Wave gear device

Abstract

To provide a wave gear device capable of reducing an n-th component of vibrations generated with the rotation of a wave generator while suppressing instability in transmission of power between a flexspline and a circular spline.SOLUTION: In a wave gear device 100, at least one of a plurality of support parts 33 of a wave generator 30 extends radially at an angular position shifted by a predetermined minute angle α from an angular position obtained by dividing 360 degrees in a circumferential direction by the number of the plurality of support parts 33.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a strain wave gear device. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there is known a strain wave gear device in which the position at which the external teeth of a flexspline mesh with the internal teeth of a circular spline is shifted in the circumferential direction of the flexspline (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses a wave gear device including a wave generator that bends a flexible gear (flexspline) into a non-circular shape to move a meshing portion with a rigid gear (circular spline) in the circumferential direction of the rigid gear. In the wave gear device described in the above-mentioned Patent Document 1, the wave generator bends the flexible gear so that multiple meshing portions are formed at equal angular intervals in the circumferential direction of the rigid gear. At least two of the multiple meshing portions have different lengths from the rotating shaft of the motor that rotates the wave generator to the portion that contacts the flexible gear in the radial direction of the rigid gear, so that the meshing states between the flexible gear and the rigid gear are different from each other. This reduces the n-th order (n is the number of multiple meshing portions) component of vibration generated with the rotation of the wave generator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 198348 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional wave gear device described in the above Patent Document 1, at least two of the meshing portions have different lengths in the radial direction of the rigid gear (circular spline) from the rotating shaft of the motor that rotates the wave generator to the portion that contacts the flexible gear (flexspline). Therefore, at least one of the meshing portions has a relatively short length in the radial direction from the rotating shaft of the motor that rotates the wave generator to the portion that contacts the flexible gear. In this case, a meshing portion between the flexible gear and the rigid gear is generated where the meshing between the flexible gear and the rigid gear is relatively shallow, so that the transmission of power between the flexible gear and the rigid gear is likely to become unstable. For this reason, there is a demand for a wave gear device that can reduce the n-th component of the vibration generated by the rotation of the wave generator while suppressing the instability of the transmission of power between the flexible gear (flexspline) and the rigid gear (circular spline).

[0006] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a wave gear device that is capable of reducing the n-th order component of vibration generated in conjunction with rotation of the wave generator while suppressing instability in the transmission of power between the flexspline and the circular spline. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, a wave gear device in one aspect of the present invention comprises: an annular circular spline provided with a plurality of internal teeth; an annular flexspline provided with a plurality of external teeth that mesh with the internal teeth and whose number is different from the number of the internal teeth; a motor; a plurality of contact portions that contact the inner surface of the flexspline from inside in the radial direction of the circular spline so as to deform the flexspline into a non-circular shape; and a plurality of support portions that extend radially to connect the rotating shaft of the motor to each of the plurality of contact portions and support each of the plurality of contact portions, and a wave generator that moves a position where the external teeth of the flexspline mesh with the internal teeth of the circular spline in the circumferential direction of the circular spline, and at least one of the plurality of support portions extends radially at an angular position that is shifted by a predetermined small angle from an angular position obtained by dividing 360 degrees in the circumferential direction by the number of the plurality of support portions.

[0008] In a wave gear device according to one aspect of the present invention, as described above, at least one of the support parts of the wave generator extends in the radial direction at an angular position (offset angular position) that is shifted a predetermined small angle from an angular position (division angular position) obtained by dividing 360 degrees in the circumferential direction by the number of the support parts. This allows at least one of the contact parts supported by each of the support parts to come into contact with the inner circumferential surface of the flexspline at the offset angular position. This allows the portion where the external teeth of the flexspline and the internal teeth of the circular spline mesh most deeply in the circumferential direction (center of meshing) to be shifted from the division angular position toward the offset angular position by the small angle shift of the contact part that contacts the inner circumferential surface of the flexspline from the division angular position to the offset angular position. This makes it possible to make the meshing state between the external teeth of the flexspline and the internal teeth of the circular spline at a division angle position where the contact portion in contact with the inner circumferential surface of the flexspline is shifted toward the shifted angle position different from the meshing state between the external teeth of the flexspline and the internal teeth of the circular spline at a division angle position where the contact portion in contact with the inner circumferential surface of the flexspline is at the division ... each other, even without making the radial lengths of the multiple support portions different from each other. In other words, it is possible to make the meshing state between the external teeth of the flexspline and the internal teeth of the circular spline different from each other at at least two division angle positions out of the multiple division angle positions, even without making the radial lengths of the multiple support portions different from each other. As a result, it is possible to reduce the n-th order (n is the number of meshing portions at multiple locations) component of vibration generated with the rotation of the wave generator while suppressing instability in the transmission of power between the flexspline and the circular spline. Furthermore, since the angle by which the divided angular position is shifted to the offset angular position is a very small angle, the contact portion that comes into contact with the inner circumferential surface of the flexspline does not shift excessively from the divided angular position.This makes it possible to shift the angular position of the contact portion that comes into contact with the inner surface of the flexspline to a deviated angular position from the division angle position, while preventing the external teeth of the flexspline and the internal teeth of the circular spline from coming into contact with each other in areas where the external teeth of the flexspline and the internal teeth of the circular spline should not actually mesh, which would cause a hindrance to the operation of deforming the flexspline into a non-circular shape, due to the contact portion being excessively deviated from the division angle position.

[0009] In the wave gear device according to the above aspect, the multiple support portions of the wave generator preferably include two support portions, a first support portion and a second support portion, the first support portion extending radially at a first angular position in the circumferential direction, and the second support portion extending radially at a second angular position shifted by a small angle from an opposing angular position shifted 180 degrees from the first angular position in the circumferential direction.

[0010] With this configuration, in which two contact portions contact the inner circumferential surface of the flexspline so as to deform the flexspline into an elliptical shape and two support portions support each of the two contact portions, it is possible to reduce the nth-order component of the vibration generated by the rotation of the wave generator while suppressing instability in the transmission of power between the flexspline and the circular spline.

[0011] In a configuration in which the second support portion extends radially at a second angular position shifted by a small angle from an opposing angular position shifted 180 degrees from the first angular position in the circumferential direction, the small angle is preferably 10 degrees or less.

[0012] With this configuration, the small angle does not become excessively large, so in a configuration in which two contact portions contact the inner surface of the flexspline so as to deform the flexspline into an elliptical shape and two support portions support each of the two contact portions, it is possible to easily realize a configuration in which the contact portions that contact the inner surface of the flexspline do not deviate excessively from the division angle position.

[0013] In the above-mentioned configuration in which the minute angle is 10 degrees or less, the minute angle is preferably an angle corresponding to the pitch (0.5×m (m is an odd number)) of the external teeth of the flexspline.

[0014] With this configuration, the angular position at which the contact portion presses the inner circumferential surface of the flexspline radially outward is shifted in the circumferential direction by (0.5 × m (m is an odd number)) pitch of the external teeth of the flexspline, so that the change in the difference in the depth of meshing between the external teeth of the flexspline and the internal teeth of the circular spline when the meshing center is shifted from the divided angle position toward the shifted angle position can be made relatively large, compared to when the minute angle is, for example, 1.0 × p (p is an integer) pitch, such as 1 pitch or 2 pitches of the external teeth of the flexspline. This makes it possible to effectively make the meshing states between the external teeth of the flexspline and the internal teeth of the circular spline differ from each other at least at two divided angle positions out of the multiple divided angle positions.

[0015] In the present application, the following configuration is also considered in the wave gear device according to the above aspect.

[0016] (Additional note 1) That is, in a configuration in which the above-mentioned minute angle is an angle corresponding to the (0.5 x m (m is an odd number)) pitch of the external teeth of the flexspline, the minute angle is preferably an angle corresponding to 0.5 or 1.5 pitches of the external teeth of the flexspline.

[0017] With this configuration, the minute angle becomes a relatively small angle among the angles corresponding to the pitch of the external teeth of the flexspline (0.5 × m (m is an odd number)), so it is easy to realize a configuration in which the minute angle corresponds to the pitch of the external teeth of the flexspline (0.5 × m (m is an odd number)) and is 10 degrees or less. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view showing a strain wave gear device according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a plan view showing a wave gear device according to an embodiment of the present invention. [Diagram 3] FIG. 3 is an enlarged view of a portion III in FIG. [Figure 4] FIG. 3 is an enlarged view of a portion IV in FIG. [Diagram 5] FIG. 1 is a plan view showing a wave gear device according to a comparative example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] The configuration of a strain wave gear device 100 according to one embodiment of the present invention will be described with reference to Figures 1 to 4. The strain wave gear device 100 is installed in, for example, a device for opening and closing a vehicle door (power sliding door), a vehicle steering device, a device for opening and closing a vehicle sunroof, etc.

[0021] In the following description, the axial, radial, and circumferential directions of the circular spline 10 (see FIG. 1) included in the wave gear device 100 are referred to as the Z direction, R direction, and C direction, respectively. One side and the other side in the axial direction (Z direction) are referred to as the Z1 side and the Z2 side, respectively. The inside and outside in the radial direction (R direction) are referred to as the R1 side and the R2 side, respectively. One side and the other side in the circumferential direction (C direction) are referred to as the C1 side and the C2 side, respectively.

[0022] (Overall configuration of strain wave gear device) As shown in FIG. 1, the wave gear device 100 includes a circular spline 10, a flexspline 20, and a wave generator 30.

[0023] 2, the circular spline 10 is formed in an annular shape. A plurality of internal teeth 11 are provided on the R1 side surface of the circular spline 10 around the entire circumference so as to be aligned in the C direction.

[0024] The circular spline 10 is fixed to an output shaft (not shown) of the strain wave gear device 100. In other words, as the circular spline 10 rotates, the output shaft of the strain wave gear device 100 rotates so that vehicle doors can be opened and closed, vehicle steering can be performed, the sunroof can be opened and closed, and the like.

[0025] The flexspline 20 is formed in an annular shape. A plurality of external teeth 21 are provided on the R2 side portion of the flexspline 20 around the entire circumference so as to be aligned in the C direction. The plurality of external teeth 21 of the circular spline 10 are configured to mesh with the plurality of internal teeth 11 of the circular spline 10.

[0026] The number of external teeth 21 of the flexspline 20 is less than the number of internal teeth 11 of the circular spline 10. In other words, the number of external teeth 21 of the flexspline 20 is different from the number of internal teeth 11 of the circular spline 10. The number of external teeth 21 of the flexspline 20 is 2w (w is an integer) less than the number of internal teeth 11 of the circular spline 10.

[0027] As shown in FIG. 1, the wave generator 30 includes a motor 31, a plurality of contact portions 32, and a plurality of support portions 33.

[0028] The motor 31 has a motor body 31a which is the power source of the strain wave gear device 100, and a rotation shaft 31b which is rotationally driven by the motor body 31a. The motor 31 rotates about a rotation axis 90 which extends along the Z direction.

[0029] 2, the multiple contact portions 32 are disposed on the R2 side with respect to the rotation axis 90 of the motor 31. Each of the multiple contact portions 32 is a roller (rolling bearing). The multiple contact portions 32 are in contact with the inner circumferential surface 22 of the flexspline 20 from the R1 side (the radially inner side of the circular spline 10) so as to deform the flexspline 20 into a non-circular shape.

[0030] Each of the multiple support portions 33 extends in the R direction (radial direction) so as to connect the rotating shaft 31b of the motor 31 and each of the multiple contact portions 32. Each of the multiple support portions 33 extends along the R direction such that the R direction and the C direction are the longitudinal direction and the transverse direction, respectively, when viewed from the Z direction. Each of the multiple support portions 33 supports each of the multiple contact portions 32.

[0031] The position where the external teeth 21 of the flexspline 20 mesh with the internal teeth 11 of the circular spline 10 is moved in the C direction (circumferential direction of the circular spline 10). Specifically, the rotation of the motor body 31a rotates the rotating shaft 31b of the motor 31. Then, as the rotating shaft 31b of the motor 31 rotates, the positions of the multiple contact portions 32 connected to the rotating shaft 31b of the motor 31 by the multiple support portions 33 move in the C direction. Accordingly, the position where the external teeth 21 of the flexspline 20 mesh with the internal teeth 11 of the circular spline 10 moves in the C direction.

[0032] The wave generator 30 is provided with two each of the contact portions 32 and the support portions 33. Specifically, the multiple contact portions 32 of the wave generator 30 include two, a first contact portion 32a and a second contact portion 32b. The multiple support portions 33 of the wave generator 30 include two, a first support portion 33a and a second support portion 33b. The first support portion 33a extends in the R direction so as to connect the rotating shaft 31b of the motor 31 and the first contact portion 32a. The second support portion 33b extends in the R direction so as to connect the rotating shaft 31b of the motor 31 and the second contact portion 32b.

[0033] (Detailed configuration of multiple contact parts and multiple support parts) As shown in Fig. 2, at least one of the multiple support parts 33 of the wave generator 30 extends in the R direction (radial direction) at an angular position shifted by a predetermined minute angle α from an angular position obtained by dividing 360 degrees in the C direction (circumferential direction) by the number of the multiple support parts 33. That is, one of the two support parts 33 (the first support part 33a and the second support part 33b) extends in the R direction at an angular position shifted by a predetermined minute angle α from an angular position obtained by dividing 360 degrees in the C direction into two. Specifically, the first support part 33a extends in the R direction (radial direction) at a first angular position P1 in the C direction (circumferential direction). And the second support part 33b extends in the R direction at a second angular position P2 shifted by the minute angle α from an opposing angular position PX shifted by 180 degrees from the first angular position P1 in the C direction. The lengths of the two support portions 33 (the first support portion 33a and the second support portion 33b) in the R direction are approximately equal.

[0034] 3 and 4, the position where the first contact portion 32a contacts the inner circumferential surface 22 of the flexspline 20 is a first angular position P1 in the direction C, while the position where the second contact portion 32b contacts the inner circumferential surface 22 of the flexspline 20 is a second angular position P2 in the direction C. In this case, the meshing state between the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 can be made to differ between the first angular position P1 and an opposing angular position PX that is shifted 180 degrees from the first angular position P1 in the direction C. This makes it possible to reduce the secondary component of the vibration generated as the wave generator 30 rotates.

[0035] 2, the minute angle α is equal to or smaller than 10 degrees. Specifically, the minute angle α is an angle corresponding to 1.5 pitches of the external teeth 21 of the flexspline 20. In other words, the minute angle α is an angle corresponding to a pitch of (0.5×m (m is an odd number)) of the external teeth 21 of the flexspline 20.

[0036] (Effects of the embodiment) In this embodiment, the following effects can be obtained.

[0037] In this embodiment, as described above, at least one of the multiple support parts 33 of the wave generator 30 extends in the radial direction at an angle position (offset angle position) shifted by a predetermined minute angle α from an angle position (division angle position) obtained by dividing 360 degrees in the circumferential direction by the number of the multiple support parts 33. This allows at least one of the multiple contact parts 32 supported by each of the multiple support parts 33 to come into contact with the inner circumferential surface 22 of the flexspline 20 at the offset angle position. This allows the portion (meshing center) where the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 mesh most deeply in the circumferential direction to be shifted from the division angle position toward the offset angle position by the amount of shift of the contact part 32 that contacts the inner circumferential surface 22 of the flexspline 20 from the division angle position to the offset angle position by the minute angle α. This makes it possible to make the meshing state between the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 at a division angle position where the contact portion 32 in contact with the inner circumferential surface 22 of the flexspline 20 is shifted toward the shifted angle position different from the meshing state between the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 at a division angle position where the contact portion 32 in contact with the inner circumferential surface 22 of the flexspline 20 is at the division angle position. In other words, even if the radial lengths of the multiple support portions 33 are made different from each other, the meshing states between the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 can be made different from each other at least two division angle positions out of the multiple division angle positions. As a result, it is possible to reduce the n-th order (n is the number of meshing portions at multiple locations) component of vibration generated with the rotation of the wave generator 30 while suppressing instability in the transmission of power between the flexspline 20 and the circular spline 10. In addition, since the angle by which the divided angular position is shifted to the offset angular position is a small angle α, the contact portion 32 that comes into contact with the inner circumferential surface 22 of the flexspline 20 does not deviate excessively from the divided angular position.This makes it possible to shift the angular position of the contact portion 32 that comes into contact with the inner peripheral surface 22 of the flexspline 20 to a shifted angular position from the divided angle position, while preventing the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 from coming into contact with each other in areas where the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 should not actually mesh with each other, which would cause a hindrance to the operation of deforming the flexspline 20 into a non-circular shape, due to the contact portion 32 being excessively shifted from the divided angle position.

[0038] In the present embodiment, as described above, the multiple support portions 33 of the wave generator 30 include two support portions, the first support portion 33a and the second support portion 33b. The first support portion 33a extends in the radial direction at a first angular position P1 in the circumferential direction. The second support portion 33b extends in the radial direction at a second angular position P2 that is shifted by a small angle α from the opposing angular position PX that is shifted by 180 degrees from the first angular position P1 in the circumferential direction. With this configuration, in which the two contact portions 32 contact the inner circumferential surface 22 of the flexspline 20 so as to deform the flexspline 20 into an elliptical shape and the two contact portions 32 are supported by the two support portions 33, it is possible to reduce the n-th order component of the vibration generated with the rotation of the wave generator 30 while suppressing instability in the transmission of power between the flexspline 20 and the circular spline 10.

[0039] In this embodiment, as described above, the minute angle α is 10 degrees or less. This prevents the minute angle α from becoming excessively large, and therefore, in a configuration in which two contact portions 32 contact the inner circumferential surface 22 of the flexspline 20 so as to deform the flexspline 20 into an elliptical shape and two support portions 33 support each of the two contact portions 32, a configuration can be easily realized in which the contact portions 32 that contact the inner circumferential surface 22 of the flexspline 20 do not deviate excessively from the divided angle position. Note that, as the minute angle α increases, the gap between the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 gradually widens between the first angular position P1 on one side of the second angular position P2 in the circumferential direction, and the gap between the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 gradually narrows between the first angular position P1 on the other side of the second angular position P2 in the circumferential direction. For example, as in the comparative wave gear device 200 shown in FIG. 5, when the infinitesimal angle α is an angle corresponding to 2.5 pitches of the external teeth 21 of the flexspline 20, the gap between the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 comes into contact with each other at the first angular position P1 on the other side of the second angular position P2 in the circumferential direction.

[0040] Furthermore, in this embodiment, as described above, the minute angle α is an angle corresponding to the (0.5×m (m is an odd number)) pitch of the external teeth 21 of the flexspline 20. As a result, the angular position at which the contact portion 32 presses the inner peripheral surface 22 of the flexspline 20 radially outward is shifted in the circumferential direction by the (0.5×m (m is an odd number)) pitch of the external teeth 21 of the flexspline 20, so that the change in the difference in the meshing depth between the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 when the meshing center is shifted from the division angle position toward the shifted angle position can be made relatively large, compared to when the minute angle α is, for example, 1.0×p (p is an integer) pitch, such as 1 pitch or 2 pitches, of the external teeth 21 of the flexspline 20. This makes it possible to effectively make the meshing state between the external teeth 21 of the flexspline 20 and the internal teeth 11 of the circular spline 10 different from each other at least at two divided angular positions among the plurality of divided angular positions.

[0041] Furthermore, in this embodiment, as described above, the minute angle α is an angle corresponding to 1.5 pitches of the external teeth 21 of the flexspline 20. As a result, the minute angle α becomes a relatively small angle among the angles corresponding to the (0.5×m (m is an odd number)) pitches of the external teeth 21 of the flexspline 20, so it is possible to easily realize a configuration in which the minute angle is an angle corresponding to the (0.5×m (m is an odd number)) pitch of the external teeth 21 of the flexspline 20 and is 10 degrees or less.

[0042] [Variations] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the description of the embodiments above, and further includes all modifications (variations) within the meaning and scope of the claims.

[0043] For example, in the above embodiment, an example was shown in which the minute angle α is an angle corresponding to 1.5 pitches of the external teeth 21 of the flexspline 20, but the present invention is not limited to this. In the present invention, the minute angle may be an angle corresponding to 0.5 pitches of the external teeth of the flexspline.

[0044] Also, in the above embodiment, an example was shown in which the infinitesimal angle α is an angle corresponding to the (0.5×m (m is an odd number)) pitch of the external teeth 21 of the flexspline 20, but the present invention is not limited to this. In the present invention, the infinitesimal angle may be an angle corresponding to a pitch other than the (0.5×m (m is an odd number)) pitch of the external teeth of the flexspline (for example, a 1.0×p (p is an integer) pitch such as 1 pitch or 2 pitches, a pitch that is neither a 0.5×m (m is an odd number) pitch nor a 1.0×p (p is an integer) pitch).

[0045] In addition, in the above embodiment, an example was shown in which the minute angle was 10 degrees or less, but the present invention is not limited to this. In the present invention, the minute angle may be greater than 10 degrees.

[0046] In the above embodiment, the multiple support parts 33 of the wave generator 30 include two parts, the first support part 33a and the second support part 33b, and the first support part 33a extends in the radial direction at a first angular position P1 in the circumferential direction, and the second support part 33b extends in the radial direction at a second angular position P2 that is shifted by a small angle α from the opposing angular position PX that is shifted by 180 degrees from the first angular position P1 in the circumferential direction, but the present invention is not limited to this. In the present invention, the multiple support parts of the wave generator may include v support parts from the first support part to a vth support part (v is an integer of 3 or more), and at least one of the v support parts from the first support part to the vth support part may extend in the radial direction at an angular position shifted by a small angle from an angular position obtained by dividing 360 degrees in the circumferential direction by v. [Explanation of symbols]

[0047] Reference Signs List 10...circular spline, 11...internal teeth (of circular spline), 20...flexspline, 21...external teeth (of flexspline), 22...inner peripheral surface (of flexspline), 30...wave generator, 31...motor, 32...contact portion, 33...support portion, 33a...first support portion, 33b...second support portion, 100...wave gear device, P1...first angular position, P2...second angular position, PX...opposing angular position, α...small angle

Claims

1. an annular circular spline having a plurality of internal teeth; an annular flexspline having a plurality of external teeth that mesh with the internal teeth and is different in number from the plurality of internal teeth; a motor; a plurality of contact portions that contact an inner circumferential surface of the flexspline from a radially inner side of the circular spline so as to deform the flexspline into a non-circular shape; and a plurality of support portions that extend in the radial direction so as to connect a rotating shaft of the motor to each of the plurality of contact portions and support each of the plurality of contact portions, and a wave generator that moves a position at which the external teeth of the flexspline mesh with the internal teeth of the circular spline in a circumferential direction of the circular spline, at least one of the plurality of support portions of the wave generator extends in the radial direction at an angular position that is shifted by a predetermined small angle from an angular position obtained by dividing 360 degrees in the circumferential direction by the number of the plurality of support portions.

2. the plurality of support portions of the wave generator include two support portions, a first support portion and a second support portion; The first support portion extends in the radial direction at a first angular position in the circumferential direction, 2. The strain wave gear device according to claim 1, wherein the second support portion extends in the radial direction at a second angular position that is shifted by the small angle from an opposing angular position that is shifted 180 degrees from the first angular position in the circumferential direction.

3. The strain wave gear device according to claim 2 , wherein the small angle is equal to or less than 10 degrees.

4. 4. The strain wave gear device according to claim 3, wherein the small angle corresponds to a pitch of the external teeth of the flexspline (0.5×m, where m is an odd number).

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