Charging scheme for electric propulsion systems

1. An engine system for an aircraft comprising:

a propulsor configured to drive the aircraft;

a thermal combustion engine configured to drive the propulsor;

an electric motor-generator connected to the thermal combustion engine and configured to drive the propulsor;

a power converter configured to apply a torque to the electric motor-generator and generate electric energy from the torque applied to the electric motor; and

an engine controller configured to:

determine a current power output of the thermal combustion engine;

determine a most fuel efficient an optimum power output of the thermal combustion engine based on current operating conditions;

compare the current power output (P) with the most fuel efficient power output (P 2 ); and

increase or decrease the torque applied to the electric motor so as to increase or decrease a load on the thermal combustion engine, wherein the torque is varied increased or decreased by an amount required to increase or decrease the power output of the thermal combustion engine to the determined most fuel efficient power output.

2. The engine system of claim 1 , wherein the engine controller is configured to increase the torque applied to the electric motor-generator by the power converter if the current power output is below the most fuel efficient power output, so as to increase the load on the thermal combustion engine.

3. The engine system of claim 2 , wherein the engine controller is configured to decrease the torque applied to the electric motor-generator by the power converter if the current power output is above the most fuel efficient power output, so as to decrease the load on the thermal combustion engine.

4. The engine system of claim 3 , wherein the engine controller is configured to increase or decrease the torque by an amount required to increase or decrease the power output of the thermal combustion engine to the optimum power output.

5. The engine system of claim 1 , wherein the engine controller is configured to decrease the torque applied to the electric motor-generator by the power converter if the current power output is above the most fuel efficient power output, so as to decrease the load on the thermal combustion engine.

6. The engine system of claim 1 , wherein the most fuel efficient power output corresponds to a power output determined to be the most fuel efficient for the current operating conditions of the engine system.

7. The engine system of claim 6 , wherein the engine controller further comprises a database and the most fuel efficient power output is determined from a schedule of most fuel efficient power outputs stored on the database.

8. The engine system of claim 6 , wherein the most fuel efficient power output is a fixed and/or predetermined value based on one or more operating conditions.

9. The engine system of claim 1 , wherein the power converter comprises a variable torque actuator.

10. The engine system of claim 1 , further comprising an energy storage device, wherein the electric energy generated from the torque applied to the electric motor-generator is used to charge the energy storage device.

11. A method for operating an engine system for an aircraft as recited in claim 1 , the method comprising:

determining a current power output of the thermal combustion engine;

determining a most fuel efficient power output of the thermal combustion engine based on current operating conditions;

comparing the current power output (P) with the most fuel efficient power output (P 2 ); and

increasing or decreasing the torque applied to the electric motor-generator so as to increase or decrease a load on the thermal combustion engine, wherein the torque is increased or decreased by an amount required to increase or decrease the power output of the thermal combustion engine to the determined most fuel efficient power output and varying the torque applied to the electric motor so as to vary a load on the thermal combustion engine, wherein the torque is varied by an amount required to vary the power output of the thermal combustion engine to the determined optimum power output.

12. The method as claimed in claim 11 , further comprising:

increasing the torque applied to the electric motor-generator by the power converter if the current power output is below the most fuel efficient power output, so as to increase the load on the thermal combustion engine, and by an amount required to increase the power output of the thermal combustion engine to the most fuel efficient power output.

13. The method as claimed in claim 11 ,

decreasing the torque applied to the electric motor-generator by the power converter if the current power output is above the most fuel efficient power output, so as to decrease the load on the thermal combustion engine, and by an amount required to decrease the power output of the thermal combustion engine to the most fuel efficient power output.

14. An aircraft propulsion system having an engine system comprising:

an engine system as recited in claim 1 ; and

an engine controller configured to:

determine a current power output of the thermal combustion engine;

determine a most fuel defficient power output of the thermal combustion engine based on current operating conditions;

compare the current power output (P) with the most fuel efficient power output (P 2 ); and

increase or decrease the torque applied to the electric motor so as to increase or decrease a load on the thermal combustion engine, wherein the torque is increased or decreased by an amount required to increase or decrease the power output of the thermal combustion engine to the determined most fuel efficient power output.

15. The engine system of claim 1 , wherein the current power output (P) is determined with sensor data from the thermal combustion engine, a connection means connected between the electric motor-generator connected to the thermal combustion engine or the propulsor.

16. The engine system of claim 1 , wherein the current power output (P) is determined with data collected from or associated with the electric motor-generator.