Low Noise Design Of Valve Train Cam Profile In Internal Combustion Engine

As one of the most important sources of vibration and noise in internal combustion engine,the performance of the valve train directly affects the dynamic performance and stability of the engine.The cam profile plays a decisive role in the valve train.So this paper from the perspective of reducing the vibration and noise level of the valve train,study on the optimization design of cam profile,with 4102 BG diesel engine as the research object.The multi-mass dynamics model of the valve train is taken as the calculation tool in this paper,the dynamic response of the valve train,such as the inflatable performance,the moving stability of the followers and the exciting force level of the system are taken as evaluation indexes,through the analysis of the performance indexs with the variation of cam profile parameters,the optimal design methods of cam profile is summarized;Then,according to the influence of cam profile parameters on the performance of the valve train,two sets of cam profiles with better performance are selected,the excitation force of the valve train is calculated and loaded on the diesel engine model,and the vibration intensity level,vibration velocity level and acceleration level,and total radiation sound pressure level is calculated to evaluate the vibration and noise level of the engine.The results show that in the FB2 type cam profile,the value of parameter m is the most influential to the system performance than the other two parameters;The results of vibration and noise response show that the optimized cam profile will cause the lower surface vibration and radiated noise,the total sound pressure level has reduced 4.5dB compared with the prototype profile,which verify the validity of the low noise design method of cam profile.Based on the concept of system optimization,matching degree analysis is carried out for the whole valve system including cam profile.The results show that the cam profile parameters,working speed and system structure parameters must meet certain matching relationship,in order to ensure the system has a relatively good stability,this match relationship can be measured by the cycle ratio K,generally,the K is larger,the stability of system is higher,when part of the parameters change,the rest of the parameters must be adjusted accordingly to ensure good stability of the system.Aiming at the current impact problem of cam profile exists in the junction,a new design method of cosine-constant velocity buffer section and a new integral cam without buffer section is proposed.The new buffer section can not only improve the plumpness of the lift curve,make the tappet motion curve smoother,but also reduce the moving speed of the valve and improve the smoothness.Compared with the prototype profile,the new integral quadratic Fourier cam profile has better inflatable performance,the acceleration and jump curve is more smooth,there is no sharp changes and mutation in the integral profile,and the positive acceleration section width becomes larger,the transition of positive and negative acceleration section becomes smooth,which can reduce the possibility of "fly off",at the same time,the value of cycle ratio K is improved,and the overall optimization effect is better.Therefore,the analysis results of this paper can provide effective theoretical support and reference for low noise design of valve train.