For three and a half years, TWT has been working together with Mercedes-Benz AG on the project "Development of an overall model for electrified drives". A Matlab-based tool has been developed to investigate and optimize the cooling concept on electric machines. An outstanding feature of this tool is a method developed by TWT to quickly calculate physically meaningful heat transfer coefficients.
As part of this project, a scientific article about "Fluid Choice Based on Thermal Model and Performance Testing for Direct Cooled Electric Drive" was published. In this publication, the cooling fluid for direct oil-cooled electric traction drive is investigated. A dedicated thermal resistance model was developed in order to show the influence of the fluid properties on the continuous performance. For this purpose, the heat transfer parameters are adjusted in the simulation using an exponential approach in order to evaluate the cooling fluid. In a sensitivity study, density, heat capacity, thermal conductivity, and viscosity are investigated. Because viscosity, within the range investigated, shows the largest percentage deviation from the reference fluid, the greatest effect on performance can be seen here. In order to check the plausibility of the calculated results of the thermal simulation, two fluids were chosen for performance testing on a dedicated electro motor cooling (EMC) test. Beyond the investigation of heat transfer, aging of the defined fluid at maximum heat input over several hours is also evaluated. Only slight changes of the fluid properties are detected. This publication presents a thermal model for direct oil-cooled drive trains, which consider fluid properties. Furthermore, the model was tested for plausibility on real hardware.
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