| The tripod universal joint is a new type of coupling developed by Qingdao University of Science and Technology for automobile transmission shafts.It has a simple structure and high reliability.However,both theoretical and experimental studies have shown that the wear between the sliding rod and the sleeve is serious.In order to further prolong the service life of the coupling and speed up its promotion and application,this paper took the tripod universal coupling as the research object,and conducted structural optimization and microscopic lubrication characteristics analysis,under the actual vehicle conditions.The fatigue analysis of the optimized coupling structure was carried out.Firstly,based on the topology optimization theory,the tripod universal joint was lightweighted by using finite element software;secondly,based on the fractal theory,the elastohydrodynamic lubrication model of the sliding rod-sleeve contact pair of the coupling was established,and the influence of the surface topography parameters of the contact pair and different design parameters on the microscopic lubrication characteristics of the coupling was discussed;finally,the transient dynamic analysis and fatigue life calculation of the coupling was carried out under the actual vehicle gears.The main contents of this article include:（1）The research background of topology optimization theory and fractal theory was introduced,and the research status of topology optimization application,microlubrication characteristic analysis,finite element fatigue analysis and the tripod universal joint research at home and abroad was summarized,which leads to the main research content of this paper.（2）The finite element model of the tripod universal coupling was established.The static strength analysis of the key parts of the sleeve,trigeminal rod and sliding rod was carried out.Based on the strength analysis,the topological optimization of the sleeve,the trigeminal rod and the sliding rod were carried out,and their structures were modified.Co MPared the results before and after optimization,the mass of the sleeve is reduced from 6.8917 kg to 4.1999 kg,a decrease of 39.1%;the mass of sliding rod is reduced from 0.2787 kg to 0.2308 kg,a decrease of 17.2%;the mass of trigeminal rod is optimized by the former 0.1814 kg is reduced to 0.1695 kg,a reduction of 7%;the overall weight of the coupling is reduced by 2.7516 kg,a reduction of 37.4%.（3）The elastohydrodynamic lubrication model of the sliding rod-sleeve contact pair of the tripod universal coupling was established.On the basis of analyzing the traditional roughness description method,the fractal theory was introduced to find the relationship between the surface roughness and the fractal theory.The average Reynolds equation of the pressure flow factor was introduced,and the basic equations of the microscopic elastohydrodynamic lubrication of the trigeminal universal coupling based on fractal theory were established.At the same time,the equations were dimensionless and discretized into algebraic equations.The co MParative analysis of the examples verifies the correctness of the numerical solution program and lays a solid foundation for the next analysis and calculation.（4）With the mathematical model of the coupling micro-elastohydrodynamic lubrication and the kinematics equations and dynamic equations of the coupling being simultaneously solved,the influence of surface roughness and topography parameters like viscosity,equivalent elastic modulus,equivalent radius of curvature,radius and shaft intersection angle on the lubrication characteristics of the coupling were analyzed.Kriging model combined with NCGA-Ⅱ algorithm was used to optimize the lubrication performance of coupling under the condition of first gear.The results show that the smaller the fractal dimension and the larger the scale coefficient,the greater the surface roughness,and the greater the surface roughness,the greater the fluctuation of the oil film pressure and oil film thicknes.Increasing the viscosity of lubricating oil,the intersection angle of the shaft,the equivalent radius of curvature and the rotating radius are conducive to the improvement of the lubrication performance of the sliding rodsleeve pair of the coupling;while increasing the equivalent elastic modulus has no obvious influence on the lubrication of rod-sleeve pair.In addition,after optimization,the maximum oil film pressure is reduced by 27.3%,the thickness of the central oil film is increased by 72.7%,and the friction coefficient is reduced by 52.5%.Coupling lubrication performance has been significantly improved.（5）Based on the finite element method,the dynamic characteristics of the optimized the tripod universal coupling in different gears were analyzed,and the fatigue life of the coupling in different gears is calculated based on the dynamic analysis results.The results show that under any gear position,when the load of the tripod universal coupling is stable,the maximum equivalent stress presents a periodic change,and the maximum stress is mainly concentrated in the squeezed position on the sliding rod that is in contact with the sleeve hole.In addition,the location where fatigue failure occurs is the same as the location where the stress is the largest.Under the condition of the first gear,the force of the coupling is the largest,and the corresponding coupling fatigue life is the lowest.As the gear position increases,the overall force of the coupling decreases,and the fatigue life increases.When the gear is fixed,the fatigue life of the parts with low equivalent stress is higher,and the fatigue failure of the coupling is mainly the cumulative effect of the contact stress between the sliding rod and the sleeve hole. |
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