The electrification of vehicle powertrains is ac- celerating. This also increases the demands placed on the lubricants used. Con- ventional transmission oils, developed for standard powertrains, are reaching their limits with highly integrated e-axles. Zeller+Gmelin from Eislingen has de- veloped Divinol Synthogear ETF, an electronic transmission fluid specifically tailored to the operating conditions of modern e-mobility platforms.
E-axles combine an electric motor, gearbox and power electronics in a single compact component. In dry systems, the fluid is solely responsible for lubricating the gearbox. Here, low friction, reliable wear protection and thermal stability are crucial. In wet sys- tems, the motor and gearbox operate in a shared oil bath. The fluid provides electrical insulation, facilitates heat dissipation from windings and inverters and remains com- patible with materials such as copper, elastomers, and insulating varnishes.
The gearbox architecture also influences the requirements. Single-stage gearboxes are subject to relatively moderate loads, while multi-stage systems generate higher shear forces and varying pressure and temperature zones. Therefore, developers need a fluid that covers a broad range of properties and adapts flexibly to different operating conditions.
Performance profile of Divinol Synthogear ETF
The new e-axle fluid is based on fully synthetic base oils. The combination of PAO and ester components and a specifically tailored additive technology enables it to meet the diverse requirements of both dry and wet systems. Divinol Synthogear ETF is charac- terised by high dielectric strength, which reliably protects windings. Wear protection for gears, bearings and sealing surfaces, as well as thermal and oxidative stability, ensure operation even at continuous temperatures above 150°C. The low viscosity improves the system’s energy efficiency and supports reliable cold-start performance.
Controlled foaming behavior and low air absorption ensure that cooling performance and lubrication remain stable even under dynamic load conditions. At the same time, the fluid is compatible with a wide variety of materials, thus reducing seal failures and electrical short circuits.
Benefits for manufacturers and developers
Divinol Synthogear ETF offers clear advantages for OEMs and system developers. It protects all system components, reduces friction losses and supports heat dissipation, thereby optimising energy consumption and range. Its universal applicability in dry and wet electric motors, as well as in single- and multi-stage transmissions, facilitates the modularisation of drive concepts. High aging resistance extends service intervals and reduces maintenance requirements.
“With Divinol Synthogear ETF, we deliver a fluid that meets the requirements of both dry and wet systems,” explains Andreas Krapf, Product Manager Automotive/Special Vehicle Products at Zeller+Gmelin. “During development, we placed particular empha- sis on electrical properties and material compatibility, as these factors are crucial for the safety and service life of modern e-axles.”
Wide range of applications
The fluid is suitable for various platforms and designs of electric drives. These include dry gearboxes with a separate electric motor as well as integrated axle systems where the motor and gearbox share a common oil bath. It can be used in vehicles with high- voltage architectures from 400 to 800 volts, including systems with direct oil cooling of the electric motor.
Ready for future generations
Divinol Synthogear ETF also meets future requirements. It is compatible with voltages above 800 volts, reduces bearing currents and erosion through targeted additives and remains stable at higher oil temperatures, such as those resulting from downsizing and increasing power densities. Its long service life and energy efficiency also contrib- ute to reducing the CO₂ footprint.
“We are seeing that OEMs are increasingly demanding fluids that meet not only cur- rent but also future requirements,” adds Andreas Krapf. “With Divinol Synthogear ETF, we can meet this demand and simultaneously simplify our customers’ development work, as one fluid can be used for various axle and drive concepts.”
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With Divinol Synthogear ETF, Zeller+Gmelin offers a lubricant solution tailored to the specific requirements of electric drive trains. It covers the needs of dry and wet sys- tems, single- and multi-stage gearboxes, and integrated or modular architectures. This fluid thus provides a flexible application range for a wide variety of current and future e-axle generations.
