Power transmission device and method for manufacturing power transmission device

Abstract

Provided is a technology for improving the support rigidity of a bearing in the event of moisture absorption and expansion of a support member. A power transmission device includes a rotating shaft (50), a support member (52A) disposed radially outward of the rotating shaft (50), and a bearing (54A) disposed between the rotating shaft (50) and the support member (52A). The power transmission device further includes an engagement member (56A) that engages with an outer peripheral portion of the support member (52A), the engagement member (56A) being made of a material having a lower moisture absorption than the material of the support member (52A).

Description

[0001] This application claims priority based on Japanese Patent Application No. 2021-144515, filed on September 6, 2021. The entire contents of that Japanese application are incorporated herein by reference. Technical Field

[0002] This invention relates to a power transmission device. Background Technology

[0003] Patent document 1 discloses a power transmission device having a rotating shaft, a support member disposed radially outside the rotating shaft, and a bearing disposed between the support member and the rotating shaft.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2018-155313

[0005] The inventors of this application have conducted research on power transmission devices and discovered the following new problem: The support components of power transmission devices sometimes absorb moisture and expand, depending on their material. Typically, when a support component absorbs moisture and expands, it tends to deform significantly outward in a radial direction. As a result, the gap between the support component and the bearing widens, leading to a decrease in the bearing's support rigidity. Currently, no technology has been proposed to address this issue, and a corresponding solution is anticipated. Summary of the Invention

[0006] One of the objectives of this invention is to provide a technique that can improve the bearing's support rigidity when the support component absorbs moisture and expands.

[0007] The power transmission device of the present invention includes a rotating shaft, a support member disposed radially outside the rotating shaft, and a bearing disposed between the rotating shaft and the support member. The power transmission device also includes a fitting member that fits into the outer periphery of the support member. The fitting member is made of a material with lower hygroscopicity than the material of the support member.

[0008] According to the present invention, the bearing support rigidity can be improved when the support component absorbs moisture and expands. Attached Figure Description

[0009] Figure 1 This is a side sectional view of the power transmission device according to the first embodiment.

[0010] Figure 2 Diagram (A) shows the state of the support component under expansion conditions in the reference configuration. Figure 2 Figure (B) shows the state of the support member in the first embodiment when it expands.

[0011] Figure 3It is a humid air graph representing the temperature and humidity in the operating environment of the power transmission device.

[0012] Figure 4 It is a diagram showing the intermediate state of the fitting process between the supporting component and the fitting component.

[0013] Figure 5 This is a side sectional view of the power transmission device according to the second embodiment.

[0014] Figure 6 This is a side sectional view of the power transmission device according to the third embodiment.

[0015] In the diagram: 10 - Power transmission device; 20A, 20B, 20C, 20D, 20E - Cover; 26A, 26B - Gears; 50 - Rotating shaft; 52A, 52B, 52C, 52D, 52E - Support components; 54A, 54B, 54C, 54D, 54E - Bearings; 56A, 56B, 56C, 56D - Fitting components; 78 - Through hole; 122 - Motor; 124 - Motor housing; 128 - Stator. Detailed Implementation

[0016] The embodiments will now be described. Identical components are labeled with the same symbols, and repeated descriptions are omitted. In the accompanying drawings, components are appropriately omitted, enlarged, or reduced for ease of explanation. Refer to the orientation of the symbols in the drawings.

[0017] (First Embodiment)

[0018] refer to Figure 1 The power transmission device 10 of this embodiment is a gear device. This power transmission device 10 includes an input shaft 12, a gear mechanism 14 that transmits rotation of the input shaft 12, an output component 16 that outputs the output from the gear mechanism 14 to the driven machine, and a housing 18 that houses the gear mechanism 14. Furthermore, the power transmission device 10 of this embodiment also includes a first housing 20A disposed axially relative to the gear mechanism 14 on one side (right side in the figure) and a second housing 20B disposed axially relative to the gear mechanism 14 on the other side (left side in the figure). The output component 16 of this embodiment is the second housing 20B. The input shaft 12 functions as the rotating shaft 50, which will be described later. In this specification, the axial, radial, and circumferential directions of the rotating shaft 50 are simply referred to as "axial," "radial," and "circumferential," respectively.

[0019] The gear mechanism 14 in this embodiment is a flexural meshing gear mechanism. This gear mechanism 14 includes an external gear 24 and internal gears 26A and 26B that mesh with each other, one of which is a flexural gear 22. The gear mechanism 14 causes one of the external gear 24 and internal gears 26A and 26B to rotate by flexing the flexural gear 22, and can output this rotational component as output rotation from the output member 16. In this embodiment, the external gear 24 becomes a flexural gear 22, thereby enabling the external gear 24 to rotate. The gear mechanism 14 in this embodiment is a cylindrical flexural meshing gear mechanism using a first internal gear 26A and a second internal gear 26B.

[0020] The input shaft 12 can rotate via rotational power transmitted from a drive source (not shown). The drive source may be, for example, a motor, a geared motor, or an engine.

[0021] In this embodiment, the input shaft 12 is a vibrator shaft. The vibrator shaft (i.e., the input shaft 12) includes a vibrator 30 that causes the flexural gear 22 to flex and deform, and shaft portions 32 disposed on both sides of the vibrator 30 in the axial direction. The outer periphery of the vibrator 30 is elliptical in a cross-section orthogonal to the axial direction of the input shaft 12. The term "ellipse" in this specification is not limited to an ellipse in a strictly geometric sense, but also includes approximately elliptical shapes. The outer periphery of the shaft portions 32 is circular in a cross-section orthogonal to the axial direction of the input shaft 12.

[0022] The flexure gear 22 is rotatably supported on the vibrator 30 via the vibrator bearing 34. The flexure gear 22 is a flexible cylindrical component. The vibrator bearing 34 corresponds to a plurality of internal gears 26A and 26B, and is respectively disposed on the inner side of the corresponding internal gears 26A and 26B.

[0023] The first internal gear 26A is disposed on one side of the axial direction (right side in the figure), and the second internal gear 26B is disposed on the other side of the axial direction (left side in the figure). The first internal gear 26A has a different number of internal teeth (e.g., 102) than the number of external teeth (e.g., 100) of the external gear 24, which is the flexural gear 22, and the second internal gear 26B has the same number of internal teeth as the external gear 24.

[0024] The housing 18 includes a first housing component 36 that also serves as the first internal gear 26A and a second housing component 38 disposed radially outward of the second internal gear 26B. The first housing component 36 and the second housing component 38 are integrally connected to each other. A main bearing 40 is disposed between the second housing component 38 and the second internal gear 26B.

[0025] The first cover 20A covers the interior space of the housing 18 that houses the gear mechanism 14 from one axial direction. The second cover 20B covers the interior space of the housing 18 that houses the gear mechanism 14 from the other axial direction. The first cover 20A is connected to the first internal gear 26A via a first threaded member 42A, thus becoming integrated with the first internal gear 26A. The second cover 20B is connected to the second internal gear 26B via a second threaded member 42B, thus becoming integrated with the second internal gear 26B.

[0026] Next, the operation of the power transmission device 10 described above will be explained. If the input shaft 12 rotates by the drive source, the gear mechanism 14 will operate. If the gear mechanism 14 operates, the output rotation after the rotation of the input shaft 12 is speed-changed (in this case, decelerated) will be output from the gear mechanism 14 via the output member 16 and output to the driven machine.

[0027] In the power transmission device 10 using the flexural gear mechanism 14, if the vibrating body shaft, which serves as the input shaft 12, rotates, the flexural gear 22 flexes and deforms into an elliptical shape that matches the shape of the vibrating body 30. Thus, if the flexural gear 22 flexes and deforms, the meshing position of the external gear 24 and the internal gear 26A changes along the rotation direction of the vibrating body 30. At this time, with each rotation of the meshing position of the external gear 24, which has different numbers of teeth, and the first internal gear 26A, their meshing teeth are sequentially staggered circumferentially. As a result, one of them (in this embodiment, the external gear 24) rotates. In this embodiment, the external gear 24 and the second internal gear 26B have the same number of teeth; therefore, even if their meshing position rotates one revolution, they do not rotate relative to each other but rotate synchronously. Therefore, the rotational component of the external gear 24 is output from the second housing 20B, which serves as the output component 16, via the second internal gear 26B, which rotates synchronously with the external gear 24.

[0028] Here, the power transmission device 10 includes: a rotating shaft 50; support members 52A and 52B disposed radially outside the rotating shaft 50; rotating shaft bearings 54A and 54B disposed between the support members 52A and 52B and the rotating shaft 50; and fitting members 56A and 56B that fit into the outer periphery of the support members 52A and 52B.

[0029] The rotating shaft 50 is capable of rotating when the power transmission device 10 is in operation. In this embodiment, the rotating shaft 50 is a vibrator shaft (input shaft 12). The rotation of the rotating shaft 50 in this embodiment enables the driven gear 58 of the gear mechanism 14 to move. In this embodiment, the driven gear 58 is a flexural gear 22.

[0030] Support members 52A and 52B support the rotating shaft 50 via rotating shaft bearings 54A and 54B. In this embodiment, the support members 52A and 52B include a first support member 52A formed by a first cover 20A and a second support member 52B formed by a second cover 20B. The support members 52A and 52B are generally disc-shaped. The support members 52A and 52B include bearing mounting portions 60 for arranging the rotating shaft bearings 54A and 54B.

[0031] Rotary shaft bearings 54A and 54B allow support members 52A and 52B to rotate relative to the rotating shaft 50. In this embodiment, the rotary shaft bearings 54A and 54B include a first rotary shaft bearing 54A disposed between the first support member 52A and the rotating shaft 50, and a second rotary shaft bearing 54B disposed between the second support member 52B and the rotating shaft 50.

[0032] The rotary shaft bearings 54A and 54B of this embodiment include: a plurality of rolling elements 54a; an outer ring 54b and an inner ring 54c for rolling the plurality of rolling elements 54a; and a sealing member 54d for sealing the internal space of the rotary shaft bearings 54A and 54B. In this embodiment, the outer ring 54b is separately provided from the support members 52A and 52B, thus serving as a dedicated part in the rotary shaft bearings 54A and 54B. Alternatively, the support members 52A and 52B can also serve as the outer ring 54b. In this embodiment, the inner ring 54c is separately provided from the rotary shaft 50, thus serving as a dedicated part in the rotary shaft bearings 54A and 54B. Alternatively, the rotary shaft 50 can also serve as the inner ring 54c.

[0033] The fitting components 56A and 56B in this embodiment include a first fitting component 56A composed of a first internal gear 26A and a second fitting component 56B composed of a second internal gear 26B. The fitting components 56A and 56B in this embodiment are generally disc-shaped.

[0034] Support members 52A and 52B each have an outer peripheral fitting portion 70 disposed on the outer periphery of the support member 52A and 52B. Fitting members 56A and 56B each have an inner peripheral fitting portion 72 disposed on the inner periphery of the fitting member 56A and 56B. The outer peripheral fitting portions 70 (outer peripheral portions) of the support members 52A and 52B and the inner peripheral fitting portions 72 (inner peripheral portions) of the fitting members 56A and 56B fit together. When viewed radially, the fitting portions (outer peripheral fitting portions 70 and inner peripheral fitting portions 72) of the support members 52A and 52B and the fitting members 56A and 56B overlap with the rotating shaft bearings 54A and 54B supported by the support members 52A and 52B.

[0035] Support members 52A and 52B each have an annular protrusion 74 protruding axially from their axial sides toward a side of the fitting members 56A and 56B that engage with them. Fitting members 56A and 56B each have a recess 76 on their axial sides, recessed axially toward the side opposite to the support members 52A and 52B that engage with them. The annular protrusion 74 of the support members 52A and 52B is locked into the recess 76 of the fitting members 56A and 56B. In this embodiment, the outer peripheral fitting portion 70 of the support members 52A and 52B is provided on the outer peripheral portion of the annular protrusion 74, and the inner peripheral fitting portion 72 of the fitting members 56A and 56B is provided on the inner peripheral portion of the recess 76.

[0036] Support members 52A and 52B have through holes 78 extending axially through the central portion of the rotation shaft 50 in the radial direction. In this embodiment, both the first support member 52A and the second support member 52B have through holes 78.

[0037] Support members 52A and 52B are fastened to mating members 56A and 56B via threaded members 42A and 42B. The first cover 20A, which becomes the first support member 52A, is fastened to the first internal gear 26A, which becomes the first mating member 56A, via the first threaded member 42A. The second cover 20B, which becomes the second support member 52B, is fastened to the second internal gear 26B, which becomes the second mating member 56B, via the second threaded member 42B. Threaded members 42A and 42B are inserted into the through holes 80 of the support members 52A and 52B and screwed into the internal threaded holes 82 of the mating members 56A and 56B.

[0038] In this embodiment, the support components 52A and 52B and the fitting components 56A and 56B are all made of resin-based materials. Here, resin-based materials refer to materials in which resin is the primary material. Examples of resins used here include general-purpose engineering plastics and special engineering plastics. Resin-based materials can be composed solely of the resin that is the primary material, or they can be composed of a composite material of the resin that is the primary material and other materials. Examples of such composite materials include carbon fiber reinforced resin and glass fiber reinforced resin.

[0039] The fitting components 56A and 56B are made of a material with lower hygroscopicity than the support components 52A and 52B that they fit with. The first fitting component 56A is made of a material with lower hygroscopicity than the first support component 52A. Furthermore, the second fitting component 56B is made of a material with lower hygroscopicity than the second support component 52B.

[0040] To quantitatively evaluate the relationship between the hygroscopicity of support components 52A, 52B and fitting components 56A, 56B, the water absorption rate can be obtained using a test based on Method A of JIS K7209. In this test, firstly, test pieces cut to specified dimensions are prepared. The test pieces are cut in any shape, either square or curved, as described in JIS K7209. Next, the test pieces are dried in an oven at 50.0 ± 2.0 °C for 24 ± 1 hours. The mass m1 (mg) of the test piece immediately after drying is measured. Then, the test pieces are cooled to room temperature in a desiccator and immersed in distilled water at 23.0 °C ± 1.0 °C for 24 ± 1 hours. The mass m2 (mg) of the test piece immediately after immersion is measured. The water absorption rate c (%) can be calculated using these masses m1 and m2 according to the following formula (1).

[0041] c={(m2-m1) / m1}×100……(1)

[0042] This test assumes that components made of resin are used as the test objects. However, hygroscopic materials other than resin can also be used as the test objects in the same test to determine the water absorption rate. Furthermore, when the material of the test object (e.g., metals such as steel) is not hygroscopic, the water absorption rate can be considered as zero.

[0043] The fitting components 56A and 56B in this embodiment are made of a material with a water absorption rate of less than 1 / 2 that of the material used for the support components 52A and 52B. To meet this condition, the water absorption rate of the fitting components 56A and 56B can also be zero. To meet this condition, the support components 52A and 52B are made of resins such as PA (polyamide) and PPA (polyphthalamide). Furthermore, the fitting components 56A and 56B are made of resins such as PEEK (polyether ether ketone). When PEEK is used, the water absorption rate is, for example, 0.1 or less, and when PA is used, the water absorption rate is, for example, 1.3 to 2.5.

[0044] The relationship between the hygroscopicity of the first fitting member 56A and the second fitting member 56B is not particularly limited. In this embodiment, the hygroscopicity of the first fitting member 56A is the same as that of the second fitting member 56B (same water absorption rate), but their hygroscopicities may also be different. Similarly, the relationship between the hygroscopicity of the first support member 52A and the second support member 52B is not particularly limited. The hygroscopicity of the first support member 52A is the same as that of the second support member 52B (same water absorption rate), but their hygroscopicities may also be different.

[0045] Furthermore, the power transmission device 10 is composed of resin components made of resin-based materials and metal components made of metallic materials. The resin components in this embodiment include: a housing 18; covers 20A and 20B; and internal gears 26A and 26B, etc. The metal components in this embodiment include: an input shaft 12 (rotating shaft 50); a flexural gear 22 (external gear 24); a vibrating body bearing 34; a main bearing 40; and rotating shaft bearings 54A and 54B, etc.

[0046] Metallic materials here refer to materials whose primary component is metal. Examples of metals used include cast iron, steel, and other ferrous materials, as well as aluminum alloys and other aluminum materials. Metallic materials can consist solely of the metal as the primary component, or they can be composite materials composed of the metal as the primary component and other materials. Examples of composite materials include alloys and fiber-reinforced metals. Metallic materials utilize materials with higher thermal conductivity than resin-based materials.

[0047] In this embodiment, the resin components, except for the fitting parts 56A and 56B, are made solely of resin. The fitting parts 56A and 56B mesh with the metal component (i.e., the external gear 24), therefore, from the viewpoint of improving strength, the fitting parts 56A and 56B are made of PEEK containing carbon fibers. The metal component in this embodiment is made solely of metal (specifically, steel). Thus, by using both the metal component and the resin component, which have a higher thermal conductivity than the resin component, the heat generated inside the power transmission device 10 can be easily transferred using the metal component. Furthermore, by expanding the heat dissipation area in the power transmission device 10, good heat dissipation can be obtained.

[0048] Next, the effects of the power transmission device 10 described above will be explained.

[0049] refer to Figure 2 (A). Hereinafter, the structure of the first support member 52A, the first rotating shaft bearing 54A, the first mating member 56A, and the second support member 52B, the second rotating shaft bearing 54B, and the second mating member 56B, which are common to the first support member 52A, the first rotating shaft bearing 54B, and the second mating member 56B, will be described with reference to the accompanying drawings. Hereinafter, in Figure 2 In (A) and other examples, for ease of explanation, the state of the support component 52A before and after expansion and deformation is exaggerated.

[0050] Consider the following scenario: When support components 52A and 52B are not constrained by other components and are about to expand due to moisture absorption. In this case, support components 52A and 52B as a whole typically expand and deform in a radially outward direction, Da. Figure 2In diagram (A), a double-dotted line represents the state before expansion and deformation, and a solid line represents the state after expansion and deformation. Based on this expansion and deformation, the bearing configuration 60 of the support components 52A and 52B displaces radially outward. Consequently, the gap between the support components 52A and 52B and the rotary shaft bearings 54A and 54B widens, which leads to a decrease in the support rigidity of the rotary shaft bearings 54A and 54B. In particular, the greater the absolute humidity of the operating environment, the greater the amount of radially outward expansion and deformation of the support components 52A and 52B. As a result, the greater the humidity of the operating environment, the wider the gap between the rotary shaft bearings 54A and 54B and the support components 52A and 52B becomes, and therefore, the support rigidity of the rotary shaft bearings 54A and 54B is more likely to decrease.

[0051] refer to Figure 2 (B) The power transmission device 10 of this embodiment includes fitting members 56A and 56B that fit into the outer periphery of the support members 52A and 52B. The fitting members 56A and 56B are made of a material with lower hygroscopicity than the support members 52A and 52B, and therefore have the following advantages.

[0052] (A) Consider the following situation: When the support members 52A and 52B are engaged with the fitting members 56A and 56B, they tend to expand due to moisture absorption, causing the outer peripheral fitting portion 70 of the support members 52A and 52B and the inner peripheral fitting portion 72 of the fitting members 56A and 56B to expand and deform radially outward. At this time, since the hygroscopicity of the fitting members 56A and 56B is lower than that of the support members 52A and 52B, the amount of expansion of the fitting members 56A and 56B due to moisture absorption is less than the amount of expansion of the support members 52A and 52B due to moisture absorption. Therefore, the amount of displacement radially outward at the inner peripheral fitting portion 72 of the fitting members 56A and 56B becomes less than the amount of displacement radially outward at the outer peripheral fitting portion 70 of the support members 52A and 52B. As a result, the expansion deformation of the support members 52A and 52B, which are intended to have a greater displacement of the outer peripheral fitting portion 70 than that of the inner peripheral fitting portion 72, is limited by the inner peripheral fitting portion 72.

[0053] Thus, by restricting the radially outward expansion deformation of support members 52A and 52B, the support members 52A and 52B can expand and deform in the radially inward direction Db. This allows the bearing mounting portion 60 of the support members 52A and 52B to displace radially inward. As a result, the clearance around the rotary shaft bearings 54A and 54B located between the support members 52A and 52B and the rotary shaft 50 can be reduced. Here, "clearance around the rotary shaft bearings 54A and 54B" refers to the clearance between the rotary shaft bearings 54A and 54B and the support members 52A and 52B, and the clearance between the rotary shaft bearings 54A and 54B and the rotary shaft 50.

[0054] Thus, by reducing the clearance around the rotary shaft bearings 54A and 54B, the interference fit of the rotary shaft bearings 54A and 54B relative to the support members 52A and 52B and the rotary shaft 50 can be increased. As a result, the support rigidity of the rotary shaft bearings 54A and 54B can be improved when the support members 52A and 52B absorb moisture and expand. Furthermore, the shaft runout of the rotary shaft 50 supported by the rotary shaft bearings 54A and 54B can be reduced.

[0055] Furthermore, according to this embodiment, the greater the absolute humidity of the operating environment, the easier it is for the support member 52A to expand and deform radially inward. Therefore, it has the following advantage: even when the absolute humidity of the operating environment increases, the clearance around the rotary shaft bearings 54A and 54B can be maintained in a reduced state, thereby maintaining a state of improved support rigidity of the rotary shaft bearings 54A and 54B.

[0056] Furthermore, when the driven gear 58 is moved via the rotating shaft 50 as in this embodiment, the shaft vibration of the rotating shaft 50 can be reduced, thereby stabilizing the meshing state of the driven gear 58 with other gears (here, the external gear 24 and the internal gears 26A, 26B). Consequently, the surface pressure on the tooth surfaces of the driven gear 58 and other gears can be made uniform, thereby extending their lifespan.

[0057] Furthermore, when the support components 52A and 52B, as well as the fitting components 56A and 56B, are all made of resin-based materials, generally, the higher the hygroscopicity, the lower the component cost. Therefore, since the support components 52A and 52B are made of a material with high hygroscopicity, it is easier to reduce component costs compared to the case where the support components 52A and 52B are made of a resin-based material with the same hygroscopicity as the fitting components 56A and 56B.

[0058] (B) In the gear, the support components 52A and 52B are made of resin-based materials, while the mating components 56A and 56B are made of resin-based materials with lower hygroscopicity than the resin-based materials used to make the support components 52A and 52B. Therefore, when the power transmission device 10 is a gear device, compared to the case where the mating components 56A and 56B and the support components 52A and 52B are made of metal-based materials, the gear device can be made lighter.

[0059] (C) Support members 52A and 52B have through holes 78 extending axially through the radial center. Therefore, when support members 52A and 52B absorb moisture and expand, thus deforming radially inward, they cannot easily limit their expansion and deformation. As a result, support members 52A and 52B easily expand and deform radially inward, thereby easily reducing the clearance around the rotating shaft bearings 54A and 54B.

[0060] (D) When viewed radially, the mating portions (outer peripheral mating portion 70 and inner peripheral mating portion 72) of the support members 52A, 52B and the mating portions 56A, 56B overlap with the rotating shaft bearings 54A, 54B. Therefore, with the expansion deformation to the radially outward restricted in the mating portions of the mating members 56A, 56B and the support members 52A, 52B, the bearing mounting portions 60 of the support members 52A, 52B can easily be displaced radially inward in a straight line. Furthermore, radial loads not anticipated in the design are difficult to be applied to the rotating shaft bearings 54A, 54B from the bearing mounting portions 60 of the support members 52A, 52B, thereby easily and stably supporting the rotating shaft 50 using the rotating shaft bearings 54A, 54B.

[0061] Next, other innovative aspects of the power transmission device 10 will be explained. In this embodiment, the power transmission device 10 is configured such that, in an environment where the absolute humidity is 0.003 (kg / kg) or higher, when the support members 52A and 52B are engaged with the fitting members 56A and 56B, the support members 52A and 52B absorb moisture and expand, thereby reducing the fastening load F (reference value). Figure 2 (B) The fastening load F acts from the support members 52A and 52B on the rotating shaft bearings 54A and 54B. This fastening load F acts from the support members 52A and 52B inwards radially. That is, the configuration is such that, at least in an environment where the absolute humidity is 0.003, the fastening load F is generated based on the hygroscopic expansion of the support members 52A and 52B. This condition is satisfied at least when the absolute humidity is 0.003 or higher and the air pressure is standard air pressure (=1.0 atm), and the support members 52A and 52B and the fitting members 56A and 56B are in an equilibrium state where the water absorption does not change.

[0062] If the support components 52A and 52B expand in size due to moisture absorption compared to their initial dimensions after being fitted with the fitting components 56A and 56B during the assembly process of the power transmission device 10 (described later), then the fastening load F is generated. Even if the support components 52A and 52B do not expand due to moisture absorption when they are fitted with the fitting components 56A and 56B via an interference fit, the fastening load will still act from the support components 52A and 52B onto the rotating shaft bearings 54A and 54B. In this case, the configuration is sufficient as follows: Under the aforementioned conditions, the support components 52A and 52B expand and deform radially inward compared to their initial dimensions after being fitted with the fitting components 56A and 56B, resulting in an increase in the fastening load F.

[0063] refer to Figure 3 . Figure 3This is a humid air curve diagram representing a standard atmospheric pressure environment. Typically, the power transmission device 10 operates in an environment with a temperature range above 15°C and below 30°C, and a relative humidity (RH) range of 30% to 70%. Figure 3 The area marked by the shaded line is the range where the absolute humidity is 0.003 or higher. Therefore, as long as the structure is configured to generate a fastening load F in an environment where the absolute humidity is at least 0.003, the fastening load F can be generated regardless of the temperature and relative humidity in the normal operating environment.

[0064] Furthermore, consider the following scenario: the operating environment and assembly environment of the power transmission device 10 have the same specific temperature. In this case, it can be configured such that, at this specific temperature and in an environment where the relative humidity is 30% or higher, the support components 52A and 52B absorb moisture and expand, thereby applying a fastening load F to the rotating shaft bearings 54A and 54B. That is, it can be configured such that, at this specific temperature and in an environment where the relative humidity is at least 30%, the support components 52A and 52B absorb moisture and expand, thereby applying a fastening load F to the rotating shaft bearings 54A and 54B. For example, it is envisioned that the operating environment and assembly environment are both controlled at this specific temperature. Therefore, at this specific temperature, the fastening load F can be generated regardless of the relative humidity (30% to 70%) of the normal operating environment.

[0065] Next, the manufacturing method of the power transmission device 10 will be described.

[0066] First, a drying process is performed to ensure that at least the support components 52A and 52B are dry. In this drying process, it is not particularly limited whether other constituent parts of the power transmission device 10 (e.g., fitting components 56A and 56B) are dried.

[0067] The specific examples of drying methods for the object to be dried in the drying process are not particularly limited. The object to be dried can be placed in an environment suitable for drying, such as vacuum drying or constant humidity drying. In the case of vacuum drying, the object is placed in a vacuum environment where the pressure is reduced during vacuum drying. In the case of constant humidity drying, the object is placed in a constant humidity environment controlled at a specified humidity level. Alternatively, a drying promoting medium can be supplied to the object to promote drying. Examples include hot air drying, far-infrared drying, and ultrasonic drying. Regarding the drying promoting medium, for example, hot air is used in hot air drying, far-infrared rays in far-infrared drying, and ultrasound in ultrasonic drying.

[0068] The specified humidity conceivable in the operating environment of the power transmission device 10 is called the reference humidity. The reference humidity is, for example, the lower limit of the absolute humidity range conceivable in the operating environment, but it can also be a humidity exceeding this lower limit. Furthermore, the amount of water absorbed by the support components 52A and 52B when they are in equilibrium under the reference humidity is called the reference water absorption. In the drying process, the support components 52A and 52B are dried such that their water absorption is less than the reference water absorption. Therefore, in the subsequent assembly process, after the support components 52A and 52B are fitted with the fitting components 56A and 56B, they only need to be placed in an operating environment with humidity exceeding the reference humidity to allow the support components 52A and 52B to absorb moisture until they reach a water absorption exceeding the reference water absorption. Furthermore, compared to the external dimensions immediately after the support components 52A and 52B are fitted with the fitting components 56A and 56B, the support components 52A and 52B can stably absorb moisture and expand. As described above, when used in an environment with an absolute humidity of 0.003 or higher, the support components 52A and 52B can be dried in the drying process in such a way that the water absorption is lower than the water absorption (reference water absorption) of the support components 52A and 52B when they are in equilibrium in an environment with an absolute humidity of 0.003 (reference humidity).

[0069] Next, the assembly process of the power transmission device 10 is carried out, which involves assembling the constituent parts of the power transmission device 10. (See reference) Figure 4 The assembly process includes a fitting process in which the support members 52A and 52B, which have been dried in the drying process, are fitted with the fitting members 56A and 56B. In this fitting process, the outer peripheral fitting portion 70 of the support members 52A and 52B is fitted with the inner peripheral fitting portion 72 of the fitting members 56A and 56B.

[0070] In the fitting process, support members 52A and 52B, which maintain a water absorption rate below the reference absorption rate, are fitted with fitting members 56A and 56B. Figure 4 In the diagram, solid lines represent the state after drying in the drying process, and double-dotted lines represent the state before drying. Because the support components 52A and 52B are dried in the drying process, compared to the case where the support components 52A and 52B are not dried, the amount of deformation due to radial outward expansion during moisture absorption is reduced, allowing the outer peripheral fitting portion 70 to shift radially inward. Furthermore, compared to the case where the support components 52A and 52B are not dried, when fitting the support components 52A and 52B with the fitting components 56A and 56B, the operation can be performed with reduced interference or with a gap between them, thereby achieving good operability.

[0071] Apart from this, the assembly process is the same as that used in the manufacturing method of the conventional power transmission device 10. That is, the power transmission device 10 is assembled using the intermediate product obtained by fitting the support members 52A, 52B with the fitting members 56A, 56B and other constituent parts of the power transmission device 10. This process itself is well known, so its detailed description is omitted.

[0072] (Second Implementation)

[0073] refer to Figure 5 In addition to the input shaft 12, gear mechanism 14, output component 16, and housing 18 described above, the power transmission device 10 of this embodiment also includes a first wheel frame 100A disposed axially on one side (right side in the figure) relative to the gear mechanism 14, a second wheel frame 100B disposed axially on the other side (left side in the figure) relative to the gear mechanism 14, and a cover 20C disposed axially on one side relative to the first wheel frame 100A. In this embodiment, the output component 16 is the second wheel frame 100B.

[0074] The difference between this embodiment and the first embodiment is that the gear mechanism 14 is an eccentric oscillating gear mechanism. This gear mechanism 14 includes an external gear 24 and an internal gear 26C that mesh with each other, one of which is an oscillating gear 106. This gear mechanism 14 causes either the external gear 24 or the internal gear 26C to rotate by oscillating the oscillating gear 106, and can output this rotational component as output rotation from the output member 16. In this embodiment, the external gear 24 becomes the oscillating gear 106, thereby enabling the external gear 24 to rotate.

[0075] In this embodiment, the input shaft 12 is a crankshaft having multiple eccentric bodies 108. Each eccentric body 108 has a shaft center CL2 eccentric to the rotation center line CL1 of the input shaft 12, and rotates around this rotation center line CL1 to cause the oscillating gear 106 (external gear 24) to oscillate. The multiple eccentric bodies 108 have different eccentric phases. When the number of eccentric bodies 108 is set to M (two in this embodiment), the eccentric phases of the multiple eccentric bodies 108 are offset from each other by an amount equivalent to (360° / M). Furthermore, the number of eccentric bodies 108 is not particularly limited and can be any number, from one to three or more.

[0076] Each oscillating gear 106 is individually provided for a plurality of eccentric bodies 108, and is rotatably supported on the corresponding eccentric body 108 via an eccentric body bearing 110.

[0077] In this embodiment, the internal gear 26C is integrated with the housing 18. A main bearing 40 is disposed between the housing 18 and the wheel frames 100A and 100B.

[0078] Wheel carriers 100A and 100B are integrated with multiple pins 112 protruding axially from wheel carriers 100A and 100B. The multiple pins 112 pass through the external gear 24 axially (X) and enable the rotational component of the external gear 24 to be synchronized with the wheel carriers 100A and 100B. "Synchronized with the rotational component" here means that, within a numerical range including zero, the rotational component of the external gear 24 is maintained at the same magnitude as the rotational component of the wheel carriers 100A and 100B.

[0079] Next, the operation of the power transmission device 10 described above will be explained. In this embodiment, the eccentric body 108 of the crankshaft constituting the input shaft 12 causes the oscillating gear 106 to oscillate. When the oscillating gear 106 oscillates, the meshing position of the external gear 24 and the internal gear 26C changes in the circumferential direction. As a result, either the external gear 24 or the internal gear 26C (in this embodiment, the external gear 24) rotates, and its rotational component is output as output rotation from the output member 16.

[0080] In addition to the aforementioned rotating shaft 50, the power transmission device 10 of this embodiment also includes a support member 52C, a rotating shaft bearing 54C, and a fitting member 56C. The main functions of the support member 52C, the rotating shaft bearing 54C, and the fitting member 56C are the same as the combination of the support member 52A, the rotating shaft bearing 54A, and the fitting member 56A described in the first embodiment. Hereinafter, the differences will be mainly explained.

[0081] In this embodiment, the rotating shaft 50 is a crankshaft (input shaft 12). The driven gear 58 that moves by rotating the rotating shaft 50 in this embodiment is an oscillating gear 106.

[0082] In this embodiment, the support member 52C is the second wheel frame 100B (output member 16). The second wheel frame 100B in this embodiment is made of a resin-based material (e.g., PA (polyamide), PPA (polyphthalamide), etc.). The support member 52C includes a bearing mounting portion 114 disposed on the outer periphery of the support member 52C for mounting the main bearing 40. The support member 52C in this embodiment does not have the through hole 78 described in the first embodiment, but has a central recess 116 recessed axially at its radial center. The bearing mounting portion 60 of the support member 52C is disposed on the inner periphery of the central recess 116.

[0083] The rotating shaft bearing 54C is positioned between the support component 52C and the rotating shaft 50.

[0084] In this embodiment, the fitting component 56C is composed of a main bearing 40 disposed between the housing 18 and the second wheel frame 100B. The main bearing 40 includes a plurality of rolling elements 40a, and an outer ring 40b and an inner ring 40c for the rolling elements 40a to roll. In this embodiment, the outer ring 40b is separately disposed from the housing 18 and is thus provided as a dedicated part in the main bearing 40. In this embodiment, the inner ring 40c is separately disposed from the support component 52C and is thus provided as a dedicated part in the main bearing 40.

[0085] The outer peripheral fitting portion 70 of the support member 52C is formed by the bearing mounting portion 114 of the support member 52C. The inner peripheral fitting portion 72 of the fitting member 56C is provided on the inner peripheral portion of the inner ring 40c of the main bearing 40. In this embodiment, the inner peripheral fitting portion 72 of the fitting member 56C fits with the outer peripheral fitting portion 70 of the support member 52C.

[0086] The main bearing 40 constituting the mating component 56C is made of a metallic material. In this embodiment, the rolling elements 40a, outer ring 40b, and inner ring 40c of the main bearing 40 are all made of a metallic material, specifically steel. Thus, as long as the hygroscopicity of the mating component is lower than that of the supporting component, it is acceptable. Specific examples are not limited to resin-based materials; as in this embodiment, it can also be made of a metallic material.

[0087] The power transmission device 10 of this embodiment also includes a fitting member 56C that fits into the outer periphery of the support member 52C. The fitting member 56C is made of a material with lower hygroscopicity than the support member 52C. Therefore, similar to the description in (A) of the first embodiment, the support rigidity of the rotating shaft bearing 54C can be improved.

[0088] Furthermore, the power transmission device 10 of this embodiment also has the constituent elements described in (D) above, and thus can also obtain the effects corresponding to that description.

[0089] Furthermore, according to this embodiment, the expansion deformation of the support member 52C is limited by using a main bearing 40 made of a metallic material constituting the fitting member 56C. Therefore, similarly to the above, the support rigidity of the rotating shaft bearing 54C can be improved. From the viewpoint of obtaining this effect, the bearing constituting the fitting member 56C is not limited to the main bearing 40, but may be other bearings.

[0090] Furthermore, the power transmission device 10 of this embodiment is also composed of resin components and metal components. The resin components of this embodiment include: a swing gear 106 (external gear 24), a first wheel frame 100A, a second wheel frame 100B, and a housing 18. The metal components of this embodiment include: a crankshaft (rotating shaft 50), a rotating shaft bearing 54C, and an internal gear 26C, etc.

[0091] (Third Implementation)

[0092] refer to Figure 6 The power transmission device 10 in this embodiment is a motor device. This power transmission device 10 includes a rotor shaft 120, a motor 122 that generates a rotating magnetic field that rotates the rotor shaft 120, a motor housing 124 on which the stator 128 of the motor 122 is fixed, and covers 20D and 20E that axially cover the motor 122. The covers 20D and 20E include a first cover 20D disposed on one side (the opposite side of the load, the right side in the figure) of the motor 122 along its axial direction, and a second cover 20E disposed on the other side (the load side, the left side in the figure) of the motor 122 along its axial direction.

[0093] The rotor shaft 120 is capable of outputting rotational power to the driven device. The motor 122 includes a stator 128 and a rotor 130 that rotates integrally with the rotor shaft 120.

[0094] The power transmission device 10 of this embodiment also includes the aforementioned rotating shaft 50, support members 52D and 52E, rotating shaft bearings 54D and 54E, and fitting member 56D. The main functions of the support member 52D, rotating shaft bearing 54D, and fitting member 56D are the same as the combination of support member 52A, rotating shaft bearing 54A, and fitting member 56A described in the first embodiment. Furthermore, the main functions of the support member 52E, rotating shaft bearing 54E, and fitting member 56D are the same as the combination of support member 52B, rotating shaft bearing 54B, and fitting member 56B described in the first embodiment. Hereinafter, the differences will be mainly explained.

[0095] In this embodiment, the rotating shaft 50 is the rotor shaft 120.

[0096] In this embodiment, the support members 52D and 52E are covers 20D and 20E. The covers 20D and 20E in this embodiment are made of resin materials (e.g., PA (polyamide), PPA (polyphthalamide), etc.). The support members 52D and 52E include a first cover 20D (i.e., the first support member 52D) and a second cover 20E (i.e., the second support member 52E). Similar to the support members 52A and 52B in the first embodiment, both the first support member 52D and the second support member 52E have through holes 78.

[0097] The rotating shaft bearings 54D and 54E include a first rotating shaft bearing 54D disposed between the support member 52D and the rotating shaft 50, and a second rotating shaft bearing 54E disposed between the support member 52E and the rotating shaft 50.

[0098] In this embodiment, the fitting component 56D is the motor housing 124. The motor housing 124 in this embodiment is made of a metallic material (e.g., aluminum alloy).

[0099] In this embodiment, the outer peripheral fitting portion 70 of the support members 52D and 52E is provided on the outer peripheral portion of the annular protrusion 74, and the inner peripheral fitting portion 72 of the fitting member 56D is provided on the inner peripheral portion of the recess 76.

[0100] The power transmission device 10 of this embodiment also includes a fitting member 56D that fits into the outer periphery of the support members 52D and 52E. The fitting member 56D is made of a material with lower hygroscopicity than the support members 52D and 52E. Therefore, similar to the description in (A) of the first embodiment, the support rigidity of the rotating shaft bearings 54D and 54E can be improved.

[0101] Furthermore, the power transmission device 10 of this embodiment also has the constituent elements described in (C) and (D) above, and thus can also obtain the effects corresponding to the description.

[0102] Furthermore, according to this embodiment, in the motor device, the motor housing 124 is used to limit the expansion deformation of the covers 20D and 20E, thus, similarly as described above, the support rigidity of the rotating shaft bearings 54D and 54E can be improved.

[0103] Furthermore, the power transmission device 10 of this embodiment is also composed of resin components and metal components. The resin components of this embodiment include: a first cover 20D and a second cover 20E. The metal components of this embodiment include: a rotor shaft 120 (rotating shaft 50), rotating shaft bearings 54D and 54E, a motor 122, and a motor housing 124, etc.

[0104] Next, other variations of each component will be explained. Hereinafter, for components (supporting parts, etc.) whose general designations end with "A, B, C…", the letters at the end of the designation will be omitted.

[0105] The specific example of gear mechanism 14 is not particularly limited. Gear mechanism 14 can be, for example, any of planetary gear mechanisms, orthogonal axis gear mechanisms, and parallel axis gear mechanisms.

[0106] As a specific type of eccentric oscillating gear mechanism, a central crank type with a crankshaft (input shaft 12) arranged on the axis of the internal gear 26 has been described. However, this type is not particularly limited; for example, a distributed type with multiple crankshafts arranged at positions radially offset from the axis of the internal gear 26 may also be used. Furthermore, in the eccentric oscillating gear mechanism, when the external gear 24 is provided as the oscillating gear 106, the housing 18 can be provided as the output component 16. Also, the internal gear 26 may be provided as the oscillating gear 106 instead of the external gear 24.

[0107] The cylindrical shape was described as a specific type of flexural gear mechanism. However, its type is not particularly limited; for example, it can also be cup-shaped or top-hat-shaped. Furthermore, in the flexural gear mechanism, when the external gear 24 is replaced by the flexural gear 22, the housing 18 can be replaced by the output component 16. Also, the internal gear 26 can be replaced by the flexural gear 22 instead of the external gear 24.

[0108] In the first and second embodiments of the power transmission device 10, the rotating shaft 50 was described as an input shaft, and in the third embodiment, it was described as a rotor shaft 120. However, specific examples are not particularly limited. The rotating shaft 50 may be, for example, an output shaft that outputs rotation to the driven device, or an intermediate shaft that transmits rotation from the input shaft to the output shaft.

[0109] The fitting member 56 only needs to fit into the outer periphery of the support member 52, and its specific example is not particularly limited. The "outer periphery of the support member 52" here does not necessarily have to be the outermost periphery forming the outermost peripheral surface of the support member 52. For example, such as... Figure 1 As shown, in addition to the outermost peripheral portion 140 forming the outermost peripheral surface of the second support member 52B, the second support member 52B also has an annular groove portion 142 disposed at a position further radially inward than the outermost peripheral portion 140. The outer peripheral portion of the annular groove portion 142 constitutes the outer peripheral portion of the annular protrusion 74 of the second support member 52B. That is, the "outer peripheral portion of the support member 52B" here can also be the outer peripheral portion of the annular groove portion 142 constituting the outer peripheral portion of the support member 52B.

[0110] The specific examples of the combination of the support member 52 and the fitting member 56 are not particularly limited. In the example of the first embodiment, when the support member 52 is used as the cover 20, the fitting member 56 may be composed of a part of the outer shell 18 which is separately disposed from the internal gear 26, or the fitting member 56 may be separately disposed from the outer shell 18 and the internal gear 26. In the example of the second embodiment, when the support member 52 is used as the wheel frame 100, the fitting member 56 may also be a retaining ring 144 (see reference) that restricts the axial movement of the main bearing 40. Figure 5 ).

[0111] In the first embodiment, an example of an internal gear 26 constituting the fitting member 56A was described, but specific examples are not particularly limited. The gear may also be an external gear, a bevel gear, etc.

[0112] When the fitting component 56 is used as a bearing, its material is not limited to metals. For example, it can also be a resin.

[0113] It can also be configured as follows: when the absolute humidity is less than 0.003, the support component 52 absorbs moisture and expands, thereby the fastening load F is applied from the support component 52 to the rotating shaft bearing 54.

[0114] The support member 52 in the first and third embodiments may not have the through hole 78, while the support member 52 in the second embodiment may have the through hole 78.

[0115] When viewed radially, the mating parts of the support member 52 and the fitting member 56 and the rotating shaft bearing 54 may not overlap.

[0116] The power transmission device 10 to which the manufacturing method described in the first embodiment is applicable is not particularly limited. The manufacturing method can be used in the power transmission devices 10 of the second and third embodiments, as well as in other power transmission devices 10.

[0117] The above embodiments and variations are examples. The abstracted technical concepts should not be limited by the content of the embodiments and variations. Regarding the embodiments and variations, various design changes can be made, such as alterations, additions, and deletions of constituent elements. In the above embodiments, the content that allows for such design changes is emphasized by the label " Embodiment." However, this does not mean that design changes are not permitted for content without this label. The shading lines on the cross-sections in the drawings are not used to limit the material of the objects marked with shading lines. The structures and values ​​mentioned in the embodiments and variations naturally include those that can be considered the same if manufacturing errors are taken into account.

Claims

1. A power transmission device comprising: Rotation axis; A support member is disposed radially outside the rotation shaft; and A bearing is disposed between the rotating shaft and the support component. The power transmission device is characterized in that... It has a fitting member that engages with the outer periphery of the support member. The supporting component and the fitting component are made of resin-based materials. The fitting component is made of a resin material with lower hygroscopicity than the resin material of the supporting component.

2. A power transmission device, comprising: Rotation axis; A support member is disposed radially outside the rotation shaft; and A bearing is disposed between the rotating shaft and the support component. The power transmission device is characterized in that... It has a fitting member that engages with the outer periphery of the support member. The fitting component is made of a material with lower hygroscopicity than the material of the supporting component. The support component is made of resin material. The fitting component is a gear made of a resin material with lower hygroscopicity than the resin material constituting the support component.

3. The power transmission device according to claim 1, characterized in that, The fitting component is a bearing made of a metallic material.

4. The power transmission device according to claim 1, characterized in that, The support component is a cover that covers the motor axially. The fitting component is the motor housing of the motor to which the stator is fixed.

5. The power transmission device according to any one of claims 1 to 4, characterized in that, The power transmission device is configured as follows: In an environment with an absolute humidity of 0.003 (kg / kg) or higher, when the support component and the fitting component are fitted together, the support component absorbs moisture and expands, thereby transferring the fastening load from the support component to the bearing.

6. The power transmission device according to any one of claims 1 to 5, characterized in that, The support member has a through hole that extends axially through the central portion of the radial direction of the rotating shaft.

7. The power transmission device according to any one of claims 1 to 6, characterized in that, When viewed radially from the rotating shaft, the mating portion of the support member and the mating member overlaps with the bearing.

8. A method for manufacturing a power transmission device, comprising the following steps: The drying process shall at least dry the supporting components; and The fitting process involves fitting the support member, which has been dried in the drying process, with the fitting member.

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