WINDTURBINE

Field of the invention

[0001] The invention is related to the area of Clean Energy Technologies, and more specifically to a hydraulic transmission for a wind turbine where the turbine main shaft is integrated in a hydraulic pump that forms an integral part of the nacelle frame structure.

Background of the Invention

[0002] The state of the art includes wind turbine power production systems with mechanical transmission with a speed-up gear box connected to the wind turbine rotor, where the gear box drives an electric generator. This type of system constitutes a major part of the deployed wind turbine power production systems. However, mechanical transmissions are quite vulnerable for wear and about 30 % of the downtime of a conventional wind turbine is related to the mechanical gearbox. A trend in the field of so-called alternative energy is that there is a demand for larger wind turbines with higher power. Currently 5MW systems are being installed and 10 MW systems are under development.

Especially for off-shore installations far away from inhabited areas larger

systems may be environmentally more acceptable and more cost effective. In this situation the weight and maintenance access of the components in the nacelle of the wind turbines is becoming a key issue when considering that the gearbox is situated 100 to 150 m above the ground or sea level.

[0003] It has therefore been proposed in several publications to use a

hydrostatic transmission system comprising a hydraulic pump and a hydraulic motor for transferring energy from the turbine rotor to the generator. By

employing a hydraulic pump and/or motor with variable displacement, it is possible to rapidly vary the gear ratio of the hydraulic system to maintain the desired generator speed under varying wind conditions.

[0004] Common for the prior art systems is the use of a main frame in the nacelle where all the components of the nacelle are deployed and fixed to the main frame individually. For a mechanical transmission this means that the hub bearing, the gearbox and the generator are all fixed to the main frame. In the same way the hub bearing, the hydraulic pump, the hydraulic motor and the generator are all fixed to the main frame when hydraulic transmission is used. In addition a mechanical break is also fixed to the main frame in most of the

applications. [0005] One of the well known problems related to the distribution of components on a main frame in the nacelle is the deflection of the main frame due to the torque between the various components. The torque on the low speed side, i.e. between the turbine hub and the hydraulic pump becomes very high and requires the supporting main frame to be dimensioned accordingly to ensure alignment of the rotating components.

[0006] Another problem related to the low speed side of wind turbines with hydraulic pumps with high torque is the lateral deflections of the turbine shaft and also the pump shaft that is connected to - and driven by the turbine shaft due to the wind forces acting on the wind turbine rotor. Such deflections of the pump shaft may increase the wear of the pump.

[0007] Most hydraulic pumps, such as cam ring pumps suffer from Hertzian contact stress that is the main contribution to the limited lifetime of such pumps. Hertzian contact stress is the localized stresses that develop as two curved surfaces come in contact and deform slightly under the imposed loads. In cam ring pumps such stresses may increase with deflections of the pump shaft.

[0008] US patent publication US 7538446 B2 discloses a gear integrated generator for a wind turbine having a tower, a nacelle, and a hub. The gear integrated generator includes: a stator supporting frame having a stator supporting portion, a radially extending portion and a rotor frame supporting portion, wherein the stator supporting frame is stationarily mountable within the nacelle. A rotor frame is rotatably supported on the rotor frame supporting portion of the stator supporting frame.

[0009] Various pump technologies exist for different industries, however, due to the low speed and high torque requirements of a pump directly driven by a wind turbine, technology from a different technological area cannot be scaled and used with success in the wind turbine industry.

[0010] The state of the art includes a closed hydraulic loop between the hydraulic pump and the hydraulic motor of the system. Pipes, tubes or hoses are used to transfer the high pressure fluid from the pump to the motor and the lower pressure fluid from the motor to the pump. As an example for a 5MW pump the diameter of the tubes or hoses must be considerable to transport sufficient fluid to the motor, and at the same time the pressure on the high pressure side is several hundred bars. The requirements for the tubes and hoses are becoming difficult to meet as stiffness will be high and forces will be transferred between the pump and motor connecting ports. Also the relative small diameters of commercially available tubes and hoses make the pressure losses substantial.

[0011] The disclosed invention has been devised and embodied to overcome these shortcomings and to obtain further advantages as will be seen from the reminder of this document.

Short summary of the invention

[0012] The invention is set forth and characterized in the main claims, while the dependent claims describe other characteristics of the invention.

[0013] The object of the invention is to make a compact and low weight hydrostatic variable transmission and further to create a hydrostatic variable transmission for a nacelle that is less vulnerable to deflections of the main frame.

[0014] Another object of the invention is to achieve reduced wear of the hydraulic pump due to Hertzian stress.

[0015] Further, an object of the invention is to reduce the size and weight of the nacelle.

[0016] The device according to an embodiment of the invention is a wind turbine rotor shaft with specific features for solving the problems addressed above.

[0017] The wind turbine rotor shaft is arranged in a first end for being directly connected to a wind turbine hub carrying wind turbine blades. The rotor shaft comprises in a longitudinal direction of the rotor shaft;

- one or more eccentric sections eccentric to a rotational axis of the rotor shaft, wherein each of the eccentric sections are arranged for driving one or more pistons in respective cylinders when the rotor shaft rotates about the rotational axis, where the cylinders are arranged mainly perpendicular to the wind turbine rotor shaft, and

- a first circular section being circular around the rotational axis of the turbine rotor shaft, the first circular section arranged between the first end and the one or more eccentric sections, and further arranged for being carried by a first bearing. The pistons and cylinders may be comprised in one or more hydraulic pumps.

[0018] In an embodiment the wind turbine rotor shaft comprises a second circular section arranged in a second end of the wind turbine rotor shaft, opposite the first end, and further arranged for being carried by a second bearing.

[0019] The wind turbine rotor shaft according to the invention allows a compact and integrated nacelle solution that has several advantages over prior art.

[0020] In prior art the turbine support and the hydraulic pump are usually arranged in series, requiring two sets of bearings and a coupling between the turbine shaft and the pump shaft. According to the invention only a single moment bearing or one pair of bearings may be used, making it a more compact and low weight solution.

[0021] It is an object of the invention to reduce the life limiting features of the drivetrain. The hydrostatic balanced piston towards the eccenter and cylinder towards the top spherical cup (top locator) is self adjustable on the spherical surfaces and will function optimal even at large shaft deflections. Also the life limiting Hertzian stresses is avoided by the use of hydrostatic balancing where the oil pressure directly works on the metal surface instead of life limiting Hertzian contact.

[0022] In an embodiment of the invention the eccentric sections are spherical segments. The use of spherical surfaces makes the design highly tolerable to shaft deflections, since the pistons, which may also have a spherical shape, will impinge the eccentric section over their whole contact surface even when the turbine shaft undergoes deflection movements as a result of forces from the turbine rotor, or from forces internally in the pump due to the high fluid pressure. The spherical eccenter drivetrain design is littlesensitive to both main shaft and main frame deflections.

[0023] In another aspect the invention is also a nacelle integrated power production system comprising a wind turbine rotor shaft as described above, and at least one hydraulic pump housing comprising the one or more pistons and respective cylinders, and a pump housing comprising the first bearing supporting the first circular section. In an embodiment the pump housing comprises also the second bearing supporting the second circular section.

[0024] The invention has the advantage that the internal structure of the nacelle becomes stiffer as the cylindrical pump housing can help to stiffen the main frame, there are fewer parts as bearings and the shaft is the same for both the hydraulic pump and the wind turbine main shaft.

[0025] According to an aspect of the invention the nacelle integrated power production system comprises one or more hydraulic motors arranged for being driven by the hydraulic pump, where the hydraulic motors comprises hydraulic motor housings directly mounted on to the pump housing. [0026] The integration of the hydraulic pump and the hydraulic motor is exploited by letting the hydraulic circuit pass through integrated flow channels of the housings of the hydraulic pump and the hydraulic motor. In an aspect of the invention the entire hydraulic circuit between a high pressure output of the hydraulic pump and a high pressure input of the hydraulic motor is arranged as one or more channels inside the pump housing and the motor housings. Flow channels inside the housings solve many of the problems experienced by the use of pipes and hoses in prior art systems.

[0027] According to an embodiment of the invention integrated flow channels in one or more hydraulic integration flanges on the pump or motor supplies the motor through large flow channels and also delivers flow from the motor to the pump. This system is not sensitive to thermal expansion, vibrations, stiffness nor limited to small internal diameters as is well known for flexible elements as hoses.

[0028] The hydraulic integration flange on the pump or motor is in one embodiment arranged for fixation of both motor and generator on the pump housing and thus minimizes alignment issues common for drivetrains.

[0029] In an aspect of the invention the nacelle integrated power production system comprises one or more electric generators directly mounted on to the pump housing, wherein each the electric generators are directly driven by a hydraulic motor. In this aspect all the heavy weight components, i.e. the turbine hub, the hydraulic pump, the hydraulic motor(s) and the electric generator(s) are all integrated with the pump, and there will be no need for the main frame to handle the forces between the main components of the nacelle since this is done by the pump housing.

[0030] In an aspect of the invention one or more electric generators are directly mounted on to the motor housing or pump housing, wherein each the electric generators are directly driven by a hydraulic motor.

[0031] According to an aspect of the invention the pump housing comprises a low pressure ring manifold and a high pressure ring manifold with radii perpendicular to the wind turbine rotor shaft wherein the low pressure ring manifold and the high pressure ring manifold are arranged in opposite first and second ends of the hydraulic pump respectively. According to an aspect one or more high pressure channels extend from a high pressure side of the cylinder top to the high pressure ring manifold, and one or more low pressure channels extend from a low pressure side of the cylinder top to the low pressure ring manifold.. [0032] An advantage of the manifold design above is the strength of the structure. The large diameter low and high pressure ring manifold and low and high pressure channels designed to withstand hydraulic fluid pressure will in addition have high load carrying capacity. The load carrying capacity can then be used for carrying part of the wind turbine loads and pump forces, ensuring optimal utilization of material resulting in a weight optimal design.

Short figure captions

[0033] Fig. 1 illustrates in a section view a nacelle integrated hydraulic transmission according to an embodiment of the invention.

[0034] Fig. 2 illustrates in a section view a turbine shaft according to an embodiment of the invention.

[0035] Fig. 3 illustrates in a section view a piston in a cylinder driven by an eccentric section of the turbine shaft, where the outer surface of the eccentric section has a spherical shape.

[0036] Fig. 4 illustrates in a perspective section view parts of a hydraulic circuit between a hydraulic pump and a hydraulic motor.

[0037] Fig. 5 illustrates in a simplified view the manifolds of the hydraulic pump according to an embodiment of the invention.

Embodiments of the invention

[0038] With reference to the attached drawings the device and system according to the invention will now be explained in more detail.

[0039] In figure 1 and figure 2 a wind turbine rotor shaft (1) is according to an embodiment of the invention arranged in a first end (A) for being directly connected to a wind turbine hub (7) carrying wind turbine blades, the rotor shaft (1) comprising in a longitudinal direction of the rotor shaft (1);

- one or more eccentric sections (5) eccentric to a rotational axis (O) of the rotor shaft (1), wherein each of the eccentric sections (5) are arranged for driving one or more pistons (3) in respective cylinders (4) when the rotor shaft (1) rotates about the rotational axis (O), where the cylinders (4) are arranged mainly perpendicular to the wind turbine rotor shaft (1), and

- a first circular section (20a) being circular around the rotational axis (O) of the turbine rotor shaft (1), the first circular section (20a) arranged between the first end (A) and the one or more eccentric sections (5), and further arranged for being carried by a first bearing (2a).

[0040] In this embodiment the first bearing (2a) is a single moment bearing that will carry the weight of the turbine hub (7) including the rotor blades.

[0041] According to an embodiment of the invention the wind turbine rotor shaft (1) comprises a second circular section (20b) arranged in a second end (B) of the wind turbine rotor shaft (1) opposite the first end (A) and further arranged for being carried by a second bearing (2b).

[0042] In this embodiment the first and second circular sections (20a, 20b) are arranged for being carried by bearings. They may therefore have different diameters and length, according to the requirements of the bearings. Typically, the first circular section (20a) closest to the turbine hub and its corresponding bearing (2a) will carry most of the weight of the turbine hub rotor, and will be of a larger dimension, e.g. diameter and length than the second circular section (20b) and its corresponding bearing (2b).

[0043] Seen from the end of the turbine rotor shaft (1), the centre of the first circular section (20a) and the second circular section (20b) coincides with the rotational axis (O). The eccentric sections (5) may in this embodiment also be circular, but their centres do not coincide with the rotational axis (O).

[0044] The pistons and cylinders may be comprised in one or more hydraulic pumps (50).

[0045] The first and second bearings (2a, 2b) may be e.g. rolling-element bearings, plain bearings, hydrostatic journal and thrust bearings or a

combination of these.

[0046] The bearings carrying the rotor shaft (1) takes the combined loads from the wind turbine rotor hub, including the rotor blades and the loads from the pumps piston/cylinder strokes.

[0047] The number of eccentric sections (5) can vary, depending on design parameters of the hydraulic pump. In Fig. 1 and 2 an example shaft with three eccentric sections is shown, but other numbers may be used . For each section a number of cylinders may be distributed around the eccentric section, where the cylinders of each section are distributed in a star topography, i.e. a radial piston pump. When an eccentric section (5) rotates, the piston (3) of a cylinder (4) will follow the eccentric section, and go through a pump cycle where the smallest volume of the cylinder (4) will occur when the eccentric section (5) pushes the piston (3) a maximum distance away from the rotation axle (O). Vice - versa, the largest volume of the cylinder (4) will occur when the eccentric section (5) pushes the piston (3) a minimum distance away from the rotation axle (O). In Fig. 1 the top, middle piston shown is at its maximum distance away from the rotation axle (O), and the cylinder (4) is therefore in its most compressed state. It can also be seen from Fig. 1 that the lower, middle piston shown is at its minimum distance away from the rotation axle (0), and the cylinder (4) is therefore in its least compressed state. Therefore opposite cylinders will be in opposite parts of the pump cycle.

[0048] In an embodiment of the invention at least one of the eccentric sections (5) have a length (I) in the longitudinal direction of the turbine rotor shaft (1) that is different from the length (I) of another of the eccentric sections (5).

[0049] The eccentric sections (5) may be individually displaced seen from the end of the rotor shaft (1) to allow balancing of the pump forces with respect to the bearings. In an embodiment of the invention at least two of the eccentric sections (5) have a reciprocal phase difference of more than 0 degree.

[0050] In an embodiment of the invention at least two of the eccentric sections (5) have a reciprocal phase difference of 180 degree.

[0051] Fig. 1 shows an example of load balancing of turbine shaft according to an embodiment of the invention. Here the middle eccentric section (5) has a length (I) that is longer than the length (I) of the two other eccentric sections (5). In this example the eccentric section in the middle has a 180 degree phase difference with regard to the two outer eccentric sections, and the forces from the pistons acting on the turbine shaft can in this way be balanced out to reduce the forces acting on the bearings (2a, 2b). In this embodiment the middle cylinder (4) volume should be equal to the sum of the volumes of the two outer cylinders (3)

[0052] However, the number of eccentric sections, the distribution of cylinders around the turbine shaft (1) and the phase difference between the eccentric sections (5) may be selected in many different ways to handle load balancing. Another examples would be four eccentric sections where the two eccentric sections in the middle have a 180 degree phase difference relative the two outer eccentric sections.

[0053] In an embodiment the eccentric sections (5) have different diameters. This gives an additional flexibility for the design of the hydraulic pump (50).

[0054] In an embodiment the one or more eccentric sections (5) are cylindrical segments.

[0055] In an embodiment an outer surface of the one or more eccentric sections (5) are spherical segments as can be seen in Fig. 2 The spherical segments can be symmetrical or non-symmetrical. The use of spherical segments allows self positioning, making the system more tolerant for deflections, since the pistons, which may also have a spherical shape, will impinge the eccentric section over their whole contact surface even when the turbine shaft undergoes deflection movements as a result of forces from the turbine rotor, or from forces internally in the pump due to the high fluid pressure.

[0056] This is shown more clearly in Fig. 3. To the left in the figure a section view of one cylinder (4) with an internal piston (3) is shown. The piston (3) is pushed into the cylinder (4) by the eccentric section (5) of the turbine shaft (1) when the turbine shaft (1) is rotated about its rotational axis (O) as illustrated, and will move up and down inside the cylinder (4).

[0057] In an embodiment of the invention the piston (3) comprises a concave spherical contact surface (31). The concave spherical contact surface (31) is arranged for allowing the piston (3) to move relative the corresponding eccentric section (5), which is convex and to maintain the piston (3) in contact with the eccentric section (5) over the entire contact surface (31) of the piston (3). In the right part of Fig. 5 this is also shown for the section A-A which is rotated 90 degree relative the sectional view in the drawing to the left.

[0058] As the piston (3) follows the eccentric section, the cylinder (4) and piston (3) assembly can follow the surface of the eccentric section (5) to ensure that the piston (3) is constantly impinging the surface of the eccentric section.

[0059] In an embodiment of the invention the pump housing (50) comprises a cylinder top (41) fixed to the pump housing (50) for each cylinder (4), wherein the cylinder top (41) has a concave spherical surface (42) and the cylinder (4) has a convex spherical surface (43). The concave spherical surface (42) is arranged to move inside the convex spherical surface (43), as can be seen in the left part of Fig. 5.

[0060] However, according to another embodiment of the invention, the cylinder top may also be designed in the opposite way, wherein the pump housing (50) comprises a cylinder top (41) fixed to the pump housing (50) for each cylinder (4), wherein the cylinder top (41) has a convex spherical surface

(42) and the cylinder (4) has a concave spherical surface (43) and the convex spherical (42) surface is arranged to move inside the concave spherical surface

(43) .

[0061] The cylinder top (41) may comprise valves arranged for controlling the fluid flow in and out of the cylinder (4).

[0062] Thus, due to the spherical ends of the cylinder (4) and piston (3) assembly towards the eccentric section (5) of the turbine shaft (1) in one end and towards the cylinder top (41) in the other end, the cylinder (4) and piston (3) assembly will follow the rotational, lateral and longitudinal movements of the turbine shaft (1) and still be able to maintain the piston (3) in contact with the eccentric section (5) over the entire contact surface (31) of the piston (3). This will reduce wear of the piston and other elements of the pump that may occur due to deflections of the turbine shaft (5) as a result of forces from the wind turbine rotor and pump internal forces.

[0063] In an embodiment of the invention the wind turbine rotor shaft (1) comprises in the first end (A) a turbine hub flange (8) for being directly connected to the wind turbine hub (7). This is illustrated in Fig. 1 and 2. In fig. 1 the turbine hub flange (8) of the turbine shaft (1) is shown mounted to the turbine hub (7). The turbine hub flange (8) may preferably be an integral part of the turbine shaft (1) or mounted by welding or other fastening means after turnery or casting.

[0064] The turbine shaft (1) may be hollow as shown in Fig. 1 or solid. A hollow structure may be preferable due to weight versus strength considerations, but this depends on the material used. A hollow structure may also be preferable for the purpose of allowing electric wiring and possibly hydraulic pipes or tubes to the turbine hub for e.g. the control of turbine pitch angle.

[0065] The different features described above for the wind turbine shaft (1) may be combined in different embodiments. E.g. the turbine shaft (1) according to the invention may comprise any combination of zero or more of the following features;

- the one or more eccentric sections (5);

- the first bearing (2a);

- the second bearing (2b);

- additional bearings not described here;

- the one or more eccentric sections (5) being spherical or cylindrical segments;

- the turbine hub flange (8);

- at least one of the eccentric sections (5) have a length (I) in the longitudinal direction of the turbine rotor shaft (1) that is different from the length (I) of another of the eccentric sections (5);

- at least two of the eccentric sections (5) have a reciprocal phase difference of more than 0 degree;

- at least two of the eccentric sections (5) have a reciprocal phase difference of 180 degree;

- the turbine shaft (1) is solid or hollow; - other features of the turbine shaft (1) described in this document.

[0066] The invention is also an integrated power production system (60). This system will now be described in more detail with reference to Fig. 1.

[0067] In an embodiment the integrated power production system (60) comprises a wind turbine rotor shaft (1) with a first circular section (2a) arranged for being carried by a first bearing (2a) as described above, at least one hydraulic pump (50) comprising the one or more pistons (3) and respective cylinders (4), and a pump housing (51) comprising the first bearing (2a) according to claim 1, wherein the first bearing (2a) supports the first circular section (20a). In this embodiment the first bearing (2a) is a single moment bearing that will carry the weight of the turbine hub (7) including the rotor blades. In this embodiment the turbine rotor shaft (1) may comprise any combination of the features for the turbine rotor shaft (1) mentioned above.

[0068] According to the invention two bearings may also be used, one on each side of the eccentric sections (5) as described previously. In this embodiment the integrated power production system (60) comprises a wind turbine rotor shaft (1) as described above, and a pump housing (51) comprises the second bearing (2b) also described above, where the second bearing (2b) supports the second circular section (20b). In this embodiment the first bearing (2a) and second bearing (2b) are carried by the pump housing (51) and the turbine shaft (1) is supported by the two bearings. In this embodiment the turbine rotor shaft (1) may comprise any combination of the features for the turbine rotor shaft (1) mentioned above.

[0069] A nacelle integrated power production system (60) comprising a wind turbine rotor shaft (1) arranged in a first end (A) for being directly connected to a wind turbine hub (7) carrying wind turbine blades, the rotor shaft (1) comprising in a longitudinal direction of the rotor shaft (1);

- one or more eccentric sections (5) eccentric to a rotational axis (O) of the rotor shaft (1), wherein each of the eccentric sections (5) are arranged for driving one or more pistons (3) in respective cylinders (4) when the rotor shaft (1) rotates about the rotational axis (O), where the cylinders (4) are arranged mainly perpendicular to the wind turbine rotor shaft (1), and

- a first circular section (20a) being circular around the rotational axis (O) of the turbine rotor shaft (1), the first circular section (20a) arranged between the first end (A) and the one or more eccentric sections (5), and further arranged for being carried by a first bearing (2a), the nacelle integrated power production system (60) further comprising and at least one hydraulic pump (50) comprising the one or more pistons (3) and respective cylinders (4), and a pump housing (51) comprising the first bearing (2a) according to claim 1, wherein the first bearing (2a) supports the first circular section (20a).

[0070] The wind turbine rotor shaft (1) comprised in any embodiment of the nacelle integrated power production system (60) above, may comprise any of the features of the turbine shaft (1) as described previously in this document.

[0071] The integrated power production system (60) comprises in an embodiment according to the invention one or more hydraulic motors (70) arranged for being driven by the hydraulic pump (50), the hydraulic motors (70) comprising hydraulic motor housings (71) directly mounted on to the pump housing (51). In Fig. l it is shown one hydraulic motor (70) with a hydraulic motor housing (71) mounted onto the pump housing (51). In the illustration the pump housing (51) comprises a hydraulic integration flange (100). The hydraulic motor housing (71) is mounted onto the hydraulic integration flange (100). The hydraulic integration flange (100) may be an integral part of the pump housing (51) or mounted by welding or other fastening means after production, such as e.g. bolting.

[0072] The hydraulic motor housing (71) can be fastened to the hydraulic integration flange (100) by any fastening means, such as screws etc.

[0073] According to another embodiment of the invention the hydraulic integration flange (100) is an integral part of the hydraulic motor housing (71) or mounted by welding or other fastening means after production, such as e.g. bolting.

[0074] According to an embodiment of the invention the pump housing comprises two integration flanges (100) for each hydraulic motor (70), arranged for being connected to a first end and a second end of the hydraulic motor housing (71) of the hydraulic motor (70).

[0075] The integrated power production system (60) comprises in an embodiment of the invention hydraulic circuit between the hydraulic pump (50) and the hydraulic motors (70). This is illustrated in Fig. 4. The integrated power production system (60) comprises a high pressure hydraulic circuit (80) between a high pressure output (not shown) of the hydraulic pump (50) and a high pressure input (not shown) of the hydraulic motor (70), wherein the entire high pressure hydraulic circuit (80) is arranged as one or more channels inside the pump housing (51) and the motor housings (71). In a preferred embodiment the high pressure hydraulic circuit (80) is also arranged as channels inside the hydraulic integration flange (100). In addition the integrated power production system (60) comprises in an embodiment a return hydraulic circuit (81) between a low pressure output (not shown) of the hydraulic motor (70) and a low pressure input (not shown) of the hydraulic pump (50). In this embodiment the high pressure hydraulic circuit (80) and the return hydraulic circuit (81) constitute a closed hydraulic loop.

[0076] According to an embodiment of the invention the high pressure hydraulic circuit (80) is arranged as one or more channels inside the pump housing (51) and inside a first end of at least one of the one or more of the motor housings (71) and a low pressure return hydraulic circuit (81) is arranged as one or more channels inside the pump housing (51) and inside a second end, opposite to the first end of the one of the one or more of the motor housings (71).

[0077] According to an embodiment of the invention where the pump housing (51) or the motor housing (71) comprises two integration flanges (100) for each hydraulic motor (70), as described above, the high pressure hydraulic circuit (80) is arranged as one or more channels inside a first of the two integration flanges (100), and the return hydraulic circuit (81) is arranged as one or more channels inside a second of the two integration flanges (100). In this

embodiment the high pressure fluid from the hydraulic pump (50) will enter into the hydraulic motor (70) via the first integration flange (100) in one end, or one side, and leave the hydraulic motor (70) on the opposite end or opposite side via the second integration flange (100) before it is returned to the hydraulic motor (50).

[0078] The hydraulic pump (50) and hydraulic motors (70) may have a fixed displacement or variable displacement to create a hydraulic transmission system with a variable gear. In an embodiment of the invention at least one of the hydraulic motors (70) is a variable displacement hydraulic motor. The hydraulic pump (50) may have fixed displacement, discrete step displacement or variable displacement.

[0079] It is an objective of the invention to reduce the life limiting features of the drivetrain. The hydrostatic balanced piston towards the surface of the eccentric section and cylinder towards the cylinder top (top locator) is self adjustable on the spherical surfaces and will function optimal even at large turbine shaft deflections.

[0080] In an embodiment of the invention the pistons (3) are hydrostatic balanced towards the eccentric sections (5) and the corresponding cylinder (4) is self adjustable on the concave spherical surface (42) of the cylinder top (41). [0081] The life limiting Hertzian stresses is avoided by the use of hydrostatic balancing where the oil pressure directly works on the metal surface instead of life limiting metal to metal contact. In an embodiment of the invention the fluid under pressure inside the piston (3) lubricates a concave spherical contact surface (31) of the piston (3).

[0082] In an embodiment of the invention the pump housing (50) and the motor housing (71) is produced as one integral piece. In this embodiment the hydraulic integration flange (100) is not needed, and the closed hydraulic loop can run directly inside the integral piece between the pump side and the motor side as channels inside the housing material.

[0083] In an embodiment the integrated power production system (60) comprises one or more electric generators (90) directly mounted on to the pump housing (51), wherein each the electric generators are directly driven by a hydraulic pump (70). In Fig. l it is shown one electric generator (90) mounted onto the pump housing (51). In the illustration the pump housing (51) comprises the hydraulic integration flange (100) that is used to integrate the motor housing (71) and pump housing (51) as described above. In this embodiment the integration flange (100) is arranged for connection of a hydraulic motor shaft to an electric generator shaft to allow the hydraulic motor to drive the electric generator directly. The electric generator (90) can be fastened to the hydraulic integration flange (100) by any fastening means, such as screws etc.

[0084] It is an object of the invention to provide an integrated nacelle solution. According to an embodiment of the invention the pump housing (51) is directly mounted onto the nacelle mainframe (6). According to another embodiment the pump housing (51) is an integral part of the nacelle mainframe (6).

[0085] According to an embodiment of the invention the pump housing (51) is directly mounted onto a yaw drive on top of a wind turbine tower. This has the advantage that the conventional main frame is not needed as an intermediate component, and a more compact and robust nacelle solution can be deployed.

[0086] According to an embodiment of the invention hydraulic pump (50) comprises flow channels arranged along, or close to the circumference of the hydraulic pump (50) as can be seen in Fig. 5. In this embodiment the pump housing (51) comprises a low pressure ring manifold (201) and a high pressure ring manifold (202) with radii perpendicular to the wind turbine rotor shaft (1) wherein the low pressure ring manifold (201) and the high pressure ring manifold (202) are arranged in opposite first and second ends of the hydraulic pump (50), respectively. In an embodiment one or more high pressure channels (204) extend from a high pressure side of the cylinder top (41) to the high pressure ring manifold (202) and one or more low pressure channels (203) extend from a low pressure side of the cylinder top (41) to the low pressure ring manifold (201). The high pressure ring manifold (202) may in an embodiment be connected to the high pressure side of one or more of the hydraulic motors (50) and the low pressure ring manifold (201) may in an embodiment be connected to the low pressure side of one or more of the hydraulic motors (50), e.g. by the first and second integration flanges (100) as described above. The low pressure channels (203) and high pressure channels (204) will in this embodiment have large radius, ensuring minimal change of direction for the hydraulic fluid flow from low pressure side to high pressure side, resulting in low pressure losses.

[0087] Valves may be used in the cylinder top (41) to control the flow of hydraulic fluid between the cylinder top (41) and the low pressure channels (203) and high pressure channels (204).

[0088] In Fig. 5 only one cylinder top (41) is illustrated. However, in an embodiment the cylinders (4) are distributed in a number of rows equal to the number of eccentric sections (5) of the wind turbine rotor shaft (1) and with a number of cylinders distributed in a circle around the wind turbine rotor shaft (1) for each row. E.g. ; if there are three eccentric sections (5) and six cylinders (4) for each sections there will be 18 cylinders (4) and 18 cylinder tops (41) in total distributed around the wind turbine rotor shaft (1), meaning that there will also be low and high pressure channels (203, 204) distributed around the wind turbine rotor shaft (1). The actual layout of the distribution may be done in several ways, where e.g . each low and high pressure channels (203, 204) may feed one or more cylinder tops (41).

[0089] Another beneficial feature of this embodiment is the strength of the structure. The large diameter low and high pressure ring manifold (201, 202) and low and high pressure channels (203, 204) designed to withstand hydraulic fluid pressure will in addition have high load carrying capacity. The load carrying capacity can then be used for carrying part of the wind turbine loads and pump forces, ensuring optimal utilization of material resulting in a weight optimal design.

[0090] The different features described above for the nacelle integrated power production system (60) may be combined in different embodiments. E.g. the nacelle integrated power production system (60) according to the invention may comprise any combination of zero or more of the following features in addition to one of the embodiments of the wind turbine rotor shaft (1) as described above;

- the at least one hydraulic pump (50) comprising the one or more pistons (3) and respective cylinders (4), and a pump housing (51) comprising the first bearing (2a);

- the pump housing (51) may comprise the second bearing (2a);

- the one or more hydraulic motors (70) comprising motor housings (71);

- the one or more hydraulic motors (70) mounted directly on to the pump housing (51);

- the high pressure hydraulic circuit (80);

- the high pressure hydraulic circuit (80) is arranged as one or more channels inside the pump housing (51) and motor housings (71);

- the high pressure hydraulic circuit (80) is arranged as one or more channels inside a first end of the motor housings (71);

- the high pressure hydraulic circuit (80) is arranged as one or more channels inside a second end of the motor housings (71) opposite the first end of the motor housings (71);

- the low pressure return hydraulic circuit (81);

- the at least one of the hydraulic motors (70) is a variable displacement hydraulic motor;

- the pump housing (51) is directly mounted onto a yaw drive on top of a wind turbine tower;

- the one or more electric generators (90) directly mounted on to the pump housing (51);

- each electric generator (90) is directly driven by a hydraulic motor (70);

- pump housing (50) comprises a cylinder top (41) fixed to the pump housing (51) for each cylinder (4);

- the cylinder top (41) has a concave spherical surface (42) and the cylinder (4) has a convex spherical surface (43) or vice-versa;

- the concave spherical (42) surface is arranged to move inside the convex spherical surface (43) or vice-versa;

- the pistons (3) are hydrostatic balanced towards the eccentric sections (5) and the corresponding cylinder (4) is self adjustable on the concave spherical surface (42) of the cylinder top (41);

- the fluid under pressure inside the piston (3) lubricates a concave spherical contact surface (31) of the piston (3);

- the pump housing (51) comprises the low pressure ring manifold (201) and/or the high pressure ring manifold (202); - the pump housing (51) comprises the one or more high pressure channels (204) and/or the one or more low pressure channels (203).

[0091] An integrated power production system (60) for a nacelle as illustrated in Fig. 1 has been described. The integrated solution has a number of

advantages over prior art that has already been mentioned. In addition to the components described here and shown in the figures additional technology, such as e.g. a tower, turbine blades, yaw system, control system, hydraulic components and valves, etc. as will be understood by a person skilled in the art will be necessary for deployment of the wind turbine power production system.

[0092] The pump housing (51) with the integrated turbine shaft (1) and one or both of the first and second bearings (2a, 2b) can in an embodiment of the invention be used where one or more hydraulic motors (70) and one or more electric generators (90) arranged on the ground or near the ground. In this case tubes or hoses may be used between the hydraulic pump (50) in the nacelle and the hydraulic motor (70) on the ground or near the ground.