Research On Measurement Of Clearance And Lip Fatigue Life Of The Variable Clearance Seal Hydraulic Cylinder

The essential difference between variable clearance seal hydraulic cylinder and ordinary hydraulic cylinder is that the different structure of the piston.The axial ends of the piston have a symmetrical lip structure.When the working pressure changes,the piston lip can adapt to the pressure change and produce deformation.The seal gap between the small piston lip and the inner wall of the cylinder to achieve a variable clearance seal.This topic focuses on the three issues of piston lip deformation law,sealing gap measurement and lip fatigue life prediction,and carries out the following researches:(1)By constructing a cantilever mechanical model with pressure on the end face of the piston lip,horizontal and vertical bending theory is used to derive the mathematical model of the deformation of the grooveless and grooved lip,and the two different structures of the piston lip are simulated and analyzed.The radial displacement deformation caused by the respective working pressure,and then obtained the theoretical value and simulation value of the seal gap;(2)For the characteristics that the small sealing gap of the hydraulic cylinder is difficult to measure directly,an ultrasonic measurement method based on"steady-state measurement+profile correction effect"is proposed,and a continuous model of vertical incident ultrasonic longitudinal wave propagation in a three-layer medium is established to pass the oil film layer.For the analysis of ultrasonic reflection coefficient,a resonant model or a spring model is used for thickness characterization,and the model is introduced to influence the correction factor?,and the experimentally measured values are corrected.(3)A set of experimental device for measuring the small sealing gap of the variable clearance sealed hydraulic cylinder was built.According to the measuring method,the sealing gap between the piston without groove and slot and the cylinder was measured respectively,and compared with the theoretical and simulated values.The results show that the errors are almost all less than 15 percent;(4)By applying the fatigue life theory,finite element software is used to analyze and predict the fatigue life of the piston lip from theoretical and simulation analysis.The theoretical calculations of the fatigue life of the grooveless piston and grooved piston lip structures were 7.5365×10~5 circles and 7.0238×10~5 circles,respectively,and the theoretical and simulation errors were within 10 percent.