Dynamic Analysis And Modified Design Of An Engine Valve Train

A valve train is one of important parts of an engine. The suitable design of a valve train isrelated with whether an engine have a good economic performance, reliability, noise and vibrationperformances. As people hope that an engine has better operation performances, an engine requiredto still operate stably and reliably under the operation point with high output power and rotationspeed. Therefore, the valve train is required to have better performances. Since the valve train isdriven by cams, a correct cam design is particularly important.The engine intake train produced by a corporation was taken as object to be researched in thispaper. The dynamic characteristics of the engine intake train have been analyzed based on the AVLEXCITE Timing Drive software and the results show that there exist some poor performances of theintake train such as poor lubrication performance between the cam and tappet, flying off of the camfollower, severe vibration and so on. The cam profile of the intake train has been modified and alarger spring preload has been set to improve the dynamic performances of the intake train. As aresult, the vibration characteristic of the modified intake train is reduced significantly, lubricationperformance between the cam and tappet is improved greatly. Moreover, the flying off of the camfollower has been eliminated completely.The main contents of this paper includes：1） The modeling theories of the one mass model and multi-mass model of the intake train havebeen introduced. The multi-mass dynamic model of the single valve of the intake train and themulti-mass dynamic model of the whole intake train have been established based on the AVLEXCITE Timing Drive software and the stiffness parameters required for the model have beenobtained on basis of UG modeling and FE analysis.2） The dynamic simulation of the intake train has been conducted and the results show that thegreatest acceleration jerk of the valve is more than the required values and there exist a severevibration of the intake train, flying off of the cam follower and a severe wear between the cam andtappet.3） The comparison between of dynamic characteristics the single valve model of the intaketrain and the whole intake train model has been conducted and the results show that the dynamiccharacteristics of each single valve of the whole intake train are greatly different from those of thesingle valve of the intake train.4）To solve the aforementioned problems of the intake train, The dynamic characteristics of theintake train with five groups of cam profile have been compared and the analysis results show that the valve vibration of the group1and5is reduced greatly, the flying off of the cam follower iseliminated completely, the lubrication performance between the cam and tappet is improved.