Carbon fibre rings tackle the scourge of bearing currents

a longstanding problem for some industrial motors – can also affect electric vehicle drivetrains, potentially leading to premature failure of bearings and other components. SKF has come up with a way to tackle the problem using conductive brush rings that provide a reliable electrical connection between an EV rotor shaft and its housing. When used in combination with ceramic ball bearings, they can alleviate bearing current effects, making EV drivetrains more reliable and longer-lasting.

EV powertrains combine powerful motors, reduction gears and control electronics in compact packages called e-axles. Putting these high-speed, high-voltage components together in a small space can produce undesirable side-effects, including bearing (or “parasitic”) currents, which circulate between stator windings and housings. They can be induced on shafts and recirculate through the bearings and other mechanical components, creating electrical discharges that erode surfaces. The resulting "micro-pitting" increases noise and vibration.

SKF’s conductive brush rings help to overcome these problems. They use pure, long-life carbon fibre bristles that offer stable, predictable electrical performance with low friction. The brush rings are available in different configurations to suit wet (oil-lubricated) or dry (sealed) motor designs.

The brush rings’ narrow profile and scalable design makes them easy to integrate into new or existing powertrains. In a typical application, the ring will be installed at one end of a motor to provide grounding, while a hybrid bearing at the other end will provide an insulated connection.