Abstract
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.
Highlights
The trend in the automotive industry towards electrified powertrains is continuously increasing.A compact drive unit including an electric traction drive, transmission, and power electronics is an established solution
The heat generated in the electric drive is one of the limiting factors in terms of driving performance
Indirect cooling systems allow the usage of cooling fluid that is optimized for heat transfer only as the fluid circulates in isolated cooling channels
Summary
The trend in the automotive industry towards electrified powertrains is continuously increasing. A compact drive unit including an electric traction drive, transmission, and power electronics is an established solution. The heat generated in the electric drive is one of the limiting factors in terms of driving performance. Thermal management and the dedicated design of cooling concepts become even more important. Depending on whether a direct or indirect cooling system is used (which refers to the direct or indirect contact of the cooling fluid with the electric drive), there are different requirements of the cooling fluid. Indirect cooling systems allow the usage of cooling fluid that is optimized for heat transfer only as the fluid circulates in isolated cooling channels
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