PLANETARY GEAR BOX

Abstract

A planetary gearbox has a sun gear, planet gears, a ring gear and plain bearing pins. A plain bearing pin is arranged in a respective planet gear, wherein the plain bearing pin and the planet gear form a lubricated plain bearing which includes a plain bearing gap, and on its contact face, the plain bearing pin forms a feed pocket which is configured to receive oil and output it to the plain bearing. On its contact face, the plain bearing pin forms an additional feed pocket which is configured to receive oil and output it to the plain bearing, is spaced from the feed pocket in the circumferential direction, and is connected to the feed pocket such that oil from the additional feed pocket can flow on the contact face of the plain bearing pin to the feed pocket.

Claims

1. Planetary gear box, which has: a sun gear, which is rotatable about an axis of rotation of the planetary gear box and defines an axial direction of the planetary gear box, a plurality of planet gears, which are driven by the sun gear, a ring gear, with which the plurality of planet gears is in engagement, a plurality of plain bearing pins which each have an external contact face, wherein a plain bearing pin is arranged in each planet gear, wherein the plain bearing pin and the planet gear form a lubricated plain bearing which comprises a plain bearing gap, and on its contact face, the plain bearing pin forms a feed pocket which is provided and configured to receive oil and output it to the plain bearing, wherein on its contact face, the plain bearing pin furthermore forms an additional feed pocket which is provided and configured to receive oil and output it to the plain bearing, is spaced from the feed pocket in the circumferential direction, and is connected to the feed pocket such that oil from the additional feed pocket can flow on the contact face of the plain bearing pin to the feed pocket.

2. Planetary gear box according to claim 1, wherein in operation, in the circumferential direction, the plain bearing gap comprises a convergent region, a minimal gap height and a divergent region, wherein the additional feed pocket is formed in the divergent region of the plain bearing gap.

3. Planetary gear box according to claim 2, wherein the additional feed pocket is formed in the plain bearing pin in the divergent region of the plain bearing gap in an angular region between 40° and 60° behind the greatest circumferential angle which corresponds to a minimal gap height.

4. Planetary gear box according to claim 2, wherein the feed pocket is formed in the plain bearing pin in the transition between the divergent region and the convergent region.

5. Planetary gear box according to claim 1, wherein the additional feed pocket is connected to the feed pocket via a circumferential groove extending in the circumferential direction.

6. Planetary gear box according to claim 1, wherein the feed pocket and/or the additional feed pocket are formed so as to be rectangular in an unrolled view from above.

7. Planetary gear box according to claim 1, wherein the feed pocket and/or the additional feed pocket are formed centrally in the plain bearing pin with respect to the axial length of the plain bearing pin.

8. Planetary gear box according to claim 1, wherein the feed pocket and the additional feed pocket have the same axial length.

9. Planetary gear box according to claim 1, wherein the feed pocket and the additional feed pocket have the same width in the circumferential direction.

10. Planetary gear box according to claim 1, wherein the feed pocket and the additional feed pocket have an axial length which corresponds to at least 50% of the axial length of the plain bearing gap.

11. Planetary gear box according to claim 1, wherein the planetary gear box has a first and a second oil supply system for the provision of lubricating oil, which are independent of one another, wherein the first oil supply system supplies oil to the feed pocket and the second oil supply system supplies oil to the additional feed pocket.

12. Planetary gear box according to claim 11, wherein the first oil supply system comprises two axially spaced oil feed bores in the feed pocket, which are provided and configured such that oil from the first oil supply system enters the feed pocket via said bores.

13. Planetary gear box according to claim 12, wherein the circumferential groove opens into the feed pocket at an axial position which lies between the two oil feed bores of the first oil supply system.

14. Planetary gear box according to claim 11, wherein the second oil supply system forms an oil feed bore in the additional feed pocket, which is provided and configured such that oil from the second oil supply system enters the additional feed pocket via said bore.

15. Planetary gear box according to claim 1, wherein two axial grooves are furthermore formed in the plain bearing pin and each extend from the feed pocket to a respective one of the axial ends of the contact face.

16. Planetary gear box according to claim 15, wherein the axial grooves have a smaller depth than the feed pocket.

17. Planetary gear box according to claim 1, wherein the feed pocket in each of the plain bearing pins of the planetary gear box is configured such that it faces radially outward relative to the axial direction of the planetary gear box.

18. Planetary gear box according to claim 1, wherein the feed pocket and the additional feed pocket are formed in the plain bearing pin symmetrically with respect to the axial centre of the plain bearing pin.

19. Plain bearing which comprises: a first bearing element having a contact face, a second bearing element having a contact face, wherein the two bearing elements are configured to rotate relative to one another and form a plain bearing gap between their contact faces, and on its contact face, the first bearing element forms a feed pocket which is provided and configured to receive oil and output it to the plain bearing, wherein on its contact face, the first bearing element furthermore forms an additional feed pocket which is provided and configured to receive oil and output it to the plain bearing, is spaced from the feed pocket in the circumferential direction, and is connected to the feed pocket such that oil from the additional feed pocket can flow on the contact face of the first bearing element to the feed pocket.

20. Gas turbine engine for an aircraft, which has: an engine core comprising a turbine, a compressor, and a turbine shaft connecting the turbine to the compressor; a fan, which is positioned upstream of the engine core, wherein the fan comprises a plurality of fan blades and is driven by a fan shaft; and a planetary gear box according to claim 1, the input of which is connected to the turbine shaft and the output of which is connected to the fan shaft.

Description

[0069] The invention will be explained in more detail below on the basis of a plurality of exemplary embodiments with reference to the figures of the drawing. In the drawings:

[0070] FIG. 1 shows a lateral sectional view of a gas turbine engine;

[0071] FIG. 2 shows a close-up lateral sectional view of an upstream portion of a gas turbine engine;

[0072] FIG. 3 shows a partially cut-away view of a gear box for a gas turbine engine;

[0073] FIG. 4 shows a sectional illustration of the elements of a planetary gear box which is suitable for use in a gas turbine engine as shown in FIG. 1;

[0074] FIG. 5 shows a plain bearing pin having a feed pocket according to the prior art, wherein the illustration is selected so as to show the unrolled outer face of the plain bearing pin;

[0075] FIG. 6 shows the plain bearing pin from FIG. 5 with additional depiction of the flow of lubricating oil in the plain bearing gap during operation;

[0076] FIG. 7 shows an exemplary embodiment of a plain bearing pin comprising a feed pocket and an additional feed pocket which are spaced apart from one another in the circumferential direction, wherein the illustration is selected so as to show the unrolled outer face of the plain bearing pin; and

[0077] FIG. 8 shows the plain bearing pin from FIG. 7 with additional depiction of the flow of lubricating oil in the plain bearing gap during operation.

[0078] FIG. 1 illustrates a gas turbine engine 10 having a main axis of rotation 9. The engine 10 comprises an air intake 12 and a thrust fan 23 that generates two air flows: a core air flow A and a bypass air flow B. The gas turbine engine 10 comprises a core 11 which receives the core air flow A. In the sequence of axial flow, the engine core 11 comprises a low-pressure compressor 14, a high-pressure compressor 15, a combustion device 16, a high-pressure turbine 17, a low-pressure turbine 19, and a core thrust nozzle 20. An engine nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass thrust nozzle 18. The bypass air flow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low-pressure turbine 19 by way of a shaft 26 and an epicyclic transmission 30.

[0079] During use, the core air flow A is accelerated and compressed by the low-pressure compressor 14 and directed into the high-pressure compressor 15, where further compression takes place. The compressed air expelled from the high-pressure compressor 15 is directed into the combustion device 16, where it is mixed with fuel and the mixture is combusted. The resulting hot combustion products then propagate through the high-pressure and the low-pressure turbines 17, 19 and thereby drive said turbines, before being expelled through the nozzle 20 to provide a certain propulsive thrust. The high-pressure turbine 17 drives the high-pressure compressor 15 by means of a suitable connecting shaft 27. The fan 23 generally provides the major part of the thrust force. The epicyclic gear box 30 is a reduction gear box.

[0080] An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low-pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun gear 28 of the epicyclic gear box assembly 30. Multiple planet gears 32, which are coupled to one another by a planet carrier 34, are situated radially to the outside of the sun gear 28 and mesh therewith. The planet carrier 34 limits the planet gears 32 to orbiting around the sun gear 28 in a synchronous manner while enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled by way of linkages 36 to the fan 23 so as to drive the rotation of the latter about the engine axis 9. Radially to the outside of the planet gears 32 and meshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary support structure 24.

[0081] It is noted that the terms “low-pressure turbine” and “low-pressure compressor” as used herein can be taken to mean the lowest pressure turbine stage and the lowest pressure compressor stage (that is to say not including the fan 23) respectively and/or the turbine and compressor stages that are connected to one another by the connecting shaft 26 with the lowest rotational speed in the engine (that is to say not including the transmission output shaft that drives the fan 23). In some documents, the “low-pressure turbine” and the “low-pressure compressor” referred to herein may alternatively be known as the “intermediate-pressure turbine” and “intermediate-pressure compressor”. Where such alternative nomenclature is used, the fan 23 can be referred to as a first compression stage or lowest-pressure compression stage.

[0082] The epicyclic gear box 30 is shown in an exemplary manner in greater detail in FIG. 3. Each of the sun gear 28, the planet gears 32 and the ring gear 38 comprise teeth about their periphery to mesh with the other gears. However, for clarity, only exemplary portions of the teeth are illustrated in FIG. 3. Although four planet gears 32 are illustrated, it will be apparent to a person skilled in the art that more or fewer planet gears 32 may be provided within the scope of protection of the claimed invention. Practical applications of an epicyclic transmission 30 generally comprise at least three planet gears 32.

[0083] The epicyclic gear box 30 illustrated by way of example in FIGS. 2 and 3 is a planetary gear box, in which the planet carrier 34 is coupled to an output shaft via linkages 36, wherein the ring gear 38 is fixed. However, any other suitable type of epicyclic gear box 30 can be used. By way of further example, the epicyclic gear box 30 can be a star arrangement, in which the planet carrier 34 is held so as to be fixed, wherein the ring gear (or annulus) 38 is allowed to rotate. In the case of such an arrangement, the fan 23 is driven by the ring gear 38. As a further alternative example, the gear box 30 can be a differential gear in which both the ring gear 38 and the planet carrier 34 are allowed to rotate.

[0084] It is self-evident that the arrangement shown in FIGS. 2 and 3 is merely an example, and various alternatives fall within the scope of protection of the present disclosure. Purely by way of example, any suitable arrangement can be used for positioning the gear box 30 in the engine 10 and/or for connecting the gear box 30 to the engine 10. By way of a further example, the connections (such as the linkages 36, 40 in the example of FIG. 2) between the gear box 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have a certain degree of stiffness or flexibility. By way of a further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts of the gear box and the fixed structures, such as the gear box housing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gear box 30 has a star arrangement (described above), the person skilled in the art would readily understand that the arrangement of output and support linkages and bearing positions would typically be different to that shown by way of example in FIG. 2.

[0085] Accordingly, the present disclosure extends to a gas turbine engine having an arbitrary arrangement of gear box types (for example star-shaped or planetary), support structures, input and output shaft arrangement, and bearing positions.

[0086] Optionally, the gear box may drive additional and/or alternative components (e.g. the intermediate-pressure compressor and/or a booster compressor).

[0087] Other gas turbine engines in which the present disclosure can be used may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of connecting shafts. By way of a further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 20, 22, meaning that the flow through the bypass duct 22 has its own nozzle that is separate from and radially outside the core engine nozzle 20. However, this is not restrictive, and any aspect of the present disclosure can also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed or combined before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) can have a fixed or variable region. Although the example described relates to a turbofan engine, the disclosure can be applied, for example, to any type of gas turbine engine, such as, for example, an open rotor engine (in which the fan stage is not surrounded by an engine nacelle) or a turboprop engine. In some arrangements, the gas turbine engine 10 possibly does not comprise a gear box 30.

[0088] The geometry of the gas turbine engine 10, and components thereof, is/are defined by a conventional axis system, which comprises an axial direction (which is aligned with the axis of rotation 9), a radial direction (in the direction from bottom to top in FIG. 1), and a circumferential direction (perpendicular to the view in FIG. 1). The axial, radial and circumferential directions are mutually perpendicular.

[0089] For better understanding of the background of the invention, a planetary gear box known from the prior art is explained in more detail with reference to FIG. 4. FIG. 4 shows a sectional illustration of an exemplary embodiment of a planetary gear box 30 of a gas turbine engine designed as a geared fan engine as shown in FIG. 1. The planetary gear box 30 comprises a sun gear 28, which is driven by a drive shaft 26 or sun shaft. The drive shaft 26 is the shaft 26 in FIGS. 1 and 2 or, more generally, a turbine shaft. In this arrangement, the sun gear 28 and the drive shaft 26 rotate around the axis of rotation 9. The axis of rotation of the planetary gear box 30 is identical with the axis of rotation 9 or engine axis of the gas turbine engine 10.

[0090] The planetary gear box 30 furthermore comprises a plurality of planet gears 32, one of which is illustrated in the sectional illustration in FIG. 4. The sun gear 28 drives the plurality of planet gears 32, wherein a toothing of the sun gear 28 is in engagement with a toothing of the planet gear 32.

[0091] The planet gear 32 is of hollow cylindrical design and forms an outer lateral surface and an inner lateral surface. Driven by the sun gear 28, the planet gear 32 rotates around an axis of rotation 90, which is parallel to the axis of rotation 9. The outer circumferential surface of the planet gear 32 forms a toothing, which is in engagement with the toothing of a ring gear 38. The ring gear 38 is arranged in a fixed manner, i.e. in such a way that it does not rotate. However, attention is drawn to the fact that the present invention is not restricted to planetary gear boxes with a stationary ring gear. It can likewise be implemented in planetary gear boxes with a stationary planet carrier and a rotating ring gear.

[0092] Owing to their coupling with the sun gear 28, the planet gears 32 rotate and, in so doing, move along the circumference of the ring gear 38. The rotation of the planet gears 32 along the circumference of the ring gear 38 and simultaneously around the axis of rotation 90 is slower than the rotation of the drive shaft 26, thereby providing a reduction ratio.

[0093] Adjoining its inner lateral surface, the planet gear 32 has a centred axial opening. A plain bearing pin 6, which itself also has an axial bore 60, is introduced into the opening, wherein the longitudinal axis of the bore is identical to the axis of rotation 90 of the planet gear 32. The plain bearing pin 6 and the planet gear 32 form a plain bearing 65 at their mutually facing surfaces. The plain bearing pin 6 is also called a planet pin, planet gear pin or planet gear bearing pin.

[0094] The mutually facing surfaces of the plain bearing pin 6 and the planet gear 32 are an at least approximately cylindrical, external contact face or outer face 61 of the plain bearing pin 6 and an at least approximately cylindrical inner face 320 of the planet gear 32. These surfaces form the running surfaces of the plain bearing. Lubricating oil is present between the running surfaces 61, 320, and on rotation builds up a hydrodynamic lubricant film which separates the running surfaces from one another. Here the plain bearing forms a plain bearing gap 650 between the running surfaces 61, 320. The height of the plain bearing gap 650, which is a radial height, varies in the circumferential direction, as will be explained in more detail below with reference to FIGS. 5 to 8. The height of the plain bearing gap 650 defines the lubricant film thickness of the oil. The smaller the lubricant film thickness, the greater the lubricant film pressure and the greater the temperature development in the lubricant film or oil.

[0095] It is pointed out that the plain bearing pin 6 may have numerous designs. Its outer face 61 may be cylindrical or alternatively spherical, as described in US 2019/162294 A1. The axial bore 60 of the plain bearing pin 6 may be hollow cylindrical or alternatively have an inner diameter which varies over the axial length, as also described in US 2019/162294 A1. It is also conceivable that the plain bearing pin 6 for example has a stiffness which varies over its axial length, for example by means of different wall thicknesses, as described in US 2021/025477 A1. Moreover, the design of the plain bearing pin 6 with an axial bore 60 should be considered merely exemplary. It may alternatively be provided that the plain bearing pin 6 has no axial bore and is solid. Furthermore, embodiment variants may be provided in which the plain bearing pin is structured in the radial direction, for example comprises a main body and a plain bearing ring which is radially spaced from the main body, forming the plain bearing 65 together with the planet gear 32.

[0096] FIG. 4 furthermore shows a front carrier plate 341 and a rear carrier plate 342, which are constituent parts of the planet carrier 34, cf. FIG. 2. The planet pin 6 is fixedly connected to the front carrier plate 341 and to the rear carrier plate 342. The front carrier plate 341 is for example connected to a torque-transmitting member, which is coupled to a fan shaft.

[0097] To lubricate the bearing 65 between the plain bearing pin 6 and the planet gear 32, one or more oil supply systems are provided, which comprise oil feed channels (not shown) which each terminate in an oil feed pocket (not shown) formed on or machined into the outer contact face 61 of the plain bearing pin 6. Oil from a circulating oil system is conducted into the feed pockets in the plain bearing pin 6 via the oil feed channels. The oil is supplied for example via the axial inner bore 60 of the plain bearing pin 6.

[0098] In the context of the present invention, the provision of effective cooling of the plain bearing gap is of importance. The principles of the present invention have been described with reference to plain bearings in a planetary gear box of a gas turbine engine, but in principle however also apply to plain bearings in any gear boxes.

[0099] Before the invention is explained with reference to an exemplary embodiment shown in FIGS. 7 and 8, for better understanding of the background of the invention, initially a plain bearing pin known from the prior art is presented with reference to FIGS. 5 and 6.

[0100] FIG. 5 shows the contact face 61 of a plain bearing pin 6 in an unrolled illustration. The angular degree φ in the circumferential direction is shown at the left-hand edge. The contact face 61 has a depression which forms a feed pocket 4 for oil from an oil supply system. In the exemplary embodiment shown, the feed pocket 4 is rectangular and formed in the plain bearing pin 6 symmetrically with respect to its axial centre.

[0101] In general, the 0° angular degree in the local coordinate system of the plain bearing pin 6 is defined by the radial direction in the coordinate system of the planetary gear box, i.e. at 0°, the radial direction extends effectively radially outward from the plain bearing pin 6. In the exemplary embodiment illustrated, the feed pocket 4 is positioned such that the position of its centre line lies on the 0° angular degree. However, this is not necessarily the case. The rotational direction n in which the angle is measured corresponds to the rotational direction of the planet gear which rotates on the plain bearing pin 6.

[0102] The feed pocket 4 may for example be configured such that its maximum depth in the axial direction is constant along the centre line 43, and at its long sides 41, 42, which are spaced apart in the circumferential direction, it transforms smoothly and without edges into the contact face 61.

[0103] The contact face 61 comprises an axially front end face 62 and an axially rear end face 63. It is pointed out that the end face of the plain bearing pin 6 need not correspond to the axial positions of the end faces 62, 63 of the contact face 61.In particular, according to FIG. 4, it may be provided that the plain bearing pin 6 forms end regions which extend axially to the front and axially to the rear beyond the plain bearing 65, and connect the plain bearing pin 6 to a front carrier plate and a rear carrier plate of a planet carrier.

[0104] FIG. 6 shows the plain bearing pin 6 from FIG. 5 in operation, when a plain bearing 65 according to FIG. 4 is formed between the contact face 61 and an associated contact face of a planet gear. FIG. 6 also shows oil feed bores 71, 72 from two oil supply systems, which terminate in and supply oil to the feed pocket 4. For safety reasons, in order to create redundancy, two independent oil supply systems are provided.

[0105] FIG. 6 furthermore shows the flow of oil in the plain bearing gap or on the contact face 61.The gap height of the plain bearing gap here varies in the circumferential direction. This is because, during operation of the planetary gear box, because of the rotational movement of the planet gears and the interaction between the toothing of the planet gear and the ring gear, the acting load reaches a maximum at a specific circumferential angle φ. Accordingly, adjacent to the 0° position in the circumferential direction, the plain bearing gap forms a convergent region 610, a minimal gap height 620 which corresponds to the maximum acting load, and a divergent region 630, wherein the minimal gap height 620 - in the exemplary embodiment illustrated, but not necessarily - lies at around 170°. Depending on the position to which the maximum of the external load points, the angular coordinate of the minimal gap height 620 may vary, for example over a range of 40°.

[0106] According to FIG. 6, fresh oil flows along the arrows D1 from the feed pocket 4 into the convergent region 610, and is heated there as far as the minimal gap height 620. The maximum oil temperature is reached at the minimal gap height 620. In the adjacent divergent region 630 of the plain bearing gap, the oil collects along arrows D2 into an oil stream D3 which runs centrally and opens into the feed pocket 4. This is however disadvantageous, since the heated oil heats the adjacent components, i.e. the plain bearing pin 6 and the planet gear. In addition, its backflow to the feed pocket 4 prevents the inflow of fresh oil into the feed pocket 4.

[0107] FIG. 7 shows an exemplary embodiment of a plain bearing pin 6 with a contact face 61 in an unrolled illustration. Insofar as the plain bearing pin 6 corresponds to the plain bearing pin of FIGS. 5 and 6, reference is made to the statements concerning these. The plain bearing pin 6 from FIG. 7 differs from the plain bearing pin of FIGS. 5 and 6 in that, in addition to the feed pocket 4, a further feed pocket, called the additional feed pocket 5, is provided. Like the feed pocket 4, this is also provided to receive oil from an oil supply system and output it to the plain bearing. The additional feed pocket 5 is spaced apart from the feed pocket 4 in the circumferential direction. The additional feed pocket 5 and the feed pocket 4 are connected together via a circumferential groove 8 extending in the circumferential direction. The angular spacing between the feed pocket 4 and the additional feed pocket 5 in some embodiments is at least 90°.

[0108] In the unrolled illustration, the additional feed pocket 5 is rectangular with two long sides 51, 52 spaced apart from one another in the circumferential direction. It is formed for example such that its maximal depth in the axial direction is constant along the centre line 43, and at its long sides 51, 52, it transforms smoothly and without edges into the contact face 61.

[0109] In the exemplary embodiment illustrated, the additional feed pocket has the same axial length and same width in the circumferential direction as the feed pocket 4. This is however to be understood merely as an example. The additional feed pocket 5 and the feed pocket 4 may alternatively differ with respect to these and other parameters.

[0110] The feed pocket 4 and the additional feed pocket 5 are arranged parallel to one another.

[0111] The plain bearing pin of FIG. 7 differs from the plain bearing pin of FIGS. 5 and 6 furthermore by the formation of two axial grooves 91, 92, which each extend from the feed pocket 4 to the respective adjacent end face 62, 63 of the contact face 61.The axial grooves 91, 92 serve for improved axial discharge of dirt particles present in the lubricating oil.

[0112] FIG. 8 shows an illustration of the plain bearing pin 6 from FIG. 7 which, like FIG. 6, additionally shows the flow of oil and the oil feed bores. It is provided that the oil feed bores 71 of a first oil supply system terminate in and supply oil to the feed pocket 4. Two oil feed bores 71 are provided, which are spaced apart from one another in the axial direction. An oil feed bore 72 of a second oil supply system terminates in the additional oil feed pocket 5 and is arranged centrally therein. It is thus provided that the two oil supply systems each supply oil to only one of the pockets 4, 5. This is however to be understood merely as an example.

[0113] The two oil feed bores 71 of the feed pocket 4 are positioned in the feed pocket 4 such that the circumferential groove 8 opens into the feed pocket 4 at an axial position which lies between these two oil feed bores 71. It may be provided that the circumferential groove 8 runs in the axial centre of the plain bearing pin 6. It may however, alternatively, run offset to the axial centre.

[0114] FIG. 8 furthermore shows that the position of the additional feed pocket 6 in the circumferential direction is selected such that it lies behind the minimal gap height 620 in the divergent region 630. It may be provided that the distance in the circumferential direction is 40° to 60° behind the greatest circumferential angle in the plain bearing pin 6 which forms a minimal gap height. It is pointed out that the position of the minimal gap height 620 in the circumferential direction may vary depending on operating conditions, so that the greatest angle at which the gap height is minimal is considered with respect to said distance.

[0115] The oil flow in the plain bearing pin 6 of FIGS. 7 and 8 is such that, initially, fresh oil flows along arrows D1 from the feed pocket 4 into the convergent region 610 of the plain bearing gap and is heated there as far as the minimal gap height 620. The maximum oil temperature is reached at the minimal gap height 620. In the adjacent divergent region 630 of the plain bearing gap, the oil collects along arrows D2 centrally over an only short circumferential region, and is then displaced by the fresh oil from the additional feed pocket 5, emerging via the oil feed bore 72, and discharged in the axial direction along arrows D4 to the two axial end faces. Thus the plain bearing pin 6 and planet gear are only heated to a reduced extent. Oil is also prevented from flowing back into the feed pocket 4. At the same time, cooling is provided by the fresh oil from the additional feed pocket 5.

[0116] The cool oil entering the additional feed pocket 5 is conducted into the additional pocket 4 via the circumferential groove 8 without undergoing substantial heating. The circumferential groove 8 here minimises a heat development in the oil which is attributable to shear forces. In the additional pocket 4, the oil stream D5 from the additional feed pocket 5 mixes with fresh oil supplied via the oil feed bores 71. Thus very cool oil is transported along arrows D1 in the direction of the convergent region 610.

[0117] The additional feed pocket 5 thus ensures that hot oil in the divergent region of the plain bearing gap is rapidly transported to the axial ends and replaced by cool oil from the additional feed pocket.

[0118] The invention is not restricted to the present exemplary embodiments which should be regarded as merely exemplary. It is in particular pointed out that any of the features described may be used separately or in combination with any other features, unless they are mutually exclusive. The disclosure extends to and comprises all combinations and sub-combinations of one or a plurality of features which are described here. If ranges are defined, said ranges thus comprise all of the values within said ranges as well as all of the partial ranges that lie in a range.