GB2464467A

GB2464467A - A sealing system

Info

Publication number: GB2464467A
Application number: GB0818827A
Authority: GB
Inventors: Timothy Hal Summers
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2008-10-15
Filing date: 2008-10-15
Publication date: 2010-04-21
Also published as: GB0818827D0

Abstract

A sealing system has a piston 12 and a cylindrical bore 14 in which the piston 12 is located. The piston 12 is movable in the axial direction of the bore 14. One of the piston 12 and the 14 bore has a circumferential groove 16. The other of the piston 12 and the bore 14 has a sealing surface 15 facing the groove 16. The system further has a sealing ring 18 which is disposed within the groove 16 and seals a surface of the groove 16 to the sealing surface 15. The sealing ring 18 is a helical coil having a plurality of coil windings 18a, 18b, 18c, the axis of the coil being along the axial direction of the bore 14.

Description

SEALING SYSTEM

The present invention relates to sealing systems.

Sealing systems comprising a piston that is sealed within a cylindrical bore by means of a sealing ring are used in many applications, in particular those in which it is necessary to allow for relative axial movement of the piston within the bore. For example, piston rings are commonly used in reciprocating internal or external combustion engines to seal the combustion/expansion chamber. However, sealing rings which accommodate relative axial movement between a piston and a cylindrical bore are

also found in other fields.

US2008/0098884 describes the use of sealing rings in actuators for turbomachinery, in which the actuator's piston is sealed within a cylinder.

Sealing rings may also be used in gas turbine engines to seal e.g. a fuel injector feed arm to the combustor outer casing of the engine. The feed arm traverses the combustor outer casing at an aperture in the casing.

Relative axial movement between the feed arm and the casing can be caused by differential thermal expansion effects within the engine, pressure differences across the casing and engine vibrations. Sealing rings at the aperture help to prevent excessive leakage of working fluid across the casing while accommodating this movement.

Figure 1 shows a schematic cross-sectional view of an embodiment of such a sealing system. The sealing system comprises a seal carrier 120 of a fuel injector feed arm 110 that is held within a cylindrical aperture or bore 140 through a combustor outer casing 130. The bore has a liner 142. The seal carrier 120 has two circumferential grooves 160. Each groove holds a sealing ring 180, which is biased to exert a radially outward force against the liner 142 and which contacts the sidewalls of the groove.

The seal carrier can move axially relative to the cylindrical bore, and is thus effectively a piston within the cylindrical bore. The sealing rings 180 provide a seal for the gap between the seal carrier 120 and the liner 142 under such motion.

A space 170 between the inner surface of each sealing ring 180 and the bottom of the corresponding groove 160 also allows the sealing system to accommodate lateral movement of the feed arm relative to the bore 140. The lateral movement is caused by differential thermal expansion effects and is predominantly in the fore-aft direction of the engine. The space allows the sealing ring to slide sideways relative to the seal carrier 120 while maintaining contact with the sidewalls of the groove.

However, this sliding motion can produce wear on the groove sidewalls, which can in turn reduce the sealing effectiveness of the sealing system.

It is desirable to reduce wear of the components of such sealing systems in order to avoid or reduce fluid leakage through the seal, and so as to increase the working life of the system.

In general terms, the present invention provides a sealing system for a piston within a cylindrical bore in which the sealing ring is provided by a helical coil.

In a first aspect, the present invention provides a sealing system having a piston and a cylindrical bore in which the piston is located, the piston being movable relative to the bore in the axial direction of the bore (and typically also being movable laterally to the bore), one of the piston and the bore having a circumferential groove, and the other of the piston and the bore having a sealing surface facing the groove, the system further having a sealing ring which is disposed within the groove and seals a surface of the groove to the sealing surface, wherein the sealing ring is a helical coil having a plurality of coil windings, the axis of the coil being along the axial direction of the bore. Successive windings of the helical coil typically occupy successive axial positions along the axis of the coil.

By providing a sealing ring that is a helical coil having a plurality of coil windings, wear occurring in the sealing system as a result of axial and/or lateral motion of the piston relative to the cylindrical bore may be reduced and/or concentrated on the coil windings of the helical spring rather than on the piston or the bore. This can be advantageous, as in many systems the coil is less expensive and easier to replace than either the component forming the piston or the component forming the cylindrical bore.

For example, successive coil windings of the sealing ring can move relative to each other in a lateral direction of the coil, whereby the ring can accommodate relative lateral movement of the piston and the bore, and can reduce or eliminate sideways movement of the sealing ring in the groove and hence reduce wear of the groove.

Thermally-induced changes in the dimensions of the helical coil can also be accommodated by relative movement of coil windings so that lock-up stresses or distortion that might occur in conventional sealing rings may be avoided.

In general, one or more first coil windings are spring biased so as exert a radial force against a surface of the groove, and one or more second coil windings are spring biased so as exert an opposing radial force against the sealing surface.

Typically, the first coil windings have a different radius to the second coil windings. Thus, the sealing ring is typically tapered in an axial direction.

By providing a sealing ring having first coil windings that are spring biased so as to exert a radial force against a surface of the groove, close contact may be maintained between the sealing ring and the groove, and relative motion between the sealing ring and the groove may be inhibited. Thus, fluid leakage between the sealing ring and the groove may be limited, and/or wear of the groove may be reduced, and the effectiveness of the sealing system increased.

By providing a sealing ring having second coil windings that are spring biased so as to exert a radial force against the sealing surface, it is possible to maintain sealing contact between the second coil windings and the sealing surface even when the second coil windings start to wear. More particularly, as the second coil windings wear, the bias on those windings urges them towards the sealing surface. Effectively, the sealing ring adjusts itself to account for its worn state.

Typically, the first coil windings are disposed at an axial end of the sealing ring. In general, the first coil windings are disposed at each axial end of the sealing ring, the second coil windings being disposed between the axial ends of the helical coil.

Thus, the sealing ring may have a first section that flares outwardly in an axial direction of the helical coil and a second section that tapers inwardly in that axial direction.

In general, the coil windings of the sealing ring are in sliding lateral contact with their neighbouring coil windings. The contact between neighbouring coil windings can help to reduce or eliminate leakage of fluid through the ring.

Typically, the coil windings have flat surfaces which make the lateral sliding contact with corresponding flat surfaces of their neighbouring coil windings. This helps to promote effective contact between neighbouring coil windings.

In general, the hardness of the sealing surface is greater than the hardness of the sealing ring. Thus relative motion between the sealing surface and the sealing ring tends to result in greater wear of the sealing ring than the sealing surface.

The sealing system of the first aspect of the present invention may be disposed in the combustor outer casing of a gas turbine engine, e.g. as a burner seal. The typically reduced wear of the sealing system of the first aspect of the present invention, relative to known burner seals, may result in reduced leakage of fluid through the combustor outer casing. As a result, specific fuel consumption of the gas turbine engine can be reduced and the occurrence of over-temperature alarms external to the combustion casing may be prevented. These benefits may be achieved without the provision of relatively costly hard coatings for the piston and/or the cylindrical bore.

Thus a second aspect of the invention provides a combustor outer casing of a gas turbine engine having a sealing system according to any one of the preceding claims, the cylindrical bore being formed at an aperture through the casing, and the piston being a portion of a fuel injector feed arm which passes through the aperture.

However, the sealing system of the first aspect of the present invention may be also be used in different applications, such as for sealing a rotor path case of a gas turbine engine to a housing for the rotor path case, or for sealing the combustion/expansion chamber of a reciprocating internal or external combustion engine.

In some applications (e.g. sealing a combustion/expansion chamber), the extent of motion in the axial direction of the bore is greater than the extent of any motion laterally to the bore. However, in other applications (e.g. sealing a fuel injector feed arm to a combustor outer casing) the extent of motion laterally to the bore can be greater than the extent of motion in the axial direction of the bore.

A third aspect of the present invention provides a sealing ring for a sealing system of the first or second aspect of the invention.

A fourth aspect of the invention provides a piston for the sealing system of the first or second aspect of the invention, the piston having the circumferential groove and the sealing ring being disposed within the groove.

A fifth aspect of the invention provides a component for the sealing system of the first or second aspect of the invention, the cylindrical bore being formed by the component, the cylindrical bore having the circumferential groove and the sealing ring being disposed within the groove.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a schematic section view of a known sealing system; and Figure 2 shows a schematic section view of a sealing system according to the present invention; and Figure 3 shows a schematic section view of a further sealing system according to the present invention.

Figure 2 shows a schematic cross-sectional view of an embodiment of a sealing system according to the present invention. The sealing system 10 includes a piston 12 that is held within a bore 14 of a component. The piston 12 may be a seal carrier portion of a gas turbine engine fuel injector feed arm. The component and bore 14 may be respectively a combustor outer casing of the engine and an aperture that passes through the casing. The piston 12 can move relative to the bore 14 in the axial direction. Also lateral movement of the piston relative to the bore is possible.

The piston 12 is cylindrical and has a groove 16 extending around its circumference. A helical coil 18 is provided within the groove 16, the axis of the coil 18 being aligned with the axis of the piston 12. The helical coil 18 serves to seal the gap between the piston 12 and the component.

The ends of the helical coil 18 make sealing contact with two opposing sidewalls 16a, 16b of the groove 16.

Further, coil windings 18a, 18b at the axial ends of the helical spring 18 have a radius in their relaxed, unloaded state that is less than the radius of the circumferential groove 16. Therefore, these coil windings exert a radially inward force against the bottom wall 16c of the groove, such that the coils make sealing contact with the surface of the groove. Thus relative motion between the helical coil 18 and the groove 16 is inhibited at the axial ends of the helical spring 18, reducing wear of the piston 12 at the groove 16.

Coil windings 18c in the middle portion of the helical spring 18 (i.e. between the axial ends of the helical coil) have a radius that is greater than that of the coil windings 18a, 18b and also greater than the radius of the piston 12. The radius of the coil windings 18c in their relaxed, unloaded state is also greater than the radius of the bore 14. Thus, the coil windings 18c of the spring 18 exert a radially outward force against a sealing surface 15 of the bore 14.

When the piston 12 moves relative to the component in a lateral direction, the coil windings 18c of the helical spring 18 will tend to deflect sideways and slide over neighbouring coil windings to accommodate the lateral movement. The windings have flat surfaces which during such sliding maintain contact with corresponding flat surfaces of their neighbour windings so that fluid leakage between windings is reduced.

When the piston 12 moves relative to the component in an axial direction, relative motion between the radially outer surface of the coil windings 18c and the sealing surface 15 occurs. As the radially outer surface of the coil windings 18c becomes worn, the radially outward bias of these windings expands them so that they remain in contact with the sealing surface 15a, thus restricting the leakage of fluid between the piston 12 and the component.

Because the windings are in close contact with their neighbours and the ends of the coil abut the two opposing sidewalls 16a, 16b, the coil has little compliance in the axial direction, which helps to maintain the shape and position of the coil windings 18c under axial motion.

The sealing surface 15 of the component may comprise a wear-resistant material, e.g. a coating that has a greater hardness than the helical spring 18. Thus the spring 18 (which in general is cheaper and more readily replaceable than the component) will tend to wear more rapidly than the cylinder 15.

Figure 3 shows a schematic cross-sectional view of an embodiment of part of a sealing system according to the present invention. In this embodiment, the sealing system includes a piston portion 22 formed by the rotor path case 23 of a gas turbine engine compressor, and a bore 24 formed by a component 27 which is a housing for the rotor path case. Due to differential thermal expansion effects in the engine, the piston portion 22 moves relative to the bore 24 in the axial direction of the engine (indicated by the dashed arrow) . Limited lateral movement of the piston portion relative to the bore (i.e. in the radial direction of the engine) can also occur.

The piston portion 22 is cylindrical and has a groove 26 extending around its circumference. A helical sealing coil 28 is provided within the groove 26, the axis of the coil 28 being aligned with the axis of the piston portion 22. The helical coil 28 seals the gap between the piston portion 22 and the housing 27. The seal partitions working fluid bleeds from different stages of the compressor into the space between the housing 27 and the rotor path case 23. More particularly, the bled fluid can be at different temperatures and pressures to either side of the coil 28 (for example the fluid from one side can be from an intermediate pressure compressor stage and the fluid from other side can be from a high pressure compressor stage) The helical coil 28 functions in a similar fashion to the helical coil 18 of the sealing system of Figure 1.

Thus the ends of the helical coil 28 make sealing contact with two opposing sidewalls 26a, 26b of the groove 26.

Coil windings 28a, 28b at the axial ends of the helical spring 28 exert a radially inward force against the bottom wall 26c of the groove. Coil windings 28c in the middle portion of the helical spring 28 exert a radially outward force against a sealing surface 25 of the bore 24.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. For example, in the embodiments of Figures 2 and 3, the helical coil is shown disposed within a groove provided on the piston. However, in other embodiments, the helical coil could be disposed within a groove provided on the bore of the component. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

Claims

CLAIMS1. A sealing system (10, 20) having a piston (12, 22) and a cylindrical bore (14, 24) in which the piston is located, the piston being movable relative to the bore in the axial direction of the bore, one of the piston and the bore having a circumferential groove (16, 26), and the other of the piston and the bore having a sealing surface (15, 25) facing the groove, the system further having a sealing ring (18, 28) which is disposed within the groove and seals a surface of the groove to the sealing surface, wherein the sealing ring is a helical coil having a plurality of coil windings, the axis of the coil being along the axial direction of the bore.
2. A sealing system according to claim 1, wherein one or more first coil windings (18a, 18b; 28a, 28b) are spring biased so as exert a radial force against a surface (16c, 26c) of the groove, and one or more second coil windings (18c, 28c) are spring biased so as exert an opposing radial force against the sealing surface.
3. A sealing system according to claim 2, wherein the first coil windings include one or more coil windings at each axial end of the helical coil.
4. A sealing system according to claim 2 or 3, wherein the second coil windings include one or more coil windings between the axial ends of the helical coil.
5. A sealing system according to any one of the previous claims, wherein the coil windings are in lateral sliding contact with their neighbouring coil windings.
6. A sealing system according to claim 5, wherein the coil windings have flat surfaces which make the lateral sliding contact with corresponding flat surfaces of their neighbouring coil windings.
7. A sealing system according to any one of the previous claims, wherein the hardness of the sealing surface is greater than the hardness of the sealing ring.
8. A combustor outer casing of a gas turbine engine having a sealing system according to any one of the preceding claims, the cylindrical bore being formed by an aperture through the casing, and the piston being a portion of a fuel injector feed arm which passes through the aperture.
9. A sealing ring for a sealing system according to any one of claims 1 to 8.
10. A piston for a sealing system according to any one of claims 1 to 8, the piston having the circumferential groove, and the sealing ring being disposed within the groove.
11. A component for a sealing system according to any one of claims 1 to 8, the cylindrical bore being formed in the component, the bore having the circumferential groove, and the sealing ring being disposed within the groove.
12. A sealing system as any one herein described, with reference to and/or as shown in Figures 2 and 3.