Patent Application
20190017496
The present subject matter relates generally to wind turbines and, more particularly, to compound main bearing arrangements for rotatable main shafts of wind turbines.
Generally, a wind turbine includes a tower, a nacelle mounted on the tower, and a rotor coupled to the nacelle. The rotor generally includes a rotatable hub and a plurality of rotor blades coupled to and extending outwardly from the hub. Each rotor blade may be spaced about the hub so as to facilitate rotating the rotor to enable kinetic energy to be converted into usable mechanical energy, which may then be transmitted to an electric generator disposed within the nacelle for the production of electrical energy. Typically, a gearbox is used to drive the electric generator in response to rotation of the rotor. For instance, the gearbox may be configured to convert a low speed, high torque input provided by the rotor to a high speed, low torque output that may drive the electric generator.
A wind turbine typically includes many bearings that provide relative movement between adjacent parts in a relatively efficient, low-friction manner. For example, in most wind turbines a “main shaft” extends from the rotor and into the nacelle and is supported by one or more “main bearings.” Additionally, the gearbox in the nacelle that steps up the angular speed of the main shaft includes several bearings. Furthermore, the yaw control system that rotates the nacelle relative to the tower to turn the rotor into/out of the wind, and the pitch control system that rotates the blades about their longitudinal axis also include various bearings that allow for enhanced operation of the wind turbine.
Conventionally, these main bearings are configured as roller element bearings characterized by having a structural element (e.g., a ball bearing) disposed between the two components which are moving relative to one another. Roller element bearings fail for any number of reasons, but ultimately their life is limited by surface fatigue and wear. Such limited-life components require regular maintenance so as to avoid larger scale failure modes. The replacement parts and maintenance for such limited-life components increase the overall costs of operating a wind turbine. Accordingly, wind turbine and bearing manufacturers strive for improved or alternate designs that extend the operating life of the bearings.
Journal bearings are generally known in the art as having a long operating life. The main reason for this is that, unlike roller element bearings, journal bearings do not have any structural element disposed between the two relative moving components, but instead have only a fluid film disposed therebetween. Thus, the wear and fatigue issues associated with roller elements, as well as the costs associated with their replacement and maintenance, may be avoided. Consequently, journal bearings appear to provide an attractive alternative to roller element bearings. Additionally, journal bearings are designed to eliminate surface-to-surface contact and thus operate with even lower friction, which may further increase efficiency.
Due to the unpredictability of the wind, start-up and shut-downs that occur with wind turbines, and the resultant range of operating conditions, manufacturers have traditionally relied on roller element bearings. However, roller element bearings alone are sometimes insufficient for wind turbines that are subject to large bending loads caused by varying wind speeds and directions around the rotor swept area. These bending loads are transferred to the rotor shaft and reacted through the rotor main bearings. The bending loads are more dominant than the other shear and axial loads and are typically reacted to the static main frame through a pair of axially spaced predominantly radially loaded bearings. When the axial spacing is short the bearings are highly loaded and expensive. When they are spaced apart they are less expensive but require a more expensive longer main shaft.
To this end, it would be desirable to utilize journal bearings, optionally in combination with roller element bearings, in a wind turbine compound main bearing that is simple, small, and compact configuration and can stably support radial loads and axial loads as well as increase the operating life of the bearings and decrease the costs associated with replacement and maintenance.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In one aspect, a drive train of a wind turbine is disclosed as having a rotatable hub, a gearbox, a rotatable rotor shaft extending between the rotatable hub and the gearbox, and a main bearing assembly supporting the rotatable rotor shaft, the main bearing assembly having a main bearing housing enclosing one or more compound bearings, each of the one or more compound bearings having at least two axial thrust bearings and a radial bearing.
In another aspect, a wind turbine is disclosed as having a tower; a nacelle mounted atop the tower; a generator and bearing pedestal coupled to a main frame within the nacelle; a gearbox coupled to the generator via a generator shaft; a rotatable hub; a rotatable rotor shaft extending between the rotatable hub and the gearbox; and a main bearing assembly coupled with the bearing pedestal and supporting the rotatable rotor shaft, the main bearing assembly having a main bearing housing enclosing one or more compound bearings, each of the one or more compound bearings having at least two axial thrust bearings and a radial bearing.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present disclosure.
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
In general, the present subject matter discloses a compound bearing arrangement to handle loads that were previously reacted to the main frame through a pair of axially spaced predominantly radially loaded bearings. When the axial spacing between the pair of bearings is short, the bearings are highly loaded and expensive. When they are spaced apart they are less expensive but require a more expensive longer shaft. If the bearings have a very short axial spacing but are larger diameter the predominant reaction load in the bearings is in the axial direction so the moments can be reacted by axial bearings which, although larger in diameter, can be more compact and hence less expensive. When using larger diameter axial bearings, the radial loads (vertical and lateral) are typically much smaller and can be reacted by a smaller inexpensive radial bearing.
Referring now to the drawings,
Referring now to
Main bearings 40, sometimes referred to as the rotor bearings, are housed in a main bearing assembly 48 that is supported by a main bearing pedestal 42 attached to the main frame 44 of the wind turbine with a main bearing housing 46 enclosing the main bearings 40. The main bearings 40 can be configured to react to loading as shown in
One embodiment of the main bearing assembly 48 can have a main bearing housing 46 (not shown) that houses the compound bearing 60 and is further shown in
It should be appreciated that the axial thrust bearings 52, 54 and the radial bearing 58 can be rolling element, for example roller bearings or ball bearings, and/or journal bearings. All bearings can also be either hydrostatic or hydrodynamic bearings. Using axially loaded thrust bearings instead of conventional vertically loaded radial bearings improves the main bearing arrangement for wind turbines. Journal hydrostatic thrust bearings instead of conventional rolling element bearings is one embodiment that enables the improvement. Another improved embodiment is a combination of rolling element and journal bearings wherein the radial bearing can be a rolling element and the thrust bearings can be journal bearings.
The compound bearing can be specifically configured such that the first and second axial thrust bearings 52, 54 are journal bearings with tilting pads 78 that enable a tilting movement in at least one direction of rotation of the bearing. A white metal or a resin overlay, low in frictional coefficient to the sliding surfaces, can be applied to the tilting pads 78. Elastic support seats can be inserted with tilting pads 78 to correct any unevenness in distribution of loads applied to the tilting pads 78.
Also, a lubricating mechanism for the compound bearing can be at least one fluid supply groove, for example oil, that can be cut in the fixed raceway annulus, and at least one fluid supply hole, communicating with the fluid supply groove(s), which can pass through the inner surface 66, the first axial surface 67, and the second axial surface 68 of the fixed raceway annulus, thus supplying lubricating fluid (oil) to the radial and axial thrust bearing pads.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
