Hybrid electric dual spool power extraction gearbox

1. A turbofan engine comprising:

a first spool including a first turbine;

a second spool including a second turbine disposed axially forward of the first turbine;

a first tower shaft engaged to the first spool;

a second tower shaft engaged to the second spool;

an accessory gearbox supporting a plurality of accessory components;

a superposition gear system disposed within the accessory gearbox, the superposition gear system including, a plurality of intermediate gears engaged to the sun gear and supported in a carrier and a ring gear circumscribing the intermediate gears, wherein the second tower shaft is engaged to drive the sun gear;

a starter selectively coupled to the sun gear through a starter clutch;

a first electric motor selectively coupled to the ring gear through a first motor clutch,

a second electric motor selectively coupled to the sun gear through a second motor clutch, wherein the first electric motor and the second electric motor are operable to input power into a corresponding one of the first and second spools.

2. The turbofan engine as recited in claim 1 , including an electric power supply providing power to the first electric motor and the second electric motor.

3. The turbofan engine as recited in claim 1 , including a first ring gear clutch for selectively coupling the first tower shaft to the ring gear and a second ring gear clutch for selectively coupling the ring gear to a static structure of the engine.

4. The turbofan engine as recited in claim 3 , wherein 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.

5. The turbofan engine as recited in claim 4 , including a sun gear shaft supporting the sun gear, the sun gear shaft coupling the second tower shaft to the starter through the starter clutch.

6. The turbofan engine as recited in claim 5 , including a ring gear shaft driven by the first tower shaft, wherein the ring gear is coupled to drive a second group of the plurality of accessory components.

7. The turbofan engine as recited in claim 6 , including a drive gear coupled to the sun gear shaft to drive a third group of the plurality of accessory components.

8. The turbofan engine as recited in claim 1 , wherein the first turbine comprises a low pressure turbine and the second turbine comprises a high pressure turbine.

9. The turbofan engine as recited in claim 1 , wherein the first tower shaft and the second tower shaft are concentric about a common axis.

10. The turbofan engine as recited in claim 1 , wherein the first tower shaft and the second tower shaft are disposed about different axes.

11. The turbofan engine as recited in claim 3 , wherein the starter clutch, first motor clutch, second motor clutch, first ring gear clutch and the second ring gear clutch comprise one-way mechanical clutches.

12. The turbofan engine as recited in claim 1 , wherein the first motor clutch couples the first electric motor to the first tower shaft to drive the first spool and 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.

13. The turbofan engine as recited in claim 12 , wherein 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.

14. The turbofan engine as recited in claim 13 , wherein the second clutch couples the second electric motor to the second tower shaft to drive the second spool in an engine starting operating condition.

15. An accessory gearbox for a turbofan engine, the accessory gearbox comprising:

a superposition gear system including a sun gear coupled to a second tower shaft of the turbofan engine;

a plurality of intermediate gears engaged to the sun gear and supported in a carrier;

a ring gear circumscribing the intermediate gears and coupled to a first tower shaft;

a starter selectively coupled to the sun gear through a starter clutch;

a first output coupled to the carrier shaft for driving a first group of accessory components;

a second output coupled to the first tower shaft for driving a second group of accessory components;

a first motor means coupled to the ring gear;

a second motor means coupled to the sun gear, wherein the first motor means and the second motor means are operable to input power into a corresponding one of the first and second tower shafts.

16. The accessory gearbox as recited in claim 15 , wherein the first output comprises a carrier shaft attached to the carrier that is coupled to a first gear system driving the first group of accessory components.

17. The accessory gearbox as recited in claim 16 , wherein the second output comprises a ring gear shaft driven by the first tower shaft that is coupled to a second gear system for driving the second group of accessory components.

18. The accessory gearbox as recited in claim 15 , wherein each of the first motor means and second motor means comprise electric motors that are powered by an electric power supply.

19. The accessory gearbox as recited in claim 18 , wherein a first motor clutch couples the first electric motor to the first tower shaft to drive a first spool and a second motor clutch couples the second electric motor to drive the second tower shaft in an engine idle operating condition.

20. The accessory gearbox as recited in claim 19 , wherein the second clutch couples the second electric motor to the second tower shaft to drive a second spool in an engine starting operating condition.

21. The accessory gearbox as recited in claim 15 , wherein the each of the first motor means and second motor means comprise electric motor/generators that are powered by an electric power supply.

22. A method of operating an accessory gearbox for a turbofan engine comprising:

coupling a first tower shaft to engage a first spool;

coupling a second tower shaft to engage a second spool;

coupling a sun gear of a superposition gear system supported within the accessory gearbox to the second tower shaft, wherein the superposition gear system includes the sun gear, a plurality of intermediate gears engaged to the sun gear and supported in a carrier and a ring gear circumscribing the intermediate gears;

coupling a first electric motor to the first tower shaft to input power to the first spool; and

coupling a second electric motor to the second tower shaft to input power to the second spool during an engine idle operating condition.

23. The method as recited in claim 22 , including coupling a starter to the sun gear, coupling the ring gear to an engine static structure, coupling the second electric motor to the second tower shaft and driving the second spool with the starter and the second electric motor to rotate the second spool and start the turbofan engine.

24. The method as recited in claim 23 , including decoupling each of the first electric motor and the second electric motor such that neither the first electric motor nor the second electric motor input power to either of the first spool and the second spool and the first tower shaft drives the ring gear and 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.

25. The method as recited in claim 22 , wherein 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.

26. The method as recited in claim 25 , wherein a third output coupled to 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.