Bearings, although buried deep within the vehicle, are on the front line in contributing to drivetrain efficiencies and delivering reliability for automotive manufacturers. Thomas M. Wolf, Application Engineering Master, power train and electrical, explains how EV drivetrains are placing new demands on components such as bearings and how these can be overcome.
Breakthroughs in technologies such as batteries, power management electronics and electric motors have paved the way for the dramatic emergence of electric mobility, but every aspect of the EV drivetrain is being advanced in the push for efficiency and reliability.
In particular, EV drivetrains are placing new demands on components such as bearings. The push for efficiency throughout the drivetrain is prompting original equipment manufacturers to explore new low-friction approaches rather than the conventional tapered roller bearings that are found in gearboxes and differentials.
Another challenge is the high speed of the electric motors in EVs up to 30,000 rpm speeds, far higher than those found in most industrial applications, are needed to ensure the drivetrain works efficiently. The speed acceleration and temperatures generated by these machines place enormous strain on bearings and their components such as cages and rolling elements.
Bearings running at such high speeds also need effective lubrication and cooling. Without this, there is a high risk of rapid degradation of the bearing components. Both races and rollers may overheat, causing premature failure and the need for early replacement.
In addition to high rotational speeds, electric motors can also present further challenges for bearings through electrical discharges. High-frequency voltage switching of the motor inverter can result in current leakage. This current can be conducted through the bearings causing arcs in the rolling contacts and may result in surface fatigue and erosion.
Manufacturers are also developing special lubricants with lower viscosity and special additives in order to reduce power losses from friction and support operations at far higher speeds. However, lower viscosity lubrication can also have an impact on the wear and fatigue characteristics of bearings. Accelerated wear can result in catastrophic failure, having an obvious impact on reliability.
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