body A (annular inner resin member 4) shown in Figure 4-5 are not undercut in shape with respect to the primary molding die where the mold opening and closing direction is axial J, so that the primary molded body A is not forcibly removed when it is removed from the primary molding die.

[0037] (Secondary molding process) With the primary molded body A set in a secondary molding die whose opening and closing direction is axial J, the secondary molding molten resin is injected into the cavity of the secondary molding die from the gate of the secondary molding die, thereby injection molding an annular outer resin member 5 provided with teeth 10, and manufacturing a power transmission resin gear 1 consisting of a core metal 2, an annular inner resin member 4, and an annular outer resin member 5. The teeth 10 shown in Figure 1-2 are formed when the annular outer resin member 5 is molded by injection molding, so there is no need to perform gear cutting after the secondary molding process.

[0038] The gate of the secondary molding die is, for example, a pin gate. This eliminates the need for a gate processing step, as the molded product can be separated from the runner by opening the secondary molding die. As shown in Figure 1-3, the gate mark G2 that occurs when the annular inner resin member 5 of the power transmission resin gear 1 is injection molded is located on one surface side in the axial direction J where the axial surface cover portion 9 is located.

[0039] As shown in Figures 4-5, axial protrusions 11 are formed on the outer circumferential surface of the primary molded body A (annular inner resin member 4) at equal intervals C in the circumferential direction, so that the annular outer resin member 5 is prevented from rotating relative to the primary molded body A. As shown in Figures 2 and 5, the axial protrusions 11 of the annular inner resin member 4 are located radially inward RI of the teeth 10 of the annular outer resin member 5, and there is an axial material removal portion 6 radially inward RI of the axial protrusions 11.

[0040] As shown in Figure 7A, the secondary molding die D has a filling portion 8 and an axial surface cover portion 9 of the annular outer resin member 5 on the PL side of the mold splitting surface.

[0041] As shown in Figures 1 and 3, the teeth 10 on the outer surface of the annular outer resin member 5 have a tooth root 10A that is arc-shaped and follows the outer shape of the worm, and a tooth surface 10B that is an arc-shaped curved surface. Therefore, it has an undercut shape with respect to a secondary molding die (for example, the movable side die M, which is the secondary molding die D in Figure 7A) whose opening and closing direction is axial J.

[0042] Therefore, after the injection molding and cooling solidification process in the secondary molding stage, when the secondary molding mold D shown in Figure 7A is opened and the molded resin gear 1 for power transmission is ejected from the movable mold M as shown by arrow E in Figure 7B, it becomes a forced ejection.

[0043] Therefore, when removing the molded power transmission resin gear 1 from the movable mold M, the deformation of the power transmission resin gear 1 propagates as the point pressed by the protrusion H of the movable mold M moves. Since the portion of the power transmission resin gear 1 that has emerged from the mold splitting surface PL is no longer constrained by the movable mold M, the side portion 10C of the teeth 10 of the annular outer resin member 5, that is, the side end of the teeth 10 on the side where the filling portion 8 and the axial surface cover portion 9 of the annular outer resin member 5 are located, attempts to deform radially outward RO as shown by arrow F1 in Figure 7B.

[0044] [Effects of the axial material removal section, filling section, and axial surface cover section] In a resin gear 1 for power transmission according to an embodiment of the present invention, the annular resin portion 3 consists of an annular inner resin member 4 that covers the outer circumference of the core metal 2 and an annular outer resin member 5 that covers the outer circumference of the annular inner resin member 4. The annular inner resin member 4 has a plurality of axial material removal portions 6 spaced apart in the circumferential direction C. The annular outer resin member 5 has a filling portion 8 that fills the axial material removal portions 6 of the annular inner resin member 4 and an axial surface cover portion 9 that covers the filling portion 8 and is located radially inward RI of the side portion 10C of the tooth 10.

[0045] Therefore, when the molded resin gear 1 for power transmission is released from the secondary molding die D, the amount of deformation of the tooth 10 radially outward RO is reduced by the axial material removal portion 6 of the annular inner resin member 4, located radially inward RI of the side portion 10C of the tooth 10, and the filling portion 8 and axial surface cover portion 9 of the annular outer resin member 5.

[0046] Furthermore, as shown in Figure 7C, when the molded resin gear 1 for power transmission is removed from the secondary molding die D, the teeth 10 on the outer surface of the annular outer resin member 5, which have been deformed radially outward RO due to forced removal, are returned to radially inward RI as shown by arrow F2 due to the molding shrinkage of the axial surface cover portion 9 that covers the filling portion 8, located radially inward RI of the side portion 10C of the teeth 10. Thus, the deformation due to forced removal is further reduced.

[0047] As described above, the axial thickness T of the axial surface cover portion 9 is 1 mm or more (T ≥ 1 mm), so the filling portion 8 is formed to fill the axial material removal portion 6, and due to the molding shrinkage of the axial surface cover portion 9, the force pulling the tooth 10 radially inward RI, as shown by arrow F2 in Figure 7C, has the desired strength. If T < 1 mm, there is a concern that the force pulling the tooth 10 radially inward RI will be weaker.

[0048] The amount of radial outward deformation of the tooth 10 due to forced extraction is reduced to, for example, 20% or less compared to the case without the axial material removal portion 6, filling portion 8, and axial surface cover portion 9. Therefore, deformation due to forced extraction can be suppressed without creating a special tooth profile.

[0049] [Trimming of the axial meat-stealing area] The shape of the axial material removal portion provided on the annular inner resin member 4 is not limited to the axial material removal portion 6 which is roughly rectangular in shape when viewed from the axial direction J, as shown in Figures 3 and 5. For example, as shown in the first modified example in Figure 8, the axial material removal portion 6 may be divided into two radially, resulting in axial material removal portions 6A and 6B, or axial material removal portions 6C and 6D which are roughly triangular when viewed from the axial direction J, as shown in the second modified example in Figure 9, may be combined.

[0050] The combination of axial material removal portions that are roughly triangular when viewed from the axial direction J may be axial material removal portions 6E, 6F as in the third modified example in Figure 10, or axial material removal portions 6G, 6H as in the fourth modified example in Figure 11.

[0051] 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]

[0052] 1. Resin gear for power transmission 2 Mandrel 3. Annular resin part 4. Annular inner resin member 5. Annular outer resin member 6, 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 7 Axial material removal section 8 Filling section 9. Axial surface cover portion 10 teeth 10A tooth root 10B Tooth surface 10C Side 11,12 Axial convexity A Primary molded body C circumferential direction D Secondary molding mold H protrusion G1, G2 Gate Site J-axis direction M Mobile type O Axis of the rotation axis PL mold cutting surface RI radially inward RO radially outward T-axis surface cover portion axial thickness W Worm Wheel

Claims

1. A resin gear for power transmission, in which gear teeth are provided on the outer surface of an annular resin part, The annular resin portion consists of an annular inner resin member that covers the outer circumference of the core metal and an annular outer resin member that covers the outer circumference of the annular inner resin member. The annular inner resin member has a plurality of axial material removal portions that are spaced apart in the circumferential direction, The annular outer resin member has a filling portion that fills the axial material removal portion and an axial surface cover portion that covers the filling portion and is located radially inward on the side of the tooth. Resin gears for power transmission.

2. The tooth has a root that is arc-shaped and follows the outer circumference of the worm, and a tooth surface that is a curved surface with an arc shape. This is a worm wheel used in combination with the aforementioned worm as a worm gear reducer. A resin gear for power transmission according to claim 1.

3. On the outer circumferential surface of the annular inner resin member, radially inward from the teeth on the outer circumferential surface of the annular outer resin member, there are a plurality of axial protrusions spaced apart in the circumferential direction, and the axial material removal portion is located radially inward from the axial protrusions. A resin gear for power transmission according to claim 1 or 2.

4. A method for manufacturing a resin gear for power transmission, wherein gear teeth are provided on the outer surface of an annular resin part, The annular resin portion consists of an annular inner resin member that covers the outer circumference of the core metal and an annular outer resin member that covers the outer circumference of the annular inner resin member. The annular inner resin member has a plurality of axial material removal portions that are spaced apart in the circumferential direction, The annular outer resin member has a filling portion that fills the axial material removal portion and an axial surface cover portion that covers the filling portion and is located radially inward on the side of the tooth. The above manufacturing method consists of a primary molding step and a secondary molding step. The aforementioned primary molding process is: With the core metal set in a primary molding die whose opening and closing direction is axial, molten resin for primary molding is injected into the cavity of the primary molding die to injection mold the annular inner resin member, thereby producing a primary molded body consisting of the core metal and the annular inner resin member. The aforementioned secondary molding process is With the primary molded body set in a secondary molding die whose opening and closing direction is axial, molten resin for secondary molding is injected into the cavity of the secondary molding die to injection mold the annular outer resin member on which the teeth are provided. The filling portion and the axial surface cover portion of the annular outer resin member are located on the mold splitting surface side of the secondary molding die. A method for manufacturing resin gears for power transmission.

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