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

Abstract

[Problem] To provide a power transmission resin gear capable of suppressing deformation caused by forced extraction without forming a specially shaped tooth profile. [Solution] A power transmission resin gear (1) in which gear teeth (10) are provided on the outer peripheral surface of an annular resin part (3). The annular resin section (3) is configured from an annular inner resin member (4) that covers the outer periphery of the core rod (2), and an annular outer resin member (5) that covers the outer periphery of the annular inner resin member (4). The annular inner resin member (4) has a plurality of axially thinned portions (6) arranged separately in the circumferential direction. The annular outer resin member (5) has a filling part (8) that fills the axial thinned part (6), and an axial surface cover part (9) that covers the filling part (8) and is positioned on the inside RI in the radial direction of the side part (10C) of the tooth (10).

Description

Technical Field

[0001] The present invention relates to a resin gear for power transmission, which is composed of a mandrel and an annular resin part. Background Technology

[0002] In order to meet the requirements of lightweight and quiet operation, a power transmission resin gear consisting of a mandrel and an annular resin part covering its outer periphery is used, for example, as a worm gear used in combination with the worm of a worm gear reducer (see, for example, Patent Documents 1-3).

[0003] When the worm gear is formed by injection molding the teeth of the worm gear formed on the outer peripheral surface of the annular resin portion, the teeth are undercut relative to the mold forming the teeth. Therefore, when the worm gear as a molded product is removed from the mold, it is forcibly pulled out, and thus the teeth of the worm gear removed from the mold are deformed.

[0004] In Patent Document 1, a mold structure is used in which multiple sliding cores for forming toothed grooves are arranged radially around the core, and the sliding cores are supported to allow for radial movement. This avoids forced removal.

[0005] In Patent Document 2, the tooth root of half the tooth width of the tooth on the side of the mold parting surface away from the mold opening and closing direction (which is axial) is set into a special tooth shape that is parallel to the axial direction. This avoids forced removal.

[0006] In Patent Document 3, the shape of the teeth on the side of the mold parting surface away from the mold opening and closing direction (axial direction) is set to a special tooth shape with a smaller undercut. This allows for forced extraction.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2002-254478 Patent Document 2: Japanese Utility Model Application Publication No. 4-49254 Patent Document 3: Japanese Patent Application Publication No. 2009-41595 Summary of the Invention

[0008] The problem that the invention aims to solve When using a mold structure including the sliding core as described in Patent Document 1, the mold is difficult to manufacture, the mold becomes large, the mold cost increases, and productivity decreases. Moreover, the quality of the molded product may be reduced due to burrs generated on the dividing surface of the sliding core.

[0009] When the tooth profile is designed with the special shape described in Patent Document 2, the design specifications of the worm gear tooth profile need to be changed. Moreover, the tooth thickness of the worm gear becomes thinner, and the contact surface of the worm meshing with the worm gear is reduced, thus reducing the strength of the worm gear.

[0010] When the tooth profile is designed with the special shape described in Patent Document 3, the design specifications of the worm gear tooth profile need to be changed. Moreover, due to forced extraction, deformation of the molded product cannot be suppressed.

[0011] The purpose of this invention is to provide a resin gear for power transmission that can suppress deformation caused by forced extraction without forming a special tooth shape.

[0012] Methods for solving problems The first aspect of the present invention discloses a power transmission resin gear having gear teeth provided on the outer circumferential surface of an annular resin portion. The annular resin portion is composed of an inner annular resin component covering the outer circumference of a mandrel and an outer annular resin component covering the outer circumference of the inner annular resin component. The inner annular resin component has a plurality of axially thinned portions arranged circumferentially. The outer annular resin component has a filling portion filling the axially thinned portions and an axially facing portion covering the filling portions and located radially inward of the side portion of the teeth.

[0013] The second aspect of the present invention provides a resin gear for power transmission, which, in the first aspect of the present invention, has teeth that are arc-shaped with tooth roots along the outer periphery of the worm and tooth surfaces that are arc-shaped curved surfaces, and is combined with the worm to serve as a worm wheel in a worm gear reducer.

[0014] The third aspect of the present invention provides a power transmission resin gear in which, in the power transmission resin gear described in the first or second aspect, the outer peripheral surface of the inner annular resin component, located radially inside the teeth on the outer peripheral surface of the outer annular resin component, has a plurality of axially spaced ridges arranged separately in the circumferential direction, and the axially thinned portion is located radially inside the axial ridges.

[0015] The fourth aspect of the present invention discloses a method for manufacturing a power transmission resin gear, wherein gear teeth are provided on the outer peripheral surface of an annular resin portion. The annular resin portion comprises an inner annular resin component covering the outer periphery of a mandrel and an outer annular resin component covering the outer periphery of the inner annular resin component. The inner annular resin component has a plurality of axially thinned portions arranged separately in the circumferential direction. The outer annular resin component has a filling portion filling the axially thinned portions and an axially facing portion covering the filling portions and located radially inward of the side portion of the teeth.

[0016] The manufacturing method includes a primary molding process and a secondary molding process. In the primary molding process, with the mandrel placed inside a primary molding mold with the mold opening and closing direction axial, molten resin for primary molding is injected into the cavity of the primary molding mold to injection mold the annular inner resin component, thereby manufacturing a primary molded body composed of the mandrel and the annular inner resin component. In the secondary molding process, with the primary molded body placed inside a secondary molding mold with the mold opening and closing direction axial, molten resin for secondary molding is injected into the cavity of the secondary molding mold to injection mold the annular outer resin component, which has the teeth. The secondary molding mold has a filling portion and an axial cover portion for the annular outer resin component on the parting surface side.

[0017] In the power transmission resin gear and its manufacturing method according to the present invention, as described above, the annular resin portion of the power transmission resin gear is composed of an annular inner resin component covering the outer periphery of a mandrel and an annular outer resin component covering the outer periphery of the annular inner resin component. The annular inner resin component has a plurality of axially thinned portions arranged circumferentially. The annular outer resin component has a filling portion filling the axially thinned portions of the annular inner resin component and an axially masking portion covering the filling portion and located radially inward of the side portion of the tooth.

[0018] When the power transmission resin gear is formed by placing a primary molded body consisting of the mandrel and the annular inner resin component in a secondary molding mold, the filling portion and the axial cover portion are provided on the parting surface side of the secondary molding mold. When the molded article is demolded from the secondary molding mold, the amount of deformation of the tooth radially outward is reduced by the axial thinning portion of the annular inner resin component located radially inward on the side of the tooth, and by the filling portion and the axial cover portion of the annular outer resin component. In addition, the tooth on the outer peripheral surface of the annular outer resin component, which deforms radially outward due to forced pulling, returns radially inward after demolding due to the molding shrinkage of the axial cover portion covering the filling portion located radially inward on the side of the tooth, thus further reducing the amount of deformation caused by forced pulling.

[0019] Invention Effects According to the present invention, the power transmission resin gear and the manufacturing method of the power transmission resin gear, by means of the axially thinned portion of the annular inner resin component, the filling portion of the annular outer resin component filling the axially thinned portion, and the axially mask portion covering the filling portion and located radially inside the side of the tooth, deformation caused by forced pull-out can be suppressed without forming a special tooth shape. Attached Figure Description

[0020] Figure 1 This is a perspective view of a resin gear for power transmission according to an embodiment of the present invention.

[0021] Figure 2 This is a front view of the resin gear used for power transmission.

[0022] Figure 3 This is a longitudinal sectional view of the resin gear used for power transmission.

[0023] Figure 4 This is a perspective view of a one-piece molded body according to an embodiment of the present invention.

[0024] Figure 5 This is the front view of the one-piece molded body.

[0025] Figure 6 This is a perspective view of the mandrel according to an embodiment of the present invention.

[0026] Figure 7A This is a longitudinal sectional view showing the injection molding of the outer ring-shaped resin component during the secondary molding process, omitting the fixed side mold, etc.

[0027] Figure 7B It is a longitudinal sectional view showing the state of the molded product being removed from the secondary molding mold after injection molding and cooling solidification in the secondary molding process.

[0028] Figure 7C This is a longitudinal sectional view of the molded product taken out of the mold used for secondary molding.

[0029] Figure 8 This is a first variation of the axially thinned portion of the annular inner resin component.

[0030] Figure 9 This is a second variation of the axially thinned portion of the annular inner resin component.

[0031] Figure 10 This is a third variation of the axially thinned portion of the annular inner resin component.

[0032] Figure 11 This is the fourth variation of the axially thinned portion of the annular inner resin component. Detailed Implementation

[0033] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0034] In this specification, the axis of rotation of the resin gear 1 for power transmission will be ( Figures 2-3The direction parallel to the reference numeral O is called the "axial direction" (reference numeral J), and the "radial" and "circumferential" directions (reference numeral C) are defined with respect to the axis. The radial direction closer to the axis is designated as the "radial inner side" (reference numeral RI), and the radial direction farther from the axis is designated as the "radial outer side" (reference numeral RO). The view taken from the axial direction is used as the front view.

[0035] [Resin gears for power transmission] like Figures 1-3 As shown, the power transmission resin gear 1 consists of a metal core rod 2 and an annular resin portion 3 covering its outer periphery. Teeth 10 are formed on the outer peripheral surface of the annular resin portion 3 in a circumferentially divided C-shaped manner.

[0036] In this embodiment, the resin gear 1 for power transmission is a worm wheel W that meshes with the worm. For example... Figure 1 and Figure 3 As shown, the tooth root 10A of tooth 10 is an arc shape along the outer periphery of the worm, and the tooth surface 10B 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.

[0037] (Core rod) Core rod 2 is, for example, Figures 1-3 The sleeve shown is an annular shape, but it may also be a component with a shaft instead of an annular shape.

[0038] (Ring-shaped resin part) like Figures 1-3 As shown, the annular resin part 3 is composed of an inner annular resin component 4 and an outer annular resin component 5. The inner annular resin component 4 covers the outer periphery of the core rod 2, and the outer annular resin component 5 covers the outer periphery of the inner annular resin component 4. The inner annular resin component 4 is, for example, made of synthetic resin reinforced with a reinforcing material such as glass fiber. The outer annular resin component 5 is, for example, made of synthetic resin without the aforementioned reinforcing material, but it can also be made of synthetic resin reinforced with the aforementioned reinforcing material.

[0039] (Axial thinning section) like Figures 2-5 As shown, the annular inner resin component 4 has a plurality of axially thinned portions 6 arranged circumferentially C on one surface of the axial direction J. Figure 3 As shown, the annular inner resin component 4 has multiple axially thinned portions 7 arranged separately along the circumferential direction C on the other surface of the axial direction J.

[0040] like Figure 2 As shown, the axially thinned portion 6 is located radially inside the tooth 10 of the power transmission resin gear 1, RI. Figure 3 The axially thinned portion 7 shown is also located radially inside the tooth 10, RI.

[0041] (Filling section and axial mask section) like Figures 1-3 As shown, the annular outer resin component 5 has a filling portion 8 that fills the axially thinned portion 6 and an axial mask portion 9 that covers the filling portion 8 and is located on the radially inner side RI of the side portion 10C of the tooth 10. Figure 3 The axial thickness T of the axial mask portion 9 shown is 1 mm or more (T≥1 mm). When the thickness T is less than 1 mm (T<1 mm), the flow of resin to the axially thinned portion 6 is poor when the annular outer resin component 5 is injection molded, and the molding of the filling portion 8 may be insufficient.

[0042] (Gate marks) like Figures 1-3 As shown, in the resin gear 1 for power transmission, the gate mark G2 generated during injection molding of the annular outer resin component 5 including the tooth 10 is located on one surface of the axial direction J, that is, on the surface side where the axial mask part 9 is located.

[0043] [Manufacturing method of resin gears for power transmission] The manufacturing method of the resin gear 1 for power transmission consists of a primary molding process and a secondary molding process. In the primary molding process, a mandrel 2 is used as an insert workpiece, and the inner annular resin component 4 is injection molded to manufacture a primary molded body A. In the secondary molding process, the primary molded body A is used as an insert workpiece, and the outer annular resin component 5 is injection molded to manufacture the resin gear 1 for power transmission.

[0044] (One-piece molded body) like Figures 4-5 As shown, the one-piece molded body A is composed of a mandrel 2 and an annular inner resin component 4. An axial protrusion 11 is formed on the outer peripheral surface of the annular inner resin component 4 in a manner that divides it into equal parts in the circumferential direction C, and an axially thinned portion 6,7 is provided on the radially inner side RI of the axial protrusion 11.

[0045] (One-time molding process) In Figure 6 The mandrel 2 is set in a mold for primary molding with the mold opening and closing direction in the axial direction J. Molten resin for primary molding is injected into the cavity of the mold for primary molding from the gate of the mold for primary molding to perform injection molding on the annular inner resin component 4, thereby manufacturing a primary molded body A composed of the mandrel 2 and the annular inner resin component 4.

[0046] The gate of the mold used for one-time molding is, for example, a needle-type gate. Therefore, by opening the mold, the molded article can be cut off from the runner, thus eliminating the need for a gate processing step. Figures 4-5As shown, the gate mark G1 generated during injection molding of the annular inner resin component 4 in the one-piece molded body A is, for example, located on one surface side of the axial J of the axially thinned portion 6.

[0047] In a one-piece molded body A, on the outer peripheral surface of the mandrel 2, as follows: Figure 6 As shown, axial protrusions 12 are formed in equal sections along the circumferential direction C, thus preventing the inner annular resin component 4 from rotating relative to the mandrel 2.

[0048] Figures 4-5 The axial protrusion 11 on the outer peripheral surface of the one-piece molded body A (circular inner resin component 4) is not undercut relative to the mold opening and closing direction of the mold. Therefore, it will not be forcibly pulled out when the one-piece molded body A is removed from the mold.

[0049] (Secondary molding process) With the primary molded body A placed inside a secondary molding mold with the mold opening and closing direction in the axial direction J, molten resin for secondary molding is injected into the cavity of the secondary molding mold through the gate of the secondary molding mold, thereby injection molding the annular outer resin component 5 with teeth 10, and manufacturing a power transmission resin gear 1 composed of a mandrel 2, an annular inner resin component 4 and an annular outer resin component 5. Figures 1-2 The tooth 10 shown is formed when the annular outer resin component 5 is formed by injection molding, so there is no need to perform tooth cutting after the secondary molding process.

[0050] The gate of the secondary molding mold is, for example, a needle-shaped gate. Therefore, by opening the secondary molding mold, the molded product can be cut off from the runner, thus eliminating the need for a gate processing step. Figures 1-3 As shown, the gate mark G2 generated during injection molding of the annular inner resin component 5 in the power transmission resin gear 1 is located on one surface side of the axial direction J where the axial mask part 9 is located.

[0051] like Figures 4-5 As shown, axial protrusions 11 are formed equally along the circumferential direction C on the outer peripheral surface of the one-piece molded body A (the inner annular resin component 4), thus preventing the outer annular resin component 5 from rotating relative to the one-piece molded body A. Figure 2 and Figure 5 As shown, the axial protrusion 11 of the inner annular resin component 4 is located on the radially inner side RI of the tooth 10 of the outer annular resin component 5, and has an axially thinned portion 6 on the radially inner side RI of the axial protrusion 11.

[0052] like Figure 7A As shown, the mold D for secondary molding has a filling part 8 and an axial mask part 9 on the parting surface PL side of the annular outer resin component 5.

[0053] like Figure 1 , Figure 3 As shown, the tooth root 10A of the tooth 10 on the outer peripheral surface of the annular outer resin component 5 is an arc shape along the outer peripheral shape of the worm, and the tooth surface 10B is an arc-shaped curved surface. Therefore, a secondary molding die with the axial direction J relative to the mold opening and closing direction (for example, as...) Figure 7A The movable side mold (M) of the secondary forming mold D becomes the bottom-cut shape.

[0054] Therefore, after injection molding and cooling curing in the secondary molding process, the opening... Figure 7A The secondary molding mold D shown is used in, as... Figure 7B When the resin gear 1 for power transmission of the molded product is pushed out from the movable mold M as shown by arrow E, it is forcibly pulled out.

[0055] Therefore, when the power transmission resin gear 1, as a molded product, is removed from the movable mold M, the power transmission resin gear 1 moves and deforms simultaneously at the part pressed by the protrusion H of the movable mold M. The portion of the power transmission resin gear 1 protruding from the parting surface PL is not constrained by the movable mold M, therefore the side portion 10C of the tooth 10 of the annular outer resin component 5, i.e., the side end of the tooth 10 on the side where the filling portion 8 and the axial mask portion 9 of the annular outer resin component 5 are located, is as follows: Figure 7B It deforms radially outwards RO like arrow F1.

[0056] [The effects of the axial thinning section, filling section, and axial mask section] In the power transmission resin gear 1 according to an embodiment of the present invention, the annular resin portion 3 is composed of an annular inner resin component 4 covering the outer periphery of the mandrel 2 and an annular outer resin component 5 covering the outer periphery of the annular inner resin component 4. The annular inner resin component 4 has a plurality of axially thinned portions 6 arranged separately in the circumferential direction C. The annular outer resin component 5 has a filling portion 8 filling the axially thinned portions 6 of the annular inner resin component 4 and an axial mask portion 9 covering the filling portion 8 and located radially inward of the side portion 10C of the tooth 10.

[0057] Therefore, when the power transmission resin gear 1, which is a molded product, is demolded from the secondary molding mold D, the amount of deformation of the gear 10 to the radially outer RO decreases due to the axial thinning portion 6 of the annular inner resin component 4 located on the radially inner side RI of the side portion 10C of the gear 10, and the filling portion 8 and axial mask portion 9 of the annular outer resin component 5.

[0058] In addition, such as Figure 7CAs shown, when the power transmission resin gear 1, which is a molded product, is removed from the secondary molding mold D, the teeth 10 on the outer peripheral surface of the annular outer resin component 5, which deformed radially outward RO due to being forcibly pulled out, return radially inward RI as shown by arrow F2 due to the molding shrinkage of the axial mask portion 9 covering the filling portion 8 located radially inward RI on the side portion 10C of the teeth 10. Therefore, the deformation caused by being forcibly pulled out is further reduced.

[0059] As described above, the axial thickness T of the axial mask portion 9 is 1 mm or more (T≥1 mm). Therefore, the filling portion 8 is formed to fill the axially thinned portion 6, and the axial mask portion 9 shrinks during molding, such as... Figure 7C The force that pulls the tooth 10 back radially inward RI, as indicated by arrow F2, has the desired strength. When T < 1 mm, the force pulling the tooth 10 back radially inward RI may be weaker.

[0060] By providing the axial thinning portion 6, the filling portion 8, and the axial mask portion 9, the amount of deformation of the tooth 10 in the radially outward direction RO caused by forced extraction is, for example, less than 20% compared to the case where they are not provided. Therefore, it is possible to suppress deformation caused by forced extraction without forming a special tooth profile.

[0061] [Example of a variation in the axially thinned section] The shape of the axially thinned portion provided on the inner side of the annular resin component 4 is not limited to... Figure 3 and Figure 5 Such an axially thinned portion 6, viewed from the axial direction J, is approximately a rectangular shape with rounded corners. For example, it can also be like... Figure 8 As in the first variation, the axially thinned portion 6 can be configured as axially thinned portions 6A and 6B that are divided into two in the radial direction, or they can be combined. Figure 9 The second variation is an axially thinned portion 6C, 6D that is approximately triangular in shape when viewed from the axial direction J.

[0062] The combination of axially thinned sections, which are approximately triangular in shape when viewed from the axial direction J, can be... Figure 10 The axially thinned portions 6E and 6F, as in the third variation example, can also be... Figure 11 The fourth variation example has axially thinned portions 6G and 6H.

[0063] The above descriptions of the embodiments are all illustrative and are not intended to limit the scope thereof. Various modifications and alterations can be made without departing from the scope of the present invention.

[0064] Explanation of reference numerals in the attached figures 1. Resin gears for power transmission 2 mandrels 3. Circular resin section 4. Circular inner resin component 5. Circular outer resin component 6, 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 7 Axial thinning sections 8. Filling section 9. Axial mask section 10 teeth 10A Tooth Root 10B tooth surface 10C Side 11, 12 Axial convex strips A one-piece molded body C Zhou Xiang D. Mold for secondary molding H convex part G1, G2 gate marks J-axis M mobile mode O The axis of rotation PL parting surface RI radial inner side RO Radial outer side T-axis thickness of the mask section W worm gear

Claims

1. A resin gear for power transmission, wherein gear teeth are provided on the outer peripheral surface of an annular resin portion, wherein... The annular resin portion is composed of an inner annular resin component covering the outer periphery of the mandrel and an outer annular resin component covering the outer periphery of the inner annular resin component. The annular inner resin component has multiple axially thinned portions arranged circumferentially. The annular outer resin component has a filling portion that fills the axially thinned portion and an axial mask portion that covers the filling portion and is located radially inside the side of the tooth.

2. The resin gear for power transmission according to claim 1, wherein, The tooth has a root that follows the arc shape of the outer periphery of the worm, and the tooth surface is an arc-shaped curved surface. The resin gear for power transmission is a worm wheel that is combined with the worm to form a worm gear reducer.

3. The resin gear for power transmission according to claim 1 or 2, wherein, The outer peripheral surface of the annular outer resin component has a plurality of axially spaced ridges arranged radially apart on the radially inner side of the teeth, and the axially thinned portion is located on the radially inner side of the axially spaced ridges.

4. A method for manufacturing a resin gear for power transmission, wherein the resin gear for power transmission has gear teeth provided on the outer peripheral surface of an annular resin portion, wherein... The annular resin portion is composed of an inner annular resin component covering the outer periphery of the mandrel and an outer annular resin component covering the outer periphery of the inner annular resin component. The annular inner resin component has multiple axially thinned portions arranged circumferentially. The annular outer resin component has a filling portion that fills the axially thinned portion and an axial mask portion that covers the filling portion and is located radially inside the side of the tooth. The manufacturing method includes a primary molding process and a secondary molding process. The one-time molding process With the mandrel positioned within 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 component, thereby manufacturing a primary molded body composed of the mandrel and the annular inner resin component. The secondary molding process With the primary molded body placed inside a secondary molding mold whose opening and closing direction is axial, molten resin for secondary molding is injected into the cavity of the secondary molding mold to injection mold the annular outer resin component with the teeth. The mold for secondary molding has a filling portion and an axial mask portion on the parting surface side of the annular outer resin component.

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