Given that ICEs and hybrids will be in the global vehicle parc for decades to come, and their numbers are likely to increase over the next 10 to 20 years, the outlook is fair for grease manufacturers, since EVs of course need greases too, and global demand for greases from all applications is on a slight upward trend.
According to 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. However, as Lubrizol points out, a number of grease applications are redundant in a BEV. 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 alternator; the fan belt tensioner pulley bearings; and bearings in starter motors. Modified applications will include pumps for the battery coolant and e-motors. E-motor transmission bearings may not need to be greased in configurations where the component is immersed in oil. Greases for BEVs will be still be expected to minimize friction but also allow batteries to operate efficiently and provide long life and effective operation of the vehicle.
On the technical side, development of greases for EVs has not advanced especially far yet, and opinion is divided over whether this will remain the case or they, like lubricants, will be optimized gradually as OEMs focus on vehicle improvements. Most feel that greases will go through evolutionary changes as opposed to dramatic changes of technology.
Still, the powertrain for a full EV is very different from today’s conventional ICE systems, whereby an e-motor drives the wheels. Engineers must select greases with this in mind and consider those differences – exposure to electromagnetic fields, noise reduction and lower torque operation (higher efficiency in EVs). This is in addition to thermal transfer properties that are becoming more critical and materials compatibility that is critical for all fluids. Experts have noted that wheel bearings will operate under more extreme conditions in EVs and over a wider range of temperatures.
Indeed, noise will become a major consideration as e-motors are significantly quieter than ICEs. The presence of an electrical current may also impact greases, similar to other fluids discussed, along with their ability to provide performance for the longer lifecycles of the vehicle. Thermal management, seals and material compatibility will also be issues common to grease and other e-mobility fluids.
Current greases are mostly lithium based, and as we know, lithium is a critical element in battery manufacture, at this stage. This creates two commercial factors that need to be considered: cost and availability. While cost can be passed on to users, supply remains a concern with the increasing demand for lithium. As a resource commodity, the price of lithium can vary greatly and new supplies can have a significant impact on the pace of change as alternatives are considered.
Water ingress into a hybrid’s ICE lubricant due to engine inactivity may allow emulsions to form, as well as organic acids, which can be highly corrosive. Current hybrids with exhaust gas recirculation technology can also suffer from accelerated oil degradation and more contaminants, such as soot.
Calcium sulfonate greases are the next most common greases and are poised to become a more prominent alternative and see increased use. Calcium-based greases are expected to deliver the same stability and wear protection under extreme pressure, as well as corrosion resistance.
Polyurea thickeners may play an important role in EVs. Polyurea greases are always the preferred grease for e-motor bearings, either tapered roller bearings, ball bearings or needle roller bearings. Huafeng Shen, senior manager of research and development for Calumet Specialties Co., explains that polyurea greases tend to have high-operating temperatures, inherent anti-oxidative properties, are not electrically conductive, have high thermal stability and low bleed characteristics.
As mentioned previously, certain driving conditions for hybrids can be conducive to increased ingress of water into fluids, which can lead to the formation of emulsions. Lubrizol demonstrated that wear can increase in the presence of an emulsion. This is more likely in hybrids, with oil cycling and operating at lower temperatures. Fuel contamination due to ICE inactivity can also lead to increased wear and oil dilution.
Engineering solutions can be applied to ensure oil operates at the appropriate temperature to minimize accumulated moisture or fuel mixing with the oil in the combustion chamber.
Hybrids have not been subject to nearly as many field tests as standard ICEs to establish longer drain situations. As experience is gained, OEMs will look to enhance the driving experience and potentially allow oil to last longer by miles or time. Some feel that in engines not subject to significant use or exposure to fuel dilution and moisture may be able to go beyond a year. Enhanced lubricants may help drive this, but for now, current engine oils having performance to spare in most operating conditions.
A new Society of Automotive Engineers committee has been formed to develop a minimum performance driveline specification for electrified vehicles. OEMs, additive companies and lubricant suppliers were invited to participate. This is part of TC-3 driveline and chassis lubrication group. Several meetings have been held to date, but progress has been limited, although one subcommittee is actively working on the impacts of copper corrosion and the types of tests that can be used to measure it. No doubt that as work advances, any specification will set minimum standards and look at material compatibility, among other things.