Freudenberg Sealing Technologies is introducing a new generation of electrically conductive seals at the virtual 2021 Vienna Motor Symposium. The seals are designed to prevent bearing damage caused by electrically-induced corrosion and to decrease electromagnetic interference.
The power semiconductors in an inverter are often positioned directly above the motor. Silicon carbide semiconductors, which are often used for 800-volt drives, switch high currents up to 20,000 times per second, and each of the switching processes causes slight voltage fluctuations. The frequency of these overshoots is one or two megahertz, which puts it in the range of medium-wave radios.
If left unmodified, this frequency is transferred to the rotor shaft of the electric drive and results in two undesired side effects: 1) the rotor shaft functions as a rod antenna and radiates electromagnetic interference; and 2) excess voltage can potentially build around the vehicle’s electrically-insulated rotor shaft, overtaxing its ability to discharge. In the latter case, the excess voltage discharges through the shaft bearings, a condition known as electro-corrosion, which reduces the performance and life cycle of bearings.
With a new generation of conductive seals, marketed under the name eCONevo, Freudenberg aims to eliminate both of these effects. The company launched the basic principle in series production in 2015, and the seals are used in a popular European EV. With eCONevo, a very thin, conductive nonwoven material is attached to the radial shaft seal ring, and provides direct electrical contact between the rotor shaft and motor housing. The development of a new material blend now makes it possible to use a nonwoven material with an AC resistance of about one ohm. As a result, the electrical conductivity of the material is high enough not only to prevent electro-corrosion but also the emission of electromagnetic waves.
“The electrically conductive seal is a small, inconspicuous component, but its impact is enormous,” said Stefan Morgenstern, Advance Developer at Freudenberg. “We can eliminate unwanted side effects from electric drives with power semiconductors made of silicon carbide. As a result, the seal contributes to the ultra-fast charging of electric cars.”
Source: Freudenberg Sealing Technologies