Method for manufacturing gear

Abstract

To provide a method for manufacturing a gear capable of suppressing deformation of a gear when a mold and a gear are separated by a pressing force from an ejector pin.SOLUTION: The present invention is a method for manufacturing a resin gear, which, when forming a gear, comprises forming a thick part in a web, the thickness dimension of which is larger in an axial direction than the surroundings, and pressing the thick part in a direction of a rotational shaft with an ejector pin to separate a mold and the gear from each other. The gear comprises: an inside rim part that is connected to the rotational shaft by injecting heated and molten resin into the mold, and is circular when viewed from the direction of the rotational shaft; an outside rim part that surrounds the inside rim part at an interval on the radial outside, and in which a plurality of teeth is arranged in a circumferential direction on its outer peripheral part; and a web that connects the inside rim part and the outside rim part, and has a dimension in the direction of the rotational shaft smaller than a dimension of the outside rim part in the direction of the rotational shaft.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a gear. [Background technology]

[0002] 2. Description of the Related Art Conventionally, as a method for manufacturing a resin gear, for example, a method of forming a gear by injecting (pouring) a resin into a mold, such as injection molding, has been known (see Patent Document 1).

[0003] In this manufacturing method, as shown in Fig. 18, a mold 100 is composed of a plurality of split molds (for example, first to third molds) 101 to 103, and when the formed gear h is removed from the mold 100, the first to third molds 101 to 103 move away from the gear h in order. In the third mold 103 which moves away from the gear h last during removal from the mold 100, an ejector pin 105 presses the gear h in a direction away from the third mold 103 (upward in Fig. 18), thereby separating the gear h from the third mold 103. At this time, the ejector pin 105 presses a web 112 which is smaller (i.e., thinner) in the dimension in the rotation axis direction (vertical direction in Fig. 18) than an outer rim 111 on which teeth 110 are formed in the gear h. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 4846631 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-described gear manufacturing method, the ejector pin 105 presses the web 112, which has a small dimension (thickness dimension) in the direction of the rotation axis of the resin gear h, to separate the gear h from the third mold 103, and the gear h may be deformed when pressed by the ejector pin.

[0006] Therefore, an object of the present invention is to provide a method for manufacturing a gear that can suppress deformation of the gear when the die and the gear are separated by pressing with an ejector pin. [Means for solving the problem]

[0007] The method for producing a gear of the present invention comprises the steps of: A method for manufacturing a resin gear, comprising the steps of: When a gear is formed by injecting heated and molten resin into a mold, the gear includes an inner rim portion connected to a rotating shaft and having a circular shape when viewed from the direction of the rotating shaft, an outer rim portion surrounding the inner rim portion at intervals on the radial outside and having a plurality of teeth arranged in the circumferential direction on its outer periphery, and a web connecting the inner rim portion and the outer rim portion and having a dimension in the direction of the rotating shaft smaller than the dimension of the outer rim portion in the direction of the rotating shaft, a thick portion is formed in the web having a thickness dimension in the direction of the rotating shaft larger than an adjacent portion; and separating the die and the gear by pressing the thick portion in the direction of the rotation axis with an ejector pin.

[0008] In this way, a thick portion is formed in the web to ensure the strength of that portion (thick portion), and the ejector pin presses against the thick portion when separating the die and the gear. This makes it possible to suppress deformation of the gear when separating the die and the gear by pressing with the ejector pin.

[0009] In the gear manufacturing method, The thick portion may be formed so as to create a gap between the thick portion and the outer rim portion in the radial direction.

[0010] With this configuration, the impact on the outer rim portion when the thick portion is pressed with the ejector pin to separate the gear and the mold is reduced, thereby preventing a decrease in the precision of the outer rim portion (deformation, etc.).

[0011] In addition, in the gear manufacturing method, the gear is a helical gear, the die is separable into at least a first portion that forms the teeth, and a second portion that holds the gear when the first portion and the gear are separated from each other by relatively rotating around the rotation axis and relatively moving in the rotation axis direction, the second portion has an abutment portion that abuts against the thick portion in a rotation direction that is a direction in which the gear rotates relatively while the gear is held, The thick portion may be pressed by the ejector pin when the gear is removed from the second portion.

[0012] In this way, when a resin helical gear is formed using a mold, by providing an abutment portion in the second portion of the mold to abut against the thick portion in the circumferential direction, it is possible to prevent the first portion of the mold from rotating together with the first portion of the gear when the first portion of the mold is separated from the gear. In other words, by utilizing the thick portion, which has a larger dimension in the rotation axis direction than adjacent portions of the web in order to ensure the strength of the portion pressed by the ejector pin, it is possible to prevent the first portion of the mold from rotating together with the first portion of the gear when the first portion of the mold is separated from the gear. Effect of the Invention

[0013] As described above, the present invention can provide a method for manufacturing a gear that can suppress deformation of the gear when the die and the gear are separated by pressing with an ejector pin. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view of a spur gear according to a first embodiment, as viewed from the other axial side. FIG. [Diagram 2] FIG. 2 is a perspective view of the spur gear as viewed from one side in the axial direction. [Diagram 3] FIG. 3 is a view of the spur gear as seen from the other axial side. [Figure 4] FIG. 4 is a view of the spur gear as viewed from one side in the axial direction. [Diagram 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a view for explaining removal of the spur gear from the die, showing the state before the second portion is moved. [Figure 7] FIG. 7 is a diagram for explaining removal of the spur gear from the mold, showing a state in which the second portion has moved and the spur gear has been pressed by an ejector pin. [Figure 8] FIG. 8 is a perspective view of the helical gear according to the second embodiment, as viewed from the other axial side. [Figure 9] FIG. 9 is a perspective view of the helical gear as viewed from one side in the axial direction. [Figure 10] FIG. 10 is a view of the helical gear as viewed from the other axial side. [Figure 11] FIG. 11 is a view of the helical gear as viewed from one side in the axial direction. [Figure 12] FIG. 12 is a cross-sectional view taken along line XII-XII in FIG. [Figure 13] FIG. 13 is a diagram for explaining removal of the helical gear from the die, showing the state before the fifth portion is moved. [Figure 14] FIG. 14 is a view for explaining removal of the helical gear from the die, showing the state after the fifth portion has been moved and before the fourth portion has been moved. [Figure 15] FIG. 15 is a view for explaining removal of the helical gear from the die, showing the state after the fourth portion has been moved. [Figure 16] FIG. 16 is a diagram for explaining removal of the helical gear from the mold, showing the state in which the helical gear is pressed by an ejector pin. [Figure 17] FIG. 17 is a diagram for explaining the arrangement of the ejector pins and the contact portion of the fourth portion of the mold. [Figure 18] FIG. 18 is a diagram for explaining a conventional method for manufacturing a gear. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

[0016] In the gear manufacturing method of the first embodiment, a resin spur gear is formed. Below, the configuration of the spur gear formed by the gear manufacturing method of the present embodiment is described, and then a method for manufacturing the spur gear using a mold is described.

[0017] As shown in Figures 1 to 5, the spur gear 1 has a through hole 9 that penetrates in the axial direction at the center when viewed from the direction of the rotation axis C (the direction in which the rotation axis C extends: hereinafter also simply referred to as the "axial direction"), and is used with the rotation axis C inserted through this through hole 9.

[0018] The spur gear 1 of this embodiment is made of two types of resin. Specifically, in the spur gear 1, the inner portion P1 is made of a resin harder than the outer portion P2 (see Figs. 3 and 5). In the spur gear 1 of this embodiment, the inner portion P1 is made of polyoxymethylene, and the outer portion P2 is made of a thermoplastic polyester elastomer.

[0019] Specifically, the spur gear 1 includes an inner rim portion 2 connected to a rotation axis C, an outer rim portion 3 surrounding the inner rim portion 2, and a web 4 connecting the inner rim portion 2 and the outer rim portion 3. The spur gear 1 of this embodiment includes a first protrusion (locking protrusion) 5 protruding in the axial direction from one surface 4a of the web 4 in the axial direction, and a second protrusion 6 protruding in the axial direction from the other surface 4b of the web 4 in the axial direction. The first protrusion 5 and the second protrusion 6 are arranged in overlapping positions when viewed from the axial direction, and form a thick portion 7 having a larger axial thickness dimension than adjacent portions of the web 4 (see FIG. 5). The spur gear 1 of this embodiment includes a plurality of first protrusions 5 and a plurality of second protrusions 6 (the same number as the first protrusions 5), i.e., a plurality of thick portions 7.

[0020] The inner rim portion 2 is a circular portion when viewed in the axial direction. Specifically, the inner rim portion 2 is a disk-shaped portion, and has an annular recess 21 on one axial surface 2a, which is recessed toward the other axial side (upper side in FIG. 5) and surrounds a central portion 20 through which the rotation shaft C is inserted. The inner rim portion 2 also has a circular protrusion 25 that protrudes toward the other axial side, at the center of the other axial surface 2b. The inner diameter α1 of the inner peripheral surface 23 of the annular recess 21 corresponds to the outer diameter α2 of the circular protrusion 25 (more specifically, it is slightly smaller than the outer diameter α2: see FIG. 5).

[0021] In this embodiment, a plurality of bottom surface recesses 22a that are recessed deeper toward the other side in the axial direction than the surrounding area are formed on the bottom surface 22 of the annular recess 21. These plurality of bottom surface recesses 22a are arranged at intervals in the circumferential direction so as to surround the central portion 20 (see FIG. 4).

[0022] The outer rim portion 3 is a portion that surrounds the inner rim portion 2 with a gap on the radial outside. A plurality of teeth 32 are formed on the outer periphery of this outer rim portion 3 and are aligned in the circumferential direction. Specifically, the outer rim portion 3 has an annular outer rim portion main body 31 that surrounds the inner rim portion 2 when viewed in the axial direction, and a plurality of teeth 32 that are aligned in the circumferential direction on the outer periphery of the outer rim portion main body 31. Each tooth trace of the plurality of teeth 32 extends in the axial direction.

[0023] The outer rim portion main body 31 is a short cylindrical portion extending in the axial direction, and the axial dimension of the outer rim portion main body 31 is the same as the axial dimension of the peripheral portion of the inner rim portion 2 (the portion outside the circular convex portion 25) (see Figure 5).

[0024] The web 4 connects the outer peripheral surface 2c of the inner rim portion 2 and the inner peripheral surface 3a of the outer rim portion 3, and its axial dimension γ1 is smaller than the axial dimension γ2 of the outer rim portion 3 (outer rim portion main body 31) (see Figure 5).

[0025] The multiple first protrusions 5 are arranged at intervals in the circumferential direction on one surface 4a of the web 4. In this embodiment, the multiple first protrusions 5 are arranged at equal intervals in the circumferential direction (see FIG. 4). Each of the multiple first protrusions 5 protrudes from one surface 4a of the web 4 to one side in the axial direction.

[0026] Specifically, each of the multiple first projections 5 has a first projection body 51 having a radial thickness dimension β1 and a circumferential length dimension β2 (see FIG. 4). Each of the multiple first projections 5 in this embodiment has a first connection portion 55 that connects the first projection body 51 and the inner rim portion 2. The axial dimension (protrusion amount) β3 of each of these first projections 5 is smaller than the dimension β4 in the axial direction from one surface 4a of the web 4 to the end of the outer rim portion 3 (see FIG. 5).

[0027] The first protrusion main body 51 has a rectangular shape that is long in the circumferential direction (in this embodiment, the direction perpendicular to the radial direction and along one surface 4a of the web 4; hereinafter, also referred to as the "longitudinal direction") when viewed from the axial direction (see FIG. 4). That is, in the first protrusion main body 51, the length dimension β2 is greater than the thickness dimension β1.

[0028] In this first protrusion main body 51, end faces 52, 53 at both ends in the longitudinal direction each extend in a plane perpendicular to the longitudinal direction. The first protrusion main body 51 has a gap γ3 between it and the outer rim portion 3 in the radial direction (see FIG. 4). An end face 54 in the protruding direction (axial direction) of the first protrusion main body 51 extends in a plane perpendicular to the axial direction.

[0029] Moreover, in the first protrusion main body 51, the central portion in the longitudinal direction bulges inward and outward in an arc shape when viewed from the axial direction. In the first protrusion main body 51 of this embodiment, the thickness dimension (radial dimension) β11 of the portion bulging in an arc shape is smaller than the length dimension β2 (see FIG. 4).

[0030] In addition, the portion of the first protrusion main body 51 in this embodiment that bulges out in an arc shape is a portion (contact portion 51a: a region indicated by dots on an end face 54 of the first protrusion main body 51 in FIG. 4) that is pressed by the first ejector pin 801 when the first ejector pin 801 pushes out in the axial direction to release the spur gear 1 from the mold 8 (first portion 81: see FIGS. 6 and 7) during injection molding described later, and the contact portion 51a has a shape and size that correspond to the first ejector pin 801 when viewed from the axial direction. The contact portion 51a in this embodiment is circular when viewed from the axial direction, and the surface pressed by the first ejector pin 801 extends in a plane direction perpendicular to the axial direction and is included in the end face 54 of the first protrusion main body 51. This contact portion 51a is disposed in the center of the first protrusion main body 51 in the longitudinal direction.

[0031] The first connecting portion 55 protrudes in the axial direction from one surface 4a of the web 4 and extends in the radial direction from the inner rim portion 2 to the first protrusion main body 51. In this embodiment, the first connecting portion 55 is connected to the center portion in the longitudinal direction of the first protrusion main body 51 (more specifically, the portion that bulges in an arc shape radially inward when viewed from the axial direction). The amount of protrusion in the axial direction of the first connecting portion 55 is the same as the amount of protrusion in the axial direction of the first protrusion main body 51.

[0032] In the multiple first projections 5 each configured as described above, the circumferential distance between the first projection bodies 51 of circumferentially adjacent first projections 5 (more specifically, the circumferential distance between the central positions of the end faces 52, 53 facing each other in the circumferential direction when viewed from the axial direction) is larger than the length dimension β2 (see FIG. 4). As a result, although the thickness dimension β1 of the first projection body 51 is smaller than the length dimension β2, the length in the longitudinal direction (or the length in the circumferential direction) of the first projection body 51 is reduced, making it difficult for deformation such as bending to occur in the first projection body 51.

[0033] The second projections 6 are arranged at intervals in the circumferential direction on the other surface 4b of the web 4. The second projections 6 are arranged at the same positions as the corresponding first projections 5 in the circumferential direction. As a result, the second projections 6 are also arranged at equal intervals in the circumferential direction (see FIG. 3). Each of the second projections 6 protrudes from the other surface 4b of the web 4 to the other side in the axial direction (i.e., the opposite side to the first projections 5).

[0034] Specifically, each of the multiple second projections 6 has a second projection body 61 having a radial thickness dimension β5 and a circumferential length dimension β6, and a second connection portion 65 that connects the second projection body 61 to the inner rim portion 2. The axial dimension (protrusion amount) β7 of each of these second projections 6 is smaller than the dimension β4 from the other surface 4b of the web 4 to the end of the outer rim portion 3 in the axial direction (see FIG. 5).

[0035] The second protrusion main body 61 has a gap γ4 between itself and the outer rim portion 3 in the radial direction (see FIG. 3). The second protrusion main body 61 in this embodiment is rectangular and elongated in the circumferential direction (in this embodiment, the long direction) when viewed from the axial direction. That is, in the second protrusion main body 61, the length dimension β6 is greater than the thickness dimension β5. The thickness dimension β5 of the second protrusion main body 61 in this embodiment is the same as the thickness dimension β1 of the first protrusion main body 51 (the thickness dimension of the portion excluding the bulging portion), and the length dimension β6 of the second protrusion main body 61 is the same as the length dimension β2 of the first protrusion main body 51.

[0036] In this second protrusion main body 61, end faces 62, 63 at both ends in the longitudinal direction each extend in a plane perpendicular to the longitudinal direction. In addition, an end face 64 in the protruding direction (axial direction) of the second protrusion main body 61 extends in a plane perpendicular to the axial direction.

[0037] The second connecting portion 65 protrudes in the axial direction from the other surface 4b of the web 4 and extends radially from the inner rim portion 2 to the second protrusion main body 61. In this embodiment, the second connecting portion 65 is connected to the longitudinal center portion of the second protrusion main body 61. The axial protrusion amount of this second connecting portion 65 and the axial protrusion amount of the second protrusion main body 61 are the same.

[0038] The first projection 5 and the second projection 6 configured as described above are arranged in overlapping positions when viewed from the axial direction, and form the thick portion 7 as described above. A plurality of the thick portions 7 are arranged on the web 4, and the plurality of the thick portions 7 are arranged at equal intervals in the circumferential direction on the web 4. Each of the thick portions 7 is arranged such that gaps γ3, γ4 are formed between the thick portions 7 and the outer rim portion 3 in the radial direction.

[0039] The spur gear 1 configured as above is formed, for example, by injection molding. Specifically, first, molten resin is injected (poured) into the mold 8 from the gate 86 (see FIG. 6). Then, after the injected resin has solidified enough to be able to be released from the first portion 81, the mold 8 is opened (divided into a plurality of portions) and the spur gear 1 is removed. The details are as follows.

[0040] As shown in Figures 6 and 7, the mold 8 has a first portion 81 that forms one axial side of the spur gear 1, a second portion 82 that forms the other axial side of the spur gear 1, and an ejector pin 80 that is arranged in the first portion 81 so that it can be inserted through the first portion 81.

[0041] In the mold 8 of this embodiment, the second portion 82 is movable upward with respect to the first portion 81 while the first portion 81 is fixed (in other words, movable relatively in the axial direction of the spur gear 1). The mold 8 of this embodiment also includes a plurality of ejector pins 80 and a push-up portion 80A that pushes up the plurality of ejector pins 80, and the push-up portion 80A pushes up the plurality of ejector pins 80, causing each ejector pin 80 to protrude upward from the first portion 81 and push up the formed spur gear 1.

[0042] The multiple ejector pins 80 include multiple first ejector pins 801 arranged at positions corresponding to the respective abutment portions 51a (see the dotted areas of each first protrusion body 51 in FIG. 4) of the multiple first protrusions 5 of the formed spur gear 1, and multiple second ejector pins 802 arranged at positions corresponding to the inner rim portion 2 of the formed spur gear 1. The multiple second ejector pins 802 are arranged at equal intervals in the circumferential direction at positions corresponding to the inner rim portion 2 (see the dotted areas (abutment portions) 2f in FIG. 4).

[0043] The spur gear 1 is injection molded by the mold 8 configured as above. More specifically, first, molten resin is injected (injected) into the mold 8 through the gate 86. Then, the resin hardens inside the mold 8, thereby forming the spur gear 1 described above.

[0044] When the spur gear 1 is formed, the second portion 82 moves upwards, thereby moving away from the spur gear 1 .

[0045] Next, the push-up portion 80A moves upward relative to the first portion 81, pushing up the first ejector pins 801 and the second ejector pins 802.

[0046] As a result, each first ejector pin 801 is pushed up and comes into contact with the contact portion 51a of the corresponding first protrusion 5 (thick portion 7) of the spur gear 1 on the first portion 81, pushing up the contact portion 51a. By providing the contact portion 51a of a shape corresponding to the first ejector pin 801 as in the spur gear 1 of this embodiment, the contact portion 51a can securely receive the first ejector pin 801, and the spur gear 1 can be reliably released from the mold 8 (more specifically, the first portion 81). Moreover, by arranging the contact portion 51a in the center of the first protrusion main body 51 (thick portion 7) in the longitudinal direction, the first protrusion main body 51 (thick portion 7) is less likely to deform when pressed by the first ejector pin 801.

[0047] Additionally, together with each first ejector pin 801, each second ejector pin 802 is also pushed up by the push-up portion 80A and comes into contact with each abutment portion 2f of the inner rim portion 2, pushing up the inner rim portion 2. In this manner, the load on each first projection 5 (thick portion 7) and web 4 is reduced by the pressing of the first protrusion 5 (abutment portion 51a) by each first ejector pin 801 and the pressing of the inner rim portion 2 (abutment portion 2f) by each second ejector pin 802, and deformation of these first projections 5 (thick portion 7) and web 4 is further suppressed.

[0048] In the spur gear 1 injection molded as described above, marks of the ejector pins 801, 802 remain at the locations pressed by the ejector pins 801, 802.

[0049] The above-described gear manufacturing method is a method for manufacturing a resin gear, and includes the steps of injecting heated and molten resin into a mold 8 to form a spur gear 1 including an inner rim portion 2 connected to the rotation axis C and circular when viewed from the axial direction (rotation axis direction), an outer rim portion 3 surrounding the inner rim portion 2 at intervals on the radial outside and having a plurality of teeth 32 arranged in the circumferential direction on its outer periphery, and a web 4 connecting the inner rim portion 2 and the outer rim portion 3 and having an axial dimension γ1 smaller than the axial dimension γ2 of the outer rim portion 3, forming a thick portion 7 (first protrusion 5 and second protrusion 6) in the web 4 whose axial thickness dimension is larger than that of adjacent portions, and pressing the thick portion 7 in the axial direction with a first ejector pin (ejector pin) 801 to separate the mold 8 (more specifically, the first portion 81) and the spur gear 1.

[0050] In this way, a thick portion 7 is formed in the web 4 to ensure the strength of the area (thick portion) 7, and then the first ejector pin 801 presses the thick portion 7 when the mold 8 (first portion 81) and the spur gear 1 are separated. This makes it possible to suppress deformation of the spur gear 1 when the mold 8 and the spur gear 1 are separated by pressing with the first ejector pin 801.

[0051] In the gear manufacturing method of the first embodiment, the thick portion 7 is formed so that gaps γ3, γ4 are generated between the thick portion 7 and the outer rim portion 3 in the radial direction. This reduces the effect on the outer rim portion 3 when the thick portion 7 is pressed by the first ejector pin 801 when separating the spur gear 1 from the mold 8 (more specifically, the first portion 81), thereby preventing a decrease in the accuracy (deformation, etc.) of the outer rim portion 3. Furthermore, by forming the spur gear 1 so that gaps γ3, γ4 are generated between the thick portion 7 and the outer rim portion 3, deformation of the outer rim portion 3 caused by the difference in the shrinkage rate between the thick portion 7 and the outer rim portion 3 when the resin injected into the mold 8 cools and hardens is also reduced.

[0052] Furthermore, in the gear manufacturing method of the first embodiment, when the thick-walled portion 7 is formed, it is connected to the inner rim portion 2. This improves the rigidity of the thick-walled portion 7 and the web 4 of the formed spur gear 1, and more reliably suppresses deformation of the web 4 when pressed by the first ejector pin 801.

[0053] In the manufacturing method for a gear of the first embodiment, thick portions 7 are formed on one surface 4a side and the other surface 4b side of the web 4 in the axial direction, respectively, which are thick portions (first protrusion 5 and second protrusion 6). This ensures a sufficient thickness (dimension in the axial direction) while keeping the thick portion 7 within a range where it does not protrude in the axial direction from the outer rim portion 3, thereby ensuring sufficient rigidity of the thick portion 7. As a result, deformation of the web 4 when pressed by the first ejector pin 801 is suppressed.

[0054] Next, a method for manufacturing a gear according to the second embodiment will be described with reference to FIGS.

[0055] In the gear manufacturing method of the second embodiment, a resin double gear is formed. Below, the configuration of the double gear formed by the gear manufacturing method of this embodiment is described, and then a method for manufacturing the double gear using a mold is described. Note that the same components as in the first embodiment are simply described using the same reference numerals, and components different from the first embodiment are described in detail.

[0056] Helical gear H is a double gear in which two gears 1A, 10 of different diameters are arranged in the axial direction, as shown in Figures 8 to 12. Of the two gears 1A, 10 arranged in the axial direction, the gear with the larger diameter is referred to as the first gear 1A, and the gear with the smaller diameter is referred to as the second gear 10. This helical gear H has a through hole 9 in the center when viewed in the axial direction, and is used with a rotation shaft C inserted through this through hole 9.

[0057] Incidentally, the helical gear H of this embodiment is also formed from two types of resin, like the spur gear 1 of the first embodiment. Specifically, in the helical gear H, the second gear 10 is formed from a resin harder than the first gear 1A (see Figs. 10 and 12). In the helical gear H of this embodiment, the second gear 10 is formed from polyoxymethylene, and the first gear 1A is formed from a thermoplastic polyester elastomer. Of the axial surface of the helical gear H of this embodiment, the inner portion P1 is the second gear 10, and the outer portion P2 is the first gear 1A.

[0058] The helical gear H has an inner rim portion 2, and the first gear 1A has an outer rim portion 3 and a web 4. The first gear 1A also has a first protrusion 5 protruding from one surface 4a of the web 4 and a second protrusion 6 protruding in the axial direction from the other surface 4b of the web 4. The first protrusion 5 and the second protrusion 6 form a thick portion 7, similar to the spur gear 1 of the first embodiment (see FIG. 12). The first gear 1A of this embodiment has a plurality of first protrusions 5 and a plurality of second protrusions 6 (the same number as the first protrusions 5), that is, a plurality of thick portions 7.

[0059] The inner rim portion 2 has an annular recess 21 surrounding a central region 20 on one axial surface 2a. The inner rim portion 2 also has a circular protrusion 25 at the center of the other axial surface 2b. A plurality of bottom surface recesses 22a are formed on the bottom surface 22 of the annular recess 21. The inner rim portion 2 in this embodiment is made up of an inner rim element 26 that is located in the inner region P1 of the second gear 10 and an inner rim element 27 of the first gear 1A that is connected to the inner rim element 26.

[0060] The outer rim portion 3 has an annular outer rim portion main body 31 and a plurality of teeth 32A arranged in the circumferential direction on the outer periphery of the outer rim portion main body 31. Each of the plurality of teeth 32A has a spiral tooth trace with the rotation axis C as the spiral center.

[0061] The web 4 connects the outer peripheral surface 2c of the inner rim portion 2 and the inner peripheral surface 3a of the outer rim portion 3, and its axial dimension γ1 is smaller than the axial dimension γ2 of the outer rim portion 3 (outer rim portion main body 31) (see Figure 12).

[0062] The multiple first projections 5 are arranged at intervals in the circumferential direction on one surface 4a of the web 4 (see FIG. 11). Each of the multiple first projections 5 has a first projection body 51 having a radial thickness dimension β1 and a circumferential length dimension β2, and a first connection portion 55 connecting the first projection body 51 and the inner rim portion 2.

[0063] The first protrusion main body 51 has an abutment portion 52 at one circumferential end, and has a gap γ3 between itself and the outer rim portion 3 in the radial direction (see FIG. 11). In the first protrusion main body 51 of this embodiment, the length dimension β2 is greater than the thickness dimension β1.

[0064] In this first protrusion main body 51, one of the two end faces 52, 53 at both ends in the longitudinal direction constitutes the above-mentioned abutted portion. That is, the abutted portion 52 of the first protrusion main body 51 is constituted by a face facing one side in the circumferential direction. In addition, the end face 54 in the protruding direction (axial direction) of the first protrusion main body 51 spreads in a planar direction perpendicular to the axial direction. In addition, in the first protrusion main body 51, the central portion in the longitudinal direction bulges in an arc shape radially inward and outward when viewed from the axial direction. In addition to the abutted portion 52, an abutted portion may be provided at one end in the circumferential direction of the first connecting portion 55.

[0065] The first connection portion 55 protrudes axially from one surface 4a of the web 4 and extends radially from the inner rim portion 2 to the first protrusion body 51, and is connected to the center of the first protrusion body 51 in the longitudinal direction.

[0066] The second projections 6 are arranged at intervals in the circumferential direction on the other surface 4b of the web 4 (see FIG. 10). Each of the second projections 6 has a second projection body 61 having a radial thickness dimension β5 and a circumferential length dimension β6, and a second connection portion 65 connecting the second projection body 61 and the inner rim portion 2.

[0067] The second protrusion main body 61 has a gap γ4 between itself and the outer rim portion 3 in the radial direction (see FIG. 10 ). In the second protrusion main body 61 of this embodiment, the thickness dimension β5 is the same as the thickness dimension β1 of the first protrusion main body 51, and the length dimension β6 is the same as the length dimension β2 of the first protrusion main body 51.

[0068] The second connection portion 65 protrudes axially from the other surface 4b of the web 4 and extends radially from the inner rim portion 2 to the second protrusion main body 61, and is connected to the center of the second protrusion main body 61 in the longitudinal direction.

[0069] The first projection 5 and the second projection 6 configured as described above are arranged in overlapping positions when viewed from the axial direction, and form the thick portion 7 as described above. A plurality of the thick portions 7 are arranged on the web 4, and the plurality of the thick portions 7 are arranged at equal intervals in the circumferential direction on the web 4. Each of the thick portions 7 is arranged such that gaps γ3, γ4 are formed between the thick portions 7 and the outer rim portion 3 in the radial direction.

[0070] The second gear 10 extends from the center of the inner rim portion 2 as viewed in the axial direction to the other side along the axial direction. A plurality of teeth 11 are formed on the outer periphery of the second gear 10 and arranged in the circumferential direction. Each of the plurality of teeth 11 has a spiral shape with the rotation axis C as the spiral center. Each tooth 11 of the second gear 10 of this embodiment has a spiral shape in the opposite direction to each tooth 32A of the first gear 1A. The axial dimension α5 of the second gear 10 of this embodiment is larger than the axial dimension α3 at the position of the circular protrusion 25 of the inner rim portion 2 of the first gear 1A (see FIG. 12).

[0071] The helical gear H configured as above is formed by, for example, injection molding, as in the first embodiment. Specifically, first, molten resin is injected (poured) into the mold 8A from the gate 86 (see FIG. 13). Then, after the resin injected into the mold 8A has solidified, the mold 8A is opened (divided into a plurality of parts), and the helical gear H is taken out. More specifically, this is as follows.

[0072] As shown in Figures 13 to 16, the mold 8A has a third portion 83 that forms one axial side of the helical gear H, a fourth portion 84 that forms the teeth 32A (the outer peripheral portion of the outer rim portion 3) of the first gear 1A in the helical gear H, a fifth portion 85 that forms the second gear 10 and its surrounding portion on the other axial side of the helical gear H, and an ejector pin 80 that is positioned in the third portion 83 so that it can be inserted through the third portion 83.

[0073] In the mold 8A of this embodiment, the fifth portion 85 and the fourth portion 84 are movable upward in sequence with respect to the third portion 83 while the third portion 83 is fixed (in other words, movable relatively in the axial direction of the helical gear H). In this upward movement, the fifth portion 85 moves upward while rotating relatively to the helical gear H about the rotation axis C so as to follow the tooth trace of the tooth 11 of the second gear 10. In addition, the fourth portion 84 moves upward while rotating relatively to the helical gear H about the rotation axis C (the opposite direction to the fifth portion 85) so as to follow the tooth trace of the tooth 32A of the first gear 1A.

[0074] Further, the third portion 83 has a plurality of contact portions 831 for preventing the helical gear H from co-rotating with the fourth portion 84 (see FIG. 17).

[0075] These multiple contact portions 831 protrude to the other side in the axial direction and are located respectively between adjacent first protrusions 5 in the circumferential direction of the helical gear H, and abut against the contacted portions 52 of the first protrusions 5 in the circumferential direction. More specifically, the contact portions 831 are portions that face (abut) against the contacted portions 52 of the first protrusions 5 in the circumferential direction among the portions in the third region 83 that fit between the first protrusions 5 (portions that fit between the first protrusions 5 within the dotted range indicated by reference numeral 830 in FIG. 17) (see reference numeral 831 in FIG. 17).

[0076] In addition, the mold 8A of this embodiment is equipped with a plurality of ejector pins 80 and a push-up portion 80A that pushes up the plurality of ejector pins 80. As the push-up portion 80A pushes up the plurality of ejector pins 80, each ejector pin 80 protrudes from the third portion 83 and pushes up the formed helical gear H.

[0077] The multiple ejector pins 80 include multiple first ejector pins 801 arranged at positions corresponding to the contact portions 51a (see the portions indicated by dots with reference numeral 51a in FIG. 17) of the multiple first protrusions 5 of the formed helical gear H, and multiple second ejector pins 802 arranged at positions corresponding to the inner rim portion 2 (see the area indicated by dots with reference numeral 2f in FIG. 17 for details) of the formed helical gear H. The multiple second ejector pins 802 are arranged at equal intervals in the circumferential direction at positions corresponding to the inner rim portion 2.

[0078] The helical gear H is injection molded by the mold 8A configured as described above. More specifically, first, molten resin is injected (injected) into the mold 8A through the gate 86. The resin then hardens in the mold 8A to such an extent that it can be demolded from the fifth portion 85, thereby forming the helical gear H described above.

[0079] When the helical gear H is formed, the fifth portion 85 moves upward while rotating about the rotation axis C, thereby moving away from the helical gear H.

[0080] Next, the fourth portion 84 moves upward while rotating about the rotation axis C (the opposite direction to the fifth portion 85), and thereby moves away from the helical gear H. At this time, the helical gear H tries to rotate together with the fourth portion 84, but the abutment portions 831 of the third portion 83 are in abutment with the abutted portions 52 of the first protrusions 5 from the side opposite to the co-rotation direction in the circumferential direction, preventing the helical gear H from rotating together with the fourth portion 84 in the circumferential direction relative to the third portion 83. As a result, the helical gear H is prevented from rotating together with the fourth portion 84.

[0081] Next, the push-up portion 80A moves upward relative to the third portion 83, pushing up the first ejector pins 801 and the second ejector pins 802, and the helical gear H is separated (released) from the third portion 83. At this time, the second ejector pin 802 pushes up a position 2f that straddles the inner rim element 27 of the first gear 1A and the inner rim element 26 of the second gear 10 (see FIG. 17). This is because, although the inner rim element 27 of the second gear 10 should be unloaded when released from the third portion 83, if a load is applied to the inner rim element 27 of the second gear 10, and only the inner rim element 27 of the first gear 1A is pushed up by the second ejector pin 802, there is a risk that the inner rim elements 26, 27 will be deformed.

[0082] In the helical gear H injection molded as described above, marks of the ejector pins 801, 802 remain at the portions pressed by the ejector pins 801, 802.

[0083] In the above gear manufacturing method, the gear formed is a helical gear H, and the die 8A is separable into at least a fourth portion (first portion) 84 that forms the teeth 32A, and a third portion (second portion) 83 that holds the helical gear H when the fourth portion 84 and the helical gear (gear) H move relatively in the axial direction (the direction of the rotation axis C) while rotating relatively around the rotation axis C, thereby separating the fourth portion 84 from the helical gear H. The third portion 83 has an abutment portion 831 that abuts against the thick portion 7 in the rotation direction in which the helical gear H rotates relatively when held, and the thick portion 7 is pressed by the first ejector pin 801 when the helical gear H is removed from the third portion 83.

[0084] In this way, when the resin helical gear H is formed using the mold 8A, by providing the abutment portion 831 in the third portion 83 of the mold 8A and abutting the thick portion 7 in the circumferential direction, it is possible to prevent co-rotation with the fourth portion 84 of the helical gear H when the fourth portion 84 of the mold 8A is separated from the helical gear H. In other words, by utilizing the thick portion 7 whose dimension in the rotation axis direction is larger than adjacent portions of the web 4 in order to ensure the strength of the portion pressed by the first ejector pin 801, it is possible to prevent co-rotation with the fourth portion 84 of the helical gear H when the fourth portion 84 of the mold 8A is separated from the helical gear H.

[0085] It should be noted that the gear manufacturing method of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment. Furthermore, part of the configuration of one embodiment can be deleted.

[0086] The specific configuration of the thick portion 7 of the gear 1, H formed by the die 8 is not limited. The thick portion 7 in the first and second embodiments is connected to the inner rim portion 2, while having gaps γ3, γ4 between it and the outer rim portion 3, but is not limited to this configuration. The thick portion 7 may have a gap between it and the inner rim portion 2, or may be connected to the outer rim portion 3. Furthermore, the thick portion 7 may be connected to both the inner rim portion 2 and the outer rim portion 3, or may have gaps between the inner rim portion 2 and the outer rim portion 3.

[0087] In addition, the thick portion 7 in the first and second embodiments is T-shaped when viewed from the axial direction, but is not limited to this configuration. The thick portion 7 may adopt various shapes such as a circle or a polygon when viewed from the axial direction. In addition, the axial protrusion amount β3 of the thick portion 7 from one surface 4a of the web 4 and the axial protrusion amount β7 from the other surface 4b of the web 4 in the first and second embodiments are the same, but may be different. In addition, the thick portion 7 in the first and second embodiments is composed of the first protrusion 5 and the second protrusion 6, but may be composed only of the first protrusion 5 or only of the second protrusion 6. In addition, in the first and second embodiments, the shape of the part (first protrusion) 5 on the one surface 4a side of the web 4 and the part (second protrusion) 6 on the other surface 4b side when viewed from the axial direction are the same, but may be different.

[0088] That is, in the gears 1, H formed by the dies 8, 8A, the thick portion 7 only needs to have an axial dimension larger than that of the portion of the web 4 adjacent to the thick portion 7.

[0089] Furthermore, the gear formed by the manufacturing method of the first embodiment is a spur gear 1, but it may be a helical gear or a double-stage gear.

[0090] In addition, in the helical gear H formed by the manufacturing method of the second embodiment, the tooth traces of the teeth 32A, 11 of both the first gear 1A and the second gear 10 are helical (helical) in shape, but the tooth trace of the tooth 32A of the first gear 1A may be straight in the axial direction. [Explanation of symbols]

[0091] 1...spur gear, 1A...first gear, 2...inner rim portion, 2a...one surface, 2b...other surface, 2c...outer peripheral surface, 2f...contact portion for second ejector pin, 20...center portion, 21...annular recess, 22...bottom surface, 22a...bottom recess, 23...inner peripheral surface, 25...circular protrusion, 26, 27...inner rim element, 3...outer rim portion, 3a...inner peripheral surface, 31...outer rim portion main body, 32, 32A...teeth, 4...web, 4a...one surface, 4b...other surface, 5...first projection, 51...first projection main body, 51a...first edge abutment portion of ejector pin, 52...abutted portion (longitudinal end face), 53...longitudinal end face, 54...rotation axis direction end face, 55...first connection portion, 6...second projection, 61...second projection main body, 62, 63...longitudinal end face, 64...rotation axis direction end face, 65...second connection portion, 7...thick portion, 8, 8A...mold, 80...ejector pin, 80A...push-up portion, 801...first ejector pin (ejector pin), 802...second ejector pin, 81...first portion, 82...second portion, 8 3...third portion (second portion), 830...portion in the third portion that fits between the first projections, 831...contact portion, 84...fourth portion (first portion), 85...fifth portion, 86...gate, 9...through hole, 10...second gear, 11...teeth, 100...mold, 101...first mold, 102...second mold, 103...third mold, 105...ejector pin, 110...teeth, 111...outer rim, 112...web, C...rotation shaft, H...helical gear, h...gear, P1...inner portion, P2...outer portion, α1...ring Inner diameter of the circular recess, α2...Outer diameter of the circular protrusion, α3...Maximum axial dimension of the inner rim portion, α5...Axial dimension of the second gear, β1...Thickness dimension of the first projection body, β2...Length dimension of the first projection body, β4...Axial dimension from the web to the end of the outer rib portion, β5...Thickness dimension of the second projection body, β6...Length dimension of the second projection body, γ1...Axial dimension of the web, γ2...Axial dimension of the outer rim portion, γ3...Gap between the first projection and the outer rim portion, γ4...Gap between the second projection and the outer rim portion

Claims

1. A method for manufacturing a resin gear, comprising the steps of: When a gear is formed by injecting heated and molten resin into a mold, the gear includes an inner rim portion connected to a rotating shaft and having a circular shape when viewed from the direction of the rotating shaft, an outer rim portion surrounding the inner rim portion at intervals on the radial outside and having a plurality of teeth arranged in the circumferential direction on its outer periphery, and a web connecting the inner rim portion and the outer rim portion and having a dimension in the direction of the rotating shaft smaller than the dimension of the outer rim portion in the direction of the rotating shaft, a thick portion is formed in the web having a thickness dimension in the direction of the rotating shaft larger than an adjacent portion; and separating the die and the gear by pressing the thick portion in the rotation axis direction with an ejector pin.

2. The method for manufacturing a gear according to claim 1 , wherein the thick portion is formed so as to create a gap between the thick portion and the outer rim portion in the radial direction.

3. the gear is a helical gear, the die is separable into at least a first portion that forms the teeth, and a second portion that holds the gear when the first portion and the gear are separated from each other by relatively rotating around the rotation axis and relatively moving in the rotation axis direction, the second portion has an abutment portion that abuts against the thick portion in a rotation direction that is a direction in which the gear rotates relatively while the gear is held, The method for manufacturing a gear according to claim 1 or 2, wherein the thick portion is pressed by the ejector pin when the gear is removed from the second portion.

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