Patent Description:
Gears in an epicyclic gear box may rotate on journal bearings. Epicyclic gear systems placed under load may deflect and diminish the performance of gears and bearings. Rigid gear systems may not allow for deflection and thus may suffer reduced performance. At the same time, the journal bearing must be stiff enough to withstand stress in high-torque applications such as gas turbine engines. Additionally, weight in aircraft applications may also be a concern with heavy gear boxes. In that regard, improving weight, compliance, and/or stiffness characteristics of a journal pin may be a tradeoff.

A prior art epicyclic gear system having the features of the preamble to claim <NUM> is disclosed in <CIT>.

Another prior art epicyclic gear system is disclosed in <CIT>.

From one aspect, the present invention provides an epicyclic gear system in accordance with claim <NUM>.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the exemplary embodiments of the disclosure, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this disclosure and the teachings herein. Thus, the detailed description herein is presented for purposes of illustration only and not limitation. The scope of the disclosure is defined by the appended claims. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented.

Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Surface shading lines may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials.

As used herein, "distal" refers to the direction radially outward, or generally, away from the axis of rotation of a gear around a journal pin. As used herein, "proximal" refers to a direction radially inward, or generally, towards the axis of rotation of a gear around a journal pin.

As used herein, "aft" refers to the direction associated with the tail (e.g., the back end) of an aircraft, or generally, to the direction of exhaust of the gas turbine engine. As used herein, "forward" refers to the direction associated with the nose (e.g., the front end) of an aircraft, or generally, to the direction of flight or motion.

In various embodiments and with reference to <FIG>, a gas turbine engine <NUM> is provided. Gas turbine engine <NUM> may be a two-spool turbofan that generally incorporates a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>. Alternative engines may include, for example, an augmentor section among other systems or features. In operation, fan section <NUM> can drive coolant along a bypass flow-path B while compressor section <NUM> can drive coolant along a core flow-path C for compression and communication into combustor section <NUM> then expansion through turbine section <NUM>. Although depicted as a turbofan gas turbine engine <NUM> herein, 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 including three-spool architectures.

Gas turbine engine <NUM> may generally comprise a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine central longitudinal axis A-A' relative to an engine static structure <NUM> via several bearing systems <NUM>, <NUM>-<NUM>, and <NUM>-<NUM>. It should be understood that various bearing systems <NUM> at various locations may alternatively or additionally be provided, including for example, bearing system <NUM>, bearing system <NUM>-<NUM>, and bearing system <NUM>-<NUM>.

Low speed spool <NUM> may generally comprise an inner shaft <NUM> that interconnects a fan <NUM>, a low pressure (or first) compressor section <NUM> and a low pressure (or first) turbine section <NUM>. Inner shaft <NUM> may be connected to fan <NUM> through a geared architecture <NUM> that can drive fan <NUM> at a lower speed than low speed spool <NUM>. Geared architecture <NUM> may comprise a gear assembly <NUM> enclosed within a gear housing <NUM>. Gear assembly <NUM> couples inner shaft <NUM> to a rotating fan structure. High speed spool <NUM> may comprise an outer shaft <NUM> that interconnects a high pressure (or second) compressor <NUM> and high pressure (or second) turbine <NUM>. A combustor <NUM> may be located between high pressure compressor <NUM> and high pressure turbine <NUM>. A mid-turbine frame <NUM> of engine static structure <NUM> may be located generally between high pressure turbine <NUM> and low pressure turbine <NUM>. Mid-turbine frame <NUM> may support one or more bearing systems <NUM> in turbine section <NUM>. Inner shaft <NUM> and outer shaft <NUM> may be concentric and rotate via bearing systems <NUM> about the engine central longitudinal axis A-A', which is collinear with their longitudinal axes. As used herein, a "high pressure" compressor or turbine experiences a higher pressure than a corresponding "low pressure" compressor or turbine.

The core airflow C may be compressed by low pressure compressor section <NUM> then high pressure compressor <NUM>, mixed and burned with fuel in combustor <NUM>, then expanded over high pressure turbine <NUM> and low pressure turbine <NUM>. Mid-turbine frame <NUM> includes airfoils <NUM> which are in the core airflow path. Turbines <NUM>, <NUM> rotationally drive the respective low speed spool <NUM> and high speed spool <NUM> in response to the expansion.

Gas turbine engine <NUM> may be, for example, a high-bypass ratio geared aircraft engine. In various embodiments, the bypass ratio of gas turbine engine <NUM> may be greater than about six (<NUM>:<NUM>). In various embodiments, the bypass ratio of gas turbine engine <NUM> may be greater than ten (<NUM>:<NUM>). In various embodiments, geared architecture <NUM> may be an epicyclic gear train, such as a star gear system (sun gear in meshing engagement with a plurality of star gears supported by a carrier and in meshing engagement with a ring gear) or other gear system. Geared architecture <NUM> may have a gear reduction ratio of greater than about <NUM>:<NUM> and low pressure turbine <NUM> may have a pressure ratio that is greater than about five (<NUM>:<NUM>). In various embodiments, the bypass ratio of gas turbine engine <NUM> is greater than about ten (<NUM>:<NUM>). In various embodiments, the diameter of fan <NUM> may be significantly larger than that of the low pressure compressor section <NUM>, and the low pressure turbine <NUM> may have a pressure ratio that is greater than about five (<NUM>:<NUM>). Low pressure turbine <NUM> pressure ratio may be measured prior to inlet of low pressure turbine <NUM> as related to the pressure at the outlet of low pressure turbine <NUM> prior to an exhaust nozzle. It should be understood, however, that the above parameters are exemplary of various embodiments of a suitable geared architecture engine and that the present disclosure contemplates other turbine engines including direct drive turbofans.

With reference to <FIG>, an epicyclic gear system <NUM>, which is geared architecture <NUM> of <FIG>, is shown. The epicyclic gear system <NUM> comprises an annular gear <NUM>. Annular gear <NUM> has teeth facing radially inward to interface with star gears <NUM>. Star gears <NUM> may be disposed radially inward from annular gear <NUM> and may comprise teeth around an outer diameter of star gears <NUM>. Star gears <NUM> may comprise a journal pin <NUM> central to star gears <NUM>. In that regard, star gear <NUM> may be a journal housing that forms a journal bearing star gear <NUM> rotating relative to journal pin <NUM>. Oil may be delivered through internal bore <NUM> of journal pin <NUM>. The oil may pass through passage <NUM> to form a thin oil film <NUM> between journal pin <NUM> and star gear <NUM>, generally following the circumference of journal pin <NUM>. Star gear <NUM> may rotate about journal pin <NUM> with a thin oil film <NUM> filling a space between journal pin <NUM> and star gear <NUM> to provide lubrication.

In various embodiments, star gears <NUM> may be coupled to carrier <NUM>. Carrier <NUM> is ghosted in <FIG> to provide greater detail of features behind carrier <NUM>. A sun gear <NUM> may be central to epicyclic gear system <NUM>. Sun gear <NUM> may be fixed to shaft <NUM> extending axially from the center of annular gear <NUM> and the center of sun gear <NUM>.

In various embodiments, journal pin <NUM> may be fixed in place relative to a reference point outside the epicyclic gear system (such as an engine) by carrier <NUM>, and both sun gear <NUM> and annular gear <NUM> may rotate. In that regard, shaft <NUM> and annular gear <NUM> may provide an input and output to epicyclic gear system <NUM>. In various embodiments, star gears <NUM> may also move about sun gear <NUM> (star gear <NUM> may be referred to as a planet gear in this configuration) and either annular gear <NUM> or sun gear <NUM> may be fixed in place. In that regard, carrier <NUM> and the unfixed gear of sun gear <NUM> and annular gear <NUM> may provide an input and output to epicyclic gear system <NUM>.

<FIG> illustrates sun gear assembly <NUM> (as illustrated in <FIG>) having a journal pin <NUM> and collar <NUM> with improved compliance, in accordance with various embodiments. Journal pin <NUM> may be symmetric about axis of rotation <NUM>. Journal pin <NUM> is radially inward from star gear <NUM>. Thin oil film <NUM> between star gear <NUM> and journal pin <NUM> provides lubrication for star gear <NUM> to rotate about journal pin <NUM>. Journal pin <NUM> has internal bore <NUM> passing through journal pin <NUM> along axis of rotation <NUM>. Journal pin <NUM> has recessed wall <NUM> of internal bore <NUM> with recessed wall <NUM> having a diameter D1 greater than the diameter D2 at the opening of internal bore <NUM>. Internal bore <NUM> and recessed wall <NUM> may define a volume <NUM> that functions as an oil plenum to deliver oil to thin oil film <NUM> through passage <NUM> (with reference to <FIG>) to an annular volume between the inner diameter of star gear <NUM> and the outer diameter of journal pin <NUM>.

In accordance with the claims, the recessed wall is elliptical to reduce weight and provide increased compliance in response to stress between star gear <NUM> and journal pin <NUM>. Recessed wall <NUM> of journal pin <NUM> may have a diameter D1 approximately <NUM>% or less of the length of the outer diameter D3 of journal pin <NUM> or less. For example, the outer diameter D3 of journal pin <NUM> may be <NUM> inches (<NUM>) and the diameter of recessed wall D1 may be <NUM> inches (<NUM>). Recessed wall has an axial length A1 that is <NUM>% of the axial length A2 of journal pin <NUM> or less. For example, journal pin may have an axial length A2 of <NUM> inches (<NUM>) while the recessed wall has an axial length A1 of <NUM> inches (<NUM>). Journal pin <NUM> may include undercut <NUM> to increase compliance. Undercut <NUM> may be radially inward from an outer diameter of journal pin <NUM> and radially outward from internal bore of journal pin <NUM>. Undercut <NUM> may be defined by wings <NUM> of journal pin <NUM> overhanging a portion of internal bore <NUM>.

Collar <NUM> extends around journal pin <NUM>. Collar <NUM> may be welded to journal pin <NUM>. Carrier <NUM> is press fit onto collar <NUM> and thereby coupled to journal pin <NUM>. Carrier <NUM> may also be coupled to a fixed point, such as a gearbox housing. In that regard, carrier <NUM> may fix journal pin <NUM> in place relative to the fixed point. Collar <NUM> may be configured to retain journal pin <NUM> within star gear <NUM> (functioning as a bearing housing). Collar <NUM> includes recessed wall <NUM> defining cutout <NUM>. Cutout <NUM> may be radial, multi-radial, rectangular, elliptical, linear, or other shape to reduce weight and provide increased compliance. Star gear <NUM> applies torque to journal pin <NUM> while rotating about journal pin <NUM>. The force may tend to twist or deflect journal pin <NUM>. Recessed wall <NUM> of journal pin <NUM> may have a balance of moment stiffness to resist the force of star gear <NUM> and compliance to improve performance of epicyclic gear system <NUM>. Adding compliance to the system allows for deflection with reduced impact on performance, especially if the flexibility of compliant design features is sufficiently less than the journal film or gear mesh stiffness.

In various embodiments, journal pin <NUM> may be made from metal materials such as steel. Internal bore <NUM> may be drilled through journal pin <NUM>. Internal bore <NUM> may provide access for a machining tool to remove metal from internal bore <NUM> of journal pin <NUM> and create recessed wall <NUM>. Journal pin <NUM> may also be additively manufactured or cast to form internal bore <NUM> and recessed wall <NUM>.

Claim 1:
An epicyclic gear system (<NUM>), comprising:
an annular gear (<NUM>) centered about an axis;
a star gear (<NUM>) radially inward from the annular gear (<NUM>);
a journal pin (<NUM>) inside the star gear (<NUM>) and comprising an internal bore (<NUM>) with a first recessed wall (<NUM>) passing through the journal pin (<NUM>) along an axis of rotation (<NUM>);
a sun gear (<NUM>) radially inward from the star gear (<NUM>);
a collar (<NUM>) coupled to the journal pin (<NUM>); and
a carrier (<NUM>) press fit onto the collar (<NUM>),
wherein the first recessed wall (<NUM>) of the internal bore (<NUM>) has a diameter (D<NUM>) greater than a diameter (D<NUM>) at an opening of the internal bore (<NUM>), and characterised in that:
the collar (<NUM>) comprises a second recessed wall (<NUM>) defining a cutout (<NUM>); and
the first recessed wall (<NUM>) has an elliptical shape, wherein an axial length (A1) of the first recessed wall (<NUM>) is <NUM>% or less of an axial length (A2) of the journal pin (<NUM>).