Lubrication of Hybrid Electric Vehicles
Reprinted with permission from the March 2024 issue of TLT, the official monthly magazine of the Society of Tribologists and Lubrication Engineers, an international not-for-profit technical society headquartered in Park Ridge, Illinois, www.stle.org/.
A large number of lubricants and coolants could be required to meet the demands of the three types of hybrid electric vehicles (HEVs). The three available mechanical arrangements are Series, Parallel, and Series-Parallel, and are described as:
Series
An electric motor powers the wheels, receiving electricity from a battery pack which is linked to a generator run by an internal combustion engine.
Only the electric motor powers the drivetrain. The combustion engine can be run continuously, but only generates electricity to the motor and battery pack.
Parallel
An electric motor and an internal combustion engine are both connected to the transmission and can simultaneously transmit power to the wheels. In many of these HEVs, the engine can also act as a generator for supplemental charging of the battery pack.
Series-Parallel
An electric motor and an internal combustion engine can independently generate power to the drivetrain.
Each of these arrangements requires a drivetrain (transmission, drive shaft and bearings) to transfer power to the wheels. Many transmissions are the dual-clutch type, often integrated with the electric motor.
The combustion engines in HE cars typically use gasoline as the fuel, while some HE trucks and buses utilize diesel fuel.
All of these mechanical arrangements require both lubrication and cooling. Specifically, the electric motor and battery require cooling, while the engine, drivetrain, bearings and regenerative braking system require lubrication. The fluid properties and performance required to lubricate, by reducing friction and wear, are very different from those required to cool, by transferring heat.
Because the engine in a series hybrid is often smaller, its lubrication requirements are much less demanding. In the series-parallel arrangement, when in-town driving changes to highway driving, the engine may need to kick in very quickly, stressing the engine oil.
In some designs, the lubricant for the transmission also lubricates the electric motor, so it must be compatible with the copper coils in the motor.
Presently, there does not seem to be much consensus among system designers, fluid suppliers, additive manufacturers and vehicle manufacturers about which hybrid electric arrangement is optimum – unlike conventional combustion engines, whose design has been optimized over the last 120 years.
All of this means that a large number of lubricants and coolants could be required to meet the demands of the three different mechanical arrangements. This could pose a real dilemma for manufacturers, marketers, and distributors of the fluids required for HEVs.
For more details, read the full article by R. David Whitby here [pdf].
Muscle Products Corp. recommends using its Hybrid Engine Treatment™ for additional protection of your HEV’s internal combustion engine. Designed specifically for today’s hybrid and low-viscosity oil engines, it treats the metal for reduced friction and wear, enhancing engine performance.
Also, treat your fuel system and keep it clean with Fuel Treatment FT-10™ for gasoline and diesel engines, or clean and add lubricity with your diesel fuel with Diesel High Performance DHP-10™.