Shaft drive

Abstract

Wave gear (1), with a flexible gear element designed as a collar sleeve (8) which has a collar (9) which is attached to a gear housing (7), wherein a hat-shaped front cover (19) is placed in front of the collar sleeve (8) which has a flange section (22) which is arranged parallel to the collar (9), wherein passages (27) are formed on the flange section (22) which each penetrate an opening in the collar (9) and are positively locked in the gear housing (7), characterized in that the passages (27) each have a funnel-shaped widening form and hold the collar (9) on the gear housing (7) without play.

Description

[0001] The invention relates to a wave gear with a flexible gear element designed as a collar sleeve, wherein the collar sleeve is preceded by a similarly collar-shaped, i.e., hat-shaped, front cover. The invention further relates to a method for manufacturing such a wave gear.

[0002] A wave gear of the type mentioned above is known, for example, from WO 2017 / 206988 A1. This wave gear is an actuating gear which is particularly suitable for use in an electric camshaft adjuster. The actuating gear can be operated by an electric motor and has a rotation angle limiter located on the side of the front cover, i.e., on the end face of the essentially cylindrical gear housing that faces the electric motor.

[0003] Further wave gears, each comprising a flexible gear element shaped like a collar sleeve, are described in documents DE 10 2017 126 527 A1, DE 10 2017 114 069 A1, DE 10 2016 223 373 B3, DE 10 2007 004 712 A1 and DE 10 2016 223 796 A1. A wave gear of this type is known from DE 10 2016 223 513 A1.

[0004] A wave gear, by its very nature, has at least one flexible, typically externally toothed gear element. This flexible gear element is coupled in a rotationally fixed manner to a rigid gear element, which can be installed in an surrounding structure either as a rotatable or non-rotatable part. The rotationally fixed coupling between the flexible and rigid gear elements can be achieved, for example, by gear teeth or by a bolted connection.

[0005] A limited-flexibility coupling of a rigid gear element with a compliant gear element designed as a collar sleeve is also known in principle. Such solutions are described in documents WO 2017 / 041802 A1 and WO 2017 / 041800 A1.

[0006] The invention is based on the objective of providing a wave gear that is further developed compared to the prior art, particularly suitable for an electric camshaft adjuster, and which is characterized by rational manufacturing possibilities, a space-saving design, and a precisely predictable operating behavior, even under conditions of series production.

[0007] This problem is solved according to the invention by a wave gear with the features of claim 1. Likewise, the problem is solved by a method for manufacturing such a wave gear according to claim 8. The embodiments and advantages of the invention explained below in connection with the manufacturing method also apply mutatis mutandis to the device, i.e., the wave gear, and vice versa.

[0008] The wave gear, in a generally known basic design, comprises a flexible gear element shaped like a collar sleeve, the collar of which is attached to a rigid gear housing. A hat-shaped front cover is attached to the collar sleeve, featuring a flange section arranged parallel to the collar. The term "flange section" is used here to distinguish it from the "collar."

[0009] According to the invention, several through-holes are formed on the flange section, each of which penetrates an opening in the collar of the flexible transmission element and is positively locked in the transmission housing. Thus, the collar sleeve, along with the front cover, is permanently attached to the transmission housing. This forming-based connection between the front cover, collar sleeve, and transmission housing is not intended to be loosened.

[0010] Each passage describes a funnel-shaped widening. A funnel-shaped widening includes not only a conical widening, but also a widening with a curved contour.

[0011] The individual through-holes provide flat contact areas for the front cover on the one- or multi-piece gearbox housing. Simultaneously, this secures the collar sleeve to a component of the gearbox housing without separate fasteners, with this attachment preferably being designed to be free of play. This freedom of play applies to all load directions, i.e., axial, radial, and tangential loads.

[0012] The positive-locking attachment of the front cover, together with the collar of the elastic gear element to the gearbox housing, ensures, in a highly reproducible manner, that the collar sleeve has a perfectly circular cross-section when not under mechanical stress. Such an ideal cross-section of the collar sleeve reliably prevents inconsistencies in the operation of the wave gear, which could manifest as preferred positions. Preferred positions, concerning the angular relationship between a drive element rigidly coupled to the motor shaft of an electric motor and the gearbox housing, could negatively affect the controllability and energy consumption of the wave gear.

[0013] In an advantageous embodiment, the flange section of the front cover has an inner annular-shaped section and an adjoining outer annular-shaped section that rests against the collar of the elastic transmission element. The openings are located on the outer annular-shaped section, and the inner annular-shaped section is spaced apart from the collar, forming an annular gap. A further annular gap, which is delimited, among other things, by the collar, is preferably formed between the collar and the transmission housing, in particular between an axial bearing disk belonging to the transmission housing, which serves for the axial support of an output element of the wave gear designed as a ring gear. The collar is deformable between the two annular gaps.The radially outer, also ring-shaped, section of the collar is held in a fixed shape by the outer ring-shaped section of the front cover. In this outer section, the axial bearing disc is connected to another housing element, for example, by screws, with each screw passing through the flange section, the collar, and the axial bearing disc. This other housing element could be, for example, a drive element, which may be integrally connected to a sprocket or pulley.

[0014] The wave gear according to claim 8 can be manufactured as follows: - A housing element in which an internally toothed, in particular cup-shaped, output element is rotatably mounted, a flexible gear element in the form of an externally toothed collar sleeve, a hat-shaped front cover and an axial bearing disc are provided, - The front cover, the collar sleeve and the axial bearing disc, which has thicker walls compared to the collar sleeve and the front cover, are connected to each other without play by forming throughs extending from a flange section, i.e., collar, of the front cover and fixing them in a form-fitting manner in conically widening openings of the axial bearing disc. - The assembly consisting of front cover, collar sleeve and axial bearing disc is attached to the housing element, in particular by screwing it in place.

[0015] Thus, even before the wave gear assembly, the collar of the gear element and the flange section of the front cover are permanently connected to the axial bearing disc. A non-destructive connection is established between the three elements: front cover, collar sleeve, and axial bearing disc. Deformation of the collar during assembly of the wave gear is inherently impossible. This also applies in cases where a wave generator is inserted into the gearbox housing before the assembly formed from the collar sleeve and axial bearing disc is attached to the gearbox housing. In a preferred embodiment, the axial bearing disc has a wall thickness that is at least three times and at most twenty times the wall thickness of the flange section.

[0016] According to a possible further development, the front cover acts as an axially effective locking device against a flexible outer ring of the wave generator provided for deforming the collar sleeve. The front cover is preferably a sheet metal part which – like the collar sleeve – has a hat shape, that is, the shape of a sleeve with a circular cross-section to which a radially outwardly directed, annular disc-shaped section is integrally formed.

[0017] The wave gear is particularly suitable for use in an electromechanical camshaft adjuster. It can also be used in a device for adjusting the compression ratio of a reciprocating engine. Furthermore, the wave gear can be used in industrial systems, for example in a robot or a machine tool.

[0018] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1. Sectional view of a wave gear in a cross-sectional view, Fig. 2 a front cover of the wave gear in perspective view, Fig. 3 a detail of the arrangement according to Fig. 1.

[0019] A wave gear, designated by reference numeral 1, is part of an electromechanical camshaft adjuster of an internal combustion engine. Regarding the fundamental function of wave gear 1, reference is made to the prior art cited at the beginning.

[0020] The wave gear 1 has a drive element 2, which is designed as part of a rotatable gear housing 7 and, in the exemplary embodiment, is formed integrally with a sprocket 3. The sprocket 3 is driven in a manner known per se via the crankshaft of the internal combustion engine, rotating at half the crankshaft speed.

[0021] An output element 4 of the wave gear 1 is designed as a ring gear and is rigidly connected to a camshaft 26 (only partially shown), i.e., an intake or exhaust camshaft, of the internal combustion engine. A pin 5 of the output element 4 engages with the camshaft 26. The angle of rotation between the camshaft 26 and the output element 4 on the one hand, and the gear housing 7 on the other, is limited by a stop disk 24, which is rigidly connected to the output element 4.

[0022] Connecting means between the output element 4 and the camshaft 26, in particular in the form of a central screw, are in Fig. 1 not shown. In the axial direction, the output element 4 is secured in a first direction directly by the drive element 2 and in the opposite direction by an axial bearing disk 6, which is also part of the housing 7, i.e., the gearbox housing.

[0023] The housing element 2 is rotationally fixed to a flexible gear element 8, which is designed as a collar sleeve. The flange, i.e., collar, of the flexible gear element 8 is designated 9. The collar 9 transitions at its inner edge into a cylindrical section 10, which is provided with external teeth 11. The external teeth 11 partially engage, in a manner known per se, with internal teeth 12, which are formed directly by the output element 4.

[0024] A wave generator 13 is provided for deforming the flexible gear element 8 during operation of the wave gear 1. The wave generator 13 comprises a rolling bearing 14 designed as a ball bearing. Balls, acting as rolling elements 16, roll on an inner ring 15 of the rolling bearing 14 and are guided in a cage 17. The inner ring 15 has a non-circular, elliptical shape. The inner ring 15 is driven by a compensating coupling in the form of an Oldham coupling 23. The inner ring 15 is rotationally fixed to a motor shaft of an electric motor (not shown) via the Oldham coupling 23.

[0025] In addition to the inner ring 15, the rolling bearing 14 has an outer ring 18. Unlike the inner ring 15, the outer ring 18 is a flexible component. The rolling elements 16 permanently force the outer ring 18 into a non-circular shape corresponding to the shape of the inner ring 15. The area of ​​the cylindrical section 10 provided with the external teeth 11 directly surrounds the outer ring 18 without being rigidly connected to it. In a generally known manner, the teeth 11 and 12 engage with each other only at two points, namely in the region of the major axis of the inner ring 15.A slightly different number of teeth on the external gearing 11 on the one hand and the internal gearing 12 on the other ensures, in a manner known per se, that a full rotation of the inner ring 15, relative to the angular position of the gear housing 7, is converted into a comparatively small pivoting motion between the gear housing 7 and the output element 4. The wave gear 1 thus functions as a high-reduction actuator.

[0026] The outer ring 18 belonging to the rolling bearing 14 is secured axially on one side by the base of the output element 4, which is designed as a ring gear. In the opposite direction, the outer ring 18, and thus the entire shaft generator 13, is axially secured by a front cover 19, which, together with the flexible gear element 8, is attached to the housing element 2 by means of screws 25. The outer ring 18 can thus abut an inner flange 20, which is formed directly by the front cover 19 and closes off an inner sleeve-shaped section 21 of the front cover 19. The inner sleeve-shaped section 21 of the front cover 19 is arranged coaxially within the cylindrical section 10 of the collar sleeve 8. On its end face opposite the inner flange 20, the inner sleeve-shaped section 21 transitions into a flanged section 22, which is located upstream of the collar 9.

[0027] The flange section 22 comprises an outer annular section 28 and an adjoining inner annular section 29. The two annular sections 28 and 29 are slightly offset from each other in the axial direction. Only the outer annular section 28 rests against the collar 9 of the elastic gear element 8. The inner annular section 29, on the other hand, is lifted from the collar 9, forming an annular gap. A further annular gap is present on the side of the inner annular section 29 opposite the first annular gap, facing the axial bearing disk 6. This has the effect that the flange section 22 is elastically deflectable in both axial directions in the region of the inner annular section 29, which significantly contributes to the deformability of the entire gear element 8.

[0028] Unlike the inner annular section 29, the outer annular section 28 rests against the collar 9, so that the collar is held rigidly within the wave gear 1 in the corresponding area. During assembly of the wave gear 1, the through-holes 27 extending from the outer annular section 28 are deformed such that they engage positively in conical openings in the axial bearing disk 6. In doing so, the through-holes 27 also penetrate circular openings in the collar 9, which are aligned with the funnel-shaped openings in the axial bearing disk 6.

[0029] After a section was cut out of the front cover 19, the collar sleeve 8 and the axial bearing disc 6 Fig.Once the assembly shown in section 3, which cannot be disassembled without damage, has been formed, this assembly is attached to the housing element 2, into which the shaft generator 13 may already be inserted at this point, and screwed in place. This screwing process has no effect whatsoever on the previously determined circular cross-sectional shape of the collar 9. Reference symbol list 1 wave gear 2 Drive element, housing element 3 sprocket 4 Output element, ring gear 5 cones 6 axial bearing discs 7 Housings, gearbox housings 8 flexible gear element, collar sleeve 9 collars 10 cylindrical section 11 External teeth 12 Internal teeth 13 Wave generator 14 rolling bearings, ball bearings 15 inner ring 16 rolling elements, ball 17 cage 18 Outer ring 19 Front cover 20 Inboard 21 inner sleeve-shaped section 22 Flange section 23 Oldham coupling 24 Stop disc 25 screws 26 Camshaft 27 Draft 28 outer ring-shaped section 29 inner ring-shaped section

Claims

Wave gear (1), with a flexible gear element designed as a collar sleeve (8) which has a collar (9) which is attached to a gear housing (7), wherein a hat-shaped front cover (19) is placed in front of the collar sleeve (8) which has a flange section (22) which is arranged parallel to the collar (9), wherein passages (27) are formed on the flange section (22) which each penetrate an opening in the collar (9) and are positively locked in the gear housing (7), characterized in that the passages (27) each have a funnel-shaped widening form and hold the collar (9) on the gear housing (7) without play. Wave gear (1) according to claim 1, characterized in that the flange section (22) has an inner annular disc-shaped section (29) and an outer annular disc-shaped section (28) adjoining the collar (9), wherein the passages (27) are located on the outer annular disc-shaped section (28) and the inner annular disc-shaped section (29) is spaced apart from the collar (9). Wave gear (1) according to one of claims 1 to 3, characterized in that the throughs (27) are held on an axial bearing disk (6) attributable to the gear housing (7) and provided for the axial support of an output element (4). Wave gear (1) according to claims 2 and 3, characterized in that the collar is separated by an annular gap from both the outer ring-shaped section (28) and the axial bearing disc (6). Wave gear (1) according to claim 3 or 4, characterized in that the axial bearing disc (6) is screwed to a further housing element (2) with screws (25) which are each inserted through the flange section (22), the collar and the axial bearing disc (6). Wave gear (1) according to claim 5, characterized in that the further housing element (2) is designed as a drive element which is integrally connected to a sprocket (3). Wave gear (1) according to one of claims 1 to 6, characterized in that the front cover (19) is designed as an axially effective locking device against a flexible outer ring (18) of a wave generator (13) provided for deformation of the collar sleeve (8). Method for manufacturing a wave gear (1), comprising the following steps: - A housing element (2) in which an internally toothed output element (4) is rotatably mounted, a flexible gear element (8) in the form of an externally toothed collar sleeve, a hat-shaped front cover (19) and an axial bearing disc (6) are provided, - the front cover (19), the collar sleeve (8) and the axial bearing disc (6) are connected to each other without play by positively locking through passages (27) extending from a flange section (22) of the front cover (19) in conically widening openings of the axial bearing disc (6), - the assembly consisting of the front cover (19), collar sleeve (8) and axial bearing disc (6) is attached to the housing element (2). Method according to claim 8, characterized in that a shaft generator (13) is inserted into the housing element (2) before the assembly formed from front cover (19), collar sleeve (8) and axial bearing disc (6) is fastened.

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