Patent Description:
Carbon seals are commonly used to seal between relatively rotating components in gas turbine engines (used in propulsion and power applications and broadly inclusive of turbojets, turboprops, turbofans, turboshafts, industrial gas turbines, and the like). These include shaft seals (i.e., where the sealing surfaces of seal and seat face radially (e.g., within <NUM>° or essentially <NUM>°) and extend axially) and face seals (i.e., where the sealing surfaces face axially (e.g., within <NUM>° or essentially <NUM>°) and extend radially).

In typical face seal situations, the annular carbon seal is axially spring biased into engagement with an annular seat (typically metallic such as a steel). Typical bias springs are bellows springs, coil springs (multiple circumferentially-distributed springs), or wave springs. The spring(s) act axially between a seal housing (seal support) and a seal carrier (carbon carrier) carrying the seal. An example seal carrier is a full annulus metal component carrying the seal and intervening between the seal and the spring. For example, a carrier may have: an outer sidewall surrounding a portion of the seal in interference fit; and a radial flange engaged by the spring (e.g., to which a bellows spring is welded). The sprung mass of such a seal includes the mass of the carbon ring, the carrier, and effectively half of the spring(s).

The seal may be a single-piece full annulus carbon member or may be segmented (formed by an end-to-end circumferential array of segments in arch bound relation via the carrier interference fit). <CIT>, and entitled "Translating Fluid Coupling Device", discloses carbon seal having a secondary o-ring seal in an inner diameter (ID) rebate of the seal abutting a face of the seal carrier. <CIT>discloses another system of the prior art, according to the preamble of claim <NUM>.

Often, the carbon seal is on non-rotating static structure and the seat rotates with one of the engine shafts. The sliding engagement causes frictional heating. The heat must be dissipated. With a rotating seat, it is common to use oil cooling. Generally, oil cooled carbon seals are divided into two categories: "dry face" seals wherein the oil passes through passageways in the seat without encountering the interface between seal face and seat face; and "wet face" seals wherein the oil passes through the seat to the interface so that the oil that flows through the seat cools the seat but then lubricates the interface to further reduce heat generation.

For both wet face and dry face seals, the oil may be delivered through a nozzle and slung radially outward by the rotating component and collected in a radially outwardly closed and inwardly open collection channel from which the passageways extend further radially outward.

One aspect of the invention involves an apparatus comprising: a first member; a shaft rotatable relative to the first member about an axis; and a seal system. The seal system has: a seal carried by the first member and having a seal face; a seal carrier; a seat carried by the shaft and having a seat face in sliding sealing engagement with the seal face; and one or more springs biasing the seal carrier relative to the first member so as to bias the seal face against the seat face. The seal carrier has: an axially-extending wall having an inner diameter (ID) surface; and a radially-extending wall having a first surface. The seal carrier axially-extending wall ID surface has a radially inwardly open groove having a first sidewall and a second sidewall and a base. A wave-form split ring contacts the first sidewall and biases the seal into engagement with the radial wall first surface.

In an optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the seal is in a radial interference fit with the seal carrier axially-extending wall ID surface.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the radial interference fit provides a compressive stress in the seal of <NUM> MPa to <NUM> MPa.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the wave-form split ring has a compressed wave amplitude of at least <NUM> millimeters.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the wave-form split ring does not contact the second sidewall.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the seal system further comprises: a sealing ring in an inwardly (e.g., radially inwardly) and axially open rebate in the seal and contacting the seal carrier radially-extending wall first surface.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the sealing ring is a fluoroelastomer of four-lobed cross-section.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the seal carrier comprises: an inner diameter sleeve having an outer diameter (OD) surface engaging the sealing ring.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the inner diameter sleeve has an outer diameter surface with a proximal portion (i.e., the outer diameter surface has a proximal portion) contacting the sealing ring and a distal portion (i.e., the outer diameter surface has a distal portion) tapering relative to the proximal portion.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the seal has an inner diameter surface with a beveled transition to the rebate.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the rebate has an outer diameter surface angled <NUM>° to <NUM>° off-axial.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the rebate has a coating in contact with the sealing ring.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the coating comprises aluminum oxide or PTFE.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the seal is a carbon seal.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the seat is steel.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the seal is a single piece.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the apparatus is a gas turbine engine.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, the seal system isolates a bearing compartment.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, in a method for manufacturing the apparatus the seal is assembled to the seal carrier by: heating the seal carrier to a temperature of <NUM> to <NUM>; and inserting the seal into the seal carrier.

In a further optional embodiment of any of the foregoing embodiments, additionally and/or alternatively, cooling of the seal carrier leaves a radial interference fit with a compressive stress in the seal of <NUM> MPa to <NUM> MPa.

<FIG> shows a seal system <NUM> having a seal <NUM> and a seat <NUM> (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 <NUM>. 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 as one piece and the seal as part of a cartridge subassembly (cartridge) <NUM>. <FIG> further shows an outward radial direction <NUM> and a forward direction <NUM>.

The example seal <NUM> is a carbon seal (carbon element) having an axially-facing/radially-extending seal surface or face <NUM> (<FIG>). The example seal <NUM> is formed as single-piece body (monoblock) circumscribing a central axis normally coincident with the centerline A when installed.

The seat <NUM> has an axially-facing/radially-extending seat surface or face <NUM> engaging the seal face <NUM>. The faces <NUM> and <NUM> are axially-facing/radially extending faces. This engagement may allow relative radial displacement of seal and seat.

The seal system <NUM> (<FIG>) isolates a space or volume <NUM> from a space or volume <NUM>. The example space or volume <NUM> is a bearing compartment. The example seal system is at a forward end of the bearing compartment. A similar or other seal system (not shown) may be at an aft end of the bearing compartment. The example bearing compartment <NUM> contains a bearing <NUM> supporting the shaft for rotation relative to the static structure about the axis A. The example second space or volume <NUM> is a buffer chamber. In the example engine configuration and position, a case component <NUM> (e.g., a strut ring/frame) of the static structure is positioned radially inboard of a gas path (core flowpath) C (<FIG>). The example seal is a dry face uncooled seal. An alternative is an oil-cooled dry-face seal wherein an array of passageways (not shown) extend 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. The seal may alternatively be a wet face seal in that there are oil passageways to outlets on the seat face <NUM>.

The seal system further includes a seal housing (seal support) <NUM> and one or more bias springs <NUM> biasing the seal <NUM> into engagement with the seat <NUM> in the assembled engine. The housing <NUM> is mounted to the case component <NUM> such as via interference fit and/or fasteners. Example fasteners <NUM> (<FIG>) are screws extending through apertures <NUM> in mounting ears <NUM> of the housing and then into threaded bores <NUM> of the case component <NUM> (or through the case component to engage nuts (not shown)). The example housing <NUM> is machined or cast/machined of an alloy.

<FIG> further shows the cartridge <NUM> as including a seal carrier (carbon carrier) <NUM> intervening between the seal <NUM> and the spring(s) <NUM>. For forming a compartment (seal compartment) <NUM> for receiving the seal <NUM>, the seal carrier has a radial wall <NUM> and an axial wall <NUM> extending axially from the radial wall <NUM>. The radial wall <NUM> has, along the seal compartment <NUM>, a face <NUM> (an aft face in the example or a forward face if oppositely oriented). The axial wall <NUM> has, along the seal compartment, a face <NUM> (an inner diameter (ID) face). The example seal carrier <NUM> is machined or cast/machined of an alloy.

The example seal carrier <NUM> also includes a centering wall <NUM> extending from a face <NUM> of the radial wall <NUM> axially opposite the face <NUM>. The centering wall <NUM> serves to center the cartridge <NUM> relative to the housing <NUM> by closely encircling an adjacent wall <NUM> of the housing. The example seal carrier <NUM> further includes a second radial wall <NUM> extending outward from the wall <NUM>. The radial wall <NUM> may function to interact with one or more anti-rotation torque pins <NUM> (<FIG>) and a circumferentially arrayed plurality of bias coil springs <NUM> (<FIG>). The bias coil springs (or other biasing means) and anti-rotation torque pins (or other anti-rotation means) may represent conventional features of a baseline seal system which may be further modified as discussed below. Similarly, the example system includes a secondary seal such as a PTFE C-seal <NUM>. The example C-seal <NUM> is sandwiched radially between an inner diameter circumferential/axially-extending flange section of the housing and the inner diameter surface of a surrounding axially-extending circumferential flange of the seal carrier. An example C-seal is shown butting up against a radial wall of the housing flange and open to the chamber <NUM> so as to be pressure-energized. Other secondary seals are possible and no secondary seal at all is an alternative.

For economy of illustration, the circumferential position of snap ring to carrier channel contact and energizing coil spring of <FIG> and snap ring to seal contact and anti-rotation pin of <FIG> is chosen as convenient. Nevertheless, the angular position and number of cycles of the wave ring may yield other contact locations.

Discussed further below, the cartridge <NUM> further includes a wave-form split ring internal snap ring <NUM> (<FIG>) captured in a radially-inwardly open channel or groove <NUM> in the wall <NUM> to bias the seal <NUM> into engagement with the face <NUM>. An example such snap ring is the WAVERING™ ring of Smalley Steel Ring Co. , Lake Zurich, Illinois. Internal snap ring <NUM> and its mating carrier feature(s) (and other features discussed below) may be added in a reengineering from a baseline such as that discussed above. The <FIG> illustrated ring is a single-turn-nonoverlap ring. In such a non-overlap (lacking axial overlap) ring there is a circumferential gap between ends of the metal strip so that faces of the strip do not contact each other. However, the ends may be angled so that one end circumferentially overlaps at a different radius from the other and the gap is both circumferential and radial. Alternative rings are multi-turn rings where there is axial overlap of multiple turns over a circumferential span (e.g. of about <NUM>°).

<FIG> shows the groove <NUM> as having a first sidewall or face <NUM> (aft face in the example), a second sidewall or face <NUM> axially opposite thereto (forward face in the example), and an outer diameter base (base surface or face) <NUM>. The snap ring <NUM> contacts the first sidewall <NUM>. <FIG> shows such contact at one peak of the amplitude of the wave. At an opposite peak of the amplitude of the wave, <FIG> shows the spring contacting the seal <NUM> but still spaced apart from the sidewall <NUM>.

The compressed wave amplitude (peak-to-peak, cross-section center to cross-section center) may be at least <NUM> millimeters, or an example <NUM> millimeters to <NUM> millimeters or <NUM> millimeters to <NUM> millimeters or <NUM> millimeters to <NUM> millimeters. The relaxed amplitude will be greater (e.g., at least <NUM>% greater or an example <NUM>% to <NUM>% greater). An example relaxed amplitude is <NUM> millimeters to <NUM> millimeters or <NUM> millimeters to <NUM> millimeters. An example ring has at least two cycles about the axis A so as to have at least two contact locations at each axial end, more particularly at least three or an example four to twelve or six to twelve.

<FIG> shows an example two-turn ring <NUM>' where the material/tum thickness is shown as T<NUM>, the ring thickness Ts is twice that, the ring is shown as height H, and the peak-to-peak wave amplitude A is H-Ts.

<FIG> shows the seal <NUM> as having a main body section <NUM> and a lip <NUM> protruding axially therefrom to the seal surface <NUM>. The main body <NUM> has an inner diameter (ID) surface <NUM> and an outer diameter (OD) surface <NUM>. The main body has a first end face <NUM> (aft in the example) and a second end face <NUM> (forward in the example). The forward end face <NUM> contacts the face <NUM>. The surface <NUM> contacts the ID surface <NUM>. In the example, a bevel surface <NUM> joins the surfaces <NUM> and <NUM>. The lip <NUM> has an inner diameter (ID) surface <NUM> and an outer diameter (OD) surface <NUM> respectively radially recessed relative to the surfaces <NUM> and <NUM>. The surface <NUM> is radially recessed to accommodate the ring <NUM>. The ring <NUM> thus contacts a portion of the surface <NUM> (<FIG>) radially outboard of the surface <NUM>.

The example cartridge <NUM> also includes a sealing ring <NUM> sealing between the seal <NUM> and the seal carrier <NUM>. The example sealing ring <NUM> is an elastomeric ring (e.g., a four-lobed seal such as the Quad Ring™ sealing ring of Minnesota Rubber & Plastics - Quadion LLC, Minneapolis, Minnesota). Example sealing ring material is a fluoroelastomer such as Viton™ fluoroelastomer of The Chemours Company, Wilmington Delaware. Sealing rings with alternative sections may be used or the sealing ring may be eliminated.

The example sealing ring <NUM> is accommodated in an inner diameter (ID) rebate <NUM> of the seal <NUM> at a junction of the surfaces <NUM> and <NUM>. The example sealing ring <NUM> is in axial compression between the radial face <NUM> of the rebate and the carrier wall face <NUM>. The rebate <NUM> also has an outer diameter (OD) face <NUM> (to the OD of the rebate but to the ID of the seal material). The rebate <NUM> or at least the radial face <NUM> contacting the sealing ring may bear a coating (not shown) that smooths texture and seals porosity of the carbon of the seal. An example coating is aluminum oxide applied via plasma spray to a thickness of <NUM> to <NUM>, then machined to a final thickness of <NUM> to <NUM> thick. Another example coating is polytetrafluoroethylene (PTFE) applied via an air-powered spray gun to a thickness <NUM> to <NUM> thick and not requiring any post-finishing operations.

The example seal system may represent a modification or reengineering of a baseline seal or configuration thereof (lacking the wave-form split ring snap ring <NUM> and optionally lacking the sealing ring <NUM>). The baseline may have a hard interference fit (e.g., press-fit and/or thermal interference fit) between the carbon seal and the seal carrier. A conventional split ring in a housing groove may serve merely as a backup retention mechanism. The hard interference fit may itself provide robust sealing between the seal and carrier. The modified or reengineered seal system or configuration may involve a much lighter interference fit which might be light enough to potentially be overcome by in-use vibration. Accordingly, to counter any backing out of the seal from the carrier, the wave form of the snap ring <NUM> biases the seal into its fully seated condition.

Additionally, the sealing ring <NUM>, if present, helps seal against any air or oil infiltration. In an example situation, due to the higher pressure in the buffer chamber <NUM> such pressure will bias the sealing ring <NUM> outward to maintain its condition radially seated against the rebate surface <NUM>.

An alternative embodiment of <FIG> adds an inner diameter (ID) wall <NUM> to the carrier <NUM>. The carrier <NUM> and the seal <NUM> may be similar to the carrier <NUM> and seal <NUM> with further modifications discussed. Nevertheless, any physically appropriate combination of features may be interchanged between the illustrated or other embodiments. The ID wall <NUM> has an inner diameter (ID) surface <NUM>, an outer diameter (OD) surface <NUM> and an aft/distal rim or end surface <NUM>. The OD surface <NUM> radially captures the sealing ring <NUM> against the rebate OD surface <NUM>. The example sealing ring <NUM> is schematically shown as a circular-sectioned O-ring (deformed by compression) rather than a lobed section. The sealing ring <NUM> may be an elastomer (e.g., fluoroelastomer). However, other ring sections may be used. The OD surface <NUM> includes a relatively axially-extending (e.g., circular cylindrical) proximal portion <NUM>-<NUM> and a radially inwardly tapering (toward the rim <NUM>) distal portion <NUM>-<NUM>. The example distal portion has an axial span at least <NUM>% of an axial span of the proximal portion to provide a shallow lead in (e.g., <NUM>% to <NUM>% or <NUM>% to <NUM>%). The example <FIG> seal <NUM> rebate (compartment) <NUM> includes a bevel <NUM> between its main body ID face and rebate radial face <NUM>. The rebate <NUM> also includes a tapering outer diameter (OD) surface <NUM> extending from the radial face to the adjacent end face. An example taper is <NUM>° to <NUM>° off-axial, more particularly <NUM>° to <NUM>° or about <NUM>°.

The tapering of the surface <NUM> may avoid damaging the sealing ring during assembly. The bevel or chamfer <NUM> may avoid chipping of the seal <NUM> during assembly. The ID wall <NUM> may protect the sealing ring from radially-slung debris in the buffer chamber.

In one example of an assembly process, the seal carrier <NUM>, <NUM> is preheated (e.g., by thermal convection in either an air oven or a liquid (e.g., water) bath. Example heating is to a temperature of about <NUM>°F (<NUM>), more broadly, <NUM> to <NUM> or <NUM> to <NUM> or <NUM> to <NUM>. This may be in distinction to a baseline heating in the range of <NUM> to <NUM> (discussed further below).

The sealing ring <NUM> may then be located relative to the seal carrier. For the <FIG> seal carrier <NUM>, this may involve locating by the ID wall <NUM> OD surface <NUM> at the root of the ID wall. For the <FIG> seal carrier <NUM>, this may involve tool/fixture (not shown) with an OD surface similarly positioned to OD surface <NUM>.

The seal <NUM> 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., approximately room temperature such as <NUM> to <NUM> or, more broadly <NUM> to <NUM>).

A subsequent pressure test of the assembly (seal <NUM> and seal carrier <NUM> and sealing ring <NUM> if present) may involve mounting the seal assembly into a fixture (not shown) which will allow establishing a pressure differential across the two boundaries between the sealing ring <NUM> and seal carrier <NUM>, and the sealing ring <NUM> and seal <NUM>. The pressure differential may be held at approximately <NUM> MPa for approximately two minutes, and the acceptance criteria will be judged by the leakage rate. An example acceptable leakage rate is about <NUM> MPa to <NUM> MPa per minute. Higher rates will be cause for reworking the assembly, such as by disassembly and reassembly, to achieve the acceptable leakage rate.

In one example of reengineering from a baseline seal system, an essentially pure press/interference fit of the baseline seal is replaced by a lighter interference fit plus the biasing action of the split ring. 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. The reduced tensile hoop stress in the carrier will reduce chances of fatigue failure.

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.

Even with a hard interference fit, there may be a tendency for vibration to back the carbon seal out of the fully seated position in the carrier. Even with reduced interference fit, the wave-form snap ring biasing of the seal <NUM> may maintain the fully seated position or at least reduce excursion amplitudes relative to the hard interference fit alone. The wave-form snap ring allows more consistent (less variation of) sealing ring <NUM> squeeze due to biasing the seal <NUM> against the seal carrier <NUM> and constant spring-load keeping the seal <NUM> firmly seated in the carrier. In a reengineering relative to a baseline, this may allow using a smaller sealing ring <NUM> cross section, reducing sealing ring weight. This correspondingly reduces the carbon seal rebate size which, in turn, allows reduction in the carbon seal body cross section beyond the rebate for a given level of strength. All these thus provide a lighter cartridge.

For thermal interference fits, reduced interference may reduce the heating temperature and thus decreasing 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.

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.

As an example of temperature reduction for thermal interference fit, the baseline seal may use a heating temperature in the range of <NUM> to <NUM>; whereas the revised seal may use <NUM> to <NUM> or other ranges discussed above. The reduction may be of an example <NUM> to <NUM> or <NUM> to <NUM>.

As an example of interference and stress reduction, the baseline seal may have an example compressive stress (e.g., at ambient conditions of <NUM> and <NUM> atm (<NUM> Bar), more broadly <NUM> to <NUM> at <NUM> Bar to <NUM> Bar) of <NUM>,<NUM> psi (<NUM> MPa), more broadly at least <NUM> MPa or <NUM> MPa to <NUM> MPa; whereas the revised seal may have an example such a stress of <NUM>,<NUM> psi (<NUM> MPa), more broadly <NUM> MPa to <NUM> MPa or <NUM> MPa to <NUM> MPa. The reduction may be of an example <NUM>,<NUM> PSI (<NUM> MPa) to <NUM>,<NUM> PSI (<NUM> MPa).

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 anti-rotation features (not shown). 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 <NUM>% carbon by weight, more particularly, at least <NUM>% or <NUM> % or <NUM>% or even commercially pure carbon with inevitable impurities.

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).

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.

The snap rings and sealing ring and spring(s) may be off-the-shelf commercial products.

<FIG> schematically illustrates a gas turbine engine <NUM> as one of many examples of an engine in which the seal system <NUM> may be used. The fan section <NUM> may include a single-stage fan <NUM> having a plurality of fan blades <NUM>. The fan blades <NUM> may have a fixed stagger angle or may have a variable pitch to direct incoming airflow from an engine inlet. The fan <NUM> drives air along a bypass flow path B in a bypass duct <NUM> defined within a housing <NUM> 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 <NUM> then expansion through the turbine section <NUM>. A splitter <NUM> aft of the fan <NUM> divides the air between the bypass flow path B and the core flow path C. The housing <NUM> may surround the fan <NUM> to establish an outer diameter of the bypass duct <NUM>. The splitter <NUM> may establish an inner diameter of the bypass duct <NUM>.

The example engine <NUM> generally includes a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine central longitudinal axis A (forming the axis <NUM>) relative to an engine static structure <NUM> via several bearing systems <NUM>.

The inner shaft <NUM> is connected to the fan <NUM> through a speed change mechanism, which in the example gas turbine engine <NUM> is illustrated as a geared architecture <NUM> to drive the fan <NUM> at a lower speed than the low speed spool <NUM>. The inner shaft <NUM> may interconnect the low pressure compressor (LPC) <NUM> and low pressure turbine (LPT) <NUM> such that the low pressure compressor <NUM> and low pressure turbine <NUM> are rotatable at a common speed and in a common direction. In other embodiments, the low pressure turbine <NUM> drives both the fan <NUM> and low pressure compressor <NUM> through the geared architecture <NUM> such that the fan <NUM> and low pressure compressor <NUM> are rotatable at a common speed. Although this application discloses geared architecture <NUM>, its teaching may benefit direct drive engines having no geared architecture. The high speed spool <NUM> includes an outer shaft <NUM> that interconnects a second (or high) pressure compressor (HPC) <NUM> and a second (or high) pressure turbine (HPT) <NUM>. A combustor <NUM> is arranged in the example gas turbine <NUM> between the high pressure compressor <NUM> and the high pressure turbine <NUM>.

The low pressure compressor <NUM>, high pressure compressor <NUM>, high pressure turbine <NUM> and low pressure turbine <NUM> 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 <NUM> and <NUM>.

Claim 1:
An apparatus comprising:
a first member (<NUM>, <NUM>);
a shaft (<NUM>, <NUM>) rotatable relative to the first member about an axis (A); and
a seal system (<NUM>) comprising:
a seal carrier (<NUM>) having:
an axially-extending wall (<NUM>) having an inner diameter (ID) surface (<NUM>); and
a radially-extending wall (<NUM>) having a first surface (<NUM>);
a seal (<NUM>) carried by the seal carrier (<NUM>) and having a seal face (<NUM>);
a seat (<NUM>) carried by the shaft (<NUM>, <NUM>) and having a seat face (<NUM>) in sliding sealing engagement with the seal face (<NUM>); and
one or more springs (<NUM>) biasing the seal carrier (<NUM>) relative to the first member (<NUM>, <NUM>) so as to bias the seal face (<NUM>) against the seat face (<NUM>),
wherein:
the seal carrier axially-extending wall ID surface (<NUM>) has a radially inwardly open groove (<NUM>) having a first sidewall (<NUM>) and a second sidewall (<NUM>) and a base (<NUM>); and characterised in that
the seal system (<NUM>) further comprises a wave-form split ring (<NUM>) contacting the first sidewall (<NUM>) and biasing the seal (<NUM>) into engagement with the radial wall first surface (<NUM>).