Study On The Stick-slip Dynamic Characteristics Caused By Dry Friction Of Auto Disc Braking System With Shaft Crack

Automobile braking system is the most important safety component，it may have alarge impact on the performance of auto. Dry friction effect may appear between thedisc and caliper of braking system because of their relative movement during braking.The friction may lead to vibration even noise from braking system. While braking in alow speed, an unstable stick-slip motion may appear then the system will presentdifferent vibration characteristics along with the changes of parameters. In the meantime,because of the complex working conditions and high-speed revolution of wheel shaftand the changes of tire load, the crack on shaft may appear. Thus, it could providetheoretical reference for the determination of design parameters to study on thestick-slip dynamic characteristics caused by dry friction of auto disc breaking systemwith shaft crack. It also could provide methods to reduce or eliminate vibration andnoise and effective measures to detect and diagnose crack online. It takes on certaintheoretic meaning and application value.In order to investigate the vibration characteristics of disc braking system duringbraking, in this paper, a model of torsional direction, a model of disc with shaft crackand a model of disc-tire system with shaft crack were established respectively. The threemodel were investigated by numerical simulation and nonlinear theory. Though analysis,the influence rules of parameters on the vibration characteristics and effect of crack onthe system were obtained. Amethod of identifying crack on wheel shaft was also found.This paper’s main research contents are as follows:(1)A2-DOF torsional vibration model of disc and caliper was established. UsingStatic+Coulomb friction model, the influence rules of driving torsion angle velocity,ratio of the inertias of disc and caliper and braking pressure on Stick-slip motioncharacteristics were calculated and using Stribeck model, the influence rules of drivingtorsion angle velocity on Stick-slip motion characteristics were also calculated.(2) The disc was simplified to a Jeffcott rotor system.5-DOF dynamic equations of discand caliper were found considering a shaft crack near the junction between the shaft andthe disc and the dry friction. The system’s vibration characteristics and the influence ofcrack on it were calculated when without crack and with different crack depth and themethod of identifying crack in this system was also found.(3) The disc-tire was simplified to a Jeffcott-cantilever rotor system. Considering a shaftcrack near the junction between the shaft and the disc, the dry friction and the load on the tire,6-DOF dynamic equations were found, the disc and tire’s vibrationcharacteristics and the influence of crack on them were calculated when without crackand with different crack depth. The conclusion that route of the system enter into andout chaos is quasi periodic motion was gotten. The method of identifying crack indisc-tire system was also found.(4)The main work in the paper is summarized, and the further research on the subject isproposed.