Patent Description:
Traditionally, a fan drive turbine has driven the fan directly on a common spool and at a single speed. More recently, a gear reduction has been placed between the fan and the fan drive turbine. This allows the fan to rotate at slower speeds than the fan drive turbine.

<CIT> discloses a prior art turbofan engine as set forth in the preamble of claim <NUM>.

<CIT> discloses a prior art geared gas turbine engine.

<CIT>, which is prior art under Article <NUM> (<NUM>) EPC discloses a fan and low pressure compressor geared to a low speed spool of a gas turbine engine.

In one aspect, there is provided a turbofan engine as recited in claim <NUM>.

The fan section <NUM> drives air along a bypass flow path B in a bypass duct defined within a housing <NUM>, such as a fan case or nacelle, and also drives air along a core flow path C for compression and communication into the combustor section <NUM> then expansion through the turbine section <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>).

<FIG> illustrates an enlarged view of the geared architecture <NUM>. In the illustrated example, the inner shaft <NUM> drives a flexible input shaft <NUM> having a plurality of undulations <NUM>, which contribute to the flexibility of the input shaft <NUM>. The inner shaft <NUM> also drives the low pressure compressor <NUM> at the same rotational speed as the flexible input shaft <NUM> such that the low pressure compressor <NUM> rotates at a higher rotational speed than the fan <NUM>. <FIG> shows a cross-sectional view of <FIG> through geared architecture <NUM>.

The geared architecture <NUM> can include a sun gear <NUM>, a carrier <NUM> supporting star gears <NUM>, and a ring gear <NUM>. The sun gear <NUM> is driven by the flexible input shaft <NUM>. In the illustrated example, the sun gear <NUM> includes a first set of sun gear teeth <NUM> located axially forward of a second set of sun gear teeth <NUM> that are separated by a sun gear trough <NUM>. As shown in <FIG> and <FIG>, multiple star gears <NUM> are circumferentially spaced around the sun gear <NUM> and include a first set of star gear teeth <NUM> located axially forward of a second set of star gear teeth <NUM> that are separated by a star gear trough <NUM>. The first and second set of sun gear teeth <NUM>, <NUM> engage a corresponding one of the first and second set of star gear teeth <NUM>, <NUM>, respectively. In this disclosure, axial or axially and radial or radially is in relation to the engine axis A unless stated otherwise. Additionally, upstream and downstream and forward and aft are in relation to a direction of airflow through the engine <NUM>.

The carrier <NUM> includes a forward plate <NUM> fixed relative to an aft plate <NUM>. Both the forward and aft plates <NUM>, <NUM> are fixed from rotating relative to the engine static structure <NUM> by a carrier support <NUM> engaging the aft carrier plate <NUM> and a portion of the engine static structure <NUM>. The carrier support <NUM> is flexible and includes at least one undulation that contributes to the flexibility of the carrier support <NUM>. In the illustrated example, the forward and aft plates <NUM>, <NUM> support star gear shafts <NUM> that are fixed relative to the forward and aft plates <NUM>, <NUM>. Star gear bearings <NUM> include an inner race <NUM> that is fixed relative to the star gear shafts <NUM> and an outer race <NUM> that is fixed relative to the star gears <NUM> and rotates with the star gears <NUM>. Although the star gear bearings <NUM> are shown as ball bearings, other types of bearings such as roller bearings or journal bearings could be used to support the star gears <NUM>.

The ring gear <NUM> is located radially outward from the star gears <NUM> and includes a forward set of ring gear teeth <NUM> located axially forward of an aft set of ring gear teeth <NUM> that are separated by a ring gear trough <NUM>. The forward and aft sets of ring gear teeth <NUM>, <NUM> engage the forward and aft set of star gear teeth <NUM>, <NUM>, respectively. The ring gear <NUM> also includes a forward extending projection <NUM> that extends axially forward until it reaches a radially extending projection <NUM> that extends radially inward toward a flexible output shaft <NUM>.

In the illustrated example, the flexible output shaft <NUM> includes multiple undulations <NUM> that contribute to the flexibility of the flexible output shaft <NUM> while still allowing the flexible output shaft <NUM> to transmit torque and rotational forces. The fan <NUM> is supported for rotation about the engine axis A by a fan drive shaft <NUM> with fan shaft bearings <NUM> engaging the fan drive shaft <NUM> on a radially inner side and the engine static structure <NUM> on a radially outer side. In the illustrated example, the flexible output shaft <NUM> is located radially inward from the fan drive shaft <NUM> and engages the fan drive shaft <NUM> axially forward of the fan shaft bearings <NUM>. One feature of this configuration is an increased axial length of the flexible output shaft <NUM> to allow for greater flexibility and a more axially compact design of the gas turbine engine <NUM> because the fan drive shaft <NUM> and the flexible output shaft <NUM> overlap axially.

In the illustrated example, a ring gear aft extending bearing flange <NUM> extends axially downstream or aft from the radially extending projection <NUM>. The bearing flange <NUM> includes a radially outer surface <NUM> having a generally constant radial dimension. The bearing flange <NUM> is at least partially axially aligned with a forward extending bearing flange <NUM> extending axially forward from the forward plate <NUM> of the carrier <NUM>. A pair of ring gear carrier bearings <NUM> each include an inner race <NUM> that rotates with the ring gear <NUM> and the flexible output shaft <NUM> and an outer race <NUM> that is fixed relative to the forward plate <NUM> of the carrier <NUM>. In the illustrated example, there are two ring gear carrier bearings <NUM> each engaging one of the bearing flange <NUM> and the bearing flange <NUM> and the bearings <NUM> are ball bearings. However, other types of bearings, such as roller bearings, could be used and more than two ring gear carrier bearings <NUM> could be used or only one ring gear carrier bearing <NUM> could be used in the illustrated location.

Similarly, the aft carrier plate <NUM> includes an aft extending bearing flange <NUM>, the sun gear includes an aft bearing flange <NUM>, and a pair of sun gear carrier bearings <NUM> engaging both the bearing flanges <NUM>, <NUM>. Each of the sun gear carrier bearings <NUM> include an inner race <NUM> fixed to rotate with the sun gear <NUM> and an outer race <NUM> fixed relative to the bearing flange <NUM>. In the illustrated example, the sun gear carrier bearings <NUM> are ball bearings. However, other types of bearings, such as roller bearings, could be used and more than two sun gear carrier bearings <NUM> could be used or only one sun gear carrier bearing <NUM> could be used in the illustrated location.

One feature associated with utilizing at least one of the ring gear carrier bearings <NUM> and at least one of the sun gear carrier bearings <NUM> is the ability to maintain the sun gear <NUM>, the star gears <NUM>, and the ring gear <NUM> aligned and concentric. This reduces stress in the components that can result from misalignment. This arrangement further accomplishes the above feature by maintaining the sun gear <NUM>, the star gears <NUM>, and the ring gear <NUM> in a rigid arrangement through the use of the ring gear carrier bearings <NUM> and sun gear carrier bearings <NUM>. Additionally, the static nature of the geared architecture <NUM> is further accomplished with the carrier <NUM> attached to the engine static structure <NUM> though the rigid carrier support <NUM> as opposed to a flexible support that would allow for greater movement of the geared architecture <NUM>. Additionally, the flexible input shaft <NUM> and the flexible output shaft <NUM> allow forces from the fan <NUM> and inner shaft <NUM> to have little if any influence on alignment of the sun gear <NUM>, star gears <NUM>, and ring gear <NUM>.

<FIG> illustrates another example geared architecture <NUM> similar to the geared architecture <NUM> except where described below or shown in the Figures. Like numbers will be used between similar or identical components between the geared architecture <NUM> and the geared architecture <NUM>.

As shown in <FIG>, the geared architecture <NUM> includes the sun gear carrier bearings <NUM> located on an axially forward or upstream side of the geared architecture <NUM> as opposed to being located on an axially aft or downstream side as shown with the geared architecture <NUM>. When the sun gear carrier bearings <NUM> are located on the axially forward side of the geared architecture <NUM>, the inner race <NUM> rotates with the sun gear <NUM> and engages a sun gear forward bearing flange <NUM>. The forward bearing flange <NUM> extends from an axially forward side of the sun gear <NUM> and includes a bearing contact surface <NUM> on a radially outer side. The outer race <NUM> on the sun gear carrier bearings <NUM> engages a radially inner side of the bearing flange <NUM> such that the outer race <NUM> rotates with the output shaft.

<FIG> illustrates another example geared architecture <NUM> similar to the geared architectures <NUM>, <NUM> except where described below or shown in the Figures. Like numbers will be used between similar or identical components between the geared architectures <NUM>, <NUM> and the geared architecture <NUM>.

As shown in <FIG>, the geared architecture <NUM> incudes one of the sun gear carrier bearings <NUM> located on a forward side similar to the geared architecture <NUM> and one of the sun gear carrier bearings <NUM> located on an aft side similar to the geared architecture <NUM>. Additionally, one of the ring gear carrier bearings <NUM> is also located on the aft side of the geared architecture <NUM> as well as on a forward side of the geared architecture <NUM>. When at least one of the ring gear carrier bearings <NUM> is located on a forward side of the geared architecture <NUM>, it is positioned similar to the ring gear carrier bearing <NUM> shown in the geared architectures <NUM>, <NUM>. However, when one of the ring gear carrier bearings <NUM> is also located on an axially aft side with the geared architecture <NUM>, the at least one of the ring gear carrier bearings <NUM> is located between an aft ring gear projection <NUM> and the aft plate <NUM> of the carrier <NUM>. The aft ring gear projection <NUM> extends axially aft from a downstream side of the ring gear <NUM> and is located radially outward from the first and second sets of ring gear teeth <NUM>, <NUM>. In the illustrated example, the ring gear carrier bearing <NUM> engages a radially outer edge of the aft carrier plate <NUM>. However, the ring gear carrier bearing <NUM> could engage another portion of the aft plate <NUM> on the carrier <NUM>. Additionally, the carrier support <NUM> engages the aft plate <NUM> of the carrier <NUM> radially inward of the ring gear carrier bearing <NUM> in the illustrated example.

Although the different non-limiting examples are illustrated as having specific components, the examples of this disclosure are not limited to those particular combinations.

Claim 1:
A turbofan engine (<NUM>) comprising:
a fan section (<NUM>);
a compressor section (<NUM>) downstream of the fan section (<NUM>); and
a turbine section (<NUM>) in driving engagement with the fan section (<NUM>) through a speed change mechanism (<NUM>; <NUM>; <NUM>), wherein the speed change mechanism (<NUM>; <NUM>; <NUM>) comprises:
a plurality of star gears (<NUM>) surrounding a sun gear (<NUM>);
a carrier (<NUM>) supporting the plurality of star gears (<NUM>) and including a first carrier bearing flange (<NUM>);
a ring gear (<NUM>) surrounding the plurality of star gears (<NUM>) and including a ring gear bearing flange (<NUM>); and
at least one ring gear carrier bearing (<NUM>) engaging the first carrier bearing flange (<NUM>) and the ring gear bearing flange (<NUM>),
characterised in that:
the carrier (<NUM>) is fixed from rotation relative to an engine static structure (<NUM>) by a rigid support (<NUM>); and
the ring gear (<NUM>) is configured to drive the fan section (<NUM>).