US Patent 6864604 Cooling structure for multi-shaft, multi-layer electric motor

A multi-shaft, multi-layer motor includes an inner rotor, an outer rotor surrounding the inner rotor, and a stator disposed coaxially between the inner and outer rotors. The motor further includes an outer member surrounding the outer rotor and defining a first wet chamber between the outer rotor and the outer member; an inner member defining a second wet chamber surrounded by the inner rotor; and an intermediate member defining a dry chamber communicating with an outer air gap between the stator and the outer rotor, and an inner air gap between the stator and the inner rotor.