Patent Description:
<CIT> discloses a prior art gas turbine arrangement.

<CIT> discloses a prior art power transmission.

<CIT> discloses a prior art combined engine-starter and accessory drive system.

A turbine engine according to an aspect of the present invention is provided in accordance with claim <NUM>.

In a further embodiment of the foregoing turbine engine, the differential gear system includes a first differential gear and a second differential gear both coupled to a differential shaft. The core engine is coupled to the first differential gear and the accessory gearbox is coupled to the second differential gear.

In a further embodiment of any of the foregoing turbine engines, a tower shaft is coupled to one of the first spool or the second spool.

In a further embodiment of any of the foregoing turbine engines, a first gear ratio between a tower shaft gear driven by the tower shaft. The first differential gear is different than a second gear ratio between an accessory drive gear and the second differential gear.

In a further embodiment of any of the foregoing turbine engines, the first differential gear and the second differential gear are supported in a rotatable differential carrier. A boost spool input gear is coupled through a ring gear to drive rotation of the rotatable differential carrier.

In a further embodiment of any of the foregoing turbine engines, the secondary drive system comprises one of a gas turbine engine or an electric motor-generator.

A method of operating a turbine engine according to another aspect of the present invention is provided in accordance with claim <NUM>.

In a further embodiment of the foregoing method of operating a turbine engine, the differential gear system includes a brake for preventing rotation of the tower shaft. Operating the accessory gearbox according to another engine operating configuration includes engaging the brake to prevent rotation of the tower shaft and driving the accessory gear box with the boost spool through the differential gear system.

In a further embodiment of any of the foregoing methods of operating a turbine engine, the boost spool is driven with one of a secondary gas turbine engine or an electric motor-generator.

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

<FIG> schematically illustrates a turbine engine <NUM>. The turbine engine <NUM> is disclosed herein as a two-spool turbofan that generally incorporates a fan section <NUM> and a core engine section <NUM>. The core engine section <NUM> includes a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>.

The exemplary engine <NUM> generally includes a first (or low speed) spool <NUM> and a second (or high speed) spool <NUM> mounted for rotation about an engine central longitudinal axis A relative to an engine static structure <NUM> via several bearing systems <NUM>. It should be understood that the various bearing systems <NUM> may be provided at different locations and the number of bearing systems <NUM> may be varied as appropriate to the application.

The inner shaft <NUM> is connected to a fan section <NUM>.

The low pressure turbine <NUM> drives the fan section <NUM> through a fan drive gear system <NUM> such that the fan section <NUM> and the low pressure turbine <NUM> rotate at different speeds. It will be appreciated that each of the positions of the fan section <NUM>, compressor section <NUM>, combustor section <NUM>, turbine section <NUM>, and fan drive gear system <NUM> may be varied within the scope and contemplation of this disclosure.

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 tower shaft <NUM> and tower shaft gear <NUM> couple a shaft of the core engine to a differential gearbox <NUM>. The tower shaft <NUM> may be coupled to either the inner shaft <NUM> or the outer shaft <NUM>. In this example, the inner shaft <NUM> is coupled to the tower shaft gear <NUM> through the tower shaft <NUM>. The accessory gearbox <NUM> is driven by an output from a differential gear system <NUM>. The differential gear system <NUM> is driven by a coupling <NUM> with the tower shaft <NUM> of the core engine and by a boost spool <NUM>.

In this disclosed example embodiment, the boost spool <NUM> is part of a secondary turbine engine <NUM>. The secondary turbine engine <NUM> includes a compressor <NUM>, combustor <NUM> and turbine <NUM> sized to provide limited power to the turbine engine <NUM>. The secondary turbine engine <NUM> provides additional power to augment operation of the turbine engine <NUM> during low and/or partial power conditions. The secondary turbine engine <NUM> draws core airflow from the main engine <NUM> from a location within the compressor section <NUM> through and inlet duct <NUM>. In this disclosed example, the duct <NUM> draws core airflow C from a location between the compressor section <NUM> and the combustor <NUM>. Exhaust flow is returned to the main engine <NUM> through an exhaust duct <NUM>. In this disclosed example, the exhaust duct returns the exhaust flow back to a location forward of the combustor <NUM>. It should be appreciated, that other locations for drawings and returning core flow from the main engine <NUM> could be utilized and are within the scope and contemplation of this disclosure.

The differential gear system <NUM> couples power input from both the tower shaft <NUM> and the boost spool <NUM> to drive the accessory gearbox <NUM>. A controller <NUM> is provided to operate features of the differential gear system <NUM> to tailor operation based on engine operating requirements. In this disclosed example, a starter motor <NUM> is coupled to the accessory gearbox <NUM> to provide an engine starting capability.

Referring to <FIG> with continued reference to <FIG>, the boost spool <NUM> may be driven by an electric motor-generator <NUM>. The electric motor-generator <NUM> is powered and controlled by an electric power system <NUM> of the aircraft and/or engine. Operation of the motor-generator <NUM> and the secondary turbine engine <NUM> augment operation of the turbine engine <NUM> to improve engine efficiency in low and/or partial power conditions.

Referring to <FIG>, with continued reference to <FIG>, the differential gear system <NUM> enables power and torque to be input from both the core engine <NUM> through the tower shaft <NUM> and the boost spool <NUM>. The example differential gear system <NUM> also enables different output of torque between the tower shaft <NUM> and the boost spool <NUM>.

The differential gear system <NUM> includes a first differential gear <NUM> mounted to a differential shaft <NUM> and supported within a differential carrier <NUM>. A second differential gear <NUM> is also mounted to the differential shaft <NUM>. The differential carrier <NUM> is rotatable about a first axis <NUM> and the differential shaft <NUM> is rotatable about a second axis <NUM> that is transverse to the axis <NUM>. Accordingly, the first and second differential gears <NUM>, <NUM> rotate about the axis <NUM> on a common differential shaft <NUM> and rotate about the first axis <NUM> transverse to rotation about the axis <NUM>. A first spool gear <NUM> is coupled to a tower input shaft <NUM> driven by the tower shaft gear <NUM>. An accessory drive gear <NUM> is engaged to the second differential gear <NUM> and drives an input shaft <NUM> of the accessory gearbox <NUM>.

A first gear ratio is established between the first differential gear <NUM> and the first spool gear <NUM>. A second gear ratio is established between the second differential gear <NUM> and the accessory drive gear <NUM>. The first gear ratio and the second gear ratio are established by providing gears of different diameters and/or numbers of teeth. In one disclosed embodiment, the first gear ratio is different than the second gear ratio. In one disclosed embodiment, the first gear ratio is greater than the second gear ratio. It should be appreciated, that the first gear ratio and the second gear ratio are tailored to the speed of the tower shaft <NUM> and the speed at which application specific parameters require operation of the accessory gearbox <NUM>. The range of either of the first gear ratio to the second gear ratio in one example embodiment is between <NUM>:<NUM> and <NUM>:<NUM>. In another example embodiment, the range of either of the first gear ratio and the second gear ratio is between <NUM>:<NUM> and <NUM>:<NUM>. It should be appreciated, that other gear ratios could be utilized and are within the contemplation and scope of this disclosure.

Moreover, in the disclosed differential gear system <NUM>, the first differential gear <NUM> and the second differential gear <NUM> are coupled to a common shaft <NUM> such that the both gears <NUM>, <NUM> revolve at a common speed about axis <NUM>.

The first and second differential gears <NUM>, <NUM> are supported within the rotatable differential carrier <NUM>. The differential carrier <NUM> is coupled to a ring gear <NUM> and the ring gear <NUM> is engaged to the boost input gear <NUM>. The boost input gear <NUM> is coupled to a shaft <NUM>. The shaft <NUM> is selectively coupled to the boost input gear <NUM> by a boost clutch <NUM>.

It should be appreciated that the illustrated inputs into the example differential gear system <NUM> do not reflect the orientation of respective drive systems. For example, the tower shaft gear <NUM> may not be disposed along the axis <NUM>. Instead, the tower shaft coupling <NUM> may be spaced apart from the axis <NUM> and a gear coupling such as that indicated at <NUM> in <FIG> may be provided to communicate the input torque and power. Similarly, the boost spool <NUM> may not be disposed along the axis <NUM>. However, a suitable gear coupling might be provided to communicate power to the gear system <NUM> as is schematically shown. Accordingly, it is within the contemplation of this disclosure that additional gear coupling systems may be incorporated to communicate power from the different inputs to the differential gear system <NUM>.

A brake <NUM> is coupled to a tower input shaft <NUM> to prevent rotation of the tower shaft <NUM>. A locking clutch <NUM> is provided between the tower input shaft <NUM> and the shaft <NUM> that provides an input to the accessory gearbox <NUM>. Engaging the locking clutch <NUM> enables the tower shaft <NUM> to directly drive the accessory gearbox <NUM>. Directly driving the accessory gearbox <NUM> with the tower shaft <NUM> bypasses the differential gear system <NUM>. Alternatively, a brake on the differential shaft <NUM> may be used to the same effect as the differential locking clutch described.

In operation, the boost spool <NUM> is driven to augment power to the engine <NUM> in low and partial power conditions. In the configuration of the differential gear system shown in <FIG>, the boost spool <NUM> is driving the ring gear <NUM> to rotate the differential carrier <NUM>. The tower shaft gear <NUM> is also rotating. In the configuration shown in <FIG>, the controller <NUM> disengages the differential locking clutch <NUM> and the tower shaft brake <NUM>. The controller <NUM> engages the boost clutch <NUM> such that torque input by the boost spool <NUM> is communicated to both the accessory gearbox <NUM> and the tower shaft <NUM> to augment engine operation.

Referring to <FIG>, another operational configuration of the disclosed example differential gear system <NUM> is shown and is utilized for starting the engine <NUM>. In this configuration, the controller <NUM> engages the brake <NUM> to prevent rotation of the tower shaft <NUM>. The controller <NUM> commands engagement of the boost clutch <NUM> and disengages the locking clutch <NUM>. The starter motor <NUM> is coupled to the accessory gearbox <NUM> to rotate the shaft <NUM> through the differential gear system <NUM> to start the secondary engine <NUM> that drives the boost spool <NUM>. All the power and torque input from the starter motor <NUM> drives the boost spool <NUM> until the secondary engine combustor <NUM> can be ignited to generate a high energy exhaust gas flow that expands through the turbine <NUM>. Power from the accessory gearbox <NUM> is routed through the second differential gear <NUM>, carrier <NUM>, and ring gear <NUM> to drive the boost spool <NUM>.

Once the secondary engine <NUM> is started, the starter motor <NUM> is shut off and all the power and torque input from the boost spool <NUM> is routed to the drive the accessory gearbox <NUM> to maintain ground idle. Power from the boost spool <NUM> is routed through ring gear <NUM> and the differential carrier <NUM> to drive the accessory drive gear <NUM> with the second differential gear <NUM>. Once the engine <NUM> is idling, the brake <NUM> may be released to enable the high energy exhaust gas flow through the outlet duct <NUM> to rotate one of the spools <NUM>, <NUM> and operate the main engine <NUM> for higher power operation.

Referring to <FIG>, another configuration of the differential gear system <NUM> is shown with the locking clutch <NUM> engaged and the boost clutch <NUM> disengaged. In this orientation, the tower shaft coupler <NUM> powers the accessory gearbox <NUM>. The boost spool <NUM> is decoupled and does not provide additional power. The configuration shown in <FIG> may be utilized when the engine <NUM> is operating at more efficient power settings that do not require augmentation from the boost spool <NUM>.

Referring to <FIG>, a boost gear system <NUM> is shown and, according to the present invention, is utilized instead of the boost clutch <NUM>. The example boost gear system <NUM> is an epicyclic gear system that includes a plurality of intermediate gears <NUM> supported in a selectively rotatable carrier <NUM>. The intermediate gears <NUM> are coupled to an inner output gear <NUM> that is coupled to drive the differential gear system <NUM>. The intermediate gears <NUM> are circumscribed and coupled to an outer gear <NUM> that is driven by the boost spool <NUM>.

In operation when power from the boost spool <NUM> is desired to augment engine operation, the carrier <NUM> is fixed by a mechanical coupling <NUM> to prevent rotation. The boost gear system <NUM> operates as a star gear system. Power is thereby transmitted from the outer gear <NUM>, through the intermediate gears <NUM> to drive the inner output gear <NUM>. When power from the boost spool <NUM> is not desired, the mechanical coupling <NUM> is released and the carrier <NUM> will rotate freely and not communicate power to the inner output gear <NUM>. It should be appreciated, that the boost gear system <NUM> is shown schematically and may be orientated in alternate configurations to fit within different design spaces and performance requirements. Moreover, the input and output into the boost gear system <NUM> may be modified to accommodate other engine and gear system requirements.

The disclosed differential gear system <NUM> enables the tailoring of multiple inputs and outputs to augment engine operation.

Claim 1:
A turbine engine (<NUM>) comprising:
a core engine (<NUM>) including a first spool (<NUM>) and a second spool (<NUM>) rotatable about a main engine longitudinal axis (A);
a boost spool (<NUM>) powered by a secondary drive system (<NUM>, <NUM>);
an accessory gearbox (<NUM>) coupled to the core engine (<NUM>) and the boost spool (<NUM>); and
a differential gear system (<NUM>) coupled between the core engine (<NUM>), the boost spool (<NUM>) and the accessory gearbox (<NUM>) for distributing power between the boost spool (<NUM>), the core engine (<NUM>) and the accessory gearbox (<NUM>),
characterised in that the turbine engine (<NUM>) comprises:
a boost gear system (<NUM>) including a plurality of intermediate gears (<NUM>) supported in a selectively rotatable boost carrier (<NUM>), an inner output gear (<NUM>) that is coupled to drive the differential gear system (<NUM>), engaged to the intermediate gears (<NUM>) and an outer gear (<NUM>) coupled to the boost spool (<NUM>), wherein power is transmitted from the outer gear (<NUM>) through the intermediate gears (<NUM>) to the inner output gear (<NUM>) when the carrier (<NUM>) is fixed and power is not transmitted between the outer gear (<NUM>) to the inner output gear (<NUM>) when the carrier (<NUM>) is allowed to rotate.