Novel revolving heat pipe cooling structure of permanent magnet synchronous motor for electric vehicle

The high temperature rises and uneven axial temperature distribution of permanent magnet synchronous motors applied in electric vehicles can lead to demagnetization of permanent magnets and turn-to-turn short circuit failures in the windings. Thus, a cooling structure based on revolving and fixed annular heat pipes is proposed. That is the revolving heat pipes are installed in the rotor, which are further increasing the rotor's heat transfer efficiency under the centrifugal force of rotor rotation. The fixed annular heat pipes are installed in the stator to cool the windings, especially the end of the windings. The experiments are designed to derive the equivalent thermal conductivity of the proposed revolving and fixed annular heat pipes on this basis. The effectiveness of the proposed cooling structure is verified by computational fluid dynamics simulations which are conducted in three typical operating conditions of the motor used in electric vehicles. The results show that the temperature rise of the rotor, permanent magnet and winding are decreased by up to 70.39%, 69.4%, and 46.18% respectively by the proposed cooling structure. It indicated that the axial temperature rises distribution of heat generating parts can be effectively equalized, and the operating time under maximum torque condition can be effectively extended, that from 30 s to 100 s.