Efficiency is vital in EVs, and driveline lubricants can contribute to maintaining it.  -  Photo: Work Truck

Efficiency is vital in EVs, and driveline lubricants can contribute to maintaining it.

Photo: Work Truck

The electric vehicle emergence is well underway and while some sectors, such as light-duty and passenger cars may seem further ahead than others, the fleet electrification transition is already making strides.

According to a recent Geotab survey of U.S. fleet professionals, 54% have electric vehicles already in their fleet or on order, demonstrating the direction of travel. However, no one within the medium and heavy-duty vehicle industries are under any illusions that the transition will be easy.

The challenges are clear: One of the primary barriers is charging.

The electric charging infrastructure in North America is currently not suitable for the kind of long-haul journeys often undertaken by medium and heavy-duty vehicles, which can render full-scale fleet electrification plans unworkable.

Technology development is another obstacle. Petro-Canada Lubricants, an HF Sinclair brand, recently launched EVR, a new line of purpose-built lubricants and fluids for EVs, to support OEMs in designing the next generation of EV technologies.

Let’s explore some vital considerations for lubricant manufacturers as we work to help develop tomorrow’s fleet technology. 

Maintaining Efficiency in EVs

Efficiency is vital in EVs, and driveline lubricants can contribute to maintaining it. Fundamentally, avoiding viscous drag and friction is a crucial factor for electric and traditional engines alike.

One of the unique challenges to EVs is that heat must be removed from the motor as quickly as possible to improve motor performance and overall system efficiency.

EV fluids must have exceptional heat transfer characteristics to enable this. The fluid’s viscosity is critical to ensuring improved fluid thermal management, which means that EV fluids typically have lower viscosity than conventional automatic transmission fluids.

Protection Remains Key for the Next-Gen Vehicles

Electric motors run at high revolutions per minute (RPMs), meaning that EV driveline fluids must work hard to protect gears from wear damage.

Combining appropriate levels of protection with the required performance is the key challenge to enable the next generation of vehicles.

Fluids must reliably transfer power to the wheelbase with minimum drag and churning in the gear set, while providing the protection that is required to keep the asset working for longer.

As EV driveline fluids are typically low viscosity fluids, they offer better flow throughout the e-motor and parts.

An ideal fluid will support friction reduction on the gears and bearings, while allowing improved heat transfer and thermal efficiency. Combined, the motor will be able to run at its highest efficiency, keeping copper windings and motor components within optimal electrical motor efficiency.

Compatibility and Conductivity in Developing an EV Fluid

It’s no surprise that material compatibility is a key factor in developing an EV fluid due to the vehicle’s copper hairpin windings and electronic components. The hardware of an EV is fundamentally different from an internal combustion engine (ICE) and in many cases the motor is in the same compartment as the gearbox.

An ICE-based driveline fluid is primarily focused on durability and performance, so for EV fluids, it is critical to include a balance of conductivity, while avoiding issues with electrical arcing or sudden electrical discharge. 

Here is where collaboration is crucial. As there are more components for the electrical current to travel through, EV OEMs must work with fluid developers to design fluids to their optimum conductivity — with the goal of keeping it low and avoiding electrical discharge and damage to the electric drive unit.

The optimum EV fluid will protect the e-driveline unit by providing adequate antiwear protection, alongside the appropriate electrical properties, compatibility with copper, and new materials while improving the unit efficiency.    

The Battery Temperature Management Conundrum

Thermal management fluids are crucial to EVs and require a careful balance between thermal insulating quality, and electrical non-conductivity to prevent the build-up of electrostatic charges.

There are two types of fluid technologies for cooling in EVs — direct and indirect.

Most major manufacturers have, to date, used indirect cooling, where the surfaces and plates are cooled by a fluid, which subsequently cools battery cells. The current method does have safety concerns, primarily, the ability of fire to spread between cells and cause an explosion.

Comparably, direct cooling, or immersion cooling, while not directly utilized in mainstream EVs, can employ dielectric thermal transfer fluids to dissipate the heat from the battery, which can reduce the chance of thermal runaway or explosion.

EV Bearing Greases

The high operating speeds and materials compatibility requirements of the electric motors in EVs require specialized greases.

Greases designed for EVs provide extended high-speed bearing life through enhanced oxidative and thermal stability.  

High-quality greases will use carefully selected base fluids, thickeners and additive systems to provide both low friction, to extend driving range, and low noise operation. In addition, the additive systems must not use corrosive extreme pressure additives which can damage the copper motor windings.

Other unique factors will impact EV grease choices. EVs are typically significantly heavier than ICE vehicles due to the batteries.

This added weight means extra stress on driveline components such as the constant-velocity (CV) joints. EVs bring an opportunity for more specialized CV joint greases that have higher EP protection than in a traditional vehicle.

As I have detailed, there are technical considerations that fluid manufacturers, alongside hardware manufacturers need to address and overcome to enable the electrification of medium- and heavy-duty fleets.

But the transition has begun, and work is underway to bridge the gap between an electric future and today’s reality.

About the Author: Darryl Purificati is the senior technical advisor for OEM/Automotive at Petro-Canada Lubricants, an HF Sinclair brand, and the chair of the American Petroleum Institute (API) lubricants committee. This article was authored and edited according to WT editorial standards and style. Opinions expressed may not reflect that of WT.

 

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