GB2412946A

GB2412946A - A unison ring

Info

Publication number: GB2412946A
Application number: GB0407897A
Authority: GB
Inventors: Brynley Clark
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2004-04-06
Filing date: 2004-04-06
Publication date: 2005-10-12
Also published as: GB0407897D0

Abstract

A unison ring (40, fig 1) is used via lever arms (25, fig 1) to vary the angle of a number of stator vanes (20, fig 1) in the compressor (10, fig 1) of a gas turbine engine. The ring (40, fig 1) is made up of two ring halves 45,55 which may have their ends tapered and serrated 258,248, the interconnection of which, allow for a more secure connection to be made, when the two halves are joined together. Bolts 285 are also used to strengthen the joint. Alternatively, the ends may have hooks (390, 395, fig 8) which interconnect to form a joint.

Description

24 1 2946 - 1

A UNISON RING

The present invention relates to the synchronous alteration of the angle of incidence of stator vane arrays of the kind used in axial fluid flow machines, such as aerofoil - bladed turbines and compressors, to control airflow. Simultaneous movement of the vanes is accomplished through the use of a unison ring disposed circumferentially about the exterior of the compressor housing. The ring is linked to each stator vane by individual vane lever arms which rotate each vane about its corresponding pivot in response to rotation of the ring.

In order to allow unison rings to be assembled around a housing they are usually formed from two or more segments which are joined together. For example, it is known to produce a unison ring in two halves with plain ends which are clamped together using plates which flank the joins and bolts which pass through the plates and the ring.

In addition, close tolerances required for ring halves with plain ends may necessitate careful matching of the halves.

The forces to which the unison ring is subjected in use may be large and the stress placed on the joined between ring segments may also be large. Problems can arise with conventional bolted joints. A particular problem for conventional bolted joints arises when the load placed on the ring alternates in direction which can result in loosening of the joints.

The present invention seeks to improve upon known systems for joining the segments of unison rings together.

According to the present invention there is provided a unison ring for selectively adjusting the angle of incidence of stator vanes in a gas turbine engine compressor or fan, the ring having two or more circumferential segments joined together at respect adjoining circumferential ends to form the ring, the ends of each segment having engagement means for engagement with the respective adjoining end of a - 2 neighbouring segment.

The present invention therefore provides a ring in which the ends of the ring segments themselves have a means of engaging a respective adjoining end. This therefore allows formation of a join with simple construction and assembly and with the potential for greatly increased strength and resistance to loosening.

Furthermore, because the ends engage each other there is no requirement for matching of ring segments to overcome tolerencing differences.

The engagement means may be adapted substantially to resist relative circumferential movement of the segments. That is to say the engagement means resist relative circumferential movement, or slippage, in both directional senses, being movement of the respective ends towards and away from each other. In this way the risk of the joint loosening is reduced.

The ring may comprise two substantially equal segments. Production of a ring from two equal halves keeps the number of components to a minimum and also keeps the number of joints to a minimum. Of course a ring with more than two segments may be required in some circumstances and this is not beyond the scope of the present invention, because the present invention is concerned with the joins between neighbouring segments, of which there can be any number.

The engagement means may comprise one or more teeth which may be sized and positioned to cooperate with teeth on an adjoining end. The engagement means may comprise a serrated surface having a plurality of teeth to provide a serrated joint. A serrated joint is particularly suited to resisting relative circumferential movement between adjacent ends.

The respective segment ends may overlap each other which can allow for a joint with increased strength. When the ends overlap they may be formed such that there is substantially no increase in the cross-section of the ring. For example, the ends may - 3 be oppositely tapered so that they fit together to form the joint.

There may further be provided mechanical fixing means for locking the respective ends together. The mechanical fixing means may comprise one or more bolts which pass through the region of the join. This is particularly relevant in embodiments in which the engagement means do not lock the ends completely together but rather allow the ends to engage and resist some forms of movement, and are then complimented by the mechanical fixing means to produce a cumulatively high strength join.

In embodiments in which the respective ends are overlapping the bolts may pass directly through the overlapping region.

The unison ring may further comprise at least one actuating point at which a load is applied to move the ring, the actuating poinVs being located at a point circumferentially spaced from the ends of the segments. In this way, therefore, the load is applied away from the joins to minimise stress on the joins.

According to an alternative aspect of the invention there is provided a unison ring for selectively adjusting the angle of incidence of stator vanes in a gas turbine engine compressor, the ring comprising at least one circumferential ring portion having a pair of respective circumferential ends at which a joint is formable to permit assembly of the ring, wherein each circumferential end has engagement means for engagement with the other respective end of the pair.

The ring may further comprise means for locking the respective ends together.

The present invention also provides a gas turbine engine compressor or fan comprising at least one unison ring as described above.

The present invention further provides a gas turbine engine comprising at least one unison ring as described above. - 4

The present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial section of a gas turbine engine compressor including several unison rings for selectively adjusting the angle of instance of stator vanes; Figure 2 is a diagrammatic plan view of a unison ring formed from two half segments; Figure 3 is a magnified diagrammatic view of the region of a known unison ring denoted by the box in Figure 2; Figure 4 is a diagrammatic plan view of a circumferential end of a unison ring segment formed according to the present invention; Figure 5 is a magnified view of the region of the circumferential end denoted by the box in Figure 4; Figure 6 is a diagrammatic plan view of a join between two circumferential ends formed according to the present invention; Figure 7 is a diagrammatic magnified view of the region denoted by the box in Figure 6; and Figure 8 is a diagrammatic plan view of a join formed according to an alternative embodiment.

Referring first to Figure 1 there is shown a gas turbine engine compressor generally indicated 10 and being of the type to which a unison ring according to the present invention is applicable. The compressor 10 includes a 15 casing for housing several arrays of stator vanes 20 interspersed by arrays of fan blades 30. In order to allow control of airflow through the compressor 10 the stator vanes 20 can be pivoted along - 5 their length in order to adjust their angle of attack. The stator vanes 20 are pivoted by connection to lever arms 25 which in turn are connected to a unison ring structure generally indicated 40. The ring 40 has a circular cross-section and is fitted around the exterior of the compressor housing 15. The ring 40 can be rotated around the housing using, for example, hydraulic actuators; this causes the levers 25 to turn which in turn causes the vanes 20 to pivot in unison.

In order to assemble the ring 40 around the casing 15 it is assembled from two half ring segments 45, 55 as shown in Figure 2. The ring segments 45, 50 are semi-circular and are joined together at respective adjoining circumferential ends to form two joins 65, 65a which are diametrically opposed to each other on the ring 40.

In use of the ring 40 it is rotated by actuators which engage the ring 40 at diametrically opposed actuating points 70, 71 which are 90 degrees away from each of the joins 65, 65a. In use of the ring 40, rotation can be in either direction and repeated cycling can place large and changing loads on the joins 65, 65a. Accordingly the joins 65, 65a must be strong in order to avoid breaking of the ring 40 and failure of the compressor 10.

Referring now to Figure 3 there is shown a known unison ring in the region of a join 165 formed between adjoining circumferential ends 146, 156 of two ring segments 145, 150. The circumferential ends 146, 156 are plain and not adapted in any way to engage each other than by simple abutment of adjacent surfaces. In order to lock the ends 146,156 together curved side plates 175, 180 are provided on either side of the ring in the region of the interface between the ends 146, 156. The plates 175, 180 extend over the join between the ends 146,155. Bolts 185 are used to pass through both plates 175, 180 and the ring segments 145, 150 to lock the ends 146, 156 together. Because the ends 146, 156 are plain and not adapted in any way to engage each other they can move with respect to each other under the cyclical loading during use of the ring. This can lead to loosening of the bolts 185 and weakening of the join between the ends 146, 156. - 6

Referring now to Figure 4 there is shown a circumferential end 256 formed according to the present invention. The end 251 is provided with engagement means for engaging a respective adjoining end 246 of a further ring segment 245 (see Figure 6). The engagement means of the end 256 commence with a step 257 which reduces the thickness of the segment 250. Extending away from the step 252 in a tapering fashion is a serrated engagement surface 258 comprising a plurality of teeth 259 best shown in Figure 5. The serrated surface 258, and therefore the end 256, terminates with a radial abutment surface 260.

Referring now to Figures 6 and 7 the circumferential end 256 of Figures 3 and 4 is shown engaged with a circumferential end 246 provided with identical engagement means which are the mirror image of the engagement means of the end 256. The abutment surface 250 of the end 256 fits against the radial step 247 of the end 246.

Similarly the abutment surface 250 of the end 246 abuts against the step 257 of the end 256. The respective serrated surfaces 258, 248 engage each other by engagement of the teeth 249, 259. It will be noted that because the ends 246, 256 are oppositely tapered the width of the ring does not increase across the region of the join 265.

The ends 246, 256 are now engaged such that the segments 245, 255 are prevented from moving circumferentially relative to each other. The ends 246, 256 are locked together by bolts 285 which pass directly through the overlapping serrated joint between the ends 246, 256. The bolts 285 lock the ends 246, 256 together and the serrated joint between the ends 246, 256 resists slippage of the segments 245, 250 in use of the ring.

Referring now to Figure 8 there is shown an alternative embodiment in which an alternative engagement means are provided. In this embodiment adjoining circumferential ends 346, 356 are provided with hooks 390, 395 each comprising a nose portion 391, 396 and a recess 392, 397, with the nose portions 391, 396 engaging into the recesses 392, 397 to interlock the ends 346, 356. In this embodiment curved side plates 375, 380 are applied across the region of the join - 7 between the ends 346, 351 and bolted together using bolts 385. In this embodiment the bolts 385 do not pass through the overlapping region of the join 365. - 8

Claims

1 A unison ring for selectively adjusting the angle of incidence of stator vanes in a gas turbine engine compressor or fan, the ring having two or more circumferential segments joined together at respective adjoining circumferential ends to form the ring, the ends of each segment having engagement means for engagement with the respective adjoining end of a neighbouring segment.

2 A unison ring as claimed in Claim 1, in which the engagement means are adapted substantially to resist relative circumferential movement of the segments both towards and away from each other.

3 A unison ring as claimed in Claim 1 or Claim 2, in which the ring comprises two substantially equal segments.

4 A unison ring as claimed in any of Claims 1 to 3, in which the engagement means comprise one or more teeth.

A unison ring as claimed in any preceding claim, in which the engagement means comprise a serrated surface.

6 A unison ring as claimed in any preceding claim in which the respective ends are overlapping.

7 A unison ring as claimed in Claim 6, in which the respective overlapping ends are formed such that there is substantially no increase in the cross-section of the ring at the join.

8 A unison ring as claimed in any preceding claim, in which the respective ends are tapered. if - 9 -

9 A unison ring as claimed in any preceding claim, in which there are further provided mechanical fixing means for locking the respective ends together.

A unison ring as claimed in Claim 9, in which the mechanical fixing means comprise one or more bolts.

11 A unison ring as claimed in Claim 10, in which the respective ends are overlapping and the bolts pass through the overlapping region

12 A unison ring as claimed in any preceding claim, in which the ring further comprises at least one actuating point at which a load is applied to move the ring, the actuating poinVs being located at a point circumferentially spaced from the ends of the segments.

13 A unison ring for selectively adjusting the angle of incidence of stator vanes in a gas turbine engine compressor, the ring comprising at least one circumferential ring portion having a pair of respective circumferential ends at which a joint is formable to permit assembly of the ring, wherein each circumferential end has engagement means for engagement with the other respective end of the pair.

14 A unison ring as claimed in Claim 13, which ring further comprises locking means for locking the respective ends together.

A gas turbine engine compressor or fan, comprising at least one unison ring as claimed in any preceding claim.

16 A gas turbine engine comprising at least one unison ring as claimed in any preceding claim.

17 A unison ring substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.