Variable coupling of turbofan engine spools via open differential gear set or simple planetary gear set for improved power extraction and engine operability, with torque coupling for added flexibility

A method for variably coupling a high pressure spool and a low pressure spools of a turbofan engine to power a generator, the method comprising:

• providing a differential gear portion and an electromagnetic variable transmission;
• coupling the electromagnetic variable transmission with the high pressure spool and the low pressure spool;
• controllably transferring torque between the high pressure spool and the low pressure spool through the EVT;
• connecting the differential gear portion between the high pressure spool and the low pressure spool in parallel with the electromagnetically variable transmission;
• equalizing a rotational speed of the high pressure spool, a rotational speed of the low pressure spool, and an output speed of an output shaft of the differential gear portion;
• and
• driving the generator by mechanically coupling the generator to the output shaft.

A gas turbine engine comprising:

• at least one compressor, a combustor, a high pressure turbine and a low pressure turbine arranged in serial flow communication and disposed about a longitudinal shaft of the engine within an annular outer casing;
• the at least one compressor driven by the high pressure and low pressure turbines and compressor air during operation;
• a variable coupler portion for coupling of a high pressure spool and a low pressure spools to power a generator in a turbofan engine, the variable coupler portion comprising:
• a differential gear portion having a first input portion, a second input portion, and an output shaft;
• an electromagnetic variable transmission having an independently rotatable inner rotor portion and an independently rotatable outer rotor portion, the inner rotor portion coupled with one of the high pressure spool and the low pressure spool, and the outer portion connected to the other spool, to transfer torque between the high pressure spool and the low pressure spool;
• the differential gear portion being connected between the high pressure spool and the low pressure spool in parallel with the electromagnetically variable transmission;
• the generator mechanically coupled to the output shaft;
• wherein the differential gear portion being arranged to equalize a rotational speed of the high pressure spool, a rotational speed of the low pressure spool, and an output speed of the output shaft for driving the generator;
• and the EVT arranged to controllably couple power from the low pressure spool to the high pressure spool.