Patent Application
20200166021
This application claims priority to European Application No. 18380019.2, having a filing date of Nov. 28, 2018, the entire contents of which are hereby incorporated by reference.
The following describes a wind turbine bearing assembly; a wind turbine; and a method of manufacturing a bearing assembly.
A wind turbine generally comprises an aerodynamic rotor with several rotor blades. In a wind turbine with gearbox, the aerodynamic rotor turns a low-speed rotor shaft. The gearbox performs rotatory speed conversion between the low-speed rotor shaft and a high-speed generator rotor. During operation of the wind turbine, vibrations may develop and can lead to stress damage or failure in components of the drive train. For safe and efficient operation of such a generator, it is therefore very important to ensure efficient transfer of loading forces between the low-speed rotor shaft and any supporting structure, for example a machine bed. Usually, the low-speed rotor shaft of such a wind turbine is held by a front bearing (near the drive end or hub end of the wind turbine) and a rear bearing (near the gearbox). Each bearing is securely mounted to a supporting structure such as a machine bed, usually by means of diametrically opposed mounting points. A mounting point may also comprise some kind of damping means to ensure that vibrations are damped and not transferred between bearing and machine bed.
It is important to suppress torsion of the rotor shaft resulting from differences in torque at the outer and inner ends or the low-speed rotor shaft. For this reason, it is known from the prior art to provide a “complete bearing arrangement”, i.e., an arrangement in which the front bearing and the rear bearing are contained in a bearing housing that is designed to provide the desired degree of rigidity and stiffness. Such a bearing housing is generally shaped to extend over the front and rear bearings and to exactly fit about the front bearing and the second bearing. The bearing housing generally also comprises the necessary interface for mounting the entire assembly to the machine bed. While this complete bearing arrangement ensures favorable load transfer and therefore also efficient operation of the generator, the bearing housing must be designed with very high tolerance requirements. Generally, a specific generator design will also require a specific bearing housing design. This is because the shape of the bearing housing will depend directly on the diameters of the front and rear bearings, and also on the distance between front and rear bearings. For example, the front bearing diameter of one generator of a series may be a few cm larger (or smaller) than the front bearing diameter of another generator of the same series. In that case, a bearing housing of one generator of a series will not be useable for another generator of the same series. Therefore, generators that differ only slightly in component design require distinct bearing housings. This adds significantly to the manufacturing costs of a generator series.
Furthermore, a bearing housing that is dimensioned to contain a front and rear bearing will be large and cumbersome. This adds to transport, handling and installation costs. Another drawback of such a complete bearing arrangement is that the housing must generally be removed in order to obtain access to a bearing, for example to perform maintenance or repair tasks.
An aspect relates to an improved way of supporting the rotor shaft to overcome the problems outlined above.
According to embodiments of the invention, the bearing assembly comprises a front bearing for a rotor shaft; a rear bearing for the rotor shaft; and a plurality of bearing connectors arranged between the front bearing and the rear bearing, wherein each bearing connector has two outer ends, and wherein one outer end of a bearing connector is secured to the front bearing, and the other outer end of that bearing connector is secured to the rear bearing.
An advantage of the bearing assembly according to embodiments of the invention is that it permits a modular approach and can contribute to significantly reduced construction costs. Instead of realizing front and rear bearings in a single unit as known from the prior art, the inventive approach is to connect the front and rear bearings using several bearing connectors. Such connectors may also be referred to as ties or stays. Since the purpose of the bearing connectors is to provide a favorably “stiff” connection between front and rear bearings, i.e. to reduce or minimize the relative torsional movement between front and rear bearings, the bearing connectors may also be referred to as “stiffening elements” or simply “stiffeners” in the following. In the inventive bearing assembly, it is possible to provide different types of bearing connectors which can be used to connect front and rear bearings in different generator designs. The cost of manufacturing different types bearing connector is significantly lower than the cost of manufacturing different complete bearing arrangements.
According to embodiments of the invention, the wind turbine has a drive train comprising an aerodynamic rotor arranged to turn a low-speed rotor shaft; and further comprises an embodiment of the inventive bearing assembly arranged to support the low-speed rotor shaft.
The inventive wind turbine can be manufactured with less overall costs than a conventional wind turbine with a combined bearing assembly. The costs of maintenance and repair to the bearings can also be significantly reduced.
According to embodiments of the invention, the method of designing such a bearing assembly comprises the steps of obtaining design parameters of a wind turbine generator; obtaining construction parameters of physically separate front and rear bearings for the generator rotor shaft; determining expected bearing loads during operation of the generator; and determining design parameters of the plurality of bearing connectors arranged between the front bearing and the rear bearing.
Particularly advantageous embodiments and features of embodiments of the invention are given by the dependent claims, as revealed in the following description. Features of different claim categories may be combined as appropriate to give further embodiments not described herein.
In the following, without restricting embodiments of the invention in any way, it may be assumed that each bearing is mounted to a supporting structure such as a machine bed by a pair of diametrically opposed suspension points. This arrangement is referred to as a “four-point suspension”.
As explained above, various dimensions may differ between generators of the same series or different series. Relevant bearing parameters (i.e. bearing construction parameters that are relevant to the design of the stiffener elements) may be the front/rear bearing diameters and the distance between front bearing and rear bearing. Therefore, in a particularly preferred embodiment of the invention, design parameters of a bearing connector are chosen on the basis of any such relevant bearing construction parameter(s). For example, significant design parameters of a bearing connector can be the minimum mass of a bearing connector and material properties of the material from which the bearing connector is to be made.
There may be various ways of establishing the necessary design parameters. In one preferred embodiment of the invention, the method comprises determining the form of a virtual cylinder extending between the front bearing and the rear bearing, and then basing the shape of a bearing connector on the form of that virtual cylinder. For example, a virtual cylinder extending between the front and rear bearings can be divided into a number of virtual segments. The virtual cylinder may have an overall circular or polygonal cross-section and the cross-sectional shape can be used as a basis for deciding on the shape of a stiffener. The virtual cylinder can be given a thickness or wall depth, which can be used as a basis for the thickness of a stiffener.
Knowing the relevant design characteristics of the generator (e.g. rotor shaft speed, torque, bearing rigidity etc.), and assuming various parameters such as material, wall thickness etc., it is possible to compute or simulate the minimum dimensions of each segment. For example, using a suitable tool such as finite element analysis, the effect of removing sections or volumes from the virtual cylinder can be simulated in order to reach a favorable stiffener design that will fulfil the load-transfer requirements. Similarly, the effects of altering the thickness in one or more regions of the virtual cylinder can be simulated to arrive at an optimal stiffener shape.
When basing the shape of a stiffener on a cylindrical form, the resulting stiffener can have a correspondingly curved or arc shape. Of course, in a simpler alternative, a stiffener can be formed as a flat or straight part (derived from a polygonal virtual cylinder, for example), which may be significantly easier to manufacture than a curved part.
The rigidity of a stiffener can be increased by adding material as appropriate. For example, a rib may be attached to a stiffener in a direction parallel to the rotational axis of the rotor. Equally, the rigidity of a stiffener can be increased by forming the stiffener to have a ‘T’-shaped cross section. With such a cross-section, a stiffener can be made using less material than a comparable stiffener with a rectangular cross-section.
The number of stiffener elements can be chosen on the basis of various other factors or parameters. For example, the number of stiffeners can be chosen on the basis of the rated torque, rotor shaft speed, etc., of a generator. The from and rear bearings of a relatively “small” generator may be connected using two or three stiffeners, for example, while the from and rear bearings of a relatively “large” generator may require four or more stiffeners.
In a preferred embodiment of the invention, the plurality of bearing connectors comprises a set of identical bearing connectors. For example, three or four identical stiffeners may be provided to join a specific pair of front and rear bearings. Installation costs can be minimized by not having to distinguish between different stiffeners when connecting the from and rear bearings.
A stiffener can be mounted between the front and rear bearings by using appropriate fasteners (e.g. bolts) to secure the outer ends of the stiffener to the bearings. To this end, in a preferred embodiment of the invention, an end of a bearing connector comprises a number of through-holes to receive fasteners for securing the bearing connector to a bearing. In a further preferred embodiment of the invention, a stiffener has a curved end to match the curvature of a bearing. The curvature is such that the same stiffener can be mounted to bearings with different diameters.
Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:
In the inventive bearing assembly 1, the from bearing 11 and rear bearing 12 are, connected by a set S_13A of stiffeners 13A. Each stiffener 13A of the set S_13A shown in this diagram is fastened at one end to the front bearing 11 and at the other end to the rear bearing 12 to mechanically connect the front and rear bearings 11, 12 as shown in in
The set of stiffeners 13A shown in
Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.
For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18380019.2 | Nov 2018 | EP | regional |
