Fluid Choice Based on Thermal Model and Performance Testing for Direct Cooled Electric Drive

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.

Experimental Study of Systems and Oils for Direct Cooling of Electrical Machine

“…The perspectives of this study include extensive tests without water, using other injection methods (as direct cooling of the windings coupled with rotor hollow shaft cooling [21]), and the study of multifunction fluids (lubrication-cooling coupling).…”

Comparison of Commonly Used Cooling Concepts for Electrical Machines in Automotive Applications

“…Simulation of end winding cooling is the most challenging because of the complex distribution of fluid and air. Therefore, test bench measurements are particularly important for this concept in order to properly model heat flow across the affected surfaces [5]. For thermal optimization during the design process, it is crucial to understand the effects of the different heat dissipation methods.…”

“…Investigations are then limited to the volume flow rate [6], the impact of the cooling jacket channel geometry [7,8] or a combination of both [9,10]. Illustration of shaft cooling, end winding cooling and stator jacket cooling in a permanent magnet synchronous machine (adopted from [5]).…”

“…For this contribution, a thermal model of an electric motor is developed that includes several stator, shaft and end Figure 1. Illustration of shaft cooling, end winding cooling and stator jacket cooling in a permanent magnet synchronous machine (adopted from [5]).…”

“…Figure1. Illustration of shaft cooling, end winding cooling and stator jacket cooling in a permanent magnet synchronous machine (adopted from[5]). …”