JP6803273B2 - Differential reducer - Google Patents

Description

The present invention relates to an inscribed swing type differential speed reducer including an internal gear and an external gear that inscribes and meshes with the internal gear.

The differential speed reducer includes an internal gear and an external gear that meshes inscribed with the internal gear, and the external gear moves eccentrically in the internal gear due to rotational input from the input shaft. Relative rotation is generated between the gears, and the rotation is output to the output shaft at a reduction ratio due to the difference in rotation speed between the eccentric movement and the relative rotation. For example, in Patent Document 1, a hollow input shaft is pivotally supported on a pair of front and rear support flanges via a pair of bearings, and a pair of front and rear eccentric bodies provided on the outer periphery of the input shaft between the bearings are provided with roller bearings. A power transmission device is disclosed in which two external gears are arranged in different phases, and an internal pin for loosely inserting an internal pin hole provided in each external gear is installed between support flanges. That is, when the input shaft rotates, the external gear is oscillated (eccentric) in the internal gear via the eccentric body to extract the relative rotation component of the difference in the number of teeth between the internal and external teeth, thereby extracting the support flange. In particular, in order to firmly fix input members such as pulleys and gears to the input shaft, the outer diameter of the input shaft is set toward the power input side for each part corresponding to the bearing. It is expanding in stages.

International Publication No. 2006/08536

In order to increase the strength of the differential speed reducer, it is effective to increase the outer diameter of the rollers that support the external gears. However, in the invention of Patent Document 1, since the outer diameter of the input shaft is gradually expanded, the inner diameter of the roller bearing becomes larger than the inner diameter of the bearing of the input shaft, and the outer diameter of the roller is restricted. It was difficult to increase the strength.

Therefore, an object of the present invention is to provide a differential speed reducer capable of increasing the outer diameter of the roller and increasing the strength even if a roller bearing is used for the shaft support of the external gear. is there.

In order to achieve the above object, the invention according to claim 1 is for an internal gear provided in a casing, an input shaft coaxially penetrating the internal gear, and an eccentric portion provided on the input shaft. An output unit having an input shaft bearing interposed between an external gear that is externally mounted via a bearing and meshes with the internal gear inwardly and an input shaft having a pin for loosely inserting the external gear. The reduction ratio is based on the difference in the number of teeth between the internal gear and the external gear and the number of teeth of the external gear due to the eccentric movement of the external gear with respect to the internal gear due to the rotation of the input shaft. It is a differential speed reducer that rotates the output part via a pin.
An eccentric bearing is used as a full roller, and a pair of input shaft bearings are arranged in front of and behind the external gear in the axial direction of the input shaft , and the outer diameter of the eccentric portion on the input shaft is set to the input shaft bearing. The feature is that it is smaller than the outer diameter of the part.
According to the second aspect of the present invention, in the configuration of the first aspect, the input shaft bearing is in contact with the outer periphery of the input shaft between the input shaft bearing and the eccentric bearing and the side surface of the input shaft bearing in the axial direction of the input shaft. A retaining portion for restricting movement to the retaining portion is provided, and the eccentric portion is formed lower than the retaining portion over the entire circumference.
The invention according to claim 3 is characterized in that, in the configuration of claim 2, the retaining portion has a disk shape integrally formed coaxially with the input shaft.
The invention according to claim 4 is that, in any of the configurations of claims 1 to 3, a plurality of sets of eccentric portions, bearings for eccentric portions, and external gears are provided, and the outer diameters of the eccentric portions are all equal. It is a feature.
The invention according to claim 5 is characterized in that, in the configuration of claim 4, the shapes of the external gears and the bearings for the eccentric portions are the same.

According to the invention of claim 1, the eccentric bearing is a full roller, and a pair of input shaft bearings are arranged in front of and behind the external gear in the axial direction of the input shaft to form an eccentric bearing on the input shaft . By making the outer diameter smaller than the outer diameter of the portion where the input shaft bearing is provided, the outer diameter of the roller can be increased, which leads to an increase in strength.
According to the second aspect of the present invention, in addition to the effect of the first aspect, a retaining portion that abuts on the outer periphery of the input shaft and abuts on the side surface of the bearing for the input shaft to regulate the movement of the input shaft in the axial direction. By providing the eccentric portion to be lower than the retaining portion over the entire circumference, it is possible to regulate the movement of the roller in the axial direction over the entire circumference of the eccentric portion as a total roller. Further, the retaining portion can be shared with both the retaining portion and the bearing for the input shaft.
According to the third aspect of the present invention, in addition to the effect of the second aspect, since the retaining portion has a disk shape integrally formed coaxially with the input shaft, the retaining portion can be easily formed by a lathe or the like. It can be processed.
According to the invention of claim 4, in addition to the effect of any one of claims 1 to 3, a plurality of sets of eccentric portions, bearings for eccentric portions, and external gears are provided, and the outer diameter of each eccentric portion is all set. Since they are made equal, the same eccentric bearing can be arranged in each eccentric portion, and the outer diameter of the roller of each eccentric bearing can be increased.
According to the fifth aspect of the present invention, in addition to the effect of the fourth aspect, since the shapes of the external gears and the bearings for the eccentric parts are the same, further cost reduction can be expected.

It is a central vertical sectional view of a series of differential reduction gears. (A) to (C) show cross-sectional views of the differential speed reducers 1A to 1C in the line AA of FIG. It is an enlarged view of F part of FIG. It is a graph which compared the efficiency when the dislocation coefficient of the internal gear 4 is different.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIGS. 1 and 2 show a series S composed of three types of differential speed reducers 1A, 1B, and 1C. However, since the structures of the differential speed reducers 1A to 1C are substantially the same, FIG. 1 shows a central longitudinal sectional view of the differential speed reducer 1A as a representative, and FIGS. 2 (A) to 2 (C) show FIG. Cross-sectional views of the differential speed reducers 1A to 1C on the AA line are shown. Further, when distinguishing the components for each of the differential speed reducers 1A to 1C, alphabetic characters such as 14A to 14C are added.
In the differential speed reducer 1A (1B, 1C), reference numeral 2 denotes a casing, which is a cylindrical inner case 3 in which an internal gear 4 is integrally provided inside and one of the axial directions in the inner case 3. It consists of a disk-shaped case cover 5 arranged on an end surface (input side, right side in FIG. 1) and a cylindrical outer case 6 arranged on the other end surface (output side, left side in FIG. 1). The inner case 3, the case cover 5, and the outer case 6 are integrally connected by a plurality of bolts 7, 7, ... Which penetrate the inner case 3 from the case cover 5 side and are screwed into the outer case 6. ..

Inside the outer case 6, a disk-shaped output shaft 9 is rotatably supported via a cross roller bearing 8 as an outer bearing. Further, inside the casing 2, a hollow tubular input shaft 12 is coaxially and rotatably supported via ball bearings 10 and 11 which are bearings for the input shaft. However, in the ball bearing 10 as the inner bearing on the input side, the axial input side half of the outer ring 10a is supported by the case cover 5, and the axial output side half of the outer ring 10a is supported by the carrier 24 described later.
In this input shaft 12, a pair of eccentric portions 14A, 14A (14B) having outer diameters equal to each other and having a phase in which the maximum eccentric side is 180 degrees different from each other between the shaft support portions 13 and 13 on which the ball bearings 10 and 11 are arranged , 14B and 14C, 14C) are formed adjacent to each other in the axial direction. Each of the eccentric portions 14A and 14A (14B, 14B and 14C, 14C) is a total roller composed of a plurality of needles 16 and 16 having a circular cross section arranged over the entire circumference as bearings for the eccentric portion. Needle bearings 15 are provided, and external gears 17A and 17A (17B, 17B and 17C, 17C) having the same outer shape are rotatably exteriorized via the needle bearings 15. Therefore, each needle 16 is in direct contact with the inner eccentric portions 14A to 14C and the outer external gears 17A to 17C.

Here, in the input shaft 12, the outer diameter D1 of the shaft support portion 13 on which the ball bearings 10 and 11 are arranged and the outer diameter D2 of the eccentric portion 14A (14B, 14C) on which the needle bearing 15 is provided are D1> D2. It is formed so as to have a relationship of. By reducing the outer diameter D2 of the eccentric portions 14A (14B, 14C) in this way, the size (outer diameter) of each needle 16 provided on the outer circumference can be increased. Further, between the shaft support portion 13 and the eccentric portion 14A (14B, 14C), a disk-shaped retaining portion 18 projecting higher toward the outer peripheral side than the eccentric portion 14A (14B, 14C) over the entire circumference is provided. Each is installed around. The retaining portion 18 restricts the movement of the needle 16 outward in the axial direction and the movement of the ball bearings 10 and 11 inward in the axial direction over the entire circumference. As a result, the movement of the input shaft 12 in the axial direction is also restricted. The movement of the ball bearing 10 to the outside is regulated by a covering portion 19 provided on the inner peripheral edge of the case cover 5 and overlapping the outer ring 10a from the outside, and the movement of the ball bearing 11 to the outside is provided on the output shaft 9. It is regulated by the step 20.

As shown in FIG. 2, the external gears 17A to 17C have a number of teeth smaller than that of the internal gear 4 and are inscribed in the internal gear 4 at an eccentric position. Here, in the differential speed reducers 1A to 1C, the internal gears 4 having the same shape with 120 teeth are used. On the other hand, in each of the external tooth gears 17A to 17C, the external tooth gear 17A has 114 teeth, the difference in the number of teeth from the internal tooth gear 4 is 6, the reduction ratio is 1/19, and the external tooth gear 17B has. , The number of teeth is 116, the difference in the number of teeth from the internal gear 4 is 4, the reduction ratio is 1/29, and the external gear 17C has the number of teeth 118 and the difference in the number of teeth from the internal gear 4 is 2. , The reduction ratio is 1/59. Therefore, the eccentricities δ1, δ2, and δ3 from the center O1 (axis center of the input shaft 12) of the internal gear 4 of the respective centers O2 of the external gears 17A to 17C (centers of the eccentric portions 14A to 14C) are δ1. The relationship is>δ2> δ3.
Here, the internal teeth of the internal gear 4 and the external teeth of the external gear 17 have involute tooth types, respectively, and the displacement coefficient of the internal gear 4 exceeds 1 and is between 1.9. It is set.

Further, in each of the external gears 17A to 17C, eight circular pin holes 21A to 21C are formed on a concentric circle centered on the center O2 at equal intervals in the circumferential direction, and the pin holes 21A to 21C are formed at equal intervals in the circumferential direction. Pins 22, 22 ... Are loosely inserted, respectively. The pin 22 is erected between the output shaft 9 and the disk-shaped carrier 24 arranged inside the case cover 5 on a concentric circle centered on the axis of the internal gear 4 and parallel to the axis. In the shaft body, a tubular metal 23 is integrally exteriorized at the free insertion portion of the external gears 17A to 17C on the outer circumference of the pin 22. The carrier 24 supports the inner half of the outer ring 10a of the ball bearing 10 inside the case cover 5 and can rotate integrally with the output shaft 9 via the pin 22. Here, the pin 22 and the output shaft 9 connected via the pin 22 serve as the output unit.

Each pin 22 inscribes the outer circumference of the metal 23 with the inner circumferences of the pin holes 21A to 21C of the front and rear external gears 17A and 17A (17B, 17B and 17C, 17C) in phases different from each other by 180 degrees. The hole diameters of the pin holes 21A to 21C of the external gears 17A to 17C are set for each of the differential speed reducers 1A to 1C. That is, the diameter of the pin holes 21A to 21C in the external gears 17A to 17C is the diameter obtained by adding twice the eccentricity δ1 to δ3 of the external gears 17A to 17C to the diameter of the pin 22 including the metal 23. Therefore, the hole diameters of the pin holes 21A to 21C are different for each of the differential speed reducers 1A to 1C. However, even if the hole diameters are different, the center positions of the pin holes 21A to 21C of the external gears 17A to 17C are all the same.

On the other hand, the ball bearing 10 is gap-fitted on the inner peripheral surface of the case cover 5 and the carrier 24, and is input between the case cover 5 supporting the outer ring 10a and the carrier 24 as shown in FIG. A gap A is formed in the axial direction of the shaft 12 and communicates with the inside of the casing 2. Further, ring-shaped grease grooves 25 and 25 are formed on the inner peripheral surfaces of the case cover 5 and the carrier 24, respectively, over the entire circumference.
Further, an oil seal 27 as a seal member is interposed between the ring-shaped ridge 26 projecting from the front surface of the case cover 5 and the outer peripheral surface of the input shaft 12. An oil seal 28 is also interposed between the outer case 6 and the output shaft 9 on the output side of the cross roller bearing 8. An oil seal 29 is also interposed between the output shaft 9 and the input shaft 12 on the output side of the ball bearing 11.

In the differential speed reducers 1A to 1C configured as described above, when the input shaft 12 is rotationally input and the input shaft 12 rotates, the front and rear eccentric portions 14A to 14C perform eccentric movements symmetrically, and each external tooth The gears 17A to 17C are eccentric and rotate while being inscribed in the internal gear 4. Therefore, the pin holes 21A to 21C also eccentrically and rotate, but since the pin holes 21A to 21C are formed to have a larger diameter than the pin 22 including the metal 23, each pin 22 has a pin hole 21A to 21C. The eccentric component is absorbed by relatively eccentric movement in the state of being inscribed in the pin 22, and only the rotation component is extracted from each pin 22. Therefore, the output shaft 9 and the carrier 24 rotate synchronously via the pin 22, and the output shaft 9 rotates in a state of being decelerated at the reduction ratio described above. Here, in the series S, the differential speed reducer 1A has a reduced speed, the differential speed reducer 1B has a medium speed reduction, and the differential speed reducer 1C has a high speed reduction.

At this time, the grease filled in the casing 2 is supplied from the gap A between the outer ring 10a, the inner peripheral surface of the case cover 5 and the inner peripheral surface of the carrier 24 to the grease grooves 25 and 25, and lubrication is supplied. It is maintained and friction is reduced. Further, even if the grease is supplied in this way, the grease does not leak because the oil seal 27 is interposed between the case cover 5 and the input shaft 12.

(Effects of Inventions Related to Series of Differential Reducers)
As described above, according to the series S of the differential speed reducers 1A to 1C of the above-described embodiment, the pin holes 21A to 21C of the external gears 17A to 17C are respectively provided with the external gears 17A to 17A according to the number of external teeth. By forming each 17C with a different diameter and sharing the internal gear 4, the pin 22, and the metal 23, the external gears 17A to 17C have pin holes 21A to a hole diameter corresponding to one reduction ratio. It suffices to form only 21C. Therefore, the parts can be shared and the manufacturing cost can be suppressed without lowering the strength of the external gears 17A to 17C.
In particular, here, since the center positions of the pin holes 21A to 21C coincide with each other between the external gears 17A to 17C, the output shaft 9 and the carrier 24 can be shared.

Further, the tooth molds of the internal gear 4 and the external gears 17A to 17C are involute tooth molds.
According to JGMA (Japan Gear Industry Association Standard) (JGMA 611-01) "ISO standard compliant cylindrical gear shift method", which is the gear standard of the Japan Gear Industry Association, involute internal teeth are considered in consideration of gear meshing efficiency. It is recommended that the total value of the shift coefficient of the gear and the shift coefficient of the involute external gear be designed to be 1 or less.
However, in the present embodiment, by setting the displacement coefficient of the internal gear 4 to exceed 1 and up to 1.9, the diameter of the root circle of the external gears 17A to 17C that mesh with the coefficient is increased. It is possible to secure the wall thickness between the tooth bottoms of the external gears 17A to 17C and the pin holes 21A to 21C.
Note that FIG. 4 is a graph comparing changes in efficiency (transmission efficiency) when the input torque is changed to 1 Nm at an input of 2000 rpm, with the dislocation coefficients of the internal gear 4 being 1.9 and 0.2. Then, No. The solid line of 1 is the dislocation coefficient of 1.9 (76 teeth, difference of 1 tooth, reduction ratio 1/75), No. The case where the dotted line of 2 has a dislocation coefficient of 0.2 (60 teeth, difference in number of teeth 1, reduction ratio 1/59) is shown.
Here, the maximum efficiency is approximately 68% with a dislocation coefficient of 1.9 and approximately 70% with a dislocation coefficient of 0.2, indicating that even if the dislocation coefficient is 1.9, the degree of influence on efficiency is not so great. ..

Further, since the number of pins 22 of the output unit is eight, the rigidity of the differential speed reducers 1A to 1C can be increased. In particular, since it is sufficient to form only the pin holes 21A to 21C corresponding to one reduction ratio in the external gears 17A to 17C, the number of pins 22 can be easily increased to eight or more.
Further, in order to increase the rigidity of the differential speed reducers 1A to 1C, it is effective to make the pin 22 thicker. If many inner roller holes are formed in the outer gear for each reduction ratio as in the background technique mentioned above, it is difficult to make the pins thicker because the inner roller holes are close to each other. Since only the pin holes 21A to 21C corresponding to one reduction ratio are formed in the tooth gears 17A to 17C, the distance between the pin holes 21A to 21C can be secured. Therefore, it is possible to easily make the pin 22 thicker to increase the rigidity.

In addition, since it is only necessary to form the pin holes 21A to 21C corresponding to one reduction ratio in the external gears 17A to 17C, even if the series has three different reduction ratios, the differential reduction gears 1A to 1C The strength of the external gears 17A to 17C does not decrease. Therefore, three or more types of series can be configured while the internal gear 4, the pin 22, the metal 23, the output shaft 9, and the carrier 24 are shared.
Then, by making the input shaft 12 hollow, weight reduction can be achieved. Further, even if the input shaft 12 is hollow, the strength of the external gears 17A to 17C can be maintained.

In the above embodiment, a series of three types of differential reduction gears is illustrated, but the reduction ratio and the number of differential reduction gears are not limited to this, and two or four or more types of differential reduction gears having different reduction ratios are used. It is possible to standardize the internal gear and the output unit even in the series. Each reduction ratio is also not limited to the above form. The number of external gears provided in each differential speed reducer can also be increased or decreased.
Further, in the above embodiment, the pin is made of metal, but a rolling element such as a roller may be made of the pin, or such a separate member may not be made of the pin alone.

(Effect of invention of differential speed reducer relating to bearing for eccentric part and outer diameter of eccentric part)
As described above, according to the differential speed reducers 1A to 1C of the above-described embodiment, the bearing for the eccentric portion is the needle bearing 15 of the full roller, and the outer diameter D2 of the eccentric portions 14A to 14C on the input shaft 12 is a ball bearing. By making the outer diameter D1 of the shaft support 13 provided with 10 and 11 smaller, the outer diameter of the needle 16 can be increased, which leads to an increase in strength.
In particular, here, a retaining portion that abuts on the outer periphery of the input shaft 12 between the ball bearings 10 and 11 and the needle bearing 15 and abuts on the side surfaces of the ball bearings 10 and 11 to restrict the axial movement of the input shaft 12. Since 18 and 18 are provided and the eccentric portions 14A to 14C are formed lower than the retaining portion 18 over the entire circumference, the needle 16 is formed over the entire circumference of the eccentric portions 14A to 14C as a whole. Axial movement can be regulated. Further, the retaining portion 18 can be shared as a retaining portion for both the ball bearings 10 and 11 and the needle 16. Further, the retaining portion 18 also serves as a retaining portion for the input shaft 12 itself.

Further, since the retaining portion 18 has a disk shape coaxially formed with the input shaft 12, the retaining portion 18 can be easily processed by a lathe or the like.
Further, since a plurality of sets of eccentric portions 14A to 14C, needle bearings 15, and external gears 17A to 17C are provided to make the outer diameters of the eccentric portions 14A to 14C all equal, the same needle is provided for each eccentric portion 14A to 14C. Bearings 15 can be arranged and the outer diameter of the needle 16 of each needle bearing 15 can be increased.
In addition, since the external gears 17A to 17C and the needle bearings 15 have the same shape, further cost reduction can be expected.
Since the needle 16 of the needle bearing 15 can be arranged at a position close to the center O1 of the internal gear 4 (the axial center of the input shaft 12), the diameter of the pin 22 for extracting the rotation motion from the external gears 17A to 17C is increased. Can be made larger. Therefore, the strength of the differential speed reducers 1A to 1C can be increased.

The shape of the retaining portion is not necessarily a disk shape, and may be a gear shape having a plurality of protrusions formed on the outer circumference as long as the movement of the needle can be regulated, or is separate from the input shaft. It may be a member.

(Effect of Invention of Differential Reducer for Supporting Ball Bearings)
As described above, according to the differential speed reducers 1A to 1C of the above-described embodiment, the outer ring 10a of the ball bearing 10 is supported by the case cover 5 and the carrier 24 of the casing 2, so that the input shaft 12 and the casing 2 are supported. The input shaft 12 can be assembled accurately by increasing the coaxiality.
In particular, here, since the outer ring 10a of the ball bearing 10 is gap-fitted with respect to the case cover 5 and the carrier 24, it can be slid on the sliding surface, and the rotational resistance is reduced.

Further, since the grease grooves 25 and 25 are formed on the sliding surfaces of the outer ring 10a to be fitted in the gap and the case cover 5 and the carrier 24, the grease is held on the sliding surfaces and slides with low friction. be able to.
Further, since the grease groove 25 is formed in the case cover 5 and the carrier 24, the standard ball bearing 10 can be adopted, and the cost increase can be suppressed.
In addition, since the grease groove 25 is formed over the entire circumference of the sliding surface, the grease groove 25 can be easily machined by a lathe or the like.
An oil seal 27 for sealing between the casing 2 and the input shaft 12 is arranged outside the ball bearing 10 in the axial direction of the input shaft 12, so that the casing 2 having a high degree of coaxiality and the input shaft 12 The oil seal 27 can be brought into contact with the input shaft 12 with high accuracy, and the risk of grease leakage can be reduced.

In the above embodiment, the outer ring of the ball bearing is gap-fitted to both the case cover and the carrier, but it may be gap-fitted to only one of them. Therefore, the grease groove may be provided only on the sliding surface on one side where the gap is fitted.
Further, when the grease groove is provided, it can be provided over the entire circumference of the sliding surface, or can be provided intermittently in the circumferential direction.

In addition, in common with each form, the casing structure is not limited to the combination of the inner case, the case cover, and the outer case as in the above form, and the number of parts can be increased or decreased, or the casing can be formed by one member. It doesn't matter.
Further, the outer bearing is not limited to the cross roller bearing, and other bearings such as ball bearings can be adopted, and the number of bearings may be increased.
Further, the structure of the input shaft and the output shaft is not limited to the above-mentioned form, and the design can be changed as appropriate, such as making the input shaft solid instead of hollow.

1A to 1C ... Differential reducer, 2 ... Casing, 3 ... Middle case, 4 ... Internal gear, 5 ... Case cover, 6 ... Outer case, 7 ... Bolt, 8 ... Cross roller Bearing, 9 ... Output shaft, 10 ... Ball bearing, 10a ... Outer ring, 11 ... Ball bearing, 12 ... Input shaft, 13 ... Shaft branch, 14 ... Eccentric part, 15 ... Needle bearing, 16・ ・ Needle, 17A to 17C ・ ・ External gear, 18 ・ ・ Retaining part, 21A to 21C ・ ・ Pin hole, 22 ・ ・ Pin, 23 ・ ・ Metal, 24 ・ ・ Carrier, 25 ・ ・ Gris groove, 27 , 28, 29 ... Oil seal, S ... Series, A ... Gap, D1 ... Shaft support outer diameter, D2 ... Eccentric outer diameter, O1 ... Internal gear center, O2 ... Outer Center of tooth gear, δ1 to δ3 ... Eccentricity.

Claims (5)

An internal gear provided in the casing, an input shaft coaxially penetrating the internal gear, and an eccentric portion provided on the input shaft are externally provided via an eccentric bearing and inscribed in the internal gear. An external gear that meshes with an external gear and an output portion that is provided with a pin for loosely inserting the external gear and has an input shaft bearing interposed between the input shaft are included, and the rotation of the input shaft causes the above-mentioned When the external gear moves eccentrically with respect to the internal gear, the reduction ratio is based on the difference in the number of teeth between the internal gear and the external gear and the number of teeth of the external gear through the pin. A differential speed reducer that rotates the output unit.
The bearing for the eccentric portion is used as a total roller, and a pair of bearings for the input shaft are arranged in front of and behind the external gear in the axial direction of the input shaft.
A differential speed reducer characterized in that the outer diameter of the eccentric portion of the input shaft is made smaller than the outer diameter of the portion provided with the bearing for each input shaft. Between the bearing for the input shaft and the bearing for the eccentric portion, a retaining portion is provided on the outer periphery of the input shaft to abut on the side surface of the bearing for the input shaft to restrict the movement of the input shaft in the axial direction. The differential speed reducer according to claim 1, wherein the eccentric portion is formed lower than the retaining portion over the entire circumference. The differential speed reducer according to claim 2, wherein the retaining portion has a disk shape coaxially formed with the input shaft. The differential reduction gear according to any one of claims 1 to 3, wherein a plurality of sets of the eccentric portion, the bearing for the eccentric portion, and the external gear are provided, and the outer diameters of the eccentric portions are all equal. Machine. The differential speed reducer according to claim 4, wherein the external gears and the eccentric bearings have the same shape.

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