Prediction And Research On Excitation Characteristics And Vibration&Noise Of Valve Train

Nowdays the low noise design of internal combustion egine mainly focus on that thecombustion noise, the slap noise of piston and the aerodynamics nosie, neglecting of the deepresearch on the vibration and noise of valve train. With the development of requirement fromlegislations and acoustic quality of powers, the vibration and noise of valve train has becomean important research subject. Valve train is an important source of internal combustionengine noise, which is directly produced by the contact force between any two neighboringcomponents. Therefore, for low noise design of internal combustion engine, it is necessary todevelop a method for predictions of vibration and noise of valve train.The prediction of excitations in valve train needs an appropriate dynamic model. Thedynamics of valve train are influenced by cam profile, rotating speed, valve clearance,lubrication, stiffiness and mass of components and so on. All the fators shoud be taken intoconsideration correctly by dynamic model and described qualitatively and quantitativelythrough mathematical variables. Parts of valve train may be simplified and modeled bydifferent mathematical method, but the purposes are the same, that are to make results fromdynamic model even closer to the real dynamic responses of valve train.A lumped dynamic model of valve train is developed by lumped parameter method. Anew simplified method, namely mode matching method for camshaft, pushrod, rockarm,valve and valve spring is put forward in the model. The contribution made by pushrod,rockarm, valve and valve spring to the vibration of valve train should be in the low ordermodes, so the models of these components are required to match their low order modes withinthe considered frequency range of vibration and noise. Based on this idea, the computingmethod of lumped parameters such as mass, stiffness and damping is studied. The model ofcontact behaviors between cam and tappet is set up in view of its important influences ondynamic characteristics of valve train. The lubrication characteristics between cam and tappetare studied and the formula for the friction force is derived. The dynamic model is solvedusing a fourth-order Runge-Kutta method and the results are analyzed in detail.The continuous dynamic model of valve train is developed by son system method, inwhich the cam shaft, pushrod, rock arm, valve spring and valve stem are simplified ascontinuous bodies, and the rigid motions and flexible vibrations of components are coupledwith contact forces between each other. The rigid-flexible coupled dynamic equations aresolved by finite difference method, as the flexible equations are partial differential equations and the components are possible to lose contact with each other. The difference boundarycondition is developed in combination with contact constraint equations for the sake ofindependence of boundary condition and common use of the solution method. This methodcan act in submission to the variations of the boundaries at the right moment, thus the solutionproblem from separation of components is solved.The finite element models of the components of internal combustion engine aredeveloped; the composed structure model is set up by “coupled+contact” method, and all themodels for prediction of vibration are verified with the mode test results. The applied methodsof exicitation in valve train, including cam-tappet contact force, pushrod-rockarm contactforce, rockarm and valve stem contact force, valve spring force and valve-seat contact force,are developed. The vibration responses of structure exictated by every acting force and theircombination in time domain are computed.Based on the above studies, a model to predict noise of valve train in time domain isdeveloped by boundary element method, and exirior radiation noise is computed withboundary conditions from superficial vibration responses of structure exicited by every actingforce and their combination in time domain.Design and build an experimental system for dynamics, vibration and noise of valve train,test valve acceleration, pushrod force, valve stem force, superficial vibration acceleration andexirior radiation noise. The prediction method and model developed in this paper are verifiedby a comparison between the prediction results and the test results to provide directions forvibration and noise control of valve train and low noise design of internal combustion engine.