| The function of the main shaft cap bolts which installed on the diesel engine is to ensure reliable and effective coupling between the bearing cap and the engine block in the complex operating conditions.Because the main bearing cap bolts work at high temperatures and complex alternating loads such as inertial forces generated by crank links and gas forces,they are prone to fatigue failure.Therefore,the research of the dynamic characteristics and fatigue life of the main bearing cap bolts in this paper have certain academic value and engineering significance.The object of this paper is a kind of diesel engine main bearing cap bolts.The fatigue life is studied on the basis of the results of the dynamic characteristics and finite element analysis.The details are as follows:1?Based on the analysis of the actual working condition of a diesel engine,the load of the main bearing cap bolt under the engine starting,the maximum torque and the rated working conditions is analyzed.And the main mechanical properties of the main bearing cap bolts which work under preload,crank link inertia force and gas force are analyzed.At the same time,The relationship the crank link inertia and force gas between the engine crank angle(time)changes in the engine single cylinder a working cycle is explored.2?The finite element analysis software ANSYS was used to analyze the transient dynamic analysis model of the coupling structure of the main bearing cap bolts under the condition of bearing preload,crank link inertia force and gas force in this paper and research the stress distribution characteristics of main bearing cap bolts under complex excitation load and discuss the influence of important working parameters such as assembly preload,crank link inertia force and gas force on the stress distribution of the root of the bolt thread and the center of the maximum stress section.3?After analyzing the dynamic characteristics of the main bearing cap bolts,it is found that the maximum stress area is located at the first buckle thread root fitted with the screw hole of the engine block.The fatigue life of the main bearing cap under the three typical operating conditions of diesel engine maximum torque and rated torque is estimated by quasi-static nominal stress method.Then the fatigue finite element analysis software is used to predict the fatigue life of the main bearing cap bolts under the normal operation condition of the engine.After the vehicle travels about 102000 km,the main shaft cover bolts need to be replaced.4?The material composition,tensile strength,hardness,friction coefficient and fatigue life of the main bearing cap bolts are tested synthetically by using WAW-600 microcomputer control electro-hydraulic servo universal testing machine,SCHATZ multi-functional fastening analysis and testing machine,GPS200 high-frequency fatigue testing machine and HR150 A Rockwell hardness.The experimental study provides objective data for the theoretical study of the dynamic characteristics of the diesel engine main bearing cap bolts and the prediction of the fatigue life. |
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