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). 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 forms of 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.

<CIT> discloses a turbomachine and a corresponding method of assembling a face seal assembly, according to the preamble of claim <NUM> and of claim <NUM>.

<CIT> discloses a gas seal for aerospace engines.

<CIT> discloses a seal for sealing an incompressible fluid between a relatively stationary seal and a movable member.

<CIT> discloses a circumferential air-riding carbon seal on a ceramic runner.

According to an aspect of the present invention, there is provided an apparatus in accordance with claim <NUM>.

Optionally, the apparatus further comprises a plurality of caps each having a sidewall and a base. Each of the plurality of coil springs has an end portion at the second end in an associated cap of the plurality of caps.

Optionally, the plurality of spring compartments each comprise: a base portion receiving the associated cap; and a shoulder separating the base portion from a broader portion.

Optionally, the plurality of spring compartments each comprise a port open to the base portion.

Optionally, the apparatus further comprises a spring carrier within the housing and having a plurality of projections each respectively received in an associated spring of the plurality of coil springs and wherein the plurality of springs bias the seal away from the spring carrier.

Optionally, the spring carrier has an annular plate portion from which the projections axially project.

Optionally, the spring carrier plate portion and housing have complementary interfitting features restricting relative rotation.

Optionally, each compartment of the plurality of compartments is formed in an outward radial projection of the seal having respective first and second circumferential ends and interfitting with complementary features of the housing to restrict relative rotation.

Optionally, the apparatus further comprises an internal snap ring captured in an internal groove of the housing and positioned to limit movement of the seal.

Optionally, the apparatus further comprises a seal ring captured in an outwardly-open channel of the housing and engaging an inner diameter surface of the seal.

Optionally, the apparatus is a gas turbine engine.

According to another aspect of the present invention, there is provided a carbon seal in accordance with claim <NUM>.

Optionally, each compartment of the plurality of compartments is formed in an outward radial projection of the carbon seal having respective first and second circumferential ends.

Optionally, each compartment of the plurality of compartments has a second axial opening axially opposite to and smaller than that compartment's first axial opening.

Optionally, the carbon seal is at least <NUM>% carbon by weight.

Optionally, each compartment of the plurality of compartments has: a base portion (e.g., for receiving an associated spring cap); and a shoulder separating the base portion from a broader portion.

<FIG> shows a seal system <NUM> having a seal <NUM> and a seat <NUM>. 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 (<FIG>) 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>).

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

<FIG> further shows an outward radial direction <NUM> and a forward direction <NUM>. 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> 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 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. The example bearing compartment <NUM> contains a bearing (not shown) 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 an oil-cooled dry-face seal wherein an array of passageways <NUM> (<FIG>) extend from respective inlet ports (not shown) at a plenum <NUM> (between the seat and a portion <NUM> of a shaft) through outlet ports (not shown) on the seat to an outer diameter (OD) rim <NUM> 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>. Or, the seal may not have oil cooling passageways at al.

The seal system further includes a seal housing <NUM> and a circumferentially distributed plurality of compression coil 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)).

In the illustrated example, the housing <NUM> indirectly engages the springs <NUM> via a spring carrier or adaptor <NUM> (<FIG>). Alternatively, there may be direct contact. The example spring carrier <NUM> comprises a plate <NUM> (<FIG>) having a first face <NUM> (aft in this example), an opposite second face <NUM>, an inner diameter (ID) perimeter <NUM>, and an outer diameter (OD) perimeter <NUM>. A circumferentially distributed (e.g., evenly) plurality of projections <NUM> extend from the second face <NUM> to distal ends <NUM> and have lateral peripheries (peripheral surfaces) <NUM>.

Each of the projections <NUM> is received in a first end portion of the associated spring <NUM> with the associated first end <NUM> of the spring abutting the second face <NUM>. An opposite second end portion of each spring is at least partially accommodated in a respective associated compartment <NUM> (<FIG>) of the seal <NUM>. An example seal system includes, for each spring, an associated end cap or spring seat <NUM> receiving the spring second end portion and itself being received in the associated compartment <NUM>. The example cap <NUM> (<FIG>) has a sidewall <NUM> extending from a rim <NUM> to an apertured end web <NUM>. The spring second end <NUM> abuts the interior surface or face of the web. As is discussed further below, the example web <NUM> has a central circular aperture <NUM>.

With the exception of the mounting ears <NUM> and anti-rotation features (discussed below) for circumferentially registering and retaining the spring carrier <NUM> and seal <NUM>, the housing is generally formed as a body of revolution about the axis A. The housing generally includes an inner wall <NUM> (inner diameter (ID) wall) and an outer wall <NUM> (outer diameter (OD) wall). At one end, each example wall <NUM>, <NUM> (aft ends in the illustrated example) are joined to/by a radial wall or web <NUM> having an outer (aft in the example) surface or face <NUM> and an opposite inner surface or face <NUM>. A circumferential channel <NUM> is formed between the walls <NUM> and <NUM> and forms a compartment that receives the spring carrier <NUM> with the carrier plate <NUM> first face <NUM> contacting the housing web <NUM> inner face <NUM>.

The ID wall <NUM> and OD wall <NUM> each have respective ID and OD surfaces. In the example, the ID surface of the OD wall includes a circumferentially distributed plurality of inward radial projections <NUM> (<FIG>). These form the housing portion of anti-rotation means restricting relative rotation of the seal <NUM> and spring carrier <NUM> on the one hand and the housing <NUM> on the other hand.

Each projection <NUM> has a respective first surface or face <NUM> (forward in the example), an opposite second surface or face <NUM>, first circumferential end <NUM>, an opposite second circumferential end <NUM>, and an inner diameter (ID) end/surface <NUM>.

The projections <NUM> are complementary to recesses <NUM> in the OD perimeter <NUM> of the plate <NUM> of the spring carrier <NUM>. The recesses <NUM> each include first and second circumferential ends <NUM>, <NUM>, and a base <NUM>. In the assembled condition, the ends <NUM> and <NUM> closely face or contact the associated ends <NUM>, <NUM> of the associated projection <NUM>. In the example, there are four projections <NUM> and four recesses <NUM>.

The example seal <NUM>, itself also has recesses <NUM> complementary to the projections <NUM> in a similar fashion to the recesses <NUM>. However, in this example, there are eight recesses <NUM> so that the projections <NUM> can cooperate with alternate recesses <NUM>. The recesses <NUM> each have a first circumferential end <NUM>, a second circumferential end <NUM>, and a base <NUM>. The recesses <NUM> define therebetween radial outward projections <NUM> each containing a respective associated compartment <NUM>. The recess <NUM> circumferential ends thus also define projection <NUM> circumferential ends. The projections also have outer diameter (OD) ends or surfaces <NUM>.

In the example seal <NUM>, the seal face <NUM> is an inner diameter portion of an end face <NUM> having an outer diameter portion <NUM> extending outward from the inner portion and slightly axially recessed therefrom. The outer diameter portion <NUM> falls along an annular region and then the projections <NUM>. The seal has an opposite end face <NUM> (proximal and, in the example aft).

As is discussed further below, the compartments <NUM> each have a relatively wide/broad portion <NUM> near the end <NUM> and a relatively narrower portion <NUM> between the wide portion <NUM> and the end face <NUM>. In the example, respective apertures or holes <NUM> extend from the outer surface portion <NUM> to the compartment narrow portion <NUM> leaving a shoulder surface <NUM>. In the example of an assembled condition, the holes <NUM> are coaxial with the springs <NUM> and their caps <NUM>. In the example, both the compartment wide portion <NUM> and the compartment narrow portion <NUM> are radially outwardly open to/through the surface <NUM>. The outward radial opening of the narrow portion is narrower than the diameter of the spring or its cap <NUM> so that, when seated, the end portion of the spring in the compartment is radially captured in the narrow portion <NUM>. For example, the narrow portion may be formed by over <NUM>° of a circular cylindrical surface <NUM>. Because the cap (or spring if no cap) outer diameter will be slightly less than this surface diameter to allow insertion, the angle may be at least <NUM>° to still provide radial capture/retention. The radial opening provided by having this extent be less than <NUM>° reduces weight and, depending on assembly sequence may allow easy visual confirmation of seating. If the design involve slight interference, the opening accommodates strain and provides radial access to allow forcing of the cap into a seated condition. The example wide portion <NUM> is wide at the OD surface <NUM> and has lateral shoulder surfaces <NUM> with an ID section being an intact section of the circular cylindrical surface <NUM>. The shoulder surfaces may extend sufficiently radially inward to leave about <NUM>° or slightly less of intact surface <NUM>. This allows assembly steps where the springs are inserted radially inward and then shifted axially to seat in the narrow portions <NUM>.

<FIG> further shows the seal <NUM> as having an inner diameter (ID) surface with a distal (forward in the example) portion <NUM> near the seal face <NUM> and a proximal (aft) portion <NUM> spaced radially outward from the distal portion by a tapering transition <NUM>. In the example, the proximal portion <NUM> is sealed to the housing via a seal ring <NUM> captured in radially outwardly open channel <NUM> near the forward end of the ID wall <NUM> of the housing. The example seal ring <NUM> is a metallic piston ring (e.g., steel). Alternative seal rings are C-seals The piston ring has respective sealing surfaces <NUM>, <NUM> in sealing engagement with the housing <NUM> (proximal face <NUM> of channel <NUM>) and seal <NUM> (ID surface proximal portion <NUM>).

<FIG> also shows a snap ring <NUM> for axially retaining the seal to the housing. The example snap ring <NUM> is a spiral internal snap ring captured in an ID channel <NUM> (having radially-extending axial end faces and an axially-extending OD base facing radially inward) of the housing outer wall <NUM>. Although <FIG> and <FIG> show an installed compressed state with the seal <NUM> disengaged from the snap ring, a pre-use state of the cartridge <NUM> has the seal face portion <NUM> contacting an axially inboard (facing the annular housing compartment <NUM> containing the springs) surface of the snap ring.

In one example of an assembly process, the housing is held with its end wall/web <NUM> downward and an opening between the ID wall and OD wall facing upward. The spring carrier <NUM> may then be downwardly inserted into the annular compartment <NUM> between the ID and OD walls. The seal ring <NUM> may then be installed via radial expansion and then relaxation into the channel/groove <NUM>. Springs <NUM> may be installed over the projections <NUM> by being lowered into place. Similarly, the caps <NUM> (if present and not already installed to the springs) may then be lowered over the exposed end portions of the springs. The seal <NUM> may then be downwardly installed with the caps <NUM> and spring end portions passing first through the compartment <NUM> wide portion <NUM> and then into the narrow portion <NUM>. Viewing through apertures <NUM> may confirm seating of the springs in the compartments <NUM>. During this downward movement of the seal, the spring may be compressed. Viewing through the apertures <NUM> can allow visual inspection to verify spring seating in the caps and verify spring condition. Nevertheless, the apertures <NUM> and <NUM> are optional. Additionally the stepping of the compartment may help reduce weight and my help avoid binding between seal and spring (as does the radial offset provided by the cap sidewall). But such stepping is optional.

Additionally, the seal <NUM> ID surface portion <NUM> will pass into sealing engagement with the corresponding portion <NUM> of the seal <NUM>. The example <FIG> seal <NUM> has an inner diameter bevel at its inboard end <NUM>. While the seal <NUM> is held sufficiently compressed, the spiral snap ring <NUM> may be circumferentially/radially contracted and lowered into alignment with the channel <NUM> and then allowed to release and circumferentially/radially expand to be captured. Thereafter, the pre-compression force on the seal <NUM> may be released causing the seal to extend outward under spring <NUM> bias until it contacts the snap ring. The resulting cartridge <NUM> may be installed over the engine shaft and screwed to the static structure as discussed above. Then, the seat may be slid over the shaft making initial contact with the seal <NUM> and then compressing the seal against bias of the springs <NUM> until the seat is stopped by an abutment surface on the shaft.

In use, relative to alternative seal and associated spring constructions, the present embodiments and variations may have one or more of several advantages. Typical existing (baseline) seals utilizing coil springs, bellows springs, or wave springs have full annulus metal components such as carriers for 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). Even if the caps <NUM> are present, the sprung mass may be substantially less than the sprung mass of the baseline seal system being replaced. Reduced sprung mass may then facilitate reduced spring force, leading to reduced wear for a given effective sealing ability. It may also synergistically lead to further mass reduction due to lower needed robustness, there by amplifying the improvement.

Additionally or alternatively, the seal may be more axially compact than the baseline. Because the coil springs occupy only a small circumferential portion of the seal, the springs may extend substantially closer to the seal face than would the axial end of a bellows or wave spring or ends of coil springs engaging a carrier or other support plate. This may provide a more axially compact cartridge <NUM> as measured by the installed axial length between the mating seat and seal faces on the one hand and the outside surface (aft in the illustrated example) of the housing web on the other hand.

Additionally, by locating the spring compartments in discrete radial protrusions, the mass of the carbon element may be reduced relative to the baseline by eliminating material circumferentially between those protrusions. Again, this may synergistically amplify other improvements.

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 the non-annular features such as the radial protrusions and pockets. 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. The initial outer diameter of the blank may be proud of the final diameter of the projection OD surfaces <NUM>. This allows drilling of the cylindrical holes that form each circular cylindrical surface <NUM> without such holes being open to the OD of the blank. Thereafter, the OD may be machined (e.g., lathed) down to the final level of the surfaces <NUM> and the recesses <NUM> and shoulder surfaces <NUM> machined (e.g., milled).

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 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 spring carrier may also be formed of an appropriate alloy (e.g., stainless steel or a titanium alloy). It may be cast and/or machined. Precision may be of relatively low importance leaving the possibility of no machining or minimal machining of a raw casting. Additionally, it may formed as an assembly such as by cutting the plate from plate stock and cutting the protrusions from rod stock and welding or otherwise fastening to the plate. The springs may be cut from commercially-available spring stock and may formed of appropriate alloy such as a stainless steel or titanium alloy.

The caps may be formed of an appropriate alloy such as a stainless steel or a titanium alloy. The caps may be formed via stamping/drawing sheetstock or may be formed by rolling from sheetstock and welding abutting ends. Alternative caps may be cast of alloy or molded of a high temperature plastic.

The snap ring and seal ring may be off-the-shelf commercial products. As noted above, the example seal ring is a metallic piston ring (e.g., steel). Alternative rings are C-seals.

<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, for example a gas turbine engine (<NUM>), comprising:
a first member;
a shaft rotatable relative to the first member about an axis (A); and
a seal system (<NUM>) comprising:
a seal (<NUM>) carried by the first member and having a seal face (<NUM>);
a seal housing (<NUM>);
a seat (<NUM>) carried by the shaft and having a seat face (<NUM>) in sliding sealing engagement with the seal face (<NUM>); and
a plurality of coil springs (<NUM>) biasing the seal face (<NUM>) against the seat face (<NUM>), each coil spring (<NUM>) having a first end (<NUM>) and a second end (<NUM>),
wherein:
the seal (<NUM>) has a plurality of spring compartments (<NUM>); and
each of the plurality of coil springs (<NUM>) is partially within a respective associated compartment (<NUM>) of the plurality of spring compartments (<NUM>),
characterized in that:
each of the plurality of spring compartments (<NUM>) comprise an outward radial opening.