WO2017045688A1

WO2017045688A1 - Wind turbine with a gear unit and an installation method and an upgrading method thereof

Info

Publication number: WO2017045688A1
Application number: PCT/DK2016/050291
Authority: WO
Inventors: Thomas Krag Nielsen
Original assignee: Envision Energy (Denmark) Aps
Priority date: 2015-09-16
Filing date: 2016-08-30
Publication date: 2017-03-23
Also published as: CN108138752B; DK201570592A1; CN108138752A; DK178869B1

Abstract

The present invention relates to a wind turbine with a nacelle comprising a gearbox unit and methods of installation and upgrading such a gearbox unit. The nacelle comprises a mainframe structure having a first and a second opening, wherein the gearbox unit is lifted into position relative to the mainframe structure through the second opening. Two separate torque arms are positioned on opposite sides of the gearbox unit, wherein a first arm of the torque arm extends into a third opening in the mainframe structure. A set of damper elements is arranged in the third opening and connected to the first arm. At least a second arm of the torque arm is axially mounted to the gearbox unit. The present configuration saves space inside the nacelle and provides a simplified dismounting and mounting process.

Description

Wind turbine with a gear unit and an installation method and an upgrading method thereof

Field of the Invention

The present invention relates to a wind turbine comprising a rotor rotatably connected to a drivetrain located in a nacelle arranged on top of a wind turbine tower, wherein the nacelle comprises a mainframe structure in which a gear unit of the drivetrain is supportably arranged. The present invention further relates to methods for installation and upgrading the gearbox unit.

Background of the Invention

It is known that drivetrains of wind turbines optionally comprise a gearbox unit mounted between the rotor and the generator unit for increasing the rotational speed of the rotor into a more suitable rotational speed for the generator unit. Such a gear box unit forms a large and expensive component which requires periodic maintenance, or even replacement, to avoid a failure. Such a maintenance or replacement process is both time consuming and expensive and it increases the downtime of the wind turbine.

The gearbox unit is subjected to rotational torque, in example, caused by a change in the power level generated by the generator unit or by a change in the rotational speed of the rotor. Also, the generator unit may be used to reduce the rotational speed of the rotor, thus subjecting the gearbox unit to a braking torque, i.e. a counteracting generator torque. The gearbox unit is also subjected to a bending moment, in example, caused by the weight of the rotor, by the aerodynamic loads on the wind turbine blades, or by misalignment between the drivetrain components. In some conventional wind turbines, the gearbox unit is mounted directly to the mainframe structure of the nacelle via mounting feet projecting from opposite sides of the gearbox housing. The mounting feet are mounted to a mainframe structure in the shape of a bedplate and require the drivetrain, including the gearbox unit, to be lifted into the bedplate via a removable top cover or a pivotal top frame of the nacelle.

Other conventional wind turbines use torque arms and dampening units to transfer the bending moment and rotational torque to the mainframe structure. Torque arms projecting from opposite radially sides of the gearbox housing are conventionally connected to individual gear stays mounted to the mainframe structure. However, each torque arm may also be connected to two dampening units arranged on opposite axially sides of that torque arm. Said dampening units are mounted to a supporting structure, e.g. a raised section of the bedplate, projecting from the mainframe structure. These support structures and gear stays take up space inside the nacelle and, thus, limit the workers' ability to move around during assembly or servicing. The support structure also requires additional material and, thus, adds to the total weight of the mainframe structure.

Secondly, the gearbox unit must be rotated in an angled position relative to the main structure during the lifting process prior to moving the gearbox unit in or out of the mainframe structure. This added step is needed since the torque arms of the gearbox unit have an outer diameter that is greater than the inner diameter of the opening in the mainframe structure. This adds to the installation time and makes it more difficult to handle the gearbox unit during lift.

WO 2007/119953 Al discloses a wind turbine having a nacelle with a mainframe structure in which a gearbox unit is arranged. The gearbox unit is connected to the rotor via a rotational torque transferring shaft extending through an opening in the mainframe structure. The gearbox unit is further connected to the generator unit via another shaft extending through another opening in the mainframe structure. Opposite facing torque arms are mounted to the side surface of the gearbox housing via matching mounting surfaces facing in a radial direction, wherein the free ends of said torque arms extend into the mainframe structure. The torque arms are connected to dampening elements for dampening the transmittal of vibrations between the gearbox unit and the mainframe structure.

Said torque arms must be mounted prior to lifting the gearbox unit into position inside the nacelle, thus adding steps to the installation process and increasing the complexity of lifting the gearbox unit into position. Also, the transfer of forces and torque are concentrated at narrow areas defined by the mounting interface between the respective torque arm and the gearbox housing, thus increasing the risk that the bolts or nuts will break off or otherwise get damaged. This solution does not allow for an upgrade of the gearbox unit to a bigger gearbox unit.

Yet another solution is to omit the torque arms and directly mount the gearbox housing to the mainframe structure, e.g. a U-shaped bedframe. However, such a solution does not allow for an upgrade of the gearbox unit as the frame structure only fits the dimensions of that gearbox unit.

EP 2495433 Al discloses a wind turbine having a mainframe structure and a gearbox with a torque arm extending from a flange of the gearbox housing. The mainframe structure is shaped as a support bed comprising a rebate on which a set of damper elements are arranged. A removable U-shaped support element is mounted to the support bed in order to encircle the free end of the torque arm and the damper elements. The mounting interfaces define weak spots which may break or otherwise fail due to the rotational torque generated in the gearbox.

US 2013/0095972 Al discloses a wind turbine having a gearbox with a gearbox housing and a nacelle with a mainframe structure, wherein torque arms are axially mounted to flanges on the gearbox housing. The free end of the torque arms are inserted into receptacles on the mainframe structure and thus supported by the mainframe structure. The structural loads and the rotational torque of the gearbox are transferred to the mainframe via the torque arms. Additional material is added to the walls of the mainframe structure in order to provide the required structural strength, however, this adds to the total weight of the mainframe structure and requires a more complex lift. Object of the Invention

An object of the invention is to provide a wind turbine with a gearbox support structure that allows for an upgrading of the gearbox unit.

An object of the invention is to provide a wind turbine with a mainframe having a reduced weight which allows for a simplified machining process of the mainframe. An object of the invention is to provide a wind turbine with a gearbox support structure that allows for an improved transfer of forces and torque between the gearbox unit and the mainframe of the nacelle. An object of the invention is to provide a method of installing a gearbox unit of a wind turbine that allows the gearbox support structure to be mounted to the gearbox unit in an axial direction.

An object of the invention is to provide a method of installing a gearbox unit of a wind turbine that reduces the complexity and time of lifting the gearbox unit into position relative to the mainframe of the nacelle.

Description of the Invention

An object of the invention is achieved by a wind turbine comprising a nacelle arranged on a wind turbine tower, a rotor with at least two wind turbine blades rotatably connected to a gearbox unit, the nacelle comprises a mainframe structure having a first opening facing the rotor and at least a second opening facing a generator unit connected to the gearbox unit, the gearbox unit defines an axial direction and a radial direction, wherein the gearbox unit is connected to the mainframe structure via at least one torque arm and at least one dampening unit, the at least one dampening unit comprises one or more damper elements configured to dampen vibrations between the gearbox unit and the mainframe structure, the at least one torque arm extends in a radial direction and comprises a first end having mounting means configured for mounting to matching mounting means on the gearbox unit, wherein said mounting means and matching mounting means are arranged in the axial direction for axially mounting the at least one torque arm, characterised in that the at least one torque arm extends into at least one third opening of the mainframe structure, wherein said one or more damper elements are arranged in said at least one third opening, wherein at least one rib element is arranged on an inner surface of the mainframe structure, and wherein the at least one rib element extends from said at least one third opening to a fourth opening of the mainframe structure facing the wind turbine tower. This provides a gearbox arrangement that enables the torque arms to be mounted in a separate step which in turn allows for a simplified and less time consuming lifting process. This allows the gearbox unit to be aligned with the mainframe structure in the axial direction prior or after it is guided through the second opening. This in turn allows for a simpler and less time consuming dismounting and mounting process during installation or replacement. This adds flexibility and upgrade capability to the gearbox mount to accommodate different configurations and sizes of the gearbox unit.

In conventional wind turbines, the torque arms form part of the outer housing of the gearbox unit which requires the gearbox unit to be rotated into an angled position so that it can be guided through the second opening of the mainframe structure. The gearbox unit must afterwards be rotated back into alignment with the mainframe structure so that it can be installed correctly. The torque arms of the present invention may be arranged in the nacelle prior to lifting the gearbox unit into its installation position and afterwards mounted to the gearbox unit. Alternatively, the gearbox unit may be lifted into position first and then the torque arms may subsequently be arranged in the nacelle and mounted to the gearbox unit. Preferably, two torque arms are arranged relative to the gearbox unit and extend outwards in opposite directions. This saves space inside the nacelle and thus allows the worker to move around inside the nacelle more freely.

The mounting means and matching mounting means may in example be bolts and nuts or threated bolt holes, screws, mounting pins and locking clips, or other suitable mounting means. The mounting means may include one or more bushing elements, e.g. elastic deformable bushing elements. Suitable mounting tools may be used to mount the torque arms to the gearbox unit.

The mainframe structure preferably has a substantially tube shaped profile defining an axial and a radial direction. The first and second openings are arranged at opposite ends wherein the first opening acts as a mounting interface for the rotor hub. The mounting interface may comprise a main bearing unit for rotatably connecting the rotor hub to the mainframe structure. The second opening may be placed in an inclined angle relative to the first opening, e.g. between 0 and 90 degrees, or a yaw bearing unit. The dimensions, e.g. the inner diameter, of the second opening may substantially correspond to the outer dimensions of only the gearbox unit. This allows the size of the second opening to be reduced compared to conventional wind turbines. In conventional wind turbines the second opening must be designed according to the gearbox unit and the projecting torque arms, thus the peripheral edge of this opening substantially follows the above-mentioned tubular profile of the mainframe structure. This increases the overall structural strength of the mainframe structure.

According to one embodiment, the at least one torque arm further comprises a first arm extending in the radial direction having a second end configured to be connected to the mainframe structure and at least a second arm on which at least a first set of the mounting means are arranged, wherein the at least second arm extends in at least a orthogonal direction relative to the first arm.

The torque arm comprises a first arm extending in the radial direction when mounted, wherein the free end of said first arm defines a connection point for connecting the torque arm to the mainframe structure. Said first arm may be configured to contact or be mounted to one or more damper elements. The torque arm may further comprise at least a second arm connected to the opposite end of the first arm. Said second arm may extend in an orthogonal direction relative to the radial direction or in a combined radial and orthogonal direction. The longitudinal axis of the second arm may thus be angled, e.g. between 0 and 90 degrees, relative to the longitudinal axis of the first arm. The free end of the second arm may define a first mounting point for mounting the torque arm to the gearbox unit, e.g. to the outer housing of the gearbox unit. The first and second arms may define a substantially L-shaped or boomerang shaped profile of the torque arm. This enables the mounting point to be moved away from a radial line extending through the centreline of the gearbox unit and the connecting point of the first arm. This in turn allows for a more optimal transfer of the forces between the gearbox unit and the mainframe structure as less material is needed compared to conventional wind turbines. Conventional torque arms require additional material in order to provide sufficient structural strength.

The torque arms are preferably arranged relative to each other so that the second arms are facing in the same or different rotational direction, e.g. a clockwise or anti- clockwise direction, or in opposite rotational directions. The rotational direction is defined relative to the rotational axis of the gearbox unit. This allows the torque arms to counteract forces generated by the rotor when rotating in a normal direction. According to a special embodiment, the at least one torque arm further comprises a third arm on which a second set of the mounting means are arranged, wherein the second and third arms are symmetrically arranged relative to the first arm and extend in opposite orthogonal directions relative to the first arm.

The torque arm may further have at least a third arm connected to the opposite end of the first arm. Said third arm may extend in another orthogonal direction relative to the radial direction or in a combined radial and orthogonal direction. The longitudinal axis of the second arm may thus be angled, e.g. between 0 and 90 degrees, relative to the longitudinal axis of the first arm. The free end of the third arm may define a second mounting point for mounting the torque arm to the gearbox unit, e.g. to the outer housing of the gearbox unit. Preferably, the second and third arms are symmetrically arranged relative to the first arm to allow an optimal transfer of forces in opposite directions. This allows the torque arms to counteract both the forces generated by the rotor, when rotating in a normal direction, and the forces generated by the rotor, when rotating in the opposite direction. In example, said wind turbine may rotate in the normal direction when operated in the normal operating mode, i.e. producing power. Rotation in the opposite direction may occur when the wind turbine is in an idling mode. The first, second and third arms may preferably define a substantially wishbone shaped profile of the torque arm. This enables the first and second mounting points to be moved away from the radial line mentioned earlier. The distance between these mounting points of the opposite facing torque arms may define a more or less squared mounting interface which in turn allows for an optimal distribution of forces in the outer housing of the gearbox unit.

The torque arm, i.e. the first arm, the second arm, and optionally the third arm, may have a planar profile with a predetermined axial thickness. This may, in turn, save material and thus reduce the total weight as no additional material is needed to provide sufficient structural strength. The torque arm may be made of metal, e.g. steel or iron, industrial grade plastic, fibre reinforced material, or another suitable material or composite. This configuration is suitable for larger gearbox units. In an alternative embodiment, the at least one torque arm comprises a single arm extending in the radial direction having a second end arranged opposite to the first end, wherein the second end is configured to be connected to the mainframe structure.

In this configuration, the torque arm may have a solid or tubular shaped profile. The first end may comprise a mounting flange on which the first and/or second sets of mounting means are arranged. The transition area between the mounting flange and the solid or tubular shaped portion may be designed to reduce stresses in the torque arm, e.g. said transition area may have a curved or tapered portion. Said mounting flange may be mounted to a matching mounting flange of the gearbox unit, e.g. located on the outer housing. The mounting flange and the matching mounting flange may be arranged to face in both the axial direction and the radial direction, or a combined axial and radial direction. In this configuration, the mounting point and connecting point are located at opposite ends of the torque arm. This configuration is suitable for smaller gearbox units.

According to one embodiment, the at least one torque arm comprises at least one side surface extending along two adjacent arms, wherein the at least one side surface has a concave shape. The torque arm may have a peripheral side surface extending along the first arm, the second arm, and optionally the third arm. The first and second arms may define a first side surface. The second and third arms may define a second side surface, and the first and third arms may define a third side surface. Each of these side surfaces may have a concave shaped side surface, i.e. curving inwards towards the intersecting point between the three arms. The first and third side surfaces may have the same or different shapes. Optionally, all three side surfaces may have the same shape. This provides an optimal transfer of forces in the torque arms as no sharp or well-defined edges exist between the mounting points and the connecting point. In turn, it also saves weight as less material is required to provide sufficient structural strength. The second side surface may preferably be shaped to follow the outer shape of the gearbox housing. This allows for the gearbox unit to be moved axially relative to the torque arm.

According to one embodiment, the distance between the first and second sets of mounting means is at least 900 millimetres, preferably between 1000 millimetres and 1300 millimetres.

A line may extend through the first and optionally second mounting point and intersect perpendicularly with the longitudinal axis of the first arm, wherein said distance is measured along this line. The torque arm preferably has a distance between the first and second mounting points of at least 900 millimetres, preferably between 1000 millimetres and 1300 millimetres. If the torque arm only comprises two arms, then the torque arm has a distance of at least 450 millimetres, preferably between 500 and 650 millimetres, measured along this line between the first mounting point and the intersection. This provides an optimal distribution of forces in the outer housing of the gearbox unit.

According to a special embodiment, the gearbox unit has an outer housing on which the matching mounting means are arranged, wherein at least one of the outer housing and the at least one torque arm comprise two flanges arranged relative to each other and which extend in the radial direction, and where one of said flanges faces the rotor and the other flange faces the generator unit. One or two flanges may be arranged on the outer surface of the gearbox housing wherein said flanges are configured for mounting to matching flanges on the torque arms. Said flanges may extend outwards from the outer housing in the radial direction. One or more matching flanges may be arranged on the torque arm at the free end of the first arm and/or of the third arm. Alternatively, at least a third flange may be arranged on the outer housing and/or on the torque arm for improved mounting.

In example, the outer housing may comprise two flanges between which the torque arm, e.g. a flange thereof, may be arranged for axially mounting the torque arm. Alternatively, a flange of the outer housing may be arranged between two flanges of the torque arm for axially mounting the torque arm. One or more bushing, as described earlier, may extend between said flanges of the torque arm and/or the gearbox housing. This allows for improved transfer of axially forces between the gearbox unit and the mainframe structure. This also allows some axial movement of the gearbox unit during rotation of the rotor.

Said flanges may be used to indicate the installation position of the gearbox unit during installation or replacement. The flanges may form part of the gearbox housing or be separate flanges mounted to the gearbox housing.

According to one embodiment, one of the at least one torque arm and the at least one dampening unit is aligned with a centreline axis of the wind turbine tower.

Preferably, the torque arms and/or the dampening units are aligned with a centreline of a fourth opening. The fourth opening may acts as a mounting interface for the wind turbine tower. This mounting interface may comprise the yaw bearing unit which is connected to the wind turbine tower. This allows for an optimal transfer of forces from the gearbox unit to the mainframe structure and further into the wind turbine tower as the wind turbine tower and at least the dampening units or torque arms, preferably also the gearbox unit, are centred relative to each other. This saves material and weight in the upper part of the wind turbine tower and, optional, in the mainframe structure as less structural strength is required.

In a special embodiment, the first arm extends into at least one third opening of the mainframe structure, wherein said one or more damper elements are arranged.

The torque arm, e.g. the first arm, may extend into a third opening arranged on a sidewall of the mainframe structure. This allows for an optimal transfer of forces to the mainframe structure as the connecting point is located within the mainframe structure. No internal support structure or separate gear stay are needed, thus material and weight of the mainframe structure may be saved. This saves space and, thus, allows the worker to move more freely around inside the nacelle. The third opening may be dimensioned to receive the first arm and the dampening unit, e.g. a set of damper elements. This allows the mainframe structure to substantially maintain its structural strength while allowing the forces to be transferred directly into the mainframe structure. This also eliminates the need for a supporting yoke surrounding the damper elements as the mainframe structure provides support for the damper elements, thus reducing the inner diameter of the third opening. Only one set of damper elements is needed, whereas conventional wind turbines use two sets of damper elements. One, two or more damper elements arranged in one or more pairs or sets are positioned in the third opening. The damper element may be an actively driven element, e.g. a hydraulic, electrical, or pneumatic driven damper, connected to a suitable energy source, e.g. a hydraulic, electrical, or pneumatic drive unit. The damper element may comprise at least one moveable element connected to or contacting the free end of the first arm. The moveable element may be configured to move relative to at least one internal chamber. The damper element may alternatively be a passive element, e.g. a spring element or an elastic deformable element. The damper element may be activated by a control unit configured to control the communication between the individual damper elements and, optionally, drive each damper element via the energy source. This adds torsional stiffness to the connection between the torque arm and the mainframe structure and dampens the vibrations in the drivetrain.

The damper elements may be interconnected via one or more cross-connections so that they are operated in opposite modes, e.g. one is compressed and one is expanded when activated. The cross-connection may be a hydraulic, electrical, pneumatic, or another suitable connection. This allows for a better control of the torsional displacement of the torque arm while allowing for a limited horizontal or vertical offset of the torque arm.

In an alternative embodiment, the at least one dampening unit is arranged on a support structure, e.g. a shelf, projecting from an inner surface of the mainframe structure, wherein said support structure forms part of the mainframe structure. In this configuration, the mainframe structure may comprise a support structure projecting from an inner surface of the sidewall, wherein this support structure may form part of the mainframe structure. The support structure may have an outer surface which at least corresponds to the dimensions of the dampening unit. Said dampening unit may be mounted to this support structure using any known mounting techniques, e.g. bolts, screws, or a mechanical coupling. Alternatively, the dampening unit may be fixed relative to this support structure using fixing means, e.g. pins and pin holes. The dampening unit may comprise a supporting yoke and a set of damper elements. The second end of the torque arm may be arranged relative to this set of damper elements. Said support structure is arranged between the first opening and the second opening, thus allowing the gearbox unit to be installed partly or fully within the mainframe structure. Some conventional wind turbines may also comprise a support structure located within the mainframe structure, however, this support structure is used to mount the main bearing unit of the main shaft while the support structure for the gearbox unit is located outside the mainframe structure, i.e. between the second opening and the generator unit.

In a special embodiment, at least one rib element is further arranged on an inner surface of the mainframe structure, wherein the at least one rib element extends from said at least one third opening to a fourth opening of the mainframe structure facing the wind turbine tower.

The mainframe structure may comprise one or more rib elements extending from said third opening and/or support structure to the fourth opening. The third opening may have a thickening extending along its peripheral edge for added structural strength. The rib elements may be configured to add structural strength to the mainframe structure. The rib elements may further comprise one or more cut-outs for saving material and weight. Optionally one or more rib elements may further be arranged between said third opening and/or support structure and the top of the mainframe structure. This allows forces from the gearbox unit to be transferred to the mainframe structure via these rib elements.

The rib elements may form part of the mainframe structure and may be manufactured in the same manufacturing process as the mainframe structure. This allows the wall thickness of at least the sides of the mainframe structure to be reduced compared with conventional wind turbines. The weight of the mainframe structure may be reduced with about one to two metric tons. According to one embodiment, the radial distance between one of the sets of mounting means and a connecting point of the first arm is at least 600 millimetres, preferably between 700 millimetres and 1000 millimetres, wherein said connecting point is defined by the one or more damper elements. The torque arm may preferably have a radial distance between the mounting point, e.g. the first or second mounting point, and the connecting point of at least 600 millimetres, preferably between 700 millimetres and 1000 millimetres. Said radial distance is measured along the longitudinal axis of the first arm between the connecting point and the intersection mentioned earlier. The first arm has a radial length measured along its longitudinal axis that at least corresponds to the radial thickness of the sidewall of the mainframe structure, preferably said radial length is at least twice the radial thickness of the sidewall. This provides an optimal transfer of forces between the gearbox unit and the mainframe structure. This also allows for an upgrade of the gearbox unit by radial adjusting the position of the torque arm relative to the third opening in the mainframe structure.

An object of the invention is also achieved by a method of installing a gearbox unit in a nacelle of a wind turbine, the nacelle comprising a mainframe structure having a first opening facing in a first direction and a second opening facing in an opposite direction, the gearbox unit defines an axial direction and a radial direction, the mainframe structure comprises at least one third opening configured to receive at least one torque arm and at least one dampening unit, wherein at least one rib element is arranged on an inner surface of the mainframe structure, and wherein the at least one rib element extends from said at least one third opening to a fourth opening of the mainframe structure facing a wind turbine tower of the wind turbine, wherein the method comprises the steps of:

lifting the gearbox unit into position relative to the mainframe structure through the second opening, connecting the gearbox unit to the mainframe structure using the at least one torque dampening unit, wherein

said step of connecting the gearbox unit further comprises mounting said at least one torque arm to the gearbox unit in the axial direction.

This provides a simplified lifting process as the gearbox unit can be moved into position in the nacelle without having to rotate the gearbox unit in order to guide it through the second opening. This allows the gearbox unit to be aligned with the mainframe structure prior to moving it through the second opening. This also reduces the complexity of the dismounting and mounting process during installation or replacement as the mounting means can be accessed in the axial direction. This further provides more space in the nacelle so that the worker can move more freely around the gearbox unit.

The gearbox unit is initially connected to an external lifting unit, e.g. crane unit, and lifted into position relative to the second opening. The gearbox unit is then guided through the second opening and finally moved, e.g. moved axially, into its installation position relative to the mainframe structure. The torque arms may be positioned inside the nacelle before or after the gearbox unit is lifted into position. The torque arms are afterwards mounted to the gearbox unit.

The present method is suitable for installing the gearbox unit in the nacelle at the top of the wind turbine tower, either at ground level at the installation site, or at a remote location. According to one embodiment, the at least one torque arm is positioned in said at least one third opening either:

prior to lifting the gearbox unit into position, or

after the gearbox unit is lifted into position.

The present configuration allows the torque arms to be handled and mounted separately of the gearbox unit which simplifies the mounting and dismounting process. The torque arms may be placed in a temporary or retracted position relative to the third opening or support structure before lifting the gearbox into position and afterwards mounted to the outer housing of the gearbox unit. Alternatively, the gearbox unit is lifted into position and the torque arms are then positioned and subsequently mounted to the gearbox unit. The dampening unit or set of damper elements may be installed before, during or after mounting the respective torque arm to the gearbox unit. No gear stay units are needed.

Conventional wind turbines disclose an installation method wherein the torque arms must be radially mounted to the gearbox prior to lifting it into position as said mounting means are not easy to access when they are placed within the mainframe structure. This also means that the receiving means, e.g. openings, located on the mainframe structure must have an increased diameter to allow the gearbox unit with torque arms to be rotated into alignment inside the mainframe structure. Otherwise the outer diameter of the gearbox unit with torque arms must be smaller than the inner diameter of the mainframe structure.

According to one embodiment, the method further comprises the step of:

- positioning one of the at least one torque arm and the at least one dampening unit relative to the fourth opening, e.g. a yaw bearing unit, of the mainframe structure so that said one of the at least one torque arm and the at least one dampening unit is aligned with a central axis of said fourth opening. The present method allows at least the torque arm or the dampening unit or set of damper elements to be positioned on the mainframe structure so that it is aligned with the centre axis of the fourth opening and, thus, the wind turbine tower. Preferably, the gearbox unit is also aligned with the fourth opening and, thus, the wind turbine tower. This allows for optimal transfer of forces from the gearbox unit to the mainframe structure and further into the wind turbine tower.

The gearbox unit may be supportably mounted onto the main shaft connected to the rotor hub. Alternatively, the gearbox unit is rotatably connected to the rotation shaft connected to the rotor hub. The gearbox unit is further connected to a generator unit via another rotation shaft. Any type of rotation shaft may be used to connect the rotor with the gearbox unit. Similarly, any type of rotation shaft may be used to connect the generator unit with the gearbox unit.

According to one embodiment, the method further comprises the steps of: radially moving the at least one torque arm in a first direction relative to the mainframe structure,

further, radially moving the at least one torque arm in a second direction relative to the mainframe structure, and

- optionally, axially moving the gearbox unit into its installation position relative to the mainframe structure prior to moving the at least one torque arm in the second direction.

The present configuration enables the torque arms to be radially adjusted to facilitate the axial movement of the gearbox unit during installation and replacement. Also, the present configuration enables the torque arms to be placed in any positions between the temporary or retracted position and an outermost mounting position.

The torque arms may be radially moved to their temporary/retracted positions when axially moving the gearbox unit into or out of its installation position. Once the gearbox unit is correctly placed in the installation position, then the torque arms may be radially moved to their respective mounting positions on the gearbox housing.

When placed in the temporary/retracted position, the dampening unit or set of damper elements may be used to hold the torque arm in its current position. Alternatively, temporary straps, wire, support elements, etc. may be used to hold the torque arm in its current position. Once the torque arm is mounted to the gearbox unit, the temporary holding means are removed.

The dampening unit or set of damper elements may be installed in the third opening or on the support structure before positioning the torque arm. Alternatively, the dampening unit or set of damper elements may be installed after the torque arm is mounted to the gearbox unit.

An object of the invention is further achieved by a method of upgrading a gearbox unit in a nacelle of a wind turbine, the nacelle comprising a mainframe structure having a first opening facing in a first direction and a second opening facing in an opposite direction, the gearbox unit defines an axial direction and a radial direction, the gearbox unit being connected to the mainframe structure by at least one torque arm and at least one dampening unit, the mainframe structure comprises at least one third opening configured to receive the at least one torque arm and the at least one dampening unit, wherein at least one rib element is arranged on an inner surface of the mainframe structure, and wherein the at least one rib element extends from said at least one third opening to a fourth opening of the mainframe structure facing a wind turbine tower of the wind turbine, wherein the method comprises the steps of:

disconnecting the gearbox unit from the mainframe structure by dismounting the at least one torque arm,

lifting the gearbox unit out of the nacelle through the second opening, lifting a new gearbox unit into position relative to the mainframe structure through the second opening, wherein said new gearbox unit differs from the gearbox unit,

reconnecting the new gearbox unit to the mainframe structure by remounting the at least one torque arm. The present method and configuration is also suitable for upgrading the gearbox unit to a bigger gearbox unit or to a gearbox unit having a different configuration. This, in turn, means that the power output of the wind turbine can be increased from a current level to a higher level, e.g. from 3 megawatt to 3.3 megawatt. The old gearbox unit is initially disconnected from the rotor and the generator unit. The torque arms are then dismounted from the gearbox unit, and optionally the dampening unit or set of damper elements is released or dismounted to allow a radial movement of the torque arms. The torque arms are then moved into their retraction positions. The gearbox unit is then axially moved out of its installation position and lifted through the second opening.

A new gearbox unit is afterwards lifted through the second opening and axially moved into its installation position. The torque arms are then radially moved into their mounting positions on the outer housing of this new gearbox unit. The torque arms are remounted and optionally the dampening unit or set of damper elements is reconnected to the torque arms. Finally, the new gearbox unit is reconnected to the rotor and the generator unit. This provides a simple and easy replacement of the gearbox unit without having to also replace the mainframe structure or torque arms, and this saves time and costs in connection with upgrading the wind turbine. This upgrade process may further include replacing other components of the drive train, e.g. the generator unit.

According to one embodiment, said step of disconnecting the gearbox unit further comprises radially moving the at least one torque arm in a first radial direction relative to the mainframe structure after being dismounted. According to one embodiment, said step of reconnecting the gearbox unit further comprises radially moving the at least one torque arm in a second radial direction relative to the mainframe structure prior to remounting said at least one torque arm.

In a preferred configuration, each torque arm is radially moved from a first mounting position defined by the old gearbox unit to the retracted position. Once the new gearbox unit is correctly positioned relative to the mainframe structure, each torque arm is radially moved into a new mounting position defined by the new gearbox unit.

During this radial movement, the first arm is moved in or out of the third opening or moved radially relative to the support structure. This allows the position of the torque arms to be adjusted according to different sized gearbox units. Description of the Drawing

The invention is described by example only and with reference to the drawings, wherein:

Fig. 1 shows an exemplary embodiment of a wind turbine,

Fig. 2 shows a conventional gearbox unit with integrated torque arm,

Fig. 3 shows a first embodiment of the gearbox unit according to the invention,

Fig. 4 shows a second embodiment of the gearbox unit according to the invention,

Fig. 5 shows a third embodiment of the gearbox unit according to the invention,

Fig. 6 shows a perspective view of the mainframe structure shown in figs. 3-5,

Fig. 7 shows an exemplary embodiment of the torque arms and the flanges of the gearbox housing, and

Fig. 8 shows an exemplary embodiment of the torque dampening unit. In the following text, the figures will be described one by one and the different parts and positions seen in the figures will be numbered with the same numbers in the different figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure. Reference list

1. Wind turbine

2. Wind turbine tower

3. Nacelle

4. Wind turbine blades

5. Tip end

6. Blade root

7. Leading edge

8. Trailing edge

9. Conventional torque arm

10. Gearbox housing, outer housing

11. Gearbox unit

12. Mainframe structure

13. First opening

14. Inner surface

15. Support structure

16. Fourth opening

17. Dampening unit

18. Torque arm

19. Torque arm

20. Third opening

21. First set of mounting means

22. Second set of mounting means

23. Torque arm

24. Rotational direction

25. Second opening

26. Rib element

27. Flanges

28. Damper elements 29. Yoke

Detailed Description of the Invention

Fig. 1 shows an exemplary embodiment of a wind turbine 1 comprising a wind turbine tower 2. A nacelle 3 is arranged on top of the wind turbine tower 2 and connected to the wind turbine tower 2 via a yaw mechanism (not shown). A rotor comprising at least two wind turbine blades 4, here three blades are shown, is rotatably connected to a rotor hub which in turn is connected to a drive train arranged inside the nacelle 3 via a rotation shaft. The wind turbine blade 4 is rotatably connected to the hub via a pitch mechanism (not shown). Each wind turbine blade 4 has a tip end 5, a blade root 6 and a body having an aerodynamic profile which defines a leading edge 7 and a trailing edge 8.

Fig. 2 shows a conventional gearbox unit with two torque arms 9 projecting from an outer housing 10 of the gearbox unit, here only one torque arm is shown for illustrative purposes. The torque arms 9 form part of this gearbox housing 10 wherein the free ends of the torque arms are configured to be connected to a gear stay unit (not shown) arranged inside the nacelle 3. The gearbox unit and torque arms 9 thus form a single unit which is lifted into position and installed inside the nacelle 3. Fig. 3 shows a first embodiment of a gearbox unit 11 according to the invention wherein only a part of the outer housing of the gearbox unit 11 is shown for illustrative purposes. The gearbox unit 11 is arranged relative to a mainframe structure 12 of the nacelle 3. The mainframe structure 12 comprises a first opening 13 which faces the rotor when mounted and a second opening (shown in fig. 6) which faces a generator unit when mounted. The mainframe structure 12 further comprises an inner surface 14 which faces the gearbox unit 11.

At least one support structure 15 located between the first opening 13 and the second opening projects inwards from the inner surface 14. Preferably, two opposite facing support structures 15 are located on either side of the mainframe structure 12. The support structure 15 forms part of the mainframe structure as indicated in fig. 3. One or more rib elements extend from the support structure 15 towards an opening 16 facing the wind turbine tower 2 for adding structural strength. The support structure 15 and thus the gearbox unit 11 are preferably aligned with a central axis of the opening 16. This allows for optimal transfer of forces from the mainframe structure 12 to the wind turbine tower 2. A dampening unit 17 is arranged on an outer surface of each support structure 15. The dampening unit 17 is arranged relative to a torque arm 18 having a rod or tubular shaped profile extending along its longitudinal axis. A first end of the torque arm 18 comprises one or more mounting means, e.g. a mounting flange, for mounting to matching mounting means, e.g. a mounting flange, on the outer housing of the gearbox unit 12. Preferably, the first end comprises at least one set of mounting means which defines at least one mounting point. A second end of the torque arm 18 is connected to damper elements (shown in fig. 8) in the dampening unit 17. Torque and other forces from the gearbox unit 11 are transferred to the mainframe structure 12 via the torque arm 18, the dampening unit 17 and the support structure 15.

The torque arm 18 is here mounted radially to the gearbox housing 10. However, the torque arm 18 may also be mounted axially by changing the orientation of the mounting means and the matching mounting means. Fig. 4 shows a second embodiment of the gearbox unit and the torque arms. Here, the torque arms 19 are axially mounted to the gearbox unit 1 as shown in fig. 7. The mainframe structure 12' comprises at least one third opening 20, e.g. a through hole, arranged in the inner surface 14'. Each torque arm 19 has a wishbone shaped profile comprising a first arm extending in the radial direction which defines a connecting point between the torque arm 19 and the mainframe structure 12' . The connection point is defined by a set of damper elements (shown in fig. 7). The torque arm 19 further comprises a second arm and a third arm arranged symmetrically relative to the first arm. The second and third arms extend at least partly in an orthogonal direction relative to the longitudinal direction of the first arm as indicated in fig. 4. A first set 21 of mounting means is arranged on the second arm which defines a first mounting point. A second set 22 of mounting means is arranged on the third arm which defines a second mounting point. Preferably, two opposite facing torque arms 19 are located on either side of the gearbox unit I V . Each torque arm 19, e.g. the first arm, extends into a corresponding third opening 20 in the mainframe structure 12' as shown in fig. 4. This torque arm 19 allows for a greater distance between the mounting points compared to the torque arm 18 of fig. 3. This, in turn, allows for a more optional distribution of the forces in the outer housing of the gearbox unit 11 ' and allows the torque arms 19 to transfer forces in both rotational directions, i.e. in the clockwise and anti-clockwise directions.

Fig. 5 shows a third embodiment of the gearbox unit and the torque arms. Here, the torque arms 23 differ from the torque arms 19 by only comprising two arms.

Each torque arm 23 has a boomerang shaped profile comprising a first arm extending in the radial direction which defines the connecting point between the torque arm 23 and the mainframe structure 12'. The torque arm 23 further comprises another arm extending at least partly in an orthogonal direction relative to the longitudinal direction of the first arm as indicated in fig. 5. A set of mounting means is arranged on that arm and defines a mounting point for the gearbox unit 11" .

Preferably, two opposite facing torque arms 23 are located on either side of the gearbox unit 11". The two torque arms 23 are arranged relative to each other so that the at least partly orthogonal arms both face in the same rotational direction (indicated by arrow 24) relative to the gearbox unit 11" as shown in fig. 5. One torque arm 23 is thus mounted to the matching mounting means of the first set 21 while the other torque arm 23 is mounted to the matching mounting means of the second set 22. This allows the torque arms 23 to transfer forces in a selected rotational direction, e.g. the anti-clockwise direction, during normal rotation of the rotor.

Fig. 6 shows a perspective view of the mainframe structure 12' wherein the gearbox unit 11 ' is arranged. Here, only part of the outer housing of the gearbox unit 11 ' is shown for illustrative purposes.

The mainframe structure 12' has a tube shaped profile defining an axial and a radial direction, wherein the first opening 13 and the second opening 25 are arranged at opposite ends as indicated in fig. 6. The second opening 25 is placed at an inclined angle relative to the first opening 13 and the opening 16, i.e. the fourth opening. The dimensions of the second opening 25 substantially correspond to the outer dimensions of the gearbox unit 1 , thus the second opening 25 is smaller than the dimensions of the tube shaped profile. This, in turn, adds structural strength to the mainframe structure 12' .

The third opening 20 and, thus, the gearbox unit 11 ' are preferably aligned with the central axis of the fourth opening 16. This allows for an optimal transfer of forces to the mainframe structure 12'. At least one rib element 26 extends from the peripheral edge of the third opening 20 to the peripheral edge of the fourth opening 16. This further adds structural strength to the mainframe structure 12' .

The mounting and dismounting process will now be described in reference to fig. 6. The gearbox unit 11 ' is lifted into position relative to the second opening 25 and guided through this opening. The gearbox unit 11 ' is then moved, e.g. axially, into position relative to the mainframe structure 12' and installed. The torque arms 19 are preferably placed inside the mainframe structure 12' in their retracted positions prior to performing the lift. The torque arms 19 are then moved, e.g. radially, into their mounting positions and then mounted to the gearbox unit 11' . During replacement or upgrading, the torque arms 19 are moved back into their retracted positions and the old gearbox unit 11 ' is dismounted and removed from the mainframe structure 11 ' in a reversed order. The new gearbox unit 11 ' is afterwards lifted into a position as described above and the torque arms 19 are moved into their new mounting positions and then mounted. The gearbox unit 11 ' is finally installed in the mainframe structure 12'.

Fig. 7 shows an exemplary embodiment of the outer housing of the gearbox unit 11 where two flanges 27 are arranged on the gearbox housing. The flanges 27 project radially from the outer housing wherein the second and third arms of the torque arms 19 are placed between these flanges 27 when mounted. The sets 21, 22 of mounting means and matching mounting means extend in the axial direction as illustrated in fig. 7 and, thus, allows for an axial mounting of the torque arms 19. The torque arm 19 is, at the connecting point, connected to a set of damper elements 28 configured to dampen the torsional movement and vibrations of the gearbox unit 11. The damper elements 28 are arranged inside the third opening 20 when mounted. Fig. 8 shows an exemplary embodiment of the dampening unit 17 wherein the damper elements 28 are arranged relative to a supporting yoke 29. The torque arm 18 is positioned between the damper elements 28 as illustrated in fig. 8. Here, only a part of the torque arm 18 is shown for illustrative purposes. The yoke 29 is configured to hold the damper elements 28 in place and transfer the forces from the gearbox unit 11 further into the mainframe structure 12. The yoke 29 comprises suitable fixing or mounting means, e.g. bolts or pins, for holding the dampening unit 17 in place on the support structure 15.

Claims

1. A wind turbine comprising a nacelle arranged on a wind turbine tower, a rotor with at least two wind turbine blades rotatably connected to a gearbox unit, the nacelle comprises a mainframe structure having a first opening facing the rotor and at least a second opening facing a generator unit connected to the gearbox unit, the gearbox unit defines an axial direction and a radial direction, wherein the gearbox unit is connected to the mainframe structure via at least one torque arm and at least one dampening unit, the at least one dampening unit comprises one or more damper elements configured to dampen vibrations between the gearbox unit and the mainframe structure, the at least one torque arm extends in the radial direction and comprises a first end having mounting means configured for mounting to matching mounting means on the gearbox unit, wherein said mounting means and matching mounting means are arranged in the axial direction for axially mounting the at least one torque arm, characterised in that the at least one torque arm extends into at least one third opening of the mainframe structure, wherein said one or more damper elements are arranged in said at least one third opening, wherein at least one rib element is arranged on an inner surface of the mainframe structure, and wherein the at least one rib element extends from said at least one third opening to a fourth opening of the mainframe structure facing the wind turbine tower.

2. A wind turbine according to claim 1, characterised in that the at least one torque arm further comprises a first arm extending in the radial direction having a second end configured to be connected to the mainframe structure and at least a second arm on which at least a first set of the mounting means are arranged, wherein the at least second arm extends in at least a orthogonal direction relative to the first arm.

3. A wind turbine according to claim 2, characterised in that the at least one torque arm further comprises a third arm on which a second set of the mounting means are arranged, wherein the second and third arms are symmetrically arranged relative to the first arm and extends in opposite orthogonal directions relative to the first arm.

4. A wind turbine according to claim 2 or 3, characterised in that the at least torque arm comprises at least one side surface extending along two adjacent arms, wherein the at least one side surface has a concave shape.

5. A wind turbine according to any one of claims 2 to 4, characterised in that the distance between the first and second sets of mounting means is at least 900 millimetres, preferably between 1000 millimetres and 1300 millimetres.

6. A wind turbine according to any one of claims 1 to 5, characterised in that the gearbox unit has an outer housing on which the matching mounting means are arranged, wherein at least one of the outer housing and the at least one torque arm comprises two flanges arranged relative to each other and which extend in the radial direction, and where one of said flanges faces the rotor and the other flange faces the generator unit.

7. A wind turbine according to any one of claims 1 to 6, characterised in that one of the at least one torque arm and the at least one dampening unit is aligned with a centreline axis of the wind turbine tower.

8. A wind turbine according to any one of claims 2 to 5, characterised in that the radial distance between one of the sets of mounting means and a connecting point of the first arm is at least 600 millimetres, preferably between 700 millimetres and 1000 millimetres, wherein said connecting point is defined by the one or more damper elements.

9. A method of installing a gearbox unit in a nacelle of a wind turbine, the nacelle comprising a mainframe structure having a first opening facing in a first direction and a second opening facing in an opposite direction, the gearbox unit defines an axial direction and a radial direction, the mainframe structure comprises at least one third opening configured to receive at least one torque arm and at least one dampening unit, wherein at least one rib element is arranged on an inner surface of the mainframe structure, and wherein the at least one rib element extends from said at least one third opening to a fourth opening of the mainframe structure facing a wind turbine tower of the wind turbine, wherein the method comprises the steps of: lifting the gearbox unit into position relative to the mainframe structure through the second opening,

connecting the gearbox unit to the mainframe structure using the at least one torque dampening unit, characterised in that

- said step of connecting the gearbox unit further comprises mounting said at least one torque arm to the gearbox unit in the axial direction.

10. A method according to claim 9, characterised in that the at least one torque arm is positioned in said at least one third opening either:

- prior to lifting the gearbox unit into position, or

after the gearbox unit is lifted into position.

11. A method according to claim 9, characterised in that the method further comprises the step of:

positioning one of the at least one torque arm and the at least one dampening unit relative to the fourth opening, e.g. a yaw bearing unit, of the mainframe structure so that said one of the at least one torque arm and the at least one dampening unit is aligned with a central axis of said fourth opening.

12. A method according to any one of claims 9 to 11, characterised in that the method further comprises the steps of:

radially moving the at least one torque arm in a first direction relative to the mainframe structure,

optionally, axially moving the gearbox unit into its installation position relative to the mainframe structure prior to moving the at least one torque arm in the second direction.

13. A method of upgrading a gearbox unit in a nacelle of a wind turbine, the nacelle comprising a mainframe structure having a first opening facing in a first direction and a second opening facing in an opposite direction, the gearbox unit defines an axial direction and a radial direction, the gearbox unit being connected to the mainframe structure by at least one torque arm and at least one dampening unit, the mainframe structure comprises at least one third opening configured to receive the at least one torque arm and the at least one dampening unit, wherein at least one rib element is arranged on an inner surface of the mainframe structure, and wherein the at least one rib element extends from said at least one third opening to a fourth opening of the mainframe structure facing a wind turbine tower of the wind turbine, wherein the method comprises the steps of:

lifting the gearbox unit out of the nacelle through the second opening,

- lifting a new gearbox unit into position relative to the mainframe structure through the second opening, wherein said new gearbox unit differs from the gearbox unit,

reconnecting the new gearbox unit to the mainframe structure by remounting the at least one torque arm.

14. A method according to claim 13, characterised in that said step of disconnecting the gearbox unit further comprises radially moving the at least one torque arm in a first radial direction relative to the mainframe structure after being dismounted.

15. A method according to claim 13 or 14, characterised in that said step of reconnecting the gearbox unit further comprises radially moving the at least one torque arm in a second radial direction relative to the mainframe structure prior to remounting said at least one torque arm.