| In the actual braking process of trains,there are many factors that affect the dynamic behavior of the system,such as braking pressure,train speed and wear state of braking components,which make the braking system produce friction self-excited vibration and noise.Among them,the influence of the response process of the braking pressure on the braking system can not be ignored.If the response of the braking pressure is reasonable,it will help to ensure the smooth deceleration or accurate parking of the train,and reduce the vibration,wear and noise pollution.At present,the braking conditions of high-speed train are more complex and diverse,so the simulation of the dynamic response of braking pressure under two braking conditions can provide the corresponding theoretical reference for the design and optimization of the system structure.According to the structure and installation position of the basic components of the train disc brake system,a dynamic model of the disc brake system is established based on the dynamic friction model and dynamic brake pressure.By selecting specific parameters,the braking pressure curves affected by different characteristic parameters(λ)of the brake control valve under two braking conditions,as well as the phase diagram and time history diagram of the system motion are numerically simulated.The complex dynamic characteristics of the system such as friction induced stick-slip vibration under the influence of dynamic response of braking pressure are analyzed,and the way for the system to enter a stable state is also analyzed.The main contents are as follows:According to the structure of brake clamp unit,the mathematical model of dynamic brake pressure is obtained by using multi parameter mathematical simplification method.Then,the mathematical models of dynamic braking pressure under service braking condition and emergency braking condition are coupled with Dankowicz and modified LuGre dynamic friction models to obtain the dynamic friction model including dynamic braking pressure.Specific parameters are selected to simulate and analyze the relationship between the braking pressure that different λ has influenced and time under emergency and service braking conditions,which provides the basis for the follow-up system dynamics modeling and dynamic characteristics research.According to the relationship between the structure and installation position of the basic components of the braking system,only the vertical vibration of the system is studied.Considering the mass conveyor belt model,a two DOF system dynamic model based on dynamic friction model and dynamic braking pressure is obtained.Dimensionless parameters and variables are introduced for dimensionless processing.Specific parameters are selected,then the dynamic characteristics of the two DOF braking system considering the dynamic response of the braking pressure are analyzed by numerical simulation with C language.It is found that the amplitude of the displacement and velocity of the system decreases from λ=1 to λ=7,and the time needed to enter the stable state is shortened.Compared with the emergency braking condition,the amplitude of the displacement and velocity of the system under the service braking condition is smaller,and the time to enter the stable state is shorter.Integrating multiple factors that affect the vibration of the brake system,considering the interaction among the bilateral brake pads,brake disc and frame,the vertical vibration of the system is only studied to simplify the braking system,a relatively complex four DOF system dynamic model based on dynamic friction model and dynamic braking pressure is obtained.After dimensionless processing,select specific parameters,use C language for numerical simulation,analyze the dynamic characteristics of four DOF braking system and the way to enter the stable state under the action of two dynamic friction models after dynamic braking pressure coupling.It is found that the system vibrates at low frequency and sticking motion appears under the action of Dankowicz dynamic friction.Under the action of modified LuGre dynamic friction,the system vibrates at high frequency and does not appear sticking motion.Compared with the two DOF system model,the four DOF system model can better simulate the system dynamic characteristics in the actual braking process.The coupling effect of the dynamic braking pressure mathematical model and Dankowicz dynamic friction model is better,so that the system can reflect very complex dynamic behavior.On the premise of meeting the braking requirements,matching reasonable brake control valve characteristic parameters can provide corresponding theoretical references for the structural design and parameter optimization of the braking system. |
