Research On Friction-induced Stick-Slip And Pure-Slip Nonlinear Vibration Of Brake System

During the braking process of the vehicle,the brake system may generate self-excited vibration induced by dry friction.Dry friction is one of the main factors that cause the brake to produce self-excited vibration.Many nonlinear factors such as friction characteristics,damping nonlinearity,stiffness nonlinearity,geometric nonlinearity,etc.,can supplement or consume system energy when acting alone or at the same time,which may affect the brake system Generate frictional self-excited vibration.This may cause the system to produce strong nonlinear vibration and noise,thereby reducing braking stability and reliability,and even more catastrophic accidents.Therefore,it is necessary to study the influence of nonlinear factors on the self-excited vibration mechanism and vibration characteristics of brakes.The thesis focuses on the self-excited vibration mechanism of brakes,and the main contents are as follows:(1)A single-degree-of-freedom brake dynamic model with Stribeck friction characteristics is established,and the self-excited vibration phenomena such as stick-slip and pure-slip vibrations of the system when the brake disc acts on different tangential speeds are analyzed.The first-order approximate analytical solutions for this dynamic model of the displacements,amplitudes and frequencies of the pure slip and stick-slip vibration are obtained by the application of homotopy perturbation method and small parameter method.In addition,the approximate analytical expressions are derived for the critical brake disc tangential velocity of conversions between stick-slip and pure-slip vibration,as well as pure-slip vibration and pure-slip motion.According to the vibration equation of the dynamic model,it is found that the root cause of the self-excited vibration of the system is the negative damping caused by the change of the relative speed between the brake disc and the friction pad.(2)On the basis of the dynamic model with Stribeck friction characteristics,a single-degree-of-freedom brake dynamic model that simultaneously considers nonlinear viscous damping and nonlinear stiffness is established.Firstly,the approximate analytical solutions of displacement,amplitude and frequency of pure slip vibration and stick-slip vibration are obtained by homotopy perturbation method and small parameter method.And then the effect on the vibration characteristic of nonlinear viscous damping and nonlinear stiffness is analyzed.The influence of system parameters and other system parameters on the vibration characteristics and conversion mechanism of stick-slip vibration and pure-slip vibration.By analyzing the vibration equation of the model,it is found that nonlinear viscous damping and nonlinear stiffness will not produce negative damping.Therefore,the root cause of the self-excited vibration of the system is the negative damping introduced to the system due to the change of dry friction on the effect of relative speed between the brake disc and the friction pad.(3)A single-degree-of-freedom brake dynamic model considering geometric nonlinearity,nonlinear viscous damping and Stribeck friction characteristics is established.Firstly,the model is analyzed by the small parameter method and the multi-scale homotopy perturbation method to obtain the analytical expressions of the displacement,amplitude and frequency of the stick-slip and pure-slip vibrations,and then the affect of geometric nonlinearity,nonlinear viscous damping and other non-linear factors on stick-slip and pure-slip vibration conversion mechanism and their vibration characteristics for this model are analyzed.The vibration equation of this model shows that geometric nonlinearity will cause the elastic restoring force to change,and the change of elastic restoring force will cause the change of dry friction.The coupling term produced by the elastic restoring force and dry friction force causes negative damping,which induces self-excited vibration of the system.(4)A single-degree-of-freedom system dynamic model with Stribeck friction characteristics,geometric nonlinearity,nonlinear viscous damping and nonlinear stiffness is established.The numerical integration method is used to analyze the influence of these nonlinear factors on the mechanism and vibration characteristics of the self-excited vibration of the system.According to the analysis results,it is found that geometric nonlinearity will cause the nonlinear elastic restoring force to be coupled with the dry friction force,resulting in negative damping.The negative damping causes self-excited vibration of the system.