Patent Description:
Certain sections of gas turbine engines may operate at high temperatures and pressures and some engine components may be sensitive thereto. Typically, seal systems are positioned at main shaft bearing compartments to minimize the high temperature and pressure air from flowing into sensitive areas and prevent the oil used for cooling and lubrication from escaping the compartment. Such seal systems may utilize carbon seals and labyrinth seals. Conventional seal systems utilize materials which have properties that may result in less favorable operating radial gaps/clearances or may also have strength or structural limitation.

Advanced gas turbine engines require higher performance seals which are higher in rubbing velocity while also meeting more aggressive cost, weight, size, environmental, and reliability metrics.

Prior art includes <CIT>, <CIT>, <CIT>, <CIT>, <NPL>", and <CIT>.

A seal system for a gas turbine engine according to one aspect of the present invention is claimed in claim <NUM>.

Optionally, the sealing interface at the hot operating condition is essentially zero (or essentially near zero).

Optionally, the sealing interface at the hot operating condition is about <NUM> inches (<NUM>).

Optionally, the seal system is an arch-bound seal.

Optionally, the seal ring comprises a multiple of segments.

Optionally, the seal runner provides an approximately <NUM>,<NUM>-<NUM>,<NUM> psi (<NUM>-<NUM> MPa) tensile yield strength, an elastic modulus of <NUM> lbfx10^<NUM>/in^<NUM> (alternatively <NUM> GPa) and a CTE of <NUM> inE-<NUM>/in/°F (alternatively <NUM>/m/°K).

Optionally, the seal system is from <NUM> to <NUM> inches (<NUM> - <NUM>) in diameter.

Optionally, the seal system is operable at revolutions per minute of <NUM>-<NUM>,<NUM> RPM.

Optionally, the seal system is operable at from -<NUM> F to <NUM> F (-<NUM> C to <NUM> C) and <NUM> psia to <NUM> psia (<NUM> bar to <NUM> bar).

Optionally, the hot operating condition is above <NUM> F (<NUM> C).

These features and elements as well as the operation of the invention will become more apparent in light of the following description and the accompanying drawings.

Although depicted as a high bypass gas turbofan engine architecture in the disclosed non-limiting embodiment, it should be appreciated that the concepts described herein are not limited only thereto.

The engine <NUM> generally includes a low spool <NUM> and a high spool <NUM> mounted for rotation about an engine central longitudinal axis A relative to an engine static structure <NUM> via several bearing compartments <NUM>. The low spool <NUM> generally includes an inner shaft <NUM> that interconnects a fan <NUM>, a low pressure compressor <NUM> ("LPC") and a low pressure turbine <NUM> ("LPT"). The inner shaft <NUM> drives the fan <NUM> directly or through a geared architecture <NUM> to drive the fan <NUM> at a lower speed than the low spool <NUM>. An exemplary reduction transmission is an epicyclic transmission, namely a planetary or star gear system. The high spool <NUM> includes an outer shaft <NUM> that interconnects a high pressure compressor <NUM> ("HPC") and high pressure turbine <NUM> ("HPT"). A combustor <NUM> is arranged between the HPC <NUM> and the HPT <NUM>. The inner shaft <NUM> and the outer shaft <NUM> are concentric and rotate about the engine central longitudinal axis A which is collinear with their longitudinal axes.

Core airflow is compressed by the LPC <NUM> then the HPC <NUM>, mixed with fuel and burned in the combustor <NUM>, then expanded over the HPT <NUM> and the LPT <NUM>. The turbines <NUM>, <NUM> rotationally drive the respective low spool <NUM> and high spool <NUM> in response to the expansion. The main engine shafts <NUM>, <NUM> are supported at a plurality of points by the bearing compartments <NUM>. It should be understood that various bearing compartments <NUM> at various locations may alternatively or additionally be provided.

Each of a multiple of bearing compartments <NUM> include one or more bearings <NUM> (illustrated schematically; <FIG>) and one or more seal system <NUM>. The bearings <NUM> and seal system <NUM> respectively support and interface with the shafts <NUM>, <NUM> of the respective low spool <NUM> and high spool <NUM>.

The seal system <NUM> operates to seal a "wet" zone from a "dry" zone. In other words, regions or volumes that contain oil may be referred to as a "wet" zone and an oil-free region may be referred to as a "dry" zone. So, for example, the interior of each bearing compartment <NUM> may be referred to as a wet zone that ultimately communicates with an oil sump while the region external thereto may be referred to as a dry zone. That is, the bearings <NUM> support the low spool <NUM> and the high spool <NUM> and the seal system <NUM> separate the "wet" zone from the "dry" zone to define the boundaries of each bearing compartment <NUM>. Although particular bearing compartments and bearing arrangements are illustrated in the disclosed non-limiting embodiment, other bearing compartments and bearing arrangements in other engine architectures such as three-spool architectures will also benefit herefrom.

With reference to <FIG>, the seal system <NUM> generally includes a seal ring <NUM>, a seal runner <NUM>, and a seal housing <NUM>. The seal ring <NUM> may include springs <NUM> or other features that position one or more ring segments of the seal ring <NUM>. The seal housing <NUM> may include secondary seals such as knife seals.

The seal system <NUM>, which provides relatively small clearance segmented circumferential, split ring, controlled gap, or radial clearance style seals are sometimes referred to as an arch bound seal. As used herein, "arch-bound" refers to the configuration of a series of segments of a ring in which the ends of the segments are held in mutual contact in a circumferential direction by a radially inwardly directed force such that the radius of the ring cannot be further decreased in a non-destructive manner. The radially inwardly directed force may be produced, for example, by a spring such as garter springs. Conventional seal systems utilize materials which have properties that may result in less favorable operating radial clearances which may also contain strength or structural limitations that are typically limited by the capabilities of their materials.

The seal system <NUM> may be utilized, for example, to cap the bearing compartment <NUM> for effective oil containment and preclude hot air ingestion. In one embodiment, the seal system <NUM> typical of gas turbine engine usages may be from <NUM> to <NUM> inches (<NUM> - <NUM>) in diameter and operate at <NUM>-<NUM>,<NUM> revolutions per minute, and temperatures and pressures of -<NUM> F to <NUM> F (-<NUM> C to <NUM> C) and <NUM> psia to <NUM> psia (<NUM> bar to <NUM> bar).

The seal system <NUM> may be located between a rotational component <NUM> such as the shafts <NUM>, <NUM> (<FIG>) and a non-rotational structure such as support <NUM> to define a sealing interface <NUM> (also shown in <FIG>). The seal ring <NUM> is a rotationally stationary component that mounts to the support <NUM> via the seal housing <NUM>. The seal runner <NUM> is mounted to the rotational component <NUM> and interfaces with the seal ring <NUM> to form the sealing interface <NUM>. The sealing interface <NUM> varies in response to operational conditions between a cold operating condition such as at build to low power operational condition (<FIG>) and a hot operating condition such as cruise flight conditions (<FIG>) during gas turbine engine operation.

The air side <NUM>, or high pressure side, is here illustrated as to the right of the seal system <NUM>. The bearing compartment <NUM> air/oil side is here illustrated to the left of the seal system <NUM> and may be considered the low pressure side. The seal system <NUM> provides a combination of materials to achieve the desired lower operational gap/air leakage/oil weepage at the sealing interface <NUM>. Materials for the rotating runner contain structural limitations, e.g., strength, etc., when a low coefficient of expansion material, e.g., ceramic, etc. is used.

The seal ring <NUM>, in the disclosed embodiment, is manufactured of a graphitic or electrographitic carbon based material. The seal ring <NUM> provides a higher coefficient of thermal expansion, relative to conventional materials, with a reduced heat generation design for reduced overall component temperature changes. The relatively higher coefficient of thermal expansion material of the seal ring <NUM> permits thermal growth at a higher rate to more closely match the total thermo-mechanical deformation of the seal runner <NUM>. This facilities a lower effective radial effective sealing interface <NUM>.

The seal runner <NUM>, in the disclosed embodiment, is manufactured of a Molybdenum alloy such as Titanium-Zirconium-Molybdenum (TZM) alloys. The seal runner <NUM> provides a low coefficient of thermal expansion less than that of the seal ring <NUM>, and a relatively high elastic modulus and high strength characteristic greater than that of conventional materials that also have low coefficients of expansion such as ceramics. In one example, the Titanium-Zirconium-Molybdenum (TZM) alloy seal runner <NUM> provide an approximately <NUM>,<NUM>-<NUM>,<NUM> psi (<NUM>-<NUM> MPa) tensile yield strength, elastic modulus of <NUM> lbfx10^<NUM>/in^<NUM> (alternatively <NUM> GPa) and a CTE of <NUM> inE-<NUM>/in/°F (alternatively <NUM>/m/°K).

The seal runner <NUM>, using a Molybdenum alloy such as Titanium-Zirconium-Molybdenum (TZM), also contains a relatively higher minimum value for the range of yield strengths compared to that of conventional materials used with a low coefficient of expansion, e.g., ceramics. This higher value for the range of yield strength characteristic enable the TZM material to be used in more challenging structural applications. The combination of low coefficient of expansion, higher elastic modulus and higher strength of the seal runner <NUM>, combined with the characteristics of the seal ring <NUM>, provides for an optimized lower effective sealing interface <NUM> during build and operation, thus optimizing seal system performance and reliability.

The optimized effective sealing interface <NUM> of the Molybdenum alloy seal runner <NUM> and the graphitic seal ring <NUM> in the illustrative embodiment as compared to other conventional materials may be defined by a comparison factor of the effective sealing interface <NUM> at the cold or build / low power operating condition (<FIG>) and a hot or normal operational condition (<FIG>). The comparison factor may be defined by setting an equivalent effective sealing interface <NUM> at the hot operating condition to be essentially near zero, e.g., <NUM> inches (<NUM>). This results in the sealing interface <NUM> providing a clearance in both the hot operating condition and the cold operating condition. That is, a desired baseline hot operating condition provides minimal air leakage without operational interference to provide seal reliability and performance which then results in a cold operating condition sealing interface <NUM> that can be compared by the comparison factor.

For an equivalent hot operating condition (<FIG>) sealing interface <NUM> of the Molybdenum alloy seal runner <NUM> and the graphitic seal ring <NUM> of the illustrative embodiment, the resultant cold operating condition (<FIG>) sealing interface <NUM> provides a comparison factor that is approximately <NUM>%-<NUM>% smaller than that of conventional alloys such as steel alloys, titanium alloys, nickel based alloys which have equivalent tensile yield strength capability of <NUM>,<NUM> -<NUM>,<NUM> psi (<NUM>-<NUM> MPa) tensile yield strength. Although some ceramic materials may have an equivalent or better effective sealing interface <NUM> at the cold operating condition, such ceramic materials provide unacceptable tensile yield strength capability for gas turbine operations as compared to the Molybdenum alloy seal runner <NUM> of the illustrative embodiment. The seal runner <NUM>, using a Molybdenum alloy such as titanium-zirconium-Molybdenum (TZM), also typically provides a higher minimum value for the range of yield strengths as compared to that of conventional materials used with a relatively lower coefficient of expansion, e.g., ceramics which have a <NUM>,<NUM>-<NUM>,<NUM> psi (<NUM>-<NUM> MPa) tensile yield strength.

The seal system <NUM> provides essentially no limit to rotor speed, e.g., over <NUM>,<NUM> rpm; low to no oil cooling requirements at hot operating conditions, e.g., <NUM> F (<NUM> C); provides a torturous path for oil to egress; and maintains a healthy delta pressure at engine operating conditions.

It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.

Claim 1:
A seal system (<NUM>) for a gas turbine engine comprising:
a seal runner (<NUM>) manufactured of a Molybdenum alloy material that provides a first coefficient of thermal expansion; and
a seal ring (<NUM>) manufactured of a graphitic material that provides a second coefficient of thermal expansion greater than the first coefficient of thermal expansion,
wherein the seal ring (<NUM>) is assembled to the seal runner (<NUM>) to form a radial sealing interface (<NUM>) that provides a radial clearance in both a hot operating condition and a cold operating condition,
characterised in that:
the seal runner (<NUM>) is manufactured of a Titanium-Zirconium-Molybdenum (TZM) alloy; and
the seal ring (<NUM>) is manufactured of electrographitic carbon materials.