Research On The Influence Of Dynamic Parameters Of Cam On The Movement Of Valve Train

Valve train,as an important mechanism of engine system,is responsible for the opening and closing of the valve and is a structural device to ensure timely ventilation during the working process of the automobile engine.As an important component of valve train,cam mechanism is often degraded because of inappropriate selection of kinetic parameters.In severe cases,it may cause abnormal operation or even failure of the valve system,thereby bringing safety risks.Therefore,in order to ensure that the valve is opened and closed on time during the operation of the valve train system,it is necessary to investigate the influence of dynamic parameters on the dynamic characteristics of the valve.In this work,the influence of the dynamic parameters for the cam mechanism in the valve train on the output displacement of the short rocker arm end of the valve opening and closing section and the cam lift error was analyzed,and Adams was used to verify the research results.Meanwhile,the influence of parameters on residual valve vibration during intermittent period was analyzed.A five-degree-of-freedom dynamic model of a set of valve train units was established by introducing Hertz contact and elastohydrodynamic lubrication theory to found a cam pair contact model and using a linear transformation method to eliminate the transmission ratio on both sides of the rocker arm.The output displacement of each component of the valve train was obtained after solving this model.The results show that in the valve opening and closing section,there is an error between the output displacement of the short rocker arm and the cam lift stroke;during the cam intermittent period,the valve train produces serious residual vibration.The influence of the stiffness and damping of the cam mechanism,guide pillar,tappet,rocker arm and valve spring on the output displacement of the short rocker arm end of the valve opening and closing section was analyzed.The results show that the damping has little effect on it.Moreover,a curve similarity measurement index was established to study the error between the short rocker arm end and the cam lift curve and improve the conventional curve similarity judging method.The main parameters of cam pair equivalent contact stiffness K_HE,equivalent contact stiffness between tappet and tappet K_TP,tappet and short rocker arm contact stiffness K_PA,and valve spring stiffness K_E were studied for the effect of the short rocker arm end and cam lift range error.The results show that with the increase of K_HE,K_TP,K_PA,the error of the short rocker arm end and the cam lift range gradually decreases to be basically stable;with the increase of K_E,the error between the two is basically unchanged at first and then gradually increases.A simulation model of the valve train unit was established by Adams,and the influence of different dynamic parameters on the output displacement of the short rocker arm end of the valve opening and closing section and the cam lift error was analyzed to verify the correctness of the theoretical analysis.The influence of the stiffness and damping of the cam mechanism,guide pillar,tappet,rocker arm and valve spring on the residual vibration of the valve train in the intermittent period is analyzed by taking the effective value of the vibration displacement as the evaluation index.The results show that with the increase of K_HE,K_TP,K_PA,rocker arm stiffness K_A,rocker arm and valve contact stiffness K_AV,and rocker arm structure damping C_A,the residual valve vibration gradually decreases to be basically stable;with K_E,cam pair The equivalent damping C_HE,the equivalent contact damping C_TP between the tappet and the tappet,the contact damping C_PA between the tappet and the short rocker arm and the valve spring damping C_E increase,the residual vibration gradually decreases;as the long rocker arm end and the valve indirect contact damping C_AV increases,the residual vibration gradually increases.Finally,the PSO algorithm was used to solve the optimal value of the valve train to weigh the overall motion characteristics,and the correctness of the set of values was verified based on Adams.In this work,the influence of valve train dynamics parameters on the output displacement of the short rocker arm end of the valve opening and closing section,the cam lift error and the residual valve vibration during the intermittent period was systematically analyzed.The purpose is to make the components can be stable according to the predetermined requirements.The work provides a reference for the selection of dynamic parameters in the valve system,and is of great significance to the precise operation and design improvement for the valve mechanism.