Flexing meshing gear device

Abstract

The present invention aims to improve the durability of the root face of an external gear. The external gear of a flexing meshing type gear device has a first meshing face, a second meshing face, and a root portion having a first root portion and a second root portion on both sides of the center of the root portion, and in a state in which the external gear is not flexed, the first root portion has a first root inner side portion and a first root outer side portion from the center of the root portion toward the outside, and the second root portion has a second root inner side portion and a second root outer side portion from the center of the root portion toward the outside, and with respect to the outer peripheral shape when viewed from the axial direction, the absolute value of the curvature of the first root inner side portion increases as it goes toward the outside, the absolute value of the curvature of the first root outer side portion decreases as it goes toward the outside, the absolute value of the curvature of the second root inner side portion increases as it goes toward the outside, the absolute value of the curvature of the second root outer side portion decreases as it goes toward the outside, and all continuously change.

Description

[0001] This application claims priority based on Japanese Patent Application No. 2021-123332, filed on July 28, 2021. The entire contents of that Japanese application are incorporated herein by reference. Technical Field

[0002] This invention relates to a flexural meshing gear device. Background Technology

[0003] Patent document 1 discloses a flexural meshing gear device, which includes a vibrating body, an external gear that is flexed and deformed by the vibrating body, and an internal gear that meshes with the external gear.

[0004] In this flexural meshing gear device, the load capacity of the external gear is increased by setting the tooth flanks on the upper part of the pitch circle of the external and internal gears to a specified shape.

[0005] Patent Document 1: Japanese Patent Application Publication No. 64-83972

[0006] In the flexural meshing gear device of Patent Document 1, there is room for improvement in the durability of the tooth root surface of the external gear. Summary of the Invention

[0007] The purpose of this invention is to improve the durability of the tooth root surface of external gears.

[0008] This invention relates to a flexural meshing gear device, comprising a vibrating body, an external gear flexed and deformed by the vibrating body, and an internal gear, wherein...

[0009] The external gear has a first meshing surface that meshes with the internal gear, a second meshing surface arranged circumferentially with the first meshing surface, and a tooth root located between the first meshing surface and the second meshing surface.

[0010] The tooth root portion has a first tooth root portion located between the center of the tooth root portion and the first meshing surface, and a second tooth root portion located between the center of the tooth root portion and the second meshing surface.

[0011] Before the external gear is assembled onto the vibrating body, the external gear is in a state where it has not flexed.

[0012] The first tooth root portion has an inner portion extending from the center of the tooth root portion toward the first meshing surface and an outer portion located between the inner portion of the first tooth root and the first meshing surface.

[0013] The second tooth root has an inner portion extending from the center of the tooth root toward the second meshing surface and an outer portion located between the inner portion of the second tooth root and the second meshing surface.

[0014] Regarding the outer perimeter shape when viewed from the axial direction

[0015] In the inner portion of the first tooth root, the absolute value of the curvature increases and changes continuously as it moves away from the center of the tooth root.

[0016] In the outer portion of the first tooth root, the absolute value of the curvature decreases and changes continuously as it moves away from the center of the tooth root.

[0017] In the inner portion of the second tooth root, the absolute value of the curvature increases and changes continuously as it moves away from the center of the tooth root.

[0018] In the outer portion of the second tooth root, the absolute value of the curvature decreases and changes continuously as it moves away from the center of the tooth root.

[0019] According to the present invention, the durability of the tooth root surface of the external gear can be improved. Attached Figure Description

[0020] Figure 1 This is a cross-sectional view showing the flexural meshing gear device according to the first embodiment.

[0021] Figure 2 The upper, middle, and lower sections are line graphs representing the radial shape at various positions along the circumferential direction of the outer periphery of the tooth root when viewed from the axial direction, the curvature at various positions along the circumferential direction, and the distribution of stress amplitude at various positions along the circumferential direction.

[0022] Figure 3 The upper, middle, and lower sections are line graphs representing the radial shape at various positions along the circumferential direction of the outer periphery of the tooth root of Comparative Example 1 when viewed from the axial direction, the curvature at various positions along the circumferential direction, and the distribution of stress amplitude at various positions along the circumferential direction.

[0023] Figure 4 The upper, middle, and lower sections are line graphs representing the radial shape, curvature, and stress amplitude distribution at various positions along the circumferential direction of the outer periphery of the tooth root of Comparative Example 2 when viewed from the axial direction.

[0024] Figure 5 This is an explanatory diagram showing the ratio of the maximum stress amplitude at the root of the external tooth of Comparative Example 2 and the Example when the maximum value of the stress amplitude at the root of the external tooth of Comparative Example 1 is set to 1.

[0025] Figure 6The upper, middle, and lower sections are line graphs showing the radial shape at each position in the circumferential direction of the outer periphery of the tooth root of the external tooth according to the second embodiment when viewed from the axial direction, the curvature at each position in the circumferential direction, and the distribution of stress amplitude generated at each position in the circumferential direction.

[0026] In the diagram: 2-wave generator, 4-external gear, 6-first internal gear, 8-second internal gear, 10-housing, 16-main bearing, 22-vibrator shaft, 22a-vibrator, 50, 50A, 50B, 50D-external teeth, 51, 51A, 51B, 51D-first meshing surface, 52, 52A, 52B, 52D-second meshing surface, 53, 53A, 53B, 53D-tooth root, 53c, 53Ac, 53Bc 53Dc - Center of tooth root; 531, 531B, 531D - First tooth root; 531a, 531Da - Inner part of first tooth root; 531b, 531Db - Outer part of first tooth root; 532, 532B, 532D - Second tooth root; 532a, 532Da - Inner part of second tooth root; 532b, 532Db - Outer part of second tooth root; 533B - Third tooth root; 100 - Gear assembly; R - Rotating shaft. Detailed Implementation

[0027] In the following figures, identical or equivalent components, parts, and processes will be labeled with the same symbols, and repeated descriptions will be omitted where appropriate. Furthermore, for ease of understanding, the dimensions of components will be appropriately enlarged or reduced in the figures. Also, parts of components that are not essential to the description of the embodiments will be omitted in the figures.

[0028] [First Implementation]

[0029] Figure 1 This is an axial sectional view showing the flexural gear device 100 according to the first embodiment of the present invention. The flexural gear device 100 decelerates the input rotation and outputs it. The flexural gear device 100 is a so-called flat type flexural gear device, which includes: a wave generator 2; an external gear 4, which is flexed and deformed by the wave generator 2; a first internal gear 6, which meshes with the external gear 4; a second internal gear 8, which is arranged (adjacent) to the first internal gear 6 in the circumferential direction and meshes with the external gear 4; a housing 10; a first limiting member 12; a second limiting member 14; a main bearing 16; a first bearing housing 18; and a second bearing housing 20. A lubricant (e.g., grease) is sealed in the flexural gear device 100. The lubricant lubricates the meshing portions of the external gear 4 with the first internal gear 6 and the second internal gear 8, as well as the bearings, etc.

[0030] [Wave Generator]

[0031] The wave generator 2 includes: a vibration-initiating shaft 22; a first vibration-initiating bearing 21a disposed between the vibration-initiating shaft 22 and the external gear 4 (the first external tooth portion 4a); and a second vibration-initiating bearing 21b disposed between the vibration-initiating shaft 22 and the external gear 4 (the second external tooth portion 4b). The first vibration-initiating bearing 21a includes: a plurality of first rolling elements 24a; a first retainer 26a for retaining the plurality of first rolling elements 24a; and a first outer ring member 28a embedded in the external gear 4. The second vibration-initiating bearing 21b includes: a plurality of second rolling elements 24b; a second retainer 26b for retaining the plurality of second rolling elements 24b; and a second outer ring member 28b embedded in the external gear 4.

[0032] The vibrator shaft 22 is the input shaft, which is connected to a rotary drive source such as a motor and rotates around the rotation axis R. An vibrator 22a, with a generally elliptical shape and a cross-section orthogonal to the rotation axis R, is integrally formed on the vibrator shaft 22. Here, "generally elliptical" is not limited to an ellipse in a strictly geometric sense; it includes any shape that can be considered generally elliptical due to having both a major axis and a minor axis.

[0033] In addition, in the following description, the direction along the rotation axis R will be called the "axial direction", the direction perpendicular to the rotation axis R will be called the "radial direction", and the direction of rotation centered on the rotation axis R will be called the "circumferential direction".

[0034] Multiple first rolling elements 24a each have a generally cylindrical shape and are spaced apart circumferentially with their central axes oriented in a direction generally parallel to the rotation axis R. The first rolling elements 24a are held in place by a first retainer 26a to roll freely and roll on the outer peripheral surface 22b of the vibrating body 22a. That is, the inner ring of the first vibrating body bearing 21a is integral with the outer peripheral surface 22b of the vibrating body 22a, but it is not limited to this and may also have a dedicated inner ring separate from the vibrating body 22a.

[0035] The structure of the second rolling element 24b is the same as that of the first rolling element 24a. Multiple second rolling elements 24b are held in a rolling position by a second retainer 26b arranged axially with the first retainer 26a, and roll on the outer peripheral surface 22b of the vibrator 22a. That is, the inner ring of the second vibrator bearing 21b is integral with the outer peripheral surface 22b of the vibrator 22a, but this is not a limitation; a separate inner ring may also be provided, separate from the vibrator 22a.

[0036] Hereinafter, the first rolling element 24a and the second rolling element 24b are sometimes collectively referred to as "rolling element 24". And the first retainer 26a and the second retainer 26b are sometimes collectively referred to as "retainer 26".

[0037] The first outer ring component 28a surrounds a plurality of first rolling elements 24a. The first outer ring component 28a is flexible, and the vibrating body 22a is flexed into an elliptical shape by the plurality of first rolling elements 24a. If the vibrating body 22a (i.e., the vibrating body shaft 22) rotates, the first outer ring component 28a continuously flexes and deforms in accordance with the shape of the vibrating body 22a. The structure of the second outer ring component 28b is the same as that of the first outer ring component 28a. The second outer ring component 28b is formed separately from the first outer ring component 28a. Alternatively, the second outer ring component 28b may be formed integrally with the first outer ring component 28a. Hereinafter, the first outer ring component 28a and the second outer ring component 28b are sometimes collectively referred to as "outer ring component 28".

[0038] [External gear]

[0039] The external gear 4 is a flexible ring-shaped component made of a metallic material (e.g., nickel-chromium-molybdenum steel), with the vibrating body 22a, rolling element 24, and outer ring component 28 embedded inside it. The external gear 4, with the vibrating body 22a, rolling element 24, and outer ring component 28 fitted together, is thus flexed into an elliptical shape. If the vibrating body 22a rotates, the external gear 4 continuously flexes and deforms in accordance with the shape of the vibrating body 22a.

[0040] The external gear 4 includes a first external tooth 4a located outside the first outer ring member 28a, a second external tooth 4b located outside the second outer ring member 28b, and a base material 4c. The first external tooth 4a and the second external tooth 4b are formed on a single base material (i.e., base material 4c) and have the same number of teeth.

[0041] [Internal Gear]

[0042] The first internal gear 6 is a rigid annular component with a first internal tooth portion 6a formed on its inner circumference. The first internal tooth portion 6a surrounds the first external tooth portion 4a of the external gear 4, which is flexed into an elliptical shape, and meshes with a predetermined region (two regions) near the long axis of the vibrating body 22a of the first external tooth portion 4a. The first internal tooth portion 6a has more teeth than the first external tooth portion 4a.

[0043] The second internal gear 8 is arranged (adjacent) to the first internal gear 6 in the axial direction. The second internal gear 8 is a rigid cylindrical component with a second internal tooth portion 8a formed on its inner circumference. The second internal tooth portion 8a surrounds the external gear 4, which is flexed into an elliptical shape, and meshes with a predetermined region (two regions) near the long axis of the vibrating body 22a of the second external tooth portion 4b. The second internal tooth portion 8a has the same number of teeth as the second external tooth portion 4b. Therefore, the second internal gear 8 rotates synchronously with the rotation of the second external tooth portion 4b (and even the external gear 4).

[0044] [Limited Components]

[0045] The first limiting member 12 is a flat, annular member disposed between the external gear 4, the first outer ring member 28a, the first retainer 26a, and the first bearing housing 18. The second limiting member 14 is a flat, annular member disposed between the external gear 4, the second outer ring member 28b, the second retainer 26b, and the second bearing housing 20. The first limiting member 12 and the second limiting member 14 restrict the axial movement of the external gear 4, the outer ring member 28, and the retainer 26.

[0046] [shell]

[0047] The housing 10 is a generally cylindrical component that surrounds the second internal gear 8. The first internal gear 6 is latched into the housing 10 and integrated with it by bolts (not shown). A main bearing 16 is disposed between the housing 10 and the second internal gear 8. In this embodiment, the main bearing 16 is a crossed roller bearing, which includes a plurality of rollers (rolling elements) 46 arranged circumferentially at intervals. The plurality of rollers 46 roll on the rolling surface 8b of the second internal gear 8 and the rolling surface 10a of the housing 10. That is, the outer peripheral side of the second internal gear 8 functions as the inner ring of the main bearing 16, and the inner peripheral side of the housing 10 functions as the outer ring of the main bearing 16. The housing 10 supports the second internal gear 8 via the main bearing 16 so that it can rotate freely relative to it. In addition, the type of bearing of the main bearing 16 is not particularly limited, for example, it can be composed of a plurality of bearings (angular contact ball bearings, tapered roller bearings, etc.) arranged axially separated between the second internal gear 8 and the housing 10, or it can be a four-point contact ball bearing. Furthermore, the main bearing 16 may also have a dedicated inner or outer ring that is different from the second internal gear 8 or the housing 10.

[0048] [case]

[0049] The first bearing housing 18 is an annular component and surrounds the vibrator shaft 22. Similarly, the second bearing housing 20 is an annular component and surrounds the vibrator shaft 22. The first bearing housing 18 and the second bearing housing 20 are configured to axially sandwich the external gear 4, rolling element 24, retainer 26, outer ring component 28, first limiting component 12, and second limiting component 14. The first bearing housing 18 is latched into the first internal gear 6 and fixed to the first internal gear 6 by bolts. The second bearing housing 20 is latched into the second internal gear 8 and fixed to the second internal gear 8 by bolts. A bearing 30 is assembled on the inner periphery of the first bearing housing 18, and a bearing 32 is assembled on the inner periphery of the second bearing housing 20. The vibrator shaft 22 is supported by the first bearing housing 18 and the second bearing housing 20 via the bearings 30 and 32, allowing it to rotate freely relative to the first bearing housing 18 and the second bearing housing 20.

[0050] [Sealing Structure]

[0051] An oil seal 40 is disposed between the vibrating body shaft 22 and the first bearing housing 18; an O-ring 34 is disposed between the first bearing housing 18 and the first internal gear 6; an O-ring 36 is disposed between the first internal gear 6 and the outer housing 10; an oil seal 42 is disposed between the outer housing 10 and the second internal gear 8; an O-ring 38 is disposed between the second internal gear 8 and the second bearing housing 20; and an oil seal 44 is disposed between the second bearing housing 20 and the vibrating body shaft 22. This effectively suppresses lubricant leakage within the flexural meshing gear device 100.

[0052] [Basic Movements]

[0053] The operation of the flexural gear assembly 100 configured as described above will be explained. Here, examples will be given where the first external gear 4a has 100 teeth, the second external gear 4b has 100 teeth, the first internal gear 6a has 102 teeth, and the second internal gear 8a has 100 teeth. Furthermore, examples will be given where the second internal gear 8 and the second bearing housing 20 are connected to the driven component.

[0054] If the vibrating body shaft 22 rotates while the two parts of the elliptical shape of the first external tooth 4a are engaged with the first internal tooth 6a along its major axis, the meshing position of the first external tooth 4a and the first internal tooth 6a also moves circumferentially. Since the number of teeth in the first external tooth 4a and the first internal tooth 6a is different, the first external tooth 4a rotates relative to the first internal tooth 6a. Because the first internal gear 6 and the first bearing housing 18 are fixed, the rotation of the first external tooth 4a is equivalent to the difference in the number of teeth. That is, the rotation of the vibrating body shaft 22 is significantly reduced before being output to the first external tooth 4a. The reduction ratio is as follows.

[0055] Reduction ratio = (Number of teeth in the first external gear section 4a - Number of teeth in the first internal gear section 6a) / Number of teeth in the first external gear section 4a

[0056] = (100-102) / 100

[0057] =-1 / 50

[0058] Since the second external tooth 4b and the first external tooth 4a are formed as one piece, the second external tooth 4b and the first external tooth 4a rotate as one. Since the second external tooth 4b and the second internal tooth 8a have the same number of teeth, no relative rotation occurs, and the second external tooth 4b and the second internal tooth 8a rotate as one. Therefore, the rotational speed, the same as that of the first external tooth 4a, is output to the second internal tooth 8a. As a result, an output that reduces the rotation of the vibrating body shaft 22 to -1 / 50 can be output from the second internal gear 8.

[0059] [Characteristic shape of the tooth root of an external gear]

[0060] Here, the characteristic shape of the outer teeth formed on the outer periphery of the first outer tooth portion 4a and the second outer tooth portion 4b of the outer gear 4 will be described.

[0061] Furthermore, since the external teeth of the first external tooth portion 4a and the external teeth of the second external tooth portion 4b have the same shape and structure, they are marked with the same symbols and are subject to the same descriptions.

[0062] Furthermore, the external gear 4 is flexible and is flexed into an approximately elliptical shape by the vibrating body 22a when assembled in the flexural meshing gear device 100. However, in the following description, the state of the external gear 4 before it is assembled in the vibrating body 22a (i.e., no flexing occurs, so that its inner circumferential surface is a perfect circle when viewed from the axial direction) will be described as a premise.

[0063] Regarding the outer peripheral shape of the root 53 of the external tooth 50 when viewed from the axial direction, in Figure 2 The upper section shows the radial shape at various locations along the circumference in a line graph format, the middle section shows the curvature at various locations along the circumference in a line graph format, and the lower section shows the distribution of stress amplitude at various locations along the circumference in a line graph format. Figure 2 The shape features of the external tooth 50 shown apply to all external teeth of the external gear 4.

[0064] in addition, Figure 2 The stress amplitude distribution of the lower section is obtained by simulation test of the stress amplitude applied to the external gear 50 when the external gear 4 is assembled into the flexural meshing gear device 100 and driven.

[0065] exist Figure 2 On the horizontal axis, the center of the tooth root 53c, which will become the center of the tooth root 53 in the circumferential direction, is taken as the origin (0 point) in the circumferential direction. One side of the circumferential direction is represented as positive (+), and the other side of the circumferential direction is represented as negative (-).

[0066] The vertical axis at the top represents the distance from the center of external gear 4.

[0067] In the curvature of the longitudinal axis in the middle section, the curvature that bulges outward toward the outer side of the external tooth 50 is represented as positive (+), and the curvature that bulges inward toward the inner side of the external tooth 50 is represented as negative (-).

[0068] like Figure 2 As shown in the upper section, the external tooth 50 has a tooth root portion 53, and also has a first meshing surface 51 and a second meshing surface 52 that are adjacent to the tooth root portion 53 in the circumferential direction.

[0069] Here, the first meshing surface 51 and the second meshing surface 52 are respectively the extent of all or part of the tooth lateral surface including the upper part of the pitch circle.

[0070] Furthermore, the root portion 53 is a portion or all of the root surface and the root lateral surfaces on both sides of the tooth.

[0071] Furthermore, the external gear 4 assembled in the flexural gear assembly 100 is sometimes used to rotate only in one direction of rotation. Under this premise, even if only one of the first meshing surface 51 and the second meshing surface 52 (for example, the first meshing surface 51) meshes with the first internal gear 6 or the second internal gear 8, while the other (for example, the second meshing surface 52) does not mesh with the first internal gear 6 or the second internal gear 8, for convenience, the two sides of the tooth root 53 are referred to as "the first meshing surface 51" and "the second meshing surface 52" respectively.

[0072] Furthermore, the tooth root portion 53 has a first tooth root portion 531 located between the tooth root portion center 53c and the first meshing surface 51, and a second tooth root portion 532 located between the tooth root portion center 53c and the second meshing surface 52. In addition, the tooth root portion center 53c is the midpoint of the tooth root portion 53 in the circumferential direction, and it is located at the innermost side in the radial direction.

[0073] Furthermore, the first tooth root portion 531 has a side extending from the center 53c of the tooth root portion toward the first meshing surface 51 ( Figure 2 The inner portion 531a of the first tooth root (on the left side) and the outer portion 531b of the first tooth root located between the inner portion 531a of the first tooth root and the first meshing surface 51.

[0074] Furthermore, the second tooth root 532 has a side extending from the center 53c of the tooth root towards the second meshing surface 52 ( Figure 2 The inner side portion 532a of the second tooth root (on the right side) and the outer side portion 532b of the second tooth root located between the inner side portion 532a of the second tooth root and the second meshing surface 52.

[0075] Furthermore, the root portion 53 of the external tooth 50 has a characteristic curvature in its peripheral shape when viewed from the axial direction.

[0076] Here, the curvature of the outer circumferential shape of the first meshing surface 51 and the second meshing surface 52, which are adjacent to the tooth root 53 on both sides, becomes a positive constant value when viewed from the axial direction.

[0077] In contrast, in the tooth root 53, the curvature of the outer peripheral shape when viewed from the axial direction is negative overall, and the curvature curves continuously change within each range of the first tooth root 531 and the second tooth root 532.

[0078] like Figure 2 As shown in the middle section, the term "continuous variation" here refers to the fact that the curvature in each range of the first tooth root 531 and the second tooth root 532 is formed by a curve without any bends. Alternatively, a straight section may be included as long as there are no bends.

[0079] Furthermore, the curvature of the outer periphery when viewed from the axial direction in the four regions of the inner side 531a and outer side 531b of the first tooth root 531, the inner side 532a and outer side 532b of the second tooth root 532, and the center 53c of the tooth root has the following characteristics (1) to (6).

[0080] (1) The absolute value of the curvature of the inner side 531a of the first tooth root increases as it moves away from the center 53c of the tooth root. Figure 2 (Left side) and increases and changes continuously.

[0081] (2) The absolute value of the curvature of the outer part 531b of the first tooth root increases as it moves away from the center 53c of the tooth root. Figure 2 (Left side) decreases and changes continuously.

[0082] (3) The absolute value of the curvature of the inner side 532a of the second tooth root increases as it moves away from the center 53c of the tooth root. Figure 2 (On the right side) it increases and changes continuously.

[0083] (4) The absolute value of the curvature of the outer part 532b of the second tooth root increases as it moves away from the center 53c of the tooth root. Figure 2 (On the right side) it decreases and changes continuously.

[0084] (5) The absolute rate of change (e.g. maximum value) of the curvature of the inner part 531a of the first tooth root, the outer part 531b of the first tooth root, the inner part 532a of the second tooth root, and the outer part 532b of the second tooth root is more than ten times greater than the absolute rate of change (e.g. maximum value) of the curvature of the first meshing surface 51 and the second meshing surface 52.

[0085] (6) At the center 53c of the tooth root portion, which forms the boundary between the first tooth root portion 531 and the second tooth root portion 532, the absolute value of the curvature is the lowest within the tooth root portion 53. Alternatively, the curvature of the center 53c of the tooth root portion may also be zero.

[0086] Based on these features (1) to (6), the outer periphery of the tooth root 53 when viewed from the axial direction is a curved shape that is almost entirely concave towards the radial inward side.

[0087] Furthermore, in the outer peripheral shape of the tooth root portion 53 when viewed axially, the absolute value of the curvature gradually increases from the end on the side of the first meshing surface 51, becomes the largest at the boundary between the inner portion 531a and the outer portion 531b of the first tooth root, and then gradually decreases toward the center 53c of the tooth root portion.

[0088] Next, the absolute value of curvature becomes the smallest (flattest shape) at the center 53c of the tooth root, then gradually increases again towards the side of the second meshing surface 52, becomes the largest at the boundary between the inner part 532a and the outer part 532b of the second tooth root, and then gradually decreases towards the end of the tooth root 53 towards the side of the second meshing surface 52.

[0089] As described above, the curvature of the outer periphery of the tooth root portion 53 when viewed longitudinally varies continuously in a curved manner within each range of the inner portion 531a of the first tooth root, the outer portion 531b of the first tooth root, the inner portion 532a of the second tooth root, and the outer portion 532b of the second tooth root.

[0090] Furthermore, even at the boundaries between the inner portion 531a and the outer portion 531b of the first tooth root and between the inner portion 532a and the outer portion 532b of the second tooth root, the absolute value of the curvature changes continuously in a curve.

[0091] However, at the center 53c of the tooth root, which forms the boundary between the first tooth root 531 and the second tooth root 532, the absolute value of the curvature does not change continuously.

[0092] [Comparative Example]

[0093] Here, the external teeth 50A and 50B of Comparative Examples 1 and 2, which do not have the characteristic shape of the external teeth 50 of the external gear 4 described above, will be described with reference to the accompanying drawings.

[0094] For external gear 50A, in Figure 3 The upper section shows the radial shape at various positions along the circumference using a line graph. Figure 3 The middle section is shown as a line graph illustrating the curvature at various positions along the circumference. Figure 3 The lower section shows, in line graph form, the stress amplitude generated at various positions in the circumferential direction of the external tooth 50A when assembled in the flexural meshing gear device.

[0095] Furthermore, for the external tooth 50B, in Figure 4 The upper section shows the radial shape at various positions along the circumference using a line graph. Figure 4 The middle section is shown as a line graph illustrating the curvature at various positions along the circumference. Figure 4 The lower section shows, in line graph form, the stress amplitude generated at various positions in the circumferential direction of the external tooth 50B when assembled in the flexural gear assembly. For external teeth 50A and 50B, the stress amplitude at each position was also determined through simulation experiments.

[0096] The external tooth 50A has a tooth root portion 53A and a first meshing surface 51A and a second meshing surface 52A that are adjacent to the tooth root portion 53A in the circumferential direction.

[0097] Similar to the external tooth 50, the curvature of the outer periphery of the first meshing surface 51A and the second meshing surface 52A when viewed from the axial direction is positive as a whole, and they have a shape with constant curvature.

[0098] In contrast, the curvature of the outer periphery of the tooth root 53A as a whole, when viewed from the axial direction, becomes a constant negative value.

[0099] The external tooth 50B has a tooth root portion 53B and a first meshing surface 51B and a second meshing surface 52B that are adjacent to the tooth root portion 53B in the circumferential direction.

[0100] Similar to the external tooth 50, the curvature of the outer periphery of the first meshing surface 51B and the second meshing surface 52B when viewed from the axial direction is positive as a whole, and they have a constant curvature shape.

[0101] However, the tooth root portion 53B is composed of a first tooth root portion 531B and a second tooth root portion 532B with a constant negative curvature of the outer peripheral shape when viewed from the axial direction, and a third tooth root portion 533B located between the first tooth root portion 531B and the second tooth root portion 532B with a zero curvature of the outer peripheral shape when viewed from the axial direction.

[0102] [Technical Effects of the Embodiments of the Invention]

[0103] To illustrate the technical effect of the characteristic shape of the external tooth 50 based on the external gear 4, the distribution of stress amplitude applied to the external gear is compared with that of the comparative examples external teeth 50A and 50B.

[0104] Figure 5 This is an explanatory diagram showing the ratio of the maximum stress amplitudes at the roots 53A and 53B of external teeth 50 and 50B when the maximum stress amplitude at the root 53A of external tooth 50A is set to 1. Additionally, Figure 5 Comparative Example 1 represents external tooth 50A, Comparative Example 2 represents external tooth 50B, and the Example represents external tooth 50.

[0105] Since the external gear 4 of the flexural gear mechanism 100 is deformed from the inner circumference by the vibrating body 22a in an elliptical rotational manner, the radial wall thickness is limited in order to ensure flexibility, and the root portion 53 of each external tooth 50 becomes particularly thin in the radial direction. Therefore, it is important to reduce the stress amplitude applied to the root portion 53 during drive.

[0106] If Figures 2-4 Comparing the stress amplitudes at various positions along the circumference of the lower segment, it is found that in the external tooth 50, the stress amplitude decreases throughout the tooth root 53. Furthermore, as... Figure 5 As shown, the maximum stress amplitude of external tooth 50 also becomes lower than that of external tooth 50A and external tooth 50B.

[0107] In particular, in the external tooth 50, the deviation in the distribution of stress amplitude is suppressed and smoothed around the center 53c of the tooth root where the wall thickness is thinnest.

[0108] In contrast, since the entire root portion 53A of the external tooth 50A has the same curvature, the central portion 53Ac of the root portion is recessed downwards, the wall thickness becomes the thinnest, and the stress amplitude becomes the largest at the central portion 53Ac of the root portion.

[0109] Furthermore, in the external tooth 50B, the curvature of the third tooth root 533B, including the central tooth root 53Bc, is 0. However, since the boundary between the third tooth root 533B and the first tooth root 531B and the second tooth root 532B on both sides has a shape with a sharp change in curvature, the stress will be concentrated around the location of the curvature change, and the stress amplitude value will become the maximum.

[0110] Thus, by comparing with external teeth 50A and 50B, it can be seen that in external teeth 50, the outer circumferential shape when viewed from the axial direction in each range of the first tooth root inner side portion 531a, the first tooth root outer side portion 531b, the second tooth root inner side portion 532a, and the second tooth root outer side portion 532b constituting the tooth root portion 53 is a shape in which the absolute value of curvature increases or decreases and changes continuously. Therefore, stress concentration can be suppressed, thereby reducing the stress amplitude of the entire tooth root portion 53 and suppressing fracture from the tooth root portion 53, thereby improving the durability of the external gear and further improving the durability of the flexural meshing gear device 100.

[0111] In particular, the curvature curves of the inner portion 531a of the first tooth root, the outer portion 531b of the first tooth root, the inner portion 532a of the second tooth root, and the outer portion 532b of the second tooth root change continuously, thus achieving a shape with a smoother curvature change, thereby suppressing stress concentration and further reducing the stress amplitude of the entire tooth root portion 53.

[0112] Furthermore, within the root portion 53 of the external tooth 50, since the curvature of the central portion 53c of the root portion, which serves as the boundary between the inner side portion 531a of the first tooth root and the inner side portion 532a of the second tooth root, is set to the minimum, stress concentration can be suppressed for the part where stress amplitude needs to be minimized to the maximum extent, thereby further improving durability.

[0113] Furthermore, within the root portion 53 of the external tooth 50, although the curvature at the boundary between the inner side portion 531a of the first tooth root and the inner side portion 532a of the second tooth root (i.e., the center 53c of the tooth root) does not change continuously, by sufficiently reducing the curvature of the center 53c of the tooth root, the effect of the discontinuous change can be sufficiently reduced, thereby suppressing stress concentration and reducing the stress amplitude of the entire tooth root portion 53.

[0114] Furthermore, within the root portion 53 of the external tooth 50, the inner portion 531a of the first tooth root, the outer portion 531b of the first tooth root, the inner portion 532a of the second tooth root, and the outer portion 532b of the second tooth root each have a portion in which the absolute value of the curvature changes at a rate more than 10 times greater than the absolute value of the curvature changes at the first meshing surface 51 and the second meshing surface 52.

[0115] Since the first meshing surface 51 and the second meshing surface 52 require positive curvature and the tooth root 53 requires negative curvature, although it is necessary to change the curvature of the tooth root 53, the effect of the curvature change can be sufficiently reduced, thereby suppressing stress concentration and reducing the stress amplitude of the entire tooth root 53.

[0116] [Second Implementation]

[0117] Regarding the outer peripheral shape of the tooth root 53D of the external tooth 50D according to the second embodiment of the present invention when viewed from the axial direction, in Figure 6 The upper section shows the radial shape at various positions along the circumference in a line graph, the middle section shows the curvature at various positions along the circumference in a line graph, and the lower section shows the distribution of stress amplitude at various positions along the circumference in a line graph. The stress amplitude distribution in the lower section is obtained by simulation experiments to determine the stress amplitude applied to the external gear 50D when it is assembled in the flexural gear assembly 100 and driven.

[0118] The external tooth 50D shown here can replace the external tooth 50 described above and be applied to all external teeth of the external gear 4.

[0119] like Figure 6 As shown in the upper section, the external tooth 50D has a tooth root portion 53D and a first meshing surface 51D and a second meshing surface 52D that clamp the tooth root portion 53D.

[0120] Furthermore, in the tooth root portion 53D, with the center of the tooth root portion 53Dc in the circumferential direction, there are a first tooth root portion 531D and a second tooth root portion 532D on both sides.

[0121] Furthermore, the first tooth root portion 531D has a side extending from the center 53Dc of the tooth root portion toward the first meshing surface 51D ( Figure 6 The inner portion 531Da of the first tooth root (on the left side) and the outer portion 531Db of the first tooth root located between the inner portion 531Da of the first tooth root and the first meshing surface 51D.

[0122] Furthermore, the second tooth root portion 532D has a side extending from the center 53Dc of the tooth root portion toward the second meshing surface 52D ( Figure 6The inner side portion 532Da of the second tooth root (on the right side) and the outer side portion 532Db of the second tooth root located between the inner side portion 532Da of the second tooth root and the second meshing surface 52D.

[0123] Both the first meshing surface 51D and the second meshing surface 52D have a shape with constant curvature.

[0124] In the tooth root 53D, the curvature of the outer peripheral shape when viewed from the axial direction is negative overall, and the curvature of the tooth root 53D as a whole changes continuously in a curved shape.

[0125] Furthermore, the four regions of the inner part 531Da of the first tooth root, the outer part 531Db of the first tooth root, the inner part 532Da of the second tooth root, and the outer part 532Db of the second tooth root have the same features as the features (1) to (5) of the inner part 531a of the first tooth root, the outer part 531b of the first tooth root, the inner part 532a of the second tooth root, and the outer part 532b of the second tooth root of the external tooth 50.

[0126] Furthermore, the central part 53Dc at the root of the external tooth 50D also has the following characteristics (7).

[0127] (7) At the center 53Dc of the tooth root, which forms the boundary between the first tooth root 531D and the second tooth root 532D, the absolute value of the curvature is the lowest, zero, within the tooth root 53D. Moreover, the curvature of the inner side of the first tooth root 531Da and the inner side of the second tooth root 532Da change continuously in a curved manner at the center 53Dc of the tooth root.

[0128] Based on these features (1) to (5) and (7), in the external tooth 50D, the curvature of the inner part 531Da of the first tooth root, the outer part 531Db of the first tooth root, the inner part 532Da of the second tooth root, and the outer part 532Db of the second tooth root continuously changes within each range, and the curvature of each boundary portion of the inner part 531Da of the first tooth root, the outer part 531Db of the first tooth root, the inner part 532Da of the second tooth root, and the outer part 532Db of the second tooth root also continuously changes.

[0129] Therefore, it can more effectively suppress stress concentration and further reduce the stress amplitude of the tooth root 53D as a whole, further improve the durability of the external gear, and thus further improve the durability of the flexural meshing gear device 100.

[0130] Furthermore, since the curvature of the central part 53Dc of the tooth root 53D, which serves as the boundary between the inner side of the first tooth root 531Da and the inner side of the second tooth root 532Da, becomes 0, stress concentration can be further suppressed for the part where stress amplitude needs to be minimized, thereby further improving durability.

[0131] Furthermore, within the root portion 53D of the external tooth 50D, since the curvature continuously changes at the center 53Dc of the root portion, the stress concentration can be further suppressed compared to the external tooth 50, thereby reducing the overall stress amplitude of the root portion 53D.

[0132] [other]

[0133] The various embodiments of the present invention have been described above. However, the present invention is not limited to the embodiments described above. For example, in the embodiments described above, an example is shown of assembling an external gear having the characteristic external teeth of the present invention in a flat-type flexible meshing gear device, but it can also be applied to other forms of flexible meshing gear devices (e.g., cup-shaped or top-hat-shaped).

[0134] Furthermore, without departing from the spirit of the invention, the details shown in the embodiments may be appropriately modified.

Claims

1. A flexural meshing gear device, comprising a vibrating body, an external gear flexed and deformed by the vibrating body, and an internal gear, characterized in that, The external gear has a first meshing surface that meshes with the internal gear, a second meshing surface arranged circumferentially with the first meshing surface, and a tooth root located between the first meshing surface and the second meshing surface. The tooth root portion has a first tooth root portion located between the center of the tooth root portion and the first meshing surface, and a second tooth root portion located between the center of the tooth root portion and the second meshing surface. The external gear is in a state where it has not flexed before being assembled onto the vibrating body. The first tooth root portion has an inner portion extending from the center of the tooth root portion toward the first meshing surface and an outer portion located between the inner portion of the first tooth root and the first meshing surface. The second tooth root has an inner portion extending from the center of the tooth root toward the second meshing surface and an outer portion located between the inner portion of the second tooth root and the second meshing surface. Regarding the outer perimeter shape when viewed from the axial direction, In the inner portion of the first tooth root, the absolute value of the curvature increases and changes continuously as it moves away from the center of the tooth root. In the outer portion of the first tooth root, the absolute value of the curvature decreases and changes continuously as it moves away from the center of the tooth root. In the inner portion of the second tooth root, the absolute value of the curvature increases and changes continuously as it moves away from the center of the tooth root. In the outer portion of the second tooth root, the absolute value of the curvature decreases and changes continuously as it moves away from the center of the tooth root.

2. The flexural meshing gear device according to claim 1, characterized in that, The curvature of the inner part of the first tooth root, the outer part of the first tooth root, the inner part of the second tooth root, and the outer part of the second tooth root changes continuously in a curve-like manner.

3. The flexural meshing gear device according to claim 1 or 2, characterized in that, At the boundary between the inner side of the first tooth root and the inner side of the second tooth root, the curvature is set to zero.

4. The flexural meshing gear device according to claim 1 or 2, characterized in that, At the boundary between the inner side of the first tooth root and the inner side of the second tooth root, the curvature does not change continuously.

5. The flexural meshing gear device according to claim 1 or 2, characterized in that, The absolute rate of change of the curvature of the inner portion of the first tooth root, the outer portion of the first tooth root, the inner portion of the second tooth root, and the outer portion of the second tooth root is greater than the absolute rate of change of the curvature of the first meshing surface and the second meshing surface.

6. The flexural meshing gear device according to claim 1 or 2, characterized in that, The absolute rate of change of the curvature of the inner part of the first tooth root, the outer part of the first tooth root, the inner part of the second tooth root, and the outer part of the second tooth root is more than 10 times the absolute rate of change of the curvature of the first meshing surface and the second meshing surface.

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