Planetary gear unit

Abstract

The invention discloses a planetary gear mechanism (1) comprising a first and a second ring gear (2, 4) and at least four dual planetary gears (6, 8, 10, 12), where each dual planetary gear (6, 8, 10, 12) has a first and a second gear (14, 16; 18, 20; 22, 24; 26, 28), wherein the first gear (14; 18; 22; 26) meshes with the teeth of the first ring gear (2), and wherein the second gear (16; 20; the teeth of the double planetary gears (6, 8, 10, 12) mesh with the teeth of the second ring gear (4), wherein the number and dimensions of the double planetary gears (6, 8, 10, 12) are adjusted such that a predetermined dimension, a predetermined torsional stiffness and / or a predetermined load bearing capacity of the interior (30) of the given planetary gear mechanism (1) are provided.

Description

Technical Field

[0001] The invention relates to a planetary gear unit according to the preamble of patent claim 1 , which has a first and a second ring gear and at least four double planetary gears. Background Art

[0002] Planetary gear units are used in various fields of technology, for example in the field of industrial robotics. For various functions, such as gripping arms, cables, wires, tubes etc. are required that can supply power or hydraulic fluid or can transmit signals. However, routing cables etc. along planetary gear units is currently a complicated matter. Summary of the invention

[0003] It is therefore an object of the present invention to provide a planetary gear unit which enables a simple and cost-effective feed-through of cables or the like.

[0004] This object is achieved by a planetary gear unit according to patent claim 1 .

[0005] The planetary gear unit has a first and a second gear ring and at least four double planetary gears. Each of the double planetary gears has a first and a second gear, which are arranged to rotate around a common axis. The teeth of the first gear of each double planetary gear engage in the teeth of the first gear ring, and the teeth of the second gear of each double planetary gear engage in the teeth of the second gear ring.

[0006] The drive member, i.e. the element driven by the shaft, provided in the planetary gear unit can be realized, for example, by one of the ring gears, wherein the other ring gear serves as the output. Since the double planetary gears are in contact with the first ring gear via a gear in each case and with the second ring gear via another gear, the movement of the ring gear serving as the drive member is transmitted to the ring gear serving as the output. However, other combinations are also possible. For example, a planetary gear carrier connected to the double planetary gear and serving as the drive member can be provided. In this case, both ring gears can serve as the output. The opposite arrangement is also possible, i.e. the ring gear serves as the drive member and the planetary gear carrier serves as the output. The ring gear can also be fixedly arranged. In this way, a 3-axis gear unit can be realized in which all axes can be arbitrarily free, driven for input, driven for output or fixed.

[0007] Now, in order to enable cables, wires, tubes etc. to be fed through the planetary gear unit, the number and size of the double planetary gears are adjusted so as to provide a predetermined size of the interior space of the planetary gear unit. This means that the double planetary gears are selected so that cables etc. can be fed through the interior space of the planetary gear unit. Alternatively, the number and size of the double planetary gears can be adjusted so as to provide a predetermined torsional stiffness and / or a predetermined load-bearing capacity. The number and size of the double planetary gears are preferably adjusted so as to meet at least two of these predetermined conditions, most preferably all three. For example, the number and size of the double planetary gears can be adjusted so as to provide a high torsional stiffness and / or load-bearing capacity of the planetary gear unit while providing sufficient space for feeding cables, wires etc. through. In this way, the planetary gear unit can be optimized with respect to one or more parameters.

[0008] According to an embodiment, the number and size of the double planetary gears are adjusted so that a predetermined size of the interior space of the planetary gear unit, a predetermined torsional stiffness and / or a predetermined load-bearing capacity are maximized and the outer diameter of the ring gear is minimized. This can be achieved in particular by correspondingly adjusting the ratio of the inner diameter of the first and second ring gears to the number and size of the double planetary gears. By taking into account the outer diameter of the ring gear, the available installation space, i.e. the maximum possible outer diameter of the planetary gear unit, will also be taken into account. In this way, in addition to high load-bearing capacity, torsional stiffness and space for feeding cables etc. through, smaller requirements are set with regard to the required installation space for the application in which the planetary gear unit is used.

[0009] The ratio of the inner diameter of the first and second ring gears to the number of double planetary gears is preferably optimized so that the diameter of the available internal space is large enough to be able to feed through cables, wires or other lines as required in the application.

[0010] For this purpose, for example, when four double planetary gears are used in a planetary gear unit, the four double planetary gears can in each case use a diameter of at least 18 teeth x module and a ring gear diameter of at least 48 teeth x module. If the ring gear diameter is increased to at least 60 teeth x module, the number of double planetary gears can be increased by 2 to 6 without increasing the diameter, in particular the module, of the double planetary gears. This process increases the bending and torsional stiffness of the gear unit in particular on the one hand, and increases the load-bearing capacity. In addition, the gear unit now provides a larger space inside the gear unit, which concentrically surrounds the gear unit axis, for example, to feed cables or tubes through the gear unit. An increase in the ring gear diameter to at least 76 teeth x module allows eight double planetary gears to be provided; an increase to at least 92 teeth allows ten double planetary gears to be provided; and an increase to at least 104 teeth allows twelve double planetary gears to be provided. With the increase in the number of teeth and the increase in the number of planetary gears, the bending and torsional stiffness, the load-bearing capacity and the ability to feed relatively large cables and tubes through the gear unit increase significantly, without changing the individual planetary gears in the process.

[0011] This correlation also applies, for example, to a double planetary gear with a tooth count of 31, wherein the ring gear tooth counts of four, six, eight, ten or twelve double planetary gears are in this case 80, 100, 120, 140 and 160. An increase in the number of planetary gear teeth to more than 31 and in the number of double planetary gears to more than twelve is likewise possible.

[0012] Advantageously, the double planetary gears are identical to one another, and the ring gear can be adjusted in terms of its size depending on the application. In this case, the scaling of the planetary gear unit is achieved only by the size of the ring gear and the number of the double planetary gears.

[0013] According to an embodiment, a tube is arranged in the inner space of the planetary gear unit. Here, the longitudinal axis of the tube is coaxial with the rotation axis of the ring gear, in particular coincides with the rotation axis of the ring gear. The tube can be a hollow shaft or a sleeve, through which wires such as cables, wires or the like can be fed. By using such a tube, it is possible to prevent the wires from coming into contact with the teeth of the double planetary gear and thus prevent damage.

[0014] When the teeth of the gears of the planetary gear unit, i.e. the teeth of the double planetary gear and the teeth of the ring gear, engage in one another, play may occur between the teeth. This can be particularly disadvantageous when the gears change their direction of rotation, for example when performing a forward movement as well as a reverse movement, because the play between the gears may cause the teeth of the gears to collide with one another unevenly in certain circumstances. This can lead to undesirable wear of the gears.

[0015] According to another embodiment, two of the at least four double planetary gears arranged adjacent to one another are therefore arranged in each case such that the first gear of a first of the two adjacent double planetary gears is preloaded in the clockwise direction so that the teeth of the first gear of the first double planetary gear are in contact with the teeth of the first gear ring, and the second gear of the first double planetary gear is preloaded in the counterclockwise direction so that the teeth of the second gear of the first double planetary gear are in contact with the teeth of the second gear ring. Furthermore, the first gear of a second of the two adjacent double planetary gears is preloaded in the counterclockwise direction so that the teeth of the first gear of the second double planetary gear are in contact with the teeth of the first gear ring, and the second gear of the second double planetary gear is preloaded in the clockwise direction so that the teeth of the second gear of the second double planetary gear are in contact with the teeth of the second gear ring.

[0016] In this way, the teeth of the gears of the first double planetary gear are (tangentially) preloaded in two different directions relative to the ring gear, one in the clockwise direction and one in the counterclockwise direction. Therefore, due to the preload, there is already contact between the teeth of the ring gear and the teeth of the gears of the double planetary gear. Moreover, due to the preload in different directions, this contact is also maintained during operation and any play between the teeth is avoided. At the same time, the teeth of the gears of the second double planetary gear are (tangentially) preloaded in a diametrically opposite manner relative to the ring gear, i.e. one in the counterclockwise direction and one in the clockwise direction.

[0017] When viewed on the inner circumference of the ring gear, two adjacent double planetary gears are always preloaded in an opposite manner, in particular. This results in a particularly good force distribution of the preload of the ring gear and thus in a stable assembly.

[0018] When the gears of the corresponding double planetary gear are preloaded, the gears can be fixed in their relative position to each other. This can be achieved, for example, by welding, soldering / brazing, gluing, radial or axial friction fit or form fit.

[0019] According to a further embodiment, the first gear ring and the second gear ring in each case have helical teeth, wherein the first gear ring and the second gear ring are designed to rotate in a first rotational direction and in an opposite second rotational direction, and wherein the teeth of the first and second gears of at least four double planetary gears are in each case helical teeth, wherein each helical tooth has a first tooth flank and a second tooth flank opposite the first tooth flank, wherein the surface normal of the first tooth flank points in the first rotational direction and the surface normal of the second tooth flank points in the second rotational direction.

[0020] In order to prevent any play between the teeth of the ring gear and the double planetary gears, according to this embodiment, two of the at least four double planetary gears arranged adjacent to each other are arranged in each case so that a first force application element applies a first force in a first direction so that the first tooth flanks of the helical teeth of the first gear of the first double planetary gear of the two adjacent double planetary gears come into contact with the second tooth flanks of the helical teeth of the first ring gear, and the second tooth flanks of the helical teeth of the second gear of the first double planetary gear come into contact with the first tooth flanks of the helical teeth of the second ring gear, thereby providing a preload on the ring gear in the first and second rotational directions. Furthermore, a second force application element applies a second force in a second direction opposite to the first direction so that the second tooth flanks of the helical teeth of the first gear of the second double planetary gear of the two adjacent double planetary gears come into contact with the first tooth flanks of the helical teeth of the first ring gear, and the first tooth flanks of the helical teeth of the second gear of the second double planetary gear come into contact with the second tooth flanks of the helical teeth of the second ring gear, thereby providing a preload on the ring gear in the first and second rotational directions.

[0021] Due to the preload, during the start-up process, there is already contact between the helical teeth of the ring gear and the helical teeth of the gear of the double planetary gear. In addition, this contact can be maintained by the force element during operation, because the preload is maintained, and the tooth play between the helical teeth can be avoided in this way.

[0022] The first and second gears of each double planetary gear are fixed relative to each other. Due to this fixing, the first and second forces can be applied simultaneously to the two gears of the double planetary gear, so that the first and second tooth flanks are in each case in contact with the first or second tooth flanks of the helical teeth of the first and second ring gears.

[0023] Due to the use of preloaded double planetary gears, tooth play between the two ring gears and the double planetary gears is avoided. Since the preload on the second double planetary gear is in the opposite direction to the preload on the first double planetary gear, tooth play between the teeth can be avoided and further improved.

[0024] According to another embodiment, the first half of the double planetary gear is preloaded in the first rotational direction and the second half of the double planetary gear is preloaded in the second rotational direction, wherein the first half and the second half of the double planetary gear are arranged alternately. In this way, the first and second forces as well as the preload in the first rotational direction and the preload in the second rotational direction can be evenly distributed and thus further improved.

[0025] According to another embodiment, the first force and the second force are greater than the axial force, which is applied during rotation due to the meshing of the helical teeth of the double planetary gear and the ring gear. The elastic behavior of the system can be reduced by such a distribution between the first force and the second force and the axial force. This means that during operation of the planetary gear unit, a movement of the double planetary gear in the first and second direction can be avoided. The first force and the second force in the planetary gear unit are preferably identical.

[0026] According to another embodiment, the force applying element may be a spring element, a magnetic element and / or a hydraulic element. Any other type of force applying element is also possible.

[0027] As described above, according to a further embodiment, the number of double planetary gears is a multiple of 2. Therefore, there are always two double planetary gears with diametrically opposed preloads, whereby the different preloads are evenly distributed in a rotational manner. By using four or more double planetary gears, play between the two ring gears and the double planetary gears and mutual twisting of the ring gears in all rotational directions, i.e. forward and backward, can be optimally prevented. Preferably, six or more double planetary gears are provided. The load capacity of the planetary gear unit can be increased in particular by a greater number of double planetary gears.

[0028] Further advantages and advantageous embodiments are set forth in the description, the drawings and the claims.The combinations of features set forth in the description and the drawings herein are in particular purely exemplary, so that these features may also exist alone or in other combinations.

[0029] The present invention will be described in more detail below based on the exemplary embodiments shown in the accompanying drawings. Here, the exemplary embodiments and the combinations shown in the exemplary embodiments are purely illustrative and are not intended to limit the scope of protection of the present invention. The scope is limited only by the attached claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In the attached picture:

[0031] Figure 1 shows a plan view of a first embodiment of a planetary gear unit;

[0032] Figure 2 shows a plan view of a second embodiment of a planetary gear unit;

[0033] Figure 3 shows a plan view of a third embodiment of a planetary gear unit;

[0034] Figure 4 Shown for Figures 1 to 3 Schematic diagram of different numbers of double planetary gears in a planetary gear unit, and tooth ratios of the ring gear and the double planetary gears;

[0035] Figure 5 A first variant of the preloading in the planetary gear unit is shown. Figure 1 A plan view of a planetary gear unit;

[0036] Figure 6 A second variant of the preload in the planetary gear unit is shown. Figure 1 a plan view of a planetary gear unit; and

[0037] Figure 7 Shows Figure 6 Cross-sectional view of a planetary gear unit.

[0038] In the following, identical or functionally equivalent elements are denoted by the same reference numerals. DETAILED DESCRIPTION

[0039] Figure 1 A planetary gear unit 1 is shown, which has a first ring gear 2 and a second ring gear ( Figure 1 In addition, the planetary gear unit 1 has a first double planetary gear 6 , a second double planetary gear 8 , a third double planetary gear 10 and a fourth double planetary gear 12 .

[0040] The double planetary gears 6, 8, 10, 12 each have two gears, wherein Figure 1 In each case, only the first gearwheel 14, 18, 22, 26 can be seen. Here, the first gearwheel 14, 18, 22, 26 is in contact with the first ring gear 2, and the second gearwheel is in contact with the second ring gear.

[0041] Now, in order to enable cables, wires, tubes etc. to be fed through the planetary gear unit 1, the number and size of the double planetary gears 6, 8, 10, 12 are adjusted so as to provide a predetermined size of the inner space 30 of the planetary gear unit 1. This means that the double planetary gears 6, 8, 10, 12 are selected so that cables etc. can be fed through the inner space 30 of the planetary gear unit 1. The number and size of the double planetary gears 6, 8, 10, 12 are in particular adjusted so as to provide a high torsional stiffness and / or load-bearing capacity of the planetary gear unit 1 while providing sufficient space for feeding cables, wires etc. through.

[0042] If more space is needed for feeding cables etc. through, the inner space 30 can be enlarged by using more double planetary gears 6, 8, 10, 12 having the same size or number of teeth x module. Figure 2 and 3 As shown, the number of double planetary gears can be increased to, for example, six ( Figure 2 ) or eight ( Figure 3). If six double planetary gears 6, 8, 10, 12, 32, 34 are used, the interior space becomes already larger. If eight double planetary gears 6, 8, 10, 12, 32, 34, 36, 38 are used, the interior space becomes even larger. Accordingly, the size or the number of teeth x module of the ring gear 2 is also increased accordingly. Therefore, the same double planetary gears 6, 8, 10, 12, 32, 34, 36, 38 can be used in Figures 1 to 3 In all three variants of the planetary gear unit 1 shown in FIG, the outer circumference is correspondingly enlarged.

[0043] If in an application where the planetary gear unit 1 is used, the outer circumference of the planetary gear unit 1 is limited by the available space, smaller double planetary gears 6, 8, 10, 12, 32, 34, 36, 38 may be used instead in order to still maintain the inner space 30 at a predetermined size. The selection of the size and number of the double planetary gears 6, 8, 10, 12, 32, 34, 36, 38 may be made based on the desired torsional stiffness, load carrying capacity and inner space size, as already explained.

[0044] In order to optimize torsional rigidity, load-bearing capacity and internal space dimensions, for a specific size of the ring gear defined by the ring gear diameter (number of teeth x module), a specific number of double planetary gears can be used as a function of its size, which is also defined by the diameter (number of teeth x module). For different numbers of double planetary gears, possible variations of the ring gear diameter and the double planetary gear diameter are Figure 4 Here, the number of teeth z2 of the ring gear is shown on the x-axis, and the number of teeth z1 of the planetary gear is shown on the y-axis.

[0045] from Figure 4 It can be seen that, for example, when four double planetary gears are used in a planetary gear unit (solid line), these four double planetary gears can each use a diameter of at least 18 teeth x module and a ring gear diameter of at least 48 teeth x module. If the ring gear diameter is increased to at least 60 teeth x module, the number of double planetary gears can be increased from two to six without increasing the diameter of the double planetary gears.

[0046] A larger number of double planetary gears 6, 8, 10, 12, 32, 34, 36, 38 can also be used. Preferably, a number of double planetary gears 6, 8, 10, 12, 32, 34, 36, 38 is always provided as a multiple of 2. Due to this number of double planetary gears, a particularly good force distribution and clearance reduction can occur between the teeth of the ring gear 2, 4 and the teeth of the double planetary gears 6, 8, 10, 12, 32, 34, 36, 38, which will be described below with reference to Figures 5 to 7In the figures, four double planetary gears 6, 8, 10, 12 are shown in each case. However, the same principle can also be applied to a planetary gear unit 1 having six, eight, ten, ... double planetary gears.

[0047] Figure 5 A first variant with reduced play is described. In the embodiment shown here, the double planetary gears 6, 8, 10, 12 are connected to one another via a planet carrier 40. In order to enable the feeding through of cables etc., the planet carrier 40 can have a passage opening (not shown).

[0048] exist Figure 5 In the embodiment shown, the first ring gear 2 is larger than the second ring gear 4. In addition, the first ring gear 2 is fixed, wherein the planetary gear carrier 40 acts as a drive member, which rotates in the direction of the arrow, and the second ring gear 4 acts as an output. Other design embodiments and size ratios of the ring gears 2, 4 and the double planetary gears 6, 8, 10, 12 are also possible.

[0049] The double planetary gears 6, 8, 10, 12 each have two gears 14, 16 (first double planetary gear 6), 18, 20 (second double planetary gear 8), 22, 24 (third double planetary gear 10), 26, 28 (fourth double planetary gear 12). Here, the first gear 14, 18, 22, 26 is in contact with the first ring gear 2, and the second gear 16, 20, 24, 28 is in contact with the second ring gear 4.

[0050] In order to prevent any play between the gears 14, 16, 18, 20, 22, 24, 26, 28 and the teeth of the ring gears 2, 4, the gears 14, 16, 18, 20, 22, 24, 26, 28 of all double planetary gears 6, 8, 10, 12 are preloaded. For this purpose, the first gear 14 of the first double planetary gear 6 is preloaded in the clockwise direction relative to the teeth of the first ring gear 2, as indicated by the arrow. The second gear 16 of the first double planetary gear 6 is preloaded in the counterclockwise direction relative to the teeth of the second ring gear 4, also as indicated by the arrow.

[0051] In the mirror image, the first gear 20 of the second double planetary gear 8 is preloaded in the counterclockwise direction relative to the teeth of the first gear ring 2, as shown by the arrow. At the same time, the second gear 22 of the second double planetary gear 8 is preloaded in the clockwise direction relative to the teeth of the second gear ring 4, as shown by the arrow.

[0052] The same is true for the double planetary gears 10, 12: the first gear 22 of the third double planetary gear 10 is preloaded in the clockwise direction relative to the teeth of the first gear ring 2, as indicated by the arrow. The second gear 24 of the third double planetary gear 10 is preloaded in the counterclockwise direction relative to the teeth of the second gear ring 4, also as indicated by the arrow. In a mirror image, the first gear 26 of the fourth double planetary gear 12 is preloaded in the counterclockwise direction relative to the teeth of the first gear ring 2, as indicated by the arrow. At the same time, the second gear 28 of the fourth double planetary gear 8 is preloaded in the clockwise direction relative to the teeth of the second gear ring 4, as indicated by the arrow.

[0053] In this way, the double planetary gears 6, 8, 10, 12 are preloaded alternately in a diametrically opposed manner. This results in a uniform distribution of the preload in the circumferential direction and prevents any play between the gears 14, 16, 18, 20, 22, 24, 26, 28 and the ring gears 2, 4, which could have a destructive effect on the planetary gear unit 1 during operation.

[0054] Figure 6 and Figure 7 Another variation to reduce the play is shown. Figure 6 In the embodiment shown, the first ring gear 2 is larger than the second ring gear 4. The first ring gear 2 can act as a drive, while the second ring gear 4 can act as an output. Other embodiments and ratios of the ring gears 2, 4 and the double planetary gears 6, 8, 10, 12 are also possible.

[0055] Also in Figure 5 In the embodiment shown, the double planetary gear 6, 8, 10, 12 has two gears 14, 16; 18, 20; 22, 24; 26, 28 in each case. The first gear 14, 18, 22, 26 is in contact with the first ring gear 2, and the second gear 16, 20, 24, 28 is in contact with the second ring gear 4. Due to this contact between the double planetary gear 6, 8, 10, 12 and the ring gear 2, 4, the movement of the first ring gear 2 in the first rotational direction 46 or the second rotational direction 48 is transmitted to the second ring gear 4, and vice versa. The rotational direction 46, 48 of the ring gear 2, 4 is indicated in the figure by arrows 46, 48.

[0056] Figure 7 A cross-sectional view of each of the double planetary gears 6, 8, 10, 12 coupled to the ring gears 2, 4 is shown. Figure 7 As shown, the ring gears 2, 4 and the double planetary gears 6, 8, 10, 12 each have a helical tooth 50. Each helical tooth 50 has a first tooth flank and a second tooth flank opposite the first tooth flank. The surface normal of the first tooth flank points to the first rotational direction 46 of the first and second ring gears 2, 4, and the surface normal of the second tooth flank points to the second rotational direction 48 of the ring gears 2, 4.

[0057] When the gears (ring gears 2, 4 and gears 14, 16; 18, 20; 22, 24; 26, 28 of the double planetary gears 6, 8, 10, 12) change their direction of rotation 46, 48, i.e. perform forward and backward movements and / or perform swinging movements between two directions of rotation, the tooth play between the teeth 50 can lead to an uneven movement profile of the gears.

[0058] In order to minimize the tooth play between the gears 14, 16; 18, 20; 22, 24; 26, 28 of the double planetary gears 6, 8, 10, 12 and the helical teeth 50 of the ring gears 2, 4, one or more force application elements 52, 54 are provided in this variation. The first force application element 52 applies a first force in a first direction, and the second force application element 54 applies a second force in a second direction opposite to the first direction. The first direction and the second direction are perpendicular to the first and second rotation directions 46, 48.

[0059] exist Figure 6 and 7 In the illustrated embodiment, a first force is applied to the first and fourth double planetary gears 6, 12, and a second force is applied to the second and third double planetary gears 8, 10. Due to the first force, the first tooth flanks of the helical teeth 50 of the first gears 14, 26 of the first and fourth double planetary gears 6, 12 are in contact with the second tooth flanks of the helical teeth of the first ring gear 2. In addition, the second tooth flanks of the helical teeth 50 of the second gears 16, 28 of the first and fourth double planetary gears 6, 12 are in contact with the first tooth flanks of the helical teeth of the second ring gear 4. Due to this contact, a preload is provided on the ring gears 2, 4 in the first rotational direction 46.

[0060] Furthermore, due to the second force, the second tooth flanks of the helical teeth 50 of the first gears 18, 22 of the second and third double planetary gears 8, 10 are in contact with the first tooth flanks of the helical teeth of the first ring gear 2. Furthermore, the first tooth flanks of the helical teeth 50 of the second gears 20, 24 of the second and third double planetary gears 8, 10 are in contact with the second tooth flanks of the helical teeth of the second ring gear 4. Due to this contact, a preload is provided on the ring gears 2, 4 in the second rotational direction 48.

[0061] Since the first and fourth double planetary gears 6, 12 are pushed in the direction of the first ring gear 2, the helical teeth 50 of the first and fourth double planetary gears 6, 12 are in contact with the helical teeth of the first and second ring gears 2, 4. Since the second and third double planetary gears 8, 10 are pushed in the direction of the second ring gear 4, the helical teeth 50 of the second and third double planetary gears 8, 10 are in contact with the helical teeth of the first and second ring gears 2, 4.

[0062] Due to this preload, during startup there is already contact between the helical teeth 50 of the ring gears 2, 4 and the gears 14, 16; 18, 20; 22, 24; 26, 28 of the double planetary gears 6, 8, 10, 12. Furthermore, this contact can be maintained during operation by force elements 52, 54, so that the preload is maintained and tooth play between the helical teeth 50 can be avoided in this way.

[0063] The force-applying elements 52, 54 can be implemented, for example, as springs, magnetic elements, hydraulic elements or any other type of element capable of applying a force on the double planetary gears 6, 8, 10, 12. This force can also be generated by the different tooth angles between the ring gears 2 and 4. The total amount of the first force applied by the first force-applying element 52 and the total amount of the second force applied by the second force-applying element 54 are preferably the same.

[0064] Therefore, by the above planetary gear unit, in some cases, the number and size of the double planetary gears can be optimized in terms of the required internal space while taking into account the size of the ring gear, the predetermined torsional stiffness and / or the load capacity. In addition, any tooth play between the ring gear and the double planetary gears can be avoided.

[0065] Reference numerals list

[0066] 1 Planetary gear unit

[0067] 2 First ring gear

[0068] 4 Second ring gear

[0069] 6 First double planetary gear

[0070] 8 Second double planetary gear

[0071] 10 Third double planetary gear

[0072] 12 Fourth double planetary gear

[0073] 14First gear of the first double planetary gear

[0074] 16 The second gear of the first double planetary gear

[0075] 18 The first gear of the second double planetary gear

[0076] 20 The second gear of the second double planetary gear

[0077] 22 The first gear of the third double planetary gear

[0078] 24 The second gear of the third double planetary gear

[0079] 26First gear of the fourth double planetary gear

[0080] 28 The second gear of the fourth double planetary gear

[0081] 30 Internal Space

[0082] 32 Fifth double planetary gear

[0083] 34 Sixth double planetary gear

[0084] 36 Seventh double planetary gear

[0085] 38 Eighth double planetary gear

[0086] 40 Planetary gear carrier

[0087] 46 First rotation direction

[0088] 48 Second rotation direction

[0089] 50 Helical teeth

[0090] 52 first force applying element

[0091] 54 Second force applying element

Claims

1. A planetary gear unit (1), comprising: first and second ring gears (2, 4), and At least four double planetary gears (6, 8, 10, 12), wherein each double planetary gear (6, 8, 10, 12) has a first and a second gear (14, 16; 18, 20; 22, 24; 26, 28) arranged to rotate about a common axis, wherein the teeth of the first gear (14; 18; 22; 26) engage in the teeth of the first gear ring (2), and wherein the teeth of the second gear (16; 20; 24; 28) engage in the teeth of the second gear ring (4), It is characterized in that The number and size of the double planetary gears (6, 8, 10, 12) are adjusted so as to provide a predetermined size of the inner space (30) of the planetary gear unit (1), a predetermined torsional stiffness and / or a predetermined load-bearing capacity.

2. The planetary gear unit according to claim 1, wherein: The number and size of the double planetary gears (6, 8, 10, 12) are adjusted, in particular the ratio of the inner diameter of the first and second ring gears (2, 4) to the number and size of the double planetary gears (6, 8, 10, 12) is selected so as to maximize the predetermined torsional stiffness and / or the predetermined load-bearing capacity and minimize the outer diameter of the ring gears (2, 4).

3. The planetary gear unit according to claim 1 or 2, wherein: The tube is arranged in the inner space (30) of the planetary gear unit (1).

4. A planetary gear unit (1) according to any one of the preceding claims, wherein: Two of the at least four double planetary gears (6, 8; 10, 12) arranged adjacent to each other are arranged in each case such that the first gear (14; 22) of the first double planetary gear (6; 10) of the two adjacent double planetary gears (6, 8; 10, 12) is preloaded in the clockwise direction so that the teeth of the first gear (14; 22) of the first double planetary gear (6; 10) are in contact with the teeth of the first ring gear (2), and the second gear (16; 24) of the first double planetary gear (6; 10) is preloaded in the counterclockwise direction so that the first double planetary gear (6; 10) is in contact with the teeth of the first ring gear (2). The teeth of the second gear (16; 24) of the first double planetary gear (10) are in contact with the teeth of the second gear ring (4), and the first gear (18; 26) of the second double planetary gear (8; 12) of the two adjacent double planetary gears (6, 8; 10, 12) is preloaded in the counterclockwise direction so that the teeth of the first gear (18; 26) of the second double planetary gear (8; 12) are in contact with the teeth of the first gear ring (2), and the second gear (20; 28) of the second double planetary gear (8; 12) is preloaded in the clockwise direction so that the teeth of the second gear (20; 28) of the second double planetary gear (8; 12) are in contact with the teeth of the second gear ring (4).

5. The planetary gear unit according to claim 4, wherein: Two adjacent double planetary gears (6, 8, 10, 12) of the at least four double planetary gears (6, 8, 10, 12) are in each case preloaded in opposite directions.

6. The planetary gear unit according to claim 4 or 5, wherein: The gears (8, 10) of each double planetary gear (6, 8, 10, 12) are fixed in their position relative to each other.

7. The planetary gear unit according to any one of claims 1 to 3, wherein: The first gear ring (2) and the second gear ring (4) each have helical teeth (50), wherein the first gear ring (2) and the second gear ring (4) are designed to rotate in a first rotational direction (46) and in an opposite second rotational direction (48), and wherein the teeth of the first and second gear wheels (14, 16; 18, 20; 22, 24; 26, 28) of the at least four double planetary gears (6, 8, 10, 12) are each helical teeth (50), wherein each helical tooth (50) has a first tooth flank and a second tooth surface opposite to the first tooth surface, wherein a surface normal of the first tooth surface points in a first rotational direction (46) and a surface normal of the second tooth surface points in a second rotational direction (48), wherein two double planetary gears (6, 8; 10, 12) arranged adjacent to each other of the at least four double planetary gears (6, 8; 10, 12) are each arranged such that a first force application element (52) applies a first force in a first direction so that a first double planetary gear (6; 10) of the two adjacent double planetary gears (6, 8; 10, 12) The first tooth surface of the helical teeth (50) of the first gear (14; 22) contacts the second tooth surface of the helical teeth (50) of the first gear ring (2), and the second tooth surface of the helical teeth (50) of the second gear (16; 24) of the first double planetary gear (6; 10) contacts the first tooth surface of the helical teeth (50) of the second gear ring (4), thereby providing a preload on the gear rings (2, 4) in the first and second rotational directions (46, 48), and wherein the second force applying element (54) applies a second force in a second direction opposite to the first direction, so that The second tooth surface of the helical teeth (50) of the first gear (18; 26) of the second double planetary gear (8; 12) of the two adjacent double planetary gears (6, 8; 10, 12) contacts the first tooth surface of the helical teeth (50) of the first ring gear (2), and the first tooth surface of the helical teeth (50) of the second gear (20; 28) of the second double planetary gear (8; 12) contacts the second tooth surface of the helical teeth (50) of the second ring gear (4), thereby providing a preload on the ring gears (2, 4) in the first and second rotational directions (46, 48).

8. The planetary gear unit according to claim 7, wherein: A first half of the at least four double planetary gears (6, 8, 10, 12) are preloaded in a first rotational direction (46), and a second half of the at least four double planetary gears (6, 8, 10, 12) are preloaded in a second rotational direction (48), wherein the first half and the second half of the double planetary gears (6, 8, 10, 12) are alternately arranged.

9. A planetary gear unit according to any one of the preceding claims, wherein: The number of the double planetary gears (6, 8, 10, 12, 32, 34, 36, 38) is a multiple of 2.

10. A planetary gear unit according to any one of the preceding claims, wherein: The number of the double planetary gears (6, 8, 10, 12, 32, 34, 36, 38) is greater than or equal to six.

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