Gear manufacturing process

Abstract

Gear manufacturing method, the gear (100) comprising an annular gear section (10) having teeth on an outer circumference, an annular bearing section (20) provided on an inner circumferential surface (10a) of the gear section (10) and supporting the gear section (10), and a core section (30) provided inside the bearing section (20), the method comprising: a bearing section forming step of the forming of the bearing section (20) by arranging the gear section (10) and the core section (30) in a ring-shaped mold (60) and filling a resin between the gear section (10) and the core section (30); and a bearing section cooling step of cooling the bearing section (20) which is formed in the bearing section forming step, characterized in that a radial gap (80) between the teeth of the gear section (10) and the mold (60) is defined before the bearing section forming step, such that it is smaller than a radial shrinkage amount (B) of the bearing section (20) in the bearing section cooling step, and a radial expansion of the gear section (10) is limited by the shape (60), such that a radial expansion amount (A) in the bearing section forming step is smaller than the radial shrinkage amount (B) of the bearing section (20) in the bearing section cooling step.

Description

[0001] The present invention relates to a gear manufacturing method according to the preamble of independent claim 1. Such a gear manufacturing method is known from publication JP H11-294 543 A.

[0002] A gear is known as a device for transmitting a rotational force from a drive shaft to a driven shaft. A gear disclosed in JP 2018-017302 A comprises an annular gear section having teeth on an outer circumference, an annular resin bearing section provided on an inner circumferential surface of the gear section and supporting the gear section, and a metal core section located inside the bearing section. The bearing section of the gear is formed by placing the core section in a mold and filling a molten resin between the gear section, which is a primary molded product, and the core section.

[0003] The gear section of the gear disclosed in JP 2018-017302 A is made of resin. Therefore, when the bearing section is formed by pouring molten resin between the gear section and the core section, the gear section expands due to the heat and pressure of the molten resin. Subsequently, when the bearing section cools, the gear section shrinks due to the thermal shrinkage of the molten resin. Consequently, the outer diameter of the gear section changes between the time before forming and after cooling the bearing section, creating residual stress within the gear section. This residual stress can compromise the durability of the gear section.

[0004] One object of the present invention is to provide a gear manufacturing method that reduces the influence on the durability of a gear section of a gear.

[0005] This problem is solved according to the invention by a gear manufacturing method with the features of independent claim 1. Preferred embodiments are set out in the dependent claims. Brief description of the drawings Fig. Figure 1 is a front view of a gear according to an embodiment of the present invention in a state of engagement with a worm shaft. Fig. 2 is a cross-sectional view along line II-II in Fig. 1. Fig. 3A is a cross-sectional view of a gear section according to Fig. 2. Fig. 3B is a front view of the gear section. Fig. 4A is a cross-sectional view of a bearing section accordingly Fig. 2. Fig. 4B is a cross-sectional view along the line IVB-IVB in Fig. 4A. Fig. 5A is a cross-sectional view of the gear before the bearing section forming step. Fig. 5B is a front view of the gear before the bearing section forming step. Fig. 6A is a cross-sectional view of the gear after the bearing section forming step. Fig. Figure 6B is a front view of the gear after the bearing section forming step. Fig. Figure 7A is a cross-sectional view of the gear after a bearing section cooling step. Fig. 7B is a front view of the gear after the bearing section cooling step. Fig. Figure 8A is a view showing a manufacturing step of the gear according to a comparative example of the embodiment of the present invention. Fig. Figure 8B is a view showing a manufacturing step of the gear according to the embodiment of the present invention. Fig. Figure 9 is a diagram showing the outside diameters of each gear section in the manufacturing step in samples where an anomaly occurs in the gear section and in samples where no anomaly occurs in a fatigue test of the gear. Description of the exemplary embodiment

[0006] A gear 100 according to an embodiment of the present invention is described below with reference to the drawings.

[0007] As in Fig. As shown in Figure 1, gear 100 is used in a worm gear reduction unit 1. Gear 100 is, for example, a worm gear.

[0008] In the worm gear 1, the gear 100 meshes with a worm shaft 6. The worm shaft 6 is connected to a rotating shaft (not shown) of a motor, and the gear 100 is connected, for example, to a pinion (not shown).

[0009] When the worm shaft 6 rotates with the motor, the gear 100 rotates. At this point, the rotation of the worm shaft 6 is slowed down and transmitted to the gear 100. The pinion rotates with the rotation of the gear 100. In this way, the worm reduction gear 1 slows down the rotation of the motor via the worm shaft 6 and the gear 100 and transmits the slowed rotation to the pinion.

[0010] In the following, a direction along an axis of rotation of the gear 100 is referred to as the "axial direction", a direction of radiation around the axis of rotation of the gear 100 as the "radial direction" and a direction along the circumference of the axis of rotation of the gear 100 as the "circumferential direction".

[0011] The worm shaft 6 comprises a columnar shaft body 6a and shaft teeth 6b, which are spirally arranged around an outer circumference of the shaft body 6a. The worm shaft 6 is made of an iron alloy, and the shaft body 6a and the shaft teeth 6b are formed in one piece.

[0012] A plurality of gear teeth 11, which mesh with the shaft teeth 6b, are formed on an outer circumference of the gear 100.

[0013] When the worm shaft 6 moves towards D1, which is in the Fig. As shown in Figure 1, when the gear rotates, the gear teeth 11 are pressed against the shaft teeth 6b. Accordingly, the gear 100 rotates in a direction D3, which is shown in Fig. 1 is shown. If the worm shaft 6 moves in a direction D2 which is in Fig. As shown in Figure 1, when the gear rotates, the gear teeth 11 are pressed by the shaft teeth 6b in a direction opposite to the case above. Accordingly, the gear 100 rotates in the direction D4, which is shown in Figure 1. Fig. 1 is shown.

[0014] Fig. 2 is a cross-sectional view along line II-II in Fig. 1. As in the Fig. 1 and Fig. As shown in Figure 2, the gear 100 includes an annular gear section 10 having gear teeth 11 on its outer circumference. The gear section 10 includes an annular gear body 12, and the gear teeth 11 project radially outward from the outer circumference of the gear body 12. The gear teeth 11 and the gear body 12 are, for example, made of resin and are formed in one piece by casting. Examples of the resin used for the gear section 10 include, but are not limited to, polyamide 6, polyamide 66, polyamide 46, polyacetal, polyetheretherketone (PEEK), and polyphenylene sulfide (PPS).

[0015] An annular bearing section 20, which supports the gear section 10, is provided on an inner circumferential surface 10a of the gear section 10. The bearing section 20 is formed from a fiber-reinforced resin. The fiber-reinforced resin is, for example, a resin obtained by mixing a fiber-reinforcing material such as glass fibers or carbon fibers with a base resin such as polyamide 6, polyamide 66, polyamide 46, polyacetal, PEEK, and PPS.

[0016] The fiber-reinforced material is not mixed into the resin used for gear section 10. The resin used for gear section 10 is softer than the fiber-reinforced resin, and the elastic modulus of gear section 10 is lower than that of bearing section 20. Therefore, when the shaft teeth 6b mesh with the gear teeth 11, the shaft teeth 6b are less likely to wear down, and the durability of the worm gear 1 can be improved.

[0017] Inside the bearing section 20, a core section 30 is provided in close contact with the bearing section 20. The core section 30 is made of metal. The core section 30 is ring-shaped, and a shaft (not shown) of the pinion is attached to an inner circumferential surface 30a of the core section 30.

[0018] Fig. 3A is a cross-sectional view of gear section 10. Fig. 3B is a front view of gear section 10. As shown in the Fig. 3A and Fig. As shown in Figure 3B, in the gear section 10, an annular projection 51a, which projects radially inwards, is formed on an inner circumferential surface 10a, and a plurality of rod-shaped projections 52a, which project in the axial direction, are formed on both axial end surfaces of the annular projection 51a.

[0019] Fig. 4A is a cross-sectional view of bearing section 20. Fig. 4B is a cross-sectional view along a line IVB-IVB in Fig. 4A. As in the Fig. 4A and Fig. As shown in Figure 4B, an annular groove 51b extending in the circumferential direction is formed on an outer circumferential surface 20b of the bearing section 20, and a plurality of holes 52b extending in the axial direction are formed on both axial end surfaces of the annular groove 51b.

[0020] As in Fig. As shown in Figure 2, the annular projection 51a of the gear section 10 is arranged in the annular groove 51b of the bearing section 20. The gear section 10 and the bearing section 20 are prevented from moving relative to each other by the annular projection 51a and the annular groove 51b, which are in axial contact with each other. Therefore, separation between the gear section 10 and the bearing section 20 can be prevented.

[0021] The rod-shaped projections 52a of the gear section 10 are each arranged in the holes 52b of the bearing section 20. The gear section 10 and the bearing section 20 are prevented from rotating relative to each other because the rod-shaped projections 52a and the holes 52b are in contact with each other in the circumferential direction. Therefore, a rotational force can be reliably transmitted between the gear section 10 and the bearing section 20.

[0022] In gear 100, the annular projection 51a extends over the entire circumference of the gear section 10, and the annular groove 51b extends over the entire circumference of the bearing section 20. Alternatively, the annular projection 51a can also extend circumferentially in a portion of its length. In this case, the annular groove 51b can extend circumferentially in a portion corresponding to the annular projection 51a.

[0023] The annular projection 51a can be formed on the outer circumferential surface 20b of the bearing section 20 instead of the inner circumferential surface 10a of the gear section 10. In this case, the annular groove 51b is formed on the inner circumferential surface 10a of the gear section 10 instead of the outer circumferential surface 20b of the bearing section 20.

[0024] The rod-shaped projections 52a can be formed on the side faces of the annular groove 51b instead of the annular projection 51a itself. In this case, the holes 52b are formed on the end faces of the annular projection 51a instead of the side faces of the annular groove 51b.

[0025] Next, a method for manufacturing the gear 100, in particular a manufacturing step for the bearing section 20, is described with reference to the Fig. 5 to 8 described. In the Fig. Figures 5 to 8 represent the radial length of a gap 80, which will be described later, as well as the extent and shrinkage amount of the gear section 10, shown in exaggerated size.

[0026] The bearing section 20 is produced by a bearing section forming step, in which an annular mold 60 is filled with molten material, and a bearing section cooling step, in which the formed bearing section 20 is cooled. Before the production of the bearing section 20, a radial shrinkage amount B (see Fig. 7A and Fig. 7B) of the bearing section 20 in the bearing section cooling step. In particular, the radial shrinkage amount B of the bearing section 20 is predetermined based on a composition of the molten material, a filling temperature, a filling pressure, a filling quantity, and the like. < Bearing section forming step >

[0027] First, as in the Fig. 5A and Fig. Figure 5B shows the gear section 10, which is a primary molded product that is pre-molded, positioned in the mold 60, and the core section 30 is positioned in the gear section 10. When the gear section 10 is positioned in the mold 60, the gap 80 is formed between an inner circumferential surface of the mold 60 and upper sections of the gear teeth 11 of the gear section 10.

[0028] Here, an inner diameter of the form 60 is determined based on the radial shrinkage amount B of the bearing section 20 in the bearing section cooling step, which was predetermined, and a design value of an outer diameter of the gear section 10. In particular, the inner diameter of the form 60 is determined such that it is a sum of a design value L1 (see Fig. 7B) of the outer diameter of the gear section 10 and a value obtained by doubling the radial shrinkage amount B of the bearing section 20. An outer diameter L2 of the gear section 10 before the bearing section forming step is determined based on the inner diameter of the mold 60 and the radial shrinkage amount B of the bearing section 20 in the bearing section cooling step, which is predetermined. In particular, the outer diameter L2 of the gear section 10 is determined such that a radial length A of the gap 80 is less than the radial shrinkage amount B of the bearing section 20. By determining the inner diameter of the mold 60 and the outer diameter L2 of the gear section 10 in this way, the radial length A of the gap 80 is determined such that it is less than the radial shrinkage amount B of the bearing section 20, which is predetermined.

[0029] Next, as in Fig. 6A and Fig. As shown in Figure 6B, the molten fiber-reinforced resin is poured between the gear section 10 and the core section 30, and the bearing section 20 is formed. In the bearing section forming step, the core section 30 and the bearing section 20 are joined together, and the bearing section 20 and the gear section 10 are fixed to one another via the annular groove 51b and the holes 52b of the bearing section 20 and the annular projection 51a and the rod-shaped projections 52a of the gear section 10. A resin section 71 is formed corresponding to a sprue of the mold. The gear section 10 consists of resin, and when the molten fiber-reinforced resin is poured between the gear section 10 and the core section 30, the gear section 10 expands radially due to the heat and pressure of the fiber-reinforced resin, as shown in the Fig. 6A and Fig. Figure 6B shows that the radial extension of the gear section 10 is limited by the form 60. That is, the gear section 10 extends until it comes into contact with the inner circumferential surface of the form 60, and extends by the length A in the radial direction during the bearing section forming step. <Lagerabschnitt-Kühlschritt>

[0030] Next, the bearing section 20, which was formed in the bearing section forming step, is cooled and solidified. As in the Fig. 7A and Fig. As shown in Figure 7B, in the bearing section cooling step, bearing section 20 shrinks by a length B in the radial direction due to heat shrinkage. Correspondingly, gear section 10 also shrinks by length B with the heat shrinkage of bearing section 20.

[0031] After the bearing section cooling step, the gear section 10, the bearing section 20, and the core section 30 are removed from the mold 60, and the resin section 71, which is not required for a gear 100 configuration, is removed. Accordingly, the in Fig. 2 gears shown 100 completed.

[0032] In this way, the gear section 10 of the gear 100 expands during the bearing section forming step and shrinks during the bearing section cooling step. Therefore, the outer diameter of the gear section 10 changes between before forming and after cooling of the bearing section 20, and residual stress is generated in the gear section. This residual stress can impair the durability of the gear section 10.

[0033] The residual stress generated in gear section 10 is discussed below with reference to the Fig. 8A and Fig. 8B described. Fig. 8A is a view showing a manufacturing step of the gear 100 when the radial length A of the gap 80 is greater than the radial shrinkage amount B of the bearing section 20 in the bearing section cooling step. Fig. Figure 8B is a view showing a manufacturing step of the gear 100 of the present embodiment, in which the radial length A of the gap 80 is smaller than the radial shrinkage amount B of the bearing section 20 in the bearing section cooling step. Fig. 8A and Fig. Figure 8B shows (a) a state before the bearing section forming step, (b) a state after the bearing section forming step, and (c) a state after the bearing section cooling step. In the Fig. 8A and Fig. Figure 8B shows the radial length of the gap 80 as well as the expansion and contraction of the gear section 10 in exaggerated size.

[0034] As in Fig. As shown in Figure 8A, if the radial length A of the gap 80 is greater than the radial shrinkage B of the bearing section 20 during the bearing section cooling step, then the radial expansion A of the gear section 10 during the bearing section forming step is greater than the radial shrinkage B of the gear section 10 during the bearing section cooling step. Therefore, the outer diameter of the gear section after the bearing section cooling step is larger than the outer diameter of the gear section before the bearing section forming step. Consequently, a tensile residual stress is generated in the gear section 10.

[0035] In contrast, in the case of the Fig. In the embodiment shown in Figure 8B, if the radial length A of the gap 80 is smaller than the radial shrinkage B of the bearing section 20 during the bearing section cooling step, the radial expansion A of the gear section 10 during the bearing section forming step is smaller than the radial shrinkage B of the gear section 10 during the bearing section cooling step. Therefore, the outer diameter of the gear section after the bearing section cooling step is smaller than the outer diameter of the gear section before the bearing section forming step. Accordingly, a compressive residual stress is generated in the gear section 10.

[0036] Here it shows Fig.9. The outer diameters of each gear section 10 before, after, and after the bearing section forming step are measured in samples (sample 1 and 2) of the fatigue test NG, in which an anomaly occurs in the gear section 10, and in samples (sample 3 and 4) of the fatigue test OK, in which no anomaly occurs in the gear section 10 in a fatigue test of the gear 100. In the fatigue test NG samples, the outer diameter of the gear section 10 after the bearing section cooling step is larger than the outer diameter of the gear section 10 before the bearing section forming step. This means that a tensile residual stress was generated in the gear section 10 in the fatigue test NG samples.In contrast, in the OK fatigue test samples, the outer diameter of gear section 10 after the bearing section cooling step is smaller than the outer diameter of gear section 10 before the bearing section forming step. This means that compressive residual stress was induced in gear section 10 in the OK fatigue test samples. This confirms that the durability of gear section 10 of gear 100 is high in the samples where compressive residual stress is induced in gear section 10.

[0037] As described above, in the present embodiment, by predetermining the radial length A of the gap 80 to a value smaller than the radial shrinkage B of the bearing section 20, compressive residual stress is generated in the gear section 10 instead of tensile residual stress. Accordingly, the impact on the durability of the gear section 10 of the gear 100 can be reduced. The inner diameter of the mold 60 is determined based on the radial shrinkage B of the bearing section 20 and the design value L1 of the outer diameter of the gear section 10, and the outer diameter L2 of the gear section 10 before the bearing section forming step is determined based on the inner diameter of the mold 60 and the radial shrinkage B of the bearing section 20.Accordingly, the gear 100 can be manufactured with the outer diameter of the design value, while the influence on the durability of the gear section 10 is reduced.

[0038] A method for adjusting the inner diameter of the mold 60 and the outer diameter of the gear section 10 before the bearing section forming step is not limited to what has been said above. At a minimum, the radial length A of the gap 80 must be determined before the bearing section forming step so that it is smaller than the radial shrinkage amount B of the bearing section 20. Accordingly, compressive residual stress is generated in the gear section 10 instead of tensile residual stress, and the influence on the durability of the gear section 10 of the gear 100 can be reduced.

[0039] According to the embodiment described above, the following functions and effects are achieved.

[0040] The radial expansion of the gear section 10 during the bearing section forming step is limited by the mold 60, such that the radial expansion of the gear section 10 during the bearing section forming step is less than the radial shrinkage B of the gear section during the bearing section cooling step. Therefore, the outer diameter of the gear section 10 after the bearing section cooling step is smaller than the outer diameter of the gear section 10 before the bearing section forming step, and thus compressive residual stress is generated in the gear section instead of tensile residual stress. Therefore, the impact on the durability of the gear section 10 of the gear 100 can be reduced.

[0041] The gear 100, which has the outer diameter of the design value, can be manufactured by setting the radial shrinkage amount B of the bearing section 20 in the bearing section cooling step.

[0042] The following section describes a design, functions and effects of the exemplary embodiment of the present invention.

[0043] Method for manufacturing the gear 100, the gear 100 comprising the annular gear section 10 having gear teeth 11 on its outer circumference, the annular bearing section 20 provided on the inner circumferential surface 10a of the gear section 10 and supporting the gear section 10, and the core section 30 provided inside the bearing section 20, the method comprising: the bearing section forming step of forming the bearing section 20 by arranging the gear section 10 and the core section 30 in the annular mold 60 and filling the fiber-reinforced resin between the gear section 10 and the core section 30;and the bearing section cooling step of cooling the bearing section 20, which is formed in the bearing section forming step, in which the radial gap A between the gear teeth 11 of the gear section 10 and the shape 60 is set before the bearing section forming step, such that it is smaller than the radial shrinkage amount B of the bearing section 20 in the bearing section cooling step.

[0044] In this configuration, the radial expansion of the gear section 10 during the bearing section forming step is limited by the die 60, such that the radial expansion of the gear section 10 during the bearing section forming step is less than the radial shrinkage B of the gear section during the bearing section cooling step. Therefore, the outer diameter of the gear section 10 after the bearing section cooling step is smaller than the outer diameter of the gear section 10 before the bearing section forming step. Consequently, compressive residual stress is generated in the gear section instead of tensile residual stress. Therefore, it is possible to provide a gear manufacturing process that reduces the impact on the durability of the gear section.

[0045] The inner diameter of the form 60 is determined on the basis of the radial shrinkage amount B of the bearing section 20 in the bearing section cooling step and the design value L1 of the outer diameter of the gear section 10.

[0046] The outer diameter L2 of the gear section 10 before the bearing section forming step is determined on the basis of the inner diameter of the mold 60 and the radial shrinkage amount B of the bearing section 20 in the bearing section cooling step, which is determined beforehand.

[0047] In this configuration, the gear 100, which has the outer diameter of the design value, can be manufactured by determining the radial shrinkage amount B of the bearing section 20 in the bearing section cooling step.

[0048] The gear 100 comprises the annular gear section 10, which has gear teeth 11 on its outer circumference, the annular bearing section 20, which is provided on the inner circumferential surface 10a of the gear section 10 and supports the gear section 10, and the core section 30, which is provided within the bearing section 20, in which the radial gap A between the gear teeth 11 of the gear section 10 and the annular mold 60 is determined before the bearing section forming step of the bearing section 20 by arranging the gear section 10 and the core section 30 in the mold 60 and filling the space between the gear section 10 and the core section 30 with fiber-reinforced resin, such that it is smaller than the radial shrinkage B of the bearing section 20 in the bearing section cooling step of the formed bearing section 20. is shaped.

[0049] In this configuration, compressive residual stress is generated in gear section 10 instead of tensile residual stress. Therefore, the impact on the durability of gear section 10 of gear 100 is lower.

[0050] Embodiments of the present invention have been described above, but the above-mentioned embodiments are merely examples of applications of the present invention, and the technical scope of the present invention is not limited to the specific embodiments of the above-mentioned embodiments.

[0051] In the embodiment described above, gear 100 was described as the worm gear which meshes with the worm shaft 6, but gear 100 is not limited to the worm gear.

[0052] In the embodiment described above, the bearing section 20 is formed from fiber-reinforced resin, but is not limited to fiber-reinforced resin.

[0053] For example, a resin layer with a different composition than that of bearing section 20 can be inserted between bearing section 20 and core section 30.

Claims

[1] Gear manufacturing method, the gear (100) comprising an annular gear section (10) having teeth on an outer circumference, an annular bearing section (20) provided on an inner circumferential surface (10a) of the gear section (10) and supporting the gear section (10), and a core section (30) provided inside the bearing section (20), the method comprising: a bearing section forming step of the forming of the bearing section (20) by arranging the gear section (10) and the core section (30) in a ring-shaped mold (60) and filling a resin between the gear section (10) and the core section (30); and a bearing section cooling step of cooling the bearing section (20) which is formed in the bearing section forming step, characterized bythat a radial gap (80) between the teeth of the gear section (10) and the mold (60) is specified before the bearing section forming step, such that it is smaller than a radial shrinkage amount (B) of the bearing section (20) in the bearing section cooling step, and a radial expansion of the gear section (10) is limited by the shape (60), such that a radial expansion amount (A) in the bearing section forming step is smaller than the radial shrinkage amount (B) of the bearing section (20) in the bearing section cooling step. [2] The gear manufacturing method according to claim 1, characterized by that an inner diameter of the shape (60) is determined on the basis of the radial shrinkage amount (B) of the bearing section (20) in the bearing section cooling step and a design value of an outer diameter of the gear section (10). [3] The gear manufacturing method according to claim 1, characterized bythat an outer diameter of the gear section (10) is determined before the bearing section forming step on the basis of an inner diameter of the mold (60) and the radial shrinkage amount (B) of the bearing section (20) in the bearing section cooling step.

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