In accordance with a preferred embodiment of the rotor assembly according to the invention the cooling channel arrangement extends through the rotor core into the second shaft portion. The sealing means of the separation element then allows a particularly advantageous seal of the shaft portions through which fluid passes, if a cooling path guided back into the shaft through the cooling channel arrangement is to be formed.

The rotor assembly according to the invention for example comprises an end plate, which is arranged on an end face of the rotor core and which, at least in some sections, forms a second cooling channel of the cooling channel arrangement, which second cooling channel adjoins the first cooling channel. Furthermore, the second cooling channel can be adjoined by a third cooling channel of the cooling channel arrangement, which third cooling channel extends through the rotor core. A particularly favourable dissipation of heat from the rotor core is thus made possible.

It is particularly preferably provided that a fourth cooling channel of the cooling channel arrangement adjoins the third cooling channel and is formed at least in part by a further end plate arranged on the rotor core and leads into the second shaft portion. Conventional rotor cores advantageously can be easily retrofitted with end plates of this kind.

The end plate or one end plate can be sealed off with respect to the rotor core by means of a further sealing means. The further sealing means is preferably arranged in a collar, which is situated in an outer radial position on the side of the end plate facing the rotor core. Expediently, a groove is formed in the collar and receives further sealing means. The further sealing means sealing off the end plate with respect to the rotor core can be an O-ring.