Flexible meshing type gear device

Abstract

The purpose of the present disclosure is to provide a flexural meshing type gear device capable of suppressing a reduction in tooth strength and a reduction in life of an external gear. The flexural meshing type gear device is provided with an oscillation starting body, an external gear which is flexurally deformed by the oscillation starting body, a first internal gear which is meshed with the external gear, and a second internal gear which is arranged side by side with the first internal gear in the axial direction and is meshed 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 second outer tooth portion has a second outer tooth thickest portion having the largest tooth thickness, and a second outer tooth inner side tooth thickness reduction portion having a tooth thickness reduction from the second outer tooth thickest portion toward the axial inner side. The internal tooth portion of the second internal gear has a second internal-tooth thickest portion having the largest tooth thickness and a second internal-tooth inner-side tooth thickness decreasing portion having a tooth thickness decreasing from the second internal-tooth thickest portion toward the axial inner side.

Description

Technical Field

[0001] The present invention relates to a flexure engagement type gear device. Background Art

[0002] There is known 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 side by side with the first internal gear in the axial direction and meshes with the external gear (for example, refer to Patent Document 1).

[0003] Patent Document 1 discloses the following technique: In a flat flexure engagement type gear device, by improving the tooth line shape of the external gear, excessive wear of the teeth of the external gear, the first internal gear, and the second internal gear is suppressed.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-120325 Summary of the Invention

[0007] Technical Problem to be Solved by the Invention

[0008] In the flexure engagement type gear device of Patent Document 1, although the effect of suppressing excessive wear of the teeth of the external gear, the first internal gear, and the second internal gear can be confirmed, there is still room for improvement from the viewpoints of the tooth strength and life of the external gear.

[0009] An object of the present invention is to provide a flexure engagement type gear device capable of suppressing a decrease in tooth strength and shortening of the life of an external gear.

[0010] Means for Solving the Technical Problem

[0011] A flexure engagement type gear device according to an embodiment of the present invention includes: 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 side by side with the first internal gear in the axial direction and meshes with the external gear, wherein 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 second external tooth portion has a second external tooth thickest portion with the maximum tooth thickness and a second external tooth inner tooth thickness decreasing portion whose tooth thickness decreases from the second external tooth thickest portion toward the axial inner side, and the internal tooth portion of the second internal gear has a second internal tooth thickest portion with the maximum tooth thickness and a second internal tooth inner tooth thickness decreasing portion whose tooth thickness decreases from the second internal tooth thickest portion toward the axial inner side.

[0012] Advantageous Effects of the Invention

[0013] According to the present invention, there is provided a flexure engagement type gear device capable of suppressing a reduction in tooth strength and a shortening of the life of an external gear. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG. is a cross-sectional view showing a flexure engagement type gear device according to the first embodiment.

[0015] Figure 2 for explaining Figure 1 the tooth line shapes of the external gear, the first internal gear, and the second internal gear.

[0016] Figure 3 for explaining Figure 1 the tooth tip shapes of the external gear, the first internal gear, and the second internal gear.

[0017] Figure 4 FIG. is a diagram for explaining the tooth line 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.

[0018] Figure 5 FIG. is a diagram for explaining the tooth tip 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.

[0019] Figure 6 FIG. is a diagram for explaining the tooth line 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. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, one or more embodiments will be described with reference to the drawings. The features and technical effects of the embodiments can be understood from the following detailed description and the drawings. However, the scope of the present invention is not limited to the embodiments disclosed below. The drawings are provided for illustrative purposes only, and thus the scope of the present invention is not limited by the examples in the drawings. The same or equivalent components, parts, and processes shown in the respective drawings are denoted by the same reference numerals, and repeated descriptions are appropriately omitted. For ease of understanding, the sizes of the components are appropriately enlarged or reduced in the respective drawings. Also, in the respective drawings, parts of the components that are not important for explaining the embodiments are omitted. Terms including numbers such as "first" and "second" are used to explain various components, but the numbers of these terms are only for the purpose of distinguishing one component from other components, and the components are not limited by the numbers of these terms.

[0021] (First Embodiment)

[0022] Figure 1This 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 (the flat type is also called the cylindrical type) flexure engagement type gear device. In addition, the present invention can be applied not only to the flat type flexure engagement type gear device 100 but also to, for example, a so-called cup type or top hat type flexure engagement type gear device.

[0023] The flexure engagement type gear device 100 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) side by side with the first internal gear 6 in the axial direction 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 each bearing, etc.

[0024] The wave generator 2 has an oscillator shaft 22, a first oscillator bearing 21a disposed between the oscillator shaft 22 and the external gear 4 (specifically, the first external tooth portion 4a of the external gear 4), and a second oscillator bearing 21b disposed between the oscillator shaft 22 and the external gear 4 (specifically, the second external tooth portion 4b of the external gear 4). The first oscillator bearing 21a includes a plurality of first rolling elements 24a, a first cage 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 oscillator bearing 21b includes a plurality of second rolling elements 24b, a second cage 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 oscillator shaft 22 is an input shaft and is connected to a rotational drive source such as a motor, and rotates about the rotation axis R. An oscillator 22a having a substantially elliptical cross-section orthogonal to the rotation axis R is integrally formed on the oscillator shaft 22.

[0025] The plurality of first rolling elements 24a each have a substantially cylindrical shape, and are arranged at intervals in the circumferential direction in a state where the axial direction is substantially parallel to the direction of the rotation axis R. The first rolling elements 24a are held by the first cage 26a so as to be freely rotatable, and roll on the outer peripheral surface 22b of the vibrator 22a. That is, the inner ring of the first vibrator bearing 21a and the outer peripheral surface 22b of the vibrator 22a are integrally formed, but not limited thereto, and a dedicated inner ring separated from the vibrator 22a may also be provided. The second rolling elements 24b have the same structure as the first rolling elements 24a. The plurality of second rolling elements 24b are held by the second cage 26b arranged side by side with the first cage 26a in the axial direction so as to be freely rotatable, and roll on the outer peripheral surface 22b of the vibrator 22a. That is, the inner ring of the second vibrator bearing 21b and the outer peripheral surface 22b of the vibrator 22a are integrally formed, but not limited thereto, and a dedicated inner ring separated from the vibrator 22a may also be provided. Hereinafter, the first rolling elements 24a and the second rolling elements 24b are also collectively referred to as "rolling elements 24". Further, the first cage 26a and the second cage 26b are also collectively referred to as "cage 26".

[0026] The first outer ring member 28a surrounds the plurality of first rolling elements 24a. The first outer ring member 28a has flexibility and is flexed into an elliptical shape by the vibrator 22a via the plurality of first rolling elements 24a. When the vibrator 22a (i.e., the vibrator shaft 22) rotates, the first outer ring member 28a continuously flexes and deforms following the shape of the vibrator 22a. The second outer ring member 28b has the same structure as 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 are also collectively referred to as "outer ring member 28".

[0027] The external gear 4 is a flexible annular member, and the vibrator 22a, the rolling elements 24, and the outer ring member 28 are fitted inside thereof. The external gear 4 is flexed into an elliptical shape by fitting the vibrator 22a, the rolling elements 24, and the outer ring member 28. When the vibrator 22a rotates, the external gear 4 continuously flexes and deforms following the shape of the vibrator 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.

[0028] 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 external gear 4 that is flexed into an elliptical shape, and meshes with the first external tooth portion 4a in two specified regions near the major axis of the vibrating body 22a. The first internal tooth portion 6a has more teeth than the first external tooth portion 4a.

[0029] The second internal gear 8 and the first internal gear 6 are arranged side by side in the axial direction, and the second internal gear 8 is adjacent to the first internal gear 6. 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 external gear 4 that is flexed into an elliptical shape, and meshes with the second external tooth portion 4b in two specified regions near the major axis of the vibrating body 22a. 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 further with the rotation of the external gear 4.

[0030] The first restricting member 12 is a flat annular member, and is disposed between the external gear 4, the first outer ring member 28a, the first cage 26a, and the first bearing housing 18. The second restricting member 14 is a flat annular member, and is disposed between the external gear 4, the second outer ring member 28b, the second cage 26b, and the second bearing housing 20. The first restricting member 12 and the second restricting member 14 are used to restrict the axial movement of the external gear 4, the outer ring members 28, and the cages 26. The first restricting member 12 and the second restricting member 14 are also referred to as thrust plates.

[0031] The housing 10 is a substantially cylindrical member that surrounds the second internal gear 8. The first internal gear 6 is embedded in the housing 10, and the first internal gear 6 is assembled with the housing 10 into one body 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, and includes a plurality of rollers (rolling elements) 46 that are 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 rotatably supports the second internal gear 8 via the main bearing 16. 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.

[0032] 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 fitted into the first internal gear 6 and fixed by bolts. The second bearing housing 20 is fitted into the second internal gear 8 and fixed by bolts. A bearing 30 is assembled on the inner circumference of the first bearing housing 18, and a bearing 32 is assembled on the inner circumference of the second bearing housing 20. The oscillation body shaft 22 is rotatably supported on the first bearing housing 18 and the second bearing housing 20 by the bearing 30 and the bearing 32.

[0033] An oil seal 40 is arranged between the oscillation body shaft 22 and the first bearing housing 18, an O-ring 34 is arranged between the first bearing housing 18 and the first internal gear 6, an O-ring 36 is arranged between the first internal gear 6 and the housing 10, an oil seal 42 is arranged between the housing 10 and the second internal gear 8, an O-ring 38 is arranged between the second internal gear 8 and the second bearing housing 20, and an oil seal 44 is arranged between the second bearing housing 20 and the oscillation body shaft 22. Thereby, leakage of the lubricant within the flexure engagement type gear device 100 can be suppressed.

[0034] The first restricting member 12 is clamped between the outer ring of the bearing 30 and the external gear 4. The thickness T12 of the first restricting member 12 is set according to the interval in the axial direction from the outer ring of the bearing 30 to the external gear 4 in consideration of the interval in the axial direction from the internal gear 6 to the internal gear 8. For example, a thrust plate having a thickness equal to the interval in the axial direction from the outer ring of the bearing 30 to the external gear 4 is selected from a plurality of thrust plates having different thicknesses, and the selected thrust plate is assembled between the external gear 4, the first outer ring member 28a, the first cage 26a, the first bearing housing 18, and the outer ring of the bearing 30. The selected thrust plate is the first restricting member 12. The interval in the axial direction from the outer ring of the bearing 30 to the external gear 4 can be actually measured when assembling the flexure engagement type gear device 100, or can be calculated based on the actual dimensions of the respective parts and assembled components when assembling the flexure engagement type gear device 100. In addition, the thickness T12 of the first restricting member 12 can also be set according to the interval in the axial direction from the first bearing housing 18 to the external gear 4.

[0035] A second restricting member 14 is clamped between the outer ring of the bearing 32 and the external gear 4. The thickness T14 of the second restricting member 14 is set according to the interval in the axial direction from the outer ring of the bearing 32 to the external gear 4 in consideration of the interval in the axial direction from the internal gear 6 to the internal gear 8. For example, a thrust plate having a thickness equal to the interval in the axial direction from the outer ring of the bearing 32 to the external gear 4 is selected from a plurality of thrust plates with different thicknesses, and the selected thrust plate is assembled between the external gear 4, the second outer ring member 28b, the second cage 26b, the second bearing housing 20, and the outer ring of the bearing 32. The selected thrust plate is the second restricting member 14. The interval in the axial direction from the outer ring of the bearing 32 to the external gear 4 can be actually measured when assembling the flexure engagement type gear device 100, or can be calculated based on the actual dimensions of the respective parts and respective assembled components when assembling the flexure engagement type gear device 100. In addition, the thickness T14 of the second restricting member 14 can also be set according to the interval in the axial direction from the second bearing housing 20 to the external gear 4.

[0036] The thickness T14 of the second restricting member 14 can also be different from the thickness T12 of the first restricting member 12. The thickness T14 of the second restricting member 14 can also be the same as the thickness T12 of the first restricting member 12.

[0037] 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. In addition, a case where the second internal gear 8 and the second bearing housing 20 are connected to the driven member will be exemplified.

[0038] 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, if the oscillation body shaft 22 rotates, then accordingly, the meshing position of the first external tooth portion 4a and the first internal tooth portion 6a also moves in the circumferential direction. Since the number of teeth of the first external tooth portion 4a and the first internal tooth portion 6a is different, at this time, 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 tooth number difference. That is, the rotation of the oscillation body shaft 22 is greatly decelerated and then output to the first external tooth portion 4a. The reduction ratio is as follows:

[0039] 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

[0040] =(100 - 102) / 100

[0041] =-1 / 50

[0042] Since the second external tooth portion 4b is formed integrally with the first external tooth portion 4a, it rotates integrally with the first external tooth portion 4a. Since the number of teeth of the second external tooth portion 4b is the same as that of the second internal tooth portion 8a, relative rotation does not occur, and the second external tooth portion 4b rotates integrally with the second internal tooth portion 8a. Therefore, the same rotation as the self-rotation of the first external tooth portion 4a is output to the second internal tooth portion 8a. As a result, an output in which the rotation of the oscillation body shaft 22 is decelerated to -1 / 50 can be taken out from the second internal gear 8.

[0043] Next, the structures of the external gear 4, the first internal gear 6, and the second internal gear 8 will be described in more detail. In addition, the external gear 4, the first external tooth portion 4a, the second external tooth portion 4b, the first internal gear 6, the first internal tooth portion 6a, the second internal gear 8, and the second internal tooth portion 8a in the present embodiment respectively correspond to the external gear, the first external tooth portion, the second external tooth portion, the first internal gear, the first internal tooth portion, the second internal gear, and the second internal tooth portion in the technical solution. In contrast, the external gear 4, the first external tooth portion 4a, the second external tooth portion 4b, the first internal gear 6, the first internal tooth portion 6a, the second internal gear 8, and the second internal tooth portion 8a in the present embodiment can also be regarded as corresponding to the external gear, the second external tooth portion, the first external tooth portion, the second internal gear, the second internal tooth portion, the first internal gear, and the first internal tooth portion in the technical solution, respectively.

[0044] <Tooth line shape>

[0045] Figure 2 is for explaining Figure 1 the tooth line shapes of the external gear 4, the first internal gear 6, and the second internal gear 8. Figure 2 is a cross-sectional view showing the external gear 4, the first internal gear 6, and the second internal gear 8 cut by an imaginary cylinder passing through the pitch circle of the external gear 4. In Figure 2 , one of the external teeth of the external gear 4 and two adjacent internal teeth in the circumferential direction are shown. For ease of understanding, in Figure 2 , the first internal tooth portion 6a and the second internal tooth portion 8a are shown in a state of sliding away from the external gear 4 in the circumferential direction, and the tooth line 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 enlarged and depicted. Figure 2 The horizontal axis in is parallel to the axial direction, and this horizontal axis represents the position in the axial direction starting from a certain reference position. The axial direction and the tooth line direction are parallel to each other, and the axial direction can also be said to be the tooth line direction. The vertical axis represents the circumferential dimension. That is, the vertical axis can also be said to represent the tooth thickness of the external teeth of the external gear 4.

[0046] In the present embodiment, the first external tooth portion 4a and the first internal tooth portion 6a have a range in the axial direction. The range of the first external tooth portion 4a is wider than the range of the first internal tooth portion 6a, and the first internal tooth portion 6a meshes with the first external tooth portion 4a throughout its range. The second external tooth portion 4b and the second internal tooth portion 8a have a range in the axial direction. The range of the second external tooth portion 4b is wider than the range of the second internal tooth portion 8a, and the second internal tooth portion 8a meshes with the second external tooth portion 4b throughout its range.

[0047] The first external tooth portion 4a may have a shape symmetric about the tooth thickness center plane S4 of the first external tooth portion 4a, or may include a partially asymmetric portion. The tooth thickness center plane S4 refers to the plane passing through the center in the tooth thickness direction of the thickest portion with the maximum tooth thickness of the first external tooth portion 4a and the rotation axis R. The tooth thickness of the first external tooth portion 4a refers to the distance from the tooth thickness center plane S4 to the tooth surface.

[0048] Similarly, the second external tooth portion 4b may have a shape symmetric about the tooth thickness center plane of the second external tooth portion 4b, or may include a partially asymmetric portion. The tooth thickness center plane of the second external tooth portion 4b coincides with the tooth thickness center plane S4 of the first external tooth portion 4a.

[0049] Similarly, the first internal tooth portion 6a may have a shape symmetric about the tooth thickness center plane S6 of the first internal tooth portion 6a, or may include a partially asymmetric portion.

[0050] Similarly, the second internal tooth portion 8a may have a shape symmetric about the tooth thickness center plane S8 of the second internal tooth portion 8a, or may include a partially asymmetric portion. Since the number of teeth of the first internal tooth portion 6a and the second internal tooth portion 8a is different, the tooth thickness center plane S8 of the second internal tooth portion 8a does not coincide with the tooth thickness center plane S6 of the first internal tooth portion 6a.

[0051] <<Tooth line shape of the first external tooth portion 4a and the first internal tooth portion 6a>>

[0052] Reference Figure 2 , the tooth line shapes of the first external tooth portion 4a and the first internal tooth portion 6a will be described. In the following description, the tooth line shapes of the first external tooth portion 4a and the first internal tooth portion 6a on the cylindrical cross section along the pitch circle will be representatively described. However, the tooth line shapes of the first external tooth portion 4a and the first internal tooth portion 6a on the cylindrical cross section radially displaced from the pitch circle along the cylindrical cross section are also the same as the tooth line shapes described below. The tooth line shape of the first external tooth portion 4a described below can be integrally reflected in the range from the tooth root to near the tooth tip of the first external tooth portion 4a, or can be partially reflected in a part of the range from the tooth root to near the tooth tip of the first external tooth portion 4a. The tooth line shape of the first internal tooth portion 6a described below can be integrally reflected in the range from the tooth root to near the tooth tip of the first internal tooth portion 6a, or can be partially reflected in a part of the range from the tooth root to near the tooth tip of the first internal tooth portion 6a.

[0053] If the first external tooth part 4a is divided axially, the first external tooth part 4a has a first external tooth thickest part 4a1, a first external tooth inner tooth thickness reducing part 4a2, and a first external tooth outer tooth thickness reducing part 4a3. The first external tooth inner tooth thickness reducing part 4a2 is located at a position axially more inner than the first external tooth thickest part 4a1, and the first external tooth outer tooth thickness reducing part 4a3 is located at a position axially more outer than the first external tooth thickest part 4a1. Here, the axial inner side means the direction along the axis closer to the center between the first external tooth part 4a and the second external tooth part 4b. The axial outer side means the direction along the axis away from the center between the first external tooth part 4a and the second external tooth part 4b. And the center between the first external tooth part 4a and the second external tooth part 4b means the boundary between the range of the first external tooth part 4a in the axial direction and the range of the second external tooth part 4b in the axial direction. The imaginary plane P0 passing through the center between the first external tooth part 4a and the second external tooth part 4b and perpendicular to the axis is called the central plane P0. The position of the central plane P0 in the axial direction is located between the first internal tooth part 6a and the second internal tooth part 8a.

[0054] The tooth thickness of the first external tooth part 4a changes axially. Specifically, the tooth thickness of the first external tooth thickest part 4a1 corresponds to the maximum tooth thickness of the first external tooth part 4a, the tooth thickness of the first external tooth inner tooth thickness reducing part 4a2 gradually decreases from the first external tooth thickest part 4a1 toward the axial inner side, and the tooth thickness of the first external tooth outer tooth thickness reducing part 4a3 gradually decreases from the first external tooth thickest part 4a1 toward the axial outer side.

[0055] If the first internal tooth part 6a is divided axially, the first internal tooth part 6a has a first internal tooth thickest part 6a1 and a first internal tooth inner tooth thickness reducing part 6a2. The first internal tooth inner tooth thickness reducing part 6a2 is located at a position axially more inner than the first internal tooth thickest part 6a1.

[0056] The tooth thickness of the first internal tooth part 6a changes axially. Specifically, the tooth thickness of the first internal tooth thickest part 6a1 corresponds to the maximum tooth thickness of the first internal tooth part 6a, and the tooth thickness of the first internal tooth inner tooth thickness reducing part 6a2 gradually decreases from the first internal tooth thickest part 6a1 toward the axial inner side.

[0057] The first external tooth thickest part 4a1 may have a range with a specified width axially, or may not have a range axially and be a point. In Figure 2 the example shown, the first external tooth thickest part 4a1 does not have a range axially and is a point.

[0058] The first internal tooth thickest part 6a1 may have a range with a specified width axially, or may not have a range axially and be a point. In Figure 2In the illustrated example, the thickest portion 6a1 of the first internal tooth has a range in the axial direction. Further, when the thickest portion 6a1 of the first internal tooth has a range in the axial direction, the axially outer end of the thickest portion 6a1 of the first internal tooth corresponds to the axially outer end of the first internal tooth portion 6a; when the thickest portion 6a1 of the first internal tooth does not have a range but is a point in the axial direction, the thickest portion 6a1 of the first internal tooth corresponds to the axially outer end of the first internal tooth portion 6a.

[0059] As Figure 2 shown, when the thickest portion 4a1 of the first external tooth does not have a range but is a point in the axial direction and the thickest portion 6a1 of the first internal tooth has a range in the axial direction, the position of the thickest portion 4a1 of the first external tooth in the axial direction is located inside the range of the thickest portion 6a1 of the first internal tooth. Further, when the thickest portion 4a1 of the first external tooth has a range in the axial direction and the thickest portion 6a1 of the first internal tooth does not have a range but is a point in the axial direction, the position of the thickest portion 6a1 of the first internal tooth in the axial direction may also be located inside the range of the thickest portion 4a1 of the first external tooth. And, when the thickest portion 4a1 of the first external tooth has a range in the axial direction and the thickest portion 6a1 of the first internal tooth has a range in the axial direction, the ranges of the thickest portion 4a1 of the first external tooth and the thickest portion 6a1 of the first internal tooth may partially or entirely overlap. When the thickest portion 4a1 of the first external tooth does not have a range but is a point in the axial direction and the thickest portion 6a1 of the first internal tooth does not have a range but is a point in the axial direction, the positions of the thickest portion 4a1 of the first external tooth and the thickest portion 6a1 of the first internal tooth in the axial direction may be aligned with each other.

[0060] The thickness reduction portion 4a2 of the inner side of the first external tooth has a range in the axial direction. As Figure 2 shown in the example, when the thickest portion 6a1 of the first internal tooth has a range in the axial direction, the range of the thickness reduction portion 4a2 of the inner side of the first external tooth partially overlaps with the range of the thickest portion 6a1 of the first internal tooth. Further, the axially inner end of the thickness reduction portion 4a2 of the inner side of the first external tooth corresponds to the center between the first external tooth portion 4a and the second external tooth portion 4b.

[0061] The range of the thickness reduction portion 6a2 on the inner side of the first internal tooth is in the axial direction. The range of the thickness reduction portion 6a2 on the inner side of the first internal tooth is smaller than the range of the thickness reduction portion 4a2 on the inner side of the first external tooth, and the entire range of the thickness reduction portion 6a2 on the inner side of the first internal tooth is included in the range of the thickness reduction portion 4a2 on the inner side of the first external tooth. The range of the thickness reduction portion 4a2 on the inner side of the first external tooth extends to a position more axially inward than the axially inner end of the range of the thickness reduction portion 6a2 on the inner side of the first internal tooth. In contrast, the position of the axially inner end of the range of the thickness reduction portion 4a2 on the inner side of the first external tooth may also be aligned with the position of the axially inner end of the range of the thickness reduction portion 6a2 on the inner side of the first internal tooth. The range of the thickness reduction portion 4a2 on the inner side of the first external tooth extends to a position more axially outward than the axially outer end of the range of the thickness reduction portion 6a2 on the inner side of the first internal tooth. In addition, the axially inner end of the thickness reduction portion 6a2 on the inner side of the first internal tooth corresponds to the axially inner end of the first internal tooth portion 6a. The thickness reduction ratio of the thickness reduction portion 6a2 on the inner side of the first internal tooth is greater than the thickness reduction ratio of the thickness reduction portion 4a2 on the inner side of the first external tooth. Therefore, in Figure 2 In the cross-section shown, the tooth line curve depicted by the thickness reduction portion 6a2 on the inner side of the first internal tooth is steeper than the tooth line curve depicted by the thickness reduction portion 4a2 on the inner side of the first external tooth. Here, the thickness reduction ratio of the thickness reduction portion 6a2 on the inner side of the first internal tooth refers to the value obtained by dividing the amount of thickness reduction of the thickness reduction portion 6a2 on the inner side of the first internal tooth when displaced a unit distance axially inward in the tooth line direction by the unit distance. That is, the thickness reduction ratio of the thickness reduction portion 6a2 on the inner side of the first internal tooth can also be said to be the amount of thickness reduction of the thickness reduction portion 6a2 on the inner side of the first internal tooth per unit distance in the tooth line direction. The thickness reduction ratio of the thickness reduction portion 4a2 on the inner side of the first external tooth refers to the value obtained by dividing the amount of thickness reduction of the thickness reduction portion 4a2 on the inner side of the first external tooth when displaced a unit distance axially inward in the tooth line direction by the unit distance. The thickness reduction ratio of the thickness reduction portion 4a2 on the inner side of the first external tooth can also be said to be the amount of thickness reduction of the thickness reduction portion 4a2 on the inner side of the first external tooth per unit distance in the tooth line direction.

[0062] The maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 6a2 of the first inner tooth is greater than the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 4a2 of the first outer tooth. Regarding the ratio of the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 6a2 of the first inner tooth to the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 4a2 of the first outer tooth, the relationship of "the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 4a2 of the first outer tooth: the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 6a2 of the first inner tooth = 1:2 to 4" is satisfied. Here, the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 6a2 of the first inner tooth refers to the value obtained by subtracting the minimum tooth thickness of the inner tooth thickness reduction portion 6a2 of the first inner tooth at the axially inner end of the inner tooth thickness reduction portion 6a2 of the first inner tooth from the maximum tooth thickness of the inner tooth thickness reduction portion 6a2 of the first inner tooth at the axially outer end of the inner tooth thickness reduction portion 6a2 of the first inner tooth. The maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 4a2 of the first outer tooth refers to the value obtained by subtracting the minimum tooth thickness of the inner tooth thickness reduction portion 4a2 of the first outer tooth at the axially inner end of the inner tooth thickness reduction portion 4a2 of the first outer tooth from the maximum tooth thickness of the inner tooth thickness reduction portion 4a2 of the first outer tooth at the axially outer end of the inner tooth thickness reduction portion 4a2 of the first outer tooth.

[0063] The first outer tooth outer tooth thickness reduction portion 4a3 has a range in the axial direction. As Figure 2 shown in the example, when the thickest portion 6a1 of the first inner tooth has a range in the axial direction, the range of the first outer tooth outer tooth thickness reduction portion 4a3 partially overlaps with the range of the thickest portion 6a1 of the first inner tooth. The range of the first outer tooth outer tooth thickness reduction portion 4a3 extends to a position axially outside the thickest portion 6a1 of the first inner tooth. In addition, the axially outer end of the first outer tooth outer tooth thickness reduction portion 4a3 corresponds to the axially outer end of the first outer tooth portion 4a.

[0064] The tooth thickness reduction ratio of the first outer tooth outer tooth thickness reduction portion 4a3 is greater than the tooth thickness reduction ratio of the first outer tooth inner tooth thickness reduction portion 4a2. Therefore, in Figure 2 the cross-section shown, the tooth line curve depicted by the first outer tooth outer tooth thickness reduction portion 4a3 is steeper than the tooth line curve depicted by the first outer tooth inner tooth thickness reduction portion 4a2. Here, the tooth thickness reduction ratio of the first outer tooth outer tooth thickness reduction portion 4a3 refers to the value obtained by dividing the reduction amount of the tooth thickness of the first outer tooth outer tooth thickness reduction portion 4a3 when displaced by a unit distance axially outward in the tooth line direction by the unit distance. The tooth thickness reduction ratio of the first outer tooth outer tooth thickness reduction portion 4a3 can also be said to be the reduction amount of the tooth thickness of the first outer tooth outer tooth thickness reduction portion 4a3 per unit distance in the tooth line direction.

[0065] <<Tooth line shape of the second outer tooth portion 4b and the second inner tooth portion 8a>>

[0066] The tooth line shapes of the second external tooth portion 4b and the second internal tooth portion 8a will be described. In the following description, the tooth line shapes of the second external tooth portion 4b and the second internal tooth portion 8a on the cylindrical cross-section along the pitch circle are representatively described. However, the tooth line shapes of the second external tooth portion 4b and the second internal tooth portion 8a on the cylindrical cross-section radially displaced from the pitch circle along the cylindrical cross-section are also the same as the tooth line shapes described below. The tooth line shape of the second external tooth portion 4b described below can be integrally reflected in the range from the tooth root to near the tooth tip of the second external tooth portion 4b, or can be partially reflected in a part of the range from the tooth root to near the tooth tip of the second external tooth portion 4b. The tooth line shape of the second internal tooth portion 8a described below can be integrally reflected in the range from the tooth root to near the tooth tip of the second internal tooth portion 8a, or can be partially reflected in a part of the range from the tooth root to near the tooth tip of the second internal tooth portion 8a.

[0067] If the second external tooth portion 4b is divided axially, the second external tooth portion 4b has a second external tooth thickest portion 4b1, a second external tooth inner tooth thickness reducing portion 4b2, and a second external tooth outer tooth thickness reducing portion 4b3. The second external tooth inner tooth thickness reducing portion 4b2 is located axially inward of the second external tooth thickest portion 4b1, and the second external tooth outer tooth thickness reducing portion 4b3 is located axially outward of the second external tooth thickest portion 4b1.

[0068] The tooth thickness of the second external tooth portion 4b changes axially. Specifically, the tooth thickness of the second external tooth thickest portion 4b1 corresponds to the maximum tooth thickness of the second external tooth portion 4b. The tooth thickness of the second external tooth inner tooth thickness reducing portion 4b2 gradually decreases from the second external tooth thickest portion 4b1 toward the axial inner side, and the tooth thickness of the second external tooth outer tooth thickness reducing portion 4b3 gradually decreases from the second external tooth thickest portion 4b1 toward the axial outer side.

[0069] If the second internal tooth portion 8a is divided axially, the second internal tooth portion 8a has a second internal tooth thickest portion 8a1 and a second internal tooth inner tooth thickness reducing portion 8a2. The second internal tooth inner tooth thickness reducing portion 8a2 is located axially inward of the second internal tooth thickest portion 8a1.

[0070] The tooth thickness of the second internal tooth portion 8a changes axially. Specifically, the tooth thickness of the second internal tooth thickest portion 8a1 corresponds to the maximum tooth thickness of the second internal tooth portion 8a. The tooth thickness of the second internal tooth inner tooth thickness reducing portion 8a2 gradually decreases from the second internal tooth thickest portion 8a1 toward the axial inner side.

[0071] The second external tooth thickest portion 4b1 may have a range axially, or may not have a range axially and be a point. In Figure 2 the example shown, the second external tooth thickest portion 4b1 does not have a range axially and is a point.

[0072] The thickest part 8a1 of the second internal tooth may have a range in the axial direction or may not have a range in the axial direction but be a point. In Figure 2 the example shown, the thickest part 8a1 of the second internal tooth has a range in the axial direction. In addition, when the thickest part 8a1 of the second internal tooth has a range in the axial direction, the axially outer end of the thickest part 8a1 of the second internal tooth corresponds to the axially outer end of the second internal tooth part 8a. When the thickest part 8a1 of the second internal tooth does not have a range in the axial direction but is a point, the thickest part 8a1 of the second internal tooth corresponds to the axially outer end of the second internal tooth part 8a.

[0073] As Figure 2 shown, when the thickest part 4b1 of the second external tooth does not have a range in the axial direction but is a point and the thickest part 8a1 of the second internal tooth has a range in the axial direction, the position of the thickest part 4b1 of the second external tooth in the axial direction is located inside the range of the thickest part 8a1 of the second internal tooth. In addition, when the thickest part 4b1 of the second external tooth has a range in the axial direction and the thickest part 8a1 of the second internal tooth does not have a range in the axial direction but is a point, the position of the thickest part 8a1 of the second internal tooth in the axial direction may also be located inside the range of the thickest part 4b1 of the second external tooth. And, when the thickest part 4b1 of the second external tooth has a range in the axial direction and the thickest part 8a1 of the second internal tooth has a range in the axial direction, the ranges of the thickest part 4b1 of the second external tooth and the thickest part 8a1 of the second internal tooth may partially or completely overlap. When the thickest part 4b1 of the second external tooth does not have a range in the axial direction but is a single point and the thickest part 8a1 of the second internal tooth does not have a range in the axial direction but is a single point, the positions of the thickest part 4b1 of the second external tooth and the thickest part 8a1 of the second internal tooth in the axial direction may also be aligned with each other.

[0074] The inner tooth thickness reduction part 4b2 of the second external tooth has a range in the axial direction. As Figure 2 shown in the example, when the thickest part 8a1 of the second internal tooth has a range in the axial direction, the range of the inner tooth thickness reduction part 4b2 of the second external tooth partially overlaps with the range of the thickest part 8a1 of the second internal tooth. In addition, the axially inner end of the inner tooth thickness reduction part 4b2 of the second external tooth corresponds to the center between the first external tooth part 4a and the second external tooth part 4b.

[0075] The range of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth has a range in the axial direction. The range of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth is smaller than the range of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth, and the entire range of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth is included within the range of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth. The position of the axially inner end of the range of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth is aligned with the position of the axially inner end of the range of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth. In contrast, the range of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth may also extend to a position axially inner than the axially inner end of the range of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth. The range of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth extends to a position axially outer than the axially outer end of the range of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth. In addition, the axially inner end of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth corresponds to the axially inner end of the second inner teeth portion 8a.

[0076] The thickness reduction ratio of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth is greater than the thickness reduction ratio of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth. Therefore, in Figure 2 the cross-section shown, the tooth line curve depicted by the thickness reduction portion 8a2 of the inner teeth of the second inner teeth is steeper than the tooth line curve depicted by the thickness reduction portion 4b2 of the inner teeth of the second outer teeth. Here, the thickness reduction ratio of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth refers to the value obtained by dividing the amount of reduction in the thickness of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth when displaced by a unit distance in the tooth line direction, specifically axially inward, by the unit distance. The thickness reduction ratio of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth can also be said to be the amount of reduction in the thickness of the thickness reduction portion 8a2 of the inner teeth of the second inner teeth per unit distance in the tooth line direction. The thickness reduction ratio of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth refers to the value obtained by dividing the amount of reduction in the thickness of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth when displaced by a unit distance in the tooth line direction, specifically axially inward, by the unit distance. The thickness reduction ratio of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth can also be said to be the amount of reduction in the thickness of the thickness reduction portion 4b2 of the inner teeth of the second outer teeth per unit distance in the tooth line direction.

[0077] The maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 8a2 of the second inner tooth is greater than the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 4b2 of the second outer tooth. Regarding the ratio of the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 8a2 of the second inner tooth to the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 4b2 of the second outer tooth, the relationship of "the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 4b2 of the second outer tooth: the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 8a2 of the second inner tooth = 1:2 to 4" is satisfied. Here, the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 8a2 of the second inner tooth refers to the value obtained by subtracting the minimum tooth thickness of the inner tooth thickness reduction portion 8a2 of the second inner tooth at the axially inner end of the inner tooth thickness reduction portion 8a2 of the second inner tooth from the maximum tooth thickness of the inner tooth thickness reduction portion 8a2 of the second inner tooth at the axially outer end of the inner tooth thickness reduction portion 8a2 of the second inner tooth. The maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 4b2 of the second outer tooth refers to the value obtained by subtracting the minimum tooth thickness of the inner tooth thickness reduction portion 4b2 of the second outer tooth at the axially inner end of the inner tooth thickness reduction portion 4b2 of the second outer tooth from the maximum tooth thickness of the inner tooth thickness reduction portion 4b2 of the second outer tooth at the axially outer end of the inner tooth thickness reduction portion 4b2 of the second outer tooth.

[0078] The maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 8a2 of the second inner tooth is greater than the maximum amount of tooth thickness reduction of the inner tooth thickness reduction portion 6a2 of the first inner tooth.

[0079] The second outer tooth outer tooth thickness reduction portion 4b3 has a range in the axial direction. As Figure 2 shown in the example, when the thickest portion 8a1 of the second inner tooth has a range in the axial direction, the range of the second outer tooth outer tooth thickness reduction portion 4b3 partially overlaps with the range of the thickest portion 8a1 of the second inner tooth. The range of the second outer tooth outer tooth thickness reduction portion 4b3 extends to a position more axially outer than the thickest portion 8a1 of the second inner tooth. In addition, the axially outer end of the second outer tooth outer tooth thickness reduction portion 4b3 corresponds to the axially outer end of the second outer tooth portion 4b.

[0080] The tooth thickness reduction ratio of the second outer tooth outer tooth thickness reduction portion 4b3 is greater than the tooth thickness reduction ratio of the second outer tooth inner tooth thickness reduction portion 4b2. Therefore, in Figure 2 the cross-section shown, the tooth line curve depicted by the second outer tooth outer tooth thickness reduction portion 4b3 is steeper than the tooth line curve depicted by the second outer tooth inner tooth thickness reduction portion 4b2. Here, the tooth thickness reduction ratio of the second outer tooth outer tooth thickness reduction portion 4b3 refers to the value obtained by dividing the reduction amount of the tooth thickness of the second outer tooth outer tooth thickness reduction portion 4b3 when displaced a unit distance in the tooth line direction, specifically in the axially outer direction, by the unit distance. The tooth thickness reduction ratio of the second outer tooth outer tooth thickness reduction portion 4b3 can also be said to be the reduction amount of the tooth thickness of the second outer tooth outer tooth thickness reduction portion 4b3 per unit distance in the tooth line direction.

[0081] <Tooth tip shape>

[0082] Figure 3 is a diagram for explaining Figure 1 the tooth tip shapes of the external gear 4, the first internal gear 6, and the second internal gear 8. In Figure 3 , 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 are shown as viewed in the circumferential direction. For ease of understanding, in Figure 3 , the tooth tips of the first internal tooth portion 6a and the second internal tooth portion 8a are shown in a state of being separated radially outward from the external gear 4, and the tooth tip 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 depicted in an enlarged manner. In Figure 3 , the horizontal axis is the axial position starting from a certain reference position. The radial dimension is shown on the vertical axis.

[0083] <<Tooth tip shapes of the first external tooth portion 4a and the first internal tooth portion 6a>>

[0084] Refer to Figure 3 to explain the tooth tip shapes of the first external tooth portion 4a and the first internal tooth portion 6a. Additionally, the first external tooth portion 4a and the first internal tooth portion 6a may have the above-described tooth line shape, but they may also not have the tooth tip shapes described below. When the first external tooth portion 4a and the first internal tooth portion 6a do not have the tooth tip shapes described below, the tooth tip shapes of the first external tooth portion 4a and the first internal tooth portion 6a may be flat, for example.

[0085] If the tooth tip of the first external tooth portion 4a is divided axially, the first external tooth portion 4a has a first external tooth maximum outer diameter portion 4a6, a first external tooth inner side outer diameter reducing portion 4a7, and a first external tooth outer side outer diameter reducing portion 4a8. The first external tooth inner side outer diameter reducing portion 4a7 is located axially inward of the first external tooth maximum outer diameter portion 4a6, and the first external tooth outer side outer diameter reducing portion 4a8 is located axially outward of the first external tooth maximum outer diameter portion 4a6.

[0086] The outer diameter of the first external tooth portion 4a changes axially. Specifically, the outer diameter of the first external tooth maximum outer diameter portion 4a6 corresponds to the maximum outer diameter of the first external tooth portion 4a, the outer diameter of the first external tooth inner side outer diameter reducing portion 4a7 gradually decreases from the first external tooth maximum outer diameter portion 4a6 toward the axial inner side, and the outer diameter of the first external tooth outer side outer diameter reducing portion 4a8 gradually decreases from the first external tooth maximum outer diameter portion 4a6 toward the axial outer side. The outer diameter of the first external tooth portion 4a refers to the distance from the rotation axis R to the tooth tip of the first external tooth portion 4a.

[0087] If the tooth tip of the first internal tooth portion 6a is divided axially, the first internal tooth portion 6a has a first internal tooth minimum inner diameter portion 6a6 and a first internal tooth inner side inner diameter increasing portion 6a7. The first internal tooth inner side inner diameter increasing portion 6a7 is located at a position axially more inner than the first internal tooth minimum inner diameter portion 6a6.

[0088] The inner diameter of the first internal tooth portion 6a changes axially. Specifically, the inner diameter of the first internal tooth minimum inner diameter portion 6a6 corresponds to the minimum inner diameter of the first internal tooth portion 6a, and the inner diameter of the first internal tooth inner side inner diameter increasing portion 6a7 gradually increases from the first internal tooth minimum inner diameter portion 6a6 toward the axially inner side. The inner diameter of the first internal tooth portion 6a refers to the distance from the rotation axis R to the tooth tip of the first internal tooth portion 6a.

[0089] The first external tooth maximum outer diameter portion 4a6 may have a range axially or may not have a range axially and be a point. In Figure 3 the example shown, the first external tooth maximum outer diameter portion 4a6 does not have a range axially and is a point.

[0090] The first internal tooth minimum inner diameter portion 6a6 may have a range axially or may not have a range axially and be a point. In Figure 3 the example shown, the first internal tooth minimum inner diameter portion 6a6 has a range axially. In addition, when the first internal tooth minimum inner diameter portion 6a6 has a range axially, the axially outer end of the first internal tooth minimum inner diameter portion 6a6 corresponds to the axially outer end of the first internal tooth portion 6a, and when the first internal tooth minimum inner diameter portion 6a6 does not have a range axially and is a point, the first internal tooth minimum inner diameter portion 6a6 corresponds to the axially outer end of the first internal tooth portion 6a.

[0091] As Figure 3As shown, when the maximum outer diameter portion 4a6 of the first external teeth has no range in the axial direction and is a single point, and the minimum inner diameter portion 6a6 of the first internal teeth has a range in the axial direction, the position of the maximum outer diameter portion 4a6 of the first external teeth in the axial direction is located inside the range of the minimum inner diameter portion 6a6 of the first internal teeth. Further, when the maximum outer diameter portion 4a6 of the first external teeth has a range in the axial direction and the minimum inner diameter portion 6a6 of the first internal teeth has no range in the axial direction and is a single point, the position of the minimum inner diameter portion 6a6 of the first internal teeth in the axial direction may also be located inside the range of the maximum outer diameter portion 4a6 of the first external teeth. Also, when the maximum outer diameter portion 4a6 of the first external teeth has a range in the axial direction and the minimum inner diameter portion 6a6 of the first internal teeth has a range in the axial direction, the ranges of the maximum outer diameter portion 4a6 of the first external teeth and the minimum inner diameter portion 6a6 of the first internal teeth may partially or entirely overlap. When the maximum outer diameter portion 4a6 of the first external teeth has no range in the axial direction and is a single point, and the minimum inner diameter portion 6a6 of the first internal teeth has no range in the axial direction and is a single point, the positions of the maximum outer diameter portion 4a6 of the first external teeth and the minimum inner diameter portion 6a6 of the first internal teeth in the axial direction may also be aligned with each other.

[0092] The first external teeth inner side outer diameter reduction portion 4a7 has a range in the axial direction. As Figure 3 shown in the example, when the minimum inner diameter portion 6a6 of the first internal teeth has a range in the axial direction, the range of the first external teeth inner side outer diameter reduction portion 4a7 partially overlaps with the range of the minimum inner diameter portion 6a6 of the first internal teeth. Further, the axially inner end of the first external teeth inner side outer diameter reduction portion 4a7 corresponds to the center between the first external teeth portion 4a and the second external teeth portion 4b.

[0093] The first internal teeth inner side inner diameter increase portion 6a7 has a range in the axial direction. The range of the first internal teeth inner side inner diameter increase portion 6a7 is smaller than the range of the first external teeth inner side outer diameter reduction portion 4a7, and the entire range of the first internal teeth inner side inner diameter increase portion 6a7 is included in the range of the first external teeth inner side outer diameter reduction portion 4a7. The range of the first external teeth inner side outer diameter reduction portion 4a7 extends to a position axially inner than the axially inner end of the range of the first internal teeth inner side inner diameter increase portion 6a7, but the position of the axially inner end of the range of the first external teeth inner side outer diameter reduction portion 4a7 may also be aligned with the position of the axially inner end of the range of the first internal teeth inner side inner diameter increase portion 6a7. The range of the first external teeth inner side outer diameter reduction portion 4a7 extends to a position axially outer than the range of the first internal teeth inner side inner diameter increase portion 6a7. Further, the axially inner end of the first internal teeth inner side inner diameter increase portion 6a7 corresponds to the axially inner end of the first internal teeth portion 6a.

[0094] The inner diameter increase ratio of the first internal teeth inner side inner diameter increase portion 6a7 is greater than the outer diameter reduction ratio of the first external teeth inner side outer diameter reduction portion 4a7. Therefore, in Figure 3In [the above], the tooth tip curve depicted by the inner diameter increasing portion 6a7 of the first inner tooth is steeper than the tooth tip curve depicted by the outer diameter decreasing portion 4a7 of the first outer tooth. Here, the inner diameter increasing ratio of the inner diameter increasing portion 6a7 of the first inner tooth refers to the value obtained by dividing the increase amount of the inner diameter of the inner diameter increasing portion 6a7 of the first inner tooth when displaced by a unit distance toward the axial inner side by this unit distance. The inner diameter increasing ratio of the inner diameter increasing portion 6a7 of the first inner tooth can also be said to be the increase amount of the inner diameter of the inner diameter increasing portion 6a7 of the first inner tooth per unit distance in the axial direction. The outer diameter decreasing ratio of the outer diameter decreasing portion 4a7 of the first outer tooth refers to the value obtained by dividing the decrease amount of the outer diameter of the outer diameter decreasing portion 4a7 of the first outer tooth when displaced by a unit distance toward the axial inner side by this unit distance. The outer diameter decreasing ratio of the outer diameter decreasing portion 4a7 of the first outer tooth can also be said to be the decrease amount of the inner diameter of the outer diameter decreasing portion 4a7 of the first outer tooth per unit distance in the axial direction.

[0095] The maximum increase amount of the inner diameter of the inner diameter increasing portion 6a7 of the first inner tooth is greater than the maximum decrease amount of the outer diameter of the outer diameter decreasing portion 4a7 of the first outer tooth. Regarding the ratio of the maximum increase amount of the inner diameter of the inner diameter increasing portion 6a7 of the first inner tooth to the maximum decrease amount of the outer diameter of the outer diameter decreasing portion 4a7 of the first outer tooth, the relationship of "the maximum decrease amount of the outer diameter of the outer diameter decreasing portion 4a7 of the first outer tooth : the maximum increase amount of the inner diameter of the inner diameter increasing portion 6a7 of the first inner tooth = 1:2 to 4" is satisfied. Here, the maximum increase amount of the inner diameter of the inner diameter increasing portion 6a7 of the first inner tooth refers to the value obtained by subtracting the minimum inner diameter of the inner diameter increasing portion 6a7 of the first inner tooth at the axial inner end of the inner diameter increasing portion 6a7 of the first inner tooth from the maximum inner diameter of the inner diameter increasing portion 6a7 of the first inner tooth at the axial outer end of the inner diameter increasing portion 6a7 of the first inner tooth. The maximum decrease amount of the outer diameter of the outer diameter decreasing portion 4a7 of the first outer tooth refers to the value obtained by subtracting the minimum outer diameter of the outer diameter decreasing portion 4a7 of the first outer tooth at the axial inner end of the outer diameter decreasing portion 4a7 of the first outer tooth from the maximum outer diameter of the outer diameter decreasing portion 4a7 of the first outer tooth at the axial outer end of the outer diameter decreasing portion 4a7 of the first outer tooth.

[0096] The outer diameter decreasing portion 4a8 of the first outer tooth has a range in the axial direction. As Figure 3 shown in the example, when the minimum inner diameter portion 6a6 of the first inner tooth has a range in the axial direction, the range of the outer diameter decreasing portion 4a8 of the first outer tooth partially overlaps with the range of the minimum inner diameter portion 6a6 of the first inner tooth. The range of the outer diameter decreasing portion 4a8 of the first outer tooth extends to a position more axially outer than the minimum inner diameter portion 6a6 of the first inner tooth. In addition, the axial outer end of the outer diameter decreasing portion 4a8 of the first outer tooth corresponds to the axial outer end of the first outer tooth portion 4a.

[0097] The outer diameter reduction ratio of the outer diameter reduction portion 4a8 on the outer side of the first external teeth is greater than the outer diameter reduction ratio of the outer diameter reduction portion 4a7 on the inner side of the first external teeth. Therefore, in Figure 3 In the cross-section shown, the tooth tip curve depicted by the outer diameter reduction portion 4a8 on the outer side of the first external teeth is steeper than the tooth tip curve depicted by the outer diameter reduction portion 4a7 on the inner side of the first external teeth. Here, the outer diameter reduction ratio of the outer diameter reduction portion 4a8 on the outer side of the first external teeth refers to the value obtained by dividing the reduction amount of the outer diameter of the outer diameter reduction portion 4a8 on the outer side of the first external teeth when displaced by a unit distance in the axial outer direction by the unit distance.

[0098] <<Tooth tip shapes of the second external teeth portion 4b and the second internal teeth portion 8a>>

[0099] The tooth tip shapes of the second external teeth portion 4b and the second internal teeth portion 8a will be described. Additionally, the second external teeth portion 4b and the second internal teeth portion 8a may have the above-described tooth line shape, but may also not have the tooth tip shapes described below. In the case where the second external teeth portion 4b and the second internal teeth portion 8a do not have the tooth tip shapes described below, the tooth tip shapes of the second external teeth portion 4b and the second internal teeth portion 8a may also be flat, for example.

[0100] If the tooth tip of the second external teeth portion 4b is divided in the axial direction, the second external teeth portion 4b has a second external teeth maximum outer diameter portion 4b6, a second external teeth inner side outer diameter reduction portion 4b7, and a second external teeth outer side outer diameter reduction portion 4b8. The second external teeth inner side outer diameter reduction portion 4b7 is located at a position more axially inner than the second external teeth maximum outer diameter portion 4b6, and the second external teeth outer side outer diameter reduction portion 4b8 is located at a position more axially outer than the second external teeth maximum outer diameter portion 4b6.

[0101] The outer diameter of the second external teeth portion 4b changes in the axial direction. Specifically, the outer diameter of the second external teeth maximum outer diameter portion 4b6 corresponds to the maximum outer diameter of the second external teeth portion 4b. The outer diameter of the second external teeth inner side outer diameter reduction portion 4b7 gradually decreases from the second external teeth maximum outer diameter portion 4b6 toward the axial inner side, and the outer diameter of the second external teeth outer side outer diameter reduction portion 4b8 gradually decreases from the second external teeth maximum outer diameter portion 4b6 toward the axial outer side. The outer diameter of the second external teeth portion 4b refers to the distance from the rotation axis R to the tooth tip of the second external teeth portion 4b.

[0102] If the second internal teeth portion 8a is divided in the axial direction, the second internal teeth portion 8a has a second internal teeth minimum inner diameter portion 8a6 and a second internal teeth inner side inner diameter increase portion 8a7. The second internal teeth inner side inner diameter increase portion 8a7 is located at a position more axially inner than the second internal teeth minimum inner diameter portion 8a6.

[0103] The inner diameter of the second inner tooth portion 8a varies axially. Specifically, the inner diameter of the second inner tooth minimum inner diameter portion 8a6 corresponds to the minimum inner diameter of the second inner tooth portion 8a, and the inner diameter of the second inner tooth inner diameter increasing portion 8a7 gradually increases from the second inner tooth minimum inner diameter portion 8a6 toward the inner side in the axial direction. The inner diameter of the second inner tooth portion 8a refers to the distance from the rotation axis R to the tooth tip of the second inner tooth portion 8a.

[0104] The second outer tooth maximum outer diameter portion 4b6 may have a range in the axial direction or may not have a range in the axial direction and be a point. In Figure 3 the example shown, the second outer tooth maximum outer diameter portion 4b6 does not have a range in the axial direction and is a point.

[0105] The second inner tooth minimum inner diameter portion 8a6 may have a range in the axial direction or may not have a range in the axial direction and be a point. In Figure 3 the example shown, the second inner tooth minimum inner diameter portion 8a6 has a range in the axial direction. In addition, when the second inner tooth minimum inner diameter portion 8a6 has a range in the axial direction, the axially outer end of the second inner tooth minimum inner diameter portion 8a6 corresponds to the axially outer end of the second inner tooth portion 8a. When the second inner tooth minimum inner diameter portion 8a6 does not have a range in the axial direction and is a point, the second inner tooth minimum inner diameter portion 8a6 corresponds to the axially outer end of the second inner tooth portion 8a.

[0106] As Figure 3 shown, when the second outer tooth maximum outer diameter portion 4b6 does not have a range in the axial direction and is a point and the second inner tooth minimum inner diameter portion 8a6 has a range in the axial direction, the position of the second outer tooth maximum outer diameter portion 4b6 in the axial direction is located inside the range of the second inner tooth minimum inner diameter portion 8a6. In addition, when the second outer tooth maximum outer diameter portion 4b6 has a range in the axial direction and the second inner tooth minimum inner diameter portion 8a6 does not have a range in the axial direction and is a point, the position of the second inner tooth minimum inner diameter portion 8a6 in the axial direction may also be located inside the range of the second outer tooth maximum outer diameter portion 4b6. And when the second outer tooth maximum outer diameter portion 4b6 has a range in the axial direction and the second inner tooth minimum inner diameter portion 8a6 has a range in the axial direction, the range of the second outer tooth maximum outer diameter portion 4b6 and the range of the second inner tooth minimum inner diameter portion 8a6 may partially or entirely overlap. When the second outer tooth maximum outer diameter portion 4b6 does not have a range in the axial direction and is a point and the second inner tooth minimum inner diameter portion 8a6 does not have a range in the axial direction and is a point, the positions of the second outer tooth maximum outer diameter portion 4b6 and the second inner tooth minimum inner diameter portion 8a6 in the axial direction may also be aligned with each other.

[0107] The second outer tooth inner diameter decreasing portion 4b7 has a range in the axial direction. As Figure 3In the example shown, when the range of the minimum inner diameter portion 8a6 of the second internal teeth is in the axial direction, the range of the inner diameter reduction portion 4b7 of the second external teeth partially overlaps with the range of the minimum inner diameter portion 8a6 of the second internal teeth. In addition, the axially inner end of the inner diameter reduction portion 4b7 of the second external teeth corresponds to the center between the first external teeth portion 4a and the second external teeth portion 4b.

[0108] The inner diameter increase portion 8a7 of the second internal teeth has a range in the axial direction. The range of the inner diameter increase portion 8a7 of the second internal teeth is smaller than the range of the inner diameter reduction portion 4b7 of the second external teeth, and the entire range of the inner diameter increase portion 8a7 of the second internal teeth is included in the range of the inner diameter reduction portion 4b7 of the second external teeth. The position of the axially inner end of the range of the inner diameter reduction portion 4b7 of the second external teeth is aligned with the position of the axially inner end of the range of the inner diameter increase portion 8a7 of the second internal teeth. In contrast, the range of the inner diameter reduction portion 4b7 of the second external teeth may also extend to a position axially inner than the axially inner end of the range of the inner diameter increase portion 8a7 of the second internal teeth. The range of the inner diameter reduction portion 4b7 of the second external teeth extends to a position axially outer than the axially outer end of the range of the inner diameter increase portion 8a7 of the second internal teeth. In addition, the axially inner end of the inner diameter increase portion 8a7 of the second internal teeth corresponds to the axially inner end of the second internal teeth portion 8a.

[0109] The inner diameter increase ratio of the inner diameter increase portion 8a7 of the second internal teeth is greater than the outer diameter reduction ratio of the inner diameter reduction portion 4b7 of the second external teeth. Therefore, in Figure 3 the tooth tip curve described by the inner diameter increase portion 8a7 of the second internal teeth is steeper than the tooth tip curve described by the inner diameter reduction portion 4b7 of the second external teeth. Here, the inner diameter increase ratio of the inner diameter increase portion 8a7 of the second internal teeth refers to the value obtained by dividing the increase amount of the inner diameter of the inner diameter increase portion 8a7 of the second internal teeth when displaced by a unit distance in the axial direction by the unit distance. The inner diameter increase ratio of the inner diameter increase portion 8a7 of the second internal teeth can also be said to be the increase amount of the inner diameter of the inner diameter increase portion 8a7 of the second internal teeth per unit distance in the axial direction. The outer diameter reduction ratio of the inner diameter reduction portion 4b7 of the second external teeth refers to the value obtained by dividing the reduction amount of the outer diameter of the inner diameter reduction portion 4b7 of the second external teeth when displaced by a unit distance in the axial direction by the unit distance. The outer diameter reduction ratio of the inner diameter reduction portion 4b7 of the second external teeth can also be said to be the reduction amount of the outer diameter of the inner diameter reduction portion 4b7 of the second external teeth per unit distance in the axial direction.

[0110] The maximum increase in the inner diameter of the second inner tooth inner diameter increasing portion 8a7 is greater than the maximum decrease in the outer diameter of the second outer tooth inner diameter decreasing portion 4b7. Regarding the ratio of the maximum increase in the inner diameter of the second inner tooth inner diameter increasing portion 8a7 to the maximum decrease in the outer diameter of the second outer tooth inner diameter decreasing portion 4b7, the relationship of "the maximum decrease in the outer diameter of the second outer tooth inner diameter decreasing portion 4b7: the maximum increase in the inner diameter of the second inner tooth inner diameter increasing portion 8a7 = 1:2 to 4" is satisfied. Here, the maximum increase in the inner diameter of the second inner tooth inner diameter increasing portion 8a7 refers to the value obtained by subtracting the minimum inner diameter of the second inner tooth inner diameter increasing portion 8a7 at the axial outer end of the second inner tooth inner diameter increasing portion 8a7 from the maximum inner diameter of the second inner tooth inner diameter increasing portion 8a7 at the axial inner end of the second inner tooth inner diameter increasing portion 8a7. The maximum decrease in the outer diameter of the second outer tooth inner diameter decreasing portion 4b7 refers to the value obtained by subtracting the minimum outer diameter of the second outer tooth inner diameter decreasing portion 4b7 at the axial inner end of the second outer tooth inner diameter decreasing portion 4b7 from the maximum outer diameter of the second outer tooth inner diameter decreasing portion 4b7 at the axial outer end of the second outer tooth inner diameter decreasing portion 4b7.

[0111] The maximum increase in the inner diameter of the second inner tooth inner diameter increasing portion 8a7 is greater than the maximum decrease in the tooth thickness of the first inner tooth inner diameter increasing portion 6a7.

[0112] The second outer tooth outer diameter decreasing portion 4b8 has a range in the axial direction. As Figure 3 shown in the example, when the second inner tooth minimum inner diameter portion 8a6 has a range in the axial direction, the range of the second outer tooth outer diameter decreasing portion 4b8 partially overlaps with the range of the second inner tooth minimum inner diameter portion 8a6. The range of the second outer tooth outer diameter decreasing portion 4b8 extends to a position more axially outward than the second inner tooth minimum inner diameter portion 8a6. In addition, the axial outer end of the second outer tooth outer diameter decreasing portion 4b8 corresponds to the axial outer end of the second outer tooth portion 4b.

[0113] The outer diameter reduction ratio of the second outer tooth outer diameter decreasing portion 4b8 is greater than the outer diameter reduction ratio of the second outer tooth inner diameter decreasing portion 4b7. Therefore, in Figure 3 the tooth line curve depicted by the second outer tooth outer diameter decreasing portion 4b8 is steeper than the tooth line curve depicted by the second outer tooth inner diameter decreasing portion 4b7. Here, the outer diameter reduction ratio of the second outer tooth outer diameter decreasing portion 4b8 refers to the value obtained by dividing the reduction amount of the outer diameter of the second outer tooth outer diameter decreasing portion 4b8 when displaced by a unit distance in the axial outer direction by the unit distance. The outer diameter reduction ratio of the second outer tooth outer diameter decreasing portion 4b8 can also be said to be the reduction amount of the outer diameter of the second outer tooth outer diameter decreasing portion 4b8 per unit distance in the axial direction.

[0114] <Advantageous technical effects>

[0115] The tooth thickness of the first outer tooth inner tooth thickness reduction part 4a2 of the first outer tooth part 4a gradually decreases towards the inner side in the axial direction. Therefore, the tooth surfaces of the first outer tooth part 4a and the first inner tooth part 6a can be in smooth contact, thereby reducing the eccentric load generated at the inner end in the axial direction of the first outer tooth part 4a, and further reducing the excessive wear of the first outer tooth part 4a and the first inner tooth part 6a. The tooth thickness of the first inner tooth inner tooth thickness reduction part 6a2 of the first inner tooth part 6a gradually decreases towards the inner side in the axial direction, which also brings the same effect.

[0116] The first outer tooth part 4a and the first inner tooth part 6a respectively have the first outer tooth inner tooth thickness reduction part 4a2 and the first inner tooth inner tooth thickness reduction part 6a2, so the tooth thicknesses of the first outer tooth part 4a and the first inner tooth part 6a are not too small. That is, it is not necessary to make the maximum reduction amount of the tooth thickness of the first outer tooth inner tooth thickness reduction part 4a2 and the maximum reduction amount of the tooth thickness of the first inner tooth inner tooth thickness reduction part 6a2 too large. Therefore, while both the first outer tooth part 4a and the first inner tooth part 6a maintain a good balance of appropriate strength, the excessive wear of both the first outer tooth part 4a and the first inner tooth part 6a can be reduced, thereby extending the service life of the outer gear 4 and the first inner gear 6. This effect is particularly significant when the relationship of "the maximum reduction amount of the tooth thickness of the first outer tooth inner tooth thickness reduction part 4a2: the maximum reduction amount of the tooth thickness of the first inner tooth inner tooth thickness reduction part 6a2 = 1:2 to 4" is satisfied.

[0117] One or both of the first outer tooth thickest part 4a1 and the first inner tooth thickest part 6a1 have a range covering a specified width in the axial direction. Therefore, even if there is a positional error of the first inner gear 6 in the axial direction, the first outer tooth thickest part 4a1 and the first inner tooth thickest part 6a1 will contact each other. Therefore, there will be no looseness in the meshing of the first outer tooth part 4a and the first inner tooth part 6a.

[0118] The second outer tooth part 4b and the second inner tooth part 8a also produce the same effects as the first outer tooth part 4a and the first inner tooth part 6a.

[0119] Even if the components of the flexure meshing type gear device 100 have dimensional errors, etc., the above-listed advantageous technical effects can be reliably achieved by restricting the components 12 and 14. This is because the thickness T12 of the first restricting component 12 is appropriately set corresponding to the interval from the outer ring of the bearing 30 to the outer gear 4 in the axial direction, and the thickness T14 of the second restricting component 14 is appropriately set corresponding to the interval from the outer ring of the bearing 32 to the outer gear 4 in the axial direction. That is, the thicknesses T12 and T14 of the restricting components 12 and 14 appropriately determine the tooth line of the outer gear 4 in the axial direction (refer to Figure 2 ) relative to the tooth lines of the inner gears 6 and 8 (refer to Figure 2) position, thus, reliably reducing the eccentric load generated at the axially inner end of the first external tooth portion 4a, and also reliably reducing excessive wear of the first external tooth portion 4a and the first internal tooth portion 6a.

[0120] (Second Embodiment)

[0121] Reference Figure 4 and Figure 5 , the second embodiment will be described. The second embodiment is different from the first embodiment in the following aspects. Except for the following description, the second embodiment is the same as the first embodiment.

[0122] Regarding the tooth line of the second internal tooth portion 8a, as Figure 4 shown, the second internal tooth inner tooth thickness reducing portion 8a2 has an outer region 8a2o and an inner region 8a2i. The inner region 8a2i is located at a position axially more inner than the outer region 8a2o. The range of the inner region 8a2i in the axial direction occupies the axially inner part of the entire range of the second internal tooth inner tooth thickness reducing portion 8a2 in the axial direction, and the range of the outer region 8a2o in the axial direction occupies the axially outer part of the entire range of the second internal tooth inner tooth thickness reducing portion 8a2 in the axial direction. The tooth thickness of the outer region 8a2o gradually decreases from the thickest part 8a1 of the second internal tooth toward the axial inner side, and the tooth thickness of the inner region 8a2i gradually decreases from the outer region 8a2o toward the axial inner side. The tooth thickness reduction ratio of the inner region 8a2i is greater than the tooth thickness reduction ratio of the outer region 8a2o.

[0123] By having the outer region 8a2o and the inner region 8a2i in the second internal tooth inner tooth thickness reducing portion 8a2, while the tooth thickness of the second internal tooth portion 8a can be reduced toward the axially inner end, the tooth thickness reduction at the center of the second internal tooth portion 8a in the axial direction can be suppressed. Therefore, the rigidity of the second internal gear 8 is increased, and the torsional rigidity of the flexural engagement type gear device 100 is increased.

[0124] In Figure 4 the example shown, the second internal tooth inner tooth thickness reducing portion 8a2 has an outer region 8a2o and an inner region 8a2i. Similarly, the first internal tooth inner tooth thickness reducing portion 6a2 may also have an outer region and an inner region located axially more inner than the outer region, and the tooth thickness reduction ratio of the inner region is greater than the tooth thickness reduction ratio of the outer region.

[0125] As Figure 5As shown, regarding the tooth tip of the second internal tooth portion 8a, the second internal tooth inner diameter increasing portion 8a7 has an outer region 8a7o and an inner region 8a7i. The inner region 8a7i is located axially more inward than the outer region 8a7o. The range of the inner region 8a7i in the axial direction occupies the axially inner part of the entire range of the second internal tooth inner diameter increasing portion 8a7 in the axial direction, and the range of the outer region 8a7o in the axial direction occupies the axially outer part of the entire range of the second internal tooth inner diameter increasing portion 8a7 in the axial direction. The inner diameter of the outer region 8a7o gradually increases from the second internal tooth minimum inner diameter portion 8a6 toward the axial inner side, and the inner diameter of the inner region 8a7i gradually increases from the outer region 8a7o toward the axial inner side. The inner diameter increase ratio of the inner region 8a7i is greater than the inner diameter increase ratio of the outer region 8a7o.

[0126] In Figure 5 the example shown, the second internal tooth inner diameter increasing portion 8a7 has an outer region 8a7o and an inner region 8a7i. Similarly, the first internal tooth inner diameter increasing portion 6a7 can also have an outer region and an inner region located axially more inward than the outer region, and the inner diameter increase ratio of the inner region is greater than the inner diameter increase ratio of the outer region.

[0127] (Third Embodiment)

[0128] Refer to Figure 6 and the third embodiment will be described. The third embodiment is different from the first embodiment in the following aspects. Except as described below, the third embodiment is the same as the first embodiment.

[0129] Similar to the first external tooth portion 4a having the first external tooth outer tooth thickness reducing portion 4a3, the first internal tooth portion 6a further has the first internal tooth outer tooth thickness reducing portion 6a3. The first internal tooth outer tooth thickness reducing portion 6a3 is located axially more outward than the first internal tooth thickest portion 6a1. The tooth thickness of the first internal tooth outer tooth thickness reducing portion 6a3 gradually decreases from the first internal tooth thickest portion 6a1 toward the axial outer side. The first internal tooth outer tooth thickness reducing portion 6a3 has a range in the axial direction, and the range of the first internal tooth outer tooth thickness reducing portion 6a3 partially or entirely overlaps with the range of the first external tooth outer tooth thickness reducing portion 4a3.

[0130] Similar to the second outer tooth thickness reduction portion 4b3 of the second outer tooth portion 4b, the second inner tooth portion 8a also has a second inner tooth outer tooth thickness reduction portion 8a3. The second inner tooth outer tooth thickness reduction portion 8a3 is located axially outward of the thickest portion 8a1 of the second inner tooth. The tooth thickness of the second inner tooth outer tooth thickness reduction portion 8a3 gradually decreases from the thickest portion 8a1 of the second inner tooth toward the axially outer side. The second inner tooth outer tooth thickness reduction portion 8a3 has a range in the axial direction, and the range of the second inner tooth outer tooth thickness reduction portion 8a3 partially or entirely overlaps with the range of the second outer tooth outer tooth thickness reduction portion 4b3.

[0131] The first inner tooth outer tooth thickness reduction portion 6a3 helps the tooth surface of the first inner tooth portion 6a to smoothly contact the tooth surface of the first outer tooth portion 4a, and reduces the eccentric load generated at the axially outer end of the first inner tooth portion 6a. The second inner tooth outer tooth thickness reduction portion 8a3 helps the tooth surface of the second inner tooth portion 8a to smoothly contact the tooth surface of the second outer tooth portion 4b, and reduces the eccentric load generated at the axially outer end of the second inner tooth portion 8a.

[0132] In addition, the case where the first inner tooth portion 6a has the first inner tooth outer tooth thickness reduction portion 6a3 can be applied to the second embodiment. Similarly, the case where the second inner tooth portion 8a has the second inner tooth outer tooth thickness reduction portion 8a3 can also be applied to the second embodiment.

[0133] Moreover, in addition to the first inner tooth minimum inner diameter portion 6a6 and the first inner tooth inner side inner diameter increasing portion 6a7, the first inner tooth portion 6a may further have a first inner tooth outer side inner diameter increasing portion. The first inner tooth outer side inner diameter increasing portion is located axially outward of the first inner tooth minimum inner diameter portion 6a6, and the inner diameter of the first inner tooth outer side inner diameter increasing portion gradually increases from the first inner tooth minimum inner diameter portion 6a6 toward the axially outer side. The case where the first inner tooth portion 6a has the first inner tooth outer side inner diameter increasing portion can also be applied to the second embodiment.

[0134] Moreover, in addition to the second inner tooth minimum inner diameter portion 8a6 and the second inner tooth inner side inner diameter increasing portion 8a7, the second inner tooth portion 8a may further have a second inner tooth outer side inner diameter increasing portion. The second inner tooth outer side inner diameter increasing portion is located axially outward of the second inner tooth minimum inner diameter portion 8a6, and the inner diameter of the second inner tooth outer side inner diameter increasing portion gradually increases from the second inner tooth minimum inner diameter portion 8a6 toward the axially outer side. The case where the second inner tooth portion 8a has the second inner tooth outer side inner diameter increasing portion can also be applied to the second embodiment.

[0135] Symbolic Explanation

[0136] 4 - external gear, 4a - first external tooth part, 4a1 - thickest part of the first external tooth, 4a2 - inner tooth thickness reduction part of the first external tooth, 4a3 - outer tooth thickness reduction part of the first external tooth, 4a6 - largest outer diameter part of the first external tooth, 4a7 - inner outer diameter reduction part of the first external tooth, 4a8 - outer outer diameter reduction part of the first external tooth, 4b - second external tooth part, 4b1 - thickest part of the second external tooth, 4b2 - inner tooth thickness reduction part of the second external tooth, 4b3 - outer tooth thickness reduction part of the second external tooth, 4b6 - largest outer diameter part of the second external tooth, 4b7 - inner outer diameter reduction part of the second external tooth, 4b8 - outer outer diameter reduction part of the second external tooth, 6 - first internal gear, 6a - first internal tooth part, 6a1 - thickest part of the first internal tooth, 6a2 - inner tooth thickness reduction part of the first internal tooth, 6a3 - outer tooth thickness reduction part of the first internal tooth, 6a6 - smallest inner diameter part of the first internal tooth, 6a7 - inner inner diameter increase part of the first internal tooth, 8 - second internal gear, 8a - second internal tooth part, 8a1 - thickest part of the second internal tooth, 8a2 - inner tooth thickness reduction part of the second internal tooth, 8a2i - inner region, 8a2o - outer region, 8a3 - outer tooth thickness reduction part of the second internal tooth, 8a6 - smallest inner diameter part of the second internal tooth, 8a7 - inner inner diameter increase part of the second internal tooth, 8a7i - inner region, 8a7o - outer region, 8b - rolling surface, 22 - vibration - starting body axis, 22a - vibration - starting body, 100 - flexural engagement type gear device.

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 side by side with the first internal gear in the axial direction and meshes with the external gear; wherein, 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 second external tooth portion has a second external tooth thickest portion with the maximum tooth thickness and a second external tooth inner tooth thickness reduction portion where the tooth thickness decreases from the second external tooth thickest portion toward the axial inner side, the internal tooth portion of the second internal gear has a second internal tooth thickest portion with the maximum tooth thickness and a second internal tooth inner tooth thickness reduction portion where the tooth thickness decreases from the second internal tooth thickest portion toward the axial inner side.

2. The flexure engagement type gear device according to claim 1, wherein, the first external tooth portion has a first external tooth thickest portion with the maximum tooth thickness and a first external tooth inner tooth thickness reduction portion where the tooth thickness decreases from the first external tooth thickest portion toward the axial inner side, the internal tooth portion of the first internal gear has a first internal tooth thickest portion with the maximum tooth thickness and a first internal tooth inner tooth thickness reduction portion where the tooth thickness decreases from the first internal tooth thickest portion toward the axial inner side.

3. The flexure engagement type gear device according to claim 2, wherein, the number of teeth of the first external tooth portion is different from that of the first internal gear, the number of teeth of the second external tooth portion is the same as that of the second internal gear, the maximum reduction amount of the tooth thickness is such that the second internal tooth inner tooth thickness reduction portion is greater than the first internal tooth inner tooth thickness reduction portion.

4. The flexure engagement type gear device according to any one of claims 1 to 3, wherein, the second external tooth portion has a second external tooth outer tooth thickness reduction portion where the tooth thickness decreases from the second external tooth thickest portion toward the axial outer side.

5. The flexure engagement type gear device according to any one of claims 1 to 3, wherein, the internal tooth portion of the second internal gear has a second internal tooth outer tooth thickness reduction portion where the tooth thickness decreases from the second internal tooth thickest portion toward the axial outer side.

6. The flexure engagement type gear device according to any one of claims 1 to 3, wherein, at least one of the second external tooth thickest portion and the second internal tooth thickest portion has a predetermined width range in the axial direction.

7. The flexure engagement type gear device according to any one of claims 1 to 3, wherein, the reduction amount of the tooth thickness per unit distance in the tooth trace direction is such that the second internal tooth inner tooth thickness reduction portion is greater than the second external tooth inner tooth thickness reduction portion.

8. The flexure engagement type gear device according to any one of claims 1 to 3, wherein, the second internal tooth inner tooth thickness reduction portion has an outer region continuous from the second internal tooth thickest portion and an inner region located on the axial inner side of the outer region, the reduction amount of the tooth thickness per unit distance in the tooth trace direction is such that the inner region is greater than the outer region.

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