Research On Transient Thermoelastic Instability Of Friction Pair In Hydro-Viscous Clutch

The hydro-viscous clutch is widely used in the stepless speed regulation of the fan and the water pump,as well as the soft start of the heavy scraper conveyor and the belt conveyor used in mining.Friction pair is the core component of the hydro-viscous clutch.Thermal failure caused by local high temperature often occurs,which directly affects the performance,reliability and service life of the hydro-viscous clutch.Thermoelastic instability theory considers the coupling effect of circumferential non-uniform temperature field,heat flux density,thermoelastic stress and other physical quantities,which is an important means to study local high temperature problems.Therefore,it is essential to carry out in-depth research on the transient thermoelastic instability of the friction pair in order to lay a theoretical foundation for improving the reliability and service life of the friction pair of the hydro-viscous clutch.A two dimensional theoretical model of thermoelastic instability of friction pair in hydro-viscous clutch was established based on disturbance method,considering the thickness of each layer of multilayer material friction disc and the thickness of steel disc.The four kinds of system matrix of thermoelastic instability under symmetric mode and antisymmetric mode for friction disc and steel disc respectively are obtained,the variation rule of critical speed under each deformation mode is studied,and the main mode of the system under symmetric(friction disc)-antisymmetric(steel disc)mode is determined.A method to determine the relationship between the disturbance growth rate and the relative slip speed of the friction pair using the system matrix is proposed.The critical speed and growth rate at each radius under the main mode are determined,and the transient distribution of the disturbance pressure field and temperature field on the contact surface of the wet friction pair is obtained.The influence law of relative rotation speed and number of hot spots on growth rate is proved,and the influence law of slip time and initial pressure disturbance amplitude on disturbance pressure field and temperature field on contact surface of friction pair is determined,which provides a preliminary condition for the study of transient thermoelastic instability of hydro-viscous clutch in the variable speed sliding process.Based on the average flow model and rough contact model,the variation rule of the average pressure of the friction pair in the variable speed sliding process is obtained.According to the relationship between the growth rate and the relative sliding speed,the variation laws of the growth rate and the total pressure of hot spot in the variable speed sliding process are obtained.The three-dimensional transient heat conduction model of friction pair was established,and the radial non-uniform temperature field distribution of friction pair in the variable speed sliding process is obtained.Combined with the disturbance of circumfluence temperature field caused by thermoelastic instability of friction pair,the variation law of total hot spot temperature of friction pair in the variable speed sliding process of hydro-viscous clutch was summarized.Introducing the wear law to the theoretical model of thermoelastic instability,the finite element model of the influence of wear law on thermoelastic instability was established,the accuracy of which is validated using the existing bi-material analytical method.The analytical method is difficult to solve the thermoelastic instability problem considering wear of friction pairs used in traditional hydro-viscous clutch.Therefore,the finite element method is mainly used to study the comprehensive influence of wear rate and thickness of friction pair on the critical speed of thermoelastic instability.According to the requirements of thermoelastic instability test of friction pair,a test bench for thermoelastic instability of friction pair in hydro-viscous clutch was built.The dynamic change of temperature of friction pair was measured in the process of sliding friction,and the influence law of relative speed of friction pair,contact pressure and lubricating oil flow rate on the disturbance temperature field was sorted out.The theoretical results are in good agreement with the experimental results,which verifies the effectiveness of the theoretical method and shows that the proposed method can be used to predict the actual temperature field of the friction pair accurately.