Planetary gear unit and drive unit with such a planetary gear

Abstract

The invention relates to a planetary gear (1) comprising a drive shaft (2) with a sun gear (2.1) arranged thereon in a rotationally fixed and axially displaceable manner and having an outer cone, a first ring gear (3) with an inner cone which is secured against rotation relative to a housing (11.1), several first planet gears (4) which have an outer cone and which mesh with the sun gear (2.1) and the first ring gear (3), wherein the sun gear (2.1) is supported by at least one first spring element (8.1) is preloaded against the first planet gears (4), a second ring gear (5) configured as an output shaft with an internal cone, wherein the second ring gear (5) has a different number of teeth compared to the first ring gear (3), several second planet gears (6) having an external cone and meshing with the second ring gear (5), and several shafts (7), wherein each shaft (7) accommodates a first and a second planet gear (4, 6) in a rotationally fixed manner, wherein at least the first ring gear (3) is arranged to be axially displaceable and is preloaded into the conical teeth of the first planet gears (4) via at least one second spring element (8.2).

Description

[0001] The invention relates to a planetary gear unit and a drive unit comprising such a planetary gear unit. Furthermore, the invention also relates to a robot comprising such a planetary gear unit or such a drive unit. Alternatively, the planetary gear unit or drive unit can also be used in a machine tool and / or as an actuator.

[0002] For example, DE 10 2012 015 051 A1 discloses a planetary gear with a tapered spur gear pair comprising a first spur gear axially displaceable along a first axis of rotation, a second spur gear with a second axis of rotation, and an adjusting device. An axial effective force and / or an axial adjustment path can be adjusted by means of the adjusting device acting axially on the first spur gear. The axial effective force presses a tapered toothing of the first spur gear axially into a tapered toothing of the second spur gear such that, during operation, the toothings of the first and second spur gears mesh with each other without play.

[0003] The object of the invention is to develop an alternative, essentially backlash-free planetary gear with a high reduction ratio. This object is achieved by the subject matter of patent claim 1. Preferred embodiments can be found in the dependent claims, the description, and the figures.

[0004] A planetary gear according to the invention comprises an input shaft with a sun gear arranged thereon in a rotationally fixed and axially displaceable manner and having an outer cone, a first ring gear secured against rotation relative to a housing and having an inner cone, a plurality of first planet gears having an outer cone and meshing with the sun gear and the first ring gear, wherein the sun gear is preloaded against the first planet gears via at least one first spring element, a second ring gear configured as an output shaft with an inner cone, wherein the second ring gear has a different number of teeth than the first ring gear, a plurality of second planet gears having an outer cone and meshing with the second ring gear, and a plurality of shafts, wherein each shaft rotatably receives a first and a second planet gear,At least the first ring gear is arranged to be axially displaceable and is preloaded into the conical toothing of the first planetary gears via at least one second spring element. The respective spring element can be designed as a compression spring, in particular a spiral spring or a wave spring.

[0005] In other words, the at least one first spring element preloads the sun gear against the first planetary gears, thereby compensating for any backlash between the respective first planetary gear and the sun gear. For example, the at least one first spring element is arranged axially between a shaft shoulder or a bearing inner ring and the sun gear, with essentially no relative rotation between the components on which the at least one first spring element is supported.

[0006] Furthermore, the at least one second spring element preloads the ring gear or a ring gear carrier, which is screwed to the ring gear, for example, against the first planetary gears, thereby compensating for any tooth play between the respective first planetary gear and the first ring gear. In particular, this can also at least partially compensate for any tooth play between the respective second planetary gear and the second ring gear. For example, the at least one second spring element is arranged axially between a stationary housing component and the first ring gear or the ring gear carrier, which is connected in a rotationally fixed manner to the first ring gear. Preferably, a plurality of second spring elements are arranged axially, evenly distributed in the circumferential direction, between the stationary housing component and the first ring gear or the ring gear carrier, which is connected in a rotationally fixed manner to the first ring gear.

[0007] The planetary gear train preferably comprises at least two shafts, each shaft having a first and a second planet gear. In particular, the planetary gear train comprises three to five shafts, each shaft having a first and a second planet gear. The drive shaft with the sun gear is provided as the central shaft of the planetary gear train, so that the shafts with the first and second planet gears arranged thereon are arranged around the drive shaft with the sun gear. The first planet gears mesh with both the sun gear and the first ring gear shaft, which is fixed to the housing. The second planet gears mesh only with the second ring gear shaft. The difference in the number of teeth between the first ring gear and the second ring gear can create a particularly large transmission or reduction ratio. For example, the second ring gear has at least one more tooth than the first ring gear. This creates a particularly large reduction ratio.Such a planetary gear is particularly suitable for actuators and robotics applications. To generate a gear ratio, the second ring gear has at least one fewer tooth than the first ring gear.

[0008] The gear pairing of the first planetary gears and the first ring gear has a different module than the gear pairing of the second planetary gears and the second ring gear. For example, the respective first planetary gear, the respective second planetary gear, and the respective shaft are monolithic and thus formed as a common component. In particular, the respective monolithic component, consisting of the first planetary gear, the second planetary gear, and the shaft, is formed either by forming or primary forming. Extrusion and powder metallurgy manufacturing processes are particularly suitable, as no rework is required due to tolerance compensation.

[0009] If the planetary gear set is designed for low forces, the planetary gears and / or ring gears can be made of thermoplastics. In particular, the spring elements for generating the preload can then be monolithically integrated into the ring gear or ring gear carrier. Alternatively, the planetary gears and / or ring gears can be made of aluminum and coated with hard anodizing for wear protection.

[0010] Preferably, the respective monolithic component, consisting of the first planetary gear, the second planetary gear, and the shaft, has at least one or more rotationally symmetrical recesses for weight reduction. The respective recess can extend through at least part of the monolithic component or through the entire monolithic component.

[0011] According to a preferred embodiment of the invention, the respective shaft is rotatably mounted on at least a first carrier, wherein the first carrier is arranged in a region on the shafts adjacent to the second planet gears on the end face and is designed to receive a respective axial end section of the respective shaft. In particular, the respective shaft protrudes at least partially axially from the second planet gears with the end section. For example, the first carrier is designed as a carrier disk and is designed to guide or radially support the axial end sections of the shafts. Axial or radial recesses with or without an undercut structure are preferably formed on the first carrier to receive the shafts. Alternatively, axial openings are formed on the first carrier to receive the shafts.By supporting the shafts on the first support, the shafts always rotate in the correct position in orbit around the central shaft axis, even under greater loads, and do not deform radially inwards.

[0012] According to a preferred embodiment of the invention, the first carrier is designed as a cylindrical disk and, to support the shafts, is arranged at least partially axially overlapping the shafts, with an outer circumferential surface of the cylindrical disk radially abutting the shafts. This represents a particularly compact and weight-optimized first carrier, which is positioned in a space radially within the shafts. For example, this space is bounded on one axial side by the end face of the second planet gears and on another axial side by a housing cover.

[0013] According to a preferred embodiment of the invention, the respective shaft is rotatably mounted on at least one second carrier, wherein the second carrier is arranged in a region on the shafts adjacent to the first planet gears on the end face and is designed to receive a respective axial end section of the respective shaft. In particular, the respective shaft protrudes at least partially axially from the first planet gears with an end section. For example, the second carrier is designed as an annular carrier disk and is designed to guide or radially support the axial end sections of the shafts, wherein the drive shaft is guided axially through a central opening in the second carrier. Axial or radial recesses with or without an undercut structure are preferably formed on the second carrier to receive the shafts. Alternatively, axial openings are formed on the second carrier to receive the shafts.By supporting the shafts on the second support, the shafts always rotate in the correct position in orbit around the central shaft, even under greater loads.

[0014] For example, the respective shaft has at least one bearing journal for receiving a carrier, wherein the at least one bearing journal is formed on the end face of the respective planetary gear or on the axial end sections of the respective shaft. Preferably, the respective monolithic component has cylindrically shaped bearing journals on the respective end face, which are supported by plain bearings or roller bearings in the respective carrier. In particular, the respective monolithic component has inner ring raceways for rolling elements integrated into the bearing journals.

[0015] According to a preferred embodiment of the invention, each shaft is rotatably mounted on a single carrier, said carrier being arranged on a cylindrical shaft section axially between the first and second planet gears of each shaft. This allows both weight and component numbers to be saved. Furthermore, the axial compactness of the planetary gear can be increased. For example, the cylindrical shaft section is arranged axially between the first and second planet gears for plain bearing or rolling bearing in a carrier designed as a bearing disk. The monolithic component, consisting of the first planet gear, the second planet gear, and the shaft, is preferably manufactured using powder metallurgy. In particular, the monolithic component has an integrated inner ring raceway for rolling elements on the cylindrical shaft section axially between the first and second planet gears.By supporting the shafts on the supports that are essentially located in the center, the shafts always rotate in the correct position in orbit around the central shaft, even under greater loads.

[0016] According to a preferred embodiment of the invention, at least the drive shaft, in particular the drive shaft and a drive motor designed as an electric motor, together with at least the first ring gear, are axially displaceable via the at least one second spring element. In other words, the at least one second spring element not only preloads the first ring gear or a ring gear carrier, which is screwed to the first ring gear, for example, but also at least indirectly the electric motor and the drive shaft with the sun gear arranged thereon. As a result, on the one hand, the first ring gear is preloaded against the first planet gears, thereby compensating for any tooth play between the respective first planet gear and the first ring gear.Secondly, the drive shaft is preloaded with the sun gear against the first planet gears, thereby at least partially compensating for any tooth play between the respective first planet gear and the sun gear. A first spring element can thus be made smaller because it needs to generate less preload force to preload the sun gear against the respective first planet gear. This reduces both the costs and the weight of the planetary gear set. For example, the at least one second spring element is arranged axially between a stationary housing component and the first ring gear or the ring gear carrier, which is connected in a rotationally fixed manner to the first ring gear, wherein the drive shaft can be driven in the axial direction via the ring gear carrier.Preferably, a plurality of second spring elements are arranged axially distributed uniformly in the circumferential direction between the stationary housing component and the first ring gear or the ring gear carrier, which is connected to the first ring gear in a rotationally fixed manner.

[0017] Alternatively, it is also conceivable to design the second ring gear to be axially displaceable and to preload it into the conical toothing of the second planetary gears via at least one spring element in order to compensate for at least some tooth play between the respective second planetary gear and the second ring gear. This can be particularly advantageous in a planetary gear designed as a transmission gear.

[0018] The invention also relates to a drive unit with a planetary gear according to the invention and a drive motor, preferably designed as an electric motor, which is arranged coaxially with the planetary gear and is drivingly connected to the drive shaft. In particular, the rotor shaft of the electric motor is rotationally fixedly connected to the drive shaft of the planetary gear.

[0019] Furthermore, the invention also relates to a robot with a planetary gear according to the invention, in particular with a drive unit according to the invention. Alternatively, the planetary gear according to the invention can be used in an actuator, for example, in a machine tool.

[0020] Further measures improving the invention are described in more detail below together with the description of preferred embodiments of the invention with reference to the figures. Fig. 1 a simplified schematic sectional view of a section of the drive unit according to the invention according to a first embodiment, Fig. 2 a simplified schematic representation of a partially shown robot with a drive unit according to the invention, Fig. 3 a simplified schematic sectional view of a section of the drive unit according to the invention according to a second embodiment, Fig. 4 a simplified schematic sectional view of a monolithic component, consisting of the first planetary gear, the second planetary gear and the shaft, according to a first embodiment, Fig. 5 a simplified schematic sectional view of a monolithic component, consisting of the first planetary gear, the second planetary gear and the shaft, according to a second embodiment and Fig. 6 a simplified schematic representation of a monolithic component consisting of the first planetary gear, the second planetary gear and the shaft, according to a third embodiment.

[0021] In Fig. 1 shows a section of a drive unit 14 according to the invention with a planetary gear 1. In addition to the planetary gear 1, the drive unit 14 comprises an electric motor 15 arranged coaxially with the planetary gear 1. In the present case, the electric motor 15 is shown very schematically. A rotor shaft of the electric motor 15 is connected in a driving manner, in particular in a rotationally fixed manner, to a drive shaft 2 of the planetary gear 1. The drive shaft 2 of the planetary gear 1 is rotationally fixedly connected to a sun gear 2.1 and extends at least partially axially through a first stationary housing component 11.1 of the planetary gear 1. In the present case, the housing of the planetary gear 1 is designed in several parts and, in addition to the first stationary housing component 11.1, also comprises a second rotatable housing component 11.2. The rotatable housing component 11.2 is rotatably mounted on the stationary housing component 11.1 via a bearing 21.The bearing 21 is axially fixed to the second housing component 11.2 by a disc 22.

[0022] The planetary gear 1 further comprises a first ring gear 3 with an inner cone that is secured against rotation relative to the housing 11.1, a ring gear carrier 3.1 that is firmly connected to the first ring gear 3 via a screw connection, and a plurality of first planet gears 4 that have an outer cone and mesh with the sun gear 2.1 and the first ring gear 3. The ring gear carrier 3.1 is mounted on the rotatable housing component 11.2 via a bearing 20 and is secured against rotation relative to the housing 11.1. The sun gear 2.1 has an outer cone and is preloaded against the first planet gears 4 via a first spring element 8.1. The first spring element 8.1 is indicated by a force arrow and is arranged on the drive shaft 2. For example, the first spring element 8.1, designed as a wave spring, is supported axially on the drive shaft 2 and the sun gear 2.1. To form the rotationally fixed but axially movable connection between the drive shaft 2 and the sun gear 2.1, a positive-locking element designed as a key is arranged on the outer peripheral surface of the drive shaft 2 and engages in a groove provided for this purpose on the inner peripheral surface of the sun gear 2.1. Alternatively, a toothing can be provided as a rotationally fixed but axially displaceable connection so that the first spring element 8.1 can axially preload the sun gear 2.1. In particular, this compensates for any tooth play between the sun gear 2.1 and the respective first planetary gear 4.

[0023] Furthermore, a second spring element 8.2 is arranged axially between the stationary housing component 11.1 and the ring gear carrier 3.1 with the first ring gear 3 arranged thereon in a rotationally and axially fixed manner, and is designed to preload the first ring gear 3 against the respective first planet gear 4. In this case, the second spring element 8.2 is indicated by two force arrows on the first housing component 11.1. As indicated, the second spring element 8.2 presses against the ring gear carrier 3.1, whereby the first ring gear 3 is preloaded against the first planet gears 4, thereby compensating for any tooth play between the respective first planet gear 4 and the first ring gear 3.

[0024] The planetary gear 1 further comprises a second ring gear 5 configured as an output shaft, having an inner cone, a plurality of second planet gears 6 having an outer cone and meshing with the second ring gear 5, and a plurality of shafts 7, each shaft 7 rotationally fixedly accommodating a first and a second planet gear 4, 6. The respective first planet gear 4, the respective second planet gear 6, and the respective shaft 7 are monolithic and thus form a single component.

[0025] The second ring gear 5 has a different number of teeth than the first ring gear 3. In this case, the second ring gear 5 has one more tooth than the first ring gear 3. The number of teeth of the respective first and second planet gears 4, 6 has the same value in this case. This creates a particularly large reduction ratio. The second ring gear 5 is designed as an output shaft and is connected in a rotationally fixed manner to the second housing component 11.2 via a screw connection. The drive shaft 2 is designed as a central shaft, with the other shafts of the planetary gear 1 being arranged around the drive shaft 2. Due to the illustration, two of four shafts 7 are shown here with the first and second planet gears 4, 6 arranged thereon, the other two shafts 7 being designed essentially identically to the two shafts 7 shown.

[0026] To ensure that the shafts 7 always rotate in the correct position in orbit around the central shaft axis, even under greater loads, and do not deform radially inward, each shaft 7 is rotatably mounted on a first support 9.1. The first support 9.1 is arranged on the shafts 7 in an area adjacent to the second planet gears 6 on the end face and is designed to receive a respective axial end section of the respective shaft 7. In this case, a pin-shaped end section of the shafts 7 is guided in openings on the first support 9.1. Furthermore, each shaft 7 is also rotatably mounted on a second support 9.2, wherein the second support 9.2 is arranged on the shafts 7 in an area adjacent to the first planet gears 4 on the end face and is designed to receive a respective axial end section of the respective shaft 7. In this case, a pin-shaped end section of the shafts 7 is guided in openings on the second support 9.2.In this case, the shafts 7 are supported by plain bearings in the respective supports 9.1, 9.2. Alternatively, and not shown here, rolling bearings can be provided in the respective supports 9.1, 9.2 to support the shafts 7.

[0027] Fig. Figure 2 shows a section of a robot 12. A joint 13 is arranged between a first robot arm segment 12a and a second robot arm segment 12b, which connects the two robot arm segments 12a, 12b to one another in an articulated manner. To change the position of the two robot arm segments 12a, 12b relative to one another, the robot 12 has the drive unit 14 according to the invention with the electric motor 15 and the planetary gear 1.

[0028] In Fig. 3 shows a second embodiment of the drive unit 14. According to Fig. 3, the respective shaft 7 is rotatably mounted on a single carrier 9, wherein this carrier 9 is arranged on a shaft section axially between the first and second planetary gears 4, 6 of a respective shaft 7. By supporting the shafts 7 on the carrier 9, the shafts 7 always rotate in the correct position in orbit around the central shaft axis, even under greater loads. Thus, compared to the first embodiment of the planetary gear 1, not only is one carrier saved, but also weight and installation space. Furthermore, the electric motor 15 and thus also the drive shaft 2, together with the first ring gear 3 and the ring gear carrier 3.1, are axially displaceable via the second spring element 8.2. The ring gear carrier 3.1 is arranged on a motor flange 15.1 of the drive, wherein a seal 23 for sealing the motor flange 15.1 from the first housing component 11.1 is also arranged on the motor flange 15.1.Due to the short axial travel and the otherwise identical circumferential speed, this can be designed, for example, as a bellows. In particular, the ring gear carrier 3.1 pulls the drive shaft 2 and thus also the sun gear 2.1 with it during an axial displacement. This allows the first spring element 8.1 to be manufactured significantly more compactly, since only a small differential force is required to compensate for the preload of the sun gear 2.1 and to compensate for any tooth play on the sun gear 2.1. Otherwise, the second embodiment of the drive unit 14 corresponds to the first embodiment of the drive unit 14, to which reference is made.

[0029] In Fig. 4 is the monolithic component according to Fig. 3, consisting of the first planetary gear 4, the second planetary gear 6, and the shaft 7. The monolithic component has a rotationally symmetrical conical recess 24 in the area of ​​the first and second planetary gears 4, 6 to reduce weight.

[0030] In Fig. 5 is an alternative embodiment of the monolithic component according to Fig. 3, consisting of the first planetary gear 4, the second planetary gear 6, and the shaft 7. The monolithic component has a rotationally symmetrical cylindrical recess 24 extending over the entire axial length to reduce weight.

[0031] Fig. 6 shows an alternative embodiment of the monolithic component according to Fig.1, consisting of the first planetary gear 4, the second planetary gear 6, and the shaft 7. The monolithic component has a recess 24 for weight reduction, which is formed axially circumferentially on the shaft 7 between the first planetary gear 4 and the second planetary gear 6. Due to the circumferential recess 24, the shaft 7 has a smaller diameter in this area. The free end sections of the shaft 7, which protrude axially from the first planetary gear 4 and the second planetary gear 6, are pin-shaped. List of reference symbols 1 planetary gear 2 drive shaft 2.1 Sun gear 3 first ring gear 3.1 Ring gear carrier 4 first planetary gear 5 second ring gear 6 second planetary gear 7 Wave 8.1 first spring element 8.2 second spring element 9 carriers 9.1 first carrier 9.2 second carrier 11.1 first housing component 11.2 second housing component 12 robots 12a first robot arm segment 12b second robot arm segment 13 Joint 14 Drive unit 15 Electric motor 15.1 Motor flange 20 warehouses 21 camps 22 discs 23 Seal 24 recess QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2012 015 051 A1

[0002]

Claims

[1] Planetary gear (1) comprising • a drive shaft (2) with a sun gear (2.1) arranged thereon in a rotationally fixed and axially displaceable manner with an outer cone, • a first ring gear (3) secured against rotation relative to a housing component (11.1) with an inner cone, • a plurality of first planetary gears (4) which have an outer cone and are in meshing engagement with the sun gear (2.1) and the first ring gear (3), wherein the sun gear (2.1) is prestressed against the first planetary gears (4) via at least one first spring element (8.1), • a second ring gear (5) arranged as an output shaft with an inner cone, wherein the second ring gear (5) has a difference in the number of teeth compared to the first ring gear (3), • several second planetary gears (6) which have an outer cone and are in meshing engagement with the second ring gear (5), • and several shafts (7), each shaft (7) receiving a first and a second planetary gear (4, 6) in a rotationally fixed manner, • wherein at least the first ring gear (3) is arranged to be axially displaceable and is pre-tensioned into the conical toothing of the first planet gears (4) via at least one second spring element (8.2). [2] Planetary gear (1) according to claim 1, characterized by that at least the drive shaft (2) together with at least the first ring gear (3) is axially displaceable via the at least one second spring element (8.2). [3] Planetary gear (1) according to one of the preceding claims, characterized by that the second ring gear (5) has at least one tooth more than the first ring gear (3). [4] Planetary gear (1) according to one of the preceding claims, characterized by that the respective first planetary gear (4), the respective second planetary gear (6) and the respective shaft (7) are monolithic. [5] Planetary gear (1) according to claim 4, characterized by that the respective monolithic component, consisting of the first planetary gear (4), the second planetary gear (6) and the shaft (7), has at least one rotationally symmetrical recess (24) for weight saving. [6] Planetary gear (1) according to one of the preceding claims, characterized by that the respective shaft (7) is rotatably mounted at least on a first carrier (9.1), wherein the first carrier (9.1) is arranged on the shafts (7) in an area adjacent to the second planetary gears (6) on the end face and is designed to receive a respective axial end section of the respective shaft (7). [7] Planetary gear (1) according to claim 6, characterized bythat the respective shaft (7) is rotatably mounted on at least one second carrier (9.2), wherein the second carrier (9.2) is arranged in an area on the shafts (7) adjacent to the front side of the first planet gears (4) and is designed to receive a respective axial end section of the respective shaft (7). [8] Planetary gear (1) according to one of claims 1 to 5, characterized by that the respective shaft (7) is rotatably mounted on a single carrier (9), said carrier (9) being arranged on a shaft section axially between the first and second planetary gears (4, 6) of a respective shaft (7). [9] Drive unit (14) comprising a planetary gear (1) according to one of the preceding claims and an electric motor (15) which is arranged coaxially to the planetary gear (1) and is connected in a rotationally fixed manner to the drive shaft (2). [10] Robot (12) comprising a planetary gear (1) according to one of claims 1 to 8.

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