| With the development of automobile industry, cars have become one of the necessary means of transportation in our daily life. And the improvement of people's living standard also leads to higher requirements on the riding comfort of passenger cars. As one of the most important parameters affecting the riding comfort, the NVH (Noise?Vibration? Harshness)performance has become an important problem to be solved in the process of vehicle development. The analysis of the main causes and influencing factors of the braking noise has become the focus of current researches. To enhance the NVH performance of vehicles, noise reduction schemes should be proposed by suppressing the generation of brake noise from the source or attenuating the spread of brake noise, and it would lead to a great theoretical and practical value in the development of automobiles and related industries.The subject in this thesis is based on the practical engineering problems of a vehicle parts manufacturer in Zhejiang Provence: Aiming at the brake noise problem occurred on a specific brake system,fellowing studies were taken:In this thesis, massive domestic and foreign related literature were referred and the corresponding brake assembly was studied (Chapter 1 & 2). The finite element analysis model of sliding caliper disc brake was established based on the dynamometer test data. ABAQUS was used to calculate the finite element model and extract the eigenvalues and mode shapes of each mode. The simulation results were compared with the dynamometer test data, the mode shapes of each noisy mode was analyzed, and the brake pads were found to be the main components causing brake noise (Chapter 3).Based on finite element method, study on combination of different material parameters were carried out in view of the limitations of single factor analysis in existing studies. The influence of elastic modulus, friction coefficient and the interaction between them on brake noise was studied, and the limitations of univariate analysis were confirmed, which lead to the necessity of constructing a full response model for predicting braking noise. Based on the results of finite element analysis and the mathematical vibration model of brake system, the existing modal coupling theory was improved, and the theory of modal self-instability was proposed (Chapter 4).Aiming at the structure optimization of brake pads, the compressive strain was introduced as the adjusting variable for the first time, and the problem of lacking unified reference between different structural parameters was solved. The noise reduction effect of three different ways to change the lining structure including modifying the contour of lining,adjusting the width of lining and chamfering on lining were studied. Combined with the engineering practice, the best technical mean was analyzed. Considering that the existing researches were limited to unweared brake pads,the effect of brake pad wearness on brake noise was investigated, which provided the basis for the whole life noise control of braking pads (Chapter 5).The influence of various working conditions on the noise proneness of brake assembly were studied based on actual condition, the effects of operating parameters including brake pressure, speed and temperature on brake noise were studied. A 9-dof mathematical vibration modal of sliding caliper disc brake system was established based on the Steibeck friction effect.Combined with the results of finite element analysis, the mechanism of the influence of the operating parameters on the braking noise was revealed, and the necessity of introducing the operation parameters into the optimization algorithm was illustrated (Chapter 6).Based on the researches above,a brake lining parameter optimization algorithm based on Monte Carlo sampling were presented considering the charastics of the material properties,the structural parameters, and the braking conditions of the brake pads. A blocked response surface has 27 blocks with the instability tendency of the brake assembly as the response variable was constructed, and Monte Carlo sampling was performed in the search space according to the probability density function of the parameters obtained from the dynamometer test, the optimal design parameters were obtained by considering the change of friction material performance caused by braking condition parameters, and the noise characteristics of brake system in the whole life cycle of the brake pads were evaluated(Chapter 7).At last, model 3900 NVH drake dynamometer manufactured by LINK was used to carry out a dynamometer noise test on the optimization scheme based on the procedure SAE J2521.The results of the test shows that the NVH performance of the optimization scheme has been significantly improved compared with the original scheme, which meets the requirements of the vehicle manufacturer. |
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