May 27, 2021
Posted by Gareth Fish, PhD, DIC, BSc (Hons), ARCS, CSci, CLS, GLGS, Technical Fellow, Industrial Additives
This article highlights the key takeaways from our recent Influence of Vehicle Electrification on Future Automotive Lubricating Greases webinar, part of our Lubrizol360 Webinar Series featuring Lubrizol experts discussing important industry trends.
The battle against air pollution is nothing new. Residents in London, England, have complained about foul-smelling air since the Middle Ages. In 1952, the Great Smog of London, which plunged the city into smoky darkness for five days, led to the Clean Air Act of 1956. In 2003, the city had to impose a traffic congestion charge after air pollution increased from the 1970s to 1990s. Finally, in 2008, the Climate Change Act aimed to reduce greenhouse gas emissions from all sources.
But the battle hasn’t just taken place in England. In the United States, the battle against pollution has been almost as long. Whether it was the Air Pollution Control Act of 1955, the Clean Air Act of 1963, Air Quality Act of 1967 or the Clean Air Act of 1970, the U.S. government has also fought to make the air cleaner for its citizens.
As the fight continues today, a movement is afoot to reduce the number of internal combustion engines (ICE) on the road by introducing more electrical vehicles (EVs) into the transportation sector around the world. It is forcing lubricant manufacturers to rethink their approach to the greases used in such vehicles. In this webinar, we examined the current state of vehicle lubrication and how the evolution of hybrid EVs (HEVs) and EVs will, by necessity, change the way greases are manufactured and used.
Today’s Automotive Greases
In common current conventional vehicles, approximately 26 of more than 50 parts require grease lubrication. There were 483,000 metric tons of grease sold in 2019 (the most recent year for which data is known; sources: NLGI and Kline). In most vehicles, there are four different types of greases used, either alone or in combination:
There may be as many as 50 greases in a typical passenger car or light truck. Inside the passenger compartment, greases serve mostly light lubrication duties like providing noise-reduction qualities. They must be plastic-compatible and are applied for the life of the components. Externally, greases are frequently used in antiwear, anticorrosion and antioxidant capabilities.
The major uses for grease include steering racks, suspension joints of light trucks, door hinges, locks and handles, brake mechanisms, shock absorbers and wheel bearings, among others. In contrast, small volumes of specialty greases are necessary for electrical contact switches, pedal mechanisms, accessory drive bearings, seat adjusters, window winders and other applications.
The majority of greases on an HEV will be the same as on today’s ICE cars, although starter-motor greases will no longer need to have high shock-load resistance. On stop-start vehicles, the starter motor can be permanently engaged, which acts as a generator when not restarting the engine. Transmission electric motor bearings may be grease- or oil-lubricated when they are incorporated in the gearbox.
Electric motor bearing greases must have the following characteristics:
- Long life
- Low noise
- Conducting or insulating
- Energy efficient
All greases will need to be optimized for energy efficiency and longer life to reduce drain on batteries.
Of all the more than 50 grease applications on an ICE vehicle, only four areas of a vehicle influence energy efficiency:
- Drivetrain joints and bearings
- Front-end accessory drive bearings
- Wheel bearings
- Steering mechanisms
One of the challenges for vehicles’ energy efficiency is their duty cycle. At low speeds, good lubrication films are not generated. There is a tendency to have in-boundary lubrication, which leads to energy losses. While moving to a thicker base oil will increase lower speed film thickness, it will lead to higher speed churning losses.
At higher speeds, the lubrication films generated are thicker. Therefore, using a lower-viscosity oil will lead to thinner films being formed, which reduces churning losses. But if the film is too thin, component durability may be compromised.
For the next few years, it is anticipated that there will be little change in the majority of automotive greases. In HEVs, there will be changes in the starter motor greases and in the greases for the electric motor bearings. The EV market still has a lot of unknowns, but it is clear that greases that have an impact on vehicle range will need to be upgraded to have higher performance in energy efficiency, durability and long life. Finally, conductivity/resistivity is known to be an issue but is vehicle hardware-specific.
For more information about future of EV lubrication, download the webinar slides here, or contact your Lubrizol representative today.