An ultrasonic measurement method to measure lubricant film thickness in thin-liner bearing is proposed to solve the problem that the existing ultrasonic measurement methods could not be used to analyze the overlapped reflected pulses from sliding bearings with thin liner. The proposed ultrasonic measurement methods are theoretically analyzed based on the spectrum analysis method of overlapped signal. The signal from bearing substrate-liner interface is required

in addition to get the reference signal from bear liner-air interface. Then the frequency-domain amplitude ratios of overlapped signals and signal from substrate-liner interface are obtained. The amplitude ratio of film-thickness information composition from the overlapped signal and the constant composition from substrate-liner interface is obtained. The reflection coefficient is then obtained by comparing the amplitude ratio with the amplitude ratio of reference signal reflected from bearing bush-air interface

and the lubricant film thickness is then obtained from the reflection coefficient. Experimental results show that measurement results coincide well with the actual film thickness when the film thickness is less than 5 μm

and that the variation of lubricant film and its thickness are represented by the mean value of the multiple measurements when the film thickness increases. The multiple experimental results of film thickness in a range of 2.3-10.3 μm show that the method has a high measurement accuracy.