Cam Profile Design And Dynamics Analysis For The Valve Train Of High Power Diesel Engine

The increase of power and explosion pressure brings greater challenges to the design of diesel engine.And it also puts forward higher requirements for the performance of valve train.The key to the design of valve train is the design of cam profile.In this paper,the kinematics and dynamics model of single valve train is established by using AVL Timing Drive which is a professional design and analysis software.On the basis of the model,various cam profiles are designed.And the kinematics and dynamics characteristics of the profiles are analyzed.In the process of profile design,it is necessary to ensure the valve train does not fly off,rebound and spring coiling when the crankshaft speed exceeds 20%.The symmetrical polydyne cam profile was designed based on the kinematics model.The influence of various parameters in the function on the fullness coefficient,contact stress,jerk and lubrication coefficient is analyzed.Then the orthogonal test is designed and obtain a parameter combination that meet the kinematics indexes.Through the range analysis,the influence of each parameter on the fullness coefficient,contact stress,jerk and the lubrication coefficient is obtained.It can be used as a reference for the design of cam profiles.On the basis of the symmetrical polydyne cam profile,the asymmetric cam profile is designed.Asymmetric cam profiles include polydyne-polydyne(P-P)cam profile,polydyne-ISAC(P-I)cam profiles and ISAC-ISAC(I-I)cam profiles.Three groups of P-P cam profiles were designed by choosing different combination of closing side parameters.The effects of positive acceleration width,peak acceleration and negative acceleration absolute value of profile on dynamics are analyzed.The closing side of P-I cam profile is designed with 3,6 and 8 segments.Through analysis and comparison,the 6 segments design is the best.The I-I cam profile also designed three groups of schemes.By comparison and analysis,the flexible adjustment of the opening side and the closing side can effectively improve the kinematic and dynamic characteristics of the valve train.Finally,with the design of I-I cam profile,the kinematics and dynamics curves of intake and exhaust valves are calculated and analyzed in detail.The analysis results show that both the intake and exhaust valves can meet the requirements of kinematics design well,and thatthe intake and exhaust valves do not flying off,rebound and spring coiling when the crankshaft speed exceeds 20%.