Lube-Tech
Fluids for Electric Drive Units The architecture of next-generation electric vehicles will call for the development of a single type of fluid for their Electric Drive Units (EDU) [5], combining high-performance lubrication of the transmission and efficient motor cooling.
Early-generation electric motors were entirely air-cooled [6], but air’s low specific heat capacity in relation to its volume necessitated a different approach. Water cooling systems [6] began to appear as a potential solution, but these were soon superseded by the use of dielectric cooling fluids, a switch explained by the findings of digital simulation work illustrated in Figure 2 [5].
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.139 page 2
The uppermost graph in Figure 2 shows the maximum temperatures reached by an electric motor cooled indirectly by glycolated water. Temperatures in excess of 200°C can lead to component deterioration. In the case of the electric motor cooled directly using the fluid developed by TotalEnergies, the temperatures recorded were more than 100°C lower, which means the motor is able to run in more extreme environments than permitted by glycolated water. A high number of tests was carried out before this conclusion was reached [7, 8] and the level of performance obtained thanks to this technology is today recognised by automobile manufacturers, many of whom now plan to use it for their upcoming vehicles.
Fluid performance has led to a step forward being taken in terms of heat flux-related research and the rules established following the analysis of the motor’s architecture can be expressed by the following equation:
Although the coefficients can vary depending on the configuration in question, an initial approach suggests that the three chief levers capable of optimising heat flow are low viscosity, a high specific heat capacity and high thermal conductivity. As is frequently the case in formulation work, however, the difficulty resides in striking the ideal compromise between opposing properties. For example, while low viscosity may favour thermal performance, a high-viscosity fluid can prevent wear and extend component life. Solutions are already available for OEMs, but research into fluid optimisation continues.
Figure 2: The peak winding and magnet temperatures recorded for the two types of cooling system tested. The difference achieved using Quartz EV-Drive MP compared with the water-jacket system is highlighted in yellow.
Fluids for power electronics Power electronics enable the transfer of energy from the battery to the motor. Recent developments suggest that this technology will enable higher quantities of energy to be handled in the future. This
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