Products and ser vices / AF TON CHEMICAL
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Electrified transmission fluid design Despite increasing electrification, some manufacturers still use existing lubricants to both cool and protect transmissions and electric motors roven performance history is attractive for OEMs hoping to avoid the need for dedicated electrified transmission fluid (ETF) in the supply chain. However, the rapid pace of change in hybrid and electric vehicle development brings additional lubricant demands and opportunities for enhanced performance, neither of which should be overlooked. Higher e-motor power and speeds require better cooling: fluids need the right thermal conductivity and viscosity characteristics. Direct cooling is most effective, but when the lubricant is in contact with e-motor components, properties not needed for automatic or manual transmission fluid become relevant. Electrical properties such as fluid conductivity, resistance and breakdown voltage must be appropriate. Compatibility with highly sensitive materials such as copper, silver, tin and plastics in e-motors and related electronics becomes a priority – in the oil’s liquid and vapor phases. Where dedicated hybrid transmissions (DHTs) are used, the absence of torque convertors and launch clutches results in higher power transfer across gears and bearings, significantly increasing the risk of wear. As well as efficiency, OEMs seek extended drain intervals – up to 400,000km. Fluid aging becomes a primary factor: thermal and oxidative stability is vital for preventing lubricant breakdown over longer periods and ensuring that electrical compatibility and wear performance is maintained right up to the oil change. These new requirements mean it is no longer enough for ETF to pass existing industry tests. Balancing all-round performance with reliability and longevity means working closely with manufacturers at the earliest stage of system development, devising more suitable lubricant tests, based on prototype hardware, to better predict realworld performance.
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1. Testing compared a transmission fluid with one modified to the performance needs of evolving DHT and e-drive applications
CHEMICAL HARMONY By asking more of the ETF, higher concentrations of performance additives might seem inevitable. But this is akin to asking an orchestra to play louder in order to sound better. In DHTs and e-drives, several new performance demands are placed on the lubricant, while other conventional requirements can be de-emphasized. Formulation changes to achieve this new balance require a different style and methodology, analogous to quietening the violins so that you can better appreciate the flute solo. “ETF solutions are not necessarily best achieved by striving to achieve harmony through the use of more and more additives,” explains Dr Susie Hurley, senior R&D advisor at Afton Chemical. “Instead, a contrasting tactic is to pare back use of components for conventional performance to allow those that deliver new performances to shine through.” Test data (Figure 1) compares a fully formulated transmission fluid against a modified version to better emphasize the performance requirements for evolving DHT and e-drive applications. While not fully balanced and optimized, the gear protection shows a marked 123% improvement (+166Nm) in pinion torque at failure. Improvements in both resistivity and oxidation performance were also noted. The speed of hardware evolution means the lifespan of today’s new lubricants can be as short as 12-36 months instead of the typical six or seven years. It is vital for OEMs to review regularly and discuss with additive partners whether fluids and fluid testing are still fit for purpose and any new opportunities that arise as the right balance of performance is reached. Traditional fluids cannot match the performance credentials of bespoke lubricants developed and tested alongside the latest hardware. Close supplier partnerships are vital to ensure that ETF enables OEMs to keep driving powertrain designs forward without being held back.
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Transmission Technology International / 2021 77