The fourth fluid-guiding element 37 is formed as a protrusion pointing centrally from the collar 27 into the cooling channel portion 21 and optimises the flow cross-section for the cooling fluid flowing into the radially outer clearances of the radially outer magnet pockets 7a, 7b.

As can be seen in FIG. 1, a radially inner part of the fourth cooling channel 18 is also formed in some sections by through-holes 38 in the shaft 4, which are arranged in an axial position corresponding to the end face 19 of the rotor core 2. As is the case with the second cooling channel 15, a radially outer part of each of the cooling channel portions 39, 40 is also delimited by the end face 19 and an end plate 41 arranged thereon. The structure of the end plate 41 corresponds to the previously described structure of the end plate 25, and therefore the cooling channel portions 39, 40 are formed similarly to the cooling channel portion 21, 22 of the second cooling channel 15.

At a free end 4b of the shaft 4 opposite the separation element 5, the rotor assembly 1 has a termination element 42 in the form of a blind stopper, which axially delimits the second shaft portion 9.

In addition, the rotor assembly 1 has multiple sealing means, which prevents the cooling fluid from escaping from the cooling channel arrangement 13: