The Dynamic Failure Analysis On Valve Train Of A High-Speed Diesel

Valve train, which controlled engine intake and exhaust process, has important impact on engine's performance and useful life. With the development of engine technology, the failure about valve train get attention gradually. Valve and cam, the key parts of valve train, is the fateful factors of valve train and is the important effect factors of engine's performance. As for the high-power high-speed diesel engines, the importance of the two parts is prominent. In order to ensure valve and cam work reliably in poor condition, the dynamic failure analysis on them have great theoretical and engineering applied significance.This dissertation investigates it on the basis of a host of reference, and combines the real situation of valve train produced by a diesel company. The failure factors of valve and cam are discussed. The kinematics and dynamics model on valve train of the engine are built up with ANSYS and AVL TYCON. The performances on the valve train are calculated and some problems on the valve train are made certain. In order to solve the problems, the reformative suggestion about cam profiles is presented.Firstly, based on the real situation of valve face, the dissertation use the finite element method coupled with the thermo-mechanical effect and construct the planar FEM model of valve face. According to the actual temperature and actual working condition of valve face, this paper meshed the valve face and analyzed valve face under complex boundary conditions of displacement and thermal transfer by a commercially available finite element code ANSYS. The temperature field and stress field were present. According to the result, maximum deformation and stress places were predicted, and thermal stress was major factor causing failure. The result can provide reference to improve cooling design of valve train.Then, the actual valve train is simplified properly by centralized mass method and construct multi-mass mathematical model. The mass of all parts are obtained under the condition of building overall solid model. In order to acquire the stiffness of parts of valve train, this paper analyze all parts by FEM and concerned software, and obtain the displacement vector sum of parts, and then get the exact stiffness of all parts.And then, this dissertation analyzed the dynamic and kinematic performance of valve train by dynamic and kinematic simulation. The result indicate that spring force surplus,fullness coefficient,Lubrication factor and vibration character meet the design limits, and valve contact velocities,dynamic behavior of springs,contact losses and impacts are fall in the range of reasonable index. According valve contact velocities of dynamic analysis, this paper make dynamic analysis of impact between valve face and valve seat, and the result indicate that the contact stress , which less than the allowable stress ,can not make valve failure. However, the contact pressure between cam and tappet overrun the allowable stress, and that is the main reason for the abrasion of cam.Finally, on the basis of dynamic failure analysis, the papers suggest the methods of decreasing the contact stress between cam and tappet. The methods provide reference for the optimal design and the reliability research on valve train.