Research On The Influence Of Pad Parameters On Disc Brake Squeal

Due to continuous attention from customers on vehicle NVH performanceand gradually rigorous regulations for environment protection, brake noise hasdrawn growing attention from both manufactures and researchers. Among manykinds of brake noise, squeal, featured by its high frequency, has been a key topic.Taking a disc brake for passenger vehicles as the object, studies based oncomplex eigenvalue analysis are presented in this dissertation to understand theinfluence of design parameters of the brake pad on occurrences of the brakesqueal.In order to ensure accurate material parameters of the brake components toestablish finite element models with high fidelity, modal tests were conductedon main components of the disc brake under free-free boundary conditions.After directly calculating material density of each component in terms ofmeasured volume and mass, the Young’s modulus and Poisson’s ratio of thematerials for the main component are adjusted by comparing dynamiccharacteristics of the component from modal testing and simulation.Two models were established in ABAQUS, namely a simplified one whichincludes only the disc and pads, and a comprehensive one which consists of allthe components in the brake. Complex modal analyses were performedrespectively on both models. Some interesting conclusions were drawn fromresults comparison. The unstable models predicted by the simplified model havefrequencies in the lower frequency band, which are the coupling ones betweencertain out-of-plane mode of the disc and the bending mode of the pads. Theunstable model calculated by the comprehensive model on the other hand, havehigher natural frequency, featuring the combination of some in-plane mode ofthe disc and the pads. With a properly adjusted load area, the simplified modelis found to predict almost the same unstable modes as the comprehensive one.Statistical analysis was carried out on measured surface profiles of the pads.Several groups of random rough surfaces were generated based on statisticalproperties corresponding to the actual or imagined pad surfaces, using a randomsurface generating method in Tribology. The height distributions of these random surfaces were separately used to modify coordinates of some pad nodeswhich are in contact with the disc in the finite element model of the brake,previously established for a pad with ideal flat contact surface. With themodified finite element model for the brake with actual pads of a rough contactsurface, complex modal analyses were then conducted. It is shown fromsimulation that frequencies of the unstable modes appear randomly, whichagrees with existing engineering observation.It is well known that the appearance of the pads changes with brakingoperation, and that the chamfers and groove in the pads affect the distribution ofthe contact pressure. Analyses were thus applied to reveal the influence of thelining thickness, the chamfers and groove in the pads on the distribution of thecomplex eigenvalues of the brake. It is noted that variation of the liningthickness changes the sensitivity of the model to the friction coefficient, andthat the groove and chamfer are helpful with reducing unstable frequencies.As to the position where the pads are assembled to the disc, the assumedmode method and the finite element procedure in ABAQUS take differenttreatments. In order to have a better understanding with both treatments, a prettysystematic analysis was tried based on a series of complex eigenvalue analysis.It is demonstrated that position change can make some difference with theunstable modes.