Carbon Face Seal

Abstract

An apparatus has: a first member (120); a shaft (40; 50) rotatable relative to the first member about an axis; and a seal system (100). The seal system has a seal carrier (150) having: an axially-extending wall (156) having an inner diameter (ID) surface (160); and a radially-extending wall (154) having a first surface (158). A seal (102) is carried by the first member and has: an outer diameter (OD) surface (206); and a seal face (106). A seat (104) is carried by the shaft and has a seat face (108) in sliding sealing engagement with the seal face. One or more springs (132) bias the seal carrier relative to the first member so as to bias the seal face against the seat face. A key (240; 280; 300; 338) spans an interface between the seal carrier and the seal.

Claims

1. An apparatus comprising: a first member (120); a shaft (40; 50) rotatable relative to the first member about an axis; and a seal system (100) comprising: a seal carrier (150) having: an axially-extending wall (156) having an inner diameter (ID) surface (160); and a radially-extending wall (154) having a first surface (158); a seal (102) carried by the seal carrier in a radial interference fit with the seal carrier axially-extending wall ID surface and having: an outer diameter (OD) surface (206); and a seal face (106); a seat (104) carried by the shaft and having a seat face (108) in sliding sealing engagement with the seal face; and one or more springs (132) biasing the seal carrier relative to the first member so as to bias the seal face against the seat face, wherein: a key (240; 280; 300; 338) spans an interface between the seal carrier and the seal.

2. The apparatus of claim 1 wherein: the key spans the seal carrier ID surface and the seal OD surface.

3. The apparatus of claim 2 wherein: the radial interference fit provides a compressive stress in the seal of 10 MPa to 150 MPa.

4. The apparatus of claim 1 wherein: the key (300; 338) comprises an epoxy.

5. The apparatus of claim 4 wherein the key (338) has: a first portion (302) in a hole (316) in the seal carrier axially-extending wall; and a second portion (340) in an axially-extending channel (341) formed by respective grooves (346, 344) in the seal carrier axially-extending wall ID surface and seal OD surface.

6. The apparatus of claim 5 wherein the key has: a third portion (304) in a circumferentially-extending channel (320) formed by respective grooves (324, 322) in the seal carrier and seal and joining the first portion to the second portion.

7. The apparatus of claim 4 wherein the key (300) has: a first portion (302) in a hole (316) in the seal carrier axially-extending wall; a second portion (306) in a hole (318) in the seal carrier axially-extending wall; and a third portion (304) in a circumferentially-extending channel (320) formed by respective grooves (346, 344) in the seal carrier and seal and joining the first portion to the second portion.

8. The apparatus of claim 1 wherein: the key (240; 280) comprises a metallic pin.

9. The apparatus of claim 8 wherein the metallic pin has a shaft having: an outboard portion (242) in a hole (244; 282) in the seal carrier; an inboard portion (246) in a hole (248; 284) in the seal; and a lateral protrusion (252) backlocked against the seal carrier to resist outward displacement.

10. (canceled)

11. (canceled)

12. (canceled)

13. (canceled)

14. The apparatus of claim 1 wherein: the seal is a carbon seal.

15. (canceled)

16. The apparatus of claim 1 wherein: the seal is a single piece.

17. The apparatus of claim 1 being a gas turbine engine.

18. A method for manufacturing the apparatus of claim 1, the method comprising: thermal interference fitting the seal (102) to the seal carrier (150); and installing the key (240; 280) or forming the key (300; 338) in situ.

19. The method of claim 18 comprising said forming the key in situ wherein: the forming the key (300; 338) in situ comprises curing epoxy.

20. The method of claim 19 wherein: the forming the key in situ is after the thermal interference fitting; and the forming the key in situ further comprises injecting the epoxy before the curing.

21. The method of claim 20 wherein: the injecting the epoxy passes the epoxy through an inlet and an outlet, at least one of the inlet and the outlet being in the seal carrier.

22. The method of claim 21 wherein: the injecting the epoxy passes the epoxy through an inlet leg from the inlet, an outlet leg to the outlet, and an intermediate leg circumferentially offsetting the outlet leg from the inlet leg.

23. The method of claim 21 wherein: the injecting the epoxy passes the epoxy through a leg formed by mating grooves in the seal and seal carrier.

24. The method of claim 18 comprising said installing the key wherein: the installing the key (240; 280) comprises driving the key through the seal carrier into the seal.

25. (canceled)

26. The method of claim 24 wherein: the key has a projection (252); and the driving the key through the seal carrier compresses the projection and then allows the projection to expand to backlock against reverse movement.

27. (canceled)

28. (canceled)

29. (canceled)

30. An apparatus comprising: a first member (120); a shaft (40; 50) rotatable relative to the first member about an axis; and a seal system (100) comprising: a seal carrier (150) having: an axially-extending wall (156) having an inner diameter (ID) surface (160); and a radially-extending wall (154) having a first surface (158); a seal (102) carried by the seal carrier in a radial interference fit with the seal carrier axially-extending wall ID surface and having: an outer diameter (OD) surface (206); and a seal face (106); a seat (104) carried by the shaft and having a seat face (108) in sliding sealing engagement with the seal face; and one or more springs (132) biasing the seal carrier relative to the first member so as to bias the seal face against the seat face, further comprising: a means (240; 280; 300; 338) interlocking the seal carrier and the seal to prevent relative movement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 is a first axial sectional view of a seal system in a turbomachine.

[0045] FIG. 1A is an enlarged view of the seal system of FIG. 1.

[0046] FIG. 2 is an end view of a seal and seal carrier of the seal system of FIG. 1.

[0047] FIG. 3 is an axial sectional view of key.

[0048] FIG. 4 is an enlarged axial sectional view of key holes in the seal and seal carrier before key installation.

[0049] FIG. 5 is an enlarged axial sectional view of a second seal system.

[0050] FIG. 6 is an end view of a third seal and seal carrier.

[0051] FIG. 7 is a first sectional view of the third seal and seal carrier.

[0052] FIG. 8 is a second sectional view of the third seal and seal carrier.

[0053] FIG. 9 is a sectional view of a fourth seal and seal carrier.

[0054] FIG. 10 is a schematic view of a gas turbine engine in which the seal system may be included.

[0055] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0056] To supplement the retention provided by the interference fit, additional keying may retain the seal to the carrier axially and/or circumferentially. As discussed below, the keying may take the form of a plurality of circumferentially distributed keys differently/separately formed from and spanning junctions between the carrier and the seal. In some embodiments, the keys may be pre-formed and then inserted (e.g., metallic pins). In some embodiments, the keys may be formed in situ (e.g., epoxy or other flowable key-forming material injected into a seal-carrier preassembly and allowed to cure and/or otherwise harden).

[0057] The key installation or formation may be after the thermal interference fitting. This may be particularly relevant to in situ formation where the material that forms the key may not be able to withstand the temperatures of the thermal interference fitting process.

[0058] FIG. 1 shows a seal system 100 having a sealing element (seal) 102 and a seat 104 (seal plate). As is discussed further below, the seal system is used in a turbomachine such as a gas turbine engine for a purpose such as isolating a bearing compartment 600. The seal is mounted to a first structure such as an engine static structure and the seat is mounted to rotate relative thereto (e.g., mounted to a shaft) about an axis A which may be the engine centerline or central longitudinal axis. As discussed below, the example seal system includes the seat 104 as one piece and the seal 102 as part of a cartridge subassembly (cartridge) 105. FIG. 1 further shows an outward radial direction 502 and a forward direction 504.

[0059] The example seal 102 is a carbon seal (carbon element) having an axially-facing/radially-extending seal surface or face 106. The example seal 102 is formed as single-piece body circumscribing a central axis normally coincident with the centerline A when installed.

[0060] The seat 104 has an axially-facing/radially-extending seat surface or face 108 engaging the seal face 106. This engagement may allow relative radial displacement of seal and seat.

[0061] The seal system 100 (FIG. 1) isolates a space or volume 600 from a space or volume 602. The example space or volume 600 is a bearing compartment. The example seal system is at an aft end of the bearing compartment. A similar or other seal system (not shown) may be at a forward end of the bearing compartment (e.g., oppositely oriented). The example bearing compartment 600 contains a bearing supporting the shaft for rotation relative to the static structure about the axis A. The example second space or volume 602 is a buffer air chamber.

[0062] In the example engine configuration and position, a case component 120 (FIG. 1, e.g., a strut ring/frame) of the static structure is positioned radially inboard of a gas path (core flowpath) C (FIG. 10). An example seal system is an oil-cooled dry-face seal system wherein an array of passageways (not shown) extend through the seat from respective inlet ports (not shown) at a plenum (between the seat and a portion of a shaft) through outlet ports (not shown) on the seat to an outer diameter (OD) rim for carrying oil is a dry face uncooled seal system. An alternative is a dry face uncooled seal system. The seal system may alternatively be a wet face seal system in that there are oil passageways to outlets on the seat face 108.

[0063] The seal system 100 cartridge 105 further includes a seal housing (seal support) 130 and one or more bias springs 132 (e.g., a bellows spring or an array of coil springs) biasing the seal 102 into engagement with the seat 104 in the assembled engine. The seal housing 130 is mounted to the case component 120 such as via interference fit and/or fasteners (not shown), directly, or indirectly (e.g., via a seal support forming a portion of a larger cartridge assembly). The example seal housing 130 is machined or cast/machined of an alloy. An end wall 144 extends radially inward from the opposite end of the sidewall 142. The adjacent end(s) of the spring(s) 132 contact the interior radial face 145 of the end wall 144. For a bellows spring 132, the spring end may be welded, brazed, or otherwise secured to the face 145. For coil springs (not shown), coil spring ends may be captured in bores in the face 145 or may capture projections from the face 145.

[0064] FIG. 1 further shows the cartridge 105 as including a seal carrier (carbon carrier) 150 intervening between the seal 102 and the spring(s) 132. For forming a compartment (seal compartment) 152 for receiving the seal 102, the seal carrier has a radial wall 154 and an axial wall 156 extending axially from the radial wall 154. The radial wall 154 has, along the seal compartment 152, a face 158 (an aft face of the seal compartment and forward face of the wall in the example or a forward face of the seal compartment and aft face of the wall if oppositely oriented). The axial wall 156 has, along the seal compartment, a face 160 (an inner diameter (ID) face). The axial wall 156 has an outer diameter (OD) face 161. The example seal carrier 150 is machined or cast/machined of an alloy. In the example, the radial wall 154 has a face 162 axially opposite the face 158 that also forms an axial end (aft in the example) face of the seal carrier. The example adjacent bellows spring end may be welded, brazed, or otherwise secured to the face 162. In the example embodiment, the bellows spring 132 restricts rotation of the seal carrier 150 about the engine centerline A but also provides a relatively robust centering force. In alternative embodiments, additional anti-rotation and/or centering means may be provided. For example, when using an array of compression coil springs instead of the bellows spring the seal system may need such means. Example such means are one or more anti-rotation pins fixed relative to case structure received in holes in cars and/or a flange of the seal carrier to restrict rotation and limit radial excursions. Additionally, in various implementations, there may be secondary seals including labyrinth seals, C-seals, and the like.

[0065] FIG. 1 shows the seal 102 as having a main body section 200 and a nose 202 protruding axially therefrom to the seal surface 106. The main body 200 has an inner diameter (ID) surface 204 and an outer diameter (OD) surface 206. The main body has a first end face 208 (forward in the example) and a second end face 210 (aft in the example). The second end face 210 contacts the face 158. The surface 206 contacts the seal carrier axial wall ID surface 160. The nose 202 has an inner diameter (ID) surface 220 and an outer diameter (OD) surface 222 respectively radially recessed relative to the surfaces 204 and 206.

[0066] The example seal system includes a key 240 spanning an interface between the seal 102 and seal carrier 150. The example key 240 (FIG. 1A) spans an interface between the seal OD surface 206 and seal carrier ID surface 160. The example key 240 is formed as a metallic rod (e.g., right circular cylinder potentially modified such as discussed below). An outboard portion 242 of the key is accommodated in a hole 244 in the carrier (e.g., a through hole between the seal carrier ID surface and the OD surface). The key may be in an interference fit (e.g., press fit and/or thermal interference fit) in the hole 244. An inboard portion 246 of the key is accommodated in a hole 248 in the seal (e.g., a blind hole extending radially inward from the seal OD surface 206). The key may be in a non-interference fit or an interference fit (e.g., press fit and/or thermal interference fit) in the seal hole 246.

[0067] FIG. 2 shows a circumferential distribution of such keys 240. The example distribution is an array of four keys at even 90? intervals about the engine/seal system centerline (central longitudinal axis) A. More broadly, an example number is three to twelve.

[0068] FIG. 3 shows an example key 240 prior to installation. The example key is metallic such as a steel. FIG. 4 shows the holes 244 and 248 prior to key insertion (e.g., having been co-drilled (line drilled) after interference fitting of the seal to the seal carrier). The example key 240 is formed as a pin and has a projection formed as a radially protruding barb 252 at an upper (radially outboard viewed in the engine frame of reference) end of the inboard portion 246. The example key also has a radial recess 250 immediately above at a lower (radially inboard viewed in the engine frame of reference) end of the outboard portion 242. In the example, the recess and barb are co-formed by displacement of material (e.g., from an initially right circular cylindrical rod stock). The barb has a relatively radial outboard surface 254 and a relatively tapering inboard surface 256 meeting at an apex 258. The barb may be made by rolling with a shaped indenter to indent at the recess 250 and raise the barb as if a burr. To facilitate such rolling and elastic deformation in assembly, the pin may be of a mild steel (e.g., AISI/SAE 4340). The pin may thus be softer than the carrier (e.g., a carrier of 17-4PH/AMS 5643 stainless steel).

[0069] During installation, the key may be forcibly driven radially inward with the inboard portion 246 first passing through the carrier hole 244 and then into the seal hole 248. While passing through the carrier hole, interference may substantially elastically depress the barb 252 into the recess 250. However, as the barb 252 passes radially inward beyond the ID face 160 and encounters the relatively lower strength and modulus material of the seal, the deformation of the barb will at least partially relieve, causing the barb to radially expand and at least partially relax and the surface 254 to backlock against the carrier ID surface 160 to resist/prevent outward radial displacement of the key.

[0070] FIG. 3 shows an example diameter D.sub.1 of the key inboard portion and outboard portion away from the recess 250 and barb 252. An example D.sub.1 is 1.0 mm to 5.0 mm, more narrowly 2.0 mm to 4.0 mm. An example diameter D.sub.2 at the barb 252 is 105% to 150% of D.sub.1, more particularly, 110% to 130%. For an interference fit, relaxed hole diameters D.sub.3 (FIG. 4relaxed in as-drilled lacking interference with the pin but reflecting any interference between the seal and carrier) will be in the same range but slightly less than actual D.sub.1 in accordance with conventional interference fit engineering practice. Example key length is 300% to 1000% of D.sub.1.

[0071] FIG. 5 shows an alternate key 280 which may be identical to the key 240 but oriented axially passing through an axial hole 282 in the carrier radial wall and to a blind hole 284 in the seal. Thus, the barb of the key 280 backlocks against the radial wall face 158. In various examples, the keys 240 and 280 may coexist in the same seal system and may be circumferentially co-aligned or out-of-phase with each other and, in various implementations there may be different numbers of the two types of keys in any seal system.

[0072] As noted above, alternative keys may be formed in situ. FIG. 6 schematically shows keys 300 formed in situ via injection of a liquid material that ultimately hardens (e.g., epoxy). An example epoxy is a two-part epoxy, and may be a filled or an unfilled epoxy. The example keys have three legs: a first terminal leg 302; a circumferentially extending intermediate leg 304; and a second terminal leg 306. The example terminal legs have ends 308, 310 at openings or ports 312, 314 of the combined seal carrier and seal. In the FIG. 6 illustration, the openings are along the OD surface 161 of the seal carrier (FIG. 7).

[0073] The example terminal legs are radially extending in respective radial passageways or holes 316, 318 (e.g., drilled). The intermediate leg 304 is within a circumferential passageway or channel 320 (FIG. 8) spanning the junction or interface between the seal and the carrier. The example passageway 320 is formed by respective open channels or grooves 322 and 324 in the seal OD surface and carrier sidewall ID surface. Each of these channels 322 and 324 extends between respective first and second circumferential ends. In the example, when in nominal circumferential alignment, the ends of the channels may extend circumferentially past the passageways 316, 318 (see FIG. 6) to allow some degree of misalignment while still having full contiguity/communication between the passageways 316, 318. Thus, the initial thermal interference fitting of seal to carrier may provide direct seal to carrier interference contact beyond the channels. For example, in a reengineering from a baseline configuration lacking the channels, such direct contact area may represent a majority (e.g., at least 70% or at least 80%) of the baseline configuration's contact area.

[0074] To install the keys 300, after thermal interference fitting of seal to carrier (e.g., at least after sufficient cooling so that the seal will be retained to the carrier during in situ formation), the key material may be injected through one of the ports (e.g., 312) and ultimately pass out the other (e.g., 314). The key may then be allowed to cure. Any excess material may be trimmed at the ports (post-curing/hardening (e.g., cut) and/or pre-curing/hardening (e.g., cut or simply wiped off if sufficiently viscous to avoid undue outflow).

[0075] Other configurations are possible. For example, FIG. 9 shows a key 338 having an axial terminal leg 340 accommodated in an axially extending passageway or channel 341 extending along the interface. For example, the axially extending passageway or channel 341 may be formed by mating channels or grooves 344 and 346 in the seal OD surface and carrier sidewall ID surface, respectively. Thus, the corresponding port 342 may also be at the seal-carrier junction and may face axially. Such axial terminal leg(s) may replace one or both of the radial legs 302, 306. For example, such an axial leg 340 may replace the radial outlet leg of each key. This allows radially inward injection with axial discharge allowing axial observation of all outlets at once to confirm sufficient injection and also allowing curing without any leakage out leaving voids.

[0076] FIG. 8 shows the circumferential passageway 320 and associated contained epoxy 304 as having a radial span ?R formed by the combination of channel/groove 322 and 324 depth or heights H.sub.1 and H.sub.2. Example H.sub.1 and H.sub.2 are 0.10 millimeters to 3.0 millimeters, more particularly, 0.50 millimeters to 2.5 millimeters to provide advantageous flow and subsequent strength.

[0077] FIG. 9 shows the leg 340 and the grooves forming the channel 341 as having associated heights H.sub.3 and H.sub.4 in the seal and carrier, respectively. Example H.sub.3 and H.sub.4 are about the same as or smaller than H.sub.1 and H.sub.2 (e.g., 40% to 110%, more particularly, 60% to 100%). Example transverse or circumferential dimensions of the leg 340 and channel 341 may be of a similar magnitude to the radial (e.g., 30% to 300% or 50% to 200% of H.sub.3 and H.sub.4). Example axial lengths of the leg 340 and channel 341 may be substantially greater (e.g., 200% to 1000% of H.sub.3 and H.sub.4).

[0078] Example end-to-end circumferential spans of the channels or grooves 322 and 324 will depend on the number of keys. For the example four keys, the example is slightly less than 90? (e.g., 80? to 88?). But a broader range is 20? to 88?.

[0079] As with the pre-formed keys, there may be additional variations involving the carrier-to-seal interface at the radial wall. These variations may thus provide circumferential retention without significant axial retention (adhesion rather than mechanical keying/interfitting may provide some axial retention).

[0080] The example seal systems may represent a modification or reengineering of a baseline seal or configuration thereof (lacking the key). The baseline may have a tight interference fit (e.g., press-fit and/or thermal interference fit) between the carbon seal and the seal carrier. The tight interference fit may itself provide robust sealing between the seal and carrier. The modified or reengineered seal system or configuration may involve a lighter interference fit in some embodiments.

[0081] In one example of an assembly process, the seal carrier 150 is preheated (e.g., by thermal convection in either an air oven or a liquid (e.g., water) bath). Example heating in an existing baseline range is to a temperature in the range of 280? C. to 340? C. Example heating for a reduced temperature range for reduced stress is to a temperature of about 120? C., more broadly, 90? C. to 150? C. or 90? C. to 200? C. or 90? C. to 250? C.

[0082] The seal 102 may be inserted to the seal carrier via translation (e.g., held by a tool (not shown)). The seal may then be held in its fully seated condition while the carrier is allowed to cool (e.g., in ambient or forced air) to a threshold temperature (e.g., by at least 50% of the peak temperature difference or at least 80%). Thereafter, it may be released from the tool for any further cooling and subsequent assembly to additional components. Depending on configuration, prior to assembling the seal to the seal carrier the seal carrier may be assembled to the bellows spring.

[0083] In one example of reengineering from a baseline seal system, an interference fit of the baseline seal is replaced by a lighter interference fit plus the action of the keys. Seal construction may otherwise be preserved. This interference reduction may be achieved by a slight increase in the diameter of the seal carrier ID surface or by a slight decrease in the diameter of the seal OD surface. In some embodiments, the reduced tensile hoop stresses in the carrier enable the use of lower strength carrier materials that may have more favorable characteristics for seal performance such as lower coefficients of thermal expansion that more closely match that of the seal carbon. For example, an iron-nickel alloy such as ASTM F30 (e.g., Alloy 42 or UNS N94100), may replace a steel (e.g., 17-4PH/AMS 5643 stainless steel). Additionally, the lower stresses in the carbon and carrier may enable cross-sectional geometries that may be more favorable to seal performance but would otherwise not have sufficient structural strength to be acceptable.

[0084] However, further advantages may be achieved and may have a cumulative effect and any particular embodiment may involve tradeoffs among the possible advantages. For example, the reduced interference fit reduces stresses in the seal. This may allow a reduction in the cross-sectional area of the seal due to not having to withstand the stresses at a given level of interference. This cross-sectional reduction reduces the weight of the seal.

[0085] For thermal interference fits, reduced interference may reduce the heating temperature and thus decrease cycle time and energy used in heating. Similarly, reduced interference may be associated with reduced need for robustness of the seal carrier, allowing material removal from the seal carrier and, thereby, lightening of the seal carrier. Lightening of the seal carrier may have positive feedback by further reducing energy and cycle time for heating in the thermal interference fit.

[0086] Lightening of the seal and/or seal carrier and/or sealing ring also allows reduction in the needed bias force from the bias spring(s). This reduced bias force may be associated with reduced spring weight. However, the reduced biased force may have a number of other advantages. Reduced bias force will, all things being equal, reduce seal wear and heat generation. This may improve longevity.

[0087] As an example of temperature reduction for thermal interference fit, the baseline seal may use a heating temperature in the range of 280? C. to 340? C.; whereas the revised seal may use 90? C. to 150? C. or other ranges discussed above. The reduction may be of an example 190? C. to 220? C. or 100? C. to 220? C.

[0088] As an example of interference and stress reduction, the baseline seal may have an example compressive stress (e.g., at ambient conditions of 21? C. and 1.0 atm (1.0 Bar), more broadly 18? C. to 25? C. at 0.95 Bar to 1.05 Bar) of 18,500 psi (128 MPa), more broadly at least 75 MPa or 75 MPa to 150 MPa; whereas the revised seal may have an example such a stress of 5,735 psi (39.5 MPa), more broadly at least 10 MPa or 10 MPa to 60 MPa or 20 MPa to 50 MPa. The reduction may be of an example at least 10 MPa, if present.

[0089] Additionally, the reduced interference may allow reduced tolerance requirements.

[0090] Component materials and manufacture techniques and assembly techniques may be otherwise conventional. For example, there are numerous commercially available annular carbon seal blanks. Such a stock blank may be lathed to profile and may then have material milled and drilled away to reveal any non-annular features such as the groove segments. These commercial blanks are available in a variety of base carbon materials (e.g., carbon graphite and electrographite) with various impregnants (e.g., for strength/cohesion and/or lubricity) suitable for particular operating environments and conditions. Example material is at least 50% carbon by weight, more particularly, at least 90% or 95% or 99% or even commercially pure carbon with inevitable impurities.

[0091] Example seats may be machined from an appropriate metal alloy (e.g., a stainless steel). This may be via lathing of an annular blank to a basic profile and then milling and drilling departures from annular (e.g., mounting splines, ID oil channels, and the like if present).

[0092] The housing and seal carrier may be formed of an appropriate metal alloy (e.g., stainless steel or a titanium alloy) and may be formed such as by pure machining/drilling of a blank or by casting and finish machining. There may be a turning to form annular surfaces such as the basic ID surface 160 with subsequent machining of the non-annular features such as grinding or milling of the groove(s), if any and drilling of the hole(s), if any.

[0093] FIG. 10 schematically illustrates a gas turbine engine 20 as one of many examples of an engine in which the seal system 100 may be used. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. The fan section 22 may include a single-stage fan 42 having a plurality of fan blades 43. The fan blades 43 may have a fixed stagger angle or may have a variable pitch to direct incoming airflow from an engine inlet. The fan 42 drives air along a bypass flow path B in a bypass duct 13 defined within a housing 15 such as a fan case or nacelle, and also drives air along a core flow path C for compression and communication into the combustor section 26 then expansion through the turbine section 28. A splitter 29 aft of the fan 42 divides the air between the bypass flow path B and the core flow path C. The housing 15 may surround the fan 42 to establish an outer diameter of the bypass duct 13. The splitter 29 may establish an inner diameter of the bypass duct 13. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures.

[0094] The example engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A (forming the axis 500) relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.

[0095] The low speed spool 30 generally includes an inner shaft 40 that interconnects, a first (or low) pressure compressor 44 and a first (or low) pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in the example gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The inner shaft 40 may interconnect the low pressure compressor (LPC) 44 and low pressure turbine (LPT) 46 such that the low pressure compressor 44 and low pressure turbine 46 are rotatable at a common speed and in a common direction. In other embodiments, the low pressure turbine 46 drives both the fan 42 and low pressure compressor 44 through the geared architecture 48 such that the fan 42 and low pressure compressor 44 are rotatable at a common speed. Although this application discloses geared architecture 48, its teaching may benefit direct drive engines having no geared architecture. The high speed spool 32 includes an outer shaft 50 that interconnects a second (or high) pressure compressor (HPC) 52 and a second (or high) pressure turbine (HPT) 54. A combustor 56 is arranged in the example gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 may be arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is collinear with their longitudinal axes.

[0096] Airflow in the core flow path C is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded through the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core flow path C. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of the low pressure compressor, or aft of the combustor section 26 or even aft of turbine section 28, and fan 42 may be positioned forward or aft of the location of gear system 48.

[0097] The low pressure compressor 44, high pressure compressor 52, high pressure turbine 54 and low pressure turbine 46 each include one or more stages having a row of rotatable airfoils. Each stage may include a row of static vanes adjacent the rotatable airfoils. The rotatable airfoils and vanes are schematically indicated at 47 and 49.

[0098] The use of first, second, and the like in the following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order. Similarly, the identification in a claim of one element as first (or the like) does not preclude such first element from identifying an element that is referred to as second (or the like) in another claim or in the description.

[0099] One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, when applied to an existing baseline configuration, details of such baseline may influence details of particular implementations. Accordingly, other embodiments are within the scope of the following claims.