Modal Analysis And Experiment Research For The Cab Of Heavy Duty Commercial Vehicle

With the rapid development of China's economic,and commercial vehicle has won increasingly wider range of applications. As heavy commercial vehicles traveling a long time, driver and passenger put forward higher demand to riding comfort. So how to reduce the cab vibration and reduce vehicle noise have been regarded by a growing number of manufacturers and research staffs. In many factors of producing vibration and noise, Cab structural vibration is one of the main factors, to reduce vibration and noise,we must first understand the dynamic characteristics of cab. Using modal analysis techniques obtain the parameters of the dynamic characteristics of cab structure, on the one hand, it can also understand the weak regional of structure, and on the other hand, it can avoid the main frequency excitation source in the design. We can overall evaluate that cab structure is reasonable whether or not. It can provide the basis for establishing a sound structural design and adopting appropriate measures for improving. So using modal analysis techniques analysis the dynamic characteristics of structure is of great significance to research on the noise and vibration of structure.Firstly,this paper introduces the development of modal analysis techniques at home and abroad, the sort of modal analysis techniques and the characteristics of modal analysis techniques currently, and indicates the specific application of modal analysis techniques in the automotive body, chassis as well as components in the example way. It introduces the basic theory of modal analysis, the estimation method of parameter identification and identification methods of modal test parameter- least squares complex frequency domain method. It simply introduces the theory of relativity analysis on modal shape.Secondly, this paper introduces the basic concepts of finite element method and the general steps that applying finite element analysis resolves various problems; it introduces finite element software Hypermesh in briefly, we predigest the geometric model under the principles of predigesting finite element model, establish finite element model of various components, and then carry out an inspection and quality amended to elements by built-in tools, finally simulate connections to accomplish finite element model of Cab BIW.Then this paper introduces the dynamics analysis features of finite element analysis software MSC.Nastran, eigenvalue calculation method, the form of mass matrix, eigenvector of the normalized method, the input method of mass matrix, it has prepare for calculation modal analysis; finally calculates the first 50 bands modal of Cab BIW with MSC.Nastran, obtains the modal parameters of model, analysis and evaluates the results.Finally, the article dissertates the general steps of experimental modal analysis and components of test system, the support way of test target, vibrator and the choice of excitation signal, the layout of incentive points and response point, it has prepare for experimental modal analysis; secondly discusses test equipment models, test data reliability test and steady-state plans, and other relevant information pilot; with software LMS.Testlab obtains modal parameters of actual Cab BIW, and detailed analyses of the frequency of 0～50 Hz mode and gives an evaluation; finally compares the calculation modal and experimental modal, finds both agreement and analyses relativity of modal shape, proves that the finite element model has sufficient credibility.It can be seen from the results of analysis that the natural frequency of fourth and fifth-order experimental mode close to the main frequency excitation of engines. It easily arouses resonance and makes noise in the indoor of cab. This paper recommends that taking measures to enhance the stiffness of roof avoid the vibration frequency of engine.