Electrical impedance spectroscopy enabled in-depth lubrication condition monitoring

Abstract

Electrical contact resistance or capacitance as measured between two interfaces of a lubricated contact has been used in tribometers, partially reflecting the lubrication condition. In contrast, the electrical impedance spectroscopy (EIS) provides rich information of magnitude/phase spectrum, which is thoroughly investigated using a combination of electrical circuit models (equivalent to the lubricated contact) and in-situ measurements with a ball-on-disc contact. Results indicate a promising potential of EIS in lubrication condition monitoring, including the variation of lubricant film thickness as estimated using high-frequency magnitude response; the transition between full-film, mixed, and boundary lubrication regimes, as differentiated using extracted electrical resistance together with phase spectrum; the forming of anti-wear boundary film, where extra resistor/capacitor are added; and the degradation of lubricant, such as fuel dilution, oil oxidization, and water emulsifying.