It is also provided preferably in the case of the rotor assembly according to the invention that the second cooling channel is designed for connection to the first cooling channel in part by through-holes penetrating the shaft. Alternatively or additionally, the fourth cooling channel can be designed for connection to the second shaft portion in part by through-holes penetrating the shaft. Conventional rotor assemblies can thus advantageously be retrofitted with little effort and without a cooling of the permanent magnets, by merely forming additional through-holes at appropriate axial positions of the shaft. A through-hole is typically provided in the shaft for each cooling channel portion of the second or fourth cooling channel.

In addition, in the rotor assembly according to the invention the second cooling channel can be designed for connection to the third cooling channel in part by elevations in the end plate. Alternatively or additionally, the fourth cooling channel can be designed for connection to the third cooling channel in part by elevations in the end plate. The second cooling channel and the fourth cooling channel are consequently delimited on the one hand by the end plate with its elevations and on the other hand by an end face of the rotor core.