Abstract:
A wind turbine includes a vertically standing non-uniform tower adapted to support a horizontally oriented rotor. A fixed base portion of the turbine is adapted to support a separate rotatable tower having an upper rotor swept portion along the main body of the tower. The tower is adapted to be secured to the base for being rotatably yawed into the wind. A bearing system is housed between the base and lower tower extremity includes a pair of vertically spaced tracks situated on an annular support rail adapted to be fixed to a ground structure, for example a reinforced concrete foundation. The bearing system is further defined by pluralities of yaw bearing cartridge assemblies adapted to extend through flanged apertures of a skirt portion in the lower extremity of the tower.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to mechanical systems for enhancing operations of wind turbines. More particularly, the disclosure relates to a wind turbine tower that includes a yaw bearing system at the tower base adapted to permit the entire tower to rotate. 
       BACKGROUND 
       [0002]    The rotor blades of a utility scale wind turbine are ideally pitched toward or “yawed” into the wind. This orientation optimizes the amount of wind energy captured by the rotor, and in turn maximizes torque produced on a main shaft of the wind turbine to drive associated electric generators, for example. 
         [0003]    Accordingly, the traditional wind turbine tower structure incorporates a rotor, a rotor shaft and bearings, collectively referred to as a turbine, along with a nacelle to support such structure. All are generally situated atop of a fixed tower, and are designed to rotate on the fixed tower structure for the purpose of maintaining the rotor in a position to always directly face the wind. 
         [0004]    The typical tower has traditionally been constructed as a nonrotating vertically upstanding structure having a circular cross-section and generally adapted to accommodate wind forces in any given azimuthal direction. As such, traditional tower construction has tended to be relatively robust, requiring more physical material than towers that might otherwise employ, for example, aerodynamic configurations including airfoil and other non-uniform cross-sections adapted to rotate or yaw with the turbine and nacelle to face the wind. Such structures might require less robust configurations, utilizing reduced cross-sections to save construction material costs. Construction of such towers might require less strength and/or have reduced thickness in those circumferential portions or areas that are normal to the wind and/or otherwise not subject to direct wind forces. 
         [0005]    A major limitation with respect to use of aerodynamic tower structures may have historically been related to difficulties of designing bearings adapted to accommodate the relatively high bending moments typically present near the bases of tower structures. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    This disclosure proposes a wind turbine tower that incorporates a yaw bearing system at the base of the tower, rather than having the traditional yaw bearing situated atop of the tower. 
         [0007]    In one aspect of the disclosure, a yaw track bearing system accommodates wind induced azimuthal rotation of the entire tower, along with the turbine and the nacelle, on a fixed annular rail that rotatably supports the tower. 
         [0008]    Another aspect of the disclosure is the provision of a non-uniform tower structure, with at least an upper rotor swept tower portion having a relatively smaller cross-section in a direction normal to wind forces than that of a traditional tower. 
         [0009]    In yet another aspect of the disclosure, a wind turbine base mounted bearing system incorporates a plurality of yaw bearing cartridge assemblies supported on spindles integral with conical wheels adapted to rotate at the tower base in annular tracks of a fixed support rail. 
         [0010]    In a still further aspect of the disclosure, the tracks are vertically spaced by an amount marginally greater than the diameter of the conical wheels. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is an elevational view of a wind turbine that embodies elements of the disclosure, depicting a tower that includes the disclosed yaw bearing system. 
           [0012]      FIG. 2  is a cross-sectional view of a tower portion of the wind turbine, taken along lines  2 - 2  of  FIG. 1 . 
           [0013]      FIG. 3  is an elevational view of a flared bottom portion of the same wind turbine, depicting a plurality of yaw bearing cartridge assemblies rotatably secured in the circumferentially extending bottom extremity of the tower. 
           [0014]      FIG. 4  is a side view of one of the yaw bearing cartridge assemblies. 
           [0015]      FIG. 5  is a cross-sectional view, taken along lines  5 - 5  of  FIG. 3 , of the lower tower extremity, depicting the manner in which one of the cartridge assemblies is rotatably secured via conical wheel and spindle to a tower base support rail. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring initially to  FIG. 1 , a wind turbine  10  is constructed in accordance with at least one embodiment of the present disclosure. While all components of the wind turbine are not necessarily shown nor described herein, the wind turbine  10  may include an upstanding tower  12 , having a vertical axis “a-a”, and supporting a rotor  14 . The rotor may be defined by a plurality of circumferentially arrayed, equally spaced, rotatable blades  16 ,  18 , and  20 , along with a hub  22  to which each of the blades is radially connected. 
         [0017]    The blades  16 ,  18 ,  20  (only three of which are employed in this example; there may be more or less) may be rotated by wind energy, such that the rotor  14  may transfer that energy via a main shaft (not shown) to one or more generators (not shown). Those skilled in the art will appreciate that such wind-power driven generators may produce commercial electric power for transmission to an electric grid (not shown). Those skilled in the art will also appreciate that a plurality of such wind turbines may be effectively employed on a so-called wind turbine farm to generate significant amounts of electric power. Although the disclosed embodiment focuses on wind only, this disclosure is pertinent to fluids generally, including other gases and even liquids, such as water, which may be used to drive similar turbine structures. 
         [0018]    The tower  12  of this disclosure includes a nacelle  24  which houses a rotor main shaft (not shown) as well as supporting bearings (not shown). The nacelle  24  may also include at least one generator (also not shown) adapted to convert wind energy into electricity, as those skilled in the art will appreciate. 
         [0019]    The tower  12  has an integral annular base  26  that may be rotatably secured to a support rail  50  ( FIG. 5 ), as will be further described below. The rail  50  is adapted to be secured to foundation  30  or other fixed supporting structure, such as a reinforced concrete mass. The entire tower  12  is thus rotatable about such internally fixed support rail  50  (not shown in  FIG. 1 ). 
         [0020]    An upper portion of the main body  32  of the tower  12  is defined by a rotor swept portion  27 . The rotor swept portion  27  of the tower  12  is herein defined as that tower area most adjacent to, and spaced immediately behind, the spinning rotor  14 . For optimizing efficiency, main body  32  may have a non-uniform cross-section ( FIG. 2 ) to accommodate any demanded azimuthal orientation of the tower  12 , to the extent that the tower may in real time be rotatably, and hence angularly, yawed according to prevailing wind direction. Such non-uniform cross-sections may allow use of reduced amounts of materials for construction. For example, the use of an airfoil shape has been demonstrated to permit employment of smaller tower cross-sections in a direction normal to the wind. 
         [0021]    Continuing reference to  FIG. 1 , the tower  12  has a cone shaped or flared bottom portion  34  situated immediately above its base  26  to accommodate transition from the non-uniform cross-section  36  ( FIG. 2 ) of its upper main body  32  to a circular cross-section at its base  26 . 
         [0022]    Referring now specifically to  FIG. 2 , the non-uniform cross-section  36  of the main body  32  of the tower  12  is depicted as having an aerodynamic or airfoil shape, as shown. The aerodynamic shape has a minor axis XX situated orthogonally to wind direction, arrow W, and a major axis YY situated parallel with the wind. The major axis YY has a greater dimension than the orthogonal-to-the-wind minor axis XX. As earlier noted, the use of non-uniform, including aerodynamic, shapes may require use of less tower construction materials, and thus may result in reduced construction costs. 
         [0023]    As shown, those skilled in the art will appreciate that the prevailing wind W is ideally always directed toward the leading edge  38  of the main body  32  of the tower  12 . Accordingly, the trailing edge  40  will optimally be positioned downwind to assure wind turbine operating efficiency. 
         [0024]      FIG. 3  depicts the flared bottom  34  of the tower  12  as terminating at a radially extending stepped interface  37  with the circular tower base  26 . As shown, the base  26  may have a relatively thicker wall structure than other portions of the tower  12 , thus providing for enhanced structural support. A plurality of yaw bearing cartridge assemblies  28  may be retained circumferentially about and within the base  26  as shown, for the rotatable support of the tower as earlier noted. 
         [0025]    Referring now also to  FIG. 4 , it will be appreciated that each yaw bearing cartridge assembly  28  includes an exterior housing  42  and a bearing cap  44  for reasons that will be made apparent below. 
         [0026]    Referring now specifically to  FIG. 5 , the earlier noted support rail  50  contains an interior bottom flange  52  adapted to be secured to a fixed foundation  30  ( FIG. 1 ). As such, the bottom flange  52  includes securement apertures  54  to accommodate bolts (not shown) for securing the support rail to the foundation  30 . Radially outer tracks extend from the support rail  50 , to comprise an upper track  56  and a lower track  58 . The tracks are adapted to accommodate respective top and bottom surfaces  64  and  66  of rolling conical wheels  60 . The wheels  60  have integral spindles  62 , and each spindle is carried within one of the yaw bearing cartridge assemblies  28 , as depicted. Although the particular spindle  62  is shown to have a hollow cross-section, the spindle could alternatively have a solid cross-section, depending on particular sizing and tower load requirements, etc. A hollow structure may be easier to fabricate, while a solid structure may present an opportunity for use of an even smaller cross-section. 
         [0027]    Those skilled in the art will appreciate that each conical wheel  60  is adapted to engage and roll within the pair of respective upper and lower tracks  56 ,  58  by means of an upper conical rolling contact surface  64  (which may interface with the upper track  56 ) and a lower track conical rolling contact surface  66  (which may interface with the lower track  58 ). For the respective conical rolling contact surfaces  64  and  66  to satisfactorily engage the tracks  56 ,  58 , it may be appreciated that the tracks may be flared slightly angularly in a radially outward direction, such that, as viewed in  FIG. 5 , the track  58  angles slightly downwardly, while the track  56  angles slightly upwardly. In addition, the tracks  56 ,  58  should be spaced a marginally greater distance apart than any given diameter of the conical wheel  60  at the point of engagement or contact. This expedient will facilitate proper operation of the rotatable tower even under high wind conditions wherein the tower may be cocked, i.e. one side of the tower may be lifted or raised relative to the opposite side of the tower, as may be appreciated by those skilled in the art. 
         [0028]    The base  26  of the tower  12  is constructed in the nature of a downwardly depending annular skirt that may be flanged, or otherwise have a thicker construction than other portions of the tower, as previously noted. Thus, the aperture  70  is depicted to be considerably thicker than the adjoining wall of the flared tower bottom  34 . As such, each aperture  70  may be effective to securely retain one yaw bearing cartridge assembly  28 . 
         [0029]    Each bearing cartridge  28  contains radially inner rollers  80  and radially outer rollers  82 , as shown. Although depicted as roller bearings, other types of bearings may be employed, including spherical, thrust, conical, and even plain bearings (bushings). 
         [0030]    The plurality of cartridge assemblies  28  collectively carries the weight of the entire tower  12  on the spindles  62  for providing relative rotation about the annular support rail  50 , as has been shown and described. 
         [0031]    Although only conical wheels in mating tracks have been described in reference to the embodiment as shown and described herein, the use of round rails with concave wheels (similar to that employed in roller coasters), or flat rails with cylindrical wheels, or even concave rails with convex wheels, constitute just a few of numerous alternative approaches that may fall within the spirit and scope of this invention. 
         [0032]    In addition, the support rail could be positioned outside of the circular tower base  26 , with the bearing cartridges inserted from inside of the tower, and extending radially outwardly of the tower (opposite of that as shown and described in this embodiment). 
         [0033]    Further, the bearing cartridges could alternatively be mounted to the fixed inner (or outer) fixed ring, with the rail mounted to the rotating tower as an alternative to the structure shown and described herein. 
         [0034]    Further, the described embodiment has the integral spindle; those skilled in the art will appreciate that the conical wheel could alternatively be attached to a separate axle. 
         [0035]    Finally, the described embodiment uses only one set of wheels in conjunction with an upper and lower rail. With some modification of structure, a single rail could be used, with a pair of wheel assemblies engaging opposed sides of the rail; i.e. with one wheel assembly above the rail and one wheel assembly below the rail. 
         [0036]    Numerous other expedients will be recognized by those skilled in the art to fall within the spirit and scope of this invention. 
       INDUSTRIAL APPLICABILITY 
       [0037]    The present disclosure generally sets forth a yaw bearing system that may enhance the utility of wind towers by making them more cost efficient. A reduction in capital costs, due to reduction in raw material usage required to fabricate a wind turbine tower, may be achieved by designing the tower to be rotatable, and to incorporate an aerodynamic or otherwise non-uniform tower cross-section requiring less materials than would a standard traditional circular cross-section. 
         [0038]    The disclosure offers an improved wind turbine tower that incorporates a yaw bearing system at the tower base, rather than a single yaw bearing for turbine and nacelle structures at the top of the tower. Replacement of the traditional single yaw bearing in this manner supports rotation of the entire tower structure, thus permitting the wind turbine, nacelle structures, and the tower to rotate as a unit about an annular dual track base support rail. In such a manner, azimuthal wind alignment of the tower with nacelle and turbine structures can be always assured, while permitting the tower to be constructed with smaller cross-sections in directions normal to the wind forces. 
         [0039]    Current wind turbine structures require having to disassemble the turbine and to remove the entire nacelle in order to replace a worn-out yaw bearing atop of the tower. The tower base-level bearing structure of this disclosure offers at least the particular advantages of (a) avoiding safety dangers inherent in having to change bearings at high elevations, and (b) individual removal and replacement of bearing cartridge assemblies without need for disassembly of the turbine and/or removal of the nacelle as required in current wind turbine structures. Moreover, the costs associated with use of small bearings are relatively low as compared to costs of using the large yaw bearings of current wind turbines. 
         [0040]    The result is a relatively robust bearing system adapted to accommodate a) significant non-uniform wind forces on the yawing tower structure, while b) using a non-uniform, e.g. aerodynamic, cross-section in the main body of the tower to reduce costs of manufacture.