Hybrid gas turbine engine starting control

1 . A system of an aircraft, the system comprising:

a gas turbine engine comprising a fan, a low speed spool comprising a low pressure compressor and a low pressure turbine coupled to an inner shaft, a high speed spool comprising a high pressure compressor and a high pressure turbine coupled to an outer shaft, and a combustor;

a low spool motor configured to augment rotational power of the low speed spool, wherein the low spool motor is coupled to a first mechanical power transmission that is coupled between the inner shaft and the low spool motor;

a high spool motor configured to augment rotational power of the high speed spool, wherein the high spool motor is coupled to a second mechanical power transmission that is coupled between the outer shaft and the high spool motor; and

a controller configured to cause fuel flow, the controller configured to:

control a thrust response of the gas turbine engine to a thrust target between zero and a thrust level to move the aircraft during engine start and during engine idle;

control the low spool motor to drive rotation of the low speed spool responsive a thrust command to produce thrust by the fan while the controller does not command fuel flow to the combustor in an e-taxi mode;

control the low spool motor to drive rotation of the low speed spool responsive to the thrust command to produce thrust by the fan during a starting operation, wherein the starting operation includes driving rotation of the high speed spool and initiation of fuel flow and combustion, and wherein during control of the fuel flow during the starting operation in a starting mode the low spool motor is controlled to achieve a target thrust response using a throttle lever angle at a power setting lower than an idle level between a lower operating limit associated with a fuel-off detent of the throttle lever angle and the idle level associated with an idle detent of the throttle lever angle; and

control the high spool motor to accelerate the high speed spool during the starting operation of the gas turbine engine and provide compression for light off in the combustor while the low spool motor controls thrust of the gas turbine engine on the low speed spool in the starting mode.

2 . The system of claim 1 , wherein the starting operation comprises a ground-based start or an in-flight restart.

3 . The system of claim 1 , further comprising:

a low spool generator configured to extract power from the low speed spool, wherein the low spool generator is coupled to the first mechanical power transmission; and

a high spool generator configured to extract power from the high speed spool, wherein the high spool generator is coupled to the second mechanical power transmission.

4 . The system of claim 3 , wherein the controller is configured to: selectively provide electrical power from the low spool generator to the high spool motor by controlling a first rectifier electronics to condition current from the low spool generator to power motor drive electronics of the high spool motor.

5 . The system of claim 4 , wherein the controller is configured to: selectively provide electrical power from the high spool generator to the low spool motor by controlling a second rectifier electronics to condition current from the high spool generator to power motor drive electronics of the low spool motor.

6 . The system of claim 5 , wherein the electrical power selection from the low spool generator and the high spool generator is based on one or more operational schedules and transition limits to maintain operation of the gas turbine engine.

7 . The system of claim 6 , wherein the controller is configured to selectively engage either or both of the low spool generator and the high spool generator to adjust a load and speed of either or both of the low speed spool and the high speed spool through a first gearbox of the first mechanical power transmission and a second gearbox of the second mechanical power transmission wherein the selective engagement is based on the one or more operational schedules and transition limits to maintain operation of the gas turbine engine.

8 . The system of claim 1 , wherein controller is operable to control the low spool motor to drive rotation of the low speed spool responsive to the thrust command at or above engine idle.

9 . A method comprising:

receiving a thrust command at a controller, the controller configured to cause fuel flow for a gas turbine engine of an aircraft, the gas turbine engine comprising a low speed spool comprising a low pressure compressor and a low pressure turbine coupled to an inner shaft, a fan driven by the low speed spool, a high speed spool comprising a high pressure compressor and a high pressure turbine coupled to an outer shaft, and a combustor;

determining, by the controller, an allocation of the thrust command between commanding fuel flow to the combustor and electric current to a low spool motor based on an operating state of the gas turbine engine and a throttle lever angle wherein the low spool motor is coupled to a first mechanical power transmission that is coupled between the inner shaft and the low spool motor;

controlling, by the controller, a thrust response of the gas turbine engine to a thrust target between zero and a thrust level to move the aircraft during engine start and during engine idle;

controlling, by the controller, the low spool motor to drive rotation of the low speed spool responsive the thrust command to produce thrust by the fan while the controller does not command fuel flow to the combustor in an e-taxi mode;

controlling, by the controller, the low spool motor to drive rotation of the low speed spool responsive to the thrust command to produce thrust by the fan during a starting operation, wherein the starting operation includes driving rotation of the high speed spool and initiation of fuel flow and combustion, wherein during control of the fuel flow during the starting operation in a starting mode the low spool motor is controlled to achieve a target thrust response using the throttle lever angle at a power setting lower than an idle level between a lower operating limit associated with a fuel-off detent of the throttle lever angle and an idle level associated with an idle detent of the throttle lever angle; and

controlling a high spool motor to accelerate the high speed spool during the starting operation of the gas turbine engine and provide compression for light off in the combustor while the low spool motor controls thrust of the gas turbine engine on the low speed spool in the starting mode, wherein the high spool motor is coupled to a second mechanical power transmission that is coupled between the outer shaft and the high spool motor.

10 . The method of claim 9 , wherein the starting operation comprises a ground-based start or an in-flight restart.

11 . The method of claim 9 , wherein a low spool generator is configured to extract power from the low speed spool, and a high spool generator is configured to extract power from the high speed spool, wherein the low spool generator is coupled to the first mechanical power transmission, and the high spool generator is coupled to the second mechanical power transmission.

12 . The method of claim 11 , further comprising:

selectively providing electrical power from the low spool generator to the high spool motor.

13 . The method of claim 12 , further comprising:

selectively providing electrical power from the high spool generator to the low spool motor.

14 . The method of claim 13 , further comprising:

selectively engaging either or both of the low spool generator and the high spool generator to adjust a load and speed of either or both of the low speed spool and the high speed spool through a first gearbox of the first mechanical power transmission and a second gearbox of the second mechanical power transmission.

15 . The method of claim 14 , wherein the selectively engaging either or both of the low spool generator and the high spool generator is based on one or more operational schedules and transition limits to maintain operation of the gas turbine engine.

16 . The method of claim 9 , further comprising:

controlling the low spool motor to drive rotation of the low speed spool responsive to the thrust command at or above engine idle.