Study of Bolt Model to Improve Accuracy of Engine Vibration Analysis 2010-32-0026

To improve the accuracy of engine vibration analysis, the bolt model which fastens an engine head and an engine block had been developed. In the conventional method of engine vibration analysis, the bolt was modeled with a rigid bar. However, it is seen that the power plant rigidity becomes higher in proportion to the rigid bar bolt length. So, to precisely predict the vibration property of engine parts, the elastic deformation of the bolt was considered in this paper. It is known that the parameters, which are Young's modulus, the length of bolts, the distance between bolts, the area of contact plane, the tightening torque and so on, have a great influence on the performance of the engine vibration model. This paper describes a study of FE bolt model to correlate eigenvalue and mode shapes with the test result. The effects of following parameters were investigated: 1) Bolt model with elastic material 2) Rigidity of bolted-connection in tightening plane. To study the proposed model, firstly, the simple modal vibration tests were conducted using two aluminum sheets fastened by some bolts. In these tests, the influence of the tightening torque, the number of bolts and the area of the contact plane on the natural frequencies of the sheets were studied. Also the natural frequencies were calculated using the computational model of the test apparatus. And the proposed model was tuned up by correlation between the computational and experimental results. To verify the validity of this bolt model, secondly, the modal vibration tests and the computation were performed using the actual engine block with four cylinders. And the natural frequencies of the block were compared, which represented the bending mode, the twisted mode and the local mode of boss. It was confirmed that the differences of the natural frequencies under 2 kHz between the computational and the experimental results were less than 3.3 %.