Oil system for turbine engine and related method

1. A turboprop gas turbine engine comprising:

a shaft configured to be driven by a turbine;

a gear train system configured to transfer power from the shaft to a propeller coupled to the turbine engine; and

an oil system comprising:

an oil pump in fluid communication with one or more lubrication loads of the turbine engine;

a first electric motor drivingly engaged to the oil pump for driving the oil pump during a first mode of operation; and

a coupling device configured to:

drivingly disengage the gear train system from the oil pump during the first mode of operation; and

drivingly engage the gear train system to the oil pump to drive the oil pump with the gear train system during a second mode of operation.

2. The turboprop gas turbine engine as defined in claim 1 , wherein the first electric motor is configured to operate as a generator and be driven by the gear train system during the second mode of operation.

3. The turboprop gas turbine engine as defined in claim 2 , comprising a battery configured to power the first electric motor during the first mode of operation and be charged by the first electric motor operating as a generator during the second mode of operation.

4. The turboprop gas turbine engine as defined in claim 1 , comprising a second electric motor configured to drive the gear train system during the first mode of operation.

5. The turboprop gas turbine engine as defined in claim 1 , wherein the coupling device is configured to transfer motive power from the gear train system to the oil pump when a driving speed from the gear train system is higher than a driving speed from the first electric motor.

6. The turboprop gas turbine engine as defined in claim 1 , wherein the coupling device is configured to drivingly engage and disengage an accessory drive shaft of the gear train system to and from the oil pump based on a rotational speed of the accessory drive shaft.

7. An oil system of a turbine engine, the oil system comprising:

an oil pump for fluid communication with one or more lubrication loads of the turbine engine;

a first source of motive power drivingly engaged to the oil pump for driving the oil pump during a first mode of operation; and

a coupling device configured to:

drivingly disengage a second source of motive power from the oil pump during the first mode of operation; and

drivingly engage the second source of motive power to the oil pump to drive the oil pump with the second source of motive power during a second mode of operation.

8. The oil system as defined in claim 7 , wherein the first source of motive power comprises an electric motor.

9. The oil system as defined in claim 8 , wherein the electric motor is configured to operate as a generator and be driven by the second source of motive power during the second mode of operation.

10. The oil system as defined in claim 9 , comprising a battery configured to power the electric motor during the first mode of operation and be charged by the electric motor operating as a generator during the second mode of operation.

11. The oil system as defined in claim 7 , wherein the coupling device is configured to transfer motive power from the second source of motive power to the oil pump when a driving speed from the second source of motive power is higher than a driving speed from the first source of motive power.

12. The oil system as defined in claim 7 , wherein the coupling device comprises a one-way rotation coupling device.

13. The oil system as defined in claim 7 , wherein the coupling device comprises a sprag clutch.

14. The oil system as defined in claim 7 , wherein the coupling device is configured to drivingly engage and disengage the second source of motive power to and from the oil pump based on an operational speed of the second source of motive power.

15. A method for driving an oil pump in fluid communication with one or more lubrication loads of a gas turbine engine, the method comprising:

driving the oil pump with a first source of motive power during a first mode of operation where the oil pump is drivingly disengaged from a second source of motive power;

drivingly engaging the second source of motive power to the oil pump; and

driving the oil pump with the second source of motive power during a second mode of operation.

16. The method as defined in claim 15 , wherein:

the first mode of operation comprises a condition where a driving speed from the first source of motive power is higher than a driving speed from the second source of motive power; and

the second mode of operation includes a condition where a driving speed from the second source of motive power is higher than a driving speed from the first source of motive power.

17. The method as defined in claim 15 , wherein the second source of motive power comprises a gear train system configured to transfer motive power to a load applied to the turbine engine and the method comprises:

driving the gear train system with an electric motor during the first mode of operation; and

driving the gear train system with a shaft driven by a turbine during the second mode of operation.

18. The method as defined in claim 15 , comprising transferring motive power from the second source of motive power to the first source of motive power during the second mode of operation.

19. The method as defined in claim 15 , wherein the first source of motive power is an electric motor driven by an electric power source and the method comprises operating the electric motor as a generator during the second mode of operation to charge the electric power source.

20. The method as defined in claim 15 , wherein the first source of motive power is an electric motor and the second source of motive power is a gear train system configured to transfer power from the gas turbine engine to a propeller coupled to the gas turbine engine.