Advancements in ultrasonic methods for in-situ lubricant monitoring.

Monitoring lubricant condition, and thus machine health, has been a major focus of interest for several decades. Although various in-situ measurement techniques are available, including electrical capacitance, optical methods, acceleration measurements and acoustic emission, active ultrasonic techniques offer an unparalleled combination of diagnostic insight, non-destructive operation and non-invasive applicability. By actively transmitting an ultrasonic pulse, film thickness and viscosity can be measured in test rigs as well as in real machinery with only minimal modifications.

This presentation highlights recent advances achieved in ultrasonic technology in three areas: 1) tribological testing — the Triboacoustic Pin, a novel active sensing element integrated into tribological specimens was developed and validated against optical interferometry film-thickness measurements and Elastohydrodynamic theory; results from tribological tests with induced contamination during the experiment will also be presented. 2) bearing lubricant health assessment — film-thickness measurements in bearings combined with a sensor-data-driven digital twin model to predict bearing condition, including algorithmic advances beyond the current state of the art. 3) viscosity measurement — non-invasive ultrasonic measurement of lubricant viscosity at ambient pressure, at high pressures of up to 4000 bar, and during liquid phase changes while drying.

Together, these achievements demonstrate the potential of ultrasonic methods for condition monitoring, tribological testing, and lubricant development and design in a non-invasive manner.