Heat transfer assembly for electric motor rotor

An electric motor (12) comprises a housing, a stator assembly (28) mounted within the housing, a shaft (26A, 26B) extending axially through the stator assembly (28) and supported by the housing, and a rotor assembly (30) mounted to the shaft. A corrugated fin heat transfer structure (44) is positioned within the shaft (26A, 26B) and is configured to draw heat from the rotor assembly (30). The corrugated fin heat transfer structure (44) can comprise a sheet forming a plurality of radially extending loops (54), which may have radially outer crests (58) and radially inner troughs (54). The crests may be offset relative to the troughs.