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), characterized in that the collar (9) is connected to a stabilizing disc (24) to form a unit, wherein the collar (9) is connected to the stabilizing disc (24) by a connection that cannot be removed without damage, and the unit is attached to the gear housing (7).

Description

The invention relates to a wave gear with a flexible gear element designed as a collar sleeve. The invention further relates to a method for manufacturing such a wave gear. 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. Further wave gears, each comprising a flexible gear element shaped as 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 2009 017 875 A1, DE 10 2016 216 924 A1, US 2013 / 0 327 179 A1, DE 10 2016 220 916 A1, DE 10 2016 223 474 B3 and DE 10 2016 223 796 A1. DE 695 19 423 T2 shows a wave gear of this type. A wave gear, by its very nature, has at least one flexible gear element, typically with external teeth. 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. 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. 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 easy to assemble, and which is characterized by a precisely predictable operating behavior, even under conditions of series production. 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. The wave gear, in a generally known basic design, comprises a flexible gear element shaped like a collar sleeve, wherein the collar of this gear element is attached to a rigid gear housing. According to the invention, the collar is attached to the gear housing together with a stabilizing disc, which has increased mechanical stability compared to the collar. For the assembly of the wave gear, in addition to the gear housing, the collar sleeve, and the ring-shaped stabilizing disc, a wave generator must also be provided. An internally toothed output element, for example designed as a ring gear, is rotatably mounted in the gear housing. In the fully assembled wave gear, the internal teeth of the output element mesh with external teeth on the collar sleeve. Even before the wave gear is assembled, the collar of the gear element is permanently connected to the stabilizing disc. During the joining process, the collar is held in a circular shape, for example, using a suitably contoured auxiliary device. This prevents any deformation of the collar during assembly of the wave gear. This also applies in cases where the wave generator is inserted into the gearbox housing before the assembly consisting of the collar sleeve and stabilizing disc is attached to the gearbox housing. In every case, the collar of the flexible gear element is connected to the stabilizing disc by a non-destructive connection that is established before the complete wave gear is assembled. The invention is based on the consideration that the cylindrical, sleeve-shaped section of a collar sleeve in a wave gear should have a cross-section as precisely as possible in the mechanically unloaded state. If such a circular cross-section is not present, preferential positions arise during operation of the wave gear, which can negatively affect the operation of the wave gear, in particular its controllability. When a collar sleeve is fastened to an surrounding component, particularly a housing component, using several screws, the collar sleeve may initially have an ideal circular cross-sectional shape. Deviations from such an ideal shape, for example, due to heat treatment, are also conceivable. In any case, a merely point-fixed collar sleeve to the surrounding component can lead to inconsistencies in the operation of the wave gear. This can be attributed to the fact that, during normal operation, the deformation of the collar sleeve by the wave generator not only deforms the cylindrical, externally toothed section of the collar sleeve, but also, to a lesser extent, the collar itself. This deformation of the collar is limited or prevented at specific points by the individual screws with which the collar sleeve is fastened to the gear housing.Ultimately, even when using a collar sleeve with perfect geometry and completely error-free assembly, undesired preferred positions of the wave gear can occur. According to the invention, such preferential positions are reliably avoided by permanently attaching the collar, i.e., flange, of the collar sleeve to a stabilizing disc before assembly with the gearbox housing. In a preferred embodiment, the stabilizing disc has a wall thickness that is at least twice and at most ten times the wall thickness of the collar. Preferably, the stabilizing sleeve is connected to the collar at its outer circumference, with the connection between the stabilizing sleeve and the collar preferably being continuous, i.e., extending around the entire circumference of said parts. Various joining technologies are suitable for creating a strong, permanent connection between the stabilizing sleeve and the collar. For example, the stabilizing sleeve can be welded to the collar. Forming processes such as embossing or crimping are also suitable for attaching the collar to the stabilizing sleeve. According to a possible further development, a front cover is attached to the stabilizing disc, which serves as an axially effective locking device against a flexible outer ring of the wave generator provided for deforming the collar sleeve. The front cover contacting the stabilizing disc is preferably a sheet metal part which – like the collar sleeve – has a hat shape. 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. An embodiment of the invention is explained in more detail below with reference to a drawing. Figure 1 shows a partial section of a wave gear in a sectional view, Figure 2 shows a collar sleeve of the wave gear in a perspective view, and Figure 3 shows the collar sleeve with a stabilizing washer attached to it. 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. 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. An output element 4 of the wave gear 1 is designed as a ring gear and is rigidly connected to a camshaft (not shown), i.e., intake or exhaust camshaft, of the internal combustion engine. A pin 5 of the output element 4 engages with the camshaft. Connecting means between the output element 4 and the camshaft, in particular in the form of a central screw, are not shown in Fig. 1. In the axial direction, the output element 4 is secured in one 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 gear housing. 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. A wave generator 13 is provided to deform 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. 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. 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. However, the flange section 22 does not rest against the collar 9. Instead, a stabilizing disc 24 is positioned in front of the collar 9. This stabilizing disc 24 is permanently connected to the collar 9 by welding before the assembly consisting of the collar sleeve 8 and the stabilizing disc 24 is attached to the housing 7. During the fastening process, in this case the welding process, by which the collar 9 is permanently attached to the rigid stabilizing disc 24, the collar sleeve 8, including the collar 9, is fixed in its normal shape with a circular cross-section by means of an auxiliary device. Details of the collar sleeve 8 and the stabilizing disc 24 are shown in Figures 2 and 3. The collar sleeve 8 is flush with the stabilizing disc 24 on its outer circumferential surfaces. Radially inwards, however, the collar 9 projects beyond the stabilizing disc 24. Thus, the collar 9 retains deformability in this area. In contrast, the shape of the collar 9, in particular its circular cross-section, is precisely defined in the area where it is rigidly connected to the stabilizing disc 24. Reference symbol list 1 Wave gear 2 Drive element, housing element 3 Sprocket 4 Output element, ring gear 5 Pin 6 Thrust bearing washer 7 Housing, gear housing 8 Flexible gear element, collar sleeve 9 Collar 10 Cylindrical section 11 External toothing 12 Internal toothing 13 Wave generator 14 Rolling bearing, ball bearing 15 Inner ring 16 Rolling element, ball 17 Cage 18 Outer ring 19 Front cover 20 Inner flange 21 Inner sleeve-shaped section 22 Flange section 23 Oldham coupling 24 Stabilizing washer 25 Screw

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), characterized in that the collar (9) is connected to a stabilizing disc (24) to form a unit, wherein the collar (9) is connected to the stabilizing disc (24) by a connection that cannot be removed without damage, and the unit is attached to the gear housing (7). Wave gear (1) according to claim 1, characterized in that the stabilizing disc (24) has a wall thickness which is at least twice and at most ten times the wall thickness of the collar (9). Wave gear (1) according to claim 1 or 2, characterized in that the stabilizing disk (24) and the collar (9) are connected to each other at their outer circumference. Wave gear (1) according to claim 1, characterized in that the stabilizing disk (24) and the collar (9) are connected to each other at their entire circumference. Wave gear (1) according to claim 3 or 4, characterized in that the stabilizing disc (24) is welded to the collar (9). Wave gear (1) according to claim 3 or 4, characterized in that the collar (9) is held by crimping on the stabilizing disc (24). Wave gear (1) according to one of claims 1 to 6, characterized in that a front cover (19) is placed in front of the stabilizing disc (24), which is designed as an axially effective safeguard 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 gear housing (7) 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, and an annular stabilizing disc (24) are provided,- the collar (9) of the collar sleeve (8) is firmly connected to the stabilizing disc (24), whereby the collar (9) is held in a circular shape during the connection process,- the assembly consisting of the collar sleeve (8) and the stabilizing disc (24) is attached to the gear housing (7). Method according to claim 8, characterized in that a shaft generator (13) is inserted into the gearbox housing (7) before the assembly formed from collar sleeve (8) and stabilizing disc (24) is fastened.

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