Patent Description:
A gas turbine engine typically includes 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 the compressor and a ground-based generator for industrial gas turbine engine applications. The compressor and turbine sections include a plurality of rotating blades and vanes spaced between the rows of blades. The vanes serve to direct and control the flow of air through the rows of blades.

One type of vane is a variable vane. In a variable vane, a vane pivots relative to a radial axis taken from a central axis of the engine. An actuator rotates a first side of the vane to pivot and a second opposed side of the vane is supported for rotation in a shroud. Typically, the actuator is at a radially outer location. In the event of a variable inlet vane failure, the rotated and supported sides of the vane may become disconnected from one another. The supported side of the vane may become liberated from the shroud and may be ingested by the rotating fan or other downstream rotating engine components. The supported side of the vane may include a retention feature to allow it to be retained in the shroud.

The supported side of the vane generally includes a bushing to facilitate rotation in the shroud. In some current designs, the bushing may be split to allow for the incorporation of a retention feature, reducing the contact area between the bushing and the supported side of the vane and the shroud. Additionally, material selection for bushings is typically limited due to the high-wear conditions in which they operate and the necessity for material matching with the supported side of the vane.

<CIT> discloses a bushing for a variable-pitch vane pivot in a turbomachine.

A further example of prior art is given by the patent documentation <CIT>.

According to the invention, a variable vane assembly includes a variable vane, a trunnion arranged on one end of the variable vane, an inner bushing mated to the trunnion, an outer bushing configured to rotatably receive the inner bushing and a retention feature configured to retain the trunnion with respect to the outer bushing and to mate the inner bushing to the outer bushing by preventing axial movement of the inner bushing in a direction towards the variable vane.

In a further embodiment of the foregoing embodiments, the retention feature is a flange formed on the inner bushing.

In a further embodiment of any of the foregoing embodiments, the flange is configured to abut an end of the outer bushing and prevent axial movement of the inner flange and the trunnion with respect to the outer bushing.

In a further embodiment of any of the foregoing embodiments, the outer bushing includes an anti-rotation feature.

In a further embodiment of any of the foregoing embodiments, the anti-rotation feature is at least one protrusion extending radially from an outer surface of the outer bushing.

In a further embodiment of any of the foregoing embodiments, the outer bushing includes at least one outer bushing flange.

In a further embodiment of any of the foregoing embodiments, the anti-rotation feature is at least one flat edge formed in the at least one outer bushing flange.

In a further embodiment of any of the foregoing embodiments, at least one of the inner and outer bushings are metallic.

In a further embodiment of any of the foregoing embodiments, the inner and outer bushings are made from the same material.

In a further embodiment of any of the foregoing embodiments, the inner bushing is mated to the trunnion in a press fit relationship.

In another exemplary embodiment, a gas turbine engine includes a shroud having a recesses, a variable vane including first and second trunnions at first and second ends of the variable vane, respectively, an inner bushing configured to receive the first trunnion in a press fit relationship, an outer bushing configured to rotatably receive the inner bushing, the outer bushing arranged in the recess, a retention feature configured to retain the first trunnion axially with respect to the outer bushing, and an actuator configured to rotate the variable vane via the second trunnion.

In a further embodiment of any of the foregoing embodiments, the retention feature is a flange formed on the inner bushing.

In a further embodiment of any of the foregoing embodiments, the shroud is configured to mate with the anti-rotation feature.

In a further embodiment of any of the foregoing embodiments, the first trunnion is radially inwards from the second trunnion with respect to a central axis of the gas turbine engine.

In another exemplary embodiment, a method of assembling a variable vane assembly includes installing a trunnion of a variable vane into an inner bushing in a press fit relationship, installing the inner bushing into an outer bushing to create a bushing assembly, and retaining the trunnion in the bushing assembly via a retention feature on the inner bushing.

In a further embodiment of any of the foregoing embodiments, the method further includes the step of installing the bushing assembly into a shroud.

In another embodiment of any of the forgoing embodiments, the method further includes the step of rotating the variable vane with respect to the shroud.

In another embodiment of any of the forgoing embodiments, the method includes the step of preventing rotation of the outer bushing relative to the shroud via an anti-rotation feature.

<FIG> schematically illustrates an example gas turbine engine <NUM> that includes a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>. Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section <NUM> drives air along a bypass flow path B while the compressor section <NUM> draws air in along a core flow path C where air is compressed and communicated to a combustor section <NUM>. In the combustor section <NUM>, air is mixed with fuel and ignited to generate a high pressure exhaust gas stream that expands through the turbine section <NUM> where energy is extracted and utilized to drive the fan section <NUM> and the compressor section <NUM>.

Although the disclosed non-limiting embodiment depicts a turbofan gas turbine engine, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines; for example a turbine engine including a three-spool architecture in which three spools concentrically rotate about a common axis and where a low spool enables a low pressure turbine to drive a fan via a gearbox, an intermediate spool that enables an intermediate pressure turbine to drive a first compressor of the compressor section, and a high spool that enables a high pressure turbine to drive a high pressure compressor of the compressor section.

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 X relative to an engine static structure <NUM> via several bearing systems <NUM>. It should be understood that various bearing systems <NUM> at various locations may alternatively or additionally be provided.

The low speed spool <NUM> generally includes an inner shaft <NUM> that connects a fan <NUM> and a low pressure (or first) compressor section <NUM> to a low pressure (or first) turbine section <NUM>. The inner shaft <NUM> drives the fan <NUM> through a speed change device, such as a geared architecture <NUM>, to drive the fan <NUM> at a lower speed than the low speed spool <NUM>. The high-speed spool <NUM> includes an outer shaft <NUM> that interconnects a high pressure (or second) compressor section <NUM> and a high pressure (or second) turbine section <NUM>. The inner shaft <NUM> and the outer shaft <NUM> are concentric and rotate via the bearing systems <NUM> about the engine central longitudinal axis X.

A combustor <NUM> is arranged between the high pressure compressor <NUM> and the high pressure turbine <NUM>. In one example, the high pressure turbine <NUM> includes at least two stages to provide a double stage high pressure turbine <NUM>. In another example, the high pressure turbine <NUM> includes only a single stage. As used herein, a "high pressure" compressor or turbine experiences a higher pressure than a corresponding "low pressure" compressor or turbine.

The example low pressure turbine <NUM> has a pressure ratio that is greater than about five (<NUM>). The pressure ratio of the example low pressure turbine <NUM> is measured prior to an inlet of the low pressure turbine <NUM> as related to the pressure measured at the outlet of the low pressure turbine <NUM> prior to an exhaust nozzle.

The mid-turbine frame <NUM> further supports bearing systems <NUM> in the turbine section <NUM> as well as setting airflow entering the low pressure turbine <NUM>.

The core airflow C is compressed by the low pressure compressor <NUM> then by the high pressure compressor <NUM> mixed with fuel and ignited in the combustor <NUM> to produce high speed exhaust gases that are then expanded through the high pressure turbine <NUM> and low pressure turbine <NUM>. The mid-turbine frame <NUM> includes vanes <NUM>, which are in the core airflow path and function as an inlet guide vane for the low pressure turbine <NUM>. Utilizing the vane <NUM> of the mid-turbine frame <NUM> as the inlet guide vane for low pressure turbine <NUM> decreases the length of the low pressure turbine <NUM> without increasing the axial length of the mid-turbine frame <NUM>. Reducing or eliminating the number of vanes in the low pressure turbine <NUM> shortens the axial length of the turbine section <NUM>. Thus, the compactness of the gas turbine engine <NUM> is increased and a higher power density may be achieved.

The disclosed gas turbine engine <NUM> in one example is a high-bypass geared aircraft engine. In a further example, the gas turbine engine <NUM> includes a bypass ratio greater than about six (<NUM>), with an example embodiment being greater than about ten (<NUM>). The example geared architecture <NUM> is an epicyclical gear train, such as a planetary gear system, star gear system or other known gear system, with a gear reduction ratio of greater than about <NUM>.

In one disclosed embodiment, the gas turbine engine <NUM> includes a bypass ratio greater than about ten (<NUM>:<NUM>) and the fan diameter is significantly larger than an outer diameter of the low pressure compressor <NUM>. It should be understood, however, that the above parameters are only exemplary of one embodiment of a gas turbine engine including a geared architecture and that the present disclosure is applicable to other gas turbine engines.

The fan section <NUM> of the engine <NUM> is designed for a particular flight condition -- typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>,<NUM>). The flight condition of <NUM> Mach and <NUM>,<NUM> ft. , with the engine at its best fuel consumption - also known as "bucket cruise Thrust Specific Fuel Consumption ('TSFC')" - is the industry standard parameter of pound-mass (lbm) of fuel per hour being burned divided by pound-force (lbf) of thrust the engine produces at that minimum point.

In another non-limiting embodiment the low fan pressure ratio is less than about <NUM>.

"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 °R = K x <NUM>/<NUM>). The "Low corrected fan tip speed", as disclosed herein according to one non-limiting embodiment, is less than about <NUM> ft/second (<NUM>/s).

Referring to <FIG>, an example variable vane assembly <NUM> is shown. A variable vane <NUM> includes first and second trunnions <NUM>, <NUM> and an airfoil <NUM>. The first trunnion <NUM> is arranged in a recess <NUM> in a shroud <NUM>. The shroud <NUM> may be circumferentially split into first and second halves <NUM>, <NUM>. In one example, the first trunnion <NUM> is located on a radially inner side of the variable vane <NUM> with respect to the engine axis X, and the second trunnion <NUM> is located on a radially outer side of the variable vane <NUM>. The second trunnion <NUM> may be actuated by an actuator <NUM>. The actuator <NUM> causes the vane to pivot about an axis T of the trunnion <NUM>. In another example, the first trunnion <NUM> may be connected to the actuator <NUM> and the second trunnion <NUM> may be supported in the shroud.

The trunnion <NUM> is arranged in an inner bushing <NUM>. The inner bushing <NUM> includes a retention feature. The retention feature may be a flange <NUM>. In this example, the trunnion <NUM> and the inner bushing <NUM> are mated in a press fit relationship. However, in another example, the trunnion <NUM> may be mated to the inner bushing <NUM> in another fashion. The inner bushing <NUM> is arranged in an outer bushing <NUM>. The outer bushing is received in the recess <NUM>.

<FIG> shows the inner and outer bushings <NUM>, <NUM> which together form a bushing assembly <NUM>. The flange <NUM> mates the inner bushing <NUM> to the outer bushing <NUM> by preventing axial movement of the inner bushing <NUM> away from the engine axis X. In one example, the vane <NUM> may be installed in the bushing assembly <NUM>. Then, the bushing assembly <NUM> may be installed into the shroud <NUM>. The inner bushing <NUM> is retained in the outer bushing <NUM> by the flange <NUM>. The press fit relationship between the trunnion <NUM> and the inner bushing <NUM> (<FIG>) retains the vane <NUM> in the inner bushing <NUM>. This arrangement serves to retain the vane <NUM> in the bushing assembly <NUM> and the shroud <NUM> via the inner and outer bushings <NUM>, <NUM>.

The outer bushing <NUM> includes one or more anti-rotation features. The anti-rotation features may be protrusions <NUM> which extend radially outward from an outer surface of the outer bushing <NUM>. Referring to <FIG>, the protrusions <NUM> are received in a slot <NUM> in the first half <NUM> of the shroud <NUM>, preventing the outer bushing <NUM> from rotating about the trunnion axis T (<FIG>).

Because the primary wear takes place between the inner and outer bushings <NUM>, <NUM>, a variety of materials can be matched to provide the desired wear characteristics. In one example, both the inner and outer bushings <NUM>, <NUM> may be metallic. For example, the metal may be a steel or steel alloy, a nickel-chromium alloy such as Inconel <NUM> or Inconel <NUM>, or a cobalt-chromium alloy such as Haynes <NUM>. The inner and outer bushings <NUM>, <NUM> may be made of the same or different materials, and may have coatings or surface treatments.

<FIG> show an alternate bushing <NUM> and shroud <NUM>. In this example, the outer bushing <NUM> includes first and second outer bushing flanges 219a, 219b. The first and second outer bushing flanges are on the radially inner and outer ends of the outer bushing <NUM> with respect to the engine axis X, respectively. The outer flange 219b is retained in the shroud <NUM> by shoulders <NUM>, preventing radial movement of the outer bushing <NUM> towards the engine axis X. Similarly, the inner flange 219a is retained by shoulders <NUM>, preventing radial movement of the outer flange away from the engine axis X. The inner bushing <NUM> is received inside the outer bushing <NUM>. The flange <NUM> on the inner bushing <NUM> is also retained by the shoulders <NUM>, and is disposed radially inward from the inner outer bushing flange 219a with respect to the engine axis X.

The flanges 219a, 219b may include at least one flat edge <NUM> which serves as an anti-rotation feature. In the example shown, the outer bushing flanges 219a, 219b each include two flat edges <NUM> spaced circumferentially opposite from one another. Referring to <FIG>, the flat edges <NUM> of the inner flanges 219a abut first and second axial lips 234a, 234b formed in the shroud <NUM>, preventing the outer bushing <NUM> from rotating along the trunnion axis T.

Similar to the previous example, the trunnion <NUM> and the inner bushing <NUM> are mated in a press fit relationship, retaining the trunnion <NUM> in the inner bushing <NUM>. The inner bushing <NUM> is retained in the outer bushing <NUM> by the inner bushing flange <NUM>. The outer bushing <NUM> is retained in the shroud <NUM> by the inner and outer flanges 219a, 219b.

Claim 1:
A variable vane assembly (<NUM>), comprising:
a variable vane (<NUM>);
a trunnion (<NUM>) arranged on one end of the variable vane (<NUM>);
an inner bushing (<NUM>) mated to the trunnion (<NUM>); and
an outer bushing (<NUM>; <NUM>) configured to rotatably receive the inner bushing (<NUM>),
characterized by:
a retention feature configured to retain the trunnion (<NUM>) with respect to the outer bushing (<NUM>; <NUM>); and
the retention feature is configured to mate the inner bushing (<NUM>) to the outer bushing (<NUM>; <NUM>) by preventing axial movement of the inner bushing (<NUM>) in a direction towards the variable vane.