HARMONIC DRIVE AND METHOD FOR PRODUCING HARMONIC DRIVE

Abstract

A harmonic drive, more particularly in an electromechanical camshaft phaser, comprises a drive element (2), a flexible transmission element (26) connected to the drive element (2) and having external teeth (29), and an output element (4) that is designed as a ring gear and has internal teeth (30) that partially mesh with the external teeth (29). The flexible transmission element (26) is pot-shaped, and is coupled in a torque-transmitting manner to the drive element (2) radially inside the outer teeth (29).

Claims

1. A harmonic drive comprising: a drive element; a flexible transmission element connected to the drive element and having outer external teeth; and an output element configured as a ring gear and having internal teeth that partially mesh with the external teeth, the flexible transmission element being pot-shaped, and being coupled in a torque-transmitting manner to the drive element radially inside the external teeth.

2. The harmonic drive according to claim 1, wherein the flexible transmission element is coupled to the drive element in a form-fitting manner.

3. The harmonic drive according to claim 2, wherein the flexible transmission element has a bottom with openings, into which form-fitting elements of the drive element engage.

4. The harmonic drive according to claim 3, wherein the openings are delimited in both peripheral directions of the transmission element by contact flanks bent out of the bottom of the flexible transmission element.

5. The harmonic drive according to claim 1, wherein a rotation angle limitation is formed between the drive element and the output element.

6. The harmonic drive according to claim 5, wherein the rotation angle limitation is formed by a stop segment of the drive element and a recess in an otherwise ring-shaped, circumferential end face strip of the output element.

7. The harmonic drive according to claim 5, wherein the rotation angle limitation is formed by an opening in the drive element and a stop segment of the output element engaging in the opening.

8. The harmonic drive according to claim 1, wherein the drive part is a sintered part.

9. A method for producing a harmonic drive, comprising the following steps: providing a pot-shaped drive element configured as a transmission element of a continuously variable transmission, first form-fitting elements being formed on a bottom of the pot-shaped drive element; providing a flexible pot-shaped externally toothed transmission element, second form-fitting elements being formed on a bottom of the flexible pot-shaped externally toothed transmission element; providing a wave generator configured to deform the pot-shaped externally toothed flexible transmission element; providing a pot-shaped internally toothed output element; inserting the wave generator into the flexible pot-shaped externally toothed transmission element to form an assembly; inserting the assembly into the pot-shaped internally toothed output element; sliding the pot-shaped drive element onto the pot-shaped internally toothed output element until a connection suitable for transmitting a torque is established between the first form-fitting elements and the second form-fitting elements; and securing the pot-shaped internally toothed output element with respect to the pot-shaped drive element in an axial direction by a locking ring.

10. The method according to claim 9, wherein a chain wheel produced by forming technology is used as the pot-shaped drive element.

11. A harmonic drive comprising: a drive element being pot-shaped and including a bottom and a cylindrical outer peripheral surface radially outside the bottom and adjoined to the bottom; a flexible transmission element connected to the drive element and having external teeth; and an output element configured as a ring gear and having internal teeth that partially mesh with the external teeth, the flexible transmission element being coupled in a torque-transmitting manner to the bottom of the drive element radially inside the external teeth.

12. The harmonic drive as recited in claim 11, wherein the flexible transmission element is pot-shaped and includes a bottom and a cylindrical section radially outside the bottom and adjoined to the bottom, the bottom of the flexible transmission element being coupled in a torque-transmitting manner to the bottom of the drive element.

13. The harmonic drive as recited in claim 12, wherein the bottom of the drive element includes first form-fitting elements and the bottom of the flexible transmission element includes second form-fitting elements, the first form-fitting elements engaging the second form-fitting elements in the torque-transmitting manner.

14. The harmonic drive as recited in claim 13, wherein lateral surfaces of the first form-fitting elements bear against contact flanks of the second form-fitting elements to form a form-fitting coupling between the flexible transmission element and the drive element.

15. The harmonic drive as recited in claim 11, wherein the output element is received inside of the cylindrical outer peripheral surface of the drive element.

16. The harmonic drive as recited in claim 11, further comprising a wave generator configured to deform the flexible transmission element, the wave generator being received inside of the flexible transmission element.

17. The harmonic drive as recited in claim 16, wherein the wave generator is received axially between the bottom of the drive element and a bottom of the output element.

18. The harmonic drive as recited in claim 11, wherein the harmonic drive is a camshaft adjuster, the drive element including a first stop contour and the output element including a second stop contour, the first stop contour and the second stop contour forming a rotation angle limitation delimiting an adjustment range of the camshaft adjuster.

Description

BRIEF SUMMARY OF THE DRAWINGS

[0044] In the following, several exemplary embodiments of the present disclosure are explained in more detail by means of a drawing. In the figures:

[0045] FIG. 1 shows a first exemplary embodiment of a harmonic drive in a sectioned, perspective view,

[0046] FIG. 2 shows a drive element, designed as a chain wheel, of the harmonic drive according to FIG. 1,

[0047] FIGS. 3 and 4 show a flexible transmission element of the harmonic drive according to FIG. 1, designed as a toothing pot,

[0048] FIG. 5 shows the drive element according to FIG. 2 with inserted toothing pot,

[0049] FIG. 6 shows an output element of the harmonic drive according to FIG. 1,

[0050] FIG. 7 shows the chain wheel according to FIG. 2 with inserted output element according to FIG. 6 as well as toothing pot according to FIG. 3 and the associated wave generator in a sectional perspective view,

[0051] FIG. 8 shows a second exemplary embodiment of a harmonic drive in a sectional perspective view,

[0052] FIGS. 9 and 10 show the harmonic drive according to FIG. 8 in exploded views,

[0053] FIG. 11 shows a detailed view of the harmonic drive according to FIG. 8,

[0054] FIG. 12 shows a drive element, namely a chain wheel, of the harmonic drive according to FIG. 8 with an inserted output element and flexible transmission element,

[0055] FIG. 13 shows a detail section of the arrangement according to FIG. 12 in a sectional perspective view,

[0056] FIG. 14 shows the output element of the arrangement according to FIG. 12,

[0057] FIG. 15 shows a detail section of the output element according to FIG. 14,

[0058] FIG. 16 shows the drive element of the harmonic drive according to FIG. 8,

[0059] FIG. 17 shows a detail section of the drive element according to FIG. 16,

[0060] FIG. 18 shows the drive element according to FIG. 16 with inserted toothing pot,

[0061] FIG. 19 shows components of a third exemplary embodiment of a harmonic drive in a perspective sectional view,

[0062] FIG. 20 shows the harmonic drive according to FIG. 19 in a further sectional perspective view,

[0063] FIG. 21 shows an output-side perspective view of the harmonic drive according to FIG. 19.

DETAILED DESCRIPTION

[0064] Unless otherwise stated, the following explanations relate to all exemplary embodiments. Parts that correspond to each other or have basically the same effect are always marked with the same reference symbols in the figures.

[0065] A harmonic drive, identified as a whole by reference numeral 1, is provided for use as an adjusting gear of an electromechanical camshaft adjuster of an internal combustion engine. The harmonic drive 1 is a three-shaft drive, with regard to the basic function of which reference is made to the prior art mentioned at the outset.

[0066] The harmonic drive 1 has a drive element 2 which at the same time represents the housing of the harmonic drive 1. A chain wheel 3 is an integral part of the drive element 2. In the exemplary embodiment according to FIG. 1, the drive element 2 is manufactured as a sintered part. In the exemplary embodiment according to FIG. 8, the drive element 2 is a transmission element produced by a forming process.

[0067] The drive element 2 is driven in all cases by a chain, wherein it rotates at half the crankshaft speed. A ring gear, which is rotatably mounted in the drive element 2, is provided as the output element 4 of the harmonic drive 1. The ring gear 4 is firmly connected to the shaft to be adjusted, that is, the camshaft of the internal combustion engine, by means of a central screw, not shown. The end face of the harmonic drive 1 to which the camshaft to be adjusted is connected is referred to as the output-side end face S.sub.AB. The opposite end face is referred to as the first end face S.sub.1. On the first end face S.sub.1, there is an electric motor, not shown, which is provided for actuating the harmonic drive 1.

[0068] The drive element 2, like the output element 4, has the basic shape of a pot. At a bottom of the drive element 2, designated in all cases with 5, which is located on the first end face S.sub.1 of the harmonic drive 1, a peripheral surface which, in the case of FIG. 1, is designed as a conical outer peripheral surface 6, adjoins. In the case of FIG. 8, the bottom 5 is adjoined by a cylindrical outer peripheral surface 7, which merges into the chain wheel 3. In the case of FIG. 19, a first conical outer peripheral surface 6 adjoins the bottom 5 and extends as far as the chain wheel 3. The opposite end face of the chain wheel 3 merges into a second conical outer peripheral surface 9 which tapers toward the output-side end face S.sub.AB. Such a second conical outer peripheral surface 9 is also given in the exemplary embodiment according to FIG. 1, but less distinctly.

[0069] In all cases, the outer peripheral surfaces 6, 7, 8, 9 are arranged radially outside of a cylindrical inner peripheral surface 10, which functions as a radial slide bearing surface with respect to the output element 4. The associated radial slide bearing surface of the output element 4 is formed by a cylindrical section 11 of the output element 4. The cylindrical section 11 is secured toward the output-side end face S.sub.AB by a locking ring 12 in the drive element 2. The locking ring 12 engages in a peripheral groove 13 on the inner peripheral surface of the drive element 2. In the opposite axial direction, that is to say, toward the first end face S.sub.1, the output element 4 is mounted by means of an axial slide bearing surface 14 which is formed directly by the bottom 5. The bottom 5 of the drive element 2 lies opposite the bottom of the output element 4, denoted by 15, on the output-side end face S.sub.AB. Each bottom 5, 15 is not closed, that is, it is only designed to be annular disc-shaped, wherein the bottom 15 extends further toward the central axis of the harmonic drive than the bottom 5. The inner delimitation of the bottom 15 is formed by a pin 16 which protrudes from the output-side bottom 15. When the harmonic drive 1 is installed, the aforementioned central screw, which is screwed tightly into the camshaft, is inserted through the opening marked 17, which is formed by the hollow pin 16. The camshaft to be adjusted can be a cam shaft or an exhaust camshaft of the internal combustion engine.

[0070] The adjustment range of the camshaft adjuster, which works with the harmonic drive 1 as an adjusting gear, is delimited by a rotation angle limitation designated overall by 18. The rotation angle limitation 18 is formed by a drive-side stop contour 19 and an output-side stop contour 20. The drive-side stop contour 19 is formed directly by the drive element 2 and the output-side stop contour 20 is formed directly by the output element 4. In the exemplary embodiments according to FIGS. 1 and 19, a stop segment 21 is formed on the inside of the bottom 5. This stop segment 21 extends over an angle of less than 60° in the peripheral direction of the bottom 5, which is generally annular disc-shaped. The stop segment 21 cooperates with an adjustment window 22 on the open, that is to say, first end face of the output ring gear 4. The adjustment window, also generally referred to as a recess, extends over an angle of more than 120° on the circumference of the cylindrical section 11 of the output element 4 and thus interrupts an end face bar 23 of the output element 4.

[0071] In the exemplary embodiment according to FIG. 8, on the other hand, the drive element 2 has an opening 24 which is curved in the shape of a circular arc as part of the rotation angle limitation 18. A stop segment 25 of the output element 4 engages in the opening 24. The stop segment 25 extends over an angle of less than 45° on the open end face of the output ring gear 4.

[0072] In all the exemplary embodiments, a pot-shaped, flexible transmission element 26 is placed on the inside of the bottom 5, as shown in isolation in FIGS. 3 and 4. The bottom of the pot-shaped transmission element 26, which is designated by 27, that is to say, the flexible pot, has the basic shape of an annular disk which is attached to the bottom 5, which is also annular disc-shaped. The radially outer edge of the bottom 27 merges into a cylindrical section 28 of the flexible pot 26. On the outer peripheral surface of the cylindrical section 28, external teeth 29 are formed, which partially engage in internal teeth 30 of the output ring gear 4. Two diametrically opposite engagement areas between the teeth 29, 30 are determined by a wave generator 31. The wave generator 31 comprises a ball bearing designated by 32. The inner ring of the ball bearing 32, denoted by 33, is non-rotatably coupled to the motor shaft of the electric motor which is used to operate the harmonic drive 1 via bolts 34, which are to be assigned to a compensating coupling, not shown.

[0073] In a manner known per se, the outer peripheral surface of the inner ring 33 is designed as a non-circular, elliptical rolling element raceway for spheres 35, that is to say, rolling elements. The spheres 35 are guided in a cage 36 and contact an outer ring 37 which, in contrast to the inner ring 33, is resilient. The cylindrical section 28 of the flexible pot 26 directly surrounds the outer ring 37 without being permanently connected thereto. A slightly different number of teeth of the external teeth 29 on the one hand and internal teeth 30 on the other hand ensures that a full rotation of the inner ring 33 in relation to the drive element 2 is converted into only a slight pivoting between the drive element 2 and the output element 4.

[0074] The outer ring 37 and thus the entire wave generator 31 is secured in the axial direction with respect to the flexible transmission element 26 by several impressions 38, which can be seen in the form of almost point-like knobs on the inner peripheral surface of the cylindrical section 28. In the opposite axial direction, that is to say, toward the output-side end face SAB, the wave generator 31 is secured directly in the axial direction by the bottom 15 of the output element 4.

[0075] With regard to details of the flexible transmission element 26, reference is made below to FIGS. 3 and 4, which relate to all exemplary embodiments. The bottom 27 of the flexible transmission element 26 has a plurality, eighteen in the exemplary embodiments, of openings 39. The peripheral boundaries of the openings 39 are delimited by contact flanks 40, which are also referred to as tabs for short and are formed by material which is bent out of the bottom 27. Each opening 39 merges radially inward into an inner widened section 41. Each opening 39 merges radially outward into an outer widened section 42. The widening compared to the central section delimited by the tabs 40 relates in each case to the peripheral direction of the annular disc-shaped bottom 27. Overall, each opening 39 thus has the basic shape of a double-T when viewed from the end face. In the radial direction of the transmission element 26, the outer widened section 42 is broader than the inner widened section 41. This results in an asymmetry of the double-T shape. Overall, each opening 37 extends almost over the full width to be measured in the radial direction of the annular disc-shaped bottom 27. A ring-shaped, peripheral inner edge strip of the bottom 27 is denoted by 43. The inner edge strip 43 represents the radially inner delimitation of all the openings 39. At their radially outer edge, the openings 39 extend approximately to the cylindrical section 28 of the transmission element 26. Overall, the bottom 27 thus has a significant elastic resilience.

[0076] In the peripheral direction, the bottom 27 and thus the entire flexible transmission element 26 is coupled to the bottom 5 of the drive element 2 in a form-fitting manner. For this purpose, a number of form-fitting elements 44 corresponding to the number of openings 39 is present on the inside of the bottom 5. When looking into the pot-shaped drive element 2, the form-fitting elements 44 each have a cuboid shape, with a form-fitting element 44 engaging in each opening 39. Lateral surfaces of the form-fitting elements 44 bear against the contact flanks 40 in such a way that a form-fitting coupling with little play, suitable for transmitting torque, is formed between the drive element 2 and the transmission element 26 in the peripheral direction of the elements 2, 26 mentioned. In the axial direction and the radial direction of the elements 2, 26, mobility is maintained between the bottom 27 of the flexible pot 26 and the bottom 5 so that the transmission element 26 is mounted on the drive element 2 with play.

[0077] In the exemplary embodiments according to FIGS. 1 and 19, the form-fitting elements 44 are produced by powder metallurgy as integral components of the drive element 2. In the exemplary embodiment according to FIG. 8, on the other hand, the form-fitting elements 44, like the entire drive element 2, are produced by means of forming. In this case, essentially rectangular depressions 45 can be seen on the outside of the bottom 5, which depressions were produced in the course of the shaping of the form-fitting elements 44 by material displacement. In any case, the form-fitting elements 44 interact directly with the openings 39 delimited by the contact flanks 40, which represent corresponding form-fitting elements.

[0078] When assembling the harmonic drive 1, the wave generator 31 is first inserted into the pot-shaped flexible transmission element 26 in all cases. The resulting assembly is also referred to as adjusting shaft 46. The adjusting shaft 46 is then pushed into the output ring gear 4. Here, the external teeth 29 engage in the internal teeth 30 in two mutually opposite peripheral areas. The drive element 2 is then pushed onto the output element 4 from the first end face S.sub.1 until the form-fitting connection between the flexible transmission element 26 and the drive element 2 is established. As the last assembly step, the locking ring 12 is inserted into the groove 13. This provides the full functionality of the harmonic drive 1, wherein no screw connections exist within the harmonic drive 1.

LIST OF REFERENCE SYMBOLS

[0079] 1 Harmonic drive [0080] 2 Drive element [0081] 3 Chain wheel [0082] 4 Output element, output ring gear [0083] 5 Bottom [0084] 6 Conical outer peripheral surface [0085] 7 Cylindrical outer peripheral surface [0086] 8 First conical outer peripheral surface [0087] 9 Second conical outer peripheral surface [0088] 10 Cylindrical inner peripheral surface; radial slide bearing surface [0089] 11 Cylindrical section of the output element [0090] 12 Locking ring [0091] 13 Groove [0092] 14 Axial slide bearing surface [0093] 15 Bottom [0094] 16 Pin [0095] 17 Opening [0096] 18 Rotation angle limitation [0097] 19 Drive-side stop contour [0098] 20 Output-side stop contour [0099] 21 Stop segment [0100] 22 Recess, adjustment window [0101] 23 Strip [0102] 24 Opening [0103] 25 Stop segment [0104] 26 Flexible transmission element, flex ring [0105] 27 Bottom [0106] 28 Cylindrical section [0107] 29 External teeth [0108] 30 Internal teeth [0109] 31 Wave generator [0110] 32 Ball bearing [0111] 33 Inner ring [0112] 34 Bolt [0113] 35 Rolling elements, sphere [0114] 36 Cage [0115] 37 Outer ring [0116] 38 Impression [0117] 39 Opening [0118] 40 Contact flank [0119] 41 Inner widened section [0120] 42 Outer widened section [0121] 43 Inner edge strip [0122] 44 Form-fitting element [0123] 45 Depression [0124] 46 Adjusting shaft [0125] S.sub.AB Output-side end face [0126] S.sub.1 First end face