BACKGROUND 1. Field

[0001] The present invention relates to seals for sealing a circumferential gap between two machine components that are relatively rotatable with respect to each other, and, more particularly, to a seal having at least one shoe extending along one of the machine components in a position to create a non-contact seal therewith.

2. Description of the Related Art

[0002] Turbomachinery, such as gas turbine engines, currently is dependent on either labyrinth, brush or carbon seals for critical applications. Labyrinth seals provide adequate sealing, but they are extremely dependent on maintaining radial tolerances at all points of engine operation. The radial clearance must take into account factors such as thermal expansion, shaft motion, tolerance stack-ups, rub tolerance, etc. Minimization of seal clearance is necessary to achieve maximum labyrinth seal effectiveness. In addition to increased leakage if clearances are not maintained, there is the potential for increases in engine vibration. Straight-thru labyrinth seals are the most sensitive to clearance changes, with large clearances resulting in a carryover effect. Stepped labyrinth seals are very dependent on axial clearances, as well as radial clearances, which limits the number of teeth possible on each land. Pregrooved labyrinth seals are dependent on both axial and radial clearances and must have an axial clearance less than twice the radial clearance to provide better leakage performance than stepped seals.

[0003] Turbomachinery, such as gas turbines engines, are becoming larger, more efficient, and more robust. Large blades and vanes are being utilized, especially in the hot section of the engine system. In view of high pressure ratios and high engine firing temperatures implemented in modem engines, certain components, such as airfoils, e.g., stationary vanes and rotating blades, require more efficient sealing capabilities than the ones that exist currently. [0004] In current assemblies, clearance between the rotating and stationary components in turbomachinery are regions of low performance. There are several drivers of aerodynamic loss in the compressor- vane carrier, turbine-shroud cavity configuration, intermediate shaft, and the like, which lowers the turbomachinery’s efficiency. One driver is the flow over the rotating components. The mixing losses that occur downstream of clearance areas are high and contribute to a reduction in stage efficiency and power. Additional mixing losses occur when the flow through the tip cavity combines with the main flow and the two streams have different velocities. Tip leakage is essentially lost opportunity for work extraction. Tip leakage also contributes towards aerodynamic secondary losses.

SUMMARY

[0005] In an aspect of the present invention, a seal assembly for sealing a circumferential gap between a first machine component and a second machine component which is rotatable relative to the first machine component about a longitudinal axis in the axial direction, comprises: a primary seal comprising: a plurality of circumferentially spaced shoes extending along one of the first and second machine components, producing a non-contact seal therewith, each of the plurality of shoes being formed with a slot; a plurality of spring elements, adapted to connect to one of the first and second machine components, and each spring element being connected to one of the plurality of shoes, the plurality of spring elements being effective to deflect and move with the plurality of shoes in response to fluid pressure applied to the plurality of shoes by a fluid stream to assist in the creation of a primary seal of the circumferential gap between the first and second machine components; a mid plate extending into the slot formed in the plurality of shoes; at least one secondary seal divided into secondary seal segments, each secondary seal segment extending into the slot and connected to one of the plurality of shoes, allowing independent movement of the plurality of shoes, sealing the plurality of spring elements in the axial direction; and a seal carrier that holds at least the primary seal, the mid plate, and the at least one secondary seal of the seal assembly together along an outer ring.

[0006] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following drawings, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention.

[0008] FIG. 1 is an exploded view of a seal assembly of the prior art;

[0009] FIG. 2 is an end view of a portion of a seal assembly of the prior art;

[0010] FIG. 3 is an elevational view of a portion of a seal assembly of the prior art;

[0011] FIG. 4 is an elevational view of a portion of a seal assembly of the prior art;

[0012] FIG. 5 is an elevational view of a portion of a seal assembly of the prior art;

[0013] FIG. 6 is an elevational view of a portion of a seal assembly of the prior art;

[0014] FIG. 7 is an elevational view of a portion of a seal assembly of the prior art;

[0015] FIG. 8 is an elevational view of a portion of a seal assembly of the prior art;

[0016] FIG. 9 is an end view of a schematic view of second seal position in a seal assembly of an exemplary embodiment of the present invention;

[0017] FIG. 10 is perspective view of a portion of an exemplary embodiment of the present invention with the front plate removed for clarity;

[0018] FIG. 11 is perspective view of a layer of a secondary seal of an exemplary embodiment of the present invention; [0019] FIG. 12 is a detailed perspective view of ends of a layer of a secondary seal of an exemplary embodiment of the present invention; [0020] FIG. 13 is a detailed perspective view of ends of a layer of a secondary seal of an exemplary embodiment of the present invention; and

[0021] FIG. 14 is a perspective view of a mid plate and secondary seal of an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0022] In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized, and that changes may be made without departing from the spirit and scope of the present invention.

[0023] Broadly, an embodiment of the present invention provides a seal assembly for sealing a circumferential gap between a first machine component and a second machine component which is rotatable relative to the first machine component about a longitudinal axis. The seal assembly includes a seal carrier, a primary seal that includes a plurality of shoes, a mid plate, at least one secondary seal, and can include a front plate. The at least one secondary seal is split up into secondary seal segments that match up with each shoe of the primary seal.

[0024] Turbomachinery typically includes a compressor section, a combustor, and a turbine section. The compressor section ingests ambient air and compresses it. The compressed air from the compressor section enters one or more combustors in the combustor section. The compressed air is mixed with fuel in the combustors, and an air-fuel mixture is combusted in the combustors to form a hot working gas. The hot working gas is routed to the turbine section, where it is expanded through alternating rows of stationary airfoils and rotating airfoils and used to generate power that can drive a rotor. The expanded gas exiting the turbine section then exhausts from the engine via an exhaust section.

[0025] The compressor and turbine sections may include several locations in which there may be gaps, or clearances, between the rotating and stationary components. During engine operation, system loss may occur through fluid leakage through clearances in the compressor and turbine sections. This system loss decreases the operational efficiency of the system. An example of the flow leakage is across a clearance between the tips of rotating blades and a surrounding stationary structure or boundary, such as an outer shroud or a vane carrier.

[0026] Seals are necessary to prevent leakage across areas within the gas turbine engine. A secondary seal that is durable in a non-contact seal assembly is desired.

[0027] FIG. 1 shows an exploded view of a traditional seal assembly 10 that may be included in turbomachinery, such as a gas turbine. FIG. 2 shows the traditional seal assembly 10 in its assembled form. The seal assembly 10 includes a front plate 12, two secondary seals 14, a mid plate 22, a primary seal 26, and a seal carrier 36. The assembled traditional seal assembly 10 illustrated in FIG. 2 creates a non-contact seal of a circumferential gap 11 between two relatively rotating components, i.e. a first machine component 38 and a second machine component 40, such as a fixed stator 72 and a rotating rotor 48.

[0028] Each traditional seal assembly 10 includes a plurality of circumferentially spaced shoes 28 that are located in a non-contact position along an exterior surface of the rotor 48, as part of the primary seal 26. Each shoe 28 has a sealing surface 70 (FIG. 6) and a slot 30 that extends radially inward toward the sealing surface 70 as can be seen in FIG. 2. Each of the plurality of shoes 28 is formed with two or more projections 84, or fins, relative to one of the machine components, and is the bottom portion of the primary seal 26, as can be seen in FIG. 6. For purposes of this discussion, the term “axial” or“axially spaced” refers to a direction along the longitudinal axis 42 of the stator 72 and rotor 48, whereas“radial” refers to a direction perpendicular to the longitudinal axis 42. The seal assembly 10 may extend along a circumferential direction C relative to the turbine longitudinal axis 42.

[0029] In certain operating conditions, especially at higher pressures, it is desirable to limit the extent of radial movement of the shoes 28 with respect to the rotor 48 to maintain clearances, e.g. the spacing between the shoes 28, and the facing surface of the rotor 48. The primary seal 26 includes a number of circumferentially spaced spring elements 34, as can be better seen in FIG. 6. Each spring element 34 is formed with an inner band 52, and an outer band 54 radially outwardly spaced from the inner band 52. One end of each of the bands 52 and 54 is mounted to, or integrally formed with, the stator 72 and the opposite end thereof is connected to a first stop 32. The first stop 32 includes a leg 56 which is connected to, or integrally formed with a shoe 28, and an arm 58 opposite to the shoe 28, which may be received within a recess formed in the stator 72. The recess has a shoulder 74 positioned in alignment with the arm 58 of the first stop 32.

[0030] A second stop 60 is connected to, or integrally formed with, the shoe 28. The second stop 60 is circumferentially spaced from the first stop 32 in a position near the point at which the inner and outer bands 52 and 54 connect to the stator 72. The second stop 60 is formed with a leg 62 and an arm 64. The arm 64 may be received within a recess in the stator 72. The recess has a shoulder 74 positioned in alignment with the arm 64 of the second stop 60.

[0031] In certain situations, when seal assemblies are used in applications such as gas turbine engines, aerodynamic forces are developed that can apply a fluid pressure to the shoe 28, causing it to move radially inwardly toward the rotor 48. The spring elements 34 deflect, and move with the shoe 28, to create a primary seal of the circumferential gap 11 between the rotor 48 and stator 72, for instance. The first and second stops 32 and 60 can limit the extent of radially inward and outward movement of the shoe 28, with respect to the rotor 48 in the radial direction R. A gap is provided between the arm 58 of the first stop 32, and the shoulder, and between the arm 64 of the second stop 60, and the shoulder, such that the shoe 28 can move radially inwardly relative to the rotor 48. The inward motion mentioned above is limited by engagement of the arms with the shoulders to prevent the shoe 28 from contacting the rotor 48, or exceeding design tolerances for the gap between the two. The arms can also contact the carrier 36 in the event that the shoe 28 moves radially outwardly relative to the rotor 48, to limit movement of the shoe 28 in that direction.

[0032] Traditionally, the seal assembly 10 includes two secondary seals 14, an aft secondary seal 80 and a forward secondary seal 82 that are identical and reversed at assembly. Each secondary seal 14 includes a base sealing element 16 that spans across four shoes 28. Each base sealing element 16 of the secondary seal 14 includes spring members 18, or whiskers. At least one spring member 18 is positioned radially outward from the base sealing element 16, as is shown in FIG. 4, along an outer ring surface 20. The aft secondary seal 80 and the forward secondary seal 82 are oriented side-by-side in the axial direction A and positioned so that the plate segments extend into the slot 30 of the at least one shoe 28. The base sealing elements 16 help to radially deflect and move with the at least one shoe 28, in response to the application of fluid pressure to the at least one shoe 28, in a way that assists in the creation of a secondary seal 14 of the circumferential gap 11 between the first and second machine components 38 and 40.

[0033] These spring members 18 are highly loaded at the base of each spring member 18. These spring members 18 crack at their base under constant high cycle fatigue loading. Within larger turbomachinery, the spring members 18 see increased stress (around 150 Mpa at times) that does not allow for the spring members 18 to operate successfully. High stress locations include the base of the spring members 18 close to the outer ring surface 20. Further, the spring members 18 increase the difficulty of assembling of the seal assembly 10.

[0034] To complete the traditional seal assembly 10 there is the mid plate 22, the front plate 12, and the seal carrier 36. FIG. 5 shows a traditional mid plate 22. The mid plate 22 includes a groove 24 along a face of the mid plate 22. The mid plate 22 extends into the slot 30 formed in the at least one shoe 28, and is positioned between the two secondary seals 14 and the plurality of shoes 28 of the primary seal 26. The spring members 18 of the two secondary seals 14 are preloaded and fit into the groove 24 of the mid plate 22 along with the rest of the secondary seals 14.

[0035] The front plate 12, shown in FIG. 3, is used to cover the components of the seal assembly 10 in the axial direction A. The seal assembly 10 includes having the two secondary seals 14 positioned between the front plate 12 and the mid plate 22. The primary seal 26 supports the inner diameter of the secondary seals 14, and the mid plate 22 supports the outer diameter of the secondary seals 14. During operation, each spring member 18 of the secondary seal 14 react against the mid plate 22. [0036] The seal carrier 36, shown in FIG. 2, holds all the components of the seal assembly 10 together along a radially outward position of a radially outer ring 50 of the seal carrier 36. Along the radially outward surface of the primary seal 26, the mid plate 22, and the front plate 12, there is a cutout 66. The seal carrier 36 has a protruding edge 68 that extends radially inward, that aligns with the cutouts 66 of the other components to help the components to stay in the relative area.

[0037] An improvement of the seal assembly 10, and specifically the secondary seals 14 is needed due to a concern for excessive wear of the secondary seals 14. The secondary seals 14 with these spring members 18 were functioning successfully on smaller engines due to smaller diameters and lower loading. These secondary seals 14 crack during cold flow and have durability issues in turbomachinery such as large gas turbine applications.

[0038] FIGS. 9 through 14 show embodiments of a new seal assembly 86. The primary seal 26 breaks into segments. In an approximately sixty-degree segment of the primary seal 26, such as shown in FIG. 6, there are four shoes 28 and spring elements 34. Instead of the secondary seal 14 mentioned above, a new secondary seal 44 is combined with a new mid plate 46 in the seal assembly 86. The optional front plate 12 is shown. The secondary seal 44 is now connected to the primary seal 26 to eliminate motion. The secondary seal 44 may be welded, caulked, braze, or similarly connected to the shoes 28 of the primary seal 26. Each shoe 28 receives a separate secondary seal segment 76 in the seal assembly 86. This segmenting of the secondary seal 44 allows for each shoe 28 to move and operate independent of each adjacent shoe 28. The new secondary seal 44 in these embodiments include a single layer instead of the multiple bands with spring members 18. In certain embodiments, the layer thickness can have a range from 0.25 mm to 2 mm in the axial direction A. In certain embodiments, the layer thickness is within a smaller range of .25 mm to .5 mm in thickness. In certain embodiments the layer thickness is approximately 0.5 mm in the axial direction A. The thickness can be greater than the multiple secondary seals with spring members 18. The mid plate 46 is a solid form that does not have a groove like in previous iterations. The secondary seal 44 is preloaded axially. Embodiments can include interlocking joints, such as a rabbet joint, or ship-lap joint, end 78, spanning in the circumferential direction, at the ends of the secondary seal segments 76. These embodiments allow for the prevention of air leakage between the shoes. In other embodiments, there is no connection between the ends of the secondary seal segments 76, however, the minimization of leakage is still taken into consideration. The space between each secondary seal segment 76 can be parallel, or in line, to the shoes.

[0039] In some of these embodiments with an overlap or interlock, the thickness decreases near the circumferential ends, providing an angled seal. The changing thickness of the overlap along the ends of the secondary seal 44 allows for the overlap when the shoe 28 is not activated (i.e. when the shoe is away from the rotor). The overlap will increase when the shoe is moved down radially, reducing the distance in the circumferential direction C, improving the seal.

[0040] The changes to the secondary seal remove the impediment of motion of adjacent shoes as was an issue in previous assemblies. The new assembly 86 provides a tighter seal than in previous traditional seal assemblies 10. Each shoe 28 in the seal assembly 86 receives its own separate secondary seal segment 76. The secondary seal 44 does not arrest the motion of adjacent shoes as is the case in traditional designs. The embodiments are cost efficient since there is less material being used. The manufacturing of the seal assembly 86 is improved with decreased times and increased efficiency. The secondary seal 44 of the seal assembly 86 allows for the ability to seal and separate a forward pressure zone 88 from an aft pressure zone 90 while undergoing constant motion along with the shoes 28. The forward pressure zone 88 having a higher pressure than the aft pressure zone 90. The seal assembly 86 can withstand high cycle fatigue cycles with the lack of high load areas in assemblies with spring members 18 giving the seal assembly 86 a longer lifespan than traditional assemblies 10.

[0041] While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only, and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.