On The Mechanism And Simulation Of Friction-induced Squeal Based On A Disc/pad Test Rig

With the continuous development of China’s automobile industry,the demand for automobiles from customers is in the increase.However,the brand recognition of consumers can be reduced by brake noise,which may contribute to a decrease in market share.Therefore,significant financial resources and efforts have been invested by major automotive OEMs and suppliers to reduce brake noise.In this study,the current research process of brake squeal is analyzed,and a new simplified dynamic model of the disc/pad device is established,focusing on the analysis of brake squeal caused by friction of the disc/pad device.In addition,the influence of friction coefficient,disc/pad contact stiffness and disc surface inclination angle on the stability of the disc/pad device is investigated.A laser vibrometer is used to test the operational deflection shape(ODS)of the disc/pad device when brake squeal occurs.Based on the vibration characteristics,a simplified two-degree-of-freedom model of the disc/pad device is constructed.The disc and pads are reduced to two masses,and the contact between the masses is simulated by a contact stiffness.Since the vibration mode of the disc is an out-of-plane mode when brake squeal is generated,an inclined plane with an angle is used to describe it.The effect of the lateral stiffness of the pad and the normal stiffness of the disc on the system is also considered.Differential equations of the disc/pad system are derived according to the simplified model.The complex eigenvalue method is then used to study the instability of the system as the friction coefficient,the disc/pad contact stiffness,and the tilt angle of the disc change,revealing the mechanism of friction squeal due to the instability of the system caused by modal coupling.The actual disc/pad assembly is simulated and analyzed.Since the friction lining is pressed from fiber,iron powder and phenolic resin,the friction lining material parameters are set to be isotropic in cross section.The FRF method,modal analysis method,and optimal design method are used to determine the mechanical parameters of the transversely isotropic material in all directions.Optimized brake pad modal analysis reduces the errors between calculated and measured values of each frequency order,improving the accuracy of the simulation model.By determining the unstable frequencies using finite element complex eigenvalue analysis of the disc/pad friction test apparatus,the effects of the disc/pad friction coefficient,the modulus of elasticity of the disc,and the brake pressure on the stability of the system are simulated and analyzed.It is found that reducing the friction coefficient between the discs/pads can reduce the tendency of friction squeal.The influence of Young’s modulus of the disc is greater on the stability of the disc/pad system,and increasing it appropriately can reduce the possibility of brake squeal.Surprisingly,it is found that there is no effect of brake pressure on the stability of the disc/pad assembly,which is inconsistent with actual disc/pad test results.Therefore,it is necessary to find a better analysis model.The actual test results show that the friction coefficient and brake pressure have a significant effect on the occurrence of friction squeal.The effect of brake pressure and friction coefficient between the disc/pad on the vibration characteristics of the disc/pad device is investigated using the transient dynamic analysis method.The vibration acceleration signals of the disc,friction pad of the brake pad,and back plate of the brake pad are obtained separately and subjected to FFT(fast Fourier transform).The analysis shows that the vibration acceleration of the disc,friction lining of the brake pad and back plate of the brake pad are different under different brake pressure.The vibration frequencies of the brake pad appear more than those of the disc,and are closer to those of the brake squeal test,but the transient dynamic analysis extracts more brake pad frequencies than the actual brake squeal frequencies.