Abstract:
The invention generally relates to two-bladed turbine nacelles and associated teetering hinges. In certain embodiments, the invention provides a hinge assembly encompassing a hub and two double elastomeric teeter bearings. In some aspects, the bearings are self-contained elements that can be preloaded in a controlled manner prior to their incorporation into the larger assembly.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/484,343, filed May 10, 2011, the content of which is herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention generally relates to offshore wind turbines and associated teetering hinges. 
       BACKGROUND 
       [0003]    Wind power refers to the conversion of wind energy into more useful forms of energy, such as electricity. Wind energy is an attractive alternative to fossil fuels because it is plentiful, renewable, widely distributed, clean, and produces no greenhouse gas emissions. Wind energy currently accounts for about 1.5% of worldwide electricity usage, and approximately eighty countries around the world use wind power on a commercial basis (World Wind Energy Report 2008: Report, World Wind Energy Association, February 2009; and Worldwatch Institute: Wind Power Increase in 2008 Exceeds 10-year Average Growth Rate, May 2009). Further, world wind generation capacity has more than quadrupled between the years 2000 and 2006, doubling about every three years. 
         [0004]    Offshore wind turbines harness the energy of powerful winds native to deep sea waters to provide electricity. Although necessary for energy production, these same strong winds result in asymmetrical loads that act on the rotor blades of the turbine, in what are known as bending moments. These high loads are subsequently transferred to the turbine shaft and ultimately, to the gearbox of the turbine, which results in gearbox failure and the unavailability of the turbine. Attempts to mitigate the high structural loads associated with bending moments include attaching the rotor blades to a flexible structure with limited pivoting capability, known as teetering hinge. 
         [0005]    Conventional teetering hinges are based on mechanical devices that use bushings or ball bearings. Due to the rigid nature of these devices, conventional teetering hinges lack substantial capability to absorb sharp dynamic loads. Furthermore, the continued exposure to high loads combined with the limited angling ability of the hinge results in the degradation of the metallic bearings by pitting. Also, the need to center the rotor blade axis back to a point perpendicular to the shaft axis requires complicated centering devices based on metallic or elastomeric springs outside the bearing itself. 
         [0006]    Other conventional teetering hinges are based on single metal-elastomeric bearings. In these devices, the preload cannot be controlled or adjusted. Rather, the preload is obtained by permanently transferring loads to the hub and the shaft, which causes unnecessary and potentially dangerous stress over the life of the system Like the conventional teeter hinges based on mechanical devices, these hinges also provide less than optimal reliability. 
         [0007]    Accordingly, there is a need for a teetering hinge suitable for two-bladed wind turbines with improved reliability, better durability, and the enhanced ability to handle high structural loads. 
       SUMMARY 
       [0008]    The invention generally relates to teetering hinge assemblies encompassing two double elastomeric teeter bearings. It has been found that a teetering hinge assembly encompassing two double elastomeric teeter bearings offers improved reliability and enhanced capability to handle load peaks over existing teetering hinges based on bushings or ball bearings. Unlike existing teeter hinges based on metallic bearings, the use of elastomeric elements in the encompassed teeter hinge confers the ability to absorb sharp dynamic loads produced by strong winds and handle the small teetering angles that would result in the degradation of typical hinge assemblies. 
         [0009]    The present invention encompasses the adoption of double elastomeric teeter bearings that comprise preloadable elastomeric elements spaced by metal shims, which provides certain benefits over conventional assemblies. The elastomeric layers are not subject to the same types of wear and tear associated with conventional mechanical hinges and furthermore offer enhanced dampening of load peaks, which reduces the stress placed on the rotor and shaft. In certain aspects of the invention, the inclusion of a safety element, such as a radial sliding bearing, restricts the stress transferred to the elastomeric layers and serves as a fallback measure should the elastomeric layers collapse. 
         [0010]    The double teeter bearing encompassed by the invention is designed to be pre-stressed through a preload prior to its incorporation into the hub and further designed so that the preload can be adjusted throughout the life of the assembly. In addition, the contemplated teeter bearing is composed of a plurality of metal-elastomeric elements. Each metal-elastomeric element is individually preloadable and furthermore, can be individually removed from the bearing without affecting the other elements. In addition to the elastomeric elements, many other components of the contemplated assembly can be removed individually without affecting the other components. These individually removable components encompassed by the invention facilitate maintenance and repair of the teeter bearing. The invention also encompasses teeter bearings that are self-contained units, even when incorporated into the turbine hub. Because the teeter bearings encompassed by the invention can function as self-contained units, the preload of the elastomeric elements is confined to the teeter system and not transferred into any associated hub. 
         [0011]    In certain embodiments of the invention, an assembly is provided. The assembly includes a hub and at least two double elastomeric teeter bearings that are positioned at openings in the hub. In certain aspects, the teeter bearings are preloadable teeter bearings. The preloadable teeter bearings can be preloaded prior to integration with the hub. The teeter bearings can also comprise self-contained units that are separate from the hub. In other embodiments of the invention, the self-contained teeter bearings are operably configured not to transfer a preload to the hub. The teeter bearings, in some embodiments, are mounted on opposite ends of a T-shaped turbine shaft head placed inside the hub. In certain embodiments the teeter bearing has, among its components, a plurality of metal-elastomeric elements. Each metal-elastomeric element can be independently preloadable and furthermore, each metal-elastomeric element can be individually removed from the teeter bearing. Other embodiments of the invention include a sliding bearing coupled to the elastomeric teeter bearing which is operably configured to receive a force in excess of the rated force bearable by the elastomeric elements or to constrain the displacements of the rotor hub in case the elastomeric elements fail. In addition to these embodiments, additional aspects of the invention will become evident upon reading the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIGS. 1A ,  1 B,  1 C,  1 D, and  1 E depict an embodiment of the invention, from different perspectives. 
           [0013]      FIGS. 2A ,  2 B,  2 C,  2 D, and  2 E depict another embodiment of the invention, from different perspectives. 
           [0014]      FIGS. 3A ,  3 B,  3 C,  3 D, and  3 E depict yet another embodiment of the invention, from different perspectives. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The invention provides a hinge assembly encompassing a hub and two double elastomeric teeter bearings. In contrast to conventional assemblies that incorporate metallic bearings or bushings, the use of elastomeric elements results in an assembly with improved resistance to degradation and enhanced ability to dampen load peaks and reduce stress on the turbine rotor and shaft. 
         [0016]    In certain embodiments of the invention, the teeter bearings are positioned at openings in the hub. The openings for the teeter bearings can be anywhere in the hub, but in some embodiments, there are two openings for the bearings, each located directly opposite from each other on the hub. In certain embodiments, the teeter bearings are operably configured to be mounted on the opposite ends of a T-shaped turbine shaft head, i.e., the horns of the shaft head. The horns of the shaft head would correspond to openings on the hub so that the mounted teeter bearings are positioned at the openings. 
         [0017]    Each double elastomeric teeter bearings comprises two elastomeric layers, hence, a double elastomeric teeter bearing. The elastomeric layers themselves are comprised of a plurality of elastomeric elements. Accordingly, each elastomeric teeter containing these layers comprises a plurality of elastomeric elements. Due to the elastomeric elements, the teeter bearing encompassed by the invention are preloadable, in which a certain amount of compression can be introduced into the elastomeric element. The elastomeric elements contemplated by the invention allow for controlled preloading. As described in detail in the embodiments below, the preload of each elastomeric element can be adjusted independently of one another. Furthermore, as explained in detail below, each elastomeric element in the teeter bearing can be removed independently of the other elastomeric elements. In addition, the other components of the teeter assembly can be removed independent of other components in the assembly. For example, each elastomeric element can be coupled with a segmented inner part of the bearing on one end of the element and a segmented outer part on the other end of the element. Each segmented section (inner part, outer part, and elastomeric element in between) can be associated with individual wedges, which, in combination with fastening devices (e.g. screws) permit individually adjusting the preload. The pre-stress of the elastic parts can be obtained by compressing them in a prevalently radial direction, which is in the direction of the prevalent external loads, through the use of a system of wedges arranged between them and the external shell of the teeter bearing. The independence of the components also facilitates their removal from and installation into the bearing. Thus, the components encompassed by certain embodiments of the invention are more accessible for the maintenance and repair of the hinge assembly. 
         [0018]    In some embodiments, the teeter bearing further comprises a sliding bearing operably configured to receive a force from elastomeric element. The sliding bearings can be coupled to the elastomeric teeters and protect the elastomeric parts from excessive stress, enhancing the overall reliability of the teeter bearing. As further described in the embodiments below, the teetering bearings can be equipped with monitoring sensors that enable early detection of possible wear in the elastomeric elements, as well as optical sensors that permit visual examination of the boundaries of elastomeric parts. Furthermore, the teetering bearings can be equipped with sensors able to monitor the behavior of the elastomeric elements in the operating hinge as they undergo cycles of oscillations. In other embodiments, the teeter bearings can be equipped with covers that protect the bearing from the effects of sun and salty air, which can potentially corrode the components within the bearing. 
         [0019]    One assembly in accordance with the invention is presented in  FIGS. 1A ,  1 B,  1 C,  1 D, and  1 E.  FIG. 1A  shows an arrangement of two-bladed rotor and associated hub. The hub  101  is essentially a shell in which the two blades (not shown) are mounted at attachment points  102 . The hub  101  contains an opening for a shaft head  103  and two openings located on opposite sides for teeter bearings  104  (not shown in  FIG. 1A ) that are mounted under a cover  105 .  FIG. 1B  is a cross-sectional view of the hub assembly, and shows the inside of the hub  101 , along with the shaft head  103  and two teeter bearings  104  located on opposite horns of the shaft head  103 . 
         [0020]      FIG. 1C  presents a magnified view of the teeter bearing  104 . The teeter bearing  104  is composed of an outer shell  107 , an inner shell  108 , a central sleeve  109 , and two couples of metal-elastomeric elements,  110  and  111 , stacked one into the other, with each element comprising alternating metal shims  112  and elastomeric layers  113 . Keys  114  have been installed to prevent mutual rotation of the parts, however, other anti-rotation devices can be used in accordance with the present invention. The teeter bearing  104  is fixed to the hub  101  by screws  115 , although other fastening devices can be used. The sliding bearing  116 , which protects the teeter bearings from excess stress and assists in the event of elastomeric layer failure, is secured by a retaining element  117  onto the end of the horn of the shaft head  103 . In certain embodiments, multiple slide bearings could be mounted as desired. A ring  118 , which gives the slide bearing freedom to move axially and with a limited radial gap, can be installed to receive position sensors or angular sensors such as the differential transformer  119  shown. The number of sensors and their positions can be adjusted as desired. A cover  105  protects the teeter bearing  104  from the deleterious effects of the sun and salty air typical of an offshore environment. 
         [0021]      FIG. 1D  depicts the teeter bearing  104  removed from the hub  101  and without the cover  105 . As shown, the teeter bearing  104  includes an outer shell  107 , an inner shell  108 , a central sleeve  109 , and two couples of metal-elastomeric elements  110  and  111  stacked one into the other. The tapered shape of metal-elastomeric elements  110  and  111 , matches the tapered shape of central sleeve  109 , the outer shell  107 , and the inner shell  108 . Accordingly, the preload of the teeter bearing  104  can be obtained by axially forcing the inner shell  108  against the outer shell  107  by tightening the associated fixing screws  115 . The arrangement of components encompassed by the invention allows the preassembly of the teeter bearing  104  prior to its installation into the hub  101  with its initial preload adjusted at the manufacturer. 
         [0022]      FIG. 1E  shows metal-elastomeric elements  110  and  111  in detail. As shown, both metal-elastomeric elements  110  and  111  are tapered. The number of such elements can be changed as needed. Furthermore, the metal-elastomeric elements can be composed of only one annular element or composed of more sectors if desired. Keys  114  have been installed to prevent mutual rotation of the parts, however, other anti-rotation devices can be used. The metal-elastomeric elements  110  and  111  are each composed of alternating metal shims  112  and elastomeric bonded layers  113 . The number and thickness of the shims  112  and elastomeric layers  113  can be adjusted as desired. 
         [0023]    Another embodiment of the invention is shown in  FIGS. 2A ,  2 B,  2 C,  2 D, and  2 E.  FIG. 2A  shows an arrangement of two-bladed rotor and associated hub. The hub  201  is essentially a shell in which the two blades (not shown) are mounted at attachment points  202 . The hub  201  contains an opening for a shaft head  203  and two openings located on opposite sides for teeter bearings  204  (not shown in this Figure) that are mounted under a cover  205 . 
         [0024]      FIG. 2B  is a cross-sectional view of the hub assembly, and shows the inside of the hub  201 , along with the shaft head  203  and two teeter bearings  204  located on opposite horns of the shaft head  203 .  FIG. 2B  also shows the arrangement of the teeter bearings  204  and components between the horns of the shaft head  203  and the hub  201 . Further, a cross-section of the teeter bearing  204  is presented, with a detailed view of the outer shell  211 , the segmented inner shell  206 , the segmented central sleeve  207 , and two couples of metal-elastomeric elements  208  stacked one against the other. In order to avoid mutual rotation of the parts, the elements  208  have square or quasi-square ends that fit the corresponding recesses machined in the adjoining parts. Undesired mutual rotation can also be prevented with the use of keys, pins, and other devices with similar functions. The teeter bearing  204  is fixed to the hub  201  and to the shaft head  203  by screws  209 , although other fastening devices, can be used. A slide bearing  210 , which protects teetering bearings from stress peaks and assists in the event of elastomeric layer failure, is installed and secured to the inner end of the outer shell  211 . The shape and location of the slide bearing  210  can be modified as needed. In addition, the invention encompasses multiple sliding bearings, which could be mounted internally or parallel to the metal-elastomeric elements  208  as needed. In certain embodiments, position sensors can be installed to monitor the displacements of the teeter bearing  204  in operation. A cover  205  protects the teeter bearing  204  from the deleterious effects of sun and salty air in offshore environments. 
         [0025]      FIG. 2C  presents a magnified view of the teeter bearing  204 . The teeter bearing  204  includes an outer shell  211 , a segmented outer sleeve  206 , a segmented central sleeve  207 , and two segmented metal-elastomeric elements  208  arranged in two circular arrays stacked one against the other. In certain embodiments, the segments of the outer sleeve  206 , the central sleeve  207 , and the metal-elastomeric elements  208  are obtained by cutting the hinge by radial planes along the axis of the horn of the shaft head  203 . The number of segments in the various sleeves can be modified as needed. In certain embodiments, the sleeves are not segmented. Each element of the central sleeve  207  can be double wedged shaped and is jointed to the horn of the shaft head  203  by screws  209 . Each component of the outer sleeve  206  can be simple wedge shaped and is jointed to the outer shell  211  by the screws  209 . Furthermore, each double element of the metal-elastomeric elements  208  is confined within the space between the outer shell  211 , the component of the central sleeve  207  and the component of the outer sleeve  206 . 
         [0026]    As shown in  FIG. 2D , the metal-elastomeric elements  208  are each composed of metal shims  212  interposed by elastomeric bonded layers  213 . The number and thickness of the layers can be adjusted as desired. The metal shims  212  at the end of each metal-elastomeric element  208  fit the corresponding recesses machined in the adjoining parts, and as shown in  FIG. 2E  may have a square or quasi-square shape. The fitting of the squared end into the recessed part helps prevent undesired rotation of the metal-elastomeric elements  208 . Other means can be used to prevent rotation, including but not limited, to keys or pins. The geometry of the end shims  212  allows mounting the metal-elastomeric elements  208  in two possible positions, with either the x-axis or the y-axis parallel to the axis of the horn of the shaft head  203 , as shown in  FIG. 2E . The tapered shape of the metal-elastomeric elements  208  matches the tapered shape of the central sleeve  207 , the outer shell  211 , and the outer sleeve  206 . Accordingly, each metal- elastomeric element  208  of the teeter bearing can be preloaded separately by forcing the central sleeve element  207  by tightening its fixing screws  209  for the inner array of metal-elastomeric elements  208  and the outer sleeve element  206  into the outer shell  211  by tightening its screws  209  for the outer array of metal-elastomeric elements  208 . The resulting preload will have an axial component as well as a radial component. Depending on the specific application, the tapered shape of the metal elastomeric element  208  can be designed to meet the required ratio of these two components.  FIG. 2E  depicts the tapered shape of the metal-elastomeric elements  208 , which in some embodiments, are mounted with the larger diameter against the central sleeve  207  for optimized distribution of the shear stress. 
         [0027]    Another embodiment of the invention is provided in  FIGS. 3A ,  3 B,  3 C,  3 D, and  3 E.  FIG. 3A  shows an arrangement of two-bladed rotor and associated hub. The hub  301  is essentially a shell in which the two blades (not shown) are mounted at attachment points  302 . The hub  301  contains an opening for a shaft head  303  and two openings located on opposite sides for teeter bearings  304  (not shown in this Figure) that are mounted under a cover  305 . 
         [0028]      FIG. 3B  is a cross-sectional view of the hub assembly, and shows the inside of the hub  301 , along with the shaft head  303  and teeter bearings  304  located on opposite horns of the shaft head  303 .  FIG. 3B  shows the arrangement of the teeter bearing  304  and components between the horns of the shaft head  303  and hub  301 . As shown in  FIG. 3B , the teeter bearing  304  includes an outer shell  306 , a double crown of metal-elastomeric elements  307 , and a crown of wedges  308  and  309  between the metal-elastomeric elements  307  and the outer shell  306 . After positioning the shaft head  303  into the hub  301  and installed the shell  306 , the inner crowns of metal-elastomeric elements  307  are installed between the horns of the shaft head  303  and the shell  306 , and are secured into their final position by inserting the wedges  309 . The outer crowns of the metal-elastomeric elements  307  are installed between the horns of the shaft head  303  and the upper end of the wedges  309  and secured by the insertion of the wedges  308 . Both crowns of metal-elastomeric elements  307  are axially restrained by the locking piece  311  along the horn of the shaft head  303 . Due to the tapered shape of the metal-elastomeric elements  307 , the preload can be obtained by forcing wedges between them and the outer shell  306  for the inner crown and wedges  308  between them and the upper part of the wedges  309  for the outer crown by tightening the wedge fixing screws  310 . A gap can be left between the wedge fixing lip and its stop face, to be filled with proper shims. This would permit a later individual adjustment of the preload to compensate for relaxation of the elastomeric compound. 
         [0029]    As further shown in  FIG. 3B , the outer shell  306  of the teeter bearing  304  is jointed at the hub  301  through a crown of screws  318 . In some embodiments, a shim can be used under the flange of shell  306  in relation to the chain of tolerances. There are two sliding bearings,  316  and  317 , on each horn of the shaft head  303 . The sliding bearings  316  and  317  protect the teeter bearings  304  from stress peaks and help in case the elastomeric layers fail. The sliding bearings  316  and  317  also allow free axial displacement between the horns of the shaft head  303  and the outer shell  306 . Sliding bearing  316  is installed on the locking piece  311  and secured by the retaining element  318 . Sliding bearing  317  is made of sectors screwed to outer shell  306 . The shape, number, and location of the sliding bearings can vary as needed. Also, multiple sliding bearings could be mounted internally or on each metal shim  18  as needed. Furthermore, in certain embodiments, transducers can be installed to monitor radial and angular displacements. In addition, anti-rotation devices, such as keys  319 , can be used to prevent mutual rotation of the parts. For the same reason, the metal-elastomeric elements  307  are guided laterally by the wedges  308  and  309  and the outer shell  306 . A cover  305  protects the teeter bearing  304  from the deleterious effects of the sun and the salty air in an offshore environment. 
         [0030]      FIG. 3C  provides a magnified view of the teeter bearing  304 , removed from the hub  301  and without the cover  305 .  FIG. 3D  shows the metal-elastomeric element  307  in greater detail. The metal-elastomeric element  307  has a tapered shape and is composed of a wedge shaped metallic piece  312  that fits the horn of the shaft head  303 , an external plate  313  that fits within the recesses of wedges  308  and  309 , and metal shims  314  interposed by elastomeric bonded layers  315 . The number and thickness of the layers can be modified as needed. In some embodiments of the invention, the metal-elastomeric elements  307  are identical for both crowns, while in other embodiments, the elements  307  are different. Furthermore, the number and shape of the metal-elastomeric elements can be modified as needed.  FIG. 3E  provides a top view of the metal-elastomeric element  307  shown in  FIG. 3D . 
         [0031]    The embodiments depicted above describe a hinge assembly, where the link between the hub of a two-bladed turbine rotor and the shaft head is achieved through a teetering hinge that permits the flap-wise rotation of the blades without causing yaw and lateral moments. The hinge assembly comprises two preloaded double teeter bearings. Each double teeter bearing can be composed of two crowns of metal-elastomeric elements constrained between the external metal parts and the diametrically opposed ends, i.e., the horns, of the central T-shaped shaft head. The torsional stiffness of the assembly is provided by the teeters working in parallel and securing substantial stiffness in the radial and axial directions. The number of metal-elastomeric layers can be modified accordingly to limit the shear strains caused by the teetering cycles and also to obtain sufficient compression modulus. The radial sliding bearings encompassed by the invention limit the radial displacement and consequent possible damage of the elastomeric elements. The sliding bearings also serve handle the radial load should the elastomeric elements fail. As presented in the embodiments above, assemblies encompassed by the invention can also include sensors able to detect the radial, axial, and torsional deformation of the elastomeric parts as well as teeter covers, to protect the underlying assembly from the harmful effects of the sun and salty air typical of offshore environments. 
         [0032]    The use of two double elastomeric bearings in the hinge assembly is able to significantly reduce the drivetrain bending moments that ultimately result in gearbox failure. Other elements depicted in the various embodiments further enhance the reliability and durability of the contemplated hinge assembly as well as its capability to handle high peak loads 
       INCORPORATION BY REFERENCE 
       [0033]    References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes. 
       Equivalents 
       [0034]    The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting on the invention described herein. Scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.