Transmission arrangement for a wind turbine

Abstract

A transmission arrangement for a wind turbine, comprising a gearbox having a drive output, an electrical generator having a drive input, a drive shaft extending between the drive output and drive input and which defines a rotational axis. In use, torque is transmitted from the drive output to the drive input through the drive shaft. The transmission arrangement further comprises a torque bypass arrangement associated with the drive shaft, wherein the torque bypass arrangement is configured such that torque is transmitted by the torque bypass arrangement, in use, from the drive output of the gearbox to the drive input to the generator upon mechanical failure of the drive shaft. A benefit of the transmission arrangement is that the torque bypass arrangement serves as a failsafe mechanism in the event that the drive shaft experiences a failure event which compromises its capacity to transmit torque between its input end and its output end.

Description

[0001] TRANSMISSION ARRANGEMENT FOR A WIND TURBINE

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a transmission arrangement, with particular utility in the context of a wind turbine generator.

[0004] BACKGROUND OF THE INVENTION

[0005] A typical Horizontal Axis Wind Turbine (HAWT) comprises a tower, a nacelle on top of the tower, a rotor hub mounted to the nacelle and a set (usually three) of wind turbine rotor blades coupled to the rotor hub. Depending on the direction of the wind, the nacelle and rotor blades are turned and directed into an optimal direction by a yaw system for rotating the nacelle and a pitch system for rotating the blades.

[0006] The nacelle houses many functional components of the wind turbine, including for example a generator, gearbox and rotor brake assembly, as well as convertor equipment for converting the mechanical energy at the rotor into electrical energy for provision to the grid. The gearbox steps up the rotational speed of a low-speed main shaft and drives a gearbox output shaft. The gearbox output shaft in turn drives the generator, which converts the rotation of the gearbox output shaft into electricity. The electricity generated by the generator may then be converted as required before being supplied to an appropriate consumer, for example an electrical grid distribution system.

[0007] It is known that the gearbox output shaft is a single point of failure. Typically, gearbox output shafts are made from high strength machined steel. However, in recent advances it is known to manufacture gearbox output shafts, or at least portions of such shafts, from composite materials. This can bring benefits in reducing emitted sound from the rotating components of the gearbox and generator since composite components can be manufactured to have more flexibility than steel components which changes the sound profile.

[0008] It is against this background that the examples of the invention have been devised.

[0009] SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a transmission arrangement for a wind turbine, comprising a gearbox having a drive output, an electrical generator having a drive input, a drive shaft extending between the drive output and drive input and which defines a rotational axis. In use, torque is transmitted from the drive output to the drive input through the drive shaft. The transmission arrangement further comprises a torque bypass arrangement associated with the drive shaft, wherein the torque bypass arrangement is configured such that torque is transmitted by the torque bypass arrangement, in use, from the drive output of the gearbox to the drive input to the generator upon mechanical failure of the drive shaft.

[0010] A benefit of the transmission arrangement is that the torque bypass arrangement serves as a failsafe mechanism in the event that the drive shaft experiences a failure event which compromises its capacity to transmit torque between its input end and its output end. In such an event, the torque bypass arrangement becomes active to ensure continue of torque transmission. The examples of the invention are particularly beneficial for drive shafts which have some composite construction. Drive shafts having a composite construction offer some benefits in terms of increased flexibility which can reduce sound emission. However, in general composite components are known to have a less predictable failure profile compared to steel equivalents. Therefore, the torque bypass arrangement of the invention can provide a backup means of torque transmission in the event that the drive shaft undergoes a failure. Moreover, the torque bypass arrangement may be configured so that it activates to transmit torque between the drive output of the gearbox to the drive input to the generator in addition to the torque transmitted along the drive shaft itself. This may be the case where there is sufficient flexibility in the drive shaft to allow some torsional movement along the drive shaft in use, for example during heavy loading conditions. However, it may be necessary to limit the amount of torsional movement that occurs. In this case, the torque bypass arrangement can be configured so that torque transmission along a load path defined by the torque bypass arrangement can occur when there is relevant angular movement between input and output ends of the drive shaft in excess of a predetermined angular internal. Expressed another way, if there is excessive torsional movement of the driveshaft can cause torque to be transmitted along the load path defined by the torque bypass arrangement.

[0011] Further optional and advantageous features are provided in the dependent claims. In yet another aspect, the examples of the invention provide a wind turbine comprising a transmission arrangement as described above.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will now be described, by way of example only, with reference to the attached drawings, in which:

[0014] Figure 1 is a schematic diagram of a typical wind turbine, which shows the main functional components housed within a wind turbine nacelle;

[0015] Figure 2 is a view of an example of a drive shaft of the wind turbine that is used to couple the gearbox to the generator, wherein the drive shaft is provided with a torque bypass arrangement;

[0016] Figures 3 and 4 are schematic views of the drive shaft in Figure 2 which show the torque bypass arrangement operating in a ‘normal’ state and a ‘failure’ state, respectively;

[0017] Figure 5 and Figures 6a, 6b illustrate other examples of torque bypass arrangements;

[0018] Figure 7 is a view of another example of a drive shaft of a wind turbine having a torque bypass arrangement;

[0019] Figure 8 is a view of another example of drive shaft with associated torque bypass arrangement, wherein the drive shaft is shown connected between a gearbox and a generator rotor;

[0020] Figure 9 is a section view through a part of Figure 8 showing the torque bypass arrangement;

[0021] Figures 10 and 11 are simplified views, like that of Figure 9, of further examples of the invention. DETAILED DESCRIPTION

[0022] A specific example of the invention will now be described in which numerous features will be discussed in detail in orderto provide a thorough understanding of the inventive concept as defined in the claims. However, it will be apparent to the skilled person that the invention may be put into effect without the specific details and that in some instances, well known methods, techniques and structures have not been described in detail in order not to obscure the invention unnecessarily.

[0023] In order to place the examples of the invention in a suitable context, reference will firstly be made to Figure 1 , which illustrates a typical Horizontal Axis Wind Turbine (HAWT) 1 in which a transmission in accordance with the examples of the invention may be implemented. Although the wind turbine 1 is referred to as ‘horizontal axis’, it will be appreciated by the skilled person that for practical purposes, the axis is usually slightly inclined to prevent contact between the rotor blades and the wind turbine tower in the event of strong winds. The examples of the invention are considered to be applicable to other types of wind turbines, for example vertical axis machines. Further, the examples of the invention are considered to be applicable to other types of renewable energy generators using similar transmissions, which may include water-flow turbines.

[0024] The wind turbine 1 comprises a tower 2, a nacelle 4 rotatably coupled to the top of the tower 2 by a yaw system 6, a rotor hub 8 mounted to the nacelle 4 and a plurality of wind turbine rotor blades 10 coupled to the rotor hub 8. The nacelle 4 and rotor blades 10 are turned and directed into the wind direction by the yaw system 6.

[0025] The nacelle 4 houses many functional components of the wind turbine, including a gearbox 12, a generator 14 and a power converter system 16 for converting the mechanical energy of the wind into electrical energy for provision to the grid.

[0026] The gearbox 12 is driven by a low-speed main shaft 20 that is coupled to the rotor hub 8 and which extends into the nacelle 4. The main shaft 20 is supported on a suitable bearing (not shown). The main shaft 20 is driven by the rotor hub 8 and provides input drive to the gearbox 12. The gearbox 12 steps up the rotational speed of the low-speed main shaft 20 via internal gears (not shown) and drives a high-speed drive shaft 22. The drive shaft 22 in turn drives the generator 14, which converts the rotation of the drive shaft 22 into electricity. The electricity generated by the generator 14 is then converted by the power converter system 16 as required before being supplied to an appropriate consumer (e.g. an electrical grid), by a suitable conductor 26. The gearbox 12, drive shaft 22 and generator 14 therefore constitute a transmission arrangement for the wind turbine 1 .

[0027] In some arrangements the gearbox 12 and generator 14 may be coupled together in an integrated unit. However, in these cases there is still a drive shaft providing a coupling between the high-speed output of the gearbox 12 and the input of the generator 14.

[0028] The gearbox 12 may be configured in various ways. For example, conventional ‘parallel shaft’ gearboxes may be used in some applications, in which the input and output shafts of the gearbox are in a common plane and parallel to each other. Another type of gearbox to which the invention applies is an epicyclic or ‘planetary’ gearbox. As the skilled person would know, an epicyclic gearbox comprises a series of planet gears that are arranged about a central sun gear, and which collectively are arranged within an encircling ring gear. The ratio of the number of teeth between the ring gear, the planet gear and the sun gears determines the gear ratio of the gearbox. For clarity, detail of the gearbox will not be described in further detail here as the gearbox is not the principal subject of the invention. Suffice to say that other gearbox configuration could also be used, although it is currently envisaged that an epicyclic gearbox provides an elegant solution suitable for the confines of a wind turbine nacelle.

[0029] Whereas the drive shaft 22 is shown in schematic form in Figure 1 , it is shown in more detail in Figure 2, by way of example.

[0030] The drive shaft 22 is generally cylindrical in form, as is usual with drive shafts in general, and configured to be coupled between a drive output of the gearbox 12 and a drive input of the generator 14. For this purpose, the drive shaft 22 extends along a longitudinal / rotational axis X between a first end 30 and a second end 32.

[0031] The first end 30 of the drive shaft 22 is provided with a first fixing 34 and the second end 32 is provided with a second fixing 36. Both fixings 34,36 are shown as flanges in this example although the skilled person would understand that other fixings may be used, for example splined shafts, universal joints, and other couplings. The fixings 34,36, being flanges, are provided with a circular array of holes 38 which serve as bolting points when assembling the drive shaft 22 to adjacent drive components. For example, the fixing 34 would be coupled to a drive output of a gearbox 12 and the fixing 36 would be connected to a drive input of a generator 12.

[0032] The drive shaft 22 may be solid or may be a hollow component. Moreover, it may be manufactured from different materials. Typically drive shafts in this technical context are made from a high strength steel alloy, although other metallic materials are of course acceptable, subject to them having the necessary material characteristics for a particular application.

[0033] It is also known to manufacture drive shafts for wind turbine applications from composite materials. For example, a drive shaft may be formed from a carbon composite material in which carbon fibres are encased in a resin substrate. Such composite materials are generally known in the art, so a detailed discussion will not be provided here. However, composite material in this context can provide some advantageous characteristics such as a higher strength-weight ratio compared to steel and increased torsional flexibility, but they can also provide a beneficial change in the emitted noise profile. Moreover, composite materials used in the context of drive shafts can offer some electrical isolation which may be beneficial.

[0034] At least a portion of the drive shaft 22 in the illustrated example may be formed from a composite material. For example, a cylindrical section of the drive shaft extending between the first and second fixings 34,36 may be a composite material whereas the first and second fixings 34,36 may be made from metal, e.g. steel, for the purposes of providing a strong bolted connection. In other examples, substantially the entire drive shaft 22 may be formed from a composite material, including the end fixings 34,36.

[0035] In other examples, the drive shaft 22 may be integrated with an output of a gearbox 12 and / or integrated with an input to the generator 14. That is to say, the end fixings 34,36 may form an integral part of a respective rotating component of the gearbox 12 and generator 14 ratherthan coupling to specific input / output components of the generator and gearbox.

[0036] The drive shaft 22 is provided with a torque bypass arrangement 40. The function of the torque bypass arrangement 40 is to serve as a fail-safe device in the event that the drive shaft 22 experiences a mechanical failure between the first and second ends 30,32 during use such that it is unable to transmit torque along the longitudinal extent of the drive shaft 22. For example, the drive shaft 22 may develop a circumferential crack during use such that it is not able to transmit torque generated at the first end fixing 34 at the output of the gearbox 12 to the second end fixing 36 at the input to the generator 14.

[0037] In the event that such a mechanical failure of the drive shaft 22 develops, the torque bypass arrangement 40 is operable to transmit torque from the drive output of the gearbox 12 to the drive input of the generator 14.

[0038] As shown in Figure 2, the torque bypass arrangement 40 comprises a torque transmitting member 42 and a torque receiving member 44. The torque transmitting member 42 and the torque receiving member 44 are configured so that torque can only be transmitted between them upon mechanical failure of the drive shaft 22.

[0039] As can be appreciated by Figure 2, the torque transmitting member 42 comprises a main body 46 from which extends a plurality of torque arms 48. In this example, there are six (6) torque arms 48 which extend along a direction aligned with the longitudinal axis X, and in this case parallel to the axis X. The main body 46 is disc-shaped in this example, having a circular outer profile, but this is not essential. Further, the torque arms 48 are integral parts with the main body 46 in this example but, again, this is just for ease of illustration and it should be understood that this configuration is not essential.

[0040] The torque arms 48 engage with the torque receiving member 44. Here, the torque receiving member 44 comprises a main body 50 that is also disc-shaped, in the same manner as the main body 46 of the torque transmitting member 42.

[0041] In the illustrated example, the torque arms 48 engage with the main body 50 of the torque receiving member 44 by means of ends 52 of the torque arms that are received into respective sockets 54 of the torque receiving member 44.

[0042] The sockets 54 in the illustrated example are apertures that are shaped to define a gap or clearance C between the outer surface of the respective torque arm 48 and the inner surface of the socket 54. This can be seen by the inset panel in Figure 2 which shows the circular-shaped end 52 of one of the torque arms 48 that is received into the similarly- shaped socket 54. The socket 54 has a greater diameter than the end 52 of the torque arm 48 to define the clearance C. The purpose of the clearance C is to allow some relative movement between the torque transmitting member 42 and the torque receiving member 44 without torque being transmitted between these components. So, the clearance C serves to accommodate torsional flex in the drive shaft in the section between the torque transmitting member 42 and the torque receiving member 44. Typically, this will be high frequency relative movement that could otherwise result in the generation of noise. Moreover, in the context of a wind turbine there can be significant torque reversals in the drive shaft due to variable dynamic loads. So, the clearance C serves to ensure that the torque transmitting member 42 and the torque receiving member 44 do not come into contact during normal operation of the transmission.

[0043] It is considered within the capabilities of the skilled person to design an acceptable clearance between the torque transmitting member 42 and the torque receiving member 44. By way of example, the clearance C may be configured to allow a small amount of angular movement between the torque transmitting member 42 and the torque receiving member 44. The amount of angular movement permitted is not intended to be limiting, but may be at least 1 degree, for example between 5 and 10 degrees. So, in the above example, the absolute value of the clearance C may be a diametric clearance (i.e. difference of diameters) of at least 1mm, for example around 10mm to 20mm, although it is to be understood that these values are not to be considered limiting.

[0044] In the event of a mechanical failure of the drive shaft 22 between the locations of the torque transmitting member 42 and the torque receiving member 44, torque input will still be applied to the torque transmitting member 42 which will rotate with respect to the torque receiving member 44 until the ends 52 of the torque arms 48 engage with the sockets 54. As a result, the torque transmitting member 42 will move angularly greater than a distance set by the clearance C and so torque will therefore be transmitted between the ends of the drive shaft 22 indirectly, through the torque bypass arrangement 40 rather than directly along the length of the drive shaft 22 itself. It should be noted that in the illustrated example the torque transmitting member 42 and the torque receiving member 44 are joined to the drive shaft 22 at spaced apart positions such the torque bypass arrangement 40 does not cover the full length of the drive shaft 22, as shown. It should be appreciated that a greater length of the drive shaft 22 may be encompassed by the torque bypass arrangement 40 with suitable modifications. For example, the full length of the drive shaft 22 as illustrated in Figure 2 may be spanned by the torque bypass arrangement 40 by designing the main body 46 of the torque transmitting member 42 to be nearer to or integrated with the first end fixing 34 of the drive shaft 22 and, similarly, by designing the main body 50 of the torque receiving member 44 to be nearer to or integrated with the second end fixing 36 of the drive shaft 22.

[0045] Beneficially, the torque bypass arrangement 40 may also come into operation in circumstances other than mechanical failure of the drive shaft, for example in circumstances where the drive shaft undergoes torsional flex by more than a predetermined amount. In such a situation, torque would still be transmitted along a load path defined by the drive shaft, but torque would also be transmitted along a second load path defined by the torque bypass arrangement. It will be appreciated therefore that in this situation the torque bypass arrangement 40 provides a torque limiting function for the drive shaft 22 to guard against excessive torque being applied which may cause excessive wear to the material of the drive shaft 22.

[0046] This is demonstrated pictorially by Figures 3 and 4. Figure 3 illustrates the drive shaft 22 and associated torque bypass arrangement 40 in a ‘normal’ operational state. In this context, a ‘normal’ state means that the gearbox 12 and drive shaft 22 are operating as intended by their design to transmit torque along the drive shaft 22 in its rotational axis from the first end 30 of the drive shaft 22 to the second end 32, whereas the torque transmitting member 42 is not engaged with the torque receiving member 44 so torque cannot be transmitted along this path. This is shown by the inset panel where the end 52 of the torque arm 48 is shown spaced from the corresponding socket 54 of the torque receiving member 44.

[0047] In contrast, Figure 4 shows the drive shaft 22 and the associated torque bypass arrangement 40 in a ‘failure’ state. In this context, a failure state is considered to be present where there exists a mechanical failure of the drive shaft 22 at a point between its ends 30,32 and, more specifically at a point between the axial locations where the torque transmitting member 42 and the torque receiving member 44 are coupled to the drive shaft 22. In this Figure, the torque bypass arrangement 40 has been activated such that the torque transmitting member 42 is engaged with the torque receiving member 44 as can be seen in the inset panel where the end 52 of the torque arm 48 has shifted to the right so as to come into contact with the socket 54.

[0048] At this point it should be noted that the torque transmitting member 42 and the torque receiving member 44 may be coupled to the drive shaft 22 in any suitable manner. This may be by welding, or they may be bolted to the drive shaft through an appropriate flanged connection (not shown) merely by way of example.

[0049] In Figure 3, the drive shaft 22 is operating normally and so is transmitting torque between its first end 30 and its second end 22 along the length of the drive shaft 22. Here it can be seen in the inset panel that the clearance C is maintained between the ends 52 of the torque arms 48 and the respective sockets 54 of the torque receiving member 44.

[0050] In Figure 4, it can be seen that there is a breakage ‘B’ in the drive shaft 22 between the torque transmission route between the first end 30 and the second end 32. It should be noted that the breakage B does not have to be a complete destruction of the drive shaft 22 at a particular point but may include significant structural weakening such that the torque transmission capabilities of the drive shaft 22 are compromised. In either scenario, the driven end 30 of the drive shaft 22 is caused to move angularly about the longitudinal axis X with respect to the output end 32. This means that the torque transmitting member 42 also moves relative to the torque receiving member 44 which means the torque arms 48 bear against the sockets 54. This is shown in the inset panel on Figure 4. As a result, torque is transmitted along the torque bypass arrangement 40 thereby ‘bypassing’ the breakage B in the drive shaft 22 between the coupling locations of the torque transmitting member 42 and torque receiving member 44. It will be appreciated therefore that in the case of serious failure of the drive shaft 22, the torque bypass arrangement 40 provides a backup route for torque transmission. This can be particularly useful in systems where a rotor brake system engages with the transmission at a point further on or ‘downstream’ from the drive shaft, for example through a rotor brake disc integrated into the rotating components of the generator.

[0051] Configurational changes may be made to the torque bypass arrangement 40 discussed above in order to enhance functionality.

[0052] A first variant is shown in Figure 5. Here, there is shown a portion of the torque receiving member 44 similar to the inset panels in Figures 3 and 4, where a torque arm 48 is shown received in its respective socket 54 thereby defining clearance C. In this example, the clearance C accommodates a resilient bushing 60. The bushing 60 may be made from a relatively soft material such as a polymer. In addition, or as an alternative to the above example, it should also be understood that the geometry of the sockets 54 and the associated protrusions 52, or equivalent components in other non-illustrated examples, may be configured to deform plastically to result in a controlled yield in the event of contact between them. This may be combined with suitable material selection, if appropriate. For example, the material of the torque receiving member could be selected to be softer than the material of the torque transmitting member.

[0053] The bushing 60 provides the torque bypass arrangement 40 with an impact cushion 62 that serves to soften the impact of the torque transmitting member 42 on the torque receiving member 44 upon failure of the drive shaft 22. The resilient characteristics of the bushing 60 may be adapted as required to change the impact cushioning provided.

[0054] An alternative configuration of impact cushion 62 is shown in Figures 6a and 6b. In a similar manner to Figure 5, Figures 6a and 6b provide a view of a torque arm 48 received in its respective socket. However, Figure 6a shows a normal operational state of the drive shaft and torque bypass arrangement 40 whereas Figure 6b shows a failure state, the definition of which has been discussed above.

[0055] As can be seen, the socket 54 is not circular in shape as in the previous embodiment but is now formed as non-circular in form or, more specifically, oval or elliptical. The reason for this is to create an engagement of mutually inclined surfaces when the torque arm 48 engages with the socket 54 which creates a wedging effect as the end of the torque arm 48 moves laterally within the socket 54 and is forced into the elongated narrower end of the socket 54. Note that it is permissible that the torque arm 48 and the socket 54 may deform slightly in this area to achieve the wedging effect and therefore provide the impact cushion functionality as discussed above. Other forms may also be acceptable. For example, the socket 54 may have a rectilinear form other than elliptical, and the end of the torque arm 48 may also be rectilinear. Moreover, it is envisaged that the ends 52 of the torque arms 48 may be provided with a central hollow or recess (not shown) which would permit a degree of plastic deformation to occur to the ends 52 of the torque arms 48 when they are forced into engagement with the respective sockets 54. The skilled person would also conceive of other arrangements that provide comparable functionality.

[0056] An alternative example of the drive shaft 22 and bypass arrangement 40 shown in Figures 2 to 6b will now be described with reference to Figure 7, wherein the bypass arrangement will be referred to as ‘140’. The bypass arrangement 140 of Figure 7 has many similarities to the bypass arrangement 40 of Figures 2 to 6b so only the differences will be described here, for brevity.

[0057] In Figure 7, a torque transmitting member 142 and a torque receiving member 144 are coupled to the drive shaft 22 as in the previous example and are disc-shaped in form.

[0058] A plurality of torque arms 148 are coupled to the torque transmitting member 142. The torque arms 148 may be formed integrally with the torque transmitting member 142, as seen in Figure 7 or may be separate components but fixed by a suitable technique.

[0059] In this illustrated example, there are four (4) torque arms 148 that extend from the torque transmitting member 142 at equal angularly-spaced positions. As shown, the torque arms 148 extend from positions spaced about the circumference of the torque transmitting member 142.

[0060] As in the previous example, ends 152 of the torque arms 148 engage with respective sockets 154 provided at the torque receiving member 144. In this example, however, the sockets 154 are provided as recesses defined about the circumferential edge of the torque receiving member 144. A clearance C is defined between the ends 152 of the torque arms 148 and the respective sockets 154, to provide the same functionality as has already been described.

[0061] The torque bypass arrangement 140 is further provided with a bracing structure 160. The bracing structure 160 is configured to constrain the torque arms 148 from moving in a radial direction with respect to the longitudinal axis X.

[0062] The bracing structure 160 is shown here as a structural member 162 that extends in a circumferential direction and links each of the torque arms 148. The structural member 162 is shown as being monolithic with the torque arms 148 in this example, although this is not essential. Other configurations are acceptable. For example, the structural member 162 may be in the form of a band or hoop that extends around the outside of the torque arms 148 in a circumferential direction. The hoop may be separate to the torque arms 148 and secured to them by an appropriate technique, e.g. welding or by suitable mechanical fasteners such as bolts. A further example will now be described with reference to Figure 8 and 9. Due to similarities with the previous examples, the same reference numerals will be used to refer to like parts, but using the prefix ‘2’.

[0063] In Figure 8, the gearbox 212 is shown attached to the generator 214 by a drive shaft 222.

[0064] The generator 214 is shown in schematic form and an outer casing 215 of the generator 214 is shown in dashed lines. The generator 214 is shown in cross section in Figure 8.

[0065] The generator 214 comprises a stator 224 and a rotor 226. The rotor 226 is supported to rotate within the confines of the stator 224. In some examples, the rotational support for the rotor 226 may be provided by the gearbox 212, as shown here. Therefore, the rotor

[0066] 226 may be considered to be supported by the gearbox 212 in a cantilevered fashion because it is only supported on one of its ends. In other examples, the rotor 226 may be supported at both of its ends.

[0067] The stator 224 comprises a set of windings 228, as is conventional with generator structures. Likewise, the rotor 226 comprises a generally cylindrical magnetic structure

[0068] 227 that supports a set of magnetic elements (not shown). This construction of rotor therefore is able to generate a rotating magnetic field which interacts with the windings

[0069] 228 to generate an electrical current. This is conventional technology and so will not be discussed further here, for brevity. An example of such a generator is disclosed in W02020 / 143888, to Vestas Wind Systems A / S.

[0070] The structure of the rotor 226 may be known as a ‘hollow rotor’ design due to the absence of a drive shaft running the entirety of the way through the interior space of the rotor. Instead, the cylindrical rotor 216 is supported by a support structure 229 on one of its ends only.

[0071] The support structure 229 has two ends. A first or ‘outer’ end 230 is connected to a circumferentially-extending end of the magnetic structure or ‘ring’ 227 and serves as a mounting point for the magnetic ring 227. The outer end 230 will be referred to as a ‘ring mount’ from now on. A second or ‘inner’ end 232 provides a connecting hub 234 of the rotor 226. The connecting hub 234 is circular in this example. The connecting hub 234 is positioned at a radially inward position relative to the ring mount 230 of the support structure 229. A body 246 of the support structure 229 extends between the hub 234 and the ring mount 230. The body 246 extends in a radial direction between the hub 234 and the ring mount 230. The precise form of the body 246 is not crucial, since its main function is to support the ring mount 230 in a fixed radial position with respect to the hub 234. The body 246 may therefore be in the form of a solid disk, or a set of spokes, by way of example.

[0072] The drive shaft 222 is connected between the gearbox 212 and the generator 214. More specifically, the drive shaft 222 is connected between an output of the gearbox 212 and the connecting hub 234 of the generator 214.

[0073] The drive shaft 222 comprises a first end 240 and a second end 242. The first end 240 is coupled to the generator 212 and the second end 242 is coupled to the connecting hub 234 of the generator 212.

[0074] The drive shaft 222 may be a conventional shaft in the form of a cylindrical metal shaft (e.g. steel) of a single-piece design that extends between the first end 240 and the second end 242. The drive shaft 222 may also be of composite construction as discussed above, for example a carbon fibre composite of solid or, more typically, cylindrical form.

[0075] In the illustrated example, the drive shaft 222 has a compound form and includes a first section 244 and a second section 246. The first section 244 and the second section 246 are different materials. For instance the first section 244 is of a solid metal construction, whilst the second section 246 is of composite construction. In a specific example the first section 244 is steel and the second section 246 is carbon fibre composite.

[0076] Although both the first section 244 and the second section 246 may be connected together in an ‘end-to-end’ manner, in the illustrated example the second section 246 is positioned radially outward from the first section 244.

[0077] The first section 244 of the drive shaft 222 provides the first end 240 of the drive shaft 222. The first section 244 of the drive shaft 244 has a second end 248 that that connects to a first end 250 of the second section 246. A second end 252 of the second section 246 connects to the connection hub 234. The first section 244 of the drive shaft 222 is elongated and extends through the open centre of the connection hub 234. A connection flange 254 at the second end 252 of the first section 244 provides a connection interface with the first end 250 of the second section 246. This is because the outer diameter of the connection flange 254 is less than the internal diameter of the first end 250 of the second section 246 of the drive shaft 222.

[0078] The interface between the first section 244 and the second section 246 at the connection flange 254 may be achieved by any suitable means, but it is shown here as a bolted connection as provided by way of a circumferential ring of bolts 256.

[0079] Due to the arrangement of the radially outer second section 246 of the drive shaft 222 compared to the radially inner first section 244, the drive shaft 222 can be considered to have a complex load path because torque is transmitted along the first section 244 and then along the radially outer second section 246. Usefully, in the case where the radially outer second section 246 is formed from a composite material, the additional flexibility in this part can provide a useful reduction in emitted noise.

[0080] The configuration of the drive shaft 222 also provides an opportunity to achieve a second connection between the drive shaft 222 and the connecting hub 234 of the rotor. In Figure 8 this is illustrated by a torque bypass arrangement 260.

[0081] As in the example of the invention discussed previously, the torque bypass arrangement 260 of this example serves as a fail-safe device in the event that the drive shaft 222 experiences a mechanical failure between the first and second ends 240,242. For example, in the Figure 8 configuration it may be the case that the second section 246 of the drive shaft 222, being a composite component, experiences a mechanical failure which means that it is unable to transmit torque effectively to the connecting hub 234 of the rotor.

[0082] The torque bypass arrangement 260 in the illustrated example also comprises a torque transmitting member 264 and a torque receiving member 266. The torque transmitting member 264 is constituted by a disc-shaped part, whereas the torque receiving member 266 is constituted by the connecting hub 234 of the rotor.

[0083] A cross-section through the torque transmitting member 264 along the line A-A can be seen in Figure 9. With reference also to Figure 9, it can be appreciated that the torque transmitting member 264 is a separate component to the drive shaft 222 and is fixed to it by a set of bolts 267 that couple the torque transmitting member 264 to an integral flange 269 formed on the drive shaft. Other arrangements would be acceptable.

[0084] In this Figure, it can be seen that the set of bolts 267 are in a circular array which connects the torque transmitting member 264 securely to the ring-shaped flange 269.

[0085] As has been mentioned, the torque transmitting member 264 is disc-shaped in form. The torque transmitting member 264 and the torque receiving member 266 are configured in a complimentary manner so as not to come into contact with one another during normal operation of the gearbox 212 and the generator 214.

[0086] To this end, the torque transmitting member 264 is shaped to define one or more protrusions 270. There are four protrusions 270 in the illustrated example, equi-spaced about the disc angularly at 90-degree intervals. This creates a balanced transfer of torque.

[0087] In a complimentary way to the torque transmitting member 264, the torque receiving member 266 is shaped to define four sockets 272, one each in respect of the four protrusions 270.

[0088] Although in this example the torque transmitting member 264 provides protrusions 270 and the torque receiving member 277 provides the sockets 272, it should be appreciated that this configuration may be reversed.

[0089] It will be noticed that the geometry of the respective protrusions 270 and the sockets 272 are such that there is a gap or clearance C defined between them. As in the previous example, this means that the protrusions 270 and the sockets 272 do not come into contact with one another during normal operation of the gearbox 212 and the generator 214.

[0090] The clearance C provides for relative movement between the torque transmitting member 264 and the torque receiving member 266 in the circumferential direction, which may be in the form of high frequency vibration and lower frequency torque reversals. The clearance C accommodates this relative angular movement and ensures that no transmission of torque occurs during normal operation. However, in the event of mechanical failure of the drive shaft 222, for example at the second section 246, it will be appreciated that the first section 244 will twist relative to the second section 246. This will cause the torque transmitting member 264 to rotate with respect to the torque receiving member 266.

[0091] The outer surfaces of the respective protrusions 270 will therefore be forced into contact with the interior surfaces of the respective sockets 272.

[0092] The functionality of an impact cushion may be provided by various means. One option would be to incorporate a relatively soft bushing (not shown) in the clearance space C between the protrusions 27 and the sockets 272. This would provide some dissipation of energy of the impact load between the torque transmitting member 264 and the torque receiving member 266. Furthermore, it will be noticed in Figure 9 that the protrusions 270 and the sockets 272 define mutually inclined surfaces that come into contact when the torque transmitting member 264 is activated, those inclined surfaces providing a wedging effect, as discussed above.

[0093] Another option is shown in Figure 9. Here, each of the protrusions 270 is provided with an aperture 276. The apertures 276 are circular in this example although this is not essential. The apertures 276 provide a weakened region of the respective protrusions 270 such that some deformation is permitted when the protrusions 270 impact the sockets 272. The deformation of the protrusions 270 at the point of impact provide some energy dissipation and so provide the functionality of an impact cushion as discussed above thereby enhancing the wedging effect discussed above.

[0094] The skilled person would appreciate that modifications may be made to the illustrated examples without departing from the inventive concept, as defined by the claims.

[0095] For example, it will be noted in that the example illustrated in Figure 9, there are four protrusions 270 which are equi-spaced about the disc angularly at 90-degree intervals, and four respective sockets 272. However, there may be fewer or more pairs of protrusions and sockets compared to the illustrated example. Moreover, in one envisaged variant, the torque transmitting member 264 may be generally oval or elliptical in its outer profile, when seen in cross-section whereas the torque receiving member 266 may have a generally elliptical inner cross-sectional profile. Such a configuration is shown in Figure 10 in a simplified form. The complementary profiles of the torque transmitting member 264 and the torque receiving member 266 would operate in a manner that is comparable to the example illustrated in Figure 9. It will be appreciated therefore that in this example there are provided two pairs of protrusions 270 and sockets 272 having an enlarged form compared to the previously-illustrated example.

[0096] A further example is shown in Figure 11 , also in simplified form. In this example, the torque transmitting member 264 comprises a protrusion 270 which is in the form of a bar 274. The bar 274 extends radially outward and has an outer end that is received within a respective socket 272 defined in the torque receiving member 266. The geometry of the socket 272 is configured so that it is larger than the end of the bar 274 so that the result is a comparable functionality to the examples described previously. It should be noted that this configuration may be reversed so that the bar 274 may extend inwardly in a radial direction and be received into a socket defined by the torque transmitting member 264.

Claims

CLAIMS1 . A transmission arrangement for a wind turbine, comprising: a gearbox (12) having a drive output, an electrical generator (14) having a drive input, a drive shaft (22,222) extending between the drive output and drive input and which defines a rotational axis (X), wherein, in use, torque is transmitted from the drive output to the drive input through the drive shaft (22), the transmission arrangement further comprising a torque bypass arrangement (40,140,260) associated with the drive shaft, wherein the torque bypass arrangement is configured such that torque is transmitted by the torque bypass arrangement, in use, from the drive output of the gearbox to the drive input to the generator upon mechanical failure of the drive shaft.

2. The transmission arrangement of Claim 1 , wherein the torque bypass arrangement (40,140,260) comprises: a torque transmitting member (42,142,264) and a torque receiving member (44,144,266), wherein the torque transmitting member and the torque receiving member are configured such that torque is transmitted to the torque receiving member only upon mechanical failure of the drive shaft.

3. The transmission arrangement of Claim 2, wherein the torque transmitting member (42,142,264) is engageable with the torque receiving member (44,144,266) such that a clearance (C) is defined between the torque transmission member and the torque receiving member during normal operation of the transmission arrangement.

4. The transmission arrangement of Claim 3, wherein an impact cushion (62) is provided between the torque transmitting member and the torque receiving member.

5. The transmission arrangement of Claim 4, wherein the impact cushion (62) is provided by or in the clearance (C) between the torque transmitting member and the torque receiving member.

6. The transmission arrangement of Claim 5, wherein the impact cushion (62) is provided by a resilient component (60) received in the clearance (C) between the torque transmitting member and the torque receiving member.

7. The transmission arrangement of Claim 5 or 6, wherein the impact cushion (62) is further provided by mutually inclined surfaces of the torque transmitting member (42,142,264) and the torque receiving member (44,144,266), respectively such that, upon rotation of the torque transmitting member with respect to the torque receiving member exceeding a predetermined angular threshold, the mutually inclined surfaces wedge together thereby to transmit torque.

8. The transmission arrangement of any one of Claims 5 to 7, wherein the impact cushion (62) is further provided by selecting the material of at least parts of the torque transmitting member and the torque receiving member such that a controlled yield is achieved when the torque transmitting member transmits torque to the torque receiving member, in use.

9. The transmission arrangement of any one of the preceding claims, wherein the torque transmitting member (42,142,264) is coupled to the drive shaft (22,222) at a first axial position and the torque receiving member is coupled to the drive shaft at a second axial position spaced from the first axial position along the rotational axis.

10. The transmission arrangement of any one of the preceding claims, wherein the drive shaft (22,222) is formed at least in part by a composite material.

11. The transmission arrangement of Claim 10, when dependent on Claim 9, wherein the drive shaft (22,222) comprises a composite section extending at least between the first axial position and the second axial position.

12. The transmission arrangement of Claim 10, wherein the drive shaft (22,222) has a first section (244) and a second section (246), wherein the second section (246) is formed from the composite material.

13. The transmission arrangement of Claim 12, wherein the first section (244) of the drive shaft (22,222) is formed from a metallic material.

14. The transmission arrangement of Claims 12 or 13, wherein the torque transmitting member (264) is coupled to the first section (244) of the drive shaft (222).

15. The transmission arrangement of Claims 12 to 14, wherein the torque receiving member (266) is coupled to the second section (246) of the drive shaft (222).

16. The transmission arrangement of Claims 12 to 15, wherein the second section (246) of the drive shaft (222) is radially outward of the first section (244) of the drive shaft (222) relative to a rotational axis (X).

17. The transmission arrangement of Claims 10 to 16, wherein the torque receiving member (266) comprises the drive input (234) to the electrical generator (14,214).

18. A wind turbine comprising the transmission arrangement of any one of the preceding claims.

Images