A cup (28) of a external rotor with symmetry of revolution about the axis comprises: a first cylindrical portion (68) which is radially internal, a second cylindrical portion (32) which is radially external and a third portion (70) between the two cylindrical portions (32, 68). When viewed in cross-section, the third portion (70) extends between two points (P1, P2) which define a straight line which forms, with the axis of the rotor cup (28), an angle (a) of between 65° and 80°. The ratio between the distance (R-P1, R-p2) between the first point (P1, P2) which is radially internal or radially external, respectively, and the axis of symmetry of the rotor cup (28), on the one hand, and the radius (R32) of the second cylindrical portion (32), on the other hand, is between 0.04 and 0.32 or between 0.65 and 1.0, respectively.

A rotor magnet installation structure includes: a first shaft including a shrinkage-fit portion in which an accommodation space is formed; at least one magnet inserted in the accommodation space, an installation outer diameter of the magnet being greater than an inner diameter of the accommodation space before the magnet is inserted in the accommodation space; and a second shaft comprising a connection portion inserted in the accommodation space, an outer diameter of the connection portion being greater than the inner diameter of the accommodation space before the connection portion is inserted in the accommodation space.

A rotor magnet installation structure includes: a first shaft including a shrinkage-fit portion in which an accommodation space is formed; at least one magnet inserted in the accommodation space, an installation outer diameter of the magnet being greater than an inner diameter of the accommodation space before the magnet is inserted in the accommodation space; and a second shaft comprising a connection portion inserted in the accommodation space, an outer diameter of the connection portion being greater than the inner diameter of the accommodation space before the connection portion is inserted in the accommodation space.

The disclosure provides a pole-piece structure for a magnetic gear, comprising a plurality of laminate plates, wherein each plate comprises one or more apertures and an aperture in each plate aligns with an aperture in an adjacent plate to form one or more channels extending from a first end of the laminate plates to a second, opposite end of the laminate plates, wherein a resin cast is provided within each channel to hold the plurality of laminate plates together.

A stator for interacting with magnets carried by a rotor of an electric machine, the stator comprising: an active region arranged to be aligned with the magnets carried by the rotor; a first inactive region and a second inactive region, wherein the first and second inactive regions are separated by the active region; and a slotless phase winding comprising a plurality of conductive elements, wherein each conductive element comprises a conductor provided in an insulating housing, and wherein the slotless phase winding is arranged in a serpentine structure comprising: a first active segment in which the conductive elements extend across the active region from the first inactive region to the second inactive region; a second active segment in which the conductive elements extend across the active region from the second inactive region to the first inactive region; and an inactive segment coupling the first active segment to the second active segment, wherein the inactive segment comprises a turn provided in the second inactive region, and wherein at least one of the conductive elements is twisted in the second inactive region.

A rotor for an electric machine is disclosed herein. The rotor comprises: a central shaft; a rotor drum arranged radially outward of the central shaft, wherein the rotor drum comprises a hollow cylinder for carrying permanent magnets on an inner and/or outer surface of the hollow cylinder, and wherein the rotor drum is coaxial with both the central shaft and a rotational axis of the rotor; and a cap arranged to couple the central shaft to the rotor drum to enable the rotor drum and central shaft to rotate together about the rotational axis. An inner portion of the cap is coupled to the central shaft at a first position along the length of the rotational axis, and an outer portion of the cap is coupled to the rotor drum at a second position along the length of the rotational axis. The first position is at a different length along the rotational axis to the second position.

A rotor for an electric machine is disclosed herein. The rotor comprises: a central shaft; a rotor drum arranged radially outward of the central shaft, wherein the rotor drum comprises a hollow cylinder for carrying permanent magnets on an inner and/or outer surface of the hollow cylinder, and wherein the rotor drum is coaxial with both the central shaft and a rotational axis of the rotor; and a cap arranged to couple the central shaft to the rotor drum to enable the rotor drum and central shaft to rotate together about the rotational axis. An inner portion of the cap is coupled to the central shaft at a first position along the length of the rotational axis, and an outer portion of the cap is coupled to the rotor drum at a second position along the length of the rotational axis. The first position is at a different length along the rotational axis to the second position.

A rotor includes a rotor hub including a through-hole to which the shaft is fixed. An upper end and a lower end of an opposing region where an outer peripheral surface of the shaft and an inner peripheral surface of the through-hole oppose each other in a radial direction are respectively provided with an upper gap portion and a lower gap portion opposing each other through a space in the radial direction. The upper gap portion and the lower gap portion each include a bottom portion extending in a direction intersecting the center axis and a peripheral wall portion connected to a radial outer edge of the bottom portion and extending along the center axis.

A rotor includes a rotor hub including a through-hole to which the shaft is fixed. An upper end and a lower end of an opposing region where an outer peripheral surface of the shaft and an inner peripheral surface of the through-hole oppose each other in a radial direction are respectively provided with an upper gap portion and a lower gap portion opposing each other through a space in the radial direction. The upper gap portion and the lower gap portion each include a bottom portion extending in a direction intersecting the center axis and a peripheral wall portion connected to a radial outer edge of the bottom portion and extending along the center axis.

A gas turbine engine includes a fan and a rotor assembly. The rotor assembly includes a rotor, a plurality of magnets, and an annular retaining sleeve. The rotor includes a radially outer wall spaced apart from a central axis of the engine by an axially forward and an axially aft annular end wall. The magnets are located radially outward of the rotor and arranged on the outer wall in axial alignment with each other, the magnets being configured to move radially relative to each other and remain in contact with the outer wall in response to elastic deformation of the outer wall. The sleeve radially surrounds the magnets so as to structurally support and secure the magnets to the rotor, the sleeve being elastically deformable in the radial direction and configured to elastically deform based on the radial movement of the magnets.