Electric machine cooling systems and methods

An electric machine shaft comprising:

• an inner shaft core having a first composition;
• said first composition having a first thermal conductivity;
• and
• an outer shaft portion surrounding at least some of the inner shaft core, said outer shaft portion having a different composition than the inner shaft core, said second composition having a second thermal conductivity that is less than the first thermal conductivity.

A method of cooling an electric machine comprising:

• providing the electric machine comprising;
• a shaft comprising;
• an inner shaft core having a first composition;
• and
• an outer shaft portion surrounding at least some of the inner shaft core, said outer shaft portion having a different composition than the inner shaft core;
• a rotor back assembly surrounding a portion of the shaft;
• and
• a plurality of permanent magnets radially positioned around radial perimeter of the rotor back assembly;
• conducting heat from the rotor back assembly to the shaft;
• and
• exporting heat from the electric machine through the shaft to an apparatus attached to the shaft.