Torque path coupling assemblies for tiltrotor aircraft

1. A rotary propulsion system for a tiltrotor aircraft operable to transition between rotary and non rotary flight modes, the rotary propulsion system comprising:

an engine having an engine rotating speed in the non rotary flight mode;

a freewheeling unit coupled to the engine;

a gear system having a torque path coupling assembly between first and second gear assemblies, the first gear assembly coupled to the freewheeling unit and having an output with an outer conical face, the second gear assembly having an input; and

a proprotor assembly coupled to the second gear assembly, the proprotor assembly having a plurality of proprotor blades with a radially extended orientation and a proprotor rotating speed in the non rotary flight mode;

wherein, the torque path coupling assembly has an engaged position wherein the output of the first gear assembly is coupled to the input of the second gear assembly thereby providing a torque path between the engine and the proprotor assembly and a disengaged position wherein the output of the first gear assembly is independent of the input of the second gear assembly thereby interrupting the torque path between the engine and the proprotor assembly;

wherein, the torque path coupling assembly includes a coupling sleeve and a synchronizing ring, the coupling sleeve having internal splines that are in mesh with the input of the second gear assembly and in mesh with the output of the first gear assembly when the torque path coupling assembly is in the engaged position, the synchronizing ring having outer splines and an inner friction cone, the outer splines operable to selectively align with the internal splines of the coupling sleeve; and

wherein, the inner friction cone of the synchronizing ring is shifted into friction contact with the outer conical face of the output of the first gear assembly responsive to shifting the coupling sleeve to synchronize a rotating speed of the output of the first gear assembly and a rotating speed of the input of the second gear assembly.

2. The rotary propulsion system as recited in claim 1 wherein the freewheeling unit further comprises a sprag clutch.

3. The rotary propulsion system as recited in claim 1 wherein the internal splines of the coupling sleeve are not in mesh with the output of the first gear assembly when the torque path coupling assembly is in the disengaged position.

4. The rotary propulsion system as recited in claim 1 wherein the torque path coupling assembly further comprises a hub coupled to the input of the second gear assembly and a plurality of struts spring mounted to the hub; and

wherein axially shifting the coupling sleeve toward the output of the first gear assembly from the disengaged position causes the struts to contact the synchronizing ring to shift the inner friction cone of the synchronizing ring into friction contact with the outer conical face of the output of the first gear assembly.

5. The rotary propulsion system as recited in claim 1 wherein the output of the first gear assembly has an output rotating speed that is proportional to the engine rotating speed;

wherein the input of the second gear assembly has an input rotating speed that is proportional to the proprotor rotating speed;

wherein the torque path coupling assembly is shiftable from the disengaged position to the engaged position when the output rotating speed and the input rotating speed are synchronized; and

wherein the input rotating speed is greater than the output rotating speed prior to synchronizing the output rotating speed and the input rotating speed.

6. The rotary propulsion system as recited in claim 5 wherein the input rotating speed is between about 0.5 percent and about 1 percent greater than the output rotating speed prior to synchronizing the output rotating speed and the input rotating speed.

7. The rotary propulsion system as recited in claim 5 wherein the input rotating speed is between about 1 percent and about 2 percent greater than the output rotating speed prior to synchronizing the output rotating speed and the input rotating speed.

8. A tiltrotor aircraft operable to transition between rotary and non rotary flight modes, the tiltrotor aircraft comprising:

an engine having an engine rotating speed in the non rotary flight mode;

a freewheeling unit coupled to the engine;

a proprotor assembly having a plurality of proprotor blades with a radially extended orientation and a proprotor rotating speed in the non rotary flight mode; and

a gear system having a torque path coupling assembly between first and second gear assemblies, the first gear assembly coupled to the freewheeling unit and having an output with an outer conical face and an output rotating speed that is proportional to the engine rotating speed, the second gear assembly coupled to the proprotor assembly and having an input with an input rotating speed that is proportional to the proprotor rotating speed;

wherein, the torque path coupling assembly has an engaged position wherein the output of the first gear assembly is coupled to the input of the second gear assembly thereby providing a torque path between the engine and the proprotor assembly;

wherein, the torque path coupling assembly has a disengaged position wherein the output of the first gear assembly is independent of the input of the second gear assembly thereby interrupting the torque path between the engine and the proprotor assembly;

wherein, the torque path coupling assembly includes a coupling sleeve and a synchronizing ring, the coupling sleeve having internal splines that are in mesh with the input of the second gear assembly and in mesh with the output of the first gear assembly when the torque path coupling assembly is in the engaged position, the synchronizing ring having outer splines and an inner friction cone, the outer splines operable to selectively align with the internal splines of the coupling sleeve; and

wherein, the inner friction cone of the synchronizing ring is shifted into friction contact with the outer conical face of the output of the first gear assembly responsive to shifting the coupling sleeve to synchronize a rotating speed of the output of the first gear assembly and a rotating speed of the input of the second gear assembly; and

wherein, the torque path coupling assembly is shiftable from the disengaged position to the engaged position when the rotating speeds of the output and the input are synchronized.

9. The tiltrotor aircraft as recited in claim 8 wherein the engine is operable in a turboshaft mode and a turbofan mode.

10. The tiltrotor aircraft as recited in claim 8 wherein the input rotating speed is greater than the output rotating speed prior to synchronizing the output rotating speed and the input rotating speed.

11. The tiltrotor aircraft as recited in claim 8 wherein the proprotor rotating speed in the non rotary flight mode is generated responsive to aerodynamic forces acting on the proprotor blades.

12. The tiltrotor aircraft as recited in claim 8 wherein the proprotor blades further comprise a non rotating and folded configuration in the non rotary flight mode.

13. A method of transitioning a tiltrotor aircraft from a non rotary flight mode to a rotary flight mode, the method comprising:

operating an engine in a turbofan mode at an engine rotating speed;

rotating an output of a first gear assembly at an output rotating speed that is proportional to the engine rotating speed, a freewheeling unit coupled between the engine and the first gear assembly;

rotating a proprotor assembly at a proprotor rotating speed responsive to aerodynamic forces acting on a plurality of proprotor blades;

rotating an input of a second gear assembly at an input rotating speed that is proportional to the proprotor rotating speed, the input rotating speed greater than the output rotating speed; and

actuating a torque path coupling assembly from a disengaged position, wherein the output of the first gear assembly is independent of the input of the second gear assembly, thereby interrupting a torque path between the engine and the proprotor assembly, to an engaged position including synchronizing the output rotating speed with the input rotating speed by shifting an inner friction cone of a synchronizing ring into friction contact with an outer conical face of the output of the first gear assembly and coupling the output of the first gear assembly to the input of the second gear assembly by shifting internal splines of a coupling sleeve in mesh with outer splines of the synchronizing ring and in mesh with the output of the first gear assembly, thereby providing the torque path between the engine and the proprotor assembly to operate the engine in a turboshaft mode.

14. The method as recited in claim 13 further comprising establishing the input rotating speed between about 0.5 percent and about 1 percent higher than the output rotating speed prior to synchronizing the output rotating speed with the input rotating speed.

15. The method as recited in claim 13 further comprising establishing the input rotating speed between about 1 percent and about 2 percent higher than the output rotating speed prior to synchronizing the output rotating speed with the input rotating speed.

16. The method as recited in claim 13 further comprising increasing the engine rotating speed to transition the freewheeling unit from an over running mode to a driving mode after actuating the torque path coupling assembly.