Mechanical Analysis Of Key Components In 4G20 Automobile Engine

Due to the direct and indirect relationship between engine performance and vehicle technology,engine is called the "heart" of vehicle.Besides,whether the engine functions properly also directly affect car's safety performance.Cylinder block,cylinder head,connecting rod and piston are among the most critical parts of an engine.At present,with the fast-changing development of computer technology,the finite element method plays an increasingly important part in design and analysis result.Making use of finite element method to analyze these parts'mechanical property can provides guiding significance to engine optimization design.Consequently,the finite element method was used to do analysis in this thesis.The solid model of connecting rod,piston,cylinder block and cylinder head were built with Pro/E based on features.And took ANSYS Workbench as main analytical platform,Pro/Mechanica as optimization design implement of connecting rod,hypermesh as free modal analysis implement of cylinder block.(1)The connecting rod plays an essential role in a four-stroke engine.However,the loads that the connecting rod endued vary constantly as the engine is running.Specifically,piston pin delivers the gas pressure whose magnitude and direction change periodically,with the reciprocating inertia force of piston and the inertia force caused by swing of connecting rod hindering the motion.As a result,the connecting rod suffered alternating loads including tension load,compressive load and bending load,which meant requiring sufficient stiffness and strength of the connecting rod.This thesis analyzed the actual forces and boundary conditions,then applied loads so as to establish the FEA model.The stress and displacement results which derived from the working condition of maximum compression and maximum stretching at rated speed were obtained by computer analysis and calculating.Then made further efforts to impose restrained conditions to do structure optimization analysis which aims at working out the optimal structural parameter,and the peak stress of maximum tensile was reduced by 3.4%and the maximum total displacement was reduced by 1.7%.Furthermore,the total mass of the connecting rod has slightly decreased.(2)Piston as important part of the combustion chamber,the working environment was very bad,not only bore the periodic heat load of the high temperature gas,but also withstood the gas pressure,the reciprocating inertia force and other mechanical load,and were the reason for piston cylinder scoring,cracking,deformation.Therefore,it was necessary to do finite element analysis under thermal load and mechanical load on the piston,calculated and analyzed its stress and strain distribution,to provide a theoretical basis for structural optimization and improvements of the piston.In combination with the empirical formula and related examples,heat transfer boundary conditions of every region of piston model was determined,and then,the steady state thermal analysis of piston was performed under rated condition.With indirect coupling method,taking the steady-state temperature field of the piston as the temperature boundary conditions of the structural analysis,stress and strain distribution of the part were analyzed and calculated in the case of thermal load,mechanical load and thermo-mechanical coupling load.By comparing and analyzing stress and strain distribution of piston in the three load conditions,dominant factors of stress concentration and excessive deformation of different regions were put forward and analyzed their reasons.(3)In order to get the Dynamic Characteristics of 4G20 petrol engine cylinder block,first of all,used Hypermesh to clean up and repair the defeatured geometry of the cylinder block's IGS model,and then,free modal analysis was carried out in optistruct module using lanczos algorithm,the front six order natural frequency and vibration mode were obtained.According to the result,weak region of cylinder block was found and some improvements were proposed.In a similar way,free modal analysis of cylinder head was also carried out taking advantage of ANSYS Workbench,and obtained the first order natural frequency is 1264.8Hz,which was far away from 166.7 Hz-4G20 petrol engine rated excitation frequency,and so that the engine can avoid the occurring of resonance.Meanwhile,the weak area of the cylinder head was expounded.