A cooling channel arrangement 13 is formed inside the rotor assembly 1. This cooling channel arrangement comprises a first cooling channel 14, which extends inside the shaft along the first shaft portion 8 in the axial direction. A second cooling channel 15 of the cooling channel arrangement 13 extends in the radial direction along the end face 16 of the rotor core 2 and directly adjoins the first cooling channel 14. In addition, a third cooling channel 17 is provided, which, adjoining the second cooling channel, extends in the axial direction through the clearances into the magnet pockets 7a-7d. A fourth cooling channel 18 of the cooling channel arrangement adjoining the third cooling channel 17 extends in the radial direction along the other end face 19 of the rotor core 2 and leads into the second shaft portion 9, which forms a fifth cooling channel 20. Consequently, a cooling path (denoted by arrows in FIG. 1) for the cooling fluid is thus formed and extends from the free end 4a of the shaft 4 through the first shaft portion 8, the rotor core 2, and the second shaft portion 9 back to the free end 4a of the shaft 4.

The second cooling channel 15 has a plurality of mutually separated cooling channel portions 21, 22, adjoined in each case by a cooling channel portion 23a, 23b of the third cooling channel 17. Each cooling channel portion 23a, 23b of the third cooling channel 17 is formed here from the clearances of a magnet pocket arrangement 6. In other words, each cooling channel portion 23a, 23b is divided eight times by the clearances.