Analysis And Experiment For Squeal Noise Of Disc Brake On Vehicle

In this dissertation,from the theory of complex modal analysis,with the help of finite analysis technology and via the experimental approaches,the mechanism of brake squeal noise is researched.In this way the root cause of squeal noise is introduced by the author from his own point of view.In the end,the proper local optimization proposals are raised from the angels of sensitivity analysis and pressure distribution optimization.The dissertation firstly introduces the current research status of squeal noise on disc brake system in the world,also the fundamental structure and the operating principle of the disc brake system are explained.Then according to the existing research theory,the mechanism of squeal noise is analyzed from the aspect of system instability analysis.Also,the sensitivity of sub-structure modal frequency about the real part of eigenvalue of the unstable complex modals of brake assembly and the effect of load distribution between pad and disc on instability are discussed.In brief,the research object of this dissertation can be summarized as below:(1)A simplified physical model of disc brake is established.The basic mechanism of brake squeal noise is expounded by deducing and analyzing the corresponding dynamic differential equations and the matrices.Also the general analysis method and optimization approach of disc brake are briefly introduced,which leads to the key points of research.(2)Through a series of bench tests and sub-structure tests,such as bench SAE J2521 standard tests and sub-structure nature frequency tests,the frequency and working condition of squeal noise of target brake system are determined.Then the experimental results are preliminarily analyzed and summarized as the basis and reference for the subsequent finite element simulation.(3)The 3D model of disc brake is established.Then after meshing,determining the constraint conditions and the material parameters in the software,the modal parameters of substructure,the complex modal simulation of brake and the distribution of complex eigenvalues are calculated according to the simulation process.Based on the results,the consistency between the modal parameters and the test results and the influence of braking pressure on the distribution of complex eigenvalues of unstable modal are analyzed.(4)Combining with the simulation result of finite element software,using 3D Polytec laser vibrometer,the dissertation discusses about the sensitivity of sub-structure modal frequency to the real part of complex eigenvalue of unstable modal of brake assembly on the basis of operational deflection shape experiment when the 2.1kHz squeal noise occurs.Depending on this,a structure optimization proposal is raised.Finally,the feasibility of this proposal is verified by analysis of system stability and bench test result.It is found that by increasing the 6th order free modal frequency of the bracket,the stability of the system near 2kHz can be effectively improved,and the squeal noise of 2.1kHz can be reduced.(5)On the basis of original simplified theoretical model,the influence factor of load distribution between pad and brake disc is introduced.Through the study of finite element calculation result and actual experiment result about pressure distribution,combining with the factors which will affect the actual pressure distribution,the optimization direction based on the improvement of pressure distribution is put forward.Then according to the result of orthogonal experiments,the optimal combination of factors can be determined,and the simulation and test verification is carried out.The results show that the improvement of pressure distribution can effectively reduce the risk of squeal noise.The experimental and simulation results show that the optimization proposals based on the improvement of pressure distribution and the sensitivity of substructure modal frequency to the complex modal instability of system can effectively solve the brake squeal noise in some specific frequency bands and working conditions.In the dissertation,the theory and experimental methods used are elaborated in depth,which has a certain guiding significance for solving the squeal noise of disc brake in the follow-up.