Fatigue Analysis And Experimental Study Of Timing Silent Chain For Gasoline Engine

Nowadays, silent chain is widely used in the timing chain system of automobileengine with the increasing demand of NVH performance. At the beginning ofdesigning the silent chain of timing system, the structure need to meet the staticstrength, but more importantly the fatigue performance of silent chain has become oneof key factors to evaluate the reliability of the timing system, so the fatigue test isusually used to predict the strength and life of the silent chain in the domesticenterprises，which will lead to long test cycle and high cost. In order to evaluate thefatigue performances of silent chain efficiently, the paper uses the Computer AidedEngineering method and fatigue test result to analyze the silent chain reliability basedon the key project of science and technology in the Jilin province, which is known asthe key technology research of silent chain system development for modern gasolineengine. Therefore, the research results of the thesis have important theoreticalsignificance and reference value to improve the efficiency and reliability of timingsilent chain in the gasoline engine.This paper firstly introduces the difference of high cycle fatigue and low cyclefatigue, S-N curve, Haigh Diagram, the safety coefficient and other related theories,and explained reliability evaluation methods and failure mechanism of silent chain,which is theoretical foundation of evaluating the fatigue performance of structural.According to the requirements for the fatigue life and specifications of the gasolineengine timing system, this paper analyses the linear fatigue performance of the silentchain based on CAE methods. The static analysis is the first step in the whole fatigueanalysis process, which can verify the chain structure under actual load conditionswhether meet the static strength or not, and analyze stress distribution to find outthe key component of the maximum stress using finite element software ANSYS. Theanalysis result shows that the key component is chain plate of inner link, and the staticstrength of chain plate meets the material requirement，then compare the result oftraditional strength calculation method to finite element analysis results, both ofthem are coincident, which verify the accuracy of the finite element analysis and theresult is reliability. Based on multi-body dynamics software RecurDyn the key chainplate will be turned into flexible body to analyze rigid-flexible coupling dynamicperformance between the rigid parts and the flexible parts. At the same time, apply theboundary conditions and set the system parameter, then simulate the whole chain structure under the actual working condition to calculate the stress changing with timein the dangerous position of silent chain. Then export the finite element model fileand the maximum stress data of flexible body to fatigue analysis software FEMFAT,and analyze fatigue performance of the key chain. This paper evaluates the fatigue lifeand strength level mainly from S-N curve, fatigue safety factor, fatigue damage andthe position of fatigue failure. According to the fatigue test data of silent chain afterheat treatment, the CAE fatigue results are the same as the fatigue test. The fatiguelife of the silent chain after heat treatment reached1.13×107circles and its strengthis significantly better than that of untreated chain plate, moreover, the fatigue damageis easy to occur in the middle of tooth profile of chain plate and the position aroundthe chain plate holes, which is consistent with the results of the fatigue test. Thereforeit verifies the reliability of CAE fatigue analysis methods.The research results provide accurate and reliable analytical methods forpredicting the fatigue strength and life of silent chain of gasoline engine timingsystem, so as to achieve the forward design for developing the new chain products.This CAE method not only can be used in the chain transmission productionenterprises, but also be applied to other mechanical industries, so this research makesa certain contribution for improving the reliability of silent chain of automobileengine timing system and reducing the fatigue test cycle and cost for enterprises.