Variable magnetic coupling of rotating machinery

A gas turbine engine comprising:

• a low pressure turbine spool and a high pressure turbine spool, at least one compression stage, a combustion chamber, an exhaust system and a rotary fan blade arrangement, the low pressure turbine spool and the high pressure turbine spool being magnetically coupled through a magnetic gearbox;
• the magnetic gearbox including:
• a first ring structure, a second ring structure and an intermediate ring structure, each of the first, second and intermediate ring structure having an annular aperture therethrough and a plurality of magnetic pole pieces embedded therein, the intermediate ring structure disposed between the first ring structure and the second ring structure, each of the first, second and intermediate ring structure being coaxially disposed, concentric with, and independently rotatable with respect to the remaining ring structures;
• the first and second ring structures each being coupled to one of the HP turbine spool and the LP turbine spool, and the intermediate ring co-operable to transfer torque between the HP turbine spool and the LP turbine spool.

A method of transferring torque between first and second independently rotating shafts of a gas turbine engine, the method comprising the steps of:

• providing an adjustable magnetic gearbox having a first ring structure, a second ring structure and an intermediate ring structure, each of the first, second and intermediate ring structure having an annular aperture therethrough and a plurality of magnetic pole pieces embedded therein, the intermediate ring structure disposed between the first ring structure and the second ring structure, each of the first, second and intermediate ring structure being coaxially disposed, concentric with, and independently rotatable with respect to the remaining ring structures;
• coupling the first shaft of the magnetic gearbox to the first ring structure;
• coupling the second shaft of the magnetic gearbox to the second ring structure;
• coupling a rotating machine to the intermediate ring structure,
• concurrently rotating at least two of the first and second shafts and the rotating machine;
• and
• controlling the ratio of torque transferred between the first and second ring structures by operating the rotating machine to supply or extract power from the intermediate ring structure.