Research On Measurement Technology Of Cylinder Lubricant Film Thickness Based On Ultrasonic Reflection Coefficient

Piston assembly-cylinder liner friction pair is one of the most important friction pairs of diesel engine.The lubrication performance of the piston assembly-cylinder liner friction pair is significant to ensure the stable operation and improve the mechanical efficiency of diesel engine.In this dissertation,the ultrasonic measurement method of lubricant film thickness and its application in diesel engine cylinder are studied,aiming to establish the ultrasonic lubricant film thickness measurement method to meet the requirements of piston assembly-cylinder liner friction pair lubrication performance monitoring.Firstly,the theoretical relationship between the ultrasonic reflection coefficient and lubricant film thickness is studied by combining acoustic equations and acoustic boundary conditions.The resonant model,spring model and phase shift model suitable for different lubricant film thickness measurement range are established,and the analytic formula of the phase shift model is proposed to overcome the limitation that the phase shift model can not solve the lubricant film thickness directly.Then the ultrasonic measurement method of diesel engine cylinder full range lubricant film thickness based on three theoretical models is established.Secondly,the influence law of the frequency resolution,noise signal,pulse repetition frequency,spatial resolution and acoustic coupling performance on ultrasonic measurement accuracy of diesel engine cylinder lubricant film thickness are analyzed.Then the compensation scheme to improve the measurement accuracy of diesel engine cylinder lubricant film thickness is established.Thirdly,the lubricant film thickness calibration and ultrasonic measurement experiment system is designed and set up,then the lubricant film thickness calibration and ultrasonic measurement experiments in the range of 4.5-125.1 μm are carried out by three theoretical models.The measurement results show good agreement and consistency with the calibration thickness,the maximum error occurs at 85.7 μm,and the error is 5.22 μm,which can verify the accuracy of the ultrasonic measurement method of diesel engine cylinder full range lubricant film thickness based on three theoretical models.Finally,the ultrasonic measurement scheme of cylinder lubricant film thickness is proposed according to the structure of diesel engine,and the simulation experiment system for diesel engine cylinder lubricant film thickness measurement is established.The reflected signal from the inner wall-air interface is considered as the reference signal,and the spring model is used to measure the piston ring lubricant film thickness in the speed range of 10-100r/min.Then the applicability of ultrasonic measurement method of diesel engine cylinder lubricant film thickness is verified preliminarily,which has great significance to further research on ultrasonic lubricant film thickness measurement in diesel engine cylinder under combustion state.