Novel capacitive measuring method to determine the complex impedance behavior of machine elements

This study presents a novel method for in situ monitoring of the condition of elastohydrodynamically (EHL) lubricated contacts, as occurring in rolling bearings and gears, using a capacitance-based evaluation of the electrical charging behavior. A nonlinear regression model is applied to segmented portions of the voltage response curve following a defined voltage pulse. This enables accurate extraction of the contact capacitance and parallel resistance, which reflect the thickness and electrical integrity of the EHL film. The method is validated against LCR meter readings on reference circuits, showing deviations below 5%. It is then applied to deep-groove ball bearings (6008 HSMB) under oil-air lubrication, varying temperatures (60°C and 100°C), and rotational speeds up to 30 000 1/min. Over 500 measurements per speed step confirm the method’s robustness and sensitivity to changes in lubrication regime, including detection of starvation effects. The extracted electrical parameters serve both for condition monitoring and for populating equivalent circuit models in the context of inverter-fed electric drive systems. The method thus contributes to improved understanding and monitoring of bearing durability, tribological film behavior, and electrical system integration. • Non-invasive evaluation of lubrication state via capacitive charging response. • Accurate extraction of capacitance and parallel resistance from time-domain signals. • Applicable to system monitoring, electrical modeling, and film thickness estimation. • Robust against noise and signal distortions through nonlinear segment fitting. • Enables identification of starvation and mixed lubrication in rolling bearings.