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Thermal Analysis

Thermal analysis of an electro motor

In order to gain detailed insight into the thermal behavior of the drive motor of an electric car, a thermal FEA model of this motor was created.

Transient temperature data obtained from measurements on the subsystems rotor and stator with housing were compared with equivalent simulation results in order to determine the relevant thermal coupling parameters in detail. Besides the coupling between the windings and the lamination stacks, the pressure fit between stator stack and housing was found to be of importance.

CFD simulations at various rotation speeds were performed in order to determine the thermal coupling between rotor and stator. Vortices already occur at moderate speed. At maximum speed, these vortices improve the thermal coupling between rotor stator compared to the pure shear flow conditions by a factor of 5.

Finally, the subsystems were assembled to the complete motor and, in turn, transient thermal simulations were performed. The simulated spatial and temporal temperature profiles were confirmed by measurements.

The figure shows the spatial temperature profile after 1 hour of operation along the radial coordinate of the motor. Despite the improvements due to the vortices, the coupling between the rotor and stator represents the highest thermal resistance. Additionally, the coupling between rotor stack and rotor winding as well as the radial conductance through the stator stack and the shrinkage coupling between stator and housing contribute significantly to the maximum temperature at the rotor winding.

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