Patent Description:
A gas turbine engine typically includes a fan section, a compressor section, a combustor section, and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive rotation of the compressor and the fan section.

A mid-turbine frame (MTF) is positioned between a high pressure turbine stage and a low pressure turbine stage in the gas turbine engine. The MTF supports one or more bearings and transfers bearing loads from an inner portion of the gas turbine engine to an outer engine frame. The MTF also serves to route air from the high pressure turbine stage to the low pressure turbine stage.

<CIT> discloses a prior art mid-turbine frame. <CIT> discloses a prior art vane insertable tie rods with keyed connections.

<CIT> discloses a prior art mid-turbine frame with fairing attachment.

A1 discloses a prior art gas turbine engine buffer cooling system. <CIT> discloses a prior art split-zone flow metering T-tube. <CIT> discloses a prior art mid-turbine bearing support. <CIT> discloses a prior art oil line insulation system for mid turbine frame. <CIT> discloses a prior art oil purge system for a mid turbine frame. <CIT> discloses a prior art shaft seal used in gas turbine engines. <CIT> discloses a prior art system for regulating a cooling fluid within a turbomachine.

According to a first aspect of the present invention, there is provided a mid-turbine frame for a gas turbine engine as set forth in claim <NUM>.

In another exemplary embodiment of any of the above mid-turbine frames, each of the spokes further includes a redirection tube directing cooling fluid flowing through the cooling passage aft such that the cooling fluid bypasses the torque box.

In another exemplary embodiment of any of the above mid-turbine frames, the connection feature includes: a flange portion and an extension portion, the extension portion extending radially into the bearing support passage, a seal plate radially outward of the flange portion, and a seal element sealing the seal plate to the inner frame case.

In another exemplary embodiment of any of the above mid-turbine frames, the seal element sealing the seal plate to the inner frame case is a piston seal.

Another exemplary embodiment of any of the above mid-turbine frames, further includes a service line seal disposed between an outward facing surface of the extension portion and an inward facing surface of the bearing support passage.

In another exemplary embodiment of any of the above mid-turbine frames, the bearing support passage includes at least a first opening for providing fluid from the bearing support passage to a component disposed radially inward of the mid-turbine frame.

In another exemplary embodiment of any of the above mid-turbine frames, the at least a first opening is sealed to the inner frame case, such that fluid passing through the opening does not pass into the torque box.

In another exemplary embodiment of any of the above mid-turbine frames, the inner frame case is configured such that all cooling air provided to an engine segment adjacent to the inner frame case bypasses the torque box.

According to a further aspect of the present invention, there is provided a method as set forth in claim <NUM>.

Another embodiment of the above exemplary method further comprises providing cooling air to a turbine section of the gas turbine engine through said mid-turbine frame, the cooling air bypassing a torque box of the mid-turbine frame.

In another embodiment of any of the above exemplary methods, providing cooling air to said turbine section through said mid-turbine frame by bypassing said torque box includes passing cooling air through a cooling passage in at least one of said spokes and redirecting the cooling air from the spoke to the turbine section via a redirection tube.

Another embodiment of any of the above exemplary method further includes sealing every opening in the torque box.

According to a further aspect of the present invention, there is provided a gas turbine engine as set forth in claim <NUM>.

In an exemplary embodiment of the above gas turbine engine, the at least one service line is connected to the bearing support passage in the sealed torque box such that fluid is passed through the torque box through the bearing support passage to the bearing.

In another exemplary embodiment of any of the above gas turbine engines each opening in the sealed torque box is sealed such that fluid exchange between the torque box and fluid external to the torque box is minimized.

The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>.

The flight condition of <NUM> Mach and <NUM>,<NUM> ft (<NUM>,<NUM>), with the engine at its best fuel consumption - also known as "bucket cruise Thrust Specific Fuel Consumption ("TSFC')" - is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. "Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (<NUM> °R)]^<NUM> (where <MAT>). The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about <NUM> ft / second (<NUM>/s).

The exemplary gas turbine engine <NUM> described above includes a mid-turbine frame (MTF) <NUM> that has an inner frame case. The inner frame case surrounds and supports a high spool bearing. Defined within the inner frame case is a cavity referred to as a torque box. The mid-turbine frame <NUM> is positioned between the low pressure turbine section <NUM> and the high pressure turbine section <NUM>. As a result of the position of the mid-turbine frame <NUM> in the flow path, the mid-turbine frame <NUM> is exposed to high temperatures.

In order to pass oil through the primary flow path to the radially inward portions of the gas turbine engine <NUM>, such as a high spool bearing supported by the mid-turbine frame <NUM>, service lines pass through the torque box.

In some designs, cooling air for the low pressure turbine is fed into the torque box, and directed from the torque box to the low pressure turbine. In the event that an oil leak from the bearing compartment, or the service lines occurs, oil can leak into the torque box. In systems directing cooling air through the torque box to the low pressure turbine, compounds, such as oil, within the torque box can be directed toward the low pressure turbine along the same flow path as the cooling air.

<FIG> schematically illustrates an isometric view of an exemplary mid-turbine frame <NUM> for a gas turbine engine, such as the gas turbine engine <NUM> of <FIG>. The mid-turbine frame <NUM> includes multiple spokes <NUM> extending radially outwardly from an inner frame case <NUM> and distributed circumferentially about the inner frame case <NUM>. Each of the spokes <NUM> is hollow, and includes a cooling passage <NUM> allowing cooling air to be passed radially inward toward the torque box defined within the inner frame case <NUM>. A radially outward end of each spoke <NUM> includes a flange <NUM>, or other connection feature, for connecting the spoke <NUM> to an engine case and to a cooling air system. In addition to including a cooling passage <NUM> for providing cooling air to the low pressure turbine, each of the spokes <NUM> structurally supports the inner frame case <NUM>. The inner frame case <NUM>, in turn, structurally supports a high spool bearing (not pictured) disposed radially inward of the inner frame case <NUM>. Alternatively, the mid-turbine frame <NUM> can support different bearing systems depending on the structural needs of a given turbine engine including the mid-turbine frame <NUM>.

Also protruding radially outward from the inner frame case <NUM> are multiple service lines <NUM>. Each of the service lines <NUM> includes a connection feature <NUM> at a radially outward end of the service line <NUM>. The connection feature <NUM> can be any known connection feature type and allows the service line <NUM> to be fluidly connected to an oil source radially outward of the primary flow path. In alternative systems, fluids distinct from oil can be passed through one or more of the service lines <NUM>. At the radially outward surface of the inner frame case <NUM>, each service line <NUM> passes through a corresponding service line seal <NUM> into the torque box. The service line <NUM> exits the torque box at a radially inward surface through a corresponding service line seal, and provides the oil to the high spool bearing, or any other system radially inward of the mid-turbine frame <NUM>. The torque box <NUM> is sealed at each opening for the service line <NUM> pass through, and at the radially inner end of each spoke <NUM>.

Further, any additional openings in the torque box <NUM> are sealed using appropriate sealing features. The sealing of the torque box <NUM> in this manner minimizes fluid leakage into the torque box, and minimizes leakage of fluids out of the torque box.

With continued reference to <FIG>, and with like numerals indicating like elements, <FIG> schematically illustrates a cross sectional view of the exemplary mid-turbine frame <NUM> of <FIG> along cross section A-A. Illustrated in <FIG> is a single spoke <NUM> with the cooling passage <NUM> described above. A practical implementation will include multiple approximately identical spokes <NUM> distributed circumferentially about an axis defined by the mid-turbine frame <NUM>. Disposed radially inward of the spoke <NUM>, and defined by the inner frame case <NUM> is a torque box <NUM>. A plug <NUM> blocks the radially inward end <NUM> of the cooling passage <NUM> through the spoke <NUM>. The plug <NUM> completely seals the radially inward opening of the cooling passage <NUM>.

In order to provide coolant to the low pressure turbine section <NUM>, a coolant redirection tube <NUM> protrudes aft from the spoke <NUM> and provides a coolant flow path from the cooling passage <NUM> into the low pressure turbine section <NUM>. By redirecting coolant flowing through the spoke <NUM>, the illustrated mid-turbine frame <NUM> avoids passing coolant through the torque box <NUM> entirely. The torque box <NUM> also includes multiple service line pass throughs and bearing support passages that are out of plane in the cross section of <FIG>. The exemplary bearing support passages are illustrated in <FIG>, and are described below. The joint between the spoke <NUM> and the torque box <NUM> is sealed using any known seal type, thereby preventing fluid transferring into and out of the torque box <NUM>.

With continued reference to <FIG> and <FIG>, and with like numerals indicating like elements, <FIG> schematically illustrates a radial cross sectional view of the exemplary mid-turbine frame <NUM> of <FIG> along cross section B-B. Cross section B-B is drawn radially along a service line <NUM>, and illustrates the torque box <NUM>, and bearing support passage <NUM> surrounded by the torque box <NUM>.

The service line <NUM> includes a connection feature <NUM> including flanges <NUM> and a seal element <NUM>. The connection feature <NUM> of the service line <NUM> connects to the bearing support passage <NUM> within the torque box <NUM>. The service line connection feature <NUM> is sealed to the bearing support passage <NUM> via a seal element <NUM>. The seal element <NUM> in the illustrated example is a piston seal. In alternative examples, any sealing element capable of sealing the service line <NUM> to the bearing support passage <NUM> can be utilized in place of the piston seal. The seal element <NUM> is disposed between an outward facing surface of an extension portion <NUM> of the service line connection feature <NUM> and an inward facing surface of the bearing support passage <NUM>. The extension portion <NUM> extends into the bearing support passage <NUM>. By sealing the interface between the service line <NUM> and the bearing support passage <NUM> in this manner, oil leaks from the service line <NUM> into the torque box <NUM> are minimized.

Disposed radially outward of the service line connection feature <NUM> is an inner frame case seal plate <NUM>. The inner frame case seal plate <NUM> is sealed to the inner frame case via a piston seal <NUM>. In alternative examples, alternative seal types capable of functioning in the mid-turbine frame environment could be utilized in place of the piston seal. The piston seal <NUM> prevents oil, and mid-turbine frame air, from outside of the inner frame case <NUM> from leaking into the torque box <NUM> through the interface between the connection feature <NUM> and the bearing support passage <NUM>. The piston seal <NUM> also prevents any fluids within the torque box <NUM>, from being passed out of the torque box <NUM> into the adjacent portions of the turbine engine.

The bearing support passage <NUM> inside the torque box <NUM> provides oil to a bearing supported by the mid-turbine frame <NUM>. The radially inward openings <NUM>, <NUM> through which the bearing support passage <NUM> passes are similarly sealed at each opening <NUM>, <NUM>, preventing flow into and out of the torque box <NUM> at the radially inward portion of the bearing support passage <NUM>.

As a result of the sealing features described above with regards to <FIG> and <FIG>, the torque box <NUM> is a sealed torque box, and fluids are not communicated into or out of the torque box <NUM>.

With continued reference to <FIG>, the above described configuration provides a configuration that is capable of minimizing the possibility for mid-turbine frame air from entering into the torque box <NUM>. The possibility is further reduced by sealing the torque box from adjacent engine sections, and prevent the exchange of fluids between the torque box and adjacent engine portions including the cooling air flow being directed to the low pressure turbine. One of skill in the art, having the benefit of this disclosure will understand that while an ideal seal prevents all fluid exchange between both sides of the seal, practical seals will have a minimal amount of fluid exchange. Reference herein to minimized transfer of fluids across a seal is in reference to this practical reality.

Claim 1:
A mid-turbine frame (<NUM>) for a gas turbine engine (<NUM>) comprising:
an inner frame case (<NUM>) structurally supporting a bearing or bearing system and defining a sealed torque box (<NUM>), the torque box representing a cavity defined within the inner frame case (<NUM>);
a plurality of spokes (<NUM>) protruding radially outward from the inner frame case (<NUM>), wherein said plurality of spokes (<NUM>) are distributed circumferentially about said inner frame case (<NUM>), a joint between a radially inward end of each of said spokes (<NUM>) and said inner frame case (<NUM>) is sealed such that fluid transfer into said torque box (<NUM>) at said joint is minimized, each of said spokes (<NUM>) comprises a cooling passage (<NUM>) extending from a radially outward end of the spoke (<NUM>) toward said inner frame case (<NUM>), and each of said cooling passages (<NUM>) extends to said inner frame case (<NUM>),
characterized in that:
a radially inward opening between said cooling passage (<NUM>) and said torque box (<NUM>) at said joint between the spoke and the inner frame case is sealed via a plug seal (<NUM>), wherein the plug seal (<NUM>) blocks a radially inward end (<NUM>) of the cooling passage (<NUM>) through the spoke (<NUM>) and completely seals the radially inward opening of the cooling passage (<NUM>); and in that
the mid-turbine frame (<NUM>) further comprises at least one service line (<NUM>) connected to the inner frame case (<NUM>) via a connection feature (<NUM>), the connection feature (<NUM>) interfacing the service line (<NUM>) with a corresponding bearing support passage (<NUM>) in the torque box (<NUM>), wherein the torque box (<NUM>) is sealed at each opening for the service line (<NUM>) passing through the torque box (<NUM>).