| The booming noise of automobile has been a common problem in the research of NVH’s performance of Multipurpose FR automobile, which performance is the subjective feeling of oppression eardrum. It is mainly caused by the strong acoustic energy which radiated within a narrow range of frequencies after the excitation of vehicle body panels structures. For vehicle system, in the process of moving automobile, which usually affected by variety of excitation at the same time, which makes a strong ambiguity exists in the mechanistic studies of the booming noise, thereby it is difficult to accurately determine the particular vibration source in the diagnostic process. Therein, because it has more drive train components and has longer power transmission path, FR usually exists more abundant intrinsic mode in the low frequency band (0～200Hz), which is easily lead to the resonance of system structure and expand the amount of unbalance vibration via the action of the unbalanced torsional vibration excitation effect, thereby likely to cause the booming phenomenon. In the domestic models, influenced by the lowly market positioning, this phenomenon is particularly prominent.Accordingly, with the study highlights of the booming noise, which caused by torsional vibration, it helps to reveal the mechanism of the problem of booming noise. To achieve this research goal, conduct test analysis of object models on purpose. According to the experiment, using CAE analysis tools, following the transfer path, constructed simulation model of driveline torsional vibration, anti-vibration suspension, body structure vibration and interior acoustic response. The models also provide a comprehensive and clear idea of the simulation method for the Torsional Vibration Control, get rid of the status of the project application that assess and improve the impact of torsional vibration on the vehicle NVH performance from the angle of the drive train itself.Simultaneously, combined with the existing NVH engineering experience and governance processes of Trouble Shooting discovered that Torsion System diagnostic work are often based on experiment or simulation at the present stage, with the existing empirical limits, complete determination of the problem point. In this mode, the accuracy and completeness of the limits has become a prerequisite which can quickly and efficiently determine the fault source or not. Moreover, limited to the difference in ability level and experienced of technical staff, it is often difficult to guarantee the diagnosis and treatment period. Therefore, currently, with the existing engineering experience it has become the requirement to develop diagnostic criteria workable, form specialized diagnostic analysis process, and develop a diagnostic analysis software which has good human-computer interaction, accurate diagnostic logic and could satisfied technical operations staffs requirement base on the process.Around this study points, carried out research work in the following areas:(1)In connection with the characteristics of power train arrangement and vehicle for the object model, designed and carried out the test of driveline torsional vibration and vehicle noise and vibration testing. Test data shows that, torsional vibration test data, suspension and body connection point vibration test data and interior sound pressure measuring point test data are existing apparent distinct peaks in the vicinity of 1500r/min, combine the subjective experimental analysis, preliminary determination that the obviously roar which object models exhibited in the vicinity of 1500r/min is caused by the driveline torsional vibration.(2) Based on the engine Torque fluctuation signal transmission path, build a complete simulation model of car roar problem coursed by torsional vibration combined with equivalent analysis, multi-body dynamics analysis and finite Element Analysis. Among them, focusing on the simplification of driveline equivalent model in building the model’s power train equivalents, avoid the ambiguity in the process of stiffness and inertia divided. In the building of suspension seismic model, referring to the structural characteristics of the actual vehicle, substitute wireframe model for missing CAD structure, after the horizontal comparison of variety of modeling methods, proposed a more streamlined suspension shock, vibration isolation model, in the building of acoustic response model, extract the simulation data which the connection points of Suspension and body as a excitation signal, avoid the plight which is difficultly to obtain the force signal of suspension connection point.(3) According to the experimental results from (1), the cars roar which objects models exhibited in the vicinity of 1500r/min are caused by the driveline torsional vibration. In order to clearly reveal the mechanism, combine the results of the simulation analysis from (2) find that, engine crankshaft torque fluctuation caused by periodic cylinder gas pressure acting on the body connection points which in the form of power fluctuations which through the action of main reduction gear after the effect of clutch, transmission and drive shaft, and transferred to the suspension system through bearing, rear axle, shock and vibration absorption effect of the suspension system. Through that, arousing the vibration of body structure, triggering the acoustic energy of structure radiating and then forming a roar. Analysis of the Mechanism covers all aspects which excitation signal change to an acoustic signal. It provides a comprehensive analysis of ideas and means of governance to achieve the governance f the roar.(4) According to the characteristics of the Diagnosis Fault Tree Analysis method, to extract the model of "improved Fault Tree" which adapted to the torsional vibration diagnosis, achieve the quantified controllable of all levels of events of fault Tree by introducing limits. Based on the diagnostic logic and needs of users, using python language, prepare and complete diagnostic analysis software which meets the diagnostic method of improved Fault Tree Model. Achieve the import, display, diagnosis of the test or simulation curve and automatically generates corresponding diagnostic analysis report, further get rid of dependence on manual diagnostic mode.(5) Based on the above analysis, combined with the engineering practice background of the subject, refine diagnosis, analysis, treatment technology roadmap of vehicle NVH issues coursed by drive train, it can be used to standardize and guide the vehicle and parts same types of problems to improve.Subject innovation:(1) Set up a complete analysis model of the issue which coursed by torsional vibration, considering all aspects of the transitive of torque fluctuation signal, get rid of the engineering application status which analyzes the torsional vibration problems only from driveline angle, provides a more comprehensive analysis of ideas for roar governance.(2) Establish an improved fault tree analysis model of the issue which coursed by torsional vibration, and conducted a focus on the branch of driveline torsional vibration, explores the way which effect of each event on top events. Provide a clearer and specific rectification idea to solve the engineering problems. Through the self-prepared diagnostic analysis software, it achieved a "dominant" expression for improved Fault tree diagnosis mode; get rid of the excessive reliance on engineering and technical personnel, effectively guarantee the efficiency and accuracy of diagnosis. Simultaneously, combine with the company’s existing diagnostic mode "Trouble Shooting", establish the diagnosis process of the vehicle NVH issues which coursed by drive train, and provide a standardized technical requirement to solve the similar problems. |
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