A motor drive system with a rotor assembly having an insert, which is received into a blind hollow rotor space in a rotor shaft. The insert is unitarily and integrally formed and defines a central hole, which is disposed along a rotational axis of the rotor assembly, and a plurality of slots that extend through an outer circumferential surface of the insert. The insert is disposed in the rotor shaft such that the outer circumferential surface of the insert is engaged to the inside circumferential surface of the rotor shaft. The central hole forms a first fluid passage through the insert, while the slots form a plurality of second fluid passages through the insert.