Wave gear for an electric camshaft adjuster for variable valve control of an internal combustion engine, use of a flexible toothed ring for a wave gear and method for producing a flexible toothed ring

Abstract

Wave gear for an electric camshaft adjuster for variable valve control of an internal combustion engine, with a wave generator (1) which can be driven with a torque, and a flexible toothed ring (2) with external teeth (3) formed on the outer circumference for transmitting the torque, wherein the toothed ring (2) is radially mounted on the inner circumference on the wave generator (1), characterized in that the flexible toothed ring (2) is formed with internal teeth (5) running around the inner circumference, which form axial bearing surfaces (6) on its teeth, on which the wave generator (1) is axially mounted at least in sections.

Description

Field of the invention

[0001] The invention relates to a wave gear for an electric camshaft adjuster for variable valve control of an internal combustion engine, a use of a flexible toothed ring for a wave gear and a method for producing a flexible toothed ring according to the type defined in more detail in the preamble of patent claims 1, 8 and 9.

[0002] DE 10 2017 111 682 A1 discloses an adjustment gear in an electric camshaft adjuster. This gear is designed as a wave gear with a flexible gear element and a wave generator. A cover on the actuator side also serves as the axial support for the wave generator. The disadvantage of this cover is the complex design and assembly.

[0003] Further wave gears are known from KR 10 2016 0 001 344 A, DE 10 2013 216 183 A1, DE 10 2016 218 927 A1, DE 10 2016 223 796 A1, KR 10 2011 0 124 681 A, WO 2020 / 111 129 A1. Summary of the invention

[0004] The invention is therefore based on the object of simplifying the structure of a strain wave gear of the aforementioned type and making it cost-effective. It is also an object of the invention to propose a use of a flexible gear ring for a strain wave gear and a method for producing a flexible gear ring.

[0005] The problem is solved by the features of patent claim 1 and alternatively by the features of patent claim 8 or 9. Further advantageous embodiments emerge from the respective subclaims, the description and the drawings.

[0006] A wave gear for an electric camshaft adjuster for variable valve timing of an internal combustion engine is proposed. The wave gear has a wave generator that can be driven by a torque and a flexible toothed ring with external teeth on the outer circumference for transmitting a torque. The toothed ring is radially mounted on the wave generator on the inner circumference. Since the flexible toothed ring is designed according to the invention with internal teeth running around the inner circumference, the teeth of which form axial bearing surfaces, the wave generator can be axially mounted on these at least in sections. In this way, it is possible to use the flexible toothed ring simultaneously for the axial mounting of the wave generator. Additional components and additional manufacturing and assembly effort for mounting the wave generator are thus avoided.

[0007] Preferably, the external and internal teeth of the toothed ring are arranged coaxially one behind the other.

[0008] In a further preferred embodiment of the invention, the wave generator and the internal gearing are arranged coaxially one behind the other. Preferably, the wave generator is designed with a flexible outer ring on which the gear ring is mounted with its inner circumference. Simple axial mounting of the wave generator on the outer ring is possible if the outer ring and the internal gearing are arranged coaxially one behind the other, and the outer ring forms an annular bearing surface on its axial end face facing the internal gearing, with which it is axially mounted on the bearing surfaces formed on the axial end faces of the teeth of the internal gearing.

[0009] In a particularly preferred embodiment of the invention, the teeth of the internal toothing of the gear ring each have a tooth width in the circumferential direction of less than one millimeter. In this way, the internal toothing can be designed to be bend-optimized, and a local increase in the flexural rigidity of the gear ring caused by the internal toothing can be minimized. This avoids, in particular, a tendency toward preferential positions and increased stresses during operation, and thus a reduction in the service life of the wave generator and gear ring.

[0010] The flexural rigidity can be further optimized or minimized if the internal gearing is designed with a radial tooth height on the inner circumference of the gear ring that is less than one millimeter.

[0011] It is also advantageous if the distance between the teeth in the circumferential direction of the internal toothing of the gear ring is less than or equal to the circumferential width of the teeth. This reliably prevents jumps in the bending stiffness of the gear ring.

[0012] A further minimization of the bending stiffness of the gear ring is possible if the internal and external teeth of the gear ring are arranged coaxially one behind the other with the teeth and the tooth gaps in the circumferential direction in the same position, ie with each tooth of the external tooth on the tooth of the internal tooth and with each tooth gap of the external tooth on the tooth gap of the internal tooth.

[0013] The object of the invention is also achieved by using a flexible gear ring for a wave gear in an electric camshaft adjuster for variable valve control of an internal combustion engine. The gear ring is connected on the drive side to a coaxially arranged drive gear of the camshaft adjuster for transmitting torque, and on the output side, it has external teeth on the outer circumference for transmitting torque. According to the invention, the gear ring is designed with internal teeth running around the inner circumference, the teeth of which form axial bearing surfaces for the axial mounting of a coaxially arranged wave generator of the wave gear.

[0014] In a particularly advantageous manner, a flexible toothed ring can be used for a wave gear according to one of the claims described above.

[0015] The object of the invention is further achieved by a method for producing a flexible gear ring for a strain wave gear. To transmit torque, the flexible gear ring has external teeth on its outer circumference. On its inner circumference, it can be radially mounted on a strain wave generator of the strain wave gear. According to the invention, a circumferential internal toothing on the inner circumference of the flexible gear ring, with bearing surfaces formed on its teeth for supporting the strain wave generator, is produced by non-cutting forming. In this way, the flexible gear ring with an additional bearing function for the strain wave generator can be manufactured from sheet metal particularly easily and cost-effectively.

[0016] Preferably, the internal gearing is formed by rolling on the outer circumference using a die on the inner circumference. This die serves as a mold for creating the internal gearing on the inner circumference during rolling from radially outside to radially inside. Alternatively, the internal gearing can also be produced by axial extrusion.

[0017] In a particularly advantageous manner, the method for producing a flexible toothed ring for a wave gear according to one of the claims described above can be used. Short description of the drawings

[0018] Further features of the invention will become apparent from the following description and the drawings, which illustrate an exemplary embodiment of the invention in simplified form. They show: Fig. 1 and Fig. 2 a wave gear according to the invention in a partial view in an electric camshaft adjuster for variable valve control of an internal combustion engine, Fig. 3 an enlarged section of Fig. 1, Fig. 4 a flexible toothed ring of the wave gear according to the invention in a single view, Fig. 5 an enlarged section of Fig. 4. Detailed description of the drawings

[0019] In Fig. 1 and Fig. Figure 2 shows a wave gear according to the invention arranged in an electric camshaft adjuster for variable valve control of an internal combustion engine. The wave gear has a wave generator 1 driven by a torque and a flexible toothed ring 2 as a so-called flex ring, which Fig. 4 is shown in a single view and is made of sheet metal. The toothed ring 2 is formed on the outer circumference with external teeth 3 for transmitting a torque ( Fig. 1 and Fig. 2). In the area of ​​the external toothing 3, it is designed to be flexible and is radially mounted on the wave generator 1 on the inner circumference with a contact surface 4. An internal toothing 5 formed circumferentially on the inner circumference of the toothed ring 2 and the wave generator 1 are arranged coaxially one behind the other. The internal toothing 5 forms axial bearing surfaces 6 ( Fig. 3 to 5). The wave generator 1 is axially mounted on these with an annular axial bearing surface 7 on its axial end face facing the internal toothing 5 and is guided with slight axial play.

[0020] The teeth of the internal toothing 5 each have a tooth width B in the circumferential direction which is less than 1 mm, ie B < 1 mm ( Fig. 4 and Fig. 5). The radial tooth height H of the teeth on the inner circumference of the gear ring 2 is less than 1 mm, i.e., H < 1 mm. In this way, an increase in the flexural rigidity of the gear ring 2 caused by the internal toothing 5 is kept to a minimum. Furthermore, on the internal toothing 5, a tooth spacing S of the teeth in the circumferential direction is provided that is less than or equal to the tooth width B, i.e., S < B, thereby avoiding jumps in the flexural rigidity.

[0021] The internal and external gears 3, 5 are arranged coaxially one behind the other, with the teeth and tooth gaps in the same circumferential direction, i.e., the tooth of the external gear is aligned with the tooth of the internal gear, and the tooth gap of the external gear is aligned with the tooth gap of the internal gear. This further minimizes the flexural rigidity of the gear ring 2.

[0022] The wave gear is arranged in an electric camshaft adjuster ( Fig. 1 to 3). This has a drive wheel 8 which can be driven by a crankshaft (not shown) of the internal combustion engine with a drive torque. The drive torque can be transmitted from the drive wheel 8 via the strain gauge gear to a camshaft (not shown) of the internal combustion engine. The drive wheel 8 is designed here as a chain wheel which can be connected to the crankshaft via a chain drive (not shown) to transmit the drive torque. It is also conceivable to design the drive wheel 8 as a belt wheel which can be connected to the crankshaft via a belt drive, in particular a dry-running belt drive. The drive wheel 8 forms a cylindrical housing section 9 radially on the inside, which encloses the strain gauge gear radially on the outside.

[0023] The flexible toothed ring 2 has a sleeve-shaped section on which external and internal teeth 3, 5 are formed. At an axial end facing away from the wave generator 1, the toothed ring 2 is radially widened in a collar-like manner on the outer circumference with a fastening section 10 ( Fig. 1, Fig. 3 and Fig. 4). In this way, the flexible gear ring 2 is designed as a so-called collar sleeve. It is axially connected to the fastening section 10 via several fastening screws 11 to the housing section 9 of the drive gear 8 for torque transmission in a rotationally fixed manner. The fastening screws 11 are guided through screw openings 17 arranged radially on the outside of the fastening section 10. At the end region axially remote from the fastening section 10, the gear ring 2 engages with the external toothing 3 in the internal toothing of a coaxially arranged output ring gear 12.

[0024] The wave generator 1 consists of a flexible outer ring 13 and an inner ring 14, which is slightly non-circular oval, in particular elliptical, on the outer circumference, on which the flexible outer ring 13 is roller-bearing mounted via rolling elements, here balls, guided in a cage, which in turn carries the flexible toothed ring 2 ( Fig. 1 to 3). The outer ring 13 and the internal toothing 5 of the toothed ring 2 are arranged coaxially one behind the other. The outer ring 13 forms, on its axial end face facing the internal toothing 5, the annular contact surface 7, with which the wave generator 1 is axially mounted on the bearing surfaces 6 of the internal toothing 5.

[0025] The inner ring 14 is connected via the coupling 15 indicated by two axial coupling pins to an electric actuator (not shown) for transmitting an adjusting torque ( Fig. 2). The coupling 15 is preferably designed as a so-called Oldham coupling, which allows for axial offset compensation. An adjusting torque can be transmitted to the wave generator 1 of the harmonic drive by the electric actuator via the coupling 15 and the inner ring 14. At the same time, the toothed ring 2 is elastically pressed into the internal toothing of the output ring gear 12 at discrete engagement points, in particular at two opposite engagement points with a few teeth, by the slightly non-circular oval, in particular elliptical, shape of the rotating inner ring 14. Fig. 1 and Fig.3). In this way, with one rotation of the inner ring 14, a rotational angle adjustment of the output ring gear 12 relative to the drive gear 8 and thus a corresponding adjustment of the camshaft with a large reduction ratio is achieved. The adjusting torque is supported on the drive gear 8 via the fastening section 10 of the gear ring 2 and transmitted to the output ring gear 12 via the external toothing 3 of the gear ring 2 with a large reduction ratio. This achieves a rotational angle adjustment of the output ring gear 12 relative to the drive gear 8 or the crankshaft and thus a corresponding phase position of the camshaft, which is connected in a rotationally fixed manner to the output ring gear 15, relative to the drive gear 8. In this way, the control times of the gas exchange valves of the internal combustion engine, which can be controlled by the camshaft, can be variably adjusted. The strain wave gear serves as the adjustment gear for the electric camshaft adjuster.Here, the clutch 15, the wave gear with the toothed ring 2, the drive wheel 8 and the camshaft are arranged coaxially to a central axis 16, which also forms an axis of rotation. List of reference symbols 1 wave generator 2 toothed ring 3 External gearing 4 Contact surface 5 Internal gearing 6 storage space 7 Contact surface 8 drive wheel 9 Housing section 10 Fastening section 11 Fixing screw 12 Output ring gear 13 Outer ring 14 inner ring 15 Clutch 16 Central axis 17 Screw opening B Tooth width H Tooth height S tooth spacing

Claims

[1] Wave gear for an electric camshaft adjuster for variable valve control of an internal combustion engine, with a wave generator (1) which can be driven with a torque, and a flexible toothed ring (2) with an external toothing (3) formed on the outer circumference for transmitting the torque, wherein the toothed ring (2) is radially mounted on the inner circumference on the wave generator (1), characterized by that the flexible toothed ring (2) is formed with an internal toothing (5) running around the inner circumference, which forms axial bearing surfaces (6) on its teeth, on which the wave generator (1) is axially mounted at least in sections. [2] Wave gear according to claim 1, characterized by that the external and internal teeth (3, 5) of the toothed ring (2) are arranged coaxially one behind the other. [3] Wave gear according to one of claims 1 or 2, characterized bythat the wave generator (1) has a flexible outer ring (13) on which the toothed ring (2) is mounted with the inner circumference, wherein the outer ring (13) and internal toothing (5) are arranged coaxially one behind the other, the latter forming bearing surfaces (6) on the axial end faces of its teeth, on which bearing surfaces the outer ring (13) is axially mounted with an annular axial bearing surface (7) formed on its axial end face facing the internal toothing (5). [4] Wave gear according to one of claims 1 to 3, characterized by that the internal toothing (5) of the toothed ring (2) each has a circumferential tooth width (B) which is less than 1 mm. [5] Wave gear according to one of claims 1 to 4, characterized by that the internal toothing (5) of the toothed ring (2) is designed with a radial tooth height (H) on the inner circumference of the toothed ring (2) of less than 1 mm. [6] Wave gear according to one of claims 1 to 5, characterized bythat the circumferential distance (S) of the teeth of the internal toothing (5) of the toothed ring (2) is less than or equal to the tooth width (B). [7] Wave gear according to one of claims 1 to 6, characterized by that the internal and external teeth (5, 3) of the toothed ring (2) are arranged with the respective teeth and the respective tooth gaps in the same position in the circumferential direction. [8] Use of a flexible toothed ring (2) for a wave gear in an electric camshaft adjuster for variable valve control of an internal combustion engine, wherein the toothed ring (2) is connected on the drive side to a coaxially arranged drive wheel (8) of the camshaft adjuster in a rotationally fixed manner for transmitting a torque and has on the output side on the outer circumference an external toothing (3) for transmitting a torque, characterized bythat the toothed ring (2) is formed with an internal toothing (5) running around the inner circumference, which forms axial bearing surfaces (6) on its teeth for the axial mounting of a coaxially arranged wave generator (1) of the wave gear. [9] Method for producing a flexible toothed ring (2) for a wave gear, wherein the flexible toothed ring (2) can be radially mounted on the inner circumference on a wave generator (1) of the wave gear, characterized by that on the inner circumference of the flexible toothed ring (2) a circumferential internal toothing (5) with axial bearing surfaces (6) formed on its teeth for the axial mounting of the wave generator (1) is produced by non-cutting forming. [10] Method according to claim 9, characterized by that the internal toothing (5) is formed by rolling on the outer circumference with a die on the inner circumference or is produced by axial extrusion.

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