Modern lubricants work exceptionally hard to deliver the right balance of cooling, protection, efficiency and reliability for a myriad of vehicle systems. The additives in these fluids can dramatically enhance performance and be pivotal in bringing new hardware to market. From the latest EV technology such as direct-cooled eMotors and multi-speed eAxles, to emerging technology such as immersion-cooled battery modules, all can benefit from targeted lubricant additive solutions.
Future-proofing
‘Lubricant is not just an interchangeable part within a system; it makes a fundamental contribution to successful design,’ explains Adam Banks, eMobility marketing manager at lubricant additive specialist Afton Chemical.
‘Every lubricant contains additives that ensure it has the right balance of properties to support a given application. While additives can often make up less than ten per cent of the finished lubricant, they are responsible for much of its performance. That’s why Afton works closely with OEMs and engineering firms: by identifying early the challenges brought by new materials and hardware, we can help to deliver future-proof performance gains.’
Being fit for the future means that lubricants for electrified vehicles must be ready to handle a host of new demands – particularly the ability to lubricate and cool the eMotor. Direct exposure to high speed and temperature eMotors, power electronics and sensitive electronic controls and sensors – on top of the usual gears, bearings and friction devices – places additional, and sometimes conflicting, pressures on the lubricant and its additives.
Keeping it real
‘Lubricants for EV applications require robust testing to ensure that they are fit for purpose: not just at the outset, but throughout their service life,’ says Dr Chris Cleveland, R&D Director at Afton. ‘For electrified vehicles to be reliable for consumers, it’s vital that these test results translate effectively to real world operation.’
Compared to conventional lubricants, EV fluids need to excel in three additional ways: electrical properties, thermal stability and compatibility with new materials.Afton has developed leading test methodologies that don’t just verify the laboratory properties of fresh fluid but go further, aiming to identify all the relevant factors that can affect lubricant performance over time.
Electric performance
The right fluid electrical properties don’t just improve safety, they also help protect components from the potential damage caused by sudden electrical discharges.
‘As a start point, any lubricant coming into contact with electrical equipment should therefore be a dielectric fluid, with low electrical conductivity and limited ability to store electrical charge,’ explains Dr Cleveland.
For any lubricant, thermal breakdown is accelerated by exposure to high temperatures and eMotors generate considerable heat. Thermal breakdown increases the number of polar particles in the fluid, which increases its electrical conductivity, so thermal stability is essential to guarantee performance over the long term.
The test of time
‘Standard electrical property testing is a good start for fresh fluid, but very often the changes in electrical properties that occur with age are not carefully examined,’ reveals Dr Cleveland. ‘Because thermal stability is crucial for EV lubricants, the in-house testing of aged fluid that we do at Afton is really important: it’s what helps us to predict the behaviour and longevity of lubricants in service.’
Compatibility is the third key area. eMotor windings and power electronics both contain copper, either coated or held within a sealed unit, so fluid compatibility with the wide range of new coating and sealing materials and lacquers is essential. The lubricant must also be compatible with the copper itself, as coatings can shrink and crack over time and expose the metal to direct fluid contact.
Above and beyond
‘We believe the basic copper corrosion test doesn’t go far enough,’ says Dr Cleveland, ‘so our own testing extends the copper strip immersion time and also measures the amount of copper in the fluid at the end of the test. That gives us a much more accurate indication of metal loss, correlating better with real world performance.’
Another aspect that is overlooked by standard tests is copper compatibility when the fluid is in its vapour phase. ‘Given the high temperatures created by eMotors and the increased numbers of sensors and controls, it is likely that lubricant will come into contact with copper elements while in its vapour form,’ adds Dr Cleveland. ‘With no industry standard test to examine the implications of this contact, Afton has developed a vapour phase copper compatibility test. This test shows that for some standard transmission fluids, copper corrosion is more severe in the gas phase than in liquid form. This challenging aspect was informed by our extensive testing and can be solved by blending a careful choice of additive chemistries.’
Unlocking new tech
Afton’s test methodologies are driving a new generation of dedicated EV lubricants. With its conventional transmission fluid chemistries already featuring in over a third of the world’s cars, Afton’s latest solutions now offer coverage for everything from hybrid transmission platforms – derived from step-type, DCT or CVT designs – to the latest fully electric drivetrain technology, including direct-cooled eMotors and multi-speed eAxles.
‘Our HiTEC® 35701 additive package has enabled the first ETF – Electrified Transmission Fluid – to be developed specifically to meet all the requirements of direct-cooled multi-speed eAxles. This package delivers the right balance over time of cooling, wear protection, optimised friction, electrical properties and compatibility,’ says Dr Harald Maelger, European OEM Relationship Manager at Afton. ‘We know from our work with OEMs that efficiency, reliability and value are core concerns for engineers, so we also reached out to Ricardo for an independent assessment of the benefits of using dedicated ETF.’
Independent analysis
The Ricardo modelling identified overall efficiency improvements as high as 2-3% from direct cooling the eMotor, enabled by appropriate lubricants. Analysis also showed that further efficiency gains of 2-4%, from using 2- and 3- speed instead of single-speed transmissions, could also be realised by using lubricant with the right friction properties. ‘These savings could support a valuable increase in driving range or a net reduction in eMotor and battery costs,’ explains Dr Maelger.
Even for emerging technology such as battery immersion cooling, Ricardo analysis shows that direct cooling can help to support the demand for faster charging, faster power output and greater efficiency.
‘While specialist battery immersion cooling technology and fluids are not yet mainstream, we’re always looking well ahead to explore the value that advanced lubricants can bring to every corner and every tier of the EV market,’ adds Dr Maelger.
Prototype tests
Afton’s work is not only based on additive and modelling expertise, but also on practical in-house evaluation of designs that are in the commercial pipeline.
With its OEM partners, the company continues to take testing to the next level. As recently published, prototype eMotor rig testing based on pre-production OEM hardware has shown that improving the thermal conductivity of the lubricant generates measurable improvements in eMotor peak torque.
Bringing balance
Afton’s value lies in its ability to unlock new technology for engineering partners through the right blend of additives.
‘Successful engineering is all about balance,’ concludes Adam Banks. ‘This is achieved most efficiently through close and early partnerships between those providing the specialist lubricant technology and those developing the hardware.’
With so much chemistry, modelling and testing expertise at their disposal, the OEM teams at Afton Chemical continue to offer a guiding hand to help each partner find – and keep – their balance.
