Gear structure, gear device, and method for manufacturing a gear structure

Abstract

This technology provides an advantage in suppressing cracking at the fixed portion. [Solution] The gear comprises an outer gear 24 having a fitting hole 42 and an inner gear 26 having a fitting portion 48 that is fitted integrally with the fitting hole 42 so as to be rotatable. One of the gears, the outer gear 24 and the inner gear 26, is a one-side gear 80, which has a fixing portion 84 that fixes the outer gear 24 and the inner gear 26 in the axial direction. The hardness of the fixing portion 84 is lower than the hardness of the tooth surface of the one-side gear 80. This is advantageous in suppressing cracking at the fixing portion.

Description

Technical Field

[0001] The present disclosure relates to a gear structure.

Background Art

[0002] Patent Document 1 discloses a gear structure including an outer gear having a fitting hole and an inner gear having a fitting portion that is fitted to rotate integrally with the fitting hole. In this gear structure, a fixing portion for fixing the outer gear and the inner gear in the axial direction is formed on one of the outer gear and the inner gear, which is one gear.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the inventor of the present application examined the disclosed technology of Patent Document 1, it was recognized that there are the following problems. On the tooth surface of one gear, usually, high hardness is required to ensure fatigue strength. Suppose a case where the fixing portion of one gear has the same hardness as such a tooth surface is considered. In this case, when forming the fixing portion on one gear by caulking, the hardness of the portion to be caulked becomes high, resulting in a small elongation, which may cause cracking at the fixing portion.

[0005] Therefore, one object of the present disclosure is to provide a technique for advantageously suppressing cracking at the fixing portion.

Means for Solving the Problems

[0006] A gear structure according to one aspect of the present disclosure comprises an outer gear having a fitting hole and an inner gear having a fitting portion that is rotatably fitted integrally with the fitting hole, wherein one of the outer gear and the inner gear has a fixing portion that fixes the outer gear and the inner gear in the axial direction, and the hardness of the fixing portion is lower than the hardness of the tooth surface of the inner gear.

[0007] A method for manufacturing a gear structure according to one aspect of the present disclosure is a method for manufacturing a gear structure comprising an outer gear having a fitting hole and an inner gear having a fitting portion that is rotatably fitted integrally with the fitting hole, the method comprising a heat treatment step of hardening at least the tooth surface of one of the outer gear and the inner gear by heat treatment, and a crimping step of forming a fixing portion on the inner gear that fixes the outer gear and the inner gear in the axial direction, wherein the crimping step is performed by crimping a location to be crimped that has a lower hardness than the tooth surface after the heat treatment step, thereby forming the fixing portion on the inner gear. [Effects of the Invention]

[0008] According to this disclosure, it is advantageous in suppressing cracking at the fixed portion. [Brief explanation of the drawing]

[0009] [Figure 1] This is a side cross-sectional view showing a gear device according to the first embodiment. [Figure 2] This is a perspective view showing a gear structure according to the first embodiment. [Figure 3] This is a side cross-sectional view showing a gear structure according to the first embodiment. [Figure 4] This is a cross-sectional view AA in Figure 3. [Figure 5] This is a front view showing a gear structure according to the first embodiment. [Figure 6] This is a magnified view of a portion of Figure 5. [Figure 7] This is a schematic side cross-sectional view showing the hardness distribution of the gear structure of the first embodiment. [Figure 8]This is a flowchart showing the first manufacturing method. [Figure 9] Figure 9(A) is an explanatory diagram showing the hardness distribution of one gear after the first heat treatment step in the first manufacturing method, Figure 9(B) is an explanatory diagram showing the hardness distribution of the other gear after the second heat treatment step, and Figure 9(C) is an explanatory diagram showing the state of the outer gear and inner gear after the insertion step. [Figure 10] This is an explanatory diagram showing the crimping process. [Figure 11] This is a flowchart showing the second manufacturing method. [Figure 12] Figure 12(A) is a schematic side cross-sectional view showing the hardness distribution of one gear after the first heat treatment step in the second manufacturing method, and Figure 12(B) is a schematic side cross-sectional view showing the hardness distribution after the softening treatment. [Figure 13] This is a front view showing a gear structure of the second embodiment. [Figure 14] Figure 14(A) is a cross-sectional view of section BB of Figure 13, and Figure 14(B) is a cross-sectional view of section CC of Figure 13. [Modes for carrying out the invention]

[0010] Embodiments for carrying out the gear structure of this disclosure are described below. Identical or equivalent elements are denoted by the same reference numeral, and redundant descriptions are omitted. For the sake of clarity, components are omitted, enlarged, or reduced in each drawing. The drawings should be viewed in accordance with the orientation of the reference numerals.

[0011] (First Embodiment) Refer to FIG. 1. The gear structure 10 is used in the gear device 12. An input rotation with a first rotational speed output from a drive source is input to the gear device 12. The drive source is, for example, a motor, an engine, or the like. The gear device 12 can output the input rotation with the first rotational speed after shifting it to an output rotation with a second rotational speed. The gear device 12 of this embodiment functions as a reduction device for reducing the input rotation, but may also function as a speed increasing device for increasing the input rotation. The gear device 12 is used in, for example, (1) robots such as industrial robots, service robots, and assist robots, (2) industrial machines such as machine tools and construction machines, (3) conveying machines such as conveyors and film conveying devices, and (4) various machines such as vehicles.

[0012] The gear structure 10 of this embodiment is incorporated into a planetary gear mechanism. The gear device 12 using this planetary gear mechanism includes, in addition to the gear structure 10, a sun gear 14, a carrier 16, a first internal gear 18, and a second internal gear 20.

[0013] An input rotation is input to the sun gear 14 via an input shaft 22. The input shaft 22 is rotatably supported by a bearing in a casing (not shown).

[0014] The gear structure 10 is arranged as a planetary gear on the radially outer side of the sun gear 14. In this embodiment, three gear structures 10 are arranged at equal angular intervals in the circumferential direction of the sun gear 14, but the number thereof is not particularly limited. The gear structure 10 includes an outer gear 24 that meshes with the sun gear 14 and the first internal gear 18, and an inner gear 26 that meshes with the second internal gear 20. Details of the gear structure 10 will be described later.

[0015] A central hole 28 penetrating the gear structure 10 in the axial direction is formed at the center of the gear structure 10. A pin 30 fixed to the carrier 16 is inserted into the central hole 28. A gear bearing 32 is arranged between the central hole 28 of the gear structure 10 and the pin 30. The gear structure 10 is rotatably supported by the gear bearing 32. The gear bearing 32 is, for example, a needle bearing, but is not limited thereto, and various bearings such as ball bearings may be used.

[0016] The carrier 16 is arranged in the axial direction of the gear structure 10 with respect to the gear structure 10. In the carrier 16 of this embodiment, a window hole 16a extending in the radial direction of the sun gear 14 from the center portion of the carrier 16 is formed. The gear structure 10 is arranged in the window hole 16a of the carrier 16.

[0017] The first internal gear 18 is arranged on the outer side in the radial direction of the sun gear 14. The first internal gear 18 is fixed to a casing (not shown).

[0018] The second internal gear 20 is provided on the output side with respect to the first internal gear 18. The second internal gear 20 is rotatably supported with respect to a casing (not shown) via a bearing (not shown). A bearing 34 is arranged between the carrier 16 and the second internal gear 20. The number of teeth of the second internal gear 20 is different from the number of teeth of the first internal gear 18. The second internal gear 20 is provided so as to be integrally rotatable with an output shaft 36 for outputting an output rotation.

[0019] The operation of the above-described gear device 12 will be described. When an input rotation with a first rotational speed is input to the sun gear 14, the gear structure 10 rotates on its own due to the meshing between the sun gear 14 and the outer gear 24 of the gear structure 10. The gear structure 10 revolves around the sun gear 14 as it rotates on its own due to the meshing between its outer gear 24 and the first internal gear 18. At this time, the gear structure 10 revolves at an intermediate rotational speed lower than the first rotational speed. As the gear structure 10 revolves, the second internal gear 20 rotates with respect to the first internal gear 18 at a rotational speed corresponding to the difference in the number of teeth between the first internal gear 18 and the second internal gear 20. At this time, the second internal gear 20 rotates at a second rotational speed lower than the intermediate rotational speed. As a result, the second internal gear 20 and the output shaft 36 rotate at a second rotational speed decelerated from the first rotational speed, and an output rotation with the second rotational speed is output from the output shaft 36.

[0020] Refer to FIGS. 2 and 3. Move on to the description of the gear structure 10. Hereinafter, there may be cases where the description is made simply by referring to the "axial direction", "circumferential direction", and "radial direction" with respect to the axial direction, circumferential direction, and radial direction of the gear structure 10.

[0021] The outer gear 24 comprises a plurality of first gear teeth 40 and a fitting hole 42 provided in the center of the outer gear 24. The inner gear 26 comprises a plurality of second gear teeth 44, a gear portion 46 provided with the plurality of second gear teeth 44, and a fitting portion 48 that fits into the fitting hole 42.

[0022] Multiple first gear teeth 40 are for meshing with other first external gears and are provided on the outer circumference of the outer gear 24. In this embodiment, the first external gears are the sun gear 14 and the first internal gear 18.

[0023] Multiple second gear teeth 44 are for meshing with other second external gears and are provided on the outer circumference of the gear portion 46 of the internal gear 26. In this embodiment, the second external gear is the second internal gear 20. In this embodiment, although not shown in the figures, the tip circle diameter of the second gear teeth 44 is less than the tip circle diameter of the first gear teeth 40. Alternatively, the tip circle diameter of the second gear teeth 44 may be greater than or equal to the tip circle diameter of the first gear teeth 40.

[0024] The fitting portion 48 of the inner gear 26 is inserted into the fitting hole 42 of the outer gear 24 in the insertion direction D1. The fitting portion 48 is fitted into the fitting hole 42 by, for example, a clearance fit or an intermediate fit, but may also be fitted by an interference fit. The fitting portion 48 is provided on the insertion direction D1 side of the gear portion 46 of the inner gear 26.

[0025] The outer gear 24 has a first side surface 50 facing the insertion direction D1. The first side surface 50 has a first outer surface 52 facing the insertion direction D1. The inner gear 26 has a second side surface 54 facing the insertion direction D1. The second side surface 54 has a second outer surface 56 facing the insertion direction D1. In this embodiment, the axial positions of the first outer surface 52 and the second outer surface 56 are aligned.

[0026] The inner gear 26 is provided with a movement restraint portion 58 that is provided with respect to the fitting portion 48 in the axial direction opposite to the insertion direction D1 (hereinafter referred to as the anti-insertion direction D2). The movement restraint portion 58 has a stepped shape that protrudes radially outward toward the anti-insertion direction D2. The outer gear 24 is restrained from axial movement toward the anti-insertion direction D2 by contacting the movement restraint portion 58 of the inner gear 26. In this embodiment, the movement restraint portion 58 is formed at the end of the second gear tooth 44 on the insertion direction D1 side.

[0027] The inner gear 26 is provided with the aforementioned central hole 28 in which the contact member 60 is positioned on the inside. The central hole 28 is formed in the center of the inner gear 26. In this embodiment, the central hole 28 penetrates the inner gear 26 in the axial direction, but it does not have to penetrate. In this embodiment, the contact member 60 is the rolling element 32a of the gear bearing 32 (see also Figure 1). The specific example of the contact member 60 is not particularly limited and may be a pin 30, a roller, etc. A contact surface 62 is provided on the inner circumferential surface of the central hole 28, into which the contact member 60 makes rolling or sliding contact. In this embodiment, the rolling element 32a, which is the contact member 60, makes rolling contact with the contact surface 62.

[0028] Refer to Figure 4. The fitting hole 42 of the outer gear 24 is provided with a female spline structure 70. The female spline structure 70 is provided on the inner circumference of the fitting hole 42. The female spline structure 70 is provided with a plurality of female spline teeth 70a that protrude radially inward. The plurality of female spline teeth 70a are spaced apart in the circumferential direction, and tooth grooves 70b are formed between adjacent female spline teeth 70a.

[0029] The mating portion 48 of the internal gear 26 is provided with a male spline structure 72 that mates with a female spline structure 70. The male spline structure 72 is provided on the outer circumference of the mating portion 48. The male spline structure 72 is provided with a plurality of male spline teeth 72a that protrude radially outward. The male spline teeth 72a have a shape that is an extension of the second gear tooth 44 in the axial direction, and the tooth tip portion of the second gear tooth 44 has been cut off.

[0030] Each of the multiple male spline teeth 72a is fitted into the tooth groove 70b between the female spline teeth 70a. This fitting of the male spline teeth 72a and the tooth groove 70b between the female spline teeth 70a enables torque to be transmitted between the fitting portion 48 and the fitting hole 42. It can also be said that torque can be transmitted between the fitting portion 48 and the fitting hole 42 by fitting the male spline structure 72 and the female spline structure 70. As a result, the fitting portion 48 is fitted so as to be able to rotate integrally with the fitting hole 42.

[0031] Refer to Figures 2, 3, and 5. Of the outer gear 24 and the inner gear 26, one gear is called the inner gear 80, and the other gear is called the outer gear 82. In this embodiment, the inner gear 80 is the inner gear 26, and the outer gear 82 is the outer gear 24.

[0032] One gear 80 (in this case, the inner gear 26) has a fixing portion 84 formed therein that fixes the inner gear 26 and the outer gear 24 in the axial direction. The fixing portion 84 is made up of the crimped portion of the one gear 80. The fixing portion 84 is made up of a part of the one gear 80. It can also be said that the fixing portion 84 fixes the inner gear 26 and the outer gear 24 in the axial direction by crimping. To achieve this, the fixing portion 84 of the one gear 80 may fix the inner gear 26 and the outer gear 24 in the axial direction by being in close contact with the other gear 82. The fixing portion 84 is formed on the side surface 54 of the one gear 80 that faces the insertion direction D1. The fixing portion 84 is formed to be recessed in the axial direction toward the opposite insertion direction D2 than the outer surface 56 of the side surface 54 of the one gear 80. In this embodiment, the fixing portion 84 is formed on the side surface 54 of the one gear 80 on at least one of the multiple spline teeth 72a of the one gear 80. In this embodiment, the fixing portion 84 is formed on all the spline teeth 72a of the spline structure 72 of the gear 80, but it may also be formed on one or more of the spline teeth 72a.

[0033] The first side surface portion 50 of the outer gear 24 is optionally formed with an axial recess 86 that is recessed in the axial direction compared to the first outer surface portion 52. The axial recess 86 is provided on the periphery of the fitting hole 42 of the outer gear 24 on the first side surface portion 50. In this embodiment, the axial recess 86 is provided in a circumferential shape that extends in the circumferential direction, and as an example, it is provided in an annular shape that is continuous in the circumferential direction.

[0034] Refer to Figures 3 and 6. The fixing portion 84 of the inner gear 26 overlaps with the outer gear 24 when viewed from the axial direction on the insertion direction D1 side relative to the outer gear 24. As a result, the fixing portion 84 of the inner gear 26 restricts the movement of the outer gear 24 in the insertion direction D1 side. The fixing portion 84 formed on the male spline tooth 72a in this embodiment is provided so as to overlap with a part of each adjacent female spline tooth 70a when viewed from the axial direction. An intertooth gap 88 is provided between the tooth tip of the male spline tooth 72a and the tooth root of the female spline tooth 70a. A part of the fixing portion 84 in this embodiment is located radially outward from this intertooth gap 88 when viewed from the axial direction, and is also provided so as to overlap with a portion 90 radially outward from the tooth root of the female spline tooth 70a.

[0035] The fixing portion 84 of the inner gear 26 is positioned within the axial recess 86 of the outer gear 24. The fixing portion 84 is positioned so as to fit within the axial recess 86 when viewed from the radial direction, and does not protrude axially outward from the axial recess 86. Multiple fixing portions 84 are positioned within the common axial recess 86 of the outer gear 24.

[0036] The axial recess 86 only needs to be located on at least one side in the circumferential direction and radially outward from the male spline tooth 72a (radially convex portion described later) on which the fixed portion 84 is formed, when viewed from the axial direction. In this embodiment, the axial recess 86 is located on both sides in the circumferential direction and radially outward from the male spline tooth 72a. In the case of being located circumferentially from the male spline tooth 72a, the axial recess 86 in this embodiment is formed on the female spline tooth 70a of the outer gear 24. In the case of being located radially from the male spline tooth 72a, the axial recess 86 in this embodiment is formed on the portion 90 radially outward from the female spline tooth 70a of the outer gear 24.

[0037] Refer to Figure 7. In Figure 7, different hatching is used to indicate areas with different hardness in the cross-section of the same member. The same applies to subsequent cross-sectional views. On the outer surface of one gear 80, there is a first high-hardness region 100 and a first low-hardness region 102 which is less hard than the first high-hardness region 100. On the outer surface of the other gear 82, there is a second high-hardness region 104 and a second low-hardness region 106 which is less hard than the second high-hardness region 104. The outer surface here refers to the surface of the member being referred to that is exposed to the external space. This outer surface includes the tooth surface 108 of the first gear 80, the tooth surface 110 of the other gear 82, and the side surfaces 50 and 52. It also includes the contact surface 62 of the first gear 80 (inner gear 26). The tooth surface 108 of the first gear 80 here refers to the surface of the gear teeth 44 of the first gear 80 that meshes with the outer gear. Furthermore, the tooth surface 110 of the other gear 82 refers to the surface of the gear teeth 40 of the other gear 82 that meshes with the external gear.

[0038] On the other hand, the hardness of the fixed portion 84 of the gear 80 is lower than the hardness of the tooth surface 108 of the gear 80. Hereinafter, this condition will be referred to as the first hardness condition. In order to satisfy the first hardness condition, a high-hardness region 100 is provided on at least the tooth surface 108 of the gear 80, and a low-hardness region 102 is provided on the fixed portion 84 of the gear 80. The tooth surface 108 of the gear 80 is prone to wear due to meshing with the external gear, and high hardness is required to ensure fatigue strength. Compared to the required hardness of such a tooth surface 108, the hardness of the fixed portion 84 is made lower.

[0039] The difference in hardness between the fixed portion 84 and the tooth surface 108 is, for example, at least 50 Hv on the Vickers hardness scale. In this embodiment, the hardness of the fixed portion 84 of the gear 80 is lower than the hardness of the entire outer surface within the axial range in which the gear teeth 44 are provided, but it is sufficient that it is lower than the hardness of the tooth surface 108. The first hardness condition only needs to be satisfied in the relationship between at least one fixed portion 84 and the tooth surface 108 of the gear 80 if there are multiple fixed portions 84. The first hardness condition may be satisfied in relation to all fixed portions 84, or in relation to one or more fixed portions 84.

[0040] On the other hand, the hardness of the fixed portion 84 of the gear 80 is lower than the hardness of the contact surface 62 of the gear 80 (inner gear 26). Hereinafter, this condition will be referred to as the second hardness condition. In order to satisfy the second hardness condition, a high-hardness region 100 is also provided on the contact surface 62 of the gear 80. The contact surface 62 of the gear 80 is prone to wear due to rolling or sliding contact with the contact member 60, and high hardness is required to ensure fatigue strength. The hardness of the fixed portion 84 is lower than the required hardness for such a contact surface 62.

[0041] The difference in hardness between the hardness of the fixed portion 84 and the hardness of the contact surface 62 is, for example, at least 50 Hv on the Vickers hardness scale. In this embodiment, the hardness of the fixed portion 84 of the internal gear 26 is lower than the hardness of the entire inner circumferential surface of the central hole 28, but it is sufficient that it is lower than the hardness of the contact surface 62. The second hardness condition only needs to be satisfied in the relationship between at least one fixed portion 84 and the contact surface 62 if there are multiple fixed portions 84. The second hardness condition may be satisfied in relation to all fixed portions 84, or it may be satisfied by one or more fixed portions 84.

[0042] The high-hardness regions 100 and 104 are provided by hardening the base material 112 of each gear 80 and 82 through heat treatment of the intermediate products of each gear 80 and 82. Here, the base material 112 refers to the part of the member that is heat-treated that exists before the heat treatment. The low-hardness regions 102 and 106 are provided, for example, by either (1) or (2) below.

[0043] (1) is the case in which the aforementioned heat treatment is partially applied to at least the tooth surfaces 108 and 110 of the outer surfaces of the gears 80 and 82, and the heat treatment is not applied to the areas on the outer surfaces where low-hardness regions 102 and 106 should be provided. In the case of (1), in the areas where heat treatment is applied, a high-hardness region 100 is provided by the partial hardening of the base material 112 of the gear 80, and in the areas where heat treatment is not applied, a low-hardness region 102 is provided by the base material 112 itself. This embodiment shows the case of (1).

[0044] (2) is a case in which the aforementioned heat treatment is applied to at least the tooth surface 108 and the areas where low hardness regions 102 and 106 are to be provided on the outer surface of one gear 80, and then the areas where low hardness regions 102 and 106 are to be provided are softened by a softening treatment. In the case of (2), high hardness regions 100 are provided in the areas where heat treatment has been applied but softening treatment has not been applied, and low hardness regions 102 are provided separately from the base material 112 in the areas where softening treatment has been applied.

[0045] The heat treatments used in (1) and (2) are, for example, quenching and nitriding. On the other hand, when partially heat-treating the outer surface of the gear 80, partial quenching such as laser quenching and high-frequency induction quenching may be used. Alternatively, in this case, the outer surfaces of the gears 80 and 82 may be partially heat-treated by masking parts of the gears 80 and 82 with a carburizing treatment and then heat-treating the unmasked parts of the gears 80 and 82 in a heat treatment furnace. The softening treatment used in (2) is achieved, for example, by partially tempering the hardened areas due to quenching by laser irradiation.

[0046] In this embodiment, the hardness of the fixed portion 84 of the one gear 80 is lower than the hardness of the tooth surface 110 of the other gear 82. To satisfy this condition, a second high-hardness region 104 is provided on the tooth surface 110 of the other gear 82. The hardness of the tooth surface 108 of the one gear 80 and the hardness of the tooth surface 110 of the other gear 82 may be the same or different.

[0047] The effects of the gear structure 10 described above will now be explained.

[0048] (A) On the other hand, the hardness of the fixed portion 84 of the gear 80 is lower than the hardness of the tooth surface 108 of the gear 80. Therefore, compared to the case where the hardness of the fixed portion 84 is the same as that of the tooth surface 108, when forming the fixed portion 84 on the gear 80 by crimping, the elongation is greater because the hardness of the planned crimping location (described later) is lower. This is advantageous in suppressing cracking in the fixed portion 84 due to crimping. Also, compared to the case where the hardness of the tooth surface 108 is the same as that of the fixed portion 84, increasing the hardness of the tooth surface 108 is advantageous in improving the fatigue strength of the tooth surface 108. In other words, lowering the hardness of the fixed portion 84 is advantageous in suppressing cracking in the fixed portion 84 due to crimping, while increasing the hardness of the tooth surface 108 is advantageous in improving the fatigue strength of the tooth surface 108. These effects become more pronounced as the difference in hardness between the hardness of the tooth surface 108 and the hardness of the fixed portion 84 increases. On the other hand, the hardness of the tooth surface 108 of the gear 80 and the fixed part 84 increases as the carbon content increases when carbon steel, such as carbon steel for machine structures, is used and heat treatment such as quenching is performed. Furthermore, when it is stated in this specification that it is "advantageous for suppressing cracks in the fixed part 84", it is also advantageous for suppressing internal cracks in the fixed part 84.

[0049] The fixing portion 84 is formed on the inner gear 26 and overlaps with the outer gear 24 when viewed from the axial direction on the insertion direction D1 side relative to the outer gear 24. This allows the fixing portion 84 of the inner gear 26 to restrain the movement of the outer gear 24 in the insertion direction D1 side. Therefore, the strength of the fixing portion 84 can be increased compared to simply forming the fixing portion 84 so that the fitting hole 42 of the outer gear 24 and the fitting portion 48 of the inner gear 26 are in close contact. In particular, this is advantageous in maintaining the axial fixed state of the outer gear 24 and the inner gear 26 by the fixing portion 84, even when large loads are repeatedly applied.

[0050] The fixing portion 84 of the inner gear 26 is positioned within the axial recess 86 of the outer gear 24. This allows the axial length of the gear structure 10 to be reduced by the axial length of the fixing portion 84 within the axial recess 86, compared to the case where the fixing portion 84 of the inner gear 26 is positioned outside the axial recess 86 of the outer gear 24.

[0051] The hardness of the fixing portion 84 of the internal gear 26 is lower than the hardness of the contact surface 62 of the internal gear 26. Therefore, compared to the case where the hardness of the fixing portion 84 is the same as that of the contact surface 62, lowering the hardness of the fixing portion 84 is advantageous in suppressing cracking at the fixing portion 84 due to crimping. Also, compared to the case where the hardness of the contact surface 62 is the same as that of the fixing portion 84, increasing the hardness of the contact surface 62 is advantageous in improving the fatigue strength of the contact surface 62.

[0052] The fixed portion 84 is formed on at least one spline tooth 72a of the spline structure 70. This allows the fixed portion 84 to be formed using the spline tooth 72a of the spline structure 70, which is used to enable the outer gear 24 and the inner gear 26 to rotate together. Therefore, when forming the fixed portion 84, it is not necessary to provide a separate part for the fixed portion 84 from the spline structure 70, and the gear structure 10 can be simplified.

[0053] An example of a manufacturing method for obtaining the gear structure 10 described above will be explained. Two manufacturing methods will be described here. Refer to Figure 8. First, the first manufacturing method will be explained. The first manufacturing method mainly includes a preparation step S10, a first heat treatment step S12, a second heat treatment step S14, an insertion step S16, and a crimping step S18.

[0054] In preparation step S10, intermediate products of the outer gear 24 and inner gear 26 are prepared. These intermediate products may have the same components as the inner gear 26 and outer gear 24 used in the finished gear structure 10, except for the fixing portion 84. For example, the intermediate product of the outer gear 24 may have a plurality of first gear teeth 40 and a fitting hole 42. The intermediate product of the inner gear 26 may have a plurality of second gear teeth 44, a gear portion 46 and a fitting portion 48. The intermediate product of the inner gear 26 does not have the fixing portion 84 in a step prior to the crimping step S18. Each subsequent step is performed on the intermediate products of the inner gear 26 and outer gear 24.

[0055] Refer to Figure 9(A). In the first heat treatment step S12, at least the tooth surface 108 of the outer surface of the one gear 80 (in this case, the inner gear 26) is partially hardened by heat treatment. In the first heat treatment step S12 of this embodiment, the contact surface 62 of the one gear 80 is also hardened by heat treatment. For example, laser hardening is used for this heat treatment. In the heat-treated areas of the one gear 80, the base material 112 hardens, creating a first high-hardness region 100. In contrast, in the areas that are not heat-treated, a first low-hardness region 102 is created by the base material 112. In this first heat treatment step S12, the crimping area 120 of the one gear 80 is not heat-treated. As a result, the hardness of the tooth surface 108 of the one gear 80 becomes higher than the hardness of the crimping area 120. In this embodiment, the hardness of the contact surface 62 of the gear 80 is also higher than the hardness of the crimping location 120. The crimping location 120 here refers to the location on the gear 80 of the finished gear structure 10 obtained by this manufacturing method where the fixing portion 84 is to be formed. In this embodiment, the location of the spline teeth 72a on the side surface 54 of the gear 80 is the crimping location 120.

[0056] Refer to Figure 9(B). In the second heat treatment step S14, at least the tooth surface 110 of the other gear 82 (in this case, the outer gear 24) is hardened by heat treatment. Here, similar to the first heat treatment step S12, an example is shown in which at least the tooth surface 110 of the outer surface of the other gear 82 is partially hardened by heat treatment. In the heat-treated areas of the other gear 82, a second high-hardness region 104 is provided by the hardening of the base material. In contrast, in the areas that are not heat-treated, a second low-hardness region 106 is provided, which is composed of the base material. This heat treatment may be the same as or different from the heat treatment used in the first heat treatment step S12.

[0057] Refer to Figure 9(C). In insertion step S16, the fitting portion 48 of the inner gear 26 is inserted into the fitting hole 42 of the outer gear 24 in the insertion direction D1, thereby fitting the fitting portion 48 into the fitting hole 42.

[0058] Refer to Figure 10. In the crimping process S18, a fixed portion 84 is formed on the gear 80 by crimping the crimping target location 120 on the gear 80. In the crimping process, a crimping jig 122 such as a pin is placed on the insertion direction D1 side relative to the crimping target location 120 of the gear 80. After this, the crimping jig 122 is pressed against the crimping target location 120 of the gear 80, and the fixed portion 84 is formed by plastically deforming (plastic flow) the crimping target location 120. At this time, the crimping target location 120 is crimped at a hardness lower than the tooth surface 108 of the gear 80 after the first heat treatment process S12.

[0059] In the manufacturing method described above, a fixed portion 84 is formed on one gear 80 by crimping a crimping target area 120 that has a lower hardness than the tooth surface 108 of one gear 80 after the heat treatment process. Therefore, as with (A) described above, this method is advantageous in suppressing cracking at the fixed portion 84 due to crimping, compared to the case where the hardness of the crimping target area 120 is the same as the hardness of the tooth surface 108. In addition, the same effects as with (A) described above can be obtained.

[0060] Furthermore, in the first heat treatment step of the first manufacturing method, at least the tooth surface 108 of the outer surface of the one gear 80 is partially hardened by heat treatment, while the crimping area 120 of the one gear 80 is not subjected to heat treatment. This makes it possible to make the hardness of the crimping area 120 of the one gear 80 lower than the hardness of the tooth surface 108 when the crimping step S18 is performed after the first heat treatment step S12.

[0061] Refer to Figure 11. Next, the second manufacturing method will be described. The second manufacturing method differs in that, in addition to the first heat treatment step S12, it includes a softening step S20 in which a softening treatment is applied to the crimping area 120 of the gear 80.

[0062] Refer to Figure 12(A). In this first heat treatment step S12, at least the tooth surface 108 and the crimping area 120 of the outer surface of the gear 80 are hardened by heat treatment. As a result, a first high-hardness region 100 is provided not only on the tooth surface 108 of the gear 80 but also on the crimping area 120. Here, we show an example in which the spline teeth 72a, including the crimping area 120, in addition to the tooth surface 108 and contact surface 62 of the outer surface of the gear 80, are partially hardened by heat treatment. Alternatively, the entire outer surface of the gear 80 may be heat treated.

[0063] Refer to Figure 12(B). The softening step S20 is performed after the first heat treatment step S12. In this softening step S20, a softening treatment is applied so that the crimping area 120 of the one gear 80 that has been hardened by the first heat treatment step S12 is softened. At this time, the softening treatment is applied so that the hardness of the crimping area 120 is lower than the hardness of the tooth surface 108 of the one gear 80 that has been hardened by the first heat treatment step. As a result, a first low hardness area 102 is provided at the crimping area 120 of the one gear 80, which is softer than the first high hardness area 100. This first low hardness area 102 is provided separately from the base material 112. For example, the heat treatment used in the first heat treatment step S12 may be achieved by partial hardening by laser irradiation, and the softening treatment used in the softening step S20 may be achieved by partially tempering the hardened area by irradiation with a laser or the like. The rest of the process is the same as described above.

[0064] This makes it possible to make the hardness of the planned crimping location 120 of the gear 80 lower than the hardness of the tooth surface 108 when the crimping process S18 is performed after the first heat treatment process S12.

[0065] Next, other features of the gear structure 10 will be described. The materials that make up each gear 80, 82 are not particularly limited. For example, each gear 80, 82 may be made of any metal that can be hardened by heat treatment, such as iron or aluminum. Also, each gear 80, 82 may be made of either carbon steel or alloy steel. In this case, both gears 80, 82 may be made of carbon steel, or both may be made of alloy steel.

[0066] Here, carbon steel follows the definition in "JIS G 0203:2009" section "4.1.1 (Types of Steel) No. 1104". In other words, carbon steel here refers to "steel that is an alloy of iron and carbon, with a carbon content typically in the range of 0.02 to approximately 2%". Examples of this carbon steel include carbon steel for machine structures and carbon steel for general structural use. Furthermore, alloy steel here follows the definition in "JIS G 0203:2009" section "4.1.1 (Types of Steel) No. 1105". In other words, alloy steel here refers to "steel that contains one or more alloying elements in order to improve or enhance the properties of the steel, or to give it specific properties", and the content of at least one alloying element is equal to or greater than the specified content. Steel with an alloying element content below the specified content is classified as carbon steel. Examples of this alloy steel include alloy steel for machine structures, stainless steel, and high-tensile steel.

[0067] The gear 80 on which the fixed portion 84 is formed may be made of alloy steel, while the gear 82 on the other side may be made of carbon steel. The advantages of this will be explained. Alloy steel generally has superior elongation properties compared to carbon steel. Also, carbon steel is generally less expensive than alloy steel. The gear 80 on the other side is made of alloy steel with such superior elongation properties. Therefore, compared to the case where carbon steel is used for the gear 80 on the other side, when forming the fixed portion 84 by crimping, the elongation of the crimping location 120 will be greater, which may be advantageous in suppressing cracking at the fixed portion 84. Also, the gear 82 on the other side, which does not have a fixed portion 84, is made of carbon steel. Therefore, compared to the case where alloy steel is used for the gear 82 on the other side, this may be advantageous in reducing the cost of the gear structure 10. In particular, when the fixed portion 84 of the inner gear 26 overlaps with the outer gear 24 when viewed from the axial direction, the amount of plastic deformation when crimping the crimping location becomes large, making it easier for cracking due to crimping to occur. Even under the premise that such problems are likely to occur, this is effective in suppressing them.

[0068] (Second Embodiment) Refer to Figures 13, 14(A), and 14(B). In subsequent embodiments, the same content as in the first embodiment may apply to components described in the first embodiment that are not described below.

[0069] In this embodiment, the fixing portion 84 is formed on some of the spline teeth 72a among the multiple spline teeth 72a, but not on the other spline teeth 72a. For the sake of explanation, the spline teeth 72a on which the fixing portion 84 is formed will be referred to as crimped spline teeth 72a-A (first spline teeth), and the spline teeth 72a on which the fixing portion 84 is not formed will be referred to as uncrimped spline teeth 72a-B (second spline teeth). In this embodiment, an example is shown where only one of the spline teeth 72a is a crimped spline tooth 72a-A, but the number of crimped spline teeth 72a-A is not particularly limited.

[0070] The hardness of the fixed portion 84 is lower than the hardness of at least a portion of the uncrimped spline teeth 72a-B. This condition is called the third hardness condition. In order to satisfy the third hardness condition, in this embodiment, a first high-hardness region 100 is formed on the uncrimped spline teeth 72a-B, and a first low-hardness region 102 is formed on the fixed portion 84. In this embodiment, the hardness of the fixed portion 84 is lower than the hardness of the tooth surface over the entire axial range of the uncrimped spline teeth 72a-B, and also lower than the hardness of the end face on the insertion direction D1 side of the uncrimped spline teeth 72a-B. In this embodiment, an example is shown where the hardness of the fixed portion 84 is lower than the overall hardness of the uncrimped spline teeth 72a-B in order to satisfy the third hardness condition. However, it is not limited to this, and the hardness of the fixed portion 84 only needs to be lower than a portion of the uncrimped spline teeth 72a-B (for example, a portion of either the tooth surface or the end face). These hardness differences are, for example, at least 50 Hv on the Vickers hardness scale. The third hardness condition only needs to be satisfied in relation to one fixed part 84 and at least one of the multiple uncrimped spline teeth 72a-B. Also, if there are multiple fixed parts 84, the third hardness condition only needs to be satisfied in relation to at least one fixed part 84 and the uncrimped spline teeth 72a-B.

[0071] The hardness of the fixed portion 84 is lower than the hardness of the uncrimped spline teeth 72a-B. Therefore, compared to the case where the hardness of the fixed portion 84 is the same as that of the uncrimped spline teeth 72a-B, lowering the hardness of the fixed portion 84 is advantageous in suppressing cracking of the fixed portion 84 due to crimping. Also, compared to the case where the hardness of the uncrimped spline teeth 72a-B is the same as that of the fixed portion 84, increasing the hardness of the uncrimped spline teeth 72a-B is advantageous in improving their strength.

[0072] Consider the case where, as in the second manufacturing method described above, heat treatment is applied to each spline tooth 72a of the intermediate product of the gear 80 in the first heat treatment step, and then the hardness of the crimping area 120 is lowered by a softening treatment. In this case, if the hardness of the fixed part 84 is lower than the hardness of the uncrimped spline teeth 72a-B, it is sufficient to apply the softening treatment only to the crimping area 120, and it is not necessary to apply the softening treatment to the uncrimped spline teeth 72a-B. Therefore, the labor required for the softening treatment can be reduced.

[0073] Next, we will describe the transformation forms of each component described so far.

[0074] The specific examples of the gear mechanism into which the gear structure 10 is incorporated are not particularly limited. This gear mechanism may be, for example, a planetary gear mechanism having a sun gear and a plurality of planetary gears as in the embodiment, an eccentric oscillating gear mechanism having an oscillating gear that oscillates by an eccentric body, or a flexible meshing gear mechanism having a flexible gear that flexes and deforms by a vibrating body, or other planetary gear mechanisms. In addition, the gear mechanism may be various other gear mechanisms other than planetary gear mechanisms, such as orthogonal axis gear mechanisms or parallel axis gear mechanisms.

[0075] An example has been described in which the fixed portion 84 is formed on one side of the gear 80, and the gear 80 is an inner gear 26. The fixed portion 84 is formed on one side of the gear 80, and the gear 80 may be an outer gear 24 instead of an inner gear 26. In this case as well, the manufacturing method described above may be applied.

[0076] The specific configuration for how the fitting portion 48 and the fitting hole 42 are fitted together so as to be rotatable as a whole is not particularly limited. For example, to achieve this, one gear 80 may have a radial projection 150 that protrudes radially from either the fitting hole 42 or the fitting portion 48 provided on the one gear 80, as shown in Figure 4. In this case, the other gear 82 only needs to be fitted into a radial recess 152 that is recessed radially from either the fitting hole 42 or the fitting portion 48 provided on the other gear 82. The fitting of the radial projection 150 of the one gear 80 and the radial recess 152 of the other gear 82 enables torque to be transmitted between the fitting portion 48 and the fitting hole 42, and the fitting portion 48 is fitted together so as to be rotatable as a whole with the fitting hole 42. In this embodiment, the radial projection 150 of one gear 80 refers to the male spline tooth 72a provided in the fitting portion 48 of the inner gear 26, and the radial recess 152 of the other gear 82 refers to the tooth groove 70b provided in the fitting hole 42 of the outer gear 24. In this case, the number of radial projections 150 of one gear 80 is not particularly limited and may be single. The radial projections 150 are not limited to spline teeth.

[0077] In the case where one gear 80 is provided with a radial projection 150, as in the embodiment, a fixing portion 84 may be formed on the radial projection 150 of the one gear 80. This makes it easier to reduce the cross-sectional area in the axial section of the part to be crimped when forming the fixing portion 84 on the one gear, compared to crimping a portion closer to the base of the radial projection 150 of the one gear 80. Consequently, this is advantageous in reducing the crimping force required when forming the fixing portion 84 on the one gear 80.

[0078] The fixing portion 84 may be formed to partially bring the fitting hole 42 of the outer gear 24 and the fitting portion 48 of the inner gear 26 into close contact. In this case, the fixing portion 84 may be formed to bring the tooth surface of the male spline tooth 72a and the tooth surface of the female spline tooth 70a into close contact. In this case, the inner gear 26 and the outer gear 24 are fixed in the axial direction by the frictional force of the parts that are brought into close contact. In this case as well, as described above, the fitting portion 48 of the inner gear 26 may be fitted to the fitting hole 42 of the outer gear 24 by clearance fitting or intermediate fitting. In this case, the fixing portion 84 may be formed on either the outer gear 24 or the inner gear 26. In this case, the fixing portion 84 may be formed on the inner gear 26 and may not overlap with the outer gear 24 when viewed from the axial direction.

[0079] The relationship between the hardness of the fixed portion 84 of the internal gear 26 and the hardness of its contact surface 62 is not particularly limited. For example, the hardness of the fixed portion 84 may be greater than or equal to the hardness of the contact surface 62.

[0080] The first and second manufacturing methods may be performed in the order of insertion step S16 → first and second heat treatment steps S12, S14 → crimping step S18 instead of the order of first and second heat treatment steps S12, S14 → insertion step S16 → crimping step S18. Alternatively, the first manufacturing method may be performed in the order of insertion step S16 → crimping step S18 → first and second heat treatment steps S12, S14.

[0081] The contents of each component described in the embodiments above are illustrative. The abstract technical ideas derived from these should not be interpreted restrictively to the contents of this specification. Many design changes, such as modifications, additions, and deletions, are possible for the contents of each component described in the embodiments. Such design changes are emphasized with the notations "this form" and "embodiment." However, design changes are also permitted for contents without such notations. Any combination of the above components is also valid. Components composed of a single member in the description herein may be composed of multiple members. Similarly, components composed of multiple members may be composed of a single member. [Explanation of Symbols]

[0082] 10...Gear structure, 12...Gear device, 24...Outer gear, 26...Inner gear, 28...Center hole, 42...Matching hole, 48...Matching part, 50...Side part, 54...Side part, 60...Contact member, 62...Contact surface, 70...Spline structure (male spline structure), 72...Spline structure (female spline structure), 72a...Spline tooth (male spline tooth), 80...One-sided gear, 84...Fixed part, 86...Axial recess, 108...Tooth surface, 120...Crimping location, 150...Radial protrusion.

Claims

1. An external gear having a fitting hole, The gear comprises an internal gear having a fitting portion that is rotatably fitted integrally with the fitting hole, One of the gears, which is the outer gear and the inner gear, has a fixing portion formed on it that fixes the outer gear and the inner gear in the axial direction. The gear structure wherein the hardness of the fixed portion is lower than the hardness of the tooth surface of the one gear.

2. The fitting portion is inserted into the fitting hole in the insertion direction, The gear structure according to claim 1, wherein the fixing portion is formed on the inner gear and overlaps with the outer gear when viewed from the axial direction on the insertion direction side with respect to the outer gear.

3. An axial recess is formed in the side surface of the outer gear facing the insertion direction, The gear structure according to claim 2, wherein the fixing portion is arranged in the axial recess.

4. The aforementioned internal gear has a central hole in which the contact member is positioned on the inside, The inner circumferential surface of the central hole is provided with a contact surface on which the contact member makes rolling or sliding contact. The aforementioned fixing portion is formed on the inner gear, The gear structure according to claim 1, wherein the hardness of the fixed portion is lower than the hardness of the contact surface.

5. The aforementioned gear has a spline structure having a plurality of spline teeth, The gear structure according to claim 1, wherein the fixing portion is formed on at least one of the spline teeth.

6. The aforementioned fixing portion is formed on some of the spline teeth among the plurality of spline teeth, and not on the other spline teeth. The gear structure according to claim 5, wherein the hardness of the fixed portion is lower than the hardness of at least some of the spline teeth on which the fixed portion is not formed.

7. The aforementioned gear is made of alloy steel, The gear structure according to claim 1, wherein the other gear among the outer gear and the inner gear is made of carbon steel.

8. The aforementioned one gear is provided with a radial projection that protrudes radially from either the fitting hole or the fitting portion provided in the one gear, The gear structure according to claim 1, wherein the fixing portion is formed on the radially protruding portion.

9. A gear device comprising the gear structure described in any one of claims 1 to 8.

10. An external gear having a fitting hole, A method for manufacturing a gear structure comprising an internal gear having a fitting portion that is fitted integrally and rotatably into the fitting hole, A heat treatment step of hardening at least the tooth surface of one of the gears, which is one of the outer gear and the inner gear, by heat treatment, The process includes a crimping step in which a fixing portion is formed on the one gear to fix the outer gear and the inner gear in the axial direction, A method for manufacturing a gear structure in which the fixing portion is formed on one gear by crimping a location to be crimped that has a lower hardness than the tooth surface after the heat treatment process in the crimping step.

11. The method for manufacturing a gear structure according to claim 10, wherein in the heat treatment step, at least the tooth surface of the outer surface of the one gear is hardened by heat treatment, and the area of ​​the one gear to be crimped is not subjected to heat treatment.

12. In the heat treatment step, the tooth surface of the one gear and the area to be crimped are hardened by heat treatment. A method for manufacturing a gear structure according to claim 10, comprising a softening step of performing a softening treatment so that the crimping portion hardened by the heat treatment step becomes soft.

Images