JP7756583B2 - Components and power transmission devices - Google Patents

Description

The present invention relates to components and power transmission devices.

Conventionally, reduction gears used as power transmission devices have included a sealing member as a component between the outer cylinder and carrier, which rotate relative to each other, to prevent leakage of the internal lubricant (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2017-219134

The above-mentioned sealing member is made of an elastic sealing material, and when the internal pressure increases due to the driving of the reduction gear device and the sealing member is subjected to axial pressure, the sealing member is distorted in the radial direction, which increases the contact pressure of the lip portion that slides against the carrier, making the sealing member more susceptible to wear.
The present invention has been made in view of the above circumstances, and has as its object to suppress the influence of sliding of various components including a seal member.

The present invention provides
A component of a power transmission device,
At least the sliding portion of the component is made of a material having a negative Poisson's ratio and a material having a positive Poisson's ratio ,
Of the sliding parts, the parts that come into direct sliding contact are made of a material with a positive Poisson's ratio .
Another aspect of the present invention is
A component of a power transmission device,
At least the sliding portion of the component is made of a material having a negative Poisson's ratio and a material having a positive Poisson's ratio,
The component is an oil seal,
The waist portion between the core and the lip portion serving as the sliding portion is made of a material with a positive Poisson's ratio.

This invention makes it possible to reduce the effects of sliding between components.

1 is an axial cross-sectional view showing a flexible mesh gear device as a power transmission device according to an embodiment of the present invention. FIG. 2 is an axial cross-sectional view of the oil seal. FIG. 10 is an axial cross-sectional view showing an example in which a material with a positive Poisson's ratio and a material with a negative Poisson's ratio are arranged in a lattice pattern. FIG. 2 is an axial cross-sectional view of a bearing and its rolling elements. FIG. 5A is a perspective view of a piston-cylinder mechanism serving as a power transmission device, with a portion cut away, and FIG. 5B is a cross-sectional view of an O-ring along the direction of reciprocating motion of the piston.

Embodiments of the present invention will be described in detail below with reference to the drawings.

[Configuration of flexure mesh gear device]
1 is an axial cross-sectional view of a flexible mesh gear device 1, which is an example of a power transmission device. Note that the upper half of this cross-sectional view illustrates a cross section along the minor axis of a vibrator 10A (described later), and the lower half illustrates a cross section along the major axis of the vibrator 10A.

As shown in FIG. 1, the flexible mesh gear device 1 is a cylindrical flexible mesh gear device and includes a vibrator shaft 10, an external gear 11, a first internal gear 31G and a second internal gear 32G as internal gears, a vibrator bearing 12, a casing 33, a first cover 34, and a second cover 35.

The vibrator shaft 10 is a hollow cylindrical shaft that rotates around a rotation axis O1, and includes a vibrator 10A whose cross section perpendicular to the rotation axis O1 has a non-circular (e.g., elliptical) outer shape, and shaft portions 10B and 10C provided on both sides of the vibrator 10A in the axial direction. The elliptical shape is not limited to a geometrically strict ellipse, but also includes an approximate ellipse. The shaft portions 10B and 10C are shafts whose cross section perpendicular to the rotation axis O1 has a circular outer shape.
In the following description, the direction along the rotation axis O1 is referred to as the "axial direction," the direction perpendicular to the rotation axis O1 as the "radial direction," and the direction of rotation about the rotation axis O1 as the "circumferential direction." In addition, within the axial direction, the side (left side in the drawing) that is connected to an external driven member and outputs decelerated motion to the driven member is referred to as the "output side," and the side opposite the output side (right side in the drawing) is referred to as the "anti-output side."

The external gear 11 is a flexible cylindrical member centered on the rotation axis O1, with teeth provided on its outer periphery.

The first internal gear 31G and the second internal gear 32G rotate around the rotation axis O1 around the vibrator shaft 10. The first internal gear 31G and the second internal gear 32G are arranged side by side in the axial direction and mesh with the external gear 11. Specifically, one of the first internal gear 31G and the second internal gear 32G meshes with teeth on one side of the axial center of the external gear 11, and the other meshes with teeth on the other side of the axial center of the external gear 11.
Of these, the first internal gear 31G is configured by providing internal teeth at a corresponding location on the inner periphery of the first internal gear member 31. On the other hand, the second internal gear 32G is configured by providing internal teeth at a corresponding location on the inner periphery of the second internal gear member 32.

The vibrator bearing 12 is, for example, a roller bearing, and is arranged between the vibrator 10A and the external gear 11. The vibrator 10A and the external gear 11 are capable of relative rotation via the vibrator bearing 12.
The vibrator bearing 12 has an outer ring 12a fitted inside the external gear 11, a plurality of rolling elements (rollers) 12b, and a cage 12c that holds the plurality of rolling elements 12b.
The multiple rolling elements 12b include a first group of rolling elements 12b arranged radially inward of the first internal gear 31G and aligned circumferentially, and a second group of rolling elements 12b arranged radially inward of the second internal gear 32G and aligned circumferentially. These rolling elements 12b roll on the outer peripheral surface of the vibrator 10A and the inner peripheral surface of the outer ring 12a as their rolling surfaces. Two outer rings 12a of the same shape are provided side by side in the axial direction to correspond to the arrangement of the multiple rolling elements 12b. The vibrator bearing 12 may have an inner ring separate from the vibrator 10A.

Spacer rings 41, 42 are provided on both axial sides of the vibrator bearing 12 and the external gear 11, abutting against them and acting as restricting members that restrict their axial movement.

The casing 33 is connected to the first internal gear member 31 with bolts 51 and covers the outer diameter side of the second internal gear 32G. The casing 33 has an outer ring portion of a main bearing 38 (e.g., a cross roller bearing) formed on its inner periphery, and rotatably supports the second internal gear member 32 via the main bearing 38. When the flexible mesh gear device 1 is connected to an external mating device, the casing 33 and first internal gear member 31 are connected to the mating device by tightening them together.

The first cover 34 is connected to the first internal gear member 31 by bolts 52 and covers the meshing point between the external gear 11 and the first internal gear 31G from the non-output side in the axial direction. A bearing 36 (e.g., a ball bearing) is arranged between the first cover 34 and the shaft portion 10B of the vibrator shaft 10, and the first cover 34 rotatably supports the vibrator shaft 10 via the bearing 36.

The second cover 35 is connected to the second internal gear member 32 by bolts 53 and covers the meshing point between the external gear 11 and the second internal gear 32G from the axial output side. A bearing 37 (e.g., a ball bearing) is arranged between the second cover 35 and the shaft portion 10C of the vibrator shaft 10, and the second cover 35 rotatably supports the vibrator shaft 10 via this bearing 37. When the flexible mesh gear device 1 is connected to an external mating device, the second cover 35 and the second internal gear member 32 are fastened together to connect to the driven member of the mating device, and output reduced rotation to the driven member.

Furthermore, the flexible mesh gear device 1 includes oil seals 43, 44, and 45 and O-rings 46, 47, and 48 as sealing components.
The oil seal 43 is disposed at the end of the axial direction on the non-output side, between the shaft portion 10B of the vibrator shaft 10 and the first cover 34, and prevents the outflow of lubricant to the non-output side. The oil seal 44 is disposed at the end of the axial direction on the output side, between the shaft portion 10C of the vibrator shaft 10 and the second cover 35, and prevents the outflow of lubricant to the output side. The oil seal 45 is disposed between the casing 33 and the second internal gear member 32, and prevents the outflow of lubricant from this portion.
O-rings 46, 47, and 48 are respectively provided between the first internal gear member 31 and the first cover 34, between the first internal gear member 31 and the casing 33, and between the second internal gear member 32 and the second cover 35, and prevent the movement of lubricant between them.

[Characteristic structure of oil seals]
The characteristic structures of the oil seals 43, 44, and 45 of the flexible mesh gear device 1 will now be described in detail.
Since the oil seals 43, 44, and 45 have a common structure, the oil seal 43 will be described in detail here. Figure 2 is an axial cross-sectional view of the oil seal 43. Note that the left-right direction in Figure 2 indicates the axial direction, and the up-down direction in Figure 2 indicates the radial direction.
The oil seal 43 is made of a rotating body whose cross section is the same as the cross section shown in FIG. 2 over the entire circumference centered on the rotation axis O1.

The oil seal 43 is disposed between two members, namely, the casing 33 located on the radially outer side and the second internal gear member 32 located on the radially inner side (the vertical direction in FIG. 2).
The oil seal 43 comprises a cylindrical fitting portion 431 fitted into the inner circumference of the casing 33, a partition portion 432 separating the lubricant-containing space S from the external space, a waist portion 433 extending from the radially inner edge of the partition portion 432 toward the containing space S, a seal lip portion 434 as a sliding portion protruding radially inward at the tip of the waist portion 433, a core metal 435 consisting of a metal ring with an approximately L-shaped cross section built into the fitting portion 431 and the partition portion 432, and a spring 436 that applies radially inward pressure to the seal lip portion 434.
The term "sliding portion" refers to a portion formed continuously from the sliding surface, more preferably a portion formed continuously including a direction perpendicular to the sliding surface. In other words, the term refers to a portion where strain occurs due to external pressure in the direction along the external pressure and in the direction perpendicular to the external pressure, and the strain in the direction perpendicular to the external pressure is directly transmitted to the sliding surface.

As described above, the fitting portion 431 is cylindrical, and its outer circumferential surface is in close contact with the inner circumferential surface of the casing 33 .
The partition portion 432 is formed integrally with the fitting portion 431 so as to close the outer end of the enclosed space S in the fitting portion 431. The radially inner side of the fitting portion 431 forms part of the enclosed space S, and the partition portion 432, together with the seal lip portion 434, closes the fitting portion 431, separating the enclosed space S from the external space.

The core metal 435 is embedded from near the inner end of the fitting portion 431 to almost the entire area of the partition portion 432, and has higher rigidity than the materials constituting the fitting portion 431 and the partition portion 432. The core metal 435 is covered with the materials constituting the fitting portion 431 and the partition portion 432.
The core metal 435 has high rigidity and prevents the fitting portion 431 and the partition portion 432 from bending.

The waist portion 433 is formed integrally with the partition portion 432 and is located radially inward of the mating portion 431. The waist portion 433 is flexible and elastically supports the seal lip portion 434.

The seal lip portion 434 has a cross-sectional shape that is convex radially inward, and its tip portion contacts the outer peripheral surface of the second internal gear member 32 over the entire circumference, thereby sealing the lubricant.
The spring 436 is, for example, an endless annular coil spring that goes around the outer periphery of the seal lip portion 434 and presses the seal lip portion 434 radially inward by contracting in the circumferential direction.

Adhesive wear occurs at the tip of the seal lip portion 434 of the oil seal 43 due to sliding against the outer peripheral surface of the second internal gear member 32. Adhesive wear occurs when minute irregularities on the sliding surface bond together due to high pressure, and when these are broken by friction, the area around the bond falls off and becomes wear powder.
The following Holm's wear equation (1) is known as a basic formula for estimating the amount of wear during adhesive wear.
W=zARl …(1)
(W: wear amount, AR: actual contact area, l: friction distance, z: friction coefficient)

This wear equation indicates that adhesive wear occurs based on the actual state of adhesion at the real contact area. If the load when materials with positive Poisson's ratios come into contact is P and the flow pressure of the material is pm, then the real contact area AR is given by the following equation (2):
AR = P/pm …(2)

Here, Poisson's ratio refers to the value obtained by dividing the lateral strain that occurs in a direction perpendicular to the stress direction when a uniaxial stress acts on an object by the longitudinal strain that occurs in the stress direction and multiplying the result by -1.
Therefore, in the case of an object with a positive Poisson's ratio, for example, when a compressive longitudinal strain occurs due to stress, an expanding lateral strain occurs in the direction perpendicular to the stress direction.
In the conventional oil seal, the entire seal including the seal lip portion, except for the core metal 435 and the spring 436, is mainly formed only from a material having a positive Poisson's ratio.

The above equation (2) shows that when a material with a positive Poisson's ratio is subjected to a load, the real contact area (hereinafter referred to as the contact area) increases, and the amount of wear increases.
For example, in conventional oil seals, the seal lip is made of a resin made of a positive Poisson material. When the seal lip is subjected to axial pressure (compressive stress: see the black arrow in Figure 2) due to an increase in internal pressure caused by a rise in temperature, lateral strain occurs, causing radial expansion. This increases the binding force of the seal lip, increases the contact area of the seal lip, and causes significant adhesive wear.

In order to suppress such adhesive wear that occurs in conventional oil seals, the oil seal 43 shown in this embodiment has a seal lip portion 434 that is made of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio.
Various materials such as steel, aluminum, and resin can be used as materials with a positive Poisson's ratio.
Materials with negative Poisson's ratios include, for example, metamaterials such as pentagraphene, special structure materials such as aggregates of three-dimensional unit lattice structures formed using 3D printing technology, and materials with negative Poisson's ratios due to their structure, such as paper (including paper folded into special structures), or materials with negative Poisson's ratios of their own.

Specifically, as shown in FIG. 2, the seal lip portion 434 of the oil seal 43 is formed by alternating layers 434a of a material with a positive Poisson's ratio and layers 434b of a material with a negative Poisson's ratio in the radial direction. Each layer 434a of a material with a positive Poisson's ratio and each layer 434b of a material with a negative Poisson's ratio are both approximately cylindrical and centered on the rotation axis O1. The innermost layer of the seal lip portion 434, which directly contacts the outer peripheral surface of the second internal gear member 32, is preferably made of the layer 434a of a material with a positive Poisson's ratio, but may also be made of a material with a negative Poisson's ratio.

Furthermore, for the seal lip portion 434 formed from a layer 434a of a material with a positive Poisson's ratio and a layer 434b of a material with a negative Poisson's ratio, when the axial direction is the longitudinal strain and the radial direction is the lateral strain, the overall Poisson's ratio is 0 or greater and is smaller than when the seal lip portion 434 is made only of materials with a positive Poisson's ratio, preferably less than half that value, and more preferably close to 0.

In addition, the layer surfaces of each layer 434a made of a material with a positive Poisson's ratio and each layer 434b made of a material with a negative Poisson's ratio may not be completely parallel to the rotation axis O1, but may be slightly inclined.
That is, the layers 434a made of a material with a positive Poisson's ratio and the layers 434b made of a material with a negative Poisson's ratio may have layer surfaces that are inclined relative to the axial direction as long as the overall Poisson's ratio of the seal lip portion 434 satisfies the above-mentioned numerical range conditions.
The orientation of the layer surfaces of each layer 434a, 434b indicates the orientation when the oil seal 43 is disposed between the casing 33 and the second internal gear member 32, not when it is not attached to the flexible meshing gear device 1.

In addition, the portion of the oil seal 43 that comes into contact with the casing 33 in which the oil seal 43 is placed without any relative movement, i.e., the aforementioned mating portion 431, is also made up of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio.
Note that "parts that come into contact without relative movement" refers to parts that are not bonded or welded to each other, and so may undergo slight sliding with the opposing member, but do not undergo relative movement such as rotation or linear movement.

Specifically, as shown in FIG. 2, the fitting portion 431 is formed so that layers 431a of material with a positive Poisson's ratio and layers 431b of material with a negative Poisson's ratio are repeatedly arranged alternately in the radial direction. In this case, each layer 431a of material with a positive Poisson's ratio and each layer 431b of material with a negative Poisson's ratio are both approximately cylindrical and centered on the rotation axis O1. Furthermore, the outermost layer of the fitting portion 431, which is in direct contact with the inner circumferential surface of the casing 33, is made of the layer 431a of material with a positive Poisson's ratio.

In the case of this fitting portion 431, the Poisson's ratio when the axial direction is the longitudinal strain and the radial direction is the lateral strain is 0 or more, and is smaller than when the material is made only of a material with a positive Poisson's ratio, preferably less than half of that, and more preferably a Poisson's ratio close to 0.
Furthermore, the layer surfaces of the layers 431a and 431b may not be completely parallel to the rotation axis O1, but may be inclined within a range in which the overall Poisson's ratio satisfies the above condition.

On the other hand, the partition portion 432 and waist portion 433 are formed only from a material with a positive Poisson's ratio, such as resin.

Note that the portions of the seal lip portion 434 and mating portion 431 of the oil seal 43 that are made up of layers of material with a positive Poisson's ratio and layers of material with a negative Poisson's ratio are not limited to a layered structure. For example, powder, granules, cells, small pieces, etc. made of material with a negative Poisson's ratio may be mixed with material with a positive Poisson's ratio.

Furthermore, the portions 431c, 434c made of a material with a positive Poisson's ratio and the portions 431d, 434d made of a material with a negative Poisson's ratio in the mating portion 431 and the seal lip portion 434 of the oil seal 43 may be arranged around the axis so as to form an alternating lattice pattern when viewed from an axial cross section, as shown in Figure 3. Note that the number of lattices shown in Figure 3 is an example, and the lattice unit may be made finer and the number of lattices may be increased.

[Technical Effects of the Invention Embodiments]
As described above, the oil seal 43 of the flexible mesh gear device 1 has a seal lip portion 434 serving as a sliding portion that is made up of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio, and so can suppress distortion due to radial expansion even when subjected to axial pressure (compressive stress) due to an increase in the internal pressure of the lubricant confinement space S. This makes it possible to suppress an increase in the contact area at the tip end of the seal lip portion 434 and reduce the amount of wear.

The oil seal 43 is configured such that the seal lip portion 434, which is made up of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio, has an overall Poisson's ratio of 0 or greater.
Therefore, when pressure (compressive stress) is applied in the axial direction, distortion such as shrinkage in the radial direction does not occur, and the surface pressure can be maintained at a certain level or higher. Therefore, it is possible to reduce the amount of wear without impairing the sealing performance of the oil seal 43.

In addition, because the waist portion 433 of the oil seal 43 is made of a material with a positive Poisson's ratio, when it is subjected to axial pressure (compressive stress) due to an increase in the internal pressure of the lubricant-containing space S, distortion occurs that causes it to expand radially, making it possible to maintain good surface pressure on the seal lip portion 434 that is supported at its tip.

Furthermore, the fitting portion 431 of the oil seal 43, which comes into contact with the casing 33 without any relative movement, is also made of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio.
The mating portion 431 does not undergo relative movement with respect to the casing 33 like the seal lip portion 434, but there is a possibility that minute sliding may occur during operation of the flexible mesh gear device 1. Therefore, by making the mating portion 431 also out of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio, it is possible to suppress an increase in the contact area when the internal pressure of the lubricant confinement space S increases, and it is possible to reduce the amount of wear.
Furthermore, the fitting portion 431 is also configured so that the overall Poisson's ratio is 0 or greater, so that it is possible to reduce the amount of wear without impairing the sealing performance.

Furthermore, materials with negative Poisson's ratios and materials with positive Poisson's ratios are laminated in the seal lip portion 434 and the fitting portion 431 of the oil seal 43. In particular, in the portion made up of materials with negative Poisson's ratios and materials with positive Poisson's ratios, the materials with negative Poisson's ratios and materials with positive Poisson's ratios are arranged in layers in the compressive load direction of the component, with the materials with negative Poisson's ratios and the materials with positive Poisson's ratios overlapping each other.
As a result, the amount of strain that occurs in the direction opposite the layer surface of each layer is made more uniform along the layer surface, variations in surface pressure are suppressed, and it is possible to further reduce the amount of wear while maintaining better sealing properties.

The technical effects of the oil seal 43 can also be said to be the same for the oil seals 44 and 45.
Furthermore, the flexible meshing gear device 1 equipped with the above-mentioned oil seals 43 to 45 can reduce the amount of wear while maintaining the sealing properties of each oil seal 43 to 45, thereby reducing the frequency of maintenance and enabling stable operation over a long period of time.

[Application to rolling elements of bearings]
For example, it is possible to apply a material with a negative Poisson's ratio to the rolling elements (components) of the bearings 36 and 37 provided in the flexible mesh gear device 1. Since the bearings 36 and 37 have the same structure, application to the bearing 36 will be described.

4 shows an axial cross-sectional view of the bearing 36 and its rolling elements 361. The left-right direction in FIG. 4 indicates the axial direction, and the up-down direction in FIG. 4 indicates the radial direction.
The bearing 36 mainly has an outer ring 362 located on the radially outer side, an inner ring 363 located on the radially inner side, and rolling elements 361 arranged between the two members consisting of the outer ring 362 and the inner ring 363. The bearing 36 is a rolling ball bearing, and the rolling elements 361 are spherical. The entire spherical surface of the rolling elements 361 can be in sliding contact with the rolling surfaces of the outer ring 362 and the inner ring 363, so the entire rolling elements 361 serve as a sliding part.

4, the rolling element 361 is laminated such that spherical shell-shaped layers 361a of material with a positive Poisson's ratio and spherical shell-shaped layers 361b of material with a negative Poisson's ratio are alternately arranged in the radial direction from the center of the rolling element 361. In this case, each layer 361a of material with a positive Poisson's ratio and each layer 361b of material with a negative Poisson's ratio are spherical shell-shaped with the same center.
Furthermore, the outermost layer of the rolling element 361 that comes into direct sliding contact with the rolling surfaces of the outer ring 362 and the inner ring 363 is preferably a layer 361a of a material with a positive Poisson's ratio, but may also be a layer of a material with a negative Poisson's ratio. The center of the rolling element 361 is a sphere rather than a spherical shell, and the sphere may be formed from either a material with a positive Poisson's ratio or a material with a negative Poisson's ratio.

In the case of the rolling element 361, when one diameter direction is treated as longitudinal strain and the other diameter direction perpendicular to that direction is treated as lateral strain, the overall Poisson's ratio is greater than or equal to 0, and is smaller than when the rolling element is made entirely of materials with a positive Poisson's ratio, preferably less than half of that, and more preferably close to 0.

In the above-mentioned bearing 36, the rolling elements 361 serving as sliding parts are composed of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio. This makes it possible to suppress radial expansion distortion even when subjected to axial pressure (compressive stress) due to an increase in the internal pressure of the lubricant-enclosed space S. This makes it possible to suppress an increase in the contact area of the rolling elements 361 with the rolling surfaces of the outer ring 362 and the inner ring 363, thereby reducing the amount of wear.

The rolling element 361 is made of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio, and is configured so that the overall Poisson's ratio in the diameter direction is 0 or greater.
Therefore, when pressure (compressive stress) is applied in either diameter direction (axial direction of the bearing 36), distortion such as contraction does not occur in the diameter direction perpendicular to the pressure (radial direction of the bearing 36), and the occurrence of gaps can be suppressed. Therefore, it is possible to reduce the amount of wear on the rolling elements 361 while maintaining stable rotation of the vibrator shaft 10 supported by the bearing 36.
Furthermore, the bearing 37 also provides the same technical effect as the bearing 36 .

Furthermore, it is also possible to use materials with a negative Poisson's ratio for the main bearing 38 of the flexible mesh gear device 1 and the rolling elements of the vibrator bearing 12 .
Because the rolling elements of the main bearing 38 and the exciter bearing 12 are cylindrical, the rolling elements are formed so that layers of material with a positive Poisson's ratio and layers of material with a negative Poisson's ratio are alternately arranged in the radial direction of the rolling element. That is, each layer of material with a positive Poisson's ratio and each layer of material with a negative Poisson's ratio are both approximately cylindrical. Furthermore, the outermost layer of the rolling element, which forms the sliding surface with the rolling surface, is made of a layer of material with a positive Poisson's ratio.
Also, in the case of rolling elements, the overall Poisson's ratio, when the axial direction is the longitudinal strain and the radial direction is the lateral strain, is 0 or more, and is smaller than when the material is made only of materials with a positive Poisson's ratio, preferably less than half of that, and more preferably a Poisson's ratio close to 0.

It is possible to reduce the amount of wear on the rolling elements while maintaining stable rotation of the components supported by these main bearings 38 and vibrator bearings 12.

[others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments.
For example, in the above embodiment, a flexible mesh gear device is used as an example of a power transmission device, but the present invention is applicable to any power transmission device, regardless of type, as long as it includes a component having a sliding part that slides against other components, such as an oil seal or a rolling element of a bearing.
For example, the present invention is not limited to flexible mesh gear devices, and can be used to apply materials with negative Poisson's ratios to components such as oil seals and bearings used in all kinds of power transmission devices, including eccentric oscillating speed reducers, parallel shaft gear reducers, other gear devices, traction drive mechanisms, transmissions, wet brakes, pumps, and cam mechanisms.

Furthermore, components to which a material with a negative Poisson's ratio is applied are not limited to oil seals and rolling elements of bearings.
For example, when the power transmission device is a cam mechanism, a rolling element such as a roller may be used for the follower link that slides against the main link, and a structure similar to that of the rolling element of the bearing described above can also be applied to this rolling element.

The present invention can also be applied to O-rings as components used in power transmission devices.
FIG. 5A is a partially cutaway perspective view of a piston-cylinder mechanism 60 serving as a power transmission device, and FIG. 5B is a cross-sectional view of an O-ring along the reciprocating direction of the piston.

The piston-cylinder mechanism 60 has a cylinder 61 and a piston 62 with an O-ring 63 provided between them.
5(B), the O-ring 63 is an annular body, and the outer periphery of the O-ring 63 is in sliding contact with the inner periphery of the cylinder 61, and therefore corresponds to the "sliding part." On the other hand, the inner periphery of the O-ring 63 hardly slides against the outer periphery of the piston 62, and therefore corresponds to the "part that comes into contact without relative movement," similar to the fitting part 431 of the oil seal 43 described above.
The left-right direction in FIG. 5B indicates the axial direction, and the up-down direction in FIG. 5B indicates the radial direction.

Specifically, the O-ring 63 is formed so that layers 631 of material with a positive Poisson's ratio and layers 632 of material with a negative Poisson's ratio are repeatedly arranged radially alternately. In this case, each layer 631 of material with a positive Poisson's ratio and each layer 632 of material with a negative Poisson's ratio are also approximately cylindrical. Furthermore, the outermost layer of the O-ring 63 that comes into direct sliding contact with the inner surface of the cylinder 61 and the innermost layer of the O-ring 63 that comes into direct sliding contact with the outer surface of the piston 62 are preferably made of the layer 631 of material with a positive Poisson's ratio, but they can also be made of material with a negative Poisson's ratio.

Also, in the case of the O-ring 63, the overall Poisson's ratio when the axial direction is the longitudinal strain and the radial direction is the lateral strain is 0 or more, and is smaller than when the O-ring is made only of materials with a positive Poisson's ratio, preferably less than half of that, and more preferably a Poisson's ratio close to 0.
Furthermore, the layers 631 and 632 may not be completely parallel to the reciprocating direction (axial direction) of the piston 62, but may be inclined within a range in which the overall Poisson's ratio satisfies the above condition.

The O-ring 63 is made of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio, so even when it is subjected to pressure (compressive stress) in the direction of reciprocating motion of the piston 62 due to an increase in the internal pressure of the cylinder 61, it is possible to suppress distortion due to radial expansion. This prevents an increase in the contact area between the outer and inner peripheries of the O-ring 63, making it possible to reduce the amount of wear.

Furthermore, by setting the overall Poisson's ratio of the O-ring 63, where the axial direction is the longitudinal strain and the radial direction is the lateral strain, to 0 or greater, when pressure is applied in the direction of the piston 62's reciprocating motion, distortion that causes contraction in the radial direction does not occur, and the surface pressure can be maintained at a constant level or higher. Therefore, it is possible to reduce the amount of wear without compromising the sealing performance of the O-ring 63.

Note that while Figure 5 illustrates an O-ring 63 with a substantially rectangular cross section, there is no limitation to the cross-sectional shape, and it may, for example, have a circular cross section.

1. Flexible mesh gear device (power transmission device)
12 vibrator bearing 12b rolling element (component)
33 Casing 36, 37 Bearing 361 Rolling element (component)
38 Main bearing 43, 44, 45 Oil seal (component)
46, 47, 48, 63 O-ring 60 Piston-cylinder mechanism 61 Cylinder 62 Pistons 361a, 361b, 431a, 431b, 434a, 434b, 631, 632 Layer 362 Outer ring 363 Inner ring 431 Fitting portion 432 Partition portion 433 Waist portion 434 Seal lip portion (sliding portion)
O1 Rotation axis S Enclosed space

Claims (8)

A component of a power transmission device,
At least the sliding portion of the component is made of a material having a negative Poisson's ratio and a material having a positive Poisson's ratio ,
Of the sliding parts, the parts that come into direct sliding contact are components made of a material with a positive Poisson's ratio . 2. The component according to claim 1, wherein the sliding portion has a portion made up of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio, and the portion has a Poisson's ratio of 0 or more as a whole. A component of a power transmission device,
At least the sliding portion of the component is made of a material having a negative Poisson's ratio and a material having a positive Poisson's ratio,
The component is an oil seal,
A component in which a waist portion between the mandrel and the lip portion serving as the sliding portion is made of a material having a positive Poisson's ratio. a portion of the component that is made up of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio is formed by laminating a material with a negative Poisson's ratio and a material with a positive Poisson's ratio;
a portion of the component that is in contact with the member on which the component is disposed without any relative motion is also made of a material having a negative Poisson's ratio and a material having a positive Poisson's ratio;
At least a part of the portion where the component is not in contact with the member where the component is placed is made of a material with a positive Poisson's ratio, and no material with a negative Poisson's ratio is laminated thereon.
Component according to any one of claims 1 to 3 . The portion of the component that is made up of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio is arranged in layers in the load direction of the component, with the material with a negative Poisson's ratio and the material with a positive Poisson's ratio overlapping each other.
5. The component of claim 4 . The component is a rolling element,
The component according to claim 1 , wherein the rolling elements that form the sliding portions are made of a material with a positive Poisson's ratio and a material with a negative Poisson's ratio. a portion of the component that is made up of a material with a negative Poisson's ratio and a material with a positive Poisson's ratio is formed by laminating a material with a negative Poisson's ratio and a material with a positive Poisson's ratio;
7. The component according to claim 6, wherein the lamination direction of the material with a negative Poisson's ratio and the material with a positive Poisson's ratio is configured such that the material with a negative Poisson's ratio and the material with a positive Poisson's ratio are alternately arranged in a radial direction from the center of the rolling element. A power transmission device having a component according to any one of claims 1 to 7.