Planetary gear, planetary reducer, and manufacturing method of planetary gear

Abstract

Provided are a planetary gear, a planetary reducer, and a manufacturing method for a planetary gear. The planetary gear has a first planetary gear and a second planetary gear that is smaller in diameter than the first planetary gear. The first planetary gear has a first spline on an inner peripheral surface. The first spline has a plurality of inner teeth extending in an axial direction. The second planetary gear has a second spline on an outer peripheral surface. The second spline has a plurality of outer teeth extending in the axial direction. The first spline and the second spline are fitted by a clearance fit or a transition fit. In addition, the planetary gear has a fixing portion on an end surface in the axial direction. In the fixing portion, a tooth profile cross section of the second spline is larger than a tooth profile cross section of other portions of the second spline. In addition, in the fixing portion, the inner teeth are in close contact with the outer teeth.

Description

TECHNICAL FIELD

[0001] The present application relates to a planetary gear, a planetary reducer, and a manufacturing method of a planetary gear. BACKGROUND

[0002] Conventionally, a planetary reducer having a sun gear, a plurality of planetary gears arranged around the sun gear, and a ring gear surrounding the plurality of planetary gears is known. In addition, a planetary reducer of a differential type that realizes a high reduction ratio by two ring gears meshing with a two-stage planetary gear constituted by two gears having different numbers of teeth is known.

[0003] A conventional planetary reducer of the differential type is described, for example, in Japanese Patent Application Publication No. H54-183566.

[0004] Patent Document 1: Japanese Patent Application Publication No. H54-183566

[0005] The two-stage planetary gear used in the planetary reducer of the differential type is constituted by a first planetary gear and a second planetary gear having a smaller diameter than the first planetary gear. When the two-stage planetary gear is manufactured, a portion of the second planetary gear is inserted inside the first planetary gear. At this time, a spline provided on an outer circumferential surface of the second planetary gear is fitted with a spline provided on an inner circumferential surface of the first planetary gear. Thereby, the rotation of the second planetary gear relative to the first planetary gear is restricted.

[0006] However, if the spline of the first planetary gear and the spline of the second planetary gear are inserted by clearance fit, the first planetary gear cannot be fixed in the axial direction relative to the second planetary gear. On the other hand, if the spline of the second planetary gear is press-fitted into the spline of the first planetary gear, there is a problem in that the first planetary gear is distorted and the tooth shape of the first planetary gear is changed. SUMMARY

[0007] An object of the present application is to provide a technology that enables the first planetary gear and the second planetary gear to be fixed while suppressing the change in the tooth shape of the first planetary gear when manufacturing a planetary gear having a first planetary gear and a second gear having a smaller diameter than the first planetary gear.

[0008] The first invention of the present application is a planetary gear for a planetary reducer, wherein the planetary gear has: a first planetary gear that is circular ring-shaped; and a second planetary gear that is fixed to the first planetary gear and has a smaller diameter than the first planetary gear, the first planetary gear has a first spline on an inner peripheral surface, the first spline having a plurality of inner teeth extending in an axial direction, the second planetary gear has a second spline on an outer peripheral surface, the second spline having a plurality of outer teeth extending in the axial direction, the first spline and the second spline are fitted by a clearance fit or a transition fit, at an axial end surface, a boundary between the first spline and the second spline has one or more fixed portions, at the fixed portions, a tooth profile cross section of the second spline is larger than a tooth profile cross section of other portions of the second spline, and at the fixed portions, the inner teeth and the outer teeth are in close contact.

[0009] The second invention of the present application is a planetary gear for a planetary reducer, wherein the planetary gear has: a first planetary gear that is circular ring-shaped; and a second planetary gear that is fixed to the first planetary gear and has a smaller diameter than the first planetary gear, the first planetary gear has a first spline on an inner peripheral surface, the first spline having a plurality of inner teeth extending in an axial direction, the second planetary gear has a second spline on an outer peripheral surface, the second spline having a plurality of outer teeth extending in the axial direction, the first spline and the second spline are fitted by a clearance fit or a transition fit, at an axial end surface, a boundary between the first spline and the second spline has one or more fixed portions, at the fixed portions, a first gap between a tooth top of the first spline and a tooth bottom of the second spline is smaller than other first gaps or a second gap between a tooth bottom of the first spline and a tooth top of the second spline is smaller than other second gaps, and at the fixed portions, the inner teeth and the outer teeth are in close contact.

[0010] The third invention of the present application is a manufacturing method of the planetary gear of the first invention or the second invention, wherein the manufacturing method of the planetary gear includes the following steps: a) fitting the second spline of the second planetary gear to an inner side of the first spline of the first planetary gear; and b) forming the fixed portions by extruding a boundary between the first spline and the second spline in the axial direction at an end surface of the planetary gear.

[0011] The fourth invention of the present application is a manufacturing method of the planetary gear of the first invention or the second invention, wherein the manufacturing method of the planetary gear includes the following steps: a) fitting the second spline of the second planetary gear to an inner side of the first spline of the first planetary gear; and b) forming the fixed portions by extruding the outer teeth of the second spline in the axial direction at an end surface of the planetary gear.

[0012] According to the first to fourth inventions of the present application, the first and second planetary gears can be fixed without press-fitting the second spline with respect to the first spline. Thus, the first and second planetary gears can be fixed while suppressing deformation of the gear teeth of the first planetary gear. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a longitudinal sectional view of a planetary reducer.

[0014] Figure 2 is a sectional view of a sun gear, a plurality of planetary gears, and a first internal gear along Figure 1 A-A line in FIG. 1.

[0015] Figure 3 is a partial longitudinal sectional view of a planetary gear.

[0016] Figure 4 is a plan view of a planetary gear.

[0017] Figure 5 is a flowchart showing manufacturing steps of a planetary gear.

[0018] Figure 6 is a longitudinal sectional view of a first planetary gear and a second planetary gear at the time of manufacturing of a planetary gear.

[0019] Figure 7 is a view of a vicinity of a fixing portion viewed in an axial direction.

[0020] Figure 8 is a plan view of a planetary gear of a first modification example.

[0021] Figure 9 is a plan view of a planetary gear of a second modification example.

[0022] REFERENCE NUMERALS

[0023] 1: planetary reducer; 10: sun gear; 11: input shaft; 12: external teeth; 20: planetary gear; 21: first planetary gear; 22: second planetary gear; 23: pin hole; 25: fixing portion; 26: first gap; 27: second gap; 30: planetary support portion; 31: carrier; 32: carrier pin; 33: window portion; 34: bearing; 35: bearing; 40: first internal gear; 41: first internal teeth; 50: second internal gear; 51: second internal teeth; 60: output shaft; 70: first spline; 71: internal teeth; 80: second spline; 81: external teeth; 91: central axis; 92: planetary axis; 211: first gear tooth; 221: second gear tooth; 222: gear portion; 223: insertion portion; P: press pin. DETAILED DESCRIPTION

[0024] Hereinafter, an example of the embodiment of the present application will be described with reference to the drawings. In addition, in this application, the direction parallel to the central axis of the sun gear will be referred to as "axial direction", the direction perpendicular to the central axis will be referred to as "radial direction", and the direction along the circular arc centered on the central axis will be referred to as "circumferential direction". However, the "parallel direction" described above also includes a substantially parallel direction. In addition, the "perpendicular direction" described above also includes a substantially perpendicular direction.

[0025] In addition, in the following description, the right side in Figure 1 will be referred to as "input side", and the left side in Figure 1 will be referred to as "output side".

[0026] <1. Planetary Reducer of One Embodiment>

[0027] Figure 1 is a longitudinal sectional view of a planetary reducer 1 of one embodiment of the present application. The planetary reducer 1 is a device that reduces the rotational motion of a first rotational speed input from a motor to the rotational motion of a second rotational speed lower than the first rotational speed and outputs it. The planetary reducer 1 is used in a joint of a robot, for example, assembled with the motor. However, the planetary reducer 1 can also be used in other devices such as an assist device, an automated guided vehicle, and the like.

[0028] As shown in Figure 1 , the planetary reducer 1 of the present embodiment has one sun gear 10, a plurality of planetary gears 20, a planetary support portion 30, a first internal gear 40, a second internal gear 50, and an output shaft 60.

[0029] The sun gear 10 is a gear arranged along a central axis 91. The sun gear 10 is connected to a motor as a driving source through an input shaft 11. The input shaft 11 is rotatably supported on an omitted housing via a bearing. The sun gear 10 and the input shaft 11 are rotated at a first rotational speed before reduction by a driving force input from the motor, with the central axis 91 as the center. A plurality of external teeth 12 are provided on the outer peripheral surface of the sun gear 10. The plurality of external teeth 12 are provided at a certain angular pitch with the central axis 91 as the center. Each external tooth 12 protrudes to the radially outer side on the outer peripheral surface of the sun gear 10.

[0030] The planetary gear 20 is a gear arranged on the radially outer side of the sun gear 10. Figure 2 is a sectional view along the A-A line in Figure 1 of the sun gear 10, the plurality of planetary gears 20, and the first internal gear 40. However, in Figure 2 , in order to avoid the complication of the drawing, the sectional line indicating the section and the teeth of each gear are omitted. As Figure 2As shown, in this embodiment, three planetary gears 20 are arranged at equal intervals around the sun gear 10. However, the number of planetary gears 20 included in the planetary speed reducer 1 may be 1 to 2, or may be 4 or more.

[0031] Each planetary gear 20 has a pin hole 23 at its center. A carrier pin 32, described later, is inserted into the pin hole 23. Each planetary gear 20 is supported by the carrier pin 32 so as to be rotatable about a planetary axis 92 parallel to the central axis 91.

[0032] like Figure 1 As shown, the planetary gear 20 has a first planetary gear 21 and a second planetary gear 22. The first planetary gear 21 and the second planetary gear 22 are separate components fixed to each other. The first planetary gear 21 is an annular gear that meshes with the sun gear 10. The first planetary gear 21 has a plurality of first gear teeth 211 on the outer peripheral surface. The plurality of first gear teeth 211 are arranged at a certain angular interval with the planetary axis 92 as the center. Each first gear tooth 211 protrudes outward from the outer peripheral surface of the first planetary gear 21. The first gear teeth 211 mesh with the outer teeth 12 of the sun gear 10 mentioned above.

[0033] The second planetary gear 22 has a smaller diameter than the first planetary gear 21. The second planetary gear 22 has a plurality of second gear teeth 221 on its outer circumference. These second gear teeth 221 are arranged at regular angular intervals around the planetary axis 92. Each second gear tooth 221 protrudes outward from the outer circumference of the second planetary gear 22. The plurality of second gear teeth 221 are positioned closer to the output side than the plurality of first gear teeth 211. Furthermore, the number of first gear teeth 211 on the first planetary gear 21 is different from the number of second gear teeth 221 on the second planetary gear 22.

[0034] The planetary support portion 30 is a unit that supports the plurality of planetary gears 20. Figure 1 As shown, the planetary support portion 30 includes a cage-shaped planetary carrier 31 and a plurality of planetary carrier pins 32. The planetary carrier 31 is an annular member centered on the central axis 91. The planetary carrier 31 is rotatably supported about the central axis 91. The planetary carrier 31 has a plurality of windows 33. The windows 33 are holes that penetrate the planetary carrier 31 in the radial direction. The plurality of windows 33 are arranged at equal intervals about the central axis 91. The plurality of planetary carrier pins 32 are fixed to the planetary carrier 31 at intervals in the circumferential direction. Each planetary carrier pin 32 extends axially along the planetary axis 92 in the window 33.

[0035] The planetary gears 20 are disposed in the window portions 33 of the carrier 31. In addition, the planetary gears 20 are rotatably supported with respect to the carrier pins 32 via bearings 34. The bearings 34 use, for example, needle bearings. However, other bearings such as ball bearings or the like can be used instead of the needle bearings. The planetary gears 20 are able to revolve around the central axis 91 while simultaneously rotating on their own axes centered on the planetary axes 92.

[0036] The first ring gear 40 is a circular ring-shaped gear that meshes with the first planetary gears 21 radially outward of the plurality of planetary gears 20. The first ring gear 40 is disposed coaxially with the central axis 91. The first ring gear 40 is fixed to an omitted housing. Thus, the first ring gear 40 also remains in a stationary state when the planetary reducer 1 is driven. The first ring gear 40 has a plurality of first internal teeth 41. The plurality of first internal teeth 41 are disposed at a certain angular pitch centered on the central axis 91. Each of the first internal teeth 41 protrudes toward the radially inner side on the inner peripheral surface of the first ring gear 40. The first gear teeth 211 of the first planetary gears 21 described above mesh with the first internal teeth 41 of the first ring gear 40.

[0037] The second ring gear 50 is a circular ring-shaped gear that meshes with the second planetary gears 22 radially outward of the plurality of planetary gears 20. The second ring gear 50 is located on the output side of the first ring gear 40. In addition, the second ring gear 50 is disposed coaxially with the central axis 91. The second ring gear 50 is rotatably supported on an omitted housing via a bearing. In addition, a bearing 35 is present between the carrier 31 and the second ring gear 50. Thus, the carrier 31 and the second ring gear 50 are able to rotate at different rotational speeds from each other.

[0038] The second ring gear 50 has a plurality of second internal teeth 51. The plurality of second internal teeth 51 are disposed at a certain angular pitch centered on the central axis 91. Each of the second internal teeth 51 protrudes toward the radially inner side on the inner peripheral surface of the second ring gear 50. The second gear teeth 221 of the second planetary gears 22 described above mesh with the second internal teeth 51 of the second ring gear 50. The number of the first internal teeth 41 possessed by the first ring gear 40 is different from the number of the second internal teeth 51 possessed by the second ring gear 50.

[0039] The output shaft 60 is a shaft disposed along the central axis 91. The output shaft 60 is located on the output side of the carrier 31. In the present embodiment, the second ring gear 50 and the output shaft 60 are formed by one component. However, the second ring gear 50 and the output shaft 60 can be separate components.

[0040] When the sun gear 10 rotates at the first rotational speed, the planetary gears 20 rotate about the planetary axis 92 due to meshing with the sun gear 10. Furthermore, the planetary gears 20 revolve around the sun gear 10 along the first internal gear 40 due to meshing with the first internal gear 40. In other words, the multiple planetary gears 20 rotate about the planetary axis 92 while revolving about the central axis 91. At this time, the orbital speed of the planetary gears 20 revolving about the central axis 91 is an intermediate speed lower than the first rotational speed.

[0041] Furthermore, as described above, the number of first internal teeth 41 of the first internal gear 40 differs from the number of second internal teeth 51 of the second internal gear 50. Therefore, as the planetary gears 20 revolve, the second internal gear 50 rotates relative to the first internal gear 40 at a speed corresponding to the difference in the number of teeth. This rotational speed of the second internal gear 50 becomes a second speed lower than the intermediate speed. As a result, the second internal gear 50 and the output shaft 60 rotate at the second speed about the central axis 91. Therefore, the output shaft 60 can extract reduced rotational motion at the second speed.

[0042] <2. Planetary Gear>

[0043] Next, a more detailed structure of the planetary gear 20 will be described. Figure 3 It is a partial longitudinal sectional view of the planetary gear 20 . Figure 4 It is a plan view of the input-side end face of the planetary gear 20 as viewed in the axial direction.

[0044] like Figure 3 as well as Figure 4 As shown, the first planetary gear 21 has a first spline 70 on its inner circumference. The first spline 70 has a plurality of internal teeth 71 protruding inward. The plurality of internal teeth 71 are arranged at regular angular intervals around the planetary axis 92. Each internal tooth 71 extends linearly in the axial direction.

[0045] The second planetary gear 22 has a second spline 80 on its outer circumferential surface. Specifically, the second planetary gear 22 includes a gear portion 222 having the plurality of second gear teeth 221 and an insertion portion 223 having the second spline 80. The insertion portion 223 is located closer to the input side than the gear portion 222. The second spline 80 has a plurality of external teeth 81 protruding outward. The plurality of external teeth 81 are arranged at regular angular intervals around the planetary axis 92. Each external tooth 81 extends linearly in the axial direction. The number of internal teeth 71 of the first spline 70 is the same as the number of external teeth 81 of the second spline 80.

[0046] In addition, in the second planetary gear 22, the number of the second gear teeth 221 is the same as the number of the external teeth 81. The second gear teeth 221 and the external teeth 81 are connected in the axial direction. However, the height of the external teeth 81 is lower than the height of the second gear teeth 221. That is, the external teeth 81 of the second spline 80 have a shape in which the second gear teeth 221 are extended toward the input side and the front ends thereof are cut. According to this structure, when the second planetary gear 22 is manufactured, the external teeth 81 are easily machined together with the second gear teeth 221. Therefore, the working hours when the second planetary gear 22 is manufactured can be reduced.

[0047] Figure 5 is a flowchart showing the manufacturing steps of the planetary gear 20. As shown in Figure 5 , when the planetary gear 20 is manufactured, first, the first planetary gear 21 and the second planetary gear 22 are prepared (step S1). Also, the insertion portion 223 of the second planetary gear 22 is inserted from the output side of the first planetary gear 21 to the inside of the first planetary gear 21. Thereby, the insertion portion 223 of the second spline 80 is fitted to the inside of the first spline 70 (step S2).

[0048] In step S2, the external teeth 81 of the second spline 80 are respectively inserted between the adjacent internal teeth 71 of the first spline 70. Further, the front ends of the internal teeth 71 of the first spline 70 and the tooth bottoms of the external teeth 81 of the second spline 80 are opposed to each other. Also, the front ends of the external teeth 81 of the second spline 80 and the tooth bottoms of the internal teeth 71 of the first spline 70 are opposed to each other.

[0049] In step S2, the first spline 70 and the second spline 80 are fitted not by press-fitting but by clearance fitting or transition fitting. That is, the internal teeth 71 of the first spline 70 and the external teeth 81 of the second spline 80 are formed in sizes that do not contact each other in at least a part of the tolerance range. In this way, the distortion of the first planetary gear 21 accompanying the fitting can be suppressed. Therefore, the change in the tooth profile of the first gear teeth 211 can be suppressed.

[0050] Figure 6 is a longitudinal sectional view of the first planetary gear 21 and the second planetary gear 22 after step S2 is completed. When the fitting of the second spline 80 with respect to the first spline 70 is completed, as shown in Figure 6 , the axial positions of the end faces of the input side of the first planetary gear 21 and the end faces of the input side of the second planetary gear 22 coincide with each other.

[0051] Next, the boundary of the first spline 70 and the second spline 80 is pressed in the axial direction at the end faces of the input side of the first planetary gear 21 and the second planetary gear 22 (step S3). Specifically, as shown in Figure 6As shown, a press pin P for extrusion pressing is pushed against the boundary of the first spline 70 and the second spline 80 from the input side of the first planetary gear 21 and the second planetary gear 22. Thereby, the end surface of the input side of the first spline 70 and the second spline 80 is partially plastically deformed. As a result, as shown in FIG. 6, the first spline 70 and the second spline 80 are fixed to each other. Figure 3 Further, as shown in FIG. 7, the fixed portion 25 is formed in the boundary of the first spline 70 and the second spline 80. Figure 4 Further, as shown in FIG. 7, the fixed portion 25 is formed in the boundary of the first spline 70 and the second spline 80.

[0052] The fixed portion 25 is formed, for example, at one portion in the circumferential direction. However, the fixed portion 25 can be formed at a plurality of portions in the circumferential direction.

[0053] Figure 7 FIG. 8 is a view of the vicinity of the fixed portion 25 as viewed in the axial direction. In FIG. 8, the tooth profile of the second spline 80 before extrusion is indicated by a two-dot chain line. As shown in FIG. 8, the fixed portion 25 is located in the boundary of the tooth top of the inner tooth 71 of the first spline 70 and the tooth bottom of the outer tooth 81 of the second spline 80. Figure 7 Figure 7 As shown in FIG. 8, the fixed portion 25 is formed in the boundary of the first spline 70 and the second spline 80.

[0054] As shown in FIG. 8, the fixed portion 25 is formed in the boundary of the first spline 70 and the second spline 80. Figure 7 As shown in FIG. 8, the fixed portion 25 is formed in the boundary of the first spline 70 and the second spline 80.

[0055] Further, in the fixed portion 25, the side surface of the inner tooth 71 of the first spline 70 and the side surface of the outer tooth 81 of the second spline 80 are in close contact with each other. Thereby, the first planetary gear 21 and the second planetary gear 22 are fixed. That is, the positional shift of the first planetary gear 21 in the axial direction with respect to the second planetary gear 22 is prevented.

[0056] As described above, the planetary gear 20 of the planetary reducer 1 has the fixed portion 25 formed by extrusion in the end surface of the input side. Therefore, the first planetary gear 21 and the second planetary gear 22 can be fixed without press-fitting the second spline 80 with respect to the first spline 70. Thereby, the tooth profile of the first gear teeth 211 of the first planetary gear 21 can be suppressed from changing, and the first planetary gear 21 and the second planetary gear 22 can be fixed.

[0057] In the end surface of the input side of the planetary gear 20, the fixed portion 25 is recessed toward the output side more than other portions. Therefore, the first planetary gear 21 and the second planetary gear 22 can be fixed without enlarging the size of the planetary gear 20 in the axial direction. Further, the fixed portion 25 does not come into contact with the first internal gear 40. Thereby, the sliding friction at the time of driving the planetary reducer 1 is suppressed.​

[0058] like Figure 7 As shown, when viewed axially, the tooth tips of the internal teeth 71 of the first spline 70 and the tooth tips of the external teeth 81 of the second spline 80 are both flatly chamfered. Furthermore, when viewed axially, the side surfaces of the internal teeth 71 of the first spline 70 and the side surfaces of the external teeth 81 of the second spline 80 are both involute curves. Forming the internal teeth 71 and external teeth 81 in this manner facilitates aligning the phases of the first planetary gears 21 and the second planetary gears 22. Furthermore, the first gap 26 between the tooth tips of the internal teeth 71 of the first spline 70 and the tooth bottoms of the external teeth 81 of the second spline 80 is reduced. Consequently, the area of ​​the fixing portion 25, when viewed axially, can be reduced.

[0059] <3. Modifications>

[0060] While one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. Various modifications will be described below, focusing on differences from the above embodiment.

[0061] <3-1. First Modification>

[0062] Figure 8 This is a top view of a planetary gear 20 according to a first modification. In this first modification, the fixing portion 25 is located at the boundary between the tooth bottoms of the internal teeth 71 of the first spline 70 and the tooth tips of the external teeth 81 of the second spline 80. In this fixing portion 25, the second gap 27 between the tooth bottoms of the internal teeth 71 of the first spline 70 and the tooth tips of the external teeth 81 of the second spline 80 is smaller than the second gap 27 in the portion outside of the fixing portion 25. Even with this structure, the first and second planetary gears 21 and 22 can be fixed using the fixing portion 25 formed by extrusion.

[0063] However, before the fixing portion 25 is formed, the first gap 26 between the tooth tips of the internal teeth 71 of the first spline 70 and the tooth bottoms of the external teeth 81 of the second spline 80 is smaller than the second gap 27 between the tooth bottoms of the internal teeth 71 of the first spline 70 and the tooth tips of the external teeth 81 of the second spline 80. Therefore, as in the above-described embodiment, providing the fixing portion 25 near the first gap 26 makes it easier to achieve close contact between the internal teeth 71 and the external teeth 81.

[0064] <3-2. Second Modification>

[0065] Figure 9is a plan view of the planetary gear 20 of the second modification. In this second modification, not the boundary of the first spline 70 and the second spline 80, but only the outer teeth 81 of the second spline 80 are pressed in the axial direction. Thereby, the fixing portion 25 is formed in the outer teeth 81 of the second spline 80. In this case, the tooth profile section of the outer teeth 81 is also larger than the tooth profile section of the outer teeth 81 other than the fixing portion 25, so that the side surfaces of the outer teeth 81 and the side surfaces of the inner teeth 71 are in close contact with each other. Thereby, the first planetary gear 21 and the second planetary gear 22 can be fixed.

[0066] <3-3. Other Modifications>

[0067] As for the shape of the details of the planetary reducer, it can be different from the shape shown in each drawing of the present application. In addition, each element appearing in the above-described embodiments or modifications can be appropriately combined within a range not causing contradiction.

[0068] Industrial Applicability

[0069] The present application can be utilized in a planetary gear, a planetary reducer, and a manufacturing method of a planetary gear.

Claims

1. A planetary gear for a planetary reducer, wherein: The planetary gear has: a first annular planetary gear; and a second planetary gear fixed to the first planetary gear and having a diameter smaller than that of the first planetary gear; The first planetary gear has a first spline on its inner circumferential surface, and the first spline has a plurality of internal teeth extending in the axial direction. The second planetary gear has a second spline on its outer peripheral surface, and the second spline has a plurality of external teeth extending in the axial direction. The first spline and the second spline are engaged with each other through a clearance fit or a transition fit without pressing the second spline into the first spline. The axial end surface has one or more fixing portions formed by pressing with a pressing pin. In the fixing portion, the tooth profile cross section of the second spline is larger than the tooth profile cross section of other parts of the second spline. At the fixing portion, the inner teeth are in close contact with the outer teeth.

2. A planetary gear for a planetary reducer, wherein: The planetary gear has: a first annular planetary gear; and a second planetary gear fixed to the first planetary gear and having a diameter smaller than that of the first planetary gear; The first planetary gear has a first spline on its inner circumferential surface, and the first spline has a plurality of internal teeth extending in the axial direction. The second planetary gear has a second spline on its outer peripheral surface, and the second spline has a plurality of external teeth extending in the axial direction. The first spline and the second spline are engaged with each other through a clearance fit or a transition fit without pressing the second spline into the first spline. The axial end surface has one or more fixing portions formed by pressing with a pressing pin. In the fixing portion, a first gap between the tooth top of the first spline and the tooth bottom of the second spline is smaller than the other first gaps, or a second gap between the tooth bottom of the first spline and the tooth top of the second spline is smaller than the other second gaps. At the fixing portion, the inner teeth are in close contact with the outer teeth.

3. The planetary gear according to claim 1 or 2, wherein: The fixing portion is located at a boundary between a tooth top of the first spline and a tooth bottom of the second spline.

4. The planetary gear according to claim 1 or 2, wherein: The fixing portion is located at a boundary between a tooth bottom of the first spline and a tooth top of the second spline.

5. The planetary gear according to claim 1 or 2, wherein: The fixing portion is recessed in the axial direction compared to other portions of the end surface.

6. The planetary gear according to claim 1 or 2, wherein: The first planetary gear has a plurality of first gear teeth on its outer peripheral surface. The second planetary gear has a plurality of second gear teeth on the outer peripheral surface. The number of the first gear teeth is different from the number of the second gear teeth. The number of the second gear teeth is the same as the number of the external teeth of the second spline.

7. The planetary gear according to claim 1 or 2, wherein: When viewed in the axial direction, the side surfaces of the inner teeth and the outer teeth are shaped like involute curves.

8. A planetary reducer comprising the planetary gear according to any one of claims 1 to 7, wherein: The planetary reducer has: The sun gear rotates at a first speed before deceleration about the central axis; a plurality of planetary gears meshing with the sun gear on a radially outer side of the sun gear; a first annular internal gear meshing with the first planetary gear on a radially outer side of the plurality of planetary gears; as well as a second annular internal gear meshing with the second planetary gears on the radially outer sides of the plurality of planetary gears; The second internal gear rotates at a second rotational speed that is reduced relative to the first internal gear.

9. A method for manufacturing a planetary gear, the method for manufacturing a planetary gear according to any one of claims 1 to 7, wherein: The manufacturing method of the planetary gear comprises the following steps: a) fitting the second splines of the second planetary gear to the inner side of the first splines of the first planetary gear without press-fitting the second splines of the second planetary gear relative to the first splines; and b) The fixing portion is formed by pressing a boundary between the first spline and the second spline in the axial direction on the end surface of the planetary gear.

10. A method for manufacturing a planetary gear, the method for manufacturing a planetary gear according to any one of claims 1 to 7, wherein: The manufacturing method of the planetary gear comprises the following steps: a) fitting the second splines of the second planetary gear to the inner side of the first splines of the first planetary gear without press-fitting the second splines of the second planetary gear relative to the first splines; and b) The fixing portion is formed on the end surface of the planetary gear by pressing the external teeth of the second spline in the axial direction.

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