Afton supports pioneering direct-cooled power electronics

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Afton supports pioneering direct-cooled power electronics Afton Chemical, Mercedes-Benz AG and ZFW Stuttgart (Institute for Thermal Management) have collaborated to establish a reliable way to measure the cooling efficiency of transmission fluids used to direct cool power electronics. This can help the EV industry to benefit further from the efficiencies offered by direct cooling.

Controlling eMotor operation and power flow in an electric drivetrain requires power electronics: critical yet sensitive systems that generate considerable heat. Power electronics are traditionally cooled using a water/glycol jacket, although with indirect cooling the heat transfer is inferior to direct cooling.

Being able to determine the heat transfer coefficient for a fluid is a significant step forward. This coefficient represents not only the heat transfer property of the fluid, but also the design-dependent heat transfer that takes place between surfaces and the coolant. Together, these enable a much more meaningful comparison of indirect versus direct cooling.

The modelling indicated that direct oil cooling with transmission fluids would be significantly more efficient than indirect cooling. Practical measurements showed that the heat transfer coefficient could be increased by a factor of 3 to 8, demonstrating much improved thermal management with direct cooling.

Increasingly OEMs are looking to make efficiency gains through direct cooling. This has already been documented for eMotors using dedicated electrified transmission fluids (ETF). There is also OEM interest in using one fluid to directly cool the power electronics, eMotor and transmission.

Our 3-way collaboration began with modelling the cooling housing of the power electronics. Potential fluids were assessed for thermal conductivity properties and viscosity, while accounting for electrical conductivity.

Demonstrating the practical application of this modelling was challenging and required an innovative measurement method, developed by ZFW Stuttgart, based on the thermal transient method. The actual thermal resistance between the heat sink surface and test fluid was measured to derive a heat transfer coefficient for each fluid.

‘The most challenging part of developing additive technology for new hardware is understanding the functional requirements before that hardware exists,’ says Arthur Petuchow, OEM Relationship Manager at Afton. ‘Fortunately, we were able to solve this in close collaboration with the Institute for Thermal Management.’

The modelling and practical measurements agreed well, demonstrating that the robustness of this method for assessing cooling efficiency of different fluids.

Comparison of calculated heat transfer coefficients of direct oil spray cooling and water/glycol (50/50) tube cooling as a function of volume flow.

A new operating mode for electrified transmission fluid that incorporates direct cooling of the power electronics must meet at least three criteria: low electrical conductivity, high compatibility with new materials and good thermal conductivity. In addition, it must also meet the lubrication needs of a conventional transmission. Achieving this balance of performance could help simplify EV cooling circuits and increase efficiency even further.

Developing any dedicated EV fluid is always boosted by early access to OEM prototype hardware. This enables the most appropriate tests to be designed for measuring fluid performance, so that additives can be developed accordingly.

© 2022. Afton Chemical Corporation is a wholly owned subsidiary of NewMarket Corporation (NYSE:NEU). 09/22.

The information in this bulletin is, to our best knowledge, sure and accurate, but all recommendations or suggestions are made without guarantee since the conditions of use are beyond our control. Afton Chemical Corporation and its affiliates disclaim any liability incurred in connection with the use of these data or suggestions. Furthermore, nothing contained herein shall be construed as a recommendation to use any product in conflict with existing patents covering any material or its use.

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Afton supports pioneering direct-cooled power electronics ‘A fluid is not a typical machine element.’ explains Arthur Petuchow. ‘Optimizing the fluid and its additive package requires an interdisciplinary approach. On the one hand a deep and fundamental chemical expertise in combination with experience is required. On the other hand, the understanding of future hardware is key to develop and prove the performance of the chemistry for the application.’

Hardware testing starting with single components over the assembly groups and up to vehicle testing is a key part of fluid development, bridging the realms of chemistry and mechanical engineering. Access to hardware and operating conditions, combined with chemical understanding, enables definition of relevant tests, allows more efficient interpretation of the results and ultimately aids optimization of drivetrain designs.

Even the earliest incarnation of new hardware can help focus fluid specification and test development processes.

While collaboration can, at first, bring IP and confidentiality challenges, they are outweighed by the benefits.

Developing critical hardware iteratively, in parallel with fluid chemistry, enables delivery of optimum efficiency and reliability.

Afton’s pioneering cooling work continues, helping OEMs to futureproof their drivetrains and their lubricants.

For more details, please see the joint paper published in the Journal of Electronics Cooling and Thermal Control, or contact your Afton representative.

© 2022. Afton Chemical Corporation is a wholly owned subsidiary of NewMarket Corporation (NYSE:NEU). 09/22.

The information in this bulletin is, to our best knowledge, sure and accurate, but all recommendations or suggestions are made without guarantee since the conditions of use are beyond our control. Afton Chemical Corporation and its affiliates disclaim any liability incurred in connection with the use of these data or suggestions. Furthermore, nothing contained herein shall be construed as a recommendation to use any product in conflict with existing patents covering any material or its use.