Flexural engagement type gear device

Abstract

The present invention provides a flexure engagement type gear device that suppresses a reduction in tooth life and can improve torsional rigidity. The flexure engagement type gear device includes: an oscillation body; an external gear that is flexurally deformed by the oscillation body; and a first internal gear and a second internal gear that mesh with the external gear. The external gear has a first external tooth portion that meshes with the first internal gear and a second external tooth portion that meshes with the second internal gear. The first external tooth portion has a first maximum tooth thickness portion with the maximum tooth thickness and a first inner tooth thickness reduction portion that extends toward the axial inner side from the first maximum tooth thickness portion and has a decreasing tooth thickness as it extends toward the axial inner side. The first inner tooth thickness reduction portion has an outer region and an inner region within the meshing range with the first internal gear. The inner region is provided on the axial inner side of the outer region and has a greater tooth thickness reduction ratio than the outer region. The boundary between the outer region and the inner region is a portion where the change rate of the tooth thickness reduction ratio is discontinuous, and the axial length of the outer region is greater than the axial length of the inner region.

Description

[0001] This application claims priority based on Japanese Patent Application No. 2021-170593 filed on October 19, 2021. The entire content of this Japanese application is incorporated herein by reference. Technical Field

[0002] The present invention relates to a flexure engagement type gear device. Background Art

[0003] There is known a so-called flat type flexure engagement type gear device, which includes: an exciting body; an external gear that is flexurally deformed by the exciting body; a first internal gear that meshes with the external gear; and a second internal gear that is arranged axially with the first internal gear and meshes with the external gear.

[0004] Patent Document 1 discloses a technique for suppressing excessive tooth wear by carefully designing the tooth line shape of the external gear, the first internal gear, or the second internal gear in a flat type flexure engagement type gear device.

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-120325

[0006] In the flexure engagement type gear device of Patent Document 1, although the effect of suppressing excessive tooth wear can be obtained, there is room for improvement in the torsional rigidity of the flexure engagement type gear device. Summary of the Invention

[0007] An object of the present invention is to provide a flexure engagement type gear device that can suppress a reduction in tooth life while improving torsional rigidity.

[0008] A flexure engagement type gear device according to an embodiment of the present invention includes: an exciting body; an external gear that is flexurally deformed by the exciting body; a first internal gear that meshes with the external gear; and a second internal gear that is arranged axially with the first internal gear and meshes with the external gear, wherein,

[0009] the external gear has a first external tooth portion that meshes with the first internal gear and a second external tooth portion that meshes with the second internal gear,

[0010] the first external tooth portion has a first maximum tooth thickness portion where the tooth thickness is maximum and a first inner tooth thickness reducing portion that extends from the first maximum tooth thickness portion toward the axial inner side and whose tooth thickness decreases as it goes toward the axial inner side,

[0011] the first inner tooth thickness reducing portion has an outer region and an inner region within the meshing range with the first internal gear, and the inner region is provided on the axial inner side of the outer region and the tooth thickness reduction ratio is greater than that of the outer region,

[0012] The boundary between the outer region and the inner region is a portion where the rate of change of the reduction ratio of the tooth thickness is discontinuous, and the axial length of the outer region is greater than the axial length of the inner region.

[0013] A flexural engagement type gear device according to another embodiment of the present invention includes: an oscillation body; an outer gear that is flexurally deformed by the oscillation body; a first inner gear that meshes with the outer gear; and a second inner gear that is arranged axially with the first inner gear and meshes with the outer gear, wherein,

[0014] The outer gear has a first outer tooth portion that meshes with the first inner gear and a second outer tooth portion that meshes with the second inner gear,

[0015] The first outer tooth portion has a first maximum tooth thickness portion where the tooth thickness is the largest and a first inner tooth thickness reduction portion that extends from the first maximum tooth thickness portion toward the axial inner side and whose tooth thickness decreases as it goes toward the axial inner side,

[0016] Between the inner end of the meshing range of the first inner gear and the first outer tooth portion and the first maximum tooth thickness portion, the reduction ratio of the tooth thickness of the first inner tooth thickness reduction portion in the axially inner 1 / 3 range is 2.5 times or more the reduction ratio of the tooth thickness of the first inner tooth thickness reduction portion in the axially outer 2 / 3 range.

[0017] A flexural engagement type gear device according to still another embodiment of the present invention includes: an oscillation body; an outer gear that is flexurally deformed by the oscillation body; a first inner gear that meshes with the outer gear; and a second inner gear that is arranged axially with the first inner gear and meshes with the outer gear, wherein,

[0018] The first inner gear has a first inner tooth portion that meshes with the outer gear,

[0019] The first inner tooth portion has a first maximum tooth thickness portion where the tooth thickness is the largest and a first inner tooth thickness reduction portion that extends from the first maximum tooth thickness portion toward the axial inner side and whose tooth thickness decreases as it goes toward the axial inner side,

[0020] The first inner tooth thickness reduction portion has an outer region and an inner region within the meshing range with the outer gear. The inner region is provided axially inner of the outer region and the reduction ratio of the tooth thickness is greater than that of the outer region,

[0021] The boundary between the outer region and the inner region is a portion where the rate of change of the reduction ratio of the tooth thickness is discontinuous, and the axial length of the outer region is greater than the axial length of the inner region.

[0022] Another embodiment of the present invention relates to a flexure engagement type gear device including: an oscillation body; an external gear that is flexurally deformed by the oscillation body; a first internal gear that meshes with the external gear; and a second internal gear that is arranged axially with the first internal gear and meshes with the external gear, wherein,

[0023] the first internal gear has a first internal tooth portion that meshes with the external gear,

[0024] the first internal tooth portion has a first maximum tooth thickness portion with the maximum tooth thickness and a first inner tooth thickness decreasing portion that extends from the first maximum tooth thickness portion toward the axial inner side and whose tooth thickness decreases as it goes toward the axial inner side,

[0025] between the inner end of the meshing range of the first internal tooth portion and the external gear and the first maximum tooth thickness portion, the tooth thickness reduction ratio of the first inner tooth thickness decreasing portion in the 1 / 3 range on the axial inner side is 2.5 times or more the tooth thickness reduction ratio of the first inner tooth thickness decreasing portion in the 2 / 3 range on the axial outer side.

[0026] According to the present invention, there is provided a flexure engagement type gear device capable of suppressing a reduction in tooth life and improving torsional rigidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a cross-sectional view showing the flexure engagement type gear device according to the first embodiment.

[0028] Figure 2 is for explaining Figure 1 the shapes of the external gear, the first internal gear, and the second internal gear.

[0029] Figure 3 is showing Figure 1 the tooth thickness reduction ratio and the change rate of the reduction ratio of the external gear.

[0030] Figure 4 is for explaining Figure 1 the shapes of the external gear, the first internal gear, and the second internal gear.

[0031] Figure 5 is showing Figure 1 the outer diameter reduction ratio and the change rate of the reduction ratio of the external gear.

[0032] Figure 6 is a view for explaining the shapes of the external gear, the first internal gear, and the second internal gear of the flexure engagement type gear device according to the second embodiment.

[0033] Figure 7This is a diagram showing the shapes of the external gear, the first internal gear, and the second internal gear of the flexure engagement type gear device according to the second embodiment.

[0034] Figure 8 This is a diagram showing the shapes of the external gear, the first internal gear, and the second internal gear of the flexure engagement type gear device according to the third embodiment.

[0035] In the figure: 4 - external gear, 4a - first external tooth part, 4b - second external tooth part, 4a1 - first maximum tooth thickness part, 4a2 - first inner tooth thickness reduction part, 4a2i - inner region, 4a2o - outer region, 4a3 - first outer tooth thickness reduction part, 4a4 - first additional inner region, 4b1 - second maximum tooth thickness part, 4b2 - second inner tooth thickness reduction part, 4b2i - inner region, 4b2o - outer region, 4b3 - second outer tooth thickness reduction part, 4b4 - second additional inner region, 4a6 - first maximum outer diameter part, 4a7 - first inner outer diameter reduction part, 4a7i - inner region, 4a7o - outer region, 4a8 - first outer outer diameter reduction part, 4a9 - first additional inner region, 4b6 - second maximum outer diameter part, 4b7 - second inner outer diameter reduction part, 4b7i - inner region, 4b7o - outer region, 4b8 - second outer outer diameter reduction part, 4b9 - second additional inner region, 6 - first internal gear, 6a - first inner tooth part, 6a1 - first maximum tooth thickness part, 6a2 - first inner tooth thickness reduction part, 6a2i - inner region, 6a2o - outer region, 6a3 - first outer tooth thickness reduction part, 6a6 - first maximum outer diameter part, 6a7 - first inner outer diameter reduction part, 6a7i - inner region, 6a7o - outer region, 6a8 - first outer outer diameter reduction part, 8 - second internal gear, 8a - second inner tooth part, 8a1 - second maximum tooth thickness part, 8a2 - second inner tooth thickness reduction part, 8a2i - inner region, 8a2o - outer region, 8a3 - second outer tooth thickness reduction part, 8a6 - second maximum outer diameter part, 8a7 - second inner outer diameter reduction part, 8a7i - inner region, 8a7o - outer region, 8a8 - second outer outer diameter reduction part, R - rotation axis, 22a - vibration generating body, 100 - flexure engagement type gear device. Detailed Embodiments

[0036] Hereinafter, with reference to the accompanying drawings, each embodiment of the present invention will be described in detail. In each drawing, the same or equivalent components, parts, and processes are denoted by the same reference numerals, and repeated descriptions are appropriately omitted. Also, for ease of understanding, in each drawing, the dimensions of the components are appropriately enlarged or reduced. Further, in each drawing, a part of the components that are not important for explaining the embodiment is omitted.

[0037] (First Embodiment)

[0038] Figure 1 This is a cross-sectional view showing the flexure engagement type gear device 100 according to the first embodiment. The flexure engagement type gear device 100 decelerates the input rotation and then outputs it. The flexure engagement type gear device 100 is a so-called flat type flexure engagement type gear device, which includes: a wave generator 2; an external gear 4 that is flexurally deformed by the wave generator 2; a first internal gear 6 that meshes with the external gear 4; a second internal gear 8 that is arranged (adjacent) in the axial direction to the first internal gear 6 and meshes with the external gear 4; a housing 10; a first restricting member 12; a second restricting member 14; a main bearing 16; a first bearing housing 18; and a second bearing housing 20. A lubricant (such as grease) is enclosed in the flexure engagement type 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 and various bearings, etc.

[0039] The wave generator 2 includes: an oscillating body shaft 22; a first oscillating body bearing 21a disposed between the oscillating body shaft 22 and the external gear 4 (the first external tooth portion 4a); and a second oscillating body bearing 21b disposed between the oscillating body shaft 22 and the external gear 4 (the second external tooth portion 4b). The first oscillating body bearing 21a includes: a plurality of first rolling elements 24a; a first retainer 26a that holds the plurality of first rolling elements 24a; and a first outer ring member 28a that is embedded in the external gear 4. The second oscillating body bearing 21b includes: a plurality of second rolling elements 24b; a second retainer 26b that holds the plurality of second rolling elements 24b; and a second outer ring member 28b that is embedded in the external gear 4. The oscillating body shaft 22 is an input shaft, which is connected to a rotational drive source such as a motor and rotates about the rotation axis R. On the oscillating body shaft 22, an oscillating body 22a having a substantially elliptical cross-section orthogonal to the rotation axis R is integrally formed.

[0040] The plurality of first rolling elements 24a each have a substantially cylindrical shape, and are circumferentially arranged at intervals in a state where their axial directions are substantially parallel to the direction of the rotation axis R. The first rolling elements 24a are held by the first retainer 26a so as to be freely rotatable, and roll on the outer peripheral surface 22b of the vibration generating body 22a. That is, the inner ring of the first vibration generating body bearing 21a is integrally formed with the outer peripheral surface 22b of the vibration generating body 22a, but is not limited thereto, and may also have a dedicated inner ring that is separate from the vibration generating body 22a. The structure of the second rolling elements 24b is the same as that of the first rolling elements 24a. The plurality of second rolling elements 24b are held by the second retainer 26b arranged in the axial direction with the first retainer 26a so as to be freely rotatable, and roll on the outer peripheral surface 22b of the vibration generating body 22a. That is, the inner ring of the second vibration generating body bearing 21b is integrally formed with the outer peripheral surface 22b of the vibration generating body 22a, but is not limited thereto, and may also have a dedicated inner ring that is separate from the vibration generating body 22a. Hereinafter, the first rolling elements 24a and the second rolling elements 24b may sometimes be collectively referred to as "rolling elements 24". Also, the first retainer 26a and the second retainer 26b may sometimes be collectively referred to as "retainer 26".

[0041] The first outer ring member 28a surrounds the plurality of first rolling elements 24a. The first outer ring member 28a has flexibility, and the vibration generating body 22a flexes it into an elliptical shape via the plurality of first rolling elements 24a. When the vibration generating body 22a (i.e., the vibration generating body shaft 22) rotates, the first outer ring member 28a continuously flexes and deforms in accordance with the shape of the vibration generating body 22a. The structure of the second outer ring member 28b is the same as that of the first outer ring member 28a. The second outer ring member 28b is formed separately from the first outer ring member 28a. Alternatively, the second outer ring member 28b may be formed integrally with the first outer ring member 28a. Hereinafter, the first outer ring member 28a and the second outer ring member 28b may sometimes be collectively referred to as "outer ring member 28".

[0042] The external gear 4 is a flexible annular member, and the vibration generating body 22a, the rolling elements 24, and the outer ring member 28 are embedded inside it. The external gear 4 is fitted with the vibration generating body 22a, the rolling elements 24, and the outer ring member 28, and thus is flexed into an elliptical shape. When the vibration generating body 22a rotates, the external gear 4 continuously flexes and deforms in accordance with the shape of the vibration generating body 22a. The external gear 4 includes a first external tooth portion 4a located outside the first outer ring member 28a, a second external tooth portion 4b located outside the second outer ring member 28b, and a base material 4c. The first external tooth portion 4a and the second external tooth portion 4b are formed on a single base material (i.e., the base material 4c), and have the same number of teeth.

[0043] The first internal gear 6 is a rigid annular member, and a first internal tooth portion 6a is formed on its inner circumference. The first internal tooth portion 6a surrounds the first external tooth portion 4a of the outer gear 4 flexed into an elliptical shape, and meshes with a specified region (two regions) near the major axis of the vibration 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.

[0044] 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 member, and a second internal tooth portion 8a is formed on its inner circumference. The second internal tooth portion 8a surrounds the second external tooth portion 4b of the outer gear 4 flexed into an elliptical shape, and meshes with a specified region (two regions) near the major axis of the vibration 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 outer gear 4).

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

[0046] The housing 10 is a substantially cylindrical member, which surrounds the second internal gear 8. The first internal gear 6 is snap-fitted into the housing 10 and integrated therewith by bolts (not shown). A main bearing 16 is disposed between the housing 10 and the second internal gear 8. In the present embodiment, the main bearing 16 is a crossed roller bearing, which includes a plurality of rollers (rolling elements) 46 arranged at intervals in the circumferential direction. 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 as to be relatively rotatable. In addition, the type of the bearing of the main bearing 16 is not particularly limited, and for example, it may also be a four-point contact ball bearing.

[0047] The first bearing housing 18 is an annular member and surrounds the oscillation body shaft 22. Similarly, the second bearing housing 20 is an annular member and surrounds the oscillation body shaft 22. The first bearing housing 18 and the second bearing housing 20 are arranged to sandwich the external gear 4, the rolling elements 24, the cage 26, the outer ring member 28, the first restricting member 12, and the second restricting member 14 in the axial direction. The first bearing housing 18 is snap-fitted to the first internal gear 6 and fixed to the first internal gear 6 by bolts. The second bearing housing 20 is snap-fitted to the second internal gear 8 and fixed to the second internal gear 8 by bolts. A bearing 30 is assembled to the inner periphery of the first bearing housing 18, and a bearing 32 is assembled to the inner periphery of the second bearing housing 20. The oscillation body shaft 22 is supported by the first bearing housing 18 and the second bearing housing 20 via the bearing 30 and the bearing 32 so as to be rotatable relative to the first bearing housing 18 and the second bearing housing 20.

[0048] An oil seal 40 is disposed between the oscillation 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 housing 10, an oil seal 42 is disposed between the 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 oscillation body shaft 22. Thus, leakage of the lubricant within the flexure engagement type gear device 100 can be suppressed.

[0049] The operation of the flexure engagement type gear device 100 configured as described above will be described. Here, a case where the number of teeth of the first external tooth portion 4a is 100, the number of teeth of the second external tooth portion 4b is 100, the number of teeth of the first internal tooth portion 6a is 102, and the number of teeth of the second internal tooth portion 8a is 100 will be exemplified. Also, a case where the second internal gear 8 and the second bearing housing 20 are connected to a driven member will be exemplified.

[0050] If the oscillation body shaft 22 rotates in a state where the first external tooth portion 4a meshes with the first internal tooth portion 6a at two positions in the major axis direction of the elliptical shape of the first external tooth portion 4a, the meshing position of the first external tooth portion 4a and the first internal tooth portion 6a also moves circumferentially. Since the number of teeth of the first external tooth portion 4a and the first internal tooth portion 6a is different, the first external tooth portion 4a rotates relative to the first internal tooth portion 6a. Since the first internal gear 6 and the first bearing housing 18 are in a fixed state, the first external tooth portion 4a rotates by an amount corresponding to the difference in the number of teeth. That is, the rotation of the oscillation body shaft 22 is significantly decelerated and output to the first external tooth portion 4a. The reduction ratio is as follows.

[0051] Reduction ratio = (Number of teeth of the first external tooth portion 4a - Number of teeth of the first internal tooth portion 6a) / Number of teeth of the first external tooth portion 4a

[0052] =(100 - 102) / 100

[0053] =-1 / 50

[0054] Since the second external tooth part 4b and the first external tooth part 4a are integrally formed, the second external tooth part 4b rotates integrally with the first external tooth part 4a. Since the number of teeth of the second external tooth part 4b is the same as that of the second internal tooth part 8a, no relative rotation occurs, and the second external tooth part 4b rotates integrally with the second internal tooth part 8a. Therefore, the same rotation as the self-rotation of the first external tooth part 4a is output to the second internal tooth part 8a. As a result, an output that decelerates the rotation of the oscillation body shaft 22 to -1 / 50 can be output from the second internal gear 8.

[0055] Next, the structures of the external gear 4, the first internal gear 6, and the second internal gear 8 will be described in further detail.

[0056] <Tooth line shape>

[0057] Figure 2 is for explaining Figure 1 the tooth line shapes of the external gear, the first internal gear, and the second internal gear. Figure 2 is a cross-sectional view when the external gear 4, the first internal gear 6, and the second internal gear 8 are cut by an imaginary cylinder passing through the pitch circle of the external gear 4. In Figure 2 two internal teeth adjacent to one external tooth of the external gear 4 in the circumferential direction are shown. For ease of understanding, Figure 2 a state in which the first internal tooth part 6a and the second internal tooth part 8a are slid in the circumferential direction to move away from the external gear 4 is shown, and in Figure 2 the shape of the tooth surface of the tooth part is exaggeratedly depicted. In Figure 2 the horizontal axis is the position in the axial direction from a certain reference position. The vertical axis represents the dimension in the circumferential direction. That is, it can also be said that the vertical axis represents the tooth thickness of the external tooth of the external gear 4. And in Figure 2 the plane P1 represents the plane perpendicular to the rotation axis R ( Figure 2An imaginary plane that is orthogonal (not shown in the figure) and passes through the axial center of the meshing range Wa between the first external tooth part 4a and the first internal tooth part 6a. In the present embodiment, the axial length of the first internal tooth part 6a is shorter than the axial length of the first external tooth part 4a, and the entire axial range of the first internal tooth part 6a meshes with the first external tooth part 4a. Therefore, the axial length of the meshing range Wa between the first external tooth part 4a and the first internal tooth part 6a is equal to the axial length of the first internal tooth part 6a, and the plane P1 passes through the axial center of the first internal tooth part 6a. And, the plane P2 represents an imaginary plane that is orthogonal to the rotation axis R and passes through the axial center of the meshing range Wb between the second external tooth part 4b and the second internal tooth part 8a. In the present embodiment, the axial length of the second internal tooth part 8a is shorter than the axial length of the second external tooth part 4b, and the entire axial range of the second external tooth part 4b meshes with the second external tooth part 4b. Therefore, the axial length of the meshing range Wb between the second external tooth part 4b and the second internal tooth part 8a is equal to the axial length of the second internal tooth part 8a, and the plane P2 passes through the axial center of the second internal tooth part 8a.

[0058] The first external tooth part 4a has, in the axial direction: a first tooth thickness maximum part 4a1, which has the maximum tooth thickness; and a first inner tooth thickness decreasing part 4a2, which extends from the first tooth thickness maximum part 4a1 toward the axial inner side (i.e., toward the direction close to the center between the first external tooth part 4a and the second external tooth part 4b) and whose tooth thickness decreases as it extends toward the axial inner side.

[0059] The first tooth thickness maximum part 4a1 is located within the meshing range Wa between the first external tooth part 4a and the first internal tooth part 6a in the axial direction, and is located at a position more outward than the axial center (P1) of the meshing range Wa. The first tooth thickness maximum part 4a1 can be a point or have a length in the axial direction.

[0060] The first inner tooth thickness decreasing part 4a2 has an outer region 4a2o on the axial outer side and an inner region 4a2i provided on the axial inner side of the outer region 4a2o within the meshing range Wa with the first internal tooth part 6a, and the decreasing ratio of the tooth thickness in the inner region 4a2i is greater than that in the outer region 4a2o. The boundary E1 between the outer region 4a2o and the inner region 4a2i is a part where the change rate of the decreasing ratio of the tooth thickness is discontinuous. The axial length of the outer region 4a2o is greater than the axial length of the inner region 4a2i.

[0061] As described above, since the first inner tooth thickness reduction portion 4a2 exists, one-end contact loads generated at the inner tooth width ends of the first outer tooth portion 4a and the first inner tooth portion 6a can be reduced, thereby reducing excessive wear of the gear. Further, since the first inner tooth thickness reduction portion 4a2 includes an outer region 4a2o and an inner region 4a2i having the above-described tooth thickness reduction ratio, the tooth thickness can be continuously reduced to the inner tooth width end, and reduction of the tooth thickness at the center of the tooth width can be suppressed. Therefore, the rigidity of the external gear 4 is increased, and the torsional rigidity of the flexure engagement type gear device 100 is increased. Further, by means of the inner region 4a2i in which the change rate of the tooth thickness reduction ratio is not continuously changed, the above-described increase in rigidity can be achieved, and an increase in tooth surface pressure within the inner region of the engagement range Wa can be suppressed. The tooth surface pressure generated in this region includes elements that promote pitting fatigue of the first outer tooth portion 4a and the first inner tooth portion 6a. Therefore, by suppressing the increase in the tooth surface pressure, reduction of the pitting life of the tooth surface can be suppressed.

[0062] Here, the boundary E1 between the outer region 4a2o and the inner region 4a2i is a portion where the change rate of the tooth thickness reduction ratio is discontinuous. Figure 3 represents Figure 1 a graph of the tooth thickness reduction ratio and the change rate of the reduction ratio of the external gear. The tooth thickness refers to the distance from the tooth thickness center plane S4 to the tooth surface. As Figure 3 shown in the "reduction ratio" curve graph, the tooth thickness reduction ratio of the first inner tooth thickness reduction portion 4a2 is continuous and becomes larger as it approaches the inner side in the axial direction. Further, as shown in the "change rate of the reduction ratio" curve graph, the change rate of the reduction ratio is discontinuous at the boundary E1. Note that the discontinuity of the change rate of the reduction ratio is not limited to a complete discontinuity, and includes a case where the change rate changes stepwise. The stepwise change can be defined, for example, as a case where a change rate difference of Δy or more is included between one end and the other end of a minute interval Δx in the axial direction. The minute interval Δx is set to an interval of 5% of the total axial length of the inner region 4a2i and the outer region 4a2o, and the difference Δy is set to 30% of the difference between the maximum value and the minimum value of the change rate on the inner region 4a2i and the outer region 4a2o.

[0063] Next, the detailed shape of the first outer tooth portion 4a will be further described. As Figure 2As shown, the first external tooth portion 4a has a first additional inner region 4a4 with tooth thickness from the inner end of the meshing range Wa to the axial center of the external gear 4, and the axial length of the outer region 4a2o can be greater than the sum of the axial lengths of the inner region 4a2i and the first additional inner region 4a4. According to this structure, it is possible to improve the rigidity of the external gear 4 corresponding to the spacing between the first internal tooth portion 6a and the second internal tooth portion 8a and to improve the pitting resistance life of each tooth surface. The first additional inner region 4a4 can have a decreasing ratio of tooth thickness continuous with the inner region 4a2i, or its tooth thickness can be constant near the axial center of the external gear 4 or increase as it approaches the center. The first additional inner region 4a4 can overlap with a part of the first inner tooth thickness reduction portion 4a2.

[0064] The decreasing ratio of the inner region 4a2i can be 2.5 times or more, preferably 3.1 times or more, of the decreasing ratio of the outer region 4a2o. According to this structure, it is possible to suppress the reduction of the pitting resistance life of the first external tooth portion 4a and the first internal tooth portion 6a, and to further improve the rigidity of the external gear 4. Here, regarding the decreasing ratio of the tooth thickness in any region in the axial direction, this decreasing ratio is defined as "(the difference in tooth thickness between one end and the other end of the above region) / (the axial length of the above region from one end to the other end)". Therefore, the decreasing ratio of the tooth thickness of the outer region 4a2o corresponds to the slope of the line segment q1 between point p1 and point p2. The decreasing ratio of the tooth thickness of the inner region 4a2i corresponds to the slope of the line segment q2 between point p2 and point p3. In addition, the above Figure 3 The decreasing ratio shown represents the decreasing ratio at each point in the axial direction. When calculating the decreasing ratio of the tooth thickness and the change rate of the decreasing ratio, it is only necessary to first find the decrease amount of the tooth thickness at each position with a certain interval in the axial direction and then calculate the decreasing ratio and the change rate of the decreasing ratio between the above positions based on the decrease amounts obtained at each position. As an example of the above certain interval, an interval of 0.1 mm or 0.2 mm can be adopted.

[0065] The axial length of the outer region 4a2o can be 2 times or more of the axial length of the inner region 4a2i. According to this structure, it is possible to suppress the reduction of the pitting resistance life of the first external tooth portion 4a and the first internal tooth portion 6a, and to further improve the rigidity of the external gear 4.

[0066] The curve representing the tooth trace shape of the inner region 4a2i and the curve representing the tooth trace shape of the outer region 4a2o can be curves represented by different functions.

[0067] In addition, between the inner end (point p3) of the meshing range Wa of the first internal gear 6 and the first tooth thickness maximum portion 4a1 of the first external tooth portion 4a, the reduction ratio of the tooth thickness of the first inner tooth thickness reduction portion 4a2 in the axially inner 1 / 3 range T1 can be 2.5 times or more, preferably 3.1 times or more, the reduction ratio of the tooth thickness of the first inner tooth thickness reduction portion 4a2 in the axially outer 2 / 3 range T2. By adopting this structure, it is also possible to reduce the one-end contact load generated at the inner tooth width end portions of the first external tooth portion 4a and the first internal gear portion 6a, thereby reducing excessive wear of the gear. Moreover, by reducing the tooth thickness in the axially outer 2 / 3 range T2, the tooth thickness can be continuously reduced to the inner tooth width end portion, and the reduction of the tooth thickness at the center of the tooth width can be suppressed, thereby improving the rigidity of the external gear 4. Therefore, the torsional rigidity of the flexural meshing type gear device 100 is improved. Moreover, by reducing the tooth thickness in the axially inner 1 / 3 range T1, the above-mentioned improvement in rigidity can be achieved, and the increase in tooth surface pressure in the inner region of the meshing range Wa can be suppressed. The tooth surface pressure generated in this region includes elements that promote pitting fatigue of the first external tooth portion 4a and the first internal gear portion 6a. Therefore, by suppressing the increase in the above-mentioned tooth surface pressure, the reduction of the pitting life of the tooth surface can be suppressed.

[0068] Moreover, the first external tooth portion 4a may further include a first outer tooth thickness reduction portion 4a3 that extends axially outward (i.e., in a direction away from the center between the first external tooth portion 4a and the second external tooth portion 4b) from the first tooth thickness maximum portion 4a1 and whose tooth thickness decreases as it extends axially outward. According to this structure, it is possible to reduce the one-end contact load generated at the outer tooth width end portions of the first external tooth portion 4a and the first internal gear portion 6a, thereby reducing excessive wear of the gear also at the outer tooth width end portions.

[0069] <Tooth line shape of the second external tooth portion 4b>

[0070] As Figure 2 shown, the second external tooth portion 4b includes, in the axial direction: a second tooth thickness maximum portion 4b1, which has the maximum tooth thickness; a second inner tooth thickness reduction portion 4b2, which extends axially inward (i.e., in a direction closer to the center between the first external tooth portion 4a and the second external tooth portion 4b) from the second tooth thickness maximum portion 4b1 and whose tooth thickness decreases as it extends axially inward; and a second outer tooth thickness reduction portion 4b3, which extends axially outward (i.e., in a direction away from the center between the first external tooth portion 4a and the second external tooth portion 4b) from the second tooth thickness maximum portion 4b1 and whose tooth thickness decreases as it extends axially outward.

[0071] The second inner tooth thickness reduction portion 4b2 has an axially outer outer region 4b2o and an inner region 4b2i provided axially inward of the outer region 4b2o and having a greater tooth thickness reduction ratio than the outer region 4b2o within the meshing range Wb with the second inner tooth portion 8a. The boundary E2 between the outer region 4b2o and the inner region 4b2i is a portion where the rate of change of the tooth thickness reduction ratio is discontinuous.

[0072] Moreover, the second inner tooth thickness reduction portion 4b2 further includes a second additional inner region 4b4 having a tooth thickness from the inner end of the meshing range Wb to the axial center of the external gear 4.

[0073] Each component of the second external tooth portion 4b (the second tooth thickness maximum portion 4b1, the second inner tooth thickness reduction portion 4b2, the second outer tooth thickness reduction portion 4b3, the meshing range Wb between the second external tooth portion 4b and the second inner tooth portion 8a, the outer region 4b2o, the inner region 4b2i, and the second additional inner region 4b4) may have the same characteristics and the relationships between the components as those of each component of the first external tooth portion 4a (the first tooth thickness maximum portion 4a1, the first inner tooth thickness reduction portion 4a2, the first outer tooth thickness reduction portion 4a3, the meshing range Wa between the first external tooth portion 4a and the first inner tooth portion 6a, the outer region 4a2o, the inner region 4a2i, and the first additional inner region 4a4). By having the same characteristics or the same relationships, the same effects are obtained at the meshing portion between the second external tooth portion 4b and the second inner tooth portion 8a.

[0074] In addition, the first external tooth portion 4a in the first embodiment corresponds to an example of the first external tooth portion according to the present invention, but it can also be regarded that the second external tooth portion 4b in the first embodiment corresponds to an example of the first external tooth portion according to the present invention.

[0075] <Tooth tip shape>

[0076] Figure 4 is a diagram for explaining Figure 1 the tooth tip shapes of the external gear, the first internal gear, and the second internal gear. Figure 4 shows the tooth tips of the first external tooth portion 4a and the second external tooth portion 4b, and the tooth tips of the first internal tooth portion 6a and the second internal tooth portion 8a when viewed in the circumferential direction. In Figure 4 for ease of understanding, a state is shown in which the tooth tips of the first internal tooth portion 6a and the second internal tooth portion 8a are slid radially outward to move away from the external gear 4. In Figure 4 the horizontal axis is the axial position from a certain reference position. The vertical axis represents the radial dimension. And in Figure 4 the center line C1 represents the rotation axis R ( Figure 3a line that is orthogonal (not shown in the figure) and passes through the axial center of the meshing range Wa between the first external tooth portion 4a and the first internal tooth portion 6a. In the present embodiment, the axial length of the first internal tooth portion 6a is shorter than the axial length of the first external tooth portion 4a, and the entire axial range of the first internal tooth portion 6a meshes with the first external tooth portion 4a. Therefore, the axial length of the meshing range Wa between the first external tooth portion 4a and the first internal tooth portion 6a is equal to the axial length of the first internal tooth portion 6a, and the center line C1 passes through the axial center of the tooth tip of the first internal tooth portion 6a. And, the center line C2 represents a line that is orthogonal to the rotation axis R and passes through the axial center of the meshing range Wb between the second external tooth portion 4b and the second internal tooth portion 8a. In the present embodiment, the axial length of the second internal tooth portion 8a is shorter than the axial length of the second external tooth portion 4b, and the entire axial range of the second external tooth portion 4b meshes with the second external tooth portion 4b. Therefore, the axial length of the meshing range Wb between the second external tooth portion 4b and the second internal tooth portion 8a is equal to the axial length of the second internal tooth portion 8a, and the center line C2 passes through the axial center of the tooth tip of the second internal tooth portion 8a.

[0077] The first external tooth portion 4a has, in the axial direction: a first maximum outer diameter portion 4a6, which has the maximum outer diameter; and a first inner side outer diameter reducing portion 4a7, which extends from the first maximum outer diameter portion 4a6 toward the axial inner side (i.e., toward the direction close to the center between the first external tooth portion 4a and the second external tooth portion 4b) and whose outer diameter decreases as it goes toward the axial inner side.

[0078] The first maximum outer diameter portion 4a6 is located in the meshing range Wa between the first external tooth portion 4a and the first internal tooth portion 6a in the axial direction, and is located at a position more outside than the axial center (C1) of the meshing range Wa. The first maximum outer diameter portion 4a6 can be a point or have a length in the axial direction.

[0079] The first inner side outer diameter reducing portion 4a7 has an outer side region 4a7o on the axial outer side and an inner side region 4a7i provided on the axial inner side of the outer side region 4a7o within the meshing range Wa with the first internal tooth portion 6a, and the reduction ratio of the outer diameter in the inner side region 4a7i is greater than that in the outer side region 4a7o. The boundary E6 between the outer side region 4a7o and the inner side region 4a7i is a part where the change rate of the reduction ratio of the outer diameter is discontinuous. The axial length of the outer side region 4a7o is greater than the axial length of the inner side region 4a7i.

[0080] As described above, due to the presence of the first inner outer diameter reduction portion 4a7, it is possible to reduce the one-end contact load generated at the inner tooth width end portions of the first outer tooth portion 4a and the first inner tooth portion 6a, thereby reducing excessive wear of the gear. Moreover, since the first inner outer diameter reduction portion 4a7 includes an outer region 4a7o and an inner region 4a7i having the above-described outer diameter reduction ratio, the outer diameter can be continuously reduced to the inner tooth width end portion, and the reduction of the outer diameter at the center of the tooth width can be suppressed. Therefore, the rigidity of the external gear 4 is improved, and the torsional rigidity of the flexure engagement type gear device 100 is improved. Further, through the inner region 4a7i in which the change rate of the outer diameter reduction ratio is not continuously changed, the above-described improvement in rigidity can be achieved, and the increase in tooth surface pressure within the inner region of the meshing range Wa can be suppressed. The tooth surface pressure generated in this region includes elements that promote pitting fatigue of the first outer tooth portion 4a and the first inner tooth portion 6a. Therefore, by suppressing the increase in the above-described tooth surface pressure, the reduction of the pitting life of the tooth surface can be suppressed.

[0081] Here, the boundary E6 between the outer region 4a2o and the inner region 4a2i is a portion where the change rate of the outer diameter reduction ratio is discontinuous. Figure 5 represents Figure 1 a graph of the outer diameter reduction ratio and the change rate of the reduction ratio of the external gear. As Figure 5 shown in the "outer diameter reduction ratio" curve graph, the outer diameter reduction ratio of the first inner outer diameter reduction portion 4a7 is continuous and becomes larger as it approaches the inner side in the axial direction. Moreover, as shown in the "change rate of the reduction ratio" curve graph, the change rate of the reduction ratio is discontinuous at the boundary E6. In addition, the discontinuity of the change rate of the reduction ratio is not limited to being completely discontinuous, and also includes cases where the change rate changes in a stepwise manner. The stepwise change can be defined, for example, as a case where the difference in the change rate is Δy or more between one end and the other end of a minute interval Δx in the axial direction. The minute interval Δx is set to an interval of 5% of the total axial length of the inner region 4a7i and the outer region 4a7o, and the difference Δy is set to 30% of the difference between the maximum value and the minimum value of the change rate on the inner region 4a7i and the outer region 4a7o. Further, when calculating the outer diameter reduction ratio and the change rate of the reduction ratio, it is sufficient to first calculate the reduction amount of the outer diameter at each position having a certain interval in the axial direction and then calculate the reduction ratio and the change rate of the reduction ratio between the above-described positions based on the calculated reduction amounts at each position. As an example of the above-described certain interval, an interval of 0.1 mm or 0.2 mm can be adopted.

[0082] Next, the detailed shape of the first outer tooth portion 4a will be further described. As Figure 4As shown, the first external tooth part 4a has a first additional inner region 4a9 with an outer diameter from the inner end of the meshing range Wa to the axial center of the external gear 4. The axial length of the outer region 4a7o can be greater than the sum of the axial lengths of the inner region 4a7i and the first additional inner region 4a9. According to this structure, it is possible to improve the rigidity of the external gear 4 corresponding to the spacing distance from the first internal tooth part 6a and the second internal tooth part 8a, and to improve the pitting resistance life of each tooth surface. The first additional inner region 4a9 can have a decreasing ratio of the outer diameter continuous with the inner region 4a7i, or its outer diameter can be constant near the axial center of the external gear 4 or increase as it approaches the center. The first additional inner region 4a9 can overlap with a part of the first inner outer diameter reducing part 4a7.

[0083] The decreasing ratio of the inner region 4a7i can be 2.5 times or more, preferably 3.1 times or more, of the decreasing ratio of the outer region 4a7o. According to this structure, it is possible to suppress the reduction of the pitting resistance life of the first external tooth part 4a and the first internal tooth part 6a, and to further improve the rigidity of the external gear 4. Here, regarding the decreasing ratio of the outer diameter of any region in the axial direction, this decreasing ratio is defined as "(the difference between the outer diameter at one end and the outer diameter at the other end of the above region) / (the axial length of the above region from one end to the other end)". Therefore, the decreasing ratio of the outer diameter of the outer region 4a7o corresponds to the slope of the line segment q5 between point p5 and point p6. The decreasing ratio of the outer diameter of the inner region 4a7i corresponds to the slope of the line segment q6 between point p6 and point p7. In addition, the above Figure 5 The shown decreasing ratio represents the decreasing ratio at each point in the axial direction.

[0084] The axial length of the outer region 4a7o can be 2 times or more of the axial length of the inner region 4a7i. According to this structure, it is possible to suppress the reduction of the pitting resistance life of the first external tooth part 4a and the first internal tooth part 6a, and to further improve the rigidity of the external gear 4.

[0085] The curve representing the tip shape of the inner region 4a7i and the curve representing the tip shape of the outer region 4a7o can be curves represented by different functions.

[0086] In addition, between the inner end (point p7) of the meshing range Wa of the first internal gear 6 and the first outer diameter maximum portion 4a6 of the first external tooth portion 4a, the reduction ratio of the outer diameter of the first inner outer diameter reduction portion 4a7 in the 1 / 3 range T5 on the axial inner side can be 2.5 times or more, preferably 3.1 times or more, of the reduction ratio of the outer diameter of the first inner outer diameter reduction portion 4a7 in the 2 / 3 range T6 on the axial outer side. By adopting this structure, it is also possible to reduce the one-end contact load generated at the inner tooth width end portions of the first external tooth portion 4a and the first internal gear portion 6a, thereby reducing excessive wear of the gear. Moreover, by reducing the outer diameter in the 2 / 3 range T6 on the axial outer side, the outer diameter can be continuously reduced to the inner tooth width end portion, and the reduction of the outer diameter at the center of the tooth width can be suppressed, thereby improving the rigidity of the external gear 4. Therefore, the torsional rigidity of the flexural meshing type gear device 100 is improved. Moreover, by reducing the outer diameter in the 1 / 3 range T5 on the axial inner side, the above-mentioned improvement in rigidity can be achieved, and the rise in tooth surface pressure in the region inside the meshing range Wa can be suppressed. The tooth surface pressure generated in this region includes elements that promote pitting fatigue of the first external tooth portion 4a and the first internal gear portion 6a. Therefore, by suppressing the rise in the above-mentioned tooth surface pressure, the reduction of the pitting life of the tooth surface can be suppressed.

[0087] Moreover, the first external tooth portion 4a may further include a first outer outer diameter reduction portion 4a8 that extends from the first outer diameter maximum portion 4a6 toward the axial outer side (i.e., toward the direction away from the center between the first external tooth portion 4a and the second external tooth portion 4b) and whose outer diameter decreases as it extends toward the axial outer side. According to this structure, it is possible to reduce the one-end contact load generated at the outer tooth width end portions of the first external tooth portion 4a and the first internal gear portion 6a, thereby reducing excessive wear of the gear also at the outer tooth width end portions.

[0088] In addition, the first external tooth portion 4a has the above-mentioned tooth line shape, but may not have the above-mentioned tooth tip shape. For example, the tooth tip shape may be flat, or may have other concavities and convexities and / or other curved shapes. In this case, the effects based on the tooth thickness shown in the description of the tooth line shape can also be obtained.

[0089] <Tooth tip shape of the second external tooth portion 4b>

[0090] As Figure 4 shown, the second external tooth portion 4b includes, in the axial direction: a second outer diameter maximum portion 4b6, which has the largest outer diameter; a second inner outer diameter reduction portion 4b7, which extends from the second outer diameter maximum portion 4b6 toward the axial inner side (i.e., toward the direction close to the center between the first external tooth portion 4a and the second external tooth portion 4b) and whose outer diameter decreases as it extends toward the axial inner side; and a second outer outer diameter reduction portion 4b8, which extends from the second outer diameter maximum portion 4b6 toward the axial outer side (i.e., toward the direction away from the center between the first external tooth portion 4a and the second external tooth portion 4b) and whose outer diameter decreases as it extends toward the radial outer side.

[0091] The second inner outer diameter reducing portion 4b7 has an outer region 4b7o on the axially outer side within the meshing range Wb with the second inner tooth portion 8a and an inner region 4b7i provided on the axially inner side of the outer region 4b7o and having a greater ratio of reduction in outer diameter than the outer region 4b7o. The boundary E7 between the outer region 4b7o and the inner region 4b7i is a portion where the rate of change of the ratio of reduction in outer diameter is discontinuous.

[0092] Moreover, the second inner outer diameter reducing portion 4b7 further includes a second additional inner region 4b9 having an outer diameter from the inner end of the meshing range Wb to the axial center of the external gear 4.

[0093] The above-described constituent elements of the second external tooth portion 4b (the second outer diameter maximum portion 4b6, the second inner outer diameter reducing portion 4b7, the second outer outer diameter reducing portion 4b8, the meshing range Wb between the second external tooth portion 4b and the second inner tooth portion 8a, the outer region 4b7o, the inner region 4b7i, and the second additional inner region 4b9) may have the same characteristics and the relationships between the constituent elements as those of the first external tooth portion 4a (the first outer diameter maximum portion 4a6, the first inner outer diameter reducing portion 4a7, the first outer outer diameter reducing portion 4a8, the meshing range Wa between the first external tooth portion 4a and the first inner tooth portion 6a, the outer region 4a7o, the inner region 4a7i, and the first additional inner region 4a9). By having the same characteristics or the same relationships, the same effects are also obtained at the meshing portion between the second external tooth portion 4b and the second inner tooth portion 8a.

[0094] In addition, the second external tooth portion 4b has the above-described tooth line shape, but may not have the above-described tooth tip shape. For example, the tooth tip shape may be flat or may have other irregularities and / or other curved shapes. In this case, the effects based on the tooth thickness shown in the description of the tooth line shape can also be obtained.

[0095] <Shape of the first inner tooth portion 6a and the second inner tooth portion 8a>

[0096] The tooth line shape of the first inner tooth portion 6a is a shape that is symmetric with respect to its tooth thickness center plane (not shown) and the tooth thickness is substantially constant in the axial direction. The tooth tip shape of the first inner tooth portion 6a is flat. Similarly, the tooth line shape of the second inner tooth portion 8a is a shape that is symmetric with respect to its tooth thickness center plane (not shown) and the tooth thickness is substantially constant in the axial direction. The tooth tip shape of the second inner tooth portion 8a is flat.

[0097] <Shape of the entire tooth>

[0098] The first external tooth portion 4a may have a shape that is symmetric with respect to the tooth thickness center plane S4 ( Figure 2)A symmetric shape may also include a partially asymmetric portion. The tooth thickness center plane S4 is a plane that contains the rotation axis R and passes through the thickest portion with the maximum tooth thickness in the central direction in the tooth thickness direction. Similarly, the second external tooth portion 4b may have a shape that is Figure 2 )symmetric with respect to the tooth thickness center plane S4, or may also include a partially asymmetric portion.

[0099] Moreover, in the description of the tooth line shape of the first external tooth portion 4a and the second external tooth portion 4b, the shape of the cylindrical cross-section along the pitch circle of the external gear 4 was described. However, on a cylindrical cross-section that is radially displaced from the cylindrical cross-section along the pitch circle, the first external tooth portion 4a and the second external tooth portion 4b also have the same tooth line shape. The same tooth line shape can similarly exist on cylindrical cross-sections with any radius from the tooth root to near the tooth tip, and may also include cylindrical cross-sections that do not have the same tooth line shape within a certain radius range. The cylindrical cross-section refers to a cross-section along a cylindrical surface centered on the rotation axis R.

[0100] In addition, in each of the reducing portions such as the first inner tooth thickness reducing portion 4a2, the first outer tooth thickness reducing portion 4a3, the second inner tooth thickness reducing portion 4b2, and the second outer tooth thickness reducing portion 4b3, both tooth surfaces are configured such that the reduction ratio of the distance between the tooth surface and the tooth thickness center plane S4 with respect to the axial direction satisfies the following formula.

[0101] Reduction ratio = Reduction amount of the distance between the tooth surface and the tooth thickness center (mm) / Movement amount in the axial direction (mm) ≤ 0.05 (Formula 1)

[0102] Among them, the reduction ratio of the distance between the tooth surface in the case of chamfering and the tooth thickness center plane S4 with respect to the axial direction generally satisfies the following formula.

[0103] Reduction amount of the distance between the tooth surface based on chamfering and the tooth thickness center plane S4 (mm) / Movement amount in the axial direction (mm) ≥ 0.5 (Formula 2)

[0104] Therefore, each tooth thickness reducing portion and the chamfering have different orders, and there is a clear difference between the two.

[0105] Moreover, each of the reducing portions such as the first inner outer diameter reducing portion 4a7, the first outer outer diameter reducing portion 4a8, the second inner outer diameter reducing portion 4b7, and the second outer outer diameter reducing portion 4b8 is configured such that the reduction ratio of the outer diameter with respect to the axial direction satisfies the following formula.

[0106] Reduction ratio = Reduction amount of the outer diameter (diameter) (mm) / Movement amount in the axial direction (mm) ≤ 0.1 (Formula 3)

[0107] Among them, the reduction ratio of the outer diameter in the case of chamfering with respect to the axial direction generally satisfies the following formula.

[0108] Reduction amount (mm) of the outer diameter (diameter) of the chamfer / Axial movement amount (mm) ≥ 1.15 (Equation 4)

[0109] Therefore, the reduction levels of the respective outer diameters are different from that of the chamfer, and there is a clear difference between the two.

[0110] (Second Embodiment)

[0111] Figure 6 It is a diagram for explaining the shapes of the external gear, the first internal gear, and the second internal gear of the flexure engagement type gear device according to the second embodiment. The difference between the second embodiment and the first embodiment is that the shapes of the first external tooth portion 4a, the second external tooth portion 4b, the first internal tooth portion 6a, and the second internal tooth portion 8a are different, while other components are the same as those in the first embodiment. Figure 6 in accordance with Figure 2 the method shows the shapes of the first external tooth portion 4a and the second external tooth portion 4b of the external gear 4, the first internal tooth portion 6a of the first internal gear 6, and the second internal tooth portion 8a of the second internal gear 8. In Figure 6 the central plane P0, the plane P1, the plane P2, and the tooth thickness center plane S4 are the same as those described in the first embodiment. The tooth thickness center plane S6 is a plane passing through the thickest portion with the maximum tooth thickness of the first internal tooth portion 6a in the tooth thickness direction and including the rotation axis R. The tooth thickness center plane S8 is a plane passing through the thickest portion with the maximum tooth thickness of the second internal tooth portion 8a in the tooth thickness direction and including the rotation axis R.

[0112] <Tooth trace shape>

[0113] The first internal tooth portion 6a has, in the axial direction: a first maximum tooth thickness portion 6a1, which has the maximum tooth thickness; and a first inner tooth thickness reduction portion 6a2, which extends from the first maximum tooth thickness portion 6a1 toward the axial inner side (i.e., toward the direction closer to the center between the first internal tooth portion 6a and the second internal tooth portion 8a) and whose tooth thickness decreases as it moves toward the axial inner side.

[0114] The first maximum tooth thickness portion 6a1 is located within the meshing range Wa between the first external tooth portion 4a and the first internal tooth portion 6a in the axial direction, and is located at a position more outward than the center (P1) of the meshing range Wa in the axial direction. The first maximum tooth thickness portion 6a1 can be a point or have a length in the axial direction.

[0115] The first inner tooth thickness reduction portion 6a2 has an outer region 6a2o on the axial outer side and an inner region 6a2i provided on the axial inner side of the outer region 6a2o within the meshing range Wa with the first external tooth portion 4a, and the tooth thickness reduction ratio of the inner region 6a2i is greater than that of the outer region 6a2o. The boundary E11 between the outer region 6a2o and the inner region 6a2i is a portion where the change rate of the tooth thickness reduction ratio is discontinuous. The axial length of the outer region 6a2o is greater than the axial length of the inner region 6a2i.

[0116] As described above, since there is the first inner tooth thickness reduction portion 6a2, it is possible to reduce the one-end contact load generated at the inner tooth width end portions of the first outer tooth portion 4a and the first inner tooth portion 6a, and thus it is possible to reduce excessive wear of the gear. Further, since the first inner tooth thickness reduction portion 6a2 includes an outer region 6a2o and an inner region 6a2i having the above-described tooth thickness reduction ratio, it is possible to continuously reduce the tooth thickness to the inner tooth width end portion and suppress the reduction of the tooth thickness at the center of the tooth width. Therefore, the rigidity of the first inner gear 6 is increased, and the torsional rigidity of the flexure engagement type gear device 100 is increased. Further, by the inner region 6a2i in which the change rate of the tooth thickness reduction ratio is not continuously changed, the above-described increase in rigidity can be achieved, and the tooth surface pressure rise in the inner region of the engagement range Wa can be suppressed. The tooth surface pressure generated in this region includes elements that promote pitting fatigue of the first outer tooth portion 4a and the first inner tooth portion 6a. Therefore, by suppressing the rise of the above-described tooth surface pressure, it is possible to suppress the reduction of the pitting life of the tooth surface.

[0117] The reduction ratio of the inner region 6a2i may be 2.5 times or more, preferably 3.1 times or more, the reduction ratio of the outer region 6a2o. According to this structure, it is possible to suppress the reduction of the pitting life of the first outer tooth portion 4a and the first inner tooth portion 6a, and further increase the rigidity of the first inner gear 6. The reduction ratio of the tooth thickness of the outer region 6a2o corresponds to the slope of the line segment q11 between the point p11 and the point p12. The reduction ratio of the tooth thickness of the inner region 6a2i corresponds to the slope of the line segment q12 between the point p12 and the point p13.

[0118] The axial length of the outer region 6a2o may be 2 times or more the axial length of the inner region 6a2i. According to this structure, it is possible to suppress the reduction of the pitting life of the first inner tooth portion 6a and the first outer tooth portion 4a, and further increase the rigidity of the first inner gear 6.

[0119] The curve representing the tooth line shape of the inner region 6a2i and the curve representing the tooth line shape of the outer region 6a2o may be curves represented by different functions.

[0120] In addition, between the inner end (point p12) of the meshing range Wa of the external gear 4 and the first maximum tooth thickness portion 6a1 of the first internal gear 6, the reduction ratio of the tooth thickness of the first inner tooth thickness reduction portion 6a2 in the axially inner 1 / 3 range T11 can be 2.5 times or more, preferably 3.1 times or more, the reduction ratio of the tooth thickness of the first inner tooth thickness reduction portion 6a2 in the axially outer 2 / 3 range T12. By adopting this structure, it is also possible to reduce the one-end contact load generated at the inner tooth width end portions of the first external tooth portion 4a and the first internal tooth portion 6a, thereby reducing excessive wear of the gear. Moreover, by reducing the tooth thickness in the axially outer 2 / 3 range T12, the tooth thickness can be continuously reduced to the inner tooth width end portion, and the reduction of the tooth thickness at the center of the tooth width can be suppressed, thereby improving the rigidity of the first internal gear 6. Therefore, the torsional rigidity of the flexural meshing type gear device 100 is improved. Moreover, by reducing the tooth thickness in the axially inner 1 / 3 range T11, the above-mentioned improvement in rigidity can be achieved, and the rise of the tooth surface pressure in the area inside the meshing range Wa can be suppressed. The tooth surface pressure generated in this area includes elements that promote pitting fatigue of the first external tooth portion 4a and the first internal tooth portion 6a. Therefore, by suppressing the rise of the above-mentioned tooth surface pressure, the reduction of the pitting life of the tooth surface can be suppressed.

[0121] Moreover, the first internal tooth portion 6a may further include a first outer tooth thickness reduction portion 6a3 that extends from the first maximum tooth thickness portion 6a1 toward the axially outer side (i.e., toward the direction away from the center between the first internal tooth portion 6a and the second internal tooth portion 8a) and whose tooth thickness decreases as it extends toward the axially outer side. According to this structure, it is possible to reduce the one-end contact load generated at the outer tooth width end portions of the first external tooth portion 4a and the first internal tooth portion 6a, thereby reducing excessive wear of the gear also at the outer tooth width end portions.

[0122] <Shape of tooth line of the second internal tooth portion 8a>

[0123] The second internal tooth portion 8a has in the axial direction: a second maximum tooth thickness portion 8a1 with the largest tooth thickness; a second inner tooth thickness reduction portion 8a2 that extends from the second maximum tooth thickness portion 8a1 toward the axially inner side (i.e., toward the direction closer to the center between the first internal tooth portion 6a and the second internal tooth portion 8a) and whose tooth thickness decreases as it extends toward the axially inner side; and a second outer tooth thickness reduction portion 8a3 that extends from the second maximum tooth thickness portion 8a1 toward the axially outer side (i.e., toward the direction away from the center between the first internal tooth portion 6a and the second internal tooth portion 8a) and whose tooth thickness decreases as it extends toward the axially outer side.

[0124] The second inner tooth thickness reduction portion 8a2 has an axially outer outer region 8a2o and an inner region 8a2i provided axially inward of the outer region 8a2o within the meshing range Wb with the second outer tooth portion 4b. The boundary E12 between the outer region 8a2o and the inner region 8a2i is a portion where the rate of change of the tooth thickness reduction ratio is discontinuous.

[0125] Each component of the second inner tooth portion 8a (the second tooth thickness maximum portion 8a1, the second inner tooth thickness reduction portion 8a2, the second outer tooth thickness reduction portion 8a3, the meshing range Wb between the second outer tooth portion 4b and the second inner tooth portion 8a, the outer region 8a2o, and the inner region 8a2i) may have the same characteristics and the relationships between the components as those of each component of the first inner tooth portion 6a (the first tooth thickness maximum portion 6a1, the first inner tooth thickness reduction portion 6a2, the first outer tooth thickness reduction portion 6a3, the meshing range Wa between the first outer tooth portion 4a and the first inner tooth portion 6a, the outer region 6a2o, and the inner region 6a2i). By having the same characteristics or the same relationships, the same effects are obtained at the meshing portion between the second outer tooth portion 4b and the second inner tooth portion 8a.

[0126] <Tooth tip shape>

[0127] Figure 7 It is a diagram for explaining the shapes of the external gear, the first internal gear, and the second internal gear of the flexural meshing type gear device according to the second embodiment. Figure 7 In accordance with Figure 3 the method shows the shapes of the first outer tooth portion 4a and the second outer tooth portion 4b of the external gear 4, the first inner tooth portion 6a of the first internal gear 6, and the second inner tooth portion 8a of the second internal gear 8. In Figure 7 the central plane P0, the center line C1, and the center line C2 are the same as those described in the first embodiment.

[0128] The first inner tooth portion 6a has, in the axial direction: a first outer diameter maximum portion 6a6, which has the maximum outer diameter; and a first inner outer diameter reduction portion 6a7, which extends from the first outer diameter maximum portion 6a6 toward the axial inner side (i.e., toward the direction closer to the center between the first inner tooth portion 6a and the second inner tooth portion 8a) and whose outer diameter decreases as it goes toward the axial inner side.

[0129] The first outer diameter maximum portion 6a6 is located within the meshing range Wa between the first outer tooth portion 4a and the first inner tooth portion 6a in the axial direction and at a position more outward than the center (C1) of the meshing range Wa in the axial direction. The first outer diameter maximum portion 6a6 may be a point or may have a length in the axial direction.

[0130] The first inner outer diameter reducing portion 6a7 has an outer region 6a7o on the axially outer side within the meshing range Wa with the first outer tooth portion 4a, and an inner region 6a7i provided on the axially inner side of the outer region 6a7o and having a greater reduction ratio of the outer diameter than the outer region 6a7o. The boundary E16 between the outer region 6a7o and the inner region 6a7i is a portion where the change rate of the reduction ratio of the outer diameter is discontinuous. The axial length of the outer region 6a7o is greater than the axial length of the inner region 6a7i.

[0131] As described above, due to the presence of the first inner outer diameter reducing portion 6a7, one - end contact load generated at the inner tooth width end portions of the first outer tooth portion 4a and the first inner tooth portion 6a can be reduced, thereby reducing excessive wear of the gear. Moreover, since the first inner outer diameter reducing portion 6a7 has the outer region 6a7o and the inner region 6a7i with the above - mentioned reduction ratio of the outer diameter, the outer diameter can be continuously reduced to the inner tooth width end portion, and the reduction of the outer diameter at the center of the tooth width can be suppressed. Therefore, the rigidity of the first inner gear 6 is improved, and the torsional rigidity of the flexural meshing type gear device 100 is improved. Moreover, through the inner region 6a7i where the change rate of the reduction ratio of the outer diameter is not continuously changed, the above - mentioned improvement of rigidity can be achieved, and the rise of the tooth surface pressure within the inner region of the meshing range Wa can be suppressed. The tooth surface pressure generated in this region includes elements that promote pitting fatigue of the first outer tooth portion 4a and the first inner tooth portion 6a. Therefore, by suppressing the rise of the above - mentioned tooth surface pressure, the reduction of the pitting life of the tooth surface can be suppressed.

[0132] The reduction ratio of the inner region 6a7i can be 2.5 times or more, preferably 3.1 times or more, of the reduction ratio of the outer region 6a7o. According to this structure, the reduction of the pitting life of the first outer tooth portion 4a and the first inner tooth portion 6a can be suppressed, and the rigidity of the first inner gear 6 can be further improved. The reduction ratio of the outer diameter of the outer region 6a7o corresponds to the slope of the line segment q15 between the point p15 and the point p16. The reduction ratio of the outer diameter of the inner region 6a7i corresponds to the slope of the line segment q16 between the point p16 and the point p17.

[0133] The axial length of the outer region 6a7o can be 2 times or more of the axial length of the inner region 6a7i. According to this structure, the reduction of the pitting life of the first outer tooth portion 4a and the first inner tooth portion 6a can be suppressed, and the rigidity of the first inner gear 6 can be further improved.

[0134] The curve representing the tip shape of the inner region 6a7i and the curve representing the tip shape of the outer region 6a7o can be curves represented by different functions.

[0135] In addition, between the inner end (point p17) of the meshing range Wa of the first internal tooth portion 6a and the outer gear 4 and the first maximum outer diameter portion 6a6, the reduction ratio of the outer diameter of the first inner outer diameter reduction portion 6a7 in the 1 / 3 range T15 on the axial inner side can be more than 2.5 times, preferably more than 3.1 times, the reduction ratio of the outer diameter of the first inner outer diameter reduction portion 6a7 in the 2 / 3 range T16 on the axial outer side. By adopting this structure, it is also possible to reduce the one-end contact load generated at the inner tooth width end portions of the first external tooth portion 4a and the first internal tooth portion 6a, thereby reducing excessive wear of the gear. Moreover, by reducing the outer diameter in the 2 / 3 range T16 on the axial outer side, the outer diameter can be continuously reduced to the inner tooth width end portion, and the reduction of the outer diameter at the center of the tooth width can be suppressed, thereby improving the rigidity of the first internal gear 6. Therefore, the torsional rigidity of the flexural meshing type gear device 100 is improved. Moreover, by reducing the outer diameter in the 1 / 3 range T15 on the axial inner side, the above-mentioned improvement in rigidity can be achieved, and the rise in tooth surface pressure in the region inside the meshing range Wa can be suppressed. The tooth surface pressure generated in this region includes elements that promote pitting fatigue of the first external tooth portion 4a and the first internal tooth portion 6a. Therefore, by suppressing the rise in the above-mentioned tooth surface pressure, the reduction of the pitting life of the tooth surface can be suppressed.

[0136] Moreover, the first internal tooth portion 6a may further include a first outer outer diameter reduction portion 6a8 that extends from the first maximum outer diameter portion 6a6 toward the axial outer side (i.e., toward the direction away from the center between the first internal tooth portion 6a and the second internal tooth portion 8a) and whose outer diameter decreases as it extends toward the axial outer side. According to this structure, it is possible to reduce the one-end contact load generated at the outer tooth width end portions of the first external tooth portion 4a and the first internal tooth portion 6a, thereby reducing excessive wear of the gear also at the outer tooth width end portions.

[0137] In addition, the first internal tooth portion 6a has the above-mentioned tooth line shape, but may not have the above-mentioned tooth top shape. For example, the tooth top shape may be flat, or may have other irregularities and / or other curved shapes. In this case, the effects based on the tooth thickness shown in the description of the tooth line shape can also be obtained.

[0138] <Tooth Top Shape of the Second Internal Tooth Portion 8a>

[0139] The second internal tooth portion 8a includes, in the axial direction: a second maximum outer diameter portion 8a6, which has the largest outer diameter; a second inner outer diameter reduction portion 8a7, which extends from the second maximum outer diameter portion 8a6 toward the axial inner side (i.e., toward the direction close to the center between the first external tooth portion 4a and the second internal tooth portion 8a) and whose outer diameter decreases as it extends toward the axial inner side; and a second outer outer diameter reduction portion 8a8, which extends from the second maximum outer diameter portion 8a6 toward the axial outer side (i.e., toward the direction away from the center between the second internal tooth portion 8a and the second internal tooth portion 8a) and whose outer diameter decreases as it extends toward the axial outer side.

[0140] The second inner diameter reduction portion 8a7 has an axially outer outer region 8a7o within the meshing range Wb with the external gear 4 and an inner region 8a7i provided axially inside the outer region 8a7o and having a greater reduction ratio of the outer diameter than the outer region 8a7o. The boundary E17 between the outer region 8a7o and the inner region 8a7i is a portion where the rate of change of the reduction ratio of the outer diameter is discontinuous.

[0141] The above-mentioned constituent elements of the second internal tooth portion 8a (the second outer diameter maximum portion 8a6, the second inner diameter reduction portion 8a7, the second outer diameter reduction portion 8a8, the meshing range Wb between the second external tooth portion 4b and the second internal tooth portion 8a, the outer region 8a7o, and the inner region 8a7i) may have the same characteristics and the relationships between the constituent elements as those of the first internal tooth portion 6a (the first outer diameter maximum portion 6a6, the first inner diameter reduction portion 6a7, the first outer diameter reduction portion 6a8, the meshing range Wa between the first external tooth portion 4a and the first internal tooth portion 6a, the outer region 6a7o, and the inner region 6a7i). By having the same characteristics or the same relationships, the same effects are also obtained at the meshing portion between the second external tooth portion 4b and the second internal tooth portion 8a.

[0142] In addition, the second internal tooth portion 8a has the above-mentioned tooth line shape, but may not have the above-mentioned tooth crest shape. For example, the tooth crest shape may be flat or may have other irregularities and / or other curved shapes. In this case, the effects based on the tooth thickness shown in the description of the tooth line shape can also be obtained.

[0143] <Shape of the first external tooth portion 4a and the second external tooth portion 4b>

[0144] The tooth line shape of the first external tooth portion 4a is a shape that is symmetric with respect to its tooth thickness center plane S4 and the tooth thickness is substantially constant in the axial direction. The tooth crest shape of the first external tooth portion 4a is flat. Similarly, the tooth line shape of the second external tooth portion 4b is a shape that is symmetric with respect to its tooth thickness center plane S4 and the tooth thickness is substantially constant in the axial direction. The tooth crest shape of the second external tooth portion 4b is flat.

[0145] <Shape of the whole tooth>

[0146] The first internal tooth portion 6a may have a shape that is symmetric with respect to the tooth thickness center plane S6 or may include a partially asymmetric portion. Similarly, the second internal tooth portion 8a may have a shape that is symmetric with respect to the tooth thickness center plane S8 or may include a partially asymmetric portion. The tooth thickness center planes S6 and S8 are planes that contain the rotation axis R and pass through the center in the tooth thickness direction of the thickest portion with the maximum tooth thickness.

[0147] Further, in the description of the tooth line shapes of the first inner tooth portion 6a and the second inner tooth portion 8a, the shape of the cylindrical cross section along the pitch circle of the external gear 4 was described. However, on a cylindrical cross section radially displaced from the cylindrical cross section along the pitch circle, the first inner tooth portion 6a and the second inner tooth portion 8a also have the same tooth line shape. The same tooth line shape can similarly exist on cylindrical cross sections with any radius from the tooth root to near the tooth tip, and can also include cylindrical cross sections that do not have the same tooth line shape within a certain radius range. The cylindrical cross section refers to a cross section along a cylindrical surface centered on the rotation axis R.

[0148] In addition, in each of the reduction portions such as the first inner tooth thickness reduction portion 6a2, the first outer tooth thickness reduction portion 6a3, the second inner tooth thickness reduction portion 8a2, and the second outer tooth thickness reduction portion 8a3, both tooth surfaces are configured such that the reduction ratio of the distance between the tooth surface and the tooth thickness center planes S6 and S8 with respect to the axial direction satisfies the following formula.

[0149] Reduction ratio = Reduction amount (mm) of the distance between the tooth surface and the tooth thickness center / Axial movement amount (mm) ≤ 0.05 (Formula 5)

[0150] Therefore, each tooth thickness reduction portion is different in order of magnitude from the chamfer, and there is a clear difference between the two.

[0151] Moreover, each of the reduction portions such as the first inner outer diameter reduction portion 6a7, the first outer outer diameter reduction portion 6a8, the second inner outer diameter reduction portion 8a7, and the second outer outer diameter reduction portion 8a8 is configured such that the reduction ratio of the outer diameter with respect to the axial direction satisfies the following formula.

[0152] Reduction ratio = Reduction amount (mm) of the outer diameter (diameter) / Axial movement amount (mm) ≤ 0.1 (Formula 6)

[0153] Therefore, each outer diameter reduction portion is different in order of magnitude from the chamfer, and there is a clear difference between the two.

[0154] (Third Embodiment)

[0155] Figure 8 This is a diagram for explaining the shapes of the external gear, the first internal gear, and the second internal gear of the flexure engagement type gear device according to the third embodiment. In the third embodiment, the shapes of the first external tooth portion 4a and the first inner tooth portion 6a are configured to be the same as those in the first embodiment, and the shapes of the second external tooth portion 4b and the second inner tooth portion 8a are configured to be the same as those in the second embodiment. For the reason that the contents shown in the first embodiment and the second embodiment are the same, the flexure engagement type gear device of the third embodiment can also suppress the reduction of the pitting resistance life of the tooth surface and can improve the torsional rigidity of the flexure engagement type gear device 100.

[0156] In addition, although the illustration is omitted, the shapes of the first external tooth portion 4a and the first internal tooth portion 6a may also be configured to be the same as those in the second embodiment, and the shapes of the second external tooth portion 4b and the second internal tooth portion 8a may also be configured to be the same as those in the first embodiment. For the same reasons as those shown in the first embodiment and the second embodiment, it is also possible to suppress a reduction in the pitting resistance life of the tooth surface and to increase the torsional rigidity of the flexure engagement type gear device 100 at this time.

[0157] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments. For example, in the first embodiment, as the tooth trace shape, a structure in which the first external tooth portion 4a has a first inner tooth thickness reduction portion 4a2 and a first outer tooth thickness reduction portion 4a3 is shown. However, the first external tooth portion 4a may have the first inner tooth thickness reduction portion 4a2 and the tooth thickness may be constant on the axially outer side of the first tooth thickness maximum portion 4a1. At this time, the first internal tooth portion 6a may have the first outer tooth thickness reduction portion 6a3 of the second embodiment and the tooth thickness may be constant on the axially inner side of the first tooth thickness maximum portion 6a1. The same applies to the second external tooth portion 4b and the second internal tooth portion 8a. Further, in the first embodiment, as the tooth tip shape, a structure in which the first external tooth portion 4a has a first inner outer diameter reduction portion 4a7 and a first outer outer diameter reduction portion 4a8 is shown. However, the first external tooth portion 4a may have the first inner outer diameter reduction portion 4a7 and the outer diameter may be constant on the axially outer side of the first outer diameter maximum portion 4a6. At this time, the first internal tooth portion 6a may have the first outer outer diameter reduction portion 6a8 of the second embodiment and the outer diameter may be constant on the axially inner side of the first outer diameter maximum portion 6a6. The same applies to the second external tooth portion 4b and the second internal tooth portion 8a. In addition, the details shown in the embodiments may be appropriately changed without departing from the gist of the invention.

Claims

1. A flexure engagement type gear device, comprising: an oscillation body; an external gear that is flexurally deformed by the oscillation body; a first internal gear that meshes with the external gear; and a second internal gear that is arranged axially with the first internal gear and meshes with the external gear. The flexure engagement type gear device is characterized in that, the external gear has a first external tooth portion that meshes with the first internal gear and a second external tooth portion that meshes with the second internal gear, the first external tooth portion has a first maximum tooth thickness portion with the maximum tooth thickness and a first inner tooth thickness decreasing portion that extends from the first maximum tooth thickness portion toward the axial inner side and whose tooth thickness decreases as it goes toward the axial inner side, the first inner tooth thickness decreasing portion has an outer region and an inner region within the meshing range with the first internal gear. The inner region is arranged axially inside the outer region and the tooth thickness decreasing ratio is greater than that of the outer region, the boundary between the outer region and the inner region is a portion where the change rate of the tooth thickness decreasing ratio is discontinuous, and the axial length of the outer region is greater than the axial length of the inner region.

2. The flexure engagement type gear device according to claim 1, characterized in that, The first external tooth portion has a first additional inner region from the inner end of the meshing range to the axial center of the external gear, and the axial length of the outer region is greater than the sum of the axial lengths of the inner region and the first additional inner region.

3. The flexure engagement type gear device according to claim 1 or 2, characterized in that, The reduction ratio of the inner region is 2.5 times or more that of the outer region.

4. The flexure engagement type gear device according to any one of claims 1 to 3, characterized in that, The axial length of the outer region is 2 times or more that of the inner region.

5. A flexure engagement type gear device, comprising: an oscillation body; an external gear that is flexurally deformed by the oscillation body; a first internal gear that meshes with the external gear; and a second internal gear that is arranged axially with the first internal gear and meshes with the external gear. The flexure engagement type gear device is characterized in that, the external gear has a first external tooth portion that meshes with the first internal gear and a second external tooth portion that meshes with the second internal gear, the first external tooth portion has a first maximum tooth thickness portion with the maximum tooth thickness and a first inner tooth thickness decreasing portion that extends from the first maximum tooth thickness portion toward the axial inner side and whose tooth thickness decreases as it goes toward the axial inner side, between the inner end of the meshing range of the first internal gear and the first external tooth portion and the first maximum tooth thickness portion, the tooth thickness decreasing ratio of the first inner tooth thickness decreasing portion in the axially inner 1 / 3 range is 2.5 times or more that of the first inner tooth thickness decreasing portion in the axially outer 2 / 3 range.

6. The flexure engagement type gear device according to any one of claims 1 to 5, characterized in that The first external tooth portion has a first maximum outer diameter portion with the largest outer diameter and a first inner outer diameter reduction portion that extends axially inward from the first maximum outer diameter portion and whose outer diameter decreases as it extends axially inward. The first inner outer diameter reduction portion has an outer region and an inner region within the meshing range with the first internal gear. The inner region is arranged axially inward of the outer region, and the reduction ratio of the outer diameter is greater than that of the outer region. The boundary between the outer region and the inner region of the first inner outer diameter reduction portion is a portion where the change rate of the reduction ratio of the outer diameter is discontinuous. The axial length of the outer region of the first inner outer diameter reduction portion is greater than the axial length of the inner region of the first inner outer diameter reduction portion.

7. The flexure engagement type gear device according to any one of claims 1 to 5, characterized in that The first external tooth portion has a first maximum outer diameter portion with the largest outer diameter and a first inner outer diameter reduction portion that extends axially inward from the first maximum outer diameter portion and whose outer diameter decreases as it extends axially inward. Between the inner end of the meshing range of the first internal gear and the first external tooth portion and the first maximum outer diameter portion, the reduction ratio of the outer diameter of the first inner outer diameter reduction portion in the axially inner 1 / 3 range is 2.5 times or more that of the axially outer 2 / 3 range of the first inner outer diameter reduction portion.

8. A flexure engagement type gear device, comprising: an oscillating body; an external gear that is flexurally deformed by the oscillating body; a first internal gear that meshes with the external gear; and a second internal gear that is arranged axially in line with the first internal gear and meshes with the external gear, wherein the flexure engagement type gear device is characterized in that the first internal gear has a first internal tooth portion that meshes with the external gear, the first internal tooth portion has a first maximum tooth thickness portion where the tooth thickness is the largest and a first inner tooth thickness decreasing portion that extends from the first maximum tooth thickness portion toward the axial inner side and whose tooth thickness decreases as it goes toward the axial inner side, the first inner tooth thickness decreasing portion has an outer region and an inner region within the meshing range with the external gear, the inner region is provided axially inside the outer region and the decreasing ratio of the tooth thickness is greater than that of the outer region, the boundary between the outer region and the inner region is a portion where the change rate of the decreasing ratio of the tooth thickness is discontinuous, and the axial length of the outer region is greater than the axial length of the inner region.

9. The flexure engagement type gear device according to claim 8, characterized in that The reduction ratio of the inner region is 2.5 times or more that of the outer region.

10. The flexure engagement type gear device according to claim 8 or 9, characterized in that The axial length of the outer region is 2 times or more that of the inner region.

11. A flexure engagement type gear device, comprising: an oscillating body; an external gear that is flexurally deformed by the oscillating body; a first internal gear that meshes with the external gear; and a second internal gear that is arranged axially side by side with the first internal gear and meshes with the external gear, wherein the flexure engagement type gear device is characterized in that the first internal gear has a first internal tooth portion that meshes with the external gear, the first internal tooth portion has a first maximum tooth thickness portion where the tooth thickness is the largest and a first inner tooth thickness decreasing portion that extends from the first maximum tooth thickness portion toward the axial inner side and whose tooth thickness decreases as it goes toward the axial inner side, Between the inner end of the meshing range of the first internal tooth portion and the outer gear and the first tooth thickness maximum portion, the reduction ratio of the tooth thickness of the first inner tooth thickness reduction portion in the axially inner 1 / 3 range is 2.5 times or more than the reduction ratio of the tooth thickness of the first inner tooth thickness reduction portion in the axially outer 2 / 3 range.

12. The flexure engagement type gear device according to any one of claims 8 to 11, characterized in that The first internal tooth portion has a first maximum outer diameter portion with the largest outer diameter and a first inner outer diameter reduction portion that extends axially inward from the first maximum outer diameter portion and whose outer diameter decreases as it extends axially inward. The first inner outer diameter reduction portion has an outer region and an inner region within the meshing range with the external gear. The inner region is arranged axially inward of the outer region, and the reduction ratio of the outer diameter is greater than that of the outer region. The boundary between the outer region and the inner region of the first inner outer diameter reduction portion is a portion where the change rate of the reduction ratio of the outer diameter is discontinuous. The axial length of the outer region of the first inner outer diameter reduction portion is greater than the axial length of the inner region of the first inner outer diameter reduction portion.

13. The flexure engagement type gear device according to any one of claims 8 to 11, characterized in that The first internal tooth portion has a first maximum outer diameter portion with the largest outer diameter and a first inner outer diameter reduction portion that extends axially inward from the first maximum outer diameter portion and whose outer diameter decreases as it extends axially inward. Between the inner end of the meshing range of the first inner tooth portion and the outer gear and the first maximum outer diameter portion, the reduction ratio of the outer diameter of the first inner outer diameter reduction portion in the axially inner 1 / 3 range is more than 2.5 times the reduction ratio of the outer diameter of the first inner outer diameter reduction portion in the axially outer 2 / 3 range.

Images