Patent Description:
Increasing amounts of power for aircraft accessory items are extracted from the turbine engine. Engine architectures include a single tower shaft coupled to a high speed spool of the engine. The tower shaft is used to start the engine and also to extract power during engine operation. Increasing loads on the single spool of the engine can limit potential engine performance capabilities.

Turbine engine manufacturers continue to seek further improvements to engine performance including improvements to thermal, transfer and propulsive efficiencies.

<CIT> discloses a turbofan engine comprising a gearbox to drive auxiliary components. <CIT> discloses a turbofan engine including a multi-speed transmission between the high pressure and low pressure turbines and associated high pressure and low pressure starter-generators. <CIT> discloses a turbofan engine comprising a differential gear assembly coupled to a low pressure input gear assembly by a clutch assembly for driving generators. <CIT> discloses a gas turbine engine comprising an accessory gearbox assembly having an accessory drive and a planetary gear train.

A turbofan engine according to an aspect of the present invention is provided as claimed in claim <NUM>.

In an embodiment of the foregoing turbofan engine, an electric power supply provides power to the first electric motor and the second electric motor.

In another embodiment of any of the foregoing turbofan engines, a second ring gear clutch is included to selectively couple the ring gear to a static structure of the engine.

In another embodiment of any of the foregoing turbofan engines, a carrier shaft is coupled to drive a first gear system within the accessory gearbox for driving a first group of the plurality of accessory components.

In another embodiment of any of the foregoing turbofan engines, a sun gear shaft supports the sun gear. The sun gear shaft couples the second tower shaft to the starter through the starter clutch.

In another embodiment of any of the foregoing turbofan engines, a ring gear shaft is driven by the first tower shaft. The ring gear is coupled to drive a second group of the plurality of accessory components.

In another embodiment of any of the foregoing turbofan engines, a drive gear is coupled to the sun gear shaft to drive a third group of the plurality of accessory components.

In another embodiment of any of the foregoing turbofan engines, the first tower shaft and the second tower shaft are concentric about a common axis.

In another embodiment of any of the foregoing turbofan engines, the first tower shaft and the second tower shaft are disposed about different axes.

In another embodiment of any of the foregoing turbofan engines, the starter clutch, first motor clutch, second motor clutch, first ring gear clutch and the second ring gear clutch comprise one-way mechanical clutches.

In another embodiment of any of the foregoing turbofan engines, the first motor clutch couples the first electric motor to the first tower shaft to drive the first spool. The second motor clutch couples the second electric motor to the second tower shaft to drive the second spool in an engine idle operating condition.

In another embodiment of any of the foregoing turbofan engines, the first motor clutch and the second motor clutch are not coupled during a normal operating condition such that neither the first electric motor nor the second electric motor input power to either of the first spool and the second spool.

In another embodiment of any of the foregoing turbofan engines, the second clutch couples the second electric motor to the second tower shaft to drive the second spool in an engine starting operating condition.

A method of operating an accessory gearbox for a turbofan engine according to another aspect of the present invention is provided as claimed in claim <NUM>.

In an embodiment of the foregoing method of operating an accessory gearbox for a turbofan engine, a starter is coupled to the sun gear, the ring gear is coupled to an engine static structure. The method includes driving the second spool with the starter and the second electric motor to rotate the second spool and start the turbofan engine.

In a further embodiment of any of the foregoing methods of operating an accessory gearbox for a turbofan engine, each of the first electric motor and the second electric motor are decoupled such that neither the first electric motor nor the second electric motor input power to either of the first spool nor the second spool. The first tower shaft drives the ring gear. The second tower shaft drives the sun gear once both the first spool and the second spool are rotating independent of rotation of the starter such that both the first tower shaft and the second tower shaft combine to drive a first output coupled to the carrier and a second output coupled to the ring gear.

In a further embodiment of any of the foregoing methods of operating an accessory gearbox for a turbofan engine, a first output of the superposition gear system drives a first group of accessory components at a first speed, and a second output of the superposition gear system drives a second group of accessory components at a second speed different than the first speed.

In a further embodiment of any of the foregoing methods of operating an accessory gearbox for a turbofan engine, a third output coupled to the sun gear drives a third group of accessory components at a third speed that is different that both the first speed and the second speed.

Although the different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations.

The inner shaft <NUM> is connected to a fan section <NUM> through a speed change mechanism, which in exemplary gas turbine engine <NUM> is illustrated as a geared architecture <NUM> to drive fan blades <NUM> at a lower speed than the low speed spool <NUM>.

For example, gear system <NUM> may be located aft of the low pressure compressor <NUM> and the fan blades <NUM> may be positioned forward or aft of the location of the geared architecture <NUM> or even aft of 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 = <NUM>/<NUM> x K).

The example gas turbine engine includes the fan section <NUM> that comprises in one non-limiting embodiment less than about <NUM> fan blades <NUM>. In another non-limiting embodiment, the fan section <NUM> includes less than about <NUM> fan blades <NUM>. Moreover in one disclosed embodiment the low pressure turbine <NUM> includes no more than about <NUM> turbine rotors schematically indicated at <NUM>. In another non-limiting example embodiment, the low pressure turbine <NUM> includes about <NUM> turbine rotors. A ratio between the number of fan blades <NUM> and the number of low pressure turbine rotors is between about <NUM> and about <NUM>. The example low pressure turbine <NUM> provides the driving power to rotate the fan section <NUM> and, therefore, the relationship between the number of turbine rotors <NUM> in the low pressure turbine <NUM> and the number of blades <NUM> in the fan section <NUM> disclose an example gas turbine engine <NUM> with increased power transfer efficiency.

The example engine <NUM> includes an accessory drive system <NUM> that receives power from both the high speed spool <NUM> and the low speed spool <NUM>. The accessory drive system <NUM> includes an accessory gearbox <NUM> for driving a plurality of accessory components <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. The accessory components <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> support operation of the gas turbine engine <NUM> and include pumps, generators and other devices driven to enable operation of different engine and aircraft systems. The accessory gearbox <NUM> is also coupled to a starter <NUM>. The starter <NUM> is capable of driving the accessory drive system <NUM> to start the engine <NUM>. In this example, a tower shaft assembly <NUM> including first and second tower shafts <NUM>, <NUM> is coupled to both the low speed spool <NUM> and the high speed spool <NUM> to distribute and extract power between the two spools <NUM>, <NUM>.

A first electric motor <NUM> and a second electric motor <NUM> are coupled through the drive system <NUM> to input power into the engine and aid in driving the accessory components <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. Excessive power extraction from a single spool, such as the high speed spool <NUM>, can limit operation and degrade overall performance and engine efficiency. Accordingly, the example accessory drive system <NUM> extracts power from both the low speed spool <NUM> and the high speed spool <NUM> to meet the overall power demands of the engine <NUM> and the aircraft associated with the engine. The power extracted from the spools <NUM>, <NUM> is combined in a superposition gear system <NUM> disposed within the accessory gearbox <NUM>. Moreover, the first and second electric motors <NUM>, <NUM> input power to the accessory gearbox <NUM> to reduce the load on the low and high speed spools <NUM>, <NUM> of the engine.

Referring to <FIG>, with continued reference to <FIG>, the superposition gear system <NUM> is an epicyclic gearbox that includes a sun gear <NUM> that rotates about an axis <NUM>. A plurality of intermediate gears <NUM> are engaged with the sun gear <NUM> and supported by a carrier <NUM>. A ring gear <NUM> circumscribes and engages the plurality of intermediate gears <NUM>.

In the disclosed example, the tower shaft assembly <NUM> includes the first tower shaft <NUM> that is driven by a gear <NUM> disposed on the low speed spool <NUM>. A first gear <NUM> on the tower shaft <NUM> is coupled to the gear <NUM>. A second gear <NUM> is disposed on a second end of the tower shaft <NUM> and engages a drive gear <NUM> disposed on a ring gear shaft <NUM>.

A second tower shaft <NUM> is coupled to a drive gear <NUM> that is driven by the high speed spool <NUM>. The second tower shaft <NUM> includes a first gear <NUM> driven by the gear <NUM> on the high speed spool <NUM>. A second gear <NUM> of the second tower shaft <NUM> is engaged to drive gear <NUM> disposed on a sun gear shaft <NUM>.

In this example, the first tower shaft <NUM> and the second tower shaft <NUM> are disposed concentrically about a common axis <NUM>. Moreover, the axis <NUM> is disposed at an angle relative to the engine longitudinal axis A and an axis <NUM> of the superposition gear system <NUM>. It should be appreciated that although the specific disclosed embodiment includes concentric tower shafts <NUM>, <NUM>, other configurations and orientations of tower shafts are within the contemplation and scope of this disclosure.

First tower shaft <NUM> is coupled to the ring gear shaft <NUM> that is selectively coupled to the ring gear <NUM> through a first ring gear clutch <NUM>. The second tower shaft <NUM> is coupled to the sun gear shaft <NUM> that is coupled to drive the sun gear <NUM>. The sun gear shaft <NUM> directly couples to the sun gear <NUM> and extends past the sun gear <NUM> to the starter <NUM>.

The superposition gear system <NUM>, therefore, has a first input provided by the first tower shaft <NUM> through the ring gear shaft <NUM> to drive the ring gear <NUM> and a second input provided by the second tower shaft <NUM> to drive the sun gear shaft <NUM> and, thereby, the sun gear <NUM>.

A first output from the superposition gear system <NUM> is provided by the carrier <NUM>. The carrier <NUM> drives an accessory group <NUM> in the disclosed example embodiment. The ring gear shaft <NUM> provides a second output to drive the accessory group <NUM>. Another accessory group <NUM> is driven by the sun gear shaft <NUM>.

The sun gear shaft <NUM> provides both another input into the gear system <NUM> by being driven by the starter <NUM> and the third output to drive the accessory group <NUM>. In this example embodiment, the accessory group <NUM> includes the fuel pump <NUM>. However, other components could be driven from the sun gear shaft <NUM>. The starter <NUM> provides a driving input to the sun gear <NUM> through the sun gear shaft <NUM>.

The example superposition gear system <NUM> includes a direct connection between the starter <NUM> and the sun gear shaft <NUM> to provide for direct driving of the high speed spool <NUM>. The sun gear shaft <NUM> is coupled to the starter <NUM> through a starter clutch <NUM>. The starter clutch <NUM> in this example is a mechanical one-way clutch that enables direct driving of the high speed spool <NUM> during starting operations. Once the high speed spool <NUM> is operating, the starter clutch <NUM> prevents back driving or over driving of the starter <NUM>. The sun gear shaft <NUM> is directly connected to the starter rather than being driven through a gear system. The direct drive of the high speed spool <NUM> through the direct connection simplifies operation and the mechanical connections.

The example superposition gear system <NUM> provides the first output through the carrier <NUM> that drives the accessory group <NUM> through a first gear system <NUM>. In this example the first group of accessory components <NUM>, <NUM>, and <NUM> are driven at a first speed. Once the engine is started, the first output through the carrier <NUM> provides the driving input required to power the accessory components <NUM>, <NUM> and <NUM> through the first gear system <NUM>.

The accessory group <NUM> is driven by the ring gear shaft <NUM> through a second gear system <NUM>. In this example, only one accessory component <NUM> is shown as being driven by the second gear system <NUM>, however, other components could be included.

The accessory group <NUM> is driven by a gear <NUM> coupled to the sun gear shaft <NUM>. The gear <NUM> is operable to rotate at the speed of the sun gear shaft <NUM> during engine operation and when driven by the starter <NUM> during starting operations.

The superposition gear system <NUM> includes a first ring gear clutch <NUM> that couples the ring gear shaft <NUM> to the ring gear <NUM>. A second ring gear clutch <NUM> couples the ring gear <NUM> to a static engine structure <NUM>. In this example, both the first ring gear clutch <NUM> and the second ring gear clutch <NUM> are mechanical one-way clutches. Moreover, in this example, the first and second mechanical one-way clutches <NUM>, <NUM> are sprag clutches. It should be appreciated that although sprag clutches are disclosed by way of example, other mechanical clutch systems could be utilized and are within the contemplation of this disclosure.

The second ring gear clutch <NUM> couples the ring gear <NUM> to the engine static structure <NUM> during a starting operation to prevent rotation of the ring gear <NUM> and thereby the first tower shaft <NUM> and the low speed spool <NUM>. When the ring gear <NUM> is fixed, the starter <NUM> will drive the sun gear shaft <NUM> such that it will be the only driving output back to the high speed spool <NUM>.

Power extracted from the low and high speed spools <NUM>, <NUM> can reduce engine efficiency. Power extraction for the spools <NUM>, <NUM> may not meet the capacity required by the engine and aircraft without degrading engine performance and efficiency. Accordingly, the first and second electric motors <NUM>, <NUM> are coupled through the superposition gearbox <NUM> to input power to the corresponding spools <NUM>, <NUM>. The first electric motor <NUM> is selectively coupled to the first tower shaft <NUM> by a coupling to the ring gear shaft <NUM> provided by a first motor clutch <NUM>. The second electric motor <NUM> is selectively coupled to the second tower shaft <NUM> through the sun gear shaft <NUM> provided by a second motor clutch <NUM>. The electric motors <NUM>, <NUM> are powered by an electrical power source <NUM> provided on-board the aircraft or by a connection to a ground power system when the aircraft is on the ground. The electric motors <NUM>, <NUM> are operable to input power into the superposition gearbox <NUM> to reduce loads on the spools <NUM>, <NUM> during specific engine operating conditions. Moreover, in another exemplary embodiment, the electric motors may operate as motor/generators. When motor/generators are utilized, the clutches <NUM>, <NUM> may not be required. Additionally, although electric motors are disclosed by way of example, any drive means could be utilized to input power through the superposition gearbox <NUM>.

Referring to <FIG> with continued reference to <FIG>, a schematic power flow diagram is shown for the system <NUM> for an idle engine operating condition. An engine idling with the aircraft on the ground is inefficient as much of the power is extracted for operation of aircraft accessory items. The engine is therefore required to operate at increased power settings.

The disclosed system <NUM> engages the motors <NUM>, <NUM> to the superposition gearbox <NUM> to drive the accessory items and reduce the load on the engine spools <NUM>, <NUM>. In the disclosed example, mechanical power flow is schematically indicated by arrows between the structural features. Accordingly, mechanical power is input from both the low and high spools <NUM>, <NUM> into the superposition gearbox <NUM>. The first and second electric motors <NUM>, <NUM> are coupled by corresponding clutches <NUM> and <NUM> to supplement the mechanical power from the spools <NUM>, <NUM>. The first motor clutch <NUM> is coupled to the low speed spool <NUM> through a mechanical coupling schematically indicated at <NUM>. The second electric motor <NUM> is coupled to the high speed spool <NUM> through a mechanical coupling indicated at <NUM> between the second motor clutch <NUM> and the sun gear shaft <NUM>. The power input into the superposition gearbox <NUM> from the first and second electric motors <NUM>, <NUM> reduces the load on the spools <NUM>, <NUM> to enable more efficient engine operation at the idle condition.

In this example, the power for the first and second electric motors <NUM>, <NUM> is provided by a battery system schematically indicated at <NUM>. The battery system <NUM> can be within the aircraft or as part of a ground system providing power to the aircraft.

Referring to <FIG>, with continued reference to <FIG> and <FIG>, an alternate power source in the form of an auxiliary power unit (APU) <NUM> could also be utilized to power the electric motors <NUM>, <NUM>. The battery system <NUM> and the APU <NUM> are power sources that are separate from the system <NUM> such that the spools <NUM>, <NUM> do not incur additional loads for power generation to drive the motors <NUM>, <NUM>. Instead, the example disclosed embodiment provides power for driving the motors <NUM>, <NUM> from a source separate from the engine <NUM>. However, power from the engine could be utilized in some engine operating conditions and is within the scope and contemplation of this disclosure.

Referring to <FIG>, with continued reference to <FIG>, the example system <NUM> is shown in a condition where the engine is operating at cruise or other efficient engine operating conditions. At cruise or other operating conditions, the engine is operating at or near designed conditions and additional power from the motors <NUM>,<NUM> is not required. Accordingly, the first and second mechanical clutches <NUM>, <NUM> are not engaged. In this example, the clutches <NUM>, <NUM> are one-way mechanical clutches that prevent back driving of the motors <NUM>, <NUM> by the spools <NUM>, <NUM>. Moreover, at engine operating conditions where the spools <NUM>, <NUM> are rotating at increased speeds, the clutches prevent overrunning of the motors <NUM>, <NUM>.

The first ring gear clutch <NUM> is engaged as is schematically shown at <NUM> to couple power from the first tower shaft <NUM> to the ring gear <NUM>. The second ring gear clutch <NUM> will free wheel and allow rotation of the ring gear <NUM>. The second tower shaft <NUM> will drive the sun gear <NUM> and thereby the gear <NUM> and the carrier <NUM>. The carrier <NUM> will in turn drive the first sear system <NUM> within the accessory gearbox <NUM>. Power from each of the high spool <NUM> and the low spool <NUM> will be split to drive the carrier <NUM> and power the accessory group schematically indicated at <NUM>. The accessory group <NUM> includes accessory components <NUM>, <NUM>, <NUM> and <NUM>.

The accessory group <NUM> includes auxiliary oil pump <NUM> driven by the gear coupling <NUM> to the ring gear shaft <NUM>. The accessory group <NUM> includes the fuel pump <NUM> driven by the gear coupling <NUM> to the sun gear shaft <NUM>. Each of the ring gear shaft <NUM>, sun gear shaft <NUM> and carrier <NUM> rotate at different speeds and therefore the accessory components <NUM>, <NUM>, <NUM>, <NUM> and <NUM> are driven by the corresponding one of the ring gear shaft <NUM>, sun gear shaft <NUM> and carrier <NUM> that best corresponds with a desired speed and operation of each accessory component.

In the disclosed example embodiment, the fuel pump <NUM> is driven by the sun gear shaft <NUM> that is in turn driven by the high speed spool <NUM>. Fuel flow requirements are tied closely to the speed of the high speed spool <NUM>. Coupling the fuel pump <NUM> to the sun gear shaft <NUM> enables driving of the fuel pump <NUM> by only the high speed spool <NUM> at a speed that corresponds and changes proportionally with operation of the engine <NUM> to provide a more desirable corresponding variation in operation. Moreover, the gear coupling <NUM> can be set to generate the desired proportional speed of the fuel pump in direct relationship to the speed of the high speed spool <NUM>.

The accessory group <NUM> including the main oil pump <NUM>, generator <NUM> and hydraulic pump <NUM> all demand significant power without a strong tie or correlation to a speed of either of the spools <NUM>, <NUM>. Accordingly, the accessory group <NUM> is driven through a coupling to the carrier <NUM>. The carrier <NUM> is driven by power extracted from both spools <NUM>, <NUM> to provide a steady consistent power output.

The accessory group <NUM> in this example includes the auxiliary oil pump <NUM> driven through the gear coupling <NUM> by the ring gear shaft <NUM>. The ring gear shaft <NUM> is coupled to the low speed spool <NUM>. The auxiliary oil pump <NUM> is desired to operate during low and negative G environments as well as operate when the engine is not operating but the fan is rotating to drive the low speed spool <NUM>. In configurations where the accessory components are driven only by the high speed spool <NUM>, the auxiliary oil pump <NUM> is not engaged and therefore does not produce an output flow of oil <NUM>. However, the third output from the superposition gear system <NUM> enables direct driving by the low speed spool <NUM> as needed to provide the desired operation. The gear couplings driving each of the accessory groups <NUM>, <NUM>, and <NUM> are each defined in consideration of the accessory component driven and are tailored to provide the most efficient speeds for each accessory component <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

It should be understood that although disclosed groups of accessory components are driven by specific gear couplings to specific locations and features of the superposition gear system <NUM>, each accessory component could be configured to be driven by gear couplings in combinations that differ from the disclosed examples. Each accessory component could be driven by any of the outputs provided by the superposition gear system <NUM>. Moreover, not all the outputs need to drive an accessory component to be considered within the contemplation of this disclosure. Any configuration of the example superposition gear system <NUM> will be determined by the design and operational requirements for each accessory.

Referring to <FIG> with continued reference to <FIG>, the mechanical and electrical power flow during a starting operation is schematically shown. During the starting operation, the starter <NUM> drives the sun gear shaft <NUM> in a first direction. The starter clutch <NUM> engages to enable driving of the sun gear shaft <NUM> by the starter <NUM>. The same rotation provided by the starter <NUM> will engage the ring gear <NUM> such that the second ring gear clutch <NUM> is engaged as is schematically shown at <NUM> to lock the ring gear <NUM> to the static structure <NUM> to prevent rotation of the ring gear <NUM>. The first ring gear clutch <NUM> is not locked in this direction, but does not receive a driving input and therefore does not rotate the corresponding first tower shaft <NUM>.

The second electric motor <NUM> is engaged to aid in the starting operation. The second motor clutch <NUM> engages the sun gear shaft <NUM> as is schematically shown at <NUM>. The additional power provided by the second electric motor <NUM> enables the starter <NUM> to be of a reduced power capacity. Moreover, the electric motor <NUM> may also operate as a backup to the starter <NUM> to provide an aided redundancy for non-standard starting operations.

Once the engine has started and the high speed spool <NUM> is rotating at speed, the starter <NUM> and the electric motor <NUM> are disengaged. The high speed spool <NUM> will begin driving the second tower shaft <NUM> and thereby the sun gear shaft <NUM>. The higher speed provided by the driving of the high speed spool <NUM> disengages the starter <NUM> and second electric motor <NUM>. Additionally, once the low speed spool <NUM> begins operation, the first tower shaft <NUM> will begin rotating. The first ring gear clutch <NUM> will engage to couple the ring gear shaft <NUM> to the ring gear <NUM>. In this operating condition, both the low speed spool <NUM> and the high speed spool <NUM> will drive portions of the superposition gear system <NUM>.

According, the example accessory drive system <NUM> includes the superposition gear system <NUM> that automatically distributes input driving torque between the low speed spool <NUM>, the high speed spool <NUM> as required during engine operation. The drive system <NUM> further includes first and second electric motors that selectively couple to the superposition gear system <NUM> to supplement power from the spools <NUM>, <NUM>.

Claim 1:
A turbofan engine (<NUM>) comprising:
a first spool (<NUM>) including a low pressure turbine (<NUM>);
a second spool (<NUM>) including a high pressure turbine (<NUM>) disposed axially forward of the low pressure turbine (<NUM>);
a first tower shaft (<NUM>) engaged to the first spool (<NUM>);
a second tower shaft (<NUM>) engaged to the second spool (<NUM>);
an accessory gearbox (<NUM>) supporting a plurality of accessory components (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>);
a superposition gear system (<NUM>) disposed within the accessory gearbox (<NUM>), the superposition gear system (<NUM>) including a plurality of intermediate gears (<NUM>) engaged to a sun gear (<NUM>) and supported in a carrier (<NUM>) and a ring gear (<NUM>) circumscribing the intermediate gears (<NUM>), wherein the second tower shaft (<NUM>) is engaged to drive the sun gear (<NUM>) and the first tower shaft (<NUM>) is selectively coupled to the ring gear (<NUM>) through a first ring gear clutch (<NUM>);
a starter (<NUM>) selectively coupled to the sun gear (<NUM>) through a starter clutch (<NUM>);
a first electric motor (<NUM>) selectively coupled to the ring gear (<NUM>) through a first motor clutch (<NUM>); and
a second electric motor (<NUM>) selectively coupled to the sun gear (<NUM>) through a second motor clutch (<NUM>), wherein the first electric motor (<NUM>) and the second electric motor (<NUM>) are each operable to input power into a corresponding one of the first and second spools (<NUM>, <NUM>).