As the global automotive industry faces its most significant transformation for a century, SKF’s capabilities support the industry in overcoming challenges and taking advantage of opportunities within electric vehicles.
Passenger electric vehicle (BEV) sales reached 2.1 million vehicles in 2019, up from less than half a million five years earlier. Despite a short-term fall in sales at the start of the global Covid-19 pandemic, demand for EVs remains strong and sales are rebounding.
Around the world, the electrification of passenger transport is picking up momentum. As part of their commitments to the Paris agreement on climate change, a growing number of countries are set to phase out the production of new combustion-engine vehicles over the next two decades. Public opinion is also enabling major cities to start imposing bans or extra charges on fossil-fuel vehicles to improve local air quality.
In several important markets, including China and Germany, governments have increased or extended purchase incentives for new energy vehicles as part of their post-pandemic crisis economic stimulus programmes. Industry analyst Bloomberg New Energy Finance expects sales to reach 8.5 million vehicles by 2025, and to pass the 50 million mark before 2040.
Extreme rotation speeds place increased demand on bearings
Electric vehicle powertrains may be mechanically simpler than their combustion-engine counterparts. But building an efficient, reliable and enjoyable electric drivetrain is extremely challenging.
“Motors used in automotive applications are designed to operate at very high speeds. For example, traction motors used in EVs rotate today at up to 20,000 RPM, and are expected to reach up to 25-30,000 RPM in future designs, as engineers strive to improve performance, whilst at the same time minimising the size and weight of powertrain components” explains Hugh Zhu, Manager Product Development DGBB at SKF.
This race for higher rotational speed ratio prompts challenging and demanding conditions on the bearings used in EV transmissions. Although the number of bearings is about the same in an E-axle compared to a traditional one, the technical challenge is higher than before. To withstand high centrifugal forces, and minimize self-heating generated by rapid rotation, these bearings require specialized cage designs, internal geometry and lubricant characteristics. Manufacturers also need them to operate reliably for the design-life of the vehicle, around ten years or 300,000 km today, and up to 500,000 km or even more in a near future.
Speed isn’t the only challenge, though. High and fast switching voltages of the electric motor inverter bring a greatly increased risk of stray currents in powertrain components. If they pass through conventional steel bearings, such currents can damage their surfaces, leading to higher friction, increased vibration and early failure. That’s where ceramic bearings come in.
Hybrid bearings with high-class performance
SKF has been helping the automotive industry meet these challenges since the beginning of the EV revolution. That’s why many OEMs in Asia, Europe and North America alike have selected SKF bearings as part of their electric drivetrain set-up.
SKF hybrid Deep Groove Ball Bearings (DGBB), for example, use ceramic rolling elements and steel rings. Bearings of this type offer improved high-speed performance and best-in-class electrical insulation characteristics, making them the premium choice for high performance EV powertrains. In addition, SKF is also developing tailored solutions to mitigate current leakage at system level and to protect the entire EV transmission.
Investing in the leading EV market
EV manufacturers don’t just need high-performing products. They also require supply chains and engineering capabilities that fit well with their manufacturing and product development footprint. China has become the world’s most important electric vehicle market, both in terms of demand and supply. It is also a key source for components for carmakers around the world. In short: to be a significant player on the EV market, component suppliers need to be successful in China.
SKF has adopted a full value chain approach here, investing in product development, manufacturing and testing targeting the local EV market. For example, the Group has invested SEK 770 million over the past two years in expanding its DGBB manufacturing capabilities in Xinchang. The site has also become the company’s global R&D centre for these bearings, enabling greater flexibility and speed when developing bearings for the fast-paced EV market.
In addition to its product development work, the SKF technical centre also supports car makers in application-specific engineering. One area of particular interest for this market is noise and vibration. “An EV is much quieter than a conventional car, so even small amounts of noise from the powertrain become noticeable,” explains Hugh Zhu, Manager Product Development DGBB at SKF. “Our expert teams work with leading international automakers to identify sources of undesirable noise and develop ways to address them at both bearing and system level to ultimately improve the experience of the end-user.”
Application-specific engineering and close cooperation with customers at early phase of the electric powertrain development also allows to design high efficiency bearing solutions and arrangement in order to decrease overall system power losses and therefore maximize vehicle electric mileage.
Carmakers are set to launch around 450 new battery and plug-in-hybrid vehicle models over the next two years. SKF has the technical, manufacturing and supply chain capabilities needed to support the sector’s accelerating growth.