GB2204364A - Mounting members in casings - Google Patents

Abstract

A compressor inlet of a gas turbine engine has movable guide vanes 3 mounted by an arrangement which permits the vanes to be mounted in a one piece casing 2. The vanes each carry a shaft 5 which is passed through a relatively wide bore in the casing 2, at an angle to the bore axis (Fig. 2), and which is wider at the inner end where a recess is formed to receive a locating collar 14 loosely fitted on the shaft 5. The collar and shaft are located transversely by a bush 15 and the vane is held in place by a spring lever 7 pivotally attached to a circumferential unison ring 16 which controls the angle of the vanes. <IMAGE>

Description

MOUNTING ARRANGEMENT The present invention concerns an arrangement for mounting a member inside a casing providing limited longitudinal clearance.

In particular, the invention finds use for mounting stator vanes or blades in an axial flow gas turbine engine, especially for the mounting of variable pitch vanes.

Stator guide vanes are used to direct, or redirect, a gas stream onto rotor blades in compressor or turbine stages. In the initial compressor stages the pitch of the stator vanes is commonly variable by turning in the blade about its longitudinal axis in order to match the compressor flow rate. The rotor vanes or blades are attached at their radially inner ends to a central shaft. Interdigitated with the various stages of rotor vanes are stator vanes which are attached at their radially outer ends to the engine casing. The inner ends of the stator vanes do not contact the rotor but, in order to minimise gas leakage paths, an absolute minimum of clearance is provided. This can make it very difficult to mount the stator vanes in the casing with the rotor in situ.Conventionally, the casing is made in annular sections which are bolted together at outside flange joints, and the line of the flange joints passes circumferentially through the mounting line of the ring of stator vanes.

Thus, the stator vanes can be assembled in position before the adjacent casing sections are bolted together.

It is an object of the present invention to provide a vane mounting arrangement which will permit the vanes to be assembled into an already complete casing. As a result it will be possible to employ one piece engine casings, or at least axially longer casing sections into which stator vanes can be mounted intermediate the ends of the casing.

In accordance with the present invention there is provided an arrangement for mounting a member inside a casing providing limited longitudinal clearance for the member comprising at the or each mounting location a structure formed in the casing defined in a bore for receiving a longitudinal shaft carried by a member, the bore being wider at its inner end than at its outer end and having a minimum dimension sufficiently greater than the diameter of the shaft to permit the shaft to be inserted at an inclined angle into the bore from inside the casing, a collar which fits loosely on the shaft and which engages the wider end of the bore to limit penetration of the member, and a bush for subsequent assembly onto the shaft from outside the casing to positively locate the shaft and collar in the bore.

Preferably, the wider inner end of the bore is formed as a part spherical recess and the collar has a corresponding part spherical outer surface for engagement with the recess. Advantageously, the bore and the inner surface of the collar are parallel sided to receive a plain bush co-axial with the axis of the shaft whereby the member may be mounted for rotation about the axis.

The invention will now be described further, by way of example only, with reference to the accompanying drawings, in which: Fig 1 is a partially sectioned view of a variable pitch stator vane, and Fig 2 illustrates the manner of assembly of the vane into the outer casing.

Referring now to the drawings, Fig 1 shows a fragment of a partially sectioned side view through the centre line of an axial flow gas turbine engine, the view shows a mounting arrangement for a variable pitch compressor guide vane or stator blade.

The blade 1 is mounted in an engine casing 2 by means of an arrangement shown in its assembled for in Fig 1, and partially dismantled in Fig 2. The vane 1 comprises an aerofoil section blade 3 which is formed with an integral circular shoulder 4 at one end. The plane of this shoulder 4 is generally perpendicular to the plane of the blade 3. Disposed to lie normal to the shoulder 4 is a shaft 5 which may also be formed integrally with the blade, or may be rigidly fixed to the shoulder, for example, by welding.

The distal end of the shaft 5 is preferably formed with a keyed section 6 for engagement with a turning lever 7. The end of the shaft is also threaded to receive a locking nut 8 for securing the lever 7 to the keyed portion 6 of the shaft 5.

At each stator vane mounting location there is formed integral with the casing 2 a hollow frusto-conical, outwardly extending projection 9.

This hollow projection defines a bore 10 which is wider at its inner end than its outer end. In the described example the bore 10 is formed towards its inner end as a part spherical recess 11 and towards its outer end as a parallel sided hole.

The diameter of the parallel sided portion of the bore 10 is substantially greater than the diameter of the shaft 5 carried by the vane, and is sufficiently greater to admit the shaft 5 to be inserted into the housing in the manner shown in Fig 2. That is, for the shaft 5 to be passed through the bore 10 at an angle inclined to the ax-s of the frusto-conical projection, in the direction indicated by the arrows 12a and 12b. This permits the vane to be mounted in position in the casing 2 although its overall length, that is including the length of the blade 3 and the shaft 5, is much greater than the radial spacing between the casing 2 and a rotor shaft 13 at that particular location.

Penetration of the shoulder 4 into the recess 11 is limited by an annular collar 14 which is fitted over the shaft 5 adjacent the shoulder 4. As shown in the drawing the adjacent faces of the collar 14 and shoulder 4 are planar. The inner circumference of the collar is also substantially greater than the diameter of the shaft portion 5 so that the collar 14 fits loosely on the shaft and is free to move transversely with respect thereto, as can be seen from Fig 2.

Upon assembly a bush 15 is inserted into the bore 10 and the collar 14 and acts to positively locate the shaft 5 with respect thereto in transverse directions. Longitudinal location of the vane 1 is achieved by means of a bias applied by the spring lever 7 one end of which is engaged with the keyed portion 6 of shaft 5 and locked thereto by lock nut 8.

The other end of the spring lever 7 is pivotally attached to a unison ring which is rotatably mounted on the casing 2. The unison ring 16 encircles the casing in a plane parallel te another plane containing the longitudinal axis of vane 1 through its shaft 5.

As illustrated, the bush 15 is parallel sided and fits closely with within the bore 16, which is also parallel sided, and extends substantially through the collar 14 almost to its bottom face, thereby to positively locate the collar 14 with respect to the shaft 5. The outer end of the bush 15 may be flanged, as shown, for engagement with the top face of housing 9 to limit penetration. The collar 14 has, as shown in the drawings, a part spherical outer surface although other forms of collar may serve as well, however, for example, a frusto-conical outer surface will serve to react the bias forces pacting outwardly to urge the shoulder 4 of the vane against the under face of collar 14 The sprung lever 7 is arranged to act quite strongly to urge the vane 1 in an outward direction thereby positively locating it in position In casing 2.

The vane particularly described above is one of a plurality of such vanes distributed circumferentially, at equally spaced locations, around a compressor inlet for a gas turbine engine.

Each blade is mounted in a similar manner and the plurality of sprung levers, such as lever 7, are pivotally attached to common unison ring 16 which encircle the compressor casing a short axial distance to one side of the plane containing the guide vanes. I$hen the unison ring 16 is rotated circumferentially all of the movable guide vanes are rotated by their respective levers through the same angle.

Claims (12)

1. An arrangement for mounting a member inside a casing providing limited longitudinal clearance for the member comprising at the or each mounting location a structure formed in the casing defining a bore for receiving a longitudinal shaft carried by a member, the bore being wider at its inner end than at its outer end and having a minimum dimension sufficiently greater than the diameter of the shaft to permit the shaft to be inserted at an inclined angle into the bore from inside the casing, a collar which fits loosely on the shaft and which engages with the wider end of the bore to limit penetration of the member, and a bush for subsequent assembly onto the shaft from outside the casing to positively locate the shaft and collar in the bore.

2. An arrangement as claimed in claim 1 wherein the wider end of the bore is formed in a part spherical recess.

3. An arrangement as claimed in claim 2 wherein the collar has a part-spherical outer surface for engagement in the recess.

4. An arrangement as claimed in any preceding claim wherein the collar has an inside diameter equal to the minimum dimension of the bore and the components are located transversely by a bush inserted in the bore.

5. An arrangement as claimed in claim 4 wherein the bore, the inner surface of the collar and the bush are parallel sided.

6. All arrangement as claimed in any preceding claim wherein the member is mounted for rotation about a longitudinal axis.

7. An arrangement as claimed in any preceding claim wherein the member is biased outwardly against the casing.

8. An arrangement as claim in claim 7 wherein a lever mounted on the shaft for rotating a member is sprung outwardly for said bias.

9. An arrangement as claimed in any preceding claim provided at each of a plurality of locations spaced apart around the circumference of a casing for mounting a plurality of stator blades.

10. The arrangement of claim 9 wherein each blade is rotatable about a longitudinal axis and carries a lever connected with a rotatory ring encircling the casing by means of which all the blades may be rotated in unison.

11. The arrangement of claim 9 or claim 10 wherein the blades comprise stator guide vanes in a gas turbine engine.

12. An arrangement substantially as described with reference to the accompanying drawings.