Ultrasonic measurement of lubricant film thickness in sliding bearings with thin liners

Abstract

When conducting ultrasonic measurements of the lubricant film thickness in sliding bearings with thin liners, the ultrasonic pulse reflected from the bearing liner–lubricant film interface will superimpose on the pulse reflected from the bearing substrate–liner interface. The thickness information of the lubricant film is contained in the reflected pulse from the liner–lubricant film interface. In this case, the film thickness could not be obtained directly from the superimposed reflected signals. The thin liner indicates that the thickness of the bearing liner is less than half the ultrasonic pulse width. Based on the spectrum analysis method of superimposed signals, a new method is proposed to measure the lubricant film thickness in sliding bearings with thin liners. The frequency-domain amplitude ratio between the echo component containing thickness information and the steady echo component from the bearing substrate–liner interface is extracted from the superimposed signal. The reflection coefficient of the liner–lubricant film interface is obtained by this amplitude ratio to determine the film thickness. The lubricant films of different thicknesses in a thin-liner thrust pad were measured in a high-precision experimental apparatus. The measurement results were compared with the known film thickness set by the experimental apparatus. In the thinner film region, the measurement results agreed well with the set film thickness. In the thicker film region, the mean values of the multiple measurement results represented the film thickness. The experimental results show that the method can be used to measure the lubricant film thickness in sliding bearings with thin liners.

Review of ultrasonic-based technology for oil film thickness measurement in lubrication

“…To extract the reflection coefficient of the oil layer from the overlapping echoes in a thrust bearing with a thin coating, Geng et al have referred to the reflected signal of the substratecoating interface [36]. Zhang et al have directly processed the overlapped signal with the superposition of some Gaussian echoes [37][38].…”

“…Therefore, the minimum point frequency is directly extracted to calculate the oil film thickness. However, the measurement error increases with the fewer echoes used [36]. The time-frequency method proposed by Jiao et al is also able to achieve the measurement of thick oil film without a reference signal [23].…”

“…The time-domain model, the unified time-domain model, is a unified solution of the film thickness model, but the algorithm needs to be improved to reduce the calculation time [20]. For some special multi-layer friction pairs, such as thin liner sliding bearing, the high-order reflected signals of multi-reflection should be considered to improve the calculation accuracy of the ultrasonic model [36]. Besides, the measurement range covering the blind zone should be considered by exploring more information from the spectrum of phase and amplitude [35].…”

Effect of Oil Acoustic Properties on Film Thickness Measurement by Ultrasound Using Spring and Resonance Models

“…Since then, it has been used for measuring lubricant film thickness [3][4][5], lubricant viscosity [6], thermoelastic compliance [7], contact forces [8], friction [9,10], contact dimensions [11], contact surface roughness [2], among other relevant information about tribological contacts. In addition to a number of works under laboratory conditions, this technique has been adapted to a range of real applications, varying from typical engineering applications such as the piston/liner system in engines [3,7,12,13], sliding bearings [14][15][16][17], roller bearings [18,19], and metal-forming applications [11,20], to a much broader realm of applications, such as measuring the thickness of leaves in tree canopies [21].…”

“…Lubricants 2024, 12, 108 2 of 16 In lubricated systems, monitoring the thickness of the lubricating film layer is fundamental to guaranteeing the correct functioning of mechanical components and equipment [22,23]. One of the main difficulties for real-time monitoring of the lubricating film layer is the complexity involved in developing non-invasive systems that can be directly applied to mechanical components [24].…”