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

The normal operation of a diesel engine is closely related to the friction and wear phenomenon generated by its mechanical structure.As one of its important friction pairs,the piston component cylinder liner has good lubrication performance,which has important research significance and scientific value in ensuring the reliable operation of the diesel engine,reducing the friction loss of the piston component cylinder liner,and improving the working efficiency of the diesel engine.Because the lubricity performance has a great relationship with the lubricating oil film thickness,this paper takes the lubricating oil film thickness as the research goal,and conducts theoretical analysis and experimental measurement research based on the diesel engine cylinder lubricating oil film thickness measurement method,in order to obtain the change rule of the lubricating oil film thickness in the diesel engine working process,and then make up for the research blank of the domestic diesel engine piston ring dynamic oil film thickness measurement.Firstly,the principle of ultrasonic measurement was studied.Based on the characteristics of ultrasonic measurement and its propagation boundary conditions,the relationship between ultrasonic frequency,reflection coefficient,and lubricating oil film thickness was studied.Resonance models,spring models,and phase models were established based on different thickness measurement ranges.Direct calculation formulas for resonance models,spring models,and phase models were derived based on Taylor expansion,This lays a theoretical foundation for ultrasonic measurement of lubricating oil film thickness.Then,a sound pressure transfer model at the impedance boundary and a sound pressure attenuation model inside the friction pair material were established using COMSOL Multiphysics simulation software.The reflected signals received by piezoelectric ceramic components were studied,and the attenuation of sound pressure at different friction pair boundaries and inside was quantitatively analyzed.The simulation results provided assistance for subsequent experimental equipment selection.On this basis,a piezoelectric acoustic transducer was used to study the effect of friction pair materials on ultrasonic measurement of lubricating oil film thickness under the same thickness;A study was conducted on the influence of probe center frequency on ultrasonic measurement of lubricating oil film thickness under the same thickness using ultrasonic probes with center frequencies of 2.25 MHz and 5MHz;Independently designed and built a static oil film thickness calibration experimental platform with stainless steel as the friction pair,and based on this experimental platform,calibrated 0～130 μ The lubricating oil film thickness within the range of m was measured and calibrated,and the experimental results proved the measurement ability and accuracy of the static oil film thickness calibration experimental platform.Finally,a dynamic lubricating oil film thickness ultrasonic measurement system was constructed on the HS400 single cylinder air-cooled diesel engine.Combined with the measurement scheme,the diesel engine shell structure was partially modified,and a diesel engine cylinder oil film thickness measurement experimental system was established.By measuring the thickness of lubricating oil film at a speed of 10-100r/min using a measurement system,the variation pattern of lubricating oil film thickness under diesel engine operating conditions was obtained,providing certain support for subsequent measurement of lubricating oil film thickness under diesel engine combustion conditions.