Research Of High-Speed EMU’s Air Spring Dynamics Characteristics And Its Failure Modes

With the rapid development of high-speed railway in China, the course mileage, the operation density and the passenger traffic of high-speed EMU have been increasing, so how to guarantee the safety and the reliability of high-speed EMU under high operating strength has become the research focus of the vast scholars. As one of the key technologies of high speed bogie, air spring suspension system has the advantage of improving the EMU dynamics performance. However, at the same time, its complicated pneumatic devices, material nonlinearity and gas flow characteristics of vibration reduction cause the modeling difficulty in the study of vehicle dynamics. Especially, few researches are related to the dynamic running states of vehicles in the failure modes of air spring suspension system. In view of this, taking the domestic high-speed EMU air spring as the research object, this paper established a three-dimensional coupled dynamics model of air spring suspension system and analyzed the effect of the various air spring failure modes on the vehicle dynamics performance for the sake of providing the certain theory reference to ensure the running safety of high-speed EMU in the air spring failure modes.Because the air spring’s vertical nonlinear characteristics are obvious, the vertical pneumatic dynamics model of air spring suspension system was first established on the basis of the principles of fluid dynamics and pneumatics. This model not only takes the nonlinear aerodynamic characteristics of the air spring into consideration, but also contains the height adjustment valve, the differential pressure valve and some other pneumatic devices and their roles in the overall suspension system. In order to verify the correctness of the vertical pneumatic dynamics model, in accordance with the relevant standards, the simulation tests and the bench tests were carried out for the air spring, in which the comparison of the tests’results shows that the model can truly reflect the air spring’s actual vertical characteristics.Even though the vertical pneumatic dynamics model of air spring doesn’t consider the air spring’s lateral nonlinear characteristics, compared to the conventional model, this model can solve the vehicle dynamics research problems in a wider range. In the high-speed trains passing analysis, air spring vertical pneumatic dynamics model can reflect passing flow field effects on the pneumatic characteristics of the air spring, in which the results show that the higher passing speed, the greater the internal pressure changes in the air spring. When the passing speed is 450 km/h, the largest air spring’s internal pressure fluctuation can reach about 30%. In the air spring suspesnsion morphologies analysis, the vertical pneumatic air spring model can effectively simulate all kinds of pneumatic devices’ connection modes in various suspesnsion morphologies. Through the analysis of the effect of various suspesnsion morphologies on the vehicle dynamic performance, the 4 points support mode with anti rolling bar can not only guarantee the vehicle running safety in the fault support mode, but also to a certain extent, can improve the ride comfort of the vehicle. In the analysis of high-speed EMU vertical ride comfort, the vertical pneumatic air spring model was used to study the effective factors of vehicle vertical ride comfort by changing the structral parameters of air spring. The results suggested that adding rubber bellow volume and selecting the appropriate orifice diameter can make the vertical ride comfort to achieve the best.Lateral characteristics of air spring are largely related to the rubber material, bellow outline, cord layer layout and other factors. Based on the nonlinear finite element model of air spring, which takes the rubber creep property, the fluid-solid coupling effect and the apron friction into consideration, the lateral dynamic characteristics of air spring is studied under different internal pressure and lateral displacement. Reference to the analytical solution of the lateral stiffness, the lateral quadratic model and the longitudinal correction model were established by function fitting method, and combined with vertical pneumatic model, the three-dimensional coupled dynamics model of air spring suspension system was set up. When the 3D coupled dynamics model of air spring was applied in the vehicle dynamics simulation, as the nonlinear characteristic of the lateral stiffness of air spring was taken into consideration, the curve passing index of vehicle is about 30% higher than that of the conventional model.Through the co-simulation between the air spring 3D coupled dynamics model and the vehicle multi-body dynamics model, the leakage process of air spring was studied and the law of time domain response of the pneumatic devices was obtained under different leakage area. In allusion to the different air spring failure modes, the dynamic running states of vehicle were analyzed. The results show that, the stability and the ride comfort of the vehicle firstly become worse, then level off with the increase of the leakage area; air spring leakage will not lead to instability of vehicle, but can make the ride comfort index overstep the optimal level standard; differential pressure valve can effectively guarantee the vehicle’s dynamic performance in the leakage of air spring and the peaks of vehicle’s vertical and horizontal safety index appeare when the leakege area is 15mm2 and 30mm2 respectively, but the peak values can still meet the safety requirements according to the standards. If the direction of the vehicle passing curve is consistent with the leakage side of air spring, the wheel partial load caused by the centrifugal force and that caused by the leakage of air spring will be superposition, which makes wheel load reduction rate about 20% higher than that of straight track. The failure of differential pressure valve in air spring leakage will seriously affect the veihicle’s curve passing ability, especially for the wheel load reduction rate which is about 27% higher than that of normal conditions. Height adjustment valve failure will cause both the lateral and vertical dynamics performance of the vehicle to become worse. The burst of rubber bellow on one side will cause car body’s rolling movement by sudden and all safety indexes will produce sharp oscillation after burst occurred, but the indexes will be leveled off after 3s and not beyond the standard limit. The effect of orifice clogging on the vehicle’s curve passing ability is little, but this failure mode can cause the deterioration in the vertical ride comfort of vehicle.In order to improve the dynamic performance of high-speed EMU in the flat air spring condition, the optimization of 4 parameters of emergency rubber spring, including the stiffness in three directions and the friction coefficient of wear plate, was carried out. Taking the 4 characteristic parameters of emergency rubber spring as the input, the consolidated dynamics comprehensive index as the output, the approximate model of vehicle was established through the RBF approximation method. Based on the approximate model, the characteristic parameters of emergency rubber spring were optimized by the particle swarm optimization strategy. The dynamics calculation results before and after optimization show that, the application of the optimized parameters in the emergency rubber spring results in the improvement of vehicle stability, ride comfort and curve passing ability in different degree.