Motor rotating shaft, rotor assembly, motor and vehicle

The motor rotating shaft comprises an inner rotating shaft and an outer rotating shaft, the inner rotating shaft comprises a first body, a cavity with an opening in one end is formed in the first body, a first shoulder part is formed at the end, facing the opening, of the first body, and the outer diameter of the first shoulder part is larger than that of the first body; a second shoulder is formed at one end, far away from the opening, of the first body, and the outer diameter of the second shoulder is larger than that of the first body; the two ends of the outer rotating shaft fixedly sleeve the first shoulder part and the second shoulder part respectively, so that a first cooling liquid channel is formed between the inner rotating shaft and the outer rotating shaft; the inner rotating shaft is provided with a liquid separation opening communicated with the first cooling liquid channel and the cavity, the outer rotating shaft is provided with at least one first liquid spraying opening and at least one secon