Harmonic wave reduction and bearing assembly and electric motor arrangement

Abstract

The present invention concerns a harmonic wave reduction and bearing assembly (10, 10'; 11, 11'), comprising a housing (26) housing an input side bearing (12, 12'), a harmonic wave reduction stage (30, 30') and an output side bearing (14, 14') that are aligned on a common central axis (22), wherein the harmonic wave reduction stage (30, 30') is sandwiched between the input side bearing (12, 12') and the output side bearing (14, 14'), wherein the input side bearing (12, 12') and the output side bearing (14, 14') are each of the radial or the radiaxial bearing type and have a plurality of rolling elements (16) positioned between a radially outer bearing ring (20, 20') and a radially inner bearing ring (18, 18'), wherein the reduction stage (30, 30') comprises, in a radial direction, an inner reduction stage ring (32), a central reduction stage ring (34) and an outer reduction stage ring (36) that are concentric with each other and configured to cooperate to perform the harmonic wave-type reduction action, wherein the inner reduction stage ring (32) is configured to rotate with the inner bearing ring (18) of the input side bearing (12, 12'), the central reduction stage ring (34) is configured to rotate with the inner bearing ring (18') of the output side bearing (14, 14') and the outer reduction stage ring (36) is configured to be coupled to the outer bearing rings (20, 20') of both the input side bearing (12, 12') and the output side bearing (14, 14').

Description

[0001] Harmonic wave reduction and bearing assembly and electric motor arrangement

[0002] Description

[0003] The invention relates to a harmonic wave reduction and bearing assembly and electric motor arrangement having radial or radiaxial bearings and one or more harmonic wave reduction stages.

[0004] Reduction assemblies are also known as gearboxes. Such gearboxes translate a fast rotation of a shaft on the input side into a slow rotation at enhanced torque on the output side of the gearbox. Many technical applications require reduction action but are faced with the problem that commonly known gearboxes in combination with bearings are prohibitively large. One such field of technology is robotics, which has a particularly strong need for miniaturization combined with robust and precise rotary speed reduction. Another field of technology, in which the invention can be used, is automotive, especially electric cars and electric wheels.

[0005] The translation of the rotational speed from fast to slow is sometimes done using a harmonic wave type reduction action known in the art. Gearboxes employing a harmonic wave type reduction action have three concentric rings. The innermost ring and outermost ring have races facing each other whose shape deviate from circular shapes. The innermost race has a small number Nin of valleys and peaks, in particular at least one of each, whereas the outermost race has a much larger number Nout of valleys and peaks with Nout > Nin, the gear ratio being equal to the quotient (Nout - Nin) / Nin. The central one of the three rings provides cages for rolling elements that are caught between the innermost race and the outermost race. The peaks and valleys are shaped to ensure that, within production tolerances, the rolling elements are always contacted by both the innermost race and the outermost race at the same time, thus ensuring a harmonic wave type movement of the rolling elements when the innermost, i.e. , input side, ring is driven to turn.

[0006] Either the outermost ring or the central ring may be affixed to a supporting structure, leaving the other ring, that is, the central ring or, respectively, the outermost ring, to constitute the output of the gearbox. The choice of outermost ring and central ring as output also determines whether the output will rotate in the same direction or in the opposite direction to the input shaft.

[0007] Commonly known gearboxes providing harmonic wave type reduction action are not capable of or ill-suited to bearing radial forces and are therefore usually used in combination with external or additional radial bearings. Most such known gearboxes are combined with three or more radial bearings for the dual purpose of bearing radial forces and sealing the gearbox from both sides. This is especially the case, since this stepping down of the rotational speed from the input side to the output side is accompanied by an equally large stepping up in torque. Radial bearings with concentric rings interposed with concentric rings of rolling elements are commonly used to take up radial forces while allowing rotational movement of rotating parts connected with the inner bearing ring of the bearing around a common central axis of the concentric rings.

[0008] This combination makes known gearboxes quite large and cumbersome. There is demand for powerful and price friendly gearboxes mostly for new robotics, general automation, medical devices, security and defense systems, new automated guided vehicles and electric vehicles. Each contribution to price optimization and size and weight reduction is welcome.

[0009] EP 3 135 954 A1 discloses a so-called reduction bearing, merging the functionality of radial bearings with that of a gearbox. It exhibits at least three concentric rings, namely an inner ring, a central ring and an outer ring, between which bearings are arranged, which consist of rings of rolling elements in rolling element cages, in effect constituting a concentric radial double-bearing. Each concentric ring further exhibits an extension section, where a harmonic wave-type reduction action is transmitted between the inner ring extension and the outer ring extension. One ring is connectable to a rotor of an electric motor, another ring is connectable to an output and the third ring is connectable to a stator of the electric motor. In effect, this reduction bearing provides a reduction action while simultaneously bearing radial forces.

[0010] It is an object of the present invention to improve over the known design with respect to simplicity, cost effectiveness, durability and performance.

[0011] This object is achieved with a harmonic wave reduction and bearing assembly, comprising an input side bearing, a harmonic wave reduction stage and an output side bearing that are aligned on a common central axis, wherein the harmonic wave reduction stage is sandwiched between the input side bearing and the output side bearing, wherein the input side bearing and the output side bearing are each of the radial or the radiaxial bearing type and have a plurality of rolling elements (16) positioned between a radially outer bearing ring and a radially inner bearing ring (18, 18’), wherein the reduction stage comprises, in a radial direction, an inner reduction stage ring, a central reduction stage ring and an outer reduction stage ring that are concentric with each other and centred on the common central axis and configured to cooperate to perform the harmonic wave-type reduction action, wherein the inner reduction stage ring is configured to rotate with the inner bearing ring of the input side bearing, the central reduction stage ring is configured to rotate with the inner bearing ring of the output side bearing and the outer reduction stage ring is configured to be coupled to the outer bearing rings of both the input side bearing and the output side bearing.

[0012] In contrast to the concentric double bearing of EP 3 135 954 A1 , which necessitates very small production tolerances and provides an inherent axial asymmetry, the bearing taking place on one side of the reduction stage, the harmonic wave reduction and bearing assembly of the present disclosure is well-balanced by utilizing at least two common radial or radiaxial bearings, between which the reduction stage is sandwiched. This arrangement also provides for good sealing of the gearbox. The use of commonly known radial or radiaxial bearings is cost-effective and provides the gearbox with simplicity and good durability. Since the reduction stage is protected on either side, axially, from radial forces, bending moments acting on the reduction stage are minimized, thus ensuring that the concentric rings of the reduction stage stay in concentric alignment with each other and the rolling elements of the reduction stage are not exposed to excessive forces at certain places along the circumference of the ring of rolling elements. Rolling elements may be of spherical shape, cylindrical shape, or other suitable shape allowing for rolling according to the setup and orientation of the race surfaces of the reduction stage. Furthermore, on either the input side or the output side or on both the input and the output sides, there may be two or more bearings present in axial alignment to each other forming the input and / or output side bearings, or bearings having two parallel rows of rolling elements.

[0013] In embodiments, the inner reduction stage ring has a first race surface having one or more peaks and the outer reduction stage ring has a second race surface facing the first race surface and having a plurality of grooves, the number of grooves being greater than the number of peaks, wherein the central reduction stage ring has structures defining a plurality of channels containing rolling elements held movable in the direction of the channel and in contact with both the first race surface and the second race surface, wherein the number of channels in the central reduction stage ring equals the difference between the number of grooves and the number of peaks. The gear ratio is determined by the quotient of the number of rolling elements and the number of peaks on the first race surface.

[0014] The channels need not be fully closed inside the central reduction stage ring, but may be open to one side, with the opening being closed by an opposing surface of, for example, the inner bearing ring of the input side bearing. Furthermore, the number of channels may be doubled if the rolling elements are provided in pairs for increased robustness. In this case, the number of pairs of channels count as the number of channels being equal to the difference between the number of grooves and the number of peaks. In embodiments, the first race surface, the second race surface and the channels are oriented such that, when in action, the rolling elements follow a radially oriented harmonic wave pattern, an axially oriented harmonic wave pattern or a radiaxially oriented harmonic wave pattern tilted at an oblique angle with respect to both the radial and the axial orientations. An oblique angle is to be understood as an angle between, but not including the radial orientation and the axial orientation. In the case of an axial orientation of the harmonic wave pattern, the central reduction stage ring will have a disk shape or disk like shape, wherein the front face of the disc in the axial direction bears the first race surface, the peaks and valleys defining different amplitudes in the axial direction. The second race surface is oriented facing the first race surface, its peaks and valleys likewise being oriented to provide a profile whose peaks are at a different axial position closer to the first race surface than its valleys.

[0015] In an embodiment, the housing has a cylindrical shape, giving it an easy to handle and well-balanced form. In further embodiments, the housing may be implemented as a common housing out of one peace into which the bearings and the reduction stage are placed, or as a composite housing composed of the input side and output side outer bearing rings and the outer reduction stage ring coupled together by removable coupling means. Such a one piece housing or composite housing provides a stable holding structure for the moving parts of the assembly inside the housing. A composite housing provides for easy assembly, a one piece housing, such as a housing cylinder or housing ring, eliminates the necessity of providing coupling means for the outer bearing rings and the outer reduction stage rings. In the composite housing, in other words, the outer bearing rings of the input side bearing, the reduction stage and the output side bearing, or the outer seating ring thereof, respectively, are connected with each other such as to form a common, in particular cylindrical, housing. This requires intricate machining of the inside of the housing, or can be achieved by combining and converting the individual outer rings into the common housing by means such as welding or soldering.

[0016] In an embodiment, the inner reduction stage ring is implemented as an extension connected to or of one piece with the inner bearing ring of the input side bearing and / or wherein the central reduction stage ring is implemented as an extension connected to or of one piece with the inner bearing ring of the output side bearing. The extensions of the inner and outer bearing rings of the input side bearing and the inner bearing ring of the output side bearing may radially mesh with each other to form the reduction stage. This embodiment provides a compact gearbox with few separate parts that have to be assembled and connected with each other, thereby providing few weak points.

[0017] In an embodiment, the inner reduction stage ring is connected to or of one piece with an extension on its input side that is configured as an inner seating ring, onto which the input side bearing is or can be fitted, in particular press-fitted, concentrically, and / or wherein the central reduction stage ring is connected to or of one piece with an extension on its output side that is configured as an inner seating ring onto which the output side bearing is or can be fitted, in particular press-fitted, concentrically. Furthermore, the housing may define on its inside an outer seating ring into which the input side bearing is or can be fitted, in particular press-fitted, concentrically, and / or wherein the housing defines on its inside an outer seating ring into which the output side bearing is or can be fitted, in particular press-fitted, concentrically. The housing may be of a one piece or of a composite type. In this context, an inner seating ring may have a convex, i.e. , radially exterior, cylindrical surface, an outer seating ring may have a concave, i.e., radially interior, cylindrical surface providing seatings for the fitting of the bearings. In other words, the outer circumferential seating surface of the inner seating ring and the inner circumferential seating surface of the outer seating ring are of cylindrical shape, as are the inner and outer surfaces of the cylindrical rolling bearing fitted therein and have inner and, respectively, outer diameters that allow the rolling bearing to be fitted inside the ring shaped space such as to be clamped in place therein. The rolling bearing may be a radial bearing or a radiaxial bearing.

[0018] In this embodiment, one or both of the bearings are cylindrical rolling bearings that can be standardized or off-the-shelf products from external rolling bearing manufacturers and do not have to be machined to specifications of the harmonic wave reduction and bearing assembly or in any way adapted for assembly. In the reverse, the seating rings are designed to accommodate the standardized bearings. These, in some cases self-contained, cylindrical rolling bearings can be accommodated in the harmonic wave reduction and bearing assembly by providing concentric inner and outer seating rings that define a space of the size of the chosen rolling bearing into which the rolling bearing is easily fitted, such as wedged, for a tight fit. The machining of the seating rings is simple, since it is not necessary to provide the seating rings with bearing races for rolling elements, since that feature is provided by the rolling bearing itself.

[0019] The embodiment having rolling bearings fitted into ring shaped spaces between an inner seating ring and an outer seating ring may be especially simple to machine since the outer seating ring may extend through the whole assembly and serve as a common housing. The embodiments including cylindrical rolling bearings fitted inside a ring shaped space between seating rings provide an easy way for accommodating the design for different sizes, bearing loads, etc., since the variability is achieved by choosing between a variety of different available cylindrical rolling bearings having known sizes and load capacities and by providing seating rings with the appropriate dimensions adapted to the sizes of the cylindrical rolling bearings. This opens the possibility of customizing the bearings according to the needs or wishes of customers, or the requirements for individual applications. In terms of production costs, it is most suitable to use the same bearings, where it is possible to get a better price for the purchase of a larger quantity of one type of bearings, it simplifies assembly and at the same time it makes warehouse management cheaper and more efficient.

[0020] This embodiment has technological advantages, because the processing of individual parts that do not have bearing races is easier than when they are part of bearing rings. Their processing in this case is independent of the supply of bearings. At the same time, it is possible to work with larger diameters of the reduction system and the use of larger diameters of rotating elements, which has a significant effect on increasing the rated torque from a gearbox with the same installation diameter. The maximum diameter of the main inner ring of the bearing does not present a limitation in this regard

[0021] In this embodiment, it is important to achieve radial and at the same time axial stability of the entire structure, therefore it is advantageous to use either double-row bearings, angular bearings, or cross-rollers bearings at least for the output side.

[0022] In an alternative embodiment, the reduction stage is formed as a separate unit of three concentric rings, the unit being placed between the input side bearing and the output side bearing and in axial alignment with the input side bearing and the output side bearing, wherein the inner reduction stage ring is connected with the inner bearing ring of the input side bearing, the central reduction stage ring is connected with the inner bearing ring of the output side bearing and the outer reduction stage ring is connected with the outer bearing rings of both the input side bearing and the output side bearing.

[0023] Whereas in this alternative embodiment, the reduction stage is formed as a separate unit to be combined with the input side bearing and the output side bearing, thus requiring a more elaborate assembly and more locations where the different parts have to be connected to each other, the individual components are more easily fabricated in the first place, requiring less elaborate machining.

[0024] In embodiments, the input side bearing and the output side bearing have equal dimensions and bearing load specifications, in particular are of the same model, resulting in a well-balanced assembly that is easy to produce.

[0025] In further embodiments, an input side end face of the input side bearing is at least partially covered with a radially inner end cap and / or a radially outer end cap, and / or wherein an output side end face of the output side bearing is at least partially covered with a radially inner end cap and / or a radially outer end cap, wherein the inner end cap or caps and / or the outer end cap or caps are ring shaped and concentric. Such end caps effectively seal open spaces on the end faces of the assembly that need to be closed to the environment and simultaneously allow for the relative rotation of the various rings against each other.

[0026] The gear ratio of the assembly may be enhanced with the assembly having two or more reduction stages coupled to each other in series from an input side reduction stage to an output side reduction stage, each reduction stage being sandwiched between an input side bearing and an output side bearing, the coupling in series being realized such that, in a pair of coupled reduction stages, the central reduction stage ring of an inputward reduction stage of the pair drives the inner reduction stage ring of an outputward reduction stage of the pair. The gear ratios of the individual reduction stages multiply. For example, such a combination of two reduction stages each having a gear ratio of 10: 1 will result in an overall gear ratio of 100: 1 , meaning that 100 revolutions of the input shaft will be stepped down to one revolution of the output ring. Since the torque is converted inverse proportional to the speed of rotation, it is enhanced by a factor of 100 in this example. Each of the two, three or more reduction stages of the assembly may be sandwiched between two bearings, thus decoupling subsequent stages from each other with respect to radial and / or axial forces.

[0027] Adjacent reduction stages of the pair share a common bearing between each other in embodiments of such stacked reduction stages. In other words, the output side bearing of the inputward reduction stage is at the same time the input side bearing of the outputward reduction stage of the pair. This reduces the number of radial or ra- diaxial bearings and the size and complexity of the assembly.

[0028] The present objective is also achieved with an electric motor arrangement comprising an electric motor and a harmonic wave reduction and bearing assembly according to the present disclosure, wherein the outer bearing ring of an input side radial or radiaxial bearing of the harmonic wave reduction and bearing assembly is connected with a housing or a stator of the electric motor and the inner bearing ring of the input side bearing is connected to a rotor of the electric motor. The electric motor arrangement thereby embodies the same characteristics, advantages and features as the above-described harmonic wave reduction and bearing assembly.

[0029] In an embodiment, a radial or radiaxial bearing of the electric motor is at the same time the input side bearing of the harmonic wave reduction and bearing assembly connected to the electric motor. The radial or radiaxial bearing of the electric motor is located next to or at the output of the motor and abutting the reduction stage of the assembly.

[0030] Further characteristics of the invention will become apparent from the description of the embodiments according to the invention together with the claims and the included drawings. Embodiments according to the invention can fulfill individual characteristics or a combination of several characteristics.

[0031] The invention is described below, without restricting the general intent of the invention, based on exemplary embodiments, wherein reference is made expressly to the drawings with regard to the disclosure of all details according to the invention that are not explained in greater detail in the text. The drawings show in:

[0032] Fig. 1A - 1 D schematic representations of a first embodiment of a harmonic wave reduction and bearing assembly,

[0033] Fig. 2 schematic representations of harmonic wave type reduction stages with different gear ratios,

[0034] Fig. 3A - 3B schematic representations of a second embodiment of a harmonic wave reduction and bearing assembly,

[0035] Fig. 4A - 4C schematic representations of a third embodiment of a harmonic wave reduction and bearing assembly, Fig. 5A - 5B schematic representations of a fourth embodiment of a harmonic wave reduction and bearing assembly,

[0036] Fig. 6A - 6B schematic representations of a fifth embodiment of a harmonic wave reduction and bearing assembly, and

[0037] Fig. 7A - 7B schematic representations of an embodiment of an electric motor arrangement.

[0038] In the drawings, the same or similar types of elements or respectively corresponding parts are provided with the same reference numbers in order to prevent the item from needing to be reintroduced.

[0039] Figs. 1 A to 1 D show schematic representations of a first embodiment of a harmonic wave reduction and bearing assembly 10, progressing in level of detail from Fig. 1 A to Fig. 1 C, and the separated constituent parts of a harmonic wave type reduction stage 30 in Fig. 1 D. In all figures showing gearboxes, the input of the gearbox displayed on the right side, the output on the left side.

[0040] Fig. 1A shows two radial bearings 12, 14 of the ball bearing type aligned on a common central axis 22, without a reduction stage. Input side bearing 12 comprises an inner bearing ring 18 and, concentric to the inner bearing ring 18, an outer bearing ring 20. Rolling elements 16 are located between a bearing race of the inner bearing ring 18 and a bearing race of the outer bearing ring 20. Likewise, output side bearing 14 comprises concentric inner bearing ring 18’, outer bearing ring 20’ and rolling elements 16 located between respective bearing races thereof. The bearing rings have screw holes or boreholes therein (without reference numbers) for assemblage. Fig. 1 B additionally shows a disassembled harmonic wave reduction stage 30 located between input side radial bearing 12 and output side radial bearing 14 and in axial alignment with both. The harmonic wave reduction stage 30 comprises an inner reduction stage ring 32, a central reduction stage ring 34, an outer reduction stage ring 36 and a plurality of rolling elements 38. The inner reduction stage ring 32 is connected to the inner bearing ring 18 of input side bearing 12. The central reduction stage ring 34 is connected to the inner bearing ring 18’ of output side bearing 14. The outer reduction stage ring 36 is connected to the outer bearing ring 20 of input side bearing 12. The rolling elements 38 are located at a radial distance from central axis 22 so as to coincide with the central reduction stage ring 34, which provides channels to accommodate the rotating elements 38. The channels of the central reduction stage ring 34 may be closed in axial direction, or open, to be closed when brought into direct opposition to the opposing surface of the inner bearing ring 18 of input side bearing 12. In both cases, the rolling elements 38 have only a freedom of movement in the radial direction inside their respective channels.

[0041] In this first embodiment, the inner, central and outer reduction stage rings 32, 34, 36 are provided as extensions of the respective inner and outer bearing rings 18, 18’, 20 of the input side bearing and 12 and the output side bearing 14, in the above described relationship. In this embodiment, the extensions are of one piece with their respective bearing rings 12, 14, 18, 18’, 20, but they may also be manufactured separate and connected to the respective bearing rings 12, 14, 18, 18’, 20 by connecting means such as soldering, welding, or through screws, bolts or the like.

[0042] Fig. 1 C shows the assembled harmonic wave reduction and bearing assembly 10 of the first embodiment. As can be seen, the three rings of the reduction stage 30 and the rolling elements 38 mesh tightly into one another, providing a very compact and balanced gearbox with good radial bearing functionality from both the input side and the output side. The extensions of the various bearing rings that form the reduction stage 30 require machining, but there are only very few parts that need to be connected, providing for a sturdy product. As can also be seen, the outer rings are combined into a composite common housing 26 housing the input and output side bearings 12, 14 sandwiching the reduction stage 30.

[0043] In addition, Fig. 1 C shows seals 40 applied from the outside to the gaps between inner and outer bearing rings 18, 20 of the input side bearing 12 and the inner and outer bearing rings 18’, 20’ of the output side bearing 14, respectively, as well as an internal seal 40 towards the central axis 22, sealing the internal gap between the extension of inner bearing ring 18 of input side bearing 12 and the inner bearing ring 18’ of output side bearing 14. This latter seal 40 is accommodated in two slits within the faces of inner bearing rings 18, 18’ facing each other, as can be better seen in Fig. 1 B. The seal 40 ensures that the input and output shafts, which are independent, are shut off from each other with respect to leakage of lubricants. Such seals may, in all of the embodiments disclosed herein, be positioned axially between the input and the output shafts in the radial position of the inner, central or outer reduction stage rings or therebetween.

[0044] Fig. 1 D shows schematic illustrations of constituent parts of harmonic wave reduction stage 30, lined up on a common central axis. From left to right, the central reduction stage ring 34 is displayed having eighteen channels 35 for the accommodation of eighteen rolling elements 38 displayed next to central reduction stage ring 34. The next item is the inner reduction stage ring 32. Reduction stage ring 32 has a non-circular circumferential first race surface 33, which in this embodiment has two peaks 33A located at the top and the bottom of the depiction and, consequently, two valleys 33B on the left and right. The shape of the first race surface 33 is an ellipse or close to an ellipse. To the right of the inner reduction stage ring 32, Fig. 1 D shows outer reduction stage ring 36 having an inward facing second race surface 37 with twenty grooves 37B, each separated from its neighbouring grooves by separators 37A.

[0045] The rightmost part of Fig. 1 D shows the reduction stage 30 with its constituent parts in an assembled state. As can be seen, each of the rolling elements 38 is accommodated inside a channel 35 of the central reduction stage ring 34, allowing movement relative to the central reduction stage ring 34 only in the radial direction. Upon rotation of the inner reduction stage ring 32, however, the turning of its peaks 33A forces the rolling elements 38 into the respective grooves 37B of the outer reduction stage ring 36, thereby forcing the central reduction stage ring 34 to slowly rotate with respect to outer reduction stage ring 36. With each passing peak 33A, a rolling element 38 will be guided into the next groove 37B from the one it had just been in. This harmonic wave like pattern of movement of the rolling elements 38 gives rise to the reduction of rotational speed from the input side to the output side. The gear ratio is determined by the ratio of the number of rolling elements 38 (18) to the number of peaks 33A (2), i.e. , in this case 9: 1. Accordingly, the number of grooves 37B of the outer reduction race ring 36 is 20, which is the sum of the number of rolling elements 38 and peaks 33A, fulfilling the requirement that the number of rolling elements 38 (or channels 35) is the difference between the number of grooves 37B and peaks 33A.

[0046] To illustrate this further, Fig. 2 provides a schematic illustration of how to achieve different gear ratios. The leftmost part of Fig. 2 shows an assembled reduction stage 30 according to Fig. 1 D, i.e., with a gear ratio of 9: 1. To the right, the respective inner reduction stage ring 32 is shown with the two peaks 33A on its first race surface 33 clearly indicated. The gear ration / = nR / 2 is indicated with nR being the number of rolling elements 38 and 2 being the number of peaks 33A, with the number of grooves 37B again being 20.

[0047] Next to this embodiment, an inner reduction stage ring 32 having only one peak 33A is displayed. The gear ratio in this case is / = nR. If this inner reduction stage ring 32 were to be used inside the reduction stage 30 shown in the leftmost place in Fig. 2, in order to keep fulfilling the requirement that the number of channels 35 is the difference between the number of grooves 37B and the number of peaks 33A, either the number of rolling elements 38 and channels 35 in the central reduction stage ring 34 would have to be increased to 19, providing a gear ration of 19: 1 , or the number of grooves 37B in the outer reduction stage ring 36 would have to be decreased by 1 , providing a gear ratio of 18: 1.

[0048] In the rightmost example in Fig. 2, the inner reduction stage ring 32 has three peaks 33A spaced 120° apart. The resulting gear ratio is then / = nR / 3. Used in the reduction stage 30 displayed left in Fig. 2, either the number of rolling elements 38 and channels 35 would have to be reduced to 17 or the number of grooves 37B would have to be increased to 21 . In the former case, the gear ratio would be 17:3, i.e., approx. 5,667: 1 , in the latter case it would be 6: 1 .

[0049] Fig. 3A to 3D show a schematic illustration of a second embodiment of a harmonic wave reduction and bearing assembly 10 in various stages of assembly progressing from Fig. 3A to Fig. 3C. Input side bearing 12 and output side bearing 14 are preassembled.

[0050] In this case, in contrast to the first embodiment of Fig. 1 , the reduction stage 30 is made of separate inner, central and outer reduction stage rings 32, 34, 36 that are aligned and assembled step by step. Progressing from Fig. 3A to Fig. 3B, first the input side components of reduction stage 30 are assembled and connected to their counterparts of the input side bearing 12 by screws, such as the screws shown in screw holes between inner reduction stage ring 32 and inner bearing ring 18 of input side bearing 12 (Fig. 3B). Likewise, outer reduction stage ring 36 is connected with outer bearing ring 20 of input side bearing 12. At this time, central reduction stage ring 34 is connected with inner bearing ring 18’ of the output side bearing 14 with a plurality of screws as well.

[0051] Next, as shown in Fig. 3C, the rolling elements 38 are placed inside their respective channels 35 of central reduction stage ring 34, likewise the internal seal 40 is placed inside its respective accommodating slit in either the inner reduction stage ring 32 or the central reduction stage ring 34, and the components aligned axially, brought into contact and connected, e.g. by screwing them together. Fig. 3C displays the finished harmonic wave reduction and bearing assembly 10 of the second embodiment, having a composite type common housing 26 that comes into being by connection of the bearings and the reduction stage, whereas Fig. 3D displays the reduction stage 30 of this embodiment without the bearings 12, 14.

[0052] As can be seen in Figs. 3C and 3D, the reduction stage 30 has additional structures on its input side and its output side needed for connecting the reduction stage 30 components to the input side bearing 12 and the output side bearing components 14 that are missing from the first embodiment depicted in Fig. 1 C, in which the rings 32, 34, 36 of the reduction stage 30 were built as extensions of the rings 18, 18’, 20 of the input side and output side bearings 12, 14. This difference makes the second embodiment slightly longer than the first em- bodiment. On the other hand, the components of the second embodiment are easier to produce than the extensions of the rings of the bearings, which makes the second embodiment more cost effective and easier to repair in case of a failure of a single part. However, because of the higher number of connection points, i.e., points of failure, given equivalent sizes, the second embodiment is slightly less robust than the first embodiment.

[0053] Figs. 4A to 4C illustrate a third embodiment of a harmonic wave reduction and bearing assembly. In this case, a difference to the previous embodiments of Figs. 1 and 3 lies in the fact that the input side bearing 12 and the output side bearing 14 are standard cylindrical rolling bearings that have not been adapted to be connected to any other parts of the assembly with boreholes, screw holes or the like. As can be seen in, for example, Fig. 1A or Fig. 3A, each of the input side bearing 12 and the output side bearing 14 have boreholes and / or screw holes in their inner and outer bearing rings 18, 18’, 20, 20’ into or through which screws are screwed for mechanical connection with the outer reduction stage ring 36 or other external parts.

[0054] The input side bearing 12 and output side bearing 14 of the embodiment of Figs. 4A to 4C, on the other hand, have not been machined to have such boreholes or screw holes. Instead, input side bearing 12 and output side bearing 14 are accommodated in the assembly 10 by being fitted, in particular press-fitted, into ring-shaped spaces 23, 23’, most clearly seen in Fig. 4C, defined by inner seating rings 19, 19’ and outer seating rings 21 , 21 ’ having cylindrical outer and inner surfaces, respectively, whose diameters are adapted to conform to the inner and outer diameters of the inner and outer bearing rings 18, 18’, 20, 20’ of the input and output side bearings 12 and 14, respectively. Furthermore, in case of a need of a greater load capacity, it is possible to dimension the ring-shaped spaces 23, 23’ such as to accommodated pairs of cylindrical rolling bearings in axial alignment to each other, or more than two rolling bearings each.

[0055] The outer seating rings 21 , 21 ’ of the input side bearing 12 and the output side bearing 14 are of one piece, namely a common housing 26 in the form of a housing ring, in other words, a hollow housing cylinder connecting all three stages of the assembly 10, that is, the input side bearing 12, the harmonic wave reduction stage 30 and the output side bearing 14.

[0056] Fig. 4A shows the components of the assembly 10 in a disassembled state. The housing 26 houses in its center the outer reduction stage ring 36 of the harmonic wave reduction stage 30. The inner reduction stage ring 32 and the central reduction stage ring 34 are in this case connected to or of one piece with the inner seating rings 19, 19’ of the input side bearing 12 and the output side bearing 14, respectively. The rolling elements 38 and seal 40 occupy the same space as shown in the previous embodiments. The harmonic wave reduction and bearing assembly 10 is closed to both sides axially by inner end caps 24, 24’ and outer end caps 25, 25’, which contain holes for screws for connecting the end caps 24, 24’, 25, 25’ with the housing 26 and the inner seating rings 19, 19’, respectively. In this case, the outer end caps 25, 25’ prevent the cylindrical rolling bearings, i.e., input side bearing 12 and output side bearing 14, from moving axially and out of the ring-shaped spaces 23, 23’ under load. The inner end caps 24, 24’ prevent the inner seating rings 19, 19’ from moving axially, thus also keeping the end of the reduction stage ring 32 and the central reduction stage ring 34 in place.

[0057] The fourth embodiment of harmonic wave reduction and bearing assemblies shown in Figs. 5A and 5B illustrates the principle of stacking two single-stage reduction and bearing assemblies 10, 10’ in series, in axial alignment with each other, as illustrated by the double-headed arrows between the two separate assemblies 10, 10’ in Fig. 5A. Fig. 5B shows the two-stage harmonic wave reduction and bearing assembly 1 1 , assembled out of inputward harmonic wave reduction and bearing assembly 10 and outputward harmonic wave reduction and bearing assembly 10’, wherein the assemblies 10, 10’ are connected such that the inner bearing rings and the outer bearing rings of the two radial bearings 14, 12’ brought into contact are connected to each other, respectively. By this, the outer bearing rings 20 are joined into a common housing and the central reduction stage ring 34 (hatched horizontally) of inputward assembly 10 is conntected to and drives the inner reduction stage ring 32 (hatched diagonally) of outputward assembly 10’. If both harmonic wave reduction and bearing assemblies 10, 10’ each have gear ratios of 9: 1 , for example, as in the case of the embodiment of Fig. 1 , the combined gear ratio is 81 : 1. This principle can be extended by adding more stages in the same manner. Since torque increases by the same factor as the speed of rotation decreases, a robust radial bearing is advantageous in such instances.

[0058] Figs. 6A and 6B show an alternative fifth embodiment of a two-stage harmonic wave reduction and bearing assembly 11’, wherein, in contrast to the fourth embodiment, the two reduction stages 30, 30’ are built as extensions of three radial bearings 12, 12714 and 14’. The middle bearing 12714 doubles as output side bearing 14 of inputward reduction stage 30 and as input side bearing 12’ of outputward reduction stage 30’ and bears extensions for the central reduction stage ring 34 of the inputward reduction stage 30 and of the inner and outer reduction stage rings 32’, 36’ of the outputward reduction stage 30’. The overall construction of each stage 30, 30’ is similar to the one shown in Figs. 1A to 1 C. Inner reduction stage ring 32 and outer reduction stage ring 36 of the inputward reduction stage 30 are built as extensions of the input side bearing’s 12 inner and outer bearing rings 18, 20, respectively, whereas central reduction stage ring 34’ of the outputward reduction stage 30’ is built as an extension of inner bearing ring 18’ of the output side bearing 14’ of the outputward reduction stage 30’. This assembly makes use of one fewer radial bearing than the one shown in Figs. 5A and 5B and thus lends itself to a more compact design.

[0059] Figs. 7A and 7B illustrate schematic representations of an embodiment of an electric motor arrangement 100 having, aligned on a common central axis, an electric motor 102 having a housing or stator 104 and a rotor 106, and on its output side a harmonic wave reduction and bearing assembly 10 according to a fifth embodiment. In this case, the function of the input side radial bearing is taken over by a radial bearing (not shown) of the electric motor itself. In all other respects, the setup of harmonic wave reduction and bearing assembly 10 is similar to the first embodiment shown in Figs. 1A to 1 C. In this way, the rotary output of electric motor 102 is immediately stepped down and torque increased in a compact design.

[0060] In all of the embodiments, the bearings 12, 12’, 14, 14’ are of the radial bearing type. It is understood that the bearings may also be of a radiaxial type in which the bearings will take up radial as well as axial stresses, depending on the intended use of the harmonic wave reduction and bearing assembly. Furthermore, the reduction stages 30, 30’ are of a type having a radial harmonic wave motion pattern of the rolling elements 38, but they may equally be of an axial or oblique type, such as are disclosed, for instance, in EP 3 366 937 A1 , the content of which is incorporated by reference in its entirety herein. All named characteristics, including those taken from the drawings alone, and individual characteristics, which are disclosed in combination with other characteristics, are considered alone and in combination as important to the invention. Embodiments according to the in- vention can be fulfilled through individual characteristics or a combination of several characteristics.

[0061] List of References

[0062] 10, 10’ harmonic wave reduction and bearing assembly

[0063] 11 , 11 ’ multi stage harmonic wave reduction and bearing assembly

[0064] 12, 12’ input side radial bearing

[0065] 14, 14’ output side radial bearing

[0066] 16 rolling element

[0067] 18, 18’ inner bearing ring

[0068] 19, 19’ inner seating ring

[0069] 20, 20’ outer bearing ring

[0070] 21 , 21 ’ outer seating ring

[0071] 22 central axis

[0072] 23, 23’ ring shaped space

[0073] 24, 24’ inner end cap

[0074] 25, 25’ outer end cap

[0075] 26 housing

[0076] 30, 30’ harmonic wave reduction stage

[0077] 32, 32’ inner reduction stage ring

[0078] 33 first race surface

[0079] 33A peak

[0080] 33B valley

[0081] 34, 34’ central reduction stage ring

[0082] 35 channel

[0083] 36, 36’ outer reduction stage ring

[0084] 37 second race surface

[0085] 37A separator

[0086] 37B groove

[0087] 38 rolling elements

[0088] 40 seal

[0089] 50, 50’ rolling bearing

[0090] 100 electric motor arrangement

[0091] 102 electric motor 04 housing 06 rotor i gear ratio nR number of rolling elements

Claims

Claims1. Harmonic wave reduction and bearing assembly (10, 10’; 11 , 11 ’), comprising a housing (26) housing an input side bearing (12, 12’), a harmonic wave reduction stage (30, 30’) and an output side bearing (14, 14’) that are aligned on a common central axis (22), wherein the harmonic wave reduction stage (30, 30’) is sandwiched between the input side bearing (12, 12’) and the output side bearing (14, 14’), wherein the input side bearing (12, 12’) and the output side bearing (14, 14’) are each of the radial or the radiaxial bearing type and have a plurality of rolling elements (16) positioned between a radially outer bearing ring (20, 20’) and a radially inner bearing ring (18, 18’), wherein the reduction stage (30, 30’) comprises, in a radial direction, an inner reduction stage ring (32), a central reduction stage ring (34) and an outer reduction stage ring (36) that are concentric with each other and configured to cooperate to perform the harmonic wave-type reduction action, wherein the inner reduction stage ring (32) is configured to rotate with the inner bearing ring (18)of the input side bearing (12, 12’), the central reduction stage ring (34) is configured to rotate with the inner bearing ring (18’) of the output side bearing (14, 14’) and the outer reduction stage ring (36) is configured to be coupled to the outer bearing rings (20, 20’) of both the input side bearing (12, 12’) and the output side bearing (14, 14’).

2. The harmonic wave reduction and bearing assembly (10, 10’; 11 , 11 ’) of claim 1 , wherein the inner reduction stage ring (32) has a first race surface (33) having one or more peaks (33A) and the outer reduction stage ring (36) has a second race surface (37) facing the first race surface (33) and having a plurality of grooves (37B), the number of grooves (37B) being greater than the number of peaks (33A), wherein the central reduction stage ring (34) has structures defining a plurality of channels (35) containing rolling elements (38) held movable in the direction of the channel (35) and in contact with both the first race surface (33) and the second race surface (37), wherein the number of channels (35) in the central reduction stage ring (34) equals the difference between the number of grooves (37B) and the number of peaks (33A), wherein in particular the first race surface (33), the second race surface (37) and the channels (35) are oriented such that, when in action, the rolling elements (38) follow a radially oriented harmonic wave pattern, an axially oriented harmonic wave pattern or a radiaxially oriented harmonic wave pattern tilted at an oblique angle with respect to both the radial and the axial orientations.

3. The harmonic wave reduction and bearing assembly (10, 10’; 11 , 11 ’) of claim 1 or 2, wherein the housing (26) has a cylindrical shape.

4. The harmonic wave reduction and bearing assembly (10, 10’; 11 , 11 ’) of one of claims 1 to 3, wherein the housing (26) is implemented as a common housing out of one peace into which the bearings and the reduction stage are placed, or as a composite housing composed of the input side and output side outer bearing rings (12, 12’, 14, 14’) and the outer reduction stage ring (36) coupled together by removable coupling means.

5. The harmonic wave reduction and bearing assembly (10, 10’; 11 , 11 ’) of one of claims 1 to 4, wherein the inner reduction stage ring (32) is implemented as an extension connected to or of one piece with the inner bearing ring (18) of the input side bearing (12, 12’) and / or wherein the central reduction stage ring (34) is implemented as an extension connected to or of one piece with the inner bearing ring (18’) of the output side bearing (14, 14’).

6. The harmonic wave reduction and bearing assembly (10, 10’; 11 , 11 ’) of one of claims 1 to 4, wherein the inner reduction stage ring (32) is connected to or of one piece with an extension on its input side that is configured as an inner seating ring (19), onto which the input side bearing (12, 12’) is or can be fitted, in particular press-fitted, concentrically, and / or wherein the central reduction stage ring (34) is connected to or of one piece with an extension on its output side that is configured as an inner seating ring (19’) onto which the output side bearing (14, 14’) is or can be fitted, in particular press-fitted, concentrically.

7. The harmonic wave reduction and bearing assembly (10, 10’; 11 , 11 ’) of claim 6, wherein the housing (26) defines on its inside an outer seating ring (21 ) into which the input side bearing (12, 12’) is or can be fitted, in particular press-fitted, concentrically, and / or wherein the housing (26) defines on its inside an outerseating ring (21 ’) into which the output side bearing (14, 14’) is or can be fitted, in particular press-fitted, concentrically.

8. The harmonic wave reduction and bearing assembly (10, 10’; 11 , 11 ’) of one of claims 1 to 4, wherein the reduction stage (30, 30’) is formed as a separate unit of three concentric rings (32, 34, 36; 32’, 34’, 36’), the unit being placed between the input side bearing (12, 12’) and the output side bearing (14, 14’) and in axial alignment with the input side bearing (12, 12’) and the output side bearing (14, 14’), wherein the inner reduction stage ring (32; 32’) is connected with the inner bearing ring (18) of the input side bearing (12, 12’), the central reduction stage ring (34, 34’) is connected with the inner bearing ring (18’) of the output side bearing (14, 14’) and the outer reduction stage ring (36, 36’) is connected with the outer bearing rings (20, 20’) of both the input side bearing (12, 12’) and the output side bearing (14, 14’).

9. The harmonic wave reduction and bearing assembly (11 , 1 1 ’) of one of claims 1 to 8, wherein the input side bearing (12, 12’) and the output side bearing (14, 14’) have equal dimensions and bearing load specifications, in particular are of the same model.

10. The harmonic wave reduction and bearing assembly (11 , 1 1 ’) of one of claims 1 to 9, wherein an input side end face of the input side bearing (12, 12’) is at least partially covered with a radially inner end cap (24) and / or a radially outer end cap (25), and / or wherein an output side end face of the output side bearing (14, 14’) is at least partially covered with a radially inner end cap (24’) and / or a radially outer end cap (25’), wherein the inner end cap or caps (24, 24’) and / or the outer end cap or caps (25, 25’) are ring shaped and concentric.11 . The harmonic wave reduction and bearing assembly (11 , 1 1 ’) of one of claims 1 to 10, the assembly (1 1 , 1 1 ’) having two or more reduction stages (30, 30’) coupled to each other in series from an input side reduction stage (30) to an output side reduction stage (30’), each reduction stage (30, 30’) being sandwiched between an input side bearing (12, 12’) and an output side bearing (14, 14’), the coupling in series being realized such that, in a pair of coupled reduction stages (30, 30’), the central reduction stage ring (34) of an inputward reduction stage (30) of the pair drives the inner reduction stage ring (32) of an outputward reduction stage (30’) of the pair.

12. The harmonic wave reduction and bearing assembly (11 , 1 1 ’) of claim 1 1 , wherein adjacent reduction stages (30, 30’) of the pair share a common bearing (14 / 12’) between each other.

13. Electric motor arrangement (100) comprising an electric motor (102) and a harmonic wave reduction and bearing assembly (10, 10’; 11 , 11 ’) according to one of claims 1 to 12, wherein the outer bearing ring (20) of an input side radial or radiaxial bearing (12) of the harmonic wave reduction and bearing assembly (10, 10’; 11 , 1 1 ’) is connected with a housing (104) or a stator of the electric motor (102) and the inner bearing ring (18) of the input side bearing (12) is connected to a rotor (106) of the electric motor (102).

14. The electric motor arrangement (100) of claim 13, wherein a radial or radiaxial bearing of the electric motor (102) is at the same time the input side bearing (12) of the harmonic wave reduction and bearing assembly (10, 10’; 1 1 , 1 1 ’) connected to the electric motor (102).

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