A2.3 - Online Bearing Lubricant Sensing by Mode Conversi¬on of Surface Acoustic Waves

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
A2 - Surface Acoustic Wave Sensors
G. Lindner, C. Brückner, M. Schmitt - Coburg Universität of Applied Sciences, Coburg (Germany)
45 - 52


A novel approach to online condition monitoring of the lubricant status in bearings is introduced, which is based on the mode conversion effect of surface acoustic waves: The excitation of Lamb waves on an outer surface of a bearing by attached piezoelectric interdigital transducers results in an interaction of these Lamb waves with the lubricant at the inner surface. This interaction influences the transmission of the Lamb waves to a second transducer due to the mode conversion effect of surface acoustic waves in contact with a liquid. The presence of the lubricant causes a loss of acoustic energy from the Lamb waves by a compression sound wave radiated into the liquid. Therefore, both the amplitude and the transmission time of such leaky Lamb waves depend on the presence and the status of the lubricant within the bearing.

This concept has been tested with different types of bearings - axial cylinder roller bearings, radial ball bearings and radial cylinder roller bearings - at different rotation conditions and with oil and grease lubricants. Up to now these tests have been performed without mechanical loads on the bearings. In all cases an influence of the amount of lubricant both on the amplitude and the transmission time of the acoustic signal has been observed. In addition, a modulation of signal amplitude and transmission time was registered, which was correlated with the rotational movement of the rolling elemets within the bearing. The comparison of the modulation frequency with the rotational frequency allows a determination of the motion and the slip of the bearing cage.