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New age fluid testing Partnering on new, more targeted tests for electrified transmission fluids can better predict real-world lubricant performance Drivetrain electrification is a real challenge for lubricant, the one component that touches every part of the transmission. Welldesigned lubricants can unlock new engineering ideas, although it’s often hard to correlate laboratory performance with real-world use. Still, next-generation lubricants could support a wide range of hardware, from transmissions hybridised with e-motors to new, dedicated hybrid transmissions and full e-drive solutions. Fluid compatibility and electrical and cooling properties will have to supplement core friction performance and parts protection. Determining fluid and additive needs will be essential for controlling risk. “Unfortunately, current industry tests aren’t always wholly relevant to or predictive of lubricant performance in EVs,” says Dr Harald Maelger, senior OEM relationship manager at Afton Chemical. “Avoiding the pitfalls requires close partnerships with additive and lubricant suppliers,
New lubricants are tested extensively through five phases before they are allowed to enter production
so OEMs can really benefit from nonstandard testing to bridge the gap between laboratory, rig and road.” Afton Chemical is at the forefront of EV fluid testing, with recent advances in three areas: friction durability with thermal stress; gas and liquid phase compatibility; and electrical property changes in ageing fluid. Tests are specifically designed to correlate with field performance to generate robust, reliable fluid recommendations. Unsurprisingly, Afton examined friction durability first. “The FVA’s recent GK test round robin was worrying. The same reference fluid,
Afton conducted a copper corrosion test, using an ATF used by a large OEM, in which the wiring was destroyed by the lubricant vapour
1 // January 2020 // www.electrichybridvehicletechnology.com
under identical conditions, showed friction failure anywhere between 3,500 and 9,300 cycles,” says Dr Susie Hurley, senior adviser in ATF R&D at Afton Chemical. “This raises a red flag: fluids meeting OEM specifications on one test rig might not meet them on another, making it even harder to translate results into the real world. Standard testing also overlooks the role of heat, as found in a hybrid transmission.” Afton’s own HEV friction durability test combined dedicated friction apparatus with a thermal loop to simulate cooling stresses. Results showed an antagonistic effect, limiting effective fluid life more than anticipated. “We wanted a reliable indicator of field performance, so we tested used as well as new clutch plates,” Hurley says. “Plate analysis showed that fluid formulation is paramount, but that if problems do occur, shorter oil drain intervals are effective at restoring performance.” Sensitive e-motor components also demand lubricant compatibility. “Our initial recommendation was to extend the standard copper corrosion test and also measure end-of-test copper in oil,” says Hurley. “Screening tests revealed that some commercial fluids are especially aggressive in the gas phase, which is important given the higher temperatures associated with e-motors. We worked very closely with an OEM to develop a simple screener test that correlates to problems experienced in the field.”
Fluid conductivity is a third focus. “Naturally, OEMs want to know what the right tests and the right limits are,” says Dr Maelger. Again, Afton moved away from the standard DC conductivity tests to field-based assessment. “Hybrid taxis being rare, we used taxis with conventional step ATs to obtain real-world used lubricant samples. They were taken at intervals and tested for suitability in hybrid transmissions. This allowed real-world evaluation with everything present except the e-motor. “Fluid conductivity increased only slightly overall; there was a balance between the increase from iron wear particles and the natural decrease seen in ageing fluids; and the used lubricant still had a solid all-round performance reserve.” The rapid pace of e-mobility development continues to generate questions. “Our additive chemistry has the advantage of inherent thermal stability and excellent friction characteristics, but we are never satisfied. We’re always looking for new ways to assess real-world component and additive interactions,” says Dr Maelger. “Our ability to develop robust, reliable lubricant tests that predict how fluids age in service will prove every bit as important for our OEM partners as their nextgeneration hardware.” FREE READER INQUIRY SERVICE To learn more about Afton Chemical, visit: www.magupdate.co.uk/PEHV