GB2440346A

GB2440346A - Bearing assembly for a variable vane

Info

Publication number: GB2440346A
Application number: GB0614712A
Authority: GB
Inventors: Dale Edward Evans
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2006-07-25
Filing date: 2006-07-25
Publication date: 2008-01-30
Also published as: GB0614712D0

Abstract

A bearing assembly for a variable vane of a gas turbine engine comprises an actuating lever 31 with a generally annular end portion and a cooperating pin 47 passing through the generally annular end portion, the pin 47 being secured at both ends in a unison ring 33. A bearing 343 is interposed between the generally annular end portion and the pin 47 and limiting means 349 are present to prevent movement of the bearing 343 in the axial direction of the pin 47. The bearing 343 preferably comprises a spherical bearing that includes a housing portion 345 and a ball portion 343, with the ball portion preferably having extensions 349 which act as the limiting means, that extend in use in the axial direction of the pin 47 to cooperate with the unison ring 33 so as to substantially prevent movement of the ball portion 343 in the axial direction of the pin 47. Since movement is occurring between the annular end portion and the housing 345, it is preferable to coat these surfaces with a low-friction coating.

Description

BEARING ASSEMBLY FOR A VARIABLE VANE

This invention relates to gas turbine engines. More specifically, it relates to mechanisms for variable stator vanes in such engines.

Variable stator vanes are widely used in the compressors of gas turbine engines to improve their part-speed behaviour. In a typical arrangement, each vane in a circumferential array is pivotable about a spindle. A unison ring extending around the engine is connected to actuating levers attached to the spindle of each vane. In operation, the unison ring is moved in a circumferential direction by an actuator. This causes the actuating levers to move, thereby turning the vanes. The unison ring ensures each vane is pivoted by the same amount.

In use, a spherical bearing is typically provided on the pin joint between the actuating lever and the unison ring, to accommodate any misalignment as the variable vanes operate. This misalignment arises because the actuating lever rotates about the axis of rotation of the vane, but the unison ring rotates about the engine centreline. The result is that the spherical bearing moves up and down the pin in use, and this leads to bending and wear of the pin.

This bending and wear may eventually affect the integrity of the mechanism, but even before that will have a detrimental effect on the accuracy of movement of the variable vanes, and consequently a detrimental effect on the engine performance.

It is therefore an object of this invention to provide a bearing assembly for a variable vane which reduces the bending and wear inherent in known arrangements, and which consequently provides more accurate and reliable movement of the variable vanes.

According to the present invention, there is provided a bearing assembly as claimed in claim 1.

An embodiment of the present invention will now be described, with reference to the accompanying drawings, in which: Figure 1 illustrates a typical prior art arrangement of variable vanes; Figure 2 is a cross-section of part of the prior art arrangement of Figure 1 and shows, in more detail, the attachment of the actuating lever to the unison ring; and Figure 3 is a cross-section of part of an arrangement of variable vanes according to the invention.

Referring first to Figure 1, interposed between the rows of rotating compressor blades 11, 13, 15, 17 are rows of variable stator vanes 19, 21, 23. Looking particularly at the row 19, each stator vane 25 has a spindle 27 about which it can rotate. At the radially-outer end of each spindle 27, a nut 29 secures one end of an actuating lever 31 to the spindle 27. The other end of the actuating lever 31 is attached to a unison ring 33, by a pin 47. The details of this attachment will be explained presently. In use, an actuator (not shown) can move the unison ring 33 in the directions shown by the double-headed arrow A. This movement is transferred to the actuating lever 31, which in turn causes the spindle 27, and therefore the vane 25, to rotate. The unison ring 33 ensures that each vane 25 in the row 19 is moved uniformly by the same amount.

Figure 2 is a cross-section of part of the prior art arrangement of Figure 1 and shows, in more detail, the attachment of the actuating lever to the unison ring. The end of the actuating lever 31 remote from the spindle 27 is generally annular. A spherical bearing 37 of known type is fitted into this annular end. The spherical bearing 37 is swaged into the actuating lever 31 so there is no relative movement between the inner surface 39 of the annular end and the outer surface 41 of the spherical bearing 37. The spherical bearing is mounted on a pin 47 which is secured to the unison ring 33 at its ends. The spherical bearing 37 is free to move on the pin 47.

In use, the ball portion 43 of the spherical bearing 37 can rotate within the housing portion 45 of the spherical bearing 37, to accommodate any angular misalignment as the variable vanes operate. This misalignment arises because the actuating lever 31 rotates about the axis X, but the unison ring 33 rotates about the engine centreline. The result is that the spherical bearing moves up and down the pin 47, in the directions shown by the arrows Y. This leads to bending and wear of the pin 47.

Figure 3 is a cross-section of part of an arrangement of variable vanes according to the invention. Some features in Figure 3 are identical to corresponding features in Figure 2, and for these the same reference numbers have been used.

A spherical bearing 337 of novel design is fitted into the annular end of the actuating lever 31. In contrast to the prior art, the spherical bearing 337 is not swaged into the annular end. Instead, there is a sliding fit between the inner surface 39 of the annular end and the outer surface 341 of the spherical bearing 337. A suitable low-friction coating is applied to one or both of the surfaces 39, 341.

The ball portion 343 of the spherical bearing 337 is extended in the axial direction of the pin 47, by the addition of extensions 349. These extensions bridge the gap between the two sides of the unison ring 33, so that the ball portion 343 cannot move relative to the pin 47 in the directions Y. Further to ensure no relative movement between the pin 47 and the ball portion 343, these two components are press-fitted together.

This arrangement ensures that the ball portion 343 cannot move in use relative to the pin 47, and so the problems of bending and wear in known arrangements are avoided. The misalignment caused by the rotation of the actuating lever 31 and the unison ring 33 about different axes is instead accommodated by sliding movement between the inner surface 39 of the annular end of the actuating lever 31 and the outer surface 341 of the spherical bearing 337, as explained above. Because the surfaces 39 and 341 have greater area than the contact area between the ball portion 37 and the pin 47 in the prior art arrangement, the pressure and therefore the wear in the system is reduced.

Furthermore, the primary loading is not bending (as in the prior art) but double shear, and so the integrity of the pin 47 is improved.

It will be appreciated that certain modifications may be made to the arrangement described, without departing from the scope of the invention.

For example, the spherical bearing may be replaced by a bearing of a different type, provided that it can accommodate the angular misalignment referred to above.

The extensions need not be formed integrally with the ball portion of the spherical bearing, but may be separate components, or may be formed integrally with another part of the assembly.

Claims

CLAI MS

1. A bearing assembly for a variable vane of a gas turbine engine, comprising an actuating lever with a generally annular end portion and a cooperating pin passing through the generally annular end portion, the pin being located at both ends in a unison ring, and further comprising a bearing interposed between the generally annular end portion and the pin, characterised in that the assembly comprises limiting means to substantially prevent movement of the bearing in the axial direction of the pin.

2. A bearing assembly as in claim 1 in which the limiting means are formed integrally with the bearing.

3. A bearing assembly as in claim 1, in which the bearing is a spherical bearing comprising a housing portion and a ball portion.

4. A bearing assembly as in claim 3, in which the limiting means are formed integrally with the ball portion.

5. A bearing assembly as in claim 1 or claim 2, in which sliding movement is possible between the annular end portion and the bearing to accommodate misalignment.

6. A bearing assembly as in claim 5, in which a low-friction coating is applied to one or both of the annular end portion and the bearing to facilitate the sliding movement.

7. A bearing assembly as in claim 3 or claim 4, in which sliding movement is possible between the annular end portion and the housing portion to accommodate misalignment.

8. A bearing assembly as in claim 7, in which a low-friction coating is applied to one or both of the annular end portion and the housing portion to facilitate the sliding movement.

9. A bearing assembly substantially as described in this specification, with reference to and as shown in Figure 3 of the accompanying drawings.