CN114542666A

CN114542666A - Gear device

Info

Publication number: CN114542666A
Application number: CN202111389287.8A
Authority: CN
Inventors: 村越温子; 石塚正幸; 南云稔也; 五十岚纯; 门井幸太
Original assignee: Sumitomo Heavy Industries Ltd
Current assignee: Sumitomo Heavy Industries Ltd
Priority date: 2020-11-26
Filing date: 2021-11-19
Publication date: 2022-05-27
Also published as: JP2022084176A; DE102021130948A1

Abstract

One of the objects of the present invention is to provide a gear device which is advantageous in weight reduction of the entire device. One embodiment of the present invention provides a gear device (100) having a hollow structure at a center portion thereof, the gear device (100) including: a cylindrical member (82) which constitutes a hollow portion; and an outer member (32) disposed radially outward of the tubular member (82) with a gap between the outer member and the tubular member (82). The specific gravity of the tubular member (82) is smaller than that of the outer member (32), and the linear expansion coefficient of the tubular member (82) is smaller than that of the outer member (32).

Description

Gear device

The present application claims priority based on japanese patent application No. 2020 and 195859, filed on 26/11/2020. The entire contents of this Japanese application are incorporated by reference into this specification.

Technical Field

The present invention relates to a gear device.

Background

Patent document 1 describes an orthogonal axis speed reducer having a hollow cylindrical member. The orthogonal axis speed reducer comprises: a 1 st speed reduction part having a hollow input shaft; a 2 nd speed reduction unit centered on an axis orthogonal to the axis of the input shaft; a cylindrical member coaxially penetrating the input shaft; and a frame body for accommodating the deceleration parts. The cylindrical member is fixed to the housing in a cantilever state.

Patent document 1: japanese patent laid-open publication No. 2019-167966

In a gear device provided with a tubular member, the weight of the tubular member increases the overall weight of the gear device. The reduction gear described in patent document 1 has room for improvement in terms of weight reduction of the entire device.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a gear device which is advantageous in weight reduction of the entire device.

In order to solve the above problem, one embodiment of the present invention provides a gear device having a hollow structure at a center portion thereof, the gear device including: a cylindrical member constituting a hollow portion; and an outer member disposed radially outward of the tubular member with a gap therebetween. The tubular member has a specific gravity lower than that of the outer member, and the tubular member has a linear expansion coefficient lower than that of the outer member.

Any combination of the above-described constituent elements or a mode in which constituent elements or expressions of the present invention are substituted for each other in a method, a system, or the like is also effective as an embodiment of the present invention.

According to the present invention, a gear device advantageous for weight reduction of the entire device can be provided.

Drawings

Fig. 1 is a sectional view showing the overall configuration of a gear device according to embodiment 1.

Fig. 2 is an enlarged sectional view of a main portion of the gear device of fig. 1.

Fig. 3 is a sectional view showing the entire configuration of the gear device according to embodiment 2.

Fig. 4 is an enlarged sectional view of a main portion of the gear device of fig. 3.

Fig. 5 is a sectional view showing the entire configuration of the gear device according to embodiment 3.

In the figure: 16-1 st speed reducer, 18-2 nd speed reducer, 22-output member, 22 a-1 st inner peripheral surface portion, 22 b-2 nd inner peripheral surface portion, 32-outer member, 34-input shaft, 34 a-hollow portion, 44-outer gear, 48-inner gear, 53-inner pin, 54-1 st carrier, 56-2 nd carrier, 81-body portion, 81 a-1 st outer peripheral surface portion, 81 b-2 nd outer peripheral surface portion, 82-cylindrical member, 82 a-hollow portion, 82 b-flange portion, 83-abutment portion, 86-bearing, 88-oil seal, 88 d-lip portion, 100-gear device.

Detailed Description

Preferred embodiments of the present invention will be described below with reference to the drawings. In the embodiment and the modifications, the same or equivalent constituent elements and components are denoted by the same reference numerals, and overlapping description is appropriately omitted. In the drawings, the dimensions of the respective members are appropriately enlarged or reduced for easy understanding. In the drawings, parts that are not essential to the description of the embodiments are omitted.

Further, although the terms including the numbers 1, 2, and the like are used to describe various constituent elements, the terms are used only for the purpose of distinguishing one constituent element from other constituent elements, and the constituent elements are not limited by the terms.

[ embodiment 1 ]

The structure of a gear device 100 according to embodiment 1 of the present invention will be described below with reference to fig. 1 and 2. Fig. 1 is a sectional view showing the overall configuration of a gear device 100 according to the present embodiment. Fig. 2 is an enlarged sectional view of a main portion of fig. 1.

The gear device 100 of the present embodiment is a gear device having a hollow structure at the center, and includes: a cylindrical member 82 constituting a hollow portion; and an outer member 32 disposed radially outward of the tubular member 82 with a gap between the outer member and the tubular member 82. The outer member 32 is a member disposed with a gap from the cylindrical member 82, and is not limited thereto. The outer member 32 may or may not rotate around the cylindrical member 82. The outer member 32 in this example includes an input shaft 34 and an output member 22, which will be described later. The outer member 32 may include

external gears

44 and 46 described later. A plurality of electric wirings including a power cable or a signal cable pass through the hollow portion 82a of the cylindrical member 82. In addition to the harness, an air pipe for supplying air also passes through the hollow portion 82 a. The cylindrical member 82 is also sometimes referred to as a center tube.

First, the overall structure of the gear device 100 will be described. The gear device 100 includes: a 1 st speed reducer 16 that receives a driving force from a motor (not shown) and performs primary speed reduction; and a 2 nd speed reducer 18 for receiving the output of the 1 st speed reducer 16 and performing a subsequent speed reduction. The 2 nd speed reducer 18 drives the output member 22 to rotate relative to the outer case 20.

(1 st speed reducer)

The 1 st speed reducer 16 is an orthogonal speed reducer, and includes a pinion gear member 24 and a gear member 26 that rotate integrally with a motor. The pinion member 24 is rotatably supported by the outer case 20 via a pair of

bearings

28 and 30. A bevel pinion gear 24a is formed by straight cutting at an end of the pinion member 24 opposite to the motor.

The gear member 26 includes a bevel gear portion 26a meshing with the bevel pinion portion 24a on the opposite side of the 2 nd speed reducer in the axial direction. The gear member 26 is coupled to an end of the input shaft 34 of the 2 nd speed reducer 18 via a bolt B1.

(speed reducer 2)

Referring to fig. 1, the 2 nd speed reducer 18 will be described. The 2 nd speed reducer 18 of the present embodiment is an eccentric oscillating planetary gear reducer. Hereinafter, a direction along the central axis La of the ring gear 48 in the 2 nd reduction gear 18 described later is referred to as an "axial direction", a circumferential direction of a circle centered on the central axis La is referred to as a "circumferential direction", and a radial direction is referred to as a "radial direction". For convenience, hereinafter, one side in the axial direction (left side in the drawing) is referred to as an input side, and the other side in the axial direction (right side in the drawing) is referred to as an opposite-to-input side.

The input shaft 34 of the 2 nd speed reducer 18 is a hollow shaft disposed along the central axis La and having a hollow portion 34 a. Two

eccentric bodies

36, 38 are integrally formed on the outer periphery of the input shaft 34, and the input shaft 34 also serves as an eccentric body shaft. The axial centers of the

eccentric bodies

36 and 38 are eccentric with a phase difference of 180 degrees.

External gears

44 and 46 are assembled to the outer peripheries of the

eccentric bodies

36 and 38 via

roller bearings

40 and 42. The

external gears

44, 46 internally mesh with the internal gear 48.

The internal gear 48 in this example is composed of an internal gear main body 48a integrated with an inner case 50, and outer pins 48b rotatably supported by the internal gear main body 48a and constituting internal teeth of the internal gear 48. The number of teeth of the

external gears

44 and 46 is set to be slightly smaller (only 1 smaller in this example) than the number of teeth of the internal gear 48 (the number of outer pins 48 b). The

external gears

44 and 46 are formed with

inner pin holes

44a and 46a, and an inner pin 53 fitted with a sleeve 52 is inserted through the

inner pin holes

44a and 46 a. The

inner pin holes

44a, 46a have an inner diameter larger than the outer diameter of the sleeve 52, and the sleeve 52 is always in contact with the

inner pin holes

44a, 46a when the

outer gears

44, 46 eccentrically oscillate.

On both axial sides of the

external gears

44 and 46, a 1 st carrier 54 and a 2 nd carrier 56 are provided, respectively, and are rotatably supported by the inner casing 50 via angular

contact roller bearings

58 and 60, respectively. The inner pin 53 is fixed to the 1 st wheel carrier 54 and the 2 nd wheel carrier 56 by press fitting.

The outer gears 44 and 46 have carrier pin holes 44b and 46b formed therein, and the carrier pins 62 pass through the carrier pin holes 44b and 46 b. The wheel frame pins 62 are loosely fitted into the wheel frame pin holes 44b and 46b with a gap therebetween. The threaded portion 62a of the carrier pin 62 is screwed into the 1 st carrier 54, and is screwed with the nut 64. With this structure, the carrier pin 62 is coupled to and integrated with the 1 st carrier 54 and the 2 nd carrier 56.

The input shaft 34 is rotatably supported by the 1 st carrier 54 and the 2 nd carrier 56 via a pair of seal ball bearings (input bearings) 66 and 68.

Outer rings

66a, 68a of the pair of

ball seal bearings

66, 68 abut the

step portions

54a, 56a of the 1 st carrier 54 and the 2 nd carrier 56, respectively. The

inner rings

66b, 68b abut against the stepped

portions

34c, 34b formed on the input shaft 34 via

rings

70, 72. The

rings

70, 72 function as positioning rings for positioning the

roller bearings

40, 42. Therefore, the movement of the input shaft 34 of the 2 nd speed reducer 18 in the axial direction is restricted by the 1 st carrier 54 and the 2 nd carrier 56 via the pair of

ball sealing bearings

66, 68, and the input shaft 34 is supported rotatably in the circumferential direction by the 1 st carrier 54 and the 2 nd carrier 56 via the pair of

ball sealing bearings

66, 68.

Inner case 50 is coupled to outer case 20 via bolt B2. The 2 nd carrier 56 is coupled to the output member 22 via a bolt B4. The output member 22 is coupled to a driven device (not shown) by a bolt hole 78. The output member 22 has a through hole 22h at the radial center, and is formed in an annular shape as a whole.

Next, the structure of the gear member 26 and the vicinity of the input shaft 34 will be described. At the end of the input shaft 34, the gear member 26 is provided via a bolt B1. A bevel gear portion 26a that meshes with the bevel pinion portion 24a of the pinion gear member 24 is formed on the outer periphery of the gear member 26. An inner bearing 80 that supports the gear member 26 is disposed on the gear member 26. The outer ring 80a of the inner bearing 80 is sandwiched between the step portion 26c formed in the gear member 26 and the retainer ring 90 fitted in the gear member 26. The inner race 80b of the inner bearing 80 abuts against the step 82c of the tubular member 82. The cylindrical member 82 is fitted into the inner periphery of the inner bearing 80.

The cylindrical member 82 has a hollow portion 82a, and the cylindrical member 82 axially penetrates the radial center of the 2 nd speed reducer 18. The cylindrical member 82 has a flange 82B at an input-side end portion, and the cylindrical member 82 is fixed to and integrated with the outer case 20 via a bolt B3 in the vicinity of the outer periphery of the flange 82B. The cylindrical member 82 penetrates the 2 nd speed reducer 18 and is inserted into the through hole 22h of the output member 22. The cylindrical member 82 is supported by a bearing 86 in the through hole 22h of the output member 22. The input-side end of the tubular member 82 is fixed to the outer case 20 via a bolt B3, and the opposite-input-side end is rotatably supported by the output member 22 via a bearing 86.

An oil seal 88 for sealing between the cylindrical member 82 and the output member 22 is disposed at the end portion of the cylindrical member 82 on the opposite side to the input side. As described above, the output member 22 is included in the outside member.

A characteristic structure of the present embodiment will be described with reference to fig. 2. In the gear device 100 having the tubular member 82, the weight of the tubular member 82 increases the weight of the entire device. If the gear device 100 becomes heavy, the range of equipment on which the gear device 100 can be mounted is limited. Therefore, it is conceivable to form the cylindrical member 82 from a material having a small specific gravity. However, if the linear expansion coefficient of the tubular member 82 is larger than that of the outer member 32, the gap between the two members decreases when the temperature rises, and the possibility of the two members contacting each other increases. It is conceivable to provide a large gap between the two, but the gear device 100 becomes larger accordingly.

Therefore, in the present embodiment, the specific gravity of the tubular member 82 is smaller than that of the outer member 32, and the linear expansion coefficient of the tubular member 82 is smaller than that of the outer member 32. The outer member 32 (i.e., the output member 22 and the input shaft 34) may be made of, for example, a ferrous metal such as carbon steel or stainless steel. In this case, the tubular member 82 may be made of a resin material such as Carbon Fiber Reinforced Plastics (CFRP) having a specific gravity and a linear expansion coefficient smaller than those of ferrous metals, or a light metal (metal having a specific gravity of 4 to 5 or less) such as titanium.

Referring to fig. 2, the oil seal 88 will be explained. The oil seal 88 is disposed between the inner cylindrical member 82 and the outer output member 22. The oil seal 88 has a ring portion 88b fitted into the output member 22, a lip portion 88d abutting against the tubular member 82, and a connecting portion 88c connecting the ring portion 88b and the lip portion 88 d. By bringing the lip portion 88d into contact with the tubular member 82, the oil seal 88 seals the gap between the tubular member 82 and the output member 22. When the output member 22 rotates, the oil seal 88 rotates integrally with the output member 22. At this time, the lip 88d slides and rotates with respect to the cylindrical member 82. The oil seal 88 and the bearing 86 are adjacent to each other and arranged in an axial direction. Adjacent to each other is not limited to being directly adjacent, but includes the case where a space or other member exists between each other.

When the surface roughness of the portion in contact with the lip portion 88d is large (the surface roughness is large), the wear of the lip portion 88d is accelerated, and the life is shortened. On the other hand, if the surface roughness of the entire cylindrical member 82 is processed to be small, the number of processing steps increases, which is disadvantageous in terms of cost. Therefore, the tubular member 82 of the present embodiment includes a main body portion 81 and an abutting portion 83 abutting against the lip portion 88d of the oil seal 88, and the abutting portion 83 is configured to have a surface roughness smaller than that of the main body portion 81. By providing the main body 81 and the contact portion 83 as separate parts (separate members), the surface roughness of the contact portion 83 can be reduced while suppressing an increase in the cost of the tubular member 82. Here, as an index indicating the surface roughness, for example, an arithmetic average roughness Ra can be used.

If the contact portion 83 is soft, the sliding resistance increases, and the wear becomes easy. On the other hand, if the entire cylindrical member 82 is hardened, the number of working steps increases, which is disadvantageous in terms of cost. Therefore, the contact portion 83 of the present embodiment is configured to have a hardness higher than that of the main body portion 81. In this case, abrasion of the contact portion 83 can be reduced while suppressing an increase in cost of the cylindrical member 82. The specific gravity of the contact portion 83 may be equal to or higher than that of the body portion 81, or may be lower than that of the body portion 81. The linear expansion coefficient of the abutment portion 83 may be equal to or higher than the linear expansion coefficient of the outer member 32, or may be smaller than the linear expansion coefficient of the outer member 32. The abutting portion 83 of the present embodiment is made of an iron-based metal.

The shape of the contact portion 83 is not limited, but the contact portion 83 of the present embodiment is a thin tubular member. The axial width of the abutment portion 83 is set to a value obtained by adding a margin to the axial range in which the lip portion 88d abuts.

As described above, the bearings 86 are disposed adjacent to the input side of the contact portion 83. When the outer diameter Dg1 of the 1 st outer circumferential surface portion 81a of the body 81 fitted with the contact portion 83 is larger than the outer diameter Dg2 of the 2 nd outer circumferential surface portion 81b of the body 81 fitted with the bearing 86, positioning of the contact portion 83 becomes difficult. Therefore, in the present embodiment, the outer diameter Dg1 of the 1 st outer peripheral surface portion 81a is set to be smaller than the outer diameter Dg2 of the 2 nd outer peripheral surface portion 81 b. The contact portion 83 is positioned based on the difference in outer diameters between the 1 st outer peripheral surface portion 81a and the 2 nd outer peripheral surface portion 81 b.

The operation of the gear device 100 will be described with reference to fig. 1. When the motor rotates and the pinion member 24 of the 1 st speed reducer 16 rotates, the pinion gear portion 24a formed at the end of the pinion member 24 rotates integrally. When the pinion gear part 24a rotates, the gear member 26 meshing with the pinion gear part 24a and the bevel gear part 26a rotates integrally with the input shaft 34.

When the

eccentric bodies

36, 38 rotate with the rotation of the input shaft 34, the

eccentric bodies

36, 38 mesh with the internal gear 48 while oscillating the

external gears

44, 46 via the

roller bearings

40, 42. Since the number of teeth of the

external gears

44 and 46 is set to be one less than the number of teeth of the internal gear 48 (the number of outer pins), the

external gears

44 and 46 rotate so that their phases are shifted by one tooth in the circumferential direction with respect to the internal gear 48 every time the input shaft 34 rotates and the

external gears

44 and 46 oscillate once. The rotation components of the

external gears

44 and 46 are transmitted to the 1 st carrier 54 and the 2 nd carrier 56 through the contact of the

inner pin holes

44a and 46a with the sleeve 52 and the inner pin 53.

The 1 st carrier 54 and the 2 nd carrier 56 are firmly coupled together via the inner pins 53 and the carrier pins 62, and therefore rotate relative to the inner case 50. The outer case 20 is fixed to the inner case 50 by a bolt B2, and the output member 22 is fixed to the 2 nd carrier 56 by a bolt B4. The 1 st carrier 54 and the 2 nd carrier 56 rotate relative to the inner case 50, whereby the output member 22 rotates relative to the outer case 20. When the output member 22 rotates, the driven device coupled to the output member 22 rotates integrally with the output member 22.

Next, the features of the gear device 100 will be described. The tubular member 82 has a specific gravity smaller than that of the outer member 32 (output member 22), and the tubular member 82 has a linear expansion coefficient smaller than that of the outer member 32 (output member 22), which contributes to weight reduction. Further, even if the temperature rises, a gap is secured between the both, and the possibility of the both contacting each other can be reduced.

Hereinafter, embodiment 2 and embodiment 3 of the present invention will be described. In the drawings and the description of embodiment 2 and embodiment 3, the same or equivalent constituent elements and components as those of embodiment 1 are denoted by the same reference numerals. Description of the structure different from that of embodiment 1 will be omitted as appropriate, and the description will be repeated. Therefore, the same or equivalent constituent elements and components as those of embodiment 1 in embodiment 2 and embodiment 3 are explained with reference to embodiment 1.

[ 2 nd embodiment ]

The structure of a gear device 100 according to embodiment 2 of the present invention will be described below with reference to fig. 3 and 4. Fig. 3 is a sectional view showing the entire configuration of the gear device 100 according to the present embodiment. Fig. 4 is an enlarged sectional view of a main portion of fig. 3.

The difference between embodiment 2 and embodiment 1 is that the cylindrical member 82 does not have the contact portion 83, and the lip portion 88d of the oil seal 88 is provided on the output member 22 (outer member 32) side, but the other configurations are the same. Therefore, the structure of the oil seal 88 will be mainly explained. As shown in fig. 4, the oil seal 88 of the present embodiment includes a ring portion 88b externally fitted to the tubular member 82, a lip portion 88d abutting against the output member 22, and a connecting portion 88c connecting the ring portion 88b and the lip portion 88 d.

The oil seal 88 of the present embodiment seals the gap between the cylindrical member 82 and the output member 22 by bringing the lip portion 88d into contact with the output member 22. When the output member 22 rotates, the oil seal 88 does not rotate, and the output member 22 slides and rotates with respect to the lip portion 88 d. By disposing the lip portion 88d radially outward, the lip portion 88d is less likely to be affected by the material of the tubular member 82 being made of a material having a lower specific gravity than the material of the outer member 32. For example, when the cylindrical member 82 is made of resin and the output member 22 is made of an iron-based metal, it is possible to prevent a problem caused by insufficient hardness. Further, the surface roughness of the output member 22 abutting the lip 88d can be reduced while suppressing an increase in cost of the tubular member 82.

From the viewpoint of ensuring the sealing property of the oil seal 88, the circumferential length of the portion abutting the lip portion 88d is preferably small. Therefore, in the present embodiment, the inner diameter Dn1 of the 1 st inner peripheral surface portion 22a of the output member 22 (outer member 32) that abuts the lip 88d is smaller than the inner diameter Dn2 of the 2 nd inner peripheral surface portion 22b of the output member 22 that fits in the bearing 86. At this time, since the circumferential length of the portion in contact with the lip portion 88d is reduced, the sealing property is easily ensured.

This embodiment can achieve the same operation and effect as those of embodiment 1.

[ embodiment 3 ]

A structure of a gear device 100 according to embodiment 3 of the present invention will be described with reference to fig. 5. Fig. 5 is a sectional view showing the entire configuration of the gear device 100 according to the present embodiment. The difference between the embodiment 3 and the embodiment 1 is that a lip portion 88d of the oil seal 88 is provided on the output member 22 (outer member 32) side, a flared portion 82e is provided on the cylindrical member 82, and the bevel gear portion 26a of the gear member 26 is disposed offset to the input-opposite side, but the other configurations are the same. Therefore, these structures will be explained.

As shown in fig. 5, the oil seal 88 of the present embodiment includes a ring portion 88b externally fitted to the contact portion 83, a lip portion 88d contacting the output member 22, and a connecting portion 88c connecting the ring portion 88b and the lip portion 88 d.

The oil seal 88 of the present embodiment seals the gap between the cylindrical member 82 and the output member 22 by bringing the lip portion 88d into contact with the output member 22. When the output member 22 rotates, the oil seal 88 does not rotate, and the output member 22 slides and rotates with respect to the lip portion 88 d.

As shown in fig. 5, the flared portion 82e of the tubular member 82 is connected to the flange portion 82b with the diameter gradually increasing from the input side of the inner bearing 80 toward the flange portion 82 b. The radius of curvature of the flared portion 82e is larger than the radius of curvature of the connecting portion on the inner peripheral side of the flange portion 82b of embodiment 1.

As shown in fig. 5, since the bevel gear portion 26a of the gear member 26 is disposed closer to the input-side opposite side, the device can be made smaller and the hollow diameter of the input side of the tubular member 82 can be made larger. Further, since inner bearing 80 is disposed near the head of bolt B1, bolt B1 can be prevented from falling even if bolt B1 is loosened. Further, since the outer ring 80a of the inner bearing 80 is used as the locking portion of the bevel gear portion 26a, it is more advantageous in terms of cost than the case where a dedicated member is provided. Further, since a space is provided on the input-opposite side of the bevel gear portion 26a, the lubricant discharged from the angular contact roller bearing 58 is guided to the inner direction of the 2 nd speed reducer 18.

In the present embodiment, the tubular member 82 has a housing portion 82s that falls radially inside the outer member 32 and a protruding portion 82g that protrudes in the axial direction from the outer member 32, and the inner diameter of the protruding portion 82g is larger than the inner diameter of the housing portion 82 s. In this example, the protrusion 82g includes a flared portion 82 e. The maximum inner diameter of the projection 82g is larger than the inner diameter of the outer member 32. The maximum inner diameter of the projection 82g is larger than the outer diameter of the

input bearings

66, 68 that support the outer periphery of the outer member 32. In the present embodiment, the inner diameter of the projecting portion 82g is larger than the inner diameter of the angular contact roller bearing 58 or the outer diameter of the 1 st carrier 54. Since the inner diameter of the protruding portion 82g of the cylindrical member 82 is larger than the inner diameter of the housing portion 82s, the space on the inner diameter side of the protruding portion 82g can be used more largely.

The present embodiment can also achieve the same operation and effect as those of embodiment 1. Further, according to the present embodiment, not only the strength around the bevel gear portion 26a can be maintained, but also the axial length of the device can be shortened, and weight reduction can be achieved.

The above description explains an example of the embodiment of the present invention in detail. The above embodiments are merely specific examples for carrying out the present invention. The contents of the embodiments are not intended to limit the technical scope of the present invention, and various design changes such as changes, additions, deletions, and the like of the constituent elements may be made without departing from the scope of the inventive concept defined in the claims. In the above-described embodiments, the description has been given with the addition of a mark such as "in the embodiments" or "in the embodiments" to the content that can be subjected to such a design change, but it does not mean that the design change is not permitted without the content of such a mark. The hatching attached to the cross section of the drawing does not limit the material of the object to be hatched.

Hereinafter, a modified example will be described. In the drawings and the description of the modified examples, the same or equivalent constituent elements and components as those of the embodiment are denoted by the same reference numerals. The description overlapping with the embodiment is appropriately omitted, and the description is repeated for the configuration different from the embodiment.

[ modified examples ]

Although the embodiment 1 has been described with the example in which the 1 st speed reducer 16 is provided, the present invention is not limited to this. For example, the rotation may be directly transmitted from the motor to the 2 nd speed reducer 18 without providing the 1 st speed reducer 16.

In the description of embodiment 1, the example in which the 2 nd speed reducer 18 is a center crank type eccentric oscillating type speed reducer is shown, but the present invention is not limited to this. The 2 nd speed reducer 18 is not particularly limited in type as long as it is a gear device having a hollow structure at the center. For example, a so-called distributed eccentric oscillating type reduction gear, a flexible meshing type reduction gear, a simple planetary reduction gear, or the like may be employed in which a plurality of crankshafts are arranged at positions offset from the center. Further, an internal-gear-swinging-type eccentric swinging reduction gear in which an eccentric body swings an internal gear (a swinging gear) may be used.

In the description of the embodiment, the example in which the number of the external gears is two is shown, but the number of the external gears may be one or three or more.

In the description of the embodiment, the example in which the inner pins 53 contributing to the transmission of the driving force of the

external gears

44 and 46 and the carrier pins 62 not involved in the transmission of the driving force are provided as the pin members for connecting the 1 st carrier 54 and the 2 nd carrier 56 is shown, but the carrier pins 62 are not necessarily provided.

The above modifications can also exhibit the same operational effects as the above embodiments.

Any combination of the constituent elements and the modified examples of the above embodiments is also effective as an embodiment of the present invention. The new embodiment resulting from the combination has the effects of both the combined embodiment and the modified example.

Claims

1. A gear device having a hollow structure at a center portion thereof, comprising:

a cylindrical member constituting a hollow portion; and

an outer member disposed radially outward of the cylindrical member with a gap therebetween,

the cylindrical member has a specific gravity smaller than that of the outer member,

the tubular member has a linear expansion coefficient smaller than that of the outer member.

2. The gear arrangement according to claim 1,

an oil seal is disposed between the cylindrical member and the outer member,

the cylindrical member has a main body portion and an abutting portion abutting against a lip portion of the oil seal,

the abutting portion has a surface roughness less than a surface roughness of the main body portion.

3. The gear arrangement according to claim 2,

the abutment portion has a hardness higher than that of the main body portion.

4. Gear unit according to claim 2 or 3,

the abutting part is formed as a separate body from the main body part,

a bearing adjacent to the contact portion is disposed between the cylindrical member and the outer member,

the main body part is provided with a 1 st outer circumferential surface part for externally embedding the abutting part and a 2 nd outer circumferential surface part for externally embedding the bearing,

the outer diameter of the 1 st outer peripheral surface portion is smaller than the outer diameter of the 2 nd outer peripheral surface portion.

5. The gear arrangement according to claim 1,

an oil seal is disposed between the cylindrical member and the outer member,

the lip portion of the oil seal is provided on the outer member side.

6. The gear arrangement according to claim 5,

a bearing adjacent to the oil seal is disposed between the cylindrical member and the outer member,

an inner diameter of a 1 st inner circumferential surface portion of the outer member abutting the lip portion is smaller than an inner diameter of a 2 nd inner circumferential surface portion of the outer member fitted to the bearing.

7. Gear unit according to one of the claims 1 to 6,

the gear device is an eccentric oscillating gear device, and is provided with an eccentric body shaft having an eccentric body for oscillating an oscillating gear,

the eccentric body shaft constitutes the outer member.

8. Gear unit according to one of the claims 1 to 7,

the cylindrical member has a receiving portion that falls radially inside the outer member and a projecting portion that projects in the axial direction from the outer member,

the inner diameter of the protruding portion is larger than that of the accommodating portion.

9. The gear arrangement according to claim 8,

the maximum inner diameter of the projection is larger than the inner diameter of the outer member.

10. The gear arrangement according to claim 9,

the maximum inner diameter of the projection is larger than the outer diameter of an input bearing that supports the outer periphery of the outer member.