Research On The Stability Of Disc Brakes With Random And Fuzzy Parameters

The performance about noise & vibration & harshness(NVH) is the key indicator for vehicle performance, which has a direct infulence on selecting a car for customers. The developers and researchers of car industry have paid great attention to reducing the level of noise inside the car and improving the NVH performance of vehicles. As the important component of chassis, disc brake may generate noise which makes people uncomfortable, if it is in unstable condition. In rencent years, complaint rate about brake noise has been very high in sales service. Meanwhile, how to reduce the propensity of brake noise has became the focus in car industry.The thesis was supported by the Graduate Student Research Innovation of Hunan Province(No. CX2013B143), and the National Natural Science Foundation(No. 11572121 and No. 11402083). On the basis of a simplifed FEM model of disc brake, the parameterized model of disc brake was built by using complex eigenvalue method and response surface method(RSM). Considering the impact of parameter uncertainty on the stable reliability of the disc brake, several methods were proposed to improve the systems’ stability. A stability analysis method for the disc brake systems with random and fuzzy parameters and a time-variant stable reliability analysis & optimiazation method for disc brake systems were proposed.The main researches and the acquired innovative achievements in the thesis are as follows:(1) The simpified FEM model of disc brake was bulit, and then the system’s squeal propensity was analysed by using the complex eigenvalue method. It can be found from the complex eigenvalues that the corresponding eigenvalue damping ratio on the 7th modal was the minimum, so the 7th modal was the main unstable modal. In order to illustrate the impact of friction for brake noise, the eigenvalues on the 7th order in different friction coefficience were calculated. The result shows that with the increasing of friction coefficience, the real part of the 7th order eigenvalue became larger and the change of the imaginary part is very small, which means the system were getting unstable and would generate brake noise at last.(2) A stability analysis method of disc brake systems with random and fuzzy parameters was proposed. The proposed method was mainly based on the techniques of response surface methodology(RSM), complex eigenvalue analysis and reliability analysis. In the proposed method, the hybrid uncertainties existing in a disc brake system were described by random and fuzzy parameters, and the parameterized model of the damping ratio of unstable mode was established by RSM. The limit state function used to evaluate the system stable reliability was built up, and the reliability analysis was carried out for the uncertain brake system with random and fuzzy parameters. In order to explore the influence of system parameters on system stability, the parameter sensitivities were carried out by the global sensitivity analysis of Morris method. By introducing the proposed method for the stability analysis of a disc brake system with random and fuzzy parameters, the reliability and the parameter sensitivities were calculated. The numerical results show that the stability of this brake system can be improved by reducing the densities of back plates or by increasing the thicknesses of back plates.(3) Considering the wear in lifetime of disc brake systems, the time-variant parameter was introduced into disc brake system, namely the thicknesses of disc and pads were decribled as fuctions of time t. so the uncertainties existing in a disc brake system were described by random and stochastic process parameters, and the time-variant stable reliability of system were sloved by using Monte-Carlo method. When the time-variant stable reliability failed to meet the requirement in its lifetime, an opitimization process is developed by using Genetic Algorithm(GA), and the target is to minimize the negative damping ratio, the thicknesses and densities of backplate were setted as design variables, the result showed that time-variant disc brake system could be stable enough after opitimization.Based on the techniques of response surface methodology(RSM), complex eigenvalue analysis and reliability analysis,the ananlysis and optimization of stable relibility for disc brake systems with random parameters and fuzzy parameters was developed in this paper, which has been proved as an effective way to improve the systems’ stable reliability, reduce squeal propensity and provide a good guidance for engineering practices.