Voltage shaft gear

Description

[0001] The invention relates to a stress wave transmission with a wave generator which is rotatably mounted relative to a flexspline by means of a radially flexible rolling bearing, wherein the radially flexible rolling bearing has several rolling elements which are not balls and whose rolling surfaces have no cylindrical portion over their axial length, and wherein the radially flexible rolling bearing has two running surfaces, namely an inner running surface and an outer running surface, between which the rolling elements are arranged and on which the rolling elements roll.

[0002] A stress wave gear typically comprises a rigid, internally toothed gear, also called a circular spline, with a cross-section perpendicular to the axial direction, and a flexible externally toothed gear, also called a flex spline, which is arranged within the volume enclosed by the rigid, internally toothed gear. A usually elliptical shaft generator is rotatably mounted within the externally toothed gear, and its outer circumference features a bearing seat for a radially flexible rolling bearing. The shaft generator is in contact with the radially flexible, externally toothed gear via this radially flexible rolling bearing. The radially flexible rolling bearing allows the shaft generator to rotate relative to the radially flexible, externally toothed gear.The shaft generator bends the radially flexible rolling bearing and the radially flexible, externally toothed gear into an elliptical shape to engage the teeth of the internally toothed gear and the flexible externally toothed gear at each end of the ellipse's main axis (vertical axis). The radially flexible rolling bearing is typically a rolling bearing with rolling elements designed as balls.

[0003] The radially flexible, externally toothed gear typically has fewer teeth than the rigid, internally toothed gear. When the shaft generator rotates, the outer surface of the externally toothed gear rolls against the inner surface of the rigid, internally toothed gear, with the teeth of the flexible externally toothed gear engaging and disengaging with the teeth of the rigid, internally toothed gear on opposite sides. Due to the difference in the number of teeth, the radially flexible, externally toothed gear rotates relative to the rigid, internally toothed gear when the shaft generator rotates. The shaft generator does not necessarily have to be elliptical. Rather, any shape other than circular is possible, as long as it results in the described engagement of the teeth of the flexible, externally toothed gear with the teeth of the internally toothed gear.It is also possible to design the shaft generator in such a way that the toothing of the radially flexible, externally toothed gear engages with the toothing of the internally toothed gear at three or more points.

[0004] There are stress wave gears in ring design that have two rigid, internally toothed gears with different numbers of teeth, each circular in cross-section, which are also called circular spline and dynamic spline.

[0005] From DE 11 2013 001 496 T5 a ring gear is known whose radially flexible rolling bearing is designed as a needle bearing.

[0006] From EP 3 492 775 B1 a stress wave gear with a rolling bearing is known, the rolling elements of which are designed as hollow rollers.

[0007] WO 2020 / 234945 discloses a stress wave gear with a rolling bearing whose rolling elements are designed as cylindrical rollers.

[0008] From DE 10 2017 106 712 A1, a stress wave transmission is known, comprising a shaft generator rotatably mounted in a radially flexible, externally toothed sleeve, and comprising a first rigid, internally toothed ring gear whose teeth mesh with the external teeth of the radially flexible, externally toothed sleeve, and a second rigid, internally toothed ring gear whose teeth also mesh with the external teeth of the radially flexible, externally toothed sleeve. The stress wave transmission is characterized in that the shaft generator is rotatably mounted relative to the radially flexible, externally toothed sleeve by means of a single radially flexible rolling bearing, which comprises a first row of rolling elements with first rolling balls and at least a second row of rolling elements with second rolling balls, offset axially from the first row of rolling elements.

[0009] From EP 2 676 049 B1 a stress wave gear is known whose radially flexible rolling bearing has two rows of rolling elements, the rolling elements overlapping in the axial direction.

[0010] From DE 10 2018 123 915 A1, a wave gear is disclosed, comprising a shaft generator, a radially deformable and flexible ring element having external teeth, and a rigid ring element having internal teeth. The external teeth of the flexible ring element mesh with the internal teeth of the rigid ring element at at least one tooth engagement area to transmit torque. The shaft generator includes a non-circular bearing element consisting of an inner ring, an outer ring, and rolling elements arranged radially between them. The bearing element projects axially, at least partially, into the flexible ring element. The inner ring is rotationally fixed to a shaft, and the outer ring is rotationally fixed to the flexible ring element. The bearing element is designed as a spherical roller bearing.DE 10 2018 123 915 A1 highlights as an advantage the ability to transmit higher loads and the improved radial stiffness of the shaft generator, the torsional stiffness of the entire wave gear, and the precision of the wave gear. However, it has been shown that such wave gears have a reduced service life.

[0011] A self-centering rolling bearing is known from US 4 929 098 A.

[0012] From US 2 595 121 A, a low-friction rolling bearing is known with a shell and a cone having opposing curved surfaces, and a plurality of rollers whose surfaces are curved to fit and bear against the opposing curved surfaces of the shell and the cone.

[0013] US Patent 2011 274382 A1 discloses a lightweight hybrid bearing assembly and a method for its manufacture. The hybrid bearing assembly comprises an inner ring and an outer ring radially spaced from the inner ring. One or both of the inner and outer rings have a convex bearing surface. A plurality of ceramic roller elements are arranged between the inner and outer rings. The ceramic roller elements have a concave bearing surface that rests against the convex bearing surface(s). This compensates, among other things, for axial misalignment of the raceways relative to each other.

[0014] From DE 10 2019 117 853 A1, a gear device of the bending engagement type is known in which a double-row rolling bearing with crowned rollers is used for a shaft generator bearing. The crowned rollers roll on rolling surfaces that run straight in a cross-sectional plane along the axial direction, with spacer elements provided to suppress misalignment of the rollers.

[0015] It is therefore the object of the present invention to provide a tension wave gear which, with the same size, has greater performance and service life.

[0016] The problem is solved by a stress wave gear according to claim 1, which is characterized in that the running surfaces are curved in a cross-sectional plane along the axial direction and have a smaller curvature in the cross-sectional plane along the axial direction (for example, a larger radius of curvature in the case of a circular arc curvature) than the rolling surfaces of the rolling elements.

[0017] In accordance with the invention, it was recognized that the service life and load-bearing capacity of the radially flexible rolling bearing are two important factors for the service life and performance of a stress wave drive. As described above, the radially flexible rolling bearing has the task of transferring the generator function circumferentially to the flexspline and ensuring tooth engagement. In addition to the radial tooth engagement forces, the radially flexible rolling bearing is also subjected to stress from the oval, in particular elliptical, pre-deformation and the so-called coning forces in the cup or hat drive. The "coning" of the flexspline that occurs in a stress wave drive with a cup or hat design is due to the fact that the toothed end of the flex cup (or hat) is subjected to excessive stress.The flexible cup wall (Flexhutes) is bent radially outwards in the radial plane of the shaft generator's vertical axis, resulting in the portions of the flexible cup wall lying in the plane of the vertical axis conically converging towards the cup base (or towards the cup rim), and the toothed end of the flexible cup being bent radially inwards in the radial plane of the shaft generator's low axis, resulting in the portions of the flexible cup wall lying in the plane of the low axis conically diverging towards the cup base (or towards the cup rim). It has been found that, according to the invention, the coning process adversely alters the pressure angles in the rolling bearing and, in particular, induces axial forces. Specifically, the coning process adversely leads to edge bearing and edge pressure, which negatively affects the load-bearing capacity and service life.In ring gears, similar adverse loads occur on the radially flexible rolling bearing due to the deformation of the flexspline during operation.

[0018] One disadvantage of ball bearings (regardless of the design of a conventional tension shaft drive) results from the unfavorable kinematics of the ball. A ball can move in all three spatial directions within a ball bearing and, due to point contact with the raceways, experiences not only rolling motion but also sliding and slipping. This effect is particularly pronounced with continuously changing contact angles and negatively impacts the spin / roll ratio, which is a major contributor to wear and the resulting heating of the rolling bearing. Especially under unfavorable lubrication conditions, this can lead to exponential wear and premature bearing failure, for example, because the bearing clearance becomes too large and disrupted gear meshing results.

[0019] In accordance with the invention, it was recognized that the service life of the radially flexible rolling bearing cannot simply be increased by permanently creating a larger contact area between the rolling elements and the raceways through the use of barrel rollers instead of balls. It has been shown that, for example, even in the stress wave gear known from DE 10 2018 123 915 A1, edge bearing and edge pressure inevitably occur, which has a negative impact on the load-bearing capacity and service life.In fact, while the use of crowned barrel rollers as rolling elements does achieve a larger contact area between the rolling elements and the raceways, the forces and kinematics described above, particularly coning, cause a shift in the pressure load away from the center of the rolling elements and towards their axial ends. As a result, the end edges of the rolling elements bear the majority of the load, leading to high Hertzian contact stress and premature wear of the rolling elements and the raceway areas stressed by these end edges. The effect of edge bearing and edge pressure is greater with higher torque loads on the tension wave drive.

[0020] Furthermore, according to the invention, it was initially recognized that an increased service life and load-bearing capacity of the radially flexible rolling bearing can be achieved by using rolling elements that are not spheres and whose rolling surfaces have no cylindrical portion along their axial length, wherein the running surfaces are curved and exhibit less curvature in a cross-sectional plane along the axial direction than the rolling surfaces of the rolling elements. In this way, it is advantageously exploited that, under a torque load of the stress wave drive exceeding the no-load load, point contact of the rolling elements with the running surfaces of the inner and outer rings is avoided in favor of line contact, while at the same time edge bearing (which is disadvantageous as described above) and the resulting edge pressure must also be avoided.The latter is achieved according to the invention by the fact that the running surfaces in a cross-sectional plane along the axial direction have a lesser curvature than the rolling surfaces of the rolling elements, which causes the end edges of the rolling elements to be spaced away from the running surfaces and the running surfaces to increasingly conform to the rolling elements axially from the center of the rolling elements towards their ends as the torque load of the tension wave drive increases due to the forces occurring as a result of the increasing load.

[0021] It has been shown that this effect can only be achieved if the running surfaces are curved in a cross-sectional plane along the axial direction. If the running surfaces are straight in a cross-sectional plane along the axial direction, no measurable advantage is achieved compared to the use of spheres simply by using rolling elements that are not spheres and whose rolling surfaces do not have a cylindrical portion over their axial length.

[0022] In a special design, the rolling elements and their running surfaces are in point contact when the tension wave drive is under no-load load. This design is particularly smooth-running under no-load load. Alternatively, it is also possible for the rolling elements and their running surfaces to be in line contact when the tension wave drive is under no-load load.

[0023] In a particularly advantageous embodiment of the tension wave drive according to the invention, the curvatures of the rolling elements and the running surfaces (in a cross-sectional plane along the axial direction) are selected such that, under a torque load of the tension wave drive exceeding the no-load load, the rolling elements are in line contact with the running surfaces along a contact line, the length of which increases with increasing torque load. In this way, it is advantageously achieved that, with increasing torque load of the tension wave drive, the running surfaces conform to the rolling elements and the pressing forces acting on the rolling elements and the running surfaces are increasingly distributed over a larger area.In particular, the curvatures of the rolling elements and the raceways in a cross-sectional plane along the axial direction (preferably taking quantitative account of the properties of the other components of the stress wave drive described above, especially the coning) can be selected such that a doubling of the torque load on the stress wave drive causes a change in the Hertzian contact pressure between the rolling elements and the raceways by a factor k, wherein the factor k is preferably less than 1.8, and in particular less than 1.5. It is also possible to select the curvatures such that the Hertzian contact pressure even decreases with an increase in the torque load on the stress wave drive. In particular, the stress wave drive according to the invention can advantageously be designed such that the factor k is in the range of 1.0 to 1.7, and in particular in the range of 1.0 to 1.5.In a design where the rolling surfaces of the rolling elements and the running surfaces each have the shape of a body of revolution whose generating curve is a rolling element circular segment, this can be achieved, for example, by ensuring that the ratio of the radius of the running surface circular segment to the radius of the rolling element circular segment is in the range of 1.01 to 1.5.

[0024] As described in detail below, the shape of the running surfaces in a cross-sectional plane along the axial direction is not limited to a circular segment. Rather, a wide variety of shapes are possible. The same applies analogously to the rolling elements. However, the following exemplary consideration of a stress wave drive, in which the rolling surfaces of the rolling elements each have the shape of a solid of revolution whose generating curve is a rolling element circular segment, and in which each running surface has the shape of a solid of revolution whose generating curve is a running surface circular segment, is also revealing with regard to other possible shapes of the rolling elements and running surfaces.

[0025] For example, it has been shown that it is particularly advantageous if the radius of the rolling element circular segment is in the range of 0.3 to 2.0 times the pitch circle diameter of the flexspline gearing. In particular, it can be advantageously provided that the radius of the rolling element circular segment is in the range of 0.3 to 1.5 times, or in the range of 0.7 to 1.3 times, or in the range of 0.9 to 1.18 times, or in the range of 1.0 to 1.08 times the pitch circle diameter of the flexspline gearing.

[0026] Alternatively or additionally, it may be advantageously provided that the radius of the running surface circular segment is in the range of 0.3 to 2.1 times the pitch circle diameter of the flexspline gearing. In particular, the radius of the running surface circular segment may be in the range of 0.4 to 1.6 times, or in the range of 0.95 to 1.23 times, or in the range of 1.04 to 1.12 times the pitch circle diameter of the flexspline gearing.

[0027] Alternatively or additionally, as already mentioned, it can also be advantageously provided that the ratio of the radius of the running surface circular segment to the radius of the rolling element circular segment is in the range of 1.01 to 1.5.

[0028] For example, the radius of the rolling element circular segment in a stress wave gear according to the invention, whose flexspline gearing has a pitch circle diameter of 91 mm, can advantageously be 95 mm. Here, the radius of the inner running surface circular segment can be 95.0 mm and the radius of the outer running surface circular segment can be 95.3 mm.

[0029] It is generally advantageous for the inner running surface to have the same curvature as the outer running surface (apart from their opposite orientation). In a particularly advantageous embodiment, the inner running surface has a greater curvature in a cross-sectional plane along the axial direction (i.e., a smaller radius of curvature in the case of a circular arc curvature) than the outer running surface in the cross-sectional plane along the axial direction.For example, it may be advantageously provided that the outer running surface has the shape of a body of revolution whose generating curve is a first running surface circular segment and the inner running surface has the shape of a body of revolution whose generating curve is a second running surface circular segment, and that the ratio of the radius of the first running surface circular segment to the radius of the second running surface circular segment is in the range of 0.9 to 0.999, in particular in the range of 0.99 to 0.999.

[0030] Based on this, it was also recognized that – depending on the planned application and the type of stress wave drive – very different shapes of rolling elements can be used to particular advantages. In particular, the shape of the rolling elements and the running surfaces can be selected, for example, such that the radially flexible rolling bearing heats up less under the same load and is therefore subject to less wear, while at the same time allowing the shaft generator to tilt relative to the flex spline.

[0031] In a particularly advantageous embodiment, at least a portion, especially a central portion, of the rolling surfaces of the rolling elements corresponds (with respect to the cross-sectional planes along the axial direction) to the shape of the envelope (in the mathematical sense) of the family of curves of the flexspline wall caused by coning. Such an embodiment is particularly advantageous with regard to achieving a long service life. In particular, it can be advantageously provided that at least the portion of the rolling surfaces of the rolling elements that comes into contact with the running surfaces at nominal load or at a predetermined or predefinable multiple of the nominal load has a shape that corresponds to the envelope (in the mathematical sense) of the family of curves of the flexspline wall caused by coning.In general, it can be provided that in a cross-sectional plane along the axial direction, the shape of the rolling surfaces of the rolling elements corresponds to the shape of the envelope (in the mathematical sense) of the family of curves of the flexspline wall caused by the coning.

[0032] The tension wave gear according to the invention has the particular advantage that, with the same Hertzian contact pressures between the rolling elements and the raceways, a higher overall load-bearing capacity of the radially flexible rolling bearing is achieved. This is further enhanced by the fact that, due to the line contact (instead of point contact), the rolling elements can even have a smaller radial dimension, which is particularly advantageous. This results in a significantly reduced radial installation space requirement for the radially flexible rolling bearing.

[0033] The invention makes it possible, for example, to design the tension wave gear according to the invention to be smaller than a conventional tension wave gear while maintaining the same load-bearing capacity.

[0034] Alternatively, due to the reduced radial installation space requirement of the radially flexible rolling bearing, the through-diameter of a shaft generator designed as a hollow shaft can be increased. An increased through-diameter of the shaft generator designed as a hollow shaft has the advantage, for example, that more or thicker electrical cables can be routed through it, which is particularly advantageous in robot, steering, and chassis assemblies.

[0035] Due to the advantage explained above, namely that the rolling elements can have a smaller radial dimension, it is also possible to have a larger number of rolling elements for the same radial size of the rolling bearing. This further increases the load-bearing capacity because the forces are distributed across a larger number of rolling elements. It is particularly advantageous if the rolling bearing has an even number of rolling elements, as this results in a symmetrical load distribution across the stress wave drive.

[0036] As already mentioned, according to the invention, it is possible to design the tension wave drive such that the loads on the radially flexible rolling bearing are reduced compared to a conventional tension wave drive with a ball bearing, despite the same torque load and size. In this case, the rolling bearing of the tension wave drive runs cooler, and the lubricant load due to increased temperatures is reduced.

[0037] Alternatively, without negatively affecting the service life of the tension wave gear, it is possible to allow a torque load on the tension wave gear that is not permissible for a conventional tension wave gear of the same size.

[0038] In a particularly advantageous way, the rolling bearing induces only very small axial forces into the system, because the radius of the running surfaces and the rolling surfaces (in the axial cross-section) is larger than in a ball bearing with rolling balls.

[0039] The tension wave drive according to the invention has the distinct advantage that, with the same overall dimensions, the weight of the rolling bearing and, in particular, the rolling elements is reduced compared to the weight of the rolling bearing in conventional tension wave drives. This enables higher rotational speeds and reduces inertia. Furthermore, the transmission accuracy of the tension wave drive is improved by the increased number of rolling elements, as there are more support points in the tooth engagement areas.

[0040] In general, as already mentioned, it can be advantageously provided that the rolling surfaces of the rolling elements are each designed as a lateral surface of a section of a body of revolution (in the mathematical sense), where the generating line can be any curve except a line segment perpendicular to the axis of rotation (which would result in a circular cylinder) or a semicircular arc with its ends directly adjacent to the axis of rotation (which would result in a sphere).

[0041] In geometry, a solid of revolution is a mathematical body whose surface is formed by rotating a generating curve (generator) around an axis of rotation, where the generating curve and the axis of rotation always lie in the same plane.

[0042] In particular, it can be advantageously provided that the rolling surfaces of the rolling elements each have the shape of a body of revolution whose generating curve is a circular segment, especially a circular segment shorter than a quarter circle or an eighth circle. It can also be provided that the rolling elements each have the form of an ellipsoid of revolution or a segment of an ellipsoid of revolution, and / or that the rolling surfaces of the rolling elements each have the form of a lateral surface of a segment of an ellipsoid of revolution.

[0043] In a special design, the rolling elements and / or the rolling surfaces of the rolling elements have a synclastic shape. In particular, the rolling elements and / or the rolling surfaces of the rolling elements can be convex.

[0044] Alternatively, the rolling surfaces of the rolling elements can have an anticlastic shape. For example, the rolling elements and / or their rolling surfaces can advantageously be tapered. It can also be advantageous for the rolling elements to be designed as a hyperboloid of revolution or as a section of a hyperboloid of revolution, and / or for the rolling surfaces of the rolling elements to be designed as a lateral surface of a section of a hyperboloid of revolution.

[0045] Preferably, all rolling elements of the radially flexible rolling bearing are of the same design.

[0046] The rolling elements can be arranged, in particular, within a rolling element cage. It is also possible to insert spacers, for example made of plastic, between adjacent rolling elements to maintain a distance between them. In particular, the spacers can have a shape complementary to the rolling elements and bear against them over a flat surface.

[0047] In a special design, the rolling elements are mirror-symmetrical with respect to a plane perpendicular to the axial direction. Depending on the application, however, it is also possible to design the rolling elements asymmetrically.

[0048] It is particularly advantageous that the axial length of the rolling elements and / or the rolling surfaces can be greater than their largest diameter. Such a design can be made especially compact.

[0049] In particular, the axial lengths of the bearing rings and / or the rolling surfaces can be the same. However, it is also possible that the inner bearing ring is axially longer than the outer bearing ring, or vice versa. Alternatively or additionally, it is also possible that one of the raceways is axially longer than the other.

[0050] Preferably, the radial material thicknesses of the bearing rings in the radially flexible rolling bearing are selected such that continuous elastic deformation during the rotation of the shaft generator is possible, just as with conventional stress shaft drives.

[0051] According to the invention, the radially flexible rolling bearing has two running surfaces between which the rolling elements are arranged and on which the rolling elements roll. In particular, it can be advantageously provided that the running surfaces have a mirror-symmetrical shape relative to each other in a cross-sectional plane extending in the axial direction.

[0052] The radially flexible rolling bearing can be designed such that no axial securing of the rolling elements is required. In particular, it can be advantageously provided that the rolling elements are secured axially solely by their contact with the raceways.

[0053] The cross-sectional shape of the running surfaces can (if the size differs) advantageously correspond to the cross-sectional shape of the rolling elements.

[0054] It can be advantageously provided that the rolling surface of each rolling element has the shape of a solid of revolution (in the mathematical sense), whose generating curve is, for example, a circular segment. In this case, the raceways can also be designed as solids of revolution (in the mathematical sense), whose generating curve is, for example, each a circular segment (preferably with a slightly larger radius). However, other generating curves are also possible, for example, sections of a conic section (ellipse, parabola, hyperbola). The same applies to the raceways.

[0055] The radially flexible rolling bearing can have an inner ring with one of the raceways on its outer surface. The radially flexible rolling bearing can have an outer ring with one of the raceways for the rolling elements on its inner surface. However, it is also possible to omit at least one of the rings (inner ring and / or outer ring) by having the shaft generator and / or the flexspline provide one of the raceways.

[0056] As already mentioned, the shaft generator can be advantageously designed as a hollow shaft, particularly if the voltage shaft drive is designed as a ring drive or a hat drive. This makes it possible, for example, to route other shafts or electrical cables through the shaft generator.

[0057] Preferably, the shaft generator has a bearing seat for the radially flexible rolling bearing. The bearing seat can, in particular, be designed as a straight cylinder with a basic shape different from a circular disk.

[0058] In a particular embodiment and according to an independent inventive concept, the wave generator is designed such that it has several rollers rolling on the inner circumference of the flexspline, each roller being mounted on a rotating carrier by means of a rolling bearing. The carrier has several rolling elements that are not spheres and whose rolling surfaces do not have a cylindrical portion over their axial length. In particular, such a wave generator can be designed as a two-roller or a three-roller.

[0059] There are no fundamental limitations regarding the design of the tension wave drive according to the invention. The tension wave drive according to the invention can advantageously be designed as a pot drive, a hat drive, or a ring drive.

[0060] The voltage wave drive according to the invention can be designed as an internal rotor, in which the wave generator is surrounded by the flexspline. Alternatively, the voltage wave drive according to the invention can also be designed as an external rotor, in which the wave generator surrounds the flexspline.

[0061] A particularly advantageous design is one in which the shaft generator is mounted in a tiltable position relative to the flexspline by means of a radially flexible rolling bearing. Such a stress wave drive offers the advantage of a particularly large installation tolerance without requiring additional components such as couplings and / or other compensating elements.

[0062] The shaft generator and / or a shaft directly connected to the shaft generator can be supported exclusively by means of the radially flexible rolling bearing. This allows for a floating mounting (relative to the other gearbox components). However, it is also possible for the shaft generator and / or a shaft directly connected to the shaft generator to be additionally mounted to rotate at another location.

[0063] According to the invention, it is possible to manufacture the remaining components of the tension wave drive according to the invention, apart from the radially flexible rolling bearing, in the usual manner, in particular with the usual dimensions and from the usual materials. Preferably, the components of the tension wave drive, in particular the radially flexible rolling bearing and / or the flex spline and / or the circular spline, are made of steel.

[0064] The radially flexible rolling bearing of the tension wave drive according to the invention can advantageously be designed as a single-row rolling bearing. However, it is also possible to design the radially flexible rolling bearing of the tension wave drive according to the invention as a multi-row rolling bearing, in particular a double-row rolling bearing.

[0065] A robot, particularly an industrial robot, that incorporates at least one tension wave drive according to the invention is of particular advantage. In particular, the tension wave drive according to the invention can be used in a robot joint. By using the tension wave drive according to the invention, the robot joint can be designed for higher loads than with a conventional tension wave drive.

[0066] A vehicle that has at least one tension wave transmission according to the invention, or a vehicle component that has at least one tension wave transmission according to the invention, is of particular advantage.

[0067] A chassis, especially an active chassis for a motor vehicle, that includes at least one tension wave transmission according to the invention is particularly advantageous. A significant benefit here is that less of the installation space, which is already limited in a vehicle, is required.

[0068] A steering system, particularly for passenger cars or trucks, that incorporates at least one tension wave transmission according to the invention is especially advantageous. The steering system can, in particular, be a power steering system and / or a superimposed steering system.

[0069] The axial direction of a stress wave drive, and in particular of the stress wave drive according to the invention, is the direction along which the rotational center axis of the drive component and / or the output component extends. For example, the wave generator can function as the drive component, while the flexspline functions as the output component.

[0070] The invention is shown in the drawing in an exemplary and schematic manner and is described below with reference to the figures, whereby identical or similarly functioning elements are usually provided with the same reference numerals even in different embodiments. The figures show: Fig. 1 a first embodiment of a tension wave drive according to the invention, Fig. 2 a second embodiment of a tension wave drive according to the invention, Fig. 3 a third embodiment of a tension wave drive according to the invention, Fig. 4 a fourth embodiment of a tension wave drive according to the invention, Fig. 5 a fifth embodiment of a tension wave drive according to the invention, Fig. 6 a sixth embodiment of a tension wave drive according to the invention, Fig. 7 a seventh embodiment of a tension wave drive according to the invention, Fig. 8 an eighth embodiment of a tension wave drive according to the invention, Fig. 9 an embodiment of a rolling element for a tension wave drive according to the invention in a side view, Fig. 10 the embodiment of a rolling element for a tension wave drive according to the invention in a top view in the axial direction, Fig.11. Another embodiment of a rolling element for a tension wave drive according to the invention in a side view, Fig. 12. Another embodiment of a rolling element for a tension wave drive according to the invention in a top view in the axial direction, Fig. 13. Another embodiment of a rolling element for a tension wave drive according to the invention in a side view, Fig. 14. Another embodiment of a rolling element for a tension wave drive according to the invention in a top view in the axial direction, Fig. 15. A detailed view of the rolling bearing of a tension wave drive according to the invention in a cross-sectional plane along the axial direction, Fig. 16. A ninth embodiment of a tension wave drive according to the invention in a top view in the axial direction, Fig.Fig. 17 shows a representation of the contact surface between the most heavily loaded rolling element and a running surface of the ninth embodiment of a tension wave drive according to the invention under no-load load; Fig. 18 shows a representation of the contact surface between the most heavily loaded rolling element and a running surface of the ninth embodiment of a tension wave drive according to the invention under a load with the rated torque; Fig. 19 shows a representation of the contact surface between the most heavily loaded rolling element and a running surface of the ninth embodiment of a tension wave drive according to the invention under a load with twice the rated torque; and Fig. 20 shows an exaggerated representation of an advantageous possibility with regard to the shape of the rolling surfaces of the rolling elements.

[0071] Fig. 1Figure 1 shows an embodiment of a stress wave drive according to the invention, comprising a shaft generator 1 which is rotatably mounted relative to a flexspline 3 by means of a radially flexible rolling bearing 2. The flexspline 3 is a flexible pot comprising a flex pot base 4 and a flexspline wall 22. An output shaft 5 is coupled to the flex pot base 4. A drive shaft 6 is coupled to the shaft generator 1.

[0072] The tension wave gear also features a circular spline 7 with internal teeth 8.

[0073] The flexspline 3 has a circumferential external toothing 9 at its end facing away from the pot base 4, which lies in the radial plane of the vertical axis of the shaft generator (the plane of the drawing of the Figure 1 (corresponds) engages at two points in the internal teeth 8 of the circular spline 7.

[0074] The radially flexible rolling bearing 2 has an inner ring 10 and an outer ring 11, between which several rolling elements 12 are arranged. These rolling elements are not spheres and their rolling surfaces 15 do not have a cylindrical portion over their axial length. Specifically, the rolling elements 12 are convex.

[0075] The inner ring 10 has an inner running surface 13. The outer ring 11 has an outer running surface 14, which is in contact with the rolling elements 12. The cross-sectional shape of the running surfaces 13, 14 corresponds to the cross-sectional shape of the rolling elements 12. The running surfaces 13, 14 have a slightly lesser curvature in a cross-sectional plane along the axial direction (corresponding to the plane of the drawing) than the rolling surfaces 15 of the rolling elements 12. This causes the end edges of the rolling elements 12 to be spaced apart from the running surfaces 13, 14, and the running surfaces 13, 14 to increasingly conform axially to the rolling elements 12 as the torque load of the tension wave drive increases, starting from the center of the rolling elements 12 towards the ends.

[0076] For example, it may be advantageously provided that the rolling surface 15 of each rolling element 12 has the form of a solid of revolution (in the mathematical sense) whose generating curve is a circular segment. In this case, the running surfaces can also be designed as solids of revolution (in the mathematical sense), each of which has a circular segment with a slightly larger radius.

[0077] In the Figure 1 It can be seen that the flanks of the flexspline 3 diverge conically from the bottom of the pot 4 in the depicted plane of the vertical axis of the shaft generator 1, a phenomenon known as coning. In the Figure 1It can also be seen that the radially flexible rolling bearing 2 advantageously adapts to the shape of the flexspline 3 caused by coning. In particular, the special shape of the rolling elements 12 and the inner ring 10 as well as the outer ring 11 allows the outer ring 11 to twist and partially tilt relative to the inner ring 10.

[0078] Furthermore, the illustrated tension wave drive has the distinct advantage that an axial angular error of the shaft generator 1 and the drive shaft 6 is compensated for by means of the radially flexible rolling bearing 2 and is not transmitted to the flex spline 3 and / or the circular spline 7, thus preventing additional stress on the radially flexible rolling bearing 2. In this respect, the tension wave drive according to the invention offers the advantage of a particularly large installation tolerance.

[0079] Figure 2Figure 1 shows a second embodiment of a tension wave drive according to the invention, which, in contrast to the one in Figure 2, Figure 1 The illustrated embodiment is designed as a hat gear. The Flexspline 3 has, instead of a flexible pot base 4, an outwardly directed circumferential rim 16, which can, for example, be designed as a flange.

[0080] Figure 3 Figure 1 shows a third embodiment of a voltage wave drive according to the invention. In this embodiment, the wave generator 1 has the inner running surface 13 on its outer circumference. Therefore, an inner ring 10 is not present in this embodiment.

[0081] Figure 4 Figure 1 shows a fourth embodiment of a tension wave drive according to the invention. In this embodiment, the flex spline 3 has the outer running surface 14 along its inner circumference. Therefore, an outer ring 11 is not present in this embodiment.

[0082] Figure 5Figure 1 shows a fifth embodiment of a stress wave drive according to the invention. In this embodiment, the wave generator 1 has the inner running surface 13, while the flex spline 3 has the outer running surface 14 along its inner circumference. In this embodiment, neither an inner ring 10 nor an outer ring 11 is present.

[0083] Figure 6Figure 6 shows a sixth embodiment of a tension wave drive according to the invention. The tension wave drive is designed as a ring drive which, in addition to a circular spline 7, has a dynamic spline 17 with a further internal toothing 18 that also meshes with the external toothing 9 of the flex spline 3. The number of teeth of the internal toothing 8 of the circular spline 7 differs from the number of teeth of the further internal toothing 18 of the dynamic spline 17. A particular advantage of this drive is that axial angular deviations of the drive shaft 6 and the shaft generator 1 are not transmitted to the flex spline 3, the circular spline 7, or the dynamic spline 17 due to the radially flexible rolling bearing according to the invention, and therefore do not lead to an additional load on the radially flexible rolling bearing 2.

[0084] Figure 7Figure 1 shows a seventh embodiment of a stress wave drive according to the invention. The stress wave drive is designed as a ring drive with a circular spline 7 and a dynamic spline 17. The wave generator 1 is designed as a hollow shaft.

[0085] Figure 8 Figure 8 shows an eighth embodiment of a tension wave drive according to the invention. In this embodiment, the rolling elements 12 are tapered. The running surfaces 13, 14 are correspondingly counter-shaped such that line contact is ensured between the running surfaces 13, 14 and the rolling surfaces 15 of the rolling elements 12.

[0086] The Figures 9 and 10Figure 1 shows a possible embodiment of a rolling element 12 for a tension wave drive according to the invention, in a side view and an axial top view. The rolling element 12 has a rolling surface 15 along its circumference. The rolling surface 15 can, for example, have a circular segment or an elliptical segment in cross-section.

[0087] The Figures 11 and 12 show another embodiment of a possible rolling element. The one in the Figures 11 and 12 The depicted rolling element 12 differs from the one shown in the Figures 9 and 10 The rolling elements 12 shown are provided by chamfers 19 applied to their ends, which are not part of the rolling surfaces 15. This design is particularly insensitive to tilting relative to the running surfaces 13, 14.

[0088] The Figures 13 and 14 Figure 1 shows a further embodiment of a rolling element 12 for a tension wave drive according to the invention, in a side view and in an axial top view. The figure 12 is shown in the side view and in an axial top view. Figures 13 and 14The depicted rolling element 12 is shaped with a waisted profile. The rolling surface 15 can, for example, have a circular segment or an elliptical segment in cross-section.

[0089] Fig. 15 Figure 1 shows a detailed view of the rolling bearing of a stress wave drive according to the invention in a cross-sectional plane along the axial direction. The radially flexible rolling bearing 2 has an inner ring 10 and an outer ring 11, between which several rolling elements 12 are arranged. These rolling elements are not spheres and their rolling surfaces 15 do not have a cylindrical portion over their axial length. Specifically, the rolling elements 12 are convex. The inner ring 10 has an inner running surface 13. The outer ring 11 has an outer running surface 14, which is in contact with the rolling elements 12.

[0090] The running surfaces 13, 14 have a slightly lesser curvature in a cross-sectional plane along the axial direction (corresponding to the plane of the drawing) than the rolling surfaces 15 of the rolling elements 12, which causes the end edges of the rolling elements 12 to be spaced away from the running surfaces 13, 14 and the running surfaces 13, 14 to increasingly conform to the rolling elements 12 axially from the center 20 of the rolling elements 12 towards the ends as the torque load of the stress wave drive increases.

[0091] The running surfaces 13, 14 can generally (apart from their opposite orientation) have the same curvature in a cross-sectional plane along the axial direction. However, it is also possible for the inner running surface 13 to have a different, particularly greater, curvature (for example, a smaller radius of curvature in the case of a circular arc) than the outer running surface 14. Such a design is particularly advantageous with regard to a long service life. Alternatively, it is also possible for the inner running surface 13 to have a smaller curvature (for example, a larger radius of curvature in the case of a circular arc) than the outer running surface 14.

[0092] In this embodiment, the rolling surfaces of the rolling elements 12 each have the shape of a solid of revolution whose generating curve is a circular segment of the rolling element with radius R1. The inner running surface 13 has the shape of a solid of revolution whose generating curve is a circular segment of the running surface with radius R2. The outer running surface 14 has the shape of a solid of revolution whose generating curve is a circular segment of the running surface with radius R3.

[0093] It has been found to be particularly advantageous if the radius R1 is in the range of 0.3 to 2.0 times the pitch circle diameter of the flexspline gearing. It has also been found to be particularly advantageous if the radii R2 and R3 are each in the range of 0.3 to 2.1 times the pitch circle diameter of the flexspline gearing. It can be particularly advantageous for the radius R2 to be larger than the radius R3.

[0094] Fig. 16 Figure 9 shows a ninth embodiment of a stress wave drive according to the invention in a top view in the axial direction, which serves as a simulation basis for the [missing information] in the Figures 17 to 19 The simulation results shown, which were obtained using the ANSYS simulation program, serve as a basis.

[0095] The stress wave drive is designed as a pot drive and features a shaft generator 1, which is rotatably mounted relative to a flexspline 3 by means of a radially flexible rolling bearing 2. The flexspline 3 is a flexible pot that has a (not shown) flex pot base 4. The stress wave drive also features a circular spline 7 with internal teeth 8.

[0096] The flexspline 3 has a circumferential external toothing 9 at its end facing away from the cup base 4, which engages the internal toothing 8 of the circularspline 7 at two points in the radial plane of the vertical axis of the shaft generator. The radially flexible rolling bearing 2 has an inner ring 10 and an outer ring 11, between which several rolling elements 12 are arranged. These rolling elements are not spheres and their rolling surfaces 15 do not have a cylindrical portion over their axial length. Specifically, the rolling elements 12 are convex.

[0097] The flexspline has a pitch circle diameter of 50 mm. The rolling surfaces of the rolling elements 12 each have the shape of a solid of revolution, the generating curve of which is a rolling element circular segment with a radius R1 of 16 mm. The rolling element diameter (in the radial direction) is 16 mm at the center of the rolling element. The inner running surface 13 has the shape of a solid of revolution, the generating curve of which is a running surface circular segment with a radius R2 of 22 mm. The outer running surface 14 has the shape of a solid of revolution, the generating curve of which is a running surface circular segment with a radius R3 of 22 mm.

[0098] The Figures 17 to 19Figure 1 shows a representation of the contact surface 21 between the most heavily loaded rolling element 12 and the outer running surface 14 of the ninth embodiment of a stress wave drive according to the invention under no-load conditions, under a load of the rated torque of the stress wave drive, and under a load of twice the rated torque of the stress wave drive. It can be seen that the length of the linear contact surface 21 of the rolling elements increases with increasing torque load. The simulation shows that the outer running surface 14 conforms to the rolling elements 12 with increasing torque load of the stress wave drive, and the pressing forces acting on the rolling elements 12 and the outer running surface 14 are increasingly distributed over a larger area. The same applies analogously to the (not shown) inner running surface 13.

[0099] Fig. 20This extremely exaggerated representation illustrates an advantageous possibility regarding the shape of the rolling surfaces of the rolling elements. Here, in a cross-sectional plane along the axial direction, the shape of the rolling surface 15 of each rolling element 12 corresponds to the shape of the envelope (in the mathematical sense) of the family of curves of the flexspline wall 22 of the flexspline 3 caused by the coning. Figure 20The figure does not show the arrangement of the rolling elements in a wave gear according to the invention, but serves solely to illustrate the aforementioned feature regarding the shape of the rolling surfaces. In particular, the invention does not provide for the rolling elements to roll on a running surface of the flexspline 3 that is not curved in the cross-sectional plane along the axial direction. Specifically, an outer ring 11, comprising the outer running surface 14, can be arranged between the rolling elements and the flexspline 3. It is also possible for the flexspline 3 to have the curved outer running surface 14. Reference symbol list:

[0100] 1 Shaft generator 2 Radially flexible rolling bearing 3 Flex spline 4 Flex cup base 5 Output shaft 6 Input shaft 7 Circular spline 8 Internal toothing 9 External toothing 10 Inner ring 11 Outer ring 12 Rolling element 13 Inner running surface 14 Outer running surface 15 Rolling surface 16 Rim 17 Dynamic spline 18 Further internal toothing 19 Chamfer 20 Center 21 Contact surface 22 Flex spline wall R1 Radius R2 Radius R3 Radius

Claims

1. Strain wave gear comprising a wave generator (1), which is rotatably mounted relative to a flexspline (3) by means of a radially flexible rolling bearing (2), wherein the radially flexible rolling bearing (2) comprises a plurality of rolling bodies (12) which are not balls and whose rolling surfaces (15) have no cylindrical portion over their axial length, and wherein the radially flexible rolling bearing (2) comprises two running surfaces (13, 14), namely an inner running surface (13) and an outer running surface (14), between which the rolling bodies (12) are arranged and on which the rolling bodies (12) roll, characterized in that the running surfaces (13, 14) are curved in a cross-sectional plane extending along the axial direction and, in the cross-sectional plane extending along the axial direction, have a smaller curvature than the rolling surfaces (15) of the rolling bodies (12).

2. Strain wave gear according to claim 1, characterized in that a. the rolling surfaces (15) of the rolling bodies (12) each have the shape of a solid of revolution whose generating curve is a rolling-body circular segment, and / or that b. each running surface (13, 14) has the shape of a solid of revolution whose generating curve is a running-surface circular segment.

3. Strain wave gear according to claim 1 or 2, characterized in that a. the rolling bodies (12) and / or the rolling surfaces (15) of the rolling bodies (12) have a synclastic shape, and / or that b. the rolling bodies (12) and / or the rolling surfaces (15) of the rolling bodies (12) are crowned, and / or that c. the rolling bodies (12) are each configured as a rotational ellipsoid or as a section of a rotational ellipsoid and / or that the rolling surfaces (15) of the rolling bodies (12) are each configured as a lateral surface of a section of a rotational ellipsoid.

4. Strain wave gear according to claim 1 or 2, characterized in that a. the rolling surfaces (15) of the rolling bodies (12) have an anticlastic shape, and / or that b. the rolling bodies (12) and / or the rolling surfaces (15) of the rolling bodies (12) are of waisted design, and / or that c. the rolling bodies (12) are each configured as a rotational hyperboloid or as a section of a rotational hyperboloid and / or that the rolling surfaces (15) of the rolling bodies (12) are each configured as a lateral surface of a section of a rotational hyperboloid.

5. Strain wave gear according to one of claims 2 to 4, characterized in that a. the radius of the rolling-body circular segment lies within a range from 0.25 times to 2.0 times the pitch circle diameter of the flexspline toothing, and / or that b. the radius of the running-surface circular segment lies within a range from 0.3 times to 2.1 times the pitch circle diameter of the flexspline toothing.

6. Strain wave gear according to one of claims 1 to 5, characterized in that, in a cross-sectional plane extending along the axial direction, the inner running surface (13) has a different, in particular stronger, curvature than the outer running surface (14).

7. Strain wave gear according to one of claims 1 to 6, characterized in that a. the radially flexible rolling bearing comprises a bearing inner ring (10) which comprises one of the running surfaces (13, 14) on its outer side, and / or that b. the radially flexible rolling bearing comprises a bearing outer ring (11) which comprises one of the running surfaces (13, 14) on its inner side.

8. Strain wave gear according to one of claims 1 to 7, characterized in that a. the wave generator (1) comprises one of the running surfaces (13, 14) and / or the flexspline (3) comprises one of the running surfaces (13, 14), or that b. the radially flexible rolling bearing comprises a bearing ring which comprises one of the running surfaces (13, 14), and the wave generator (1) or the flexspline (3) comprises the other one of the running surfaces (13, 14).

9. Strain wave gear according to one of claims 1 to 8, characterized in that the ratio of the radius of the running-surface circular segment to the radius of the rolling-body circular segment lies within a range from 1.01 to 1.5.

10. Strain wave gear according to one of claims 1 to 9, characterized in that, in a cross-sectional plane extending along the axial direction, at least a part of the shape of the rolling surfaces (15) of the rolling bodies (12) has the shape of the envelope of the family of curves of the flexspline wall caused by coning.

11. Radially flexible rolling bearing for a strain wave gear according to one of claims 1 to 10, wherein the radially flexible rolling bearing (2) comprises a plurality of rolling bodies (12) which are not balls and whose rolling surfaces (15) have no cylindrical portion over their axial length, and wherein the radially flexible rolling bearing (2) comprises two running surfaces (13, 14), namely an inner running surface (13) and an outer running surface (14), between which the rolling bodies (12) are arranged and on which the rolling bodies (12) roll, characterized in that the running surfaces (13, 14) are curved in a cross-sectional plane extending along the axial direction and, in the cross-sectional plane extending along the axial direction, have a smaller curvature than the rolling surfaces (15) of the rolling bodies (12).

12. Robot, in particular industrial robot, comprising at least one strain wave gear according to one of claims 1 to 10.

13. Robot joint comprising at least one strain wave gear according to one of claims 1 to 10.

14. Vehicle component, in particular a running gear, in particular an active running gear for a motor vehicle, or a steering system, in particular a passenger car steering system or a truck steering system, comprising at least one strain wave gear according to one of claims 1 to 10.