The Changing Requirements For Lubricants In EVs

A Pangea SI Expert

The world of electric-powered vehicles has arrived upon us and is definitely here to stay. Just one quick glance at TV adverts shows virtually all the OEMs advertising their hybrid or fully electric-powered vehicles at the expense of internal combustion engine (ICE) options. The International Energy Agency has produced statistics looking at the passenger cars stock over the last decade and it shows that globally, hybrid and battery electric vehicles (BEVs) have grown in the marketplace exponentially. In 2020, there were over 10 million hybrid or electric vehicles present across the globe, and in all regions, BEVs have outstripped the traditional plug-in hybrid.

With all the work and emphasis placed on electrically powered vehicles, we have to stop and think about the lubrication regimes for these vehicles.

Consideration Factors for Lubricants in Electric Vehicles

Traditional combustion engine vehicles require the use of an engine oil, a transmission oil, maybe an axle oil and some greases. A new modern battery-powered vehicle does not require engine oil and most of the focus now sits with the transmission oil, however, this is now no ordinary transmission oil. Even though all of the traditional requirements of the transmission oil are still needed, such as anti-wear, extreme pressure protection, frictional balance and high levels of antioxidancy, there are now added demands placed on the fluid. These demands come in the shape of electrical compatibility as the transmissions are now driven by an electric motor and this motor is directly in contact with the transmission fluid.

The formulator now must consider several factors:

• Electric motors contain copper windings and electronic circuitry, and the fluid has to protect and not attack these yellow metals, both when the copper is submerged in the fluid and also when it sits outside the fluid, in order to maintain the optimum operation of the transmissions.
• There are also new materials found in these E-motors or E-axles in the form of new plastics such as polyamides and other polymers, and the fluid must be benign to these new materials. The fluids must also have optimum conductivity properties, too high a conductivity and there is a risk of electrical shock, too low a conductivity and there is a risk of unwanted electrical discharge.
• Another consideration is the speed at which these motors or axles operate. Traditional engines operate at a maximum speed of around 7000 rpm but the new E-motors can rotate in the region of 30 to 50,000 rpm. This brings a risk of high foaming in the lubricant as the fluid churning is very high. If the foam remains uncontrolled then the user runs the risk of starving the axle of fluid and potentially inflicting irreparable damage on it.

So the formulator has an exceptionally difficult job balancing all the requirements of a new modern E-axle with the needs of a traditional transmission system, and of course, they have to do this in a low viscosity fluid in order to maintain the high expectations of fuel economy required by the market and the end user.

The Role of Fluids in Cooling Batteries

All this work does not take into account one major new component in an electric vehicle and that is the battery. The battery is the most expensive component of the electric vehicle and requires protection and maintenance to keep up longevity and efficiency for as long as possible. Rechargeable batteries operate within a temperature window, and fast charging and high power draws will raise the temperature significantly in contrast to very low ambient temperatures which cool the battery to temperatures outside of its optimum operating range.

Today, traditional methods of temperature control are utilised such as air cooling and indirect water-glycol mixtures. The issue with these techniques is that the heating or cooling is inefficient and significant temperature gradients can be experienced across the battery. This limits the life of the battery and reduces its operating capability. More modern methods involve full immersion of the battery in a liquid coolant, to maximise the cooling and minimise the temperature gradient, but this also brings its own problems.

• The fluid needs to have excellent heat transfer properties to remove heat from a hot battery. It also needs to have low viscosity to allow efficient movement of the fluid to keep the temperature constant.
• Most importantly, the fluid has to have excellent dielectric properties to prevent short-circuiting.
• The fluid must also have excellent oxidation properties, very high flash points, and low volatility.

Ultimately a battery coolant fluid needs to be a specialist fluid, designed for the job, and specialist esters are generally taking centre stage for this application.

The new world of electric-powered vehicles is very exciting but it brings with it a new set of problems for the lubricant engineers but is a challenge that they will continue to rise to through innovative solutions.

– Speak to the leading Additives and Lubricants Formulator Expert who wrote this article

Expert Bio:
Expert is an additives and lubricants formulator with over 25 years of experience working for industry leaders such as BP Castrol, Lubrizol, and Afton Chemical.

Key roles and experiences include:

– Works in the Chemical Distribution industry with a focus on lubricant additives and electric vehicles

– Has technical experience from roles such as technical advisor, global technology manager, development chemist and program manager engine oils.

– Has direct experience working with driveline additives, manual transmission fluids, industrial hydraulic fluids and more.

Expert has extended knowledge on:
– Lubricants and additive technology
– E-Mobility and EVs
– Lubricant Blending

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