Speed reducer

Abstract

The invention provides a speed reducer. A speed reducer according to one embodiment of the present invention is provided with: an internal gear; a carrier (3) provided so as to be rotatable with respect to the internal gear; a sun shaft rotatably supported by the carrier (3); and a planetary shaft which is rotatably supported by the carrier (3) and which revolves relative to the sun shaft. The planetary shaft is provided with a first planetary gear that meshes with the sun gear, and a second planetary gear (28) that meshes with the internal teeth. The carrier (3) is present in a region between two circumferentially adjacent planetary shafts and between two second straight lines (L2) that are parallel to a first straight line (L1) connecting the carrier axis (A1) and the planetary axis (A2) and that are tangent to the addendum circle diameter (D) of the second planetary gear (28).

Description

Technical Field

[0001] The invention relates to a reducer. Background Art

[0002] The planetary gear reducer as a reducer comprises: a sun gear; a plurality of planetary gears meshing with the sun gear; a gear carrier supporting the plurality of planetary gears so as to rotate freely; and an internal gear disposed radially outward of the plurality of planetary gears. The plurality of planetary gears revolve around the sun gear. The internal gear meshes with the plurality of planetary gears.

[0003] In some cases, the planetary gears of the planetary gear reducer are each provided with a gear meshing with the sun gear (hereinafter referred to as a first planetary gear) and a gear meshing with the internal gear (hereinafter referred to as a second planetary gear).

[0004] The first planetary gear and the second planetary gear of this type are arranged on a planetary shaft so as to be aligned in the axial direction, and the planetary shaft is rotatably supported by a carrier.

[0005] In order to improve the overall rigidity of the reducer, the gear frame sometimes has two gear frame plates that support the two sides of the planetary shaft in the axial direction so that they can rotate freely. In order to further improve the rigidity of the reducer, multiple columns connecting the two gear frame plates are sometimes provided. In many cases, multiple columns are provided between two planetary shafts adjacent to each other in the circumferential direction (for example, refer to Patent Document 1).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: U.S. Patent Application Publication No. 2017 / 0198785 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] However, in the above-mentioned prior art, the plurality of columns are arranged at intervals in the circumferential direction, so the column cannot effectively bear the torque load due to the position (orientation) of the torque load applied to the reducer. Therefore, there is room for improvement in terms of increasing the rigidity of the reducer.

[0011] The present invention provides a reducer capable of further improving rigidity.

[0012] Solutions for solving problems

[0013] A reducer of a technical solution of the present invention comprises: an internal gear having internal teeth; a gear frame arranged to rotate freely relative to the internal gear; a sun shaft configured on the same axis as the rotation axis of the gear frame; and a plurality of planetary shafts arranged in a manner spaced apart in the circumferential direction with the rotation axis of the gear frame as the center, the sun shaft being supported on the gear frame in a manner so as to rotate freely and having a sun gear, the plurality of planetary shafts being supported on the gear frame in a manner so as to rotate freely and, relative to the revolution of the sun shaft, the plurality of planetary shafts each comprising: a first planetary gear meshing with the sun gear; and a second planetary gear meshing with the internal teeth, the gear frame being present between two of the planetary shafts adjacent in the circumferential direction, and the gear frame being present in an area between two second straight lines parallel to the first straight line when viewed axially, the first straight line connecting the rotation axis of the gear frame and the rotation axis of the planetary shaft rotating relative to the gear frame, and the two second straight lines being tangent to the tooth top circle diameter of the second planetary gear.

[0014] By configuring in this way, the gear carrier can be placed between the planetary shafts adjacent to each other in the circumferential direction as much as possible. Therefore, the gear carrier can be used to bear the torque load applied to the reducer as much as possible. As a result, the rigidity of the reducer can be further improved.

[0015] In the above structure, it is also possible that the gear rack comprises: two gear rack plates, which are supported on both sides of the axial direction of the internal gear in a rotatable manner via the internal teeth of the internal gear; and a column portion, which connects the two gear rack plates, and the sun shaft and multiple planetary shafts are supported on the two gear rack plates in a rotatable manner, and the column portion is arranged between two planetary shafts adjacent to each other in the circumferential direction, and the column portion exists in the area between two second straight lines parallel to the first straight line, the first straight line connecting the rotation axis of the gear rack and the rotation axis of the planetary shaft relative to the gear rack plate, and the two second straight lines are tangent to the tooth top circle diameter of the second planetary gear.

[0016] In the above configuration, the carrier may be present in a region between two third straight lines passing through a rotation axis of the carrier, and the two third straight lines may be tangent to a diameter of a tooth tip circle of the second planetary gear.

[0017] In the above configuration, the speed reducer may include an even number of planetary shafts as the plurality of planetary shafts.

[0018] In the above structure, the column portion may also include: a plurality of column portion main bodies, which are arranged between two of the planetary shafts adjacent in the circumferential direction; and a connecting portion, which connects the two circumferentially adjacent column portion main bodies, and the connecting portion is arranged at a position radially inward of the internal gear than the plurality of planetary shafts.

[0019] In the above configuration, a side surface of the connection portion on the planetary shaft side may be formed in an arc shape when viewed in the axial direction.

[0020] Effects of the Invention

[0021] The above-mentioned speed reducer can further improve the rigidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic cross-sectional view of a speed reducer according to an embodiment of the present invention.

[0023] Figure 2 This is a plan view of the first gear carrier plate according to the embodiment of the present invention as viewed from the inner flange portion side.

[0024] Figure 3 It is an explanatory diagram of the rigidity of the speed reducer with respect to the torque load according to the embodiment of the present invention.

[0025] Figure 4 It is an explanatory diagram showing the existence region of the pillar portion under the first condition according to the embodiment of the present invention.

[0026] Figure 5 It is an explanatory diagram showing the existence region of the pillar portion under the second condition according to the embodiment of the present invention.

[0027] Description of Reference Numerals

[0028] 1. Reducer; 2. Internal gear; 3. Gear rack; 4. Sun shaft; 5. Planetary shaft; 7a. Internal gear; 11. First gear rack plate (gear rack plate); 12. Second gear rack plate (gear rack plate); 14. Column; 21. Column body; 22. Connecting part; 22b. Outer side surface (side surface); 24. Sun gear; 27. First planetary gear; 28. Second planetary gear; A1. Gear rack axis (rotation axis of gear rack); A2. Planetary axis (rotation axis of planetary shaft relative to gear rack (gear rack plate)); L1. First straight line; L2. Second straight line; L3. Third straight line; S1, S2, S3, S4, area. DETAILED DESCRIPTION

[0029] Next, embodiments of the present invention will be described based on the drawings.

[0030] <Reduction gear>

[0031] Figure 1It is a schematic cross-sectional view of the speed reducer 1 .

[0032] like Figure 1 As shown, the reducer 1 is a so-called planetary gear reducer.

[0033] The reducer 1 includes: a cylindrical internal gear 2; a gear frame 3 which is arranged to be freely rotatable relative to the internal gear 2; a sun shaft 4 which is arranged on the same axis as the rotation axis A1 of the gear frame 3; and four planetary shafts 5 which are arranged in the rotation direction of the gear frame 3 with the rotation axis A1 as the center. In the following description, the rotation axis A1 of the gear frame 3 is referred to as the gear frame axis A1. The direction parallel to the gear frame axis A1 is referred to as the axial direction. The rotation direction of the gear frame 3 is referred to as the circumferential direction. The direction orthogonal to the axial direction and the circumferential direction (radial direction of the gear frame 3) is referred to as the radial direction.

[0034] <Internal gear>

[0035] An annular outer flange portion 6 extending radially outward is formed on the outer peripheral surface 2a of the internal gear 2. The outer flange portion 6 is used to mount the reducer 1 on an external device not shown in the figure. A plurality of bolt through holes 6a are arranged on the outer flange portion 6 at equal intervals in the circumferential direction. The reducer 1 is fixed to the external device by passing bolts not shown in the figure through the bolt through holes 6a and fastening them to the external device not shown in the figure.

[0036] An annular inner flange portion 7 extending radially inward is formed on the inner peripheral surface 2b of the internal gear 2. Internal teeth 7a are formed on the inner peripheral surface of the inner flange portion 7. The internal teeth 7a are formed over the entire inner flange portion 7 in the axial direction.

[0037] In the inner peripheral surface 2b of the internal gear 2, main bearings 81 and 82 (first main bearing 81 and second main bearing 82) are provided on both sides in the axial direction across the inner flange portion 7. The two main bearings 81 and 82 are formed symmetrically with the inner flange portion 7 as the center. Therefore, in the following description, only the first main bearing 81 of the two main bearings 81 and 82 will be described. The description of each part of the second main bearing 82 is omitted by marking the same reference numerals as those of each part of the first main bearing 81.

[0038] The first main bearing 81 is, for example, a ball bearing, and includes an inner ring 81a, an outer ring 81b disposed radially outward of the inner ring 81a, and rolling elements 81c disposed between the inner ring 81a and the outer ring 81b. As the rolling element 81c, for example, a spherical body is used. However, the present invention is not limited thereto, and various rolling elements such as cylindrical rollers can be used.

[0039] The outer ring 81b is formed integrally with the internal gear 2. The inner ring 81a is formed integrally with the gear frame 3. In the internal gear 2, a cylindrical seal retaining portion 8 is formed in an axially protruding manner on the side opposite to the inner flange portion 7 across the first main bearing 81. The outer peripheral surface of the annular seal portion 9 is embedded in the inner peripheral surface 8a of the seal retaining portion 8. The seal portion 9 seals between the internal gear 2 and the gear frame 3.

[0040] <Gear rack>

[0041] The gear frame 3 is composed of two gear frame plates 11 and 12 (first gear frame plate 11 and second gear frame plate 12) overlapping in the axial direction. The first gear frame plate 11 of the two gear frame plates 11 and 12 is rotatably supported on the internal gear 2 by means of the first main bearing 81. The second gear frame plate 12 of the two gear frame plates 11 and 12 is rotatably supported on the internal gear 2 by means of the second main bearing 82.

[0042] The two gear rack plates 11 and 12 are formed symmetrically with the inner flange portion 7 as the center. Therefore, in the following description, only the first gear rack plate 11 of the two gear rack plates 11 and 12 is described. The description of each part of the second gear rack plate 12 is omitted by marking the same figure marks as the parts of the first gear rack plate 11. The description of the second gear rack plate 12 only describes the differences between it and the first gear rack plate 11.

[0043] Figure 2 It is a plan view of the first gear carrier plate 11 as viewed from the inner flange portion 7 side.

[0044] like Figure 1 , Figure 2 As shown, the first carrier plate 11 includes a disk-shaped plate body 13 and a column portion 14 for connecting the two carrier plates 11 and 12 to each other.

[0045] The outer peripheral portion 13a of the plate body 13 is formed integrally with the inner ring 81a of the first main bearing 81 on the second gear frame plate 12 side. Thus, the plate body 13 in the first gear frame plate 11 is supported by the first main bearing 81 in a rotatable manner on the internal gear 2. The side of the outer peripheral portion 13a of the plate body 13 opposite to the second gear frame plate 12 is configured as a sealing surface 13b. The inner peripheral surface of the sealing portion 9 is fitted with the sealing surface 13b. Thus, the sealing portion 9 is used to seal the internal gear 2 and the gear frame 3.

[0046] A through hole 13c is formed in the radial center of the plate body 13 and penetrates in the axial direction. The through hole 13c is arranged on the same axis as the gear frame axis A1. A first bearing seat 15 is formed on the second gear frame plate 12 side of the through hole 13c. The first bearing seat 15 is a circular recessed portion when viewed from the axial direction. The first bearing seat 15 is arranged on the same axis as the gear frame axis A1.

[0047] The first bearing seat 15 is formed by a step relative to the through hole 13c. The inner diameter of the first bearing seat 15 is larger than the inner diameter of the through hole 13c. The first bearing 17 is provided in the first bearing seat 15. The first bearing 17 is, for example, a ball bearing. However, it is not limited thereto, and various bearings such as a cylindrical roller bearing can be used for the first bearing 17. The first bearing 17 is used to support the sun shaft 4 so that it can rotate freely.

[0048] Four second bearing seats 16 are formed around the first bearing seat 15 of the plate body 13. The second bearing seats 16 are arranged at equal intervals in the circumferential direction centered on the gear frame axis A1. The second bearing seat 16 is a recessed portion formed on one surface 13d on the side of the second gear frame plate 12 of the plate body 13. The second bearing seat 16 is formed into a circular shape when viewed axially. A second bearing 18 is provided on the second bearing seat 16. The second bearing 18 is, for example, a ball bearing. However, this is not limited to this, and various bearings such as cylindrical roller bearings can be used for the second bearing 18. The second bearing 18 is used to support the planetary shaft 5 so that it can rotate freely.

[0049] The column portion 14 is formed to protrude from one surface 13d of the plate body 13 toward the second gear carrier plate 12. The column portion 14 is formed in a manner avoiding the second bearing seat 16 and the planetary shaft 5 (including the second planetary gear 28 discussed later) supported by the second bearing seat 16. That is, the column portion 14 includes: four column portion bodies 21, which are respectively arranged between two second bearing seats 16 adjacent in the circumferential direction; and a connecting portion 22, which connects two column portion bodies 21 adjacent in the circumferential direction.

[0050] The column body 21 is formed in a quadrangular column shape. The radially outer side surface 21a of the column body 21 is along the circumferential direction. Two side surfaces 21b extending orthogonally to the outer side surface 21a as viewed in the axial direction face each other in the circumferential direction.

[0051] The connecting portion 22 is formed in a manner connecting the radially inner end of the column body 21. That is, the connecting portion 22 is arranged at a position radially inner than the planetary shaft 5. The inner side surface 22a of the connecting portion 22 on the radial inner side is formed in an arc shape centered on the gear rack axis A1. The outer side surface 22b of the connecting portion 22 on the radial outer side is formed in an arc shape in a manner avoiding the second bearing seat 16. The outer side surface 22b of the connecting portion 22 is smoothly connected to the side surface 21b of the column body 21.

[0052] The connecting portion 22 does not necessarily need to be formed in a manner that spans the entirety of two circumferentially adjacent column bodies 21. In other words, the connecting portion 22 does not necessarily need to be formed in a manner that spans the entire circumference. That is, it only needs to extend from the side surface 21b of the column body 21 in the circumferential direction by a predetermined length. This aspect will be described in detail later.

[0053] The column body 21 and the connecting portion 22 protrude the same length relative to the one side 13d of the plate body 13. Therefore, the front end 14a of the column 14 is flat. Hereinafter, the protruding length of the column body 21 and the connecting portion 22 protruding relative to the one side 13d of the plate body 13 is referred to as the protruding length of the column 14.

[0054] Based on such a structure, the first gear frame plate 11 and the second gear frame plate 12 are combined in such a manner that the front ends 14a of the respective column portions 14 are butted against each other. Thus, a constant interval is formed between the plate bodies 13 of the respective gear frame plates 11 and 12. The protruding length of the column portion 14 is determined in such a manner that the constant interval is longer than the axial length of the inner flange portion 7 of the internal gear 2. The inner flange portion 7 is located between the two plate bodies 13.

[0055] A plurality of (for example, four in this embodiment) pin holes 23 are formed at the front end 14a of each column 14 at a position corresponding to the column body 21. The first gear frame plate 11 and the second gear frame plate 12 are positioned by pressing a pin (not shown) into each pin hole 23.

[0056] The sealing surface 13 b of the first gear carrier plate 11 is not formed on the second gear carrier plate 12 . Accordingly, the thickness of the second gear carrier plate 12 in the axial direction is thinner than the thickness of the first gear carrier plate 11 in the axial direction.

[0057] <Sun Axis>

[0058] The sun shaft 4 is supported in a rotatable manner by each first bearing 17 provided on each gear frame plate 11, 12. The end 4a of the sun shaft 4 on the side of the second gear frame plate 12 protrudes outward in the axial direction by means of the first bearing 17. In this protruding portion, a sun gear 24 and an input gear 25 are provided in sequence from the side of the first bearing 17. The sun gear 24 is formed integrally with the sun shaft 4. The input gear 25 is fixed in a manner that is engaged with the sun shaft 4. The input gear 25 rotates integrally with the sun shaft 4. A drive gear 26a of, for example, an electric motor 26 is meshed with the input gear 25. Thus, power is transmitted to the input gear 25.

[0059] <Planetary Axis>

[0060] The planetary shaft 5 is rotatably supported by the second bearings 18 provided on the carrier plates 11 and 12. That is, the planetary shaft 5 rotates around the rotation axis A2. Hereinafter, the rotation axis A2 is referred to as the planetary axis A2. The planetary axis A2 is parallel to the carrier axis A1.

[0061] The end portion 5a of the planetary shaft 5 on the second carrier plate 12 side protrudes outward in the axial direction via the second bearing 18. The first planetary gear 27 is fixed so as to fit into the protruding portion. The first planetary gear 27 meshes with the sun gear 24.

[0062] A second planetary gear 28 is integrally formed between the two second bearings 18 in the planetary shaft 5 . The second planetary gear 28 meshes with the internal teeth 7 a of the inner flange portion 7 .

[0063] <Operation of the speed reducer>

[0064] Next, the operation of the speed reducer 1 will be described.

[0065] When the electric motor 26 is driven, the sun gear 24 (sun shaft 4) rotates by means of the drive gear 26a and the input gear 25. Then, the first planetary gear 27 meshing with the sun gear 24 also rotates. The second planetary gear 28 rotates integrally with the first planetary gear 27. The second planetary gear 28 meshes with the internal teeth 7a of the inner flange portion 7. Therefore, each planetary gear 27, 28 and the planetary shaft 5 rotates around the planetary axis A2 while revolving around the gear carrier axis A1.

[0066] As the planetary gears 27, 28 and the planetary shaft 5 revolve, the gear frame 3 rotates relative to the internal gear 2. At this time, by fixing the internal gear 2 to an external device not shown in the figure, the gear frame 3 functions as an output unit. That is, by mounting the driven body not shown in the figure on the gear frame 3, the rotation of the driving gear 26a is decelerated by the gear frame 3 and output to the driven body. In the case where the gear frame 3 is fixed to an external device, for example, the internal gear 2 can also function as an output unit.

[0067] However, when the speed reducer 1 is driven, a torque load is applied to the carrier 3. The position (direction) of the torque load changes as the carrier 3 or the internal gear 2 rotates.

[0068] The carrier 3 is provided with a column portion 14. The column portion 14 is formed so as to extend over the entire circumference radially inside each planetary shaft 5 (second planetary gear 28). Therefore, the column portion 14 can bear the torque load regardless of the position of the torque load.

[0069] Here, a case where the connecting portion 22 is not present in the column 14 and only the column body 21 is present will be described.

[0070] Figure 3It is an explanatory diagram of the rigidity of the speed reducer 1 (carrier 3) with respect to the torque load. Figure 3 With the aforementioned Figure 2 Corresponding. Figure 3 Relative to Figure 2 Only the column body 21 is shown.

[0071] like Figure 3 As shown in FIG. 1 , when only the column body 21 is used as the column 14, the column 14 may not exist at the position of the torque load (see, for example, arrow Y1). Therefore, the rigidity of the gear carrier 3 (reducer 1) cannot be fully ensured. In particular, when the number of planetary shafts 5 (first planetary gears 27 and second planetary gears 28) is an even number, the area where the column 14 does not exist becomes larger (see FIG. 1 ). Figure 3 range S1 and range S2 in it).

[0072] In contrast, in the present embodiment, the column 14 includes the connection portion 22 in addition to the column body 21. Therefore, even when the position of the torque load changes, the connection portion 22 can ensure the rigidity of the carrier 3 with respect to the torque load.

[0073] Figure 4 , Figure 5 1 is an explanatory diagram showing the region where the column 14 exists. For convenience of explanation, Figure 4 , Figure 5 Only 1 / 4 of the circumference of the gear carrier 3 is shown.

[0074] It can also be known from the above that the connecting portion 22 does not need to be formed in a manner spanning the entire circumference. Figure 4 As shown, the connection portion 22 (column portion 14) only needs to exist in the area S3 between two second straight lines L2 which are at least parallel to the first straight line L1, and the first straight line L1 connects the gear carrier axis A1 and the planetary axis A2. The two second straight lines L2 are tangent to the tooth top circle diameter D of the second planetary gear 28. Hereinafter, this condition is referred to as the first condition.

[0075] The expectation is that Figure 5 As shown, the connection portion 22 (column portion 14) only needs to be present in the region S4 between two third straight lines L3 passing through the carrier axis A1. The two third straight lines L3 are tangent to the tip circle diameter D of the second planetary gear 28. This condition is hereinafter referred to as the second condition.

[0076] Thus, in the above-mentioned embodiment, the column portion 14 is formed in a manner that satisfies at least the first condition. Therefore, compared with, for example, a case where only the column portion main body 21 is provided on the gear frame 3, the column portion 14 (connecting portion 22) different from the column portion main body 21 can be extended on both sides of the circumferential direction of the column portion main body 21. In other words, the gear frame 3 (column portion 14) can be placed as much as possible between the circumferentially adjacent planetary shafts 5. Therefore, the gear frame 3 can be utilized as much as possible to bear the torque load applied to the reducer 1. Thereby, the rigidity of the reducer 1 can be improved.

[0077] The carrier 3 includes two carrier plates 11 and 12 and a column portion 14 connecting the two carrier plates 11 and 12. By configuring the carrier 3 in this way, the carrier 3 can be easily formed to satisfy at least the first condition. More specifically, the rigidity of the speed reducer 1 can be easily increased.

[0078] By forming the gear frame 3 in a manner that satisfies the second condition, the connection portion 22 can be further extended in the circumferential direction compared to the first condition. Accordingly, the gear frame 3 can be further located between the planetary shafts 5 adjacent in the circumferential direction. Therefore, the gear frame 3 can be further utilized to bear the torque load applied to the reducer 1. As a result, the rigidity of the reducer 1 can be reliably improved.

[0079] When the speed reducer 1 has an even number of planetary shafts 5 (the first planetary gears 27 and the second planetary gears 28) as in the present embodiment, the region that is difficult to bear the torque load becomes larger (see, for example, Figure 3 ). Therefore, the above structure can be appropriately used when the number of the planetary shafts 5 is an even number.

[0080] The column portion 14 includes a column portion body 21 and a connecting portion 22. The connecting portion 22 is arranged at a position radially inward of the planetary shaft 5. That is, in a structure such as the reducer 1 which includes a first planetary gear 27 meshing with the sun gear 24 and a second planetary gear 28 meshing with the internal teeth 7a, a space is formed radially inward of the second planetary gear 28. The connecting portion 22 is arranged by effectively and flexibly utilizing the space. Therefore, the connecting portion 22 can be formed over the entire circumference without increasing the size of the reducer 1. The rigidity of the reducer 1 can be more reliably improved.

[0081] The radially outer side surface 22b of the connection portion 22 is formed in an arc shape to avoid the second bearing seat 16. Loads other than the torque load are also applied to the connection portion 22. By forming the outer side surface 22b of the connection portion 22 in an arc shape, it is possible to prevent stress from being locally applied to the connection portion 22. Therefore, the rigidity of the speed reducer 1 can be further improved.

[0082] The present invention is not limited to the above-described embodiment, and includes embodiments in which various modifications are added to the above-described embodiment within a scope not departing from the gist of the present invention.

[0083] For example, in the above-mentioned embodiment, the following case is described: the gear frame 3 is composed of two gear frame plates 11 and 12 overlapped in the axial direction and the column portion 14 formed on each gear frame plate 11 and 12. However, this is not limited to this, and the gear frame 3 can be a structure that supports the sun shaft 4 and the planetary shaft 5 so that they can rotate freely. The gear frame 3 can be formed in a manner that satisfies the above-mentioned first condition and second condition.

[0084] In the above embodiment, the gear carrier 3 is rotatably supported by the internal gear 2. However, the present invention is not limited thereto, and the gear carrier 3 may be rotatably provided relative to the internal gear 2. The gear carrier 3 may also be rotatably supported by a member different from the internal gear 2.

[0085] In the above embodiment, the case where the reducer 1 has four planetary shafts 5 (the first planetary gear 27 and the second planetary gear 28) is described. However, this is not limited to this, and the planetary shafts 5 can be more than two. The number of planetary shafts 5 is not limited to an even number, and can also be an odd number. Even in such a case, the same effect as the above embodiment can be achieved.

[0086] In the embodiments disclosed in this specification, for a component composed of multiple objects, the multiple objects can be integrated, and conversely, for a component composed of one object, it can be divided into multiple objects. Regardless of whether it is integrated or not, it only needs to be configured to achieve the purpose of the invention.

Claims

1. A reducer, wherein: The reducer has: an internal gear having internal teeth; a gear carrier, which is arranged to be rotatable relative to the internal gear; a sun shaft arranged on the same axis as the rotation axis of the gear carrier; as well as A plurality of planetary shafts are arranged at intervals in the circumferential direction around the rotation axis of the carrier. The sun shaft is rotatably supported by the gear carrier and has a sun gear. The plurality of planetary shafts are rotatably supported on the gear carrier and revolve relative to the sun shaft. The plurality of planetary shafts are provided with: a first planetary gear meshing with the sun gear; and a second planetary gear meshing with the internal teeth, The gear carrier exists between two of the planetary shafts adjacent to each other in the circumferential direction. Furthermore, the gear carrier exists in a region between two second straight lines parallel to the first straight line when viewed axially, the first straight line connecting the rotation axis of the gear carrier and the rotation axis of the planetary shaft relative to the gear carrier. The two second straight lines are tangent to the addendum circle diameter of the second planetary gear.

2. The reducer according to claim 1, wherein: The gear rack has: two gear carrier plates rotatably supported on both sides of the internal gear in the axial direction via the internal teeth of the internal gear; and A column portion connecting the two gear frame plates, The sun shaft and the plurality of planetary shafts are rotatably supported by the two gear carrier plates. The column portion is arranged between two of the planetary shafts adjacent to each other in the circumferential direction. The column portion exists in a region between two second straight lines parallel to the first straight line, the first straight line connecting the rotation axis of the gear carrier and the rotation axis of the planetary shaft relative to the gear carrier plate. The two second straight lines are tangent to the tooth tip circle diameter of the second planetary gear.

3. The reducer according to claim 1 or 2, wherein: The gear carrier exists in a region between two third straight lines passing through the rotation axis of the gear carrier. The two third straight lines are tangent to the addendum circle diameter of the second planetary gear.

4. The reducer according to claim 1 or 2, wherein: The speed reducer has an even number of planetary shafts as the plurality of planetary shafts.

5. The reducer according to claim 2, wherein: The column portion comprises: a plurality of column bodies disposed between two of the planetary shafts adjacent to each other in the circumferential direction; and a connecting portion connecting two of the column main bodies adjacent to each other in the circumferential direction, The connection portion is arranged radially inward of the internal gear relative to the plurality of planetary shafts.

6. The reducer according to claim 5, wherein: The side surface of the connecting portion on the planetary shaft side is formed in an arc shape when viewed in the axial direction.

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