| Generally speaking,interior vehicle noise problems that people can perceive which needs to consider three essential factors: sound source,transfer path and frequency response.In the process of diagnosing the noise problem of interior vehicle,at first,the source of the excitation force related to noise is identified through subjective evaluation or with the help of professional sound measurement equipment.Then,according to the structural design and sound package of full vehicle and its power-train or outer accessory systems,all kinds of possible noise transfer paths could be able to draw a classification and conclusion.Finally,the noise generating mechanism is able to be analyzed by combining CAE simulation prediction and actual vehicle measurement work,and the real reason of interior vehicle noise is also able to be found out.However,what is the most important sound source of all vehicle interior noise after all,and how to quantify the influence of each transfer path of interior vehicle noise,it is necessary to consider comprehensively for almost all possible relative factors,above these are very complicated to deal with.To the end,how to focus on the parts or positions of main noise contribution,it becomes a feasible approach to diagnose and improve the interior vehicle noise problems.At the beginning of this thesis,several main sound sources,the definition of vehicle power-train outer accessories and evaluation indexes of interior vehicle noise and some characteristics of frequency distribution are introduced,and then mode shape and sound pressure distribution with numerical computation results through applying excitation effect also called vibration speed to the vehicle body's firewall at low and middle frequency noise domain of interior vehicle are discussed,also application with three methods FDM,FVM and FEM in room sound field are introduced in detail,compare with finite difference method(FDM),finite volume method(FVM),though finite element method(FEM)is relatively complex,but mesh subdivision is more flexible than others,especially suitable for interior vehicle space that is irregular geometry structure solution domain,what's more,FEM computation precision is more higher.In order to take a good directive effect on sound property of vehicle at the early development phase,it is necessary that points out interior vehicle's sound pressure distribution trends,noise energy concentrated zone and potential noise problems,in addition,noise peak value and its frequency domain need to be detect,furthermore,including that to predict some weak positions of sound insulation and sound absorption on vehicle body,until get better improvement effect and engineering solution direction.Based on above these,by establishing the sound three dimensions FEM model of of vehicle body,a flexible tetrahedral mesh element is adopted to treat.At last,the numerical simulation results of the sound pressure distribution of interior vehicle are compared with the measurement results.The AC compressor(air condition compressor)system is another main sound sources of interior vehicle noise and the power-train accessory systems,especially for pure electric vehicle,which differs from that of traditional vehicle with ICE(internal combustion engine),the AC compressor's noise phenomenon is a prominent problem in the initial start-up stage of pure electric vehicle or hybrid vehicle.In the early phase of product design and development,this thesis puts forward a complete system of excepts(including product design,manufacture,full vehicle composition,measurement evaluation,quality confirmation and so on)subjective evaluation noise and working process for the prototype vehicle.As a matter of fact,the main noise phenomenon of "click" in the frequency band of about 250 Hz,three effective countermeasures for noise performance improvement of interior vehicle are summarized,including improving the structural stiffness and manufacture precision and adjusting control strategy of AC compressor's rotation speed.However,as for interior vehicle noise with the internal combustion engine,the engine front-end accessory pulley belt system and timing driving system are another two important subsystems of the power-train outer accessory system and main sound sources.By use of the frequency calculation formula about every two adjacent accessory belts section,and sound source identification measurement equipment,the abnormal noise phenomenon's frequency domain of interior vehicle at idling is showed to be at about 700 Hz of noise phenomenon of "dadada",moreover it could be avoided by rationally adjustment of belt's tension.Except that,the processing of timing cover's structure design and the timing chain type selection about driving system play an important role on controlling structure resonance noise and order noise respectively.Therefore,in the vehicle conceptual design phase,the noise problem's crisis management of interior vehicle problems can be done well in advance through the investigation and analysis.In the end,the pulsating resonance noise problem of engine fuel system discussed,which is actually derived from fluid's resonance effect.Through theoretical analysis and measurement and calculation,it is proved that the harmonic noise problem generated within the fuel common rail is closely related to the fuel flow and pulsating pressure of the fuel pipe.The thesis also reveals that the noise problem of about 250 Hz produced by the fuel system is related to the length of the entire pipeline about 6m and the excitation force of the fuel pump check valve for vibration attenuation.The research work in this thesis shows that the FEM is an important and very useful numerical computation method to study the problem of interior room acoustics,and it is especially suitable for the noise diagnosis and improvement of small spatial as interior vehicle cabin.In addition,the noise source identification combined with professional sound measurement equipment can be used for reference about the diagnosis and analysis of noise problems derived from the accessory systems of the vehicle power-train.The corresponding project solutions are proposed according to the generation mechanism of each sound source.After verification and evaluation,significant improvement effect is achieved.The research conclusion in this thesis is of great significance for the design of interior vehicle noise performance. |
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