The Multi-body Dynamics Research And Torsional Vibration Analysis Of Crankshaft System Model Based On Virtual Prototype Technology

As one of the important parts of the engine, the crankshaft has been the important targetof the study of the people.With the rapid development of science and technology, mechanicalequipments that are driven by engine are increasing. People has higher requirement forengine, especially for the requirement of harshness (NVH) which is an important part of theTorsional vibration research.However, the traditional torsional vibration analysis method ofcrankshaft need to spend a lot of time and money,which is not beneficial to reduce the cost ofproduct development and to seize market quickly for company.But it is the development trendof the engine design to research the torsional vibration of crankshaft by using VirtualPrototyping Technology, which combines computer-aided design, finite element method(FEM) and multi-body dynamics simulation (MSS).Taking a6V150engine as an example, the thesis carried out the simulation research ofmulti-body dynamics and the analysis of torsional vibration on crankshaft system modelcombining with finite element software ANSYS and multi-body dynamics simulationsoftware ADAMS. According to the result of the torsional vibration simulation analysis,optimized and designed two different types of absorber to reach the purpose of reducingvibration. In the meanwhile, compare the effect of vibration to choose the best absorber.Themain points of the thesis are as follows:1) This components of the crankshaft system were modeling and assembling inPro/E.Then the multi-body dynamics model for the crankshaft assembly including flexiblecrankshaft was established by importing the three-dimensional models into the ADAMS and creating the modal neutral file.2)By using muti-body dynamics analysis software ADAMS, this paper carried out themulti-rigid body model and the rigid-body and flexible-body mixed model dynamics analysisand kinematics analysis researches and got the related parameters of the crankshaft system,including the velocity and acceleration of pistons and the force of crankpin, piston and mainjournal, ect. With comparing the differences in the two models parameters, the resultsrevealed the influence that the flexible crankshaft makes into the crankshaft dynamics.3)According to the traditional calculation method of engine crankshaft torsionalvibration, it can obtain torsional moment vector diagram of different orders. In the theory, itcould draw a conclution that the syntony of crankshaft system would happen when theharmonic order number is1.5integer times. Then, the inherent frequency of the motor shaft,relative amplitude value, vibration mode figure, the critical speed and the critical rotatingspeed spectrum diagram would be acquired by simplifying the actual crankshaft andcalculating torsional vibration. In the ADAMS software, by applying explosion pressureunder different working conditions, the software caculated the free end of a crankshafttorsional vibration and the corresponding frequency response curve. Focusing on the analysisresult of the torsional vibration under the rated speed, it showed that large torsional amplituder should be paid attention to in4.5,7.5,8.5orde.4)The paper described briefly the torsional vibration reduction methods and used optimaldesign to devise a best absorber to achieve the purpose of reducing vibration according to thesimulation results of torsional vibration. On the basis of design principle of rubber absorber, ittook to design5kinds of rubber absorber under different ratios between frequency of rubberabsorber and natural frequency of the original crankshaft system. In the virtual prototypemodel, respectively do simulating calculation. Comparing the simulation results, the secondrubber absorber is the best one. At the same time, on the basis of the theory of silicone oildamper design, the thesis adopts to solve nonlinear constrained function of two variables tooptimize and design for the best one and gains angular displacement curve of torsionalvibration at the free-end of crankshaft by simulation.Then, through comparing and analyzing the simulation curves about the two types of absorber, the result showed silicone oil damperwas the most optimized one achieving the purpose of weakening torsional vibrationThrough the research work and its analysis results mentioned before, it demonstratedthat using virtual PrototyPing technology to predict the torsional vibration performance of theengine would be a new way for vibration and noise reduction of engines.