Shaft drive

Abstract

Wave gear, with a housing element (2), an internally toothed drive element (4) connected to it in a rotationally fixed manner, a flexible, externally toothed gear element (34), and an internally toothed output element (5), wherein the drive element (4) has form-locking elements (27) with which it is connected to the housing element (2), characterized in that the form-locking elements (27) are designed as plug-in tabs which are pushed through openings (26) in the housing element (2) and by means of which stop contours which are effective in the circumferential direction and which interact with stop contours of the output element (5) are formed.

Description

The invention relates to a wave gear mechanism according to the preamble of claim 1, which is particularly suitable for use in an electromechanical camshaft adjuster.A wave gear is known, for example, from DE 10 2016 217 051 A1. This harmonic drive that can be used as an adjusting gear in a camshaft adjuster comprises a drive wheel, an adjusting element in the form of a bearing inner ring, and an output element that is provided for connection to a camshaft. In this case, the drive wheel is mounted on the camshaft by means of a sliding bearing.A further wave gear of fundamentally the same construction is disclosed in DE 10 2016 219 076 A1. This wave gear also works with a flexible, externally toothed gear component, i.e. a flex ring. The external toothing of the flex ring meshes with the internal toothing of a drive wheel and with the internal toothing of a driven wheel designed as a ring gear. In addition to the flex ring, in the case of DE 10 2016 219 076 A1, the output wheel also has elastic properties.A wave gear described in DE 10 2016 201 536 A1 has a flex ring which is modified in comparison with the two cases mentioned at the beginning in that it has an outer reinforcement running in a ring shape.In a wave gear mechanism disclosed in DE 10 2015 223 419 A1, not the flex ring but a resilient rolling bearing outer ring contacting the flex ring has a modified shape. The modification is provided here in the form of an external material weakening of the outer ring.A harmonic drive of the generic type is known from DE 10 2015 210 707 B3. Further wave gearings are known from DE 10 2008 019 586 A1, DE 10 2017 114 069 A1, U.S. Pat. No. 5,417,186 A, DE 10 2007 051 475 A1, DE 10 2015 204 822 A1 and DE 10 2009 007 065 A1.The object of the invention is to specify a wave gear which is further developed than the state of the art mentioned and which is distinguished by a particularly compact, assembly-friendly structure and low mass moments of inertia.This object is achieved according to the invention by a wave gear with the features of claim 1. The wave gear comprises, in a basic construction known per se, a housing element, a drive element which is connected to the latter in a rotationally fixed manner and is provided with an internal toothing, an elastic, externally toothed gear element, and an internally toothed output element.According to the invention, the drive element has form-fitting elements, by means of which it is connected to the housing element. The component of the harmonic drive, which is referred to as "housing element", does not necessarily imply that the harmonic drive has a closed housing. Depending on the field of application of the harmonic drive, the housing element can be a rotating or a non-rotating element. When the harmonic drive is used in an electromechanical camshaft adjuster, the housing element is typically provided as a rotating element. If, on the other hand, the wave gearing is used in a device for varying the compression ratio of a reciprocating piston engine, the housing element is typically connected in a rotationally fixed manner to a non-rotating surrounding structure or is an integral part of this surrounding structure.In any case, because a positive fit is produced between the drive element and the housing element, separate connecting elements, for example screws, securing rings or clamps, which hold the drive element on the housing element, are unnecessary. The positive connection between the drive element and the housing element produced without additional elements allows the transmission of forces and moments between the drive element and the housing element.The form-fitting elements are designed as plug-in lugs which are inserted through openings in the housing element. The plug-in lugs extend substantially in the axial direction of the drive element, that is to say parallel to the central axis of the wave gearing. The number of the tabs is not subject to any theoretical restrictions. Preferably, at least three plug-in tabs and corresponding openings are present in the housing element. A higher number of plug-in lugs, for example six or eight lugs, can also be provided.A small number of insertion lugs, in particular an embodiment with exactly three insertion lugs, has the advantage that the insertion lugs are suitable for forming stop contours which are effective in the circumferential direction and cooperate with stop contours which are formed by the output element. In the case of the use of the harmonic drive as an adjusting gear of an electromechanical camshaft adjuster, the adjustment range of the camshaft adjuster is limited by the stop contours.The stop contours on the side of the output element are formed in a preferred embodiment by radially outwardly directed vanes of the output element. The width of each wing measured in the circumferential direction deviates from the width of each plug-in tab measured in the same direction by, for example, no more than 50%.The output element is preferably slidingly mounted within the harmonic drive. In this case, the output element has two axial bearing surfaces, with which it is mounted on the one hand with respect to the drive element and on the other hand with respect to the housing element. In a particularly preferred manner, the axial bearing surface supporting the output element with respect to the housing element is formed by the mentioned vanes.In addition, the output element can also have a radial bearing surface which is effective with respect to the housing element and is preferably arranged on the side of the vanes which are remote from the input element and which describe segments of a flange which are separated from one another. In a particularly space-saving configuration, the vanes engage in an annular shoulder on an inner circumferential surface of the housing element.Regardless of whether the form-fit elements of the drive element engage in openings of the housing element which have a closed edge, i.e. are configured as bores, in particular in the form of slots, or cooperate with other retaining contours of the housing element, in the fully assembled wave gear preferably each form-fit element has a formed end section. This end section can be given its final shape, for example, by bending, caulking or flanging. In any case, the forming process holds the plurality of positive-locking elements and thus the entire drive element on the housing element without play. The freedom from play relates here at least to the tangential direction of the drive element. Preferably, there is a clearance-free connection in any direction between the drive element and the housing element. In this case, in the direction in which the drive element is inserted into the housing element, a positive fit can be provided by a shoulder on each insertion tab, wherein the shoulder directly abuts on the housing element. In the opposite axial direction, on the other hand, the positive connection that is also effective in the axial direction is only produced by the deformation of the end sections of the positive connection elements. In principle, other connection technologies, such as clip or snap connections, between the drive element and the housing element are also conceivable.The housing element of the harmonic drive can be designed as a transmission element of a belt drive, in particular as a sprocket or belt wheel. It is likewise possible to connect a sprocket or belt wheel as a separate element to the housing element.The wave gear is suitable not only for applications in motor vehicle technology, but also as an adjusting gear in industrial applications, for example within a machine tool or an industrial robot.An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. Shown herein are: FIG. 1 shows a wave gearing in a sectional illustration, FIG. 2 shows the wave gearing in an end view, FIG. 3 shows a detail of the wave gearing in a sectional view, FIG. 4 shows a drive element of the harmonic drive, FIG. 5 shows a detail of the wave gearing in a perspective view.A wave gear mechanism, which is identified overall by the reference numeral 1, is provided for use in an electromechanical camshaft adjuster of an internal combustion engine, which adjuster is not shown in any more detail. With regard to the basic function of the harmonic drive 1, reference is made to the prior art cited at the beginning.The wave gear 1 comprises a housing element 2, which in the exemplary embodiment is formed integrally with a sprocket wheel 3, which is driven via the crankshaft of the internal combustion engine. The wave gear 1 further comprises a driving annulus gear 4, which is generally referred to as a driving element and is firmly connected to the housing element 2 in a manner explained in more detail below. In addition to the input annulus gear 4, an output element in the form of an output annulus gear 5 is pivotably mounted in the housing element 2, wherein the input annulus gear 4 and the output annulus gear 5 overlap one another as viewed in the axial direction of the annulus gears 4, 5.In the cavity formed by the input ring gear 4 and the output ring gear 5 there is a wave generator 6, which has a ball bearing as a rolling bearing 7. The rolling bearing 7 comprises an inner ring 8 with a non-circular, elliptical outer contour. Bolts 9 inserted into the inner ring 8 cooperate with a non-illustrated balancing clutch. Via the compensating clutch, the inner ring 8 is driven by an electric motor, likewise not shown. Overall, the harmonic drive 1 is a three-shaft drive, wherein the three shafts are provided by the rotatable housing element 2, the output annulus gear 5, and the electrically driven inner ring 8.Balls 10 roll on the non-circular contoured raceway of the inner ring 8, which balls are guided in a cage 11. The associated outer ring, designated by 12, of the rolling bearing 7 is designed as a thin-walled, flexible part in contrast to the inner ring 8 and permanently adapts itself to the non-round shape of the inner ring 8. As a result, an external toothing 13 of a flex ring 34, which surrounds the outer ring 12 without being firmly connected to the latter, is partially brought into engagement with an internal toothing 14 of the input annulus gear 4 and with an internal toothing 18 of the output annulus gear 5. The number of teeth of the internal toothing 14 corresponds to the number of teeth of the external toothing 13. Thus, the flex ring 34, which is generally referred to as a flexible transmission element, always remains in an unchanged angular position relative to the input annulus gear 4. On the other hand, the number of teeth of the internal toothing 18 deviates slightly, namely by two, from the number of teeth of the external toothing 13. This has the effect that a full revolution of the inner ring 8 in relation to the housing element 2 is converted into a slight pivoting between the housing element 2 and the output ring gear 5. In the present case, the harmonic drive 1 is designed as a so-called positive drive, also referred to as a positive transmission ratio. This means that the output ring gear 5 rotates in the same direction as the inner ring 8. Alternatively, a design of the harmonic drive 1 as a minus drive, i.e. as a drive with a negative transmission ratio, is also possible.The internal toothing 14 is located on a cylindrical section 15 of the input ring gear 4; the cylindrical section 15 merges at an end face of the wave gearing 1 into a radially inwardly directed inner rim 16. The inner rim 16 forms an axial stop with respect to the outer ring 12 and thus the entire wave generator 6. On the end face of the input annulus gear 4 opposite the inboard side 16, the input annulus gear has an outboard side 17 which limits the mobility of the output annulus gear 5 in the axial direction. In this case, an annular axial bearing surface 24 formed by the output annulus gear 5 bears against the radially outwardly directed outboard rim 17. The axial bearing surface 24 delimits a cylindrical section 19 of the output ring gear 5, which is shaped in the manner of a flat pot. The cylindrical section 19 merges on its side facing away from the axial bearing surface 24 into a non-closed base 20, which lies in a plane normal to the central axis of the ring gears 4, 5 and thus also to the rotational axis of the camshaft to be adjusted. The bottom 20 merges at its inner edge into a pin 21 which projects out of the bottom 20 towards the side of the camshaft to be adjusted. The opening defined by the hollow pin 21 is indicated 33. A central screw, not shown, is inserted through the opening 33, with which the output ring gear 5 is screwed firmly to the camshaft.From the cylindrical section 19 of the output ring gear 5 there emerge three uniformly distributed, i.e. at 120° intervals, wings 22 distributed on the circumference, which are to be understood as individual segments of a radially outwardly directed incomplete flange. Each vane 22 provides an axial bearing surface 23, which abuts the housing element 2 in the region of an annular shoulder 32. The output annulus gear 5 is thus supported in both axial directions by the axial bearing surfaces 23, 24 within the structural unit formed from the housing element 2 and the input annulus gear 4. A radial support is provided by a radial bearing surface 25 which is located in a region of the cylindrical section 19 between the vane 22 and the base 20. Thus, the output ring gear 5, apart from any bearing play, is not displaceable relative to the housing element 2 either in the radial or in the axial direction.In the housing element 2 there are three slot-shaped openings 26, through each of which a plug-in lug 27 is guided, which is an integral component of the hollow drive wheel 4. The insertion lugs 27 are aligned substantially in the axial direction of the drive ring gear 4. Here, the outboard rim 17 is adjoined by a short, radially outward-directed section which merges into a longer, axially oriented section of the plug-in tab 27. The plug-in tab 27, which is generally referred to as a form-fit element, thus has an overall angular shape. Each plug-in tab 27 can be seen to have a shoulder 28 which, when the harmonic drive 1 is assembled, abuts on the edge of an opening 26 in each case on the housing element 2.The portion of each plug-in tab 27 protruding from the opening 26 is referred to as an end portion 29. After the drive ring gear 4 and housing element 2 have been plugged together, the end section 29 is shaped, in the present case radially outwards, to such an extent that the drive ring gear 4 is positively prevented from being pulled out of the housing element 2. In addition, the forming of the end section 29, which is to be carried out during the production of the harmonic drive 1, also brings about a play-free connection between the input ring gear 4 and the housing element 2 in the circumferential direction.The plug-in lugs 27 are not only designed for the permanently fixed connection between the input annulus gear 4 and the housing element 2, but also as limiting elements which act in the circumferential direction with respect to the output annulus gear 5. Reference numeral 30 denotes circumferential stop surfaces of the plug-in lugs 27. Circumferential stop surfaces 30 may be abutted by circumferential stop surfaces 31 provided by each vane 22. Both circumferential stop surfaces 30, 31 project into the annular shoulder 32 on the inner circumferential surface of the housing element 2. Overall, this achieves a limitation of the angle of rotation of the harmonic drive 1 in the axial direction without additional installation space requirements of the harmonic drive 1. The wave gearing 1 is thus constructed to be particularly narrow compared to conventional solutions. In addition, the elimination of fasteners, such as screws, for connecting the input ring gear 4 to the housing element 2 significantly reduces the number of parts of the harmonic drive 1.List of reference characters1 Harmonic drive 2 Housing element 3 Sprocket 4 Input annulus gear 5 Output annulus gear 6 Wave generator 7 Rolling bearing 8 Inner ring 9 Bolt 10 Ball 11 Cage 12 Outer ring 13 External toothing 14 Internal toothing of the input annulus gear 15 Cylindrical section 16 Inner rim 17 Outer rim 18 Internal toothing of the output annulus gear 19 Cylindrical section 20 Base 21 Journal 22 Vanes 23 Axial bearing surface 24 Axial bearing surface 25 Radial bearing surface 26 Opening in the housing element 27 Plug-in plate, positive locking element 28 Shoulder on the plug-in plate 29 End section of the plug-in plate 30 Circumferential stop surface of the plug-in plate 31 Circumferential stop surface of the vane 32 Annular shoulder 33 Central opening in the output element 34 Flexible transmission element, flex ring

Claims

Wave gear, having a housing element (2), an internally toothed drive element (4) connected to the latter in a rotationally fixed manner, a flexible externally toothed gear element (34), and an internally toothed output element (5), wherein the drive element (4) has positive-locking elements (27), by means of which it is connected to the housing element (2), characterized in that the positive-locking elements (27) are designed as plug-in lugs which are inserted through openings (26) in the housing element (2) and by means of which stop contours which act in the circumferential direction and cooperate with stop contours of the output element (5) are formed.Wave gear according to Claim 1, characterized in that the stop contours of the output element (5) are formed by radially outwardly directed vanes (22).Wave gear mechanism according to Claim 2, characterized in that the output element (5) has two axial bearing surfaces (24, 23), with which it is mounted on the one hand with respect to the drive element (4) and on the other hand with respect to the housing element (2), the axial bearing surface (23) mounting the output element (5) with respect to the housing element (2) being formed by the vanes (22).Wave gear according to Claim 3, characterized in that the output element (5) has a radial bearing surface (25) which acts with respect to the housing element (2) and is arranged on the side of the vanes (22) facing away from the drive element (4).Wave gear according to one of Claims 2 to 4, characterized in that the vanes (22) engage in an annular shoulder (32) of the housing element (2).Wave gear according to one of Claims 1 to 5, characterized in that the positive-locking elements (27) each have a shaped end section (29) and are held on the housing element (2) without play at least in the circumferential direction.Harmonic drive according to one of Claims 1 to 6, characterized in that the housing element (2) is designed as a transmission element of a belt transmission, in particular as a sprocket wheel (3).Use of a harmonic drive according to Claim 1 in an electromechanical camshaft adjuster.

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