Analysis And Experimental Study On The Failure Of Seal In Transmission Of Vehicle

The piston ring type seals,as the rotary sealing devices,are one of the most important components in the wet clutch unit of a heavy load vehicle,whereas the failure of the rings occurred only after a service of about a month,the expected service life was more than 3 months.The failure ring was subjected to serious wear on the sealing surfaces,but the mating metal surfaces had slight abrasion.So it is necessary to investigate the wear mechanism and failure cause of sealing rings in order to provide the essential evidence and critical feedback into the design process,and thus contributing to the prevention of the sealing failures and more successful application of this rings in the future.According to the environmental and service conditions of seals in the transmission,the characteristics of the fluid film were studied,and pressure,friction torque and their regular pattern with working conditions were obtained.The lubrication of seals was researched by fluid film.Based on the force analysis of sealing ring,the balance between closing force and bearing force was confirmed to discuss the patterns of sealing friction and wear behavior.A model to simulate leak was constructed and then leakage rate was calculated.The wear of these rings can be divided into two categories:normal wear and abnormal wear.In accordance with the different characteristics,experimental analysis and modeling method were applied respectively.In order to obtain the influence of abnormal wear,a model was established for the small perturbation and rotation of ring.To assess the friction and wear behavior of seals made from PTFE composites under heavy-pressure and high-speed conditions,effects of normal load,sliding speed and oil temperature on tribological properties were investigated using a test rig.Scanning electron microscopy(SEM) was utilized to examine composite microstructures and study the wear mechanism.According to the working conditions of sealing rings,the transfer regularity in the sealing system was investigated.This heat transfer system consists of the ring,the fluid film and the sealed medium.Then the method to calculate the frictional heating of the end face and the partition ratios of the frictional heat were presented.The temperature distribution in the sealing rings was given,and the heat transfer analysis results indicate that the temperature distribution is related to the geometric parameters,the material parameters of the sealing rings,the frictional heat of the fluid film and the coefficient of heat transfer from the sealing rings to the sealed medium.A coupled method based on heat transfer theory and experimental analysis was put forward to estimate thermal loads on sealing rings.Selecting reasonably boundary conditions exerted on seals and simulating the actual operations of the transmission,thermal responses such as temperature field and distribution,thermal deformation,and their variabilities with pressure and rotating speed were obtained by computation of heat transfer.A test rig for dynamic sealing performance under high pressure and high speed was developed and built that can be used for rotary seal.This testing system is developed to simulate the real conditions of sealing rings and its functions include measuring statistical and dynamic fluid leakage rate,evaluating sealing performance during running in process and detecting the temperature of seals,which is of high quality of practicability and universality from the results.Conducted experiments with several seals by this testing system,the performance parameters and relation curves had been obtained,and the effect of each performance parameter on sealing performance was discussed primarily.The development and exploitation of this test rig for rotary seal provides potent guarantee for design and testing verification of seals with low friction coefficient,high reliability and high values of pressure-velocity.There are some indexs that cause sealing failure including working pressure,rotation, lubrication of seals,frictional heat,temperature distribution,deformation of the end face and so on.Those key technical indexes of failure mode were discussed,which indicated that failure mechanism was mainly wear-out-failure by heat and unbalance between closing force and bearing force.The optimum design methods based on working condition parameters,geometric parameters and seals-Types were put forward.The virtual design was applied in the optimized sealing ring and the results show that the leakage rate could be reduced and the effect of the frictional heat and thermal deformation of the end faces on the characteristics of the seals were within a appropriate range.