Planetary gear reducer

Abstract

Provided is a reducer that is rigid with a small number of parts and is configured to be short in the axial direction. Provided is a reducer (W1), comprising: an input shaft (10) having an eccentric portion (12); a fixed sun gear (20) formed from an external gear that is coaxial with the input shaft (10); a first planetary gear (31) having an internal gear meshing with the fixed sun gear (20) and provided on the eccentric portion (12) of the input shaft (10); a driven sun gear (40) disposed on the same axis as the axis of rotation of the input shaft (10) and formed from an external gear that outputs a reduction output; and a second planetary gear (33) having an internal gear meshing with the driven sun gear (40) and provided on the eccentric portion (12) of the input shaft (10), wherein the first planetary gear (31) and the second planetary gear (33) are formed integrally in the axial direction and configure a planetary gear train (30). By configuring a pair of planetary gears of a 2KH type hypocycloid reducer from internal gears, the shaft length can be shortened and a large reduction ratio can be achieved.

Description

Planetary gear reducer

[0001] The present invention relates to a planetary gear reducer, and more particularly to a 2K-H type hypocycloid reducer.

[0002] A cycloid reducer can achieve a large reduction ratio with a single stage and is small and lightweight, but has a large number of parts, a complex structure, and concerns about rigidity (Patent Document 1).

[0003] On the other hand, there is a reducer that uses a 2K-H type planetary gear mechanism (Patent Document 2). The planetary gear mechanism in Patent Document 2 uses two sets of combinations of an internal gear and an external gear that meshes with it, and has high rigidity with a small number of gears used, and can also significantly reduce speed in a single stage.

[0004] JP 2012-97903 A JP 2017-106596 A

[0005] However, in the reducer of Patent Document 2, a large reduction ratio is achieved by using external gears for both the first planetary gear that meshes with the gear on the input shaft and the second planetary gear that meshes with the output shaft, but on the other hand, a small-diameter external gear is used for the second planetary gear that meshes with the gear on the output shaft, which means that the second planetary gear becomes long in the axial direction to ensure the required torque.Furthermore, because the gear provided on the output shaft is an internal gear, a support member is required to rotatably support the internal gear in the axial direction, which poses the problem of further increasing the axial length.

[0006] The present invention has been made in view of this, and provides a reducer that has a small number of parts, high rigidity, and is short in the axial direction.

[0007] In order to solve the above problems, the reducer according to the configuration of the present disclosure comprises an input shaft having an eccentric portion, a fixed sun gear consisting of an external gear arranged coaxially with the input shaft, a first planetary gear having an internal gear that meshes with the fixed sun gear and arranged on the eccentric portion of the input shaft, a driven sun gear consisting of an external gear arranged coaxially with the rotation axis of the input shaft and outputting a reduced output, and a second planetary gear having an internal gear that meshes with the driven sun gear and arranged on the eccentric portion of the input shaft, wherein the first planetary gear and the second planetary gear are formed integrally in the axial direction in the same phase with different gear ratios to form a planetary gear train.

[0008] According to this aspect, the reducer is a 2K-H type hypocycloid reducer, which does not have small driving parts such as pins, has a small number of parts, is arranged in line in the axial direction, and has high rigidity. Since the driven sun gear that extracts the reduction output is made up of an external gear, it is configured to be short in the axial direction.

[0009] In one aspect, the planetary gear train has a support portion provided between the first planetary gear and the second planetary gear, which are arranged side by side in the axial direction, and is rotatably supported by the eccentric portion at the support portion, and the support portion comprises an inner peripheral portion that forms the circumferential inside of the support portion and an outer peripheral portion that forms the circumferential outside of the support portion, the inner peripheral portion and the outer peripheral portion are offset in the axial direction, and the first planetary gear is arranged approximately coaxially with the inner peripheral portion. According to this aspect, the planetary gear train can be made short in the axial direction. Furthermore, the support portion can be arranged close to the fixed sun gear, and the reducer itself can be made short in the axial direction.

[0010] In one aspect, the internal gear of the first planetary gear and the internal gear of the second planetary gear are configured based on a trochoid curve, and the difference in the number of teeth between the first planetary gear and the fixed sun gear, and between the second planetary gear and the driven sun gear, is an integer of 2 or more and the meshing ratio is 2 or more. According to this aspect, the reducer can be configured to have high rigidity while also ensuring quietness.

[0011] As is clear from the above description, a reducer is provided which has a small number of parts, is highly rigid, and is short in the axial direction.

[0012] 6(A) is a perspective view (partially cut away) of a reducer according to the configuration of the present disclosure; FIG. 6(B) is a cross-sectional view of a reducer according to the configuration of the present disclosure; FIG. 6(C) is a skeleton diagram showing the configuration of the reducer; FIG. 6(A) shows a fixed sun gear; FIG. 6(B) is a front view of the fixed sun gear; FIG. 6(C) is a cross-sectional view of the fixed sun gear; FIG. 6(A) shows a side view of the input shaft; FIG. 7(B) is a rear view of the input shaft; FIG. 8 shows a driven sun gear; FIG. 8(A) is a front view of the driven sun gear; FIG. 8(B) is a side view of the driven sun gear; FIG. 8(C) is a cross-sectional view of the driven sun gear; FIG. 9(A) shows a front perspective view of the planetary gear train; FIG. 9(B) is a side view of the planetary gear train; FIG. 9(C) is a cross-sectional view of the planetary gear train. 9(D) is a rear perspective view of the planetary gear train, mainly showing the first planetary gear, a cross-sectional view taken along line AA in FIG. 2, and a cross-sectional view taken along line BB in FIG. 2.

[0013] Specific embodiments of the present invention will be described below with reference to the drawings. The embodiments are illustrative and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention. In addition, in the following description of the embodiments and modifications, the same components are designated by the same reference numerals, and duplicated descriptions will be omitted as appropriate.

[0014] (First embodiment) Fig. 1 is a perspective view (partially cut away) of a reducer W1 according to the configuration of the present disclosure. Fig. 2 is a cross-sectional view of the reducer W1. Fig. 3 is an exploded front perspective view of the reducer W1. Fig. 4 is an exploded rear perspective view of the reducer W1. Fig. 5 is a skeleton diagram showing the configuration of the reducer W1. In Figs. 3 and 4, only main components are shown, and bearings and the like are omitted. Note that in each drawing, directions are described with the output shaft side as the front (FR) and the input shaft side as the rear (RE) based on the input shaft and output shaft (driven sun gear) arranged side by side in the axial direction of the reducer W1.

[0015] 1 to 5, the reducer W1 is a 2K-H type hypocycloid reducer having a planetary gear mechanism. The reducer W1 mainly includes an input shaft 10, a fixed sun gear 20, a planetary gear train 30, a driven sun gear 40, and a housing 50.

[0016] 2, the reducer W1 is mounted on a wheel drive unit of a vehicle and is interposed between a motor M and a wheel hub H. The reducer W1 has an input shaft 10 as an input shaft and a driven sun gear 40 as an output shaft, and the rotation of the input shaft 10 is reduced and output from the driven sun gear 40.

[0017] The input shaft 10 is inserted into the motor M, and is rotated by the rotation of the motor M. The driven sun gear 40 is connected to a wheel hub H to which a wheel (not shown) is connected, and the rotation of the driven sun gear 40 is transmitted to the wheel through the wheel hub H. The rotation of the motor M is reduced in speed by a reducer W1 and transmitted to the wheel, causing the wheel to rotate. The input shaft 10 may be directly driven as a rotating shaft on the motor M side, or may be connected to a rotating shaft of the motor M and driven. Similarly, in addition to the configuration in which the driven sun gear 40 is directly connected to the wheel hub H to transmit driving force, a configuration in which a transmission shaft is provided to be connected to the driven sun gear 40 and connected to the wheel hub H via the transmission shaft to drive the wheel may also be used.

[0018] (Housing) The fixed sun gear 20 is made up of a housing cover portion 21 and a fixed sun gear main body 22. The housing cover portion 21, together with the housing 50, constitutes the housing of the reducer W1.

[0019] The housing 50 is composed of a cylindrical portion 51 having a substantially cylindrical shape and an end face 52 that closes one end of the cylindrical portion 51. A substantially disk-shaped housing cover portion 21 is attached with bolts (not shown) so as to close the opening of the cylindrical portion 51 (the end opposite the end face 52). Each component is held in the substantially cylindrical internal space defined thereby.

[0020] A portion of the input shaft 10 is inserted into and rotatably held in a central through-hole 23 provided in the center of the housing cover portion 21. A portion of the driven sun gear 40, which is provided coaxially with the input shaft 10, is inserted into and rotatably held in a central through-hole 54 provided in an end face 52 of the housing 50.

[0021] (Fixed Sun Gear) The configuration of the fixed sun gear 20 will be described with reference to Fig. 6. Fig. 6 shows the fixed sun gear. Fig. 6(A) is a front view of the fixed sun gear. Fig. 6(B) is a side view of the fixed sun gear. Fig. 6(C) is a cross-sectional view of the fixed sun gear.

[0022] As described above, the fixed sun gear 20 is made up of the housing cover portion 21 and the fixed sun gear main body 22. The fixed sun gear 20 is formed integrally with the substantially disk-shaped housing cover portion 21 and the ring-shaped fixed sun gear main body 22, which has a smaller diameter than the housing cover portion 21, arranged side by side in the axial direction with their axes aligned. The fixed sun gear main body 22 is provided on the surface of the housing cover portion 21 facing the housing 50. When the housing cover portion 21 is fastened to the housing 50, the fixed sun gear main body 22 is positioned inside the housing.

[0023] A plurality of screw holes 29 are formed at equal intervals on the same circumference on the side edge of the housing cover portion 21. Bolts (not shown) are inserted into these screw holes 29 and fastened to openings in the housing 50, thereby fixing the fixed sun gear 20 in place.

[0024] The fixed sun gear main body 22 is an external gear with an external gear formed on its ring-shaped outer circumferential surface. The fixed sun gear main body 22 is a trochoid gear that uses a trochoid curve in its gear shape and is a helical gear with teeth that are cut obliquely with respect to the axis.

[0025] Helical gears and trochoidal gears are used for not only the fixed sun gear main body 22 but also all of the gears of the reducer W1. Helical gears can ensure a higher meshing ratio than spur gears. Trochoidal gears have a better meshing ratio than involute gears and a smaller slip ratio. In this embodiment, a meshing ratio of 2 or more is ensured for each gear, ensuring both a high meshing ratio and quiet operation. Note that helical gears are not essential; spur gears or helical gears may also be used.

[0026] (Input Shaft) The configuration of the input shaft 10 will be described with reference to Fig. 7. Fig. 7 shows the input shaft 10. Fig. 7(A) is a side view of the input shaft 10. Fig. 7(B) is a rear view of the input shaft 10.

[0027] As shown in FIG. 7, the input shaft 10 has a connecting shaft portion 11, an eccentric portion 12, a flange portion 13, and a support shaft portion 14, each of which is configured as a substantially cylindrical column, and these are arranged in order in the axial direction and formed integrally.

[0028] The connecting shaft 11 constitutes one end of the input shaft 10, and the tip of the connecting shaft 11 protrudes from the central through-hole 23 of the housing cover 21 and is inserted into and fixed to the motor M. The base end of the connecting shaft 11 is supported in the central through-hole 23 via a bearing BR1, so that the input shaft 10 is rotatably supported by the fixed sun gear 20.

[0029] The eccentric portion 12 is provided eccentric by an eccentricity amount e with respect to the central axis X, which is the rotational axis of the input shaft 10. When the input shaft 10 rotates, the eccentric portion 12 rotates about the rotation center X1 of the eccentric portion 12 while being eccentric from the central axis X by the eccentricity amount e.

[0030] The flange portion 13 is thin and has an expanded diameter and is provided between the eccentric portion 12 and the support shaft portion 14. It guides the arrangement of the bearings of the eccentric portion 12 and the support shaft portion 14 and also serves as a spacer to prevent interference and friction between parts when the input shaft 10 rotates.

[0031] The support shaft 14 constitutes the other end of the input shaft 10, and engages with a circular recess 48 provided in the center of one end (rear side) of the driven sun gear 40 via a bearing BR3, with the rotational axis aligned with that of the driven sun gear 40 (see FIG. 2). As a result, the input shaft 10 and the driven sun gear 40 are connected so that their rotational axes are aligned and they can rotate relative to each other.

[0032] (Driven Sun Gear) The configuration of the driven sun gear 40 will be described with reference to Fig. 8. Fig. 8 shows the driven sun gear 40. Fig. 8(A) is a front view of the driven sun gear 40. Fig. 8(B) is a side view of the driven sun gear 40. Fig. 8(C) is a cross-sectional view of the driven sun gear 40.

[0033] The driven sun gear 40 is formed integrally with a cylindrical output shaft portion 41 and a generally disk-shaped driven sun gear main body 42 that is larger in diameter than the output shaft portion 41, with their central axes aligned in the axial direction. The driven sun gear 40 is arranged with the driven sun gear main body 42 side facing the input shaft 10 side.

[0034] The output shaft 41 is inserted into a central through-hole 54 formed in the center of an end face 52 of the housing 50, with its tip protruding outside the housing 50 and rotatably held via a collar C. The end face 52 of the housing 50 has a protrusion 53 formed by extending the central through-hole 54, with the peripheral wall of the central through-hole 54 extending from the surface of the end face 52. The output shaft 41 is disposed in the central through-hole 54 extended by the protrusion 53, so that the driven sun gear 40 is stably held in the housing 50 and rotatably. Note that although a collar C is used for the output shaft 41 as a bearing for a location requiring rigidity where a shear load is applied, a bearing may also be used for the bearing.

[0035] A wheel hub H is connected to the output shaft portion 41 protruding from the housing 50, and the rotation input from the input shaft 10 is decelerated and output from the driven sun gear 40, causing the wheel connected to the wheel hub H to rotate.

[0036] The driven sun gear body 42 is disposed within the housing. A circular recess 48 is formed in the center of the end face of the driven sun gear body 42 for connection with the input shaft 10. The support shaft portion 14 of the input shaft 10 is fitted into the circular recess 48, and the two are connected to each other so as to be rotatable about the central axis X.

[0037] The driven sun gear main body 42 is an external gear with an external gear formed on its ring-shaped outer circumferential surface. The rotational input received by the driven sun gear main body 42 causes the driven sun gear 40 to rotate (spin) about the central axis X.

[0038] (Planetary Gear Train) The configuration of the planetary gear train 30 will be described with reference to Figure 9. Figure 9(A) is a front perspective view of the planetary gear train 30, mainly showing the second planetary gear 33. Figure 9(B) is a side view of the planetary gear train 30. Figure 9(C) is a vertical cross-sectional view of the planetary gear train 30. Figure 9(D) is a rear perspective view of the planetary gear train 30, mainly showing the first planetary gear 31.

[0039] The planetary gear train 30 is formed by axially aligning a first planetary gear 31, a support portion 32, and a second planetary gear 33, which are integrally formed.

[0040] The first planetary gear 31 is an internal gear configured in a substantially ring shape, and has an internal gear provided on its inner circumferential surface that meshes with the fixed sun gear main body 22 of the fixed sun gear 20. The number of teeth of the first planetary gear 31 is configured to be two or more more than the number of teeth of the fixed sun gear 20.

[0041] The support portion 32 is formed in a substantially circular plate shape and is provided on the eccentric portion 12 of the input shaft 10 via a bearing BR2, and receives an eccentric input when the input shaft 10 rotates.

[0042] The second planetary gear 33 is an internal gear configured in a substantially ring shape, and has an internal gear provided on its inner circumferential surface that meshes with the driven sun gear main body 42 of the driven sun gear 40. The number of teeth of the second planetary gear 33 is two or more more than the number of teeth of the driven sun gear 40, and is different from the number of teeth of the first planetary gear 31. In other words, the first planetary gear 31 and the second planetary gear 33 are configured to have different gear ratios.

[0043] The first planetary gear 31 is arranged on the fixed sun gear 20 side (rear) of the support portion 32, and the second planetary gear 33 is arranged on the driven sun gear 40 side (front) opposite the fixed sun gear, with the support portion 32 sandwiched between the two planetary gears 31, 33. The two planetary gears are provided to protrude in the axial direction from both end faces of the approximately disk-shaped support portion 32.

[0044] The gear surfaces (inner peripheral surfaces of the ring shape) of the first planetary gear 31 and the second planetary gear 33 are eccentric with respect to the central axis X by the same eccentricity amount e in the same direction as the eccentric direction of the eccentric portion 12. In other words, the first planetary gear 31 and the second planetary gear 33 are eccentric and in the same phase.

[0045] The planetary gear train 30, particularly the support portion 32, is shaped so that the reducer W1 is short in the axial direction.

[0046] The support portion 32 is made up of an inner peripheral portion 32a that forms the inside of the approximately disk-shaped support portion 32 in the circumferential direction, and an outer peripheral portion 32b that forms the outside of the support portion 32 in the circumferential direction.

[0047] The inner peripheral portion 32a serves to be supported by the eccentric portion 12, and the outer peripheral portion 32b serves to connect to the two planetary gears.

[0048] The outer peripheral portion 32b is integrally formed with the inner peripheral portion 32a but is offset from the inner peripheral portion 32a in the axial direction. Specifically, the outer peripheral portion 32b is configured to be offset from the inner peripheral portion 32a in the axial direction toward the second planetary gear 33 (forward). Therefore, the first planetary gear 31, which protrudes from the outer edge of the outer peripheral portion 32b in the direction opposite to the direction in which the second planetary gear 33 is provided (rearward), is spaced apart from the inner peripheral portion 32a in the circumferential direction but positioned at approximately the same position in the axial direction. A substantially ring-shaped space SP1 is formed between the inner peripheral portion 32a and the first planetary gear 31, which are positioned at a distance in the circumferential direction, and the fixed sun gear main body 22 is positioned within this space SP1. In other words, the first planetary gear 31, the fixed sun gear main body 22, and the inner peripheral portion 32a are positioned at approximately the same position in the axial direction.

[0049] Therefore, the housing cover part 21 from which the fixed sun gear main body 22 protrudes is adjacent to the inner peripheral part 32a. The housing cover part 21, which is the housing, and the planetary gear train 30 having the inner peripheral part 32a arranged inside the housing are arranged close to each other. In other words, the axial gap between the housing and the mechanical parts arranged inside the housing is shortened.

[0050] The above-described shape of the support portion 32 allows the planetary gear train 30 to be configured to be short in the axial direction, and the above-described configuration also allows the axial space within the housing to be shortened, allowing the reducer W1 to be configured to be short in the axial direction.

[0051] (Movement of Reducer W1) The movement of the reducer W1 configured as described above will be explained using the skeleton diagram of Fig. 5, Fig. 10, and Fig. 11. Fig. 10 is a cross-sectional view taken along line A-A in Fig. 2. It mainly shows the fixed sun gear main body 22 and the first planetary gear 31. Fig. 11 is a cross-sectional view taken along line B-B in Fig. 2. It mainly shows the second planetary gear 33 and the driven sun gear main body 42.

[0052] As shown in Fig. 5, the reducer W1 is a hypocycloid reducer having a 2K-H type planetary gear mechanism. The reducer W1 includes an input shaft 10 having an eccentric portion 12, a fixed sun gear 20 consisting of an external gear provided coaxially with the input shaft 10, a first planetary gear 31 having an internal gear that meshes with the fixed sun gear 20, a driven sun gear 40 having an external gear that outputs a reduced output, and a second planetary gear 33 having an internal gear that meshes with the driven sun gear 40. The first planetary gear 31 and the second planetary gear 33 are integrally formed to form a planetary gear train 30.

[0053] The first planetary gear 31 and the second planetary gear 33 are formed eccentrically in the same phase and are provided in the eccentric portion 12 .

[0054] When the rotational input of the motor M is transmitted to the input shaft 10, the eccentric portion 12 performs eccentric rotational motion. This eccentric rotational motion is transmitted to the first planetary gear 31 via the bearing BR2. As the fixed sun gear main body 22, which is fixed to the housing 50, meshes with the first planetary gear 31, the first planetary gear 31 is decelerated by the gear ratio between the first planetary gear 31 and the fixed sun gear main body 22. The first planetary gear 31 rotates on its axis by the amount of gear meshing while revolving relative to the fixed sun gear main body 22 due to the eccentric rotational motion of the eccentric portion 12. Furthermore, the second planetary gear 33, which is formed integrally with the first planetary gear 31, meshes with the driven sun gear main body 42 in conjunction with the orbital motion of the first planetary gear 31, and the rotational speed is further decelerated by the gear ratio between the second planetary gear 33 and the driven sun gear main body 42 before being output. At this time, the second planetary gear 33 rotates at a speed reduced by the amount of rotation of the first planetary gear 31 and the gear ratio between the first planetary gear 31 and the fixed sun gear main body 22 relative to the input shaft 10, and the driven sun gear main body 42 is output at a speed further reduced relative to the rotation speed of the second planetary gear 33 by the gear ratio between the driven sun gear main body 42 and the second planetary gear.

[0055] (Effects) The first planetary gear 31 and the second planetary gear 33 are formed eccentrically in phase and are provided in the eccentric portion 12. If the reduction ratio based on the number of teeth Z1 of the fixed sun gear main body 22 and the number of teeth Z2 of the first planetary gear 31 is defined as the first reduction ratio R1, and the reduction ratio based on the number of teeth Z3 of the second planetary gear 33 and the number of teeth Z4 of the driven sun gear main body 42 is defined as the second reduction ratio R2, then because they are provided in phase, the difference between the first reduction ratio R1 and the second reduction ratio R2 is the total reduction ratio i of the reducer W1. This makes it possible to obtain a very large reduction ratio. For example, if the first planetary gear is an external gear and the second planetary gear is an internal gear provided in the eccentric portion, the sum of the two gear ratios is the total reduction ratio of the reducer, making it difficult to obtain a large reduction ratio. As in this embodiment, the first planetary gear 31 and the second planetary gear 33 are both internal gears, and the two gears are provided with different gear ratios, thereby realizing a large reduction ratio of the reducer W1.

[0056] The difference in the number of teeth between the two sets of gears in the reducer W1 is 2 or more. If the difference in the number of teeth is 1, a larger reduction ratio can be obtained, but the amount of eccentricity must be reduced, which poses a problem of high load on the bearings provided in the eccentric portion. By setting the difference in the number of teeth to 2 or more, the above configuration ensures a large reduction ratio while keeping the amount of eccentricity within a reasonable range.

[0057] An example of the number of teeth in this embodiment and the corresponding total reduction ratio i are as follows: Number of teeth Z1 of the fixed sun gear main body 22 = 55 Number of teeth Z2 of the first planetary gear 31 = 53 Number of teeth Z3 of the second planetary gear 33 = 39 Number of teeth Z4 of the driven sun gear main body 42 = 37 Here, 1 / i = 1 / (39 / (39-37)) - 1 / (55 / (55-53)), so the total reduction ratio i of the reducer W1 = 67

[0058] The reducer W1 has a small number of parts, and each part is roughly the same size and arranged axially, making it highly rigid. Furthermore, it can achieve a large reduction ratio without increasing its circumferential size.

[0059] Additionally, in the reducer W1, the driven sun gear 40 that extracts the reduction output is configured as an external gear, so it can be configured to be shorter in the axial direction than if it were configured as an internal gear. An internal gear is provided to protrude axially from a disk-shaped base, while an external gear does not require a base and can be directly mounted on the disk-shaped outer periphery. For the same tooth width, the internal gear can be configured to be shorter in the axial direction. In the reducer W1, the driven sun gear main body 42 is configured as an external gear, thereby shortening the axial length of the housing. As described above, the shape of the planetary gear train 30 is also configured to be shorter in the axial direction within the housing, so the reducer W1 as a whole is configured to be short in the axial direction. Therefore, the reducer W1 can be configured compactly both radially and axially, while achieving a large reduction ratio.

[0060] The above describes preferred embodiments of the present invention, but the above embodiments are merely examples of the present invention, and these can be combined based on the knowledge of those skilled in the art, and such forms are also included in the scope of the present invention.

[0061] W1: reducer, 10: input shaft, 12: eccentric portion, 20: fixed sun gear, 30: planetary gear train, 31: first planetary gear, 32: support portion, 32a: inner peripheral portion, 32b: outer peripheral portion, 33: second planetary gear, 40: driven sun gear

Claims

1. an input shaft having an eccentric portion; a fixed sun gear including an external gear provided coaxially with the input shaft; a first planetary gear having an internal gear meshing with the fixed sun gear and provided on the eccentric portion of the input shaft; a driven sun gear arranged coaxially with the rotation axis of the input shaft and configured as an external gear for outputting a reduced output; a second planetary gear provided on the eccentric portion of the input shaft, the second planetary gear having an internal gear that meshes with the driven sun gear; Equipped with a gear ratio between the first planetary gear and the fixed sun gear is different from a gear ratio between the second planetary gear and the driven sun gear, The first planetary gear and the second planetary gear are integrally formed and aligned in the axial direction to constitute a planetary gear train. A planetary gear reducer characterized by:

2. the planetary gear train has a support portion provided between the first planetary gear and the second planetary gear that are arranged side by side in the axial direction, and is rotatably supported by the eccentric portion at the support portion, The support portion includes an inner peripheral portion that configures a circumferential inside of the support portion and an outer peripheral portion that configures a circumferential outside of the support portion, The inner peripheral portion and the outer peripheral portion are provided to be offset in the axial direction, The first planetary gear is disposed substantially coaxially with the inner peripheral portion.

2. The planetary gear reducer according to claim 1 .

3. the internal gear of the first planetary gear and the internal gear of the second planetary gear are configured based on a trochoid curve, a difference in the number of teeth between the first planetary gear and the fixed sun gear, and between the second planetary gear and the driven sun gear, is an integer of 2 or more, and a meshing ratio is 2 or more; 3. The planetary gear reducer according to claim 1 or 2.