Study On Lubricating Condition Prediction And Dynamic Characteristcs Of Grooved Rotary Seal Ring For Vehicle

For the increase of pv value(pressure multiplies velocity) in vehicle transmission system, micro grooves rotary seal(MGRS) is used to some extent for its good hydrodynamic effects. However, the operating condition in vehicle transmission system is complex and horrible; researches about MGRS are limited under real vehicle conditions. Through theoretical analysis, numerical simulation and experimental research, the static and dynamic characteristics of MGRS are studied systematically. For the limitations and shortcomings of traditional film lubrication, a lubrication conditions prediction model is developed. By considering cavitation effects, a dynamic characteristics analysis model is established. By taking steady and dynamic characteristics as optimization objectives, the groove structure of MGRS is optimized. Finally, a dynamic model of MGRS is established, and the dynamic characteristics of optimized groove and traditional spiral groove are compared and analyzed, and the mechanism of the creep rotation is analyzed.Boundary fitted coordinated transformation is used to solve boundaries of micro grooves. By applying the finite volume method, the film thickness discontinuity of micro groove boundaries is avoided and a lubrication model of MGRS with grooves is developed. Asperity contact properties under mixed lubrication condition are described by statistical contact model. Based on the steady-state force balance of MGRS, a lubrication conditions prediction model is established through coupling film lubrication and asperity contact models. The concept of “separation speed” is proposed, as the critical speed to demarcate lubrication conditions. The empirical formula of separation speed with operating pressure is fitted, which can be applied to judge lubrication conditions of MGRS conveniently. The parametric study of separation properties of radial and spiral grooves is analyzed, and the optimum range of groove structure is obtained.For the traditional Reynolds boundary condition cannot solve the problem of accurately predicting the hydrodynamic performance of MGRS, a lubrication model based on the mass conservation boundary condition is established, and a cavitation observation test rig of rotary seal is built. On the basis of the linearized small perturbation method, a model to analyze dynamic characteristics of MGRS is developed under the mass conservation boundary condition, and a test system to obtain dynamic stiffness of rotary seal is established. The effects of different cavitation boundary conditions are investigated. The results indicate that stiffness coefficients are mainly influenced by hydrodynamic effects and cavitation occurrence. While damping coefficients are not impacted by hydrodynamic and hydrostatic effects directly, but by cavitation occurrence.In order to acquire better steady and dynamic characteristics of MGRS, an optimization method of grooves structure is developed on the basis of lubrication model of MGRS with grooves, by taking groove shape parameters as design variables. The results show that, MGRS with optimal grooves have better lubrication performance than traditional grooves, of which the reason is that the shapes of optimal grooves can make use of hydrodynamic effects more effectively. Also the number of grooves has great influences on the shapes of optimal grooves, yet outer diameter has little influences. By regression analysis, the regression equations of lubrication characteristics of rotary seal with optimized grooves are obtained.For the steady model cannot predict the dynamic properties of rotary seal under dynamic conditions such as transient impact, a dynamic model of MGRS is established. The dynamic performances of MGRS under real oil filling, pressure impact and speed impact conditions are analyzed. Furthermore, the dynamic model is extended to two-dimensional case to analyze creep rotation behavior. The results indicate that MGRS has stable and fast transient response, and has good tracking performance under the real oil filling condition, and has good impact resistance under extreme conditions. The axial stimulations of rotary shaft is the reason of creep rotation of seal ring. The dynamic and the creep characteristics of the optimized grooves MGRS are much better than those with conventional spiral grooves.