Rotor blade bearing for underwater turbine

Abstract

Disclosed is a rotor blade bearing arrangement (214) for an underwater turbine (1), wherein the rotor blade bearing arrangement (214) is designed to rotatably support a rotor blade shaft (204) in a rotor hub housing (202), wherein the rotor blade shaft (204) has a seaward end (207) designed to be connected in a rotationally fixed manner to a rotor blade (4), and a rotor hub-side end (208) designed to be received by a rotor hub (2), and wherein the rotor blade bearing arrangement (214) has the rotor blade shaft (204) and a first seaward bearing unit (220) and a second rotor hub-side bearing unit (230), wherein the first and the second bearing units (220; 230) are arranged at a distance W from one another, wherein the first and the second bearing units (220; 230) are designed as plain bearings (225; 235), each having an inner Sliding surface (282; 292) and an outer sliding surface (281;291), wherein the inner sliding surface (292) of the first sliding bearing (225) is formed on the seaward end (207) of the rotor blade shaft (204) and the inner sliding surface (282) of the second sliding bearing (235) is formed on the rotor hub-side end (208) of the rotor blade shaft (204), and wherein the outer sliding surfaces (281; 291) of the first and second sliding bearings (225; 235) are formed by a rotor hub housing section (252; 262), wherein the rotor hub housing section (252; 262) is formed in a hollow tube shape and has a seaward end (255), on which the sliding layer (291) for the first sliding bearing (225) is formed, and a rotor hub-side end (254), on which the sliding layer (281) for the second sliding bearing (235) is formed, has.;

Description

Technical FieldThe present invention relates to a rotor blade bearing arrangement for an underwater turbine according to the preamble of claim 1, and to a rotor hub arrangement having such a rotor blade bearing arrangement.Background ArtRotor blades of subsea turbines are typically attached to a rotor hub and may be rotatably mounted with respect to the rotor hub. By rotating or pivoting the rotor blades, the drive power can be varied. In addition, the rotor blade adjustment serves to rotate the rotor blades in such a way that no torque is introduced from the rotor blades into the rotor hub, and thus the turbine as a whole can come to a standstill. In some embodiments, the blade adjustment is used to be able to adapt to changing water flow directions without the entire subsea turbine having to be rotated.The loads induced by the rotor blades, in particular the high bending moment, however, lead to a high load on the rotor blade bearings and thus to a high risk of damage to the rotor blade bearings, which in turn leads to long downtime of the turbine. Moreover, forceful forces due to water pressure act on the blade bearings.It is therefore an object of the present invention to provide a rotor blade bearing arrangement which can withstand high loads during the operating period.SUMMARY OF THE INVENTIONThis object is achieved by a rotor blade bearing arrangement according to patent claim 1, and by a rotor hub according to patent claim 11.A rotor blade bearing arrangement for an underwater turbine is presented below, wherein the rotor blade bearing arrangement is designed to rotatably support a rotor blade shaft in a rotor hub housing. The rotor blade shaft has a sea-side end which is designed to be connected to a rotor blade in a rotationally fixed manner, and a rotor-hub-side end which is designed to be received by a rotor hub. The rotor blade bearing arrangement comprises the rotor blade shaft, a first sea-side bearing unit and a second rotor hub-side bearing unit, wherein the first and the second bearing unit are arranged at a distance W from one another.In order to provide a rotor blade bearing arrangement which withstands the high loads and the high temperature differences, it is proposed that the first and the second bearing unit are designed as slide bearings which each have an inner slide surface and an outer slide surface, wherein the inner slide surface of the first slide bearing is formed at the sea-side end of the rotor blade shaft and the inner slide surface of the second slide bearing is formed at the rotor hub-side end of the rotor blade shaft, and wherein the outer slide surfaces of the first and the second slide bearings are formed by a rotor hub housing section, wherein the rotor hub housing section is formed in the shape of a hollow tube and has a sea-side end at which the slide layer is formed for the first slide bearing and a rotor hub-side end at which the slide layer is formed for the second slide bearing.The rotor hub itself preferably has a rotor hub housing which defines an interior space. In order to configure the housing wall as thin as possible, but nevertheless to achieve a high rigidity, such that the underwater turbine can also withstand high water pressures and rotor blade loads, the rotor hub housing can furthermore be reinforced with reinforcing ribs which are arranged in the interior space and reinforce the structural stability of the rotor hub housing. In addition, as a further advantageous exemplary embodiment shows, an assembly opening can be provided in the rotor hub housing, which ensures accessibility to the interior of the rotor hub.According to a preferred embodiment, the rotor hub housing has a hollow tube-shaped rotor hub housing section which is formed integrally with the rotor hub housing and which is designed to be equipped with the outer sliding surfaces.Alternatively, an exemplary embodiment is therefore proposed in which the rotor hub housing section is designed as a housing section which is separate from the rotor hub housing and can be installed together with the rotor blade bearing arrangement and the rotor blade shaft in a rotor hub housing. The rotor hub housing section is then fastened to the rotor hub housing, for example, by means of fastening means, in particular screws. Alternatively, the rotor hub housing section can also be pressed into a correspondingly configured receptacle on the rotor hub housing.As a result, the rotor blade bearing arrangement is designed as a module which is easily inserted into the rotor hub. The module preferably has fully adjusted and / or fully prestressed bearing units and can be inserted into the rotor hub without further adjustments. As further preferred exemplary embodiments show, the rotor hub bearing module can furthermore also have a seawater seal and / or optionally further rotor blade shaft adjustment components (e.g. gearwheels), etc., which are preassembled on the rotor blade bearing arrangement outside the rotor hub and are mounted as a unit in the rotor hub in a further assembly step. The advantage of the modular construction is the simplified assembly of the bearing units, since the latter can be effected outside the rotor hub housing with good accessibility, and, as mentioned above, can be fully adjusted and pre-tensioned in the rotor hub. The individual modules can also be replaced very quickly for service work and in the event of damage.In order to achieve ideal tilting rigidity and thus high load-bearing capacity and at the same time to compensate for the effects of the thermal differences in the rotor blade bearing arrangement, it is proposed to arrange the first bearing unit and the second bearing unit at a bearing spacing W at a distance from one another in such a way that the following applies to the bearing spacing W: 0.8*D1≤W≤2*D1, preferably 1*D1≤W≤1.5*D1, wherein D1indicates a diameter of the rotor blade shaft at the location of the first sea-side bearing unit.According to a further preferred embodiment, the first bearing unit has a larger bearing diameter than the second bearing unit. Due to the smaller design of the second bearing unit, it can be produced more cost-effectively and the mounting of the first bearing unit on the shaft is simplified.According to a further preferred embodiment, at least one of the sliding surfaces has a sliding coating. Since both the rotor blade shaft and the rotor hub housing section are usually made of steel, a steel-steel sliding pairing would be present in the bearing units designed as plain bearings, which has relatively poor sliding properties. If, on the other hand, one of the sliding surfaces is coated with a sliding coating, this can significantly improve the sliding capability. Particularly preferred in this case is a slide coating with a plastic or a fiber composite material, wherein the fiber composite material in particular comprises slide fibers. The plastic or the fiber composite material can comprise in particular PTFE as sliding material.According to a further preferred embodiment, at least one slide bearing has radial slide surfaces which are formed in a wedge-like manner. As a result, a bearing arrangement can be provided in the case of plain bearings as well, which bearing arrangement exhibits an O-arrangement. As a result, a high bending stiffness can be achieved and an improved introduction of force from the rotor shaft via the bearing unit into the rotor hub and / or a stiffening rib formed on the rotor hub. The concept of the continuous force flow path is likewise embodied on the contour of possible inner stiffening ribs which are formed on the rotor hub housing. Here too, a force flow transmission can then take place from the rotor blade shaft to the inner bearing and then via the specially shaped reinforcing ribs to the outer contour of the hub. The theoretical lines of force are combined at the flange connection between the rotor hub and the rotor main shaft and are introduced here into the surrounding structure (rotor main shaft).Alternatively, at least one slide bearing has radial slide surfaces which are cylindrical. This type of slide bearings can be produced particularly easily and well, since only cylindrical sliding surfaces with a single diameter have to be formed on the rotor blade shaft or on the rotor hub housing section and it does not have to be ensured that the inclination angles of the sliding surfaces are exactly matched to one another.According to a further preferred exemplary embodiment, the rotor blade shaft has, at its sea-side end, a stop step with a first sea-side annular axial sliding surface which interacts with a first complementary annular axial sliding surface formed on the rotor hub housing section.Alternatively or additionally, the rotor blade shaft can also have a stop step at its rotor hub-side end, which stop step is designed to cooperate with a one- or multi-part fastening ring, in particular a shaft nut with a thrust washer, in order to fasten the rotor blade shaft in the rotor hub housing section with a defined installation position, wherein the fastening ring has a second rotor hub-side annular axial sliding surface, which cooperates with a second complementary annular axial sliding surface formed on the rotor hub housing section.Both stop surfaces serve to secure the rotor blade shaft in a specific position with respect to the rotor hub housing section and thus in a specific position in the rotor hub. This allows exact alignment of the components, which is necessary for the connection to a drive mechanism.It is furthermore advantageous if the inner sliding surfaces of the first and the second sliding bearing are each formed by a first and a second sliding bushing, wherein the first sliding bushing is attached to the sea-side end of the rotor blade shaft, and the second sliding bushing is attached to the rotor hub-side end of the rotor blade shaft. As a result, it is possible to dispense with coating of the rotor blade shaft or of the rotor hub housing section. The slide coating is in some cases less robust than a slide bushing and it is significantly more expensive to provide such a coating. The sliding bushing itself is usually manufactured from a fiber composite material and has fibers, in particular sliding fibers, which are embedded in a plastic matrix. In addition, the nonwoven fabric may also include solid lubricant particles that aid in the slip properties. Alternatively or additionally, the sliding bushing can also be made of a plastic which comprises solid lubricant.According to an advantageous exemplary embodiment, the sliding bushing is pressed onto the rotor blade shaft, wherein the rotor shaft and the sliding bushing are designed such that an overlap is provided between the outer diameter of the rotor blade shaft and the inner diameter of the sliding bushing. This makes it possible to ensure a secure fit of the sliding bushing on the rotor blade shaft. The inner first and second sliding surfaces are here represented by the outer lateral surfaces of the sliding bushes. The two outer sliding surfaces, which can be brought into sliding contact with the inner sliding surfaces, are formed by the rotor hub housing section. Alternatively, it is also possible to press the first and second sliding bushes into the rotor hub housing section, so that the outer first and second sliding surfaces are formed by an inner lateral surface of the sliding bushes and the inner first and second sliding surfaces are formed by the outer diameter of the rotor blade shaft. It is also conceivable for one of the two sliding bushes to be pressed onto the rotor blade shaft and for the other sliding bush to be pressed into the rotor hub housing section.The axial sliding surfaces can also be coated with a sliding coating, as described above. However, it is preferred to provide a sliding disc, which provides the axial sliding surface, instead of the coating, also in the axial sliding surfaces. An exemplary embodiment is particularly preferred in which the radial and axial sliding surface is provided via a sliding bushing, wherein a flange is then formed on the sliding bushing, which flange provides the axial sliding surface. Such sliding bushes can be easily mounted on the rotor shaft.According to a further preferred exemplary embodiment, the rotor blade bearing arrangement furthermore has at least one sea water seal arrangement with at least one sealing lip, wherein the sea water seal arrangement is designed to provide a seal between the rotor hub housing section and the rotor blade shaft, wherein the sea water seal arrangement is preferably designed such that it can be fastened to the rotor hub housing section and the at least one sealing lip starts on the rotor blade shaft. Preferably, the sea water seal arrangement is a redundant lip seal for long service intervals and may include a re-lubricating function and a condition monitoring system.By means of such a fastening, the sea water seal can easily be exchanged even in the assembled state of the subsea turbine. In addition, the configuration of the rotor blade bearing arrangement according to the above-mentioned relationship between bearing spacing and rotor blade shaft diameter allows the rotor blade shaft to have a smaller diameter overall, which in turn also leads to a smaller diameter of the dynamic seawater seal. This in turn allows the relative movement of the seal to be reduced, which in turn reduces wear of the sea water seal.As already mentioned above, the rotor blade bearing arrangement is preferably designed as a module and can advantageously also comprise the rotor hub housing section and the seawater seal in addition to the rotor blade shaft and the bearing units. This makes it possible to easily replace the entire model.According to a further preferred exemplary embodiment, the rotor blade shaft, irrespective of whether it is present as a module or not, can have at least one drive component at its first rotor-hub-side end, which drive component is designed to cooperate with a central drive for rotating the rotor blade shaft. Since the rotor shaft extends relatively far into the interior of the rotor hub through the bearing arrangement discussed above, the rotor shaft is particularly well suited for central adjustment drives. All rotor blades are connected via a mechanism and controlled centrally via an actuator (e.g. electric motor, hydraulic cylinder). In other words, the rotor blades are not adjusted individually but jointly.According to a further preferred embodiment, the drive components are bevel gears, wherein the adjustment drive is preferably driven by an electric geared motor or a hydraulic motor and the torque distribution takes place via a central bevel gear. Alternatively, the drive component can also be a push rod which is connected to the rotor blade shafts via a connecting rod / crank disk mechanism. The push rod itself is axially movable with the aid of a linear drive and ensures an adjustment of the rotor blade shafts.According to a further preferred embodiment, the first and / or second slide bearing is fluid-lubricated, wherein preferably the fluid is a corrosion-preventing fluid, in particular deionized and / or demineralized water. Fluid lubrication of the slide bearings allows a further reduction in the friction on the slide surfaces and can ensure cooling at the same time. A special form of fluid lubrication can also be provided, namely lubrication with water. Thus, for example, seawater can also be used. If seawater is used, it is also possible to dispense with a complex seawater seal since it is precisely desired that seawater penetrates into the space between the rotor blade shaft and the rotor hub housing section in order to lubricate the plain bearings arranged there.However, since seawater is relatively corrosive, it is preferable to conduct fluid lubrication with a corrosion preventive fluid. For environmental reasons, deionized and / or demineralized water is particularly suitable.However, in order to allow as little fluid exchange as possible into the surrounding seawater and also in order to reduce the buoyancy of the underwater turbine, it is furthermore preferable to flood the rotor hub housing as a whole with the lubricating fluid. The lubricating fluid should have a density similar to water.A further aspect of the present application is therefore directed to a rotor hub arrangement for an underwater turbine having a rotor hub housing which is designed to be connected to a rotor main shaft for driving a generator in a rotationally fixed manner and is designed to receive the at least one rotor blade shaft and to mount it rotatably, wherein a rotor blade bearing arrangement as described above is used for mounting the rotor blade shaft. The rotor hub arrangement in turn is usually connected in a rotationally fixed manner to a rotor main shaft which in turn drives a generator for generating power. It is particularly preferred here if the interior of the rotor hub housing is flooded with a fluid which simultaneously serves as lubricant for the slide bearings.It is particularly preferred here if the fluid has a density which has a similar density to water, or wherein the fluid is water, in particular seawater, but preferably deionized and demineralized water.In such a configuration, although the seawater seals could be completely dispensed with, it is advantageous if a relatively simple seal arrangement is arranged between the rotor blade shaft and the rotor hub housing. Such a sealing arrangement may be a sealing arrangement that merely performs a dirt retaining function in order to protect the slide bearings and drive components from dirt particles. Alternatively or additionally, the sealing arrangement can also be a sealing arrangement with a pressure compensation function, which ensures that a pressure compensation with the environment can take place in the event of a negative or positive pressure in the rotor hub housing. This minimizes wear on the seal, since these do not have to work against a pressure.According to a further preferred exemplary embodiment, the rotor hub arrangement has at least two rotor blades arranged opposite one another, which are fastened to rotor blade shafts, which in turn are each mounted and fastenable by means of the rotor blade bearing arrangement. As mentioned above, the rotor blade shafts each have a first sea-side end which can be fastened to the rotor blade in a rotationally fixed manner, and a second rotor-hub-side end which projects into an interior space of the rotor hub. Furthermore, the mutually opposite rotor blade shafts are arranged in the rotor hub with the aid of the rotor blade bearing arrangement in such a way that a diameter X of a circle described by the rotor hub-side ends of the rotor blade shafts and a diameter Y of a circle described by the sea-side ends of the rotor blade shafts satisfy the following relationship:In a preferred embodiment, in which two mutually opposite rotor shafts are used, this means that a distance X between the rotor hub-side ends of the two mutually opposite rotor blade shafts and the distance Y between the sea-side ends of the two mutually opposite rotor blade shafts satisfy the stated relationship.As a result, the rotor blade shafts, as mentioned above, extend far into the interior space of the rotor hub and allow a fully integrated, centralized rotor blade adjustment system, which connects a compact design with cost efficiency.According to a further preferred exemplary embodiment, a so-called spinner is furthermore arranged on the rotor hub, which spinner is designed to improve the flow dynamics of the turbine. A spinner is a streamline fairing mounted in the center of the rotor hub. Spinners make the turbine more streamlined overall, thereby reducing drag and smoothing the flow pattern. The spinner can furthermore be designed to accommodate drive components of the rotor blade adjustment system, for example the geared motor for the bevel gear drive or the linear drive for the latter.According to a further preferred exemplary embodiment, the rotor hub arrangement and / or the underwater turbine as a whole is additionally protected from corrosion by providing a corrosion-protecting coating and / or at least one sacrificial anode.Further advantages and advantageous embodiments are specified in the description, the drawings and the claims. In this case, in particular the combinations of the features indicated in the description and in the drawings are purely exemplary, and therefore the features can also be present individually or in a different combination.Brief description of the FiguresThe invention will be described in more detail below with reference to exemplary embodiments illustrated in the drawings. The exemplary embodiments and the combinations shown in the exemplary embodiments are purely exemplary and are not intended to define the scope of protection of the invention. This is defined solely by the appended claims.The following are shown: FIGS. 1 to 23 : schematic sectional views of various different preferred exemplary embodiments for an underwater turbine.DETAILED DESCRIPTION OF THE INVENTIONIn the following, elements that are the same or functionally the same are identified by the same reference numerals.FIG. 1 shows a schematic sectional view of an underwater turbine 1. the underwater turbine 1 comprises as main components a rotor hub 2 which is designed to support and support rotor blades 4 and a rotor main shaft 6 which is fixedly connected to the rotor hub 2 and extends into a nacelle 8 in which a generator 10 for power generation is accommodated. The rotor main shaft 6 can be fastened to the rotor hub 2, for example, by means of fastening means, in particular screws 5. A water flow flows against the rotor blades 4 and thereby cause a rotation of the rotor hub 2. The rotor 12 can be fastened directly to the rotor main shaft 6, but it is also possible for a transmission (not shown) to be arranged between the rotor main shaft 6 and the generator 10, which transmission converts the slow rotation of the rotor main shaft 6 into a fast rotation for the power generation. The rotor main shaft 4 is in turn rotatably mounted in the nacelle 8 by means of bearing units 14, 16. The bearing units 14, 16 are in particular designed in such a way that they can absorb axial and radial loads. Thus, the rotor main shaft 6 can be mounted, for example, via axial and radial bearing units.The rotor blades 4 are preferably likewise mounted rotatably, so that they can be adapted to the respective flow direction without the entire nacelle 8 having to be rotated. In addition, the adjustment of the rotor blades 4 also enables the rotor blades 4 to be rotated into the so-called flag position, in which the flow does not lead to a rotation of the rotor hub 2. As a result, the underwater turbine 1 can be shut down as a whole.The rotor blades 4 themselves are usually arranged symmetrically to one another and, in the case of two rotor blades 4- 1, 4- 2, are arranged, for example, directly opposite one another. In the case of more than two rotor blades, such as three or four rotor blades 4, for example, these can be arranged at a 120° distance or at a 90° distance from one another.In the exemplary embodiments shown in FIGS. 1 to 23, a two-blade rotor is shown in each case, which has two rotor blades 4- 1; 4- 2 lying opposite one another.Furthermore, FIGS. 2 to 23 show different details and exemplary embodiments of the subsea turbine 1. The rotor hub assembly 200 typically includes a rotor hub housing 202 into which a rotor blade shaft 204 is inserted.The rotor blade shaft 204 in turn is designed to be connected to the actual rotor blades 4 (see FIG. 1 ) and can be configured in one part or in multiple parts. It is likewise possible for the rotor blade shaft to be designed as a shaft stub. The two-division into rotor blade 4 and rotor blade shaft 204 makes it possible for the rotor hub arrangement 200 to be transported in a pre-assembled manner and for the rotor blades to be connected to the rotor hub arrangement 200 and more precisely to the rotor blade shaft 204 only at the location of use. In this case, in some configurations, it is even possible to mount the rotor blades on the rotor blade shaft under water. For this purpose, it is particularly advantageous if a rotor hub interior 210 is sealed with respect to the water into which the underwater turbine is introduced.In the case of the two-blade rotor illustrated in FIGS. 2 to 5, the rotor blade shafts 204- 1, 204- 2 each have a sea-side end 207 and a rotor-hub-side end 208. The sea-side end 206 is designed to be connected to the actual rotor blades 4, while the rotor hub-side end 208 projects into an interior space 210 of the rotor hub arrangement 200 and is designed to be connected to a preferably central rotor blade twisting device 300. In order to enable a rotation of the rotor blades or of the rotor blade hubs 204, the rotor blade shafts 204 are mounted rotatably with respect to the housing 202 of the rotor hub 2 by means of a rotor blade bearing arrangement 214.The rotor blade shafts 204 themselves define a length L of the rotor blade shaft 204 between their seawater-side end 207 and their rotor hub-side end 208. The two rotor hub-side ends 208- 1 and 208- 2 and the two sea water-side ends 207- 1, 207- 2 are in turn spaced apart by a distance X and Y, respectively. If more than two rotor blades are present, the rotor hub-side ends 207 and the seawater-side ends 208 are each located on a circle having a diameter X or Y.The rotor blade bearing arrangement 214 furthermore comprises a first sea-side bearing unit 220 and a second rotor hub-side bearing unit 230. The bearing units 220, 230 can be designed as rolling bearing units 221, 231, as shown in FIGS. 2 to 5. However, it is also possible, as shown in FIGS. 6 to 8, to configure the bearing units 214 as slide bearing units 225; 235.If the bearing units 220; 230 are designed as rolling bearings 221; 231, they each have an inner ring 222; 232 and an outer ring 223; 233, which define between them a bearing interior in which rolling bodies 224; 234 are arranged. The rolling bodies 224; 234 can optionally be guided in a rolling bearing cage (not shown).If the bearing units 220; 230 are designed as slide bearings 225; 235, slide bearing bushes 226; 236 can be provided, which ensure particularly good slide bearing.The bearing inner rings 222; 232, more precisely an inner bore 227, 237 of the bearing inner rings22; 232, or the plain bearing bushes 226; 236, each have an inner diameter d1i, d2ithat is dimensioned such that the bearing inner rings 222, 232 or the plain bearing bushes 226; 236 can be connected to the respective rotor blade shaft 204 in a rotationally fixed manner. In this case, the inner diameters d1i, d2iare usually dimensioned such that they overlap an outer diameter of the rotor blade shaft 204 such that the bearing inner rings 222, 232 or the plain bearing bushes 226; 236 can be fastened to the rotor blade shaft 204 with an interference fit.The bearing outer rings 223, 233 are attached to a rotor hub housing section 252; 262 in a rotationally fixed manner. The rotor hub housing section 252 can be embodied as an integral component of the rotor hub housing 202 (see, for example. FIGS. 2 and 3 ), however, it is also possible for the rotor hub housing section 262 to be present as a separate housing section which is connected to the rotor hub housing by means of fastening means 264 (see, for example. FIGS. 4 and 5 ).It is of course equally possible to connect the plain bearing bushes 226; 236 to the rotor hub housing section 252; 262 in a rotationally fixed manner, preferably to press them into the rotor hub housing section 252; 262.For the rotationally fixed connection, an inner diameter of the rotor hub housing section 252, 262 is usually dimensioned in such a way that it overlaps an outer diameter of the bearing outer rings 223, 233 or of the plain bearing bushes 226; 236, so that the bearing outer rings 223, 233 or the plain bearing bushes 226; 236 can be fastened in the rotor hub housing section 252; 262 with an interference fit.Furthermore, the rotor hub arrangement 200 has a preferably dynamic sea water seal arrangement 240 which is designed to seal a gap 242 between the rotor blade shaft 204 and the housing 202 in order to prevent water from entering the interior of the rotor hub 2.In order to achieve ideal tilting stiffness and thus a high load-bearing capacity and at the same time to compensate for the effects of the thermal differences in the rotor blade bearing arrangement 214, the first bearing unit 220 and the second bearing unit 230 are furthermore arranged spaced apart from one another at a specific bearing distance W, in each case measured from the center of the bearing unit (see FIGS. 2, 3 and 6, 7). At this time, the bearing distance W is set in relation to the inner diameter d1i of the inner bore 227 of the sea side bearing unit 220, so that 0.8*d1i≤W≤2*dli, preferably 1*d1i≤W≤1.5*d1i.In this way, in the case of rolling bearings 221; 231, in particular tapered roller bearings, the possible thermal growth of the rotor blade shaft 204 and the ring growth of the warm inner bearing rings 222 can be compensated for in relation to the colder outer bearing rings 223, which ensures that the bearing units 220, 230 are operated without jamming. In addition, if the bearing units 220, 230 are installed with a prestress, as is customary, for example, in tapered roller bearings, a prestress loss in the bearing can also be counteracted.The special spaced arrangement of the bearing units 220, 230 furthermore enables the rotor blade shaft 204 to be longer and thus to extend further into the interior 210 of the rotor hub 2. In addition, the diameter of the rotor blade shaft 204 can thereby be reduced, since the forces which are exerted by the rotor blade 4 on the rotor blade shaft 204 and on the bearings 220, 230 are distributed over a longer distance. The smaller shaft diameter, in turn, allows the sea water side seal assemblies 240 that seal the rotor hub to also have a smaller diameter. As a result, the relative movement of the seals is reduced, which contributes to the fact that the seals wear less quickly overall.It is particularly preferred that a length L of the rotor blade shaft 204 is adapted such that a distance X of the rotor hub-side ends 208- 1, 208- 2 of two rotor blade shafts 204- 1, 204- 2 lying opposite one another and a distance of the seawater-side ends 207- 1, 207- 2 of the rotor blade shafts 204- 1, 204- 2 lying opposite one another (or alternatively the diameters X, Y of the circles described by the corresponding ends 208 or 207) satisfy the following relationship: X: Y≈6:1.This enables a short distance of the rotor blade shafts 204- 1, 204- 2 from one another at a relatively large rotor blade spacing.FIG. 9 further shows that the rotor hub housing 202 has rib structures 250 that structurally reinforce the housing 202 and make it possible to provide a relatively thin-walled housing 202 that, however, resists high loads, in particular also a high water pressure at greater depths.As can be seen in particular from FIGS. 2 to 6, the bearing units are arranged in such a way that they form an O-arrangement, wherein the O-arrangement is designed in such a way that a force flow can be absorbed by the rib structures 250 arranged in the housing 202 and is transmitted to the rotor main shaft 6. This is possible both in the case of rolling bearing units, in particular tapered roller bearings, and in the case of a corresponding plain bearing configuration (see FIG. 6 ).Furthermore, FIGS. 2, 3 and 6 to 8 show that the rotor blade shaft 204 can be inserted together with the bearing units 220 and 230 into the rotor hub housing 202, wherein the rotor hub housing 202 in this exemplary embodiment has the rotor hub housing section 252 which is formed integrally with the rotor hub housing and extends in a tubular manner inwards and which can be formed as a bearing seat for the outer rings 223; 233 or as a sliding surface or seat for the plain bearing bushes 226; 236.Alternatively, however, the rotor blade shaft 204 and the bearing units 220 and 230 can also be designed as a module 260, which can be inserted in its entirety into the rotor hub housing 202 (see in particular FIGS. 4 and 5 ). For this purpose, the module 260 furthermore has the likewise tubular separate rotor hub housing section 262, which is referred to below as module housing section 262 and is designed as a bearing seat for the outer rings 223; 233 or as a sliding surface or seat for the plain bearing bushes 226; 236 for the bearing units 220 or 230. The tubular module housing portion 262 may be secured to the rotor hub assembly housing 202 by fasteners 264. The embodiment as a module 260 has the advantage that the bearing units 220 and 230 can be fully assembled and, if necessary, can be provided in a fully prestressed manner and only have to be inserted into the housing. Furthermore, in this case, the seawater seal 240 can already be fastened to the module 260, so that the assembly steps during the assembly of the module 260 into the rotor hub housing 202 can be significantly simplified.Tapered roller bearings are particularly suitable as bearing units 220; 230, since they can absorb a high external load, especially bending moments, in an O-arrangement and make possible a continuous introduction of force into the rotor main shaft 6. As a result, the bearings can, however, also be dimensioned smaller overall.Alternatively, FIGS. 6 to 8 show the above-mentioned sliding bearing of the rotor blade shaft 204, wherein FIGS. 6 to 8 show a rotor shaft 204 which is inserted into the housing 202 of the rotor hub 2, wherein a sliding pairing is formed between the tubular housing section 252 of the tube hub housing 202 or the module housing section 262 and the rotor blade shaft 204, which sliding pairing forms a first sliding surface pairing 280 on the sea side and a sliding surface pairing 290 on the rotor hub side, respectively. In FIGS. 6 to 8, only the integrated embodiment with a housing section 252 is shown, and not the modular embodiment. However, the following applies analogously.In order to form the rotor hub-side sliding surface pair 280 or the sea water-side sliding surface pair 290 with outer sliding surfaces 281; 291 and inner sliding surfaces 282, 292, the housing section 252 has, in particular, a first rotor hub-side 254 and a second sea-side section 255, which are designed as outer sliding surfaces 281, 291. The inner sliding surfaces 282; 292 are formed in this exemplary embodiment by the sliding bearing bushes 226; 236. The inner and outer sliding surfaces 281, 291, 282, 192 are designed as radial sliding surfaces which serve for radial bearing of the rotor blade shaft 204 with respect to the rotor hub housing section 252.Analogously, an outer lateral surface 203 of the rotor blade shaft 204 can serve as counter-sliding surfaces. FIG. 8 illustrates an embodiment of this type in which the plain bearing bushes 226, 236 are pressed into the rotor hub housing section 252 and the rotor blade shaft 204 has a first lateral surface section 203- 1 and a second lateral surface section 203- 2, which are formed as inner sliding surfaces 282, 292.In addition, axial sliding surfaces 283, 293 (outer); 284, 294 (inner) can also be provided. The axial sliding surfaces 283, 293; 284, 294 allow, for example, the rotor blade shaft 204 to be equipped at its sea-side end 207 with a stop surface 206 which interacts with a corresponding counterstop surface 256 on the rotor hub housing section 252 in order to define a defined insertion position of the rotor blade shaft 204 into the rotor hub housing 202. The outer axial sliding surface 293 is then formed on the stop surface 206, while the inner axial sliding surface 294 is formed on the counterstop surface 256 of the rotor hub housing section 252.Analogously, an axial slide bearing can also be formed on the rotor hub-side end 208 of the rotor blade shaft 204 or the rotor hub-side end 254 of the rotor hub housing section 252. In the illustrated exemplary embodiments of FIGS. 7 and 8, a stop surface 257 is also formed on the rotor hub housing section 252 on the rotor hub side, said stop surface being formed as an outer axial sliding surface 283 for the sliding bearing 235 on the rotor hub side. On this sliding surface 283, for example, a shaft nut 246, which is equipped with an inner sliding surface 284, can cooperate. The shaft nut 246 serves, for example, to secure the rotor blade shaft 204 in the rotor hub housing 202.Instead of the plain bearing bushes 226; 236 shown in the figures, the corresponding sliding surfaces 281, 291; 282, 292; 283; 293; 284; 294 can also be provided with a sliding coating, for example made of a fiber composite, in order to avoid a steel-steel sliding pairing. The plain bearing bush 226; 236 can also be produced from a fiber composite material. Such a fiber composite material preferably comprises a sliding fiber and / or a plastic matrix made of a slidable material, such as, for example. PTFE.In the exemplary embodiments illustrated in FIGS. 6 and 7, plain bearing bushes 226; 236 are used, which are fastened to the rotor blade shaft 204 in a rotationally fixed manner, while in FIG. 8 the plain bearing bushes are pressed into the rotor hub housing section 252.FIG. 6 shows an exemplary embodiment in which, analogously to an O-arrangement of a tapered roller bearing, conical plain bearing bushes are used, which are likewise arranged in an O-arrangement. In this case, the rotor blade shaft 204 can have a conical slide bearing bush receiving surface (or sliding surface) 205, but it is also possible for an additional bearing element, such as an inner ring 286, for example, to be arranged on the rotor blade shaft 204 and bears the conical slide bearing bush 236 or serves as sliding surface for the conical slide bearing bush. The angle of attack of the conical slide bearing arrangement is in turn selected such that a force introduction into the reinforcing ribs 250 is possible.As shown in FIGS. 7 and 8, the plain bearing bushes 226, 236 can also form cylindrical sliding surfaces. Furthermore, it is shown in FIGS. 7 and 8 that the plain bearing bushes 226; 236 have a cylindrical sleeve portion 228; 238 serving as a radial bearing, with the aid of which the radial sliding surfaces 281, 291; 282, 292 are formed, and a flange portion 229, 239 serving as a axial bearing, with the aid of which the axial sliding surfaces 283, 293, 284, 294 are formed.According to a further preferred embodiment, the slide bearing is additionally lubricated in fluid terms, in particular with water. For this purpose, the entire interior 210 of the rotor hub 2 can preferably be flooded with a fluid, so that not only the plain bearing bushes 226; 236, as shown in FIGS. 6 to 8, are lubricated with the fluid, but also other bearing units arranged in the rotor hub interior 210. The fluid can be water, in particular a deionized and demineralized water which, compared to seawater, has corrosion-reducing properties, or else a fluid which has an analogous density to water.If water is used as the fluid, it is also possible to dispense with the seawater seal 240 which completely seals off the intermediate space 242 between the rotor housing 202 and the rotor blade shaft 204 and to provide only a simple seal 244 having a dirt retention function (see FIG. 7 ). Since the same pressure prevails both in the rotor hub interior 210 and in the surrounding medium, this seal 244 is not heavily loaded and merely ensures retention of dirt particles which could jeopardize the sliding bearing pairing between the rotor housing 202 and the rotor blade shaft 204.In the case of such a fluid-lubricated mounting, it is also possible to dispense with sealing devices at the rotor hub-side end 208 of the rotor blade shaft 204. Namely, usually, both an inner space of the rotor blade shaft 204 and the rotor blade 4 is filled with water in order to prevent floating due to trapped air. As a result, the rotor blade shaft 204 can be configured as a hollow shaft overall, as is shown in particular in FIG. 8, which is closed off, for example, merely with the aid of crank disks. It is of course likewise possible for the rotor blade shaft 204 not to be designed completely as a hollow shaft, as illustrated in FIGS. 6 and 7.Furthermore, the exemplary embodiments of FIGS. 2, 4 and 10 to 13 show that a bevel gear drive 310 is used as the central rotor blade twisting device 300 for adjusting the rotor blade shafts 204. For adjustment with the aid of a bevel gear drive 310, in the exemplary embodiments shown, a respective bevel gear 312- 1 or 312- 2 is attached to the rotor blade shaft 204 at the rotor hub-side end 208, which bevel gear meshes with a central bevel gear 314. The central bevel gear 314 is in turn driven via a drive unit 316 or an electric motor and enables an adjustment of the rotor blades by 360°. This solution is possible both in the case of a modular construction as illustrated in FIG. 4 and in the case of installation of the rotor blade shaft into the housing 202 itself (see FIGS. 2 and 10 to 13 ). The electric motor 316 can be configured compactly and can be arranged in the interior 210 and rotor hub 2 (see FIG. 11 ) or in the rotor main shaft 6 (see FIG. 12 ) configured as a hollow shaft.In the exemplary embodiment shown in FIG. 11, the drive motor 316 is of compact design and can therefore directly transmit the required torque. In order to provide the required torque on the rotor blade shaft 204, a gear mechanism 317 is provided between the bevel gear 312 and the rotor blade shaft 204 in the exemplary embodiment shown. The bevel gears 312- 1, 312- 2 are coupled to a transmission input shaft 318. The rotational speed is reduced and the torque is increased via a transmission stage 319. On the transmission output side, the rotor blade shaft is attached in a rotationally fixed manner. The transmission 317 is preferably formed with one or more planetary stages.However, if the electric motor 316 is structurally relatively discharging, it may furthermore be provided to provide an additional housing section 272 on the housing 202 of the rotor hub arrangement 200, which is designed to receive the electric motor 316. In order in this case not to impair the streamlineness of the underwater turbine 1 or to improve the flow against the rotor blades 4, a so-called spinner 274 can be attached to the housing section 272 (see in particular FIGS. 2, 10 and 13).Instead of an electric motor 316, the housing section 272 can of course also accommodate other types of drive units.Furthermore, in particular FIGS. 4, 10 and 12 show that the rotor main shaft 6 is of hollow design and cables 270 can be guided through it, which can be used for controlling the electric motor 316. Furthermore, FIGS. 2, 4 and 10 to 13 show that the rotor blade shafts 204 can also have a bore 209, through which cables 270 can be guided, for example, in order to provide a continuous flow. In order to supply current to sensors (not shown) and to conduct signals which detect, for example, a deformation of the rotor blades 4 and / or a load which acts on the rotor blades 4.Since the rotor blades do not have to move continuously to new positions and it is sometimes expedient to move the rotor blades into a so-called flag position and to hold them there in which no torque can be transmitted from the water flow to the rotor blades, for example for maintenance purposes, it is furthermore expedient to provide a blocking device 320 which fixes the rotor blades in a specific position. For this purpose, as shown in FIG. 13, a locking device 320 can be provided which is fixed in a rotationally fixed manner to the rotor hub housing 202 and which likewise has a bevel gear 322 which can be brought into engagement with the bevel gears 312- 1 and 312- 2 by means of actuating elements 324 in order to prevent these from further rotation. If the locking bevel gear 322 is in engagement with the bevel gears 312, the drive unit 316 can be de-energized and does not have to constantly hold the bevel gears 312 and thus the respective rotor blade shafts 204 in their position. This is also advantageous in terms of energy. Furthermore, the locking device 320 can be designed such that, in the event of a power failure, the locking bevel gear 322 only engages with the bevel gears 312 when the rotor blades 4 move into the feathered position on account of the water flow and on account of no force turning the rotor blades into the water flow. The blocking device 320 then ensures that a further rotation of the rotor blades 4 is not possible.Instead of a bevel gear arrangement, a push rod arrangement 330 can also be used as the central rotor blade twisting device 300.Figures 3, 5 and 14-23 show, as an alternative central rotor blade twisting apparatus 300, the push rod assembly 330 with a push rod 332 which is axially movable and cooperates with the rotor blade shaft 204 to twist it. The pushrod 332 typically has a first rotor hub-side end 334 and a second opposing end 336, and extends through a bore 60 in the rotor main shaft 6, which bore may be sealed in the case of a flooded rotor hub using a seal 374 (see FIG. 17 ).The push rod 332 is moved axially with the aid of a linear drive 400, wherein the linear drive 400 can cooperate directly with the push rod (see FIGS. 14 and 15 ), but can also act indirectly on the push rod as a separate component (see FIG. 16 ).As can be seen in particular from FIGS. 17 and 18, the push rod 332 is connected to the rotor hub-side end 208 of the rotor blade shaft 204 with the aid of a connecting device 340.In this case, the connecting device 340 has one connecting rod 342 per rotor blade shaft 204. Each connecting rod 342 comprises a connecting rod 344, at the ends 346; 348 of which an eye 350; 352 is formed in each case. The bosses 350; 352 serve as plain bearings for bolts 354; 356 which provide for rotatable attachment of the connecting rods 342.The connecting rod 342 is rotatably connected at its first end 346 by means of the bolts 354 to a connecting rod-connecting element, in particular a connecting rod holder 358, which in turn is attached to the connecting rod 332 in a rotationally fixed manner.On the second side 348, the respective connecting rods 342- 1, 242- 2 are rotatably attached to connecting rod-rotor blade shaft connecting elements, for example crank disks 360- 1, 360- 2, by means of bolts 356, wherein each crank disk 360 is in turn connected to the corresponding rotor blade shaft 204 in a rotationally fixed manner, wherein, for example, fastening elements 362 can be used.The sectional view of FIG. 8 shows in particular a further embodiment of the connecting rod-rotor blade shaft connection, wherein here too a crank disk 360 is used, which are fastened to the rotor blade shaft 204 by fastening elements 362. Furthermore, it can be seen from this exemplary embodiment that the connecting rods 342- 1, 342- 2 each have a spherical bearing unit 380- 1, 380- 2 in their second connecting rod eyes 352, which bearing unit is designed as a spherical slide bearing in the exemplary embodiment shown. The spherical bearing unit 380 in turn has an outer ring 381 and an inner ring 382, which are arranged slidingly on one another. The spherical plain bearing 380 can be pressed into the connecting rod eye 352, for example, with the aid of a bolt 384 which carries the bearing, and can be connected to the crank disk 360.Furthermore, it can be seen in FIG. 8 that an O-ring 390 can be inserted between the crank disk 360 and the rotor blade shaft 204 as a seal, which seals a flooded rotor blade shaft, for example, against a dry rotor hub interior.If the push rod is moved axially, as shown in FIGS. 18, A, B and C, the rotor blade shaft 204 can be rotated from a first maximum position I (see FIG. 11A ) into a second maximum position II (see FIG. 11C ). In the middle position shown in FIG. 11B, the connecting rod 342 is set at a maximum angle. It is furthermore preferred that the first maximum position I corresponds to a flag position or the second maximum position II corresponds to a maximum force absorption position of the rotor blades 4 in the water flow.It is furthermore preferred that the push rod 332 is prestressed into the flag position I, so that only when the push rod 332 is actively moved is the rotor blade 4 moved into a position in which the water flow exerts a torque on the rotor blades 4.The push rod 332 can be accommodated in the rotor main shaft 6 designed as a hollow shaft, as illustrated in FIGS. 15 to 23, but it is also possible for the push rod 332 to be arranged on a side of the rotor hub 2 opposite the rotor main shaft 6, as illustrated in FIG. 14. In this case, analogously to the bevel gear drive of FIGS. 2 and 3, a housing 272 is provided, which surrounds the push rod mechanism 330, and the housing 272 can in turn be equipped with a spinner 274 as a flow optimizing element.If the push rod 332 extends through the rotor main shaft 6, which is designed as a hollow shaft, as illustrated in FIGS. 3, 5 and 15 to 23, a linear bearing unit 370 in the form of a bearing bush 372 is furthermore arranged on the rotor main shaft 6, said linear bearing unit supporting the push rod 332 with respect to the rotor main shaft 6 and ensuring an axial movability of the push rod 332. As mentioned above, the push rod 332 itself has a rotor hub-side end 334 and a second end which is designed as a pod-side end 336 in FIGS. 3, 5 and 15 to 23. The second end 336 can extend through the entire rotor shaft 6, but it is also possible, as is illustrated in particular in FIG. 15, for the pod-side end 336 of the push rod 332 also to be accommodated in the rotor main shaft 6.As mentioned above, in order to axially move the push rod 332, the second end 336 of the push rod 332 is axially acted upon directly or indirectly by means of a linear drive 400. In the exemplary embodiments illustrated in FIGS. 14 and 15, the push rod 332 is configured for this purpose at its second end 336 as a hydraulic piston 402, which is accommodated in a hydraulic cylinder 404. In FIG. 14, the hydraulic cylinder 404 is accommodated in the housing portion 272, while in the embodiment of FIG. 15, the hydraulic cylinder is inserted into the rotor main shaft 6.In addition to the hydraulic linear drive 400 shown here, it is of course also possible to use any other linear drive 400, for example a pneumatic linear drive or else a worm drive.The push rod 332, which is designed as a piston, has at its second end a flange 405 which is guided sealingly in the piston housing 404 and thus forms a first working chamber 406 and a second working chamber 408. The first working chamber 406 and the second working chamber 408 can each be charged with hydraulic fluid in order to move the push rod piston 402 and thus the push rod 332 from the first position I into the second position II. For the application of hydraulic fluid, a pump assembly 410 is also provided, which in the exemplary embodiment shown in FIG. 15 is held in a rotationally fixed manner in the nacelle 8 and is rotatably fastened to the hydraulic cylinder 404 via a rotary bushing 412. Such rotary feedthroughs 412 are known in the prior art and are therefore not further explained.The rotary feedthrough 412 is in turn fastened to the nacelle 8 in a rotationally fixed manner by means of a fastening element 414. Furthermore, control devices 416 are accommodated in a stationary manner in the nacelle 8. FIG. 15 shows that a cable feedthrough for the cable 270 is provided, which runs from the nacelle 8 or the control units 416 through the rotor main shaft 6 and extends into the rotor blades 4 in order, for example, to supply current to sensors and / or to conduct signals. This cable 270 is also connected via a rotary feedthrough 419 at the end of the rotor hub 6 to the stationary elements 416; 410 in the nacelle 8.FIGS. 16 to 23 show exemplary embodiments in which the pod-side end 336 of the push rod 332 extends into the pod interior 802. In these illustrated exemplary embodiments, too, the push rod 332 is moved from the first position I into the second position II by means of a hydraulic linear drive 400. In contrast to the exemplary embodiment shown in FIG. 12, however, in the exemplary embodiments shown in FIGS. 16 to 23, the push rod 332 or its pod-side end 336 is not directly acted upon with a hydraulic fluid, but rather the pod-side end 336 of the push rod 332 is moved from the first I into the second II position by means of a separate linear drive unit 400 which is fixed in a rotationally fixed manner in the pod 8. However, since the push rod 332 rotates with the rotor hub 2 in the same way as the rotor main shaft 6, but the linear drive 400 is stationary, a rotational decoupling must be provided between the push rod 332 and the linear drive 400.Furthermore, the figures show that the linear drive 400 in turn has an axially moving piston 402, which, however, is now configured as a separate element and acts on the pod-side end 336 of the push rod 332. For this purpose, the piston 402 has a pushrod-side end 420 and a pod-side end 422. The nacelle-side end 422 of the piston 402 is received in a piston-cylinder housing 404 and is designed to be acted upon by hydraulic fluid. For this purpose, a first working chamber 406 and a second working chamber 408 are again provided, which, analogously to the exemplary embodiment described above, is acted upon by hydraulic fluid which is supplied by the pump assembly 410 in order to move the piston 402 from the first position I into the second position II.Furthermore, in particular FIGS. 16, 19 and 20, 21 show that the push rod-side end 420 of the piston 402 and the pod-side end 336 of the push rod 332 are accommodated in a push rod-piston connecting housing 426. The push rod-piston connecting housing 426 is in turn accommodated in an axially displaceable manner in a linear drive housing 428, which in turn is coupled to the rotor main shaft 6 in a rotationally fixed manner. In this case, the piston 402, more precisely the pushrod-side end 420 of the piston 402, can be connected to the pushrod-piston connection housing 426 in a rotationally fixed manner (see FIGS. 16, 19 ), but it is also possible, as illustrated in FIGS. 20 and 21, for the pod-side end 336 of the pushrod 332 to be coupled to the pushrod-piston connection housing 426 in a rotationally fixed manner.In both cases, it should be taken into account that the linear drive housing 428 and the push rod 332 rotate together with the rotor main shaft 6, while the piston 402 of the linear drive 400 is configured to be stationary. For this reason, a first and a second bearing unit 430, 440 are arranged in the push rod-piston connecting housing 426. In the exemplary embodiment shown, the bearing units 430; 440 are designed as rolling bearings having an inner ring 432; 442, an outer ring 434; 444 and rolling elements 436; 446 arranged therebetween, but can also be a slide bearing. As can be seen in particular from the detailed views of FIGS. 19, 20 and 21, the bearing inner rings 432 and 442 are fastened in a rotationally fixed manner to the push rod 332 (see FIG. 19 ) or in a rotationally fixed manner to the piston 402 (see FIGS. 20, 21 ), while the outer rings 434; 444 are received in a rotationally fixed manner by the push rod-piston connection housing 426.By providing the bearing units 430 and 440 in the push rod-piston connection housing 426, rotational decoupling between the rotating push rod 332 and the stationary piston 402 can be achieved. Accordingly, the push rod-piston connection housing 426 of the embodiments shown in Figs. 19 to 23 is also stationary while rotating together with the rotor main shaft 6, the linear drive housing 428 and the push rod 332 in the embodiment of Figs. 20, 21.As is also shown in FIGS. 3, 5 and 16 to 23 and mentioned above, the linear drive 400 is also designed in this exemplary embodiment as a hydraulic piston drive. In this case, the piston 402 is guided in a cylinder 404 and forms with the latter a first working chamber 406 and a second working chamber 408, which are alternately acted upon with hydraulic fluid by means of a hydraulic fluid which is provided via the hydraulic pump 410 in order to move the piston 402 from a first position I into a second position II. For this purpose, the piston 402 has a flange 405 at the cylinder housing-side end 422 with which the piston 402 is guided sealingly in the piston housing 404 and separates the working spaces 406, 408 from one another. The piston housing 404 is supported in the pod in a rotationally fixed manner on the one hand with the aid of a fastening means 414 and is at least partially surrounded by the linear drive housing 428. This makes it possible to ensure a defined position and fastening of the linear drive 400 in the nacelle.However, since, as mentioned above, the linear drive housing 428 is connected to the rotor main shaft 6 in a rotationally fixed manner and therefore likewise rotates, but the piston housing 404 is configured to be stationary, a rotational decoupling must also be provided between the piston housing 404 and the linear drive housing 428.In the exemplary embodiments illustrated in FIGS. 16 and 19 to 23, this rotational decoupling takes place via two bearing units 450, 460, which are designed analogously to the bearing units 420, 430 as rolling bearings, in particular tapered roller bearings, and each have an inner ring 452, 462, an outer ring 454; 464 and rolling bodies 456; 466 arranged therebetween. The inner rings 452, 462 are arranged in a rotationally fixed manner on the piston housing 424, while the outer rings 454, 464 are arranged in a rotationally fixed manner in the linear housing 428. Of course, a slide bearing can also be used here, or the bearing units can be arranged differently.As can be seen further from the detailed views of FIGS. 19, 20 and 21, a biasing element 470 in the form of a spring is furthermore arranged on the push rod-piston connection housing 426, said biasing element providing a biasing of the push rod 332 into a first position I (see in particular FIG. 21 ). The first position I is preferably the flag position, so that in the event of a power failure or no application of hydraulic fluid, the rotor blades 4 are rotated out of the flow, so that no torque is introduced into the underwater turbine 1. If the push rod-piston connecting housing 426 is connected to the piston 402 in a rotationally fixed manner, the spring, as can be seen from FIG. 19, is preferably supported on the one hand on the push rod-piston connecting housing 426 and on the other hand on the piston housing 404. If, on the other hand, the push rod-piston connecting housing 426 is connected to the push rod 332 in a rotationally fixed manner (see FIGS. 20, 21 ), it rotates with the push rod 332 and the linear drive housing 428, so that the spring restoring element 470 can be supported on the one hand on the push rod-piston connecting housing 426 and on the other hand on the linear drive housing 428, as illustrated in FIGS. 21 and 22.In addition to the prestressing element 470, which prestresses the push rod 332 into a specific position, it is furthermore advantageous if a blocking device 480 is additionally provided, which blocks the linear movement of the push rod 332. The locking device 480 can have locking elements, for example in the form of bolts 482, 484, which, as shown in FIGS. 19 to 21, engage with the push rod-piston connecting housing 426 and fix this in a specific position. For this purpose, the push rod-piston connecting housing 426 has an opening 486, into which the bolt 482 or 484 can be inserted and holds the push rod 332 in a specific predetermined position. In this case, the first position I (see FIG. 21 ) can in turn be the feathered position of the rotor blades, while the second position II (see FIG. 20 ) can correspond to an optimum torque transmission position of the rotor blades 6. Of course, a plurality of locking bolts can also be provided.Alternatively or additionally to the bolts 482, 484 which cooperate with the push rod-piston connecting housing 426, it can likewise be provided, as can be seen from the exemplary embodiment of FIGS. 22 and 23, that the blocking device 480 acts directly on the push rod 332. Thus, for example, a bolt 488 can be arranged on the rotor main shaft 6, which bolt extends through a bore 490 in the rotor main shaft 6 in the direction of the push rod 332 and interacts there with a bolt receptacle 492 provided in the push rod 332 in order to secure the push rod 332 in a specific position. In this case too, it is advantageous that this position corresponds to the flag position of the rotor blades 4, since it is ensured in this case that even in the event of a power failure or an inactive actuation of the rotor blades, the latter remain rotated from the flow and do not introduce any further torque into the subsea turbine.The blocking device 480, as well as other elements and sensors, can in turn be energized or controlled via control units 416 which are arranged in the nacelle 8.For this purpose, cables 418 can likewise be provided, which extend via corresponding rotary feedthroughs to the blocking elements or also to the rotor blades in order to conduct signals or current.List of reference characters1 Subsea turbine 2 rotor hub 4 rotor blades 5 screws 6 rotor main shaft 8 nacelle 802 nacelle interior 10 generator 12 generator rotor 14, 16 bearing units rotor main shaft 200 rotor hub arrangement 202 rotor hub housing 203 lateral surface of rotor blade shaft 204 rotor blade shaft 205 conical support surface for conical plain bearing bush 206 stop surface 207 sea-side end of rotor blade shaft 208 rotor hub-side end of rotor blade shaft 209 bore rotor blade shaft 210 interior 214 rotor blade bearing arrangement 220 sea-side rotor blade shaft bearing unit 230 rotor hub-side rotor blade shaft bearing unit 221; 231 rolling bearings 222; 232 inner ring 223; 233 outer ring 224; 234 rolling bodies 225; 235 plain bearing 226; 236 plain bearing bushes 227; 237 inner bore of bearing rings 228; 238 sleeve section of plain bearing bush 229; 239 optional flange portion of the plain bearing bushing 240 seawater seal 242 gap between housing and rotor blade shaft 244 dirt retention seal 246 shaft nut 250 rib structures 252 rotor hub housing portion 254 rotor hub-side first housing portion 255 sea-side second housing portion 256 counterstop surface 260 module 262 tubular module housing portion 264 fastening means for module 270 cable 272 drive device housing 274 spinner 280 rotor hub-side sliding surface pairing 290 sea-side sliding surface pairing 281; 291 outer radial sliding surfaces 282; 292 inner radial sliding surfaces 283; 293 outer axial sliding surface 284; 294 inner axial sliding surface 286 inner ring 300 rotor blade twisting device 310 bevel gear drive 312 bevel gear on rotor blade shaft 314 central bevel gear 316 bevel gear drive (electric motor) 317 transmission 318 transmission input shaft 319 transmission stage 320 blocking device 322 blocking bevel gear 330 push rod arrangement 332 push rod 334 rotor hub-side first end 336 second end 338 holding element 340 connecting device 342 connecting rod 344 connecting rod 346 first connecting rod end 348 second connecting rod end 350 first connecting rod eye 352 second connecting rod eye 354 bolt 356 bolt 358 connecting rod-push rod connecting element; connecting rod holder 360 connecting rod-rotor blade shaft connecting element; Crank disk 362 Fastening means 370 Linear bearing unit 372 Bearing bush 380 Spherical slide bearing 381 Outer ring 282 Inner ring 384 Bolt 390 O-ring 400 Linear drive 402 Hydraulic piston 403 Flange 404 Hydraulic cylinder 406 First working space 408 Second working space 410 Pump 412 Rotary feedthrough 414 Fastening in pod 416 Control devices 418 Cable 419 Slip ring 420 Rotor hub-side end of the piston 422 Pod-side end of the piston 424 Piston housing = Cylinder 426 Push rod-piston connection housing 428 Linear drive housing 430; 440 Bearing units 432; 442 Bearing inner ring 434; 444 Bearing outer ring 436; 446 Rolling bodies 450; 460 Bearing units 470 Restoring element 480 Locking device 482; 484 Locking elements=Bolt 486Bolt receiving opening 488Bolt 490 Bore 492Bolt receiving means X Spacing Y Spacing d1iInner diameter d2iInner diameter W Bearing spacing L Length of the rotor blade shaft

Claims

A rotor blade bearing arrangement (214) for an underwater turbine (1), wherein the rotor blade bearing arrangement (214) is configured to rotatably support a rotor blade shaft (204) in a rotor hub housing (202), wherein the rotor blade shaft (204) has a sea-side end (207) configured to be connected to a rotor blade (4) in a rotationally fixed manner and a rotor hub-side end (208) configured to be received by a rotor hub (2), and wherein the rotor blade bearing arrangement (214) has the rotor blade shaft (204) and a first sea-side bearing unit (220) and a second rotor hub-side bearing unit (230), wherein the first and the second bearing unit (220; 230) are arranged at a distance W from each other, characterized in that the first and the second bearing unit (220; 230) are arranged as a slide bearing (225; 235), each having an inner sliding surface (282; 292) and an outer sliding surface (281; 291), wherein the inner sliding surface (292) of the first sliding bearing (225) is formed at the sea-side end (207) of the rotor blade shaft (204) and the inner sliding surface (282) of the second sliding bearing (235) is formed at the rotor hub-side end (208) of the rotor blade shaft (204), and wherein the outer sliding surfaces (281; 291) of the first and second sliding bearings (225; 235) are formed by a rotor hub housing portion (252; 262), wherein the rotor hub housing portion (252; 262); 262) is formed in the shape of a hollow tube and has a sea-side end (255) at which the sliding layer (291) for the first sliding bearing (225) is formed, and a rotor hub-side end (254) at which the sliding layer (281) for the second sliding bearing (235) is formed.The rotor blade bearing assembly (214) of claim 1, wherein the rotor hub housing portion (252) is formed integrally with a rotor hub housing (202), or wherein the rotor hub housing portion (262) is formed as a housing portion (262) separate from the rotor hub housing (202), which can be installed together with the rotor blade bearing assembly (214) and the rotor blade shaft (204) into a rotor hub housing (202).The rotor blade bearing arrangement (214) according to claim 1 or 2, wherein the rotor blade shaft (204) has a diameter D1 at the location of the first seaside bearing unit (225), and wherein the bearing distance W is 0.8*D1 ≤ W ≤ 2*D1, preferably 1*D1 ≤ W ≤ 1.5*D1.The rotor blade bearing assembly (214) of any preceding claim, wherein the first bearing unit (225) has a larger bearing diameter than the second bearing unit (235).The rotor blade bearing assembly (214) of any preceding claim, wherein at least one of the sliding surfaces (281; 291; 282; 292) comprises a sliding coating.The rotor blade bearing arrangement (214) according to any one of the preceding claims, wherein at least one slide bearing (225; 235) has radial slide surfaces (281; 291; 282; 292) which are formed in a tapered manner, and / or wherein at least one slide bearing (225; 235) has radial slide surfaces (281; 291; 282; 292) which are formed in a cylindrical manner.The rotor blade bearing assembly (214) of any preceding claim, wherein the rotor blade shaft (204) has, at its sea end (207), a stop step (206) having a first sea end annular axial slide surface (293) that cooperates with a first complementary annular axial slide surface (294) formed on the rotor hub shell portion (252; 262).Rotor blade bearing arrangement (214) according to one of the preceding claims, wherein the rotor blade shaft (204) has, at its rotor hub-side end (208), a stop step which is designed to cooperate with a one- or multi-part fastening ring, in particular a shaft nut (246) with thrust washer, in order to fasten the rotor blade shaft (204) in the rotor hub housing section (252; 262) with a defined installation position, wherein the fastening ring (246) has a second rotor hub-side annular axial sliding surface (284) which cooperates with a second complementary annular axial sliding surface (283) formed on the rotor hub housing section (252; 262).The rotor blade bearing assembly (214) according to any one of the preceding claims, wherein the inner sliding surfaces (281, 291) of the first and the second sliding bearing (225; 235) are formed by a first and a second sliding bushing (226; 236), respectively, wherein the first sliding bushing (226) is attached to the sea-side end of the rotor blade shaft (204) and the second sliding bushing (236) is attached to the rotor hub-side end of the rotor blade shaft (204).The rotor blade bearing arrangement (214) according to any one of claims 7 to 9, wherein a sliding disc is arranged between the first axial sliding surfaces (293; 294) and / or the second axial sliding surfaces (283; 284), wherein preferably at least one of the sliding discs is formed as a flange (229; 239) of the first and / or second sliding bushing (226; 236).The rotor blade bearing arrangement (214) according to any one of the preceding claims, wherein the first and / or second plain bearing (225; 235) are fluid lubricated, wherein preferably the fluid is a corrosion preventing fluid, in particular deionized and / or demineralized water.Rotor hub arrangement (200) for an underwater turbine (1) having a rotor hub housing (202) which is designed to be connected in a rotationally fixed manner to a rotor main shaft (6) for driving a generator (10), and is designed to receive and rotatably mount at least one rotor blade shaft (204), wherein a rotor blade bearing arrangement (214) according to one of the preceding claims is provided for mounting the rotor blade shaft (204).The rotor hub assembly (200) according to claim 12, wherein the rotor hub housing (202) is flooded with a fluid, wherein the fluid is configured as a lubricant for the first and second slide bearings (225; 235).The rotor hub assembly (200) according to claim 12 or 13, wherein the fluid has a density that has a similar density to water, or wherein the fluid is water, in particular seawater, but preferably deionized and demineralized water.Rotor hub arrangement (200) according to one of Claims 12 to 14, wherein a sealing arrangement (240) with a pressure compensation function is arranged between the rotor blade shaft (204) and the rotor hub housing (202).

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