GB2264984A

GB2264984A - A device for adjusting gas turbine guide vanes.

Info

Publication number: GB2264984A
Application number: GB9205454A
Authority: GB
Inventors: Georg Gotzler
Original assignee: BMW Rolls Royce GmbH
Current assignee: Rolls Royce Deutschland Ltd and Co KG
Priority date: 1992-03-12
Filing date: 1992-03-12
Publication date: 1993-09-15
Also published as: GB9205454D0; DE4216033A1

Description

1 - A device for adjusting guide vanes 2264984 The invention relates to a

device for adjusting the guide vanes of a gas turbine, comprising an adjusting ring which substantially surrounds the turbine casing and is connected, more particularly by levers, to the adjustable guide vanes. An adjusting device of this kind is disclosed e.g. in EP-B0 235 073.

Normally the rings for adjusting guide vanes are mounted for sliding directly on.the turbine casing. During operation of the gas turbine, however, the temperature of the turbine casing varies widely, resulting in variations in thermal expansion. The adjusting ring mounted on the turbine casing is also heated during operation of the gas turbine and consequently expands or is deformed, depending on its specific thermal expansion. Since there are differences in the dimensions, more particularly the thickness, and in the materials used for the individual components, the thermal expansion of the adjusting rings is different from that of the turbine casing. Consequently,the radial clearance of the adjusting rings relative to the turbine casing cannot be kept constant during all operating states of a gas turbine. This may result in inaccurate adjustment of the vanes.

The aim of the invention therefore is to disclose measures for avoiding these inaccuracies in the adjustment of the guide vanes, due to differences between the thermal expansion of the adjusting ring and that of the turbine casing.

To this end, the adjusting ring is mounted on a sliding ring which substantially surrounds the turbine casing and is supported on the turbine casing via spokes which are inclined relative to the radial direction. Advantageous C) other features of the invention are described in the subclaims.

According to the invention,the adjusting ring, in the radial direction, is not mounted or centred on the turbine casing but on a separate sliding ring which is secured to the casing via inclined spokes. As a result of the inclined arrangement of the spokes, when the turbine casing expands through heating the sliding ring rotates substantially around the longitudinal axis of the casing without being C> deformed by any substantial components of force in the radial direction. The usefulness of this effect increases with the length of the individual spokes and the extent to which they are inclined relative to the radial direction. This will be clear from an examination of a cross-section 3 - through a turbine casing according to the invention. Since the adjusting ring is rotatably mounted on the sliding ring, the position of the adjusting ring is not affected by rotation of the sliding ring caused by thermal expansion of the turbine casing, and consequently also, there are no effects on the adjustment of the guide vanes.

To enable the spokes to move relative to the sliding ring or the turbine casing, the spokes can be made somewhat flexible at the places where they are secured. The flexible places act like joints. The flexible places at the ends of the spokes can have a smaller cross-section than the spokes themselves, to prevent the spokes buckling, to ensure adequate flexibility and 'Co prevent deformation of the sliding ring. Alternatively,the spokes can be secured by actual joints to the casing at one end and to the sliding ring at the other end.

A further reduction can be made in interfering influences due to differences in thermal expansion if the thermal expansion of the slide ring is similar to that of the adjusting ring. During operation of the gas turbine, of course, the sliding ring disposed according to the invention will also undergo thermal expansion, at least slightly. This slight expansion, howeverg is not a problem if the adjusting ring expands in the same manner, since in that case the deformation of the adjusting ring through heating will not be added to by deformation of the sliding ring. More particularly, comparable thermal expansion characteristics are obtained in that the adjusting ring and the sliding ring are made of material having the same thermal expansion characteristics and substantially have the same thickness. Of course, the sliding ring must have sufficient rigidity to carry the adjusting ring, but this requirement is met practically automatically if the components are of comparable thickness and made of substantially the same material.

Advantageously, the spokes are given the maximum length to C> reduce the heat transfer from the turbine casing through the spokes to the sliding ring. If the heat conduction is reduced, with a corresponding reduction in the thermal expansion of the sliding ring and the adjusting ring, there will be a further reduction in any inaccuracy in the adjustment of the vanes. To reduce the heat conduction between the turbine casing and the sliding ring, the spokes or the spoke-securing components can also be given low thermal conductivity, i.e. be made of a different material which is a poorer conductor of heat. More particularly, plastics discs, for example, can be disposed between the - 5 casing and the spokes, and can also serve as centring discs so as to compensate tolerances in manufacture.

These and other advantages of the invention will be clear from sketches of part of a preferred embodiment, as explained hereinafter. In the drawings:

Fig. 1 is a partial longitudinal section through the vanes of a gas turbine, and Fig. 2 is a cross-section -through Fig. 1 along arrow A.

A gas turbine has adjustable guide vanes 1 mounted in a turbine easing 3 so as to be rotatable around their longitudinal axis 2. The adjustable guide vanes 1 are actuated via levers 4 which are secured to an adjusting ring 5. The adjusting ring 5 surrounds the turbine casing 3 and is mounted on a sliding ring 7 so that it can rotate around the longitudinal axis 6 of the turbine. The sliding ring 7 also surrounds the turbine casing 3 and is concentric with the longitudinal axis 6 of the turbine.

The mounting of the adjusting ring 5 on the sliding ring 7 is also shown in Fig. 2 which is a partial cross-section along arrow A in Fig. 1. Fig. 2 also shows how the sliding ring 7 is secured to the turbine easing 3. For this purpose, Spokes 8 are provided and are secured to the sliding ring 7, whereas their other end is connected to the turbine casing 3, e.g. by a screw 9. The mounting of the adjusting ring 5 on the slidin ring 7 is also shown in Fig.

C> 9 1. The ring is mounted by tightening the flanges of bushes 10 for securing the levers 4 to the adjusting ring 5. Alternatively, as shown in the left half of Fig. 1, two adjusting rings 5 can be mounted side by side on a single sliding ring 7.

As already explained at the beginning, the purpose of mounting the adjusting ring 5 on a separate sliding ring 7 t) is to ensure that the position of the adjusting ring 5, and consequently the position of the guide vanes 1, is substantially unaffected by the thermal expansion of the turbine casing 3. If the turbine casing 3 is heated and expands in the radial direction (as shown in Fig. 2 by arrows 11 extending from the longitudinal axis 6 of the turbine) the spokes 8, which are inclined relative to the radial direction (arrows 11), rotate the sliding ring 7 around the longitudinal axis 6 substantially in the direction of arrows 12. Consequently the adjusting ring 5 is not directly affected by the thermal expansion of the turbine casing 3. Any inaccuracies resulting from differences between the thermal expansion of the sliding ring 7 and the adjusting ring 5 are avoided in that the adjusting ring 5 and the sliding ring 7 have substantially the same thermal expansion. This is because ring 5 and the sliding ring 7 have the same expansion and the same rate of heating up.

the adjusting coefficients of More particularly, the sliding ring 7 and the adjusting ring 5 can be made of the same material and have the same thickness. To reduce the transfer of heat from the turbine casing 3 via the spokes 8 to the sliding ring 7, a plastics disc 13 can also be placed between the turbine casing 3 and the spokes 8, and also the spokes 8 can be made of a material having a low coefficient of heat conduction. The plastics disc 3 can also serve as a centring disc to compensate tolerances in manufacture. To sum up, this procedure eliminates or at least reduces inaccuracies in the adjustment of the guide vanes resulting from differences in thermal expansion. However, any structural detail can differ from the embodiment shown without departing from the content of the claims.

Claims

C L A I M S

1. A device for adjusting the guide vanes of a gas C turbine, comprising an adjusting ring (5) which substantially surrounds the turbine casing (3) and is connected, more particularly by levers (4), to the adjustable guide vanes (1), characterised in that the adjusting ring (5) is mounted on a sliding ring (7) which substantially surrounds the turbine casing (3) and is C, supported on the turbine casing (3) via spokes (8) which are inclined relative to the radial direction (arrows 11).

2. An adjusting device according to claim 1, characterised in that the thermal expansion of the sliding ring (7) is similar to that of the adjusting ring (5).

3. An adjusting device according to claim 1 or 2, characterised in that the adjusting ring (5) and the slidin 0 9 ring (7) are made of material having the same thermal expansion characteristics and substantially have the same thickness.

4. An adjusting device according to any of claims 1 to 3, characterised in that the spokes (8) or the spoke-securing components (9, 13) have low thermal conductivity.

An adjusting device according to any of claims 1 to 4, characterised in that plastics discs (13) are provided between the spokes (8) and the turbine easing (3) and/or between the spokes (8) and the sliding ring (7).

6. An adjusting device according to any of claims 1 to 5, charapterised in that the end regions of the spokes (8) are made flexible.like joints.

7. An adjusting device according to any of claims 1 to 5, characterised in that the spokes (8) are connected to the sliding ring (7) and to the turbine casing (3) by joints.

8. An adjusting device according to claim 1 substantially as described herei.n wi.th reference to the accompanyj.ng drawings.

9. A gas turbine i.ncorpolating a device for adjusting Lhe guide vanes of the turbine as claimed in any precedi.ng cl-aim.