Frequency Reliability Analysis For Transmission System In Valve Train

According to the firing order of cylinder,engine valve train opens or closes the exhaust valve,which makes fresh gas sucked into cylinder and exhaust gas discharged from the cylinder.The performance of designed valve-train will directly affect the technical specifications of internal-combustion engine.When the drive frequency approach the inherent frequency,resonance in the transmission system would happen,and the system would vibrate with the most severe amplitude.It will lead to a large deformation and dynamic stress in mechanical structure,even a damaging accident.Reliability design is a machine design method,which can meet the given reliability index.Through analyzing the frequency reliability of the valve train,it is found that the parameter which has great influence on the resonance of the system can be solved in the robust optimization design,which can effectively improve the design efficiency and improve the working efficiency.There are 6 Chapters in the paper,and the main research contents of the paper are as follows:Chapter 1 This paper discusses the purpose and the significance of this topic.On the basis of reading a large number of Chinese and foreign literatures,the development and research status of valve mechanism,reliability,reliability sensitivity and reliability robust design are reviewed.Chapter 2 Through the study of the actual working state of the valve train transmission system and the search of Chinese and foreign literature,the paper summarizes the four main forms of the valve mechanism failure.In order to analyze one of the failure problems,a vibration model of the transmission system.of the valve train is established,and the differential equation of motion of the valve train vibration system is deduced,which lays a foundation for the resonance reliability analysis of the transmission system of the valve train.At the same time,some basic concepts involved in reliability design and the common methods of calculating reliability are expounded,which lays a theoretical foundation for the reliability analysis based on frequency.Chapter 3 The perturbation technique and the generalized eigenvalue are combined to solve the solution of the eigenvalue based on the frequency,and the expression of the covariance of the natural frequency of each step is deduced.At the same time,according to the interference theory of reliability,the function of the resonance of stochastic dynamic system is defined,and the quasi-failure probability expression of the whole dynamic system under multiple independent failure modes is deduced.Based on this,the resonance reliability of the system is respectively calculated by the mean first order second moment and Monte Carlo method.Moreover,by comparing the results of the two algorithms,the feasibility of the proposed method is further proved.Chapter 4 According to the existing reliability sensitivity calculation method,an analysis method of frequency reliability sensitivity based on resonance problem is proposed.In order to more intuitively compare the influence of random parameters on the reliability of the system,a method for calculating the unit of random variables is proposed,that is,dimensionless of reliability sensitivity.On the basis of this,the proposed method is combined with the vibration model of the valve train system to calculate the mean sensitivity and the variance sensitivity of the seven parameters.From the results,the influence of different random parameters on the reliability of valve train transmission system is different,which provides a quantitative reference for the following optimization design of valve train.Chapter 5 By combining the reliability optimization design with the sensitivity analysis method,the reliability robust design based on the sensitivity analysis method is put forward.With MATLAB optimization toolbox,the optimization model of the valve train transmission system is solved,and the results not only guarantee the whole system reliability,but also the sensitivity of the reliability.Furthermore,the reliability and robust design method is proved to be practical and effective.Chapter 6 The main conclusions of this dissertation are summarized and the prospects of the applications of reliability design in mechanical structures are discussed.