Gearbox unit with a backlash-free reduction gear

Abstract

The invention relates to a transmission device (1) at least comprising a planetary drive (2), in which planet shafts (6) are supported at at least one bearing point (8) by means of a rolling element bearing (26), the cylindrical rollers (13) of which run directly on the planet carrier (3).

Description

[0001] Gear device with a backlash-free reduction gear

[0002] Field of the invention

[0003] The invention relates to a transmission device at least comprising a planetary drive with at least one planet carrier, at least one first planet gear, at least one second planet gear and at least one planet shaft, wherein the planet gears are seated coaxially to one another on a planetary axis on the planet shaft, the planet shaft is mounted on at least one first bearing point in the planetary drive, the first bearing point is provided with at least one first planetary shaft bearing and the planetary shaft is mounted on the planet carrier by means of the first planetary shaft bearing so as to be rotatable about a planetary axis.

[0004] Background of the invention

[0005] Such gear devices, known as reduction gears or speed reducers, are often used in actuators in robotics technology, in which the actuating mechanism is driven by electric machines. The purpose of these gear devices is to reduce the relatively high drive speeds of the electric machines. These gear devices have planetary drives with several so-called double or stepped planets. One such gear device is disclosed in US 10 352 400 B2. The stepped planets each have a first planet gear and a second planet gear on a planetary shaft. One of the planet gears is designed as a planetary pinion and is integral with the planetary shaft. In this case, the planetary drive is provided with four stepped planets, which are arranged at a radial distance from the central axis of the planetary drive. One set of the first planet gears meshes with an input sun gear.A set of planetary pinions meshes with a ring gear of the transmission device. The planetary shafts are mounted on a planet carrier with rolling bearings. The outer ring of the rolling bearing has two ribs and is fixed in the planet carrier. The inner ring of the rolling bearing sits on the planetary shaft and is designed without ribs. Transmission devices of this type must operate without backlash and are therefore internally preloaded. In the example considered according to US 10 352 400 B2, the outer contours of the tooth tips of the planetary pinion gears are conical for this purpose, and the respective planetary shaft is axially preloaded against the tooth engagement of the ring gear. For this purpose, a preload device is clamped between the planet carrier and the planetary shaft on the end face of the respective planetary shaft, which permanently pushes the externally helical toothing into that of the ring gear without backlash.This system is self-adjusting because the planetary shaft is mounted in the planet carrier with floating bearings that allow axial displacement by a certain amount. The cylindrical rollers are guided axially between the ribs of the outer ring, so their axial position relative to the planet carrier is fixed. The inner ring has no ribs, so the pins of the planetary shaft, together with the inner ring, act as floating bearings and can be displaced by the specified amount relative to the rolling elements held by the ribs.

[0006] In other arrangements of the type, for example those known from CN 1005 351 459 A, the pins of the planetary shafts are slide-mounted in the planetary carrier and are pre-tensioned at this point with a pre-tensioning device so that they can be moved axially.

[0007] Description of the invention

[0008] The object of the invention is to create a transmission device that can be manufactured easily and inexpensively.

[0009] The object is achieved with a transmission device according to the features of claim 1.

[0010] According to this, the first planetary shaft bearing is a first rolling bearing with at least one row of first cylindrical rollers and a first inner raceway formed directly on the planet carrier. The inner raceway has an inner cylindrical surface. The cylindrical rollers run radially on the outside of the inner cylindrical surface. Radial is defined perpendicular to the planetary axis. The planetary axis is defined as being axially aligned, regardless of its position in space. The axis of rotation or rolling axis of the cylindrical rollers is preferably aligned parallel to the planetary axis. The basic shape of cylindrical rollers is generally defined as cylindrical - however, deviations from the ideal cylindrical shape are included in the definition of "cylindrical rollers". Such deviations are, for example, that the transitions of the cylindrical rollers from their outer surfaces to their end faces can deviate from the cylindrical shape.In this case, the cylindrical rollers, for example, have a crowned end profile. The proportion of crowning to the total length of the respective cylindrical roller can be very small, for example in the range of a few hundredths, or it can cover the entire roller length and thus also define so-called barrel rollers. Crowning is defined by contour lines that are curved, inclined, or straight lines that deviate from the axial direction, and by combinations of these. The end faces of the cylindrical rollers are either circular or axially crowned. For the purposes of this invention, cylindrical rollers are rollers whose "length to width" ratio is less than or equal to the numerical value 2.5, both according to the classic definition for cylindrical rollers and greater than 2.5 according to the definition of needle rollers.

[0011] The cylindrical rollers are arranged in a row if they are arranged adjacent to one another in the circumferential direction one behind the other around the axis of rotation and also run on the raceways in this way during operation. Alternatively, the rolling bearing has more than one row of cylindrical rollers. In this case, more than one row of cylindrical rollers is arranged axially next to one another. It is also not excluded that several and / or possibly different bearings than the rolling bearing are arranged in the bearing location. The bearing location and / or the planetary shaft bearing is defined not only by the rolling bearing according to the invention but also by components of the planet carrier, such as a bearing bore with an inner cylindrical surface and possibly other bearings inserted into it or supported on it. The cylindrical rollers roll in the circumferential direction on the inner cylindrical surface.

[0012] A key component of the invention is that the inner raceway for the cylindrical rollers is formed directly on the planet carrier, thus no longer on an outer ring, as in the prior art. The inner raceway is provided with an inner cylindrical surface facing the planetary axis.

[0013] Due to increasing robotization, for example of production plants, the demands on the gear devices used and the bearing technology used therein are also increasing. The gear devices known to date, such as those known from US 10 352 400 B2, may under certain circumstances no longer meet the requirements with regard to the design of their bearing technology. Such requirements include, for example, increased accuracy with a higher load-bearing capacity and lower material consumption and lower manufacturing costs. The advantage of the invention is that the arrangement according to the invention eliminates the need for a bearing compared to known arrangements. This means that less material is used for the rolling bearing. The radial installation space previously required for the bearing ring and freed up by the solution according to the invention can be used either for more and / or for larger rolling elements in that location.Alternatively, the installation space can be reduced while maintaining the dimensions of the cylindrical rollers. The first measure can increase the load capacity of the rolling bearing or its rigidity. In the second case, installation space can be saved and / or used for other purposes. Since the bearing positions according to the invention, as well as previously known arrangements, require a bore in the planet carrier for the seat of the rolling bearing, the prior art arrangements may be interchangeable with the rolling bearing design according to the invention even without adapting the bearing positions.

[0014] According to one embodiment of the invention, the first outer raceway for the cylindrical rollers is formed on an inner ring. Furthermore, the inner ring is provided with the outer raceway and two ribs that axially define the outer raceway. The outer raceway has an outer cylindrical surface facing radially outward from the planetary axis, against which the cylindrical rollers roll during operation.

[0015] The outer raceway between the ribs is defined by an external cylindrical surface and, if necessary, by undercuts. The ribs form an axial stop for the end faces of the cylindrical rollers and thus serve as end stops for the cylindrical rollers. They also provide parallel guide surfaces on which the cylindrical rollers are guided in circumferential and tangential directions so that the roller axes remain aligned as parallel as possible to the planetary axis during rolling bearing operation. The axial distance between the guide surfaces corresponds to the length of the rollers plus the smallest possible axial play between the rollers and the ribs.

[0016] The planetary shaft bearing is a floating bearing designed as a cylindrical roller bearing, which acts as a radial bearing. The floating bearing is therefore a bearing that absorbs radial forces but not axial forces, because the floating bearing compensates for axial forces by a certain amount. This requires an interface between the stationary elements of the bearing location, at which axially movable elements can be displaced relative to the stationary elements. This interface is formed on the bearing according to the invention between the cylindrical rollers and the inner cylindrical surface, i.e., the cylindrical rollers move axially relative to the inner cylindrical surface of the planet carrier during compensation.

[0017] According to the prior art, the interface is designed as a sliding fit between the inner ring and a shaft or between the outer ring and the housing bore in the usual way for a loose bearing. In the case considered in US 10 352 400 B2, an interface is formed between the cylindrical rollers, which are axially fixedly guided on the outer ring, and the raceway of the inner ring, i.e. the cylindrical rollers are axially displaceable relative to the inner ring by means of the outer ring. In the arrangement according to the invention, however, the cylindrical rollers are displaceable relative to the housing or planet carrier by means of the inner ring. Due to the axial displacement of the planet pinion thus possible, it can remain preloaded in the toothing of the ring gear without play.

[0018] For the application known from US 10 352 400 B2, cylindrical roller bearings of standard design are preferably purchased as catalog bearings. For this purpose, cylindrical roller bearings of design NU according to DIN DIN5412 of bearing clearance group “C3” are used with an interference fit in the housing and on the shaft. The press fits on the inner and outer rings secure the seat of the bearing rings and reduce the bearing clearance to a minimum by expanding the inner ring and constricting the outer ring. The bearing is designed to be rigid to ensure low radial play. The axial displacement between the outer ring or the cylindrical rollers and the inner ring is adjusted by a preload device on the one hand and also radially by the change in center distance caused by the conical toothing and the radial component acting in the contact of the gears, until the cylindrical rollers rest radially on the inner ring with no radial play.

[0019] The known arrangement can have a detrimental effect on the service life of the rolling bearing because the axially compensating function of the floating bearings is limited in the axial direction by the permissible displacement between the outer and inner rings. The permissible displacement is ultimately determined by the width of the outer raceway of the standardized inner ring. This width can be too short with unfavorable tolerance positions. In the case of extensive axial displacement, this can lead to so-called edge runout, i.e. the running surfaces of the cylindrical rollers protrude beyond the outer raceway in the axial direction and rest radially on the edges of the limiting raceway chamfers. Such disadvantageous conditions, known as edge runout, can lead to premature damage to the bearing positions under high loads.The arrangement according to the invention advantageously prevents such edge runners because the inner cylindrical surface of the inner raceway can be made axially wider than the raceway width of the race rings of standardized rolling bearings.

[0020] One embodiment of the invention therefore provides that an axially directed width of the inner cylindrical surface corresponds to at least 1.1 times the axially directed length of the longest of the cylindrical rollers. The bearing seats of outer rings are usually "naturally" wider than the outer rings seated in them. The already available installation space can be used to create a wider rolling raceway, i.e. a wider inner cylindrical surface, without changing the design of previously used planet carriers. Furthermore, when redesigning the planet carriers, the maximum displacement paths that may be required due to extreme tolerances can be taken into account without having to take the dimensions of the standardized rolling bearings that can be used into account.

[0021] One embodiment of the invention provides that the first rolling bearing and optionally also the second rolling bearing is of full complement design, i.e. the first cylindrical rollers are arranged in a row directly one after the other in the circumferential direction around the planetary axis and are not separated from one another by cage webs. The loose bearings known from US 10 352 400 B2, on the other hand, are cylindrical roller bearings which consist of an outer ring, an inner ring, a cage and cylindrical rollers. One function of the cages is to keep the cylindrical rollers circumferentially spaced from one another during operation of the cylindrical roller bearing. For this purpose, the individual cylindrical roller is guided in a pocket in the cage. The pocket is delimited in the circumferential direction by axially aligned webs, so that a web runs between each two circumferentially adjacent cylindrical rollers.In contrast to this arrangement, the invention now provides for the use of the cylindrical rollers in a rolling bearing without a cage. This measure allows for more cylindrical rollers to be arranged in a row in the circumferential direction, or for the installation space required for the bearing to be reduced by using smaller-diameter cylindrical rollers. If necessary, the existing rolling bearing with a cage can be replaced with a full-complement bearing without changing the surrounding structure. Furthermore, full-complement bearings exhibit comparatively higher rigidity, allowing the transmission device to be designed more precisely and adapted to more stringent requirements.

[0022] A further embodiment of the invention provides that the planetary shaft is supported at two bearing points in the planet carrier, i.e. twice. In both bearing points, either the same cylindrical roller bearing or different cylindrical roller bearings are used. The respective cylindrical roller bearing has the aforementioned features according to the invention, so that both bearing points are designed identically, at least with regard to their loose bearing, i.e. the inner raceway is designed directly in the bore and both bearings are full complement bearings. Preferably, the same bearings are used at both bearing points. The advantage of the invention is that by using identical parts, the number of different individual parts of the device can be reduced, thus simplifying storage and assembly.The batch sizes for the production of the inner ring and the cylindrical rollers are doubled, resulting in cost-effective production.

[0023] One embodiment of the invention provides that the cylindrical rollers in the first bearing location, the second bearing location, as well as the third bearing location and fourth bearing location are part of each of the rolling bearings. One and the same cylindrical rollers are used both in the rolling bearings for supporting the planetary shafts and for supporting the planet carrier on the ring gear. It is irrelevant whether these rolling bearings are equipped with full complement cylindrical rollers or whether the cylindrical rollers are guided in cages. The advantage of this embodiment is that the batch sizes for the production of the cylindrical rollers are multiplied, which can reduce their manufacturing costs. Furthermore, the effort required, for example, to store and feed different rollers can be avoided.

[0024] The gear device preferably relates to a reduction gear. The stepped planets each have a first planet gear and a second planet gear on a planetary shaft. One of the planet gears is preferably designed as a single piece with the planetary shaft, but can also be mounted on the planetary shaft as a separate component or fastened to it. The planetary drive is provided with at least two of the stepped planets. However, the use of three, four or more of the stepped planets is also contemplated. The stepped planets are arranged at a radial distance from the central axis of the planetary drive, which, depending on the use of the gear device, is also the axis of rotation for the planet carrier and / or the ring gear. One set of the first planet gears meshes with an input sun gear. One set of the planetary pinions meshes with a ring gear of the gear device.The planetary shafts are mounted on a planetary carrier with planetary shaft bearings. The planetary gear is preloaded to eliminate backlash by conically designing the outer contours of the planetary pinion gear teeth, which preloads the respective planetary shaft against the toothing of the ring gear. For this purpose, a preload device comprising at least one spring and one ball is clamped between the planetary carrier and the planetary shaft on the end face of the respective planetary shaft.

[0025] Description of the drawings

[0026] The invention is explained in more detail below using an exemplary embodiment. Figure 1 shows a longitudinal section through a transmission device 1 along the central axis 31 of the transmission device 1.

[0027] Figure 2 shows a detail from the drawing according to Figure 1, enlarged and not to scale. Figure 1 - The gear device 1 has a planetary drive 2 and an input gear 32. The planetary drive 2 is formed from a planet carrier 3, four planetary shafts 6, a sun shaft 33 and a ring gear 7. Due to the nature of the illustration, only two of the four planetary shafts 6 are visible in the picture. The sun shaft 33 is provided with a sun gear 34. The input gear 32 is the power input element in the planetary drive 2 and is seated on the sun shaft 33. The planetary shafts 6 are each formed from a first planet gear 4 and a second planet gear 5. The planet gears 4 and 5 are coaxial with one another and aligned with a planetary axis 11. The second planet gear 5 forms a planetary pinion together with a shaft 35 of the planetary shaft 6. The first planet gear 4 is mounted on the shaft 35 as a separate component.The planet carrier 3 is preferably constructed in multiple parts and is a power output element of the planetary drive 2. The ring gear 7 is mounted on a housing 27. The sun gear 34 meshes with the first planet gear 4. The second planet gear 5 meshes with the ring gear 7. Figures 1 and 2 - The respective planetary shaft 6 is mounted at a first bearing point 8 and at a second bearing point 24 with planetary shaft bearings 9 and 23 in the planet carrier 3. The planetary shaft bearings 9 and 23 are floating bearings. The respective first bearing point 8 is formed by a first bearing bore 38 in the planet carrier 3, the planetary shaft bearing 9, and a journal 36. The journal 36 is formed on the shaft 35. The second bearing point 24 is formed by a second bearing bore 39 in the planet carrier 3, the planetary shaft bearing 23, and a bearing seat 40. The bearing seat 40 is an external cylindrical section of the shaft 35.

[0028] Figure 2 - The planetary shaft bearing 9 has a first rolling bearing 26 and the inner raceway 12. The inner raceway 12 is formed in the bearing bore 38 and is provided with an inner cylindrical surface 22 and an insertion chamfer 37.

[0029] The second planetary shaft bearing 23, like the first planetary shaft bearing 9, has a first rolling bearing 26 and an inner raceway 20. The inner raceway 20 is formed by an inner cylindrical surface 41 in the second bearing bore 39 and by an insertion chamfer 42.

[0030] The respective first rolling bearing 26 is formed by an inner ring 14 and by cylindrical rollers 13. The inner ring 14 is provided with an outer raceway 15 running around the planetary axis 11 and with ribs 17 and 18. The outer raceway 15 runs axially between the ribs 17 and 18. The cylindrical rollers 13 are arranged in a row in the circumferential direction one behind the other and without a cage, i.e. full complement, i.e. without the webs of a cage, directly following one another, radially between the inner raceway 12 and the outer raceway 15 and axially between the ribs 17 and 18.

[0031] The gear device 1 operates without backlash. For this purpose, the outer head contour of the external toothing 44 of the respective second planetary gear 5, which is constructed as a single piece and made of a single material together with its shaft 35, is conical and preloaded in an axial direction against the internal toothing 45 of the ring gear 7 by means of a preloading device 43. For this purpose, the preloading device 43 is clamped to the end face of the respective planetary shaft 6 and the planet carrier 3. The preloading device 43 is formed from a bolt 46, a spring 47, and a ball 48 in a guide bore 49. The bolt 46, the spring 47, the ball 48, and the guide bore 49 are arranged concentrically to one another and also concentrically on the planetary axis 11. The bolt 46 is either inserted or screwed into the planet carrier 3 and guides the spring 47. The spring 47 is guided on a guide pin 50 of the bolt 46 and preloaded against the ball 48.The ball 48 is guided in the guide bore 49 of the planetary shaft 6 and preloaded against the planetary shaft 6 by the spring 47. This system functions in a self-adjusting manner because the planetary shaft 6 is mounted in the planetary carrier 3 with the planetary shaft bearings 9 and 23 designed as floating bearings, allowing axial displacement by a certain sliding travel.

[0032] When the planetary shaft 6 is displaced, the inner rings 14, which are firmly seated on the shaft 35, are moved axially with the shaft 35, and thus also the cylindrical rollers 13, which are guided axially between the ribs 17 and 18 and fixed in their position relative to the shaft 35. The cylindrical rollers 13 of the respective planetary shaft bearings 9 and 10 slide by a certain compensation amount, i.e., a proportion of a dimension X or by de relative to the planet carrier 3 on the respective inner cylindrical surface 22 or 41, which is necessary to maintain / adjust the clearance. The value of X is the smallest distance required to adjust the clearance and is a difference between the minimum axial width B1 of the inner cylindrical surface 22 or 41 required for compensation and the maximum length L1 of the cylindrical rollers 13, which is technically possible due to production.In the described case, the inner cylindrical surfaces 22 and 41 are either equally wide in the axial direction or can differ in width. The width B1 of the inner cylindrical surfaces is at least 1.1 times the length L1 of the respective axially aligned cylindrical rollers 13, but can also be greater, depending on how large the distance X is to be.

[0033] Figure 1 - The planet carrier 3 is mounted at a third bearing point 25 and a fourth bearing point 28 on the housing 27 and on the ring gear 7, respectively. Each of the bearing points 25 and 28 is provided with a rolling bearing 30. The respective rolling bearing 30 is an angular contact roller bearing and is formed from an inner angular contact track 52, an outer angular contact track 51, the cylindrical rollers 13, and a cage 29. The inner angular contact track 52 is formed directly on the ring gear 7 and the housing 27, respectively. The respective outer angular contact track 51 is formed directly on the planet carrier 3. The cylindrical rollers 13 of each of the rolling bearings 30 are each guided in a cage 29. The rolling bearings 26 and 30 used in the bearing positions 8, 24, 25 and 28 all have the same type of cylindrical rollers 13, which are preferably all characterized by the same diameter and the same length L1.Although the basic shape of the cylindrical rollers, which gives their name, is cylindrical, the cylindrical rollers used in the bearings are all provided with a spherical outer surface, which is shown in the longitudinal section of their roller axes as biconvex with or without cylindrical sections.

[0034] List of reference symbols

[0035] Gear device planetary drive

[0036] Planet carrier first planet gear second planet gear planetary shaft

[0037] Ring gear first bearing point first planetary shaft bearing journal

[0038] Planetary axis inner raceway

[0039] Cylindrical roller inner ring

[0040] outdoor track

[0041] Rolling elements

[0042] Inner ring flange Inner ring flange Planetary axis Inner raceway Outer cylindrical surface Inner cylindrical surface Second planetary shaft bearing Second bearing position Third bearing position First rolling bearing

[0043] Housing fourth bearing position cage second rolling bearing central axis

[0044] Input gear sun shaft sun gear shaft

[0045] cones

[0046] Lead-in chamfer first bearing bore second bearing bore bearing seat inner cylindrical surface lead-in chamfer

[0047] Pretensioning device External gearing Internal gearing Bolt

[0048] Feather

[0049] Bullet

[0050] Guide hole

[0051] guide pin

[0052] Outer inclined track Inner inclined track

Claims

Claims: Gear device (1) comprising at least a planetary drive (2) with at least one planet carrier (3), at least one first planet gear (4), at least one second planet gear (5) and at least one planet shaft (6), wherein - the planet gears (4, 5) are aligned coaxially with each other on a planet axis (11) on the planet shaft (6), - the planetary shaft (6) is supported at at least one first bearing point (8) in the planetary drive (2), - the first bearing point (8) is provided with at least one first planetary shaft bearing (9), - the planetary shaft (6) is rotatably mounted on the planet carrier (3) by means of the first planetary shaft bearing (9) about a planetary axis (11), characterized in that the first planetary shaft bearing (9) is a first rolling bearing (26) with at least one row of first cylindrical rollers (13) and a first inner raceway (12) formed directly on the planet carrier (3), wherein the inner raceway (12) has an inner cylindrical surface (22), and wherein the inner cylindrical surface (22) is directed radially in the direction of the axially oriented planetary axis (11), wherein the cylindrical rollers (13) run radially outside the inner cylindrical surface (22), and wherein radial is perpendicular to the planetary axis (11).Gear device (1 ) according to claim 1 , characterized in that a first outer raceway (15) of the rolling bearing (26) for the cylindrical rollers (13) is formed on an inner ring (14) seated on a section of the planetary shaft (6), wherein the inner ring (14) is provided with the outer raceway (15) and two flanges (17, 18) axially adjoining the outer raceway (15) and wherein the outer raceway (15) is provided with an outer cylindrical surface (21 ) on which the cylindrical rollers (13) run radially inwards. Gearbox device (1) according to claim 2, characterized in that an axially directed width (B1) of the inner cylindrical surface (22) formed on the planet carrier (3) corresponds to at least 1.1 times the length (L1) of the longest of the first cylindrical rollers (13) of the rolling bearing (26). Gearbox device (1) according to claim 2 or 3, characterized in that the first planet shaft bearing (9) is a full complement bearing, wherein the first cylindrical rollers (13) are arranged in a cageless row circumferentially around the planet axis (11).A transmission device (1) according to one of the preceding claims, characterized in that the planetary shaft (6) is supported at the first bearing point (8) by the first planetary shaft bearing (9) and at a second bearing point (24) by a second planetary shaft bearing (23), wherein both the first planetary shaft bearing (9) and the second planetary shaft bearing (23) each comprise at least the first rolling bearing (26) according to claim 1. A transmission device (1) according to one of the preceding claims with at least one ring gear (7), wherein the second planet gear (5) is in tooth mesh with the ring gear (7), characterized in that the planet carrier (3) is supported at least at a third bearing point (25) by at least one second rolling bearing (30) on a housing (27).Gear unit (1) according to claim 6, characterized in that the ring gear (7) is formed and / or attached to the housing (27) and that the planet carrier (3) is mounted on the ring gear (7) by means of the second rolling bearing (30). Gear unit according to claim 7, characterized in that the planet carrier (3) is mounted on the ring gear (7) at a fourth bearing point (28), wherein both the third bearing point (25) and the fourth bearing point (28) have the second rolling bearing (30). RECTIFIED SHEET (RULE 91) ISA / EP Gearbox device according to claim 8, characterized in that the cylindrical rollers (13) are a component of each of the rolling bearings (26, 30) at the first bearing position (8), the second bearing position (24), as well as at the third bearing position (25) and fourth bearing position (28). Gearbox device according to claim 9, characterized in that the cylindrical rollers (13) inserted at the third bearing position (25) and the fourth bearing position (28) are each guided in at least one cage (29) at each of the bearing positions (25, 28).