Patent Application
20130170987
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Referring initially to
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.
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.
The tower 12 has an integral annular base 26 that may be rotatably secured to a support rail 50 (
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 (
Continuing reference to
Referring now specifically to
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.
Referring now also to
Referring now specifically to
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
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.
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).
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.
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.
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).
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.
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.
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.
Numerous other expedients will be recognized by those skilled in the art to fall within the spirit and scope of this invention.
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.
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.
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.
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.
