Air turbine starter with decoupler

1. An air turbine starter for starting an engine, comprising:

a housing defining an inlet, an outlet, and a flow path extending between the inlet and the outlet for communicating a flow of gas therethrough;

a turbine member journaled within the housing and disposed within the flow path for rotatably extracting mechanical power from the flow of gas;

a gear train drivingly coupled with the turbine member;

a clutch having a drive shaft that is operably coupled with the gear train;

an output shaft with a threaded portion configured to be operably coupled to and rotate with the engine; and

a backdrive decoupler, comprising:

a threaded shaft operably coupled to the output shaft and where the threaded shaft is selectively receivable and axially moveable with respect to the threaded portion of the output shaft; and

a retention mechanism having a primary axis extending axially through a portion of the output shaft and a portion of the threaded shaft and selectively operably coupling the output shaft to a first end of the threaded shaft; and

wherein when driving torque is transmitted from the drive shaft of the clutch to the output shaft, the retention mechanism is not loaded, when overrunning torque is transmitted below a certain level the output shaft, the retention mechanism, and the threaded shaft are loaded, and when the overrunning torque reaches a certain level the retention mechanism uncouples the drive shaft and the first end of the threaded shaft to define a decoupled and separated position where the output shaft is disengaged from the engine.

2. The air turbine starter of claim 1 wherein the retention mechanism is a shear pin wherein the pin shears when the overrunning torque reaches the certain level.

3. The air turbine starter of claim 1 wherein the output shaft is an output shaft having a three helical female thread.

4. The air turbine starter of claim 1 wherein the threaded shaft further comprises a stop at the first end that abuts with a portion of the output shaft.

5. The air turbine starter of claim 4 wherein the driving torque is transmitted through the stop of the threaded shaft and the output shaft.

6. The air turbine starter of claim 1 , further comprising a locking mechanism configured to secure the output shaft in the decoupled and separated position.

7. The air turbine starter of claim 6 wherein the locking mechanism comprises a spring lock.

8. The air turbine starter of claim 1 wherein the retention mechanism comprises at least one moveable element that is moveable between a first position where the moveable element engages with an interface portion of the output shaft and a second position where the moveable element is moved radially inwardly.

9. The air turbine starter of claim 8 wherein the moveable element is a ball detent that moves radially inward within a channel received in the threaded shaft when the overrunning torque reaches the certain level.

10. The air turbine starter of claim 1 wherein the threaded portion of the output shaft is an internal threaded portion.

11. The air turbine starter of claim 1 wherein the output shaft further comprises first driving surfaces and the threaded shaft comprises second driving surfaces that interengage with the first driving surfaces to transmit driving torque.

12. A decoupler assembly for decoupling an output shaft during backdrive, the output shaft having a threaded portion, comprising:

a threaded shaft having a first end with a stop and a second end configured to be operably coupled to a drive shaft of an engine and where the threaded shaft is selectively receivable and axially moveable with respect to the threaded portion of the output shaft; and

a retention mechanism having a primary axis extending axially through a portion of the output shaft and a portion of the threaded shaft and selectively operably coupling the output shaft to the first end of the threaded shaft;

wherein when driving torque is transmitted to the output shaft, the retention mechanism is not loaded, when overrunning torque is transmitted below a certain level the output shaft, retention mechanism, and threaded shaft are loaded, and when the overrunning torque reaches a certain level the retention mechanism uncouples the output shaft and the first end of the threaded shaft and the output shaft moves in a direction away from the first end of the threaded shaft.

13. The decoupler assembly of claim 12 wherein the retention mechanism is a shear pin and wherein the pin shears when the overrunning torque reaches the certain level.

14. The decoupler assembly of claim 12 wherein the driving torque is transmitted through the stop of the threaded shaft and the output shaft.

15. The decoupler assembly of claim 12 , further comprising a locking mechanism configured to secure the output shaft in a decoupled position.

16. The decoupler assembly of claim 12 wherein the retention mechanism comprises at least one moveable element that is moveable between a first position where the moveable element engages with an interface portion of the output shaft and a second position where the moveable element is moved radially inwardly.

17. The decoupler assembly of claim 16 wherein the moveable element is a ball detent that moves radially inward within a channel received in the threaded shaft when the overrunning torque reaches the certain level.

18. A method for operating a starter motor, comprising:

extracting mechanical power from a flow of gas utilizing a turbine and driving a gear train and clutch having a threaded output shaft therewith;

transmitting a driving torque from a drive shaft through a threaded shaft, which is retained within the threaded output shaft by a retention mechanism having a primary axis extending axially through a portion of the threaded output shaft and a portion of the threaded shaft, to the threaded output shaft, which is operably coupled to an engine; and

during back driving, ceasing retention by the retention mechanism when overrunning torque reaches a certain level such that the threaded output shaft decouples from the engine.

19. The method of claim 18 , further comprising retaining the output shaft in place to prevent reengagement of the output shaft and the engine.

20. The method of claim 18 wherein the clutch allows for overrun where overrunning torque is transmitted below a certain level and the output shaft, the retention mechanism, and the threaded shaft are loaded.