GB2264541A

GB2264541A - Improved sealing ring for gas turbine engines

Info

Publication number: GB2264541A
Application number: GB9204421A
Authority: GB
Inventors: John Derek Kernon; Mark John Knight
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1992-02-29
Filing date: 1992-02-29
Publication date: 1993-09-01
Also published as: JPH0626365A; EP0559312A1; GB9204421D0; US5344162A

Abstract

A sealing ring for controlling gas leakage through the annular space between two rotating concentric members; for example engine shafts. The sealing ring 20 has a generally trapezoidal cross section, and an overlapping scarf joint. The sealing ring improves sealing by providing continuous lines of contact at edges 26 and 28 between inner and outer coaxial shaft members 14 and 16 respectively. <IMAGE>

Description

2264541 IMPROVED SEALING RING FOR GAS TURBINE ENGINES fo The present

invention relates to sealing rings, and in particular sealing rings in gas turbine engines.

It is common in gas turbine engines to find annular gaps disposed between co-axial rotatable members within a rotor assembly. In use these gaps may require sealing means in order to seal a high pressure region from a low pressure region.

Conventionally, sealing rings having rectangular cross sections which fit into circumferential grooves have been employed. These rings have scarfed joints with the plane of the scarf disposed parallel to the radial surfaces of the ring.

Under rotational loading the sealing ring expands outwardly until it contacts the internal surface of the outer member. The corresponding expansion of the scarf joint establishes a leakage path for the high pressure air. Additional leakage also occurs with this type of ring, unless a costly zero clearance fit is maintained between the ring and the groove.

Accordingly, it is an object of the present invention to provide an improved sealing ring, sealing an annular gap between coaxial rotatable members, which has two adjoining surfaces defining a first edge which, in use, provides a continuous line of contact between the ring and the surface of the outer member.

The first edge is axially offset from the centroid of the ring which, in use, causes the ring to roll.

faw 4.

The invention will now be described in greater detail with reference, by way of example only, to the accompanying drawings, in which:

Figure 1 is a perspective view of a portion of the sealing ring including the scarfed joint, Figure 2 is a detailed section view of the stationary sealing ring according to the embodiment of the present invention, Figure 3 is a detailed section view of the fully expanded sealing ring, Figure 4 is a detailed section view of the sealing ring at the operating condition, and Figure 5 is a section view on the line I-I in Figure Referring to the embodiment of figures 1 and 2 a rotor assembly 10 has an annular gap 12 defined between coaxial inner and outer cylindrical shaft members 14 and 16 respectively. Inner shaft member 14 has a circumferential groove 18 formed in its external surface for receiving an inwardly sprung sealing ring 20, with axial clearance.

Sealing ring 20 has a generally trapezoidal cross section defining parallel radial surfaces 22 and 24, a radially outermost edge 26, and an edge 28. In addition chamfered surfaces 30 and 32 are defined between the rings internal surface 21 and radial surfaces 22 and 24. A scarfed joint 34 is formed at the ends of sealing ring 20, with the plane of the scarf lying between edges 26 and 28.

It will be noted that radially outermost edge 26 is axially offset from the centroid of the ring. This offset may be further increased by machining surface 30 to a greater depth and at a greater angle relative to its adjoining radial surface, than the corresponding chamfered surface 32.

Referring now to Figure 3, sealing ring 20 expands radially outwards during acceleration of rotor assembly 10. Initially sealing ring 20 expands against its inherent radial stiffness under the influence of its increasing rotational load. This expansion continues until sealing ring 20 is radially restrained at its radially outermost edge 26, by outer shaft member 16. Radially outermost edge 26 thereby defines a continuous line of contact between sealing ring 20 and outer shaft member 16. The line of contact being continuous by virtue of scarf joint 34 having sufficient overlap to accommodate the required circumferential expansion.

Referring now to Figures 4 and 5, as rotor assembly 10 accelerates further, the additional rotational load generated by sealing ring 20 is applied to outer shaft member 16, at the line of contact. Consequently, the applied and the reaction force acting on sealing ring 20 define a couple perpendicular to the plane of the ring. Under the influence of the couple the ring rolls within circumferential groove 18, until the edges of the ring contact walls 36 and 38. The roll angle is determined by axial clearances within circumferential groove 18. Edge 28 thereby defines a continuous line of contact between sealing ring 20 and inner shaft member 14, again continuous by virtue of scarf joint 34 having sufficient overlap to accommodate the required circumferential expansion. Additionally a discontinuous line of contact is defined between sealing ring 20 and edge 40 of circumferential groove 18.

fall Preferably Radially outermost edge 26 is disposed axially towards a high pressure region A. In which case the discontinuous line of contact at edge 40 combined with expanded scarf joint 34, defines a small leakage orifice 42 between cavity C and high pressure region A. Consequently sealing ring 20 is exposed to a radial pressure differential forcing it outwards.

The two continuous lines of contact defined at the radially and axially restrained edges, 26 and 28 respectively, provide a continuous annular seal in annular gap 12, sealing a high pressure region A from a low pressure region B.

Claims

01 An improved sealing ring sealing an annular gap between coaxial rotatable members, which has two adjoining surfaces defining a first edge which in use provides a continuous line of contact between the ring and the surface of the outer member.

2 A sealing ring as claimed in claim 1 wherein the edge is axially offset from the centroid of the ring which, in use, causes the ring to roll.

3 A sealing ring as claimed in claim 1 or 2 wherein the ring cross section in the radial axial plane has a generally trapezoidal shape.

4 A sealing ring as claimed in any preceding claim wherein the sealing ring has a scarfed joint.

A sealing ring as claimed in claim 4 wherein the plane of the scarf joint lies obliquely relative to the plane of the ring.

6 A sealing ring as claimed in any preceding claim wherein two adjoining surfaces define a second edge which in use provides a continuous line of contact between the sealing ring and a surface of the inner member.

A sealing ring as claimed in claim 6 wherein the plane of the scarf joint lies between the first and second edges of the ring.

8 A sealing ring as claimed in any preceding claim wherein the first edge is axially disposed towards a high pressure region and the second edge is axially disposed towards a low pressure region.

A sealing ring as claimed in any preceding claim wherein the ring is sprung into a groove formed in the external surface of the radially inner member.

A sealing ring as claimed in claim 9 wherein the axial fit between the ring and the groove is clearance.

11 A sealing ring substantially as described with reference to the accompanying drawings.