Dynamic Analysis Of Overhead Valve-train Based On Multi-body Coupled System

Valve train controls the inlet and intake procedure of engine, which means the performance of valve-train, has direct effects on performance and reliability of engine. With the development of engine technique, it is important to research on dynamic performance of valve train.Working mechanism of overhead valve train with four valves has been analyzed and the main parameters for dynamic modeling are decided by theoretical and experimental methods. Based on this study, model of camshaft—rocker—valve system has been built by AVL/TYCON software, based on which simulation and evaluation on dynamic performance have been carried out. It is concluded that valve train works smoothly under rated speed and there is no valve rebound and disjunction between valve and rocker but good dynamic performance.TYCON model is parameterized and it can not reflect the characteristics of structure, namely only stress of key parts is available but its distribution is not, which is not helpful for structure optimization. To overcome those deflects described above about TYCON model, in this paper it has been proposed to analyze dynamic characteristics based on Rigid-flexible Coupled Dynamic theory. More specifically, the 3D Rigid-flexible Coupled Dynamic Model of camshaft—rocker—valve system has been established, where rocker is considered as flexible body. And then dynamic study on this model has been accomplished by using dynamic substructure method with fixed-interface in the mechanical Multi-body Dynamic Analysis software—ADAMS. Based on this theory, valve acceleration,seating velocity and the contact stress between cam and rocker as well as lubrication between them are calculated. Moreover the calculation of stress on flexible body has been outlined and a dynamic response of valve in line with the changing rule of stress on flexible rocker is analyzed. It is obtained that valve seating velocity and contact stress are within the allowable value. It also can be seen that oil film between rocker and cam is reducing with the rotation becoming slow and the thinnest oil film occurs where the biggest contact stress does not The Rigid-flexible Coupled Dynamic model can not only reflect dynamic performance of valve train, but also stress distribution of flexible body, which is helpful for structure optimization.On the basis of these theoretical studies, experimental research on dynamic characteristics of valve-train has been fulfilled to obtain valve acceleration and dynamic strain of valve and rocker, by which the validity of analysis based on 3D Rigid-flexible Coupled Dynamic Model has been verified and it has also been proved that it can describe dynamic characteristics of valve-train more precisely. In the mean while, dynamic stress curve of flexible body can be obtained by modal synthesis method,which is the theoretical support for fatigue anticipation and structural optimization.