Analysis On Influence Of Flutter Of Vehicle Disc Brake System On Wheel-Rail Adhesion

As the most widely used basic braking device for high-speed EMU in my country,the disc brake method is of great significance in realizing stable and safe parking of vehicles.Due to the constant friction between the disc brake and brake pads when the vehicle is braking,it will cause the brake pads to appear high-frequency jitter on the brake disc(that is,produce friction flutter phenomenon).The adhesion state between wheel and rail is related to whether the vehicle can start and brake normally.If this friction chatter phenomenon affects the adhesion state between wheel and rail,it will bring more uncertainty to the effectiveness and safety of highspeed train braking.Therefore,it is of great theoretical significance and engineering application value to study the influence of friction flutter phenomenon during braking on wheel-rail adhesion state.In this thesis,the relationship between friction flutter and wheel-rail adhesion in diskshaped system is studied for the purpose of lifting adhesion utilization.The main research work is as follows:(1)By using Matlab software to establish a mathematical model of a single-degree-offreedom disc brake system,the stability of the brake system is analyzed.In order to solve the critical speed at which brake friction flutter occurs,a practical Stribeck friction force type whose negative slope characteristics is selected between the brake pads and the brake disc,and the dynamics of the brake system is studied by numerical simulation.The critical velocity of frictional flutter and the factors affecting the flutter are obtained.(2)By combining a quarter vehicle model with a disc brake model with torsional vibration,a vehicle model with a seven-degree-of-freedom disc brake system is established.The practical Stribeck friction force type is selected.The method of numerical simulation is mainly used to study the motion state and friction flutter behavior of the braking system during the braking process of the vehicle under the action of sinusoidal excitation with or without track vertical irregularities.To study and analyze the impact of the brake pads vibration convergent motion,pure sliding motion,viscous-sliding motion and the resulting friction and flutter on the bogie,car body,and wheelset.(3)Using the O Polach wheel-rail force calculation model and considering the influence of track excitation,the vertical force and the tangential force coefficient between wheel and rail caused by the frictional chatter transmitted to the wheelset by the braking system are analyzed.By using Matlab/Simulink software,a simplified single-wheel-disc braking model was established.The O Polach wheel-rail force approximate calculation model was combined with the bilinear model,and the influence of track excitation was considered.The average slip rate and the transient slip rate were introduced to analyze the creep rate and the tangential force coefficient of the wheelset when the torsional vibration of the wheelset was generated in the stable region and the critical instability region of the adhesion curve.