E-fluid Technology for Electrified Drivetrains

E-fluid Technology for Electrified Drivetrains

Jan 5, 2022
Posted by Amanda Eastwood, Product Manager, Driveline, Suzanne Patterson, Technology Manager, Driveline

This article highlights the key takeaways from our recent e-Fluid Technology for Electrified Drivetrains webinar, part of our Lubrizol360 Webinar Series featuring Lubrizol experts discussing important industry trends.

Changing legislation and tighter carbon dioxide (CO2) targets are driving original equipment manufacturers (OEMs) to develop electrified vehicles at an increasingly accelerated pace. In fact, hybrid and battery electric vehicles are forecasted to account for over 65% of the light-duty vehicle market by 2030.

The rapid expansion of the electric vehicle (EV) market is a proliferation of hardware designs. The drive for increased efficiency and performance has resulted in new hardware configurations and operating conditions. Conventional fluids will not deliver the performance required in these e-devices and lubricant manufacturers are seeing a significant shift in what lubricants will have to do in these new vehicles.

In this webinar, we examined the overall electrification market and the evolving requirements for fluids in EVs, specifically as they relate to e-axle hardware, performance and efficiency.

State of the EV Market

More than 65% of new light-duty vehicles will be either hybrid or fully electric by 2030. Digging deeper, it is expected that hybrids will represent 34% of global production during that time, with mild hybrid electric vehicles (MHEV) dominating the market. But battery electric vehicles (BEV) won’t be far behind, as they are expected to represent 32% of production by 2030, an outlook that has more than doubled in the past two years and continues to accelerate.

The trend is driven by legislation and many countries (Norway, by 2025, for example) have decided to ban internal combustion engines (ICE) within the next 20 years. Many OEMs have announced aggressive targets to retire ICEs in the same timeframe. That means electrification is an increasingly dynamic market, and e-driveline architectures are proliferating.

What This Means for Fluid Development

EV designs are increasingly combining the electric motor, and sometimes the inverter and control unit, into the gearbox. This means the amount of copper exposed to the lubricant is greater, and therefore copper corrosion protection by the lubricant is critical. Exposure to the motor also requires the lubricant to have appropriate electrical properties to maintain safety and efficiency. Furthermore, EV hardware can have different temperature properties affecting lubricant thermal stability and can incorporate new materials of construction with which the lubricant must be compatible. The lubricant must still provide requisite protection of gears and bearings, which is increasingly challenging since low viscosity fluids are desirable to optimize efficiency and heat transfer.

E-fluid Considerations

There are different performance aspects that must be taken into account when developing an e-fluid:

• Fluid electrical properties

• Material compatibility

• Oxidation and sludge control

• Corrosion protection

• Friction performance

• Gear and bearing protection

• Thermal properties

• Efficiency

E-fluids must conduct electricity at appropriate levels. If the conductivity is too low, it can cause static discharge, which leads to pitting; if it is too high, it can lead to leakage current, potentially reducing efficiency or creating shock hazards. For lubricants, the primary contributors to electrical conductivity are additive components and fluid viscosity.

In most EVs, polymeric materials are used as magnet wire insulation, wire coatings, slot liners and structural parts (such as bearing cages). E-fluids must be compatible with these materials, such as polyamides, polyimides, polyester amides, polyphenylene sulfides and polyether ether ketones. E-fluids must prevent damage to structural plastics which could lead to bearing or gear failure, as well as protect plastic coatings that would otherwise expose copper to the fluid.

Temperatures within e-devices are often similar to those of traditional transmissions and axles, but high temperature excursions can occur. Therefore, the fluid must be resistant to oxidation and sludge formation at elevated temperatures, especially when the motor is exposed to the lubricant.

An EV contains up to six kilometers of copper wiring in batteries, windings and e-motor rotors. Corroded copper wires and deposits in the e-motor circuitry and sensors could lead to shorting and vehicle malfunction or breakdown. As a result, any e-fluids that come into contact with the motor must have appropriate copper compatibility.

Gear and bearing protection require robust anti-wear protection from the additive package. This chemistry can also corrode copper, increase electrical conductivity, affect material compatibility, and increase the chance of fluid oxidation. Providing high load carrying capability while balancing other performance requirements is one of the biggest challenges in developing driveline e-fluids.

It is becoming desirable to use the lubricant to cool the motor, increasing the need for fluids with improved thermal properties. Fluid viscosity reduction improves heat transfer capability and is therefore considered desirable in the industry. Reducing the viscosity of a lubricant, however, can have a detrimental effect on other performance, especially foam, aeration, load carrying capability and electrical conductivity.

The industry agrees that efficiency gains can be achieved in e-devices by changing fluid properties such as viscosity, traction, and friction. It is unclear, however, the degree to which each property affects efficiency. For example, it is tempting to believe that lower viscosity is always better due to churn loss reductions, but under certain operating conditions, viscosity reduction hurts and other fluid properties (for example, traction and friction) become more beneficial. Understanding fluid efficiency contributions for different hardware designs and duty cycles will enable fluid design which best balances efficiency with the myriad of other performance demands.

Our View

As electrification of the vehicle market accelerates, the fluids necessary to keep EVs in proper working order will continue to evolve, with a focus on optimizing performance to meet the needs of next generation hybrid and electric vehicle drivelines. Lubricant manufacturers are developing solutions based on dedicated additive technologies to enable the growth of the EV market as more OEMs and countries try to wean themselves off ICE vehicles.

For more information about the development of e-fluids and their role in the development of the latest EV drivetrains, download the webinar slides here, or contact your Lubrizol representative today.

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