An Overview of EV Lubricants

While battery electric vehicles do not require an engine oil like their internal combustion engine counterparts, they do require a host of lubricants to keep them running safely, reliably and efficiently. So which components in an electric vehicle require lubrication, and what types of lubricants are vital for smooth operation? 

Thermal management fluids. Not surprisingly, electric motors and the batteries that power them generate a significant amount of heat, and thermal management fluids must facilitate the optimum temperatures in both components. However, it is difficult to strike the right balance between keeping the e-motor cool and the battery at an ideal—and different—temperature. 

Original equipment manufacturers—including Tesla, Jaguar and Audi—have typically used a blend of water and ethylene glycol (EG) to cool electric motors and other electronics in EVs. Some manufacturers (Nissan and Volkswagen) have tried using an air-cooled approach, and others (BMW) have even employed a refrigerant. It is generally agreed upon, though, that more work needs to be done to formulate thermal management fluids that best meet the needs of today’s—and tomorrow’s—electric vehicles. Some formulators think that the existing families of lubricating base oils might be able to do the trick, but others believe that a completely new fluid may be necessary. 

At any rate, the cooling performance of any fluid depends on its specific heat capacity and its viscosity. According to Lubes’n’Greases’ Electric Vehicles Knowledge Hub, “specific heat is a key consideration for the selection of any cooling fluid. Simple water comes out on top, but water cannot be used by itself, so it is mixed with a glycol (a substance in the alcohol family) to prevent it from boiling or freezing. These mixtures are still better than a petroleum oil at retaining heat.”

Viscosity is the measure of how easily a liquid will flow. For EV thermal management, a low-viscosity fluid is generally preferred. However, this low viscosity must be balanced against two factors: volatility, which is the propensity for the oil to evaporate in high heat and prevent potential fires, and density, which determines how much fluid the system will need. 

Driveline fluids. Many electric vehicles on the road today employ a driveline fluid that is identical or very similar to an automatic transmission fluid. However, several experts have posited that a bespoke EV driveline fluid may be a more effective solution. 

According to an article published by the Society of Tribologists and Lubrication Engineers, there are six key driveline fluid properties that formulators and equipment manufacturers are keeping top of mind while working to develop EV-specific fluids: 

• Viscosity and friction. Any reduction in friction can extend the battery life and range of an EV.
• Copper compatibility. Electric vehicles contain much more copper than ICE vehicles do, much of it carrying current and some of which comes into direct contact with lubricants. Preventing the copper components from corroding is of obvious importance and has become a new parameter for electric vehicles. 
• Load-carrying ability. Electric motors produce high torque, which places stress on gears.
• Aeration and foaming. EVs are trending toward higher-speed electric motors. These higher speeds could lead to air entrainment in the fluid.
• Electrical conductivity. There is a limit to how conductive a fluid can be without causing problems with electrical components. However, if the conductivity of a fluid is too low, buildup of static electricity is a concern.
• Thermal conductivity. Fluids with higher thermal conductivity can keep the motor and drive system running cool. However, oils are generally poor heat conductors.

Greases. According to major additive manufacturer Lubrizol, there are more than 50 applications for greases in a modern vehicle and four areas that have the most influence on energy efficiency. These include the transmission and bearings, wheel bearings, steering mechanisms and frontend accessory drive bearings. But the company also pointed out that several grease applications are redundant in a battery electric vehicle. These include the center bearings, high-speed constant velocity joints, universal joints and sliding splines in drive shafts; drive bearings for water pumps, engine cooling fans and the alternator; the fan belt tensioner pulley bearings; and bearings in starter motors.

The development of greases for electric vehicles differs from that of thermal management and driveline fluids in that it has not advanced very far yet. Furthermore, it appears that opinion is divided over whether this will remain the case or if greases will be optimized gradually. However, most feel that grease technology will go through slower, evolutionary changes as opposed to quicker, more dramatic changes. 

The fact remains that the powertrain for a fully electric vehicle is quite different from today’s ICE cars. Because of this, engineers must select greases with a few key differences in mind. These include exposure to electromagnetic fields, noise reduction and lower torque operation (i.e., higher efficiency). 

EVs’ Impact on the Lubricants Business

The inevitable shift from ICE vehicles to electric ones is expected to have notable consequences for the lubricants industry. The most concerning of these is a dip in lubricant demand, as electric vehicles will eventually slice a large chunk out of engine oil sales. (Engine oils currently make up about 20% of global automotive lubricant demand.)

But how big will that slice be? 

Analysts have said that the impact that growing EV populations will have on PCMO demand will be significant but likely not devastating for lubricant marketers. Chevron Oronite officials said that numbers of both EVs and ICE-only cars will continue rising until 2050, at which point the numbers of conventional vehicles will start to decrease. Passenger car motor oil demand will peak at roughly 8.2 million tons in 2050, Oronite predicted, then it will fall to 7.5 million tons a decade later. At that point, it will be about 20% less than it would be without the presence of any EVs.

Other analysts have differing opinions about EVs’ eventual impact on lubricant demand. Global consultancy Kline & Co. estimated that by 2040, EVs will force down combined PCMO demand in 15 major countries by about 20%. The consultancy also said that demand volume will decrease at a cumulative annual rate of 0.1% over that period, whereas it would have increased at a rate of 0.9% sans EVs.

IHS Markit said in 2018 that it expected global PCMO demand to be 7% lower in 2040 than it would be without EVs. It also posited that the transition to EVs will be slower than some forecasters have predicted, because the increasing average lifespan of cars will slow the rate of vehicle scrappage.

For more information on all things electric vehicles, check out the Electric Vehicles Knowledge Hub at https://www.lubesngreases.com/category/electric-vehicles/   

Simon Johns contributed to this article.

Sydney Moore is managing editor of Lubes’n’Greases magazine. Contact her at Sydney@LubesnGreases.com