Spur Gear Unit
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- HARMONIC DRIVE AG
- Filing Date
- 2023-09-15
- Publication Date
- 2026-06-24
AI Technical Summary
In compact spur gearing, flexsplines without tooth modification experience increased stresses, reducing performance.
The external toothing of the flexspline is modified with a radially lowered area starting from the plane between the circular spline and dynamic spline, distributing load more evenly over the tooth surface.
This configuration reduces stress peaks, improving load capacity and service life by at least 25%.
Smart Images
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Abstract
Description
[Technical Field]
[0001] The present invention relates to a spur gearing in the form of strain wave gearing, which includes a circular spline with internal toothing, a dynamic spline with internal toothing and axially adjacent to the circular spline, a flexible flexspline with at least one external toothing arranged inside the circular spline and the dynamic spline, and a wave generator arranged inside the flexspline for radially deforming the flexspline. Due to the deformation of the flexspline, a form-locking torque-transmitting connection is established between the circular spline and the flexspline at two opposing points on the flexspline, and between the flexspline and the dynamic spline at four positions on either side of the contact point with the circular spline. This type of spur gearing therefore includes four main components: the wave generator, the flexspline, the dynamic spline, and the circular spline. [Background technology]
[0002] During deceleration operation of the wave gearing, i.e., when the rotation speed is reduced, the elliptically shaped wave generator functions as the driving element. The wave generator, particularly via a thin ring-type rolling bearing, deforms the flexspline (FS), which is engaged with internally toothed hollow gears, i.e., the circular spline (CS) and the dynamic spline (DS). As the wave generator (WG) rotates, the major axis of the ellipse moves, thereby shifting the tooth engagement area. Since the flexspline has fewer teeth than the circular spline, specifically two fewer teeth, the flexspline rotates relative to the circular spline by one tooth pitch angle during half a rotation of the wave generator and by two tooth pitch angles during a full rotation. If the circular spline is fixed in position, the flexspline rotates in the opposite direction to the rotation of the wave generator.
[0003] The wave generator usually consists of an elliptical steel disk fitted with a thin ring-rolling bearing. This component is used as the drive element in reduction operation. The circular spline is a hollow gear with internal teeth whose teeth engage with the external teeth of the flexspline in the region of the major axis of the ellipse of the wave generator. The circular spline usually has two more teeth than the flexspline. The flexspline configuration allows for large elastic deformations in the radial direction. The flexspline is brought into an elliptical shape by the wave generator. In the region of the major axis of the ellipse, the external teeth of the flexspline engage with the internal teeth of both the circular spline and the dynamic spline.
[0004] A dynamic spline is a hollow gear with internal teeth that has the same number of teeth as a flexspline. This component rotates in the same direction and at the same speed as the flexspline and is used as a driven element or as a support frame in reduction gear operations. This type of spur gear can be used advantageously in various technical fields, especially in service robotics.
[0005] The above-mentioned spur gear device is described, for example, in the following Patent Document 1 (DE 10 2020 107 674 B3).
[0006] EP 3 690 280 A1 discloses a dual-type strain wave gear having an externally toothed gear with two external toothings with different numbers of teeth, with a gap formed between the teeth as a cutting gap for a tooth milling cutter.
[0007] DE 11 2012 005 159 B4 describes a flexible mesh gearing, which includes a wave generator and a cylindrical externally toothed gear, the externally toothed gear being flexible and arranged on the outer periphery of the wave generator, and further includes two internally toothed gears that engage with the externally toothed gear.
[0008] From JP 2009-133414 A, a strain wave gear reducer is known which has a flexible external gear, the external gear being partially engaged with a rigid internal gear and a sub-rigid internal gear. [Prior art documents] [Patent documents]
[0009] [Patent Document 1] German Patent Invention No. 102020107674 [Patent Document 2] European Patent Application Publication No. 3690280 [Patent Document 3] German Patent Invention No. 112012005159 [Patent Document 4] JP 2009-133414 Summary of the Invention [Problem to be solved by the invention]
[0010] It is a disadvantage that in compact spur gearing in the form of strain wave gearing, flexsplines are used without any tooth modification in the flank direction, where increased stresses occur, which reduce the performance of the spur gearing.
[0011] The object underlying the present invention is therefore to provide a spur gear of the type mentioned at the outset, which has an optimum load distribution and improved performance. [Means for solving the problem]
[0012] The above problem is solved according to the invention by the features of claim 1. DETAILED DESCRIPTION OF THE INVENTION
[0013] Hereinafter, an embodiment of the invention will be described.
[0014] According to the invention, the external toothing starts in the axial direction from the plane between the circular spline and the dynamic spline and is pulled back in the radial direction towards the gear axis, i.e. the axial transition path (axial transition line) of the radial position of the tooth flank cross section of the external toothing of the flexspline has a radially lowered (pulled back) area in the axial direction.
[0015] Advantageous configurations of the invention are the subject of the subclaims.
[0016] The present invention starts from the recognition that it is known from evaluation of actual tests and finite element calculations that in spur gearing, increased stresses occur in the meshed components near the plane between the circular spline and the dynamic spline.
[0017] Based on this understanding, the increased stress in the plane between the circular spline and the dynamic spline can be reduced by providing the teeth of the flexspline with modified (profile-shifted) teeth in a certain area in the lateral direction (tooth surface direction). When the load is small, the teeth should support more strongly in the direction of the end face of the flexspline. And when the load increases, as a result of the deformation of the flexspline, the supporting surface increases and the load is distributed more evenly over the tooth surface (than in conventional spur gears).
[0018] The radially lowered or shifted region of the axial transition path of the radial position of the tooth flank cross section of the external toothing of the flexspline can start in the axial direction from a position between the circular spline and the dynamic spline and extend up to the respective end faces of the flexspline. The region is preferably largest in the plane between the circular spline and the dynamic spline or in the region around this plane and decreases in the direction of the end faces. The shift of the transition path (transition line) means a radial shift of the flank cross section of the flexspline toothing in the direction of the central axis of the gear train, which results in a radially lowered region of the external toothing.
[0019] Advantageously, the maximum radial shift of the radially depressed area in the direction of the central axis is located in the area of the plane between the circular spline and the dynamic spline, in this way compensating for the increased load on the tooth flank of the flexspline near the plane between the circular spline and the dynamic spline caused by deformation under load.
[0020] The radially depressed areas can be symmetrical or asymmetrical with respect to the axial center of the external toothing. Both hollow gears (circular spline and dynamic spline) are preferably constructed with the same width.
[0021] If the circular spline and the dynamic spline do not have the same axial extent, the radially depressed region is located asymmetrically relative to the center of the external toothing of the flexspline. Due to geometric constraints of the hollow gears or different loads, it may be advantageous to configure the hollow gears with different widths. Hollow gears of different widths require an asymmetric configuration. Furthermore, for certain configurations, depending on the specific engagement situation, an asymmetric configuration may be more suitable for hollow gears of the same width. The shift in the radially depressed toothing region improves edge support and improves load distribution on the gears.
[0022] Advantageously, the radial shift of the front cross section of the external toothing of the flexspline in the direction of the central axis decreases linearly in the axial direction from the region of greatest radial depression on both sides in the direction of the end faces, i.e. the radial extent of the external toothing increases in each case towards the end faces.
[0023] Advantageously, the axial progression path of the radial shift of the front cross section of the external toothing of the flexspline has a constant value (in terms of radial height) in the region of one or both end faces.
[0024] The axial transition path of the radial shift of the front cross section of the external toothing of the flexspline advantageously has a convex or concave shape (as viewed in the axial direction) in the radially lowered region. A convex axial transition path makes it possible to further reduce local high contact stresses.
[0025] Preferably, the front cross section of the external toothing of the flexspline is shifted in the direction of the central axis in the region of one or both end faces.
[0026] In one preferred embodiment, the flexspline comprises two external toothings which are separated from one another, in particular completely, by a groove.
[0027] Preferably, a value between 0 and 0.2 is selected for the maximum shift of the axial transition path of the radial position of the tooth profile section of the external toothing of the flexspline in the direction of the central axis, relative to the ratio (module) of the reference circle (Teilkreis: reference circle diameter) to the number of teeth of the flexspline. The maximum shift is the difference between the maximum and minimum radial positions of the tooth profile section of the flexspline (profile shift: amount of offset).
[0028] The front cross section of the external toothing of the flexspline in the region of one or both end faces can be preferably shifted in the direction of the central axis, which shift of the toothing at the end faces can reduce the contact stresses that are increased due to the edge support.
[0029] The rolling bearings of the spur gear with rolling elements preferably comprise balls, rollers or needles as rolling elements.
[0030] The advantages of the present invention are, in particular, that due to the shift in the axial progression path of the radial position of the tooth flank cross section of the external toothing of the flexspline, the typical loads on the teeth in spur gear trains are taken into account, so that the load capacity and the service life of the gear train are increased, in particular by at least 25%.
[0031] The present invention will now be explained in more detail with reference to the drawings, in which all features described in this specification and / or shown in the drawings, by themselves or in any meaningful combination thereof, constitute the subject matter of the present invention, regardless of their association in the claims or claim dependencies. The following highly schematic figures are shown in the drawings: [Brief explanation of the drawings]
[0032] [Figure 1] FIG. 1 is a front view of a spur gear device according to a preferred embodiment. [Figure 2] FIG. 2 is a side view showing a cross section of the spur gear device of FIG. 1. [Figure 3] FIG. 2 shows a cross-section of a variant of the spur gearing of FIG. 1 with one WG bearing in side view. [Figure 4] 2 shows a cross-section of a variant of the spur gearing of FIG. 1 with hollow gears of different widths (circular spline and dynamic spline) in side view. [Figure 5] FIG. 10 is a diagram showing the axial transition path of the radial position of a tooth front cross section of an external tooth portion of a flexspline toothing portion as a first preferred embodiment. [Figure 6] FIG. 10 is a diagram showing the axial transition path of the radial position of a tooth front cross section of an external toothing portion of a flexspline toothing portion as a second preferred embodiment. [Figure 7] FIG. 10 is a diagram showing an axial transition path of the radial position of a tooth front cross section of an external tooth portion of a flexspline toothing portion as a third preferred embodiment. [Figure 8] FIG. 10 is a diagram showing the axial transition path of the radial position of a tooth front cross section of an external tooth portion of a flexspline toothing portion as a fourth preferred embodiment. [Figure 9] FIG. 10 is a diagram showing an axial transition path of the radial position of a tooth front cross section of an external tooth portion of a flexspline toothing portion as a fifth preferred embodiment. [Figure 10] FIG. 10 is a diagram showing an axial transition path of the radial position of a tooth front cross section of an external tooth portion of a flexspline toothing portion as a sixth preferred embodiment. [Figure 11] FIG. 13 is a diagram showing the axial transition path of the radial position of a tooth front cross section of an external tooth portion of a flexspline toothing portion as a seventh preferred embodiment. [Figure 12] FIG. 10 shows another preferred spur gear arrangement in side view. [Figure 13] FIG. 10 shows another preferred spur gear arrangement in side view. [Example]
[0033] In all figures, the same elements are given the same reference numerals.
[0034] The flat gearing 2 shown in FIGS. 1 and 2 is configured as a strain wave gearing (Wellgetriebe; "Wellgetriebe" or "Wellgetriebe") and includes a flexspline 4, a circular spline 6 arranged coaxially with the flexspline 4, a dynamic spline 8, and a wave generator 10. The circular spline 6 and the dynamic spline 8 are configured as cylindrical hollow gears with internal teeth. The flexspline 4 has the shape of a thin-walled hollow cylinder with external teeth 16. Inside the flexspline 4 is a wave generator 10, which consists of a centrally located disk 28, i.e., a so-called plug, whose outer cross section has an ellipse-like shape, and two rolling bearings 12 mounted on the outer side surfaces of the plug 28. The cylindrical thin-walled ring of the rolling bearing 12 and the flexspline 4 are elastically deformed by the plug into an ellipse-like cross section. Due to this deformation, the external teeth 16 of the flexspline 4 engage with the internal teeth 20 of the circular spline 6 and the internal teeth 24 of the dynamic spline 8 in two regions on both sides of the major axis of the ellipse.
[0035] In the embodiment selected here, the external toothing 16 of the flexspline has two fewer teeth than the internal toothing 20 of the circular spline 6 and the same number of teeth as the internal toothing 24 of the dynamic spline 8. As the plug 28 rotates about the gearing axis 30, the tooth engagement area of the ellipse's major axis moves circumferentially accordingly. Due to the different number of teeth of the flexspline 4 and the circular spline 6, one rotation of the plug 28 results in a relative rotation of the two components by an angle of two tooth pitches. Because the dynamic spline 8 has the same number of teeth, it assumes the same angular position as the flexspline 4, so the circular spline 6 and the dynamic spline 8 rotate relative to each other. Using the plug 28 as the driving element and the circular spline 6 and the dynamic spline 8 as the driven elements or support frames, respectively, results in a gearing with a high reduction ratio in one stage.
[0036] Figure 3 shows an alternative preferred spur gearing 2 provided with only one rolling bearing 12. In the variant with one rolling bearing, this rolling bearing fulfills the same function as both rolling bearings 12, 14 in Figures 1 and 2. The rolling bearing 12 comprises a series of rolling elements 14, here configured as balls. A gearing with only one rolling bearing has a relatively low load capacity but is relatively inexpensive.
[0037] Both hollow gears (CS and DS) are preferably constructed with the same width. Due to geometrical constraints or different loads on the hollow gears, it may be advantageous to construct them with different widths.
[0038] 2, 3 and 4, in the known spur gear 2, each front cross section of the tooth of the external toothing 16 of the flexspline 4 is at the same radial position relative to the gear axis or central axis 30. The profile shift of the flexspline toothing has the same value over its entire width.
[0039] Near the plane 34 between the circular spline 6 and the dynamic spline 8, the stresses in the toothing or external toothing 16 are greater than in the adjacent lateral areas. This causes excessive wear or damage to the flexspline teeth, thereby reducing the performance and load capacity of the spur gear. To counteract this effect, the present invention proposes to retract the external toothing 16 axially, starting from the plane 34 between the circular spline 6 and the dynamic spline 8, and radially toward the gearing axis 30.
[0040] The radially recessed axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 distributes the load better over the tooth flank. The stress peaks near the plane 34 between the circular spline 6 and the dynamic spline 8 are reduced, i.e., the stress peaks at the edges of the CS and DS teeth immediately adjacent to this plane 34 are reduced, thereby improving the performance of the spur gearing.
[0041] The axial transition paths 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 are shown in the following figures in preferred embodiments.
[0042] FIG. 5 shows an axial transition path 40 of the radial position of the tooth face cross section of the external toothing 16 of the flexspline 4 as a first preferred embodiment.
[0043] The shift of the axial transition path of the radial position of the tooth flank section of the external toothing of the flexspline characterizes the radial shift of the tooth flank section of the external toothing 16 in the direction of the central axis 30 of the spur gear 2, starting from the radial design position. The flank section is formed, as is known, by a cutting curve between the tooth and any plane lying parallel to the end face. If the radial position of the cutting curve is expressed as a function of the axial position of the cutting plane, the transition path is obtained.
[0044] The axial transition path 40 of the radial position of the tooth flap cross section of the external toothing 16 of the flexspline 4 (radial shift of the tooth flap cross section of the external toothing 16) is formed symmetrically with respect to the plane 34 between the circular spline 6 and the dynamic spline 8. The shift of the axial transition path 40 of the radial position of the tooth flap cross section of the external toothing 16 of the flexspline 4 in the direction of the central axis 30 has a maximum magnitude in a radially lowered region 44 (i.e., a region shifted in the radial direction toward the central axis 30) symmetrically with respect to the plane 34 between the circular spline 6 and the dynamic spline 8. Subsequently, in the radial direction, the axial transition path 40 of the radial position of the tooth flap cross section of the external toothing 16 of the flexspline 4 rises linearly in both sections or regions 64, 68 symmetrically with respect to the plane 34 between the circular spline 6 and the dynamic spline 8 up to the design flap cross section of the external toothing 16.
[0045] In the further transition paths in sections 48 and 52, the tooth face cross section of the external toothing 16 remains in its design position without any change in profile shift in the radial direction. The interval 60 is the maximum dimension of the radial shift of the tooth face cross section of the external toothing 16 of the flexspline 4.
[0046] 6 shows a second preferred embodiment of the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4. In this second embodiment, the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 is at its lowest in the radial direction in a radially lowered region 44 located in the region of the plane 34 between the circular spline 6 and the dynamic spline 8, and this region 44 is connected to two regions 64, 68 on both sides, and in these regions 64, 68, the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 rises linearly in the radial direction up to the design flank cross section at the end face of the flexspline 4. The preferred embodiment depends on other shape features of the flexspline 4, such as the number of teeth, the tooth profile (tooth form), and the wall thickness, and must be determined based on the tooth flank loads for a specific sample.
[0047] A third preferred embodiment of the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 is shown in Figure 7. Its structure is similar to the transition path shown in Figure 5. Unlike Figure 5, this embodiment has an asymmetric position of the plane 34 between the circular spline 6 and the dynamic spline 8 and an asymmetric transition path of the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4.
[0048] In this third embodiment, in a radially lowered region 44 located in the region of the plane 34 between the circular spline 6 and the dynamic spline 8, the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 is at its lowest point as viewed in the radial direction, and two regions 64, 68 connect to both sides of this region 44, and in these regions 64, 68, the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 rises in the radial direction. In this case, the transition path 40 has a greater gradient in the region 64 than in the region 68, and accordingly the region 68 has a greater width.
[0049] In the regions 48, 52 adjacent to the regions 64, 68, the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 is again constant. Depending on the different loads, the circular spline 6 and the dynamic spline 8 can be configured with different widths. The asymmetric embodiment takes this possibility into account.
[0050] A fourth preferred embodiment of the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 is shown in FIG. 8. Unlike the embodiment shown in FIG. 5, here the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 does not extend linearly in the axial direction in the regions 64, 68 adjacent to the constant radially depressed region 44. This transition path is convexly curved. The convex axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 makes it possible to further reduce local contact stresses on the tooth flank. Manufacturing a convex transition path is relatively difficult.
[0051] Figure 9 shows a fifth preferred embodiment of an axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4. Unlike the transition path shown in Figure 8, this embodiment has additional pullbacks (shortened radial extent) at the end face portions 70, 72 of the flexspline 4. This additional reduced area makes it possible to reduce the stresses that are increased at the end face edges of the toothing of the circular spline, dynamic spline or flexspline.
[0052] Figure 10 shows a fifth preferred embodiment of an axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4. Unlike the embodiment shown in Figure 5, here the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 extends non-linearly in the axial direction. This transition path is concavely curved in a radially depressed central region 44. A concave transition path of the axial transition path of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 is relatively easy to manufacture, but results in unfavorable local contact stresses on the tooth flank compared to the convex configuration (Figure 9).
[0053] In this embodiment too, the load on the tooth flank is more favorable compared to the known axial transition path of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4. Adjacent to the region 44, two regions 48, 52 are formed which have a constant transition path of the axial transition path of the radial tooth flank cross section.
[0054] 11 shows a sixth preferred embodiment of the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4. In this embodiment, the external toothing 16 is completely interrupted by the grooves 62 in the radially lowered central region 44, thereby forming a first external toothing 82 and a second external toothing 84, which form the common external toothing 16 of the flexspline 4. In the radially lowered region 44, the axial transition path 40 of the radial position of the tooth flank cross section of the external toothing 16 of the flexspline 4 is formed so as to be radially lowered, and the external toothing 16 is interrupted by the grooves 62 in the region of the central plane 34.
[0055] 12 shows a spur gear 2 according to a further preferred embodiment. This spur gear 2 has two rolling bearings 12, each of which has a rolling element 14 arranged therein, and in this embodiment, these rolling elements 14 are configured as rollers. Rollers can withstand higher loads than balls.
[0056] Fig. 13 shows another spur gear 2 in a preferred embodiment. The spur gear 2 according to Fig. 13 has a common rolling bearing 12 for the circular spline 6 and the dynamic spline 8, in which the common rolling elements 14 are configured as needles or rollers. [Explanation of symbols]
[0057] 2 Spur gear device 4 Flexspline 6 Circular Spline 8 Dynamic Splines 10 Wave Generator 12 Rolling bearings 14 Rolling elements 16 External teeth 20 Internal teeth 24 Internal teeth 28 Plug 30 central axis, gear device axis 34 Plane between circular spline and dynamic spline 40 Axial transition path of the radial position of the tooth front cross section of the external tooth part of the flexspline 44 Radially depressed area 48, 52 Area at the end face 60 intervals 62 Groove 64, 68 area 70, 72 End section 82 First external tooth 84 Second external teeth
Claims
1. A spur gear device of the type of wave drive gear device, comprising: a circular spline (6) having internal teeth (20); a dynamic spline (8) having internal teeth (24) and adjacent to the circular spline (6) in the axial direction; a flexible flexspline (4) having external teeth (16) and positioned inside the circular spline (6) and the dynamic spline (8); and a wave generator (10) positioned inside the flexspline (4) for deforming the flexspline (4) in the radial direction, wherein Between the circular spline (6) and the flex spline (4), a shape-engagement type torque transmission connection is established at two opposing points on the flex spline (4), and between the flex spline (4) and the dynamic spline (8), at four positions on both sides of the contact portion with respect to the circular spline (6). The axial transition path (40) of the radial position of the tooth front cross-section of the external teeth (16) of the flexspline (4) has a region (44) that is shifted radially when viewed in the direction of the central axis (30) of the spur gear device (2). A spur gear system characterized by the following.
2. The maximum radial shift of the region (44) that is reduced in the radial direction in the direction of the central axis (30) is located in the region of the plane (34) between the circular spline (6) and the dynamic spline (8). A spur gear device according to claim 1, characterized by the above.
3. The radially reduced region (44) is formed symmetrically or asymmetrically with respect to the plane (34) between the circular spline (6) and the dynamic spline (8). A spur gear device according to claim 1, characterized by the above.
4. The radial shift of the tooth front cross-section of the external teeth (16) of the flexspline (4) in the direction of the central axis (30) is linearly reduced in the axial direction from the radially reduced region (44) toward the end faces (70, 72) of the flexspline (4) on both sides. A spur gear device according to claim 1, characterized by the above.
5. The axial transition path (40) of the radial shift of the tooth front cross-section of the external tooth portion (16) of the flexspline (4) takes a constant value in the region of one or both end faces (70, 72) of the flexspline (4). A spur gear device according to claim 1, characterized by the above.
6. The axial transition path (40) of the radial shift of the tooth front cross-section of the external tooth portion (16) of the flexspline (4) has a convex shape in the radially reduced region (44). A spur gear device according to claim 1, characterized by the above.
7. The axial transition path (40) of the radial shift of the tooth front cross-section of the external tooth portion (16) of the flexspline (4) has a concave shape in the radially reduced region (44). A spur gear device according to claim 1, characterized by the above.
8. The tooth front cross-section of the external tooth portion (16) of the flexspline (4) is shifted in the direction of the central axis (30) in the region of one or both end faces (70, 72) of the flexspline (4). A spur gear device according to claim 1, characterized by the above.
9. The flexspline (4) includes two external teeth (82, 84) separated from each other by a groove (62). A spur gear device according to claim 1, characterized by the above.
10. The flexspline (4) is provided with a rolling bearing (12) located inside it in the radial direction, and the rolling elements (14) of the rolling bearing (12) are configured as balls. A spur gear device according to any one of claims 1 to 9, characterized by the above.
11. The flexspline (4) is provided with a rolling bearing (12) located inside it in the radial direction, and the rolling elements (14) of the rolling bearing (12) are configured as rollers or needles. A spur gear device according to any one of claims 1 to 9, characterized by the above.