Study On Nonlinear Mechanical Model Of Hydraulic Damper For Railway Vehicles

As an important component of railway vehicle suspension system,the hydraulic damper has a great influence on vehicle stability,operating quality and curving performance.Up to now,all the hydraulic dampers used in commercial high-speed EMUs in China are imported,which are not only restricted in technology but also high in cost.In addition,most of the high-speed EMUs in China were imported completely in the early stage.However,the domestic line conditions,climate conditions,operation and maintenance are quite different from those at abroad,which cannot make these imported dampers fully adapt to the operation demand of domestic EMUs,exposing a series of problems,such as oil leakage,abnormal noise,vehicle shaking and abnormal vibration.Therefore,it is imperative to formulate reasonable technical requirements for hydraulic dampers and to develop hydraulic dampers with good performance,high reliability and independent intellectual property rights.It is necessary to establish a highprecision mechanical model based on the structure of the damper to obtain reasonable technical requirements.The development of high-efficiency damper needs to break the traditional experience design method,clearly grasp the relationship between the internal and external characteristics of the damper,and at the same time,improve the design efficiency with the help of computer simulation technology.In view of this,the research on the nonlinear mechanical model of the hydraulic damper for railway vehicles based on the internal structure has very important theoretical significance and engineering application value.In this thesis,according to the nonlinear mechanical model of hydraulic dampers for railway vehicles,the following research work is carried out:(1)A multiphase interaction dynamic model of the hydraulic fluid is established.The characteristics of the existing hydraulic fluid models are analyzed comprehensively,and the comparative analysis and summary of each model are made.In order to make up the deficiency of the existing model,the dynamic mathematical model of each phase transformation of hydraulic fluid is established.The calculation formula of key physical properties of hydraulic fluid is derived in detail.Dynamic and static tests are carried out on a specially designed damper to verify the hydraulic fluid model established in this thesis.The results show that since the existing hydraulic fluid models cannot completely simulate the static and dynamic characteristics of hydraulic fluid,the definition of bulk modulus,the description of the dynamic process of cavitation and gas dissolution and the resonable calculation of fluid physical characteristics are very important for the hydraulic fluid modelling.The multiphase interation dynamic model established in this thesis can accurately simulate the static and dynamic characteristics of hydraulic fluid,which shows that the calcuation method of hydraulic fluid physical properties and the description method of cavitation and gas dissolution are reasonable.(2)A nonlinear mechanical model of the hydraulic damper(GC?damper model for short)is established,which considers the environmental temperature,physical properties of the medium,macro physical properties and a few micro properties.Using the idea of modular modeling,the mathematical sub models of each part of the hydraulic damper are established.Based on the principle of mass conservation and the Newton's second law,the hydraulic fluid model of hydraulic damper and its sub models are connected,and the nonlinear mechanical model based on the physical parameters of the hydraulic damper is established.(3)A force element of the hydraulic damper in SIMPACK based on the GC?damper model is developed.32 subprograms including hydraulic fluid,throttle and damping valve are written by using FORTRAN90 computer language,and a dynamic link library including these subprograms is generated.Finally,the force element of hydraulic damper is developed by using SIMPACK user interface and dynamic link library.The results show it is feasible to establish the computational model of the hydraulic damper model in the vehicle dynamics simulation environment,and it has high calculation efficiency and accuracy.(4)The hydraulic damper test and model validation are carried out.The dynamic and static tests of the sub-models of the key damping elements of hydraulic dampers are conducted by using “the progressive step-by-step verification method”.Then,the results of static and dynamic characteristics of the GC?damper model and Maxwell model are compared and compared with the test results.The results show that the sub-models of the key damping elements established in this thesis can accurately reproduce their nonlinear static and dynamic flow characteristics.The GC?damper can accurately simulate the nonlinear static and dynamic characteristics of hydraulic damper because of the detailed modelling of each component,but the Maxwell model cannot completely simulate the nonlinear static and dynamic characteristics due to the lack of detailed modelling of each component.(5)Key problems of the hydraulic damper design based on the GC?damper model are researched.Some suggestions and solutions are put forward.The results show that the computer simulation design method based on the GC?damper model is a better method in the design of hydraulic damper,which can improve the efficiency of hydraulic damper design and solve many practical problems.(6)The vehicle dynamic stability based on the GC?damper model is investigated.Taking an intercity EMU as the research object,the hunting frequency and bifurcation characteristics of vehicles are studied based on the model.The results show that the model of yaw dampers has a great influence on the simulation results of vehicle system stability and the GC?damper model can improve the accuracy of vehicle dynamics simulation.The initial air content of the yaw damper greatly affects bifurcation characteristics,critical speed and hunting frequency of vehicles,and it is a key parameter for vehicle stability research.For the yaw damper with lower unloading speed,the orifice diameter has little effect on hunting frequency and bifurcation characteristics,which means that the orifice model can be appropriately simplified.