Systems and methods for transferring mechanical power in a turbine engine

1. A system for transferring mechanical power in a turbine engine including a low pressure spool and a high pressure spool, the system comprising:

a power transfer unit coupled to an output shaft of the low pressure spool; and

an accessory gearbox including a gear train, the accessory gearbox mounted directly to the power transfer unit, the accessory gearbox coupled to a drive shaft of the high pressure spool,

wherein the power transfer unit includes a shaft configured to couple an output of the power transfer unit to the accessory gearbox to transfer power from the output shaft of the low pressure spool to the gear train of the accessory gearbox, wherein the accessory gearbox is configured to drive the high pressure spool in order to mechanically link the low pressure spool to the high pressure spool.

2. The system of claim 1 , further comprising a clutch coupled to the power transfer unit, wherein the clutch is configured to transfer power produced from the low pressure spool to the high pressure spool.

3. The system of claim 2 , wherein the turbine engine is included on an aircraft, and the system further comprises:

an engine electronic controller (EEC) including a processor for executing instructions to engage the clutch and couple the power transfer unit to the drive shaft of the high pressure spool based on a ground speed of the aircraft.

4. The system of claim 2 , wherein the turbine engine is included on an aircraft, and the system further comprises:

an engine electronic controller (EEC) including a processor for executing instructions to engage the clutch and couple the power transfer unit to the drive shaft of the high pressure spool during ground idle operation of the aircraft.

5. The system of claim 2 , wherein the turbine engine is included on an aircraft, and the system further comprises:

an engine electronic controller (EEC) including a processor for executing instructions to engage the clutch and couple the power transfer unit to the drive shaft of the high pressure spool when the aircraft is taxiing.

6. The system of claim 2 , wherein the turbine engine is included on an aircraft, and the system further comprises:

an engine electronic controller (EEC) including a processor for executing instructions to disengage the clutch to decouple the power transfer unit from the drive shaft of the high pressure spool when the aircraft enters takeoff mode.

7. The system of claim 2 , wherein the turbine engine is included on an aircraft, and the system further comprises:

an engine electronic controller (EEC) including a processor for executing instructions to engage the clutch and couple the power transfer unit to the drive shaft of the high pressure spool during flight of the aircraft to assist with restart of the turbine engine.

8. The system of claim 2 , wherein the turbine engine is included on an aircraft, and the system further comprises:

an engine electronic controller (EEC) including a processor for executing instructions to engage the clutch and couple the power transfer unit to the drive shaft of the high pressure spool based on receipt of a signal indicative of weight on wheels of the aircraft.

9. The system of claim 2 , wherein the turbine engine is included on an aircraft, and the system further comprises:

an engine electronic controller (EEC) including a processor for executing instructions to engage the clutch and couple the power transfer unit to the drive shaft of the high pressure spool during descent of the aircraft.

10. The system of claim 2 , further comprising:

a pilot operated control switch for manual control of the clutch.

11. The system of claim 1 , wherein the power transfer unit is operable to (i) detect a decrease in power provided to the high pressure spool and to (ii) cause a surge bleed valve to open.

12. The system of claim 1 , further comprising a sprag clutch assembly including a sprag clutch with a sprag clutch input shaft and an sprag clutch output shaft, where the sprag clutch input shaft is coupled to the power transfer unit and where the sprag clutch output shaft is coupled to the shaft of the power transfer unit that couples to the accessory gearbox.

13. The system of claim 12 , further comprising a first speed sensor disposed proximate to the sprag clutch input shaft and a second speed sensor disposed proximate to the sprag clutch output shaft, the first speed sensor configured to measure a rotational speed of the sprag clutch input shaft and the second speed sensor configured to measure a rotational speed of the sprag clutch output shaft.

14. The system of claim 13 , further comprising an engine electronic controller (EEC) including a processor for executing instructions to verify whether power is being transferred from the low pressure spool to the high pressure spool based on inputs received from the first speed sensor and the second speed sensor.

15. The system of claim 1 , further comprising a torque sensor configured to sense the torque being transmitted between the low pressure spool and a drive shaft of the high pressure spool.

16. A system for transferring mechanical power in a turbine engine from a low pressure spool to a high pressure spool, the system comprising:

a power transfer unit coupled to an output shaft of the low pressure spool;

an accessory gearbox including a gear train, the accessory gearbox mounted directly to the power transfer unit, the accessory gearbox coupled to a drive shaft of the high pressure spool,

a clutch that is configured to selectively couple the power transfer unit directly to the accessory gearbox, and

wherein the power transfer unit transfers power from the output shaft of the low pressure spool to the gear train of the accessory gearbox, wherein the accessory gearbox is configured to drive the high pressure spool in order to mechanically link the low pressure spool to the high pressure spool.

17. A method for transferring mechanical power in a turbine engine, wherein the turbine engine includes a low pressure spool and a high pressure spool, the method comprising:

coupling a power transfer unit to an output shaft of the low pressure spool; and

coupling an accessory gearbox coupled to a drive shaft of the high pressure spool, wherein the accessory gearbox includes a gear train, and the accessory gearbox mounted directly to the power transfer unit,

coupling an output of the power transfer unit to the accessory gearbox to transfer power from the output shaft of the low pressure spool to the gear train of the accessory gearbox, wherein the accessory gearbox is configured to drive the high pressure spool in order to mechanically link the low pressure spool to the high pressure spool.

18. The method of claim 17 further comprising coupling, by a clutch, the power transfer unit to the accessory gearbox, wherein power produced from the low pressure spool is diverted to the high pressure spool.

19. The method of claim 18 , wherein the turbine engine is included on an aircraft, and the method further comprises:

engaging the clutch and coupling the power transfer unit to the drive shaft of the high pressure spool, via the accessory gearbox, based on a ground speed of the aircraft.

20. The method of claim 18 , wherein the turbine engine is included on an aircraft, and the method further comprises:

engaging the clutch and coupling the power transfer unit to the drive shaft of the high pressure spool, via the accessory gearbox, during ground idle operation of the aircraft.

21. The method of claim 18 , wherein the turbine engine is included on an aircraft, and the method further comprises:

engaging the clutch and coupling the power transfer unit to the drive shaft of the high pressure spool, via the accessory gearbox, during flight of the aircraft to assist with restart of the turbine engine.

22. A system for transferring mechanical power in a turbine engine including a low pressure spool and a high pressure spool, the system comprising:

a power transfer unit coupled to an output shaft of the low pressure spool;

an accessory gearbox including a gear train, the accessory gearbox mounted directly to the power transfer unit, the accessory gearbox coupled to a drive shaft of the high pressure spool,

a clutch coupled directly between the power transfer unit and the accessory gearbox, wherein the clutch is configured to transfer power produced from the high pressure spool to the low pressure spool in order to mechanically link the low pressure spool to the high pressure spool.