GB1565018A - Gas turbine seals - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO GAS TURBINE SEALS (71) We, ROLLS-ROYCE LIMITED, a British Company of 65 Buckingham Gate, London, SW1E 6AT, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to seals suitable for use in a gas turbine engine and more particularly but not exclusively to intershaft seals used in multi-shaft gas turbine engines.

It is well known to provide seals which are commonly known as intershaft seals between two relatively rotatable gas turbine engine shafts. Such seals may be used for preventing the flow of lubricating oil from between the shafts or alternatively to prevent the flow of high pressure air or gas either into, or out of the space between the shafts.

One of the most common types of seal used for such applications is a labyrinth type seal which is secured to the radially outermost surface of the radially innermost shaft.

The radial extremities of the labyrinth runs in an oil reservoir provided within the radially innermost shaft. The main problem associated with such a type of seal is that the diameter of the labyrinth extremities is dictated by the internal diameter of the outer shaft in order to facilitate assembly of the shafts. This means that it is not always possible to obtain an optimum or small enough clearance between the extremities of the labyrinth and the reservoir in the outer shaft. This can result in an unsatisfactory seal. Alternatively, if either or both of the shafts vibrate or orbit slightly during operation, this could result in the labyrinth extremities contacting the outer shaft which will cause wear and an enlarged sealing clearance thus reducing sealing efficiency.

An object of the present invention is to provide a seal suitable for use in a gas turbine engine and which substantially eliminates the aforementioned disadvantages.

According to the present invention, a seal assembly for sealing between two concentric cylindrical rotatable members comprises a resilient ring which is a close fit upon the inner cylindrical member when it is stationary, and which under influence of centrifugal force, is urged into closer proximity to the internal surface of the outer cylindrical member when the inner cylindrical member is rotating.

In one embodiment of the invention the resilient ring is in the form of a split spring steel ring, and the concentric cylindrical members are two coaxially arranged gas turbine engine main shafts.

Preferably the resilient ring is located within an annular groove provided on or in the inner shaft and when expanded under the influence of centrifugal force extends into a further annular groove situated within the internal surface of the outer shaft, the further annular groove being filled with oil and thus providing the seal.

The radially innermost part of the resilient ring includes at least one spigot which extends into a recessed side wall of the groove situated on or within the outer surface of the inner shaft, the at least one spigot serving to limit the degree of expansion to which the resilient ring may be subjected thus preventing the ring contacting the bottom of the groove in the outer shaft.

For better understanding of the invention an embodiment thereof will be more particularly described by way of example only and with reference to the accompanying drawings in which: Figure 1 shows a diagramatic side view of a gas turbine engine including a seal assembly made in accordance with the present invention Figure 2 shows a cross-sectional side view of a seal assembly made in accordance with an embodiment of the present invention is in the inoperative condition Figure 3 shows a cross-sectional view of the seal assembly shown at Figure 2 in the operative condition.

Referring to the drawings a gas turbine engine shown diagramatically at 10 comprises in flow series, a low pressure compressor 12, a high pressure compressor 13, combustion equipment 14, a high pressure turbine 15, and a low pressure turbine 16, the engine terminating in an exhaust nozzle 17.

Both the low pressure compressor 12 and the low pressure turbine 16, and the high pressure compressor 13 and high pressure turbine 15 are secured to the rotatably mounted engine main shafts 19 and 18 respectively. A seal assembly 20 made in accordance with an embodiment of the present invention is located between the two shafts 18 and 19.

Figures 2 and 3 show a more detailed cross-sectional view of the seal assembly shown generally at 20. The seal assembly comprises a resilient split seal ring 21 which may be manufactured from spring steel and is provided at its radially innermost diameter with a spigot 22. The sealing ring 21 is dimensioned so that when the shaft 19 is not rotating as shown in Figure 2, the ring 21 is a close fit, on the inner shaft 19. The sealing ring 21 is restrained from axial movement by being secured within an annular groove, the annular groove being defined between a pair of annular flanges 23 and 24 which serve to form the side walls of the groove. For ease of assembly the flange 24 in this instance is removably secured to shaft 19 by means of a screw thread or any other suitable convenient mechanical fastening.

The flanges 23 and 24 are provided with axially extending lips at their radially outer ends which extend towards each other to produce the effect of recesses 25 and 26 in the sides of the groove. The recesses 25 and 26 ensure that the sealing ring 21 is restrained from expanding too far under the influence of centrifugal force. Situated opposite the groove defined by the flanges 23 and 24 on shaft 19 is a further annular groove 27 provided within the inner cylindrical surface of the shaft 18 which is dimensioned such as to receive the ring 21 when the latter is expanded under centrifugal loading.

During operation of the engine the groove 27 is provided with a supply of oil which is retained within the groove by centrifugal force acting upon it. The centrifugal force also acts upon sealing ring 21 to expand it radially outwardly from the shaft 19 and into the oil filled groove 27 until it is restrained from further movement by spigot 22 contacting the lips defining the recesses 25 and 26.

During this mode of operation the sealing ring 21 is frictionally driven by contact with the lips on the annular flanges 23 and 24. In this way a seal will be produced which will substantially prevent the flow of liquid or gas between shafts 18 and 19.

When the engine is shut down centrifugal force will cease to act upon the sealing ring 21 which by virtue of its resilience will reduce in diameter and return to close contact with the shaft 19 thus permitting the axial separation of the shafts 18 and 19 if required.

It will be appreciated that whilst the described and illustrated embodiment of the present invention concerns a gas turbine engine seal the invention is not necessarily restricted to such an application. This type of seal could equally well be utilised in any device requiring a seal between two rotatable cylindrical members where normal assembly techniques are not possible.

Modification may also be made to the above described example without departing from the scope of the invention, for example the groove defined by the flanges 23 and 24 may be cut in the surface of the shaft 19, and means equivalent to the lips on the flanges 23 and 24 e.g. sliding collars may be used to prevent excessive expansion of the ring 21.

WHAT WE CLAIM IS: 1. A seal assembly for sealing between two concentric cylindrical relatively rotatable members comprising a resilient ring which is a close fit upon the inner cylindrical member when it is stationary, and which under the influence of centrifugal force is urged into closer proximity to the internal surface of the outer cylindrical member when the inner cylindrical member is rotating.

2. A seal assembly as claimed in claim 1 in which the resilient ring comprises a split spring steel ring.

3. A seal assembly as claimed in claim 1 in which the two concentric cylindrical relatively rotatable members comprise two coaxially arranged gas turbine engine main shafts.

4. A seal assembly as claimed in claims 1 and 3 in which the resilient ring is located within an annular groove provided on or in the inner shaft and when expanded under the influence of centrifugal force extends into a further annular groove situated within the internal surface of the outer shaft.

5. A seal assembly as claimed in claim 4 in which the further annular groove provided within the outermost shaft is filled with oil thus providing an effective seal.

6. A seal assembly as claimed in claim 4 in which the radially innermost part of the resilient ring includes at least one spigot which extends into a recessed side-wall of the groove situated on or within the outer surface of the inner shaft, the at least one spigot serving to limit the degree of expansion to which the resilient ring may be subjected thus preventing the ring contacting the bottom of the groove in the outer shaft.

7. A seal assembly substantially as claimed in any preceding claim and substan

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. Figure 3 shows a cross-sectional view of the seal assembly shown at Figure 2 in the operative condition. Referring to the drawings a gas turbine engine shown diagramatically at 10 comprises in flow series, a low pressure compressor 12, a high pressure compressor 13, combustion equipment 14, a high pressure turbine 15, and a low pressure turbine 16, the engine terminating in an exhaust nozzle 17. Both the low pressure compressor 12 and the low pressure turbine 16, and the high pressure compressor 13 and high pressure turbine 15 are secured to the rotatably mounted engine main shafts 19 and 18 respectively. A seal assembly 20 made in accordance with an embodiment of the present invention is located between the two shafts 18 and 19. Figures 2 and 3 show a more detailed cross-sectional view of the seal assembly shown generally at 20. The seal assembly comprises a resilient split seal ring 21 which may be manufactured from spring steel and is provided at its radially innermost diameter with a spigot 22. The sealing ring 21 is dimensioned so that when the shaft 19 is not rotating as shown in Figure 2, the ring 21 is a close fit, on the inner shaft 19. The sealing ring 21 is restrained from axial movement by being secured within an annular groove, the annular groove being defined between a pair of annular flanges 23 and 24 which serve to form the side walls of the groove. For ease of assembly the flange 24 in this instance is removably secured to shaft 19 by means of a screw thread or any other suitable convenient mechanical fastening. The flanges 23 and 24 are provided with axially extending lips at their radially outer ends which extend towards each other to produce the effect of recesses 25 and 26 in the sides of the groove. The recesses 25 and 26 ensure that the sealing ring 21 is restrained from expanding too far under the influence of centrifugal force. Situated opposite the groove defined by the flanges 23 and 24 on shaft 19 is a further annular groove 27 provided within the inner cylindrical surface of the shaft 18 which is dimensioned such as to receive the ring 21 when the latter is expanded under centrifugal loading. During operation of the engine the groove 27 is provided with a supply of oil which is retained within the groove by centrifugal force acting upon it. The centrifugal force also acts upon sealing ring 21 to expand it radially outwardly from the shaft 19 and into the oil filled groove 27 until it is restrained from further movement by spigot 22 contacting the lips defining the recesses 25 and 26. During this mode of operation the sealing ring 21 is frictionally driven by contact with the lips on the annular flanges 23 and 24. In this way a seal will be produced which will substantially prevent the flow of liquid or gas between shafts 18 and 19. When the engine is shut down centrifugal force will cease to act upon the sealing ring 21 which by virtue of its resilience will reduce in diameter and return to close contact with the shaft 19 thus permitting the axial separation of the shafts 18 and 19 if required. It will be appreciated that whilst the described and illustrated embodiment of the present invention concerns a gas turbine engine seal the invention is not necessarily restricted to such an application. This type of seal could equally well be utilised in any device requiring a seal between two rotatable cylindrical members where normal assembly techniques are not possible. Modification may also be made to the above described example without departing from the scope of the invention, for example the groove defined by the flanges 23 and 24 may be cut in the surface of the shaft 19, and means equivalent to the lips on the flanges 23 and 24 e.g. sliding collars may be used to prevent excessive expansion of the ring 21. WHAT WE CLAIM IS:

1. A seal assembly for sealing between two concentric cylindrical relatively rotatable members comprising a resilient ring which is a close fit upon the inner cylindrical member when it is stationary, and which under the influence of centrifugal force is urged into closer proximity to the internal surface of the outer cylindrical member when the inner cylindrical member is rotating.

2. A seal assembly as claimed in claim 1 in which the resilient ring comprises a split spring steel ring.

3. A seal assembly as claimed in claim 1 in which the two concentric cylindrical relatively rotatable members comprise two coaxially arranged gas turbine engine main shafts.

4. A seal assembly as claimed in claims 1 and 3 in which the resilient ring is located within an annular groove provided on or in the inner shaft and when expanded under the influence of centrifugal force extends into a further annular groove situated within the internal surface of the outer shaft.

5. A seal assembly as claimed in claim 4 in which the further annular groove provided within the outermost shaft is filled with oil thus providing an effective seal.

6. A seal assembly as claimed in claim 4 in which the radially innermost part of the resilient ring includes at least one spigot which extends into a recessed side-wall of the groove situated on or within the outer surface of the inner shaft, the at least one spigot serving to limit the degree of expansion to which the resilient ring may be subjected thus preventing the ring contacting the bottom of the groove in the outer shaft.

7. A seal assembly substantially as claimed in any preceding claim and substan

tially as hereinbefore described by way of example only and with reference to the accompanying drawings. -