The world’s oldest car manufacturer is embarking on a new era, but it’s not being closed-minded as it does so. Its line-up of battery-electric vehicles is launching under the EQ sub-brand, gradually phasing out the combustion engine that the company’s founder was instrumental in popularizing more than a century ago.
But this step change is not happening overnight. By 2030, the company expects around half of its global sales to feature a gasoline or diesel engines, and Renato Andorf, lubricant specialist at Mercedes-Benz, says expectations placed on these powertrains are tougher than ever.
“We’ve always had challenges for engine oil development, such as the introduction of low-ash engine oils at the start of this century for vehicles equipped with new particulate filters for diesel engines,” he comments. “As a result, the partnership of Daimler and Mercedes-Benz with the oil and additive companies has been close over the last few decades and continues to be so.”
Technical challenges result, both directly and indirectly, from tightening limits on fuel consumption and the associated requirement for increasingly high-performance and low-viscosity oils. Ensuring an adequate level of wear protection has meant collaboration with suppliers is taking place much earlier than in previous programs.
Andorf continues, “In the development process, the engine oil is treated similarly to any other engine hardware component. For this reason, all new and improved oil products are developed in close partnership with companies from the oil and additive industries. The engine hardware and engine oils need to be developed as compatible tribological ‘partners’.”
Engine testing takes place at the OEM’s Stuttgart-Untertürkheim powertrain development and production facility, Mercedes-Benz operates 24 multi-axis dynamometers on a near-constant basis. These enable every possible engine load and climate scenario to be tested repeatedly, from stop-and-go traffic to 2,400-hour durability runs at angles of up to 40°, which are particularly suitable for off-road use. Oil and lubricant development not only requires validation for conditions where the engine is under heavy loads; low-load scenarios – where black sludge generation is common – are also problematic.
“The impact on fuel efficiency remains an important criterion for future engine oils, as this contributes to the CO2 emissions of the vehicle. New fuel-economy-improved engine oils need to be compatible with metal coatings, on bearings for example; as a result, specific metal coatings may also be required,” says Andorf.
The latest innovations in low-friction surface technology is filtering down from the most high-performance models. Daimler developed a twin-arc spray honing process called Nanoslide for AMG powertrains in the late 2000s, designed to solve inherent problems with reduced-weight aluminum blocks. This lightweight coating for the cylinder walls removes the need for heavy cast-iron liners, which can be up to 5mm thick and cause additional friction. It also creates a more effective tribological surface than aluminum by exposing oil-retaining pores in the material. Applications have been broad, now spanning from the OM 654 diesel as used in the company’s plug-in hybrids, to the M 139 high-performance AMG four-cylinder powerplant that was developed for its high-performance hatchbacks.
Nanoslide is one of many technologies shared with Mercedes-Benz’s motorsport programs. The latest Formula 1 cars use 1.6-liter turbo engines that experience the same hot-running characteristics as downsized road engines, and partnerships with lubricant suppliers are vital and mutually beneficial. Working with team engineers, team sponsor and partner Petronas co-developed a synthetic base oil to suit, later adapting it for road use. It features stronger oil chains to withstand evaporation and is designed to dissipate high temperatures and avoid any sludging, which Andorf says is a particular issue for applications over 134ps per liter.
Hybridization, another trend shared with Formula 1, adds complexity too. Mercedes-Benz will offer more than 20 plug-in hybrids by the end of this year, from the A-Class to the S-Class. Varied usage – including the potential to operate at high load from immediately after a cold start, or for engines to be left idle for long periods, which causes condensation build-up – places new demands on lubricants. Shared motorsport knowledge also enabled Petronas to formulate its first hybrid oil in 2016, engineered to reduce varnishing and wear on the valvetrain and piston rings caused by more frequent engine-off driving.
“The requirement is more a strong, continuous development of engine oils, rather than a breakthrough,” says Andorf, adding that the requirements are likely to continue to become more varied. “Meeting all the requirements is in fact the art of engine oil development and the real competence of oil developers. Focusing purely on only one requirement criterion, without the need to fulfill all remaining criteria, is actually relatively easy.”