Wind turbine powertrain

Abstract

The invention describes a wind turbine powertrain comprising: a low speed shaft; the high-speed assembly comprises a planetary gearbox and a generator; a coupling assembly including a first annular portion connected to the low speed shaft, a second annular portion connected to the first stage of the planetary gearbox, and a cylindrical intermediate portion extending between the annular portions; a powertrain housing arranged to enclose the low speed shaft and the coupling assembly; characterized in that: an external access opening is formed in the powertrain housing; and an interior access opening formed in the middle portion of the coupling assembly and arranged to align with the exterior access opening to facilitate access to the interior of the coupling assembly. The invention also describes a method of implementing a maintenance procedure for such a wind turbine powertrain.

Description

Background Art

[0001] A widely used design for a wind turbine power train includes a low-speed shaft coupled to a planetary gearbox, and a generator mounted to the gearbox. The low-speed shaft is supported by a housing around a bearing assembly in place (typically including a front bearing around the upwind region of the low-speed shaft, and a rear bearing around the downwind region of the low-speed shaft), and this "main bearing housing" is fixed to the nacelle floor so that loads can be transferred to the wind turbine tower. The coupling assembly and the gearbox-generator module can be attached to the main bearing housing in a cantilevered manner so that the torque reaction forces and the weight of the gearbox-generator module are substantially supported by the main bearing housing.

[0002] A known type of coupling (between the low speed shaft and the gearbox) comprises two annular discs or plates, one of which is connected to the low speed shaft and the other to the first stage of the gearbox. These plates are shaped to extend radially outward, i.e. the outer diameter of the annular plates is greater than the diameter of the downwind end of the low speed shaft. These annular plates (which may be similar in size) are connected around their outer perimeter by a relatively short annular connecting portion or "hollow shaft". The hollow shaft is preferably as short as possible to help transfer loads from the gearbox-generator assembly to the main bearing housing and the nacelle bedplate. The short coupling assembly also helps to achieve an advantageously compact powertrain. This type of coupling assembly design may be preferred because the flexibility of the annular plates combined with the spatial separation achieved by the hollow shaft allows radial and angular displacement of the gearbox input shaft relative to the low speed shaft.

[0003] However, a disadvantage of this design is that the annular connecting portion does not allow access to the fasteners that connect the annular plate to the low speed shaft and gearbox. It is also not possible to access these fasteners through apertures in the annular plate, as any such apertures would alter the flexural and torsional properties of the annular plate, thereby defeating its purpose as a coupling member in this type of powertrain.

[0004] One way to address this problem is to carefully design the coupling assembly to ensure that the fasteners do not require any maintenance over the entire service life of the wind turbine (which may be more than 20 years). However, such "maintenance-free" designs are expensive and significantly increase the overall cost of the wind turbine.

[0005] It is therefore an object of the present invention to provide an improved powertrain design which overcomes the problems outlined above.

[0006] This object is achieved by the claimed wind turbine power train and the claimed method of implementing a maintenance procedure. Summary of the invention

[0007] As described above, a wind turbine power train of the type discussed herein includes a low speed shaft or "main shaft", a planetary gearbox, and a coupling assembly between the main shaft and the gearbox. According to the present invention, the coupling assembly includes a first annular portion connected to the main shaft, a second annular portion connected to the planetary gearbox, and a substantially hollow cylindrical middle portion extending between these annular portions. A housing is provided to enclose the main shaft and the coupling assembly, as it is important to prevent contaminants from entering or leaving the space between the main shaft and the gearbox. The wind turbine power train of the present invention is characterized by: an outer access opening formed in the power train housing; and an inner access opening, which is formed in the middle portion of the coupling assembly and is arranged to align with the outer access opening to facilitate access to the interior of the coupling assembly.

[0008] In the context of the present invention, the annular portion of the coupling assembly may be referred to as a coupling portion and may be in the form of a substantially flat plate or disc. The coupling portion may also be referred to herein as a plate or disc. Such a coupling portion may be annular, with a central opening, since the components to be coupled are an annular end of the main shaft and an annular arrangement of planetary gears of the first gearbox stage.

[0009] In the context of the present invention, the middle part should be understood to include a hollow, substantially cylindrical part having a suitable diameter (e.g. similar to the diameter of the coupling plate) and a length that is preferably as short as possible. Thus, the diameter of the middle part is significantly greater than its length, so that the middle part has the shape of a shallow ring. Since this ring is connected to the coupling disc, it can be referred to as a coupling ring in this article. The coupling disc and the coupling ring together define a closed space in the interior of the coupling assembly. As will be explained below, the coupling ring can be detached from one or both coupling plates in order to decouple the main shaft from the gearbox.

[0010] An advantage of the construction of the present invention is that even if the enclosed space in the interior of the coupling assembly is very limited due to a shallow or short coupling ring, a technician still has access to components in the interior of the coupling portion and can perform maintenance procedures with relative ease. Because the method of the present invention facilitates access to components in the interior of the coupling portion, this portion of the powertrain does not need to be "over-engineered" to avoid maintenance over the service life of the wind turbine. In contrast, the connection between the main shaft and the gearbox can be achieved at an advantageous low cost using relatively inexpensive "standard" bolted connections, which can be expected to require regular maintenance during the service life of the wind turbine. In the powertrain design of the present invention, accessibility to the interior of the coupling assembly is included while maintaining an advantageous short coupling assembly length. In other words, there is no need to extend the length of the coupling assembly in order to access the fasteners in the interior of the coupling assembly.

[0011] Maintenance procedures for coupling part components may be scheduled with other routine inspection or maintenance routines so that the power train design of the present invention does not incur significant costs during the wind turbine's service life.

[0012] According to the present invention, a method of performing a maintenance procedure on such a wind turbine power train comprises the steps of: rotating the power train unit so that an internal opening in the intermediate portion is aligned with an external opening in the power train housing; and then accessing a plurality of components in the interior of the coupling assembly through the aligned openings. The now accessible components may be manipulated as appropriate, for example, fasteners may be tightened or loosened as required, fastener preload may be checked and adjusted as required, etc.

[0013] Particularly advantageous embodiments and features of the invention are given by the dependent claims, as revealed in the following description. Features of different claim categories may be combined as appropriate to give further embodiments not described herein.

[0014] In the following, without limiting the invention in any way, it may be assumed that the length of the power train is about 8-10 m and the diameter at the coupling zone may be about 1-2 m. For various reasons, the length of the power train should be kept as short as possible, and the present invention provides a method for constructing an advantageous compact coupling assembly. In a particularly preferred embodiment of the invention, the length of the coupling assembly (i.e. the distance between the non-driven end of the main shaft and the first stage of the planetary gearbox) is at most 1.0 m, more preferably at most 0.7 m.

[0015] As explained above, the powertrain housing encloses the main shaft and the coupling assembly. In a preferred embodiment of the present invention, the powertrain housing includes a first housing section shaped to enclose the front bearing and the rear bearing around the main shaft in appropriate position, and a second housing section shaped to enclose the coupling assembly. In the following, the housing section surrounding the main shaft and its bearings in appropriate position may be referred to as the main bearing housing; the housing section surrounding the coupling assembly in appropriate position may be referred to as the coupling housing. The upwind end of the coupling housing is fixed to the downwind end of the main bearing housing. The downwind end of the coupling housing is fixed to the planetary gearbox. In this way, the main shaft and bearings as well as the coupling assembly are protected from the influence of airborne contaminants. Another purpose of the powertrain housing is to be connected to the gearbox housing, which in turn supports the generator in a cantilever manner. The structural loads are transmitted to the nacelle floor via the gearbox housing and the powertrain housing, and from there to the tower.

[0016] Due to the weight load of the gearbox-generator module and any misalignment of the gearbox input shaft relative to the main shaft, some deformation of this type of power train inevitably occurs during operation of the wind turbine. The power train is usually designed with the aim of keeping such deformations within the range that the coupling assembly can accommodate under all operating conditions. As mentioned above, a compact power train length is also preferred. Therefore, the coupling assembly of the power train of the present invention is preferably as short as possible while having sufficient rigidity, since the rigidity of the coupling assembly and the coupling housing determines to a certain extent the deformation behavior of the power train. Since the access openings in the coupling housing and the coupling ring mean that material is effectively "removed" from these components, the desired degree of rigidity is preferably achieved by "adding" material (for example by increasing the wall thickness in other areas of the coupling housing and the coupling assembly).

[0017] In a particularly preferred embodiment of the invention, these access openings are arranged to align when the low speed shaft is rotated to a predetermined position (i.e., a "locked" or "maintenance" position). The size of the external access openings need not be greater than the size of the internal access openings at all. In this way, the size of these openings can be kept to a beneficial minimum, so that the provision of access openings does not adversely affect the structural strength of the coupling assembly and the coupling housing.

[0018] In a preferred embodiment of the invention, a cover or hatch may be provided at least for the external access opening and / or the internal access opening. The cover is preferably shaped to fit precisely into the corresponding access opening so that it may contribute to the rigidity of the housing.

[0019] The first annular portion of the coupling assembly is preferably fixed to the non-driven end of the main shaft by an annular arrangement of fasteners inserted into corresponding threaded holes formed in the non-driven end of the main shaft. These fasteners are preferably axially aligned, that is, the axes of the fasteners are parallel to the powertrain rotation axis of the powertrain and are inserted in the upwind direction. These fasteners are referred to herein as "upwind-facing internal fasteners". Similarly, the second annular portion of the coupling assembly is preferably fixed to the first stage of the planetary gearbox by a second annular arrangement of fasteners inserted into corresponding threaded holes formed in the first stage of the planetary gearbox. These fasteners are preferably axially aligned, that is, the axes of the fasteners are parallel to the powertrain rotation axis of the powertrain and are inserted in the downwind direction. These fasteners are referred to herein as "downwind-facing internal fasteners". In the following, without limiting the invention in any way, it can be assumed that such fasteners are metal screws with hexagonal or "hex" heads and that the hex heads of these fasteners can be accessed from within the coupling assembly. The upwind facing internal fasteners and the downwind facing internal fasteners used in the coupling assembly of the power train having the dimensions given above may be standard bolts of size approximately M48-M 100. Likewise, expansion bolts or multi-jackbolt tensioners may be used.

[0020] When shutting down a wind turbine power train for a maintenance routine, one or more rotating parts can be "locked" to prevent them from moving until the wind turbine is safely restarted. For example, the generator rotor can be kept stationary by a brake disc. The locked generator rotor prevents the rotation of any upwind components in the gearbox, and therefore also prevents the rotation of the coupling assembly and the main shaft. Therefore, after the shutdown sequence is completed, the position of the coupling assembly relative to the power train housing may be essentially random, and the external access opening (in the power train housing) and the internal access opening (in the middle part of the coupling assembly) may not be aligned. Therefore, in a preferred embodiment of the method of the present invention, a drive unit can be deployed to rotate the gearbox / generator shaft to achieve rotation of the first stage of the gearbox and the coupling assembly (relative to the main shaft) to align the openings. The drive unit used for this purpose can be equipment installed in the nacelle for this purpose. Similarly, the drive unit can be the generator itself. Alternatively or in addition, the step of rotating the power train components to align the openings can be completed by achieving rotation of the low-speed shaft (relative to the gearbox input shaft). This can be done, for example, using an external drive unit attached to the low-speed shaft.

[0021] As explained above, the coupling assembly comprises two annular plates connected by an intermediate portion or a coupling ring. In a preferred embodiment of the invention, the annular plates are fixed to the coupling ring by an arrangement of external fasteners (i.e., fasteners accessible from the outside of the coupling assembly). In a preferred embodiment of the invention, the upwind end and the downwind end of the coupling ring are formed as an inwardly facing flange or an outwardly facing flange. Depending on the choice of flange design, the external fasteners can be inserted through holes provided in the periphery of the annular plates and threaded into matching threaded blind holes provided in the outwardly facing flange; alternatively, the external fasteners can be inserted through holes provided in the inwardly facing flange and threaded into matching threaded blind holes provided at the periphery of the annular plates. A first annular arrangement of external fasteners is used to connect the first annular plate to the coupling ring; a second annular arrangement of external fasteners is used to connect the second annular plate to the coupling ring.

[0022] The powertrain housing is preferably configured to include a plurality of small apertures, each of which is positioned to facilitate access to a plurality of external fasteners so that the coupling plate can be temporarily removed from the coupling ring. A first set of (equidistantly arranged) access apertures can be provided for the external fasteners of the first coupling plate, and a similar set of access apertures can be provided for the external fasteners of the second coupling plate. For example, each access aperture can facilitate access to three or four external fasteners, thereby allowing some or all of these external fasteners to be removed as needed during maintenance procedures.

[0023] When one decoupled driveline part (e.g. main shaft) rotates relative to another driveline part (e.g. gearbox input shaft), the removed coupling plate will rotate relative to the coupling ring. Therefore, in a particularly preferred embodiment of the invention, to avoid friction between the coupling ring and the coupling plates, the coupling assembly comprises an arrangement of shims between the coupling ring and each coupling plate. As part of the decoupling procedure, the shims can be removed through the opening of the driveline housing until they are needed again.

[0024] After aligning the internal opening in the middle portion with the external opening in the powertrain housing, the technician can access the interior of the coupling assembly. For example, a maintenance procedure may require some manipulation of the fasteners facing upwind and / or the fasteners facing downwind. The tool used to loosen such fasteners and re-tighten the fasteners to the required torque can be any suitable power tool, such as a bolt tensioning device, a pneumatic impact wrench, a hydraulic socket wrench, a hydraulic puller, etc. Such tools are typically heavy and difficult to operate in the limited space available inside the coupling assembly, particularly because the technician must hold the tool while reaching in through the aligned access openings. Therefore, in another preferred embodiment of the present invention, one or more brackets are provided at suitable locations in the interior of the coupling assembly, and these brackets are formed to hold or at least partially support maintenance tools, thereby helping technicians to implement maintenance procedures.

[0025] The main shaft and / or gearbox input shaft can be rotated as needed to rotate the coupling interface relative to the stationary powertrain housing so that the next set of external fasteners can be accessed through the small access openings. An exemplary sequence of steps is explained below. In a preparatory step, most of the external fasteners are removed from the two annular plates, leaving a reduced set of external fasteners in place. For example, in an embodiment with an annular arrangement of 24 external fasteners in each annular plate and four small access windows in the powertrain housing, 20 external fasteners are removed from each annular plate, leaving four equidistantly arranged external fasteners in place, each of which can be accessed through one of the four access windows. In the next step, these remaining external fasteners can be removed without rotating the main shaft and / or gearbox input shaft. After the powertrain components are disengaged in this manner, a maintenance procedure can then be performed. After the maintenance procedure is completed, the coupling assembly is reassembled by reversing the above steps: securing the reduced set of external fasteners through the small access apertures, and then rotating the main shaft and / or gearbox input shaft an appropriate amount as needed to rotate the coupling interface relative to the stationary powertrain housing so that the next external fastener can be inserted and tightened through the access apertures.

[0026] In an exemplary maintenance routine, it may be necessary to adjust the upwind facing internal fasteners (connecting the first annular plate to the main shaft) and the downwind facing internal fasteners (connecting the second annular plate to the gearbox first stage). This may be accomplished in a two-stage procedure, for example, where the downwind facing internal fasteners are adjusted in the first stage and the upwind facing internal fasteners are adjusted in the second stage. Rotation of the second coupling plate and any object upwind of the second coupling plate is accomplished using, for example, an auxiliary drive unit mounted to the generator or gearbox.

[0027] Initially, the main shaft is in a position where the internal access opening and the external access opening are aligned and the low-speed shaft is locked. In this position, any accessible internal fastener facing downwind can be manipulated as needed (assuming that the gearbox input shaft is locked before manipulating the fastener in any way). For example, a technician may only be able to reach one internal fastener facing downwind on each side of the powertrain. In order to access the remaining internal fasteners facing downwind, it is necessary to rotate the first stage of the generator. For this purpose, as described above, the second annular plate is disconnected from the coupling ring by removing the second annular arrangement of the external fasteners. Using the auxiliary drive unit, the gearbox input shaft can then be rotated to a new position relative to the main shaft, for example, the gearbox input shaft can be rotated through 45°. Rotating the first stage of the gearbox also causes the second annular plate to be rotated, but the internal access opening in the coupling ring remains aligned with the external access opening. In this new position, the technician can now adjust one or more remaining internal fasteners facing downwind. Repeat these steps until the maintenance team has adjusted all internal fasteners facing downwind. The second annular plate is then reconnected to the coupling ring by reinserting and tightening the second annular arrangement of external fasteners.

[0028] In the second stage of the procedure, the internal fasteners facing upwind are adjusted. Here, again, the aligned access openings facilitate access to one or more internal fasteners facing upwind (assuming that the low speed shaft is always locked before the fasteners are manipulated in any way). To access the remaining internal fasteners facing upwind, the main shaft is unlocked and the auxiliary drive unit is used to rotate the main shaft (together with the coupling assembly and the gearbox input shaft) through the appropriate portion of a full circle so that the main shaft is in a new position. After rotating the main shaft, the access opening in the coupling ring is no longer aligned with the external access opening. To realign the access opening, the first annular plate is disconnected from the coupling ring by removing the first annular arrangement of external fasteners, while locking the main shaft and the gearbox input shaft. The gearbox input shaft and coupling ring can then be rotated to a certain position (for example, rotated through -45°) to realign the access opening. This can be accomplished by the auxiliary drive unit connected to the gearbox output shaft as described above. Rotating the first stage of the gearbox by this amount also realigns the external fastener bolt pattern in the coupling ring and the first coupling plate for reassembly in a subsequent step. In this new position, the maintenance personnel can now adjust one or more of the remaining upwind facing internal fasteners while locking the gearbox input shaft. Then, the first annular plate is reconnected to the aligned coupling ring using the first annular arrangement of external fasteners while locking the main shaft and the gearbox input shaft. These steps are repeated until the maintenance personnel has adjusted all of the upwind facing internal fasteners.

[0029] The above maintenance procedures for the upwind facing internal fasteners and / or the downwind facing internal fasteners are advantageously simple and can be scheduled as part of a regular service routine. Since the fasteners can be inspected relatively frequently, the coupling assembly need not be carefully designed to be maintenance-free throughout the service life of the powertrain, but can be implemented as an advantageous economical structure.

[0030] In an alternative method of accessing the remaining internal fasteners facing upwind, the main shaft is rotated relative to the gearbox input shaft, for example by means of an auxiliary drive unit arranged to rotate the main shaft or by pitching the rotor blades when the main shaft is unlocked and the gearbox input shaft is locked. For this purpose, the first annular plate is disconnected from the coupling ring by removing the first annular arrangement of external fasteners, while locking the main shaft and the gearbox input shaft. The main shaft can then be rotated to a new position, for example by 45°. Rotating the main shaft also results in rotating the first annular plate, but the internal access opening in the coupling ring remains aligned with the external access opening. In this new position, the maintenance personnel can now adjust one or more remaining internal fasteners facing upwind. Repeat these steps until all internal fasteners facing upwind have been adjusted. The main shaft can then be rotated as appropriate to realign the first annular plate and the coupling ring. The first annular plate is then reconnected to the coupling ring again by reinserting and tightening the first annular arrangement of external fasteners. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It should be understood, however, that the drawings are designed for illustration purposes only and not as a definition of the limits of the present invention.

[0032] Figure 1 A wind turbine power train of the type discussed herein is shown;

[0033] Figure 2 A simplified side elevation view showing the powertrain of the present invention;

[0034] Figure 3 A simplified plan view showing the powertrain of the present invention;

[0035] Figure 4-Figure 10 The steps of the method of the present invention are illustrated;

[0036] Fig.11 Show Figure 2 and Figure 3 phases during maintenance procedures in the power train;

[0037] Fig.12 An exploded view of a coupling assembly of an embodiment of a powertrain of the present invention is shown.

[0038] In the drawings, like reference numerals refer to like objects throughout. Objects in the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0039] Figure 1 is a schematic illustration of an exemplary wind turbine power train 2 mounted inside a nacelle 30 supported by a tower 32 of the wind turbine 3 (the aerodynamic rotor is not included in the figure for clarity). By means not shown here but familiar to those skilled in the art, the low speed unit 20 of the power train 2 is secured to a bedplate 31, which in turn is connected to the top of the tower 32, such that the power train loads are transferred to the tower 32.

[0040] In this exemplary embodiment, the wind turbine can have a rated power output of about 5 to 20 MW, and the aerodynamic rotor of the wind turbine can have a diameter of 160 m or more. When the wind turbine is operated at its rated speed, the main shaft 201 of the power transmission system 2 of such a wind turbine 3 can rotate at a relatively low rate (e.g., 8-12 rpm). To support the low-speed shaft 201, a main bearing arrangement is provided, which includes a front bearing and a rear bearing 20B at both ends of the low-speed shaft 201. The housing 2H encloses the bearing 20B and most of the low-speed shaft 201, and is sealed to prevent contaminants from entering or leaving the housing 2H. This housing 2H is fixed to the base plate 31.

[0041] The high speed unit 21 including the gearbox 211 and the generator 213 is mounted to the low speed unit 20 by means of the coupling assembly 1. Here, the high speed unit 21 includes a planetary gearbox 211 having several stages. The generator 213 is mounted in a cantilever manner to the non-drive end of the gearbox 211. The weight of the high speed unit 21 of such a powertrain 2 may be about 40-80 metric tons.

[0042] The low speed shaft 201 must be connected in some way to the planetary gears of the first stage 212 of the gearbox. Instead of connecting the non-driven end of the low speed shaft 201 directly to the first stage 212 of the gearbox, a coupling assembly 1 is used as shown here. This coupling assembly 1 is constructed to be as short as possible, i.e., to connect the low speed shaft 201 to the gearbox 211 as directly as possible, to achieve optimal torque transmission. In a preferred embodiment of the present invention, the length of the powertrain 2 can be about 6-10m, and the total axial length 1L of the coupling assembly 1 is at most 1m and can be shorter, for example, the axial length 1L can be as short as 70cm.

[0043] Figure 2A simplified side elevation view of a powertrain 2 of the present invention is shown, showing some components in cross section. The figure shows the main shaft 201 and the planetary gearbox 211 connected by an embodiment of the coupling assembly 1 of the present invention. The housing 1H encloses the coupling assembly 1. The upwind end of the coupling housing 1H is fixed to the downwind end of the main bearing housing 2H by a flange connection. The downwind end of the coupling housing 1H is fixed to the first stage 212 of the planetary gearbox 211. As shown here, a bearing 21B is provided between the stationary coupling housing 1H and the rotating gearbox first stage 212.

[0044] The coupling assembly 1 comprises two annular discs or plates 11, 12 having the same outer diameter. These annular plates 11, 12 are connected around their outer periphery by a relatively short annular connecting portion 13 (also called a "hollow shaft" or "coupling ring"). One annular plate 11 is connected to the low speed shaft 201, while the other annular plate 12 is connected to the gearbox first stage 212. The plates 11, 12 extend radially outwards, i.e. the outer diameter of the annular plates is greater than the diameter of the downwind end of the low speed shaft 201. The flexibility of the annular plates 11, 12 combined with the spatial separation achieved by the connecting portion 13 allows radial and angular displacement of the gearbox first stage 212 relative to the low speed shaft 201.

[0045] Each annular portion 11, 12 of the coupling assembly 1 has a substantially flat rim extending radially from a central aperture. The first annular portion 11 is bolted to the main shaft 201 by an annular arrangement of axially aligned fasteners F11 inserted in the upwind direction (e.g., an annular arrangement of eight equally spaced bolts of size approximately M48-M100); the second annular portion 12 is bolted to the gearbox first stage 212 by an annular arrangement of axially aligned fasteners F12 inserted in the downwind direction (e.g., a corresponding annular arrangement of eight bolts). These fasteners F11, F12 can only be accessed from the interior of the coupling assembly 1.

[0046] As shown here, the stationary coupling assembly housing 1H has an external access opening 1HA, and the rotating hollow shaft 13 of the coupling assembly 1 has a matching internal access opening 13A. In this embodiment, the openings 13A, 1HA are substantially the same size and are aligned when the main shaft 210 has been rotated to a corresponding position. This can be a predetermined locking / maintenance position, for example, that is, the shutdown procedure of the wind turbine can end with the main shaft 201 in the position shown here, resulting in the alignment of the openings 13A, 1HA, so that a technician can reach in and access the fasteners F11, F12. The figure also shows the connection between the annular parts 11, 12 and the coupling ring 13. The fasteners F13 for attaching the coupling ring 13 to the coupling parts 11, 12 can be accessed through smaller openings or "windows" 2HW, 1HW formed around the housing 2H, 1H.

[0047] exist Figure 3, this exemplary powertrain embodiment is shown in a simplified plan view. In this exemplary embodiment, the rotating hollow shaft 13 of the coupling assembly 1 has two diametrically opposed apertures 13A, and the coupling assembly housing 1H also has two diametrically opposed matching apertures 1HW. Here, the aligned openings 1HA, 13A allow a technician 5 on both sides of the powertrain 1 to reach in and access one or more of the fasteners F11, F12, for example to check the preload value of the fasteners F11, F12. By allowing direct access for this purpose, the coupling assembly 1 can be constructed using relatively economical fasteners F11, F12, and there is no need to design the coupling assembly to be "maintenance-free".

[0048] Figure 4-Figure 10 The steps of a two-stage maintenance procedure for adjusting fasteners F11, F12 are shown. Figure 4-Figure 6 Each shows a front view (seen downwind) of the second annular plate 12 to illustrate the steps of the first stage of the procedure in which the fasteners F12 facing downwind are adjusted. Figure 4 In FIG. 1 , the access openings 13A, 13HA are shown aligned, thereby allowing a technician to access two diametrically opposed bolts F12 labeled "1" and "5". Figure 5 , the external fasteners F14 have been removed, thereby disconnecting the second annular plate 12 from the coupling ring 13. This allows the gearbox first stage (together with the second annular plate 12) to rotate independently of the coupling ring, the first annular plate and the main shaft (step D1). The arrows indicate the rotation of the second annular plate 12 (and the gearbox input shaft), and the illustration appears to allow access to the diametrically opposed bolts F12 marked "2" and "6" (step D2). These steps D1 and D2 are repeated until the maintenance personnel has access to the second annular plate 12 (and the gearbox input shaft). Figure 6 Diametrically opposed bolts F12 are shown in FIG. 1 . In a final step, after any necessary rotation of the gearbox first stage, the second annular plate 12 is once again connected to the coupling ring 13 using external fasteners F14.

[0049] Figure 7 – Fig.10 Each shows a front view (seen in the upwind direction) of the first annular plate 12 to illustrate the steps of the second stage of the procedure for accessing the fastener F11 facing upwind. Figure 7, the access openings 13A, 13HA are shown aligned, allowing the technician to access the two diametrically opposed bolts F11 marked "1" and "5". To access the additional internal fasteners F11 facing upwind, the main shaft is unlocked as described above and rotated (step U1) together with the coupling assembly 11, 12, 13 and the gearbox input shaft to a new position, for example through 45°. For this step, the first coupling plate 11 and the coupling ring 13 can be connected by a reduced set of external fasteners F13, the remaining fasteners F13 having been removed. In the example shown in FIG. Figure 8 In the new position indicated in , the access opening 13A in the coupling ring 13 is no longer aligned with the external access opening 1HA. Fig. 9 In the embodiment, all external fasteners F13 have been removed, thereby disconnecting the first annular plate 11 from the coupling ring 13 (step U2). Then, the first stage of the gearbox is rotated by an appropriate amount, thereby causing the coupling ring 13 (via the second annular plate 12) to rotate in the opposite direction and independently of the first coupling plate 11, so as to Fig.10 1HA as shown in (step U3). The diametrically opposed bolts F11 marked "8" and "4" are now accessible for maintenance (step U4). The reduced set of external fasteners F13 are then installed to reconnect the first coupling plate 11 and the coupling ring 13 (step U5). These steps U1-U5 are repeated until the maintenance personnel have access to the remaining upwind facing bolts F11. In the final step, the gearbox first stage is turned to realign the external fastener bolt pattern in the coupling ring 13 and the first annular plate 11, and the components are connected once again using the complete set of external fasteners F13.

[0050] Fig.11 Show Figure 2 and Figure 3 , further stages during a maintenance procedure in an embodiment of the present invention. The figure shows a set of shims 14 between the coupling ring and the first annular plate 11, and a set of shims 14 between the coupling ring and the second annular plate 12. The purpose of the shims 14 is to leave a gap between the coupling ring and the annular plates when the shims are removed so that the powertrain components on one side of the coupling assembly (such as the main shaft) can rotate relative to the powertrain parts on the other side of the coupling assembly (such as the gearbox input shaft). Here, the fasteners F14 between the coupling ring 13 and the second annular portion 12 have been removed so that the shims 14 can be adjusted as required. To facilitate this procedure, the coupling housing 1H is shaped as shown in the figure, with "bumps" formed adjacent to the inlet and outlet openings 1HW, 2HW to allow the shims 14 to be handled as required.

[0051] The figure also shows a bracket 16 located in the interior of the coupling ring, which can be used to support the power tool 6 (indicated by the dashed line) during maintenance steps performed on the fasteners F11 , F12 .

[0052] The step of removing the annular plate from the coupling ring 13 may be required in the preparation stage of a more complex maintenance procedure, for example when access to the bearing 21B and / or its seal 21B (which may require maintenance at some point during the service life of the wind turbine) is required. Similarly, access to the front end of the gearbox may be required to perform some maintenance tasks. For this purpose, after releasing the fasteners F14 from the second annular plate 12, the coupling housing 1H is disassembled from the main bearing housing 2H, and then the entire high-speed assembly 21, 22 can be displaced in the downwind direction using a suitable lifting device to facilitate access to the components at the front end of the gearbox. Similarly, access to the downwind end of the main shaft 201 may be required to perform some maintenance tasks. For this purpose, after releasing the fasteners F14 from the first annular plate 11, the coupling housing 1H is disassembled from the main bearing housing 2H. Similarly, the entire high-speed assembly 21, 22 (including the second annular plate 12 and the hollow shaft 13 at this time) can then be displaced in the downwind direction to facilitate access to the components at the non-drive end of the main shaft 201.

[0053] Fig.12 is an exploded view of an exemplary embodiment of a coupling assembly 1 used in the powertrain of the present invention relative to the powertrain rotation axis 2R. The figure shows that each coupling plate 11, 12 is a substantially solid annular portion extending from a central aperture to its outer circumferential portion, with threaded holes 11B, 12B as described above to receive large bolts F11, F12, so as to connect the upwind annular plate 11 to the main shaft and the downwind annular plate 12 to the first stage of the gearbox. When the apertures 13A in the coupling ring 13 are aligned with the corresponding apertures in the stationary coupling housing 1H as described above, the fasteners F11, F12 can be accessed through these apertures 13A. For a coupling assembly 1 with an outer diameter of about 2.5m and an axial length of about 1m, the access opening 13A can have an elliptical shape with a width of about 0.3m and a height of about 0.6m. These dimensions may be sufficient to allow a technician to reach in with a tool, for example, to check the preload of the fasteners F11, F12.

[0054] Each plate 11, 12 has a small hole around its outer perimeter to receive external fasteners F13, F14. The hollow shaft 13 or coupling ring 13 has an inwardly facing flange with threaded holes to receive the external fasteners F13, F14. As described above, these fasteners F13, F14 can be accessed through small windows or access ports 1HW, 2HW around the housing 1H, 2H.

[0055] Although the present invention has been disclosed in the form of preferred embodiments and variations thereof, it will be appreciated that many additional modifications and variations may be made thereto without departing from the scope of the present invention. For example, instead of reaching into the interior of the coupling assembly to adjust the internal fasteners as depicted in the accompanying drawings, a coupling assembly having a sufficiently large size may allow a technician to crawl inside to perform maintenance tasks on the internal fasteners.

[0056] For the sake of clarity, it is to be understood that the use of "a" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements.

Claims

1. A wind turbine power train (2), comprising: - low speed shaft (201); - a high-speed assembly (211, 212), the high-speed assembly (211, 212) comprising a planetary gearbox (211) and a generator (212); - a coupling assembly (1) comprising a first annular portion (11) connected to the low speed shaft (201), a second annular portion (12) connected to the first stage (212) of the planetary gearbox (211), and a cylindrical intermediate portion (13) extending between the annular portions (11, 12), - a powertrain housing (1H, 2H) arranged to enclose the low-speed shaft (201) and the coupling assembly (1); Features - an external access opening (1HA) formed in the powertrain housing (1H); - an internal access opening (13A) formed in the middle portion (13) of the coupling assembly (1) and arranged to align with the external access opening (1HA) to facilitate access to the interior of the coupling assembly (1).

2. A wind turbine power train according to the preceding claim, wherein the first annular portion (11) is fixed to the low speed shaft (201) by a first annular arrangement of axial fasteners (F11).

3. A wind turbine power train according to any of the preceding claims, wherein the second annular portion (12) is fixed to the first stage (212) of the planetary gearbox (211) by a second annular arrangement of axial fasteners (F12).

4. A wind turbine power train according to any of the preceding claims, wherein the power train housing comprises a housing section (2H) adapted to enclose a bearing arrangement (20B) around the low speed shaft (201), and a separate housing section (1H) arranged to enclose the coupling assembly (1).

5. A wind turbine power train according to any of the preceding claims, wherein the annular portion (11, 12) of the coupling assembly (1) is fixed to the middle portion (13) of the coupling assembly (1) by an arrangement of external fasteners (F13, F14).

6. A wind turbine power train according to any of the preceding claims, wherein the power train housing (1H, 2H) comprises a plurality of apertures (1HW, 2HW) arranged to facilitate access to the external fasteners (F13, F14).

7. A wind turbine power train according to any of the preceding claims, wherein the coupling assembly (1) comprises an arrangement of shims (14) between the intermediate portion (13) and the annular portions (11, 12), and wherein the shims (14) are sized to fit through an opening (1HA, 13A, 1HW, 2HW) of the power train housing (1H, 2H).

8. A wind turbine power train according to any of the preceding claims, comprising at least one bracket (16) arranged in the interior of the coupling assembly (1) to support a maintenance tool (6).

9. A method of performing a maintenance procedure on a wind turbine power train (2) according to any one of claims 1 to 8, comprising the steps of: - rotating the powertrain unit so that the internal access opening (13A) is aligned with the external access opening (1HA); - inserting the tool (6) through the aligned openings (1HA, 13A) into the interior of the coupling assembly; and - Manipulating the fasteners (F11, F12) using said tool (6).

10. A method according to the preceding claim, wherein the step of rotating the powertrain unit comprises effecting rotation of the low speed shaft (201).

11. A method according to any one of the preceding method claims, wherein the step of rotating a powertrain unit comprises effecting rotation of the gearbox first stage (212).

12. The method according to any of the preceding method claims, wherein the step of manipulating a fastener (F11, F12) using an inserted tool (6) comprises checking a preload of the fastener (F11, F12) and / or adjusting the preload of the fastener (F11, F12).

13. A method according to any one of the preceding method claims, comprising the step of disconnecting the annular portions (11, 12) from the intermediate portion (13) to facilitate rotation of the first drive train unit relative to the second drive train unit.

14. The method according to any of the preceding claims, wherein the maintenance of the second annular arrangement of axial fasteners (F12) comprises the steps of: - mounting an auxiliary drive unit to a component of the high-speed assembly (211, 212) to achieve rotation of the second annular portion (12); - disconnecting the second annular portion (12) from the intermediate portion (13); D1) actuating the auxiliary drive unit to rotate the second annular portion (12) to a position in which a plurality of the fasteners (F12) are accessible through aligned access openings (13A, 1HA); D2) Perform maintenance on accessible fasteners (F12); - repeating steps D1 and D2 until maintenance of said second annular arrangement of axial fasteners ( F12 ) has been completed; and - Connecting the second annular portion (12) to the intermediate portion (13).

15. The method according to any of the preceding claims, wherein maintenance of said first annular arrangement of axial fasteners (F11) comprises the steps of: - mounting an auxiliary drive unit to a component of the high-speed assembly (211, 212) to achieve rotation of the second annular portion (12); U1) actuating the auxiliary drive unit to rotate the low speed shaft (201) through a portion of a revolution; U2) disconnecting the first annular portion (11) from the middle portion (13); U3) actuating the auxiliary drive unit to align with the inlet and outlet openings (13A, 1HA); U4) performing maintenance on the accessible fastener (F11); U5) connecting the first annular portion (11) to the middle portion (13); - Repeating steps U1 - U5 until maintenance of said first annular arrangement of axial fasteners ( F11 ) has been completed.

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