WO2015022309A1

WO2015022309A1 - Bearing assembly with mounting for spherical plain bearing

Info

Publication number: WO2015022309A1
Application number: PCT/EP2014/067217
Authority: WO
Inventors: Peter Klein Meuleman; Jascha Van Pommeren; Dennis Vervoorn; Koos WELLING
Original assignee: Aktiebolaget Skf
Priority date: 2013-08-13
Filing date: 2014-08-12
Publication date: 2015-02-19

Abstract

The invention resides in a bearing assembly (100) which forms part of a bearing construction for rotationally supporting a wind turbine blade relative to a wind turbine hub (110). The bearing assembly comprises a spherical plain bearing (130) and a mounting structure (122) for receiving the spherical plain bearing. According to the invention, the mounting structure has a tapered bore (125) and the bearing assembly further comprises a conical housing sleeve (140) with a conically shaped outer surface (145) that is adapted to fit in the tapered bore (125). An outer ring (132) of the spherical plain bearing is mounted to a cylindrical bore of the conical housing sleeve.

Description

BEARING ASSEMBLY WITH MOUNTING FOR SPHERICAL PLAIN BEARING

The present invention relates to the field of spherical plains bearings and is more particularly directed to a bearing assembly for supporting a wind turbine blade relative to a wind turbine hub, comprising a spherical plain bearing and a mounting structure for the spherical plain bearing.

BACKGROUND TO THE INVENTION

Typically, wind turbine blades are connected to the hub using a slewing bearing with a diameter that is approximately equal to the diameter of the blade root. Wind turbines are becoming larger and larger, and the blade root can have a diameter of more than 3 metres. A slewing bearing with an equivalent diameter generates a substantial amount of friction. Also, the slewing bearings experience a high level of wear, due to the relatively small back and forth rotations that the bearing undergoes during operation, especially when individual pitch control is applied, and due to the associated difficulty of maintaining a good lubrication film. Consequently, the use of slewing bearings and other types of rolling element bearings as pitch bearings in wind turbines has disadvantages. An alternative design for a pitch bearing is disclosed in WO2012/146745. In one embodiment, the pitch bearing comprises a spherical plain bearing for supporting radial loads. The spherical plain bearing is considerably smaller in diameter than the blade root diameter, meaning that relatively low friction is generated. The disclosed pitch bearing further comprises an arrangement of rod connections with swivelling rod ends, for taking up the axial loads and bending moment of the blade. The contact area of the swivelling rod ends is also relatively low, and the pitch bearing as a whole generates considerably less friction in comparison with a slewing bearing. A further alternative design for a pitch bearing assembly is disclosed in DE2855992. The assembly comprises two axially spaced bearings which are connected to the blade and hub respectively via two mutually overlapping conical structures. The two bearings are rolling element bearings with a diameter that is considerably less than the blade root diameter, which again is advantageous in terms of reducing friction.

Spherical plain bearings are better adapted than slewing bearings (and other rolling contact bearings) to withstand frequent and relatively small back and forth rotations. However, wear inevitably occurs and bearing replacement may become necessary. When a slewing bearing is replaced, the blade is detached from bearing and supported using e.g. a crane while the slewing bearing is replaced. This is an expensive process. In-situ bearing replacement, without the need for detaching the blade, becomes more feasible when the blade is supported by relatively small bearings, such as in the bearing arrangements disclosed in WO2012/146745 and DE2855992.

There is still room for improvement, however, in terms of providing a bearing assembly comprising a spherical plain bearing that is easy to mount and dismount during in-situ bearing replacement.

SUMMARY OF THE INVENTION The invention resides in a bearing assembly for rotationally supporting a wind turbine blade relative to a wind turbine hub, wherein the assembly comprises a spherical plain bearing and a mounting structure for receiving the spherical plain bearing. An outer ring of the spherical plain bearing is mounted in fixed connection with the mounting structure and an inner ring of the bearing is mounted in fixed connection with a shaft component of the assembly. According to the invention, the mounting structure has a tapered bore, and the assembly further comprises a conical housing sleeve with a conically shaped outer surface that is adapted to fit in the tapered bore, whereby an outer ring of the spherical plain bearing is received in a cylindrical bore of the housing sleeve.

An interference fit is generally prescribed for mounting the outer ring of a spherical plain bearing. In a preferred example of an assembly according to the invention, the outer ring of the spherical plain bearing is mounted in the bore of the housing sleeve with an interference fit. The housing sleeve ensures that the bearing can be mounted with the proper fit.

When the spherical plain bearing is dismounted from the bearing assembly, there is a risk of radial misalignment being created between the mounting structure and the shaft component of the bearing assembly. If the mounting structure were adapted to receive the bearing outer ring directly, the misalignment could make it impossible to press in the spherical plain bearing, without causing damage. When the conical housing is pressed into the tapered bore, the misalignment is pressed out, making it possible to mount the spherical plain bearing without damaging the mounting structure or the bearing.

Suitably, the fit between the conical housing sleeve and the tapered bore of the mounting structure is an interference fit, for optimal elimination of misalignment and a play-free connection between the mounting structure and the conical housing sleeve. Also, the interference fit exerts a radial clamping force on the bearing outer ring, which can be used to create the interference fit between the bearing outer ring and the conical housing sleeve. In a further development of the invention, the conical housing sleeve is at least partly separable, to enable easy removal and insertion of the spherical plain bearing. In one example, the housing sleeve comprises two separate segments. In an alternative example, the housing sleeve has a fracture or cut along its axial length, enabling the sleeve to be opened somewhat in radial direction to release or insert the spherical plain bearing.

In some examples, a small diameter end of the conical housing sleeve is provided with a lip that extends in a radially inward direction. The outer ring of the spherical plain bearing is mounted close to this lip, which ensures that the bearing is pulled out when the conical housing sleeve is pulled out.

The bearing assembly may comprise at least one additional bearing that is mounted within of the conical housing sleeve. In one example, a thrust spherical plain bearing or an angular contact spherical plain bearing is arranged next to the (radial) spherical plain bearing at a large diameter end of the conical housing sleeve. An outer ring of the angular contact or thrust plain bearing may be mounted in connection with the bore of the housing sleeve via a spring or other resilient means. The spring ensures that the outer ring maintains its radial position, and prevents radial loads on the sleeve bearing transmitted through the bearing. This especially advantageous when the bearing is a thrust spherical plain bearing, as radial loads reduce the life of this type of bearing.

Suitably, the thrust or angular contact spherical plain bearing is axially retained by a locking plate that is e.g. bolted to the mounting structure. In some examples, the locking plate also bears against the large diameter end of the housing sleeve, which gets pressed into the tapered bore when the locking plate is screwed on. Alternatively, the housing sleeve may comprise a flange at its large diameter end, which can be e.g. bolted to the mounting structure.

To enable the conical housing sleeve to be extracted from the tapered bore, the large diameter end may suitably be provided with tool engagement means.

When the housing sleeve has been extracted, a new bearing can be mounted in the sleeve bore. Alternatively, the housing sleeve can be rotated through e.g. 180 degrees and replaced in the tapered bore of the mounting structure. A bearing assembly that supports a wind turbine blade need only undergo a maximum rotation of approximately 90 degrees. Furthermore the loads on the bearing are applied through a limited angular range. Consequently, the bearing has a load and wear zone, whereby further sections of the inner and outer rings are not subject to wear and are not loaded. The conical mounting sleeve makes it a straightforward process to rotate the bearing, such that a relatively fresh section of both bearing rings is moved into the load and wear zone. Alternatively, the bearing can be rotated through the required angular displacement within the housing sleeve. The interval between bearing replacement can thus be extended.

Thus, a bearing assembly according to the invention has several advantages. These and other advantages will become apparent from the detailed description and accompanying drawings. DRAWINGS

The invention will now be described further, with reference to the following Figures, in which:

Fig. 1 a is a perspective, cross-sectional view of a bearing assembly according to the invention;

Fig. 1 b is a perspective, cross-sectional view of the assembly of Fig. 1 a, shown in a dismounted condition;

Fig. 2a is a schematic, cross-sectional view of a further bearing assembly according to the invention;

Fig. 2b is a schematic, cross-sectional view of the assembly of Fig. 2a, shown in a dismounted condition. DETAILED DESCRIPTION

Fig. 1 a shows an example of a first bearing assembly according to the invention, in an assembled state. Figure 1 b shows components of the assembly in a dismounted state. The first bearing assembly 100 is part of a bearing structure for rotationally supporting a wind turbine blade relative to a wind turbine hub 1 10. The bearing structure comprises a dynamic frame 120 to which the turbine blade is attached. The hub 1 10 in this example comprises a central shaft that is coupled to the turbine main shaft and which interconnects three shaft components 1 12. The hub further comprises a static frame (not shown) that cooperates with a corresponding dynamic frame 120. Each dynamic frame is rotationally supported relative to each static frame by means of first and second bearing assemblies. The first bearing assembly is mounted to the shaft component 1 12 and comprises a spherical plain bearing 130 having an inner ring 131 and an outer ring 132. The second bearing assembly (not shown) is axially spaced from the first assembly 100, and suitably also comprises a spherical plain bearing. Further, each dynamic frame 120 and each static frame has a frame construction comprising three legs with openings in between. Legs of the static frame pass between the dynamic frame legs and legs of the dynamic frame pass between the static frame legs. In use of the wind turbine, the high loads from the blade are transmitted to the hub 1 10 through the bearing structure. The high loads can cause deformation of the dynamic frame 120, leading to a risk of misalignment between the outer and inner rings of the supporting bearings. The spherical plain bearing 130 is a self-aligning 5 bearing and can accommodate misalignment. The bearing 130 also has excellent wear behaviour, but there remains a risk that bearing replacement will be necessary during the lifetime of the wind turbine. The described bearing structure enables the bearings in the first and second bearing assemblies to be replaced without removal of the blade. Suitably, an additional, temporary connection is i o established between the static and dynamic frames of the bearing structure while bearing replacement occurs.

In a bearing assembly according to the invention, the spherical plain bearing can be easily dismounted and can be replaced in a manner that ensures a proper fit for 15 the bearing.

This is achieved in that the bearing assembly comprises a housing sleeve 140 with a conically shaped outer section 145 that fits into a correspondingly tapered bore 125 of a mounting structure 122 on the dynamic frame 120. The outer ring 132 of

20 the spherical plain bearing 1 20 is mounted in a cylindrical bore of the housing sleeve 140. Preferably, as best seen in Fig. 1 b, the housing sleeve is formed from a first segment 141 and a second segment 142 that can be radially separated. This facilitates the mounting of the bearing outer ring 132 to the bore of the sleeve and facilitates its later removal. Alternatively, the sleeve may have a fracture along

25 its axial length that allows the sleeve to be opened somewhat in radial direction.

The inner ring 131 is mounted to the shaft component 1 12 of the hub. When the spherical plain bearing 130 is dismounted from the bearing assembly 100, a radial misalignment between the shaft section 1 12 and the mounting structure 122 of the 30 dynamic frame 120 can occur. Such a misalignment is eliminated when the conical housing sleeve 140 is pressed into the tapered bore 125 of the mounting structure, making it possible to remount the spherical plain bearing without causing damage. Suitably, there is an interference fit between the housing sleeve 140 and the tapered bore 125, such that when the housing sleeve has been pressed in, a radial clamping force is also exerted on the outer ring 132 of the spherical plain bearing, such that an interference fit of the outer ring in the bore of the conical housing sleeve is created. In the depicted example, the bearing assembly further comprises a first spherical thrust plain bearing 150 for transmitting axial forces acting in a direction towards the hub 1 10. An inner ring 1 51 of the first thrust plain bearing is mounted against an abutment on the shaft component 1 12. An outer ring 152 of the thrust bearing 150 is axially retained by a locking flange 160. A second spherical thrust plain bearing 170 is provided for taking up axial loads acting in a direction towards the blade, which is retained against the locking flange by a locknut or a separable ring 180.

The locking plate 1 60 has a number of connection holes for e.g. bolts 165 that are received in threaded holes 128 in the mounting structure. The locking plate 160 also bears against an axial face of the housing sleeve 140, at the large-diameter end, and the bolted connection between the mounting structure 122 and the locking plate 160 can be used to fully press in the housing sleeve 140 at the small- diameter end.

Suitably, the housing sleeve is provided with means to enable the sleeve 140 to be pushed or pulled out of the tapered bore 125. One example of such means is shown in Figures 2a and 2b, which schematically depict a further example of a bearing assembly according to the invention in an assembled state (Fig. 2a) and in a disassembled state (Fig. 2b).

The conical housing sleeve 240 is pressed into the tapered bore of the mounting structure 222 when a locking plate 260 is screwed to the mounting structure. To enable extraction of the sleeve 240, the sleeve is provided with a number of threaded holes 247 and the mounting structure is provided with a corresponding number of blind holes with an axially oriented recess surface 228. After the locking plate 260 has been removed, threaded rods 248 can be inserted into the threaded holes in the sleeve 240. When the ends of the threaded rods are screwed against the axial surface 228 of the blind holes 228, the sleeve 240 is pressed out of the tapered bore. As will be understood, many other methods and means may be used to extract the conical housing sleeve from the tapered bore of the mounting structure. A number of aspects/embodiments of the invention have been described. It is to be understood that each aspect/embodiment may be combined with any other aspect/embodiment. Moreover the invention is not restricted to the described embodiments, but may be varied within the scope of the accompanying patent claims.

Claims

1 . A bearing assembly (100) which forms part of a bearing construction for rotationally supporting a wind turbine blade relative to a wind turbine hub (1 10), the bearing assembly comprising a spherical plain bearing (130) and a mounting structure (122) for receiving the spherical plain bearing;

characterized in that

• the mounting structure has a tapered bore (1 25), and

• the bearing assembly further comprises a conical housing sleeve (140) with a conically shaped outer surface (145) that is adapted to fit in the tapered bore (125), whereby an outer ring (132) of the spherical plain bearing is received in a cylindrical bore of the housing sleeve.

2. Bearing assembly according to claim 1 , wherein the conical housing sleeve (140) is adapted for an interference fit in the tapered bore (125) of the mounting structure.

3. Bearing assembly according to claim 1 or 2, wherein the conical housing sleeve (140) is formed from two or more segments (141 , 142) which are connected together.

4. Bearing assembly according to claim 1 or 2, wherein the housing sleeve comprises a break or cut along its axial length.

5. Bearing assembly according to any preceding claim, wherein the outer ring (1 32) of the bearing is received in the bore of the housing sleeve (140) with an interference fit.

6. Bearing assembly according to any preceding claim, wherein a large diameter end of the conical housing sleeve (140) comprises receiving means for an extraction tool, for extracting the housing sleeve from the mounting structure (122).

7. Bearing assembly according to any preceding claim, wherein the large diameter end of the housing sleeve is provided with a flange having a first set of connection holes and the mounting structure (122) is provided with a second set of connection holes, in alignment with the first set.

8. Bearing assembly according to any preceding claim, further comprising a thrust or angular contact spherical plain bearing (150) mounted within the conical housing sleeve (140).

9. Bearing assembly according to claim 8, further comprising a locking plate (1 60) which axially retains the thrust or angular contact spherical plain bearing (170) and is connectable to the mounting structure (122).