Rotary electric machine with lightened rotor

19) An electric machine (1) comprising:

• a shaft (2), which is mounted so as to rotate around a central rotation axis (3);
• a rotor (4) with permanent magnets which is fitted to the shaft (2) so as to rotate together with the shaft (2);
• a stator (5) with a tubular, cylindrical shape, which is arranged around the rotor (4) so as to enclose, on the inside, the rotor (4) and has a magnetic core (6), which consists of a series of laminations made of a ferromagnetic material and is longitudinally crossed by a plurality of stator slots (7);
• and
• a stator winding (8) comprising a plurality of copper rigid bars (9), which are inserted in corresponding stator slots (7) and are covered, on the outside, with an insulating coating (14);
• wherein the shaft (2) has a hub (28) supported by bearings, a rim (29), which is arranged around the hub (28) at a given distance from the hub (28) and supports the permanent magnets (23), and a plurality of spokes (30), which develop radially and connect the hub (28) to the rim (29) so that between the hub (28) and the rim (29) there is an empty space;
• and
• wherein the spokes (30) are shaped so as to generate, during the rotation of the shaft (2), a predetermined sound.