# Automatic Transmission Fluids in Electrified Transmissions: Compatibility with Elastomers
## 4 Conclusions  
Four different ATFs were tested to check their compatibility with three elastomeric materials commonly used as seals and gaskets in the transmissions of electric vehicles, as well as for the insulation of electric wiring. These materials were tested according to the recommendations of transmissions manufacturers regarding the admissible changes in hardness, volume, and resistance properties after aging these materials in ATFs. The variations found in the mechanical properties could have been related to variations in the composition and crystalline structure of the elastomers, and therefore some complementary tests (FT-IR, XRD, and TGA) were performed to clarify the results. This research allows the readers to infer that the lubricant composition and the type of seal and gasket materials are important in terms of compatibility. This research has been conducted with three standard materials used in seals, and then, general conclusions are deduced for each combination of lubricant and material. A more detailed compatibility study for a specific EV would \begin{table}
\begin{tabular}{c c c c} \hline \hline
**ATF** & **FKM** & **EPDM** & **Silicone** \\ \hline Oil A & ** & ** & ** \\ Oil B & ** & ** & ** \\ Oil C & ** & ** & ** \\ Oil D & ** & ** & ** \\ \hline \hline \end{tabular} \({}^{*}\)Low compatibility; ** Medium compatibility; and *** High compatibility.  
\end{table} 
Table 10: Oil compatibility with the studied elastomers. require a detailed test of the specific lubricant and materials for each application, using the same methodology proposed in this manuscript. From the results, we can conclude that:  
* The four ATFs caused similar effects on each material, except for oil C and oil A, which reduced the tensile strength of the silicone and increased the volume of the EPDM, respectively, making them incompatible. * A significant reduction in the crystalline structure of the silicone was indicated by the XRD tests, this reduction being higher after aging in oil C, which led to this combination not fulfilling the specifications regarding tensile strength. The crystalline structure variation in FKM was not important, and it was not possible to make the calculations for the EPDM due to its semi-crystalline nature. * The FT-IR tests helped to confirm the presence of the oils inside the structure of the aged silicone samples, which would have contributed to the swelling and softening of the material. * Due to oil absorption in the polymeric matrix, chemical and structural changes were detected in the EPDM and silicone, causing a volume increase which led to reductions in hardness and tensile strength. The FKM did not absorb any oil during the aging process, but the evaporation of the volatile components present in the fresh rubber caused a decrease in the volume and an increase in hardness. * The non-compatibility of the EPDM with the oils from Group III was also proven. * The compatibility of these ATFs with some of the elastomers tested is an essential requirement but is not sufficient without further trials involving other properties. More compatibility tests (magnetic, electrical, corrosion, thermal, foaming at high speeds, and aeration) should be conducted on the ATFs before using them in an electrified transmission. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12126213/s1](https://www.mdpi.com/article/10.3390/app12126213/s1)]([https://www.mdpi.com/article/10.3390/app12126213/s1](https://www.mdpi.com/article/10.3390/app12126213/s1)), Figure S1. Tensile strength and elongation at break for FKM and oils A to D (Fresh and after aging periods of 168, 336, 504 and 672 h); Figure S2. Tensile strength and elongation at break for EPDM and oils A to D (Fresh and after aging periods of 168, 336, 504 and 672 h); Figure S3. Tensile strength and elongation at break for Silicone and oils A to D (Fresh and after aging periods of 168, 336, 504 and 672 h); Table S1. Characteristic FTIR spectra bands for FKM.