Patent Description:
Gas turbine engines, such as those that power modern commercial and military aircraft, generally include a compressor section to pressurize an airflow, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases.

Some gas turbine engines include variable stator vanes that can be pivoted about their individual axes to change an operational performance characteristic of the engine. Typically, the variable stator vanes are robustly designed to handle the stress loads that are applied to change the position of the vanes. A mechanical linkage is typically utilized to rotate the variable stator vanes. Because forces on the variable stator vanes can be relatively significant, forces transmitted through the mechanical linkage can also be relatively significant. Variable vanes are mounted about a pivot and are attached to an arm that is in turn actuated to adjust each of the vanes of a stage. A specific orientation between the arm and vane is required to assure that each vane in a stage is adjusted as desired to provide the desired engine operation. Newer compressor designs have resulted in higher compression ratios and loads. Further, recent designs have more vanes distributed through roughly the same space, resulting in decreased size, especially decreased diameter, of the vane stems. The point of connection of vane arms to vane stems is also subjected to even larger forces, especially torques, during surge load operation.

Sheet metal design of vane arms are used in legacy engines and are low cost but are limited in terms of grip strength to the vane stem. Current and future compressors tend to be of higher pressure ratio, generating higher loads which are limiting to the sheet metal design of a vane arm. Connection of a vane arm to a vane stem is typically made with a claw having arms which contact flat surfaces of the vane stem. However, with such a structure, as loads increase, force is applied to arms of the claw which can tend to pry open the claw.

<CIT> discloses a vane arm connection system for a gas turbine engine.

<CIT> discloses a scalable high pressure compressor variable vane actuation arm, and <CIT> discloses variable stator vane actuating levers.

According to an aspect of the present invention, a vane arm connection system for a gas turbine engine is provided in accordance with claim <NUM>. According to another aspect a method for retrofitting a vane arm for a gas turbine engine, according to claim <NUM> is provided. Various embodiments of the invention are provided by the dependent claims.

A detailed description of non-limiting embodiments of the disclosure follows, with reference to the attached drawings, wherein:.

The gas turbine engine <NUM> is disclosed herein as a two-spool geared turbofan (GTF) that generally incorporates a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>. Alternative engine architectures might include various other sections, systems or features which are not illustrated herein. The fan section <NUM> drives air along a bypass flowpath while the compressor section <NUM> drives air along a core flowpath for compression and communication into the combustor section <NUM>, and then expansion through the turbine section <NUM>. Although depicted as a GTF in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with a GTF as the teachings may be applied to other types of turbine engines such as a direct drive turbofan with high or low bypass turbofan, turbojets, turboshafts, and three spool (plus fan) turbofans wherein an intermediate spool includes an intermediate pressure compressor (IPC) between a low pressure compressor (LPC) and a high pressure compressor (HPC), and an intermediate pressure turbine (IPT) between the high pressure turbine (HPT) and the low pressure turbine (LPT).

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.

In one example, the gas turbine engine <NUM> is a high-bypass geared aircraft engine with a bypass ratio greater than about six (<NUM>:<NUM>). The geared architecture <NUM> can include an epicyclic gear train, such as a planetary gear system or other gear system. The example epicyclic gear train has a gear reduction ratio of greater than about <NUM>:<NUM>, and in another example is greater than about <NUM>:<NUM>. The geared turbofan enables operation of the low spool <NUM> at higher speeds which can increase the operational efficiency of the LPC <NUM> and LPT <NUM> to render increased pressure in relatively few stages.

A pressure ratio associated with the LPT <NUM> is pressure measured prior to the inlet of the LPT <NUM> as related to the pressure at the outlet of the LPT <NUM> prior to an exhaust nozzle of the gas turbine engine <NUM>. In one non-limiting embodiment, the bypass ratio of the gas turbine engine <NUM> is greater than about ten (<NUM>:<NUM>), the fan diameter is significantly larger than that of the LPC <NUM>, and the LPT <NUM> has a pressure ratio that is greater than about five (<NUM>:<NUM>). It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans, where the rotational speed of the fan <NUM> is the same (<NUM>:<NUM>) of the LPC <NUM>.

In one example, a significant amount of thrust is provided by the bypass flow path due to the high bypass ratio. The fan section <NUM> of the gas turbine engine <NUM> is designed for a particular flight condition - typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>,<NUM> meters). This flight condition, with the gas turbine engine <NUM> at its best fuel consumption, is also known as bucket cruise thrust specific fuel consumption (TSFC). TSFC is an industry standard parameter of fuel consumption per unit of thrust.

Fan pressure ratio is the pressure ratio across a blade of the fan section <NUM> without the use of a fan exit guide vane system. The relatively low fan pressure ratio according to one example of a gas turbine engine <NUM> is less than <NUM>. Low corrected fan tip speed is the actual fan tip speed divided by an industry standard temperature correction of ("T" / <NUM>)<NUM> in which "T" represents the ambient temperature in degrees Rankine. The low corrected fan tip speed according to one example of a gas turbine engine <NUM> is less than about <NUM> fps (<NUM>/s).

With reference to <FIG>, one or more stages of the LPC <NUM> and/or the HPC <NUM> include a variable vane system <NUM> that can be rotated to change an operational performance characteristic of the gas turbine engine <NUM> for different operating conditions. The variable vane system <NUM> may include one or more variable vane stages.

The variable vane system <NUM> may include a plurality of variable stator vanes <NUM> (see also <FIG>) circumferentially arranged around the engine central axis A. The variable stator vanes <NUM> each include a variable vane body that has an airfoil portion such that one side of the airfoil portion generally operates as a suction side and the opposing side of the airfoil portion generally operates as a pressure side. Each of the variable stator vanes <NUM> generally spans between an inner diameter and an outer diameter relative to the engine central axis A.

Each of the variable stator vanes <NUM> includes an inner trunnion <NUM> that is receivable into a corresponding socket and an outer trunnion <NUM> mounted through an outer engine case <NUM> such that each of the variable stator vanes <NUM> can pivot about a vane axis T (shown in <FIG>).

The variable vane system <NUM> further includes a synchronizing ring assembly <NUM> to which, in one disclosed non-limiting embodiment, each of the outer trunnions <NUM> are attached through a vane arm <NUM> connected to ring assembly <NUM> for example with a fastener extending along a respective axis D. It should be appreciated that although a particular vane arm <NUM> is disclosed in this embodiment, various linkages of various geometries may be utilized.

The variable vane system <NUM> is driven by an actuator system <NUM> with an actuator <NUM>, a drive <NUM> and an actuator arm <NUM> (also shown in <FIG>). Although particular components are separately described, it should be appreciated that alternative or additional components may be provided.

With reference to <FIG>, the vane arm <NUM> links each outer trunnion <NUM> to the synchronizing ring assembly <NUM>. Rotation of the synchronizing ring assembly <NUM> about the engine axis A (<FIG>) drives the vane arm <NUM> to rotate the outer trunnion <NUM> of each of the variable stator vanes <NUM>.

Each vane arm <NUM> interfaces with the synchronizing ring assembly <NUM> via a pin <NUM>. The pin <NUM> is swaged to an end section <NUM> of the vane arm <NUM> within an aperture <NUM>. Of course, other connections between vane arm <NUM> and ring <NUM> could be utilized.

<FIG> shows that vane arms <NUM> engage with vane stems <NUM>. This point of engaging is subject to potentially significant torque during operation of the engine and also the system to position the vanes as desired. Under surge loads, this torque is increased even further.

<FIG> illustrate engagement of a known vane arm and claw structure with a vane stem. As shown, vane stem <NUM> can have a base <NUM> which extends to other systems of the engine, for example to vanes which are to be positioned around axis T as discussed above. Extending from base <NUM> is a head <NUM> which defines two oppositely facing flat contact surfaces <NUM>. A typical vane stem <NUM> then also has a round portion <NUM> extending upwardly from the head <NUM>, and the vane arm can be secured to the vane stem with a nut <NUM> which can, for example, be threaded to the round portion <NUM>. Alternatively, this connection can be by way of a threaded opening in the vane stem, and a bolt threaded into the opening. This type of connection is illustrated in <FIG> discussed below.

Also as illustrated, a vane arm typically has a claw structure <NUM> (see also <FIG>) to securely engage the vane stem. Claw structure <NUM> has a central portion <NUM> which has an opening <NUM> for receiving round portion <NUM> of vane stem <NUM>. Claw arms <NUM> extend from central portion <NUM> and typically curve downwardly to define spaced, inwardly directed surfaces <NUM> which engage with flat contact surfaces <NUM> of head <NUM>. In this way, claw structure <NUM> is engaged with vane stem <NUM>. As set forth above, however, current and planned designs of gas turbine engines involve use of more vanes and therefor more vane stems, which results in the need for smaller diameter vane stems. This, in turn, results in smaller flat contact surfaces <NUM> to be engaged by inwardly directed surfaces <NUM>, and therefore an increased chance that inwardly directed surfaces <NUM> will deflect or spread relative to flat surfaces <NUM>, particularly under surge load conditions wherein the torque (see arrow X, <FIG>) is significantly increased.

Referring to <FIG>, a torque transfer member or plate <NUM> is illustrated. Torque transfer plate <NUM> in this configuration is a substantially flat member having a body portion <NUM> defining an opening <NUM>, and having at least one arm <NUM>, in this configuration two arms <NUM>, that serve to contact a claw of a vane arm and transfer some of the force due to torque that would otherwise tend to pry open the claw arms. Force is transferred to a different part of the claw where there is significantly more stiffness, such that connection of vane arm <NUM> to vane stem <NUM> is more able to withstand surge loads without prying open the claw. Thus, torque capacity before yield is increased.

<FIG> illustrate a torque transfer plate <NUM> in position in a vane arm connection system, mounted to a vane stem <NUM> within a claw <NUM> of a vane arm <NUM>. As shown, opening <NUM> engages flat contact surfaces <NUM> of head <NUM> such that torque transfer plate <NUM> is non-rotatably mounted to the vane stem <NUM>. In addition, arms <NUM> extend outside of claw <NUM> and engage with a surface of claw <NUM> that is not the opposing surfaces <NUM>, such that the engagement of torque transfer plate <NUM> with claw <NUM> does not create forces that tend to pry the claw arms open. Rather, force is transferred from where it would normally occur, illustrated by arrow A in <FIG>, to engage on an edge surface <NUM> of claw <NUM> where the claw can accept the force in a direction indicated by arrow B in <FIG>, without being pried open. In the configuration illustrated, the force is transferred <NUM> degrees around claw <NUM>.

Referring back to <FIG>, further details of this configuration of torque transfer plate <NUM> are discussed. In this non-limiting configuration, body <NUM> has a width W sized to fit between claw arms <NUM> of claw <NUM> (illustrated in <FIG> discussed below). Within the body <NUM>, opening <NUM> is defined having two spaced surfaces <NUM> which can be spaced to engage with flat contact surfaces <NUM> of head <NUM>. This can be a press fit, or a fit designed to be snug with little or no lateral play.

Opening <NUM> also has a length L which is configured to accept the flat contact surfaces <NUM> of head <NUM> as best shown in <FIG>. This length dimension can be snug or can have some play. In addition, it should be noted that other configurations of this portion of the opening are possible, for example where only one end surface <NUM> of the opening that is opposite to arms <NUM> is utilized, and the other end of the opening can be open. End surface <NUM> serves to hold torque transfer plate <NUM> in place when mounted within a claw <NUM> on head <NUM>. End surface <NUM> prevents plate <NUM> from sliding out in the direction toward arms <NUM>, while arms <NUM> engage against claw <NUM> and prevent plate <NUM> from sliding out in the other direction. Thus, the portion of body <NUM> indicated at <NUM> could alternatively be open, for example to save material and weight.

<FIG> illustrates plate <NUM> formed from stamped sheet metal such that body <NUM> and arms <NUM> are a single integral piece part. While this is beneficial from a simplicity and ease of manufacturing standpoint, other configurations are possible. For example, plate <NUM> could be made from composite or sintered metal, and could be additively manufactured, or machined instead of stamped from sheet metal, or could generally be fabricated by any known method. However, sheet metal stamping is one particularly cost-effective method for high volume production.

<FIG> shows a top view of plate <NUM> mounted within claw <NUM> on head <NUM> of vane stem <NUM>. As shown, body <NUM> is sized to fit within arms <NUM> of claw <NUM>. Arms <NUM> extend outside of claw <NUM> to a dimension wider than the space between arms <NUM> and, in this non-limiting configuration, engage against a distal edge surface <NUM> of claw <NUM>. As set forth above, this serves to transfer force of engagement between flat contact surfaces <NUM> of head <NUM> and claw <NUM> from a prying force applied to inner surfaces <NUM> of arms <NUM>, through plate <NUM> to distal edge surface <NUM> where the force is not structurally detrimental to the claw. As shown, engagement of contact surfaces <NUM> of head <NUM> with both claw <NUM> and plate <NUM> is along flat surfaces in one plane X, but engagement between plate <NUM> and claw <NUM> is along flat surfaces in another plane Y that is turned approximately <NUM> degrees, or is substantially perpendicular, to plane X. Thus, force due to a torque load as illustrated by arrow Z can be at least partially transferred from plane X to plane Y, where it will not tend to pry open claw arms <NUM>.

It should be appreciated that although plate <NUM> is shown in <FIG> with arms <NUM> engaging distal edge surface <NUM> of claw <NUM>, in some configurations (not illustrated), plate <NUM> could be assembled in the reverse position such that arms <NUM> engage against a proximal edge surface <NUM> of claw <NUM>, with substantially the same result. In either position, arms <NUM> have claw contact surfaces <NUM> that contact either distal edge surface <NUM> or proximal edge surface <NUM> of claw <NUM>. Also, while <FIG> illustrate one non-limiting configuration wherein arms <NUM> engage distal or proximal edge surfaces of the claw, other configurations are possible, with arms <NUM> engaging against other portions of claw <NUM>, so long as the contact is not with opposed surfaces <NUM> or otherwise within arms <NUM> and outwardly directed so as to pry arms <NUM> apart.

Arms <NUM> extend at least as wide as arms <NUM> so that the transferred force can be transferred to as much area as possible, thereby also potentially reducing localized stress caused by such force, in addition to transferring such force away from plane X.

In <FIG>, a configuration of vane stem is shown wherein a threaded portion <NUM> is mounted to the vane stem, and a nut <NUM> is threaded onto this threaded portion to complete assembly. <FIG> illustrate an alternative configuration wherein a bolt <NUM> is threaded into a threaded opening (not illustrated) of the vane stem. Either of these configurations serves to secure claw <NUM> and plate <NUM> in place on head <NUM>.

Referring back to <FIG> and <FIG>, plate <NUM> can have a cutout <NUM> positioned between arms <NUM>. Cutout <NUM> accepts an anti rotation tab of the claw and helps to hold all components in place during assembly. Cutout <NUM> also serves to conserve material and reduce weight.

It should be appreciated that both new and existing systems can benefit from plate <NUM> as disclosed herein. Retrofitting plate <NUM> to systems having only claw <NUM> mounted to head <NUM> is possible. Plate <NUM> can be implemented in such systems by positioning plate <NUM> within claw <NUM>, with body <NUM> below the upper body of the claw and between the claw arms and arms <NUM> extending laterally outside of claw <NUM>. Then opening <NUM> and arms <NUM> can be positioned on head <NUM> to engage flat contact surfaces <NUM> of head <NUM>. Then these components can be secured in place with bolt <NUM> or nut <NUM> depending upon the configuration in use.

Surfaces of claw <NUM> have been referred to herein as distal and proximal, and these terms should be considered when viewed from the non-claw end of the vane arm. Thus, from the non-claw end of the vane arm, distal edge surface <NUM> would be the furthest away edge of claw <NUM>, while proximal edge surface <NUM> would be the closer edge surface of claw <NUM>.

Claim 1:
A vane arm connection system for a gas turbine engine (<NUM>), comprising:
a vane stem (<NUM>) having a head (<NUM>) with flat contact surfaces (<NUM>);
a vane arm (<NUM>) having a claw (<NUM>), the claw (<NUM>) comprising opposed arms (<NUM>) having inwardly facing surfaces (<NUM>) engaging the flat contact surfaces (<NUM>) of the head (<NUM>); and
a torque transfer member (<NUM>) having a body (<NUM>) defining an opening (<NUM>) for engaging the flat contact surfaces (<NUM>) of the head (<NUM>) of the vane stem (<NUM>), and at least one arm (<NUM>) extending from the body (<NUM>) to contact the claw (<NUM>), wherein the engagement between the flat contact surfaces (<NUM>) and the opening (<NUM>) transfers load from torque away from the inwardly facing surfaces (<NUM>),
wherein the opposed arms (<NUM>) of the claw (<NUM>) have proximal (<NUM>) and distal (<NUM>) surfaces, facing toward and away from the vane arm, and characterized in that, at least one arm (<NUM>) of the torque transfer member (<NUM>) extends from the torque transfer member (<NUM>) to contact at least one of the proximal (<NUM>) and distal (<NUM>) surfaces,
wherein the claw (<NUM>) has an upper body (<NUM>) defining an opening (<NUM>) for securing to the vane stem (<NUM>) and two claw arms (<NUM>) extending downwardly from the upper body (<NUM>) and engaging the flat contact surfaces (<NUM>) of the head (<NUM>), wherein the torque transfer member (<NUM>) is positioned below the upper body (<NUM>) of the claw (<NUM>), and within the claw arms (<NUM>), and wherein the at least one arm (<NUM>) of the torque transfer member (<NUM>) extends outside of the claw arms (<NUM>) to contact the at least one of the proximal (<NUM>) and distal (<NUM>) surfaces.