Inner ring of a wave generator

Abstract

A wave generator (1) comprises a rolling bearing (2), which in turn comprises an intrinsically rigid inner ring (3) having a non-circular outer contour and a flexible outer ring (4). The inner ring (3) has a race (7) outside of the sheet-metal center plane (25).

Description

[0001] Inner ring of a wave generator

[0002] The invention relates to an inner ring of a wave generator suitable for a wave gear according to the preamble of claim 1. The invention further relates to a method for producing such an inner ring.

[0003] Such a wave generator is known, for example, from DE 10 2014 202 060 A1. The wave generator is part of an actuating gear in an electric camshaft adjuster. Other electric camshaft adjusters with a wave generator are described, for example, in documents DE 10 2004 009 128 A1,

[0004] DE 10 2008 053 ​​914 A1, DE 10 2009 037 403 A1, DE 10 2010 031 218 A1 and

[0005] DE 10 2013 220 220 A1 discloses an inner ring for a large-diameter bearing application. EP 3 343 051 A1 discloses an inner ring for a large-diameter bearing application.

[0006] Within a wave gear, a wave generator's task is to deform an elastic, toothed gear element. For this purpose, a wave generator has a rolling bearing with a non-circular, usually elliptical, bearing ring. In mass production, it is advantageous to manufacture the inner ring of the wave generator from sheet metal. However, it has been found that the bearing service life is insufficient in certain cases.

[0007] The invention is based on the object of providing an inner ring for a wave generator of a wave gear which enables a long bearing service life.

[0008] This object is achieved according to the invention by an inner ring having the features of claim 1. The inner ring is intended for a wave generator of a wave gear comprising a rolling bearing in a known basic design and therefore has a raceway for rolling elements of the rolling bearing arranged on its outer circumference. The inner ring is inherently rigid and has a non-circular, in particular elliptical, outer contour. The corresponding outer ring of the rolling bearing is designed as a flexible bearing ring.

[0009] The inner ring is made from sheet metal. A semi-finished product can be cut to length or a blank can be punched into it, preferably already having a non-circular outer contour. The sheet metal used as the starting material has a roughly constant thickness and a center plane located centrally between the two outer surfaces.

[0010] The raceway of the inner ring made from sheet metal is arranged outside the center plane of the sheet metal. This can be achieved by forming the inner ring to give it an asymmetric, particularly L-shaped longitudinal section. If a plane is drawn through the inner ring that is perpendicular to the axis of rotation of the inner ring, a longitudinal section region with an asymmetric shape, particularly an L-shape, is created. A first, outer limb of the L-shaped longitudinal section forms the non-circular circumferential surface of the inner ring, on which rolling elements roll in the case of a rolling bearing arrangement. The circumferential surface can have a rim, although the rim does not necessarily have to be completely circumferential. It can, for example, be interrupted by individual recesses that can serve as engagement points for coupling components. A second, inner L-limb extends from the aforementioned L-limb in the radial direction of the bearing inwards.The inner leg in the longitudinal section forms a ring disc.

[0011] By arranging the raceway outside the sheet center plane, the service life of the inner ring is increased. Sheet metal can contain non-metallic inclusions as a result of segregation during the casting and subsequent rolling process. A sheet metal inner ring with a raceway stamped symmetrically in its annular disc plane has this raceway in the sheet center plane and thus where the non-metallic inclusions are located. The invention is based on the finding that the service life of a sheet metal inner ring can be increased if the raceway and the sheet center plane are separated, because then fewer, ideally no, non-metallic inclusions are located in or immediately below the raceway.

[0012] It has been shown that an L-shape of the longitudinal section of the inner ring of the wave generator is sufficient compared to a symmetrical shape, such as a T-shape. By deep drawing a rim, the original sheet center plane no longer runs exactly radially, but is shifted axially, towards the rim, by the deep drawing. This leaves sufficient radial space for a sufficiently rigid area of ​​the sheet. The non-metallic inclusions are thus displaced outside the raceway. The sheet core, as the central grain, is thus deflected axially and, in a preferred embodiment, no longer meets the radially directed outer contour.

[0013] The L-profile has the additional advantage of having virtually unchanged inertia and rigidity compared to the T-profile. The inertia can be further reduced by adding additional axial recesses in the area of ​​the annular disc in addition to a central opening. The axial recesses can perform additional functions. For example, bolts can engage in a first axial recess, with the bolts forming part of an Oldham coupling. Second axial recesses can also ensure lubricant exchange.

[0014] It has been found that certain ratios of the sheet thickness of the ring disc to that of the deep-drawn rim are particularly advantageous. With a ratio between 0.7 and 0.8, sufficient surface material is available, so that even a slight deflection of the sheet center plane is sufficient to achieve a sufficient distance between the surface and the center plane.

[0015] This ensures sufficient sheet surface material is available in the area of ​​the lateral surface. At a ratio of 0.6 to 0.7, however, the degree of deformation is significantly greater. In this case, however, back-upsetting also allows for a particularly favorable displacement of the sheet core, so that its minimum distance from the raceway is sufficiently large.

[0016] According to the invention, it is proposed to produce an inner ring of a wave generator with the following steps:

[0017] Provision of a semi-finished product as a sheet with a sheet center plane, punching a non-circular blank, cold-forming production of a rim in the blank such that the sheet center plane in the area of ​​the rim is shifted from the radial direction, upsetting the blank.

[0018] Depending on the size of the inner ring, the non-circular blank can first be pre-punched to accommodate a tool. Chamfering can occur before forming, preferably deep drawing. After the forming step, the originally flat blank takes on a three-dimensional shape with a ring disk and a portion extending away from the plane of the ring disk, such as a rim. The blank is optionally upset, and a final perforation can occur. At the same time, or before or after the process, additional axial recesses can be made in the ring disk. Post-processing steps such as deburring or chamfering can follow.

[0019] Preferably, the inner ring with L-profile is produced by cold forming.

[0020] Due to the L-shaped longitudinal section on both sides of the rotation axis, the inner ring has an overall flat, open-bottomed cup shape. With this shape, the inner ring's mass inertia, radial stiffness, and torsional rigidity are comparable to a T-profile inner ring. However, the strength properties of a flat ring or flat disc are significantly exceeded by the inner ring's L-shaped longitudinal section.

[0021] Rolling bearing components manufactured by forming processes are known in principle, for example, from DE 101 32 470 A1 and from DE 10 2005 003 987 A1.

[0022] According to a possible further development, a compensating coupling, in particular an Oldham coupling, is coupled to the rolling bearing. An Oldham coupling suitable for a wave generator is known in principle, for example, from DE 10 2007 049 072 A1.

[0023] For coupling the compensating coupling with the inner ring of the wave generator, two bolts are suitable, for example, which are each held in the radially inward-pointing L-leg of the inner ring.

[0024] According to various advantageous developments, the compensating coupling is coupled to the inner ring of the wave generator without separate connecting elements, such as bolts. For example, an Oldham disc of the compensating coupling, made of plastic or metal, is guided by two guide lugs molded onto the inner ring, allowing limited radial displacement. An alternative way of guiding the Oldham disc on the inner ring is possible using guide slots formed directly through the inner ring and interacting with mating contours on the Oldham disc side.

[0025] In both cases, a torque can be transmitted to the Oldham disk, for example, by means of a two-bladed drive element. The drive element is coupled to a drive shaft, in particular rigidly connected, and is displaceable relative to the Oldham disk to a limited extent in the radial direction of the drive shaft and the compensating coupling. The drive shaft is preferably electrically driven, in particular identical to the motor shaft of an electric motor.

[0026] According to a simplified design, a two-bladed drive element mounted on a drive shaft interacts directly with the inner ring of the wave generator. As long as the drive shaft lacks radial flexibility and the drive element is rigidly connected to the drive shaft, a limited functionality of a compensating coupling is provided by a movable guide of the drive element on the inner ring. The full functionality of a compensating coupling can be achieved by using a drive shaft that can be deflected in the radial direction. Such a drive shaft can, for example, comprise a helical spring or two concentric helical springs wound in opposite directions. Instead of a two-bladed drive element, a single-finger coupling can also be used, as is known in principle, for example, from document DE 10 2004 041 769 A1.

[0027] The wave generator is suitable for use in a wave gear, which is used, for example, in an electric camshaft adjuster. The wave generator is also suitable for an adjusting gear in a device for varying the compression ratio of a reciprocating piston engine. In the latter case, the adjusting gear adjusts an eccentric shaft, which interacts with other components of a reciprocating piston engine's crankshaft via a secondary connecting rod.

[0028] Below, three embodiments of the invention are explained in more detail with reference to a drawing. In the drawings:

[0029] Fig. 1 shows a first embodiment of a wave generator with an inner ring in a sectional view, Figs. 2 and 3 show the inner ring of the wave generator according to Fig. 1,

[0030] Fig. 4 shows a second embodiment of a wave generator with an inner ring in frontal view,

[0031] Fig. 5 shows the wave generator according to Fig. 4 in a sectional view analogous

[0032] Fig. 1 ,

[0033] Fig. 6 and 7 show the inner ring of the wave generator according to Fig. 4 in representations analogous to Fig. 2 and 3,

[0034] Fig. 8 shows a third embodiment of a wave generator with an inner ring in a representation analogous to Fig. 4,

[0035] Fig. 9 shows the wave generator according to Fig. 8 in a representation analogous to Fig. 1,

[0036] Fig. 10 and 11 the inner ring of the wave generator according to Fig. 8 in representations analogous

[0037] Fig. 2 and 3,

[0038] Fig. 12 another inner ring for a wave generator.

[0039] Unless otherwise stated, the following explanations refer to all embodiments. Corresponding or essentially equivalent parts are identified by the same reference numerals in all figures.

[0040] A wave generator, designated overall by 1, comprises a rolling bearing 2, whose inner ring is designated by 3 and whose outer ring is designated by 4. The wave generator 1 is part of a wave gear (not shown in detail), whose function is described in the prior art cited above. The wave gear is used in an electric camshaft adjuster.

[0041] Balls roll as rolling elements 5 between the inner ring 3 and the outer ring 4 as bearings, and are guided in a cage 6. The inner ring 3 describes an L-profile LP in longitudinal section, with a raceway 7, on which the balls roll, being formed by an outer L-leg 8. An inner L-leg 9 pointing in the direction of the rotation axis R adjoins the outer L-leg 8. Overall, the outer L-leg 8 describes a cylindrical wall, with the portion protruding from the plane of the inner L-leg 9 forming a rim 24, which in this case is of a circumferential design. The inner L-leg 9 describes a base of a flat, one-piece, pot-shaped structure, also referred to as an annular disk 23, which adjoins the outer L-leg 8 and is open in the middle. The entire inner ring 3 is manufactured from metal, namely steel, for example 100Cr6, by forming processes.The outer circumferential surface of the inner ring 3, through which the raceway 7 is provided, has a non-circular, elliptical shape. Corresponding to this shape, the outer ring 4, which, in contrast to the inner ring 3, is designed to be flexible, is also forced into a non-circular shape. A flexible gear element 10, which directly surrounds the outer ring 4 without being rigidly connected to it, adapts to this shape. The flexible, externally toothed gear element 10 is also referred to as a flex ring and partially engages the internal toothing of inherently rigid gear elements (not shown). Instead of a flex ring 10, a collar sleeve or a flexible pot-shaped gear element could also be used as a flexible gear element.

[0042] Figure 3 schematically shows the original sheet metal center plane 25 of the sheet metal from which the inner ring 3 is made. Since the inner ring 3 has been given an asymmetrical shape through a deep-drawing and upsetting process, the sheet metal center plane 25, which represents the sheet metal core as the location with the most non-metallic inclusions, is deflected from the radial direction in the area of ​​the outer L-leg 8. The length and thickness of the rim 24 are designed such that the sheet metal center plane 25 no longer intersects the raceway 7 and, in this case, even the remaining radial wall.

[0043] The inner ring 3 is coupled to a compensating coupling 11, which in the designs according to Figs. 1 and 4 is designed as an Oldham coupling.

[0044] The compensating coupling 11, designed as an Oldham coupling, comprises an Oldham disk 12 which, in the design shown in Figs. 1 to 3, is coupled to the inner ring 3 by means of two bolts 13. The bolts 13 are fastened in the inner ring 3 and at the same time guided in elongated holes 14 of the Oldham disk 12, so that the disk can be moved relative to the inner ring 3 to a limited extent in a defined radial direction. 15 designates bores in the inner ring 3 in which the bolts 13 are fastened. In the embodiment shown in Figs. 1 to 3, the end face of the Oldham disk 12 abuts on the outer L-leg 8 of the inner ring 3 and on the heads 16 of the bolts 13, so that it is held captive on the inner ring 3 and thus on the entire rolling bearing 2.

[0045] 4 to 7, there are no bolts or other separate fastening means for holding the Oldham disk 12 on the inner ring 3. Instead, two guide lugs 17 are formed on the inner ring 3 and extend in the axial direction from the outer L-leg 8. The guide lugs 17 engage in recesses 18 in the Oldham disk 12 and thus perform a function comparable to the function of the bolts 13 of the wave generator according to Fig. 1. Furthermore, Fig. 4 shows two recesses 19 in the Oldham disk 12, which are offset by 90° from the recesses 18 and are intended to interact with a drive element not shown here. This is a two-blade drive element 20, as is also provided in the embodiment according to Figs. 8 to 11. In the design according to Figs. 8 to 11, the drive element 20 acts in contrast to the designs according to Figs.1 and 4, however, not via an Oldham disk 12, but directly with the inner ring 3. The drive element 20 of the wave generator 1 according to Fig. 8 is preferably attached to a flexible drive shaft, so that the full functionality of a compensating coupling 11 is provided without a separate compensating disk.

[0046] The two wings of the drive element 20, designated 22, engage in guide slots 21 of the inner ring 3. Similar to the embodiment shown in Fig. 4, the guide slots 21 do not provide a guiding function in the axial direction, which is advantageous for assembly purposes.

[0047] Figure 12 shows a further inner ring 3 with an annular disc 23. First axial recesses 26 and second axial recesses 27 are arranged in the annular disc 23, which in the present case are circular, wherein the first axial recesses 26 and second axial recesses 27 differ in their diameters.

[0048] List of reference symbols

[0049] Wave generator

[0050] Rolling bearings, rolling bearings

[0051] inner ring

[0052] Outer ring

[0053] Rolling elements

[0054] cage

[0055] Raceway outer L-leg inner L-leg

[0056] 10 flexible gear element

[0057] 11 Compensating coupling

[0058] 12 Oldham disc

[0059] 13 bolts

[0060] 14 slot

[0061] 15 Hole

[0062] 16 heads

[0063] 17 Guide nose

[0064] 18 recess

[0065] 19 Recess 0 Drive element 1 Guide slot 2 Wing

[0066] 23 Ring disc

[0067] 24 board

[0068] 25 Sheet metal center plane

[0069] 26 first axial recess

[0070] 27 second axial recess

[0071] LP L-profile R Rotation axis ds Thickness of the ring disc dB Thickness of the board

Claims

Patent claims 1 . Inner ring (3) of a wave generator (1 ), wherein the inner ring (3) is made of a sheet metal having a sheet metal center plane (25), has a non-circular outer contour and a raceway (7) for rolling elements (5), characterized in that the raceway (7) is arranged outside the sheet metal center plane (25).

2. Inner ring (3) according to claim 1, characterized in that the inner ring (3) is formed by an annular disc (23) with a rim (24) forming an L-shaped longitudinal section.

3. Inner ring (3) according to claim 2, characterized in that the ratio of the formed sheet thickness (dß) of the rim (24) to the sheet thickness (ds) of the annular disc (23) is between 0.7 and 0.

8.

4. Inner ring (3) according to claim 2, characterized in that the ratio of the formed sheet thickness (dß) of the rim (24) to the sheet thickness (ds) of the annular disc (23) is between 0.5 and 0.

6.

5. Inner ring (3) according to one of the preceding claims, characterized in that the annular disc has first and second axial recesses (26, 27).

6. Wave generator (1 ) with a rolling bearing (2) which has a flexible outer ring (4) and an inner ring (3) according to one of the preceding claims.

7. Wave generator (1) according to claim 6 with an inner ring according to claim 5, characterized in that the wave generator (1) has a compensating coupling (11) coupled to the rolling bearing (2) with two bolts (13) which are coupled to the first axial recesses (26) of the inner ring (3), the second axial recesses (27) forming lubricant passages.

8. Wave generator (1) according to one of claims 6 to 7, characterized in that the rolling bearing (2) is designed as a ball bearing.

9. Method for producing an inner ring (3) of a wave generator (1), comprising the following steps: - Providing a semi-finished product as a sheet with a sheet center plane (25), - Punching a non-circular blank, - cold forming a rim (24) into the round blank such that the sheet center plane (25) is displaced from the radial direction in the area of ​​the rim (24), - Upsetting the round blank.

10. The method according to claim 9, characterized in that the cold-forming production of the rim (24) is carried out by deep drawing.

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