Study On Synthetical Performances And Systemic Optimization Of Valvetrain For High Speed Diesel Engine

In order to meet the elevated requirement of modern vehicle ICE design to the performances of valvetrain, complete investigation is conducted into the synthetical performances analyzing method of OHV type valvetrain. This dissertation takes 6DF1-26 diesel engine as the objective, kinematic, dynamic, lubrication and friction models are set up, and its relative characteristics & features are analyzed, that makes evaluation to the valvetrain performances not restricted in one field.Based on the harmonic analysis to the lift curve of the cam follower, the time-frequency analysis to the dynamic response of the valvetrain is carried out. The relationship between the valvetrain dynamic response, cam profile and natural characteristics is revealed, and that makes the analysis of the components of the dynamic response of the valvetrain and of its determinants possible. This method is able to avoid the defection of weak pertinence and low precision problem through the traditional method purely in time domain or frequency domain. With the aid of the precise dynamic model, the response sequence including vibration and contact load etc. following the camshaft rotation speed & valve clearance etc. are acquired. In order to improve the precision of the dynamic model of valvetrain, adaptive random search method is used to identifiy the parameters of the dynamic model, such as M, C, K etc., with the least squares criterion to determine the measure of agreement between single mass-spring & (4+N₁+N₂) mass-spring dynamic model of the valvetrain and the physical system, and with the help of it, a method has been developed for converting the measured dynamic response of a system into estimates of its unknown physical parameters. By using a more refined model of the valvetrain with high precision and the greatly improved adaptiveness to variant working conditions, valve clearance, cam profile, valve spring etc., and the traditional try-and-error method that is lack of scientific basis is replaced by identification method.Secondly, the dynamic oil film thickness and contact Herts stress are calculated through the EHL model and Herts contact theory, on the basis of accurate data from the Kinematic and Dynamic model, the low film thickness and high stress zone is located, and that is confirmed by the 2000h reliability test.Lastly, considering the wide speed range, high speed, and individuality features of valvetrain for vehicle internal combustion engine, systemic optimal design methodology is developed which makes valve spring design an integral part of N^th degree harmonic cam profile design, with the aid of the high precision dynamic model and lubrication & friction model. Grid optimal method and random search method is adapted separately to select the best matched parameters of the valve spring (n_a, D, d) and the cam profile (ρ₁,ρ₂,ρ₃,ρ₄,ρ₅,ρ₆,ρ₇, R₁,θ_Z etc.).The systemic optimal valve-train design methodology practice on 6DF1-26 Dielsel Engine is proved that it makes spring-inertia force match characteristics and lifter-cam lubrication and fatigue-resistant properties in the cam zone more balanced. As a result, the air charging, dynamical, lifter-cam lubrication and fatigue-resistant properties are improved without lowering the valve train jump-up speed.The methodology developed in the dissertation also indicates adaptability and applicability for engineering optimal systemic design of ICE valvetrain.