Ultrasonic reflection measured oil film thickness in the slipper bearings of an aviation fuel piston pump

Running on an ultra-thin dynamic oil film, the slipper bearing in an aviation fuel piston pump is vulnerable to lubrication failure. To improve lubrication performance, the slipper surface is often grooved. However, the eventual lubrication effects remain challenging to judge qualitatively due to inaccessible measurement of oil film thickness distribution during pump operation. Eddy current sensors have been attempted, but they inevitably damage the oil film itself, and the tribo-pair test bench or incomplete pump used cannot simulate the complete working performance of a real pump. Addressing this issue, an ultrasonic-based method is investigated for online monitoring of the oil film thickness in a grooved slipper bearing. Firstly, the influence of groove texture on acoustic reflection is investigated by dividing the acoustic echoes into that from the top and bottom of the grooved surface, respectively. On this basis, a reflection coefficient extraction method fusing the reference signal and reflected signals at the top and bottom of the grooved surface is proposed, which can accurately extract the reflection coefficient and thus calculate the oil film thickness. Secondly, the finite element simulation is carried out to reveal the universal effects of the groove structure on the classical calculation method. The theoretical validity of the proposed reflection coefficient extraction method is verified by finite element simulation and experiment. A real aviation fuel piston pump is adopted for experimental validation, which is thoroughly performed under various operating conditions. The ultrasound measurement method shows promising results that are consistent with the theoretical calculations.