Technology: This is how the lubricants of the future will help electromobility
In electromobility, lubricants are just as important as before. They extend the life of the components, increase efficiency and thus help extend the range. But because of electricity, chemists have to break new ground.
For a good century, the matter was clear to automotive lubricant manufacturers. There was the combustion engine, then the transmission and then a few bearings that had to be kept supple. Over time, the drives became more powerful and the running times of the vehicles became longer and longer. The lubricants also had to be able to do more, which is why they continued to be developed and researched into additives that could handle these tasks.
But the world of lubricants has now become somewhat out of control. The global political and economic situation is becoming increasingly unstable, supply chains are breaking down, sustainability and electromobility are determining the mobility of the future. This also presents oil producers with new challenges. These are inherent in the nature of things. “A classic oil based on hydrocarbons is not a good heat store. The best heat store we know of is water. But that’s not quite so easy with electromobility,” explains Dr. Dirk Schwäbisch, Head of Automotive Lubricants at Petronas. A possible solution to this problem are ester compounds, i.e. electrical fluids whose molecules contain both hydrocarbons and oxygen.
This conflict of objectives takes on another dimension as soon as you realize that in the future, unlike now, the electric machines will also be “wet” on the inside. According to current plans, such engines will be used in VW’s further developed MEB modular system and in the SSP architecture (Scalable Systems Platform). The energy densities of these electric motors are increasing, so the rotors have to be cooled from the inside. Otherwise the engine will get too hot. Above 100 degrees the magnets demagnetize and lose power. This puts the chemists at the fuel suppliers in a quandary. Water cools excellently, liquids with hydrocarbon molecules lubricate well, but are not perfect as heat conductors. “So you look for molecules that are somewhere in between. “They have a polarity similar to that of water and the electrical resistance of the hydrocarbon,” says Dirk Schwäbisch, explaining the balancing act of the lubricant inventors and giving an outlook on the direction of development: “It will be low-viscosity oils to protect the electrical components of the electric motor cool and at the same time ensure the lubrication of the transmission components.”
As if this challenge wasn’t big enough, the drive units are becoming more and more compact and the inverter, motor and gearbox are combined in a single unit, all of which need to be cooled or lubricated. This increases performance, therefore also efficiency and ultimately also the range. A liquid that cools these three elements has to be able to do a lot. Especially since the increase in performance and the ever smaller available installation space increases the heat generation even more than it already does. In order to combine these three components, the technicians are working on so-called three-in-one oils.
The fact that electric machines will also be combined with multi-stage transmissions in the future does not make the task any easier. These components, such as friction elements or a dog clutch, increase the efficiency of the drive, but you need the right oil to lubricate these new components as well. It’s worth taking a look into the past here. Manual transmission oils have a high sulfur content to protect the gears. However, the electrical components of the electric machine and in the inverter are often made of copper and this reacts with sulfur. “That makes a chemist’s toenails curl up,” grins Dirk Schwäbisch with a healthy dose of gallows humor.
The additional task that the technicians face is to weigh up how much copper and how much gear protection is needed in order to then find the optimal properties of the oil. So fluids are developed to be sulfur-free while still providing gear protection. One solution is likely to be optimized phosphorus components, which have already ensured this wear protection. “The high torque of the electric motors generates a lot of pressure on the surfaces of the gears when accelerating. Since we use low-viscosity oils, the protective film is quite thin, so we need special additives to keep this film stable and thus chemically protect the surfaces,” says Dirk Schwäbisch.
The development of oils and lubricants basically follows a proven pattern. You calculate the viscosity and recreate it in the laboratory. The oil is then put to the test in tests that replicate the actual intended use as closely as possible. At best, the electric car should last on one charge for its entire life (around 250,000 kilometers). However, there are already electric vehicles in China where the oil has to be changed every 20,000 kilometers. Here too, a compromise must be found. To reduce weight, as little oil as possible is added. However, this increases the thermal stress of the lubricant.
The oils of the future will continue to be golden yellow due to the additives, but will probably also be more expensive than before, as these multi-talented liquids need more and higher quality additives to reliably fulfill their task. In addition, the manufacturing process for these oils must be almost clinically pure. Of course, the lubricants industry is also trying to become climate neutral. So used fossil oils are distilled and reused as base oil. Of course, oil can also be obtained from plastic. Another alternative are biogenic raw materials that are generated from plants such as algae. Similar to what is the case with biofuels. “Lubricants will support the transition to sustainable mobility through more efficient use of energy and drivetrains,” summarizes James Mark, head of the NEV lubricants department at Petronas.