Patent Description:
Carbon seals are commonly used to seal between relatively rotating components in gas turbine engines. In typical situations, the annular carbon seal is 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>, "Oil Weepage Return for Carbon Seal Plates" shows a seal with two sets of passageways through the seat. One set delivers oil to the interface as a wet face seal. Another set helps centrifugally pump out oil that has weeped radially inward from the interface.

<CIT>, "Rotating shaft seal" shows an alternative wet face seal.

<CIT>, "Hydrodynamic Seal Seat Cooling Features" shows a dry face seal wherein the oil passageways have two legs: an upstream leg receiving oil from a collection notch which in turn has collected the oil from a nozzle; and a downstream leg extending radially outward from the upstream leg generally close to and parallel to the sealing interface.

<CIT> discloses a prior art seal system as set forth in the preamble of claim <NUM>.

From one aspect of the disclosure, there is provided a seal system as recited in claim <NUM>.

There is also provided a gas turbine engine as recited in claim <NUM>.

There is also provided a method as recited in claim <NUM>.

<FIG> shows a seal system <NUM> having a first member <NUM> carrying a seal <NUM>. The exemplary seal <NUM> is a carbon seal having a seal surface or face <NUM>. The exemplary seal <NUM> is formed as a body of revolution about an axis <NUM> which is an axis of relative rotation between the first member <NUM> and a second member <NUM>. <FIG> further shows an outward radial direction <NUM>. The exemplary seal face <NUM> is a radial face. The second member <NUM> comprises a piece <NUM> (seat piece) forming a seat for the seal with a seat surface or face <NUM> in sliding sealing engagement with the seal face <NUM> at a sealing interface.

The exemplary illustrated configuration is a dry face configuration. The seal <NUM> may be biased into axially compressive engagement with the seat face <NUM> via one or more factors including pressure bias and spring loading. The seal <NUM> is shown as sealing a space or region <NUM> inboard of the sealing interface from a space or region <NUM> outboard. Depending upon configuration, the pressure difference may bias the seal in either direction. <FIG> further shows a spring <NUM> (e.g., a coil spring) providing the required bias. There may be a circumferential array of such springs about the axis <NUM> each under axial compression.

In one group of examples discussed below, the second member <NUM> is rotating in an inertial frame of reference while the first member <NUM> is either stationary or counter-rotating. The rotating of the second member <NUM> may create a centrifugal oil flow action discussed further below.

In operation, the relative rotation produces frictional heating at the sliding interface between the faces <NUM> and <NUM>. Cooling to dissipate this heat is therefore desirable. As discussed above, it is well-known to provide a circumferential array of oil flow passages through a seat. These are typically drilled after machining gross features of the seat. <FIG>, however, shows the seat piece <NUM> as having an annular channel <NUM> axially spaced from the seat face <NUM>. The exemplary annular channel <NUM> extends from a radially inboard inner diameter (ID) base <NUM> to a radially outboard outer diameter (OD) opening <NUM> in an OD surface <NUM> of the seat piece <NUM>. The channel <NUM> also has a first surface or face <NUM> and a second surface or face <NUM> axially spaced therefrom. The channel <NUM> may be machined in the piece <NUM> by conventional methods, such as turning or milling, or advanced methods, such as EDM.

<FIG> further shows a circumferential array of passageway legs (passageways) <NUM> connected to the annular channel <NUM> at respective first ends <NUM> and open to a surface portion <NUM> of the piece <NUM> at their second ends <NUM>. An exemplary number of passageways <NUM> is <NUM> to <NUM>, more particularly <NUM> to <NUM> or <NUM> to <NUM> in seal sizes used on gas turbine engines. In operation, centrifugal action causes an accumulation <NUM> of oil to be captured by the second member <NUM> in a radially outwardly closed collection channel <NUM>. The passageway second ends <NUM> form outlets from the collection channel allowing oil flows <NUM> to pass outward through the passageways to the channel <NUM>. The flows <NUM> from the individual passageways <NUM> merge to form a flow <NUM> in the channel <NUM>. The flow <NUM> flows radially outward to be discharged as a discharge flow <NUM>. The radial oil flow <NUM> in the channel cools the seat piece <NUM> and, thereby, cools the seat face and seal face.

To form the channel <NUM>, <FIG> shows a weir formed by an annular member <NUM> accommodated partially in a radially inwardly open channel <NUM> in the seat piece <NUM>. A portion of the member <NUM> protrudes radially inwardly from an opening of the channel <NUM> at the surface <NUM>. As an oil source, <FIG> shows an oil pump <NUM> delivering oil from a reservoir <NUM> via a conduit <NUM>. The conduit <NUM> may terminate at one or more nozzles <NUM>. Each nozzle may have a respective outlet <NUM> discharging a spray <NUM> of the oil. The sprayed oil collects on a surface of the first member and is slung radially outward as a flow <NUM> (<FIG>) to the channel <NUM>. Oil from the flow <NUM> may be collected and returned to the reservoir <NUM> by a conventional collection apparatus (not shown).

<FIG> further shows the seat face <NUM> having a radial span RS<NUM> and the channel <NUM> as having a radial span RS<NUM>. The exemplary radial spans are oriented so that the channel <NUM> fully radially overlaps the seal face <NUM>. This provides a short thermal conductive flowpath for heat to pass from the seat face <NUM> to the flow <NUM> in the channel <NUM>. <FIG> further shows an angle θ<NUM> between the seal face/seat face on the one hand and the adjacent channel face <NUM> on the other hand. Exemplary θ<NUM> is greater than zero. More particularly, with the seal face extending exactly or close to exactly radially, the adjacent portion of the channel face <NUM> diverges at the angle θ<NUM> in the radial outward direction. This divergence from radial helps cause the flow <NUM> to remain attached to the face <NUM>. The opposite inclination would potentially risk flow separation and loss of heat conduction. Exemplary θ<NUM>, however, may be fairly small in order to maintain cooling effectiveness as the flow <NUM> progresses radially outward toward the outer diameter (OD) extent of the seal face. Thus, exemplary θ<NUM> is <NUM>-<NUM>°, more particularly, <NUM>-<NUM>°, <NUM>-<NUM>°, or <NUM>-<NUM>° or <NUM>-<NUM>°. The second face <NUM> may similarly diverge from the first face at an angle θ<NUM>. But this divergence θ<NUM> may represent an artifact of manufacturing such as from a tapered bit. Exemplary θ<NUM> is <NUM>° to <NUM>°, more particularly <NUM>° to <NUM>° or <NUM>° to <NUM>° or <NUM>° to <NUM>°. Alternative lower ends on those ranges are <NUM>° and <NUM>°. Exemplary span S<NUM> between the seat face <NUM> and the channel face <NUM> is <NUM> inch to <NUM> inch (<NUM> to <NUM>), more narrowly <NUM> to <NUM> or <NUM> to <NUM>. Exemplary channel width S<NUM> is <NUM> inch to <NUM> inch (<NUM> to <NUM>), more narrowly <NUM> to <NUM> or <NUM> to <NUM> or <NUM> to <NUM>.

An exemplary member <NUM> may be formed by spiral winding such as used for retaining rings. Alternatively, a weir may be integrally machined into seat piece <NUM>.

In various implementations, the use of the annular channel <NUM> may have one or more of several advantages relative to any particular baseline. For example, when contrasted with a baseline arrangement as in the '<NUM> publication, the channel <NUM> may provide more circumferential uniformity of cooling which may help reduce heat generation and wear. For example, discrete passages may produce a circumferential array of cool zones interspersed with warmer zones. The differential thermal expansion of cool portions of the seat and hot portions of the seat may produce an uneven seat surface generating unnecessary heat and potentially compromising sealing.

<FIG> shows a turbofan engine <NUM> having an engine case <NUM> containing a rotor shaft assembly <NUM>. An exemplary engine is a turbofan. Alternatives include turbojets, turboprops, turboshafts, and industrial gas turbines. The exemplary turbofan is a two-spool turbofan. Via high <NUM> and low <NUM> shaft portions of the shaft assembly <NUM>, a high pressure turbine (HPT) section <NUM> and a low pressure turbine (LPT) section <NUM> respectively drive a high pressure compressor (HPC) section <NUM> and a low pressure compressor (LPC) section <NUM>. The engine extends along a longitudinal axis (centerline) <NUM> from a fore end to an aft end. Adjacent the fore end, a shroud (fan case) <NUM> encircles a fan <NUM> and is supported by vanes <NUM>. An aerodynamic nacelle <NUM> around the fan case is shown and an aerodynamic nacelle <NUM> around the engine case is shown.

Although a two spool (plus fan) engine is shown, an alternative variation involves a three spool (plus fan) engine wherein an intermediate spool comprises an intermediate pressure compressor (IPC) between the LPC and HPC and an intermediate pressure turbine (IPT) between the HPT and LPT. In another aspect a three-spool engine, the IPT drives a low pressure compressor while the LPT drives a fan, in both cases either directly or indirectly via a transmission mechanism, for example a gearbox.

In the exemplary embodiment, the low shaft portion <NUM> of the rotor shaft assembly <NUM> drives the fan <NUM> through a reduction transmission <NUM>. An exemplary reduction transmission is an epicyclic transmission, namely a planetary or star gear system.

<FIG> also shows at their outboard ends, the vanes <NUM> have flanges <NUM> bolted to an inner ring structure of the fan case to tie the outboard ends of the vanes together. Integral therewith or fastened thereto is a forward mounting structure <NUM> (e.g., clevises which form part of a four bar mechanism) and provides forward support to the engine (e.g., vertical and lateral support). To mount the engine to the aircraft wing, a pylon <NUM> is mounted to the structure <NUM> (e.g., forming the outer part thereof). The pylon is also mounted to a rear engine mount <NUM>.

In one example, <FIG> shows a location <NUM> for the seal system <NUM> wherein the first member <NUM> may be mounted to (or integrally formed with) a static bearing support <NUM> and the second member <NUM> may be mounted to (or integrally formed with) a forward portion of the low shaft <NUM>. Alternatively, in a location <NUM>, the first member <NUM> may be mounted to (or integrally formed with) a static hub <NUM> and the second member <NUM> mounted to (or integrally formed with) a fan shaft <NUM>. In these two illustrated examples, the seal system is positioned adjacent one end of a bearing system to isolate the bearing system. Similar locations may be provided for other bearings in the engine. For example, locations <NUM> and <NUM> may represent locations where the sealing is between the high spool and static structure on either side of a bearing supporting the high spool.

<FIG> shows an alternate seal system <NUM> configuration, otherwise similar to <FIG> with several exceptions. A first exception is that the cooling channel <NUM> extends radially outward to a plenum <NUM> (<FIG>). The plenum <NUM> is defined by the combination of: a further annular channel in a first seat piece <NUM>; and a second piece <NUM> encircling and attached to the first piece. The exemplary second piece <NUM> is formed as an annular sleeve having a circumferential array of apertures <NUM> extending between an inner diameter (ID) surface <NUM> and an outer diameter (OD) surface <NUM>. The ID surface is engaged to the OD surface of the first seat piece <NUM> fore and aft of the plenum <NUM> (e.g., via interference fit or a braze joint). Alternative configurations may have the second piece <NUM> as nondestructively removable from the first piece such as via a retaining clip or wire (e.g. snap ring). Similarly, in such removable configurations, separate seals may be provided between the pieces (e.g., O-rings).

The apertures <NUM> are axially offset from the outer diameter opening of the channel <NUM> to the plenum <NUM>. An exemplary number of apertures <NUM> is <NUM> to <NUM>, more particularly <NUM> to <NUM> or <NUM> to <NUM> in seal sizes used on gas turbine engines. The plenum <NUM> and apertures <NUM> may provide one or more of several functions. First, the apertures may provide a metering function (metering/restricting discharge flows <NUM>) helping ensure the flow has sufficient residence time in the channel <NUM> to not separate from the face <NUM> and to provide sufficient cooling. Additionally, residence time in the plenum <NUM> may further cool the first seat piece <NUM> to maximize the cooling. The axial offset of the apertures <NUM> from the outlet or OD end of the channel <NUM> helps ensure that flow is along the length of the plenum <NUM> to again maximize cooling efficiency. Exemplary offset S<NUM> (measured center-to-center) is <NUM> inches to <NUM> inches (<NUM> to <NUM>), more particularly, <NUM> inches to <NUM> inches (<NUM> to <NUM>) or, for non-zero values <NUM> inch to <NUM> inch (<NUM> to <NUM>) or <NUM> inch to <NUM> inch (<NUM> to <NUM>).

A further difference between the <FIG> and <FIG> systems is the <FIG> presence of an integral weir formed in the first piece. This may be more representative of conventional weirs.

Additional variations include seals where the oil is not delivered from a spray nozzle, but instead passes outward from a plenum (e.g., as in the '<NUM> and '<NUM> patents above) or via other means.

Where a measure is given in English units followed by a parenthetical containing SI or other units, the parenthetical's units are a conversion and should not imply a degree of precision not found in the English units.

Claim 1:
A seal system (<NUM>) comprising:
a first member (<NUM>);
a seal (<NUM>) carried by the first member (<NUM>) and having a seal face; and
a second member rotatable relative to the first member (<NUM>) about an axis (<NUM>) and having:
a seat (<NUM>), the seat (<NUM>) having a seat face in sliding sealing engagement with the seal face; and
a circumferential array of passageway legs,
wherein the second member further comprises:
an annular channel (<NUM>) axially spaced from the seat face, the passageway legs connected to the annular channel (<NUM>),
wherein:
the passageway legs and the annular channel (<NUM>) are in a first piece (<NUM>); and
a second piece (<NUM>) encircles and is attached to the first piece (<NUM>);
characterised in that
the second piece (<NUM>) has a circumferential array of apertures (<NUM>) and cooperates with the first piece (<NUM>) to define a plenum (<NUM>) extending from the annular channel (<NUM>).