Reliability Study Of Vehicle Disc Brakeconsidering Performance Degradationand Dependent Failure

Safety is one of the important indexes to measure the level of automobile design and manufacture,and the reliability of automobile braking performance can be used as an important evaluation index of automobile safety.During the braking process of the automobile,the brake may emit harsh noise due to road excitation and self-excited vibration of brake system,which has a great impact on vehicle comfort.On the other hand,due to the complex road conditions and driver's habits,automobiles often face long-term continuous braking or emergency braking,resulting in brake temperature rise and thermal recession,and even serious traffic accidents.Automobile disc brake is a complicated coupling mechanical system consisting of many parts,including brake disc,friction disc,brake caliper,pump and oil pipe.As the deceleration system and parking system of automobile,its reliability is very important to ride comfort and driving safety of automobile.When the brake is in an unstable state(road excitation,multi-cycle braking,friction),all these problems bring a test to the ride comfort and driving safety of automobile.This topic focuses on the problems of strength degradation,dynamic correlation of failure modes and reliability optimization of automotive disc brake system,and carries out the following research works:(1)For complex mechanical systems with strength degradation and failure mode correlation,a dynamic failure correlation reliability analysis model considering system strength degradation is established.Firstly,aiming at the problem of missing data in the process of system strength degradation,a system strength degradation model under Gamma process is established by estimating characteristic parameters with P-S-N curve of product fatigue life.Then,aiming at the problem that the correlation between random variables is not obvious,based on Vine Copula function,the dynamic Vine Copula model under GAS framework is established,and the non-parametric estimation method is used to estimate the dynamic parameters to reduce the calculation error.Finally,the reliability of the series mechanical system with multiple failure modes and dynamic correlation is analyzed by using the model.(2)Aiming at the vibration of automobile disc brake system,braking noise is emitted,which leads to modal failure.Based on the stress-strength interference model of reliability analysis,the Latin hypercube test design is used to extract sample points,and the surrogate model is constructed by response surface method.The sample data areapproximated and the quadratic response surface approximation model of target eigenvalue damping ratio is obtained by fitting.By using F test,the variance analysis of the model is carried out,which verifies that the model has smaller error and higher fitting accuracy,and provides a reference for parameter optimization of automobile disc brake.(3)Aiming at the problem of rapid heating and thermal-mechanical coupling failure of disc brake system during braking,Abaqus finite element analysis software is used to simplify the model,and the transient temperature field and stress field nephogram of the brake disc under different working conditions are obtained,and the maximum flash temperature of the brake disc is defined.Based on the sample of design parameters obtained from Latin hypercube test in Chapter 3,the response value of maximum brake temperature rise is calculated and the regression analysis model of the sample value is designed by using BP neural network.The weight and threshold of each layer of the neural network are obtained by non-linear regression analysis,and the thermal-mechanical coupling failure function of the brake system is fitted.(4)Aiming at the dynamic correlation failure and parameter optimization of disc brake failure modes,the reliability of the brake system at different time points such as1000 h,2000h,3000 h,4000H and 5000 h is calculated based on the dynamic Vine Copula model,and the high accuracy of the model is verified by Montr Carlo method.Through orthogonal test method and BP neural network algorithm,the system parameters of the disc brake are optimized,and the failure mode of the brake system is optimized by a comprehensive score,and the optimal design scheme of the brake parameters is obtained.Finally,the optimal parameter combination is substituted into the dynamic correlation failure model of the brake system,and the reliability of the system at the initial time is 0.9715,which is 1.91% higher than the original design and achieves the desired optimization effect.