Patent Description:
Gas turbine engines are known and typically include a fan delivering air into a bypass duct as propulsion and into a compressor as core airflow. The air is compressed in the compressor and delivered into a combustion section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors driving them to rotate.

Historically, the fan rotor rotated as one with the fan drive turbine. This resulted in compromise in the design as it may be desirable to have the turbine rotate at a higher speed than the fan.

Thus, it has been proposed to include a gear reduction between the fan drive turbine and the fan rotor.

More recently, the assignee of the present application has developed a commercial gas turbine engine wherein a gear reduction is placed between a low pressure compressor and a fan, such that a fan drive turbine drives the low pressure compressor at one speed and drives the fan at a slower speed.

Such commercial engines have supported the gear reduction on two bearings forwardly of the gear reduction.

It has also been proposed to straddle mount a gear reduction. In a straddle mount gear reduction, bearings are placed on a forward side and on an aft side of the gear reduction. Such an arrangement raises challenges in the event of a failure of a component in the drivetrain of the fan.

A gas turbine engine according to the prior art is shown in the document <CIT>.

The present invention provides a gas turbine engine as claimed in claim <NUM>.

In a further example, the engine <NUM> bypass ratio is greater than about six and less than twenty-five, with example embodiments being greater than about ten or between fifteen and twenty, the geared architecture <NUM> is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM> and the low pressure turbine <NUM> has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine <NUM> bypass ratio is greater than about ten, the fan diameter is significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> has a pressure ratio that is greater than about five and less than <NUM>:<NUM>, such as between about <NUM> and <NUM>. 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> and less than <NUM>, or equal to, or less than <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>.

As shown, a first bearing <NUM> is positioned forwardly of the gear reduction <NUM> and a second bearing <NUM> is positioned aft of the gear reduction <NUM>. While the bearings <NUM>/<NUM> are shown schematically, the bearing arrangement may be as shown in more detail in <FIG>.

<FIG> shows an engine embodiment <NUM>, outside the wording of the claims, wherein a fan <NUM> rotates as one with a low pressure compressor hub <NUM> having compressor blades <NUM>. The gear reduction <NUM> thus reduces the speed of a fan driven by a fan drive turbine <NUM>, but the low pressure compressor hub <NUM> and fan <NUM> rotate at the same speed.

The quantities mentioned above with regard to <FIG> might also apply to the <FIG> engine.

A flexible drive connection <NUM> connects the fan drive turbine <NUM> to drive the gear reduction <NUM> as will be better explained below. While a flexible drive connection is shown, a more rigid connection may be utilized within the scope of this disclosure. Also, a flexible mount <NUM> is schematically shown for the gear reduction <NUM>.

The fan drive turbine <NUM> is shown to have rotating blades <NUM> and static vanes <NUM>.

A high pressure compressor <NUM> is driven by a high pressure turbine <NUM>. A combustor <NUM> is intermediate turbine <NUM> and compressor <NUM>.

Bearing <NUM> is forward of gear reduction <NUM> and thrust bearing <NUM> is aft of the gear reduction <NUM>. A low turbine shaft <NUM> is located between thrust bearing <NUM> and fan drive turbine <NUM> such that it drives flexible connection <NUM>.

Note, thrust bearing <NUM> is forward of combustor <NUM> and axially between the low and high pressure compressors <NUM>/<NUM>.

With the engine shown in <FIG>, should there be a failure of the drivetrain forward of thrust bearing <NUM>, the low turbine <NUM> could over-speed since there is no resisting torsional load to slow it down. Thrust bearing <NUM> will enable the turbine to maintain an axial running position with hot gases and fuel from the combustor attempting to accelerate the turbine without having the resistive force from the fan and low compressor to slow it down. This is an undesirable condition.

Thus, <FIG> shows a detail wherein a weakened link <NUM> is formed in a turbine drive shaft <NUM> aft of the thrust bearing <NUM>. The gear reduction is a so-called planetary system. Now, should there be a failure in the drivetrain, it will tend to be at the weakened link <NUM>. When this failure occurs, rather than the turbine section overspeeding, the turbine will disengage from its axial position and move aft since thrust bearing <NUM> will no longer hold it, and the rotating blades <NUM> will contact the static vanes <NUM>. The rotation of the fan drive turbine <NUM> will be stopped or at least prevented from accelerating to an unsafe speed avoiding the undesired condition previously mentioned.

Similar undesirable conditions can happen with the fan rotor <NUM> as shown in <FIG> when it experiences bearing failure. <FIG>, an example outside the wording of the claims, depicts a gear drive <NUM> that is straddle mounted by two bearings <NUM> and <NUM>. Bearing <NUM> is a radial bearing that can react radial loads but not axial loads. Bearing <NUM> is a thrust bearing that can react both radial loads and axial thrust loads. Bearing <NUM> reacts the axial thrust load from fan <NUM>. As further shown, there is a catcher or retainer feature <NUM>. The input drive <NUM> drives the sun gear <NUM> in this example, which, in turn, engages intermediate gears <NUM>. A ring gear <NUM> in this example is static. Thus, a carrier <NUM> rotates to, in turn, drive a fan driveshaft <NUM> that rotates with the fan shaft. It should be understood this arrangement can be utilized with the engines of <FIG> or <FIG>.

A catcher <NUM> includes a frame <NUM> bolted at <NUM> to a static frame <NUM>. In the event of failure of thrust bearing <NUM>, the gear reduction <NUM> and the fan <NUM> may be urged forwardly or to the left in <FIG>. However, the catcher <NUM> has a radially inner portion <NUM> which is radially inward of a flange <NUM> on shaft the <NUM>. The catcher <NUM> is formed of sufficiently strong material that it can contact, catch and hold the flange <NUM>, and hence resist movement of the gear reduction <NUM> and fan <NUM> to the left or outwardly of the engine.

<FIG> shows an embodiment according to the present invention wherein the gear reduction is a so-called "star gear" system. Structure, which is similar to that of <FIG>, is identified by the same reference numeral. Here, however, the carrier <NUM> is static. The intermediate gears <NUM> still rotate with the sun gear <NUM> and drive a ring gear <NUM>. Ring gear <NUM> drives a shaft <NUM> to, in turn, rotate the fan. In <FIG>, the gear drive <NUM> is also straddle mounted by two bearings <NUM> and <NUM>, but their positions are reversed such that thrust bearing <NUM> is forward of gear drive <NUM>. This embodiment may also be used with the engines of <FIG> or <FIG>.

In this embodiment, a catcher <NUM> has a radially outermost edge <NUM>, which is forward of a flange <NUM> associated with the shaft <NUM>. The catcher <NUM> is again bolted to a frame structure <NUM>, which is associated with the carrier <NUM>.

Now, should thrust bearing <NUM> fail, the catcher <NUM> will catch the flange <NUM> and resist movement of the gear reduction and fan forwardly and outwardly of the engine.

<FIG> shows a detail of the catcher <NUM> having two halves 158A and 158B with an intermediate space 158C. This will facilitate assembly of the catcher, which may otherwise be complex in the environment as illustrated in <FIG>.

The thrust bearings as disclosed and claimed may be any type thrust bearing, including ball bearings, tapered roller bearings and spherical roller bearings, among others.

Claim 1:
A gas turbine engine (<NUM>) comprises:
a fan drive turbine (<NUM>) driving a gear reduction (<NUM>), said gear reduction (<NUM>), in turn, driving a fan rotor (<NUM>), said fan rotor (<NUM>) delivering air into a bypass duct as bypass air and into a compressor section (<NUM>) as core flow;
a forward bearing (<NUM>) positioned between said gear reduction (<NUM>) and said fan rotor (<NUM>) and supporting said gear reduction (<NUM>), and a second bearing (<NUM>) positioned aft of said gear reduction (<NUM>) and supporting said gear reduction (<NUM>), said forward bearing (<NUM>) being a thrust bearing (<NUM>);
a fan drive turbine drive shaft (<NUM>) driving said gear reduction (<NUM>); and
a catcher (<NUM>) provided to resist movement of said gear reduction (<NUM>) and said fan rotor (<NUM>) in an outer direction in the event of a failure of said forward bearing (<NUM>), wherein said gear reduction (<NUM>) is an epicyclic gear reduction (<NUM>),
wherein said epicyclic gear reduction (<NUM>) includes a sun gear (<NUM>), intermediate gears (<NUM>) driven by said sun gear (<NUM>), and a ring gear (<NUM>) driven by said intermediate gears (<NUM>), with a static carrier (<NUM>), and said ring gear (<NUM>) driving a fan drive shaft (<NUM>) to drive said fan rotor (<NUM>),
characterized in that:
said catcher (<NUM>) is bolted to a frame structure (<NUM>) associated with said static carrier (<NUM>).