Research On Low Noise Cam Profile Design Of Internal Combustion Engine Valve Train

With the development and progress of society,the vibration and noise level of the internal combustion engine has attracted wide attention.The valve train is one of the main noise sources of the internal combustion engine,its performance is closely related to the overall dynamics and stability of the internal combustion engine.When the valve train is working,power is transmitted from the camshaft to the rest of the components,so camshaft profile design plays a decisive role in the dynamic performance of valve train.This paper takes a certain type of diesel engine as the main research object,Improve the working stability of valve parts by improving the continuity of cam profile,thus reducing the contribution of the valve train to the overall vibration and noise level of the diesel engine.The main theme of this paper is an optimization design study,which requires an effective profile design method with an accurate and reliable valve train calculation model.The dynamic and kinematic model of the valve train is established by AVL EXCITE Timing Drive,and the model establishment method is based on the centralized mass method.The discrete method and parameter acquisition of each part of the valve train are described in detail in this paper.To verify the accuracy of the above simulation model,the author designed and completed the valve train dynamic check experiment.The experiment is based on two autonomous sensors,both of which are piezoelectric force sensors which can measure the contact force between cam tappets and the contact force between the valve and valve seat ring at different speeds of the valve train.The measured correction data were compared with the simulation prediction data,the results showed that although there were some differences between the two results,the peaks and phases could correspond to each other,which verified the accuracy of the simulation model.By discrete derivation and filtering of the measured cam profile,the original profile of this diesel engine was determined to be FB2.Through the analysis of the main excitation force of the valve,it was found that the working stability of the valve train is affected to a certain extent because the FB2 cam profile only guarantees the continuity of the acceleration curve at the segment.In order to improve this problem,the author designed an N-th harmonic cam profile for the diesel engine without changing the valve timing.In the design process,the periodic coefficient is introduced to control the symmetry of the profile line,which reduces the constraint variables of the solution,and the differential evolution algorithm is introduced in the solution process to further screen the design variables.To further investigate the low-noise optimization effect of the above method,the main excitation forces of the valve train corresponding to the harmonic profile and the FB2 profile were analyzed from the time domain and frequency domain.It is proved that the harmonic cam profile can improve the working stability of the valve train,the peak value of the main excitation force is reduced and the fluctuation situation is improved.The vibration and noise levels of the diesel engine were calculated by the finite element method and the boundary element method,and the two type profiles were evaluated by the vibration intensity,vibration acceleration level,and radiation noise sound pressure level.The results showed that the design method of the harmonic cam is effective in reducing the vibration and noise of the internal combustion engine.The research results of this paper can provide support and reference for the low-noise design of diesel engine cam profiles.