Development and Validation of an Electrical Monitoring Technique for Electrified Lubricated Contacts

Electrical currents passing through lubricated rolling contacts are an increasing reliability concern in electrified powertrains, where shaft voltages and high-frequency currents can cause lubricant-film breakdown and electrically induced surface damage. Reliable electrical monitoring is therefore essential for distinguishing separated and conductive contact states and identifying transient dielectric breakdown events.

This study presents the development and validation of an electrical excitation and monitoring technique for subsequent integration with a friction and wear testing machine. The technique was initially evaluated using a static steel ball–ball configuration under separated and direct metallic-contact conditions. A 12.5 kHz square-wave signal with a nominal amplitude of 20 V peak-to-peak was applied through a capacitively coupled, current-limiting circuit, while the applied and contact-side voltage signals were monitored simultaneously.

Distinct electrical responses were observed for the two contact conditions. Direct metallic contact produced a clear change in the contact-side voltage due to the formation of a conductive path, whereas the separated condition exhibited a weaker response influenced by electrical noise and parasitic coupling. Introducing lubricant under static direct-contact conditions did not establish a confirmed electrically insulating film, and no dielectric breakdown or electrical discharge was detected under the tested conditions.

The results validate the capability of the developed technique to distinguish electrical responses associated with separated and conductive contact states. Future work will integrate the technique with the friction and wear testing machine under lubricated dynamic rolling conditions, with improved voltage and current monitoring to investigate lubricant film dielectric breakdown, transient electrical discharge behavior, and associated surface damage.