Patent Description:
Additional demands on large military and commercial engines solely utilize the high spool rotor to extract horsepower and power accessories including fuel/oil pumps, PMAG, and aircraft accessory pumps. With increasing demand for horsepower extraction to power additional accessories and provide more electrical power, extraction limits of the high rotor are being reached and there is a need for additional horsepower. At the very least, it would be useful to better balance the extraction demands between more than one spool.

However, the "penalties" for current modes of extracting power from more than one spool at a time, add complexity, weight, cost, and maintainability that present challenges to utilizing a second lower spool.

<CIT> discloses a twin-spool turbojet with means for driving ancillary machines.

<CIT> discloses a differential power system for a multi-spool turbine engine.

In accordance with a first aspect of the disclosure, a turbine engine assembly is provided in accordance with claim <NUM>.

<FIG> is a quarter-sectional view that schematically illustrates example gas turbine engine <NUM> that includes fan section <NUM>, compressor section <NUM>, combustor section <NUM> and turbine section <NUM>. Alternative engines might include an augmenter section (not shown) among other systems or features. Fan section <NUM> drives air along bypass flow path B while compressor section <NUM> draws air in along core flow path C where air is compressed and communicated to combustor section <NUM>. In combustor section <NUM>, air is mixed with fuel and ignited to generate a high pressure exhaust gas stream that expands through turbine section <NUM> where energy is extracted and utilized to drive fan section <NUM> and 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, an industrial gas turbine; a reverse-flow gas turbine engine; and 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 gas turbine engine <NUM> generally includes low speed spool <NUM> and high speed spool <NUM> mounted for rotation about center axis A of gas turbine engine <NUM> relative to 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.

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

Combustor <NUM> is arranged between high pressure compressor <NUM> and high pressure turbine <NUM>. In one example, high pressure turbine <NUM> includes at least two stages to provide double stage high pressure turbine <NUM>. In another example, 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 <NUM>. The pressure ratio of the example low pressure turbine <NUM> is measured prior to an inlet of low pressure turbine <NUM> as related to the pressure measured at the outlet of low pressure turbine <NUM> prior to an exhaust nozzle.

Mid-turbine frame <NUM> of engine static structure <NUM> can be arranged generally between high pressure turbine <NUM> and low pressure turbine <NUM>. Mid-turbine frame <NUM> further supports bearing systems <NUM> in turbine section <NUM> as well as setting airflow entering the low pressure turbine <NUM>.

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

It will be recognized that the terms high and low, unless described in another way, are relative. For example, a low spool generally connects a low pressure compressor and a low pressure turbine, while a high spool generally connects a high pressure compressor and a high pressure turbine. Most often the high spool rotates faster than the low spool. Further, though shown as a two-spool engine, it will be appreciated by the skilled artisan that the teachings can be readily adapted to other engine configurations, such as a three-spool engine. Differential gear assembly <NUM> can be modified and relocated as needed to offtake power from a turbine assembly having any two concentric counter-rotating shafts / spools such as high and intermediate, intermediate and low, and likely, high and low.

<FIG> shows details of a first example embodiment of differential gear assembly <NUM> providing power to accessory system <NUM> from both low spool <NUM> and high spool <NUM>. As noted with respect to <FIG>, low spool <NUM> includes low spool accessory drive gear <NUM> driven by low rotor shaft <NUM>, while high spool <NUM> includes high spool accessory drive gear <NUM> driven by high rotor shaft <NUM> concentric around at least a portion of low rotor shaft <NUM>.

As noted above, these embodiments of a differential gear assembly (<NUM> in <FIG>) are designed around a counter-rotating shaft configuration. That is, low spool <NUM> rotates clockwise and high spool <NUM> rotates counter-clockwise or vice versa. Differential gear assembly <NUM> is adapted to offtake power from rotation of one or both of low spool <NUM> and high spool <NUM>, and includes one or more idler gears <NUM>. Each includes a plurality of teeth <NUM> meshed with low spool accessory drive gear <NUM> and high spool accessory drive gear <NUM>. Bearing surface <NUM> supports idler bearing assembly <NUM>, which in turn connects idler gear(s) <NUM> with differential bullgear <NUM>.

Differential bull gear <NUM> includes a plurality of differential gear teeth <NUM> and a corresponding at least differential bearing surface <NUM> engaging with idler bearing surface <NUM> of each of the one or more idler gears <NUM>. The plurality of differential gear teeth <NUM> are adapted to mesh with accessory drive system <NUM> to transfer the power offtakes from each spool and drive one or more accessory loads <NUM>. This may be via an accessory drive shaft, such as but not limited to towershaft <NUM>, or another configuration depending on the particular engine architecture.

Note that accessory drive gears <NUM>, <NUM> have heretofore been described generally. In the example embodiment of <FIG>, low spool accessory drive gear <NUM> includes at least a ring gear assembly, while high spool accessory drive gear <NUM> includes a standard bull gear. <FIG> will show an embodiment where these elements are reversed, and the configuration changes necessary to the differential gear assembly will be described accordingly.

In both cases, ring gear assembly generally includes ring gear <NUM> supported to low rotor shaft <NUM> by a plurality of ring gear bearings <NUM>, and pinion gear <NUM> meshed with ring gear <NUM>. Pinion gear <NUM> includes a fixed central portion <NUM> mounted to a fixed surface of the engine shown in <FIG>. Outer rotatable portion <NUM> of pinion gear <NUM> is rotatable about fixed central portion <NUM> to facilitate transfer between ring gear <NUM> and differential assembly <NUM>. Here, outer portion <NUM> meshes with ring gear <NUM> and low rotor shaft <NUM> (or high rotor shaft <NUM> as in <FIG>) to drive rotation of ring gear <NUM> about the low rotor shaft. Also in both example embodiments, the differential bullgear (<NUM> in <FIG>) is shown to be supported to low rotor shaft <NUM> by another plurality of bearings <NUM>. Alternatively, in both <FIG> and <FIG>, the example embodiment can be adapted in another way such that both the differential bullgear and ring gear are "free spinning" relative to any of the shafts or spools. One non-limiting alternative includes supporting one or both of these gears to fixed part of the engine such as the case, while still allowing for different rotational speeds relative to one or more shafts.

A size of differential bullgear <NUM> and a gear ratio of differential bullgear <NUM> relative to towershaft <NUM>, are selected to selectively offtake a first portion of power from the low spool and a second portion of power from the high spool to drive a plurality of accessories (loads <NUM>) connected to the towershaft. Preferably, selective offtake of first and second portions of power continuously maintain a minimum excess power margin on each of low and high spools <NUM>, <NUM>. Selective offtake from each spool <NUM>, <NUM>, can depend at least in part on instantaneous accessory load and on relative engine speed.

<FIG> shows details of a second example embodiment of differential gear assembly <NUM> providing power to accessory system <NUM> from both counter-rotating low spool <NUM> and high spool <NUM>. As with <FIG> and <FIG>, low spool <NUM> includes low spool accessory drive gear <NUM> driven by low rotor shaft <NUM>, while high spool <NUM> includes high spool accessory drive gear <NUM> driven by high rotor shaft <NUM> concentric around at least a portion of low rotor shaft <NUM>.

Differential gear assembly <NUM> is adapted to offtake power from rotation of one or both of low spool <NUM> and high spool <NUM>, and includes one or more idler gears <NUM>. Each includes a plurality of teeth <NUM> meshed with low spool accessory drive gear <NUM> and high spool accessory drive gear <NUM>. Bearing surface <NUM> supports idler bearing assembly <NUM>, which in turn connects idler gear(s) <NUM> with differential bullgear <NUM>.

Similar to <FIG>, differential bullgear <NUM> includes a plurality of differential gear teeth <NUM> and a corresponding at least one differential bearing surface <NUM> engaging with idler bearing surface <NUM> of each of the one or more idler gears <NUM>. The plurality of differential gear teeth <NUM> are adapted to mesh with accessory drive system <NUM> to transfer the power offtakes from each spool and drive one or more accessory loads <NUM>. This may be via an accessory drive shaft, such as but not limited to towershaft <NUM>, or another configuration depending on the particular engine architecture.

Note that in the example embodiment of <FIG>, low spool accessory drive gear <NUM> includes at least a ring gear assembly, while high spool accessory drive gear <NUM> includes a standard bull gear. <FIG> shows an embodiment where these elements are reversed, namely, low spool accessory drive gear <NUM> includes at least a standard bull gear, while high spool accessory drive gear <NUM> includes at least a ring gear assembly.

In both cases, the ring gear assembly generally includes ring gear <NUM> supported to low rotor shaft <NUM> by a plurality of ring gear bearings <NUM>, and pinion gear <NUM> meshed with ring gear <NUM>. Pinion gear <NUM> includes a fixed central portion <NUM> mounted to a fixed surface of the engine shown in <FIG>. Outer rotatable portion <NUM> of pinion gear <NUM> is rotatable about fixed central portion <NUM> to facilitate transfer between ring gear <NUM> and differential assembly <NUM>. Here, outer portion <NUM> meshes with ring gear <NUM> and high rotor shaft <NUM> to drive rotation of ring gear <NUM> about low rotor shaft <NUM>. Also in both example embodiments, the differential bullgear (<NUM> in <FIG>, <NUM> in <FIG>) is supported to low rotor shaft <NUM> by another plurality of bearings <NUM>. Similar to the example embodiment of <FIG>, the example embodiment in <FIG> can be adapted in another way such that both the differential bullgear and ring gear are "free spinning" relative to any of the shafts or spools. One non-limiting alternative includes supporting one or both of these gears to fixed part of the engine such as the case, while still allowing for different rotational speeds relative to one or more shafts.

A size of differential bullgear <NUM> and a gear ratio of differential bullgear <NUM> relative to towershaft <NUM>, are selected to selectively offtake a first portion of power from low spool <NUM> and a second portion of power from high spool <NUM> to drive accessories / loads <NUM> connected to towershaft. Preferably, selective offtake of first and second portions of power continuously maintain a minimum excess power margin on each of low and high spools <NUM>, <NUM>. Selective offtake from each spool <NUM>, <NUM> can depend at least in part on instantaneous accessory load and on relative engine speed.

It will be recognized that the "first" and "second" portions of power referenced in the preceding paragraph, and throughout the instant document merely are used to allow the reader to differentiate between the "first" power offtake from the low spool and the "second" power offtake from the high spool. Absent any explicit statement to the contrary, the "first" portion of power offtake is not necessarily greater than, equal to, or less than the "second" portion of power offtake at any given time or operational condition. Generally, but not exclusively, more power will be taken from the high spool during low engine speeds. Additional power may be taken from the low spool at higher engine speeds or during acceleration, but (a) this does not always exceed the amount of power taken from the high spool, and (b) other parameters and load demands will always affect the instantaneous and total distribution of power offtake between the low and high spools during any given flight cycle.

An example embodiment of a turbine engine assembly includes a low spool including a low spool accessory drive gear driven by a low rotor shaft, a high spool including a high spool accessory drive gear driven by a high rotor shaft concentric around a portion of the low rotor shaft, and a differential gear assembly adapted to offtake power from rotation of one or both of the low spool and the high spool to drive one or more accessory loads. The differential gear assembly includes a differential bullgear and one or more idler gears each including a plurality of teeth meshed with the low spool accessory drive gear and the high spool accessory drive gear, and a bearing surface. The differential bull gear includes a plurality of teeth and a corresponding at least one bearing surface engaging with the bearing surface of each of the one or more idler gears. The plurality of teeth are adapted to mesh with an accessory drive system to transfer the power offtake and drive the one or more accessory loads. The low spool accessory drive gear comprises a ring gear assembly. The ring gear assembly includes a ring gear supported to the low rotor shaft by a first plurality of bearings and a pinion gear meshed with the ring gear. The ring gear assembly is radially inward of the one or more idlers gears.

The assembly of the preceding paragraph can optionally include any one or more of the following features, configurations and/or additional components:
A further example of any of the foregoing assemblies, wherein the high spool accessory drive gear comprises a bull gear.

A further example of any of the foregoing assemblies, wherein a fixed central portion of the pinion gear is mounted to a fixed surface of the engine.

A further example of any of the foregoing assemblies, wherein an outer portion of the pinion gear is rotatable about the fixed central portion.

A further example of any of the foregoing assemblies, wherein the outer portion meshes with the ring gear and the low rotor shaft or the high rotor shaft to drive rotation of the ring gear about the low rotor shaft.

A further example of any of the foregoing assemblies, wherein the differential bullgear is supported to the low rotor shaft by a second plurality of bearings.

A further example of any of the foregoing assemblies, wherein the low rotor shaft rotates in a first direction and the high rotor shaft rotates in a second direction opposite the first direction.

A further example of any of the foregoing assemblies, further comprising an accessory drive shaft as part of the accessory drive system.

A further example of any of the foregoing assemblies, wherein the accessory drive shaft comprises a towershaft.

A further example of any of the foregoing assemblies, wherein a size of the differential bullgear and a gear ratio of the differential bullgear, relative to the towershaft, are selected to selectively offtake a first portion of power from the low spool and a second portion of power from the high spool to drive a plurality of accessories connected to the towershaft.

A further example of any of the foregoing assemblies, wherein the selective offtake of first and second portions of power continuously maintain a minimum excess power margin on each of the low and high spools.

A further example of any of the foregoing assemblies, wherein the selective offtake depends at least in part on instantaneous accessory load and on relative engine speed.

Claim 1:
A turbine engine (<NUM>) assembly comprising:
a low spool (<NUM>) including a low spool accessory drive gear (<NUM>) driven by a low rotor shaft (<NUM>);
a high spool (<NUM>) including a high spool accessory drive gear (<NUM>) driven by a high rotor shaft (<NUM>), the high rotor shaft (<NUM>) concentric around a portion of the low rotor shaft (<NUM>); and
a differential gear assembly (<NUM>) adapted to offtake power from rotation of one or both of the low spool (<NUM>) and the high spool (<NUM>) to drive one or more accessory loads (<NUM>), the differential gear assembly (<NUM>) comprising:
a first idler gear (<NUM>) and a second idler gear (<NUM>), each including a plurality of teeth (<NUM>) meshed with the low spool accessory drive gear (<NUM>) and the high spool accessory drive gear (<NUM>), and a bearing surface (<NUM>); and
a differential bull gear (<NUM>) including a plurality of teeth (<NUM>) and a corresponding at least one bearing surface (<NUM>) engaging with the bearing surface (<NUM>) of each of the first and second idler gears (<NUM>), the plurality of teeth (<NUM>) adapted to mesh with an accessory drive system (<NUM>) to transfer the power offtake and drive the one or more accessory loads (<NUM>),
characterized in that
the low spool accessory drive gear (<NUM>) comprises a ring gear assembly including a ring gear (<NUM>) supported to the low rotor shaft (<NUM>) by a first plurality of bearings (<NUM>) and a pinion gear (<NUM>) meshed with the ring gear (<NUM>), and in that the ring gear assembly is radially inward of the one or more idler gears.