CN114761683A - Wind turbine - Google Patents

Abstract

The present invention provides a wind turbine comprising: a turbine rotor including a set of turbine rotor blades and defining a rotor axis of rotation, the turbine rotor mounted on a tower; a generator for converting mechanical energy of the turbine rotor into electrical energy, the generator comprising a generator rotor drivingly coupled to the turbine rotor and mounted on the tower; a transmission system coupling the turbine rotor to the generator rotor and comprising: an upstream stepped planetary gearbox comprising: an upstream ring gear drivingly coupled to the turbine rotor; an upstream first planet gear drivingly coupled with the upstream ring gear; upstream second planet gears each rotationally coupled with the first planet gears; and an upstream sun gear drivingly coupled to the upstream second planet gears and to the generator rotor, wherein the upstream second planet gears are axially offset from each other.

Description

Wind turbine

Technical Field

The present invention relates to a wind turbine and a transmission for a wind turbine.

Background

WO2015016703 relates to a wind turbine comprising: a rotor coupled to a rotor shaft defining a rotor rotation axis, the rotor including a set of rotor blades; an outer vertical drive shaft and an inner vertical drive shaft coaxially located within the first vertical drive shaft, the inner and outer vertical drive shafts being coupled to the rotor shaft; a generator for converting mechanical rotational energy of the rotor into electrical energy and comprising coaxial inner and outer generator rotors coupled to the inner and outer vertical drive shafts; and a gear system coupling the inner and outer drive shafts to the rotor shaft. A gear system allows coupling the rotor shaft to the inner and outer vertical drive shafts, wherein the drive shaft rotation axis of the inner and outer vertical drive shafts and the rotor rotation axis allow a horizontal turbine rotor axis to tilt by an angle of between 1 and 10 degrees.

WO9521326 describes according to its abstract a wind power system comprising: a wind turbine having a horizontal rotor mounted on bearings and rotatable about a vertical axis; a primary energy unit; a mechanical transmission having reduction gears; and a system for rotating the wind turbine about a vertical axis. The mechanical transmission reduction gear has an output designed as two coaxial shafts whose dynamic connection with the reduction gear input shaft ensures that the coaxial shafts rotate in opposite directions. The mechanical transmission reduction gear has a primary energy unit in the form of two counter-rotating, cooperating working units, each connected to one coaxial reduction gear shaft. The structural design of the system compensates for the reactive torque acting on the wind turbine in the horizontal plane without any additional power consuming mechanism.

WO2015/127589 is described in its abstract: a transmission arrangement (1000) for a wind turbine is disclosed. The transmission structure is composed of a spiral bevel gear mechanism (100) arranged in a cabin (92) and a planetary gear speed-increasing gearbox (200) arranged in a tower (93), wherein an impeller (91) is connected to an input shaft of the spiral bevel gear mechanism (100), an output shaft of the spiral bevel gear mechanism is connected to an input shaft of the planetary gear speed-increasing gearbox (200), and an output shaft of the planetary gear speed-increasing gearbox (200) is connected to a generator set (94); and the output shaft of the spiral bevel gear mechanism (100) is coaxial with the input shaft of the planetary gear increasing gearbox (200) and has the same axial direction with the tower drum (93). The transmission structure (1000) has high reliability and low failure rate, and is easy to disassemble, assemble and maintain. "

US6607464 is described in its abstract: "transmission, in particular for a wind power installation, comprises a planetary stage on the input side, which is mounted upstream of at least one gear stage. The planetary stage comprises at least two power dividing planetary gears mounted in parallel. The differential gears installed downstream of the power dividing planet gears compensate for the unequal load distribution between the individual planet gears caused by their parallel arrangement. "

US2017/030335 is described in its abstract: "a drive system for a wind turbine comprises: a transmission gear configured to be connected to the wind rotor shaft, the transmission gear having a first planetary gear set and a second planetary gear set; and a generator downstream of the transmission gear. The transmission gear and the generator are mounted in plain bearings. "

WO2011/047448 describes in its abstract: the invention provides a planetary gear unit (23) for a gearbox of a wind turbine, the planetary gear unit (23) comprising a ring gear (10), a sun gear (11) and planet gears (25, 26). The ring gear (10) and the sun gear (11) each have a double helical gear and are each made from one piece. The planet gears (25, 26) are rotatably mounted on planet shafts (14) in a planet carrier (24) by means of bearings (13) and are mounted for interaction between the ring gear (10) and the sun gear (21). A first number of planet gears (25) are disposed in a first plane (a) and a second number of planet gears (26) are disposed in a second plane (B), the second plane (B) being axially displaced with respect to the first plane (a) by a distance (D), and the planet gears (25) in the first plane (a) being axially displaced with respect to the planet gears (26) in the second plane (B). According to an embodiment of the invention, the planet carrier (24) comprises two separate parts (27, 28), wherein a first part (27) of the planet carrier (24) has a first number of planet shafts (14) for the first number of planet gears (25) and a second part (28) of the planet carrier (24) has a second number of planet shafts (14) for the second number of planet gears (26), and wherein the first and second parts (27, 28) are complementary. "

In particular, applicant's WO2019022595 provides a wind turbine comprising: -a turbine rotor comprising a set of turbine rotor blades and defining a rotor rotation axis, the turbine rotor being mounted on a tower;

a gearbox drivingly coupled to the turbine rotor and having an output for increasing an output rotational speed when in operation;

a generator for converting mechanical energy of the turbine rotor into electrical energy, the generator being mounted at an end of the tower near the rotor axis of rotation and comprising a first generator rotor and a second generator rotor having an air gap therebetween and being mounted rotatable relative to each other for converting rotational motion into electrical energy;

a transmission system, comprising:

an outer drive shaft and an inner drive shaft concentrically located within the outer drive shaft;

a drive shaft gear system coupling the inner drive shaft and the outer drive shaft to the gearbox, wherein the axes of rotation of the inner drive shaft and the outer drive shaft are functionally perpendicular to the rotor axis of rotation, wherein

The drive shaft system includes a drive shaft gear drivingly coupled with the gearbox and the drive shaft gear engages a first drive gear on the inner drive shaft and engages a second drive gear on the outer drive shaft and is arranged to, in operation, rotate the inner and outer drive shafts counter to each other and wherein one of the inner and outer drive shafts is drivingly coupled to the first generator rotor and the other of the inner and outer drive shafts is drivingly coupled to the second generator rotor.

US4291233 is described according to its abstract: "A wind turbine generator system that converts rotational energy of wind-driven turbine blades into rotation of a rotor and a stator of an electric machine in opposite directions to produce electrical power. Bevel gears rotating with the turbine blades drive the two pinions and associated concentric shafts in opposite directions. The two shafts are combined with a planetary gear set to provide the required reverse rotation. A shaft is associated with the ring carrier and drives the ring gear in one rotational direction. The other shaft drives the planet carrier in the opposite rotational direction. The planetary gear sets are arranged so as to drive the sun gear in a direction opposite to that of the ring gear. The rotor is attached to the sun gear by a tripod support structure, and a stator attached to rotate with the ring gear surrounds the rotor. Thus, the rotor and stator rotate in opposite mechanical and electrical additive directions. "

Disclosure of Invention

It is an aspect of the present invention to provide an alternative wind turbine design.

There is therefore provided a wind turbine comprising:

a turbine rotor including a set of turbine rotor blades and defining a rotor axis of rotation, the turbine rotor mounted on a tower;

a generator for converting mechanical energy of the turbine rotor into electrical energy, the generator comprising a generator rotor drivingly coupled to the turbine rotor and mounted on the tower;

a transmission system coupling the turbine rotor to the generator rotor and comprising:

an upstream stepped planetary gearbox.

The upstream stepped planetary gearbox comprises: an upstream ring gear drivingly coupled to the turbine rotor; an upstream first planet gear drivingly coupled with the upstream ring gear; upstream second planet gears each rotationally coupled with the first planet gears; an upstream sun gear drivingly coupled to the upstream second planet gears and to the generator rotor, and the upstream second planet gears are axially offset from each other.

In another aspect, the upstream stepped planetary gearbox includes a common carrier that rotationally carries the upstream first and second planet gears rotatable about their axes of rotation, that rotationally carries the upstream sun gear, and that rotationally carries the upstream ring gear.

In another aspect, the upstream stepped planetary gearbox comprises each of said upstream first planet gears being rotatably carried on a fixed pin and each of said upstream second planet gears being rotatably carried on said fixed pin, and said upstream first planet gears and said upstream second planet gears on said pin are rotationally coupled, in particular via a flexible coupling, more in particular via a shaft extending through said fixed pin.

In another aspect, the upstream stepped planetary gearbox includes a common carrier that carries a pin that rotatably carries the upstream sun gear.

Stepped planetary gearboxes are also known as compound planetary gearboxes. Such gearboxes include a planetary gear train with compound planet gears. Each compound planet gear comprises a pair of rigidly connected and longitudinally arranged gears having different radii, i.e. a first and a second planet gear. The gears have a common axis of rotation. One of the two gears engages the centrally located sun gear and the other gear engages the outer ring gear.

There is further provided a wind turbine comprising:

a turbine rotor including a set of turbine rotor blades and defining a rotor axis of rotation, the turbine rotor mounted on a tower;

A generator for converting mechanical energy of the turbine rotor into electrical energy, the generator comprising a generator rotor drivingly coupled to the turbine rotor and mounted on the tower;

a transmission system coupling the turbine rotor to the generator rotor and comprising:

a bevel gear box comprising a bevel drive gear coupled to a turbine rotor and a first bevel pinion and a second bevel pinion, wherein the first and second bevel pinions have a common axis of rotation and counter-rotate when operated;

a downstream planetary gearbox comprising a downstream ring gear, downstream planet gears and a downstream sun gear, wherein the first bevel pinion is drivingly coupled to one of the downstream ring gear and the downstream planet gears, the second bevel pinion is drivingly coupled to the other of the downstream ring gear and the downstream planet gears, and the generator rotor is drivingly coupled to the downstream sun gear.

Wind turbines are suitable for new generation wind turbines with capacities of 10MW or more for various wind climates. Specifically, this design enables the next generation of large wind turbines in the 12-16MW + class. It can operate in IEC I, II, III + and IV + grade wind regions. The number of rotating parts is limited as much as possible while using journal bearings to improve reliability performance. The design is particularly suitable for large wind turbines due to specific technical solutions taking into account (minimizing) component and system deflections and deformations inherent to the large wind turbine concept and economic reasons. It allows a compact design with high speed (in the wind turbine sense) output.

The current design is suitable for both windward and downwind designs of wind turbines.

In the present description, the elements may be coaxial. Coaxial in this connection means that the elements each rotate about an axis of rotation, and that the axes of rotation are in a straight line or coincide.

Some differences from other earlier designs are particularly as follows.

In fact, the downstream planet gears may be integrated into the bevel gear box. In an embodiment, the downstream planetary gearbox is attached to, in particular integrated with, one of the bevel pinions.

The turbine shaft may be a hollow shaft held in two pre-biased bearings, in particular conical bearings in the housing. Such a construction part is also referred to as a main bearing unit or MBU. For example, the Eolotec company describes in US2015030277 examples of such construction elements that may be used in the present invention. In such shafts, the shaft includes a tapered section extending between spaced bearings. The pre-biasing or pre-loading of the bearings towards each other may be controlled using a control device. Other configurations known to the skilled person having, for example, a single rotor bearing may also be used.

Numerous other aspects are described in the appended dependent claims. In addition, many other aspects are summarized in the appended clauses.

In an embodiment of the drive train, the turbine shaft comprises a main bearing unit or MBU. In this embodiment, the bearing unit is the only major element rigidly attached to the cast main bracket, thereby forming the structural major component of the nacelle structure or chassis. The other main components are attached to this main bearing unit via a flange connection, rather than being directly connected to the chassis by other means. The main benefit of this solution is that any dynamic (non-torque) deformations and deflections in the chassis and/or the main carrier do not adversely affect the integrity of the drive train.

Typically, to avoid or bear rotor induced bending moments and additional loads and load variations, the turbine shaft is coupled to a flexible or resilient coupling. In wind turbines, various flexible couplings are known. For example, Geislinger describes an example of a suitable flexible coupling, which is referred to as a "Geislinger compoindd coupling". Generally, such couplings combine torsional stiffness with built-in flexibility in response to rotor induced bending loads, thereby providing a torsionally resilient shaft coupling. The flexible coupling may comprise different conceptual solutions, but the main functional working principle is still essentially to eliminate any possibility of harmful non-torque loads (bending moments) entering the gearbox.

Current wind turbines may include any general type of generator. For example, the generator may comprise an axial flux generator. Alternatively, a radial flux generator may be used. These generator types may have conventional generator designs.

The generator may be a permanent magnet generator but may equally comprise a synchronous machine type generator requiring an externally started generator-rotor field current. However, the use of permanent magnet generators, in particular "outer wheel" or outer rotor type generators with an outer generator rotor having permanent magnets and an inner stator having coils, greatly reduces the power coupling complexity, i.e. high currents do not have to be transmitted between the rotating generator components and the stationary body before being fed into a common power electronic converter.

In an embodiment, the first and second bevel pinions are positioned at opposite ends of a line segment intersecting the drive shaft axis of rotation.

In an embodiment, the drive train, in particular the transmission system, further comprises an upstream planetary gearbox. "upstream" herein refers to being positioned between the turbine rotor and the bevel gear box. In an embodiment thereof, the upstream planetary gearbox comprises: a ring gear drivingly coupled to the turbine rotor; and a sun gear drivingly coupled to the bevel gear of the bevel gear box. Such upstream planetary gearboxes providing a planetary transmission may be single stage. Alternatively, such a transmission may be 1.5 speed.

In an embodiment, the planetary transmission comprises a planetary gear system having first and second planet gears on a common shaft, wherein the first planet gear is drivingly coupled with the ring gear and the second planet gear is drivingly coupled with the sun gear. In a particular embodiment, the planet carrier is fixed relative to the nacelle and is therefore attached to an upstream gearbox housing that is fixed relative to the nacelle. In another particular embodiment, the sun gear shaft member facing the turbine rotor is also supported by bearings placed inside the planet carrier structure. Another sun output shaft member may be flexibly attached to the bevel gear shaft via a universal joint or instead of a flexible link. The fixed planet carrier solution provides a compact, robust and structurally rigid configuration. This particular reliability enhancement is intended to minimize the effects associated with scaling at the critical interface between the planet and sun due to inherent deflections and distortions. The combination of these latter measures with a universal or flexible joint with bevel gears is a key driving factor to further propel the drive train and wind turbines to extend to 16MW + and above.

In a 1.5 stage gearbox embodiment, the gearbox provides a step up gear ratio of at least i to 1: 10. Such gearboxes are also known as stepped (planetary) gearboxes or compound (planetary) gearboxes.

The step-up gear ratio of the upstream gearbox can be further increased by, for example, increasing the ratio of the first and second planet gears relative to each other on a common shaft. It is not always possible to increase the diameter of the second (larger) planet gear. In an embodiment, the second planet gears may be axially displaced relative to each other while being meshingly coupled with the sun gear. In an embodiment, the sun gear is longer or extends further in the axial direction.

In an embodiment thereof, the upstream planetary gearbox comprises at least two sets of planetary gear systems, wherein at least two second planet gears are substantially in one first planet plane and at least one second planet gear is axially displaced (i.e. along the turbine rotor rotation axis) with respect to the first planet plane.

In an embodiment thereof, the upstream planetary gearbox comprises at least a first and a second set of planetary gear systems, wherein each set of planetary gear systems comprises at least two second planetary gear systems. The second planet gears of the set of planetary gear systems are substantially in a first planet plane, and the second planet gears of the second set of planetary gear systems in the second planet plane are axially displaced (i.e. along the turbine rotor rotation axis) relative to the first planet plane.

These embodiments allow for an increase in the second planet gear diameter, and thus an increase in the gear ratio.

In addition to the current design, providing an upstream planetary gearbox has a number of advantages.

The bevel gearbox in earlier designs was driven directly by the rotor shaft. These designs may allow for limited input torque, as well as limitations matching rated power, since rotor torque is only transmitted to two pinions. The current design more readily achieves a 12-16MW + rating and associated greater input torque, as the input torque is here transmitted by 5 or more planets in a compact planetary gear arrangement.

Early designs described a planetary gearbox that was integrated with the generator in the joint housing and possibly placed the generator in the tower foundation. In an embodiment of the current design, the downstream planetary gearbox is integrated within the bevel gearbox. Thus. Each individual pinion drives a planet carrier or ring gear.

The fact that the downstream planetary gearbox can be fully integrated with the upper or lower pinion is a major innovative advantage, preventing slight movements (deflections and/or deformations) of the pinion from affecting the integrity and the service life of this gearbox.

The entire transmission system and generator may be located inside the nacelle, whereby the generator is placed near above the gearbox housing (e.g., 0.5m to 1.0 m).

In an embodiment, the generator is brushless and therefore does not require slip rings and brushes.

In an embodiment, the transmission system comprises a transmission housing and the generator comprises a generator housing, and wherein the generator housing is attached to the transmission housing, in particular, the generator housing is attached on top of the transmission housing, opposite the tower.

In an embodiment, a turbine rotor is mounted on the tower, wherein a rotor rotation axis of the turbine rotor is functionally perpendicular to a tower longitudinal axis. In this regard, "functionally perpendicular" encompasses slight pitch angles between 5 and 10 degrees that are typically used to compensate for the curvature of the turbine blade toward the tower.

In an embodiment, a generator includes a housing and a cooling system.

In an embodiment, the cooling system comprises a gas cooling system comprising a gas cooling inlet in the generator housing for flow of cooling gas into the generator and a gas cooling outlet for allowing gas to exit the generator housing.

In an embodiment, the fixed stator coil housing of the outer rotor generator is an annular structure filled with a positively circulating coolant. This acts as the main cooling system for generator temperature management. In an alternative embodiment, the generator is of a conventional inner rotor type, whereby the generator rotor rotates inside the stator. The stator coils of the stator housing, which now have the cooling liquid inside, face inwards.

In an embodiment, the rotor has one or more vanes for arranging the cooling gas inside the housing in motion, in particular designed to induce a flow of cooling gas from the cooling gas inlet to the cooling gas outlet when in operation. In this way, internal heat diffusion and cooling performance can be optimized by optimal gas mixing.

In an embodiment the stator has one or more facilities, in particular exhaust passages, whereby an air pump forces pressurized cooling air through the stator coils in the air gap between the moving rotor and stator to enhance generator heat dissipation. In particular, such air passages are designed to, when in operation, induce cooling gas to flow through the air gap when passing from the cooling gas inlet to the cooling gas outlet.

In an embodiment, the current design includes a transmission system with a small planetary gearbox integrated within a bevel gearbox. The counter rotating output shaft of the bevel gear box is the input to the planetary gear box. In an embodiment, this is two counter-rotating input rotations that are converted within a bevel gear box into rotation of a single high speed output shaft that is in turn coupled to a conventional generator, such as a permanent magnet outer or inner rotor generator or an electrically excited generator.

In an embodiment, the planetary gearbox is fully integrated into the bevel gear box.

In an embodiment, a planetary gearbox that is fully integrated but does not have its own outer casing has a planet carrier that is attached directly to the upper bevel pinion bottom flange inside the bevel gearbox. The lower bevel pinion is attached to the ring gear of this planetary gear box via a shaft, preferably a flexible shaft or a rigid shaft with a flexible coupling. In an alternative arrangement, the upper bevel pinion is attached to the ring gear and the lower bevel pinion is attached to the planet carrier. In an embodiment, the sun gear appears as a single assembly with the sun gear shaft. The latter passing through the upper bevel pinion. In an embodiment, the sun gear is supported by an internal journal bearing and is therefore also functionally the planetary gearbox output shaft. In an embodiment, the upper bevel pinion and the planetary gearbox provide a fully integrated assembly, whereby slight movement (shifting) of this upper bevel pinion under load does not compromise the integrity of the downstream planetary gearbox primary components. This special design feature ensures that the overall gearbox design requirements can be met for over 25 years. A second important factor to improve life is the use of journal bearings at all bevel pinion and downstream planetary gearbox locations.

In an embodiment, the upper and lower bevel pinions are supported by a fixed shaft (pin). Journal bearings are integrated within these pinions to absorb radial and axial forces. Generally, in bevel gear driving, a pinion axial force in a direction toward the center is large. Therefore, great care is taken to solve this problem by the special design of the upper and lower pins. The gearbox output shaft is supported by journal bearings incorporated inside the pins. A downstream planetary gearbox is attached to the pin.

Indeed, there are several possible alternative arrangements for the planetary gearbox:

A. the planetary gearbox is atop the upper bevel pinion. In other words outside and on top of the main gear case housing. In this layout, the ring gear or planet carrier is attached directly to the upper pinion via, for example, a flanged connection. A shaft, in an embodiment a flexible shaft, is attached to the lower bevel pinion. In this embodiment, the shaft passes through the upper bevel pinion and connects to the ring gear or planet carrier, depending on design preference. The sun gear now requires a separate bearing support solution and the sun gear with shaft assembly again forms the gearbox output shaft.

B. The planetary gearbox is on top of the lower bevel pinion inside the large bevel gear.

C. The planetary gearbox is below the lower bevel pinion outside the original gearbox.

And (3) annotation: also in arrangement A, B or C, the planet carrier or ring gear is directly connected and driven by the bevel pinion to which it is attached, and the other primary component (selected from the other primary component of the planet carrier and ring gear) is driven by the other opposing bevel pinion.

Gearbox speed

In the applicant's 12MW early design, the turbine rotor rated speed was 8 RPM. For calculation, the step-up ratios of the 1.5 stage gearbox and the bevel gearbox were slightly increased to 1:15.3 and 1:8.2(2 × 4.1), respectively. This will sum up to 1004RPM generator speed.

In the current design of 12MW, the turbine rotor rated speed is again 8RPM, and the step-up ratios for the 1.5 stage gearbox and bevel gearbox are 1:15.3 and 1:8.2(2x4.1), respectively. This doubles to 502RPM for both bevel pinions. As in earlier designs, one bevel pinion rotates clockwise while the other bevel pinion rotates counterclockwise. Each of these bevel pinions in turn drives a planetary gearbox main assembly (i.e. one selected from the ring gear and the planet carrier), but in the opposite direction, which results in a doubling of the step-up ratio of the "normal" planetary gearbox.

This results in various planetary gearbox step-up ratios in the following corresponding gearbox output speeds:

step-up ratio gearbox output speed [ RPM ]

1:3 3,012.

1:4 4,016

1:5 5,020

In an alternative embodiment, the planetary gearbox step-up ratio may be further increased to an "actual" current maximum value of, for example, 1:7, with a corresponding increase in generator speed.

If again in an alternative embodiment a larger rotor is fitted and the nominal rotor speed drops to e.g. 7RPM instead of 8RPM in the first calculation example, the generator speed can be flexibly adjusted by increasing the boost ratio of the planetary gearbox. This provides great flexibility for system tuning and LCOE optimization during expansion.

The transmission system output speed is the generator input speed. The new solution of adding a planetary gearbox thus provides a higher generator speed compared to earlier designs. This allows the size of the generator to be reduced from, for example, about

Reduction to indicative (outer rotor diameter x air gap length)

But these are only indicative data. Therefore, "disk" generators are preferred over "bucket" generators because of the reduced need for active materials (magnets, copper and magnetic steel) and the superior generator heat dissipation. Also important, smaller generators typically reduce the rare earth requirements to 2% to 4% of what is originally required for a direct drive PMG of the same rating and rotor size and similar rated tip speed (e.g., 90 m/s). These indicative rare earth data are based on comparison with direct drive and for this particular drive train concept, 600kg/MW magnet data are typically used.

Downstream planetary gearbox and generator orientation

In the design of the present operation, the imaginary central axis or the axis of rotation between or connecting the bevel pinions may be in any intermediate position between the vertical plane, the horizontal plane or measured in full circles. Thus, the generator may also be vertical, and thus face up or down, horizontal (e.g., facing right or left), or in any intermediate position between vertical and horizontal as measured in a full circle. An imaginary central axis or axis of rotation between or connecting the bevel pinions themselves may be central, for example for straight or helical bevel pinions. The cones may be offset, such as those bevel gears in which the hypoid gears correspond in shape to those used in automotive differentials.

The embodiment with an imaginary central bevel gear shaft for two pinions in horizontal position allows mounting the holding brake at the pinion opposite to the pinion with integrated planetary gearbox. This arrangement is an alternative to installing a holding brake at the low speed shaft behind the rotor, and it can significantly reduce size and cost due to lower torque resulting from combining higher speeds.

A relatively conventional inner or outer rotor generator, which may now be deployed, forms part of the present patent application. In an embodiment it has an open structure for optimal temperature management, but has a spacious light-weight housing (cover) for protecting the generator interior from the harsh ocean impacts. In addition, the housing or shell provides optimal mixing of hot and cold air streams as part of the generator temperature management/heat dissipation strategy.

Adequate generator life is achieved by using journal bearings in all bearing locations, as well as a separate oil bath system, or alternatively by integrating with the transmission system lubrication system. Advanced generator cooling features include forced cooling air into the generator air gap. An alternative (supplemental) generator cooling enhancement option is a spoke outer rotor annular support structure for promoting optimal mixing of generator internal cooling air. Another special design feature is a combined structural support structure and water cooled shroud for attaching the stator coils. Due to the spacious area within the (stationary) stator housing, it is practically uncomplicated to combine all necessary equipment, such as cooling fans, air hoses and heat exchangers.

In an embodiment, the generator comprises a bottom structure mechanically attached to the gearbox upper cover. The connecting rod between the generator rotor and the outer shaft of the gearbox is provided by an intermediate carbon reinforced plastic or other shaft material, with a flexible coupling on each side, to avoid that gearbox shifting and/or deformation may negatively affect the integrity and service life of the generator.

In an embodiment, a torque limiter (KTR or otherwise) is integrated with an upper flexible coupling connecting the gearbox output shaft and the generator rotor. The KTR Ruflex et al torque limiter with integrated flexible coupling is a semi-standard assembly and will be located at the generator (input) drive shaft and mounting flange interface.

In an embodiment, generators with very fast operating speeds (3000-.

The holding disc brake may be located at the drive train main shaft, attached to one bevel pinion, or located at the gearbox output shaft.

The torque limiter with integrated flexible coupling is a semi-standard package and will be located at the generator (input) drive shaft.

Summary of major benefits

1. A simple, cost-effective and efficient 'super-speed' gear drive train, with a minimum number of rotating elements including bearings;

2. the component and bearing count can be comparable to the medium speed gear concept with a two-stage planetary gearbox, but now using a smaller and cheaper traditional generator (one stator and one rotor);

3. the bearing count is equivalent to that of the bearing designed earlier by the applicant, but the size, the mass and the cost of the generator are greatly reduced;

4. Gearbox mass and cost are only slightly increased compared to applicant's earlier designs;

5. due to the integrated downstream planetary gearbox, the torque density (Nm/kg) performance is generally improved compared to applicant's earlier designs

6. Eliminating large current rotating emitters; the generator power is fed directly from the generator stator to the frequency converter;

7. overall drive train complexity, mass and cost are reduced compared to applicant's earlier designs;

8. with permanent magnet generators, the minimum rare earth demand is only about 2% to 4% compared to the rare earth demand for an equivalent rated direct drive generator;

9. with further rotor scaling (═ reduction of rotor speed), there is unparalleled flexibility in selecting the optimum generator rated speed achieved by the addition of a small planetary gearbox;

the invention also relates to a wind turbine comprising a turbine rotor drivingly coupled to an upstream planetary gearbox, the upstream planetary gearbox being drivingly coupled to a transmission having two opposing gears, both of which are drivingly coupled to a downstream planetary gearbox, the downstream planetary gearbox being drivingly coupled to a generator rotor for generating electrical energy. In an embodiment, the transmission with opposing gears is a functionally right angle transmission. This is also known as a bevel gear box or simply bevel gear.

In an embodiment, the bevel gear has two opposing bevel gears called bevel pinions. The upper bevel pinion is integrated with a downstream planetary gearbox located inside the bevel gear assembly. The downstream planetary sun gear shaft passes through the upper bevel pinion and is also the complete gearbox output shaft. In an embodiment, the downstream planet carrier is mechanically attached to the downstream upstream planet bottom section, and they rotate as a single assembly. The downstream ring gear is attached to the downstream planet carrier casting via a journal bearing arrangement, collectively forming a single unit that is structurally strong and rigid. The downstream ring gear is attached to the lower pinion via a flexible shaft or a rigid shaft with two flexible couplings. In an embodiment, the downstream planetary gearbox is "open," without a separate housing, and it uses the same lubrication system as the upstream planetary gearbox, i.e., the 1.5 stage planetary gearbox, and has a bevel gearbox.

In an embodiment, the downstream ring gear may be attached to the upper pinion gear and the downstream planet carrier connected to the lower pinion gear.

An alternative embodiment of the downstream planetary gearbox is above the lower pinion, below the lower pinion, or above the upper pinion, and has two variations of the downstream ring gear and the downstream planet carrier attachment.

One skilled in the art will understand that the term "substantially" herein, for example, in "consisting essentially of. The term "substantially" may also encompass embodiments having "integral," "complete," "all," and the like. Thus, in embodiments, the modifier "substantially" may also be deleted. Where applicable, the term "substantially" may also mean 90% or more, such as 95% or more, particularly 99% or more, even more particularly 99.5% or more, including 100%. The term "comprising" also encompasses embodiments in which the term "comprises" means "consisting of.

The term "functionally" will be understood and will be apparent to those skilled in the art. The terms "substantially" and "functionally" may also encompass embodiments having "entirely," "completely," "all," and the like. Thus, in embodiments, the modifier "functional" may also be deleted. When used, for example, in "functionally parallel," the skilled artisan will understand that the modifier "functionally" encompasses the term "substantially" as explained above. In particular, "functionally" should be understood to encompass an arrangement of features that allows the features to function as if the adjective "functionally" were not present. The term "functionally" is intended to cover variations of the features to which it refers, which enable a combination of features to operate or function in a functional use of the features and other features that the term may refer to in the present invention. For example, if the antenna is functionally coupled or functionally connected to the communication device, the received electromagnetic signals received by the antenna may be made available to the communication device. For example, the word "functionally parallel" used in "functionally parallel" is intended to cover completely parallel, but also embodiments covered by the word "substantially" as explained above. For example, "functionally parallel" refers to embodiments that function like components, e.g., in parallel, when operated. This covers embodiments where the skilled person is clearly aware that it operates as if it were parallel in its intended field of use.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices or apparatus herein are described with particularity during operation. As will be clear to a person skilled in the art, the invention is not limited to the method of operation or the apparatus in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device or apparatus claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention also applies to a device or an apparatus comprising one or more of the characterising features described in the description and/or shown in the attached drawings. The invention also relates to a method or a process comprising one or more of the characterising features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent may be combined to provide additional advantages. Furthermore, some features may form the basis of one or more divisional applications.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

FIG. 1 schematically depicts an embodiment of a wind turbine;

FIG. 2 is a schematic cross-sectional view of the interior of the nacelle or cabin components of FIG. 1;

FIG. 3 shows details of an embodiment of a transmission system and generator;

fig. 4 shows an embodiment of a generator, in particular an outer rotor permanent magnet generator, and

FIG. 5 is an alternative transmission component.

The figures are not necessarily to scale.

Detailed Description

Fig. 1 schematically shows an example of a two-bladed downwind wind turbine of the present invention. The wind turbine has a tower 18. The tower 18 carries a nacelle or nacelle 30. The nacelle 30 rotatably holds the turbine rotor 1. For positioning the turbine rotor 1 in the wind, the nacelle 30 may be rotatably mounted on the tower 18, thereby allowing setting the yaw angle of said nacelle 30.

The current design of wind turbines is found to be particularly advantageous for wind turbines with a capacity of 8-10MW and even more, where the rotor size is matched for different IEC wind classes, as this represents the next major step in the technological extension. It is expected that this will at least in part require new innovative solutions to technically achieve such extended steps while reducing the cost of electricity generation based on service life. The downwind wind turbine is shown in fig. 1, but the current design can also be applied to upwind wind turbines.

In this embodiment, the nacelle 30 includes a helicopter deck 31 and has an external cooling radiator 36.

In this embodiment, the nacelle 30 houses a drive train that couples the turbine rotor 1 to the generator 6 via a transmission system 5, see fig. 2.

In fig. 2 to 4, the drive train with the transmission system 5 and the generator 6 will be explained in detail. The figures are schematic and not all elements and components are of exact or relative size. The figure is a cross-section along a plane defined by the rotor rotation axis R (the fringe line) and the tower longitudinal line L.

Fig. 2 shows an embodiment of a drive train with a turbine rotor 1 coupled to a generator 6 via a transmission system 5. Fig. 3 will explain embodiments of the transmission system 5 and the generator 6 in more detail, and fig. 4 shows embodiments of the generator 6 in more detail. The transmission system may be divided into components 5A and 5B as will be explained below. Fig. 5 shows an alternative embodiment of a component 5A of the transmission system 5.

In the drawings, many examples of bearings will be indicated by the classical designation of a rectangle with a cross inside. These do not always include a separate reference numeral but are considered obvious to the skilled person.

Fig. 2 shows that the wind turbine comprises a turbine rotor 1 comprising a set of turbine blades and defining a rotor rotation axis R (striped line). The turbine rotor 1 may have two or more blades. With two blades, the installation is simplified and the helicopter deck 31 can be practically used for helicopter landing purposes, as can be seen in the figures.

Here, the turbine rotor 1 is connected to a hollow turbine rotor shaft 2, which is here depicted as of the type discussed above. The turbine rotor shaft 2 has a mechanical lock 16 which is able to lock the wind turbine in the locked position.

A nacelle or nacelle 30 is rotatably mounted on the tower 18 via bearings 17 (illustrated).

The turbine rotor shaft 2 is mounted in a housing 3 which has a front bearing and an end bearing and is conical. This construction is known per se, described and patented by Eolotec, for example. It includes front and rear preloaded tapered roller bearings. In an alternative embodiment (not depicted), a functionally equivalent solution may incorporate journal bearings. This housing 3 is attached to a frame, which is attached to the cabin. At the opposite end of the housing 3, the other components of the drive train extend.

Subsequently, the turbine rotor shaft 2 is coupled to a flexible coupling 4. Such a flexible or elastic coupling 4 may be of the type discussed above, for example. In an embodiment, the flexible coupling comprises two discs coupled using a flexible or elastic material.

The current embodiment of the wind turbine of fig. 2 comprises a transmission system 5 coupled to a flexible coupling 4, which is in turn coupled to a generator 6. In the exemplary embodiment, the transmission system 5 has two components 5A and 5B coupled to one another and can be integrated into a common housing. This will be explained in fig. 3 and 5.

In the embodiment of fig. 3, the transmission system 5 then comprises an upstream planetary gearbox 7 which is drivingly coupled at one end with the turbine rotor 1 and at the other end with an input of a bevel gearbox 8. In fig. 2, the upstream planetary gearbox is schematically indicated with 5A. The bevel gearbox 8 is drivingly coupled at an output end to a downstream planetary gearbox 9. This is indicated as 5B in fig. 2. The downstream planetary gearbox 9 is in turn drivingly coupled to a generator rotor 10 of the generator 6. In this regard, "upstream" is towards the turbine rotor 1 and "downstream" is towards the generator 6.

In fig. 3, in this embodiment, the transmission system 5 has an input upstream gearbox shaft 32 drivingly coupled to the flexible coupling 4 and an output upstream gearbox shaft 33 drivingly coupled to the bevel gearbox 8. The transmission system 5 allows the wind turbine to be designed for a greater power rating.

First, we discuss the upstream planetary gearbox in the depicted embodiment of FIG. 3.

In this embodiment, the upstream planetary gearbox 7 has a modified planetary gear design also referred to as a 1.5 stage gearbox. The upstream planetary gearbox 7 is also referred to as a multi-stage planetary transmission and enables a maximum step-up gear ratio of at least i-1: 10. Alternatively, the final gear set that together drives the central sun gear at the output shaft may be skipped. Such an embodiment would produce a conventional 1-stage planetary gearbox with a maximum step-up gear ratio of about i-1: 6.4, and thus increase the input torque load of the bevel gearbox 8. This in turn reduces the number of generator revolutions for a given rotor speed and increases the size and cost of the generator. Such an arrangement may be technically less feasible, especially for an overall drive train concept and especially with higher ratings associated with higher rated torque levels.

The presently described embodiment of the upstream planetary gearbox 7 is as follows. The input upstream gearbox shaft 32 holds the upstream ring gear 19. Here, two upstream planetary gear elements are mounted in the housing, each holding an upstream first planet gear 20 and an upstream second planet gear 21 representing the main elements of an additional "0.5 stage" of the gearbox. The upstream first planet gears 20 and the upstream second planet gears 21 are rotationally fixedly mounted on a common shaft 35. The common shaft 35 is fixed in position in the gearbox housing or alternatively within the fixed planet carrier, thereby keeping it positioned in the housing or in the fixed planet carrier. The common shaft 35 is rotatable on its respective axis of rotation. Since the diameter of the upstream second planetary gear 21 is larger than that of the upstream first planetary gear 20, the rotation speed is additionally increased. The upstream second planet gears 21 engage the upstream sun gear 34 and, when in operation, drive the upstream sun gear 34. An upstream sun gear 34 is rotationally fixed to the output gearbox upstream gearbox shaft 33. The figures show two planetary gear sets in cross section. In practice, five or more planetary gear sets may be used, all of which are meshingly engaged with the upstream sun gear 34 and positioned around the upstream sun gear 34.

In the present drive train it is also possible to provide one or more additional gearboxes in order to further increase the rotational speed of the generator 6. With the currently modified upstream planetary gearbox 7, the rotational speed is increased by at least a factor of about 10. The first gear ratio of the upstream ring gear 19 and the upstream first planet gears 20 may be up to a maximum of 1: 6.4. The second gear ratio of the upstream second planet gears 21 and the upstream sun gear 34 may be as high as 1:2 to 1: 4. Thus, the combined gear ratio can be as high as 12 or more. This reduces the load (torque) on the bevel gear box 8.

In the present transmission system 5, the upstream planetary gearbox 7 is drivingly coupled to the bevel gearbox 8. We will now describe the presently depicted embodiment of the bevel gear box 8 of fig. 3.

The output upstream gearbox shaft 33 is coupled in a rotationally fixed manner and drivingly to the gear or bevel drive gear 11. In the present embodiment, the toothed gearing of the bevel drive shaft gear 11 is here at an angle of between 60 and 70 degrees with respect to the rotor rotation axis R. Bevel drive gear 11 engages a first bevel pinion 12 and a second bevel pinion 13. Here, the first and second bevel pinions 12 and 13 each have a conical shape. They taper towards the rotor axis of rotation R. The tooth surfaces of the bevel drive gear 11 have a corresponding conical shape. In alternative embodiments, the first and second bevel pinions 12 and 13 may be bevel gears, offset gears, Zerol bevel gears, helical bevel gears, straight bevel gears, or crown gears. The tooth-shaped parts of the bevel drive gear 11 are adapted to the first bevel pinion 12 and the second bevel pinion 13. In effect, the bevel gearbox 8 defines a double right angle transmission. Both bevel pinions 12, 13 rotate in opposite directions when in operation.

In the present embodiment of fig. 3, the transmission system 5 includes a common housing 15. The second bevel pinion 13 includes a second bevel pinion shaft 22 held in the common housing 15 using a second pinion journal bearing 23.

In this embodiment, the first bevel pinion gear 12 includes a hollow bevel pinion shaft 24 that is held in a common housing using a first pinion journal bearing 26.

In the depicted embodiment, the bevel pinions 12, 13 are in-line on a common axis of rotation R1. Here, this axis of rotation R1 intersects the turbine rotor axis of rotation R. Known tilt gearboxes allow positioning such that the axis of rotation of the pinion does not intersect the turbine rotor axis of rotation R.

As previously mentioned, the downstream planetary gearbox 9 may be drivingly coupled to the bevel gearbox 8 at various locations. Generally, the generator 6 will be positioned near one of the bevel pinions 12, 13. This closest bevel pinion will be indicated as first bevel pinion 12. Furthermore, for ease of construction, the generator 6 will be positioned with the generator rotor axis of rotation aligned with the axis of rotation R1 of the two bevel pinions 12, 13. Typically, the line will intersect the rotor shaft axis of rotation R. Furthermore, generally, the generator will be placed radially outside the first bevel pinion, or on the end of the first bevel pinion remote from the rotor shaft rotation axis R.

Generally, the downstream planetary gearbox 9 may be drivingly coupled between a first bevel pinion 12 and a second bevel pinion 13.

Alternatively, the downstream planetary gearbox 9 may be located radially outside the first bevel gear 12 and between the first bevel gear 12 and the generator 6. In other words, the downstream planetary gearbox 9 is located between the bevel pinions 12, 13 and the generator 6. It only needs to pass from the second bevel pinion 13 through the first bevel pinion and be drivingly coupled to the coupling shaft of the downstream planetary gearbox 9. One end of the downstream planetary gearbox 9 is drivingly coupled to the first bevel pinion 12 and the other end of the downstream planetary gearbox 9 is drivingly coupled to the generator rotor 10. This places the generator 6 further away from the rotor shaft axis of rotation R.

Alternatively, the downstream planetary gearbox 9 may be located radially outside the second bevel pinion 13. This position, furthest away from the generator 6 and having two bevel pinions 12, 13 between the downstream planetary gearbox 9 and the generator 6, requires a coupling shaft from the first bevel pinion through the second bevel pinion and drivingly coupled to the downstream planetary gearbox 9, and a relatively long concentric shaft coupling the downstream planetary gearbox 9 to the generator 6, this shaft further extending through both bevel pinions. In order to obtain a simple and compact structure it will/can be located between the rotation axis R and one of the bevel pinions 12, 13.

In fig. 3, a first positioning of the downstream planetary gearbox 9 between the first and second bevel pinions 12, 13 is depicted. Here, the downstream planetary gearbox 9 is located close to the radially inner end of the first bevel pinion 12. A component of the downstream planetary gearbox 9 may even be integrated with the first bevel pinion 12.

The downstream planetary gearbox 9 has the following general components. The downstream ring gear 50, downstream sun gear 51 and downstream planet gears 52 are mounted on a downstream planet gear frame 53.

In the embodiment of FIG. 3, components of the downstream planetary gearbox 9 are drivingly coupled between the bevel gearbox 8 and the generator in the following manner. A downstream planet gear frame or planet carrier 53 is drivingly coupled with the first bevel pinion gear 12. Specifically, the downstream planet gear frame or planet carrier may be attached to the first bevel pinion gear 12 or integrated with the first bevel pinion gear 12. The downstream ring gear 50 is drivingly coupled to the second bevel pinion 13 or coupled with the second bevel pinion 13. This may be done, for example, using a flexible shaft 55. In the present embodiment, the downstream ring gear 50 includes a flexible coupling 54 coupled to a flexible shaft 55, which in turn is coupled to another flexible coupling 56 that is drivingly coupled to the second bevel pinion 13. The downstream sun gear 51 is drivingly coupled to/with the transmission system output shaft 27. In this embodiment, a flexible or splined coupling 28 drivingly couples the transmission system output shaft 27 to the generator rotor shaft 29.

To protect the generator 6, in particular against grid-induced events, such as sudden outages, resulting in high transient driveline peak loads, in the present embodiment of fig. 2, the internal drive shaft is coupled to the generator 6 via an overload clutch or torque limiter. Overload clutches are known per se in the art.

Functionally, the bevel gearbox 8 provides an additional gear ratio between 1 and 10 to the drive train's transmission system 5. Furthermore, the bevel gear box 8 provides a pitch transmission (angle drive; bevel pinion; miter gear; right angle bevel gear drive; bell crank; angle drive) with two counter-rotating bevel pinions 12, 13. Thus, the present transmission system 5 first provides gear ratios as high as the "gearbox engineering maximum" in the range 1: 350-. Specifically, a practical speed increasing gear ratio range between 1:375-500 can be achieved.

Thus, rotational speeds of more than 3,000 revolutions per minute of the generator rotor are possible. In embodiments, up to 3.000 to 5.000 revolutions per minute are possible. This may result in a smaller generator diameter, for example.

The rotor and complete drive train are mounted in the tower 18 perpendicular to the tower longitudinal axis L. In an alternative embodiment, in particular in an upwind wind turbine, the rotor and drive train may be mounted on the tower with the rotor rotation axis R at an angle of inclination α to the vertical (90 °) coupling. The pitch angle α can be critical as it enables the distance between the tower and the rotor (tip) to be increased, thereby minimizing the likelihood of the blade tip striking the tower and reducing the tower's disturbing influence on the rotor. The angle of inclination a is generally chosen between about 5 degrees and a maximum of 10 degrees so as not to negatively affect the aerodynamic performance.

The housing of the transmission system 5 may be a single housing. Alternatively, the housing may be divided into two coupled housing parts, for example with a split at the second planet gears 34. This may improve the possibilities of use and maintenance. In the present embodiment, the flexible coupling 4 may be removed by removing bolts, for example, and may be disengaged from the present drive train, thereby providing space for later removal of (parts of) the housing. In an alternative embodiment, the upstream planetary gearbox 7 and the bevel gearbox 8 each have a separate housing.

Fig. 3 also shows an embodiment of the generator 6 in cross-section. In fig. 4, the details of the generator 6 are shown in more detail. The generator (electrical generator)6 is simply referred to as a "generator" and has a housing 25. The housing 25 has fixing means for fixing the housing to the transmission system 5, here to the housing of the transmission system 5. Typically, the generator housing 25 will be housed inside the nacelle 30.

The generator 6 is of the external rotor type and comprises an external generator rotor 10 and an (internal) stator 38+ 57. The rotor 10 and stator 38+57 are concentric and define an air gap 39 therebetween. The rotor 10 is coupled to a drive shaft 27 produced by the downstream planetary gearbox 9. In the present embodiment, the generator drive shaft 27 may be coupled to the generator rotor 10 via a coupling 28, in one embodiment the overload clutch forms an integrated assembly with the flexible coupling. Indeed, here, as an example of a possible coupling, a plate couples the transmission system output shaft 27 to the external generator rotor 10. The flexible or rigid shaft connecting the lower pinion 13 with the downstream ring gear can be coupled by a gear spline coupling or alternatively designed flexible coupling type developed and patented by the german RENK AG. This is to compensate for slight dynamic misalignments caused by deflection and twisting, and to a lesser extent for collection length variations. Gear splines or other designed flexible couplings are attached to the downstream ring gear 50 and lower pinion gear 13 via an upper adapter unit 54 and a lower adapter unit 56, respectively.

The external generator rotor 10 may comprise permanent magnets to provide alternating magnetic poles. The stator body 57 includes coils 38 for inducing voltage and current. Since the stator 11 is fixed in relation to the frame and the nacelle in this embodiment, no electrical coupling like a wiper or sliding contacts or brushes is required. As previously discussed, axial flux generators may also be considered instead of the radial flux generator of fig. 2. In the current inventive concept, such a generator will also have a rotor and a stator fixed relative to the nacelle.

To be able to resist or bear high torsional forces while allowing some bending deflection or to be able to reduce weight, the shaft 55 may be made of a fiber-reinforced composite material. It provides a torque axis. Suitable fibre-reinforced composites include fibre materials commercially sold under the names Dyneema, Aramid and Kevlar. However, it has been found that carbon fibre reinforced composites are preferred in order to provide a higher degree of rigidity and strength.

In the present embodiment, the generator has one or two journal bearings attached to the hollow generator pin 58 and the hollow generator rotor shaft 59, and the generator forms the structural support of the generator rotor 10.

In the present embodiment, the generator 6 comprises a (lightweight) generator housing 25. The generator 6 also comprises a cooling system. In the present embodiment, the cooling system comprises a combined gas and liquid cooling system.

The gas cooling system includes a gas inlet 40 in the generator structural shell 14 and a gas outlet 41 in the generator shell 25. The inlet 40 and outlet 41 as well as the air circulation pump and the air-air or air-liquid heat exchanger are not drawn in the schematic. They may also be as far away from each other as possible.

In an embodiment, the gas cooling system, which is generally based on air circulating inside the generator 6, comprises an exhaust member in the generator rotor. In the present embodiment, the generator rotor 10 has vanes or fins and/or spokes and/or holes to set the air inside the generator 6 in motion.

In an embodiment, an exhaust member on the rotor provides a pump function to exhaust air from the gas inlet 40 to the gas outlet 41. The gas cooling system may comprise pump means for circulating air through the generator housing 25. In the present embodiment, the gas cooling system comprises a heat exchanger gas coupling the gas inlet 40 and the gas outlet 41. In the present embodiment, the heat exchanger is of the gas-liquid heat exchanger type. It allows the gas of the gas cooling system to exchange heat with the liquid of the liquid cooling system, which will be discussed further. In the embodiment discussed, the inner generator rotor 11 additionally has an exhaust member in the gas cooling system. Gas passages 28 are provided in the inner generator rotor 11 for further mixing or allowing mixing of the gas inside the generator 38.

In an embodiment, the stator structural housing is a hollow annular body 57 in which the cooling fluid circulates, and it is an integral part of the generator temperature management system. The liquid inlets and outlets 42, 43 (not drawn) are connected to a circulation pump and a liquid-liquid or liquid-air heat exchanger.

In an embodiment, the stator housing incorporates at least one inlet pipe or nozzle along the circumference of the stator along an imaginary horizontal axis and at least one gas channel or nozzle in a vertical plane. The air pump forces cooling air between the stator coils and the air gap 39 which generates most of the generator heat. If two or more gas channels are placed in a vertical plane, they may be positioned horizontally with respect to the generator base or in various oblique positions to promote optimal cooling air mixing and heat rejection.

In fig. 5, an alternative embodiment of the upstream planetary gearbox 7 of the transmission system 5 is explained. In fig. 3, the transmission system 5 is divided into two components, an upstream transmission system component 5A and a downstream transmission system component 5B. The downstream component 5B includes a bevel gearbox 8 and a downstream planetary gearbox 9. The upstream component 5A includes an upstream planetary gearbox 7. The upstream planetary gearbox 7 in fig. 3 comprises a 1.5 stage planetary gearbox 7 also referred to as a stepped planetary gearbox 7. For the sake of brevity, it will not generally be referred to as "upstream" as in the description of fig. 3 and 4. In fig. 5, the specific gearbox 7 is redesigned to further optimize the current wind turbine design. It should be noted that the particular stepped planetary gearbox of FIG. 5 may also be applied in other wind turbine designs that do not include the bevel gearbox 8 discussed thus far. For example, it may be used in more conventional wind turbine designs having other downstream planetary gearbox(s) and/or "conventional spur gears" coupling the stepped planetary gearbox of figure 5 to the generator 6. For the sake of brevity, "upstream" is not always added in the description of fig. 5. It is apparent, however, that the stepped planetary gearbox 7 of fig. 5 is proximate to and typically directly connected to the turbine rotor shaft as the first or upstream component of the transmission system 5.

In an embodiment, the redesigned stepped planetary gearbox 7 (or 1.5 stage) design of FIG. 5 focuses on meeting the large input torque requirements associated with the next generation of 12-16MW + offshore wind turbines with matching 215-260m rotor diameters. The design incorporates journal bearings whenever possible and feasible, which is a key contributor to achieving compact gearbox design with competitive torque density (Nm/kg).

Furthermore, the stepped planetary gearbox 7 of fig. 5 and associated dimensioning enables matching of specific power rating combinations according to IEC class I-III, aiming to provide optimal LCOE performance for each specific wind climate. Thus, in an embodiment, the gearbox input (rotor) side includes six planet gears instead of four in the original design for absorbing a corresponding 16-24MNm + range of input torque levels. In particular, the planet gears are provided in two sets of planetary gear systems in two planetary planes P1, P2, or respective first and second planes of upstream second planet gears P1, P2. There may be more planes and sets, thereby increasing complexity. The second planet gears may also all be axially offset relative to each other. This requires complex alignment, but may allow for a larger second planet gear and increase the transmission ratio. For example, the six second planet gears 21 may be grouped into two sets of opposing second planet gears 21 in two axially offset planes. This also allows for larger diameters.

The layout of the stepped planetary gearbox 7, which has (here) six planetary gear systems each comprising a first planet gear 20 and a second planet gear 21, thus comprises a first planet gear 20 rotating inside the ring gear 19 at the input side or upstream side of the gearbox, which in an embodiment provides a first step-up ratio of 1: 4.93. It also reduces the outer shell diameter by more than one meter, now about 4100 mm. Second planet gears 21, downstream with respect to the first planet gears 20, are individually attached to the shared drive shaft, shearing with matching first planet gears 20, each second planet gear having, in an embodiment, teeth of a slanted or helical shape. All planetary gear systems are each subdivided into two separate sets of three planetary gear systems. In this embodiment, these gear sets rotate in separate planes (P1, P2) and together drive a "double" or axially extending sun gear 34, and represent as an assembly a stepped planetary gearbox output stage. In an embodiment, the second step-up ratio in the reference step gearbox 7 is about 1: 3.73.

This provides a total step-up ratio of 1:18.33 for the particular first and second step-up ratios. This is a good first compromise between the parallel objectives of driving ring gear cost as a key gearbox cost driver and maximizing boost ratio. The latter focuses on controlling the size and cost of bevel gears through a reduced (residual) required speed increase ratio, which is supplemented by a reduced torque to be transmitted.

The stepped planetary gearbox 7 of fig. 5 includes at least nine innovative features that provide several benefits as will be explained below.

The first innovative feature is a compact central "tool" carriage 62. The central bracket 62 comprises a structurally rigid element that holds or carries an additional primary load carrying element. In the embodiment of fig. 5, the center carrier 62 is part of the transmission housing. In the embodiment of fig. 5, the center bracket couples upstream housing component 65 and right or downstream housing component 73. The element attached to the central carrier 62 comprises (here) six planet pins (fixed shafts), each rotatably housing a planet common shaft 35. The planet gear common shaft 35, which is fixed to or near the upstream end, includes the first planet gears 20 rotatably fixedly attached thereto. The planet common shaft 35 thus rotates with its first planet gears 20 about the planet axis of rotation Rp. The planet gear common shaft 35 drives the second planet gears 21. This second planet gear 21 may be rotatably fixedly attached to the planet gear common shaft 35. In the current embodiment of fig. 5, the drive disc 70 is rotatably fixedly attached to the planet common shaft 35. Via a flexible coupling 71, a drive disc 70 rotationally drives the second planet gears 21 (said planet gears 21 being downstream of the first planet gears 20). Further, the central bracket 62 includes an annular gear pin 63 fixedly attached or mounted thereto. The ring gear pin 63 holds the ring gear 19, here attached via a ring gear carrier disc 75 and a bearing 64.

Finally, the central carrier 62 holds a rear/upstream output shaft bearing 66 that carries the output upstream gearbox shaft 33. As in fig. 3, it may be attached to a bevel drive gear 11.

The second feature is the (upstream) ring gear carrier disc 75 bearing support at the fixed hollow shaft or ring gear pin 63 of spacious design, which is structurally rigid or provides structural rigidity. However, the ring gear carrier disc 75 provides an interface element that can introduce built-in design flexibility to promote optimal load transfer between the rotating upstream ring gear 19 and the planet gears 20.

A third feature is the "tool carriage" principle, including the already discussed central (tool) carriage 62 mentioned above, and further layout possibilities to achieve vertical gearbox disassembly. A first split is between the outer left/upstream housing component 65 and the central carrier 62 and a second split is between the right/downstream housing component 73 joining the bevel gearbox 8 and the auxiliary or downstream planetary gearbox 9 and in effect the transmission system component 5B (fig. 3). The center bracket 62 itself may also be individually removed and reassembled. Gearbox disassembly further enables "simple" vertical gearbox assembly during periods of operation and upper tower repair during operation without the need for expensive jack-up or other installation vessels.

The "tool carriage" provided by the introduction of the center carriage 62 also provides a compact integrated gearbox system solution that minimizes the negative impact on the gearbox and drive train interface due to deflection and deformation. The latter is a key factor in designing large mechanical drive trains for turbines of ratings of approximately >10 MW. One key interface related advantage of the new design is that the induced loads in the outer casing are almost eliminated, resulting in deflection and distortion being transferred to the critical gearbox interior.

This is because, within the new design parameters, the outer shells 65, 73 and the central bracket 62 are only connected at the outer shell mounting ring. The king pin or ring gear pin 63 attached to the central bracket 62 directly supports the rotating ring gear 19, providing a structurally rigid and robust overall solution. The left housing part 65 of the gearbox housing remains directly connected to the MBU, but through a shortened intermediate connection and now with a larger radius to optimize load transfer.

The fourth innovative element is a (here six) fixed shaft or planet pin 61 supporting the gearbox first 20 and second 21 planet gears, which are coupled together via a separate planet gear torque/common shaft 35. This couples each mating first and second planet gears 20, 21 forming a planet gear pair. Fixed shafts or planet gear pins 61 (three short and three long) are attached (here firmly pressed inside) to the central carrier 62 or mounted on the central carrier 62, resulting in a structurally strong and rigid interface connection.

Part of this solution is further that the planetary gear support function and the torque transfer function are split by applying a separate torque shaft 35 for each first planet/second planet gear set or pair. The planet gear torque/common shaft/axle 35 in turn provides a mechanical linkage between the first planet gears 20 and the second planet gears 21. The first planet gears 20 are rotationally fixedly coupled to their planet gear common shaft/axle 35. This is achieved, for example, by a splined connection, friction device or other means, and is rigid or has some built-in flexibility to optimize the load distribution between the ring gear and the planet gears.

Each of the first planetary gears 20 is rotationally coupled ("it") to one of the second planetary gears 21. It is proposed here to use a flexible coupling. Furthermore, the first planet gears 20 and their coupled second planet gears 21 are both mounted on a stationary planet gear shaft or planet gear pin 61 via one or more bearings 72. In this particular embodiment, the drive plate for the upstream second planet gears 70 is rotationally fixed to the planet gear common shaft 35. Via a flexible coupling 71, the drive disk 70 is drivingly, in particular rotationally fixedly, coupled to the second planetary gear 21. Thus, the coupling of the first planetary gear 20 with its second planetary gear 21 is done by a chain formed by the planetary gear common shaft 35, the drive disk for the upstream second planetary gear 70 and the flexible coupling 71. The mechanical linkage is thus supplemented by the shrink fit and the flexible element 71, for example between the drive element 70 and the second planet gears 21, through the intermediate drive element 70. The solution of the (fixed) planet pin 61 and torque shaft 35 combination further provides advantageous material fatigue properties compared to a single rotational shaft holding the first planet gears 20 and the second planet gears 21. This absorbs bending moments and torque transfer loads.

A fifth innovative feature is that the fixed shaft or pin 61, 63 plus central bracket 62 solution eliminates the negative effects of the shaft-gear moment that would otherwise be unavoidable (counterclockwise, with the turbine rotor on the left). These moments are generated by the combination of the ring gear 19 and the first planet gears 20 and the second planet gears 21 and the sun gear 34. For stepped planetary gearboxes such as that of figure 5, this is an inherent phenomenon but may not always be recognised. This problem is not in itself easy to solve, in particular for an alternative solution with a rotating shaft and two support bearings between the gears. If mishandled, gearbox integrity and service life may be compromised.

A sixth innovative feature is the "axially displaced second planet gear". Here, the second planetary gears 21 are in two planes P1, P2 on the output/downstream side of the stepped gear box 7. This feature allows for a significantly higher step-up ratio compared to an equivalent sized stepped planetary gearbox with a single row/plane of second/output planet gears 21. The reason for this is that for a given ring gear pitch circle, the maximum achievable pressure rise ratio decreases as the number of first planet gears increases. Another contributing factor limiting the maximum speed-increasing ratio of a "conventional" stepped planetary gearbox is that the second planet gear rings may contact or overlap each other, neither of which is functionally possible. In the present example, there are six second planet gears 21 arranged in two planes P1, P2 of every third second planet gear 21. Other configurations, numbers of planes, numbers of second planet gears, etc. are possible, such as three planes of two respective auxiliary planet gears, but there are also two planes of four respective second planet gears, two planes of five respective second planet gears.

The seventh feature is the flexible linkage of each individual drive shaft 35 with the mating second planetary gear 21. This innovative arrangement allows the gears to move slightly out of their "natural" plane of rotation.

The eighth feature relates to the hollow sun gear 34 loosely fitted over the bevel gear shaft 33. This arrangement has a dual function, serving as a support shaft for both bevel drive gear 11 and sun gear 34. The gearbox shaft 33 transmits the sun gear 34 output torque to the bevel drive gear 11 input side. In this embodiment, the sun gear 34 has a flexible mechanical linkage or coupling to the gearbox shaft 34. The whole arrangement does not need a special sun gear bearing bracket. Another benefit is that it creates a "floating" sun gear through the flexibility of the control link. This flexibility feature implies here a torsional stiffness for optimal torque transmission, plus only a minimum axial movement allowed, and necessarily finally some angular and parallel movements with respect to the central rotation axis R. In this embodiment of fig. 5, one end of the gearbox shaft 33 has a bearing 66 holding it in the central carrier 62, and the other end of the gearbox shaft 33 has a bearing 74 where it is held in a right or upstream structural bearing support 73. Here, the bevel drive gear is rotationally fixedly coupled to the gearbox shaft 33.

A drive element, such as a drive plate 67, is also rotationally fixedly coupled to the gearbox shaft 33. The sun gear 34 is freely arranged on the gearbox shaft 34. The sun gear includes a flange 69 rotationally coupled to a drive plate 67 via a flexible sun gear coupling 68.

A ninth feature relates to the opposite pitch tooth angle or the opposite helical shape when helical teeth are applied to the two second planetary gear sets (in P1 and P2) and the sun gear 34. Generally, the sun gear 34 extends axially. This measure enhances optimal interaction and load distribution within this complex dynamic subsystem involving simultaneous movement of the second planet gears 21 in plane and with the mating axially extending sun gear 34. Its parallel purpose is to minimize axial movement caused by balancing axial loads at the axially extending sun gear 34.

The eleventh feature relates to the gearbox shaft 33 having an upstream end supported by an asymmetric spherical roller bearing 66 incorporated in the central carrier 62. This arrangement allows a simple solution for absorbing substantial axial loads originating from the bevel gearbox 8 (fig. 3). In addition, it also provides the necessary additional system flexibility to counteract the negative effects that can occur from deflection and deformation between the left and right components of the overall gearbox.

The twelfth feature relates to the following. The gearbox design of fig. 5 can be shortened by about 800mm, and the linkages between the MBU and the gearbox are shortened by about 1000 mm. This allows the entire transmission system 5 to have its center of mass closer to the tower center or longitudinal axis as a key benefit. The mass of the transmission system 5 can be reduced by an estimated 80 to 125 tons.

The stepped planetary gearbox 7 of figure 3 has a large ring gear diameter and it is likely that "only" four planets rotate in a single plane. The outer circles of the respective second planet gears of the design are already very close to each other. Thus, the maximum step-up ratio of the stepped planetary gearbox 7 of FIG. 3 is most likely limited to about 1:15 in practical designs. Furthermore, the gearbox mass and cost are considerable. With five or more second planet gears 21, which may require a higher (e.g. 10MW and more) rating and corresponding input torque, the maximum step-up ratio may even drop between 1:10 and 1:12 unless the ring gear diameter is increased again. This will eventually lead to a dead-end policy. The design of fig. 5 or aspects thereof attempt to address this problem. The features described above may be combined as in fig. 5. Also, individual elements of the features may be used in the design of FIG. 3.

Compare the designs of FIGS. 3 and 5

	FIG. 3	FIG. 5
			Planet	4, indicating a 12MW reference design	6, reference design 16MW/235m
Speed increasing ratio	Maximum possible 1:15	At least 1:22 … 25 (stop not shown)
			Limiting factor	The size and cost of the ring gear;	mainly the size and cost of the ring gear
	Deformation and deflection
				Key interface
Key interface	A plurality of	Not identified; principle of tool carrier
			Modular	Possibly, by major redesign	Is, upward and finally downward
Expandable	Not easy, several bottle necks	Easy, at least as high as 24-26MNm +
					From 6 ═>8 possible planets;
		but this will limit the step-up ratio
			Limiting factor	The number of planets; ring gear, mass	Mainly the size and cost of the ring gear
	Cost, deflection and distortion
			Shell splitting	Whether or not	Is, left + right and center brackets
Serviceability	Lower than standard	Current advanced technology offshore; upper tower
			Journal bearing	Partly in the right gearbox part	Most of the bearing position
Quality of	Height of	Competitiveness of
			Size and breadth	Big (a)	Competitiveness of
Cost of	Height of	Competitiveness of

It should also be clear that the above description and accompanying drawings are included to illustrate some embodiments of the invention and not to limit the scope of protection. Further embodiments will be apparent to the skilled person from the disclosure. These embodiments are within the scope and spirit of the present invention and are an obvious combination of the prior art and the present patent disclosure.

List of reference numerals

1 turbine rotor

2 turbine rotor shaft

3 housing of a turbomachine rotor shaft

4 flexible coupling

5 Transmission System

5A upstream Transmission component

5B downstream Transmission component

6 electric generator

7 upstream planetary gearbox

8 bevel gear box

9 downstream planetary gearbox

10 Generator rotor

11-cone driving gear

12 first bevel pinion

13 second bevel pinion

14 generator stator

15 Transmission System common housing

16-hold brake + rotor lock

17 nacelle clamp bearing

18 tower frame

19 upstream ring gear

20 upstream first planetary gear

21 upstream second planetary gear

22 second bevel pinion shaft

23 second pinion journal bearing

24 hollow small bevel gear shaft

25 generator structure shell

26 first pinion journal bearing

27 Transmission system output shaft

28 (spline) coupling

29 generator rotor shaft

30 nacelle or nacelle body

31 helicopter deck

32 input upstream gearbox shaft

33 output upstream gearbox shaft

34 upstream sun gear

35 planet gear common shaft

36 cooling radiator

37 permanent magnet

38 stator coil

39 air gap

40 gas inlet

41 gas outlet

42 liquid inlet

43 liquid outlet

50 downstream ring gear

51 downstream sun gear

52 downstream planetary gear

53 downstream planetary gear frame

54 flexible shaft coupling

55 Flexible shaft

56 other Flexible shaft coupling

57 liquid cooling

58 Generator pin (stationary shaft) for holding journal bearing

XX generator journal bearing

59 hollow generator rotor shaft

61 planetary gear pin

62 center bracket

63 ring gear pin/main gearbox pin

64 ring gear bearing

65 upstream housing part

66 rear upstream gearbox shaft bearing

67 drive plate for upstream sun gear

68 Flexible coupling for upstream sun gear

69 Flange for upstream Sun Gear

70 drive disk for upstream second planetary gear

71 Flexible coupling for a drive disk of an upstream second planetary gear

72 bearing for upstream planetary gear

73 right housing part

74 downstream bearing for upstream gearbox shaft

75 upstream ring gear carrier disc

R rotor shaft axis of rotation

R1 first and second bevel pinion axes of rotation

L Tower longitudinal axis

P1 first plane of upstream second planetary gear

Second plane of P2 upstream second planetary gear

Rp planetary gear axis of rotation

The following clauses may be formulated to describe aspects of the embodiments. In addition, claims are defined on other pages.

1. A wind turbine, comprising:

a turbine rotor including a set of turbine rotor blades and defining a rotor axis of rotation, the turbine rotor mounted on a tower;

a generator for converting mechanical energy of the turbine rotor into electrical energy, the generator comprising a generator rotor drivingly coupled to the turbine rotor and mounted on the tower;

a transmission system coupling the turbine rotor to the generator rotor and comprising:

a bevel gear box including a bevel drive gear coupled to the turbine rotor and a first bevel pinion and a second bevel pinion, wherein the first and second bevel pinions have a common axis of rotation and counter-rotate when operated;

a downstream planetary gearbox comprising a downstream ring gear, a downstream planet gear, and a downstream sun gear, wherein the first bevel pinion is drivingly coupled to one of the downstream ring gear and the downstream planet gear, the second bevel pinion is drivingly coupled to the other of the downstream planet gear and the downstream ring gear, and the generator rotor is drivingly coupled to the downstream sun gear.

2. The wind turbine of clause 1, wherein the downstream planetary gearbox is disposed between the first and second bevel pinions, in particular, between the rotor axis of rotation and one of the first and second bevel pinions.

3. The wind turbine according to clause 1 or 2, wherein the first bevel pinion is connected to the downstream planet gear, the second bevel pinion is connected to the downstream ring gear by a drive shaft, and the downstream sun gear is connected to the generator rotor via a transmission system output shaft, wherein in particular the transmission system output shaft extends through the first bevel pinion.

4. The wind turbine according to any of the preceding clauses, wherein the downstream planetary gearbox comprises a downstream planet carrier for rotatably holding the downstream planet gear, wherein the one selected from the first and second bevel pinions is coupled to the downstream planet carrier.

5. The wind turbine of any preceding clause, further comprising an upstream planetary gearbox coupling the turbine rotor and the bevel gearbox, particularly the upstream planetary gearbox comprising a 1.5 stage planetary gearbox.

6. Wind turbine according to the preceding clause 5, wherein the upstream planetary gearbox comprises a planetary transmission, in particular an upstream ring gear drivingly coupled to the turbine rotor and an upstream sun gear drivingly coupled to the drive shaft gear.

7. The wind turbine according to any of the preceding clauses 5 and 6, wherein the upstream planetary gearbox comprises an upstream planetary gear system having first and second planet gears on a common shaft, wherein the first planet gear is drivingly coupled with the ring gear and the second planet gear is drivingly coupled with the sun gear.

8. The wind turbine of any of preceding clauses 5 or 6, wherein the upstream planetary gearbox provides a gear ratio of 10 to 15.

9. The wind turbine according to any of the preceding clauses, wherein the turbine rotor is mounted on the tower with its rotor axis of rotation functionally perpendicular to the tower longitudinal axis.

10. The wind turbine according to any of the preceding clauses, wherein the turbine rotor is fixed to one end of a hollow turbine rotor shaft extending through a housing, wherein the housing is fixed to a nacelle on the tower, and an opposite end of the hollow turbine rotor shaft carries the transmission system and the generator.

11. The wind turbine of any preceding clause, wherein the generator comprises a housing and a cooling system.

12. The wind turbine of the preceding clause 11, wherein the cooling system comprises a gas cooling system including a gas cooling inlet in the generator housing for cooling gas flow into the generator and a gas cooling outlet allowing gas to exit the generator housing.

13. The wind turbine according to clause 12, wherein the generator rotor has one or more vanes for arranging the cooling gas inside the housing in motion, in particular designed to induce a flow of cooling gas from the cooling gas inlet to the cooling gas outlet when in operation.

14. Wind turbine according to any of clauses 11 to 13, wherein the stator has one or more facilities, in particular passages, for arranging the cooling gas inside the housing in motion, in particular designed to induce a flow of cooling gas from the cooling gas inlet to the cooling gas outlet when in operation.

15. The wind turbine according to any of clauses 13 to 14, wherein the gas cooling system comprises a heat exchanger for exchanging heat with a liquid flow.

Claims (15)

1. A wind turbine, comprising:

a turbine rotor including a set of turbine rotor blades and defining a rotor axis of rotation, the turbine rotor mounted on a tower;

a generator for converting mechanical energy of the turbine rotor into electrical energy, the generator comprising a generator rotor drivingly coupled to the turbine rotor and mounted on the tower;

a transmission system coupling the turbine rotor to the generator rotor and including an upstream stepped planetary gearbox comprising:

an upstream ring gear drivingly coupled to the turbine rotor;

an upstream first planet gear drivingly coupled with the upstream ring gear;

upstream second planet gears, each second planet gear rotationally coupled with the first planet gear;

an upstream sun gear drivingly coupled to the upstream second planet gear and to the generator rotor, and

the upstream second planet gears are axially offset from each other.

2. Wind turbine according to claim 1, wherein the upstream stepped planetary gearbox comprises at least four upstream second planet gears, in particular at least two sets of at least 2 upstream second planet gears, more in particular at least two sets of at least 3 upstream second planet gears, wherein in particular the upstream second planet gears of each set are functionally in an axial plane and the axial planes are axially offset with respect to each other, in particular allowing the second planet gears to overlap.

3. Wind turbine according to any of the preceding claims, comprising a common carrier rotationally carrying the upstream first and second planet gears rotatable around their axis of rotation, rotationally carrying the upstream sun gear and rotationally carrying the upstream ring gear, wherein in particular the wind turbine comprises planet pins fixed to the common carrier and each planet pin holds the upstream first planet gear and the upstream second planet gear, wherein the upstream first planet gear and the upstream second planet gear are rotationally coupled.

4. Wind turbine according to any of the preceding claims, wherein each of the upstream first planet gears is rotatably carried on a fixed pin and each of the upstream second planet gears is rotatably carried on the fixed pin, and the upstream first planet gears and the upstream second planet gears on the pin are rotationally coupled, in particular via a flexible coupling, more in particular via a shaft extending through the fixed pin.

5. A wind turbine according to any of the preceding claims when dependent on claim 3, wherein the common carrier carries an annular pin which rotatably carries the upstream ring gear.

6. A wind turbine according to any of the preceding claims when dependent on claim 3, wherein the common carrier rotatably carries the upstream sun gear.

7. The wind turbine of any preceding claim, wherein the upstream sun gear is coupled to an output shaft via a flexible coupling.

8. The wind turbine of any preceding claim, wherein the transmission system further comprises a bevel gearbox coupled to the upstream sun gear, in particular further comprising a downstream planetary gearbox coupling the bevel gearbox to the generator rotor, and/or in particular wherein the bevel gearbox comprises a bevel gear coupled to the upstream sun gear and two opposing bevel pinions coupled to the bevel gear, and one said bevel pinion is coupled to a downstream ring gear and one said bevel pinion is coupled to a downstream planetary carrier, and a downstream sun gear is coupled to the generator rotor.

9. Wind turbine according to any of the preceding claims, wherein the upstream first planet gears are each rotatable around their planet rotation axis having a fixed position with respect to the rotation axis, in particular wherein the planet rotation axis is functionally parallel to the rotation axis.

10. A wind turbine comprising a turbine rotor having a turbine rotor rotation axis and being drivingly coupled to an upstream planetary gearbox which is drivingly coupled to a right angle transmission having two opposing gears which are drivingly coupled via a downstream planetary gearbox to a generator rotor of a generator, in particular an outer rotor permanent magnet generator having a central stator, the generator rotor in particular defining a generator rotation axis which is functionally at right angles to the turbine rotor rotation axis.

11. A transmission system for a wind turbine for coupling a turbine rotor to a generator including a rotor, the transmission system comprising:

a bevel gear box including a bevel drive gear for coupling to the turbine rotor and first and second bevel pinions drivingly coupled with the bevel drive gear, wherein the first and second bevel pinions have a common axis of rotation and counter-rotate when operated,

an upstream planetary gearbox comprising an upstream ring gear, upstream planet gears and an upstream sun gear drivingly coupled to the bevel drive gear, an

A downstream planetary gearbox comprising a downstream ring gear, downstream planet gears and a downstream sun gear, wherein the first bevel pinion is drivingly coupled to one of the downstream ring gear, downstream planet gears and downstream sun gear, the second bevel pinion is drivingly coupled to another of the downstream ring gear, downstream planet gears and downstream sun gear, and the downstream sun gear is for being drivingly coupled to the generator rotor.

12. A transmission system for a wind turbine for coupling a turbine rotor to a generator including a rotor, the transmission system comprising:

a bevel gear box including a bevel drive gear for coupling to the turbine rotor and first and second bevel pinions drivingly coupled with the bevel drive gear, wherein the first and second bevel pinions have a common axis of rotation and counter-rotate in operation, an

A downstream planetary gearbox comprising a downstream ring gear, downstream planet gears and a downstream sun gear, wherein the first bevel pinion is drivingly coupled to one of the downstream ring gear and the downstream planet gears, the second bevel pinion is drivingly coupled to the other of the downstream ring gear and the downstream planet gears, and the downstream sun gear is for being drivingly coupled to the generator rotor.

13. A stepped planetary gearbox, comprising: a ring gear drivingly coupled to the first planet gears; second planet gears each rotationally coupled to the first planet gear; and a sun gear drivingly coupled to the second planet gears, wherein the second planet gears are axially offset from each other.

14. The stepped planetary gearbox of claim 13, comprising at least four of said second planet gears in two sets, wherein said second planet gears in each set functionally lie in one axial plane, and said axial planes are axially offset.

15. The stepped planetary gearbox of claim 13 or 14, wherein said ring gear is rotatable about a ring gear rotation axis and said first planet gears are each rotatable about their planet rotation axis having a fixed position relative to said ring gear rotation axis, and/or wherein said planet rotation axes are functionally parallel to said ring gear rotation axis.

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